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Recovering $Λ$CDM Model From a Cosmographic Study: Using the mathematical definitions of deceleration and jerk parameters we
obtain a general differential equation for squared Hubble parameter. For a
constant jerk, this differential equation leads to an exact function for Hubble
parameter. By the aid of this exact Hubble function we can exactly reconstruct
any other cosmographic parameters. We also obtained a general function for
transition redshift as well as spacetime curvature. Our derived functions
clearly impose a lower limit on the jerk parameter which is
$j_{min}\geq-0.125$. Moreover, we found that the jerk parameter indicates the
geometry of the spacetime i.e any deviation from $j=1$ imply to a non-flat
spacetime. In other word $j\neq 1$ reefers to a dynamical, time varying, dark
energy. From obtained Hubble function we recover the analogue of $\Lambda$CDM
model. To constrain cosmographic parameters as well as transition redshift and
spacetime curvature of the recovered $\Lambda$CDM model, we used
Metropolis-Hasting algorithm to perform Monte Carlo Markov Chain analysis by
using observational Hubble data obtained from cosmic chronometric (CC)
technique, BAO data, Pantheon compilation of Supernovae type Ia, and their
joint combination. The only free parameters are $H$, $A(\Omega_{m})$ and $j$.
From joint analysis we obtained $H_{0}=69.9\pm 1.7$,
$A(\sim\Omega_{0m})=0.279^{+0.013}_{-0.017}$,
$B(\sim\Omega_{0X})=0.721^{+0.017}_{-0.013}$, $j_{0}=1.038^{+0.061}_{-0.023}$
and $z_{t}=0.706^{+0.031}_{-0.034}$. | Stellar Populations of Elliptical Galaxies in the Local Universe: We study the stellar populations of 1,923 elliptical galaxies at z<0.05
selected from the Sloan Digital Sky Survey as a function of velocity
dispersion, sigma, and environment. We construct average, high signal-to-noise
spectra and find the following: (1) lower-sigma galaxies have a bluer optical
continuum and stronger (but still weak) emission lines; (2) at fixed sigma,
field ellipticals have a slightly bluer stellar continuum, especially at
wavelengths \lesssim 4000 \AA, and have stronger (but still weak) emission
lines compared to their group counterparts, although this environmental
dependence is strongest for low-sigma ellipticals. Based on Lick indices
measured from both the individual and average spectra, we find that: (1) at a
given sigma, elliptical galaxies in groups have systematically weaker Balmer
absorption than their field counterparts, although this environmental
dependence is most pronounced at low sigma; (2) there is no clear environmental
dependence of <Fe>, while the alpha-element absorption indices such as Mgb are
only slightly stronger in galaxies belonging to rich groups. An analysis based
on simple stellar populations (SSPs) reveals that more massive elliptical
galaxies are older, more metal-rich and more strongly alpha-enhanced. We also
find that: (1) the SSP-equivalent ages of galaxies in rich groups are, on
average, ~1 Gyr older than in the field, although once again this effect is
strongest at low sigma; (2) galaxies in rich groups have slightly lower [Fe/H]
and are marginally more strongly alpha-enhanced; and (3) there is no
significant environmental dependence of total metallicity, [Z/H]. Our results
are generally consistent with stronger low-level recent star formation in field
ellipticals at low sigma, similar to recent results based on ultraviolet and
infrared observations. (Abridged) |
Distant galaxy clusters in the XMM Large Scale Structure survey: (Abridged) Distant galaxy clusters provide important tests of the growth of
large scale structure in addition to highlighting the process of galaxy
evolution in a consistently defined environment at large look back time. We
present a sample of 22 distant (z>0.8) galaxy clusters and cluster candidates
selected from the 9 deg2 footprint of the overlapping X-ray Multi Mirror (XMM)
Large Scale Structure (LSS), CFHTLS Wide and Spitzer SWIRE surveys. Clusters
are selected as extended X-ray sources with an accompanying overdensity of
galaxies displaying optical to mid-infrared photometry consistent with z>0.8.
Nine clusters have confirmed spectroscopic redshifts in the interval 0.8<z<1.2,
four of which are presented here for the first time. A further 11 candidate
clusters have between 8 and 10 band photometric redshifts in the interval
0.8<z<2.2, while the remaining two candidates do not have information in
sufficient wavebands to generate a reliable photometric redshift. All of the
candidate clusters reported in this paper are presented for the first time.
Those confirmed and candidate clusters with available near infrared photometry
display evidence for a red sequence galaxy population, determined either
individually or via a stacking analysis, whose colour is consistent with the
expectation of an old, coeval stellar population observed at the cluster
redshift. We further note that the sample displays a large range of red
fraction values indicating that the clusters may be at different stages of red
sequence assembly. We compare the observed X-ray emission to the flux expected
from a suite of model clusters and find that the sample displays an effective
mass limit M200 ~ 1e14 Msolar with all clusters displaying masses consistent
with M200 < 5e14 Msolar. This XMM distant cluster study represents a complete
sample of X-ray selected z>0.8 clusters. | Constraints on deviations from $Λ$CDM within Horndeski gravity: Recent anomalies found in cosmological datasets such as the low multipoles of
the Cosmic Microwave Background or the low redshift amplitude and growth of
clustering measured by e.g., abundance of galaxy clusters and redshift space
distortions in galaxy surveys, have motivated explorations of models beyond
standard $\Lambda$CDM. Of particular interest are models where general
relativity (GR) is modified on large cosmological scales. Here we consider
deviations from $\Lambda$CDM+GR within the context of Horndeski gravity, which
is the most general theory of gravity with second derivatives in the equations
of motion. We adopt a parametrization in which the four additional Horndeski
functions of time $\alpha_i(t)$ are proportional to the cosmological density of
dark energy $\Omega_{DE}(t)$. Constraints on this extended parameter space
using a suite of state-of-the art cosmological observations are presented for
the first time. Although the theory is able to accommodate the low multipoles
of the Cosmic Microwave Background and the low amplitude of fluctuations from
redshift space distortions, we find no significant tension with $\Lambda$CDM+GR
when performing a global fit to recent cosmological data and thus there is no
evidence against $\Lambda$CDM+GR from an analysis of the value of the Bayesian
evidence ratio of the modified gravity models with respect to $\Lambda$CDM,
despite introducing extra parameters. The posterior distribution of these extra
parameters that we derive return strong constraints on any possible deviations
from $\Lambda$CDM+GR in the context of Horndeski gravity. We illustrate how our
results can be applied to a more general frameworks of modified gravity models. |
Herschel-ATLAS: deep HST/WFC3 imaging of strongly lensed submillimeter
galaxies: We report on deep near-infrared observations obtained with the Wide Field
Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) of the first five
confirmed gravitational lensing events discovered by the Herschel Astrophysical
Terahertz Large Area Survey (H-ATLAS). We succeed in disentangling the
background galaxy from the lens to gain separate photometry of the two
components. The HST data allow us to significantly improve on previous
constraints of the mass in stars of the lensed galaxy and to perform accurate
lens modelling of these systems, as described in the accompanying paper by Dye
et al. We fit the spectral energy distributions of the background sources from
near-IR to millimetre wavelengths and use the magnification factors estimated
by Dye et al. to derive the intrinsic properties of the lensed galaxies. We
find these galaxies to have star-formation rates of approximately 400 to 2000
M_sol/yr, with approximately (6-25)x10^10 M_sol of their baryonic mass already
turned into stars. At these rates of star formation, all remaining molecular
gas will be exhausted in less than 100 Myr, reaching a final mass in stars of a
few 10^11 M_sol. These galaxies are thus proto-ellipticals caught during their
major episode of star formation, and observed at the peak epoch z=1.5-3 of the
cosmic star formation history of the Universe. | Understanding the relation between thermal Sunyaev-Zeldovich decrement
and halo mass using the SIMBA and TNG simulations: The relation between the integrated thermal Sunyaev-Zeldovich (tSZ)
$y$-decrement versus halo mass ($Y$--$M$) can potentially constrain galaxy
formation models, if theoretical and observational systematics can be properly
assessed. We investigate the $Y$--$M$ relation in the SIMBA and
IllustrisTNG-100 cosmological hydrodynamic simulations, quantifying the effects
of feedback, line-of-sight projection, and beam convolution. We find that
SIMBA's AGN jet feedback generates strong deviations from self-similar
expectations for the $Y$--$M$ relation, especially at
$M_{500}<10^{13}M_{\odot}$. In SIMBA, this is driven by suppressed in-halo $y$
contributions owing to lowered halo baryon fractions. IllustrisTNG results more
closely resemble SIMBA without jets. Projections of line-of-sight structures
weaken these model differences slightly, but they remain significant --
particularly at group and lower halo masses. In contrast, beam smearing at
$\textit{Planck}$ resolution makes the models indistinguishable, and both
models appear to agree well with $\textit{Planck}$ data down to the lowest
masses probed. We show that the arcminute resolution expected from forthcoming
facilities would retain the differences between model predictions, and thereby
provide strong constraints on AGN feedback. |
Mass accretion rates of the HectoMAP clusters of galaxies: We estimate the mass accretion rate (MAR) of the 346 clusters of galaxies in
the HectoMAP Cluster Survey. The clusters span the redshift range $0.17-0.42$
and the $M_{200}$ mass range $\approx (0.5 - 3.5)\cdot 10^{14} M_\odot$. The
MAR estimate is based on the caustic technique along with a spherical infall
model. Our analysis extends the measurement of MARs for 129 clusters at $z<0.3$
from the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS) and the
Hectospec Cluster Survey (HeCS) to redshift $z \sim 0.42$. Averaging over
redshift, low-mass clusters with $M_{200}\sim 0.7\cdot 10^{14} M_\odot$ accrete
$\sim 3\cdot 10^4 M_\odot$yr$^{-1}$; more massive clusters with $M_{200}\sim
2.8\cdot 10^{14} M_\odot$ accrete $\sim 1\cdot 10^5 M_\odot$yr$^{-1}$. Low- and
high-mass clusters increase their MAR by $\sim 46\%$ and $\sim 84\%$,
respectively, as the redshift increases from $z\sim 0.17-0.29$ to $z\sim
0.34-0.42$. The MARs at fixed redshift increase with mass and MARs at fixed
mass increase with redshift in agreement with $\Lambda$CDM cosmological model
for hierarchical structure formation. We consider the extension of MAR
measurements to $z \sim 1$. | Dwarf Galaxies and the Cosmic Web: We use a cosmological simulation of the formation of the Local Group of
Galaxies to identify a mechanism that enables the removal of baryons from
low-mass halos without appealing to feedback or reionization. As the Local
Group forms, matter bound to it develops a network of filaments and pancakes.
This moving web of gas and dark matter drifts and sweeps a large volume,
overtaking many halos in the process. The dark matter content of these halos is
unaffected but their gas can be efficiently removed by ram-pressure. The loss
of gas is especially pronounced in low-mass halos due to their lower binding
energy and has a dramatic effect on the star formation history of affected
systems. This "cosmic web stripping" may help to explain the scarcity of dwarf
galaxies compared with the numerous low-mass halos expected in \Lambda CDM and
the large diversity of star formation histories and morphologies characteristic
of faint galaxies. Although our results are based on a single high-resolution
simulation, it is likely that the hydrodynamical interaction of dwarf galaxies
with the cosmic web is a crucial ingredient so far missing from galaxy
formation models. |
Frontier Fields: Subaru Weak-Lensing Analysis of the Merging Galaxy
Cluster A2744: We present a weak-lensing analysis of the merging {\em Frontier Fields} (FF)
cluster Abell~2744 using new Subaru/Suprime-Cam imaging. The wide-field lensing
mass distribution reveals this cluster is comprised of four distinct
substructures. Simultaneously modeling the two-dimensional reduced shear field
using a combination of a Navarro--Frenk--White (NFW) model for the main core
and truncated NFW models for the subhalos, we determine their masses and
locations. The total mass of the system is constrained as $M_\mathrm{200c} =
(2.06\pm0.42)\times10^{15}\,M_\odot$. The most massive clump is the southern
component with $M_\mathrm{200c} = (7.7\pm3.4)\times10^{14}\,M_\odot$, followed
by the western substructure ($M_\mathrm{200c} =
(4.5\pm2.0)\times10^{14}\,M_\odot$) and two smaller substructures to the
northeast ($M_\mathrm{200c} = (2.8\pm1.6)\times10^{14}\,M_\odot$) and northwest
($M_\mathrm{200c} = (1.9\pm1.2)\times10^{14}\,M_\odot$). The presence of the
four substructures supports the picture of multiple mergers. Using a composite
of hydrodynamical binary simulations we explain this complicated system without
the need for a "slingshot" effect to produce the northwest X-ray interloper, as
previously proposed. The locations of the substructures appear to be offset
from both the gas ($87^{+34}_{-28}$ arcsec, 90\% CL) and the galaxies
($72^{+34}_{-53}$ arcsec, 90\% CL) in the case of the northwestern and western
subhalos. To confirm or refute these findings, high resolution space-based
observations extending beyond the current FF limited coverage to the west and
northwestern area are essential. | Fast simulations for intensity mapping experiments: We present a code to generate mock observations of 21 cm intensity mapping
experiments. The emphasis of the code is on reducing the computational cost of
running a full-blown simulation, trading computational time for accuracy. The
code can be used to generate independent realizations of the cosmological
signal and foregrounds, which are necessary, for instance, in order to obtain
realistic forecasts for future intensity mapping experiments. The code is able
to reproduce the correct angular and radial clustering pattern for the
cosmological signal, including redshift-space distortions, lightcone evolution
and bias. Furthermore, it is possible to simulate a variety of foregrounds,
including the potentially problematic polarized synchrotron emission. |
Tensor B mode and stochastic Faraday mixing: This paper investigates the Faraday effect as a different source of B mode
polarization. The E mode polarization is Faraday rotated provided a stochastic
large-scale magnetic field is present prior to photon decoupling. In the first
part of the paper we discuss the case where the tensor modes of the geometry
are absent and we argue that the B mode recently detected by the Bicep2
collaboration cannot be explained by a large-scale magnetic field rotating,
through the Faraday effect, the well established E mode polarization. In this
case, the observed temperature autocorrelations would be excessively distorted
by the magnetic field. In the second part of the paper the formation of Faraday
rotation is treated as a stationary, random and Markovian process with the aim
of generalizing a set of scaling laws originally derived in the absence of the
tensor modes of the geometry. We show that the scalar, vector and tensor modes
of the brightness perturbations can all be Faraday rotated even if the vector
and tensor parts of the effect have been neglected, so far, by focussing the
attention on the scalar aspects of the problem. The mixing between the power
spectra of the E mode and B mode polarizations involves a unitary
transformation depending nonlinearly on the Faraday rotation rate. The present
approach is suitable for a general scrutiny of the polarization observables and
of their frequency dependence. | Galaxy Zoo: dust lane early-type galaxies are tracers of recent,
gas-rich minor mergers: We present the second of two papers concerning the origin and evolution of
local early-type galaxies exhibiting dust features. We use optical and radio
data to examine the nature of active galactic nucleus (AGN) activity in these
objects, and compare these with a carefully constructed control sample. We find
that dust lane early-type galaxies are much more likely to host emission-line
AGN than the control sample galaxies. Moreover, there is a strong correlation
between radio and emission-line AGN activity in dust lane early-types, but not
the control sample. Dust lane early-type galaxies show the same distribution of
AGN properties in rich and poor environments, suggesting a similar triggering
mechanism. By contrast, this is not the case for early-types with no dust
features. These findings strongly suggest that dust lane early-type galaxies
are starburst systems formed in gas-rich mergers. Further evidence in support
of this scenario is provided by enhanced star formation and black hole
accretion rates in these objects. Dust lane early-types therefore represent an
evolutionary stage between starbursting and quiescent galaxies. In these
objects, the AGN has already been triggered but has not as yet completely
destroyed the gas reservoir required for star formation. |
Inflation and Alternatives with Blue Tensor Spectra: We study the tilt of the primordial gravitational waves spectrum. A hint of
blue tilt is shown from analyzing the BICEP2 and POLARBEAR data. Motivated by
this, we explore the possibilities of blue tensor spectra from the very early
universe cosmology models, including null energy condition violating inflation,
inflation with general initial conditions, and string gas cosmology, etc. For
the simplest G-inflation, blue tensor spectrum also implies blue scalar
spectrum. In general, the inflation models with blue tensor spectra indicate
large non-Gaussianities. On the other hand, string gas cosmology predicts blue
tensor spectrum with highly Gaussian fluctuations. If further experiments do
confirm the blue tensor spectrum, non-Gaussianity becomes a distinguishing test
between inflation and alternatives. | Cosmology with AGN dust time lags -- Simulating the new VEILS survey: The time lag between optical and near-infrared continuum emission in active
galactic nuclei (AGN) shows a tight correlation with luminosity and has been
proposed as a standardisable candle for cosmology. In this paper, we explore
the use of these AGN hot-dust time lags for cosmological model fitting under
the constraints of the new VISTA Extragalactic Infrared Legacy Survey VEILS.
This new survey will target a 9 deg^2 field observed in J- and Ks-band with a
14-day cadence and will run for three years. The same area will be covered
simultaneously in the optical griz bands by the Dark Energy Survey, providing
complementary time-domain optical data. We perform realistic simulations of the
survey setup, showing that we expect to recover dust time lags for about 450
objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of
0.1 < z < 1.2. We use the lags recovered from our simulations to calculate
precise distance moduli, establish a Hubble diagram, and fit cosmological
models. Assuming realistic scatter in the distribution of the dust around the
AGN as well as in the normalisation of the lag-luminosity relation, we are able
to constrain {\Omega}_{\Lambda} in {\Lambda}CDM with similar accuracy as
current supernova samples. We discuss the benefits of combining AGN and
supernovae for cosmology and connect the present work to future attempts to
reach out to redshifts of z > 4. |
Using Colors to Improve Photometric Metallicity Estimates for Galaxies: There is a well known correlation between the mass and metallicity of
star-forming galaxies. Because mass is correlated with luminosity, this
relation is often exploited, when spectroscopy is not available, to estimate
galaxy metallicities based on single band photometry. However, we show that
galaxy color is typically more effective than luminosity as a predictor of
metallicity. This is a consequence of the correlation between color and the
galaxy mass-to-light ratio and the recently discovered correlation between star
formation rate (SFR) and residuals from the mass-metallicity relation. Using
Sloan Digital Sky Survey spectroscopy of 180,000 nearby galaxies, we derive
"LZC relations," empirical relations between metallicity (in seven common
strong line diagnostics), luminosity, and color (in ten filter pairs and four
methods of photometry). We show that these relations allow photometric
metallicity estimates, based on luminosity and a single optical color, that are
50% more precise than those made based on luminosity alone; galaxy metallicity
can be estimated to within 0.05 - 0.1 dex of the spectroscopically-derived
value depending on the metallicity diagnostic used. Including color information
in metallicity estimates also reduces systematic biases for populations skewed
toward high or low SFR environments, as we illustrate using the host galaxy of
the supernova SN 2010ay. This new tool will lend more statistical power to
studies of galaxy populations, such as supernova and gamma-ray burst (GRB) host
environments, in ongoing and future wide field imaging surveys. | Probing Inhomogeneity in the Helium Ionizing UV Background: We present an analysis combining the simultaneous measurement of
intergalactic absorption by hydrogen (H I), helium (He II) and oxygen (O VI) in
UV and optical quasar spectra. The combination of the H I and He II Lyman-alpha
forests through $\eta$ (the ratio of column densities of singly ionized helium
to neutral hydrogen) is thought to be sensitive to large-scale inhomogeneities
in the extragalactic UV background. We test this assertion by measuring
associated five-times-ionized oxygen (O VI) absorption, which is also sensitive
to the UV background. We apply the pixel optical depth technique to O VI
absorption in high and low $\eta$ samples filtered on various scales. This
filtering scale is intended to represent the dominant scale of any coherent
oxygen excess/deficit. We find a $2\sigma$ detection of an O VI opacity excess
in the low $\eta$ sample on scales of $\sim$10 cMpc for HE 2347-4342 at
$\bar{z}\approx 2.6$, consistent with a large-scale excess in hard UV photons.
However, for HS 1700+6416 at $\bar{z}\approx 2.5$ we find that the measured O
VI absorption is not sensitive to differences in $\eta$. HS 1700+6416 also
shows a relative absence of O VI overall, which is $6\sigma$ inconsistent with
that of HE 2347-4342. This implies UV background inhomogeneities on
$\gtrsim$200 cMpc scales, hard UV regions having internal ionization structure
on $\sim$10 cMpc scales and soft UV regions showing no such structure.
Furthermore, we perform the pixel optical depth search for oxygen on the He II
Gunn-Peterson trough of HE 2347-4342 and find results consistent with post-He
II-reionization conditions. |
Structure Decomposition for the Luminous Disk Galaxies in the NGC 524
Group: Members of the NGC 524 group of galaxies are studied using data obtained on
the 6m telescope of the Special Astrophysical Observatory of the Russian
Academy of Sciences, with the SCORPIO reducer in an imaging mode. Surface
photometry has been carried out and parameters of the large-scale galactic
components - disks and bulges - have been determined for the six largest
galaxies of the group. A lower than expected percentage of bars and high
percentage of ring structures were found. Integrated B-V colours for a hundred
of dwarf galaxies in the vicinity (within 30 kpc) of the six largest galaxies
of the group have been measured. A considerable number of blue irregular
galaxies with ongoing star formation is found among dwarf satellites of the
lenticular galaxies of the group. The luminosity function for the dwarf
galaxies of the group suggests that the total mass of the group is not very
high, and that the X-ray emitting gas observed around NGC 524 relates to the
central galaxy and not to the group as a whole. | Quintessence or Phantom: Study of scalar field dark energy models
through a general parametrization of the Hubble parameter: In this work we propose a simple general parametrization scheme of the Hubble
parameter for the scalar field dark energy models. In our approach it is
possible to incorporate both the quintessence and phantom scalar field in a
single analytical scheme and write down relevant cosmological parameters which
are independent of the nature of the scalar field. A general condition for the
phantom barrier crossing has also been obtained. To test this approach, a well
behaved parametrization of the normalized Hubble parameter has been considered
and a wide variety of observational data like CMB data, Supernovae data, BAO
data etc. has been used to constraint the various cosmological parameters. It
has been found that data prefer the present value of the equation of state of
the dark energy to be in the phantom domain. One interesting outcome of this
analysis is that although the current value of the dark energy equation of
state is phantom in nature, a phantom crossing of the EOS has taken place in
the recent past. We have also carried out the Bayesian model comparison between
$\Lambda CDM$ model and the proposed model which indicates that this model is
favored by data as compared to $\Lambda CDM$ model. |
Graviton production in non-inflationary cosmology: We discuss the creation of massless particles in a Universe, which transits
from a radiation-dominated era to any other expansion law. We calculate in
detail the generation of gravitons during the transition to a matter dominated
era. We show that the resulting gravitons generated in the standard
radiation/matter transition are negligible. We use our result to constrain one
or more previous matter dominated era, or any other expansion law, which may
have taken place in the early Universe. We also derive a general formula for
the modification of a generic initial graviton spectrum by an early matter
dominated era. | The small scale power asymmetry in the cosmic microwave background: We investigate the hemispherical power asymmetry in the cosmic microwave
background on small angular scales. We find an anomalously high asymmetry in
the multipole range l=601-2048, with a naive statistical significance of 6.5
sigma. However, we show that this extreme anomaly is simply a coincidence of
three other effects, relativistic power modulation, edge effects from the mask
applied, and inter-scale correlations. After correcting for all of these
effects, the significance level drops to ~1 sigma, i.e., there is no anomalous
intrinsic asymmetry in the small angular scales. Using this null result, we
derive a constraint on a potential dipolar modulation amplitude, A(k)<0.0045 on
the ~10 Mpc-scale, at 95% C.L. This new constraint must be satisfied by any
theoretical model attempting to explain the hemispherical asymmetry at large
angular scales. |
Galaxy number-count dipole and superhorizon fluctuations: In view of the growing tension between the dipole anisotropy of number counts
of cosmologically distant sources and of the cosmic microwave background (CMB),
we investigate the number count dipole induced by primordial perturbations with
wavelength comparable to or exceeding the Hubble radius today. First, we find
that neither adiabatic nor isocurvature superhorizon modes can generate an
intrinsic number count dipole. However a superhorizon isocurvature mode does
induce a relative velocity between the CMB and the (dark) matter rest frames
and thereby affects the CMB dipole. We revisit the possibility that it has an
intrinsic component due to such a mode, thus enabling consistency with the
galaxy number count dipole if the latter is actually kinematic in origin.
Although this scenario is not particularly natural, there are possible links
with other anomalies and it predicts a concommitant galaxy number count
quadrupole which may be measurable in future surveys. We also investigate the
number count dipole induced by modes smaller than the Hubble radius, finding
that subject to CMB constraints this is too small to reconcile the dipole
tension. | Phenomenology of a Pseudo-Scalar Inflaton: Naturally Large
Nongaussianity: Many controlled realizations of chaotic inflation employ pseudo-scalar
axions. Pseudo-scalars \phi are naturally coupled to gauge fields through c
\phi F \tilde{F}. In the presence of this coupling, gauge field quanta are
copiously produced by the rolling inflaton. The produced gauge quanta, in turn,
source inflaton fluctuations via inverse decay. These new cosmological
perturbations add incoherently with the "vacuum" perturbations, and are highly
nongaussian. This provides a natural mechanism to generate large nongaussianity
in single or multi field slow-roll inflation. The resulting phenomenological
signatures are highly distinctive: large nongaussianity of (nearly) equilateral
shape, in addition to detectably large values of both the scalar spectral tilt
and tensor-to-scalar ratio (both being typical of large field inflation). The
WMAP bound on nongaussianity implies that the coupling, c, of the pseudo-scalar
inflaton to any gauge field must be smaller than about 10^{2} M_p^{-1}. |
Cosmic flow around local massive galaxies: Aims. We use accurate data on distances and radial velocities of galaxies
around the Local Group, as well as around 14 other massive nearby groups, to
estimate their radius of the zero-velocity surface, $R_0$, which separates any
group against the global cosmic expansion.
Methods. Our $R_0$ estimate was based on fitting the data to the velocity
field expected from the spherical infall model, including effects of the
cosmological constant. The reported uncertainties were derived by a Monte Carlo
simulation.
