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On the evolution of Betti curves in the Cosmic web: In this work, we study the evolution of Betti curves obtained by
persistent-homological analysis of pointclouds formed by halos in different
cosmological $N$-body simulations. We show that they can be approximated with a
scaled log-normal distribution function with reasonable precision. Our analysis
shows that the shapes and maximums of Betti curves exhibit dependence on the
mass range of the selected subpopulation of halos, but at the same time, the
resolution of a simulation does not play any significant role, provided that
the mass distribution of simulated halos is complete down to a given mass
scale. Besides, we study how Betti curves change with the evolution of the
Universe, i.e., their dependence on redshift. Sampling subpopulations of halos
within certain mass ranges up to redshift $z=2.5$ yields a surprisingly small
difference between corresponding Betti curves. We propose that this may be an
indicator of the existence of a new specific topological invariant in the
structure of the Universe. | Local Hole revisited: evidence for bulk motions and self-consistent
outflow: We revisit our mapping of the `Local Hole', a large underdensity in the local
galaxy redshift distribution that extends out to redshift, $z\approx0.05$ and a
potential source of outflows that may perturb the global expansion rate and
thus help mitigate the present `$H_0$ tension'. First, we compare local
peculiar velocities measured via the galaxy average redshift-magnitude Hubble
diagram, $\bar{z}(m)$, with a simple dynamical outflow model based on the
average underdensity in the Local Hole. We find that this outflow model is in
good agreement with our peculiar velocity measurements from $\bar{z}(m)$ and
not significantly inconsistent with SNIa peculiar velocity measurements from at
least the largest previous survey. This outflow could cause an $\approx2-3$\%
increase in the local value of Hubble's constant. Second, considering
anisotropic motions, we find that the addition of the outflow model may improve
the $\bar{z}(m)$ fit of a bulk flow where galaxies are otherwise at rest in the
Local Group frame. We conclude that the Local Hole plus neighbouring
overdensities such as the Shapley Supercluster may cause outflow and bulk
motions out to $\approx150$h$^{-1}$Mpc that are cosmologically significant and
that need to be taken into account in estimating Hubble's constant. |
Efficient Optimal Reconstruction of Linear Fields and Band-powers from
Cosmological Data: We present an efficient implementation of Wiener filtering of real-space
linear field and optimal quadratic estimator of its power spectrum Band-powers.
We first recast the field reconstruction into an optimization problem, which we
solve using quasi-Newton optimization. We then recast the power spectrum
estimation into the field marginalization problem, from which we obtain an
expression that depends on the field reconstruction solution and a determinant
term. We develop a novel simulation based method for the latter. We extend the
simulations formalism to provide the covariance matrix for the power spectrum.
We develop a flexible framework that can be used on a variety of cosmological
fields and present results for a variety of test cases, using simulated
examples of projected density fields, projected shear maps from galaxy lensing,
and observed Cosmic Microwave Background (CMB) temperature anisotropies, with a
wide range of map incompleteness and variable noise. For smaller cases where
direct numerical inversion is possible, we show that our solution matches that
created by direct Wiener Filtering at a fraction of the overall computation
cost. Even more significant reduction of computational is achieved by this
implementation of optimal quadratic estimator due to the fast evaluation of the
Hessian matrix. This technique allows for accurate map and power spectrum
reconstruction with complex masks and nontrivial noise properties. | The star formation histories of Hickson compact group galaxies: ABRIDGED: We study the Star Formation History (SFH) of 210 galaxies members
of 55 Hickson Compact Groups (HCG) and 309 galaxies from the Catalog of
Isolated Galaxies (CIG). The SFH traces the variation of star formation over
the lifetime of a galaxy, and yields consequently a snapshot picture of its
formation. Comparing the SFHs in these extremes in galaxy density, allows us to
determine the main effects of Compact Groups (CG) on the formation of galaxies.
We fit our spectra using the spectral synthesis code STARLIGHT and obtain the
stellar population contents and mean stellar ages of HCG and CIG galaxies in
three different morphological classes: early-type galaxies (EtG), early-type
spirals (EtS), and late-type spirals (LtS). We find that EtG and EtS galaxies
in HCG show larger contents of old and intermediate stellar populations as well
as an important deficit of the young stellar population, what clearly implies
an older average stellar age in early galaxies in HCG. For LtS galaxies we find
similar mean values for the stellar content and age in the two samples.
However, we note that LtS can be split into two subclasses, namely old and
young LtS. In HCG we find a higher fraction of young LtS than in the CIG
sample, in addition, most of these galaxies belong to groups where most of the
galaxies are also young and actively forming stars. The Specific Star Formation
Rate (SSFR) of spiral galaxies in the two samples differ. EtS in HCG show lower
values of the SSFR, while LtS peak at higher values when comparing with their
counterparts in isolation. We have also measured shorter Star Formation Time
Scale (SFTS) in HCG galaxies, indicating that they have less prolonged star
formation activity than CIG galaxies. |
Dark Energy Survey Year 3 Results: Measurement of the Baryon Acoustic
Oscillations with Three-dimensional Clustering: The three-dimensional correlation function offers an effective way to
summarize the correlation of the large-scale structure even for imaging galaxy
surveys. We have applied the projected three-dimensional correlation function,
$\xi_{\rm p}$ to measure the Baryonic Acoustic Oscillations (BAO) scale on the
first-three years Dark Energy Survey data. The sample consists of about 7
million galaxies in the redshift range $ 0.6 < z_{\rm p } < 1.1 $ over a
footprint of $4108 \, \mathrm{deg}^2 $. Our theory modeling includes the impact
of realistic true redshift distributions beyond Gaussian photo-$z$
approximation. To increase the signal-to-noise of the measurements, a Gaussian
stacking window function is adopted in place of the commonly used top-hat.
Using the full sample, $ D_{\rm M}(z_{\rm eff} ) / r_{\rm s} $, the ratio
between the comoving angular diameter distance and the sound horizon, is
constrained to be $ 19.00 \pm 0.67 $ (top-hat) and $ 19.15 \pm 0.58 $
(Gaussian) at $z_{\rm eff} = 0.835$. The constraint is weaker than the angular
correlation $w$ constraint ($18.84 \pm 0.50$) because the BAO signals are
heterogeneous across redshift. When a homogeneous BAO-signal sub-sample in the
range $ 0.7 < z_{\rm p } < 1.0 $ ($z_{\rm eff} = 0.845$) is considered,
$\xi_{\rm p} $ yields $ 19.80 \pm 0.67 $ (top-hat) and $ 19.84 \pm 0.53 $
(Gaussian). The latter is mildly stronger than the $w$ constraint ($19.86 \pm
0.55 $). We find that the $\xi_{\rm p} $ results are more sensitive to
photo-$z$ errors than $w$ because $\xi_{\rm p}$ keeps the three-dimensional
clustering information causing it to be more prone to photo-$z$ noise. The
Gaussian window gives more robust results than the top-hat as the former is
designed to suppress the low signal modes. $\xi_{\rm p}$ and the angular
statistics such as $w$ have their own pros and cons, and they serve an
important crosscheck with each other. | From Galaxy Clusters to Ultra-Faint Dwarf Spheroidals: A Fundamental
Curve Connecting Dispersion-supported Galaxies to Their Dark Matter Halos: We examine scaling relations of dispersion-supported galaxies over more than
eight orders of magnitude in luminosity by transforming standard fundamental
plane parameters into a space of mass (M1/2), radius (r1/2), and luminosity
(L1/2). We find that from ultra-faint dwarf spheroidals to giant cluster
spheroids, dispersion-supported galaxies scatter about a one-dimensional
"fundamental curve" through this MRL space. The weakness of the M1/2-L1/2 slope
on the faint end may imply that potential well depth limits galaxy formation in
small galaxies, while the stronger dependence on L1/2 on the bright end
suggests that baryonic physics limits galaxy formation in massive galaxies. The
mass-radius projection of this curve can be compared to median dark matter halo
mass profiles of LCDM halos in order to construct a virial mass-luminosity
relationship (Mvir-L) for galaxies that spans seven orders of magnitude in
Mvir. Independent of any global abundance or clustering information, we find
that (spheroidal) galaxy formation needs to be most efficient in halos of Mvir
~ 10^12 Msun and to become inefficient above and below this scale. Moreover,
this profile matching technique is most accurate at the high and low luminosity
extremes (where dark matter fractions are highest) and is therefore quite
complementary to statistical approaches that rely on having a well-sampled
luminosity function. We also consider the significance and utility of the
scatter about this relation, and find that in the dSph regime observational
errors are almost at the point where we can explore the intrinsic scatter in
the luminosity-virial mass relation. Finally, we note that purely stellar
systems like Globular Clusters and Ultra Compact Dwarfs do not follow the
fundamental curve relation. This allows them to be easily distinguished from
dark-matter dominated dSph galaxies in MRL space. (abridged) |
Do all QSOs have the same black hole mass?: QSOs from SDSS, 2QZ and 2SLAQ covering an order of magnitude in luminosity at
fixed redshift exhibit similar amplitudes of clustering. In addition, QSO
clustering evolution at z>0.5 is well fitted by a model that assumes a fixed
host halo mass, implying that QSOs may occur in a relatively narrow range of
halo and BH mass. We argue that the slow evolution of early-type galaxies out
to z~1-2 may also provide support for a slow evolution of QSO host BH masses.
The result would mean that if high-z QSOs radiate at Eddington rates then low-z
SyI must radiate at ~100x less than Eddington. We conclude that models where
QSOs radiate at L_Edd require M_BH and M_halo to be decoupled to circumvent the
clustering results. While single BH mass and flickering models fit the z>0.5
clustering results, they appear to be rejected by the z~0, M_BH-L relation from
reverberation mapping. We find that the inclusion of z<0.5 QSO clustering data
improves the fit of a long-lived QSO model and suggest that the predictions of
a PLE model for QSO BH masses agree reasonably with UV-bump and reverberation
estimates (abridged). | On the buildup of massive early-type galaxies at z<~1. II- The
coordinated key role of wet, mixed, and dry major mergers: Hierarchical models predict that present-day massive early-type galaxies
(mETGs) have finished their assembly at a quite late cosmic epoch (z~0.5),
conflicting directly with galaxy mass-downsizing. In Eliche-Moral et al.
(2010), we presented a semi-analytical model that predicts the increase by a
factor of ~2.5 observed in the number density of mETGs since z~1 to the
present, just accounting for the effects of the major mergers strictly-reported
by observations. Here, we describe the relative, coordinated role of wet,
mixed, and dry major mergers in driving this assembly. Accordingly to
observations, the model predicts that: 1) wet major mergers have controlled the
mETGs buildup since z~1, although dry and mixed mergers have also contributed
significantly to it; 2) the bulk of this assembly takes place during the ~1.4
Gyr time-period elapsed at 0.7<z<1, being nearly frozen at z<~0.7; 3) this
frostbite can be explained just accounting for the observational decrease of
the major merger fraction since z~0.7, implying that major mergers (and, in
particular, dry events) have contributed negligibly to the mETGs assembly
during the last ~6.3 Gyr; and 4) major mergers are responsible for doubling the
stellar mass at the massive-end of the red sequence since z~1. The most
striking model prediction is that at least ~87% of the mETGs existing at z~1
are not the passively-evolved, high-z counterparts of present-day mETGs, but
their gas-poor progenitors instead. This implies that <~5% of present-day mETGs
have been really in place since z~1. The model derives a redshift of final
assembly for present-day mETGs in agreement with hierarchical models (z~0.5),
reproducing at the same time the observed buildup of mETGs at z<~1.(Abridged) |
Probing Primordial Features with the Stochastic Gravitational Wave
Background: The stochastic gravitational wave background (SGWB) offers a new opportunity
to observe signals of primordial features from inflationary models. We study
their detectability with future space-based gravitational waves experiments,
focusing our analysis on the frequency range of the LISA mission. We compute
gravitational wave spectra from primordial features by exploring the parameter
space of a two-field inflation model capable of generating different classes of
features. Fine-tuning in scales and amplitudes is necessary for these signals
to fall in the observational windows. Once they show up, several classes of
frequency-dependent oscillatory signals, characteristic of different underlying
inflationary physics, may be distinguished and the SGWB provides a window on
dynamics of the primordial universe independent of cosmic microwave background
and large-scale structure. To connect with future experimental data, we discuss
two approaches of how the results may be applied to data analyses. First, we
discuss the possibility of reconstructing the signal with LISA, which requires
a high signal-to-noise ratio. The second more sensitive approach is to apply
templates representing the spectra as estimators. For the latter purpose, we
derive templates that can accurately capture the spectral features of several
classes of feature signals and compare them with the SGWB produced by other
physical mechanisms. | Constraining uber gravity with recent observations and studying the
$H_0$ problem: This paper studies both $\Lambda$CDM and CDM models under the \"uber gravity
theory, named \"u$\Lambda$CDM and \"uCDM respectively. We report bounds over
their parameter phase-space using several cosmological data, in particular, the
recent Pantheon+ sample. Based on the joint analysis, the best fit value of the
\"uber characteristic parameter is $z_\oplus = 0.046^{+0.047}_{-0.032}$ and
$z_\oplus = 1.382^{+0.020}_{-0.021}$ at 68\% confidence level for
\"u$\Lambda$CDM and \"uCDM respectively. Although \"uber gravity can
successfully mimics the cosmological constant, we find that the
$\mathbb{H}0(z)$ diagnostic suggests the $H_0$ tension is not alleviated.
Finally, both models are statistically compared with $\Lambda$CDM through the
Akaike and Bayesian information criteria. Both \"uber gravity models and
$\Lambda$CDM are equally preferred for most of the single samples, in
particular, \"u$\Lambda$CDM is not rejected by the CMB data. However, there is
strong evidence against them for the joint analysis. |
On the origin of intrinsic alignment in cosmic shear measurements: an
analytic argument: Galaxy intrinsic alignment can be a severe source of error in weak-lensing
studies. The problem has been widely studied by numerical simulations and with
heuristic models, but without a clear theoretical justification of its origin
and amplitude. In particular, it is still unclear whether intrinsic alignment
of galaxies is dominated by formation and accretion processes or by the effects
of the instantaneous tidal field acting upon them. We investigate this question
by developing a simple model of intrinsic alignment for elliptical galaxies,
based on the instantaneous tidal field. Making use of the galaxy stellar
distribution function, we estimate the intrinsic alignment signal and find that
although it has the expected dependence on the tidal field, it is too weak to
account for the observed signal. This is an indirect validation of the standard
view that intrinsic alignment is caused by formation and/or accretion
processes. | The Spatial Distribution of Dust and Stellar Emission of the Magellanic
Clouds: We study the emission by dust and stars in the Large and Small Magellanic
Clouds, a pair of low-metallicity nearby galaxies, as traced by their spatially
resolved spectral energy distributions (SEDs). This project combines Herschel
Space Observatory PACS and SPIRE far-infrared photometry with other data at
infrared and optical wavelengths. We build maps of dust and stellar luminosity
and mass of both Magellanic Clouds, and analyze the spatial distribution of
dust/stellar luminosity and mass ratios. These ratios vary considerably
throughout the galaxies, generally between the range $0.01\leq L_{\rm
dust}/L_\ast\leq 0.6$ and $10^{-4}\leq M_{\rm dust}/M_\ast\leq 4\times10^{-3}$.
We observe that the dust/stellar ratios depend on the interstellar medium (ISM)
environment, such as the distance from currently or previously star-forming
regions, and on the intensity of the interstellar radiation field (ISRF). In
addition, we construct star formation rate (SFR) maps, and find that the SFR is
correlated with the dust/stellar luminosity and dust temperature in both
galaxies, demonstrating the relation between star formation, dust emission and
heating, though these correlations exhibit substantial scatter. |
Superfluid dark stars: We present a superfluid dark star model consisting of relativistic dark
bosons with two-body self-interaction. The obtained masses, radii, and tidal
deformability depend in a simple way on the boson mass and interaction
strength. We report first results on binary mergers: the distinctive amplitude
and frequency of the emitted gravitational waves are well within reach of
terrestrial interferometers. | Optimizing baryon acoustic oscillation surveys II: curvature, redshifts,
and external datasets: We extend our study of the optimization of large baryon acoustic oscillation
(BAO) surveys to return the best constraints on the dark energy, building on
Paper I of this series (Parkinson et al. 2007). The survey galaxies are assumed
to be pre-selected active, star-forming galaxies observed by their line
emission with a constant number density across the redshift bin. Star-forming
galaxies have a redshift desert in the region 1.6 < z < 2, and so this redshift
range was excluded from the analysis. We use the Seo & Eisenstein (2007)
fitting formula for the accuracies of the BAO measurements, using only the
information for the oscillatory part of the power spectrum as distance and
expansion rate rulers. We go beyond our earlier analysis by examining the
effect of including curvature on the optimal survey configuration and updating
the expected `prior' constraints from Planck and SDSS. We once again find that
the optimal survey strategy involves minimizing the exposure time and
maximizing the survey area (within the instrumental constraints), and that all
time should be spent observing in the low-redshift range (z<1.6) rather than
beyond the redshift desert, z>2. We find that when assuming a flat universe the
optimal survey makes measurements in the redshift range 0.1 < z <0.7, but that
including curvature as a nuisance parameter requires us to push the maximum
redshift to 1.35, to remove the degeneracy between curvature and evolving dark
energy. The inclusion of expected other data sets (such as WiggleZ, BOSS and a
stage III SN-Ia survey) removes the necessity of measurements below redshift
0.9, and pushes the maximum redshift up to 1.5. We discuss considerations in
determining the best survey strategy in light of uncertainty in the true
underlying cosmological model. |
Renyi entropy and the holographic dark energy in flat space time: Based on Renyi entropy, we study the entropy corrected version of the
holographic dark energy (HDE) model in apparent horizon of spatially flat FLRW
universe. Applying the generalized entropy leads to the modified version of the
Friedmann evolution equations which besides pressure-less matter and HDE, there
is an extra term that is purely geometric. This extra term are assumed as
another part of dark energy. We assume the universe is filled by
non-interacting components of ideal fluids such as dark matter and holographic
dark energy. The total dark energy, which is a combination of generalized HDE
and geometric part, has a density parameter that approaches one by decreasing
the redshift. Considering the total equation of state parameter and
deceleration parameter of the universe indicates that the universe could stays
in positive accelerated expansion phase that shows an agreement with
observational data, only for the specific values of the constant $\zeta$. | SNe Ia Tests of Quintessence Tracker Cosmology in an Anisotropic
Background: We investigate the observational effects of a quintessence model in an
anisotropic spacetime. The anisotropic metric is a non-rotating particular case
of a generalized Godel's metric and is classified as Bianchi III. This metric
is an exact solution of the Einstein-Klein-Gordon field equations with an
anisotropic scalar field, which is responsible for the anisotropy of the
spacetime geometry. We test the model against observations of type Ia
supernovae, analyzing the SDSS dataset calibrated with the MLCS2k2 fitter, and
the results are compared to standard quintessence models with Ratra-Peebles
potentials. We obtain a good agreement with observations, with best values for
the matter and curvature density parameters $\Omega_M = 0.29$ and $\Omega_k=
0.01$ respectively. We conclude that present SNe Ia observations cannot, alone,
distinguish a possible anisotropic axis in the cosmos. |
The MUSIC of Galaxy Clusters III: Properties, evolution and Y-M scaling
relation of protoclusters of galaxies: In this work we study the properties of protoclusters of galaxies by
employing the MUSIC set of hydrodynamical simulations, featuring a mass-limited
sample of 282 resimulated clusters with available merger trees up to high
redshift, and we trace the cluster formation back to $z$ = 1.5, 2.3 and 4. We
study the features and redshift evolution of the mass and the spatial
distribution for all the cluster progenitors and for the protoclusters, which
we define as the most massive progenitors of the clusters identified at $z$ =
0. A natural extension to redshifts larger than 1 is applied to the estimate of
the baryon content also in terms of gas and stars budgets: no remarkable
variations with redshift are discovered. Furthermore, motivated by the proven
potential of Sunyaev-Zel'dovich surveys to blindly search for faint distant
objects, we focus on the scaling relation between total object mass and
integrated Compton $y$-parameter, and we check for the possibility to extend
the mass-observable paradigm to the protocluster regime, far beyond the
redshift of 1, to account for the properties of the simulated objects. We find
that the slope of this scaling law is steeper than what expected for a
self-similarity assumption among these objects, and it increases with redshift
mainly for the synthetic clusters where radiative processes, such as radiative
cooling, heating processes of the gas due to UV background, star formation and
supernovae feedback, are included. We use three different criteria to account
for the dynamical state of the protoclusters, and find no significant
dependence of the scaling parameters from the level of relaxation. Based on
this, we exclude that the dynamical state is the cause of the observed
deviations from self-similarity. | Synchronous Evolution of Galaxies in Groups: NGC 524 Group: By means of panoramic spectroscopy at the SAO RAS BTA telescope, we
investigated the properties of stellar populations in the central regions of
five early-type galaxies -- the NGC 524 group members. The evolution of the
central regions of galaxies looks synchronized: the average age of stars in the
bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five
galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr
ago. The only galaxy, in which the ages of stellar population in the nucleus
and in the bulge coincide (i.e. the nuclear burst of star formation did not
take place) is NGC 502, the farthest from the center of the group of all the
galaxies studied. |
On the redshift evolution of the baryon and gas fraction in simulated
groups and clusters of galaxies: We study the redshift evolution of the baryon budget in a large set of galaxy
clusters from the {\it Magneticum} suite of SPH cosmological simulations. At
high redshifts, we obtain "closed box" systems independently by the mass of the
systems on radii greater than $3R_{500,\mathrm c}$, whereas at lower redshifts,
only the most massive halos could be considered as `"closed box". The baryon
fraction shows a general decrease with the redshift and, for less massive
objects, we observe a much more prominent decrease than for massive halos. The
gas depletion parameter $Y_{\rm gas}$ shows a steeper and highly scattered
radial distribution in the central regions of less massive halos with respect
to massive objects at all redshifts, while on larger radii the gas fraction
distributions are independent of the masses or the redshifts. The hot component
of the gas traces well the total amount of gas at low redshifts. At higher
redshifts, the cold component provides a not negligible contribution to the
total amount of baryon in our systems. Moreover, the behaviour of the baryonic,
entire gas, and hot gas phase depletion parameters as a function of radius,
mass, and redshift are described by some functional forms. The evolution of
metallicity and stellar mass in halos suggests that the early enrichment
process is dominant. We investigate correlations between the time evolution of
AGN feedback and the depletion parameters. We demonstrate that the energy
injected by the AGN activity shows a particularly strong positive correlation
with $Y_{\rm bar}$, $Y_{\rm cold}$,$Y_{\rm star}$ and a negative one with
$Y_{\rm hot}$, $Z_{\rm Tot}$. These trends are consistent with previous works,
meaning that our results, combined with findings derived from current and
future X-rays observations, represent possible proxies to test the AGN feedback
models used in different suites of numerical simulations. | Scalar Field Dark Energy Parametrization: We propose a new Dark Energy parametrization based on the dynamics of a
scalar field. We use an equation of state $w=(x-1)/(x+1)$, with $x=E_k/V$, the
ratio of kinetic energy $E_k=\dot\phi^2/2$ and potential $V$. The eq. of motion
gives $x=(L/6)(V/3H^2)$ and with a solution $x=([1+2 L/3(1+y)]^{1/2}-1)(1+y)/2$
where $y\equiv \rm/V$ and $L\equiv (V'/V)^2 (1+q)^2,\, q\equiv\ddot\p/V'$.
Since the universe is accelerating at present time we use the slow roll
approximation in which case we have $|q|\ll 1$ and $L\simeq (V'/V)^2$. However,
the derivation of $L$ is exact and has no approximation. By choosing an
appropriate ansatz for $L$ we obtain a wide class of behavior for the evolution
of Dark Energy without the need to specify the potential $V$. In fact $w$ can
either grow and later decrease, or other way around, as a function of redshift
and it is constraint between $-1\leq w\leq 1$ as for any canonical scalar field
with only gravitational interaction. Furthermore, we also calculate the
perturbations of DE and since the evolution of DE is motivated by the dynamics
of a scalar field the homogenous and its perturbations can be used to determine
the form of the potential and the nature of Dark Energy. Since our
parametrization is on $L$ we can easily connect it with the scalar potential
$V(\phi)$. |
Bispectrum from open inflation: We calculate the bispectrum of primordial curvature perturbations, \zeta,
generated during "open inflation." Inflation occurs inside a bubble nucleated
via quantum tunneling from the background false vacuum state. Our universe
lives inside the bubble, which can be described as a
Friedman-Lema\^itre-Robertson-Walker (FLRW) universe with negative spatial
curvature, undergoing slow-roll inflation. We pay special attention to the
issue of an initial state for quantum fluctuations. A "vacuum state" defined by
a positive-frequency mode in de Sitter space charted by open coordinates is
different from the Euclidean vacuum (which is equivalent to the so-called
"Bunch-Davies vacuum"). Quantum tunneling then modifies the initial state away
from the original Euclidean vacuum. While most of the previous study on
modifications of the initial quantum state introduces, by hand, an initial time
at which the quantum state is modified as well as the form of the modification,
an effective initial time naturally emerges and the form is fixed by quantum
tunneling in open inflation models. Therefore, open inflation enables a
self-consistent computation of the effect of a modified initial state on the
bispectrum. We find a term which goes as <\zeta_{k_1} \zeta_{k_2} \zeta_{k_3}>
\propto 1/k_1^2k_3^4 in the so-called squeezed configurations, k_3\ll
k_1\approx k_2, in agreement with the previous study. The bispectrum in the
exact folded limit, e.g., k_1=k_2+k_3, is also enhanced and remains finite.
However, these terms are exponentially suppressed when the wavelength of \zeta
is smaller than the curvature radius of the universe. The leading-order
bispectrum is equal to the usual one from single-field slow-roll inflation; the
terms specific for open inflation arise only in the sub-leading order when the
wavelength of \zeta is smaller than the curvature radius. | Which FLRW comoving 3-manifold is preferred observationally and
theoretically?: The lack of structure greater than 10 Gpc/h in Wilkinson Microwave Anisotropy
Probe (WMAP) observations of the cosmic microwave background (CMB) favours
compact Friedmann-Lemaitre-Robertson-Walker (FLRW) models of the Universe. The
present best candidates based on observations are the Poincare dodecahedral
space S^3/I^* and the 3-torus T^3. The residual gravity effect favours the
Poincare space, while a measure space argument where the density parameter is a
derived parameter favours flat spaces almost surely. |
Applications of Bayesian model averaging to the curvature and size of
the Universe: Bayesian model averaging is a procedure to obtain parameter constraints that
account for the uncertainty about the correct cosmological model. We use recent
cosmological observations and Bayesian model averaging to derive tight limits
on the curvature parameter, as well as robust lower bounds on the curvature
radius of the Universe and its minimum size, while allowing for the possibility
of an evolving dark energy component. Because flat models are favoured by
Bayesian model selection, we find that model-averaged constraints on the
curvature and size of the Universe can be considerably stronger than non
model-averaged ones. For the most conservative prior choice (based on
inflationary considerations), our procedure improves on non model-averaged
constraints on the curvature by a factor of ~ 2. The curvature scale of the
Universe is conservatively constrained to be R_c > 42 Gpc (99%), corresponding
to a lower limit to the number of Hubble spheres in the Universe N_U > 251
(99%). | Measuring Hubble Constant with Dark Neutron Star-Black Hole Mergers: Detection of gravitational waves (GWs) from neutron star-black hole (NSBH)
standard sirens can provide local measurements of the Hubble constant ($H_0$),
regardless of the detection of an electromagnetic (EM) counterpart: The
presence of matter terms in GWs breaks the degeneracy between mass parameters
and redshift, allowing simultaneous measurement of both the luminosity distance
and redshift. Although the tidally disrupted NSBH systems can have EM emission,
the detection prospects of an EM counterpart will be limited to $z < 0.8$ in
the optical, in the era of the next generation GW detectors. However, the
distinctive merger morphology and the high redshift detectability of
tidally-disrupted NSBH makes them promising standard siren candidates for this
method. Using recent constraints on the equation-of-state of NSs from
multi-messenger observations of NICER and LIGO/Virgo/KAGRA, we show the
prospects of measuring $H_{0}$ solely from GW observation of NSBH systems,
achievable by Einstein Telescope (ET) and Cosmic Explorer (CE) detectors. We
first analyze individual events to quantify the effect of high-frequency ($\ge$
500 Hz) tidal distortions on the inference of NS tidal deformability parameter
($\Lambda$) and hence on $H_0$. We find that disruptive mergers can constrain
$\Lambda$ up to $\mathcal{O}(60\%)$ more precisely than non-disruptive ones.
However, this precision is not sufficient to place stringent constraints on the
$H_0$ for individual events. By performing Bayesian analysis on different sets
of simulated NSBH data (up to $N=100$ events, corresponding to a timescale from
several hours to a day observation) in the ET+CE detectors, we find that NSBH
systems enable unbiased 4\% - 13\% precision on the estimate of $H_0$ (68\%
credible interval). This is a similar measurement precision found in studies
analyzing populations of NSBH mergers with EM counterparts in the LVKC O5 era. |
Diffuse radio emission from non-Planck galaxy clusters in the LoTSS-DR2
fields: The presence of large-scale magnetic fields and ultra-relativistic electrons
in the intra-cluster medium (ICM) is confirmed through the detection of diffuse
radio synchrotron sources, so-called radio halos and relics. Due to their
steep-spectrum nature, these sources are rarely detected at frequencies above a
few GHz, especially in low-mass systems. The aim of this study is to discover
and characterise diffuse radio sources in low-mass galaxy clusters in order to
understand their origin and their scaling with host cluster properties. We
searched for cluster-scale radio emission from low-mass galaxy clusters in the
Low Frequency Array (LOFAR) Two-metre Sky Survey - Data Release 2 (LoTSS-DR2)
fields. We made use of existing optical (Abell, DESI, WHL) and X-ray (comPRASS,
MCXC) catalogues. The LoTSS-DR2 data were processed further to improve the
quality of the images that are used to detect and characterize diffuse sources.