Results. Testing various assumptions about a location of the group
barycentre, we found the optimal estimates of the radius to be
$0.91\pm0.05$~Mpc for the Local Group, and $0.93\pm0.02$~Mpc for a synthetic
group stacked from 14 other groups in the Local Volume. Under the standard
Planck model parameters, these quantities correspond to the total mass of the
group $\sim (1.6\pm0.2) 10^{12} M_{\odot}$. Thus, we are faced with the
paradoxical result that the total mass estimate on the scale of $R_0 \approx
(3- 4) R_{vir}$ is only $~60$% of the virial mass estimate. Anyway, we conclude
that wide outskirts of the nearby groups do not contain a large amount of
hidden mass outside their virial radius. | Correlating correlation functions of primordial perturbations: We explore the correlations between correlation functions of the primordial
curvature perturbation produced during inflation. We find that for general
single field inflation, other than the source terms which depend on the model
details, higher order correlation functions are characterized by the power
spectrum, its spectral index and running. The correlation between the
bispectrum and power spectrum is presented as an explicit example of our
systematic approach. |
How can gravitational-wave standard sirens and 21 cm intensity mapping
jointly provide a precise late-universe cosmological probe?: In the next decades, the gravitational-wave (GW) standard siren observations
and the neutral hydrogen 21-cm intensity mapping (IM) surveys, as two promising
cosmological probes, will play an important role in precisely measuring
cosmological parameters. In this work, we make a forecast for cosmological
parameter estimation with the synergy between the GW standard siren
observations and the 21-cm IM surveys. We choose the Einstein Telescope (ET)
and the Taiji observatory as the representatives of the GW detection projects
and choose the Square Kilometre Array (SKA) phase I mid-frequency array as the
representative of the 21-cm IM experiments. In the simulation of the 21-cm IM
data, we assume perfect foreground removal and calibration. We find that the
synergy of the GW standard siren observations and the 21-cm IM survey could
break the cosmological parameter degeneracies. The joint ET+Taiji+SKA data give
$\sigma(H_0)=0.28\ {\rm km\ s^{-1}\ Mpc^{-1}}$ in the $\Lambda$CDM model,
$\sigma(w)=0.028$ in the $w$CDM model, which are better than the results of
$Planck$+BAO+SNe, and $\sigma(w_0)=0.077$ and $\sigma(w_a)=0.295$ in the CPL
model, which are comparable with the results of $Planck$+BAO+SNe. In the
$\Lambda$CDM model, the constraint precision of $H_0$ and $\Omega_{\rm m}$ is
less than or rather close to 1%, indicating that the magnificent prospects for
precision cosmology with these two promising cosmological probes are worth
expecting. | Detection of molecular gas in a distant submillimetre galaxy at z=4.76
with ATCA: We have detected the CO(2-1) transition from the submillimetre galaxy (SMG)
LESSJ033229.4-275619 at z=4.755 using the new Compact Array Broadband Backend
system on the Australian Telescope Compact Array. These data have identified a
massive gas reservoir available for star formation for the first time in an SMG
at z~5. We use the luminosity and velocity width (FWHM of 160 km/s) of the
CO(2--1) line emission to constrain the gas and dynamical mass of
Mgas~1.6x10^10 Msun and Mdyn(<2kpc)~5x10^10 (0.25/sin^2(i)) Msun, respectively,
similar to that observed for SMGs at lower redshifts of z~2-4, although we note
that our observed CO FWHM is a factor of ~3 narrower than typically seen in
SMGs. Together with the stellar mass we estimate a total baryonic mass of
Mbary~1x10^11 Msun, consistent with the dynamical mass for this young galaxy
within the uncertainties. Dynamical and baryonic mass limits of high-redshift
galaxies are useful tests of galaxy formation models: using the known z~4-5
SMGs as examples of massive baryonic systems, we find that their space density
is consistent with that predicted by current galaxy formation models. In
addition, these observations have helped to confirm that z~4-5 SMGs possess the
baryonic masses and gas consumption timescales necessary to be the progenitors
of the luminous old red galaxies seen at z~3. Our results provide a preview of
the science that ALMA will enable on the formation and evolution of the
earliest massive galaxies in the Universe. |
Designing an Optimal LSST Deep Drilling Program for Cosmology with Type
Ia Supernovae: The Vera C. Rubin Observatory's Legacy Survey of Space and Time is forecast
to collect a large sample of Type Ia supernovae (SNe Ia) that could be
instrumental in unveiling the nature of Dark Energy. The feat, however,
requires measuring the two components of the Hubble diagram - distance modulus
and redshift - with a high degree of accuracy. Distance is estimated from SNe
Ia parameters extracted from light curve fits, where the average quality of
light curves is primarily driven by survey parameters such as the cadence and
the number of visits per band. An optimal observing strategy is thus critical
for measuring cosmological parameters with high accuracy. We present in this
paper a three-stage analysis aiming at quantifying the impact of the Deep
Drilling (DD) strategy parameters on three critical aspects of the survey: the
redshift completeness (originating from the Malmquist cosmological bias), the
number of well-measured SNe Ia, and the cosmological measurements. Analyzing
the current LSST survey simulations, we demonstrate that the current DD survey
plans are characterized by a low completeness ($z~\sim$ 0.55-0.65), and
irregular and low cadences (few days) that dramatically decrease the size of
the well-measured SNe Ia sample. We then propose a modus operandi that provides
the number of visits (per band) required to reach higher redshifts. The results
of this approach are used to design a set of optimized DD surveys for SNe Ia
cosmology. We show that most accurate cosmological measurements are achieved
with Deep Rolling surveys characterized by a high cadence (one day), a rolling
strategy (each field observed at least two seasons), and two sets of fields:
ultra-deep ($z \gtrsim 0.8$) and deep ($z \gtrsim 0.6$) fields. We also
demonstrate that a deterministic scheduler including a gap recovery mechanism
is critical to achieve a high quality DD survey required for SNe Ia cosmology. | Holographic dark energy at the Ricci scale: We consider a holographic cosmological model in which the infrared cutoff is
fixed by the Ricci's length and dark matter and dark energy do not evolve
separately but interact non-gravitationally with one another. This
substantially alleviates the cosmic coincidence problem as the ratio between
both components remains finite throughout the expansion. We constrain the model
with observational data from supernovae, cosmic background radiation, baryon
acoustic oscillations, gas mass fraction in galaxy clusters, the history of the
Hubble function, and the growth function. The model shows consistency with
observation. |
The separate and combined effects of baryon physics and neutrino
free-streaming on large-scale structure: We use the cosmo-OWLS and BAHAMAS suites of cosmological hydrodynamical
simulations to explore the separate and combined effects of baryon physics
(particularly feedback from active galactic nuclei, AGN) and free-streaming of
massive neutrinos on large-scale structure. We focus on five diagnostics: i)
the halo mass function; ii) halo mass density profiles; iii) the halo
mass-concentration relation; iv) the clustering of haloes; and v) the
clustering of matter; and we explore the extent to which the effects of baryon
physics and neutrino free-streaming can be treated independently. Consistent
with previous studies, we find that both AGN feedback and neutrino
free-streaming suppress the total matter power spectrum, although their scale
and redshift dependencies differ significantly. The inclusion of AGN feedback
can significantly reduce the masses of groups and clusters, and increase their
scale radii. These effects lead to a decrease in the amplitude of the
mass-concentration relation and an increase in the halo autocorrelation
function at fixed mass. Neutrinos also lower the masses of groups and clusters
while having no significant effect on the shape of their density profiles (thus
also affecting the mass-concentration relation and halo clustering in a
qualitatively similar way to feedback). We show that, with only a small number
of exceptions, the combined effects of baryon physics and neutrino
free-streaming on all five diagnostics can be estimated to typically better
than a few percent accuracy by treating these processes independently (i.e., by
multiplying their separate effects). | The QCD Axion and Gravitational Waves in light of NANOGrav results: The North American Nanohertz Observatory for Gravitational Waves (NANOGrav)
collaboration has recently reported strong evidence for a stochastic process
affecting the 12.5 yr dataset of pulsar timing residuals. We show that the
signal can be interpreted in terms of a stochastic gravitational wave
background emitted from a network of axionic strings in the early Universe. The
spontaneous breaking of the Peccei-Quinn symmetry originate the axionic string
network and the QCD axion, the dark matter particle in the model. We explore a
non-standard cosmological model driven by an exotic scalar field $\phi$ which
evolves under the influence of a self-interacting potential; the axion field
starts to oscillate during the modified cosmology, and provides the dark matter
observed. For an equation of state $w_\phi < 1/3$, the QCD axion mass is
smaller than expected in the standard cosmology and the GW spectrum from
axionic strings is larger. We assess the parameter space of the model which is
consistent with the NANOGrav-$12.5\,$yr detection, which can be explained
within 95\% limit by a QCD axion field evolving in a dust-like scenario, as
well as within 68\% limit in a cosmology with $w_\phi < 0$. |
Tidal alignment of galaxies: We develop an analytic model for galaxy intrinsic alignments (IA) based on
the theory of tidal alignment. We calculate all relevant nonlinear corrections
at one-loop order, including effects from nonlinear density evolution, galaxy
biasing, and source density weighting. Contributions from density weighting are
found to be particularly important and lead to bias dependence of the IA
amplitude, even on large scales. This effect may be responsible for much of the
luminosity dependence in IA observations. The increase in IA amplitude for more
highly biased galaxies reflects their locations in regions with large tidal
fields. We also consider the impact of smoothing the tidal field on halo
scales. We compare the performance of this consistent nonlinear model in
describing the observed alignment of luminous red galaxies with the linear
model as well as the frequently used "nonlinear alignment model," finding a
significant improvement on small and intermediate scales. We also show that the
cross-correlation between density and IA (the "GI" term) can be effectively
separated into source alignment and source clustering, and we accurately model
the observed alignment down to the one-halo regime using the tidal field from
the fully nonlinear halo-matter cross correlation. Inside the one-halo regime,
the average alignment of galaxies with density tracers no longer follows the
tidal alignment prediction, likely reflecting nonlinear processes that must be
considered when modeling IA on these scales. Finally, we discuss tidal
alignment in the context of cosmic shear measurements. | Tracing the merger rate of the Universe with APERTIF and ASKAP: OH maser emission at 1.67 GHz is known to be associated with regions of
intense star formation within ULIRGs. As these galaxies are formed through
violent mergers, studying the co-moving density of OH maser galaxies across
cosmic time will allow the merger rate of the Universe to be determined in an
independent way. This merger rate is an important parameter in galaxy formation
and evolution scenarios. The sensitivity, wide field of view and spectral
coverage of both APERTIF on the WSRT and ASKAP will allow for the first time
all-sky blind surveys for OH maser galaxies to be carried out to redshift 1.4.
We describe the prospects for such surveys, including the expected number of OH
maser galaxies that will be discovered, and what limits can be placed on the OH
maser luminosity function, and hence the merger rate out to redshift 1.4 with
various survey strategies. |
Constraining Dark Matter -- Dark Radiation interactions with CMB, BAO,
and Lyman-$α$: Several interesting Dark Matter (DM) models invoke a dark sector leading to
two types of relic particles, possibly interacting with each other:
non-relativistic DM, and relativistic Dark Radiation (DR). These models have
interesting consequences for cosmological observables, and could in principle
solve problems like the small-scale cold DM crisis, Hubble tension, and/or low
$\sigma_8$ value. Their cosmological behaviour is captured by the ETHOS
parametrisation, which includes a DR-DM scattering rate scaling like a
power-law of the temperature, $T^n$. Scenarios with $n=0$, $2$, or $4$ can
easily be realised in concrete dark sector set-ups. Here we update constraints
on these three scenarios using recent CMB, BAO, and high-resolution
Lyman-$\alpha$ data. We introduce a new Lyman-$\alpha$ likelihood that is
applicable to a wide range of cosmological models with a suppression of the
matter power spectrum on small scales. For $n=2$ and $4$, we find that
Lyman-$\alpha$ data strengthen the CMB+BAO bounds on the DM-DR interaction rate
by many orders of magnitude. However, models offering a possible solution to
the missing satellite problem are still compatible with our new bounds. For
$n=0$, high-resolution Lyman-$\alpha$ data bring no stronger constraints on the
interaction rate than CMB+BAO data, except for extremely small values of the DR
density. Using CMB+BAO data and a theory-motivated prior on the minimal density
of DR, we find that the $n=0$ model can reduce the Hubble tension from
$4.1\sigma$ to $2.7\sigma$, while simultaneously accommodating smaller values
of the $\sigma_8$ and $S_8$ parameters hinted by cosmic shear data. | SN and BAO constraints on (new) polynomial dark energy parametrizations:
current results and forecasts: In this work we introduce two new polynomial parametrizations of dark energy
and explore their correlation properties. The parameters to fit are the
equation of state values at z=0 and z=0.5, which have naturally low correlation
and have already been shown to improve the popular Chevallier-Polarski-Linder
(CPL) parametrization. We test our models with low redshift astronomical
probes: type Ia supernovae and baryon acoustic oscillations (BAO), in the form
of both current and synthetic data. Specifically, we present simulations of
measurements of the radial and transversal BAO scales similar to those expected
in a BAO high precision spectroscopic redshift survey similar to EUCLID.
According to the Bayesian deviance information criterion (DIC), which penalizes
large errors and correlations, we show that our models perform better than the
CPL re-parametrization proposed by Wang (in terms of z=0 and z=0.5). This is
due to the combination of a lower correlation and smaller relative errors. The
same holds for a frequentist perspective: our Figure-of-Merit is larger for our
parametrizations. |
Physical Properties of Spectroscopically-Confirmed Galaxies at z >= 6.
I. Basic Characteristics of the Rest-Frame UV Continuum and Lyman-alpha
emission: We present deep HST near-IR and Spitzer mid-IR observations of a large sample
of spectroscopically-confirmed galaxies at z >= 6. The sample consists of 51
Lyman-alpha emitters (LAEs) at z ~ 5.7, 6.5, and 7.0, and 16 Lyman-break
galaxies (LBGs) at 5.9 < z < 6.5. The near-IR images were mostly obtained with
WFC3 in the F125W and F160W bands, and the mid-IR images were obtained with
IRAC in the 3.6um and 4.5um bands. Our galaxies also have deep optical imaging
data from Subaru Suprime-Cam. We utilize the multi-band data and secure
redshifts to derive their rest-frame UV properties. These galaxies have steep
UV continuum slopes roughly between beta ~ -1.5 and -3.5, with an average value
of beta ~ -2.3, slightly steeper than the slopes of LBGs in previous studies.
The slope shows little dependence on UV continuum luminosity except for a few
of the brightest galaxies. We find a statistically significant excess of
galaxies with slopes around beta ~ -3, suggesting the existence of very young
stellar populations with extremely low metallicity and dust content. Our
galaxies have moderately strong rest-frame Lyman-alpha equivalent width (EW) in
a range of ~10 to ~200 \AA. The star-formation rates are also moderate, from a
few to a few tens solar masses per year. The LAEs and LBGs in this sample share
many common properties, implying that LAEs represent a subset of LBGs with
strong Lyman-alpha emission. Finally, the comparison of the UV luminosity
functions between LAEs and LBGs suggests that there exists a substantial
population of faint galaxies with weak Lyman-alpha emission (EW < 20 \AA) that
could be the dominant contribution to the total ionizing flux at z >= 6. | Angular Momentum Transfer and Lack of Fragmentation in Self-Gravitating
Accretion Flows: Rapid inflows associated with early galaxy formation lead to the accumulation
of self-gravitating gas in the centers of proto-galaxies. Such gas
accumulations are prone to non-axisymmetric instabilities, as in the well-known
Maclaurin sequence of rotating ellipsoids, which are accompanied by a
catastrophic loss of angular momentum (J). Self-gravitating gas is also
intuitively associated with star formation. However, recent simulations of the
infall process display highly turbulent continuous flows. We propose that
J-transfer, which enables the inflow, also suppresses fragmentation.
Inefficient J loss by the gas leads to decay of turbulence, triggering global
instabilities and renewed turbulence driving. Flow regulated in this way is
stable against fragmentation, whilst staying close to the instability threshold
for bar formation -- thick self-gravitating disks are prone to global
instabilities before they become unstable locally. On smaller scales, the
fraction of gravitationally unstable matter swept up by shocks in such a flow
is a small and decreasing function of the Mach number. We conclude
counterintuitively that gas able to cool down to a small fraction of its virial
temperature will not fragment as it collapses. This provides a venue for
supermassive black holes to form via direct infall, without the intermediary
stage of forming a star cluster. Some black holes could have formed or grown in
massive halos at low redshifts. Thus the fragmentation is intimately related to
J redistribution within the system: it is less dependent on the molecular and
metal cooling but is conditioned by the ability of the flow to develop virial,
supersonic turbulence. |
Remapping simulated halo catalogues in redshift space: We discuss the extension to redshift space of a rescaling algorithm, designed
to alter the effective cosmology of a pre-existing simulated particle
distribution or catalogue of dark matter haloes. The rescaling approach was
initially developed by Angulo & White and was adapted and applied to halo
catalogues in real space in our previous work. This algorithm requires no
information other than the initial and target cosmological parameters, and it
contains no tuned parameters. It is shown here that the rescaling method also
works well in redshift space, and that the rescaled simulations can reproduce
the growth rate of cosmological density fluctuations appropriate for the target
cosmology. Even when rescaling a grossly non-standard model with Lambda=0 and
zero baryons, the redshift-space power spectrum of standard LCDM can be
reproduced to about 5% error for k<0.2h Mpc^-1. The ratio of
quadrupole-to-monopole power spectra remains correct to the same tolerance up
to k=1h Mpc^-1, provided that the input halo catalogue contains measured
internal velocity dispersions. | 21cm Forest with the SKA: An alternative to both the tomography technique and the power spectrum
approach is to search for the 21cm forest, that is the 21cm absorption features
against high-z radio loud sources caused by the intervening cold neutral
intergalactic medium (IGM) and collapsed structures. Although the existence of
high-z radio loud sources has not been confirmed yet, SKA-low would be the
instrument of choice to find such sources as they are expected to have spectra
steeper than their lower-z counterparts. Since the strongest absorption
features arise from small scale structures (few tens of physical kpc, or even
lower), the 21cm forest can probe the HI density power spectrum on small scales
not amenable to measurements by any other means. Also, it can be a unique probe
of the heating process and the thermal history of the early universe, as the
signal is strongly dependent on the IGM temperature. Here we show what SKA1-low
could do in terms of detecting the 21cm forest in the redshift range z =
7.5-15. |
Machine Learning Cosmic Expansion History: We use the machine learning techniques, for the first time, to study the
background evolution of the universe in light of 30 cosmic chronometers. From 7
machine learning algorithms, using the principle of mean squared error
minimization on testing set, we find that Bayesian ridge regression is the
optimal method to extract the information from cosmic chronometers. By use of a
power-law polynomial expansion, we obtain the first Hubble constant estimation
$H_0=65.95^{+6.98}_{-6.36}$ km s$^{-1}$ Mpc$^{-1}$ from machine learning. From
the view of machine learning, we may rule out a large number of cosmological
models, the number of physical parameters of which containing $H_0$ is larger
than 3. Very importantly and interestingly, we find that the parameter spaces
of 3 specific cosmological models can all be clearly compressed by considering
both their explanation and generalization abilities. | Testing the spherical evolution of cosmic voids: We study the spherical evolution model for voids in $\Lambda$CDM, where the
evolution of voids is governed by dark energy at an earlier time than that for
the whole universe or in overdensities. We show that the presence of dark
energy suppresses the growth of peculiar velocities, causing void
shell-crossing to occur at progressively later epochs as $\Omega_{\Lambda}$
increases. We apply the spherical model to evolve the initial conditions of
N-body simulated voids and compare the resulting final void profiles. We find
that the model is successful in tracking the evolution of voids with radii
greater than $30 h^{-1} \rm Mpc$, implying that void profiles could be used to
constrain dark energy. We find that the initial peculiar velocities of voids
play a significant role in shaping their evolution. Excluding the peculiar
velocity in the evolution model delays the time of shell crossing. |
Combining clustering and abundances of galaxy clusters to test cosmology
and primordial non-Gaussianity: We present the clustering of galaxy clusters as a useful addition to the
common set of cosmological observables. The clustering of clusters probes the
large-scale structure of the Universe, extending galaxy clustering analysis to
the high-peak, high-bias regime. Clustering of galaxy clusters complements the
traditional cluster number counts and observable-mass relation analyses,
significantly improving their constraining power by breaking existing
calibration degeneracies. We use the maxBCG galaxy clusters catalogue to
constrain cosmological parameters and cross-calibrate the mass-observable
relation, using cluster abundances in richness bins and weak-lensing mass
estimates. We then add the redshift-space power spectrum of the sample,
including an effective modelling of the weakly non-linear contribution and
allowing for an arbitrary photometric redshift smoothing. The inclusion of the
power spectrum data allows for an improved self-calibration of the scaling
relation. We find that the inclusion of the power spectrum typically brings a
$\sim 50$ per cent improvement in the errors on the fluctuation amplitude
$\sigma_8$ and the matter density $\Omega_{\mathrm{m}}$. Finally, we apply this
method to constrain models of the early universe through the amount of
primordial non-Gaussianity of the local type, using both the variation in the
halo mass function and the variation in the cluster bias. We find a constraint
on the amount of skewness $f_{\mathrm{NL}} = 12 \pm 157 $ ($1\sigma$) from the
cluster data alone. | On the Density profile slope of Clusters of Galaxies: The present paper extends to clusters of galaxies the study of Del Popolo
(2012), concerning how the baryon-dark matter (DM) interplay shapes the density
profile of dwarf galaxies. Cluster density profiles are determined taking into
account dynamical friction, random and ordered angular momentum and the
response of dark matter halos to condensation of baryons. We find that halos
containing only DM are characterized by Einasto's profiles, and that the
profile flattens with increasing content of baryons, and increasing values of
random angular momentum. The analytical results obtained in the first part of
the paper were applied to well studied clusters whose inner profiles have
slopes flatter than NFW predictions (A611, A383) or are characterized by
profiles in agreement with the NFW model (MACS J1423.8+2404, RXJ1133). By using
independently-measured baryonic fraction, a typical spin parameter value
$\lambda \simeq 0.03$, and adjusting the random angular momentum, we re-obtain
the mass and density profiles of the quoted clusters. Finally, we show that the
baryonic mass inside $\simeq 10$ kpc, $M_{b,in}$ is correlated with the total
mass of the clusters, %finding a correlation among the two quantities, as
$M_{b,in} \propto M_{500}^{0.4}$. |
Non-detection of a statistically anisotropic power spectrum in
large-scale structure: We search a sample of photometric luminous red galaxies (LRGs) measured by
the Sloan Digital Sky Survey (SDSS) for a quadrupolar anisotropy in the
primordial power spectrum, in which P(\vec{k}) is an isotropic power spectrum
P(k) multiplied by a quadrupolar modulation pattern. We first place limits on
the 5 coefficients of a general quadrupole anisotropy. We also consider
axisymmetric quadrupoles of the form P(\vec{k}) = P(k){1 +
g_*[(\hat{k}\cdot\hat{n})^2-1/3]} where \hat{n} is the axis of the anisotropy.
When we force the symmetry axis \hat{n} to be in the direction (l,b)=(94
degrees,26 degrees) identified in the recent Groeneboom et al. analysis of the
cosmic microwave background, we find g_*=0.006+/-0.036 (1 sigma). With uniform
priors on \hat{n} and g_* we find that -0.41<g_*<+0.38 with 95% probability,
with the wide range due mainly to the large uncertainty of asymmetries aligned
with the Galactic Plane. In none of these three analyses do we detect evidence
for quadrupolar power anisotropy in large scale structure. | The Merger Rates and Mass Assembly Histories of Dark Matter Haloes in
the Two Millennium Simulations: We construct merger trees of dark matter haloes and quantify their merger
rates and mass growth rates using the joint dataset from the Millennium and
Millennium-II simulations. The finer resolution of the Millennium-II Simulation
has allowed us to extend our earlier analysis of halo merger statistics to an
unprecedentedly wide range of descendant halo mass (10^10 < M0 < 10^15 Msun),
progenitor mass ratio (10^-5 < xi < 1), and redshift (0 < z < 15). We update
our earlier fitting form for the mean merger rate per halo as a function of
M_0, xi, and z. The overall behavior of this quantity is unchanged: the rate
per unit redshift is nearly independent of z out to z~15; the dependence on
halo mass is weak (M0^0.13); and it is nearly a power law in the progenitor
mass ratio (xi^-2). We also present a simple and accurate fitting formula for
the mean mass growth rate of haloes as a function of mass and redshift. This
mean rate is 46 Msun/yr for 10^12 Msun haloes at z=0, and it increases with
mass as M^{1.1} and with redshift as (1+z)^2.5 (for z > 1). When the fit for
the mean mass growth rate is integrated over a halo's history, we find
excellent match to the mean mass assembly histories of the simulated haloes. By
combining merger rates and mass assembly histories, we present results for the
number of mergers over a halo's history and the statistics of the redshift of
the last major merger. |
Observational signatures of microlensing in gravitational waves at
LIGO/Virgo frequencies: Microlenses with typical stellar masses (a few ${\rm M}_{\odot}$) have
traditionally been disregarded as potential sources of gravitational lensing
effects at LIGO/Virgo frequencies, since the time delays are often much smaller
than the inverse of the frequencies probed by LIGO/Virgo, resulting in
negligible interference effects at LIGO/Virgo frequencies. While this is true
for isolated microlenses in this mass regime, we show how, under certain
circumstances and for realistic scenarios, a population of microlenses (for
instance stars and remnants from a galaxy halo or from the intracluster medium)
embedded in a macromodel potential (galaxy or cluster) can conspire together to
produce time delays of order one millisecond which would produce significant
interference distortions in the observed strains. At sufficiently large
magnification factors (of several hundred), microlensing effects should be
common in gravitationally lensed gravitational waves. We explore the regime
where the predicted signal falls in the frequency range probed by LIGO/Virgo.
We find that stellar mass microlenses, permeating the lens plane, and near
critical curves, can introduce interference distortions in strongly lensed
gravitational waves. For those lensed events with negative parity, (or saddle
points, never studied before in the context of gravitational waves), and that
take place near caustics of macromodels, they are more likely to produce
measurable interference effects at LIGO/Virgo frequencies. This is the first
study that explores the effect of a realistic population of microlenses, plus a
macromodel, on strongly lensed gravitational waves. | Electrodynamics in an LTB scenario: In this article we analyze the electrodynamics in curved space-time in LTB
metric. We calculate the most general scale factor in this inhomogeneous
Universe. We also study the presence of electromagnetic field bubbles in the
Universe. |
Stochastic dark energy from inflationary quantum fluctuations: We study the quantum backreaction from inflationary fluctuations of a very
light, non-minimally coupled spectator scalar and show that it is a viable
candiate for dark energy. The problem is solved by suitably adapting the
formalism of stochastic inflation. This allows us to self-consistently account
for the backreaction on the background expansion rate of the Universe where its
effects are large. This framework is equivalent to that of semiclassical
gravity in which matter vacuum fluctuations are included at the one loop level,
but purely quantum gravitational fluctuations are neglected. Our results show
that dark energy in our model can be characterized by a distinct effective
equation of state parameter (as a function of redshift) which allows for
testing of the model at the level of the background. | A Free-Form mass model of the Hubble Frontier Fields Cluster AS1063 (RXC
J2248.7-4431) with over one hundred constraints: We derive a free-form mass distribution for the massive cluster AS1063
(z=0.348) using the completed optical imaging from the Hubble Frontier Fields
programme. Based on a subset of 11 multiply lensed systems with spectroscopic
redshift we produce a lens model that is accurate enough to unveil new multiply
lensed systems, totalling over a 100 arclets, and to estimate their redshifts
geometrically. Consistency is found between this precise model and that
obtained using only the subset of lensed sources with spectroscopically
measured redshifts. Although a relatively large elongation of the mass
distribution is apparent relative to the X-ray map, no significant offset is
found between the centroid of our mass distribution and that of the X-ray
emission map, suggesting a relatively relaxed state for this cluster. For the
well resolved lensed images we provide detailed model comparisons to illustrate
the precision of our model and hence the reliability of our de-lensed sources.