We have detected diffuse radio emission in 28 galaxy clusters. The number of
confirmed (candidates) halos and relics are six (seven) and 10 (three),
respectively. Among these, 11 halos and 10 relics, including candidates, are
newly discovered by LOFAR. Beside these, five diffuse sources are detected in
tailed radio galaxies and are probably associated with mergers during the
formation of the host clusters. We are unable to classify other 13 diffuse
sources. We compare our newly detected, diffuse sources to known sources by
placing them on the scaling relation between the radio power and the mass of
the host clusters. | Planck 2013 Results. XXIV. Constraints on primordial non-Gaussianity: The Planck nominal mission cosmic microwave background (CMB) maps yield
unprecedented constraints on primordial non-Gaussianity (NG). Using three
optimal bispectrum estimators, separable template-fitting (KSW), binned, and
modal, we obtain consistent values for the primordial local, equilateral, and
orthogonal bispectrum amplitudes, quoting as our final result fNL^local=
2.7+/-5.8, fNL^equil= -42+/-75, and fNL^ortho= -25+\-39 (68% CL statistical).
NG is detected in the data; using skew-C_l statistics we find a nonzero
bispectrum from residual point sources, and the ISW-lensing bispectrum at a
level expected in the LambdaCDM scenario. The results are based on
comprehensive cross-validation of these estimators on Gaussian and non-Gaussian
simulations, are stable across component separation techniques, pass an
extensive suite of tests, and are confirmed by skew-C_l, wavelet bispectrum and
Minkowski functional estimators. Beyond estimates of individual shape
amplitudes, we present model-independent, 3-dimensional reconstructions of the
Planck CMB bispectrum and thus derive constraints on early-Universe scenarios
that generate primordial NG, including general single-field models of
inflation, excited initial states (non-Bunch-Davies vacua), and
directionally-dependent vector models. We provide an initial survey of
scale-dependent feature and resonance models. These results bound both general
single-field and multi-field model parameter ranges, such as the speed of
sound, c_s \geq 0.02 (95% CL), in an effective field theory parametrization,
and the curvaton decay fraction r_D \geq 0.15 (95% CL). The Planck data
significantly limit the viable parameter space of the ekpyrotic/cyclic
scenarios. The amplitude of the 4-point function in the local model tauNL <
2800 (95% CL). These constraints represent the highest precision tests to date
of physical mechanisms for the origin of cosmic structure. |
The Berry phase in inflationary cosmology: We derive an analogue of the Berry phase associated with inflationary
cosmological perturbations of quantum mechanical origin by obtaining the
corresponding wavefunction. We have further shown that cosmological Berry phase
can be completely envisioned through the observable parameters, viz. spectral
indices. Finally, physical significance of this phase is discussed from the
point of view of theoretical and observational aspects with some possible
consequences of this quantity in inflationary cosmology. | Could the Cosmological Recombination Spectrum Help Us Understand
Annihilating Dark Matter?: In this paper we explore the potential effects of DM annihilations on the
cosmological recombination spectrum. With this example we want to demonstrate
that the cosmological recombination spectrum in principle is sensitive to
details related to possible extra energy release during recombination. We
restrict ourselves to DM models which produce a negligible primordial
distortion of the CMB energy spectrum. However, since during the epoch of
cosmological recombination a large fraction of the deposited energy can
directly go into ionizations and excitations of neutral atoms, both the
cosmological recombination spectrum and ionization history can still be
affected significantly. We compute the modifications to the cosmological
recombination spectrum using our multi-level HI and HeI recombination code,
showing that additional photons are created due to uncompensated loops of
transitions which are induced by DM annihilations. As we illustrate here, the
results depend on the detailed branching of the deposited energy into heating,
ionizations and excitations. This dependence in principle should allow us to
shed light on the nature of the underlying annihilating DM model (or more
generally speaking, the mechanism leading to energy injection) when measuring
the cosmological recombination spectrum. However, for current upper limits on
the potential DM annihilation rate during recombination the cosmological
recombination spectrum is only affected at the level of a few percent.
Nevertheless, we argue here that the cosmological recombination spectrum would
provide another independent and very direct way of checking for the presence of
sources of extra ionizing or exciting photons at high redshifts. This would
open an new window to possible (non-standard) processes occurring (abridged) |
First Detection of Cosmic Microwave Background Lensing and
Lyman-α Forest Bispectrum: We present the first detection of a correlation between the Lyman-$\alpha$
forest and cosmic microwave background (CMB) lensing. For each Lyman-$\alpha$
forest in SDSS-III/BOSS DR12, we correlate the one-dimensional power spectrum
with the CMB lensing convergence on the same line of sight from Planck. This
measurement constitutes a position-dependent power spectrum, or a squeezed
bispectrum, and quantifies the non-linear response of the Lyman-$\alpha$ forest
power spectrum to a large-scale overdensity. The signal is measured at
5~$\sigma$ and is consistent with the $\Lambda$CDM expectation. We measure the
linear bias of the Lyman-$\alpha$ forest with respect to the dark matter
distribution, and constrain a combination of non-linear terms including the
non-linear bias. This new observable provides a consistency check for the
Lyman-$\alpha$ forest as a large-scale structure probe and tests our
understanding of the relation between intergalactic gas and dark matter. In the
future, it could be used to test hydrodynamical simulations and calibrate the
relation between the Lyman-$\alpha$ forest and dark matter. | Newcomers and suburbanites can drive the evolution of the size-stellar
mass relation of early type galaxies in galaxy clusters: At fixed stellar mass $M_*$, the effective radius $R_{\rm e}$ of massive
satellite early-type galaxies (ETGs) in galaxy clusters is, on average, larger
at lower redshift. We study theoretically this size evolution using the
state-of-the-art cosmological simulation IllustrisTNG100: we sampled $75$
simulated satellite ETGs at redshift $z=0$ with $M_* \ge 10^{10.4} M_{\odot}$
belonging to the two most massive ($\approx 10^{14.6} M_{\odot} $) haloes of
the simulation. We traced back in time the two clusters' main progenitors and
we selected their satellite ETGs at $z>0$ with the same criterion adopted at
$z=0$. The $R_{\rm e}-M_*$ relation of the simulated cluster satellite ETGs,
which is robustly measured out to $z=0.85$, evolves similarly to the observed
relation over the redshift range $0\lesssim z \lesssim 0.85$. In the simulation
the main drivers of this evolution are the acquisition of new galaxies
("newcomers") by the clusters and the transformation of member galaxies located
at large clustercentric distance ("suburbanites") at $z=0.85$, which end up
being massive satellite ETGs at $z=0$. Though several physical processes
contribute to change the population of satellite ETGs in the considered
redshift interval, the shape of the stellar mass function of the simulated
cluster ETGs is not significantly different at $z=0.85$ and at $z=0$,
consistent with observations. |
Primordial Magnetic Helicity from Stochastic Electric Currents: We study the possibility that primordial magnetic fields generated in the
transition between inflation and reheating posses magnetic helicity, $H_M$. The
fields are induced by stochastic currents of scalar charged particles created
during the mentioned transition. We estimate the rms value of the induced
magnetic helicity by computing different four-point SQED Feynman diagrams. For
any considered volume, the magnetic flux across its boundaries is in principle
non null, which means that the magnetic helicity in those regions is gauge
dependent. We use the prescription given by Berger and Field and interpret our
result as the difference between two magnetic configurations that coincide in
the exterior volume. In this case the magnetic helicity gives only the number
of magnetic links inside the considered volume. We calculate a concrete value
of $H_M$ for large scales and analyze the distribution of magnetic defects as a
function of the scale. Those defects correspond to regular as well as random
fields in the considered volume. We find that the fractal dimension of the
distribution of topological defects is $D = 1/2$. We also study if the regular
fields induced on large scales are helical, finding that they are and that the
associated number of magnetic defects is independent of the scale. In this case
the fractal dimension is $D=0$. We finally estimate the intensity of fields
induced at the horizon scale of reheating, and evolve them until the decoupling
of matter and radiation under the hypothesis of inverse cascade of magnetic
helicity. The resulting intensity is high enough and the coherence length long
enough to have an impact on the subsequent process of structure formation. | NGC 1300 Dynamics: II. The response models: We study the stellar response in a spectrum of potentials describing the
barred spiral galaxy NGC 1300. These potentials have been presented in a
previous paper and correspond to three different assumptions as regards the
geometry of the galaxy. For each potential we consider a wide range of
$\Omega_p$ pattern speed values. Our goal is to discover the geometries and the
$\Omega_p$ supporting specific morphological features of NGC 1300. For this
purpose we use the method of response models. In order to compare the images of
NGC 1300 with the density maps of our models, we define a new index which is a
generalization of the Hausdorff distance. This index helps us to find out
quantitatively which cases reproduce specific features of NGC 1300 in an
objective way. Furthermore, we construct alternative models following a
Schwarzschild type technique. By this method we vary the weights of the various
energy levels, and thus the orbital contribution of each energy, in order to
minimize the differences between the response density and that deduced from the
surface density of the galaxy, under certain assumptions. We find that the
models corresponding to $\Omega_p\approx16$\ksk and $\Omega_p\approx22$\ksk are
able to reproduce efficiently certain morphological features of NGC 1300, with
each one having its advantages and drawbacks. |
Forecast cosmological constraints from the number counts of
Gravitational Waves events: We present a forecast for the upcoming Einstein Telescope (ET) interferometer
with two new methods to infer cosmological parameters. We consider the emission
of Gravitational Waves (GWs) from compact binary coalescences, whose
electromagnetic counterpart is missing, namely Dark Sirens events. Most of the
methods used to infer cosmological information from GW observations rely on the
availability of a redshift measurement, usually obtained with the help of
external data, such as galaxy catalogues used to identify the most likely
galaxy to host the emission of the observed GWs. Instead, our approach is based
only on the GW survey itself and exploits the information on the distance of
the GW rather than on its redshift. Since a large dataset spanning the whole
distance interval is expected to fully represent the distribution, we applied
our methods to the expected ET's far-reaching measuring capabilities. We
simulate a dataset of observations with ET using the package
$\texttt{darksirens}$, assuming an underlying $\Lambda$CDM cosmology, and
including the possibility to choose between three possible Star Formation Rate
density (SFR) models, also accounting for possible population III stars
(PopIII). We test two independent statistical methods: one based on a
likelihood approach on the theoretical expectation of observed events, and
another applying the $\textit{cut-and-count method}$, a simpler method to
compare the observed number of events with the predicted counts. Both methods
are consistent in their final results, and also show the potential to
distinguish an incorrect SFR model from the data, but not the presence of a
possible PopIII. Concerning the cosmological parameters, we find instead that
ET observations by themselves would suffer from strong degeneracies, but have
the potential to significantly contribute to parameter estimation if used in
synergy with other surveys. | Multifrequency VLBA study of the blazar S5 0716+714 during the active
state in 2004 II. Large-scale jet kinematics and the comparison of the
different methods of VLBI data imaging as applied to kinematic studies of AGN: We study the jet kinematics of the blazar S5 0716+714 during its active state
in 2003-2004 with multi-epoch VLBI observations. Aims. We present a kinematic
analysis of the large-scale (0-12 mas) jet of 0716+714, based on the results of
six epochs of VLBA monitoring at 5 GHz. Additionally, we compare kinematic
results obtained with two imaging methods based on different deconvolution
algorithms. The blazar 0716+714 has a diffuse large-scale jet and a very faint
bright compact core. Experiments with simulated data showed that the
conventional data reduction procedure based on the CLEAN deconvolution
algorithm does not perform well in restoring this type of structure. This might
be the reason why previous kinematic studies of this source yielded ambiguous
results. In order to obtain accurate kinematics of this source, we
independently applied two imaging techniques to the raw data: the conventional
method, based on difference mapping, which uses CLEAN deconvolution, and the
generalized maximum entropy method (GMEM) realized in the VLBImager package
developed at the Pulkovo Observatory in Russia. The results of both methods
give us a consistent kinematic scenario: the large-scale jet of 0716+714 is
diffuse and stationary. Differences between the inner (0-1 mas) and outer (1-12
mas) regions of the jet in brightness and velocity of the components could be
explained by the bending of the jet, which causes the angle between the jet
direction and the line of sight to change from ~5 deg to ~11 deg. For the
source 0716+714 both methods worked at the limit of their capability. |
The Atacama Cosmology Telescope: likelihood for small-scale CMB data: The Atacama Cosmology Telescope has measured the angular power spectra of
microwave fluctuations to arcminute scales at frequencies of 148 and 218 GHz,
from three seasons of data. At small scales the fluctuations in the primordial
Cosmic Microwave Background (CMB) become increasingly obscured by extragalactic
foregounds and secondary CMB signals. We present results from a nine-parameter
model describing these secondary effects, including the thermal and kinematic
Sunyaev-Zel'dovich (tSZ and kSZ) power; the clustered and Poisson-like power
from Cosmic Infrared Background (CIB) sources, and their frequency scaling; the
tSZ-CIB correlation coefficient; the extragalactic radio source power; and
thermal dust emission from Galactic cirrus in two different regions of the sky.
In order to extract cosmological parameters, we describe a likelihood function
for the ACT data, fitting this model to the multi-frequency spectra in the
multipole range 500<ell<10000. We extend the likelihood to include spectra from
the South Pole Telescope at frequencies of 95, 150, and 220 GHz. Accounting for
different radio source levels and Galactic cirrus emission, the same model
provides an excellent fit to both datasets simultaneously, with chi2/dof=
675/697 for ACT, and 96/107 for SPT. We then use the multi-frequency likelihood
to estimate the CMB power spectrum from ACT in bandpowers, marginalizing over
the secondary parameters. This provides a simplified `CMB-only' likelihood in
the range 500<ell<3500 for use in cosmological parameter estimation. | Cosmological significance of the early bright galaxies observed with
JWST: The recent discovery of objects with redshift $z>10$ with the help of James
Webb Space Telescope (JWST) poses serious challenges to the $\Lambda$CDM
cosmological model, which has been in vogue for some time now. The new data
indicate that galaxy formation must have taken place much earlier than expected
in this model. Another viable class of cosmological models is that of the
so-called coasting models, in which the scale factor of the universe varies
proportionately with time. In these models, the universe at redshift $z=12$ has
ample time ($\sim 1070$ Myrs) for galaxy formation. The earliest such model is
the one proposed by E.A. Milne, based on his `kinematic relativity', but it is
considered unrealistic for not treating gravity as relevant at cosmological
scales. A closed version of an eternal coasting FLRW model was proposed by the
present authors even before SNe Ia data began to pour in. Subsequently we
developed a more general model of the same class, which is valid for all the
three possible geometries, with open, closed or flat spatial sections. In the
nonrelativistic era, this model makes the falsifiable prediction that the ratio
of matter density to dark energy density is 2. This avoids the cosmic
coincidence problem. Moreover, this eternal coasting model allows room for
creation of matter from dark energy, that may speed up galaxy and structure
formation at the early epochs, as implied by the JWST data. The paper also
attempts to review some similar coasting models, but emphasizes the eternal
coasting cosmology as the most probable candidate model capable of explaining
the presence of high redshift galaxies discovered by JWST. |
Measurements of Nuclear Reactions that Create and Destroy Li and Be
during BBN: I review measurements of the most important reactions involved in the
creation and destruction of Li and Be during big bang nucleosynthesis (BBN) as
well as their uncertainties and the relative contributions they make to the
uncertainty in the primordial $^7$Li abundance ($^7$Li/H). Examining the
sensitivity of calculated $^7$Li/H to these reactions as predicted by different
BBN codes I find no significant differences. I compare my calculation of
primordial $^7$Li/H to some recently published values and conclude that in the
absence of a major undetected experimental blunder, nuclear physics
uncertainties cannot account for the cosmological Li problem. With an estimated
13% uncertainty in the calculated abundance, the discrepancy with observation
amounts to some $4.6\sigma$. | Galaxy pairs in the Sloan Digital Sky Survey - VIII: The observational
properties of post-merger galaxies: In order to investigate the effects of galaxy mergers throughout the
interaction sequence, we present a study of 10,800 galaxies in close pairs and
a smaller sample of 97 post-mergers identified in the Sloan Digital Sky Survey.
We find that the average central star formation rate (SFR) enhancement (x 3.5)
and the fraction of starbursts (20 per cent) peak in the post-merger sample.
The post-mergers also show a stronger deficit in gas phase metallicity than the
closest pairs, being more metal-poor than their control by -0.09 dex. Combined
with the observed trends in SFR and the timescales predicted in merger
simulations, we estimate that the post-mergers in our sample have undergone
coalescence within the last few hundred Myr. In contrast with the incidence of
star-forming galaxies, the frequency of active galactic nuclei (AGN) peaks in
the post-mergers, outnumbering AGN in the control sample by a factor of 3.75.
Moreover, amongst the galaxies that host an AGN, the black hole accretion rates
in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in
the control sample. These results are consistent with a picture in which star
formation is initiated early on in the encounter, with AGN activity peaking
post-coalescence. |
Probing the first galaxies with the SKA: Observations of anisotropies in the brightness temperature of the 21 cm line
of neutral hydrogen from the period before reionization would shed light on the
dawn of the first stars and galaxies. In this paper, we use large-scale
semi-numerical simulations to analyse the imprint on the 21 cm signal of
spatial fluctuations in the Lyman-alpha flux arising from the clustering of the
first galaxies. We show that an experiment such as the Square Kilometer Array
(SKA) can probe this signal at the onset of reionization, giving us important
information about the UV emission spectra of the first stars and characterizing
their host galaxies. SKA-pathfinders with ~ 10% of the full collecting area
should be capable of making a statistical detection of the 21 cm power spectrum
at redshifts z < 20 (corresponding to frequencies $\nu$ > 67 MHz). We then show
that the SKA should be able to measure the three dimensional power spectrum as
a function of the angle with the line of sight and discuss the use of the
redshift space distortions as a way to separate out the different components of
the 21 cm power spectrum. We demonstrate that, at least on large scales where
the Lyman-alpha fluctuations are linear, they can be used as a model
independent way to extract the power spectra due to these Lyman-alpha
fluctuations. | Suitable Initial Conditions for Newtonian Simulations with Massive
Neutrinos: Initial conditions for cosmological N-body simulations are usually calculated
by rescaling the present day linear power spectrum obtained from an
Einstein-Boltzmann solver to the initial time employing the scale-independent
matter growth function. For the baseline Lambda-CDM model, this has been shown
to be consistent with General Relativity (GR) even in the presence of
relativistic species such as photons. We show that this approach is not
feasible in cosmologies with massive neutrinos and present an alternative
method employing the Newtonian motion gauge framework. |
Prospect for cosmological parameter estimation using future Hubble
parameter measurements: We constrain cosmological parameters using only Hubble parameter data and
quantify the impact of future Hubble parameter measurements on parameter
estimation for the most typical dark energy models. We first constrain
cosmological parameters using 52 current Hubble parameter data including the
Hubble constant measurement from the Hubble Space Telescope. Then we simulate
the baryon acoustic oscillation signals from WFIRST (Wide-Field Infrared Survey
Telescope) covering the redshift range of $z\in [0.5, 2]$ and the redshift
drift data from E-ELT (European Extremely Large Telescope) in the redshift
range of $z\in [2,5]$. It is shown that solely using the current Hubble
parameter data could give fairly good constraints on cosmological parameters.
Compared to the current Hubble parameter data, with the WFIRST observation the
$H(z)$ constraints on dark energy would be improved slightly, while with the
E-ELT observation the $H(z)$ constraints on dark energy is enormously improved. | Addressing the Hubble tension with cosmic chronometers: Twenty years after the discovery that the expansion of the Universe is
accelerating, a new finding is now challenging our understanding of the cosmos.
Recent studies have shown that the Hubble constant, the speed of expansion
measured today, provides values in significant tension when measured from the
Cosmic Microwave Background in the primordial Universe or from Cepheids and
Supernovae Type Ia in the local Universe. Whether this tension is hinting
towards new physics or some issue in the measurements, is still under debate;
but it is clearly calling for new independent cosmological probes to provide
additional pieces of evidence to solve this puzzle. This chapter introduces the
method of cosmic chronometers, a new emerging cosmological probe that can
provide cosmology-independent estimates of the Universe's expansion history.
This method is based on the fact that the expansion rate of the Universe can be
directly derived from measuring how much the Universe has changed in age
between two different redshifts, i.e. by estimating the slope of the
age--redshift relation. First, the main ingredients of the method will be
discussed, presenting the main equations involved and how to estimate from the
observables the needed quantities. After, it will be presented how to reliably
select a sample of tracers to map the age evolution of the Universe coherently.
Next, different methods to robustly measure the differential age of a
population, the fundamental quantity involved in the method, will be reviewed.
Finally, the main measurements obtained will be presented, providing forecasts
for future surveys and discussing how these data can provide useful feedback to
address the Hubble tension. |
Filling in the Gaps in the 4.85 GHz Sky: We describe a 4.85 GHz survey of bright, flat-spectrum radio sources
conducted with the Effelsberg 100 m telescope in an attempt to improve the
completeness of existing surveys, such as CRATES. We report the results of
these observations and of follow-up 8.4 GHz observations with the VLA of a
subset of the sample. We comment on the connection to the WMAP point source
catalog and on the survey's effectiveness at supplementing the CRATES sky
coverage. | Sample variance in photometric redshift calibration: cosmological biases
and survey requirements: We use N-body/photometric galaxy simulations to examine the impact of sample
variance of spectroscopic redshift samples on the accuracy of photometric
redshift (photo-z) determination and calibration of photo-z errors. We estimate
the biases in the cosmological parameter constraints from weak lensing and
derive requirements on the spectroscopic follow-up for three different photo-z
algorithms chosen to broadly span the range of algorithms available. We find
that sample variance is much more relevant for the photo-z error calibration
than for photo-z training, implying that follow-up requirements are similar for
different algorithms. We demonstrate that the spectroscopic sample can be used
for training of photo-zs and error calibration without incurring additional
bias in the cosmological parameters. We provide a guide for observing proposals
for the spectroscopic follow-up to ensure that redshift calibration biases do
not dominate the cosmological parameter error budget. For example, assuming
optimistically (pessimistically) that the weak lensing shear measurements from
the Dark Energy Survey could obtain 1-sigma constraints on the dark energy
equation of state w of 0.035 (0.055), implies a follow-up requirement of 150
(40) patches of sky with a telescope such as Magellan, assuming a 1/8^2 deg
effective field of view and 400 galaxies per patch. Assuming (optimistically) a
VVDS-like spectroscopic completeness with purely random failures, this could be
accomplished with about 75 (20) nights of observation. For more realistic
assumptions regarding spectroscopic completeness, or in the presence of other
sources of systematics not considered here, further degradations to dark energy
constraints are possible. We test several approaches for reducing the
requirements. Abridged |
Cosmic filaments in galaxy cluster outskirts: quantifying finding
filaments in redshift space: Inferring line-of-sight distances from redshifts in and around galaxy
clusters is complicated by peculiar velocities, a phenomenon known as the
"Fingers of God" (FoG). This presents a significant challenge for finding
filaments in large observational data sets as these artificial elongations can
be wrongly identified as cosmic web filaments by extraction algorithms.
Upcoming targeted wide-field spectroscopic surveys of galaxy clusters and their
infall regions such as the WEAVE Wide-Field Cluster Survey motivate our
investigation of the impact of FoG on finding filaments connected to clusters.
Using zoom-in resimulations of 324 massive galaxy clusters and their outskirts
from The ThreeHundred project, we test methods typically applied to large-scale
spectroscopic data sets. This paper describes our investigation of whether a
statistical compression of the FoG of cluster centres and galaxy groups can
lead to correct filament extractions in the cluster outskirts. We find that
within 5 R200 (~15 Mpc/h) statistically correcting for FoG elongations of
virialized regions does not achieve reliable filament networks compared to
reference filament networks based on true positions. This is due to the complex
flowing motions of galaxies towards filaments in addition to the cluster
infall, which overwhelm the signal of the filaments relative to the volume we
probe. While information from spectroscopic redshifts is still important to
isolate the cluster regions, and thereby reduce background and foreground
interlopers, we expect future spectroscopic surveys of galaxy cluster outskirts
to rely on 2D positions of galaxies to extract cosmic filaments. | An expanded M_bh-sigma diagram, and a new calibration of active galactic
nuclei masses: [Abridged] We present an updated and improved M_bh-sigma diagram containing
64 galaxies for which M_bh measurements (not just upper limits) are available.
Due to new and increased black hole masses at the high-mass end, and a better
representation of barred galaxies at the low-mass end, the "classical" (all
morphological type) M_bh-sigma relation for predicting black hole masses is
log(M_bh/M_Sun) = (5.13+/-0.34)log[sigma/200] + (8.13+/-0.05), with an rms
scatter of 0.43 dex. Modifying the regression analysis to correct for a
hitherto over-looked sample bias in which black holes with masses <10^6 M_Sun
are not (yet) detectable, the relation steepens further to give log(M_bh/M_Sun)
= (5.95+/-0.44)log[sigma/200] + (8.15+/-0.06). We have also updated the
"barless" and "elliptical-only" M_bh-sigma relations introduced by Graham and
Hu in 2008 due to the offset nature of barred/disc galaxies. These relations
have a total scatter as low as 0.34 dex and currently define the upper envelope
of points in the M_bh-sigma diagram. These relations also have a slope
consistent with the value 5, in agreement with the prediction by Silk & Rees
based on feedback from massive black holes in bulges built by
monolithic-collapse.
Using updated virial products and velocity dispersions from 28 active
galactic nuclei, we determine that the optimal scaling factor f - which brings
their virial products in line with the 64 directly measured black hole masses -
is 2.8^{+0.7}_{-0.5}. This is roughly half the value reported by Onken et al.
and Woo et al., and consequently halves the mass estimates of most
high-redshift quasars. We have explored the results after separating the
samples into barred and non-barred galaxies, and we have also developed a
preliminary corrective term to the velocity dispersion based on bar dynamics. |
Turbulence-induced deviation between baryonic field and dark matter
field in the spatial distribution of the Universe: The cosmic baryonic fluid at low redshifts is similar to a fully developed
turbulence. In this work, we use simulation samples produced by the hybrid
cosmological hydrodynamical/N-body code, to investigate on what scale the
deviation of spatial distributions between baryons and dark matter is caused by
turbulence. For this purpose, we do not include the physical processes such as
star formation, supernovae (SNe) and active galactic nucleus (AGN) feedback
into our code, so that the effect of turbulence heating for IGM can be
exhibited to the most extent. By computing cross-correlation functions $r_m(k)$
for the density field and $r_v(k)$ for the velocity field of both baryons and
dark matter, we find that deviations between the two matter components for both
density field and velocity field, as expected, are scale-dependent. That is,
the deviations are the most significant at small scales and gradually diminish
on larger and larger scales. Also, the deviations are time-dependent, i.e. they
become larger and larger with increasing cosmic time. The most emphasized
result is that the spatial deviations between baryons and dark matter revealed
by velocity field are more significant than that by density field. At z = 0, at
the 1% level of deviation, the deviation scale is about 3.7 $h^{-1}$Mpc for
density field, while as large as 23 $h^{-1}$Mpc for velocity field, a scale
that falls within the weakly non-linear regime for the structure formation
paradigm. Our results indicate that the effect of turbulence heating is indeed
comparable to that of these processes such as SN and AGN feedback. | The disappearance of a narrow Mg II absorption system in quasar SDSS
J165501.31+260517.4: In this letter, we present for the first time, the discovery of the
disappearance of a narrow Mg II $\lambda\lambda2796,2803$ absorption system
from the spectra of quasar SDSS J165501.31+260517.4 ($z_{\rm e}=1.8671$). This
absorber is located at $z_{\rm abs} =1.7877$, and has a velocity offset of
$8,423\rm ~km~s^{-1}$ with respect to the quasar. According to the velocity
offset and the line variability, this narrow Mg II $\lambda\lambda2796,2803$
absorption system is likely intrinsic to the quasar. Since the corresponding UV
continuum emission and the absorption lines of another narrow Mg II
$\lambda\lambda2796,2803$ absorption system at $z_{\rm abs}=1.8656$ are very
stable, we think that the disappearance of the absorption system is unlikely to
be caused by the change in ionization of absorption gas. Instead, it likely
arises from the motion of the absorption gas across the line of sight. |
The Extended GMRT Radio Halo Survey II: Further results and analysis of
the full sample: The intra-cluster medium contains cosmic rays and magnetic fields that are
manifested through the large scale synchrotron sources, termed as radio halos,
relics and mini-halos. The Extended Giant Metrewave Radio Telescope (GMRT)
Radio Halo Survey (EGRHS) is an extension of the GMRT Radio Halo Survey (GRHS)
designed to search for radio halos using GMRT 610/235 MHz observations. The
GRHS+EGRHS consists of 64 clusters in the redshift range 0.2 -- 0.4 that have
an X-ray luminosity larger than 5x10^44 erg/s in the 0.1 -- 2.4 keV band and
with declinations > -31 deg in the REFLEX and eBCS X-ray cluster catalogues. In
this second paper in the series, GMRT 610/235 MHz data on the last batch of 11
galaxy clusters and the statistical analysis of the full sample are presented.
A new mini-halo in RXJ2129.6+0005 and candidate diffuse sources in Z5247, A2552
and Z1953 are discovered. A unique feature of this survey are the upper limits
on the detections of 1 Mpc sized radio halos; 4 new are presented here making a
total of 31 in the survey. Of the sample, 58 clusters that have adequately
sensitive radio information were used to obtain the most accurate occurrence
fractions so far. The occurrence of radio halos in our X-ray selected sample is
~22%, that of mini-halos is 13% and that of relics is ~5%. The radio power -
X-ray luminosity diagrams for the radio halos and mini-halos with the
detections and upper limits are presented. The morphological estimators namely,
centroid shift (w), concentration parameter (c) and power ratios (P_3/P_0)
derived from the Chandra X-ray images are used as proxies for the dynamical
states of the GRHS+EGRHS clusters. The clusters with radio halos and mini-halos
occupy distinct quadrants in the c-w, c-P_3/P_0 and w - P_3/P_0 planes,
corresponding to the more and less morphological disturbance, respectively. The
non-detections span both the quadrants. | Observable induced gravitational waves from an early matter phase: Assuming that inflation is succeeded by a phase of matter domination, which
corresponds to a low temperature of reheating $T_r<10^9\rm{GeV}$, we evaluate
the spectra of gravitational waves induced in the post-inflationary universe.
We work with models of hilltop-inflation with an enhanced primordial scalar
spectrum on small scales, which can potentially lead to the formation of
primordial black holes. We find that a lower reheat temperature leads to the
production of gravitational waves with energy densities within the ranges of
both space and earth based gravitational wave detectors. |
Cold dark matter particle mass and properties and axion-like dark
radiation in $Λ$CDM cosmology: A theory is presented for the mass, size, lifetime, and other properties of
cold dark matter particles within the $\Lambda$CDM cosmology. Using Illustris
simulations, we demonstrate the mass and energy cascade in self-gravitating
collisionless dark matter that facilitates the hierarchical structure formation
of dark matter haloes. A scale-independent rate of energy cascade
$\varepsilon_u \approx 10^{-7}m^2/s^3$ can be identified. Energy cascade leads
to universal scaling laws on relevant scales $r$, i.e. a two-thirds law for
kinetic energy ($v_r^2\propto \varepsilon_u^{2/3}r^{2/3}$) and a four-thirds
law for halo density ($\rho_r\propto\varepsilon_u^{2/3}G^{-1}r^{-4/3}$), where
$G$ is the gravitational constant. Both scaling laws can be confirmed by
simulations and galaxy rotation curves. For cold and collisionless dark matter
interacting via gravity only and because of the scale independence of
$\varepsilon_u$, these scaling laws can be extended down to the smallest scale
where quantum effect is important. Combined with the uncertainty principle and
virial theorem on that scale, we estimate a mass
$m_X=(\varepsilon_u\hbar^5G^{-4})^{1/9}=10^{12}$GeV, size
$l_X=(\varepsilon_u^{-1}\hbar G)^{1/3}=10^{-13}$m, and lifetime
$\tau_X=c^2/\varepsilon_u=10^{16}$years for cold dark matter particles. Here
$\hbar$ is Planck constant, and $c$ is the speed of light. The energy scale
$E_X=(\varepsilon_u^5\hbar^7G^{-2})^{1/9}=10^{-9}$eV strongly suggests a dark
radiation to provide a viable mechanism for energy dissipation. The axion-like
dark radiation should be produced at an early time
$t_X=(\varepsilon_u^{-5}\hbar^2G^2)^{1/9}=10^{-6}$s (quark epoch) with a mass
of $10^{-9}$eV, a GUT scale decay constant $10^{16}$GeV, an axion-photon
coupling constant $10^{-18}$GeV$^{-1}$, and energy density 1$\%$ of the photon
energy in CMB. Potential extension to self-interacting dark matter is also
presented. | Cosmology and fundamental physics with the Euclid satellite: Euclid is a European Space Agency medium class mission selected for launch in
2019 within the Cosmic Vision 2015-2025 programme. The main goal of Euclid is
to understand the origin of the accelerated expansion of the Universe. Euclid
will explore the expansion history of the Universe and the evolution of cosmic
structures by measuring shapes and redshifts of galaxies as well as the
distribution of clusters of galaxies over a large fraction of the sky. Although
the main driver for Euclid is the nature of dark energy, Euclid science covers
a vast range of topics, from cosmology to galaxy evolution to planetary
research. In this review we focus on cosmology and fundamental physics, with a
strong emphasis on science beyond the current standard models. We discuss five
broad topics: dark energy and modified gravity, dark matter, initial
conditions, basic assumptions and questions of methodology in the data
analysis. This review has been planned and carried out within Euclid's Theory
Working Group and is meant to provide a guide to the scientific themes that
will underlie the activity of the group during the preparation of the Euclid
mission. |
Cosmology and fundamental physics with the ELT-ANDES spectrograph: State-of-the-art 19th century spectroscopy led to the discovery of quantum
mechanics, and 20th century spectroscopy led to the confirmation of quantum
electrodynamics. State-of-the-art 21st century astrophysical spectrographs,
especially ANDES at ESO's ELT, have another opportunity to play a key role in
the search for, and characterization of, the new physics which is known to be
out there, waiting to be discovered. We rely on detailed simulations and
forecast techniques to discuss four important examples of this point: big bang
nucleosynthesis, the evolution of the cosmic microwave background temperature,
tests of the universality of physical laws, and a real-time model-independent
mapping of the expansion history of the universe (also known as the redshift
drift). The last two are among the flagship science drivers for the ELT. We
also highlight what is required for the ESO community to be able to play a
meaningful role in 2030s fundamental cosmology and show that, even if ANDES
only provides null results, such `minimum guaranteed science' will be in the
form of constraints on key cosmological paradigms: these are independent from,
and can be competitive with, those obtained from traditional cosmological
probes. | Stochastic gravitational wave background from accreting primordial black
hole binaries during early inspiral stage: We investigate the stochastic gravitational wave background produced by
primordial black hole binaries during their early inspiral stage while
accreting high-density radiation surrounding them in the early universe. We
first show that the gravitational wave amplitude produced from a primordial
black hole binary has correction terms because of the rapid rate of increase in
masses of the primordial black holes. These correction terms arise due to
non-vanishing first and second time derivatives of the masses and their
contribution to the overall second time derivative of quadrupole moment tensor.
We find that some of these correction terms are not only significant in
comparison with the main term but even dominant over the main term for certain
ranges of time in the early Universe. The significance of these correction
terms is not only for the gravitational wave amplitude produced from an
individual PBH-binary, but persists for the overall stochastic gravitational
wave background produced from them. We show that the spectral density produced
from such accreting primordial black hole binaries lie within the detectability
range of some present and future gravitational wave detectors. |
Dark matter dominated dwarf disc galaxy Segue 1: Several observations reveal that dwarf galaxy Segue 1 has a dark matter (DM)
halo at least ~ 200 times more massive than its visible baryon mass of only ~
103 solar masses. The baryon mass is dominated by stars with perhaps an
interstellar gas mass of < 13 solar masses. Regarding Segue 1 as a dwarf disc
galaxy by its morphological appearance of long stretch, we invoke the dynamic
model of Xiang-Gruess, Lou & Duschl (XLD) to estimate its physical parameters
for possible equilibria with and without an isopedically magnetized gas disc.
We estimate the range of DM mass and compare it with available observational
inferences. Due to the relatively high stellar velocity dispersion compared to
the stellar surface mass density, we find that a massive DM halo would be
necessary to sustain disc equilibria. The required DM halo mass agrees grossly
with observational inferences so far. For an isopedic magnetic field in a gas
disc, the ratio f between the DM and baryon potentials depends strongly on the
magnetic field strength. Therefore, a massive DM halo is needed to counteract
either the strong stellar velocity dispersion and rotation of the stellar disc
or the magnetic Lorentz force in the gas disc. By the radial force balances,
the DM halo mass increases for faster disc rotation. | Polarized CMB power spectrum estimation using the pure
pseudo-cross-spectrum approach: We extend the pure pseudo-power-spectrum formalism proposed recently in the
context of the Cosmic Microwave Background polarized power spectra estimation
by Smith (2006) to incorporate cross-spectra computed for multiple maps of the
same sky area. We present an implementation of such a technique, paying
particular attention to a calculation of the relevant window functions and
mixing (mode-coupling) matrices. We discuss the relevance and treatment of the
residual $E/B$ leakage for a number of considered sky apodizations as well as
compromises and assumptions involved in an optimization of the resulting power
spectrum uncertainty. In particular, we investigate the importance of a
pixelization scheme, patch geometry, and sky signal priors used in apodization
optimization procedures. In addition, we also present results derived for more
realistic sky scans as motivated by the proposed balloon borne experiment EBEX.
We conclude that the presented formalism thanks to its speed and efficiency can
provide an interesting alternative to the CMB polarized power spectra
estimators based on the optimal methods at least on angular scales smaller than
~10 degrees. In this regime, we find that it is capable of suppressing the
total variance of the estimated $B$-mode spectrum to within a factor of ~2 of
the variance due to only the sampling and noise uncertainty of the B-modes
alone, as derived from the Fisher matrix approach. |
A Suzaku Search for Non-thermal Emission at Hard X-ray Energies in the
Coma Cluster: The brightest cluster radio halo known resides in the Coma cluster of
galaxies. The relativistic electrons producing this diffuse synchrotron
emission should also produce inverse Compton emission that becomes competitive
with thermal emission from the ICM at hard X-ray energies. Thus far, claimed
detections of this emission in Coma are controversial (Fusco-Femiano et al.
2004; Rossetti & Molendi 2004). We present a Suzaku HXD-PIN observation of the
Coma cluster in order to nail down its non-thermal hard X-ray content. The
contribution of thermal emission to the HXD-PIN spectrum is constrained by
simultaneously fitting thermal and non-thermal models to it and a spatially
equivalent spectrum derived from an XMM-Newton mosaic of the Coma field
(Schuecker et al. 2004). We fail to find statistically significant evidence for
non-thermal emission in the spectra, which are better described by only a
single or multi-temperature model for the ICM. Including systematic
uncertainties, we derive a 90% upper limit on the flux of non-thermal emission
of 6.0x10^-12 erg/s/cm^2 (20-80 keV, for photon index of 2.0), which implies a
lower limit on the cluster-averaged magnetic field of B>0.15 microG. Our flux
upper limit is 2.5x lower than the detected non-thermal flux from RXTE
(Rephaeli & Gruber 2002) and BeppoSAX (Fusco-Femiano et al. 2004). However, if
the non-thermal hard X-ray emission in Coma is more spatially extended than the
observed radio halo, the Suzaku HXD-PIN may miss some fraction of the emission.
A detailed investigation indicates that ~50-67% of the emission might go
undetected, which could make our limit consistent with these detections. The
thermal interpretation of the hard Coma spectrum is consistent with recent
analyses of INTEGRAL (Eckert et al. 2007) and Swift (Ajello et al. 2009) data. | Stress testing the dark energy equation of state imprint on supernova
data: This work determines the degree to which a standard Lambda-CDM analysis based
on type Ia supernovae can identify deviations from a cosmological constant in
the form of a redshift-dependent dark energy equation of state w(z). We
introduce and apply a novel random curve generator to simulate instances of
w(z) from constraint families with increasing distinction from a cosmological
constant. After producing a series of mock catalogs of binned type Ia
supernovae corresponding to each w(z) curve, we perform a standard Lambda-CDM
analysis to estimate the corresponding posterior densities of the absolute
magnitude of type Ia supernovae, the present-day matter density, and the
equation of state parameter. Using the Kullback-Leibler divergence between
posterior densities as a difference measure, we demonstrate that a standard
type Ia supernova cosmology analysis has limited sensitivity to extensive
redshift dependencies of the dark energy equation of state. In addition, we
report that larger redshift-dependent departures from a cosmological constant
do not necessarily manifest easier-detectable incompatibilities with the
Lambda-CDM model. Our results suggest that physics beyond the standard model
may simply be hidden in plain sight. |
3.3 μm PAH observations of the central kiloparsecs of Centaurus A: Aims. The aim of this work is to further investigate the nature of PAH
excitation and emission especially in the context of tracing star formation in
a variety of extragalactic environments. Here we turn our attention to the
energetic environment of the closest AGN in our sample, Centaurus A. Methods.
Using ISAAC on the ESO VLT UT1 (Antu) we have made high spatial resolution 3.3
{\mu}m imaging observations of the central kiloparsec of CenA. These
observations have been compared with star formation tracers in the near- and
mid-infrared, as well as with mid-infrared tracers of nuclear activity.
Results. The nucleus is not devoid of PAH emission, implying that the PAH
particles are not destroyed in the nucleus as might be expected for such a
harsh environment. However, we see the feature to continuum ratio decrease
towards the AGN. As well, the 3.3 {\mu}m PAH feature emission generally traces
the sites of star formation in Cen A, but in detail there are spatial offsets,
consistent with an earlier study of the starburst galaxies NGC 253 and NGC
1808. However, the feature-to-continuum ratio does not drop at the positions of
star formation as was previously seen in that earlier study. The cause for this
difference remains uncertain. Finally, our data reveal possible evidence for a
nearly face-on, circular or spiral, dust structure surrounding the nucleus. | Confirmation of the compactness of a z=1.91 quiescent galaxy with Hubble
Space Telescope's Wide Field Camera 3: We present very deep Wide Field Camera 3 (WFC3) photometry of a massive,
compact galaxy located in the Hubble Ultra Deep Field. This quiescent galaxy
has a spectroscopic redshift z=1.91 and has been identified as an extremely
compact galaxy by Daddi et al. 2005. We use new H-F160W imaging data obtained
with Hubble Space Telescope/WFC3 to measure the deconvolved surface brightness
profile to H = 28 mag arcsec**-2. We find that the surface brightness profile
is well approximated by an n=3.7 Sersic profile. Our deconvolved profile is
constructed by a new technique which corrects the best-fit Sersic profile with
the residual of the fit to the observed image. This allows for galaxy profiles
which deviate from a Sersic profile. We determine the effective radius of this
galaxy: r_e=0.42 +- 0.14 kpc in the observed H-F160W-band. We show that this
result is robust to deviations from the Sersic model used in the fit. We test
the sensitivity of our analysis to faint "wings" in the profile using simulated
galaxy images consisting of a bright compact component and a faint extended
component. We find that due to the combination of the WFC3 imaging depth and
our method's sensitivity to extended faint emission we can accurately trace the
intrinsic surface brightness profile, and that we can therefore confidently
rule out the existence of a faint extended envelope around the observed galaxy
down to our surface brightness limit. These results confirm that the galaxy
lies a factor of 10 off from the local mass-size relation. |
The Imprint of Warm Dark Matter on the Cosmological 21-cm Signal: We investigate the effects of warm dark matter (WDM) on the cosmic 21-cm
signal. If dark matter exists as WDM instead of cold dark matter (CDM), its
non-negligible velocities can inhibit the formation of low-mass halos that
normally form first in CDM models, therefore delaying star-formation. The
absence of early sources delays the build-up of UV and X-ray backgrounds that
affect the 21-cm radiation signal produced by neutral hydrogen. With use of the
21CMFAST, code, we demonstrate that the pre-reionization 21-cm signal can be
changed significantly in WDM models with a free-streaming length equivalent to
that of a thermal relic with mass mx of up to ~10-20 keV. In such a WDM
cosmology, the 21-cm signal traces the growth of more massive halos, resulting
in a delay of the 21-cm absorption signature and followed by accelerated X-ray
heating. CDM models where astrophysical sources have a suppressed
photon-production efficiency can delay the 21-cm signal as well, although its
subsequent evolution is not as rapid as compared to WDM. This motivates using
the gradient of the global 21-cm signal to differentiate between some CDM and
WDM models. Finally, we show that the degeneracy between the astrophysics and
mx can be broken with the 21-cm power spectrum, as WDM models should have a
bias-induced excess of power on large scales. This boost in power should be
detectable with current interferometers for models with mx < 3 keV, while next
generation instruments will easily be able to measure this difference for all
relevant WDM models. | Multi-tasking the growth of cosmological structures: Next-generation large-scale structure surveys will deliver a significant
increase in the precision of growth data, allowing us to use `agnostic' methods
to study the evolution of perturbations without the assumption of a
cosmological model. We focus on a particular machine learning tool, Gaussian
processes, to reconstruct the growth rate $f$, the root mean square of matter
fluctuations $\sigma_8$, and their product $f\sigma_8$. We apply this method to
simulated data, representing the precision of upcoming Stage IV galaxy surveys.
We extend the standard single-task approach to a multi-task approach that
reconstructs the three functions simultaneously, thereby taking into account
their inter-dependence. We find that this multi-task approach outperforms the
single-task approach for future surveys and will allow us to detect departures
from the standard model with higher significance. By contrast, the limited
sensitivity of current data severely hinders the use of agnostic methods, since
the Gaussian processes parameters need to be fine tuned in order to obtain
robust reconstructions. |
ELUCID VII: Using Constrained Hydro Simulations to Explore the Gas
Component of the Cosmic Web: Using reconstructed initial conditions in the SDSS survey volume, we carry
out constrained hydrodynamic simulations in three regions representing
different types of the cosmic web: the Coma cluster of galaxies; the SDSS great
wall; and a large low-density region at $z\sim 0.05$. These simulations, which
include star formation and stellar feedback but no AGN formation and feedback,
are used to investigate the properties and evolution of intergalactic and
intra-cluster media. About half of the warm-hot intergalactic gas is associated
with filaments in the local cosmic web. Gas in the outskirts of massive
filaments and halos can be heated significantly by accretion shocks generated
by mergers of filaments and halos, respectively, and there is a tight
correlation between gas temperature and the strength of the local tidal field.
The simulations also predict some discontinuities associated with shock fronts
and contact edges, which can be tested using observations of the thermal SZ
effect and X-rays. A large fraction of the sky is covered by Ly$\alpha$ and OVI
absorption systems, and most of the OVI systems and low-column density HI
systems are associated with filaments in the cosmic web. The constrained
simulations, which follow the formation and heating history of the observed
cosmic web, provide an important avenue to interpret observational data. With
full information about the origin and location of the cosmic gas to be
observed, such simulations can also be used to develop observational
strategies. | The Zurich Environmental Study (ZENS) of Galaxies in Groups along the
Cosmic Web. II. Galaxy Structural Measurements and the Concentration of
Morphologically Classified Satellites in Diverse Environments: We present structural measurements for the galaxies in the 0.05<z<0.0585
groups of the Zurich Environmental Study, aimed at establishing how galaxy
properties depend on four environmental parameters: group halo mass M_GROUP,
group-centric distance R/R_200, ranking into central or satellite, and
large-scale structure density delta_LSS. Global galaxy structure is quantified
both parametrically and non-parametrically. We correct all these measurements
for observational biases due to PSF blurring and surface brightness effects as
a function of galaxy size, magnitude, steepness of light profile and
ellipticity. Structural parameters are derived also for bulges, disks and bars.
We use the galaxy bulge-to-total ratios (B/T), together with the calibrated
non-parametric structural estimators, to implement a quantitative morphological
classification that maximizes purity in the resulting morphological samples. We
investigate how the concentration C of satellite galaxies depends on galaxy
mass for each Hubble type, and on M_GROUP, R/R_200 and delta_LSS. At galaxy
masses M>10^10 M_sun, the concentration of disk satellites increases with
increasing stellar mass, separately within each morphological bin of B/T. The
known increase in concentration with stellar mass for disk satellites is thus
due, at least in part, to an increase in galaxy central stellar density at
constant B/T. The correlation between concentration and galaxy stellar mass
becomes progressively steeper for later morphological types. The concentration
of disk satellites shows a barely significant dependence on delta_LSS or
R/R_200. The strongest environmental effect is found with group mass for
M>10^10 M_sun disk-dominated satellites, which are ~10% more concentrated in
high mass groups than in lower mass groups. |
The mass assembly history of black holes in the Universe: We track the growth and evolution of high redshift seed black holes over
cosmic time. This population of massive, initial black hole seeds form at these
early epochs from the direct collapse of pre-galactic gas discs. Populating
dark matter halos with seeds formed in this fashion, we follow their mass
assembly history to the present time using a Monte-Carlo merger tree approach.
Using this formalism, we predict the black hole mass function at the present
time; the integrated mass density of black holes in the Universe; the
luminosity function of accreting black holes as a function of redshift and the
scatter in observed, local Mbh{\sigma}s relation. Signatures of these massive
seed models appear predominantly at the low mass end of the present day black
hole mass function. In fact, our prediction of the shape of the Mbh{\sigma}s
relation at the low mass end and increased scatter has recently been
corroborated by observations. These models predict that low surface brightness,
bulge-less galaxies with large discs are least likely to be sites for the
formation of massive seed black holes at high redshifts. The efficiency of seed
formation at high redshifts also has a direct influence on the black hole
occupation fraction in galaxies at z = 0. This effect is more pronounced for
low mass galaxies today as we predict the existence of a population of low mass
galaxies that do not host nuclear black holes. This is the key discriminant
between the models studied here and the Population-III remnant seed model. | 21-cm power spectrum and ionization bias as a probe of long-mode
modulated non Gaussian sky: The observed hemispherical power asymmetry in cosmic microwave background
radiation can be explained by long wavelength mode (long-mode) modulation. In
this work we study the prospect of the detection of this effect in the angular
power spectrum of 21-cm brightness temperature. For this task, we study the
effect of the neutral Hydrogen distribution on the angular power spectrum. This
is done by formulating the bias parameter of ionized fraction to the underlying
matter distribution. We also discuss the possibility that the long mode
modulation is companied with a primordial non-Gaussianity of local type. In
this case, we obtain the angular power spectrum with two effects of primordial
non-Gaussianity and long mode modulation. Finally, we show that the primordial
non-Gaussianity enhances the long mode modulated power of 21-cm signal via the
non-Gaussian scale-dependent bias up to four orders of magnitude. {Accordingly,
the observation of 21-cm signal with upcoming surveys such as the Square
Kilometer Array (SKA) is probably capable of detecting hemispherical power
asymmetry in the context of the long mode modulation. |
The angular power spectrum of gravitational-wave transient sources as a
probe of the large-scale structure: We present a new, simulation-based inference method to compute the angular
power spectrum of the distribution of foreground gravitational-wave transient
events. As a first application of this method, we use the binary black hole
mergers observed during the LIGO, Virgo, and KAGRA third observation run to
test the spatial distribution of these sources. We find no evidence for
anisotropy in their angular distribution. We discuss further applications of
this method to investigate other gravitational-wave source populations and
their correlations to the cosmological large-scale structure. | Dynamics and Constraints of the Massive Gravitons Dark Matter Flat
Cosmologies: We discuss the dynamics of the universe within the framework of Massive
Graviton Dark Matter scenario (MGCDM) in which gravitons are geometrically
treated as massive particles. In this modified gravity theory, the main effect
of the gravitons is to alter the density evolution of the cold dark matter
component in such a way that the Universe evolves to an accelerating expanding
regime, as presently observed. Tight constraints on the main cosmological
parameters of the MGCDM model are derived by performing a joint likelihood
analysis involving the recent supernovae type Ia data, the Cosmic Microwave
Background (CMB) shift parameter and the Baryonic Acoustic Oscillations (BAOs)
as traced by the Sloan Digital Sky Survey (SDSS) red luminous galaxies. The
linear evolution of small density fluctuations is also analysed in detail. It
is found that the growth factor of the MGCDM model is slightly different
($\sim1-4%$) from the one provided by the conventional flat $\Lambda$CDM
cosmology. The growth rate of clustering predicted by MGCDM and $\Lambda$CDM
models are confronted to the observations and the corresponding best fit values
of the growth index ($\gamma$) are also determined. By using the expectations
of realistic future X-ray and Sunyaev-Zeldovich cluster surveys we derive the
dark-matter halo mass function and the corresponding redshift distribution of
cluster-size halos for the MGCDM model. Finally, we also show that the Hubble
flow differences between the MGCDM and the $\Lambda$CDM models provide a halo
redshift distribution departing significantly from the ones predicted by other
DE models. These results suggest that the MGCDM model can observationally be
distinguished from $\Lambda$CDM and also from a large number of dark energy
models recently proposed in the literature. |
Dark Matter Velocity Spectroscopy: Dark matter decays or annihilations that produce line-like spectra may be
smoking-gun signals. However, even such distinctive signatures can be mimicked
by astrophysical or instrumental causes. We show that velocity spectroscopy-the
measurement of energy shifts induced by relative motion of source and
observer-can separate these three causes with minimal theoretical
uncertainties. The principal obstacle has been energy resolution, but upcoming
experiments will reach the required 0.1% level. As an example, we show that the
imminent Astro-H mission can use Milky Way observations to separate possible
causes of the 3.5-keV line. We discuss other applications. | Dark Energy Survey Year 3 Results: Three-Point Shear Correlations and
Mass Aperture Moments: We present high signal-to-noise measurements of three-point shear
correlations and the third moment of the mass aperture statistic using the
first 3 years of data from the Dark Energy Survey. We additionally obtain the
first measurements of the configuration and scale dependence of the four
three-point shear correlations which carry cosmological information. With the
third-order mass aperture statistic, we present tomographic measurements over
angular scales of 4 to 60 arcminutes with a combined statistical significance
of 15.0$\sigma$. Using the tomographic information and measuring also the
second-order mass aperture, we additionally obtain a skewness parameter and its
redshift evolution. We find that the amplitudes and scale-dependence of these
shear 3pt functions are in qualitative agreement with measurements in a mock
galaxy catalog based on N-body simulations, indicating promise for including
them in future cosmological analyses. We validate our measurements by showing
that B-modes, parity-violating contributions and PSF modeling uncertainties are
negligible, and determine that the measured signals are likely to be of
astrophysical and gravitational origin. |
The Baryon Content of Cosmic Structures: We make an inventory of the baryonic and gravitating mass in structures
ranging from the smallest galaxies to rich clusters of galaxies. We find that
the fraction of baryons converted to stars reaches a maximum between M500 =
1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright
galaxies in groups. The fraction of baryons detected in all forms deviates
monotonically from the cosmic baryon fraction as a function of mass. On the
largest scales of clusters, most of the expected baryons are detected, while in
the smallest dwarf galaxies, fewer than 1% are detected. Where these missing
baryons reside is unclear. | Probing Cosmology beyond $Λ$CDM using the SKA: The cosmological principle states that the Universe is statistically
homogeneous and isotropic at large distance scales. There currently exist many
observations which indicate a departure from this principle. It has been shown
that many of these observations can be explained by invoking superhorizon
cosmological perturbations and may be consistent with the Big Bang paradigm.
Remarkably, these modes simultaneously explain the observed Hubble tension,
i.e., the discrepancy between the direct and indirect measurements of the
Hubble parameter. We propose several tests of the cosmological principle using
SKA. In particular, we can reliably extract the signal of dipole anisotropy in
the distribution of radio galaxies. The superhorizon perturbations also predict
a significant redshift dependence of the dipole signal which can be nicely
tested by the study of signals of reionization and the dark ages using SKA. We
also propose to study the alignment of radio galaxy axes as well as their
integrated polarization vectors over distance scales ranging from a few Mpc to
Gpc. We discuss data analysis techniques that can reliably extract these
signals from data. |
Utility of observational Hubble parameter data on dark energy evolution: Aiming at exploring the nature of dark energy, we use thirty-six
observational Hubble parameter data (OHD) in the redshift range $0 \leqslant z
\leqslant 2.36$ to make a cosmological model-independent test of the two-point
$Omh^2(z_{2};z_{1})$ diagnostic. In $\Lambda$CDM, we have $Omh^2 \equiv
\Omega_{m}h^2$, where $\Omega_{m}$ is the matter density parameter at present.
We bin all the OHD into four data points to mitigate the observational
contaminations. By comparing with the value of $\Omega_{m}h^2$ which is
constrained tightly by the Planck observations, our results show that in all
six testing pairs of $Omh^2$ there are two testing pairs are consistent with
$\Lambda$CDM at $1\sigma$ confidence level (CL), whereas for another two of
them $\Lambda$CDM can only be accommodated at $2\sigma$ CL. Particularly, for
remaining two pairs, $\Lambda$CDM is not compatible even at $2\sigma$ CL.
Therefore it is reasonable that although deviations from $\Lambda$CDM exist for
some pairs, cautiously, we cannot rule out the validity of $\Lambda$CDM. We
further apply two methods to derive the value of Hubble constant $H_0$
utilizing the two-point $Omh^2(z_{2};z_{1})$ diagnostic. We obtain $H_0 =
71.23\pm1.54$ ${\mathrm{km \ s^{-1} \ Mpc^{-1}}}$ from inverse variance
weighted $Omh^2$ value (method (I)) and $H_0 = 69.37\pm1.59$ ${\mathrm{km \
s^{-1} \ Mpc^{-1}}}$ that the $Omh^2$ value originates from Planck measurement
(method (II)), both at $1\sigma$ CL. Finally, we explore how the error in OHD
propagate into $w(z)$ at certain redshift during the reconstruction of $w(z)$.
We argue that the current precision on OHD is not sufficient small to ensure
the reconstruction of $w(z)$ in an acceptable error range, especially at the
low redshift | The evolving slope of the stellar mass function at 0.6 <= z < 4.5 from
deep WFC3 data: We used Early Release Science (ERS) observations taken with the Wide Field
Camera 3 (WFC3) in the GOODS-S field to study the galaxy stellar mass function
(GSMF) at 0.6<=z<4.5. Deep WFC3 near-IR data (for Y as faint as 27.3, J and H
as faint as 27.4 AB mag at 5 sigma), as well as deep Ks (as faint as 25.5 at 5
sigma) Hawk-I band data, provide an exquisite data set with which determine in
an unprecedented way the low-mass end of the GSMF, allowing an accurate probe
of masses as low as M~7.6 10^9 Msun at z~3. Although the area used is
relatively small (~33 arcmin^2), we found generally good agreement with
previous studies on the entire mass range. Our results show that the slope of
the faint-end increases with redshift, from alpha=-1.44+/-0.03 at z~0.8 to
alpha=-1.86+/-0.16 at z~3, although indications exist that it does not steepen
further between z~3 and z~4. This result is insensitive to any uncertainty in
the M* parameter. The steepness of the GSMF faint-end solves the well-known
disagreement between the stellar mass density (SMD) and the integrated star
formation history at z>2. However, we confirm the that there appears to be an
excess of integrated star formation with respect to the SMD at z<2, by a factor
of ~2-3. Our comparison of the observations with theoretical predictions shows
that the models forecast a greater abundance of low mass galaxies, at least up
to z~3, as well as a dearth of massive galaxies at z~4 with respect to the
data, and that the predicted SMD is generally overestimated at z<~2. |
HeII Ly$α$ Transmission Spikes and Absorption Troughs in Eight
High-resolution Spectra Probing the End of HeII Reionization: We present statistics of HeII Lya transmission spikes and large-scale
absorption troughs using archival high-resolution ($R=\lambda /\Delta \lambda
\simeq 12,500$-$18,000$) far-UV spectra of eight HeII-transparent quasars
obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope.