A clear linear structure is associated with one such source extending approx.
23 kpc in length, that could be an example of jet-induced star formation, at
redshift z=3.1. |
Effects of active-sterile neutrino mixing during primordial
nucleosynthesis: In the present work, we discuss the effects of the inclusion of
sterile-active neutrino oscillations during the production of primordial
light-nuclei. We assume that the sterile neutrino mass-eigenstate might
oscillate with the two lightest active neutrino mass- eigenstates, with mixing
angles ${\phi}_1$ and ${\phi}_2$. We also allow a constant renormalization
(represented by a parameter (${\zeta}$)) of the sterile neutrino occupation
factor. Taking ${\zeta}$ and the mixing angles as free parameters, we have
computed distribution functions of active and sterile neutrinos and primordial
abundances. Using observable data we set constrains in the free parameters of
the model. It is found that the data on primordial abundances are consistent
with small mixing angles and with a value of ${\zeta}$ smaller than 0.65 at
3${\sigma}$ level. | The first high-redshift cavity power measurements of cool-core galaxy
clusters with the International LOFAR Telescope: Radio-mode feedback associated with the active galactic nuclei (AGN) at the
cores of galaxy clusters injects large amount of energy into the intracluster
medium (ICM), offsetting radiative losses through X-ray emission. This
mechanism prevents the ICM from rapidly cooling down and fueling extreme
starburst activity as it accretes onto the central galaxies, and is therefore a
key ingredient in the evolution of galaxy clusters. However, the influence and
mode of feedback at high redshifts (z~1) remains largely unknown. Low-frequency
sub-arcsecond resolution radio observations taken with the International LOFAR
Telescope have demonstrated their ability to assist X-ray observations with
constraining the energy output from the AGNs (or "cavity power") in galaxy
clusters, thereby enabling research at higher redshifts than before. In this
pilot project, we test this hybrid method on a high redshift (0.6<z<1.3) sample
of 13 galaxy clusters for the first time with the aim of verifying the
performance of this method at these redshifts and providing the first estimates
of the cavity power associated with the central AGN for a sample of distant
clusters. We were able to detect clear radio lobes in three out of thirteen
galaxy clusters at redshifts 0.7<z<0.9, and use these detections in combination
with ICM pressures surrounding the radio lobes obtained from standard profiles
to calculate the corresponding cavity powers of the AGNs. By combining our
results with the literature, the current data appear to suggest that the
average cavity power peaked at a redshift of z~0.4 and slowly decreases toward
higher redshifts. However, we require more and tighter constraints on the
cavity volume and a better understanding of our observational systematics to
confirm any deviation of the cavity power trend from a constant level. |
Substructure lensing in galaxy clusters as a constraint on low-mass
sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell
2390: Certain covariant theories of the modified Newtonian dynamics paradigm seem
to require an additional hot dark matter (HDM) component - in the form of
either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs)
with a mass around 11eV - to be relieved of problems ranging from cosmological
scales down to intermediate ones relevant for galaxy clusters. Here we suggest
using gravitational lensing by galaxy clusters to test such a marriage of
neutrino HDM and modified gravity, adopting the framework of
tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter
(CDM), such HDM is subject to strong phase-space constraints, which allows one
to check cluster lens models inferred within the modified framework for
consistency. Since the considered HDM particles cannot collapse into
arbitrarily dense clumps and only form structures well above the galactic
scale, systems which indicate the need for dark substructure are of particular
interest. As a first example, we study the cluster lens Abell 2390 and its
impressive straight arc with the help of numerical simulations. Based on our
results, we outline a general and systematic approach to model cluster lenses
in TeVeS which significantly reduces the calculation complexity. We further
consider a simple bimodal lens configuration, capable of producing the straight
arc, to demonstrate our approach. We find that such a model is marginally
consistent with the hypothesis of 11eV SNs. Future work including more detailed
and realistic lens models may further constrain the necessary SN distribution
and help to conclusively assess this point. Cluster lenses could therefore
provide an interesting discriminator between CDM and such modified gravity
scenarios supplemented by SNs or other choices of HDM. | New test of the FLRW metric using the distance sum rule: We present a new test of the validity of the
Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, based on comparing the
distance from redshift 0 to $z_1$ and from $z_1$ to $z_2$ to the distance from
$0$ to $z_2$. If the universe is described by the FLRW metric, the comparison
provides a model-independent measurement of spatial curvature. The test relies
on geometrical optics, it is independent of the matter content of the universe
and the applicability of the Einstein equation on cosmological scales. We apply
the test to observations, using the Union2.1 compilation of supernova distances
and Sloan Lens ACS Survey galaxy strong lensing data. The FLRW metric is
consistent with the data, and the spatial curvature parameter is constrained to
be $-1.22<\Omega_{K0}<0.63$, or $-0.08<\Omega_{K0}<0.97$ with a prior from the
cosmic microwave background and the local Hubble constant, though modelling of
the lenses is a source of significant systematic uncertainty. |
Unifying all mass discrepancies with one effective gravity law?: A remarkably tight relation is observed between the Newtonian gravity sourced
by the baryons and the actual gravity in galaxies of all sizes. This can be
interpreted as the effect of a single effective force law depending on
acceleration. This is however not the case in larger systems with much deeper
potential wells, such as galaxy clusters. Here we explore the possibility of an
effective force law reproducing mass discrepancies in all extragalactic systems
when depending on both acceleration and the depth of the potential well. We
exhibit, at least at a phenomenological level, one such possible construction
in the classical gravitational potential theory. Interestingly, the framework,
dubbed EMOND, is able to reproduce the observed mass discrepancies in both
galaxies and galaxy clusters, and to produce multi-center systems with offsets
between the peaks of gravity and the peaks of the baryonic distribution. | Inflation with very small tensor-to-scalar ratio: We have investigated inflation models that predict a very small value of the
tensor-to-scalar ratio, $r$. The spectral index $n_s$, and the tensor-to-scalar
ratio $r$, are strictly constrained by the Planck data. $n_s$ and $r$ are
sensitive to the shape and magnitude of the inflaton potential,
respectively.The constraints by the Planck 2018 data combined with other
cosmological observations are compared with the predictions from the inflation
models regarding $n_s$ and $r$. Furthermore, we discuss the comparison of
future tensor-to-scalar ratio data with predictions from the inflation models
with a focus on part of the quantum fluctuation origin. |
Sub-millimetre galaxies in cosmological hydrodynamic simulations: Source
number counts and the spatial clustering: We use large cosmological Smoothed-Particle-Hydrodynamics simulations to
study the formation and evolution of sub-millimetre galaxies (SMGs). In our
previous work, we studied the statistical properties of ultra-violet selected
star-forming galaxies at high redshifts. We populate the same cosmological
simulations with SMGs by calculating the reprocess of stellar light by dust
grains into far-infrared to millimetre wavebands in a self-consistent manner.
We generate light-cone outputs to compare directly the statistical properties
of the simulated SMGs with available observations. Our model reproduces the
submm source number counts and the clustering amplitude. We show that bright
SMGs with flux $S > 1$ mJy reside in halos with mass of $\sim 10^{13}
M_{\odot}$ and have stellar masses greater than $10^{11}\sim \rm M_{\odot}$.
The angular cross-correlation between the SMGs and Lyman-$\alpha$ emitters is
significantly weaker than that between the SMGs and Lyman-break galaxies. The
cross-correlation is also weaker than the auto-correlation of the SMGs. The
redshift distribution of the SMGs shows a broad peak at $z \sim 2$, where
Bright SMGs contribute significantly to the global cosmic star formation rate
density. Our model predicts that there are hundreds of SMGs with $S > 0.1$ mJy
at $z > 5$ per 1 square degree field. Such SMGs can be detected by ALMA. | An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6: I.
Survey Description and Morphological Properties of Star Forming Galaxies: We present the results of a 42-orbit HST/WFC3 survey of the rest-frame
optical morphologies of star forming galaxies with spectroscopic redshifts in
the range z=1.5-3.6. The survey consists of 42 orbits of F160W imaging covering
~65 arcmin^2 distributed widely across the sky and reaching a depth of 27.9 AB
for a 5 sigma detection within a 0.2 arcsec radius aperture. Focusing on an
optically selected sample of 306 star forming galaxies with stellar masses in
the range M* = 10^9 - 10^11 Msun, we find that typical circularized effective
half-light radii range from ~ 0.7 - 3.0 kpc and describe a stellar mass -
radius relation as early as z ~ 3. While these galaxies are best described by
an exponential surface brightness profile, their distribution of axis ratios is
strongly inconsistent with a population of inclined exponential disks and is
better reproduced by triaxial stellar systems with minor/major and
intermediate/major axis ratios ~ 0.3 and 0.7 respectively. While rest-UV and
rest-optical morphologies are generally similar for a subset of galaxies with
HST/ACS imaging data, differences are more pronounced at higher masses M* > 3 x
10^10 Msun. Finally, we discuss galaxy morphology in the context of efforts to
constrain the merger fraction, finding that morphologically-identified
mergers/non-mergers generally have insignificant differences in terms of
physical observables such as stellar mass and star formation rate, although
merger-like galaxies selected according to some criteria have statistically
smaller effective radii and correspondingly larger SFR surface density. |
Radiative Transfer Modeling of Lyman Alpha Emitters. I. Statistics of
Spectra and Luminosity: We combine a cosmological reionization simulation with box size of 100Mpc/h
on a side and a Monte Carlo Lyman-alpha (Lya) radiative transfer code to model
Lyman Alpha Emitters (LAEs) at z~5.7. The model introduces Lya radiative
transfer as the single factor for transforming the intrinsic Lya emission
properties into the observed ones. Spatial diffusion of Lya photons from
radiative transfer results in extended Lya emission and only the central part
with high surface brightness can be observed. Because of radiative transfer,
the appearance of LAEs depends on density and velocity structures in
circumgalactic and intergalactic media as well as the viewing angle, which
leads to a broad distribution of apparent (observed) Lya luminosity for a given
intrinsic Lya luminosity. Radiative transfer also causes frequency diffusion of
Lya photons. The resultant Lya line is asymmetric with a red tail. The peak of
the Lya line shifts towards longer wavelength and the shift is anti-correlated
with the apparent to intrinsic Lya luminosity ratio. The simple radiative
transfer model provides a new framework for studying LAEs. It is able to
explain an array of observed properties of z~5.7 LAEs in Ouchi et al. (2008),
producing Lya spectra, morphology, and apparent Lya luminosity function (LF)
similar to those seen in observation. The broad distribution of apparent Lya
luminosity at fixed UV luminosity provides a natural explanation for the
observed UV LF, especially the turnover towards the low luminosity end. The
model also reproduces the observed distribution of Lya equivalent width (EW)
and explains the deficit of UV bright, high EW sources. Because of the broad
distribution of the apparent to intrinsic Lya luminosity ratio, the model
predicts effective duty cycles and Lya escape fractions for LAEs. | SAFIR: testing the coexistence of AGN and star formation activity and
the nature of the dusty torus in the local universe: We present the Seyfert and star formation Activity in the Far-InfraRed
(SAFIR) project, a small (15.1h) Herschel guaranteed time proposal performing
PACS and SPIRE imaging of a small sample of nearby Seyfert galaxies. This
project is aimed at studying the physical nature of the nuclear IR emission by
means of multi-component spectral energy distribution (SED) fitting and the
star formation properties of AGN hosts, as traced by cold dust. We summarize
the results achieved so far and outline the on-going work. |
When is the growth index constant?: The growth index $\gamma$ is an interesting tool to assess the phenomenology
of dark energy (DE) models, in particular of those beyond general relativity
(GR). We investigate the possibility for DE models to allow for a constant
$\gamma$ during the entire matter and DE dominated stages. It is shown that if
DE is described by quintessence (a scalar field minimally coupled to gravity),
this behaviour of $\gamma$ is excluded either because it would require a
transition to a phantom behaviour at some finite moment of time, or, in the
case of tracking DE at the matter dominated stage, because the relative matter
density $\Omega_m$ appears to be too small. An infinite number of solutions,
with $\Omega_m$ and $\gamma$ both constant, are found with $w_{DE}=0$
corresponding to Einstein-de Sitter universes. For all modified gravity DE
models satisfying $G_{\rm eff}\ge G$, among them the $f(R)$ DE models suggested
in the literature, the condition to have a constant $w_{DE}$ is strongly
violated at the present epoch. In contrast, DE tracking dust-like matter deep
in the matter era, but with $\Omega_m <1$, requires $G_{\rm eff} > G$ and an
example is given using scalar-tensor gravity for a range of admissible values
of $\gamma$. For constant $w_{DE}$ inside GR, departure from a quasi-constant
value is limited until today. Even a large variation of $w_{DE}$ may not result
in a clear signature in the change of $\gamma$. The change however is
substantial in the future and the asymptotic value of $\gamma$ is found while
its slope with respect to $\Omega_m$ (and with respect to $z$) diverges and
tends to $-\infty$. | Constraints on hybrid metric-Palatini models from background evolution: In this work, we introduce two models of the hybrid metric-Palatini theory of
gravitation. We explore their background evolution, showing explicitly that one
recovers standard General Relativity with an effective Cosmological Constant at
late times. This happens because the Palatini Ricci scalar evolves towards and
asymptotically settles at the minimum of its effective potential during
cosmological evolution. We then use a combination of cosmic microwave
background, supernovae and baryonic accoustic oscillations background data to
constrain the models' free parameters. For both models, we are able to
constrain the maximum deviation from the gravitational constant $G$ one can
have at early times to be around $1\%$. |
Dipole Anisotropy in Integrated Linearly Polarized Flux Density in NVSS
Data: We study the dipole anisotropy in integrated linearly polarization flux
density in NRAO VLA Sky Survey (NVSS). We extract the anisotropy parameters in
the number counts, number counts weighted by polarization observables, i.e.
degree of polarization (p) and polarization flux (P). We also determine the
anisotropy in the degree of polarization per source and polarization flux per
source. We consider data with several different cuts on the flux density,
S>10,20,30,40,50 mJy. For studies with degree of polarization we impose the
additional cut 0.01<p<1. Similarly for polarization flux we impose, 0.5<P<100
mJy. We find a very significant signal of dipole, both in number counts and P
(or p) weighted number counts. For the case of P weighted number counts the
significance ranges from 8 \sigma to 5 \sigma for S>20 mJy to S>50 mJy. The
corresponding direction parameters are found to be stable with the cut on flux
density. The significance is even higher for the case of p weighted number
counts. The observed anisotropy is found to be much larger in comparison to the
CMBR expectations. We find that polarization observables show a much higher
level of anisotropy in comparison to pure number counts or flux weighted number
counts. | Quintessence dynamics with two scalar fields and mixed kinetic terms: The dynamical properties of a model of dark energy in which two scalar fields
are coupled by a non-canonical kinetic term are studied. We show that overall
the addition of the coupling has only minor effects on the dynamics of the
two-field system for both potentials studied, even preserving many of the
features of the assisted quintessence scenario. The coupling of the kinetic
terms enlarges the regions of stability of the critical points. When the
potential is of an additive form, we find the kinetic coupling has an
interesting effect on the dynamics of the fields as they approach the
inflationary attractor, with the result that the combined equation of state of
the scalar fields can approach -1 during the transition from a matter dominated
universe to the recent period of acceleration. |
Calculating the Hubble diagram by perturbation theory: The effect of density fluctuations upon light propagation is calculated
perturbatively in a matter dominated irrotational universe. The starting point
is the perturbed metric (second order in the perturbation strength), while the
output is the Hubble diagram. Density fluctuations cause this diagram to
broaden to a strip. Moreover, the shift of the diagram mimics accelerated
expansion. | A Dynamical Model of the Local Group: This dynamical model for the 28 galaxies with distances less than 1.5 Mpc,
and not apparently tight satellites, is constrained by the initial condition
that peculiar velocities at high redshift are small and growing in accordance
with the standard cosmology. The solution is a satisfactory fit to most of the
measured redshifts, distances, and proper motions, with some interesting
exceptions that call for further investigation. The model predicts Milky Way
rotation speed 256 km/s, consistent with Reid et al. (2009a). Ten Local Group
galaxies emanate from low supergalactic latitude and supergalactic longitude ~
70 degrees, perhaps as remnants from failed assembly of a larger galaxy. NGC
6822 passes close to the Milky Way at redshift ~0.27, in an orbit similar to
the Magellanic Clouds. Leo I has heliocentric angular velocity 0.33 mas/yr,
perhaps measurable by the mean stellar motion, and 15 galaxies have proper
motions greater than 0.05 mas/yr, measurable for any with masers. |
Breaking the Degeneracy: Optimal Use of Three-point Weak Lensing
Statistics: We study the optimal use of third order statistics in the analysis of weak
lensing by large-scale structure. These higher order statistics have long been
advocated as a powerful tool to break measured degeneracies between
cosmological parameters. Using ray-tracing simulations, incorporating important
survey features such as a realistic depth-dependent redshift distribution, we
find that a joint two- and three-point correlation function analysis is a much
stronger probe of cosmology than the skewness statistic. We compare different
observing strategies, showing that for a limited survey time there is an
optimal depth for the measurement of third-order statistics, which balances
statistical noise and cosmic variance against signal amplitude. We find that
the chosen CFHTLS observing strategy was optimal and forecast that a joint two-
and three-point analysis of the completed CFHTLS-Wide will constrain the
amplitude of the matter power spectrum $\sigma_8$ to 10% and the matter density
parameter $\Omega_m$ to 17%, a factor of ~2.5 improvement on the two-point
analysis alone. Our error analysis includes all non-Gaussian terms, finding
that the coupling between cosmic variance and shot noise is a non-negligible
contribution which should be included in any future analytical error
calculations. | Viscous dark fluid universe: We investigate the cosmological perturbation dynamics for a universe
consisting of pressureless baryonic matter and a viscous fluid, the latter
representing a unified model of the dark sector. In the homogeneous and
isotropic background the \textit{total} energy density of this mixture behaves
as a generalized Chaplygin gas. The perturbations of this energy density are
intrinsically non-adiabatic and source relative entropy perturbations. The
resulting baryonic matter power spectrum is shown to be compatible with the
2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also
Hubble-function and supernovae Ia data, shows that, different from other
studies, there exists a maximum in the probability distribution for a negative
present value $q_0 \approx - 0.53$ of the deceleration parameter. Moreover,
while previous descriptions on the basis of generalized Chaplygin gas models
were incompatible with the matter power spectrum data since they required a
much too large amount of pressureless matter, the unified model presented here
favors a matter content that is of the order of the baryonic matter abundance
suggested by big-bang nucleosynthesis. |
A Minkowski Functional Analysis of the Cosmic Microwave Background Weak
Lensing Convergence: Minkowski functionals are summary statistics that capture the geometric and
morphological properties of fields. They are sensitive to all higher order
correlations of the fields and can be used to complement more conventional
statistics, such as the power spectrum of the field. We develop a Minkowski
functional-based approach for a full likelihood analysis of mildly non-Gaussian
sky maps with partial sky coverage. Applying this to the inference of
cosmological parameters from the Planck mission's map of the Cosmic Microwave
Background's lensing convergence, we find an excellent agreement with results
from the power spectrum-based lensing likelihood. While the non-Gaussianity of
current CMB lensing maps is dominated by reconstruction noise, a Minkowski
functional-based analysis may be able to extract cosmological information from
the non-Gaussianity of future lensing maps and thus go beyond what is
accessible with a power spectrum-based analysis. We make the numerical code for
the calculation of a map's Minkowski functionals, skewness and kurtosis
parameters available for download from GitHub. | The Ellipticity Distribution of Ambiguously Blended Objects: Using overlapping fields with space-based Hubble Space Telescope (HST) and
ground-based Subaru Telescope imaging we identify a population of blended
galaxies that are blended to such a large degree that they are detected as
single objects in the ground-based monochromatic imaging, which we label as
'ambiguous blends'. For deep imaging data, such as the depth targeted with the
Large Synoptic Survey Telescope (LSST), the ambiguous blend population is both
large ($\sim 14$%) and has a distribution of ellipticities that is different
from that of unblended objects in a way that will likely be important for the
weak lensing measurements. Most notably, for a limiting magnitude of $i \sim
27$ we find that ambiguous blending results in a ~14% increase in shear noise
(or ~12% decrease in the effective projected number density of lensed galaxies;
neff) due to 1) larger intrinsic ellipticity dispersion, 2) a scaling with the
galaxy number density $N_{gal}$ that is shallower than 1/$\sqrt{N_{gal}}$. For
the LSST Gold Sample ($i < 25.3$) there is a ~7% increase in shear noise (or
~7% decrease in $n_{eff}$). More importantly than these increases in the shear
noise, we find that the ellipticity distribution of ambiguous blends has an RMS
13% larger than that of non-blended galaxies. Given the need of future weak
lensing surveys to constrain the ellipticity distribution of galaxies to better
than a percent in order to mitigate cosmic shear multiplicative biases, the
different ellipticity distribution of ambiguous blends could be a dominant
systematic if unaccounted for. |
Topology of large scale under-dense regions: We investigate the large scale matter distribution adopting QSOs as matter
tracer. The quasar catalogue based on the SDSS DR7 is used. The void finding
algorithm is presented and statistical properties of void sizes and shapes are
determined. Number of large voids in the quasar distribution is greater than
the number of the same size voids found in the random distribution. The largest
voids with diameters exceeding 300 Mpc indicate an existence of comparable size
areas of lower than the average matter density. No void-void space correlations
have been detected, and no larger scale deviations from the uniform
distribution are revealed. The average CMB temperature in the directions of the
largest voids is lower than in the surrounding areas by 0.0046 +/- 0.0028 mK.
This figure is compared to the amplitude of the expected temperature depletion
caused by the Integrated Sachs-Wolfe effect. | Ongoing Star Formation In AGN Host Galaxy Disks: A View From
Core-collapse Supernovae: The normalized radial distribution of young stellar populations (and cold
gas) in nearby galactic disks is compared between AGN host galaxies and
starforming galaxies (both with Hubble types between S0/a and Scd) by using
type II supernovae (SNe) as tracers. A subset of 140 SNe\,II with available
supernova position measurements are selected from the SAI-SDSS image catalog by
requiring available SDSS spectroscopy data of their host galaxies. Our sample
is finally composed of 46 AGNs and 94 starforming galaxies. Both directly
measured number distributions and inferred surface density distributions
indicate that a) the SNe detected in starforming galaxies follow an exponential
law well; b) by contrast, the SNe detected in AGN host galaxies significantly
deviate from an exponential law, which is independent of both morphological
type and redshift. Specifically, we find a detection deficit around
$R_{\mathrm{SN}}/R_{25,\mathrm{cor}}\sim0.5$ and an over-detection at outer
region $R_{\mathrm{SN}}/R_{25,\mathrm{cor}}\sim0.6-0.8$. This finding provides
a piece of evidence supporting that there is a link between ongoing star
formation (and cold gas reservoir) taking place in the extended disk and
central AGN activity. |
The first bent double lobe radio source in a known cluster filament:
Constraints on the intra-filament medium: We announce the first discovery of a bent double lobe radio source (DLRS) in
a known cluster filament. The bent DLRS is found at a distance of 3.4 Mpc from
the center of the rich galaxy cluster, Abell~1763. We derive a bend angle
alpha=25deg, and infer that the source is most likely seen at a viewing angle
of Phi=10deg. From measuring the flux in the jet between the core and further
lobe and assuming a spectral index of 1, we calculate the minimum pressure in
the jet, (8.0+-3.2)x10^-13 dyn/cm^2, and derive constraints on the
intra-filament medium (IFM) assuming the bend of the jet is due to ram
pressure. We constrain the IFM to be between (1-20)x10^-29 gm/cm^3. This is
consistent with recent direct probes of the IFM and theoretical models. These
observations justify future searches for bent double lobe radio sources located
several Mpc from cluster cores, as they may be good markers of super cluster
filaments. | Strong PAH Emission from z~2 ULIRGs: Using the Infrared Spectrograph on board the Spitzer Space Telescope, we
present low-resolution (64 < lambda / dlambda < 124), mid-infrared (20-38
micron) spectra of 23 high-redshift ULIRGs detected in the Bootes field of the
NOAO Deep Wide-Field Survey. All of the sources were selected to have 1) fnu(24
micron) > 0.5 mJy; 2) R-[24] > 14 Vega mag; and 3) a prominent rest-frame 1.6
micron stellar photospheric feature redshifted into Spitzer's 3-8 micron IRAC
bands. Of these, 20 show emission from polycyclic aromatic hydrocarbons (PAHs),
usually interpreted as signatures of star formation. The PAH features indicate
redshifts in the range 1.5 < z < 3.0, with a mean of <z>=1.96 and a dispersion
of 0.30. Based on local templates, these sources have extremely large infrared
luminosities, comparable to that of submillimeter galaxies. Our results confirm
previous indications that the rest-frame 1.6 micron stellar bump can be
efficiently used to select highly obscured starforming galaxies at z~2, and
that the fraction of starburst-dominated ULIRGs increases to faint 24 micron
flux densities. Using local templates, we find that the observed narrow
redshift distribution is due to the fact that the 24 micron detectability of
PAH-rich sources peaks sharply at z = 1.9. We can analogously explain the
broader redshift distribution of Spitzer-detected AGN-dominated ULIRGs based on
the shapes of their SEDs. Finally, we conclude that z~2 sources with a
detectable 1.6 micron stellar opacity feature lack sufficient AGN emission to
veil the 7.7 micron PAH band. |
Cosmic Evolution of Star Formation In SDSS Quasar Hosts Since z=1: We present Spitzer IRS observations of a complete sample of 57 SDSS type-1
quasars at z~1. Aromatic features at 6.2 and/or 7.7 um are detected in about
half of the sample and show profiles similar to those seen in normal galaxies
at both low- and high-redshift, indicating a star-formation origin for the
features. Based on the ratio of aromatic to star-formation IR (SFIR)
luminosities for normal star-forming galaxies at z~1, we have constructed the
SFIR luminosity function (LF) of z~1 quasars. As we found earlier for
low-redshift PG quasars, these z~1 quasars show a flatter SFIR LF than do z~1
field galaxies, implying the quasar host galaxy population has on average a
higher SFR than the field galaxies do. As measured from their SFIR LF,
individual quasar hosts have on average LIRG-level SFRs, which mainly arise in
the circumnuclear regions. By comparing with similar measurements of
low-redshift PG quasars, we find that the comoving SFIR luminosity density in
quasar hosts shows a much larger increase with redshift than that in field
galaxies. The behavior is consistent with pure density evolution since the
average SFR and the average SFR/BH-accretion-rate in quasar hosts show little
evolution with redshift. For individual quasars, we have found a correlation
between the aromatic-based SFR and the luminosity of the nuclear radiation,
consistent with predictions of some theoretical models. We propose that type 1
quasars reside in a distinct galaxy population that shows elliptical morphology
but that harbors a significant fraction of intermediate-age stars and is
experiencing intense circumnuclear star formation. | The First Stars: The first stars to form in the Universe -- the so-called Population III stars
-- bring an end to the cosmological Dark Ages, and exert an important influence
on the formation of subsequent generations of stars and on the assembly of the
first galaxies. Developing an understanding of how and when the first
Population III stars formed and what their properties were is an important goal
of modern astrophysical research. In this review, I discuss our current
understanding of the physical processes involved in the formation of Population
III stars. I show how we can identify the mass scale of the first dark matter
halos to host Population III star formation, and discuss how gas undergoes
gravitational collapse within these halos, eventually reaching protostellar
densities. I highlight some of the most important physical processes occurring
during this collapse, and indicate the areas where our current understanding
remains incomplete. Finally, I discuss in some detail the behaviour of the gas
after the formation of the first Population III protostar. I discuss both the
conventional picture, where the gas does not undergo further fragmentation and
the final stellar mass is set by the interplay between protostellar accretion
and protostellar feedback, and also the recently advanced picture in which the
gas does fragment and where dynamical interactions between fragments have an
important influence on the final distribution of stellar masses. |
Cosmology with massive neutrinos III: the halo mass function and an
application to galaxy clusters: We use a suite of N-body simulations that incorporate massive neutrinos as an
extra-set of particles to investigate their effect on the halo mass function.