The sample covers the redshift range 2.5<z<3.8, thereby probing the rapidly
evolving HeII absorption at the end of the HeII reionization epoch. The
measured lengths of the troughs decrease dramatically from L>100cMpc at z>3 to
L~30cMpc at z~2.7, signaling a significant progression of HeII reionization at
these redshifts. Furthermore, unexpectedly long L~65cMpc troughs detected at
z~2.9 suggest that the UV background fluctuates at larger scales than predicted
by current models. By comparing the measured incidence of transmission spikes
to predictions from forward-modeled mock spectra created from the outputs of a
(146cMpc)^3 optically thin Nyx hydrodynamical simulation employing different UV
background models, we infer the redshift evolution of the HeII photoionization
rate $\Gamma_\mathrm{He\,II}(z)$. The photoionization rate decreases with
increasing redshift from $\simeq 4.6\times 10^{-15}\mathrm{\,s^{-1}}$ at z~2.6
to $\simeq 1.2 \times 10^{-15}\mathrm{\,s^{-1}}$ at z~3.2, in agreement with
previous inferences from the HeII effective optical depth, and following
expected trends of current models of a fluctuating HeII-ionizing background. | Systematics in the Gamma Ray Bursts Hubble diagram: Thanks to their enormous energy release which allows to detect them up to
very high redshift, Gamma Rays Bursts (GRBs) have recently attracted a lot of
interest to probe the Hubble diagram (HD) deep into the matter dominated era
and hence complement Type Ia Supernoave (SNeIa). However, lacking a local GRBs
sample, calibrating the scaling relations proposed as an equivalent to the
Phillips law to standardize GRBs is not an easy task because of the need to
estimate the GRBs luminosity distance in a model independent way. We consider
here three different calibration methods based on the use of a fiducial
$\Lambda$CDM model, on cosmographic parameters and on the local regression on
SNeIa. We find that the calibration coefficients and the intrinsic scatter do
not significantly depend on the adopted calibration procedure. We then
investigate the evolution of these parameters with the redshift finding no
statistically motivated improvement in the likelihood so that the no evolution
assumption is actually a well founded working hypothesis. Under this
assumption, we then consider possible systematics effects on the HDs introduced
by the calibration method, the averaging procedure and the homogeneity of the
sample arguing against any significant bias. We nevertheless stress that a
larger GRBs sample with smaller uncertainties is needed to definitely conclude
that the different systematics considered here have indeed a negligible impact
on the HDs thus strengthening the use of GRBs as cosmological tools. |
Searching for the Dark Force with 21-cm Spectrum in Light of EDGES: The EDGES Collaboration has recently announced the detection of the 21-cm
spectrum with an absorption profile centred at $78$ megahertz, of which the
depth is deeper than that expected by the standard cosmological paradigm. To
enrich the heating process of baryons due to scattering with dark matter during
dark ages, we in this Letter explore the possibility of extra heat transfer
between dark sector compositions and their observational signatures on the
21-cm cosmological spectrum. By parameterizing interaction models of the dark
Universe, we find that the observational constraint on the parameter space of
dark matter can be slightly relaxed but the discrepancy with the commonly
predicted parameter space of weakly interacting massive particles remains. Our
analyses also reveal that the interaction between dark compositions may leave
observational signatures on the 21-cm spectrum during dark ages and thus would
become detectable in the forthcoming 21-cm cosmology. | Small scale clustering of BOSS galaxies: dependence on luminosity,
color, age, stellar mass, specific star formation rate and other properties: We measure and analyze galaxy clustering and the dependence on luminosity,
color, age, stellar mass and specific star formation rate using Baryon
Oscillation Spectroscopic Survey (BOSS) galaxies at $0.48<z<0.62$. We fit the
monopole and quadrupole moments of the two-point correlation function (2PCF)
and its projection on scales of $0.1$ -- $60.2h^{-1}$Mpc, after having split
the catalog in a variety of ways. We find that the clustering dependence is
consistent with previous well-established results showing the broad trends
expected: For example, that brighter, redder, older, more massive and quenched
galaxies are more strongly clustered. We also investigate the dependence on
additional parameters previously derived from stellar population synthesis
model fits to the spectra. We find that galaxy clustering depends on look-back
formation time at a low level, while it has little dependence on metallicity.
To understand the physics behind these trends, we fit the clustering with a
simulation-based emulator to simultaneously model cosmology and galaxy bias
using a Halo Occupation Distribution framework. After marginalizing parameters
determining the background cosmology, galaxy bias, and a scaling parameter to
decouple halo velocity field, we find that the growth rate of large scale
structure as determined by the redshift-space distortions is consistent with
previous analysis using the full sample, and we do not find evidence that
cosmological constraints depend systematically on galaxy selection. This
demonstrates that cosmological inference using small scale clustering
measurements is robust to changes in the catalog selection. |
A method to determine the evolution history of the mean neutral Hydrogen
fraction: The light-cone (LC) effect imprints the cosmological evolution of the
redshifted 21-cm signal $T_{\rm b} ({\hat{\bf{n}}}, \nu)$ along the frequency
axis which is the line of sight (LoS) direction of an observer. The effect is
particularly pronounced during the Epoch of Reionization (EoR) when the mean
hydrogen neutral fraction ${\bar{x}_{\rm HI}}(\nu)$ falls rapidly as the
universe evolves. The multi-frequency angular power spectrum (MAPS) ${{\mathcal
C}_{\ell}}(\nu_1,\nu_2)$ quantifies the entire second-order statistics of
$T_{\rm b} ({\hat{\bf{n}}}, \nu)$ considering both the systematic variation
along $\nu$ due to the cosmological evolution and also the statistically
homogeneous and isotropic fluctuations along all the three spatial directions
encoded in ${\hat{\bf{n}}}$ and $\nu$. Here we propose a simple model where the
systematic frequency $(\nu_1,\nu_2)$ dependence of ${{\mathcal
C}_{\ell}}(\nu_1,\nu_2)$ arises entirely due to the evolution of ${\bar{x}_{\rm
HI}}(\nu)$. This provides a new method to observationally determine the
reionization history. Considering a LC simulation of the EoR 21-cm signal, we
use the diagonal elements $\nu_1=\nu_2$ of ${{\mathcal C}_{\ell}}(\nu_1,\nu_2)$
to validate our model. We demonstrate that it is possible to recover the
reionization history across the entire observational bandwidth provided we have
the value ${\bar{x}_{\rm HI}}$ at a single frequency as an external input. | Probing Cosmology with Dark Matter Halo Sparsity Using X-ray Cluster
Mass Measurements: We present a new cosmological probe for galaxy clusters, the halo sparsity.
This characterises halos in terms of the ratio of halo masses measured at two
different radii and carries cosmological information encoded in the halo mass
profile. Building upon the work of Balmes et al. (2014) we test the properties
of the sparsity using halo catalogs from a numerical N-body simulation of
($2.6$ Gpc/h)$^3$ volume with $4096^3$ particles. We show that at a given
redshift the average sparsity can be predicted from prior knowledge of the halo
mass function. This provides a quantitative framework to infer cosmological
parameter constraints using measurements of the sparsity of galaxy clusters. We
show this point by performing a likelihood analysis of synthetic datasets with
no systematics, from which we recover the input fiducial cosmology. We also
perform a preliminary analysis of potential systematic errors and provide an
estimate of the impact of baryonic effects on sparsity measurements. We
evaluate the sparsity for a sample of 104 clusters with hydrostatic masses from
X-ray observations and derive constraints on the cosmic matter density
$\Omega_m$ and the normalisation amplitude of density fluctuations at the $8$
Mpc h$^{-1}$ scale, $\sigma_8$. Assuming no systematics, we find
$\Omega_m=0.42\pm 0.17$ and $\sigma_8=0.80\pm 0.31$ at $1\sigma$, corresponding
to $S_8\equiv \sigma_8\sqrt{\Omega_m}=0.48\pm 0.11$. Future cluster surveys may
provide opportunities for precise measurements of the sparsity. A sample of a
few hundreds clusters with mass estimate errors at a few percent level can
provide competitive cosmological parameter constraints complementary to those
inferred from other cosmic probes. |
Submillimetre observations of X-ray active galactic nuclei in the
William Herschel Deep Field: We investigate the contribution made by active galactic nuclei (AGN) to the
high-redshift, luminous, submillimetre (submm) source population using deep (<
2 mJy/beam) Large Apex Bolometer Camera (LABOCA) 870 um observations within the
William Herschel Deep Field (WHDF). This submm data complements previously
obtained Chandra X-ray data of the field, from which AGN have been identified
with the aid of follow-up optical spectra. From the LABOCA data, we detect 11
submm sources (based on a detection threshold of 3.2 sigma) with estimated
fluxes of > 3 mJy/beam. Of the 11 identified submm sources, we find that 2
coincide with observed AGN and that, based on their hardness ratios, both of
these AGN appear to be heavily obscured. We perform a stacking of the submm
data around the AGN, which we group by estimated column density, and find that
only the obscured (N_H > 10^22 cm^2) AGN show significant associated submm
emission. These observations support the previous findings of Page et al and
Hill et al that obscured AGN preferentially show submm emission. Hill et al
have argued that, in this case, the contribution to the observed submm emission
(and thus the submm background) from AGN heating of the dust in these sources
may be higher than previously thought. | The Scale of Homogeneity in the $R_h=ct$ Universe: Studies of the Universe's transition to smoothness in the context of LCDM
have all pointed to a transition radius no larger than ~300 Mpc. These are
based on a broad array of tracers for the matter power spectrum, including
galaxies, clusters, quasars, the Ly-alpha forest and anisotropies in the cosmic
microwave background. It is therefore surprising, if not anomalous, to find
many structures extending out over scales as large as ~2 Gpc, roughly an order
of magnitude greater than expected. Such a disparity suggests that new physics
may be contributing to the formation of large-scale structure, warranting a
consideration of the alternative FLRW cosmology known as the $R_h=ct$ universe.
This model has successfully eliminated many other problems in LCDM. In this
paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a
function of distance, showing a transition to smoothness at ~2.2 Gpc, fully
accommodating all of the giant structures seen thus far. This outcome adds
further observational support for R_h=ct over the standard model. |
J16021+3326: New Multi-Frequency Observations of a Complex Source: We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly. | Planck 2013 results. XXII. Constraints on inflation: We analyse the implications of the Planck data for cosmic inflation. The
Planck nominal mission temperature anisotropy measurements, combined with the
WMAP large-angle polarization, constrain the scalar spectral index to $n_s =
0.9603 \pm 0.0073$, ruling out exact scale invariance at over 5 $\sigma$.
Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0.11
(95% CL). The Planck data thus shrink the space of allowed standard
inflationary models, preferring potentials with V" < 0. Exponential potential
models, the simplest hybrid inflationary models, and monomial potential models
of degree n > 2 do not provide a good fit to the data. Planck does not find
statistically significant running of the scalar spectral index, obtaining $d
n_s/d ln k = -0.0134 \pm 0.0090$. Several analyses dropping the slow-roll
approximation are carried out, including detailed model comparison and
inflationary potential reconstruction. We also investigate whether the
primordial power spectrum contains any features. We find that models with a
parameterized oscillatory feature improve the fit $\chi^2$ by ~ 10; however,
Bayesian evidence does not prefer these models. We constrain several
single-field inflation models with generalized Lagrangians by combining power
spectrum data with bounds on $f_\mathrm{NL}$ measured by Planck. The fractional
primordial contribution of CDM isocurvature modes in the curvaton and axion
scenarios has upper bounds of 0.25% or 3.9% (95% CL), respectively. In models
with arbitrarily correlated CDM or neutrino isocurvature modes, an
anticorrelation can improve $\chi^2$ by approximatively 4 as a result of
slightly lowering the theoretical prediction for the $\ell<40$ multipoles
relative to the higher multipoles. Nonetheless, the data are consistent with
adiabatic initial conditions. |
Integral Field Spectroscopy of 2.0<z<2.7 Sub-mm Galaxies; gas
morphologies and kinematics: We present two-dimensional, integral field spectroscopy covering the
rest-frame wavelengths of strong optical emission lines in nine sub-mm-luminous
galaxies (SMGs) at 2.0<z<2.7. The GEMINI-NIFS and VLT-SINFONI imaging
spectroscopy allows the mapping of the gas morphologies and dynamics within the
sources, and we measure an average Halpha velocity dispersion of
sigma=220+-80km/s and an average half light radius of r=3.7+-0.8kpc. The
average dynamical measure, V_obs/2sigma=0.9+-0.1 for the SMGs, is higher than
in more quiescent star-forming galaxies at the same redshift, highlighting a
difference in the dynamics of the two populations. The SMGs' far-infrared SFRs,
measured using Herschel-SPIRE far-infrared photometry, are on average
370+-90Mo/yr which is ~2 times higher than the extinction corrected SFRs of the
more quiescent star-forming galaxies. Six of the SMGs in our sample show strong
evidence for kinematically distinct multiple components with average velocity
offsets of 200+-100km/s and average projected spatial offsets of 8+-2kpc, which
we attribute to systems in the early stages of major mergers. Indeed all SMGs
are classified as mergers from a kinemetry analysis of the velocity and
dispersion field asymmetry. We bring together our sample with seven other SMGs
with IFU observations to describe the ionized gas morphologies and kinematics
in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the
SMG Halpha components with sub-halo offsets in the Millennium simulation
database we infer an average halo mass for SMGs of 13<log(M[h^-1Mo])<14.
Finally we explore the relationship between the velocity dispersion and star
formation intensity within the SMGs, finding the gas motions are consistent
with the Kennicutt-Schmidt law and a range of extinction corrections, although
might also be driven by the tidal torques from merging or even the star
formation itself. | Reionization process dependence of the ratio of CMB polarization power
spectra at low-$\ell$: We investigate how much the ratio of cosmic microwave background (CMB)
polarization power spectra $C^{BB}_\ell/C^{EE}_\ell$ at low-$\ell$ ($\ell
\lesssim 10$) depends on the process of reionization. Both such low-$\ell$
B-mode and E-mode polarization powers are dominantly produced by Thomson
scattering of CMB photons off the free electrons which are produced in the
process of reionization. Since the reionization should be finished until at
least the redshift $z \simeq 6$ and the low-$\ell$ polarization powers are
produced at late time, the ratio is rather insensitive by the ionization
process at higher redshifts, but it is sensitive to the value of optical
depth.The value of the ratio at $\ell=2$, however, is almost insensitive to the
reionization process including the value of optical depth, and the value is
approximately half of the value of tensor-to-scalar ratio. This fact can be
utilized for future determination of tensor-to-scalar ratio in spite of the
ambiguity due to cosmic variance. |
Remarkable Spectral Variability of PDS 456: We report on the highest to date signal-to-noise-ratio X-ray spectrum of the
luminous quasar PDS 456, as obtained during two XMM-Newton orbits in September
2007. The present spectrum is considerably different from several previous
X-ray spectra recorded for PDS 456 since 1998. The ultra-high-velocity outflow
seen as recently as February 2007 is not detected in absorption. Conversely, a
significant reflection component is detected. The reflection model suggests the
reflecting medium may be outflowing at a velocity v/c = -0.06 +/- 0.02. The
present spectrum is analyzed in the context of the previous ones in an attempt
to understand all spectra within the framework of a single model. We examine
whether an outflow with variable partial covering of the X-ray source along the
line of sight that also reflects the source from other lines of sight can
explain the dramatic variations in the broad-band spectral curvature of PDS
456. It is established that absorption plays a major role in shaping the
spectrum of other epochs, while the 2007 XMM-Newton spectrum is dominated by
reflection, and the coverage of the source by the putative outflow is small (<
20%). | Momentum power spectrum of SDSS galaxies by massE cosmic ruler: 2.1x
improvement in measure of growth rate: Peculiar motion of galaxies probes the structure growth in the Universe. In
this study we employ the galaxy stellar mass-binding energy (massE) relation
with only two nuisance parameters to build the largest peculiar-velocity (PV)
catalog to date, consisting of 229,890 ellipticals from the main galaxy sample
(MGS) of the Sloan Digital Sky Survey (SDSS). We quantify the distribution of
the massE-based distances in individual narrow redshift bins (dz=0.005), and
then estimate the PV of each galaxy based on its offset from the Gaussian mean
of the distribution. As demonstrated with the Uchuu-SDSS mock data, the derived
PV and momentum power spectra are insensitive to accurate calibration of the
massE relation itself, enabling measurements out to a redshift of 0.2, well
beyond the current limit of z=0.1 using other galaxy scaling laws. We then
measure the momentum power spectrum and demonstrate that it remains almost
unchanged if varying significantly the redshift bin size within which the
distance is measured, as well as the intercept and slope of the massE relation,
respectively. By fitting the spectra using the perturbation theory model with
four free parameters, f{\sigma}8 is constrained to f{\sigma}8
=0.459+0.068-0.069 over {\Delta}z=0.02-0.2, 0.416+0.074-0.076 over
{\Delta}z=0.02-0.1 and 0.526+0.133-0.143 over {\Delta}z=0.1-0.2. The error of
f{\sigma}8 is 2.1 times smaller than that by the redshift space distortion
(RSD) of the same sample. A Fisher-matrix forecast illustrates that the
constraint on f{\sigma}8 from the massE-based PV can potentially exceed that
from the stage-IV RSD in late universe (z<0.5). |
Measuring ISW with next-generation radio surveys: The late-time integrated Sachs-Wolfe (ISW) signal in the CMB temperature
anisotropies is an important probe of dark energy when it can be detected by
cross-correlation with large-scale structure surveys. Because of their huge sky
area, surveys in the radio are well-suited to ISW detection. We show that 21cm
intensity mapping and radio continuum surveys with the SKA in Phase~1 promise a
$\sim5\sigma$ detection if we use tomography, with a similar forecast for the
precursor EMU survey. In SKA Phase~2, the 21cm galaxy redshift survey and the
continuum survey could deliver a $\sim6\sigma$ detection. Our analysis of the
radio surveys aims for theoretical accuracy on large scales. Firstly, we
include all the effects on the radio surveys from observing on the past
lightcone: redshift-space distortions and lensing magnification can have a
significant impact on the ISW signal to noise ratio, while Doppler and other
relativistic distortions are not significant. Secondly, we use the full
information in the observable galaxy angular power spectra $C_\ell(z,z')$, by
avoiding the Limber approximation and by including all cross-correlations
between redshift bins in the covariance. Without these cross-bin correlations,
the ISW signal to noise ratio is biased. | Improved Tomographic Binning of 3x2pt Lens Samples: Neural Network
Classifiers and Optimal Bin Assignments: Large imaging surveys, such as the Legacy Survey of Space and Time, rely on
photometric redshifts and tomographic binning for 3x2pt analyses that combine
galaxy clustering and weak lensing. In this paper, we propose a method for
optimizing the tomographic binning choice for the lens sample of galaxies. We
divide the CosmoDC2 and Buzzard simulated galaxy catalogs into a training set
and an application set, where the training set is nonrepresentative in a
realistic way, and then estimate photometric redshifts for the application
sets. The galaxies are sorted into redshift bins covering equal intervals of
redshift or comoving distance, or with an equal number of galaxies in each bin,
and we consider a generalized extension of these approaches. We find that bins
of equal comoving distance produce the highest dark energy figure of merit of
the initial binning choices, but that the choice of bin edges can be further
optimized. We then train a neural network classifier to identify galaxies that
are either highly likely to have accurate photometric redshift estimates or
highly likely to be sorted into the correct redshift bin. The neural network
classifier is used to remove poor redshift estimates from the sample, and the
results are compared to the case when none of the sample is removed. We find
that the neural network classifiers are able to improve the figure of merit by
~13% and are able to recover ~25% of the loss in the figure of merit that
occurs when a nonrepresentative training sample is used. |
MASSIV: Mass Assembly Survey with SINFONI in VVDS. III. Evidence for
positive metallicity gradients in z~1.2 star-forming galaxies: A key open issue for galaxy evolution and formation models is the
understanding of the different mechanisms of galaxy assembly at various cosmic
epochs. The aim of this study is to derive the global and spatially-resolved
metal content in high-redshift galaxies. Using VLT/SINFONI IFU spectroscopy of
a first sample of 50 galaxies at z~1.2 in the MASSIV survey, we are able to
measure the Ha and [NII]6584 emission lines. Using the N2 ratio as a proxy for
oxygen abundance in the interstellar medium, we measure the metallicity of the
sample galaxies. We develop a tool to extract spectra in annular regions of
these galaxies, leading to a spatially-resolved estimate of the oxygen
abundance in each galaxy. We derive a metallicity gradient for 26 galaxies in
our sample and discover a significant fraction of galaxies with a "positive"
gradient. Using a simple chemical evolution model, we derive infall rates of
pristine gas onto the disks. Seven galaxies display a positive gradient at a
high confidence level. Four out of these are interacting and one is a chain
galaxy. We suggest that interactions might be responsible for shallowing and
even inverting the abundance gradient. We also identify two interesting
correlations in our sample: a) galaxies with higher gas velocity dispersion
have shallower/positive gradients; and b) metal-poor galaxies tend to show a
positive gradient whereas metal-rich ones tend to show a negative one. This
last observation can be explained by the infall of metal-poor gas into the
center of the disks. We address the question of the origin of this infall under
the influence of gas flows triggered by interactions and/or cold gas accretion. | Forecasting Cosmological Constraints from the Weak Lensing Magnification
of Type Ia Supernovae Measured by the Nancy Grace Roman Space Telescope: The weak lensing magnification of Type Ia Supernovae (SNe Ia) is sensitive to
the clustering of matter, and provides an independent cosmological probe
complementary to SN Ia distance measurements. The Nancy Grace Roman Space
Telescope is uniquely sensitive to this measurement as it can discover high
redshift SNe Ia and measure them with high precision. We present a methodology
for reconstructing the probability distribution of the weak lensing
magnification $\mu$ of SNe Ia, $p(\mu)$, from observational data, and using it
to constrain cosmological parameters. We find that the reconstructed $p(\mu)$
can be fitted accurately by a stretched Gaussian distribution, and used to
measure the variance of $\mu$, $\xi_\mu$, which can be compared to theoretical
predictions in a likelihood analysis. Applying our methodology to a set of
realistically simulated SNe Ia expected from the Roman Space Telescope, we find
that using the weak lensing magnification of the SNe Ia constrains a
combination of matter density $\Omega_m$ and matter clustering amplitude
$\sigma_8$. SN Ia distances alone lead to a better than 1\% measurement of
$\Omega_m$. The combination of SN Ia weak lensing magnification and distance
measurements result in a $\sim$ 10\% measurement on $\sigma_8$. The SNe Ia from
Roman will be powerful in constraining the cosmological model. |
Statistics of tidal and deformation eigenvalue fields in the primordial
Gaussian matter distribution: the two-dimensional case: We study the statistical properties of the eigenvalues of the primordial
tidal and deformation tensor for random Gaussian cosmic density fields. With
the tidal and deformation tensors, Hessians of the gravitational and velocity
potential, being Gaussian, the corresponding eigenvalue fields are distinctly
non-Gaussian. Following the extension of the Doroshkevich formula for the
joined distribution of eigenvalues to two-dimensional fields, we evaluate the
two- and three-point correlation functions of the eigenvalue fields. In
addition, we assess the number densities of singular points of the eigenvalue
fields and find their corresponding two- and three-point correlation functions.
The role of tidal forces and the resulting mass element deformation in
shaping the prominent anisotropic wall-like and filamentary components of the
cosmic web has since long been recognized based on the Zel'dovich
approximation. Less well-known is that the weblike spatial pattern is already
recognizable in the primordial tidal and deformation eigenvalue field, even
while the corresponding Gaussian density and the potential field appear merely
as a spatially incoherent and unstructured random field. Furthermore, against
the background of a full phase-space assessment of structure formation in the
Universe, the caustic skeleton theory entails a fully analytical framework for
the nonlinear evolution of the cosmic web. It describes the folding of the dark
matter sheet and the emerging caustic singularities, fully specified by the
deformation eigenvalues and eigenvectors. Finally, tidal tensor eigenvalues are
of central importance, and understanding their distribution is critical in
predicting the resulting rotation and orientation.
The current study applies to two-dimensional Gaussian random fields and will
be generalized to a three-dimensional analysis in an upcoming study. | Weak lensing by voids in modified lensing potentials: We study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies,
which are examples of theories of gravity that modify the lensing potential. We
find voids in the dark matter and halo density fields of N-body simulations and
compute their lensing signal analytically from the void density profiles, which
we show are well fit by a simple analytical formula. In the Cubic Galileon
model, the modifications to gravity inside voids are not screened and they
approximately double the size of the lensing effects compared to GR. The
difference is largely determined by the direct effects of the fifth force on
lensing and less so by the modified density profiles. For this model, we also
discuss the subtle impact on the force and lensing calculations caused by the
screening effects of haloes that exist in and around voids. In the Nonlocal
model, the impact of the modified density profiles and the direct modifications
to lensing are comparable, but they boost the lensing signal by only $\approx
10\%$, compared with that of GR. Overall, our results suggest that lensing by
voids is a promising tool to test models of gravity that modify lensing. |
Stability of Cool Cores During Galaxy Cluster Growth: A Joint
$Chandra$/SPT Analysis of 67 Galaxy Clusters Along a Common Evolutionary
Track Spanning 9 Gyr: We present the results of a joint analysis of $Chandra$ X-ray and South Pole
Telescope (SPT) SZ observations targeting the first sample of galaxy clusters
at $0.3 < z < 1.3$, selected to be the progenitors of well-studied nearby
clusters based on their expected accretion rate. We develop a new procedure in
order to tackle the analysis challenge that is estimating the intracluster
medium (ICM) properties of low-mass and high-redshift clusters with ${\sim}150$
X-ray counts. One of the dominant sources of uncertainty on the ICM density
profile estimated with a standard X-ray analysis with such shallow X-ray data
is due to the systematic uncertainty associated with the ICM temperature
obtained through the analysis of the background-dominated X-ray spectrum. We
show that we can decrease the uncertainty on the density profile by a factor
${\sim}5$ with a joint deprojection of the X-ray surface brightness profile
measured by $Chandra$ and the SZ integrated Compton parameter available in the
SPT cluster catalog. We apply this technique to the whole sample of 67 clusters
in order to track the evolution of the ICM core density during cluster growth.
We confirm that the evolution of the gas density profile is well modeled by the
combination of a fixed core and a self-similarly evolving non-cool core
profile. We show that the fraction of cool-cores in this sample is remarkably
stable with redshift although clusters have gained a factor ${\sim}4$ in total
mass over the past ${\sim}9$ Gyr. This new sample combined with our new
X-ray/SZ analysis procedure and extensive multi-wavelength data will allow us
to address fundamental shortcomings in our current understanding of cluster
formation and evolution at $z > 1$. | Detecting edges in the X-ray surface brightness of galaxy clusters: The effects of many physical processes in the intracluster medium of galaxy
clusters imprint themselves in X-ray surface brightness images. It is therefore
important to choose optimal methods for extracting information from and
enhancing the interpretability of such images. We describe in detail a gradient
filtering edge detection method that we previously applied to images of the
Centaurus cluster of galaxies. The Gaussian gradient filter measures the
gradient in the surface brightness distribution on particular spatial scales.
We apply this filter on different scales to Chandra X-ray observatory images of
two clusters with AGN feedback, the Perseus cluster and M87, and a merging
system, A3667. By combining filtered images on different scales using radial
filters spectacular images of the edges in a cluster are produced. We describe
how to assess the significance of features in filtered images. We find the
gradient filtering technique to have significant advantages for detecting many
kinds of features compared to other analysis techniques, such as
unsharp-masking. Filtering cluster images in this way in a hard energy band
allows shocks to be detected. |
Galaxy evolution in overdense environments at high redshift: passive
early-type galaxies in a cluster at redshift 2: We present a study of galaxy populations in the central region of the
IRAC-selected, X-ray detected galaxy cluster Cl J1449+0856 at z=2. Based on a
sample of spectroscopic and photometric cluster members, we investigate stellar
populations and morphological structure of cluster galaxies over an area of
~0.7Mpc^2 around the cluster core. The cluster stands out as a clear
overdensity both in redshift space, and in the spatial distribution of galaxies
close to the center of the extended X-ray emission. The cluster core region
(r<200 kpc) shows a clearly enhanced passive fraction with respect to field
levels. However, together with a population of massive passive galaxies mostly
with early-type morphologies, it also hosts massive actively star-forming,
often highly dust-reddened sources. Close to the cluster center, a
multi-component system of passive and star-forming galaxies could be the future
BCG still assembling. We observe a clear correlation between passive stellar
populations and an early-type morphology, in agreement with field studies at
similar redshift. Passive early-type galaxies in this clusters are typically a
factor 2-3 smaller than similarly massive early-types at z~0, but also on
average larger by a factor ~2 than their field analogs at z~2, lending support
to recent claims of an accelerated structural evolution in high-redshift dense
environments. These results point towards the early formation of a population
of massive galaxies, already evolved both in their structure and stellar
populations, coexisting with still-actively forming massive galaxies in the
central regions of young clusters 10 billion years ago. | Non-Gaussianity and statistical anisotropy from vector field populated
inflationary models: We present a review of vector field models of inflation and, in particular,
of the statistical anisotropy and non-Gaussianity predictions of models with
SU(2) vector multiplets. Non-Abelian gauge groups introduce a richer amount of
predictions compared to the Abelian ones, mostly because of the presence of
vector fields self-interactions. Primordial vector fields can violate isotropy
leaving their imprint in the comoving curvature fluctuations zeta at late
times. We provide the analytic expressions of the correlation functions of zeta
up to fourth order and an analysis of their amplitudes and shapes. The
statistical anisotropy signatures expected in these models are important and,
potentially, the anisotropic contributions to the bispectrum and the
trispectrum can overcome the isotropic parts. |
The clustering of dark siren host galaxies: Dark sirens are a powerful way to infer cosmological and astrophysical
parameters from the combination of gravitational wave sirens and galaxy
catalogues. Importantly, the method relies on the completeness of the galaxy
catalogues being well modelled. A magnitude-limited catalogue will always be
incomplete to some extent, requiring a completion scheme to avoid biasing the
parameter inference. Standard methods include homogeneous and multiplicative
completion, which have the advantage of simplicity but underestimate or
overestimate the amplitude of structure at low completeness, respectively. In
this work, we propose a new method to complete galaxy catalogues which uses
clustering information to incorporate knowledge of the large scale structure
into the dark sirens method. We find that if the structure of the true number
of galaxies is sufficiently well preserved in the catalogue, our estimator can
perform drastically better than both homogeneous and multiplicative completion.
We lay the foundations for a maximally informative dark sirens analysis and
discuss its limitations. | O'R Inflation in $F$-term Supergravity: The supersymmetric realization of inflation in $F$-term supergravity is
usually plagued by the well known "$\eta$" problem. In this paper, a broad
class of small-field examples is realized by employing general O' Raifeartaigh
superpotentials, where the moduli is identified as the massless inflaton. For
illustration we present the simplest example in detail, which can be considered
as a generalization of hybrid inflation. |
Instant Preheating in Quintessential Inflation with $α$-Attractors: We investigate a compelling model of quintessential inflation in the context
of $\alpha$-attractors, which naturally result in a scalar potential featuring
two flat regions, the inflationary plateau and the quintessential tail. The
"asymptotic freedom" of $\alpha$-attractors, near the kinetic poles, suppresses
radiative corrections and interactions, which would otherwise threaten to lift
the flatness of the quintessential tail and cause a 5th-force problem
respectively. Since this is a non-oscillatory inflation model, we reheat the
Universe through instant preheating. The parameter space is constrained by both
inflation and dark energy requirements. We find an excellent correlation
between the inflationary observables and model predictions, in agreement with
the $\alpha$-attractors set-up. We also obtain successful quintessence for
natural values of the parameters. Our model predicts potentially sizeable
tensor perturbations (at the level of 1%) and a slightly varying equation of
state for dark energy, to be probed in the near future. | Imprints of local lightcone projection effects on the galaxy bispectrum.
II: General relativistic imprints on the galaxy bispectrum arise from
observational (or projection) effects. The lightcone projection effects include
local contributions from Doppler and gravitational potential terms, as well as
lensing and other integrated contributions. We recently presented for the first
time, the correction to the galaxy bispectrum from all local lightcone
projection effects up to second order in perturbations. Here we provide the
details underlying this correction, together with further results and
illustrations. For moderately squeezed shapes, the correction to the Newtonian
prediction is ~30% on equality scales at z ~ 1. We generalise our recent
results to include the contribution, up to second order, of magnification bias
(which affects some of the local terms) and evolution bias. |
Morphologies of low-redshift AGN host galaxies: what role does AGN
luminosity play?: Mergers of galaxies have been suspected to be a major trigger of AGN activity
for many years. However, when compared to carefully matched control samples,
AGN host galaxies often show no enhanced signs of interaction. A common
explanation for this lack of observed association between AGN and mergers has
often been that while mergers are of importance for triggering AGN, they only
dominate at the very high luminosity end of the AGN population. In this study,
we compare the morphologies of AGN hosts to a carefully matched control sample
and particularly study the role of AGN luminosity. We find no enhanced merger
rates in AGN hosts and also find no trend for stronger signs of disturbance at
higher AGN luminosities. While this study does not cover very high luminosity
AGN, we can exclude a strong connection between AGN and mergers over a wide
range of AGN luminosities and therefore for a large part of the AGN population. | Mid-infrared spectroscopy of Spitzer-selected ultra-luminous starbursts
at z~2: We want to study the mid-infrared properties and the starburst and AGN
contributions, of 24um sources at z~2, through analysis of mid-infrared spectra
combined with millimeter, radio, and infrared photometry. Mid-infrared
spectroscopy allows us to recover accurate redshifts. A complete sample of 16
Spitzer-selected sources (ULIRGs) believed to be starbursts at z~2
("5.8um-peakers") was selected in the (0.5 sq.deg.) J1064+56 SWIRE Lockman Hole
field. These sources have S(24um)>0.5mJy, a stellar emission peak redshifted to
5.8um, and r'(Vega)>23. The entire sample was observed with the low resolution
units of the Spitzer/IRS infrared spectrograph. These sources have 1.2mm
observations with IRAM 30m/MAMBO and very deep 20cm observations from the VLA.
Nine of our sources also benefit from 350um observation and detection from
CSO/SHARC-II. The entire sample shows good quality IRS spectra dominated by
strong PAH features. The main PAH features at 6.2, 7.7, 8.6, and 11.3um have
high S/N average luminosities of 2.90, 10.38, 3.62, and 2.29x10^{10}Lsun,
respectively. We derived accurate redshifts spanning from 1.75 to 2.28. The
average of these redshifts is 2.017. This result confirms that the selection
criteria of "5.8um-peakers" associated with a strong detection at 24um are
reliable to select sources at z~2. We have analyzed the different correlations
between PAH emission and infrared, millimeter, and radio emission. Practically
all our sources are strongly dominated by starburst emission. We have also
defined two subsamples based on the equivalent width at 7.7um to investigate
AGN contributions. Our sample contains strong starbursts and represents a
particularly 24um-bright class of SMGs. The very good correlation between PAH
and far-IR luminosities is now confirmed in high-z starburst ULIRGs. These
sources show a small AGN contribution to the mid-IR, around ~20% in most cases. |
THESEUS$-$BTA cosmological tests using Multimessenger Gamma-Ray Bursts
observations: Modern Multimessenger Astronomy is a powerful instrument for performing
cosmological crucial tests of the Standard Cosmological Model in the wide
redshift interval up to $z \sim 10$. This is principally important for
discussion related to discrepancies between local and global measurements of
cosmological parameters. We present a review of multimessenger gamma-ray burst
observations currently conducted and planed for THESEUS$-$BTA cooperative
program. Such observations give a unique opportunity to test the fundamental
foundations of cosmological models: gravitation theory; cosmological principle
of homogeneity and isotropy of large-scale distribution of matter; and space
expansion paradigm. Important role of various selection effects leading to
systematic distortions of true cosmological relations is discussed. | Dark sectors with dynamical coupling: Coupled dark matter-dark energy scenarios are modeled via a dimensionless
parameter $\xi$, which controls the strength of their interaction. While this
coupling is commonly assumed to be constant, there is no underlying physical
law or symmetry that forbids a time-dependent $\xi$ parameter. The most general
and complete interacting scenarios between the two dark sectors should
therefore allow for such a possibility, and it is the main purpose of this
study to constrain two possible and well-motivated coupled cosmologies by means
of the most recent and accurate early and late-time universe observations. We
find that CMB data alone prefers $\xi(z) >0$ and therefore a smaller amount of
dark matter, alleviating some crucial and well-known cosmological data
tensions. An objective assessment of the Bayesian evidence for the coupled
models explored here shows no particular preference for the presence of a
dynamical dark sector coupling. |
The case for primordial black holes as dark matter: The aim of this paper is to present the case that stellar mass primordial
black holes make up the dark matter component of the Universe. A near critical
density of compact bodies implies that most lines of sight will be
gravitationally microlensed, and the paper focuses on looking for the predicted
effects on quasar brightness and spectral variations. These signatures of
microlensing include the shape of the Fourier power spectrum of the light
curves, near achromatic and statistically symmetric variations, and the absence
of time dilation in the timescale of variability. For spectral changes, as the
continuum varies there should be little corresponding change in the strength of
the broad lines. In all these cases, the observations are found to be
consistent with the predictions for microlensing by a population of stellar
mass compact bodies. For multiply lensed quasars where the images vary
independently it is shown that stellar populations are too small to produce the
observed microlensing effects, implying a population of compact dark matter
bodies of around a stellar mass along the line of sight. The most serious
objection to dark matter in the form of compact bodies has come from
observations of microlensing of stars in the Magellanic Clouds. In this paper
the expected event rate is re-analysed using more recent values for the
structure and dynamics of the Galactic halo, and it is shown that there is then
no conflict with the observations. Finally, the possible identity of a near
critical density of dark matter in the form of stellar mass compact bodies is
reviewed, with the conclusion that by far the most plausible candidates are
primordial black holes formed during the QCD epoch. The overall conclusion of
the paper is that primordial black holes should be seen alongside elementary
particles as viable dark matter candidates. | Galaxy Cluster Mass Estimation from Stacked Spectroscopic Analysis: We use simulated galaxy surveys to study: i) how galaxy membership in
redMaPPer clusters maps to the underlying halo population, and ii) the accuracy
of a mean dynamical cluster mass, $M_\sigma(\lambda)$, derived from stacked
pairwise spectroscopy of clusters with richness $\lambda$. Using $\sim\!
130,000$ galaxy pairs patterned after the SDSS redMaPPer cluster sample study
of Rozo et al. (2015 RMIV), we show that the pairwise velocity PDF of
central--satellite pairs with $m_i < 19$ in the simulation matches the form
seen in RMIV. Through joint membership matching, we deconstruct the main
Gaussian velocity component into its halo contributions, finding that the
top-ranked halo contributes $\sim 60\%$ of the stacked signal. The halo mass
scale inferred by applying the virial scaling of Evrard et al. (2008) to the
velocity normalization matches, to within a few percent, the log-mean halo mass
derived through galaxy membership matching. We apply this approach, along with
mis-centering and galaxy velocity bias corrections, to estimate the log-mean
matched halo mass at $z=0.2$ of SDSS redMaPPer clusters. Employing the velocity
bias constraints of Guo et al. (2015), we find $\langle \ln(M_{200c})|\lambda
\rangle = \ln(M_{30}) + \alpha_m \ln(\lambda/30)$ with $M_{30} = 1.56 \pm 0.35
\times 10^{14} M_\odot$ and $\alpha_m = 1.31 \pm 0.06_{stat} \pm 0.13_{sys}$.
Systematic uncertainty in the velocity bias of satellite galaxies
overwhelmingly dominates the error budget. |
A 5% measurement of the gravitational constant in the Large Magellanic
Cloud: We perform a novel test of General Relativity by measuring the gravitational
constant in the Large Magellanic Cloud (LMC). The LMC contains six well-studied
Cepheid variable stars in detached eclipsing binaries. Radial velocity and
photometric observations enable a complete orbital solution, and precise
measurements of the Cepheids' periods permit detailed stellar modelling. Both
are sensitive to the strength of gravity, the former via Kepler's third law and
the latter through the gravitational free-fall time. We jointly fit the
observables for stellar parameters and the gravitational constant. Performing a
full Markov Chain Monte Carlo analysis of the parameter space including all
relevant nuisance parameters, we constrain the gravitational constant in the
Large Magellanic Cloud relative to the Solar System to be
$G_\text{LMC}/G_\text{SS} = 0.93^{+0.05}_{-0.04}$. We discuss the implications
of this 5% measurement of Newton's constant in another galaxy for dark energy
and modified gravity theories. This result excludes one Cepheid, CEP-1812,
which is an outlier and needs further study: it is either a highly unusual
system to which our model does not apply, or it prefers
$G_\text{LMC}<G_\text{SS}$ at $2.6\sigma$. We also obtain new bounds on
critical parameters that appear in semi-analytic descriptions of stellar
processes. In particular, we measure the mixing length parameter to be
$\alpha=0.90^{+0.36}_{-0.26}$ (when assumed to be constant across our sample),
and obtain constraints on the parameters describing turbulent dissipation and
convective flux. | The colour of galaxies in distant groups: (Abridged) We present new optical and near-infrared imaging for a sample of
98 spectroscopically-selected galaxy groups at 0.25<z<0.55. We measure accurate
colours for group members and the surrounding field population, statistically
complete above a stellar mass limit of M=1E10 Msun. The overall colour
distribution is bimodal in both the field and group samples; but at fixed
luminosity the fraction of group galaxies populating the red peak is larger, by
20+/-7 per cent, than that of the field. In particular, group members with
early-type morphologies, as identified in HST imaging, exhibit a tight red
sequence, similar to that seen for more massive clusters. We show that
approximately 20-30 per cent of galaxies on the red sequence may be
dust-reddened galaxies with non-negligible star formation and early-spiral
morphologies. This is true of both the field and group sample, and shows little
dependence on near infrared luminosity. Thus, the fraction of bright group
members with no sign of star formation or AGN activity is 54+/-6 per cent. Our
field sample, which includes galaxies in all environments, contains 35+/-3 per
cent of such inactive galaxies, consistent with the amount expected if all such
galaxies are located in groups and clusters. This reinforces our earlier
conclusions, that dense environments at z<0.5 are associated with a premature
cessation of star formation in some galaxies; in particular we find no evidence
for significantly enhanced star formation in these environments. Simple galaxy
formation models predict a quenching of star formation in groups that is too
efficient, overpopulating the red sequence. Attempts to fix this by increasing
the timescale of this quenching equally for all group members distorts the
colour distribution in a way that is inconsistent with observations. |
Precise Clustering and Density Evolution of redMaPPer Galaxy Clusters
versus MXXL Simulation: We construct a large, redshift complete sample of distant galaxy clusters by
correlating Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) redshifts
with clusters identified with the red-sequence Matched-filter Probabilistic
Percolation (redMaPPer) algorithm. Our spectroscopic completeness is 97% for ~
7,000 clusters within the redMaPPer selection limit, $z \leqslant$ 0.325, so
that our cluster correlation functions are much more precise than earlier work
and not suppressed by photometric redshifts. We derive an accurate power-law
mass-richness relation from the observed abundance with respect to the mass
function from Millennium XXL (MXXL) simulation, adjusted to the Planck weighted
cosmology. The number density of clusters is found to decline by 20% over the
range 0.1 $< z <$ 0.3, in good agreement with the evolution predicted by MXXL.
Our projected three-dimensional correlation function scales with richness,
$\lambda$, rising from $r_0=$ 14 h$^{-1}$ Mpc at $\lambda\simeq$ 25, to $r_0=$
22 h$^{-1}$ Mpc at $\lambda\simeq$ 60, with a gradient that matches MXXL when
applying our mass-richness relation, whereas the observed amplitude of the
correlation function at $\left<z\right>=$ 0.24 exceeds the MXXL prediction by
20% at the $\simeq$ 2.5$\sigma$ level. This tension cannot be blamed on
spurious, randomly located clusters as this would reduce the correlation
amplitude. Full consistency between the correlation function and the abundances
is achievable for the pre-Planck values of $\sigma_8=$ 0.9, $\Omega_m=$ 0.25,
and h = 0.73, matching the improved distance ladder estimate of the Hubble
constant. | Cosmic Evolution of Virial and Stellar Mass in Massive Early-Type
Galaxies: We measure the average mass properties of a sample of 41 strong gravitational
lenses at moderate redshift (z ~ 0.4 - 0.9), and present the lens redshift for
6 of these galaxies for the first time. Using the techniques of strong and weak
gravitational lensing on archival data obtained from the Hubble Space
Telescope, we determine that the average mass overdensity profile of the lenses
can be fit with a power-law profile (Delta_Sigma prop. to R^{-0.86 +/- 0.16})
that is within 1-sigma of an isothermal profile (Delta_Sigma prop. to R^{-1})
with velocity dispersion sigma_v = 260 +/- 20 km/s. Additionally, we use a
two-component de Vaucouleurs+NFW model to disentangle the total mass profile
into separate luminous and dark matter components, and determine the relative
fraction of each component. We measure the average rest frame V-band stellar
mass-to-light ratio (Upsilon_V = 4.0 +/- 0.6 h M_sol/L_sol) and virial
mass-to-light ratio (tau_V = 300 +/- 90 h M_sol/L_sol) for our sample,
resulting in a virial-to-stellar mass ratio of M_vir/M_* = 75 +/- 25. Finally,
we compare our results to a previous study using low redshift lenses, to
understand how galaxy mass profiles evolve over time. We investigate the
evolution of M_vir/M_*(z) = alpha(1+z)^{beta}, and find best fit parameters of
alpha = 51 +/- 36 and beta = 0.9 +/- 1.8, constraining the growth of virial to
stellar mass ratio over the last ~7 Gigayears. We note that, by using a sample
of strong lenses, we are able to constrain the growth of M_vir/M_*(z) without
making any assumptions about the IMF of the stellar population. |
Probing Large-scale UV Background Inhomogeneity Associated with Quasars
using Metal Absorption: We study large-scale UV background inhomogeneity in three-dimensions
associated with the observed quasar populations at high redshift. We do this by
measuring metal absorption through quasar absorption spectrum stacking as a
function distance to closest quasar in SDSS-IV/eBOSS on 10s of comoving
megaparsec scales. We study both intergalactic medium absorbers and mixed
circumgalactic medium absorbers and probe absorption in O VI, C IV, and Si IV,
and Si III. Overall stronger high ionization species absorption is seen closer
to quasars at $2.4<z<3.1$. O VI absorption shows a particularly strong change,
with effects in C IV evident in some cases, and more marginal effects in Si III
and Si IV. We further study $2.05<z<2.4$ (with weak signs of increasing
homogeneity with time) and explore the study of metal absorption as a function
of integrated SDSS-r band flux quasar flux (yielding consistent but less
significant results). While the metal absorption does show sensitivity to
large-scale 3D quasar proximity, the current incomplete quasar samples limit
detailed interpretation. This work does, however, demonstrate that UV
background inhomogeneities exist on scales of several 10s of comoving
megaparsecs associated with quasars and that they can be measured with
precision by examining metal absorption in the intergalactic medium. | Discovery and Cosmological Implications of SPT-CL J2106-5844, the Most
Massive Known Cluster at z > 1: Using the South Pole Telescope (SPT), we have discovered the most massive
known galaxy cluster at z > 1, SPT-CL J2106-5844. In addition to producing a
strong Sunyaev-Zel'dovich effect signal, this system is a luminous X-ray source
and its numerous constituent galaxies display spatial and color clustering, all
indicating the presence of a massive galaxy cluster. VLT and Magellan
spectroscopy of 18 member galaxies shows that the cluster is at z =
1.132^+0.002_-0.003. Chandra observations obtained through a combined HRC-ACIS
GTO program reveal an X-ray spectrum with an Fe K line redshifted by z = 1.18
+/- 0.03. These redshifts are consistent with galaxy colors in extensive
optical, near-infrared, and mid-infrared imaging. SPT-CL J2106-5844 displays
extreme X-ray properties for a cluster, having a core-excluded temperature of
kT = 11.0^+2.6_-1.9 keV and a luminosity (within r_500) of L_X (0.5 - 2.0 keV)
= (13.9 +/- 1.0) x 10^44 erg/s. The combined mass estimate from measurements of
the Sunyaev-Zel'dovich effect and X-ray data is M_200 = (1.27 +/- 0.21) x 10^15
M_sun. The discovery of such a massive gravitationally collapsed system at high
redshift provides an interesting laboratory for galaxy formation and evolution,
and is a powerful probe of extreme perturbations of the primordial matter
density field. We discuss the latter, determining that, under the assumption of
LambdaCDM cosmology with only Gaussian perturbations, there is only a 7% chance
of finding a galaxy cluster similar to SPT-CL J2106-5844 in the 2500 deg^2 SPT
survey region, and that only one such galaxy cluster is expected in the entire
sky. |
Discovery of A Variable Broad Absorption Line in the BL Lac object PKS
0138-097: We report the discovery of a Broad Absorption Line (BAL) of \sim 10^4 km s-1
in width in the previously known BL Lac object PKS 0138-097, which we
tentatively identified as a Mg II BAL. This is the first detection of a BAL,
which is sometimes seen in powerful quasars with high accretion rates, in a BL
Lac object. The BAL was clearly detected in its spectra of two epochs at a high
luminosity state taken in the Sloan Digital Sky Survey (SDSS), while it
disappeared in three SDSS spectra taken at a low luminosity state. The BAL and
its variability pattern was also found in its historical multi-epoch spectra in
the literature, but has been overlooked previously. In its high resolution
radio maps, PKS 0138-097 shows a core plus an one-sided parsec-scale jet. The
BAL variability can be interpreted as follows: The optical emission is
dominated by the core in a high state and by the jet in a low state, and the
BAL material is located between the core and jet so that the BAL appears only
when the core is shining. Our discovery suggests that outflows may also be
produced in active galactic nuclei at a low accreting state. | Bounds on the Horndeski Gauge-Gravity Coupling: The Horndeski gauge-gravity coupling is the leading non-minimal interaction
between gravity and gauge bosons, and it preserves all the symmetries and the
number of physical degrees of freedom of the standard model of particle physics
and general relativity. In this paper we study the effects of the non-minimal
interaction in astronomy and cosmology, and obtain upper bounds on the
associated dimensionless coupling constant $\lambda$. From the modification of
equations of motion of gauge bosons applied to compact astronomical objects, we
find upper bounds $|\lambda| \lesssim 10^{88}$, $|\lambda| \lesssim 10^{75}$
and $|\lambda| \lesssim 10^{84}$ from a black hole shadow, neutron stars and
white dwarfs, respectively. The bound $|\lambda| \lesssim 10^{75}$ that is
deduced from neutron stars is the strongest and provides twenty orders of
magnitude improvement of the previously known best bound on this parameter. On
the other hand, the effects of this term on modification of the gravitational
Poisson equation lead to a weaker bound $|\lambda| \lesssim 10^{98}$. From the
propagation of gravitational waves we also find $|\lambda| \lesssim 10^{119}$,
which is even weaker. |
LSPE-STRIP on-sky calibration strategy using bright celestial sources: In this paper we describe the global on-sky calibration strategy of the
LSPE-Strip instrument. Strip is a microwave telescope operating in the Q- and
W-bands (central frequencies of 43 and 95 GHz respectively) from the
Observatorio del Teide in Tenerife, with the goal to observe and characterise
the polarised Galactic foreground emission, and complement the observations of
the polarisation of the cosmic microwave background to be performed by the
LSPE-SWIPE instrument and other similar experiments operating at higher
frequencies to target the detection of the B-mode signal from the inflationary
epoch of the Universe. Starting from basic assumptions on some of the
instrument parameters (NET, 1/f noise knee frequency, beam properties,
observing efficiency) we perform realistic simulations to study the level of
accuracy that can be achieved through observations of bright celestial
calibrators in the Strip footprint (sky fraction of 30 %) on the determination
and characterisation of the main instrument parameters: global and relative
gain factors (in intensity and in polarisation), polarisation direction,
polarisation efficiency, leakage from intensity to polarisation, beams, window
functions and pointing model. | Propagating Speed of Primordial Gravitational Waves: Primordial Gravitational Waves, i.e. a background of metric perturbations
sourced by the quantum inflationary fluctuations, if measured, could both
provide a substantial evidence for primordial inflation and shed light on
physics at extremely high energy scales. In this work we focus on their
propagating speed. Using an effective field theory approach we introduce a
time-dependent propagating speed $c_{\rm T}(t)$ showing that also small
deviations from the General Relativity (GR) prediction $c_{\rm T}(t) = c$ can
lead to testable consequences. We derive a set of equations that relate the
propagating speed and its time dependence to the inflationary parameters and
that generalize the usual slow roll consistency relations. Imposing the new
generalized consistency relations and combining small and large scales data, we
derive model independent constraints on inflation with non-trivial primordial
tensor speed. In particular we constrain its scale dependence to be $d\log
c_{\rm T} / d\log k=0.082^{+0.047}_{-0.11}$ at 68% C.L. while we only derive
the lower bound $c_{\rm T}>0.22\,c$ at 95% C.L. . We also constrain the
tensor-to-scalar ratio at the pivot scale $k_*=0.05\rm{Mpc}^{-1}$ to be
$r<0.0599$ at 95% C.L. in agreement with the result provided by the Planck
collaboration. Thanks to a proper small scale parameterization of the tensor
spectrum we derive stringent constraints on the tensor tilt $n_{\rm
T}=-0.084^{+0.10}_{-0.047}$ at 68% C.L. and on its runnings $\alpha_{\rm
T}=d\,n_{\rm T}/d\log k=0.0141^{+0.0035}_{-0.021}$ and $\beta_{\rm
T}=d\,\alpha_{\rm T}/d\log k= -0.0061^{+0.010}_{-0.0014}$ both at 68% C.L. Our
results show a remarkable agreement with the standard slow roll predictions and
prove that current data can significantly constrain deviations from GR on the
inflationary energy scales. |
HI in radio galaxies: prospects for upcoming wide-field surveys: We present results of an ongoing systematic study of the large-scale
properties of neutral hydrogen (HI) gas in nearby radio galaxies. Our main goal
is to investigate the importance of gas-rich galaxy mergers and interactions
among radio-loud AGN. From an HI study of a complete sample of classical
low-power radio galaxies we find that the host galaxies of extended Fanaroff &
Riley type-I radio sources are generally HI poor (< 10E8 M_sun) and show no
indications for gas-rich galaxy mergers or ongoing gas-rich interactions. In
contrast, the host galaxies of a significant fraction of low-power compact
radio sources contain enormous discs/rings of HI gas (with sizes up to 190 kpc
and masses up to 2 x 10E10 M_sun). This segregation in HI mass with radio
source size likely indicates that these compact radio sources are either
confined by large amounts of gas in the central region, or that their fueling
is inefficient and different from the fueling process of classical FR-I radio
sources. To a first order, the overall HI properties of our complete sample
(detection rate, mass and morphology) appear similar to those of radio-quiet
early-type galaxies. If confirmed by better statistics, this would imply that
low-power radio-AGN activity may be a short phase that occurs at some point
during the lifetime of many early-type galaxies. We discuss how upcoming HI
surveys (e.g. with ASKAP and Apertif) are essential for studying in a
statistical way the the connection between the presence and morphology of a
radio-loud AGN and the properties of the cold HI gas associated with its host
galaxy. | CLASH: Extending galaxy strong lensing to small physical scales with
distant sources highly-magnified by galaxy cluster members: We present a strong lensing system in which a double source is imaged 5 times
by 2 early-type galaxies. We take advantage in this target of the multi-band
photometry obtained as part of the CLASH program, complemented by the
spectroscopic data of the VLT/VIMOS and FORS2 follow-up campaign. We use a
photometric redshift of 3.7 for the source and confirm spectroscopically the
membership of the 2 lenses to the galaxy cluster MACS J1206.2-0847 at redshift
0.44. We exploit the excellent angular resolution of the HST/ACS images to
model the 2 lenses in terms of singular isothermal sphere profiles and derive
robust effective velocity dispersions of (97 +/- 3) and (240 +/- 6) km/s. The
total mass distribution of the cluster is also well characterized by using only
the local information contained in this lensing system, that is located at a
projected distance of more than 300 kpc from the cluster luminosity center.
According to our best-fitting lensing and composite stellar population models,
the source is magnified by a total factor of 50 and has a luminous mass of
about (1.0 +/- 0.5) x 10^{9} M_{Sun}. By combining the total and luminous mass
estimates of the 2 lenses, we measure luminous over total mass fractions
projected within the effective radii of 0.51 +/- 0.21 and 0.80 +/- 0.32. With
these lenses we can extend the analysis of the mass properties of lens
early-type galaxies by factors that are about 2 and 3 times smaller than
previously done with regard to, respectively, velocity dispersion and luminous
mass. The comparison of the total and luminous quantities of our lenses with
those of astrophysical objects with different physical scales reveals the
potential of studies of this kind for investigating the internal structure of
galaxies. These studies, made possible thanks to the CLASH survey, will allow
us to go beyond the current limits posed by the available lens samples in the
field. |
Approach to scaling in axion string networks: We study the approach to scaling in axion string networks in the radiation
era, through measuring the root-mean-square velocity $v$ as well as the scaled
mean string separation $x$. We find good evidence for a fixed point in the
phase-space analysis in the variables $(x,v)$, providing a strong indication
that standard scaling is taking place. We show that the approach to scaling can
be well described by a two parameter velocity-one-scale (VOS) model, and show
that the values of the parameters are insensitive to the initial state of the
network. The string length has also been commonly expressed in terms of a
dimensionless string length density $\zeta$, proportional to the number of
Hubble lengths of string per Hubble volume. In simulations with initial
conditions far from the fixed point $\zeta$ is still evolving after half a
light-crossing time, which has been interpreted in the literature as a
long-term logarithmic growth. We show that all our simulations, even those
starting far from the fixed point, are accounted for by a VOS model with an
asymptote of $\zeta_*=1.20\pm0.09$ (calculated from the string length in the
cosmic rest frame) and $v_* = 0.609\pm 0.014$. | A new interpretation of the far-infrared - radio correlation and the
expected breakdown at high redshift: (Abrigded) Observations of galaxies up to z 2 show a tight correlation
between far-infrared and radio continuum emission. We explain the far-infrared
- radio continuum correlation by relating star formation and magnetic field
strength in terms of turbulent magnetic field amplification, where turbulence
is injected by supernova explosions from massive stars. We calculate the
expected amount of turbulence in galaxies based on their star formation rates,
and infer the expected magnetic field strength due to turbulent dynamo
amplification. We estimate the timescales for cosmic ray energy losses via
synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung
emission, probing up to which redshift strong synchrotron emission can be
maintained. We find that the correlation between star formation rate and
magnetic field strength in the local Universe can be understood as a result of
turbulent magnetic field amplification. If the typical gas density in the
interstellar medium increases at high z, we expect an increase of the magnetic
field strength and the radio emission, as indicated by current observations.