We show that for cosmologies with massive neutrinos the mass function of dark
matter haloes selected using the spherical overdensity (SO) criterion is well
reproduced by the fitting formula of Tinker et al. (2008) once the cold dark
matter power spectrum is considered instead of the total matter power, as it is
usually done. The differences between the two implementations, i.e. using
$P_{\rm cdm}(k)$ instead of $P_{\rm m}(k)$, are more pronounced for large
values of the neutrino masses and in the high end of the halo mass function: in
particular, the number of massive haloes is higher when $P_{\rm cdm}(k)$ is
considered rather than $P_{\rm m}(k)$. As a quantitative application of our
findings we consider a Planck-like SZ-clusters survey and show that the
differences in predicted number counts can be as large as $30\%$ for $\sum
m_\nu = 0.4$ eV. Finally, we use the Planck-SZ clusters sample, with an
approximate likelihood calculation, to derive Planck-like constraints on
cosmological parameters. We find that, in a massive neutrino cosmology, our
correction to the halo mass function produces a shift in the
$\sigma_8(\Omega_{\rm m}/0.27)^\gamma$ relation which can be quantified as
$\Delta \gamma \sim 0.05$ and $\Delta \gamma \sim 0.14$ assuming one
($N_\nu=1$) or three ($N_\nu=3$) degenerate massive neutrino, respectively. The
shift results in a lower mean value of $\sigma_8$ with $\Delta \sigma_8 = 0.01$
for $N_\nu=1$ and $\Delta \sigma_8 = 0.02$ for $N_\nu=3$, respectively. Such
difference, in a cosmology with massive neutrinos, would increase the tension
between cluster abundance and Planck CMB measurements. | A Novel Test of the Modified Newtonian Dynamics with Gas Rich Galaxies: The current cosmological paradigm, LCDM, requires that the mass-energy of the
universe be dominated by invisible components: dark matter and dark energy. An
alternative to these dark components is that the law of gravity be modified on
the relevant scales. A test of these ideas is provided by the Baryonic
Tully-Fisher Relation (BTFR), an empirical relation between the observed mass
of a galaxy and its rotation velocity. Here I report a test using gas rich
galaxies for which both axes of the BTFR can be measured independently of the
theories being tested and without the systematic uncertainty in stellar mass
that affects the same test with star dominated spirals. The data fall precisely
where predicted a priori by the modified Newtonian dynamics (MOND). The scatter
in the BTFR is attributable entirely to observational uncertainty. This is
consistent with the action of a single effective force law but poses a serious
fine-tuning problem for LCDM. |
Massive primordial black holes in contemporary universe: The parameters of the original log-normal mass spectrum of primordial black
holes (PBH) are approximately adjusted on the basis of existing observational
data on supermassive black holes in the galactic centers and the mass
distribution of the near-solar mass black holes in the Galaxy. Together with
the assumption that PBHs make all or a noticeable mass fraction of the
cosmological dark matter, it allows to fix the parameters of the original mass
spectrum. The predicted, in this way, the number density of MACHOs is found to
be about an order of magnitude below the observed value. A possible resolution
of this controversy may be prescribed to the non-isotropic and inhomogeneous
distribution of MACHOs or to the modification of the original spectrum, e.g.
assuming a superposition of two-maximum log-normal spectra of PBHs. A competing
possibility is that MACHOs are not PBHs but dead primordial compact stars. | The First Galaxies: We review our current understanding of how the first galaxies formed at the
end of the cosmic dark ages, a few 100 million years after the Big Bang. Modern
large telescopes discovered galaxies at redshifts greater than seven, whereas
theoretical studies have just reached the degree of sophistication necessary to
make meaningful predictions. A crucial ingredient is the feedback exerted by
the first generation of stars, through UV radiation, supernova blast waves, and
chemical enrichment. The key goal is to derive the signature of the first
galaxies to be observed with upcoming or planned next-generation facilities,
such as the James Webb Space Telescope or Atacama Large Millimeter Array. From
the observational side, ongoing deep-field searches for very high-redshift
galaxies begin to provide us with empirical constraints on the nature of the
first galaxies. |
A comparative study of optical/ultraviolet variability of narrow-line
Seyfert 1 and broad-line Seyfert 1 active galactic nuclei: The ensemble optical/ultraviolet variability of narrow-line Seyfert 1 (NLS1)
type active galactic nuclei (AGNs) is investigated, based on a sample selected
from the Sloan Digital Sky Survey (SDSS) Stripe-82 region with multi-epoch
photometric scanning data. As a comparison a control sample of broad-line
Seyfert 1 (BLS1) type AGNs is also incorporated. To quantify properly the
intrinsic variation amplitudes and their uncertainties, a novel method of
parametric maximum-likelihood is introduced, that has, as we argued, certain
virtues over previously used methods. The majority of NLS1-type AGNs exhibit
significant variability on timescales from about ten days to a few years with,
however, on average smaller amplitudes compared to BLS1-type AGNs. About 20
NLS1- type AGNs showing relatively large variations are presented, that may
deserve future monitoring observations, for instance, reverberation mapping.
The averaged structure functions of variability, constructed using the same
maximumlikelihood method, show remarkable similarity in shape for the two types
of AGNs on timescales longer than about 10 days, which can be approximated by a
power-law or an exponential function. This, along with other similar
properties, such as the wavelength-dependent variability, are indicative of a
common dominant mechanism responsible for the long-term optical/UV variability
of both NLS1- and BLS1-type AGNs. Towards the short timescales, however, there
is tentative evidence that the structure function of NLS1-type AGNs continues
declining, whereas that of BLS1-type AGNs flattens with some residual
variability on timescales of days. If this can be confirmed, it may suggest
that an alternative mechanism, such as X-ray reprocessing, starts to become
dominating in BLS1-type AGNs, but not in NLS1-, on such timescales. | The Low-Velocity, Rapidly Fading Type Ia Supernova 2002es: SN 2002es is a peculiar subluminous Type Ia supernova (SN Ia) with a
combination of observed characteristics never before seen in a SN Ia. At
maximum light, SN 2002es shares spectroscopic properties with the underluminous
SN 1991bg subclass of SNe Ia, but with substantially lower expansion velocities
(~6000 km/s) more typical of the SN 2002cx subclass. Photometrically, SN 2002es
differs from both SN 1991bg-like and SN 2002cx-like supernovae. Although at
maximum light it is subluminous (M_B=-17.78 mag), SN 2002es has a relatively
broad light curve (Dm15(B)=1.28 +/- 0.04 mag), making it a significant outlier
in the light-curve width vs. luminosity relationship. We estimate a 56Ni mass
of 0.17 +/- 0.05 M_sun synthesized in the explosion, relatively low for a SN
Ia. One month after maximum light, we find an unexpected plummet in the
bolometric luminosity. The late-time decay of the light curves is inconsistent
with our estimated 56Ni mass, indicating that either the light curve was not
completely powered by 56Ni decay or the ejecta became optically thin to
gamma-rays within a month after maximum light. The host galaxy is classified as
an S0 galaxy with little to no star formation, indicating the progenitor of SN
2002es is likely from an old stellar population. We also present a less
extensive dataset for SN 1999bh, an object which shares similar observed
properties. Both objects were found as part of the Lick Observatory Supernova
Search, allowing us to estimate that these objects should account for ~2.5% of
SNe Ia within a fixed volume. We find that current theoretical models are
unable to explain the observed of characteristics of SN 2002es. |
The Completed SDSS-IV Extended Baryon Oscillation Spectroscopic Survey:
N-body Mock Challenge for Galaxy Clustering Measurements: We develop a series of N-body data challenges, functional to the final
analysis of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data
Release 16 (DR16) galaxy sample. The challenges are primarily based on
high-fidelity catalogs constructed from the Outer Rim simulation - a large box
size realization (3 Gpc/h) characterized by an unprecedented combination of
volume and mass resolution, down to 1.85x10^9 M_sun/h. We generate synthetic
galaxy mocks by populating Outer Rim halos with a variety of halo occupation
distribution (HOD) schemes of increasing complexity, spanning different
redshift intervals. We then assess the performance of three complementary
redshift space distortion (RSD) models in configuration and Fourier space,
adopted for the analysis of the complete DR16 eBOSS sample of Luminous Red
Galaxies (LRGs). We find all the methods mutually consistent, with comparable
systematic errors on the Alcock-Paczynski parameters and the growth of
structure, and robust to different HOD prescriptions - thus validating the
robustness of the models and the pipelines used for the baryon acoustic
oscillation (BAO) and full shape clustering analysis. In particular, all the
techniques are able to recover a_par and a_perp to within 0.9%, and fsig8 to
within 1.5%. As a by-product of our work, we are also able to gain interesting
insights on the galaxy-halo connection. Our study is relevant for the final
eBOSS DR16 `consensus cosmology', as the systematic error budget is informed by
testing the results of analyses against these high-resolution mocks. In
addition, it is also useful for future large-volume surveys, since similar
mock-making techniques and systematic corrections can be readily extended to
model for instance the Dark Energy Spectroscopic Instrument (DESI) galaxy
sample. | KiDS-1000 cosmology: Combined second- and third-order shear statistics: This paper performs the first cosmological parameter analysis of the
KiDS-1000 data with second- and third-order shear statistics. This work builds
on a series of papers that describe the roadmap to third-order shear
statistics. We derive and test a combined model of the second-order shear
statistic, namely the COSEBIs and the third-order aperture mass statistics
$\langle M_\mathrm{ap}^3\rangle$ in a tomographic set-up. We validate our
pipeline with $N$-body simulations that mock the fourth Kilo Degree survey data
release. To model the second- and third-order statistics, we use the latest
version of \textsc{HMcode2020} for the power spectrum and \textsc{BiHalofit}
for the bispectrum. Furthermore, we use an analytic description to model
intrinsic alignments and hydro-dynamical simulations to model the effect of
baryonic feedback processes. Lastly, we decreased the dimension of the data
vector significantly by considering for the $\langle M_\mathrm{ap}^3\rangle$
part of the data vector only equal smoothing radii, making a data analysis of
the fourth Kilo Degree survey data release using a combined analysis of COSEBIs
third-order shear statistic possible. We first validate the accuracy of our
modelling by analysing a noise-free mock data vector assuming the KiDS-1000
error budget, finding a shift in the maximum-a-posterior of the matter density
parameter $\Delta \Omega_m< 0.02\, \sigma_{\Omega_m}$ and of the structure
growth parameter $\Delta S_8 < 0.05\, \sigma_{S_8}$. Lastly, we performed the
first KiDS-1000 cosmological analysis using a combined analysis of second- and
third-order shear statistics, where we constrained
$\Omega_m=0.248^{+0.062}_{-0.055}$ and
$S_8=\sigma_8\sqrt{\Omega_m/0.3}=0.772\pm0.022$. The geometric average on the
errors of $\Omega_\mathrm{m}$ and $S_8$ of the combined statistics increased
compared to the second-order statistic by 2.2. |
The evolutionary sequence of sub-mm galaxies: from diffuse discs to
massive compact ellipticals?: The population of compact massive galaxies observed at z > 1 are
hypothesised, both observationally and in simulations, to be merger remnants of
gas-rich disc galaxies. To probe such a scenario we analyse a sample of 12
gas-rich and active star forming sub-mm galaxies (SMGs) at 1.8 < z < 3. We
present a structural and size measurement analysis for all of these objects
using very deep ACS and NICMOS imaging in the GOODS-North field. Our analysis
reveals a heterogeneous mix of morphologies and sizes. We find that four
galaxies (33% \pm 17%) show clear signs of mergers or interactions, which we
classify as early-stage mergers. The remaining galaxies are divided into two
categories: five of them (42% \pm 18%) are diffuse and regular disc-like
objects, while three (25% \pm 14%) are very compact, spheroidal systems. We
argue that these three categories can be accommodated into an evolutionary
sequence, showing the transformation from isolated, gas-rich discs with typical
sizes of 2-3 kpc, into compact (< 1 kpc) galaxies through violent major merger
events, compatible with the scenario depicted by theoretical models. Our
findings that some SMGs are already dense and compact provides strong support
to the idea that SMGs are the precursors of the compact, massive galaxies found
at slightly lower redshift. | On interpretation of recent proper motion data for the Large Magellanic
Cloud: Recent observational studies using the Hubble Space Telescope (HST) have
derived the center-of-mass proper motion (CMPM) of the Large Magellanic Cloud
(LMC). Although these studies carefully treated both rotation and perspective
effects in deriving the proper motion for each of the sampled fields, they did
not consider the effects of local random motion in the derivation. This means
that the average PM of the fields (i.e., the observed CMPM) could significantly
deviate from the true CMPM, because the effect of local random motion can not
be close to zero in making the average PM for the small number of the fields
(~10). We discuss how significantly the observationally derived CMPM can
deviate from the true CMPM by applying the same method as used in the
observations for a dynamical model of the LMC with a known true CMPM. We find
that the deviation can be as large as ~ 50 km/s (~0.21 mas/yr), if the LMC has
a thick disk and a maximum circular velocity of ~120$ km/s. We also find that
the deviation depends both on the total number of the sampled fields and on
structure and kinematics of the LMC. We therefore suggest that there is a
possibility that the observed CMPM of the LMC deviates from the true one to
some extent. We also show that a simple mean of PM for a large number of the
LMC fields (~1000) can be much closer to the true CMPM. |
Results on Low-Mass Weakly Interacting Massive Particles from a 11 kg d
Target Exposure of DAMIC at SNOLAB (ICRC2021 Proceedings): Experimental efforts of the last decades have been unsuccessful in detecting
WIMPs (Weakly Interacting Massive Particles) in the 10-to-10$^4$ GeV/$c^2$
range, thus motivating the search for lighter dark matter. The DAMIC (DArk
Matter In CCDs) at SNOLAB experiment aims for direct detection of light dark
matter particles ($m_\chi <$ 10 GeV/$c^2$) by means of CCDs (Charge-Coupled
Devices). Fully-depleted 675 $\mu$m-thick CCDs are used to such end. The
optimized readout noise and operation at cryogenic temperatures allow for a
detection threshold of 50 eV$_{\text{ee}}$ electron-equivalent energy. Focusing
on nuclear and electronic scattering as potential detection processes, DAMIC
has so far set competitive constraints on the detection of low mass WIMPs and
hidden-sector particles. In this work, an 11 kg-day exposure dataset is
exploited to search for light WIMPs by building the first comprehensive
radioactive background model for CCDs. Different background sources are
discriminated making conjoint use of the spatial distribution and energy of
ionization events, thereby constraining the amount of contaminants such as
tritium from silicon cosmogenic activation and surface lead-210 from radon
plate-out. Despite a conspicuous, statistically-significant excess of events
below 200 eV$_{\text{ee}}$, this analysis places the strongest exclusion limit
on the WIMP-nucleon scattering cross section with a silicon target for 1 GeV $<
m_\chi c^2<$ 9 GeV. | Multi-wavelength spectroscopic probes: prospects for primordial
non-Gaussianity and relativistic effects: Next-generation cosmological surveys will observe larger cosmic volumes than
ever before, enabling us to access information on the primordial Universe, as
well as on relativistic effects. We consider forthcoming 21cm intensity mapping
surveys (SKAO) and optical galaxy surveys (DESI and Euclid), combining the
information via multi-tracer cross-correlations that suppress cosmic variance
on ultra-large scales. In order to fully incorporate wide-angle effects and
redshift-bin cross-correlations, together with lensing magnification and other
relativistic effects, we use the angular power spectra, $C_\ell(z_i,z_j)$.
Applying a Fisher analysis, we forecast the expected precision on $f_{\rm NL}$
and the detectability of lensing and other relativistic effects. We find that
the full combination of two pairs of 21cm and galaxy surveys, one pair at low
redshift and one at high redshift, could deliver $\sigma(f_{\rm NL})\sim 1.5$,
detect the Doppler effect with a signal-to-noise ratio $\sim$8 and measure the
lensing convergence contribution at $\sim$2\% precision. In a companion paper,
we show that the best-fit values of $f_{\rm NL}$ and of standard cosmological
parameters are significantly biased if the lensing contribution neglected. |
Detecting cosmic voids via maps of geometric-optics parameters: Curved-spacetime geometric-optics maps derived from a deep photometric survey
should contain information about the three-dimensional matter distribution and
thus about cosmic voids in the survey, despite projection effects. We explore
to what degree sky-plane geometric-optics maps can reveal the presence of
intrinsic three-dimensional voids. We carry out a cosmological $N$-body
simulation and place it further than a gigaparsec from the observer, at
redshift 0.5. We infer three-dimensional void structures using the watershed
algorithm. Independently, we calculate a surface overdensity map and maps of
weak gravitational lensing and geometric-optics scalars. We propose and
implement a heuristic algorithm for detecting (projected) radial void profiles
from these maps. We find in our simulation that given the sky-plane centres of
the three-dimensional watershed-detected voids, there is significant evidence
of correlated void centres in the surface overdensity $\Sigma$, the averaged
weak-lensing tangential shear $\overline{\gamma_\perp}$, the Sachs expansion
$\theta$, and the Sachs shear modulus $\lvert\sigma\rvert$. Recovering the
centres of the three-dimensional voids from the sky-plane information alone is
significant given the weak-lensing shear $\overline{\gamma_\perp}$, the Sachs
expansion $\theta$, or the Sachs shear $\lvert\sigma\rvert$, but not
significant for the surface overdensity $\Sigma$. Void radii are uncorrelated
between three-dimensional and two-dimensional voids; our algorithm is not
designed to distinguish voids that are nearly concentric in projection. This
investigation shows preliminary evidence encouraging observational studies of
gravitational lensing through individual voids, either blind or with
spectroscopic/photometric redshifts. The former case - blind searches - should
generate falsifiable predictions of intrinsic three-dimensional void centres. | Asymmetric velocity anisotropies in remnants of collisionless mergers: Dark matter haloes in cosmological N-body simulations are affected by
processes such as mergers, accretion and the gravitational interaction with
baryonic matter. Typically the analysis of dark matter haloes is performed in
spherical or elliptical bins and the velocity distributions are often assumed
to be constant within those bins. However, the velocity anisotropy, which
describes differences between the radial and tangential velocity dispersion,
has recently been show to have a strong dependence on direction in the triaxial
halos formed in cosmological simulations. In this study we derive properties of
particles in cones parallel or perpendicular to the collision axis of merger
remnants. We find that the velocity anisotropy has a strong dependence on
direction. The finding that the direction-dependence of the velocity anisotropy
of a halo depends on the merger history, explains the existence of such trends
in cosmological simulations. It also explains why a large diversity is seen in
the velocity anisotropy profiles in the outer parts of high-resolution
simulations of cosmological haloes. |
Constraints on decaying dark matter from the extragalactic gamma-ray
background: If dark matter is unstable and the mass is within GeV-TeV regime, its decays
produce high-energy photons that give contribution to the extragalactic
gamma-ray background (EGRB). We constrain dark matter decay by analyzing the
50-month EGRB data measured with Fermi satellite, for different decay channels
motivated with several supersymmetric scenarios featuring R-parity violation.
We adopt the latest astrophysical models for various source classes such as
active galactic nuclei and star-forming galaxies, and take associated
uncertainties properly into account. The lower limits for the lifetime are very
stringent for a wide range of dark matter mass, excluding the lifetime shorter
than 10^28 s for mass between a few hundred GeV and ~1TeV, e.g., for b\bar{b}
decay channel. Furthermore, most dark matter models that explain the anomalous
positron excess are also excluded. These constraints are robust, being little
dependent on astrophysical uncertainties, unlike other probes such as Galactic
positrons or anti-protons. | The dynamics of the giant radio galaxy 3C 457: We present multi-frequency radio observations with the Giant Metrewave Radio
Telescope and Very Large Array, and X-ray observations with the X-ray
Multi-Mirror Mission ({\it XMM-Newton}) telescope of the giant radio source
(GRS) 3C 457. We have detected the core, lobes and the environment of the GRS
in X-ray. We examine the relationships between the radio and X-ray emission,
determine the radio spectrum over a large frequency range and attribute the
X-ray emission from the lobes to the inverse-Compton scattering of cosmic
microwave background (CMB) photons. The magnetic field strength of the lobes is
very close to the equipartition value. Both the lobes are in pressure balance
near the hotspots and apparently under-pressured towards the core. The X-ray
spectrum of the core of the GRS consists of an unabsorbed soft power-law
component and a heavily absorbed hard power-law component. The soft unabsorbed
component is likely to be related to the radio jets. There is no strong
evidence of Fe K$\alpha$ emission line in our data. |
Directional dark matter detection sensitivity of a two-phase liquid
argon detector: We examine the sensitivity of a large scale two-phase liquid argon detector
to the directionality of the dark matter signal. This study was performed under
the assumption that, above 50 keV of recoil energy, one can determine (with
some resolution) the direction of the recoil nucleus without head-tail
discrimination, as suggested by past studies that proposed to exploit the
dependence of columnar recombination on the angle between the recoil nucleus
direction and the electric field. In this paper we study the differential
interaction recoil rate as a function of the recoil direction angle with
respect to the zenith for a detector located at the Laboratori Nazionali del
Gran Sasso and we determine its diurnal and seasonal modulation. Using a
likelihood-ratio based approach we show that, with the angular information
alone, 100 events are enough to reject the isotropic hypothesis at three
standard deviation level. For an exposure of 100 tonne years this would
correspond to a spin independent WIMP-nucleon cross section of about 10^-46
cm^2 at 200 GeV WIMP mass. The results presented in this paper provide strong
motivation for the experimental determination of directional recoil effects in
two-phase liquid argon detectors. | Ultra-low mass PBHs in the early universe can explain the PTA signal: Pulsar Timing Array collaborations have recently announced the discovery of a
stochastic gravitational wave background (SGWB) at nanohertz frequencies. We
analyze the GW signals from the domination of ultra-low mass primordial black
holes (PBHs) in the early universe and show that they can explain this recent
discovery. This scenario requires a relatively broad peak in the power spectrum
of scalar perturbations from inflation with a spectral index in a narrow range
of $1.45$ to $1.6$. The resulting PBH population would have mass around
$10^{8}$g, and the initial abundance $\beta_f$ lies between $10^{-10}$ and
$10^{-9}$. We find that this explanation is preferred by the data over the
generic model, assuming supermassive BHs as the source. These very light PBHs
would decay before Big Bang Nucleosynthesis (BBN); however, upcoming
third-generation terrestrial laser interferometers would be able to test the
model by observing the GW spectrum produced during the formation of the PBHs.
Also, the scalar power spectra associated with our scenario will be within the
reach of PIXIE probing CMB spectral distortions. |
Imaging the Thermal and Kinematic Sunyaev-Zel'dovich Effect Signals in a
Sample of Ten Massive Galaxy Clusters: Constraints on Internal Velocity
Structures and Bulk Velocities: We have imaged the Sunyaev-Zel'dovich (SZ) effect signals at 140 and 270 GHz
towards ten galaxy clusters with Bolocam and AzTEC/ASTE. We also used Planck
data to constrain the signal at large angular scales, Herschel-SPIRE images to
subtract the brightest galaxies that comprise the cosmic infrared background
(CIB), Chandra imaging to map the electron temperature $T_e$ of the
intra-cluster medium (ICM), and HST imaging to derive models of each galaxy
cluster's mass density. The galaxy clusters gravitationally lens the background
CIB, which produced an on-average reduction in brightness towards the galaxy
clusters' centers after the brightest galaxies were subtracted. We corrected
for this deficit, which was between 5-25% of the 270 GHz SZ effect signal
within $R_{2500}$. Using the SZ effect measurements, along with the X-ray
constraint on $T_e$, we measured each galaxy cluster's average line of sight
(LOS) velocity $v_z$ within $R_{2500}$, with a median per-cluster uncertainty
of +-700 km/s. We found an ensemble-mean <$v_z$> of 430+-210 km/s, and an
intrinsic cluster-to-cluster scatter $\sigma_{int}$ of 470+-340 km/s. We also
obtained maps of $v_z$ over each galaxy cluster's face with an angular
resolution of 70". All four galaxy clusters previously identified as having a
merger oriented along the LOS showed an excess variance in these maps at a
significance of 2-4$\sigma$, indicating an internal $v_z$ rms of $\gtrsim$1000
km/s. None of the six galaxy clusters previously identified as relaxed or plane
of sky mergers showed any such excess variance. | I Zw 18 as morphological paradigm for rapidly assembling high-z galaxies: IZw18, ever since regarded as the prototypical blue compact dwarf (BCD)
galaxy, is, quite ironically, the most atypical BCD known. This is because its
large exponential low-surface brightness envelope is not due to an old stellar
host but entirely due to extended nebular emission (ne) (Papaderos et al. 2002;
P02). We study IZw18 and IZw18C down to an unprecedently faint surface
brightness level using HST ACS data.
We argue that the properties of IZw18C can be consistently accounted for by
propagating star formation over the past ~100 Myr, in combination with stellar
diffusion and the associated radial stellar mass filtering effect (P02).
As for IZw18, we find that ne extends out to ~16 stellar scale lengths and
provides at least 1/3 of the total optical emission.
The case of IZw18 suggests caution in studies of distant galaxies in dominant
stages of their evolution, rapidly assembling their stellar mass at high
specific star formation rates (SSFRs). It calls attention to the fact that ne
is not necessarily cospatial with the underlying ionizing and non-ionizing
stellar background, neither has to scale with its surface density. The
prodigious energetic output during dominant phases of galaxy evolution may
result in large exponential ne envelopes, extending much beyond the still
compact stellar component, just like in IZw18. Therefore, the morphological
paradigm of IZw18, while probably unique in the nearby Universe, may be
ubiquitous among high-SSFR galaxies at high redshift. Using IZw18 as reference,
we show that extended ne may introduce substantial observational biases and
significantly affect fundamental galaxy relations. Among others, we show that
the surface brightness profiles of distant morphological analogs to IZw18 may
be barely distinguishable from Sersic profiles with an exponent 2<n<5, thus
mimicking the profiles of massive galaxy spheroids. (abridged) |
BLAST: A Far-Infrared Measurement of the History of Star Formation: We directly measure redshift evolution in the mean physical properties
(far-infrared luminosity, temperature, and mass) of the galaxies that produce
the cosmic infrared background (CIB), using measurements from the Balloon-borne
Large Aperture Sub-millimeter Telescope (BLAST), and Spitzer which constrain
the CIB emission peak. This sample is known to produce a surface brightness in
the BLAST bands consistent with the full CIB, and photometric redshifts are
identified for all of the objects. We find that most of the 70 micron
background is generated at z <~ 1 and the 500 micron background generated at z
>~ 1. A significant growth is observed in the mean luminosity from ~ 10^9 -
10^12 L_sun, and in the mean temperature by 10 K, from redshifts 0< z < 3.
However, there is only weak positive evolution in the comoving dust mass in
these galaxies across the same redshift range. We also measure the evolution of
the far-infrared luminosity density, and the star-formation rate history for
these objects, finding good agreement with other infrared studies up to z ~1,
exceeding the contribution attributed to optically-selected galaxies. | Characterising large-scale structure with the REFLEX II cluster survey: We study the large-scale structure with superclusters from the REFLEX X-ray
cluster survey together with cosmological N-body simulations. It is important
to construct superclusters with criteria such that they are homogeneous in
their properties. We lay out our theoretical concept considering future
evolution of superclusters in their definition, and show that the X-ray
luminosity and halo mass functions of clusters in superclusters are found to be
top-heavy, different from those of clusters in the field. We also show a
promising aspect of using superclusters to study the local cluster bias and
mass scaling relation with simulations. |
Off-center observers versus supernovae in inhomogeneous pressure
universes: Exact luminosity distance and apparent magnitude formulas are applied to
Union2 557 supernovae sample in order to constrain possible position of an
observer outside of the center of symmetry in spherically symmetric
inhomogeneous pressure Stephani universes which are complementary to
inhomogeneous density Lema\^itre-Tolman-Bondi (LTB) void models. Two specific
models are investigated. The first which allows a barotropic equation of state
at the center of symmetry with no scale factor function being specified (model
IIA), and the second which has no barotropic equation of state at the center,
but has an explicit dust-like scale factor evolution (model IIB).
It is shown that even at $3\sigma$ CL, an off-center observer cannot be
further than about 4.4 Gpc away from the center of symmetry which is comparable
to the reported size of a void in LTB models with the most likely value of the
distance from the center about 341 Mpc for model IIA and 68 Mpc for model IIB.
The off-center observer cannot be farther away from the center than about 577
Mpc for model IIB at $3\sigma$ CL. It is evaluated that the best-fit parameters
which characterize inhomogeneity are: $\Omega_{inh} = 0.77$ (dimensionless -
model IIA) and $\alpha = 7.31 \cdot 10^{-9}$ $(s/km)^{2/3} Mpc^{-4/3}$ (model
IIB). | Search for Low-Mass Dark Matter with CDMSlite Using a Profile Likelihood
Fit: The Cryogenic Dark Matter Search low ionization threshold experiment
(CDMSlite) searches for interactions between dark matter particles and
germanium nuclei in cryogenic detectors. The experiment has achieved a low
energy threshold with improved sensitivity to low-mass (<10 GeV/c$^2$) dark
matter particles. We present an analysis of the final CDMSlite data set, taken
with a different detector than was used for the two previous CDMSlite data
sets. This analysis includes a data "salting" method to protect against bias,
improved noise discrimination, background modeling, and the use of profile
likelihood methods to search for a dark matter signal in the presence of
backgrounds. We achieve an energy threshold of 70 eV and significantly improve
the sensitivity for dark matter particles with masses between 2.5 and 10
GeV/c$^2$ compared to previous analyses. We set an upper limit on the dark
matter-nucleon scattering cross section in germanium of 5.4$\times$10$^{-42}$
cm$^2$ at 5 GeV/c$^2$, a factor of $\sim$2.5 improvement over the previous
CDMSlite result. |
The GALEX view of the Herschel Reference Survey - Ultraviolet structural
properties of nearby galaxies: We present GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) as well as
SDSS g, r, i photometry and structural parameters for the Herschel Reference
Survey, a magnitude-, volume-limited sample of nearby galaxies in different
environments. We use this unique dataset to investigate the ultraviolet (UV)
structural scaling relations of nearby galaxies and to determine how the
properties of the UV disk vary with atomic hydrogen content and environment. We
find a clear change of slope in the stellar mass vs. effective surface
brightness relation when moving from the optical to the UV, with more massive
galaxies having brighter optical but fainter UV surface brightnesses than
smaller systems. A similar change of slope is also seen in the radius vs.
surface brightness relation. By comparing our observations with the predictions
of a simple multi-zone chemical model of galaxy evolution, we show that these
findings are a natural consequence of a much more efficient inside-out growth
of the stellar disk in massive galaxies. We confirm that isophotal radii are
always a better proxy for the size of the stellar/star-forming disk than
effective quantities and we show that the extent of the UV disk (normalized to
the optical size) is strongly correlated to the integrated HI gas fraction.
This relation still holds even when cluster spirals are considered, with
HI-deficient systems having less extended star-forming disks than HI-normal
galaxies. Interestingly, the star formation in the inner part of HI-deficient
galaxies is significantly less affected by the removal of the atomic hydrogen,
as expected in a simple ram-pressure stripping scenario. These results suggest
that it is the amount of HI that regulates the growth of the star-forming disk
in the outskirts of galaxies. | Backreaction in Growing Neutrino Quintessence: We investigate the cosmological effects of neutrino lumps in Growing Neutrino
Quintessence. The strongly non-linear effects are resolved by means of
numerical N-body simulations which include relativistic particles, non-linear
scalar field equations and backreaction effects. For the investigated models
with a constant coupling between the scalar field and the neutrinos the
backreaction effects are so strong that a realistic cosmology is hard to
realize. This points towards the necessity of a field dependent coupling in
Growing Neutrino Quintessence. In this case realistic models of dynamical Dark
Energy exist which are testable by the observation or non-observation of large
neutrino lumps. |
Comparing X-ray and Dynamical Mass Profiles in the Early-Type Galaxy NGC
4636: We present the results of an X-ray mass analysis of the early-type galaxy NGC
4636, using Chandra data. We have compared the X-ray mass density profile with
that derived from a dynamical analysis of the system's globular clusters (GCs).
Given the observed interaction between the central active galactic nucleus and
the X-ray emitting gas in NGC 4636, we would expect to see a discrepancy in the
masses recovered by the two methods. Such a discrepancy exists within the
central ~10kpc, which we interpret as the result of non-thermal pressure
support or a local inflow. However, over the radial range ~10-30kpc, the mass
profiles agree within the 1-sigma errors, indicating that even in this highly
disturbed system, agreement can be sought at an acceptable level of
significance over intermediate radii, with both methods also indicating the
need for a dark matter halo. However, at radii larger than 30kpc, the X-ray
mass exceeds the dynamical mass, by a factor of 4-5 at the largest
disagreement. A Fully Bayesian Significance Test finds no statistical reason to
reject our assumption of velocity isotropy, and an analysis of X-ray mass
profiles in different directions from the galaxy centre suggests that local
disturbances at large radius are not the cause of the discrepancy. We instead
attribute the discrepancy to the paucity of GC kinematics at large radius,
coupled with not knowing the overall state of the gas at the radius where we
are reaching the group regime (>30kpc), or a combination of the two. | Spectator fields and their imprints on the Cosmic Microwave Background: When a subdominant light scalar field ends slow roll during inflation, but
well after the Hubble exit of the pivot scales, it may determine the
cosmological perturbations. This thesis investigates how such a scalar field,
the spectator, may leave its impact on the Cosmic Microwave Background (CMB)
radiation and be consequently constrained. We first introduce the observables
of the CMB, namely the power spectrum $P_\zeta$, spectral index $n_s$ and its
running $dn_s/d\ln k$, the non-Gaussianities $f_{NL}$, $g_{NL}$ and
$\tau_{NL}$, and the lack of isocurvature and polarization modes. Based on
these studies, we derive the cosmological predictions for the spectator
scenario, revealing its consistency with the CMB for inflection point
potentials, hyperbolic tangent potentials, and those with a sudden phase
transition. In the end, we utilize the spectator scenario to explain the CMB
power asymmetry, with a brief tachyonic fast-roll phase. |
Two analytic relations connecting the hot gas astrophysics with the cold
dark matter model for galaxy clusters: Galaxy clusters are good targets for examining our understanding of
cosmology. Apart from numerical simulations and gravitational lensing, X-ray
observation is the most common and conventional way to analyze the
gravitational structures of galaxy clusters. Therefore, it is valuable to have
simple analytical relations that can connect the observed distribution of the
hot, X-ray emitting gas to the structure of the dark matter in the clusters as
derived from simulations. In this article, we apply a simple framework that can
analytically connect the hot gas empirical parameters with the standard
parameters in the cosmological cold dark matter model. We have theoretically
derived two important analytic relations, $r_s \approx \sqrt{3}r_c$ and $\rho_s
\approx 9\beta kT/8 \pi Gm_gr_c^2$, which can easily relate the dark matter
properties in galaxy clusters with the hot gas properties. This can give a
consistent picture describing gravitational astrophysics for galaxy clusters by
the hot gas and cold dark matter models. | Spectroscopic confirmation of two Lyman break galaxies at redshift
beyond 7: We report the spectroscopic confirmation of two Lyman break galaxies at
redshift > 7. The galaxies were observed as part of an ultra-deep spectroscopic
campaign with FORS2 at the ESO/VLT for the confirmation of z~7 ``z--band
dropout'' candidates selected from our VLT/Hawk-I imaging survey. Both galaxies
show a prominent emission line at 9735A and 9858A respectively: the lines have
fluxes of ~ 1.6-1.2 x 10^(-17) erg/s/cm2 and exhibit a sharp decline on the
blue side and a tail on the red side. The asymmetry is quantitatively
comparable to the observed asymmetry in z ~ 6 Ly-alpha lines, where absorption
by neutral hydrogen in the IGM truncates the blue side of the emission line
profile. We carefully evaluate the possibility that the galaxies are instead at
lower redshift and we are observing either [OII], [OIII] or H-alpha emission:
however from the spectroscopic and the photometric data we conclude that there
are no other plausible identifications, except for Ly-alpha at redshift >7,
implying that these are two of the most robust redshift determination for
galaxies in the reionization epoch. Based on their redshifts and broad--band
photometry, we derive limits on the star formation rate and on the ultraviolet
spectral slopes of the two galaxies. We argue that these two galaxies alone are
unlikely to have ionized the IGM in their surroundings. |
A roadmap to cosmological parameter analysis with third-order shear
statistics I: Modelling and validation: In this work, which is the first of a series to prepare a cosmological
parameter analysis with third-order cosmic shear statistics, we model both the
shear three-point correlation functions $\Gamma^{(i)}$ and the third-order
aperture statistics $\langle\mathcal{M}_\mathrm{ap}^3\rangle$ from the
BiHalofit bispectrum model and validate these statistics with a series of
N-body simulations.
We then investigate how to bin the shear three-point correlation functions to
achieve an unbiased estimate for third-order aperture statistics in real data.
Finally, we perform a cosmological parameter analysis on KiDS1000-like mock
data with second- and third-order statistics. We recover all cosmological
parameters with very little bias. Furthermore, we find that a joint analysis
almost doubles the constraining power on $S_8$ and increases the
figure-of-merit in the $\Omega_\mathrm{m}$-$\sigma_8$ plane by a factor of 5.9
with respect to an analysis with only second-order shear statistics.
Our modelling pipeline is publicly available at
https://github.com/sheydenreich/threepoint/releases/. | Anisotropies of gravitational-wave standard sirens as a new cosmological
probe without redshift information: Gravitational waves (GWs) from compact binary stars at cosmological distances
are promising and powerful cosmological probes, referred to as the GW standard
sirens. With future GW detectors, we will be able to precisely measure source
luminosity distances out to a redshift $z\sim5$. To extract cosmological
information, previously proposed cosmological studies using the GW standard
sirens rely on source redshift information obtained through an extensive
electromagnetic follow-up campaign. However, the redshift identification is
typically time consuming and rather challenging. Here, we propose a novel
method for cosmology with the GW standard sirens free from the redshift
measurements. Utilizing the anisotropies of the number density and luminosity
distances of compact binaries originated from the large-scale structure, we
show that, once GW observations will be well established in the future, (i)
these anisotropies can be measured even at very high redshifts ($z\geq 2$),
where the identification of the electromagnetic counterpart is difficult, (ii)
the expected constraints on the primordial non-Gaussianity with the Einstein
Telescope would be comparable to or even better than the other large-scale
structure probes at the same epoch, and (iii) the cross-correlation with other
cosmological observations is found to have high-statistical significance,
providing additional cosmological information at very high redshifts. |
Observational Limits on Type 1 AGN Accretion Rate in COSMOS: We present black hole masses and accretion rates for 182 Type 1 AGN in
COSMOS. We estimate masses using the scaling relations for the broad Hb, MgII,
and CIV emission lines in the redshift ranges 0.16<z<0.88, 1<z<2.4, and
2.7<z<4.9. We estimate the accretion rate using an Eddington ratio L_I/L_Edd
estimated from optical and X-ray data. We find that very few Type 1 AGN accrete
below L_I/L_Edd ~ 0.01, despite simulations of synthetic spectra which show
that the survey is sensitive to such Type 1 AGN. At lower accretion rates the
BLR may become obscured, diluted or nonexistent. We find evidence that Type 1
AGN at higher accretion rates have higher optical luminosities, as more of
their emission comes from the cool (optical) accretion disk with respect to
shorter wavelengths. We measure a larger range in accretion rate than previous
works, suggesting that COSMOS is more efficient at finding low accretion rate
Type 1 AGN. However the measured range in accretion rate is still comparable to
the intrinsic scatter from the scaling relations, suggesting that Type 1 AGN
accrete at a narrow range of Eddington ratio, with L_I/L_Edd ~ 0.1. | Studying the WHIM with Gamma Ray Bursts: We assess the possibility to detect and characterize the physical state of
the missing baryons at low redshift by analyzing the X-ray absorption spectra
of the Gamma Ray Burst [GRB] afterglows, measured by a micro calorimeters-based
detector with 3 eV resolution and 1000 cm2 effective area and capable of fast
re-pointing, similar to that on board of the recently proposed X-ray satellites
EDGE and XENIA. For this purpose we have analyzed mock absorption spectra
extracted from different hydrodynamical simulations used to model the
properties of the Warm Hot Intergalactic Medium [WHIM]. These models predict
the correct abundance of OVI absorption lines observed in UV and satisfy
current X-ray constraints. According to these models space missions like EDGE
and XENIA should be able to detect about 60 WHIM absorbers per year through the
OVII line. About 45 % of these have at least two more detectable lines in
addition to OVII that can be used to determine the density and the temperature
of the gas. Systematic errors in the estimates of the gas density and
temperature can be corrected for in a robust, largely model-independent
fashion. The analysis of the GRB absorption spectra collected in three years
would also allow to measure the cosmic mass density of the WHIM with about 15 %
accuracy, although this estimate depends on the WHIM model. Our results suggest
that GRBs represent a valid, if not preferable, alternative to Active Galactic
Nuclei to study the WHIM in absorption. The analysis of the absorption spectra
nicely complements the study of the WHIM in emission that the spectrometer
proposed for EDGE and XENIA would be able to carry out thanks to its high
sensitivity and large field of view. |
Domain Adaptive Graph Neural Networks for Constraining Cosmological
Parameters Across Multiple Data Sets: Deep learning models have been shown to outperform methods that rely on
summary statistics, like the power spectrum, in extracting information from
complex cosmological data sets. However, due to differences in the subgrid
physics implementation and numerical approximations across different simulation
suites, models trained on data from one cosmological simulation show a drop in
performance when tested on another. Similarly, models trained on any of the
simulations would also likely experience a drop in performance when applied to
observational data. Training on data from two different suites of the CAMELS
hydrodynamic cosmological simulations, we examine the generalization
capabilities of Domain Adaptive Graph Neural Networks (DA-GNNs). By utilizing
GNNs, we capitalize on their capacity to capture structured scale-free
cosmological information from galaxy distributions. Moreover, by including
unsupervised domain adaptation via Maximum Mean Discrepancy (MMD), we enable
our models to extract domain-invariant features. We demonstrate that DA-GNN
achieves higher accuracy and robustness on cross-dataset tasks (up to $28\%$
better relative error and up to almost an order of magnitude better $\chi^2$).
Using data visualizations, we show the effects of domain adaptation on proper
latent space data alignment. This shows that DA-GNNs are a promising method for
extracting domain-independent cosmological information, a vital step toward
robust deep learning for real cosmic survey data. | Effects of a dark matter caustic passing through the Oort Cloud: We investigate the effect of a dark matter caustic passing through the Solar
System. We find, confirming a previous result, that the Sun tracks the caustic
surface for some time. We integrate numerically the equations of motion of the
Sun and a comet for a large number of initial conditions and of caustic passage
properties. We calculate the probability for the comet to escape the Solar
System and the probability for it to fall within 50 A.U. of the Sun, given the
initial semi-major axis and eccentricity of its orbit. We find that the average
probability for a comet to fall within 50 A.U. of the Sun is of order $3 \cdot
10^{-4}$ and that comets which are initially at a distance larger than about
$10^5$ A.U. have a probability of order one to be ejected from the Solar
System. |
Constraining stellar assembly and AGN feedback at the peak epoch of star
formation: We study stellar assembly and feedback from active galactic nuclei (AGN)
around the epoch of peak star formation (1<z<2), by comparing hydrodynamic
simulations to rest-frame UV-optical galaxy colours from the Wide Field Camera
3 (WFC3) Early-Release Science (ERS) Programme. Our Adaptive Mesh Refinement
simulations include metal-dependent radiative cooling, star formation, kinetic
outflows due to supernova explosions, and feedback from supermassive black
holes. Our model assumes that when gas accretes onto black holes, a fraction of
the energy is used to form either thermal winds or sub-relativistic
momentum-imparting collimated jets, depending on the accretion rate. We find
that the predicted rest-frame UV-optical colours of galaxies in the model that
includes AGN feedback is in broad agreement with the observed colours of the
WFC3 ERS sample at 1<z<2. The predicted number of massive galaxies also matches
well with observations in this redshift range. However, the massive galaxies
are predicted to show higher levels of residual star formation activity than
the observational estimates, suggesting the need for further suppression of
star formation without significantly altering the stellar mass function. We
discuss possible improvements, involving faster stellar assembly through
enhanced star formation during galaxy mergers while star formation at the peak
epoch is still modulated by the AGN feedback. | Lemaitre-Tolman-Bondi cosmological models, smoothness, and positivity of
the central deceleration parameter: We argued in a previous paper [R. A. Vanderveld et al. 2006,
arXiv:astro-ph/0602476] that negative deceleration parameters at the center of
symmetry in Lemaitre-Tolman-Bondi cosmological models can only occur if the
model is not smooth at the origin. Here we demonstrate explicitly the
connection between non-smoothness and the failure of positivity theorems for
deceleration. We also address some confusion that has arisen in the literature
and respond to some recent criticisms of our arguments. |
Non-tensorial Gravitational Wave Background in NANOGrav 12.5-Year Data
Set: We perform the first search for an isotropic non-tensorial gravitational-wave
background (GWB) allowed in general metric theories of gravity in the North
American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year
data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian
indication for a spatially correlated process with scalar transverse (ST)
correlations whose Bayes factor versus the spatially uncorrelated
common-spectrum process is $107\pm 7$, but no statistically significant
evidence for the tensor transverse, vector longitudinal and scalar longitudinal
polarization modes. The median and the $90\%$ equal-tail amplitudes of ST mode
are $\mathcal{A}_{\mathrm{ST}}= 1.06^{+0.35}_{-0.28} \times 10^{-15}$, or
equivalently the energy density parameter per logarithm frequency is
$\Omega_{\mathrm{GW}}^{\mathrm{ST}} = 1.54^{+1.21}_{-0.71} \times 10^{-9}$, at
frequency of 1/year. | Higgsless simulations of cosmological phase transitions and
gravitational waves: First-order cosmological phase transitions in the early Universe source sound
waves and, subsequently, a background of stochastic gravitational waves.
Currently, predictions of these gravitational waves rely heavily on simulations
of a Higgs field coupled to the plasma of the early Universe, the former
providing the latent heat of the phase transition. Numerically, this is a
rather demanding task since several length scales enter the dynamics. From
smallest to largest, these are the thickness of the Higgs interface separating
the different phases, the shell thickness of the sound waves, and the average
bubble size. In this work, we present an approach to perform Higgsless
simulations in three dimensions, producing fully nonlinear results, while at
the same time removing the hierarchically smallest scale from the lattice. This
significantly reduces the complexity of the problem and contributes to making
our approach highly efficient. We provide spectra for the produced
gravitational waves for various choices of wall velocity and strength of the
phase transition, as well as introduce a fitting function for the spectral
shape. |
The Average Optical Spectra of Intense Starbursts at z~2: Outflows and
the Pressurization of the ISM: An important property of star-forming galaxies at z~1-2 is the high local
star-formation intensities they maintain over tens of kiloparsecs at levels
that are only observed in the nearby Universe in the most powerful nuclear
starbursts. To investigate how these high star-formation intensities affect the
warm ionized medium, we present an analysis of the average spectra of about 50
such galaxies at z~1.2-2.6 and of subsamples selected according to their local
and global star-formation intensity. Stacking allows us to probe relatively
weak lines like [SII]\lambda \lambda 6716,6731 and [OI]\lambda 6300, which are
tracers of the conditions of the ISM and are undetectable in most individual
targets. We find higher gas densities (hence pressures) in intensely
star-forming regions compared to fainter diffuse gas and, overall, values that
are comparable to starburst regions and the diffuse ISM in nearby galaxies. By
modeling the H\alpha\ surface brightnesses and [SII]/H\alpha\ line ratios with
the Cloudy photoionization code, we find that our galaxies continue trends
observed in local galaxies, where gas pressures scale with star-formation
intensity. We discuss these results in the context of models of self-regulated
star formation, where star formation determines the average thermal and
turbulent pressure in the ISM, which in turn determines the rate at which stars
can form, finding good agreement with our data. We also confirm the detection
of broad, faint lines underlying H\alpha\ and [NII], which have previously been
considered evidence of either outflows or active galactic nuclei. Finding that
the broad component is only significantly detected in stacks with the highest
average local and global star-formation intensities strongly supports the
outflow interpretation, and further emphasizes the importance of star-formation
feedback and self-regulation in the early Universe. | Dwarf galaxies in CDM and SIDM with baryons: observational probes of the
nature of dark matter: We present the first cosmological simulations of dwarf galaxies, which
include dark matter self-interactions and baryons. We study two dwarf galaxies
within cold dark matter, and four different elastic self-interacting scenarios
with constant and velocity-dependent cross sections, motivated by a new force
in the hidden dark matter sector. Our highest resolution simulation has a
baryonic mass resolution of $1.8\times 10^2\,{\rm M}_\odot$ and a gravitational
softening length of $34\,{\rm pc}$ at $z=0$. In this first study we focus on
the regime of mostly isolated dwarf galaxies with halo masses
$\sim10^{10}\,{\rm M}_\odot$ where dark matter dynamically dominates even at
sub-kpc scales. We find that while the global properties of galaxies of this
scale are minimally affected by allowed self-interactions, their internal
structures change significantly if the cross section is large enough within the
inner sub-kpc region. In these dark-matter-dominated systems, self-scattering
ties the shape of the stellar distribution to that of the dark matter
distribution. In particular, we find that the stellar core radius is closely
related to the dark matter core radius generated by self-interactions. Dark
matter collisions lead to dwarf galaxies with larger stellar cores and smaller
stellar central densities compared to the cold dark matter case. The central
metallicity within $1\,{\rm kpc}$ is also larger by up to $\sim 15\%$ in the
former case. We conclude that the mass distribution, and characteristics of the
central stars in dwarf galaxies can potentially be used to probe the
self-interacting nature of dark matter. |
Reheating the Standard Model from a hidden sector: We consider a scenario where the inflaton decays to a hidden sector thermally
decoupled from the visible Standard Model sector. A tiny portal coupling
between the hidden and the visible sectors later heats the visible sector so
that the Standard Model degrees of freedom come to dominate the energy density
of the Universe before Big Bang Nucleosynthesis. We find that this scenario is
viable, although obtaining the correct dark matter abundance and retaining
successful Big Bang Nucleosynthesis is not obvious. We also show that the
isocurvature perturbations constituted by a primordial Higgs condensate are not
problematic for the viability of the scenario. | Gravitational Waves from Broken Cosmic Strings: The Bursts and the Beads: We analyze the gravitational wave signatures of a network of metastable
cosmic strings. We consider the case of cosmic string instability to breakage,
with no primordial population of monopoles. This scenario is well motivated
from GUT and string theoretic models with an inflationary phase below the
GUT/string scale. The network initially evolves according to a scaling
solution, but with breakage events resulting from confined monopoles (beads)
being pair produced and accelerated apart. We find these ultra-relativistic
beads to be a potent source of gravitational waves bursts, detectable by
Initial LIGO, Advanced LIGO, and LISA. Indeed, Advanced LIGO could observe
bursts from strings with tensions as low as $G\mu \sim 10^{-12}$. In addition,
we find that ultra-relativistic beads produce a scale-invariant stochastic
background detectable by LIGO, LISA, and pulsar timing experiments. The
stochastic background is scale invariant up to Planckian frequencies. This
phenomenology provides new constraints and signatures of cosmic strings that
disappear long before the present day. |
Cosmic Voids in Sloan Digital Sky Survey Data Release 7: We study the distribution of cosmic voids and void galaxies using Sloan
Digital Sky Survey Data Release 7 (SDSS DR7). Using the VoidFinder algorithm as
described by Hoyle 2002, we identify 1054 statistically significant voids in
the northern galactic hemisphere with radii > 10 h^{-1} Mpc. The filling factor
of voids in the sample volume is 62%. The largest void is just over 30 h^{-1}
Mpc in effective radius. The median effective radius is 17 h^{-1} Mpc. The
voids are found to be significantly underdense, with density contrast \delta <
-0.85 at the edges of the voids. The radial density profiles of these voids are
similar to predictions of dynamically distinct underdensities in gravitational
theory. We find 8,046 galaxies brighter than M_r = -20.09 within the voids,
accounting for 7% of the galaxies. We compare the results of VoidFinder on SDSS
DR7 to mock catalogs generated from a SPH halo model simulation as well as
other \Lambda -CDM simulations and find similar void fractions and void sizes
in the data and simulations. This catalog is made publicly available at
http://www.physics.drexel.edu/~pan/voidcatalog.html for download. | Effect of supersonic relative motion between baryons and dark matter on
collapsed objects: Great attention is given to the first star formation and the epoch of
reionization as main targets of planned large radio interferometries (e.g.