Such an increase would imply a modification of the far-infrared - radio
correlation. We expect a breakdown when inverse Compton losses start dominating
over synchrotron emission. For a given star formation surface density, we
calculate the redshift where the breakdown occurs, yielding z (Sigma_SFR/0.0045
M_solar kpc^{-2} yr^{-1})^{1/(6-alpha/2)}. In this relation, the parameter
\alpha describes the evolution of the characteristic ISM density in galaxies as
(1+z)^\alpha. Both the possible raise of the radio emission at high redshift
and the final breakdown of the far-infrared -- radio correlation at a critical
redshift will be probed by the Square Kilometre Array (SKA) and its
pathfinders, while the typical ISM density in galaxies will be probed with
ALMA. |
Isocurvature modes in the CMB bispectrum: We study the angular bispectrum of local type arising from the (possibly
correlated) combination of a primordial adiabatic mode with an isocurvature
one. Generically, this bispectrum can be decomposed into six elementary
bispectra. We estimate how precisely CMB data, including polarization, can
enable us to measure or constrain the six corresponding amplitudes, considering
separately the four types of isocurvature modes (CDM, baryon, neutrino density,
neutrino velocity). Finally, we discuss how the model-independent constraints
on the bispectrum can be combined to get constraints on the parameters of
multiple-field inflation models. | Deriving galaxy cluster velocity anisotropy profiles from a joint
analysis of dynamical and weak lensing data: We present an analytic approach to lift the mass-anisotropy degeneracy in
clusters of galaxies by utilizing the line-of-sight velocity dispersion of
clustered galaxies jointly with weak lensing inferred masses. More
specifically, we solve the spherical Jeans equation by assuming a simple
relation between the line-of-sight velocity dispersion and the radial velocity
dispersion and recast the Jeans equation as a Bernoulli differential equation
that has a well-known analytic solution. We first test our method in
cosmological N-body simulations and then derive the anisotropy profiles for 35
archival data galaxy clusters with an average redshift of $\langle
{z}_{c}\rangle =0.25$. The resulting profiles yield a weighted average global
value of $\langle \beta (0.2\leqslant R/{R}_{200}\leqslant 1)\rangle =0.35\pm
0.28$ (stat) \pm 0.15 (sys). This indicates that clustered galaxies tend to
globally fall on radially anisotropic orbits. We note that this is the first
attempt to derive velocity anisotropy profiles for a cluster sample of this
size utilizing joint dynamical and weak lensing data |
Examining the Radio-Loud/Radio-Quiet dichotomy with new Chandra and VLA
observations of 13 UGC galaxies: (Abridged) We present the results from new 15 ks Chandra-ACIS and 4.9 GHz
Very Large Array observations of 13 galaxies hosting low luminosity AGN. This
completes the multiwavelength study of a sample of 51 nearby early-type
galaxies described in Capetti & Balmaverde (2005, 2006); Balmaverde & Capetti
(2006). The aim of the three previous papers was to explore the connection
between the host galaxies and AGN activity in a radio-selected sample. We
detect nuclear X-ray emission in eight sources and radio emission in all but
one (viz., UGC6985). The new VLA observations improve the spatial resolution by
a factor of ten: the presence of nuclear radio sources in 12 of the 13 galaxies
confirms their AGN nature. As previously indicated, the behavior of the X-ray
and radio emission in these sources depends strongly on the form of their
optical surface brightness profiles derived from Hubble Space Telescope
imaging, i.e., on their classification as "core", "power-law" or "intermediate"
galaxies. With more than twice the number of "power-law" and "intermediate"
galaxies compared to previous work, we confirm with a much higher statistical
significance that these galaxies lie well above the radio-X-ray correlation
established in FRI radio galaxies and the low-luminosity "core" galaxies. This
result highlights the fact that the "radio-loud/radio-quiet" dichotomy is a
function of the host galaxy's optical surface brightness profile. We present
radio-optical-X-ray spectral indices for all 51 sample galaxies. Survival
statistics point to significant differences in the radio-to-optical and
radio-to-X-ray spectral indices between the "core" and "power-law" galaxies
(Gehan's Generalized Wilcoxon test probability "p" for the two classes being
statistically similar is <10^-5), but not in the optical-to-X-ray spectral
indices (p=0.25). | A tale of two GRB-SNe at a common redshift of z = 0.54: We present ground-based and HST optical observations of the optical
transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618,
both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical
light curves (LCs), and the late-time broadband spectral energy distributions
(SEDs) of the OT resemble those of local type Ic supernovae (SNe). For GRB
090618, the dense sampling of our optical observations has allowed us to detect
well-defined bumps in the optical LCs, as well as a change in colour, that are
indicative of light coming from a core-collapse SN. The accompanying SNe for
both events are individually compared with SN1998bw, a known GRB-supernova, and
SN1994I, a typical type Ic supernova without a known GRB counterpart, and in
both cases the brightness and temporal evolution more closely resemble
SN1998bw. We also exploit our extensive optical and radio data for GRB 090618,
as well as the publicly-available SWIFT -XRT data, and discuss the properties
of the afterglow at early times. In the context of a simple jet-like model, the
afterglow of GRB 090618 is best explained by the presence of a jet-break at
t-to > 0.5 days. We then compare the rest-frame, peak V -band absolute
magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large
sample of local type Ibc SNe, concluding that, when host extinction is
considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from
the peak magnitudes of non-GRB/XRF SNe. |
When Primordial Black Holes from Sound Speed Resonance Meet a Stochastic
Background of Gravitational Waves: As potential candidates of dark matter, primordial black holes (PBHs) are
within the core scopes of various astronomical observations. In light of the
explosive development of gravitational wave (GW) and radio astronomy, we
thoroughly analyze a stochastic background of cosmological GWs, induced by over
large primordial density perturbations, with several spikes that was inspired
by the sound speed resonance effect and can predict a particular pattern on the
mass spectrum of PBHs. With a specific mechanicsm for PBHs formation, we for
the first time perform the study of such induced GWs that originate from both
the inflationary era and the radiation-dominated phase. We report that, besides
the traditional process of generating GWs during the radiation-dominated phase,
the contribution of the induced GWs in the sub-Hubble regime during inflation
can become significant at critical frequency band because of a narrow resonance
effect. All contributions sum together to yield a specific profile of the
energy spectrum of GWs that can be of observable interest in forthcoming
astronomical experiments. Our study shed light on the possible joint probe of
PBHs via various observational windows of multi-messenger astronomy, including
the search for electromagnetic effects with astronomical telescopes and the
stochastic background of relic GWs with GW instruments. | The effect of recombination radiation on the temperature and ionization
state of partially ionized gas: A substantial fraction of all ionizing photons originate from radiative
recombinations. However, in radiative transfer calculations this recombination
radiation is often assumed to be absorbed 'on-the-spot' because for most
methods the computational cost associated with the inclusion of gas elements as
sources is prohibitive. We present a new, CPU and memory efficient
implementation for the transport of ionizing recombination radiation in the
TRAPHIC radiative transfer scheme. TRAPHIC solves the radiative transfer
equation by tracing photon packets at the speed of light and in a
photon-conserving manner in spatially adaptive smoothed particle hydrodynamics
simulations. Our new implementation uses existing features of the TRAPHIC
scheme to add recombination radiation at no additional cost in the limit in
which the fraction of the simulation box filled with radiation approaches 1. We
test the implementation by simulating an HII region in photoionization
equilibrium and comparing to reference solutions presented in the literature,
finding excellent agreement. We apply our implementation to discuss the
evolution of the HII region to equilibrium. We show that the widely used case A
and B approximations yield accurate ionization profiles only near the source
and near the ionization front, respectively. We also discuss the impact of
recombination radiation on the geometry of shadows behind optically thick
absorbers. We demonstrate that the shadow region may be completely ionized by
the diffuse recombination radiation field and discuss the important role of
heating by recombination radiation in the shadow region. |
The cluster gas mass fraction as a cosmological probe: a revised study: (Abriged) We present the analysis of the baryonic content of 52 X-ray
luminous galaxy clusters observed with Chandra in the redshift range 0.3-1.273.
We use the deprojected X-ray surface brightness profiles and the measured
values of the gas temperature to recover the gas and total mass profiles. By
assuming that galaxy clusters are representative of the cosmic baryon budget,
the distribution of the cluster baryon fraction in the hottest (T> 4 keV)
systems as a function of redshift is used to constrain the cosmological
parameters. We discuss how our constraints are affected by several systematics,
namely the isothermality, the assumed baryon fraction in stars, the depletion
parameter and the sample selection. By using only the cluster baryon fraction
as a proxy for the cosmological parameters, we obtain that Omega is very well
constrained at the value of 0.35 with a relative statistical uncertainty of 11%
(1 sigma level; w=-1) and a further systematic error of about (-6,+7)%. On the
other hand, constraints on Lambda (without the prior of flat geometry) and w
(using the prior of flat geometry) are definitely weaker due to the presence of
larger statistical and systematic uncertainties (of the order of 40 per cent on
Lambda and larger than 50 per cent on w). If the WMAP 5-year best-fit results
are assumed to fix the cosmological parameters, we limit the contributions
expected from non-thermal pressure support and ICM clumpiness to be lower than
about 10 per cent, leaving also room to accommodate baryons not accounted for
either in the X-ray emitting plasma or in stars of the order of 18 per cent of
the total cluster baryon budget. | A Reverberation Lag for the High-Ionization Component of the Broad Line
Region in the Narrow-Line Seyfert 1 Mrk 335: We present the first results from a detailed analysis of photometric and
spectrophotometric data on the narrow-line Seyfert 1 galaxy Mrk 335, collected
over a 120-day span in the fall of 2010. From these data we measure the lag in
the He II 4686 broad emission line relative to the optical continuum to be 2.7
\pm 0.6 days and the lag in the H\beta 4861 broad emission line to be 13.9 \pm
0.9 days. Combined with the line width, the He II lag yields a black hole mass,
MBH = (2.6 \pm 0.8)\times 10^7 Msun. This measurement is consistent with
measurements made using the H\beta 4861 line, suggesting that the He II
emission originates in the same region as H\beta, but at a much smaller radius.
This constitutes the first robust lag measurement for a high-ionization line in
a narrow-line Seyfert 1 galaxy. |
Beyond the 3rd moment: A practical study of using lensing convergence
CDFs for cosmology with DES Y3: Widefield surveys of the sky probe many clustered scalar fields -- such as
galaxy counts, lensing potential, gas pressure, etc. -- that are sensitive to
different cosmological and astrophysical processes. Our ability to constrain
such processes from these fields depends crucially on the statistics chosen to
summarize the field. In this work, we explore the cumulative distribution
function (CDF) at multiple scales as a summary of the galaxy lensing
convergence field. Using a suite of N-body lightcone simulations, we show the
CDFs' constraining power is modestly better than that of the 2nd and 3rd
moments of the field, as they approximately capture the information from all
moments of the field in a concise data vector. We then study the practical
aspects of applying the CDFs to observational data, using the first three years
of the Dark Energy Survey (DES Y3) data as an example, and compute the impact
of different systematics on the CDFs. The contributions from the point spread
function are 2-3 orders of magnitude below the cosmological signal, while those
from reduced shear approximation contribute $\lesssim 1\%$ to the signal.
Source clustering effects and baryon imprints contribute $1-10\%$. Enforcing
scale cuts to limit systematics-driven biases in parameter constraints degrades
these constraints a noticeable amount, and this degradation is similar for the
CDFs and the moments. We also detect correlations between the observed
convergence field and the shape noise field at $13\sigma$. We find that the
non-Gaussian correlations in the noise field must be modeled accurately to use
the CDFs, or other statistics sensitive to all moments, as a rigorous cosmology
tool. | Spectral optical monitoring of 3C 390.3 in 1995-2007: II. Variability of
the spectral line parameters: A study of the variability of the broad emission-line parameters of 3C390.3,
an active galaxy with the double-peaked emission-line profiles, is presented.
We give a detail analysis of variation in the broad Ha and Hb profiles, the
ratios, and the Balmer decrement of different line segments. Studying the
variability of the line profiles we explore the disk structure, that is assumed
to emit the broad double-peaked Ha and Hb emission lines. We divided the
observed spectra in two periods (before and after the outburst in 2002) and
analyzed separately the variation in these two periods. First we analyzed the
spectral emission-line profiles of Ha and Hb, measuring the peak positions.
Then, we divided lines into several segments, and we measured the line-segment
fluxes. The Balmer decrement variation for total Ha and Hb fluxes, as well as
for the line segments has been investigated and discussed. We modeled the line
parameters variation using an accretion disk model. We compared the variability
in the observed line parameters with the disk model predictions and found that
the variation in line profiles and in line segments corresponds to the emission
of a disk-like BLR. But, also there is probably one additional emission
component that contributes to the Ha and Hb line center. We found that the
variation in the line profiles is caused by the variation in the parameters of
the disk-like BLR, first of all in the inner (outer) radius which can well
explain the line parameter variations in the Period I. The Balmer decrement
across the line profile has a bell-like shape, and it is affected not only by
physical processes in the disk, but also by different emitting disk dimension
of the Ha and Hb line. The geometry of the BLR of 3C390.3 seems to be very
complex, and inflows/outflows might be present, but it is evident that the
broad line region with disk-like geometry has dominant emission. |
Inferences on the distribution of Ly-alpha emission of z~7 and z~8
galaxies: Spectroscopic confirmation of galaxies at z~7 and above has been extremely
difficult, owing to a drop in intensity of Ly-alpha emission in comparison with
samples at z~6. This crucial finding could potentially signal the ending of
cosmic reionization. However it is based on small datasets, often incomplete
and heterogeneous in nature. We introduce a flexible Bayesian framework, useful
to interpret such evidence. Within this framework, we implement two simple
phenomenological models: a smooth one, where the distribution of Ly-alpha is
attenuated by a factor \es with respect to z~6; a patchy one where a fraction
\ep is absorbed/non-emitted while the rest is unabsorbed. From a compilation of
39 observed z~7 galaxies we find \es=0.69+-0.12 and \ep=0.66+-0.16. The models
can be used to compute fractions of emitters above any equivalent width W. For
W>25\AA, we find X^{25}_{z=7}=0.37+-0.11 (0.14+-0.06) for galaxies fainter
(brighter) than M_{UV}=-20.25 for the patchy model, consistent with previous
work, but with smaller uncertainties by virtue of our full use of the data. At
z~8 we combine new deep (5-\sigma flux limit 10^{-17}ergs^{-1}cm^{-2})
Keck-NIRSPEC observations of a bright Y-dropout identified by our BoRG Survey,
with those of three objects from the literature and find that the inference is
inconclusive. We compute predictions for future near-infrared spectroscopic
surveys and show that it is challenging but feasible to constrain the
distribution of Ly-alpha emitters at z~8 and distinguish between models. | Testing General Relativity on cosmological scales at redshift z ~ 1.5
with quasar and CMB lensing: We test general relativity (GR) at the effective redshift $\bar{z} \sim 1.5$
by estimating the statistic $E_G$, a probe of gravity, on cosmological scales
$19 - 190\,h^{-1}{\rm Mpc}$. This is the highest-redshift and largest-scale
estimation of $E_G$ so far. We use the quasar sample with redshifts $0.8 < z <
2.2$ from Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic
Survey (eBOSS) Data Release 16 (DR16) as the large-scale structure (LSS)
tracer, for which the angular power spectrum $C_\ell^{qq}$ and the
redshift-space distortion (RSD) parameter $\beta$ are estimated. By cross
correlating with the $\textit{Planck}$ 2018 cosmic microwave background (CMB)
lensing map, we detect the angular cross-power spectrum $C_\ell^{\kappa q}$
signal at $12\,\sigma$ significance. Both jackknife resampling and simulations
are used to estimate the covariance matrix (CM) of $E_G$ at $5$ bins covering
different scales, with the later preferred for its better constraints on the
covariances. We find $E_G$ estimates agree with the GR prediction at
$1\,\sigma$ level over all these scales. With the CM estimated with $300$
simulations, we report a best-fit scale-averaged estimate of
$E_G(\bar{z})=0.30\pm 0.05$, which is in line with the GR prediction $E_G^{\rm
GR}(\bar{z})=0.33$ with $\textit{Planck}$ 2018 CMB+BAO matter density fraction
$\Omega_{\rm m}=0.31$. The statistical errors of $E_G$ with future LSS surveys
at similar redshifts will be reduced by an order of magnitude, which makes it
possible to constrain modified gravity models. |
Isotropic cosmic birefringence from early dark energy: A tantalizing hint of isotropic cosmic birefringence has been found in the $E
B$ cross-power spectrum of the cosmic microwave background (CMB) polarization
data with a statistical significance of $3\sigma$. A pseudoscalar field coupled
to the CMB photons via the Chern-Simons term can explain this observation. The
same field may also be responsible for early dark energy (EDE), which
alleviates the so-called Hubble tension. Since the EDE field evolves
significantly during the recombination epoch, the conventional formula that
relates $E B$ to the difference between the $E$- and $B$-mode auto-power
spectra is no longer valid. Solving the Boltzmann equation for polarized
photons and the dynamics of the EDE field consistently, we find that currently
favored parameter space of the EDE model yields a variety of shapes of the $EB$
spectrum, which can be tested by CMB experiments. | Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes
and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm
Tension with LambdaCDM: We present an expanded sample of 75 Milky Way Cepheids with Hubble Space
Telescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibrate
the extragalactic distance ladder and refine the determination of the Hubble
constant. All HST observations were obtained with the same instrument (WFC3)
and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in
Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial
scanning mode to mitigate saturation and reduce pixel-to-pixel calibration
errors, reaching a mean photometric error of 5 millimags per observation. We
use new Gaia EDR3 parallaxes, vastly improved since DR2, and the
Period-Luminosity (PL) relation of these Cepheids to simultaneously calibrate
the extragalactic distance ladder and to refine the determination of the Gaia
EDR3 parallax offset. The resulting geometric calibration of Cepheid
luminosities has 1.0% precision, better than any alternative geometric anchor.
Applied to the calibration of SNe~Ia, it results in a measurement of the Hubble
constant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions based
on earlier Gaia data releases. We also find the slope of the Cepheid PL
relation in the Milky Way, and the metallicity dependence of its zeropoint, to
be in good agreement with the mean values derived from other galaxies. In
combination with the best complementary sources of Cepheid calibration, we
reach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigma
difference with the prediction from Planck CMB observations under LambdaCDM. We
expect to reach ~1.3% precision in the near term from an expanded sample of ~40
SNe Ia in Cepheid hosts. |
The supernova delay time distribution in galaxy clusters and
implications for Type-Ia progenitors and metal enrichment: Knowledge of the supernova (SN) delay time distribution (DTD) - the SN rate
versus time that would follow a hypothetical brief burst of star formation -
can shed light on SN progenitors and physics. We compile recent measurements of
the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts z=0-1.45. Together
with the observed iron-to-stellar mass ratio in clusters, which constrains the
time-integrated number of SN Ia events in clusters, we recover the DTD of SNe
Ia in cluster environments. The DTD peaks at the shortest time-delay interval
we probe, 0<t<2.2 Gyr, with a low tail out to delays of ~10 Gyr, and is
remarkably consistent with several recent DTD reconstructions based on
different methods, in different environments. We test DTD models from the
literature, requiring that they simultaneously reproduce the observed cluster
SN rates and the observed iron-to-stellar mass ratios. A power-law DTD of the
form t^{-1.2+/-0.3}, extending to a Hubble time, can satisfy both constraints.
Shallower power laws, such as t^{-1/2} cannot, assuming a single DTD, and a
single star-formation burst (either brief or extended) at high z. This implies
50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from
double-degenerate (DD) models, which generically have ~t^{-1} shapes over a
wide range of timescales, match the data, but only if their predictions are
scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits
to the data, due to a lack of delayed SNe and overall low numbers of SNe. The
observations also permit a combination of two SN Ia populations - prompt (e.g.
SD) SNe Ia that explode within a few Gyr of star formation, and produce about
60% of the iron mass in clusters, and a DD population that contributes the
events seen at z<1.4. Our results support the existence of a DD progenitor
channel for SNe Ia, if the overall predicted numbers can be suitably increased. | The Evolution of Mass-size Relation for Lyman Break Galaxies From z=1 to
z=7: For the first time, we study the evolution of the stellar mass-size relation
for star-forming galaxies from z ~ 4 to z ~ 7 from Hubble-WFC3/IR camera
observations of the HUDF and Early Release Science (ERS) field. The sizes are
measured by determining the best fit model to galaxy images in the rest-frame
2100 \AA \ with the stellar masses estimated from SED fitting to rest-frame
optical (from Spitzer/IRAC) and UV fluxes. We show that the stellar mass-size
relation of Lyman-break galaxies (LBGs) persists, at least to z ~ 5, and the
median size of LBGs at a given stellar mass increases towards lower redshifts.
For galaxies with stellar masses of 9.5<Log(M*/Msun)<10.4 sizes evolve as
$(1+z)^{-1.20\pm0.11}$. This evolution is very similar for galaxies with lower
stellar masses of 8.6<Log(M*/Msun)<9.5 which is $r_{e} \propto
(1+z)^{-1.18\pm0.10}$, in agreement with simple theoretical galaxy formation
models at high z. Our results are consistent with previous measurements of the
LBGs mass-size relation at lower redshifts (z ~ 1-3). |
AMICO: optimised detection of galaxy clusters in photometric surveys: We present AMICO (Adaptive Matched Identifier of Clustered Objects), a new
algorithm for the detection of galaxy clusters in photometric surveys. AMICO is
based on the Optimal Filtering technique, which allows to maximise the
signal-to-noise ratio of the clusters. In this work we focus on the new
iterative approach to the extraction of cluster candidates from the map
produced by the filter. In particular, we provide a definition of membership
probability for the galaxies close to any cluster candidate, which allows us to
remove its imprint from the map, allowing the detection of smaller structures.
As demonstrated in our tests, this method allows the deblending of close-by and
aligned structures in more than $50\%$ of the cases for objects at radial
distance equal to $0.5 \times R_{200}$ or redshift distance equal to $2 \times
\sigma_z$, being $\sigma_z$ the typical uncertainty of photometric redshifts.
Running AMICO on mocks derived from N-body simulations and semi-analytical
modelling of the galaxy evolution, we obtain a consistent mass-amplitude
relation through the redshift range $0.3 < z < 1$, with a logarithmic slope
$\sim 0.55$ and a logarithmic scatter $\sim 0.14$. The fraction of false
detections is steeply decreasing with S/N, and negligible at S/N > 5. | Angpow: a software for the fast computation of accurate tomographic
power spectra: The statistical distribution of galaxies is a powerful probe to constrain
cosmological models and gravity. In particular the matter power spectrum $P(k)$
brings information about the cosmological distance evolution and the galaxy
clustering together. However the building of $P(k)$ from galaxy catalogues
needs a cosmological model to convert angles on the sky and redshifts into
distances, which leads to difficulties when comparing data with predicted
$P(k)$ from other cosmological models, and for photometric surveys like LSST.
The angular power spectrum $C_\ell(z_1,z_2)$ between two bins located at
redshift $z_1$ and $z_2$ contains the same information than the matter power
spectrum, is free from any cosmological assumption, but the prediction of
$C_\ell(z_1,z_2)$ from $P(k)$ is a costly computation when performed exactly.
The Angpow software aims at computing quickly and accurately the auto
($z_1=z_2$) and cross ($z_1 \neq z_2$) angular power spectra between redshift
bins. We describe the developed algorithm, based on developments on the
Chebyshev polynomial basis and on the Clenshaw-Curtis quadrature method. We
validate the results with other codes, and benchmark the performance. Angpow is
flexible and can handle any user defined power spectra, transfer functions, and
redshift selection windows. The code is fast enough to be embedded inside
programs exploring large cosmological parameter spaces through the
$C_\ell(z_1,z_2)$ comparison with data. We emphasize that the Limber's
approximation, often used to fasten the computation, gives wrong $C_\ell$
values for cross-correlations. |
Relic density and CMB constraints on dark matter annihilation with
Sommerfeld enhancement: We calculate how the relic density of dark matter particles is altered when
their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa
interaction between the annihilating particles. Maintaining a dark matter
abundance consistent with current observational bounds requires the
normalization of the s-wave annihilation cross section to be decreased compared
to a model without enhancement. The level of suppression depends on the
specific parameters of the particle model, with the kinetic decoupling
temperature having the most effect. We find that the cross section can be
reduced by as much as an order of magnitude for extreme cases. We also compute
the mu-type distortion of the CMB energy spectrum caused by energy injection
from such Sommerfeld-enhanced annihilation. Our results indicate that in the
vicinity of resonances, associated with bound states, distortions can be large
enough to be excluded by the upper limit |mu|<9.0x10^(-5) found by the
COBE/FIRAS experiment. | Thermal Instability & the Feedback Regulation of Hot Halos in Clusters,
Groups, and Galaxies: Observations of clusters and groups imply that such halos are roughly in
global thermal equilibrium, with heating balancing cooling when averaged over
sufficiently long time- and length-scales; the ICM is, however, very likely to
be locally thermally unstable. Using simple observationally-motivated heating
prescriptions, we show that local thermal instability (TI) can produce a
multi-phase medium---with ~ 10000 K cold filaments condensing out of the hot
ICM---only when the ratio of the TI timescale in the hot plasma (t_{TI}) to the
free-fall timescale (t_{ff}) satisfies t_{TI}/t_{ff} <~ 10. This criterion
quantitatively explains why cold gas and star formation are preferentially
observed in low-entropy clusters and groups. In addition, the interplay among
heating, cooling, and TI reduces the net cooling rate and the mass accretion
rate at small radii by factors of ~ 100 relative to cooling-flow models. This
dramatic reduction is in line with observations. The feedback efficiency
required to prevent a cooling-flow is ~ 0.001 for clusters and decreases for
lower mass halos; supernova heating may be energetically sufficient to balance
cooling in galactic halos. We further argue that the ICM self-adjusts so that
t_{TI}/t_{ff} >~ 10 at all radii. When this criterion is not satisfied, cold
filaments condense out of the hot phase and reduce the density of the ICM.
These cold filaments can power the black hole and/or stellar feedback required
for global thermal balance, which drives t_{TI}/t_{ff} >~ 10. In comparison to
clusters, groups have central cores with lower densities and larger radii. This
can account for the deviations from self-similarity in the X-ray
luminosity-temperature (L_X-T_X) relation. The high-velocity clouds observed in
the Galactic halo can also be due to local TI producing multi-phase gas close
to the virial radius. |
The Alcock Paczynski test with 21cm intensity field: Feasibility of the Alcock Paczynski (AP) test by stacking voids in the 21cm
line intensity field is presented. We analyze the Illstris-TNG simulation to
obtain the 21cm signal map. We then randomly distribute particles depending on
the 21cm intensity field to find voids by using publicly available code, VIDE.
As in the galaxy clustering, the shape of the stacked void in the 21cm field is
squashed along the line of sight due to the peculiar velocities in
redshift-space, although it becomes spherical in real-space. The redshift-space
distortion for the stacked void weakly depends on redshift and we show that the
dependency can be well described by the linear prediction, with the amplitude
of the offset being free parameters. We find that the AP test using the stacked
voids in a 21cm intensity map is feasible and the parameter estimation on
$\Omega_{\rm m}$ and $w$ is unbiased. | Qualitative interpretation of galaxy spectra: We describe a simple step-by-step guide to qualitative interpretation of
galaxy spectra. Rather than an alternative to existing automated tools, it is
put forward as an instrument for quick-look analysis, and for gaining physical
insight when interpreting the outputs provided by automated tools. Though the
recipe is of general application, it was developed for understanding the nature
of the Automatic Spectroscopic K-means based (ASK) template spectra. They
resulted from the classification of all the galaxy spectra in the Sloan Digital
Sky Survey data release 7 (SDSS-DR7), thus being a comprehensive representation
of the galaxy spectra in the local universe. Using the recipe, we give a
description of the properties of the gas and the stars that characterize the
ASK classes, from those corresponding to passively evolving galaxies, to HII
galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found
to be in excellent agreement with quantitative analyses of the same spectra. A
number of byproducts follow from the analysis. There is a tight correlation
between the age of the stellar population and the metallicity of the gas, which
is stronger than the correlations between galaxy mass and stellar age, and
galaxy mass and gas metallicity. The galaxy spectra are known to follow a
1-dimensional sequence, and we identify the luminosity-weighted mean stellar
age as the affine parameter that describes the sequence. All ASK classes happen
to have a significant fraction of old stars, although spectrum-wise they are
outshined by the youngest populations. Old stars are metal rich or metal poor
depending on whether they reside in passive galaxies or in star-forming
galaxies. |
Microlensing signatures of extended dark objects using machine learning: This paper presents a machine learning-based method for the detection of the
unique gravitational microlensing signatures of extended dark objects, such as
boson stars, axion miniclusters and subhalos. We adapt MicroLIA, a machine
learning-based package tailored to handle the challenges posed by low-cadence
data in microlensing surveys. Using realistic observational timestamps, our
models are trained on simulated light curves to distinguish between
microlensing by point-like and extended lenses, as well as from other object
classes which give a variable magnitude. We show that boson stars, examples of
objects with a relatively flat mass distribution, can be confidently identified
for $0.8 \lesssim r/r_E\lesssim 3$. Intriguingly, we also find that more
sharply peaked structures, such as NFW-subhalos, can be distinctly recognized
from point-lenses under regular observation cadence. Our findings significantly
advance the potential of microlensing data in uncovering the elusive nature of
extended dark objects. The code and dataset used are also provided. | Galaxy Zoo: Passive Red Spirals: We study the spectroscopic properties and environments of red spiral galaxies
found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated
spirals we construct a sample of truly passive disks (not dust reddened, nor
dominated by old stellar populations in a bulge). As such, our red spirals
represent an interesting set of possible transition objects between normal blue
spirals and red early types. We use SDSS data to investigate the physical
processes which could have turned these objects red without disturbing their
morphology. Red spirals prefer intermediate density regimes, however there are
no obvious correlations between red spiral properties and environment -
environment alone is not sufficient to determine if a spiral will become red.
Red spirals are a small fraction of spirals at low masses, but are a
significant fraction at large stellar masses - massive galaxies are red
independent of morphology. We confirm that red spirals have older stellar popns
and less recent star formation than the main spiral population. While the
presence of spiral arms suggests that major star formation cannot have ceased
long ago, we show that these are not recent post-starbursts, so star formation
must have ceased gradually. Intriguingly, red spirals are ~4 times more likely
than normal spirals to host optically identified Seyfert or LINER, with most of
the difference coming from LINERs. We find a curiously large bar fraction in
the red spirals suggesting that the cessation of star formation and bar
instabilities are strongly correlated. We conclude by discussing the possible
origins. We suggest they may represent the very oldest spiral galaxies which
have already used up their reserves of gas - probably aided by strangulation,
and perhaps bar instabilities moving material around in the disk. |
The linear growth rate of structure in Parametrized Post Friedmannian
Universes: A possible solution to the dark energy problem is that Einstein's theory of
general relativity is modified. A suite of models have been proposed that, in
general, are unable to predict the correct amount of large scale structure in
the distribution of galaxies or anisotropies in the Cosmic Microwave
Background. It has been argued, however, that it should be possible to
constrain a general class of theories of modified gravity by focusing on
properties such as the growing mode, gravitational slip and the effective, time
varying Newton's constant. We show that assuming certain physical requirements
such as stability, metricity and gauge invariance, it is possible to come up
with consistency conditions between these various parameters. In this paper we
focus on theories which have, at most, 2nd derivatives in the metric variables
and find restrictions that shed light on current and future experimental
constraints without having to resort to a (as yet unknown) complete theory of
modified gravity. We claim that future measurements of the growth of structure
on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on
both dark energy and modified theories of gravity. | Redshift evolution and covariances for joint lensing and clustering
studies with DESI Y1: Galaxy-galaxy lensing (GGL) and clustering measurements from the Dark Energy
Spectroscopic Instrument Year 1 (DESI Y1) dataset promise to yield
unprecedented combined-probe tests of cosmology and the galaxy-halo connection.