Square Kilometre Array). Recently, it is claimed that the supersonic relative
velocity between baryons and cold dark matter can suppress the abundance of
first stars and impact the cosmological reionization process. Therefore, in
order to compare observed results with theoretical predictions it is important
to examine the effect of the supersonic relative motion on the small-scale
structure formation. In this paper, we investigate this effect on the nonlinear
structure formation in the context of the spherical collapse model in order to
understand the fundamental physics in a simple configuration. We show the
evolution of the dark matter sphere with the relative velocity by both using
N-body simulations and numerically calculating the equation of motion for the
dark matter mass shell. The effects of the relative motion in the spherical
collapse model appear as the delay of the collapse time of dark matter halos
and the decrease of the baryon mass fraction within the dark matter sphere.
Based on these results, we provide the fitting formula of the critical density
contrast for collapses with the relative motion effect and calculate the mass
function of dark matter halos in the Press-Schechter formalism. As a result,
the relative velocity decreases the abundance of dark matter halos whose mass
is smaller than $10^8~M_\odot/h$. |
Glass-Like Random Catalogues for Two-Point Estimates on the Light Cone: We introduce grlic, a publicly available Python tool for generating
glass-like point distributions with a radial density profile $n(r)$ as it is
observed in large-scale surveys of galaxy distributions on the past light cone.
Utilising these glass-like catalogues, we assess the bias and variance of the
Landy-Szalay (LS) estimator of the first three two-point correlation function
(2PCF) multipoles in halo and particle catalogues created with the cosmological
N-body code gevolution. Our results demonstrate that the LS estimator
calculated with the glass catalogues is biased by less than $10^{-4}$ with
respect to the estimate derived from Poisson-sampled random catalogues, for all
multipoles considered and on all but the smallest scales. Additionally, the
estimates derived from glass-like catalogues exhibit significantly smaller
standard deviation $\sigma$ than estimates based on commonly used
Poisson-sampled random catalogues of comparable size. The standard deviation of
the estimate depends on a power of the number of objects $N_R$ in the random
catalogue; we find a power law $\sigma \propto N_R^{-0.9}$ for glass-like
random catalogues as opposed to $\sigma \propto N_R^{-0.48}$ using
Poisson-sampled random catalogues. Given a required precision, this allows for
a much reduced number of objects in the glass-like random catalogues used for
the LS estimate of the 2PCF multipoles, significantly reducing the
computational costs of each estimate. | Generic 3-point Statistics with Tensor Modes in Light of Swampland and
TCC: Recently proposed Swampland Criteria (SC) and Trans-Planckian Censorship
Conjecture (TCC) together put stringent theoretical constraints on slow roll
inflation, raising a question on future prospects of detection of Primordial
Gravitational Waves (PGW). As it appears, the only option to relax the
constraints is by considering Non Bunch Davies (NBD) initial states, that in
turn brings back the observational relevance of PGW via its 2-point function.
In this article we develop consistent 3-point statistics with tensor modes for
all possible correlators (auto and mixed) for NBD initial states in the light
of SC and TCC in a generic, model independent framework of Effective Field
Theory of inflation. We also construct the templates of the corresponding
nonlinearity parameters $f_{NL}$ for different shapes of relevance and
investigate if any of the 3-point correlators could be of interest for future
CMB missions. Our analysis reveals that the prospects of detecting the tensor
auto correlator are almost nil whereas the mixed correlators might be relevant
for future CMB missions. |
Overcoming real-world obstacles in 21 cm power spectrum estimation: A
method demonstration and results from early Murchison Widefield Array data: We present techniques for bridging the gap between idealized inverse
covariance weighted quadratic estimation of 21 cm power spectra and the
real-world challenges presented universally by interferometric observation. By
carefully evaluating various estimators and adapting our techniques for large
but incomplete data sets, we develop a robust power spectrum estimation
framework that preserves the so-called "EoR window" and keeps track of
estimator errors and covariances. We apply our method to observations from the
32-tile prototype of the Murchinson Widefield Array to demonstrate the
importance of a judicious analysis technique. Lastly, we apply our method to
investigate the dependence of the clean EoR window on frequency--especially the
frequency dependence of the so-called "wedge" feature--and establish upper
limits on the power spectrum from z = 6.2 to z = 11.7. Our lowest limit is
Delta(k) < 0.3 Kelvin at 95% confidence at a comoving scale k = 0.046 Mpc^-1
and z = 9.5. | Cosmological constraints from the EFT power spectrum and tree-level
bispectrum of 21cm intensity maps: We explore the information content of 21cm intensity maps in redshift space
using the 1-loop Effective Field Theory power spectrum model and the bispectrum
at tree level. The 21cm signal contains signatures of dark matter, dark energy
and the growth of large-scale structure in the Universe. These signatures are
typically analyzed via the 2-point correlation function or power spectrum.
However, adding the information from the 3-point correlation function or
bispectrum will be crucial to exploiting next-generation intensity mapping
experiments. The bispectrum could offer a unique opportunity to break key
parameter degeneracies that hinder the measurement of cosmological parameters
and improve on the precision. We use a Fisher forecast analysis to estimate the
constraining power of the HIRAX survey on cosmological parameters, dark energy
and modified gravity. |
IGM damping wing constraints on reionisation from covariance
reconstruction of two $z\gtrsim7$ QSOs: Bright, high redshift ($z>6$) QSOs are powerful probes of the ionisation
state of the intervening intergalactic medium (IGM). The detection of
Ly$\alpha$ damping wing absorption imprinted in the spectrum of high-z QSOs can
provide strong constraints on the epoch of reionisation (EoR). In this work, we
perform an independent Ly$\alpha$ damping wing analysis of two known $z>7$
QSOs; DESJ0252-0503 at $z=7.00$ (Wang et al.) and J1007+2115 at $z=7.51$ (Yang
et al.). For this, we utilise our existing Bayesian framework which
simultaneously accounts for uncertainties in: (i) the intrinsic Ly$\alpha$
emission profile (reconstructed from a covariance matrix of measured emission
lines; extended in this work to include NV) and (ii) the distribution of
ionised (H\,{\scriptsize II}) regions within the IGM using a $1.6^3$ Gpc$^3$
reionisation simulation. This approach is complementary to that used in the
aforementioned works as it focuses solely redward of Ly$\alpha$ ($1218 <
\lambda < 1230$\AA) making it more robust to modelling uncertainties while also
using a different methodology for (i) and (ii). We find, for a fiducial EoR
morphology, $\bar{x}_{\rm HI} = 0.64\substack{+0.19 \\ -0.23}$ (68 per cent) at
$z=7$ and $\bar{x}_{\rm HI} = 0.27\substack{+0.21 \\ -0.17}$ at $z=7.51$
consistent within $1\sigma$ to the previous works above, though both are
slightly lower in amplitude. Following the inclusion of NV into our
reconstruction pipeline, we perform a reanalysis of ULASJ1120+0641 at $z=7.09$
(Mortlock et al.) and ULASJ1342+0928 at $z=7.54$ (Ba\~nados et al.) finding
$\bar{x}_{\rm HI} = 0.44\substack{+0.23 \\ -0.24}$ at $z=7.09$ and
$\bar{x}_{\rm HI} = 0.31\substack{+0.18 \\ -0.19}$ at $z=7.54$. Finally, we
combine the QSO damping wing constraints for all four $z\gtrsim7$ QSOs to
obtain a single, unified constraint of $\bar{x}_{\rm HI} = 0.49\substack{+0.11
\\ -0.11}$ at $z=7.29$. | The thawing dark energy dynamics: Can we detect it?: We consider different classes of scalar field models including quintessence,
and tachyon scalar fields with a variety of generic potential belonging to
thawing type. Assuming the scalar field is initially frozen at $w=-1$, we
evolve the system until the present time. We focus on observational quantities
like Hubble parameter, luminosity distance as well as quantities related to the
Baryon Acoustic Oscillation measurement. Our study shows that with present
state of observations, one can not distinguish amongst various models which in
turn can not be distinguished from cosmological constant. This lead us to a
conclusion that there is a thin chance to observe the dark energy metamorphosis
in near future. |
Science with the space-based interferometer eLISA. II: Gravitational
waves from cosmological phase transitions: We investigate the potential for the eLISA space-based interferometer to
detect the stochastic gravitational wave background produced by strong
first-order cosmological phase transitions. We discuss the resulting
contributions from bubble collisions, magnetohydrodynamic turbulence, and sound
waves to the stochastic background, and estimate the total corresponding signal
predicted in gravitational waves. The projected sensitivity of eLISA to
cosmological phase transitions is computed in a model-independent way for
various detector designs and configurations. By applying these results to
several specific models, we demonstrate that eLISA is able to probe many
well-motivated scenarios beyond the Standard Model of particle physics
predicting strong first-order cosmological phase transitions in the early
Universe. | On The Depolarization Asymmetry Seen in Giant Radio Lobes: The depolarization asymmetry seen in double-lobed radio sources, referred to
as the Laing-Garrington (L-G) effect where more rapid depolarization is seen in
the lobe with no visible jet as the wavelength increases, can be explained
either by internal differences between the two lobes, or by an external Faraday
screen that lies in front of only the depolarized lobe. If the jet
one-sidedness is due to relativistic beaming the depolarization asymmetry must
be due to an intervening Faraday screen. If it is intrinsic the depolarization
asymmetry must be related to internal differences in the lobes. We assume in
this paper that the speed in the outer jet of several Fanaroff-Riley Class 1
(FRI) sources exhibiting the L-G effect is close to the 0.1c reported by
several other investigators. For these sources we find that the jet
one-sidedness cannot be explained by beaming and therefore must be intrinsic.
In these FRI sources the L-G effect must be due to differences that originate
inside the lobes themselves. Although it is not known if the flow in the outer
jets of FRII sources also slows to this speed it is suggested that the
explanation of the L-G effect is likely to be the same in both types. This
argument is strengthened by the recent evidence that FRII galaxies have very
large viewing angles, which in turn implies that the L-G model cannot work
regardless of the jet velocity. It may therefore be too soon to completely rule
out internal depolarization in the lobes as the true explanation for the L-G
effect. |
The Morphology of the Thermal Sunyaev-Zel'dovich Sky: At high angular frequencies the thermal Sunyaev-Zel'dovich (tSZ) effect
constitutes the dominant signal in the CMB sky. The tSZ effect is caused by
large scale pressure fluctuations in the baryonic distribution in the Universe
so its statistical properties provide estimates of corresponding properties of
the projected 3D pressure fluctuations. It's power spectrum is a sensitive
probe of the density fluctuations, and the bispectrum can be used to separate
the bias associated with pressure. The bispectrum is often probed with a
one-point real-space analogue, the skewness. In addition to the skewness the
morphological properties, as probed by the well known Minkowski Functionals
(MFs), also require the generalized one-point statistics, which at the lowest
order are identical to the skewness parameters. The concept of generalized
skewness parameters can be extended to define a set of three associated
generalized skew-spectra. We use these skew-spectra to probe the morphology of
the tSZ sky or the y-sky. We show how these power spectra can be recovered from
the data in the presence of arbitrary mask and noise templates using the well
known Pseudo-Cl (PCL) approach for arbitrary beam shape. We also employ an
approach based on the halo model to compute the tSZ bispectrum. The bispectrum
from each of these models is then used to construct the generalized
skew-spectra. We consider the performance of an all-sky survey with Planck-type
noise and compare the results against a noise-free ideal experiment using a
range of smoothing angles. We find that the skew-spectra can be estimated with
very high signal-to-noise ratio from future frequency cleaned tSZ maps that
will be available from experiments such as Planck. This will allow their mode
by mode estimation for a wide range of angular frequencies and will help us to
differentiate them from various other sources of non-Gaussianity. | Explaining low l anomalies in the CMB power spectrum with resonant
superstring excitations during inflation: We explore the possibility that both the suppression of the $\ell = 2$
multipole moment of the power spectrum of cosmic microwave background
temperature fluctuations and the possible dip for $\ell = 10-30$ can be
explained as well as a possible new dip for $\ell \approx 60$ as the result of
the resonant creation of sequential excitations of a fermionic (or bosonic)
closed superstring that couples to the inflaton field. We consider a D=26
closed bosonic string with one toroidal compact dimension as an illustration of
how string excitations might imprint themselves on the CMB. We analyze the
existence of successive momentum states, winding states or oscillations on the
string as the source of the three possible dips in the power spectrum. Although
the evidence of these dips are of marginal statistical significance, this might
constitute the first observational evidence of successive superstring
excitations in Nature. |
MACSJ1423.8+2404: Gravitational Lensing by a Massive, Relaxed Cluster of
Galaxies at z=0.54: We present results of a gravitational-lensing and optical study of MACS
,J1423.8+2404 (z=0.545, MACS, J1423). Our analysis uses high-resolution images
taken with the Hubble Space Telescope in the F555W and F814W passbands, ground
based imaging in eight optical and near-infrared filters obtained with Subaru
and CFHT, as well as extensive spectroscopic data gathered with the Keck
telescopes. At optical wavelengths the cluster exhibits no sign of substructure
and is dominated by a cD galaxy that is 2.1 magnitudes (K-band) brighter than
the second brightest cluster member, suggesting that MACS, J1423 is close to be
fully virialized. Analysis of the redshift distribution of 140 cluster members
reveals a Gaussian distribution, mildly disturbed by the presence of a loose
galaxy group that may be falling into the cluster along the line of sight.
Combining strong-lensing constraints from two spectroscopically confirmed
multiple-image systems near the cluster core with a weak-lensing measurement of
the gravitational shear on larger scales, we derive a parametric mass model for
the mass distribution. All constraints can be satisfied by a uni-modal mass
distribution centred on the cD galaxy and exhibiting very little substructure.
The derived projected mass of M(<65\arcsec [415 kpc])=(4.3\pm0.6)\times 10^{14}
M_sun is about 30% higher than the one derived from X-ray analyses assuming
spherical symmetry, suggesting a slightly prolate mass distribution consistent
with the optical indication of residual line-of-sight structure. The similarity
in shape and excellent alignment of the centroids of the total mass, K-band
light, and intra-cluster gas distributions add to the picture of a highly
evolved system [ABRIDGED] | Stringent neutrino flux constraints on anti-quark nugget dark matter: Strongly-interacting matter in the form of nuggets of nuclear-density
material are not currently excluded as dark matter candidates in the ten gram
to hundred kiloton mass range. A recent variation on quark nugget dark matter
models postulates that a first-order imbalance between matter and antimatter in
the quark-gluon plasma prior to hadron production in the early universe binds
up most of the dark matter into heavy (baryon number $B \sim 10^{25}$)
anti-quark nuggets in the current epoch, explaining both the dark matter
preponderance and the matter-antimatter asymmetry. Interactions of these
massive objects with normal matter in the Earth and Sun will lead to
annihilation and an associated neutrino flux in the $\sim 20-50$ MeV range. We
calculate these fluxes for anti-quark nuggets of sufficient number density to
account for the dark matter and find that current neutrino flux limits from
Super-Kamiokande provide stringent constraints on several possible scenarios
for such objects. Conventional anti-quark nuggets in the previously allowed
mass range cannot account for more than $\sim 1/5$ of the dark matter flux; if
they are in a color-superconducting phase, then their muon production during
matter annihilation must be suppressed by an order of magnitude below prior
estimates if they are to remain viable dark matter candidates. |
The impact of baryonic potentials on the gravothermal evolution of
self-interacting dark matter haloes: The presence of a central baryonic potential can have a significant impact on
the gravothermal evolution of self-interacting dark matter (SIDM) haloes. We
extend a semi-analytical fluid model to incorporate the influence of a static
baryonic potential and calibrate it using controlled N-body simulations. We
construct benchmark scenarios with varying baryon concentrations and different
SIDM models, including constant and velocity-dependent self-interacting cross
sections. The presence of the baryonic potential induces changes in SIDM halo
properties, including central density, core size, and velocity dispersion, and
it accelerates the halo's evolution in both expansion and collapse phases.
Furthermore, we observe a quasi-universality in the gravothermal evolution of
SIDM haloes with the baryonic potential, resembling a previously known feature
in the absence of the baryons. By appropriately rescaling the physical
quantities that characterize the SIDM haloes, the evolution of all our
benchmark cases exhibits remarkable similarity. Our findings offer a framework
for testing SIDM predictions using observations of galactic systems where
baryons play a significant dynamical role. | Planck pre-launch status: High Frequency Instrument polarization
calibration: The High Frequency Instrument of Planck will map the entire sky in the
millimeter and sub-millimeter domain from 100 to 857 GHz with unprecedented
sensitivity to polarization ($\Delta P/T_{\tiny cmb} \sim 4\cdot 10^{-6}$) at
100, 143, 217 and 353 GHz. It will lead to major improvements in our
understanding of the Cosmic Microwave Background anisotropies and polarized
foreground signals. Planck will make high resolution measurements of the
$E$-mode spectrum (up to $\ell \sim 1500$) and will also play a prominent role
in the search for the faint imprint of primordial gravitational waves on the
CMB polarization. This paper addresses the effects of calibration of both
temperature (gain) and polarization (polarization efficiency and detector
orientation) on polarization measurements. The specific requirements on the
polarization parameters of the instrument are set and we report on their
pre-flight measurement on HFI bolometers. We present a semi-analytical method
that exactly accounts for the scanning strategy of the instrument as well as
the combination of different detectors. We use this method to propagate errors
through to the CMB angular power spectra in the particular case of Planck-HFI,
and to derive constraints on polarization parameters. We show that in order to
limit the systematic error to 10% of the cosmic variance of the $E$-mode power
spectrum, uncertainties in gain, polarization efficiency and detector
orientation must be below 0.15%, 0.3% and 1\deg\ respectively. Pre-launch
ground measurements reported in this paper already fulfill these requirements. |
Simulations of galaxy cluster mergers with velocity-dependent, rare and
frequent self-interactions: Self-interacting dark matter (SIDM) has been proposed to solve small-scale
problems in $\Lambda$CDM cosmology. In previous work, constraints on the
self-interaction cross-section of dark matter have been derived assuming that
the self-interaction cross-section is independent of velocity. However, a
velocity-dependent cross-section is more natural in most theories of SIDM.
Using idealized $N$-body simulations, we study merging clusters, with
velocity-dependent SIDM. In addition to the usual rare scattering in the
isotropic limit, we also simulate these systems with anisotropic, small-angle
(frequent) scatterings. We study the qualitative features of the mergers and we
find that the effects of velocity-dependent cross-sections are observed when
comparing early-time and late-time oscillation amplitude of the brightest
cluster galaxy (BCG). Finally, we also extend the existing upper bounds on the
velocity-independent, isotropic self-interaction cross-section to the parameter
space of rare and frequent velocity-dependent self-interactions by studying the
central densities of dark matter only isolated haloes. For these upper-bound
parameters, we find that the offsets just after the first pericentre to be
$\leq$ 10 kpc. On the other hand, because of BCG oscillations, we speculate
that the distribution of BCG offsets in relaxed cluster to be a statistically
viable probe. Therefore, this motivates further studies of BCG off-centering in
cosmological simulations. | Astrophysical Plasma Instabilities induced by Long-Range Interacting
Dark Matter: If dark matter (DM) is millicharged or darkly charged, collective plasma
processes may dominate momentum exchange over direct particle collisions.
Plasma streaming instabilities can couple the momentum of the DM to
counter-streaming baryons or other DM and result in the counter-streaming
fluids coming to rest with each other, just as happens for baryonic
collisionless shocks in astrophysical systems. While electrostatic plasma
instabilities are highly suppressed by Landau damping when DM is millicharged,
in the cosmological situations of interest, electromagnetic instabilities such
as the Weibel can couple momenta, assuming that the linear instability
saturates in the manner typically found for baryonic plasmas. We find that the
streaming of DM in the pre-Recombination universe is affected more strongly by
direct collisions than collective processes, validating previous constraints.
However, when considering magnetized Weibel and Firehose instabilities, the
properties of the Bullet Cluster merger are likely to be substantially altered
if $[q_\chi/m_\chi] \gtrsim 10^{-12}-10^{-11}$, where $[q_\chi/m_\chi]$ is the
charge-to-mass ratio of the DM relative to that of the proton. The Weibel
growth rates are even faster in the case of a dark-$U(1)$ charge, potentially
ruling out $[q_\chi/m_\chi] \gtrsim 10^{-14}$ in the Bullet Cluster system, in
agreement with previous work. The strongest previous limits on millicharged DM
(mDM) arise from considering the spin-down of galactic disks. We show that
plasma instabilities or tangled background magnetic fields could lead to
diffusive propagation of the DM, weakening these spin-down limits. Thus, plasma
instabilities may place some of the most stringent constraints over much of the
millicharged, and our results corroborate previous extremely stringent
potential constraints on the dark-charged parameter space. |
Mirror matter can alleviate the cosmological lithium problem: The abundance of lithium-7 confronts cosmology with a long lasting problem
between the predictions of standard big bang nucleosynthesis and the baryonic
density determined from the cosmic microwave background observations. This
article investigates the influence of the existence of a mirror world, focusing
on models in which neutrons can oscillate into mirror neutrons. Such a
mechanism allows for an effective late time neutron injection, which induces an
increase of the destruction of beryllium-7, due to an increase of the neutron
capture, and then a decrease of the final lithium-7 abundance. Big bang
nucleosynthesis sets constraints on the oscillation time between the two types
of neutron and the possibility for such a mechanism to solve, or alleviate, the
lithium problem is emphasized. | KiDS-1000 Cosmology: Multi-probe weak gravitational lensing and
spectroscopic galaxy clustering constraints: We present a joint cosmological analysis of weak gravitational lensing
observations from the Kilo-Degree Survey (KiDS-1000), with redshift-space
galaxy clustering observations from the Baryon Oscillation Spectroscopic Survey
(BOSS), and galaxy-galaxy lensing observations from the overlap between
KiDS-1000, BOSS and the spectroscopic 2-degree Field Lensing Survey (2dFLenS).
This combination of large-scale structure probes breaks the degeneracies
between cosmological parameters for individual observables, resulting in a
constraint on the structure growth parameter $S_8=\sigma_8 \sqrt{\Omega_{\rm
m}/0.3} = 0.766^{+0.020}_{-0.014}$, that has the same overall precision as that
reported by the full-sky cosmic microwave background observations from Planck.
The recovered $S_8$ amplitude is low, however, by $8.3 \pm 2.6$ % relative to
Planck. This result builds from a series of KiDS-1000 analyses where we
validate our methodology with variable depth mock galaxy surveys, our lensing
calibration with image simulations and null-tests, and our
optical-to-near-infrared redshift calibration with multi-band mock catalogues
and a spectroscopic-photometric clustering analysis. The systematic
uncertainties identified by these analyses are folded through as nuisance
parameters in our cosmological analysis. Inspecting the offset between the
marginalised posterior distributions, we find that the $S_8$-difference with
Planck is driven by a tension in the matter fluctuation amplitude parameter,
$\sigma_8$. We quantify the level of agreement between the CMB and our
large-scale structure constraints using a series of different metrics, finding
differences with a significance ranging between $\sim\! 3\,\sigma$, when
considering the offset in $S_{8}$, and $\sim\! 2\,\sigma$, when considering the
full multi-dimensional parameter space. |
Hi intensity mapping with MeerKAT: Primary beam effects on foreground
cleaning: Upcoming and future neutral hydrogen Intensity Mapping surveys offer a great
opportunity to constrain cosmology in the post-reionization Universe, provided
a good accuracy is achieved in the separation between the strong foregrounds
and the cosmological signal. Cleaning methods rely on the frequency smoothness
of the foregrounds and are often applied under the assumption of a simplistic
Gaussian primary beam. In this work, we test the cleaning in the presence of a
realistic primary beam model with a non trivial frequency dependence. We focus
on the Square Kilometre Array precursor MeerKAT telescope and simulate a
single-dish wide area survey. We consider the main foreground components,
including an accurate full sky point source catalogue. We find that the
coupling between beam sidelobes and the foreground structure can complicate the
cleaning. However, when the beam frequency dependence is smooth, we show that
the cleaning is only problematic if the far sidelobes are unexpectedly large.
Even in that case, a proper reconstruction is possible if the strongest point
sources are removed and the cleaning is more aggressive. We then consider a
non-trivial frequency dependence: a sinusoidal type feature in the beam width
that is present in the MeerKAT beam and is expected in most dishes, including
SKA1-MID. Such a feature, coupling with the foreground emission, biases the
reconstruction of the signal across frequency, potentially impacting the
cosmological analysis. Interestingly, such contamination is present at a lower
level even when no point sources are included and the beam is Gaussian, showing
that this frequency ripple can be problematic even within the main lobe. We
show that this effect is constrained to a narrow region in $k_\parallel$ space
and can be reduced if the maps are carefully re-smoothed to a common lower
resolution. | Primordial density and BAO reconstruction: We present a new method to reconstruct the primordial (linear) density field
using the estimated nonlinear displacement field. The divergence of the
displacement field gives the reconstructed density field. We solve the
nonlinear displacement field in the 1D cosmology and show the reconstruction
results. The new reconstruction algorithm recovers a lot of linear modes and
reduces the nonlinear damping scale significantly. The successful 1D
reconstruction results imply the new algorithm should also be a promising
technique in the 3D case. |
On the dynamics of a dark sector coupling: Interacting dark energy models may play a crucial role in explaining several
important observational issues in modern cosmology and also may provide a
solution to current cosmological tensions. Since the phenomenology of the dark
sector could be extremely rich, one should not restrict the interacting models
to have a coupling parameter which is constant in cosmic time, rather allow for
its dynamical behavior, as it is common practice in the literature when dealing
with other dark energy properties, as the dark energy equation of state. We
present here a compendium of the current cosmological constraints on a large
variety of interacting models, investigating scenarios where the coupling
parameter of the interaction function and the dark energy equation of state can
be either constant or dynamical. For the most general schemes, in which both
the coupling parameter of the interaction function and the dark energy equation
of state are dynamical, we find $95\%$~CL evidence for a dark energy component
at early times and slightly milder evidence for a dynamical dark coupling for
the most complete observational data set exploited here, which includes CMB,
BAO and Supernova Ia measurements. Interestingly, there are some cases where a
dark energy component different from the cosmological constant case at early
times together with a coupling different from zero today, can alleviate both
the $H_0$ and $S_8$ tension for the full dataset combination considered here.