In such analyses, it is essential to identify and characterise all relevant
statistical and systematic errors. In this paper, we forecast the covariances
of DESI Y1 GGL+clustering measurements and characterise the systematic bias due
to redshift evolution in the lens samples. Focusing on the projected clustering
and galaxy-galaxy lensing correlations, we compute a Gaussian analytical
covariance, using a suite of N-body and log-normal simulations to characterise
the effect of the survey footprint. Using the DESI One Percent Survey data, we
measure the evolution of galaxy bias parameters for the DESI Luminous Red
Galaxy (LRG) and Bright Galaxy Survey (BGS) samples. We find mild evolution in
the LRGs in 0.4 < z < 0.8, subdominant compared to the expected statistical
errors. For BGS, we find less evolution effects for brighter absolute magnitude
cuts, at the cost of reduced sample size. We find that with a fiducial redshift
bin width delta z = 0.1, evolution effects on GGL is negligible across all
scales, all fiducial selection cuts, all fiducial redshift bins, given DESI Y1
sample size. Galaxy clustering is more sensitive to evolution due to the bias
squared scaling. Nevertheless the redshift evolution effect is insignificant
for clustering above the 1-halo scale of 0.1Mpc/h. For studies that wish to
reliably access smaller scales, additional treatment of redshift evolution is
likely needed. This study serves as a reference for GGL and clustering studies
using the DESI Y1 sample |
Distance-Redshift Relations in an Anisotropic Cosmological Model: In this paper we study an anisotropic model generated from a particular
Bianchi type-III metric, which is a generalization of G\"odel's metric and an
exact solution of Einstein's field equations. We analyse type Ia supernova
data, namely the SDSS sample calibrated with the MLCS2k2 fitter, and we verify
in which ranges of distances and redshifts the anisotropy could be observed. We
also consider, in a joint analysis, the position of the first peak in the CMB
anisotropy spectrum, as well as current observational constraints on the Hubble
constant. We conclude that a small anisotropy is permitted by the data, and
that more accurate measurements of supernova distances above z = 2 might
indicate the existence of such anisotropy in the universe. | Gravitational Lensing by Spherical Lenses: In this work we introduced a new proposal to study the gravitational lensing
theory by spherical lenses, starting from its surface mass density $\Sigma(x)$
written in terms of a decreasing function $f$ of a dimensionless coordinate $x$
on the lens plane. The main result is the use of the function $f(x)$ to find
directly the lens properties, at the same time that the lens problem is
described by a first order differential equation which encodes all information
about the lens. SIS and NIS profiles are used as examples to find their
functions $f(x)$. Using the Poisson equation we find that the deflection angle
is directly proportional to $f(x)$, and therefore the lens equation can be
written in terms of the function and the parameters of the lens. The critical
and caustic curves, as well as image formation and magnification generated by
the lens are analyzed. As an example of this method, the properties of a lens
modeled by a NFW profile are determined. Altough the puntual mass is
spherically symmetric, its mass density is not continuous so that its $f(x)$
function is discussed in the Appendix A. |
The origin of the relationship between black hole mass and host galaxy
bulge luminosity: There is a strong decrease in scatter in the black hole mass versus bulge
luminosity relationship with increasing luminosity and very little scatter for
the most luminous galaxies. It is shown that this is a natural consequence of
the substantial initial dispersion in the ratio of black hole mass to total
stellar mass and of subsequent galaxy growth through hierarchical mergers.
"Fine-tuning" through feedback between black hole growth and bulge growth is
neither necessary nor desirable. | Spontaneous symmetry breaking in inflationary cosmology: on the fate of
Goldstone Bosons: We argue that in an inflationary cosmology a consequence of the lack of time
translational invariance is that spontaneous breaking of a continuous symmetry
and Goldstone's theorem \emph{do not} imply the existence of \emph{massless}
Goldstone modes. We study spontaneous symmetry breaking in an O(2) model, and
implications for O(N) in de Sitter space time. The Goldstone mode acquires a
radiatively generated mass as a consequence of infrared divergences, and the
continuous symmetry is spontaneously broken for any finite $N$, however there
is a \emph{first order phase transition} as a function of the Hawking
temperature $T_H=H/2\pi$. For O(2) the symmetry is spontaneously broken for
$T_H < T_c= \lambda^{1/4} v/2.419$ where $\lambda$ is the quartic coupling and
$v$ is the tree level vacuum expectation value and the Goldstone mode acquires
a radiatively generated mass $\mathcal{M}^2_\pi \propto \lambda^{1/4} H$. The
first order nature of the transition is a consequence of the strong infrared
behavior of minimally coupled scalar fields in de Sitter space time, the jump
in the order parameter at $T_H=T_c$ is $\sigma_{0c} \simeq 0.61\,
{H}/{\lambda^{1/4}}$. In the strict $N\rightarrow \infty$ the symmetry cannot
be spontaneously broken. Furthermore, the lack of kinematic thresholds imply
that the Goldstone modes \emph{decay} into Goldstone and Higgs modes by
emission and absorption of superhorizon quanta. |
Multiphase Gas In Galaxy Halos: The OVI Lyman-limit System toward
J1009+0713: We have serendipitously detected a strong O VI-bearing Lyman limit system at
z_abs = 0.3558 toward the QSO J1009+0713 (z_em = 0.456) in our survey of
low-redshift galaxy halos with the Hubble Space Telescope's Cosmic Origins
Spectrograph. Its rest-frame equivalent width of W_r = 835 +/- 49 mA is the
highest for an intervening absorber yet detected in any low-redshift QSO
sightline, with absorption spanning 400 km s^-1 in its rest frame. HST/WFC3
images of the galaxy field show that the absorber is associated with two
galaxies lying at 14 and 46 kpc from the QSO line of sight. The bulk of the
absorbing gas traced by H I resides in two strong, blended component groups
that possess a total logN(HI) = 18 - 18.8. The ion ratios and column densities
of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a
simple photoionization model in which diffuse, low-metallicity halo gas is
exposed to a photoionizing field from stars in the nearby galaxies that
propagates into the halo at 10% efficiency. We constrain the metallicity firmly
within the range 0.1 - 1 Zsun, and photoionization modeling indirectly
indicates a subsolar metallicity of 0.05 - 0.5 Zsun. The appearance of strong O
VI and nine Mg II components and our review of similar systems in the
literature support the "interface" picture of high-velocity O VI: the total
strength of the O VI shows a positive correlation with the number of detected
components in the low-ionization gas, however the total O VI column densities
still far exceed the values expected from interface models for the number of
detected clouds. | Cos observations of metal line and broad lyman alpha absorption in the
multi-phase o vi and ne viii system toward he 02226-4110: Observations of the QSO HE 0226-4110 (zem = 0.495) with the Cosmic Origins
Spectrograph (COS) from 1134 to 1796 {\AA} with a resolution of ~17 km s-1 and
signal-to- noise (S/N) per resolution element of 20 to 40 are used to study the
multi-phase absorption system at z = 0.20701 containing O VI and Ne VIII. The
system was previously studied with lower S/N observations with FUSE and STIS.
The COS observations provide more reliable measures of the H I and metal lines
present in the system and reveal the clear presence of broad Lyman {\alpha}
(BLA) absorption with b = 72(+13, -6) km s-1 and logN(H I) = 13.87\pm0.08.
Detecting BLAs associated with warm gas absorbers is crucial for determining
the temperature, metallicity and total baryonic content of the absorbers. The
BLA is probably recording the trace amount of thermally broadened H I in the
collisionally ionized plasma with log T ~5.7 that also produces the O VI and Ne
VIII absorption. The total hydrogen column in the collisionally ionized gas,
logN(H) ~ 20.1, exceeds that in the cooler photoionized gas in the system by a
factor of ~22. The oxygen abundance in the collisionally ionized gas is [O/H] =
-0.89\pm0.08\pm0.07. The absorber probably occurs in the circumgalactic
environment (halo) of a foreground L = 0.25L* disk galaxy with an impact
parameter of 109h70-1 kpc identified by Mulchaey & Chen (2009). |
Galaxies and Environment of the Clusters of Galaxies CL 0024+1654 and RX
J0152.7-1357: We present the analysis and results of photometric and spectroscopic catalog
combined with X-ray data of two non-relaxed clusters CL 0024+1654 (z=0.4) and
RX J0152.7-1357 (z=0.8). Using the Spearman correlation analysis we quantify
the correlation between morphology, color, and star formation rate of each
galaxy with its surrounding number density, mass density, and temperature of
Intracluster Medium (ICM). Although our results show that the two clusters
exhibit a weaker correlation compared with relaxed clusters, it still confirms
the significant effect of the ICM in varying the star formation rates in the
galaxies. Various physical mechanisms have been suggested to explain the
relation between the properties of galaxies and their environments for example:
ram pressure stripping, mergers etc. Nonetheless, using this analysis alone, it
is difficult to identify the dominant environmental mechanism(s) operating in
clusters of galaxies and the role of the initial condition. | The enigmatic pair of dwarf galaxies Leo IV and Leo V: coincidence or
common origin?: We have obtained deep photometry in two 1x1 degree fields covering the close
pair of dwarf spheroidal galaxies (dSph) Leo IV and Leo V and part of the area
in between. We find that both systems are significantly larger than indicated
by previous measurements based on shallower data and also significantly
elongated. With half-light radii of r_h=4'.6 +- 0'.8 (206 +- 36 pc) and
r_h=2'.6 +- 0'.6 (133 +- 31 pc), respectively, they are now well within the
physical size bracket of typical Milky Way dSph satellites. Their ellipticities
of epsilon ~0.5 are shared by many faint (M_V>-8) Milky Way dSphs. The large
spatial extent of our survey allows us to search for extra-tidal features with
unprecedented sensitivity. The spatial distribution of candidate red giant
branch and horizontal branch stars is found to be non-uniform at the ~3 sigma
level. This substructure is aligned along the direction connecting the two
systems, indicative of a possible `bridge' of extra-tidal material. Fitting the
stellar distribution with a linear Gaussian model yields a significance of 4
sigma for this overdensity, a most likely FWHM of ~16 arcmin and a central
surface brightness of ~32 mag arcsec^{-2}. We investigate different scenarios
to explain the close proximity of Leo IV and Leo V and the possible tidal
bridge between them. Orbit calculations demonstrate that they are unlikely to
be remnants of a single disrupted progenitor, while a comparison with
cosmological simulations shows that a chance collision between unrelated
subhalos is negligibly small. Leo IV and Leo V could, however, be a bound
`tumbling pair' if their combined mass exceeds 8 +- 4 x 10^9 M_sun. The
scenario of an internally interacting pair appears to be the most viable
explanation for this close celestial companionship. (abridged) |
The ATLAS3D project - XVIII. CARMA CO imaging survey of early-type
galaxies: We present the Combined Array for Research in Millimeter Astronomy (CARMA)
ATLAS3D molecular gas imaging survey, a systematic study of the distribution
and kinematics of molecular gas in CO-rich early-type galaxies. Our full sample
of 40 galaxies (30 newly mapped and 10 taken from the literature) is complete
to a 12CO(1-0) integrated flux of 18.5 Jy km/s, and it represents the largest,
best-studied sample of its type to date. A comparison of the CO distribution of
each galaxy to the g-r color image (representing dust) shows that the molecular
gas and dust distributions are in good agreement and trace the same underlying
interstellar medium. The galaxies exhibit a variety of CO morphologies,
including discs (50%), rings (15%), bars+rings (10%), spiral arms (5%), and
mildly (12.5%) and strongly (7.5%) disrupted morphologies. There appear to be
weak trends between galaxy mass and CO morphology, whereby the most massive
galaxies in the sample tend to have molecular gas in a disc morphology. We
derive a lower limit to the total accreted molecular gas mass across the sample
of 2.48x10^10 Msuns, or approximately 8.3x10^8 Msuns per minor merger within
the sample, consistent with minor merger stellar mass ratios. | Angular size test on the expansion of the Universe: Assuming the standard cosmological model as correct, the average linear size
of galaxies with the same luminosity is six times smaller at z=3.2 than at z=0,
and their average angular size for a given luminosity is approximately
proportional to 1/z. Neither the hypothesis that galaxies which formed earlier
have much higher densities nor their luminosity evolution, mergers ratio, or
massive outflows due to a quasar feedback mechanism are enough to justify such
a strong size evolution. Also, at high redshift, the intrinsic ultraviolet
surface brightness would be prohibitively high with this evolution, and the
velocity dispersion much higher than observed. We explore here another
possibility to overcome this problem by considering different cosmological
scenarios that might make the observed angular sizes compatible with a weaker
evolution.
One of the models explored, a very simple phenomenological extrapolation of
the linear Hubble law in a Euclidean static universe, fits the angular size vs.
redshift dependence quite well, which is also approximately proportional to 1/z
with this cosmological model. There are no free parameters derived ad hoc,
although the error bars allow a slight size/luminosity evolution. The type Ia
supernovae Hubble diagram can also be explained in terms of this model with no
ad hoc fitted parameter.
WARNING: I do not argue here that the true Universe is static. My intention
is just to discuss which theoretical models provide a better fit to the data of
observational cosmology. |
The earliest galaxies seen in 21 cm line absorption: We investigate the 21 cm absorption lines produced by non-linear structures
during the early stage of reionization, i.e. the starless minihalos and the
dwarf galaxies. After a detailed modelling of their properties, with particular
attention to the coupling physics, we determine their 21 cm absorption line
profiles. The infalling gas velocity around minihalos/dwarf galaxies strongly
affects the line shape, and with the low spin temperatures outside the virial
radii of the systems, gives rise to horn-like line profiles. The optical depth
of a dwarf galaxy is reduced for lines of sight penetrating through its HII
region, and especially, a large HII region created by a dwarf galaxy with
higher stellar mass and/or a top-heavy initial mass function results in an
optical depth trough rather than an absorption line. We compute synthetic
spectra of 21 cm forest for both high redshift quasars and radio afterglows of
gamma ray bursts (GRBs). Even with the planned SKA, radio afterglows of most if
not all GRBs would still be too dim to be the background sources for high
resolution (1 kHz) observations, but absorption lines can be easily detected
towards a high-z quasar. Broadband observation against GRB afterglows can also
be used to reveal the evolving 21 cm signal from both minihalos and dwarf
galaxies if there was no X-ray background or it was extremely weak, but it
becomes difficult if an early X-ray background existed. Hence the 21 cm
absorption could be a powerful probe of the presence/intensity of the X-ray
background and the thermal history of the early universe. | Lower Redshift Analogues of the Sources of Reionization: Known populations of QSOs appear to fall short of producing the ionizing flux
required for re-ionizing the universe. The alternative, galaxies as sources of
ionizing photons, suffers from the problem that known types of galaxies are
almost completely opaque to ionizing photons. For reionization to happen,
either large numbers of (largely undiscovered) sources are required, or the
known populations of galaxies need to have had a much larger escape fraction
for ionizing radiation in the past. We discuss recent discoveries of faint z~3
Lyman alpha emitters with asymmetric, extended Lyman alpha emission regions,
which apparently are related to interacting galaxies. The unusually shaped line
profiles and the underlying stellar populations of these objects suggest the
presence of damaged gaseous halos, infall of gas, tidal or stripped stellar
features and young populations of hot stars, that would all be conducive to the
release of ionizing radiation. As galaxy interactions and mergers increase with
redshift, these effects can only become more important at earlier times, and so
these interacting z~3 objects may be late, lower redshift analogues of the
sources of reionization. |
Observational bounds on extended minimal theories of massive gravity:
New limits on the graviton mass: In this work, we derive for the first time observational constraints on the
extended Minimal Theory of Massive Gravity (eMTMG) framework in light of
Planck-CMB data, geometrical measurements from Baryon Acoustic Oscillation
(BAO), Type Ia supernovae from the recent Pantheon+ samples, and also using the
auto and cross-correlations cosmic shear measurements from KIDS-1000 survey.
Given the great freedom of dynamics choice for the theory, we consider an
observationally motivated subclass in which the background evolution of the
Universe goes through a transition from a (positive or negative) value of the
effective cosmological constant to another value. From the statistical point of
view, we did not find evidence of such a transition, i.e. deviation from the
standard $\Lambda$CDM behavior, and from the joint analysis using Planck + BAO
+ Pantheon+ data, we constrain the graviton mass to $< 6.6 \times 10^{-34}$ eV
at 95% CL. We use KIDS-1000 survey data to constrain the evolution of the
scalar perturbations of the model and its limits for the growth of structure
predicted by the eMTMG scenario. In this case, we find small evidence at 95% CL
for a non-zero graviton mass. We interpret and discuss these results in light
of the current tension on the $S_8$ parameter. We conclude that, within the
subclass considered, the current data are only able to impose upper bounds on
the eMTMG dynamics. Given its potentialities beyond the subclass, eMTMG can be
classified as a good candidate for modified gravity, serving as a framework in
which observational data can effectively constrain (or confirm) the graviton
mass and deviations from the standard $\Lambda$CDM behavior. | A test of MOND and Emergent Gravity with SMACS J0723.3-7327 using
eROSITA observations: We implement a test of MOND and Verlinde's Emergent Gravity using the galaxy
cluster SMACS J0723-7327, which has been recently imaged using the eROSITA
X-ray telescope as well as with JWST. We test MOND using two independent
methods. The first method involves comparing the dynamical MOND mass and
baryonic mass, while the second method entails a comparison of the
MOND-estimated temperature with the observed temperature. We then compare the
unseen mass predicted by Emergent Gravity with the estimated dark matter mass.
We find that MOND is able to explain the mass discrepancy at large radii but
not in the central regions. The observed temperature profile is also in slight
disagreement with that in the MOND paradigm. Likewise the Emergent Gravity
Theory shows a marginal discrepancy in accurately accounting for the dynamical
mass in the inner regions. Our results are qualitatively consistent with the
earlier tests on other clusters. |
Hunting for Galaxies and Halos in simulations with VELOCIraptor: We present VELOCIraptor, a massively parallel galaxy/(sub)halo finder that is
also capable of robustly identifying tidally disrupted objects and separate
stellar halos from galaxies. The code is written in c++11, use the MPI and
OpenMP API's for parallelisation, and includes python tools to read/manipulate
the data products produced. We demonstrate the power of the VELOCIraptor
(sub)halo finder, showing how it can identify subhalos deep within the host
that have negligible density contrasts to their parent halo. We find a subhalo
mass-radial distance dependence: large subhalos with mass ratios of
$\gtrsim10^{-2}$ are more common in the central regions that smaller subhalos,
a result of dynamical friction and low tidal mass loss rates. This dependence
is completely absent in (sub)halo finders in common use, which generally search
for substructure in configuration space, yet is present in codes that track
particles belonging to halos as they fall into other halos, such as HBT+.
VELOCIraptor largely reproduces the dependence seen without tracking, finding a
similar radial dependence to HBT+ in well resolved halos from our limited
resolution fiducial simulation. | z~7 Galaxies in the HUDF: First Epoch WFC3/IR Results: We present a sample of 16 robust z~7 z-drop galaxies detected by the newly
installed WFC3/IR camera on the Hubble Space Telescope. Our analysis is based
on the first epoch data of the HUDF09 program covering the Hubble Ultra Deep
Field with 60 orbits of Y, J, and H observations. These remarkable data cover
4.7 arcmin^2 and are the deepest NIR images ever taken, reaching to ~29 mag AB
(5 sigma). The 16 z~6.5-7.5 galaxies have been identified based on the Lyman
Break technique utilizing (z-Y) vs. (Y-J) colors. They have magnitudes J =
26.0-29.0 (AB), an average apparent half-light radius of ~0.16 arcsec (<~1
kpc), and show very blue colors (some even beta<~-2.5), in particular at low
luminosities. The WFC3/IR data confirms previous NICMOS detections indicating
that the dropout selection at z~7 is very reliable. Our data allow a first
determination of the faint end slope of the z~7 luminosity function, reaching
down to M_UV ~ -18, a full magnitude fainter than previous measurements. When
fixing phi*=1.4e-3/Mpc^3/mag to the value previously measured at z~6, we find a
best-fit value of alpha=-1.77+-0.20, with a characteristic luminosity of
M_*=-19.91+-0.09. This steep slope is similar to what is seen at z~2-6 and
indicates that low luminosity galaxies could potentially provide adequate flux
to reionize the universe. The remarkable depth and resolution of these new
images provide insights into the coming power of JWST. |
Runaway Stars and the Escape of Ionizing Radiation from High-Redshift
Galaxies: Approximately 30% of all massive stars in the Galaxy are runaways with
velocities exceeding 30 km/s. Their high speeds allow them to travel ~0.1-1 kpc
away from their birth place before they explode at the end of their several Myr
lifetimes. At high redshift, when galaxies were much smaller than in the local
universe, runaways could venture far from the dense inner regions of their host
galaxies. From these large radii, and therefore low column densities, much of
their ionizing radiation is able to escape into the intergalactic medium.
Runaways may therefore significantly enhance the overall escape fraction of
ionizing radiation, fesc, from small galaxies at high redshift. We present
simple models of the high-redshift runaway population and its impact on fesc as
a function of halo mass, size, and redshift. We find that the inclusion of
runaways enhances fesc by factors of ~1.1-8, depending on halo mass, galaxy
geometry, and the mechanism of runaway production, implying that runaways may
contribute 50-90% of the total ionizing radiation escaping from high-redshift
galaxies. Runaways may therefore play an important role in reionizing the
universe. | Joint Planck and WMAP CMB Map Reconstruction: We present a novel estimate of the cosmological microwave background (CMB)
map by combining the two latest full-sky microwave surveys: WMAP nine-year and
Planck PR1. The joint processing benefits from a recently introduced component
separation method coined "local-generalized morphological component analysis''
(LGMCA) based on the sparse distribution of the foregrounds in the wavelet
domain. The proposed estimation procedure takes advantage of the IRIS 100
micron as an extra observation on the galactic center for enhanced dust
removal. We show that this new CMB map presents several interesting aspects: i)
it is a full sky map without using any inpainting or interpolating method, ii)
foreground contamination is very low, iii) the Galactic center is very clean,
with especially low dust contamination as measured by the cross-correlation
between the estimated CMB map and the IRIS 100 micron map, and iv) it is free
of thermal SZ contamination. |
Testing gravity with the cosmic microwave background: constraints on
modified gravity with two tensorial degrees of freedom: We provide a cosmological test of modified gravity with two tensorial degrees
of freedom and no extra propagating scalar mode. The theory of gravity we
consider admits a cosmological model that is indistinguishable from the
$\Lambda$CDM model at the level of the background evolution. The model has a
single modified-gravity parameter $\beta$, the effect of which can be seen in
linear perturbations, though no extra scalar mode is propagating. Using the
Boltzmann code modified to incorporate the present model, we derive the
constraints $-0.047 < \beta < -0.028$ at 68$\%$ confidence from Planck CMB
data. Since our modified gravity model can hardly be constrained by the Solar
System tests and gravitational-wave propagation, our result offers the first
observational test on the model. | Induced gravitational waves from slow-roll inflation after an enhancing
phase: The primordial spectrum of fluctuations may present a large peak as a result
of enhancing features during inflation. This may include, but is not limited
to, bumps in the inflaton's potential, phases of ultra-slow-roll or turns in
multi-field space. However, in many models, inflation does not end immediately
after the enhancing feature and it is likely to continue with a second phase of
slow-roll. We show that the resulting induced gravitational waves may probe the
primordial spectrum from the second inflationary phase, even if its amplitude
is too small to directly induce detectable gravitational waves. This is
because, if there are sharp peaks in the primordial spectrum, the total
gravitational wave spectrum is not simply the sum of gravitational waves
induced by a peaked and scale-invariant primordial spectra separately, but
cross terms from interaction between these modes also become important. We also
find that such cross terms always have a characteristic slope. We discuss the
parameter space that may be probed by future gravitational waves detectors in
the presence of these signals. |
Parsec-scale dust emission from the polar region in the type 2 nucleus
of NGC 424: Advancements in infrared IR open up the possibility to spatially resolve AGN
on the parsec-scale level and study the circumnuclear dust distribution,
commonly referred to as the "dust torus", that is held responsible for the type
1/type 2 dichotomy of AGN. We used the mid-IR beam combiner MIDI together with
the 8m telescopes at the VLTI to observe the nucleus of the Seyfert 2 galaxy
NGC 424, achieving an almost complete coverage of the uv-plane accessible by
the available telescope configurations. We detect extended mid-IR emission with
a relatively baseline- and model-independent mid-IR half-light radius of (2.0
\pm 0.2) pc \times (1.5 \pm 0.3) pc (averaged over the 8-13 {\mu}m wavelength
range). The extended mid-IR source shows an increasing size with wavelength.
The orientation of the major axis in position angle -27deg is closely aligned
with the system axis as set by optical polarization observations. Torus models
typically favor extension along the mid-plane at mid-IR wavelengths instead.
Therefore, we conclude that the majority of the pc-scale mid-IR emission
(>~60%) in this type 2 AGN originates from optically-thin dust in the polar
region of the AGN, a scenario consistent with the near- to far-IR SED. We
suggest that a radiatively-driven dusty wind, possibly launched in a puffed-up
region of the inner hot part of the torus, is responsible for the polar dust.
In this picture, the torus dominates the near-IR emission up to about 5 {\mu}m,
while the polar dust is the main contributor to the mid-IR flux. Our results of
NGC 424 are consistent with recent observations of the AGN in the Circinus
galaxy and resemble large-scale characteristics of other objects. If our
results reflect a general property of the AGN population, the current paradigm
for interpreting and modeling the IR emission of AGN have to be revised.
(abridged) | The XMM deep survey in the CDF-S II. a 9-20 keV selection of heavily
obscured active galaxies at z>1.7: We present results on a search of heavily obscured active galaxies z>1.7
using the rest-frame 9-20 keV excess for X-ray sources detected in the deep
XMM-CDFS survey. Out of 176 sources selected with the conservative detection
criteria (>8 sigma) in the first source catalogue of Ranalli et al., 46 objects
lie in the redshift range of interest with the median redshift z~2.5. Their
typical rest-frame 10-20 keV luminosity is 1e+44 erg/s, as observed. Among
optically faint objects that lack spectroscopic redshift, four were found to be
strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption
features in their X-ray spectra were used to obtain X-ray spectroscopic
redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5
keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20
keV excess and were found to be strongly absorbed X-ray sources with column
density of nH > 0.6e+24 cm-2, including two possible Compton thick sources.
While they are emitting at quasar luminosity, ~3/4 of the sample objects are
found to be absorbed by nH > 1e+22 cm-2. A comparison with local AGN at the
matched luminosity suggests an increasing trend of the absorbed source fraction
for high-luminosity AGN towards high redshifts. |
Inflation-Dark Matter unified through Quantum Generation: We unify inflation and dark matter via a single scalar field phi. One of the
main difficulties for this unification is that between inflation and dark
matter one needs a successful reheating process and a long lasting period of
radiation. Therefore the amount of energy density in the inflaton-dark matter
field phi must be fine tune after reheating to give dark matter. Here we show
an alternative scheme in which the inflaton decays completely, disappearing
entirely from the spectrum. However, at low energies, before matter-radiation
equality, the same interaction term that leads to the inflaton decay,
regenerates phi. An essential feature is that the transition between the
intermediate radiation dominated to the dark matter phase is related to a
quantum generation of the scalar field \phi instead to purely classical
dynamics. Thanks to this quantum transition the inflation-dark matter
unification can take place naturally without fine tuning. The unification
scheme presented here has three parameters, the mass of the dark matter
particle m_o, the inflation parameter lambda and the coupling g for the
inflaton interaction. Phenomenology fixes the value for lambda and gives a
constraint between g and m_o, leaving only the mass of the dark matter particle
m_o as a free parameter. These same three parameters lambda, m_o, g are present
in models with inflation and a dark matter wimp particle but without
unification. Therefore our unification scheme does not increase the number of
parameters and it accomplishes the desired unification between inflaton and
dark matter for free. | Non-Gaussian Shape Recognition: A detection of primordial non-Gaussianity could transform our understanding
of the fundamental theory of inflation. The precision promised by upcoming CMB
and large-scale structure surveys raises a natural question: if a detection
given a particular template is made, what does this truly tell us about the
underlying theory? In this paper we present a systematic way to constrain a
wide range of non-Gaussian shapes, including general single and multi-field
models and models with excited initial states. We present a separable,
divergent basis able to recreate many shapes in the literature to high accuracy
with between three and seven basis functions. The basis allows shapes to be
grouped into broad "template classes", satisfying theoretically-relevant priors
on their divergence properties in the squeezed limit. We forecast how well a
Planck-like CMB survey could not only detect a general non-Gaussian signal but
discern more about its shape, using existing templates and new ones we propose.
This approach offers an opportunity to tie together minimal theoretical priors
with observational constraints on the shape in general, and in the squeezed
limit, to gain a deeper insight into what drove inflation. |
Inverse problem: Reconstruction of modified gravity action in Palatini
formalism by Supernova Type Ia data: We introduce in $f(R)$ gravity--Palatini formalism the method of inverse
problem to extract the action from the expansion history of the universe.
First, we use an ansatz for the scale factor and apply the inverse method to
derive an appropriate action for the gravity. In the second step we use the
Supernova Type Ia data set from the Union sample and obtain a smoothed function
for the Hubble parameter up to the redshift~1.7. We apply the smoothed Hubble
parameter in the inverse approach and reconstruct the corresponding action in
$f(R)$ gravity. In the next step we investigate the viability of reconstruction
method, doing a Monte-Carlo simulation we generate synthetic SNIa data with the
quality of union sample and show that roughly more than 1500 SNIa data is
essential to reconstruct correct action. Finally with the enough SNIa data, we
propose two diagnosis in order to distinguish between the $\Lambda$CDM model
and an alternative theory for the acceleration of the universe. | Euclid: Forecast constraints on consistency tests of the $Λ$CDM
model: The standard cosmological model is based on the fundamental assumptions of a
spatially homogeneous and isotropic universe on large scales. An observational
detection of a violation of these assumptions at any redshift would immediately
indicate the presence of new physics. We quantify the ability of the Euclid
mission, together with contemporary surveys, to improve the current sensitivity
of null tests of the canonical cosmological constant $\Lambda$ and the cold
dark matter (LCDM) model in the redshift range $0<z<1.8$. We considered both
currently available data and simulated Euclid and external data products based
on a LCDM fiducial model, an evolving dark energy model assuming the
Chevallier-Polarski-Linder (CPL) parameterization or an inhomogeneous
Lema\^{\i}tre-Tolman-Bondi model with a cosmological constant $\Lambda$ (LLTB),
and carried out two separate but complementary analyses: a machine learning
reconstruction of the null tests based on genetic algorithms, and a
theory-agnostic parametric approach based on Taylor expansion and binning of
the data, in order to avoid assumptions about any particular model. We find
that in combination with external probes, Euclid can improve current
constraints on null tests of the LCDM by approximately a factor of three when
using the machine learning approach and by a further factor of two in the case
of the parametric approach. However, we also find that in certain cases, the
parametric approach may be biased against or missing some features of models
far from LCDM. Our analysis highlights the importance of synergies between
Euclid and other surveys. These synergies are crucial for providing tighter
constraints over an extended redshift range for a plethora of different
consistency tests of some of the main assumptions of the current cosmological
paradigm. |
Constraining coupled quintessence with the 21cm signal: The 21cm line probes the evolution of matter perturbations over a wide range
of redshifts, from the dark ages down to the completion of reionization.