Due to the energy exchange among the dark sectors, the current values of the
matter energy density and of the clustering parameter $\sigma_8$ are shifted
from their $\Lambda$CDM-like values. This fact makes future surveys, especially
those focused on weak lensing measurements, unique tools to test the nature and
the couplings of the dark energy sector. | $Λ$CDM Tensions: Localising Missing Physics through Consistency
Checks: $\Lambda$CDM tensions are by definition model dependent; one sees anomalies
through the prism of $\Lambda$CDM. Thus, progress towards tension resolution
necessitates checking the consistency of the $\Lambda$CDM model to localise
missing physics either in redshift or scale. Since the Universe is dynamical
and redshift is a proxy for time, it is imperative to first perform consistency
checks involving redshift, then consistency checks involving scale, as the next
steps to settle the ``systematics versus new physics" debate and foster
informed model building. We present a review of the hierarchy of assumptions
underlying the $\Lambda$CDM cosmological model and comment on whether relaxing
them can address the tensions. We focus on the lowest lying fruit of
identifying missing physics through the identification of redshift dependent
$\Lambda$CDM model fitting parameters. We highlight recent progress made on
${S_8:= \sigma_8 \sqrt{\Omega_{\rm m}/0.3}}$ tension and elucidate how similar
progress can be made on $H_0$ tension. Our discussions indicate that $H_0$
tension, equivalently a redshift dependent $H_0$, and a redshift dependent
$S_8$ imply a problem with background $\Lambda$CDM cosmology. |
Large-scale periodicity in the distribution of QSO absorption-line
systems: The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe. | The blue UV slopes of z~4 Lyman break galaxies: implications for the
corrected star formation rate density: We plan to analyse dust extinction in Lyman Break Galaxies (LBGs) by
introducing a new and more reliable approach to their selection and to the
characterization of their distribution of UV slopes beta, using deep IR images
from HST. We exploit deep WFC3 IR observations of the ERS and HUDF fields over
GOODS-South, combined with HST-ACS optical data, to select z~4 LBGs through a
new (B-V) vs. (V-H) colour diagram. The UV slope of the selected galaxies is
robustly determined by a linear fit over their observed I, Z, Y, J magnitudes,
coherently with the original definition of beta. The same fit is used to
determine their rest-frame UV magnitudes M1600 through a simple interpolation.
We estimate the effect of observational uncertainties with detailed simulations
that we also exploit, under a parametric maximum-likelihood approach, to
constrain the probability density function of UV slopes PDF(beta) as a function
of rest-frame magnitude. We find 142 and 25 robust LBGs in the ERS and HUDF
fields respectively, limiting our sample to S/N(H)>10 objects. Our newly
defined criteria improve the selection of z~4 LBGs and allow us to exclude red
interlopers at lower redshift, especially z~3-3.5 objects. We find that z~4
LBGs are characterized by blue UV slopes, suggesting a low dust extinction: all
L<L* galaxies have an average UV slope <beta>\simeq-2.1, while brighter objects
only are slightly redder (<beta> -1.9). We find an intrinsic dispersion ~ 0.3
for PDF(beta) at all magnitudes. The SFRD at z~4 corrected according to these
estimates turns out to be lower than previously found: log(SFRD)\simeq-1.09
M_sun/yr/Mpc^3. Finally, we discuss how the UV slope of z~4 galaxies changes as
a function of the dust-corrected UV magnitude (i.e. SFR) showing that most
galaxies with a high SFR (> 80 M_sun/yr) are highly extincted objects.
[Abridged] |
NGC 2207/IC 2163: A Grazing Encounter with Large Scale Shocks: Radio continuum, Spitzer infrared, optical and XMM-Newton X-ray and UVM2
observations are used to study large-scale shock fronts, young star complexes,
and the galactic nuclei in the interacting galaxies NGC 2207/IC 2163. There are
two types of large-scale shock fronts in this galaxy pair. The shock front
along the rim of the ocular oval in IC 2163 has produced vigorous star
formation in a dusty environment. In the outer part of the companion side of
NGC 2207, a large-scale front attributed to disk or halo scraping is
particularly bright in the radio continuum but not in any tracers of recent
star formation or in X-rays. This radio continuum front may be mainly in the
halo on the back side of NGC 2207 between the two galaxies. Values of the flux
density ratio S(8 um)/S(6 cm) of kpc-sized, Spitzer IRAC star-forming clumps in
NGC 2207/IC 2163 are compared with those of giant H II regions in M81. We find
evidence that in 2001 a radio supernova was present in the core of feature i, a
mini-starburst on an outer arm of NGC 2207. X-ray emission is detected from the
NGC 2207 nucleus and from nine discrete sources, one of which corresponds to SN
1999ec, and another may be a radio supernova or a background quasar. The X-ray
luminosity and X-ray spectrum of the NGC 2207 nucleus suggests it is a highly
absorbed, low luminosity AGN. | Constraints on the mass-richness relation from the abundance and weak
lensing of SDSS clusters: We constrain the scaling relation between optical richness ($\lambda$) and
halo mass ($M$) for a sample of SDSS redMaPPer galaxy clusters within the
context of the {\it Planck} cosmological model. We use a forward modeling
approach where we model the probability distribution of optical richness for a
given mass, $P(\ln \lambda| M)$. To model the abundance and the stacked lensing
profiles, we use an emulator specifically built to interpolate the halo mass
function and the stacked lensing profile for an arbitrary set of halo mass and
redshift, which is calibrated based on a suite of high-resolution $N$-body
simulations. We apply our method to 8,312 SDSS redMaPPer clusters with $20\le
\lambda \le 100$ and $0.10\le z_{\lambda}\le0.33$, and show that the log-normal
distribution model for $P(\lambda|M)$, with four free parameters, well
reproduces the measured abundances and lensing profiles simultaneously. The
constraints are characterized by the mean relation, $\left\langle
\ln{\lambda}\right\rangle(M)=A+B\ln(M/M_{\rm pivot})$, with
$A=3.207^{+0.044}_{-0.046}$ and $B=0.993^{+0.041}_{-0.055}$ (68\%~CL), where
the pivot mass scale $M_{\rm pivot}=3\times 10^{14} h^{-1}M_\odot$, and the
scatter $\sigma_{\mathrm{\ln\lambda}|M}=\sigma_0+q\ln(M/M_{\rm pivot})$ with
$\sigma_0=0.456^{+0.047}_{-0.039}$ and $q=-0.169^{+0.035}_{-0.026}$. We find
that a large scatter in halo masses is required at the lowest richness bins
($20\le \lambda \lesssim 30$) in order to reproduce the measurements. Without
such a large scatter, the model prediction for the lensing profiles tends to
overestimate the measured amplitudes. This might imply a possible contamination
of intrinsically low-richness clusters due to the projection effects. Such a
low-mass halo contribution is significantly reduced when applying our method to
the sample of $30\le \lambda \le 100$. |
Radio-Quiet AGN and the Transient Radio Sky: 8.4-GHZ radio imaging study of an optically selected sample of early type
Seyfert galaxies; comparison of images taken at two epochs reveals possible
variation in the nuclear radio flux density in five of them over a seven year
period. It is shown that there is a possible correlation between the presence
of nuclear radio variability and the absence of hundred parsec-scale radio
emission, analogous with radio-loud AGN. Our results suggest that all Seyferts
may exhibit variation in their nuclear radio flux density at 8.4 GHz, but that
variability is more easily recognized in compact sources in which emission from
the variable nucleus is not diluted by unresolved, constant flux density radio
jet emission within the central 50 pc. Taken in combination with other Seyfert
properties, these results suggest a paradigm of intermittent periods of
quiescence and nuclear outburst across the Seyfert population and demonstrate
the importance of investigating the temporal domain at radio wavelengths, which
remains completely unexplored for faint radio-quiet AGN. Discovery of
intermittent activity and radio flares has important implications for the AGN
duty cycles and the origin of Ultra-High Energy Cosmic Rays. New radio
facilities, such as the EVLA/VLBA, eMERLIN, LOFAR and eVLBI on the EVN, will
revolutionise the study of radio-quiet AGN; in particular, the combination of
increased sensitivity and sampling rate with high-angular resolution and
automatic data reduction will open up the transient radio sky and bring major
future breakthroughs. | The Entrainment-Limited Evolution of FR II Sources: Maximum Sizes and A
Possible Connection to FR Is: We construct a simple theoretical model to investigate how entrainment
gradually erodes high-speed FR II jets. This process is described by embedding
a mixing-layer model developed originally to describe FR I objects in a
self-similar model for the lobe structure of classical FR II sources. Following
the classical FR II models, we assume that the lobe is dominated by the
particles injected from the central jet. The entrainment produces a boundary
shear layer which acts at the interface between the dense central jet and the
less denser surrounding lobe, and the associated erosion of the jet places
interesting limits on the maximum size of FR II sources. The model shows that
this limit depends mainly on the initial bulk velocity of the relativistic jet
triggered. The bulk velocities of FR IIs suggested by our model are in good
agreement with that obtained from direct pc-scale observations on ordinary
radio galaxies and quasars. Finally, we discuss how FR IIs may evolve into FR
Is upon reaching their maximum, entrainment-limited sizes. |
Bias in apparent dispersion measure due to de-magnification of plasma
lensing on background radio sources: The effect of ionized gas on the propagation of radio signals is known as
plasma lensing. Unlike gravitational lensing, plasma lensing causes both
magnification and strong de-magnification effects to background sources. We
study the cross section of plasma lensing for two density profiles, the
Gaussian and power-law models. In general, the cross section increases with the
density gradient. Radio sources can be used to measure the free electron
density along the line of sight. However, plasma lensing de-magnification
causes an underestimate of the electron density. Such a bias increases with the
electron density, and can be up to $\sim 15\%$ in the high density region.
There is a large probability that high density clumps will be missed due to
this bias. The magnification of plasma lensing can also change the luminosity
function of the background sources. The number density of sources on both the
high and low luminosity ends can be overestimated due to this biasing effect. | Type II Cepheids as Extragalactic Distance Candles: Extragalactic Type II Cepheids are tentatively identified in photometric
surveys of IC 1613, M33, M101, M106, M31, NGC 4603, and the SMC. Preliminary
results suggest that Type II Cepheids may play an important role as standard
candles, in constraining the effects of metallicity on Cepheid parameters, and
in mapping extinction. |
Constraining the halo mass function with observations: The abundances of dark matter halos in the universe are described by the halo
mass function (HMF). It enters most cosmological analyses and parametrizes how
the linear growth of primordial perturbations is connected to these abundances.
Interestingly, this connection can be made approximately cosmology independent.
This made it possible to map in detail its near-universal behavior through
large-scale simulations. However, such simulations may suffer from systematic
effects, especially if baryonic physics is included. In this paper we ask how
well observations can constrain directly the HMF. The observables we consider
are galaxy cluster number counts, galaxy cluster power spectrum and lensing of
type Ia supernovae. Our results show that DES is capable of putting the first
meaningful constraints on the HMF, while both Euclid and J-PAS can give
stronger constraints, comparable to the ones from state-of-the-art simulations.
We also find that an independent measurement of cluster masses is even more
important for measuring the HMF than for constraining the cosmological
parameters, and can vastly improve the determination of the halo mass function.
Measuring the HMF could thus be used to cross-check simulations and their
implementation of baryon physics. It could even, if deviations cannot be
accounted for, hint at new physics. | Simulations of the merging galaxy cluster Abell 3376: Observed galaxy clusters often exhibit X-ray morphologies suggestive of
recent interaction with an infalling subcluster. Abell 3376 is a nearby
(z=0.046) massive galaxy cluster whose bullet-shaped X-ray emission indicates
that it may have undergone a recent collision. It displays a pair of Mpc-scale
radio relics and its brightest cluster galaxy is located 970 h_70^-1 kpc away
from the peak of X-ray emission, where the second brightest galaxy lies. We
attempt to recover the dynamical history of Abell 3376. We perform a set of
N-body adiabatic hydrodynamical simulations using the SPH code Gadget-2. These
simulations of binary cluster collisions are aimed at exploring the parameter
space of possible initial configurations. By attempting to match X-ray
morphology, temperature, virial mass and X-ray luminosity, we set approximate
constraints on some merger parameters. Our best models suggest a collision of
clusters with mass ratio in the range 1/6-1/8, and having a subcluster with
central gas density four times higher than that of the major cluster. Models
with small impact parameter (b<150 kpc), if any, are preferred. We estimate
that Abell 3376 is observed approximately 0.5 Gyr after core passage, and that
the collision axis is inclined by i~40 degrees with respect to the plane of the
sky. The infalling subcluster drives a supersonic shock wave that propagates at
almost 2600 km/s, implying a Mach number as high as M~4; but we show how it
would have been underestimated as M~3 due to projection effects. |
Tensions in the dark: shedding light on Dark Matter-Dark Energy
interactions: The emergence of an increasingly strong tension between the Hubble rate
inferred from early- and late-time observations has reinvigorated interest in
nonstandard scenarios, with the aim of reconciling these measurements. One such
model involves interactions between Dark Matter and Dark Energy. Here we
consider a specific form of the coupling between these two fluids proportional
to the Dark Energy energy density, which has been studied extensively in the
literature and claimed to substantially alleviate the Hubble tension. We
complement the work already discussed in several previous analyses and show
that, once all relevant cosmological probes are included simultaneously, the
value of the Hubble parameter in this model is $H_0=69.82_{-0.76}^{+0.63}$
km/(s Mpc), which reduces the Hubble tension to $2.5\sigma$. Furthermore, we
also perform a statistical model comparison, finding a $\Delta\chi^2$ of
$-2.15$ (corresponding to a significance of 1.5$\sigma$) with the inclusion of
one additional free parameter, showing no clear preference for this model with
respect to $\Lambda$CDM, which is further confirmed with an analysis of the
Bayes ratio. | Discovery of the first giant double radio relic in a galaxy cluster
found in the PLANCK Sunyaev-Zel'dovich cluster survey: PLCK G287.0+32.9: We report the discovery of large scale diffuse non-thermal radio emission in
PLCK G287.0+32.9, an exceptionally hot (T ~ 13 keV), massive and luminous
galaxy cluster, strongly detected by the PLANCK satellite in a recent, all-sky
blind search for new clusters through Sunyaev-Zel'dovich effect. Giant
Metrewave Radio telescope 150 MHz and Very Large Array 1.4 GHz radio data
reveal a pair of giant (>1 Mpc) "arc" shaped peripheral radio-relics
(signatures of shock waves) of unprecedented scale (linear separation ~4.4 Mpc
at redshift 0.39), located at distances from the cluster center which are about
0.7 and 1.3 of the cluster's virial radius. Another possible giant relic and a
radio-halo is detected closer to the cluster center. These relic sources are
unique "signposts" of extremely energetic mergers and shocks (both ongoing and
past), that are assembling and heating up this very massive galaxy cluster.
They are also a probe of the filamentary cosmic-web structure beyond the
cluster virial radius. Optical imaging with the IUCAA 2 meter telescope and
XMM-Newton X-ray data confirm a very rich galaxy cluster with a morphologically
disturbed core region, suggesting a dynamically perturbed merging system. |
Growing Massive Black Hole Pairs in Minor Mergers of Disk Galaxies: We perform a suite of high-resolution smoothed particle hydrodynamics
simulations to investigate the orbital decay and mass evolution of massive
black hole (MBH) pairs down to scales of ~30 pc during minor mergers of disk
galaxies. Our simulation set includes star formation and accretion onto the
MBHs, as well as feedback from both processes. We consider 1:10 merger events
starting at z~3, with MBH masses in the sensitivity window of the Laser
Interferometer Space Antenna, and we follow the coupling between the merger
dynamics and the evolution of the MBH mass ratio until the satellite galaxy is
tidally disrupted. While the more massive MBH accretes in most cases as if the
galaxy were in isolation, the satellite MBH may undergo distinct episodes of
enhanced accretion, owing to strong tidal torques acting on its host galaxy and
to orbital circularization inside the disk of the primary galaxy. As a
consequence, the initial 1:10 mass ratio of the MBHs changes by the time the
satellite is disrupted. Depending on the initial fraction of cold gas in the
galactic disks and the geometry of the encounter, the mass ratios of the MBH
pairs at the time of satellite disruption can stay unchanged or become as large
as 1:2. Remarkably, the efficiency of MBH orbital decay correlates with the
final mass ratio of the pair itself: MBH pairs that increase significantly
their mass ratio are also expected to inspiral more promptly down to
nuclear-scale separations. These findings indicate that the mass ratios of MBH
pairs in galactic nuclei do not necessarily trace the mass ratios of their
merging host galaxies, but are determined by the complex interplay between gas
accretion and merger dynamics. | Reducing the $H_0$ and $σ_8$ tensions with Dark Matter-neutrino
interactions: The introduction of Dark Matter-neutrino interactions modifies the Cosmic
Microwave Background (CMB) angular power spectrum at all scales, thus affecting
the reconstruction of the cosmological parameters. Such interactions can lead
to a slight increase of the value of $H_0$ and a slight decrease of $\sigma_8$,
which can help reduce somewhat the tension between the CMB and lensing or
Cepheids datasets. Here we show that it is impossible to solve both tensions
simultaneously. While the 2015 Planck temperature and low multipole
polarisation data combined with the Cepheids datasets prefer large values of
the Hubble rate (up to $H_0 = 72.1^{+1.5}_{-1.7} \rm{km/s/Mpc}$, when
$N_{\rm{eff}}$ is free to vary), the $\sigma_8$ parameter remains too large to
reduce the $\sigma_8$ tension. Adding high multipole Planck polarization data
does not help since this data shows a strong preference for low values of
$H_0$, thus worsening current tensions, even though they also prefer smaller
value of $\sigma_8$. |
Nonparametric Dark Energy Reconstruction from Supernova Data: Understanding the origin of the accelerated expansion of the Universe poses
one of the greatest challenges in physics today. Lacking a compelling
fundamental theory to test, observational efforts are targeted at a better
characterization of the underlying cause. If a new form of mass-energy, dark
energy, is driving the acceleration, the redshift evolution of the equation of
state parameter w(z) will hold essential clues as to its origin. To best
exploit data from observations it is necessary to develop a robust and accurate
reconstruction approach, with controlled errors, for w(z). We introduce a new,
nonparametric method for solving the associated statistical inverse problem
based on Gaussian Process modeling and Markov chain Monte Carlo sampling.
Applying this method to recent supernova measurements, we reconstruct the
continuous history of w out to redshift z=1.5. | Mesoscopic Energy Ranking Constraints in the IllustrisTNG Simulations: We revisited the problem of mixing in a gravitational N-body system from the
point of view of the ordering of coarse-grained cells in the one-particle
energy space, here denoted {\it energy ranking preservation} (ERP). This effect
has been noted for some time in simulations, although individual particle
energies and their phase-space variables mix considerably. The present
investigation aimed to map ERP in terms of parameters involving the collective
range in which it is effective, as well as in terms of global and historical
characterisations of gravitational systems evolving towards equilibrium. We
examined a subset of the IllustrisTNG cosmological magnetohydrodynamical
simulations (TNG50-4 and TNG100-3), considering both their full and dark-only
versions. For each simulation, we selected the $20$ most massive haloes at
redshift $z=0$, tracing their ERP fractions back at selected redshift markers
({\tt z} $= \{1.0, 5.0, 10.0 \}$), and for a coarse-graining set ranging from
$5$ to $30$ energy bins. At the redshift marker {\tt z} $= 1$, we found high
ERP fractions (above $\sim 80 \%$) in both simulations, regardless of the
coarse-graining level. The {\it decline} in ERP fractions with redshift was
roughly a function of mass and fractional mass increase in the analysed TNG50-4
haloes, but not in the TNG100-3 ones, indicating a possible relative
susceptibility of the ERP effect to mass accretion for haloes less massive than
$\sim 10^{14} ~ M_{\odot}$. We confirmed earlier indications in the literature
concerning a possible "mesoscopic" constraint operative in a time span of at
least several Gyr. |
Constraining dark matter annihilation with the isotropic $γ$-ray
background: updated limits and future potential: The nature of the Isotropic $\gamma$-ray Background (IGRB) measured by the
Large Area Telescope (LAT) on the Fermi $\gamma$-ray space Telescope ({\it
Fermi}) remains partially unexplained. Non-negligible contributions may
originate from extragalactic populations of unresolved sources such as blazars,
star-forming galaxies or galactic milli-second pulsars. A recent prediction of
the diffuse $\gamma$-ray emission from Active Galactic Nuclei (AGN) with a
large viewing angle with respect to the line-of-sight (l.o.s.) has demonstrated
that this faint but numerous population is also expected to contribute
significantly to the total IGRB intensity. A more exotic contribution to the
IGRB invokes the pair annihilation of dark matter (DM) weakly interacting
massive particles (WIMPs) into $\gamma$-rays. In this work, we evaluate the
room left for galactic DM at high latitudes ($>10^\circ$) by including photons
from both prompt emission and inverse Compton scattering, emphasizing the
impact of the newly discovered contribution from misaligned AGN (MAGN) for such
an analysis. Summing up all significant galactic and extragalactic components
of the IGRB, we find that an improved understanding of the associated
astrophysical uncertainties is still mandatory to put stringent bounds on
thermally produced DM. On the other hand, we also demonstrate that the IGRB has
the potential to be one of the most competitive {\it future} ways to test the
DM WIMP hypothesis, once the present uncertainties are even slightly reduced.
In fact, if MAGN contribute even at 90% of the maximal level consistent with
our current understanding, thermally produced WIMPs would be severely
constrained as DM candidates for masses up to several TeV. | Broken scale invariance, $α$-attractors and vector impurity: We show that if the $\alpha$-attractor model is realized by the spontaneous
breaking of the scale symmetry, then the stability and the dynamics of the
vector field that gauges the scale symmetry can severely constrain the
$\alpha$-parameter as $5/6 < \alpha < 1$ restricting the inflationary
predictions in a very tiny region in the $n_s - r$ plane that are in great
agreement with the latest Planck data. Although the different values of
$\alpha$ do not make a tangible difference for $n_s$ and $r$, they provide
radically different scenarios for the post-inflationary dynamics which
determines the standard BBN processes and the large scale isotropy of the
universe. |
Probing the anisotropic local universe and beyond with SNe Ia data: The question of the transition to global isotropy from our anisotropic local
Universe is studied using the Union 2 catalogue of Type Ia supernovae (SNe Ia).
We construct a "residual" statistic sensitive to systematic shifts in their
brightness in different directions and use this to search in different redshift
bins for a preferred direction on the sky in which the SNe Ia are brighter or
fainter relative to the 'standard' LCDM cosmology. At low redshift (z<0.05) we
find that an isotropic model such as LCDM is barely consistent with the SNe Ia
data at 2-3 sigma. A complementary maximum likelihood analysis of peculiar
velocities confirms this finding -- there is a bulk flow of around 260 km/sec
at z \sim 0.06, which disagrees with LCDM at 1-2 sigma. Since the Shapley
concentration is believed to be largely responsible for this bulk flow, we make
a detailed study of the infall region: the SNe Ia falling away from the Local
Group towards Shapley are indeed significantly dimmer than those falling
towards us and on to Shapley. Convergence to the CMB rest frame must occur well
beyond Shapley (z>0.06) so the low redshift bulk flow can systematically bias
any reconstruction of the expansion history of the Universe. At high redshifts
z>0.15 the agreement between the SNe Ia data and the isotropic LCDM model does
improve, however, the sparseness and low quality of the data means that LCDM
cannot be singled out as the preferred cosmological model. | Cosmic rays in galaxy clusters and their non-thermal emission: Radio observations prove the existence of relativistic particles and magnetic
field associated with the intra-cluster-medium (ICM) through the presence of
extended synchrotron emission in the form of radio halos and peripheral relics.
This observational evidence has fundamental implications on the physics of the
ICM. Non-thermal components in galaxy clusters are indeed unique probes of very
energetic processes operating within clusters that drain gravitational and
electromagnetic energy into cosmic rays and magnetic fields. These components
strongly affect the (micro-)physical properties of the ICM, including viscosity
and electrical conductivities, and have also potential consequences on the
evolution of clusters themselves. The nature and properties of cosmic rays in
galaxy clusters, including the origin of the observed radio emission on
cluster-scales, have triggered an active theoretical debate in the last decade.
Only recently we can start addressing some of the most important questions in
this field, thanks to recent observational advances, both in the radio and at
high energies. The properties of cosmic rays and of cluster non-thermal
emissions depend on the dynamical state of the ICM, the efficiency of particle
acceleration mechanisms in the ICM and on the dynamics of these cosmic rays. In
this review we discuss in some detail the acceleration and transport of cosmic
rays in galaxy clusters and the most relevant observational milestones that
have provided important steps on our understanding of this physics. Finally,
looking forward to the possibilities from new generations of observational
tools, we focus on what appear to be the most important prospects for the near
future from radio and high-energy observations. |
Multiple measurements of gravitational waves acting as standard probes:
model-independent constraints on the cosmic curvature with DECIGO: Although the spatial curvature has been precisely determined via the cosmic
microwave background (CMB) observation by Planck satellite, it still suffers
from the well-known cosmic curvature tension. As a standard siren,
gravitational waves (GWs) from binary neutron star mergers provide a direct way
to measure the luminosity distance. In addition, the accelerating expansion of
the universe may cause an additional phase shift in the gravitational waveform,
which allows us to measure the acceleration parameter. This measurement
provides an important opportunity to determine the curvature parameter
$\Omega_k$ in the GW domain based on the combination of two different
observables for the same objects at high redshifts. In this study, we
investigate how such an idea could be implemented with future generation of
space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO)
in the framework of two model-independent methods. Our results show that DECIGO
could provide a reliable and stringent constraint on the cosmic curvature at a
precision of $\Delta\Omega_k$=0.12, which is comparable to existing results
based on different electromagnetic data. Our constraints are more stringent
than the traditional electromagnetic method from the Pantheon SNe Ia sample,
which shows no evidence for the deviation from the flat universe at $z\sim
2.3$. More importantly, with our model-independent method, such a
second-generation space-based GW detector would also be able to explore the
possible evolution $\Omega_k$ with redshifts, through direct measurements of
cosmic curvature at different redshifts ($z\sim 5$). Such a model-independent
$\Omega_k$ reconstruction to the distance past can become a milestone in
gravitational-wave cosmology. | Degeneracies in parametrized modified gravity models: We study degeneracies between parameters in some of the widely used
parametrized modified gravity models. We investigate how different observables
from a future photometric weak lensing survey such as LSST, correlate the
effects of these parameters and to what extent the degeneracies are broken. We
also study the impact of other degenerate effects, namely massive neutrinos and
some of the weak lensing systematics, on the correlations. |
Dark Matter 2014: This article gives an overview on the status of experimental searches for
dark matter at the end of 2014. The main focus is on direct searches for weakly
interacting massive particles (WIMPs) using underground-based low-background
detectors, especially on the new results published in 2014. WIMPs are excellent
dark matter candidates, predicted by many theories beyond the standard model of
particle physics, and are expected to interact with the target nuclei either
via spin-independent (scalar) or spin-dependent (axial-vector) couplings.