Observing the 21cm cosmological signal will extend our understanding of the
evolution of the Universe and it is thus important to investigate the
predictions of different cosmological models. In this paper we focus on the
prospect of constraining coupled quintessence models during the Epoch of
Reionization both for global signal experiments and for intensity mapping
surveys. To derive the all-sky 21cm signal and fluctuations in coupled
quintessence, we simulate cosmological volumes of the 21cm signal including the
coupling between dark matter and the quintessence field, where the strength of
the coupling is labeled by the parameter $Q$. We show that the coupling between
dark matter and quintessence modifies structure formation and expedites the
process of reionization. For the upcoming 21cm line surveys like SKA and a
fiducial global 21cm signal experiment, we perform a Fisher matrix analysis to
constrain the coupling $Q$ and the dark matter density parameter
$\Omega_\mathrm{dm}$.
The results indicate that SKA will be able to place a 68% upper limit $0.04$
to $|Q|$. At the same time, such a global 21cm detector provides a constraint
on the dark matter density parameter $\Omega_\mathrm{dm}$ around
$\Delta\Omega_{\rm dm}\approx 0.005$, whereas SKA sets a quite weaker
constraint around $\Delta\Omega_{\rm dm}\approx0.1$. These constraints are
comparable to those already obtained from the cosmic microwave background, but
explore an entirely different redshift range. | Measurement of Void Bias Using Separate Universe Simulations: Cosmic voids are biased tracers of the large-scale structure of the universe.
Separate universe simulations (SUS) enable accurate measurements of this
biasing relation by implementing the peak-background split (PBS). In this work,
we apply the SUS technique to measure the void bias parameters. We confirm that
the PBS argument works well for underdense tracers. The response of the void
size distribution depends on the void radius. For voids larger (smaller) than
the size at the peak of the distribution, the void abundance responds
negatively (positively) to a long wavelength mode. The linear bias from the SUS
is in good agreement with the cross power spectrum measurement on large scales.
Using the SUS, we have detected the quadratic void bias for the first time in
simulations. We find that $ b_2 $ is negative when the magnitude of $ b_1 $ is
small, and that it becomes positive and increases rapidly when $ |b_1| $
increases. We compare the results from voids identified in the halo density
field with those from the dark matter distribution, and find that the results
are qualitatively similar, but the biases generally shift to the larger voids
sizes. |
A Large Systematic Search for Recoiling and Close Supermassive Binary
Black Holes: [ABRIDGED] We have carried out a systematic search for close supermassive
black hole binaries among z < 0.7 SDSS quasars Such binaries are predicted by
models of supermassive black hole and host galaxy co-evolution, therefore their
census and population properties constitute an important test of these models.
We used an automatic technique based on spectroscopic principal component
analysis to search for broad H-beta lines that are displaced from the
rest-frame of the quasar by more than 1,000 km/s This method can also yield
candidates for rapidly recoiling black holes. Our search yielded 88 candidates,
several of which were previously identified and discussed in the literature.
The widths of the broad H-beta lines are typical among quasars but the shifts
are extreme. We found a correlation between the peak offset and skewness of the
broad H-beta profiles, which suggests that the profiles we have selected share
a common physical explanation. The general properties of the narrow emission
lines are typical of quasars. We carried out followup spectroscopic
observations of 68 objects to search for changes in the peak velocities of the
H-beta lines (the time interval in the observer's frame between the original
and new observations is 1-10 yr). We measured significant changes in 14
objects, with resulting accelerations between -120 and +120 km/s/yr. We
emphasize that interpretation of the offset broad emission lines as signatures
of supermassive binaries is subject to many significant caveats. Many more
followup observations over a long temporal baseline are needed to characterize
the variability pattern of the broad lines and test that this pattern is indeed
consistent with orbital motion. The possibility that some of the objects in
this sample are rapidly recoiling black holes remains open as the available
data do not provide strong constraints for this scenario. | On exact solutions for quintessential (inflationary) cosmological models
with exponential potentials: We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model. |
Chemical Evolution of the Carina Dwarf Spheroidal: We explore a range of chemical evolution models for the Local Group dwarf
spheroidal (dSph) galaxy, Carina. A novel aspect of our work is the removal of
the star formation history (SFH) as a `free parameter' in the modeling, making
use, instead, of its colour-magnitude diagram (CMD)-constrained SFH. By varying
the relative roles of galactic winds, re-accretion, and ram-pressure stripping
within the modeling, we converge on a favoured scenario which emphasises the
respective roles of winds and re-accretion. While our model is successful in
recovering most elemental abundance patterns, comparable success is not found
for all the neutron capture elements. Neglecting the effects of stripping
results in predicted gas fractions approximately two orders of magnitude too
high, relative to that observed. | Spitzer-IRS high resolution spectroscopic survey of the 12 micron
Seyfert galaxies: II. Results for the Complete Dataset: We present the Spitzer 10-37um IRS high resolution (R~600) spectroscopic
survey of the Seyfert galaxies of the 12 micron Galaxy Sample. The new spectra
of 61 galaxies, with those already published, gives us a total of 91 12micron
Seyfert galaxies observed, out of 112. We use an improved AGN classification
for Seyfert galaxies: instead of the type 1 and 2 classes, we use the
spectropolarimetric data to divide them into "AGN 1" and "AGN 2", where AGN 1's
include all broad-line objects, including the Seyfert 2's showing hidden broad
lines in polarized light, while AGN 2's contains only Seyferts with no
detectable broad lines at all. We present various mid-IR observables and we
find that these properties characterize the AGN 1's objects as a single family,
with strongly AGN-dominated spectra. In contrast, the AGN 2's can be divided in
two groups, the first one with properties similar to the AGN 1's and the second
similar to the non-Seyfert galaxies, such as LINERs or starburst galaxies. We
computed a semianalytical model to estimate the AGN and the starburst
contributions to the mid-IR galaxy emission at 19um. We find that AGN 1 have an
AGN contribution >73% and AGN 2 >45% of their total emission at 19um. The
detection of [NeV] lines is an almost perfect signature of energy production by
an AGN. We present mean spectra of the various AGN categories. We derive the
first local luminosity functions for the mid-infrared lines and the PAH
feature. No statistical difference is found in the space densities for Seyfert
1's and 2's, nor for the new classes of AGN 1's and 2's. The global output of
accretion-powered galactic nuclei in the local universe is derived from the
correlation between [NeV] line and the nonstellar IR continuum luminosity. |
The role of soft photon injection and heating in 21 cm cosmology: The ARCADE radio excess and EDGES measurement remain puzzling. A link between
the two has been previously considered, however, in this work we highlight an
important related effect that was not analyzed in detail before. By performing
cosmological thermalization calculations with soft photon injection using {\tt
CosmoTherm}, we show that for the 21 cm signal generation the interplay between
enhanced radio spectral distortions and the associated heating can hide a
significant radio excess before the reionzation era. We illustrate this effect
for a simple power-law soft photon source in decaying particle scenarios. Even
if simplistic, the uncovered link between CMB spectral distortions and 21 cm
cosmology should apply to a much broader range of scenarios. This could
significantly affect the constraints derived from existing and future 21 cm
observations on the evolution of the ambient radio background. In particular,
scenarios that would be ruled out by existing data without heating could become
viable solutions once the heating is accounted for in the modelling. Our
calculations furthermore highlight the importance of global 21 cm observations
reaching into the dark ages, where various scenarios can potentially be
distinguished. | Anisotropic bispectrum of curvature perturbations from primordial
non-Abelian vector fields: We consider a primordial SU(2) vector multiplet during inflation in models
where quantum fluctuations of vector fields are involved in producing the
curvature perturbation. Recently, a lot of attention has been paid to models
populated by vector fields, given the interesting possibility of generating
some level of statistical anisotropy in the cosmological perturbations. The
scenario we propose is strongly motivated by the fact that, for non-Abelian
gauge fields, self-interactions are responsible for generating extra terms in
the cosmological correlation functions, which are naturally absent in the
Abelian case. We compute these extra contributions to the bispectrum of the
curvature perturbation, using the delta N formula and the Schwinger-Keldysh
formalism. The primordial violation of rotational invariance (due to the
introduction of the SU(2) gauge multiplet) leaves its imprint on the
correlation functions introducing, as expected, some degree of statistical
anisotropy in our results. We calculate the non-Gaussianity parameter f_{NL},
proving that the new contributions derived from gauge bosons self-interactions
can be important, and in some cases the dominat ones. We study the shape of the
bispectrum and we find that it turns out to peak in the local configuration,
with an amplitude that is modulated by the preferred directions that break
statistical isotropy. |
NANOGrav meets Hot New Early Dark Energy and the origin of neutrino mass: It has recently been speculated that the NANOGrav observations point towards
a first-order phase transition in the dark sector at the GeV scale [1]. Here,
we show that such a phase transition might already have been predicted in the
Hot New Early Dark Energy model (Hot NEDE) [2],[3]. There, it was argued that
two dark sector phase transitions are the signature of neutrino mass generation
through the inverse seesaw mechanism. In particular, an IR phase transition
serves a double purpose by resolving the Hubble tension through an energy
injection and generating the Majorana mass entry in the inverse seesaw mixing
matrix. This usual NEDE phase transition is then accompanied by a UV
counterpart, which generates the heavy Dirac mass entry in the inverse seesaw
mass matrix of a right-handed neutrino. Here, we investigate if the UV phase
transition of the Hot NEDE model can occur at the GeV scale in view of the
recent NANOGrav observations. | The Second Byurakan Survey Galaxies. I. The Optical Database: A database for the entire catalog of the Second Byurakan Survey (SBS)
galaxies is presented. It contains new measurements of their optical parameters
and additional information taken from the literature and other databases. The
measurements were made using Ipg(near-infrared), Fpg(red) and Jpg(blue) band
images from photographic sky survey plates obtained by the Palomar Schmidt
telescope and extracted from the STScI Digital Sky Survey (DSS). The database
provides accurate coordinates, morphological type, spectral and activity
classes, apparent magnitudes and diameters, axial ratios, and position angles,
as well as number counts of neighboring objects in a circle of radius 50 kpc.
The total number of individual SBS objects in the database is now 1676. The 188
Markarian galaxies which were re-discovered by SBS are not included in this
database. We also include redshifts that are now available for 1576 SBS
objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies. |
Dark Matter in Galaxy Clusters: a Parametric Strong Lensing Approach: We present a parametric strong lensing analysis of three massive clusters.
Our aim is to probe the inner shape of dark matter haloes, in particular the
existence of a core. We adopt the following working hypothesis: any
group/cluster scale dark matter clump introduced in the modelling should be
associated with a luminous counterpart. We also adopt some additional well
motivated priors in the analysis, even if this degrades the quality of the fit,
quantified using the RMS between the observed and model generated images. In
particular, in order to alleviate the degeneracy between the smooth underlying
component and the galaxy scale perturbers, we use the results from
spectroscopic campaigns by Bergamini et al. (2019) allowing to fix the mass of
the galaxy scale component. In the unimodal galaxy cluster AS1063, a cored mass
model is favored with respect to a non cored mass model, and this is also the
case in the multimodal cluster MACSJ0416. In the unimodal cluster MACSJ1206, we
fail to reproduce the strong lensing constraints using a parametric approach
within the adopted working hypothesis. We then successfully add a mild
perturbation in the form of a superposition of B-spline potentials which allows
to get a decent fit (RMS=0.5"), finally finding that a cored mass model is
favored. Overall, our analysis suggest evidence for cored cluster scale dark
matter haloes. These findings may be useful to interpret within alternative
dark matter scenario, as self interacting dark matter. We propose a working
hypothesis for parametric strong lensing modelling where the quest for the best
fit model will be balanced by the quest for presenting a physically motivated
mass model, in particular by imposing priors. | The Swift-XRT Survey of Groups and Clusters of Galaxies: My Ph.D. Thesis is devoted to the study of groups and clusters of galaxies in
the X-ray band. This field has been very active in the last ten years, thanks
to the data gathered from the Chandra and XMM satellites. Clusters of galaxies
are prominent X-ray sources thanks to thermal bremsstrahlung emission from the
diffuse ICM heated to 10^7-10^8 K, which provides about 15% of their total
mass. The analysis of the X-ray emission from groups and clusters allows to
study the large scale structure of the Universe, to constrain the cosmological
parameters, and to investigate the interaction between the ICM and the cluster
galaxies. My scientific work is mainly focused on the realization of a new
X-ray survey of galaxy clusters, the SXCS, obtained from the previously
unexplored archive of the X-Ray Telescope (XRT) on board of the Swift
satellite. The goal is not only to build a new catalogue, but also to
characterize the thermodynamical and chemical properties of the brightest
groups and clusters in the survey catalogue. Moreover, given the overall
characteristics of the survey, I also expect to detect some clusters at
redshift z>1, which will have a strong impact in the study of the large scale
structure of the Universe and the cosmological parameters. During my work I
also contributed substantially to the image simulator code of a new proposed
X-ray mission submitted to the NASA Astro 2010 Decadal Survey: the Wide Field
X-ray Telescope (WFXT). This work represents an important part of the
scientific case of WFXT, since, for first time in the simulations I included
realistic populations of all the source types contributing to the extragalactic
X-ray sky, namely groups and clusters of galaxies, active galactic nuclei, and
star-forming galaxies. Thanks to this work, the scientific cases of WFXT can
now be tested on solid ground. |
Probing Dark Energy Dynamics from Current and Future Cosmological
Observations: We report the constraints on the dark energy equation-of-state w(z) using the
latest 'Constitution' SNe sample combined with the WMAP5 and SDSS data. Based
on the localized principal component analysis and the model selection criteria,
we find that the LCDM model is generally consistent with the current data, yet
there exists weak hint of the possible dynamics of dark energy. In particular,
a model predicting w(z)<-1 at z\in[0.25,0.5) and w(z)>-1 at z\in[0.5,0.75),
which means that w(z) crosses -1 in the range of z\in[0.25,0.75), is mildly
favored at 95% confidence level. Given the best fit model for current data as a
fiducial model, we make future forecast from the joint data sets of JDEM,
Planck and LSST, and we find that the future surveys can reduce the error bars
on the w bins by roughly a factor of 10 for a 5-w-bin model. | AGN outflow feedback: Constraints from variability: We present an overview on how variability can be used to constrain the
location of the ionized outflow in nearby Active Galactic Nuclei using
high-resolution X-ray spectroscopy. Without these constraints on the location
of the outflow, the kinetic luminosity and mass loss rate can not be
determined. We focus on the Seyfert 1 galaxy NGC 5548, which is arguably the
best studied AGN on a timescale of 10 years. Our results show that frequent
observations combined with long term monitoring, such as with the \textit{Rossi
X-ray Timing Explorer (RXTE)} satellite, are crucial to investigate the effects
of these outflows on their surroundings. |
`Standard' Cosmological model & beyond with CMB: Observational Cosmology has indeed made very rapid progress in the past
decade. The ability to quantify the universe has largely improved due to
observational constraints coming from structure formation Measurements of CMB
anisotropy and, more recently, polarization have played a very important role.
Besides precise determination of various parameters of the `standard'
cosmological model, observations have also established some important basic
tenets that underlie models of cosmology and structure formation in the
universe -- `acausally' correlated initial perturbations in a flat,
statistically isotropic universe, adiabatic nature of primordial density
perturbations. These are consistent with the expectation of the paradigm of
inflation and the generic prediction of the simplest realization of
inflationary scenario in the early universe. Further, gravitational instability
is the established mechanism for structure formation from these initial
perturbations. The signature of primordial perturbations observed as the CMB
anisotropy and polarization is the most compelling evidence for new, possibly
fundamental, physics in the early universe. The community is now looking beyond
the estimation of parameters of a working `standard' model of cosmology for
subtle, characteristic signatures from early universe physics. | The Contribution Of Inverse Compton Scattering To The Diffuse
Extragalactic Gamma-Ray Background From Annihilating Dark Matter: In addition to gamma-rays, dark matter annihilation products can include
energetic electrons which inverse Compton scatter with the cosmic microwave
background to produce a diffuse extragalactic background of gamma-rays and
X-rays. In models in which the dark matter particles annihilate primarily to
electrons or muons, the measurements of EGRET and COMPTEL can provide
significant constraints on the annihilation cross section. The Fermi Gamma-Ray
Space Telescope will likely provide an even more stringent test of such
scenarios. |
Evolution of Primordial Stars Powered by Dark Matter Annihilation up to
the Main-Sequence Stage: Primordial stars formed in the early universe are thought to be hosted by
compact dark matter (DM) halos. If DM consists of Weakly Interacting Massive
Particles (WIMPs), such stars may be powered by DM annihilation during the
early phases of their evolutions. We study the pre-main sequence evolutions of
the primordial star using a detailed stellar evolution code under the
assumption that the annihilation of adiabatically contracted WIMPs DM within
the star provides a sufficient energy to sustain the stellar equilibrium. We
follow the evolution of accreting stars using several gas mass accretion rates
derived from cosmological simulations. We show that the stellar mass becomes
very large, up to 900 - 1000 M_sun when the star reaches the main-sequence
phase for a reasonable set of model parameters such as DM particle mass and the
annihilation cross section. During the dark star phase, the star expands over a
thousand solar-radii, while the surface temperature remains below 10^4 K. The
energy generated by nuclear reactions is not dominant during this phase. We
also study models with different gas mass accretion rates and the DM particle
masses. All our models for different DM particle masses pass the dark star
phase. The final mass of the dark stars is essentially unchanged for DM mass of
m_DM <= 10 GeV. Gravitational collapse of the massive dark stars will leave
massive black holes with mass as large as 1000 M_sun in the early universe. | Observable imprints of primordial gravitational waves on the temperature
anisotropies of the Cosmic Microwave Background: We examine the contribution of tensor modes, in addition to the dominant
scalar ones, on the temperature anisotropies of the cosmic microwave background
(CMB). To this end, we analyze in detail the temperature two-point angular
correlation function $C(\theta)$ from the Planck 2018 dataset, focusing on
large angles ($\theta \gtrsim 120^{\circ}$) corresponding to small $\ell$
multipoles. A hierarchical set of infrared cutoffs are naturally introduced to
the scalar and tensor power spectra of the CMB by invoking an extra
Kaluza-Klein dimension compactifying at about the GUT scale between the Planck
epoch and the start of inflation. We associate this set of lower scalar and
tensor cutoffs with the parity of the multipole expansion of the $C(\theta)$
function. By fitting the Planck 2018 data we compute the multipole coefficients
thereby reproducing the well-known odd-parity preference in angular
correlations seen by all three satellite missions COBE, WMAP and Planck. Our
fits improve significantly once tensor modes are included in the analysis,
hence providing a hint of the imprints of primordial gravitational waves on the
temperature correlations observed in the CMB today. To conclude we suggest a
relationship between, on the one hand, the lack of (positive) large-angle
correlations and the odd-parity dominance in the CMB and, on the other hand,
the effect of primordial gravitational waves on the CMB temperature
anisotropies. |
Mapping the Clumpy Structures within Submillimeter Galaxies using
Laser-Guide Star Adaptive Optics Spectroscopy: We present the first integral-field spectroscopic observations of
high-redshift submillimeter-selected galaxies (SMGs) using Laser Guide Star
Adaptive Optics (LGS-AO). We target H-alpha emission of three SMGs at redshifts
z~1.4-2.4 with the OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) on
Keck. The spatially-resolved spectroscopy of these galaxies reveals unresolved
broad H-alpha line regions (FWHM>1000 km/s) likely associated with an AGN and
regions of diffuse star formation traced by narrow-line H-alpha emission
(FWHM<500 km/s) dominated by multiple Halpha-bright stellar clumps, each
contributing 1-30% of the total clump-integrated H-alpha emission. We find that
these SMGs host high star-formation rate surface densities, similar to local
extreme sources, such as circumnuclear starbursts and luminous infrared
galaxies. However, in contrast to these local environments, SMGs appear to be
undergoing such intense activity on significantly larger spatial scales as
revealed by extended H-alpha emission over 4-16 kpc. H-alpha kinematics show no
evidence of ordered global motion as would be found in a disk, but rather large
velocity offsets (~few x 100 km/s) between the distinct stellar clumps.
Together with the asymmetric distribution of the stellar clumps around the AGN
in these objects, it is unlikely that we are unveiling a clumpy disk structure
as has been suggested in other high-redshift populations of star-forming
galaxies. The SMG clumps in this sample may correspond to remnants of
originally independent gas-rich systems that are in the process of merging,
hence triggering the ultraluminous SMG phase. | RATAN-600 7.6-cm Deep Sky Strip Surveys at the Declination of the SS433
Source During the 1980-1999 Period. Data Reduction and the Catalog of Radio
Sources in the Right-Ascension Interval 7h < R.A. < 17h: We use two independent methods to reduce the data of the surveys made with
RATAN-600 radio telescope at 7.6 cm in 1988-1999 at the declination of the
SS433 source. We also reprocess the data of the "Cold" survey (1980-1981). The
resulting RCR (RATAN COLD REFINED) catalog contains the right ascensions and
fluxes of objects identified with those of the NVSS catalog in the
right-ascension interval 7h < R.A. < 17h. We obtain the spectra of the radio
sources and determine their spectral indices at 3.94 and 0.5 GHz. The spectra
are based on the data from all known catalogs available from the CATS, Vizier,
and NED databases, and the flux estimates inferred from the maps of the VLSS
and GB6 surveys. For 245 of the 550 objects of the RCR catalog the fluxes are
known at two frequencies only: 3.94 GHz (RCR) and 1.4 GHz (NVSS). These are
mostly sources with fluxes smaller than 30 mJy. About 65% of these sources have
flat or inverse spectra (alpha > -0.5). We analyze the reliability of the
results obtained for the entire list of objects and construct the histograms of
the spectral indices and fluxes of the sources. Our main conclusion is that all
10-15 mJy objects found in the considered right-ascension interval were already
included in the decimeter-wave catalogs. |
A Link Between Star Formation Quenching and Inner Stellar Mass Density
in SDSS Central Galaxies: We study the correlation between galaxy structure and the quenching of star
formation using a sample of SDSS central galaxies with stellar masses 9.75< log
M_*/M_sun<11.25 and redshifts z<0.075. GALEX UV data are used to cleanly divide
the sample into star-forming and quenched galaxies, and to identify galaxies in
transition (the green valley). Despite a stark difference in visual appearance
between blue and red galaxies, their average radial stellar mass density
profiles are remarkably similar (especially in the outer regions) at fixed
mass. The inner stellar mass surface density within a radius of 1 kpc,
\Sigma_1, is used to quantify the growth of the bulge as galaxies evolve. When
galaxies are divided into narrow mass bins, their distribution in the
color-\Sigma_1 plane at fixed mass forms plausible evolutionary tracks.
\Sigma_1 seems to grow as galaxies evolve through the blue cloud, and once it
crosses a threshold value, galaxies are seen to quench at fixed \Sigma_1. The
\Sigma_1 threshold for quenching grows with stellar mass, \Sigma_1 ~
M_*^{0.64}. However, the existence of some star-forming galaxies above the
threshold \Sigma_1 implies that a dense bulge is necessary but not sufficient
to quench a galaxy fully. This would be consistent with a two-step quenching
process in which gas within a galaxy is removed or stabilized against star
formation by bulge-driven processes (such as a starburst, AGN feedback, or
morphological quenching), whereas external gas accretion is suppressed by
separate halo-driven processes (such as halo gas shock heating). Quenching thus
depends on an interplay between the inner structure of a galaxy and its
surrounding dark matter halo, and lack of perfect synchrony between the two
could produce the observed scatter in color vs. \Sigma_1. (Abridged) | Broadband Photometry of 105 Giant Arcs: Redshift Constraints and
Implications for Giant Arc Statistics: We measure the photometric properties of 105 giant arcs that were identified
in systematic searches for galaxy-cluster-scale strong lenses in the Second
Red-Sequence Cluster Survey (RCS-2) and the Sloan Digital Sky Survey (SDSS).
The cluster lenses span 0.2 < z_lens < 1.2 in redshift, with a median z_lens =
0.58. Using broadband color criteria we sort the entire arc sample into
redshift bins based on u-g and g-r colors, and also r-z colors for the ~90% of
arcs that have z-band data. This analysis yields broad redshift constraints
with 71 +5 -4 % of the arcs at z > 1.0, 64 +6 -4 % at z > 1.4, 56 +5 -4 % at z
> 1.9, and 21 +4 -2 % at z > 2.7. The remaining 29 +3 -5 % have z < 1. The
inferred median redshift is z_s = 2.0 +/- 0.1, in good agreement with a
previous determination from a smaller sample of brighter arcs (g < 22.5). This
agreement confirms that z_s = 2.0 +/- 0.1 is the typical redshift for giant
arcs with g < 24 that are produced by cluster-scale strong lenses, and that
there is no evidence for strong evolution in the redshift distribution of arcs
over a wide range of g-band magnitudes (20 < g < 24). Establishing that half of
all giant arcs are at z > 2 contributes significantly toward relieving the
tension between the number of arcs observed and the number expected in a
Lambda-CDM cosmology, but there is considerable evidence to suggest that a
discrepancy persists. Additionally, this work confirms that forthcoming large
samples of giant arcs will supply the observational community with many
magnified galaxies at z > 2. |
On the Kinematic Morphology around Halos: In this paper, we report an interesting kinematic phenomenon around the
halos' edge related to the splashback radius. After the shell-crossing, cosmic
flow exhibits various rotational morphologies via stream-mixing. Vorticity is
generated in a particular way that coincides with the large-scale structure.
Notably, one specific flow morphology, which is spiraling inward and
compressing in the third direction, concentrates around halos. A detailed
examination that reveals a sharp change in the logarithmic derivative of its
volume fraction, coincides with the location of the splashback radius defined
as the outermost caustic structure. Such a feature encodes valuable phase space
information and provides a new perspective on understanding the dynamical
evolution of halos. As a volume-weighted quantity, the profile of flow
morphology is purely kinematic. And unlike other related studies, the
rotational flow morphologies capture the anisotropic phase structure in the
multi-stream region. | Diffuse Lyman-alpha Halos around Galaxies at z=2.2-6.6: Implications for
Galaxy Formation and Cosmic Reionization: We present diffuse Lyman-alpha halos (LAHs) identified in the composite
Subaru narrowband images of 100-3600 Lyman-alpha emitters (LAEs) at z=2.2, 3.1,
3.7, 5.7, and 6.6. First, we carefully examine potential artifacts mimicking
LAHs that include a large-scale point-spread function (PSF) made by
instrumental and atmospheric effects. Based on our critical test with composite
images of non-LAE samples whose narrowband-magnitude and source-size
distributions are the same as our LAE samples, we confirm that no artifacts can
produce a diffuse extended feature similar to our LAHs. After this test, we
measure the scale lengths of exponential profile for the LAHs estimated from
our z=2.2-6.6 LAE samples of L(Lyman-alpha) > 2 x 10^42 erg s^-1. We obtain the
scale lengths of ~ 5-10 kpc at z=2.2-5.7, and find no evolution of scale
lengths in this redshift range beyond our measurement uncertainties. Combining
this result and the previously-known UV-continuum size evolution, we infer that
the ratio of LAH to UV-continuum sizes is nearly constant at z=2.2-5.7. The
scale length of our z=6.6 LAH is larger than 5-10 kpc just beyond the error
bar, which is a hint that the scale lengths of LAHs would increase from z=5.7
to 6.6. If this increase is confirmed by future large surveys with significant
improvements of statistical and systematical errors, this scale length change
at z > 6 would be a signature of increasing fraction of neutral hydrogen
scattering Lyman-alpha photons, due to cosmic reionization. |
Recovering Galaxy Cluster Convergence from Lensed CMB with Generative
Adversarial Networks: We present a new method which leverages conditional Generative Adversarial
Networks (cGAN) to reconstruct galaxy cluster convergence from lensed CMB
temperature maps. Our model is constructed to emphasize structure and
high-frequency correctness relative to the Residual U-Net approach presented by
Caldeira, et. al. (2019). Ultimately, we demonstrate that while both models
perform similarly in the no-noise regime (as well as after random off-centering
of the cluster center), cGAN outperforms ResUNet when processing CMB maps
noised with 5uK/arcmin white noise or astrophysical foregrounds (tSZ and kSZ);
this out-performance is especially pronounced at high l, which is exactly the
regime in which the ResUNet under-performs traditional methods. | Escape from supercooling with or without bubbles: gravitational wave
signatures: Quasi-conformal models are an appealing scenario that can offer naturally a
strongly supercooled phase transition and a period of thermal inflation in the
early Universe. A crucial aspect for the viability of these models is how the
Universe escapes from the supercooled state. One possibility is that thermal
inflation phase ends by nucleation and percolation of true vacuum bubbles. This
route is not, however, always efficient. In such case another escape mechanism,
based on the growth of quantum fluctuations of the scalar field that eventually
destabilize the false vacuum, becomes relevant. We study both of these cases in
detail in a simple yet representative model. We determine the duration of the
thermal inflation, the curvature power spectrum generated for the scales that
exit horizon during the thermal inflation, and the stochastic gravitational
wave background from the phase transition. We show that these gravitational
waves provide an observable signal from the thermal inflation in almost the
entire parameter space of interest. Furthermore, the shape of the gravitational
wave spectrum can be used to ascertain how the Universe escaped from
supercooling. |
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