Non-WIMP dark matter candidates, especially axions and axion-like particles are
also briefly discussed. | The Extended Optical Disk of M101: We have used deep, wide-field optical imaging to study the faint outskirts of
the luminous spiral galaxy M101 (NGC 5457), as well as its surrounding
environment. Over six square degrees, our imaging has a limiting surface
brightness of mu_B ~ 29.5 mag/arcsec^2, and has revealed the stellar structure
of M101's disk out to nearly 25 arcminutes (50 kpc), three times our measured
R25 isophotal size of the optical disk. At these radii, the well-known
asymmetry of the inner disk slews 180 degrees, resulting in an asymmetric plume
of light at large radius which follows the very extended HI disk to the
northeast of M101. This plume has very blue colors (B-V ~ 0.2), suggesting it
is the somewhat more evolved (few hundred Myr to ~ 1 Gyr) counterpart of the
young far ultraviolet emitting population traced by GALEX imaging. We also
detect another, redder spur of extended light to the east of the disk, and both
structures are reminiscent of features produced during fly-by galaxy
interactions. However, we see no evidence of very extended tidal tails around
M101 or any of its companions which might be expected from a recent encounter
with a massive companion. We consider the properties of M101's outer disk in
light of possible past interactions with the nearby companion galaxies NGC 5477
and NGC 5474. The detection of optical starlight at such large radii gives us
the ability to study star formation histories and stellar populations in outer
disks over a longer timescales than those traced by the UV or Halpha emitting
populations. Our data suggest ongoing buildup of the M101's outer disk due to
encounters in the group environment triggering extended star formation and
tidal heating of existing disk populations. |
Astrophysical hydrodynamics with a high-order discontinuous Galerkin
scheme and adaptive mesh refinement: Solving the Euler equations of ideal hydrodynamics as accurately and
efficiently as possible is a key requirement in many astrophysical simulations.
It is therefore important to continuously advance the numerical methods
implemented in current astrophysical codes, especially also in light of
evolving computer technology, which favours certain computational approaches
over others. Here we introduce the new adaptive mesh refinement (AMR) code
TENET, which employs a high order discontinuous Galerkin (DG) scheme for
hydrodynamics. The Euler equations in this method are solved in a weak
formulation with a polynomial basis by means of explicit Runge-Kutta time
integration and Gauss-Legendre quadrature. This approach offers significant
advantages over commonly employed second order finite volume (FV) solvers. In
particular, the higher order capability renders it computationally more
efficient, in the sense that the same precision can be obtained at
significantly less computational cost. Also, the DG scheme inherently conserves
angular momentum in regions where no limiting takes place, and it typically
produces much smaller numerical diffusion and advection errors than a FV
approach. A further advantage lies in a more natural handling of AMR refinement
boundaries, where a fall-back to first order can be avoided. Finally, DG
requires no wide stencils at high order, and offers an improved data locality
and a focus on local computations, which is favourable for current and upcoming
highly parallel supercomputers. We describe the formulation and implementation
details of our new code, and demonstrate its performance and accuracy with a
set of two- and three-dimensional test problems. The results confirm that DG
schemes have a high potential for astrophysical applications. | The shape of CMB temperature and polarization peaks on the sphere: We present a theoretical study of CMB temperature peaks, including its effect
over the polarization field, and allowing nonzero eccentricity. The formalism
is developed in harmonic space and using the covariant derivative on the
sphere, which guarantees that the expressions obtained are completely valid at
large scales (i.e., no flat approximation). The expected patterns induced by
the peak, either in temperature or polarization, are calculated, as well as
their covariances. It is found that the eccentricity introduces a quadrupolar
dependence in the peak shape, which is proportional to a complex bias parameter
$b_\epsilon$, characterizing the peak asymmetry and orientation. In addition,
the one-point statistics of the variables defining the peak on the sphere is
reviewed, finding some differences with respect to the flat case for large
peaks. Finally, we present a mechanism to simulate constrained CMB maps with a
particular peak on the field, which is an interesting tool for analysing the
statistical properties of the peaks present in the data. |
Supermassive black hole formation by the cold accretion shocks in the
first galaxies: We propose a new scenario for supermassive star (SMS;>10^5Msun) formation in
shocked regions of colliding cold accretion flows near the centers of first
galaxies. Recent numerical simulations indicate that assembly of a typical
first galaxy with virial temperature (~10^4K) proceeds via cold and dense flows
penetrating deep to the center, where the supersonic streams collide each other
to develop a hot and dense (~10^4K, ~10^3/cc) shocked gas. The post-shock layer
first cools by efficient Ly alpha emission and contracts isobarically until
8000K. Whether the layer continues the isobaric contraction depends on the
density at this moment: if the density is high enough for collisionally
exciting H2 rovibrational levels (>10^4/cc), enhanced H2 collisional
dissociation suppresses the gas to cool further. In this case, the layer
fragments into massive (>10^5Msun) clouds, which collapse isothermally (~8000K)
by the Ly alpha cooling without subsequent fragmentation. As an outcome, SMSs
are expected to form and evolve eventually to seeds of supermassive black holes
(SMBH). By calculating thermal evolution of the post-shock gas, we delimit the
range of post-shock conditions for the SMS formation, which can be expressed
as: T>6000K/(n/10^4/cc) for n<10^4/cc and T>5000-6000K for n>10^4/cc, depending
somewhat on initial ionization degree. We found that metal enrichment does not
affect the above condition for metallicity below 10^-3Zsun if metals are in the
gas phase, while condensation of several percent of metals into dust decreases
this critical value of metallicity by an order of magnitude. Unlike the
previously proposed scenario for SMS formation, which postulates extremely
strong ultraviolet radiation to quench H2 cooling, our scenario naturally
explains the SMBH seed formation in the assembly process of the first galaxies,
even without such a strong radiation. | Weak lensing from self-ordering scalar fields: Cosmological defects result from cosmological phase transitions in the early
Universe and the dynamics reflects their symmetry-breaking mechanisms. These
cosmological defects may be probed through weak lensing effects because they
interact with ordinary matters only through the gravitational force. In this
paper, we investigate global textures by using weak lensing curl and B modes.
Non-topological textures are modeled by the non-linear sigma model (NLSM), and
induce not only the scalar perturbation but also vector and tensor
perturbations in the primordial plasma due to the nonlinearity in the
anisotropic stress of scalar fields. We show angular power spectra of curl and
B modes from both vector and tensor modes based on the NLSM. Furthermore, we
give the analytic estimations for curl and B mode power spectra. The amplitude
of weak lensing signals depends on a combined parameter $\epsilon^{2}_{v} =
N^{-1}\left( v/m_{\rm pl} \right)^{4}$ where $N$ and $v$ are the number of the
scalar fields and the vacuum expectation value, respectively. We discuss the
detectability of the curl and B modes with several observation specifications.
In the case of the CMB lensing observation without including the instrumental
noise, we can reach $\epsilon_{v} \approx 2.7\times 10^{-6}$. This constraint
is about 10 times stronger than the current one determined from the Planck. For
the cosmic shear observation, we find that the signal-to-noise ratio depends on
the mean redshift and the observing number of galaxies as $\propto z^{0.7}_{\rm
m}$ and $\propto N^{0.2}_{\rm g}$, respectively. In the study of textures using
cosmic shear observations, the mean redshift would be one of the key design
parameters. |
Observational evidence of fractality in the large-scale distribution of
galaxies: Using a sample of 133 991 galaxies distributed in the sky region $100^{\circ}
<\alpha<270^{\circ}$ and $7^{\circ}<\delta<65^{\circ}$, extracted from the SDSS
NASA/AMES Value Added Galaxy Catalog (AMES-VAGC), we estimate the fractal
dimension using two different methods. First, using an algorithm to estimate
the correlation dimension. The second method, in a novel approach, creates a
graph from the data and estimates the graph dimension purely from connectivity
information. In both methods we found a dimension $D\approx 2$ in scales below
20 Mpc, which agrees with previous works. This result shows the non-homogeneity
of galaxies distribution at certain scales. | Luminous Infrared Galaxies with the Submillimeter Array: II. Comparing
the CO(3-2) Sizes and Luminosities of Local and High-Redshift Luminous
Infrared Galaxies: We present a detailed comparison of the CO(3-2) emitting molecular gas
between a local sample of luminous infrared galaxies (U/LIRGs) and a high
redshift sample that comprises submm selected galaxies (SMGs), quasars, and
Lyman Break Galaxies (LBGs). The U/LIRG sample consists of our recent CO(3-2)
survey using the Submillimeter Array while the CO(3-2) data for the high
redshift population are obtained from the literature. We find that the
L(CO(3-2)) and L(FIR) relation is correlated over five orders of magnitude,
which suggests that the molecular gas traced in CO(3-2) emission is a robust
tracer of dusty star formation activity. The near unity slope of 0.93 +/- 0.03
obtained from a fit to this relation suggests that the star formation
efficiency is constant to within a factor of two across different types of
galaxies residing in vastly different epochs. The CO(3-2) size measurements
suggest that the molecular gas disks in local U/LIRGs (0.3 - 3.1 kpc) are much
more compact than the SMGs (3 - 16 kpc), and that the size scales of SMGs are
comparable to the nuclear separation (5 - 40 kpc) of the widely separated
nuclei of U/LIRGs in our sample. We argue from these results that the SMGs
studied here are predominantly intermediate stage mergers, and that the wider
line-widths arise from the violent merger of two massive gas-rich galaxies
taking place deep in a massive halo potential. |
The SEDs, Host Galaxies and Environments of Variability Selected AGN in
GOODS-S: Variability selection has been proposed as a powerful tool for identifying
both low-luminosity AGN and those with unusual SEDs. However, a systematic
study of sources selected in such a way has been lacking. In this paper, we
present the multi-wavelength properties of the variability selected AGN in
GOODS South. We demonstrate that variability selection indeed reliably
identifies AGN, predominantly of low luminosity. We find contamination from
stars as well as a very small sample of sources that show no sign of AGN
activity, their number is consistent with the expected false positive rate. We
also study the host galaxies and environments of the AGN in the sample.
Disturbed host morphologies are relatively common. The host galaxies span a
wide range in the level of ongoing star-formation. However, massive star-bursts
are only present in the hosts of the most luminous AGN in the sample. There is
no clear environmental preference for the AGN sample in general but we find
that the most luminous AGN on average avoid dense regions while some
low-luminosity AGN hosted by late-type galaxies are found near the centres of
groups. AGN in our sample have closer nearest neighbours than the general
galaxy population. We find no indications that major mergers are a dominant
triggering process for the moderate to low luminosity AGN in this sample. The
environments and host galaxy properties instead suggest secular processes, in
particular tidal processes at first passage and minor mergers, as likely
triggers for the objects studied. This study demonstrates the strength of
variability selection for AGN and gives first hints at possibly triggering
mechanisms for high-redshift low luminosity AGN. | MAGIC observations and multiwavelength properties of the quasar 3C279 in
2007 and 2009: Context. 3C 279, the first quasar discovered to emit VHE gamma-rays by the
MAGIC telescope in 2006, was reobserved by MAGIC in January 2007 during a major
optical flare and from December 2008 to April 2009 following an alert from the
Fermi space telescope on an exceptionally high gamma -ray state.
Aims. The January 2007 observations resulted in a detection on January 16
with significance 5.2 sigma, corresponding to a F(> 150 GeV) (3.8 \pm 0.8)
\cdot 10^-11 ph cm^-2 s^-1 while the overall data sample does not show
significant signal. The December 2008 - April 2009 observations did not detect
the source. We study the multiwavelength behavior of the source at the epochs
of MAGIC observations, collecting quasi-simultaneous data at optical and X-ray
frequencies and for 2009 also gamma-ray data from Fermi.
Methods. We study the light curves and spectral energy distribution of the
source. The spectral energy distributions of three observing epochs (including
the February 2006, which has been previously published in Albert et al. 2008a)
are modeled with one-zone inverse Compton models and the emission on January
16, 2007 also with two zone model and with a lepto-hadronic model.
Results. We find that the VHE gamma-ray emission detected in 2006 and 2007
challenges standard one-zone model, based on relativistic electrons in a jet
scattering broad line region photons, while the other studied models fit the
observed spectral energy distribution more satisfactorily. |
Parameterizing scalar-tensor theories for cosmological probes: We study the evolution of density perturbations for a class of $f(R)$ models
which closely mimic $\Lambda$CDM background cosmology. Using the quasi-static
approximation, and the fact that these models are equivalent to scalar-tensor
gravity, we write the modified Friedmann and cosmological perturbation
equations in terms of the mass $M$ of the scalar field. Using the perturbation
equations, we then derive an analytic expression for the growth parameter
$\gamma$ in terms of $M$, and use our result to reconstruct the linear matter
power spectrum. We find that the power spectrum at $z \sim 0$ is characterized
by a tilt relative to its General Relativistic form, with increased power on
small scales. We discuss how one has to modify the standard, constant $\gamma$
prescription in order to study structure formation for this class of models.
Since $\gamma$ is now scale and time dependent, both the amplitude and transfer
function associated with the linear matter power spectrum will be modified. We
suggest a simple parameterization for the mass of the scalar field, which
allows us to calculate the matter power spectrum for a broad class of $f(R)$
models. | Initial Results from the Nobeyama Molecular Gas Observations of Distant
Bright Galaxies: We present initial results from the CO survey toward high redshift galaxies
using the Nobeyama 45m telescope. Using the new wide bandwidth spectrometer
equipped with a two-beam SIS receiver, we have robust new detections of three
high redshift (z=1.6-3.4) submillimeter galaxies (SXDF 1100.001, SDP9, and
SDP17), one tentative detection (SDSS J160705+533558), and one non-detection
(COSMOS-AzTEC1). The galaxies observed during the commissioning phase are
sources with known spectroscopic redshifts from previous optical or from
wide-band submm spectroscopy. The derived molecular gas mass and line widths
from Gaussian fits are ~10^11 Msun and 430-530 km/s, which are consistent with
previous CO observations of distant submm galaxies and quasars. The
spectrometer that allows a maximum of 32 GHz instantaneous bandwidth will
provide new science capabilities at the Nobeyama 45m telescope, allowing us to
determine redshifts of bright submm selected galaxies without any prior
redshift information. |
New Developments in Spiral Structure Theory: After a short review of the principal theories of spiral structure in
galaxies, I describe two new developments. First, it now seems clear that
linear theory cannot yield a full description for the development of spiral
patterns because N-body simulations suggest that non-linear effects manifest
themselves at a relative overdensity of ~2%, which is well below the believed
spiral amplitudes in galaxies. Second, I summarize the evidence that some stars
in the solar neighborhood have been scattered at an inner Lindblad resonance.
This evidence strongly supports a picture of spirals as a recurring cycle of
transient instabilities, each caused by resonant scattering by a previous wave. | Window function dependence of the novel mass function of primordial
black holes: We investigate the ambiguity of the novel mass function of primordial black
holes, which has succeeded in identifying the black hole mass in a given
configuration of fluctuations, due to the choice of window function of smoothed
density fluctuations. We find that while the window function dependence of the
exponential factor in the novel mass function is the same as the one in the
conventional mass function around the top-hat scale, the dependences are
different on other scales, which leads to the narrower mass function in the
novel formulation for some window functions. |
How informative are summaries of the cosmic 21-cm signal?: The cosmic 21-cm signal will bring data-driven advances to studies of the
Cosmic Dawn (CD) and Epoch of Reionization (EoR). Radio telescopes such as the
SKA will eventually map the HI fluctuations over the first billion years - the
majority of our observable Universe. With such large data volumes, it becomes
increasingly important to develop "optimal" summary statistics, allowing us to
learn as much as possible about the CD and EoR. In this work we compare the
constraining power of several 21-cm summary statistics, using the determinant
of the Fisher information matrix, $\det F$. Since we do not have an established
"fiducial" model for the astrophysics of the first galaxies, we compute the
distribution of $\det F$ across the prior volume. Using a large database of
cosmic 21-cm lightcones that include realizations of telescope noise, we
compare the following summaries: (i) the spherically-averaged power spectrum
(1DPS), (ii) the cylindrically-averaged power spectrum (2DPS), (iii) the 2D
Wavelet scattering transform (WST), (iv) a recurrent neural network (RNN), (v)
an information-maximizing neural network (IMNN), and (vi) the combination of
2DPS and IMNN. Our best performing individual summary is the 2DPS, having
relatively high Fisher information throughout parameter space. Although capable
of achieving the highest Fisher information for some parameter choices, the
IMNN does not generalize well, resulting in a broad distribution. Our best
results are achieved with the concatenation of the 2DPS and IMNN. The
combination of only these two complimentary summaries reduces the recovered
parameter variances on average by factors of $\sim$6.5 - 9.5, compared with
using each summary independently. Finally, we point out that that the common
assumption of a constant covariance matrix when doing Fisher forecasts using
21-cm summaries can significantly underestimate parameter constraints. | Crab nebula at 260 GHz with the NIKA2 polarimeter. Implications for the
polarization angle calibration of future CMB experiments: The quest for primordial gravitational waves enclosed in the Cosmic Microwave
Background (CMB) polarization B-modes signal motivates the development of a new
generation of high sensitive experiments (e.g. CMB-S4, LiteBIRD) that would
allow them to detect its imprint.Neverthless, this will be only possible by
ensuring a high control of the instrumental systematic effects and an accurate
absolute calibration of the polarization angle. The Crab nebula is known to be
a polarization calibrator on the sky for CMB experiments, already used for the
Planck satellite it exhibits a high polarized signal at microwave wavelengths.
In this work we present Crab polarization observations obtained at the central
frequency of 260 GHz with the NIKA2 instrument and discuss the accuracy needed
on such a measurement to improve the constraints on the absolute angle
calibration for CMB experiments. |
Homogeneity and isotropy in the 2MASS Photometric Redshift catalogue: Using the 2MASS Photometric Redshift catalogue we perform a number of
statistical tests aimed at detecting possible departures from statistical
homogeneity and isotropy in the large-scale structure of the Universe. Making
use of the angular homogeneity index, an observable proposed in a previous
publication, as well as studying the scaling of the angular clustering and
number counts with magnitude limit, we place constraints on the fractal nature
of the galaxy distribution. We find that the statistical properties of our
sample are in excellent agreement with the standard cosmological model, and
that it reaches the homogeneous regime significantly faster than a class of
fractal models with dimensions $D<2.75$. As part of our search for systematic
effects, we also study the presence of hemispherical asymmetries in our data,
finding no significant deviation beyond those allowed by the concordance model. | Morphological Annotations for Groups in the FIRST Database: The morphology of selected groups of sources in the FIRST (Faint Images of
the Radio Sky at Twenty Centimeters) survey and catalog is examined. Sources in
the FIRST catalog (April 2003 release, 811117 entries) were sorted into
singles, doubles, triples and groups of higher-count membership based on a
proximity criteria. The 7106 groups with four or more components were examined
individually for bent types including, but not limited to, wide-angle tail
(WAT) and narrow-angle tail (NAT) types. In the process of this examination,
ring, double-double (DD), X-shaped, hybrid morphology (HYMOR), giant radio
sources (GRS), and the herein described W-shaped and tri-axial morphology
systems were also identified. For the convenience of the reader separate tables
for distinctive types were generated. A few curiosities were found. For the
16,950 three-component groups and 74,788 two-component groups, catalogs with
probability estimates for bent classification, as determined by pattern
recognition techniques, are presented. |
Two New Catalogues of Superclusters of Abell/ACO Galaxy Clusters out to
redshift 0.15: We present two new catalogues of superclusters of galaxies out to a redshit
of z = 0.15, based on the Abell/ACO cluster redshift compilation maintained by
one of us (HA). The first of these catalogues, the all-sky Main SuperCluster
Catalogue (MSCC), is based on only the rich (A-) Abell clusters, and the second
one, the Southern SuperCluster Catalogue (SSCC), covers declinations delta <
-17 deg and includes the supplementary Abell S-clusters. A tunable
Friends-of-Friends (FoF) algorithm was used to account for the cluster density
decreasing with redshift and for different selection functions in distinct
areas of the sky. We present the full list of Abell clusters used, together
with their redshifts and supercluster memberships and including the isolated
clusters. The SSCC contains about twice the number of superclusters than MSCC
for delta < -17 deg, which we found to be due to: (1) new superclusters formed
by A-clusters in their cores and surrounded by S-clusters (50%), (2) new
superclusters formed by S-clusters only (40%), (3) redistribution of member
clusters by fragmentation of rich (multiplicity m > 15) superclusters (8%), and
(4) new superclusters formed by the connection of A-clusters through bridges of
S-clusters (2%). Power-law fits to the cumulative supercluster multiplicity
function yield slopes of alpha = -2.0 and alpha = -1.9 for MSCC and SSCC
respectively. This power-law behavior is in agreement with the findings for
other observational samples of superclusters, but not with that of catalogues
based on cosmological simulations. | A fast and accurate method to compute the mass return from multiple
stellar populations: The mass returned to the ambient medium by aging stellar populations over
cosmological times sums up to a significant fraction (20% - 30% or more) of
their initial mass. This continuous mass injection plays a fundamental role in
phenomena such as galaxy formation and evolution, fueling of supermassive black
holes in galaxies and the consequent (negative and positive) feedback
phenomena, and the origin of multiple stellar populations in globular clusters.
In numerical simulations the calculation of the mass return can be time
consuming, since it requires at each time step the evaluation of a convolution
integral over the whole star formation history, so the computational time
increases quadratically with the number of time-steps. The situation can be
especially critical in hydrodynamical simulations, where different grid points
are characterized by different star formation histories, and the gas cooling
and heating times are shorter by orders of magnitude than the characteristic
stellar lifetimes. In this paper we present a fast and accurate method to
compute the mass return from stellar populations undergoing arbitrarily
complicated star formation histories. At each time-step the mass return is
calculated from its value at the previous time, and the star formation rate
over the last time-step only. Therefore in the new scheme there is no need to
store the whole star formation history, and the computational time increases
linearly with the number of time-steps. |
HI as a Probe of the Large Scale Structure in the Post-Reionization
Universe: Visibility Correlations and Prospects for Detection: Simulated maps of the HI distribution in the post-reionization era are used
to study the prospects for detection with existing and upcoming radio
telescopes. We consider detection in the redshifted radiation from the
hyperfine transition with a rest frame frequency of 1420 MHz. Possibility of a
statistical detection using visibility correlations is discussed. We show that
the MWA (Murchison Widefield Array) and the GMRT (Giant
Meterwave Radio Telescope) can potentially detect signal from the HI
distribution at high redshifts. MWA can detect visibility correlations at large
angular scales at all redshifts accessible to it in the post-reionization era.
The GMRT can detect visibility correlations at lower redshifts, specifically
there is a strong case for a survey at z = 1.3. We also discuss prospects for
direct detection of rare peaks in the HI distribution using the GMRT. We show
that direct detection should be possible with integration time that is
comparable to, or even less than, the time required for a statistical
detection. Specifically, it is possible to make a statistical detection of the
HI distribution by measuring the visibility correlation, and, direct detection
of rare peaks in the HI distribution using the GMRT in less than 1000 hours of
observations. | AGN Feedback Driven Molecular Outflow in NGC 1266: NGC 1266 is a nearby field galaxy observed as part of the ATLAS3D survey
(Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc)
molecular disk and a mass-loaded molecular outflow driven by the AGN (Alatalo
et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed
a compact (diameter < 1.2 pc), high bright- ness temperature continuum source
most consistent with a low-level AGN origin. The VLBA continuum source is
positioned at the center of the molecular disk and may be responsible for the
expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven
molecular outflow in NGC 1266 supports the picture in which AGNs do play a
significant role in the quenching of star formation and ultimately the
evolution of the red sequence of galaxies. |
Shapes and alignments of dark matter haloes and their brightest cluster
galaxies in 39 strong lensing clusters: We study shapes and alignments of 45 dark matter (DM) haloes and their
brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from
Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble
(CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of
the DM haloes by strong gravitational lensing, whereas BCG shapes are derived
from their light profiles in Hubble Space Telescope images. Our measurements
from a large sample of massive clusters presented here provide new constraints
on dark matter and cluster astrophysics. We find that DM haloes are on average
highly elongated with the mean ellipticity of $0.482\pm 0.028$, and position
angles of major axes of DM haloes and their BCGs tend to be aligned well with
the mean value of alignment angles of $22.2\pm 3.9$ deg. We find that DM haloes
in our sample are on average more elongated than their BCGs with the mean
difference of their ellipticities of $0.11\pm 0.03$. In contrast, the
Horizon-AGN cosmological hydrodynamical simulation predicts on average similar
ellipticities between DM haloes and their central galaxies. While such a
difference between the observations and the simulation may well be explained by
the difference of their halo mass scales, other possibilities include the bias
inherent to strong lensing measurements, limited knowledge of baryon physics,
or a limitation of cold dark matter. | Cold gas in the inner regions of intermediate redshift clusters: Determining gas content and star formation rate has known remarkable progress
in field galaxies, but has been much less investigated in galaxies inside
clusters. We present the first CO observations of luminous infrared galaxies
(LIRGs) inside the virial radii of two intermediate redshift clusters,
CL1416+4446 (z=0.397) and CL0926+1242 (z=0.489). We detect three galaxies at
high significance (5 to 10 sigma), and provide robust estimates of their CO
luminosities, L'CO. In order to put our results into a general context, we
revisit the relation between cold and hot gas and stellar mass in nearby field
and cluster galaxies. We find evidence that at fixed LIR (or fixed stellar
mass), the frequency of high L'CO galaxies is lower in clusters than in the
field, suggesting environmental depletion of the reservoir of cold gas. The
level of star formation activity in a galaxy is primarily linked to the amount
of cold gas, rather than to the galaxy mass or the lookback time. In clusters,
just as in the field, the conversion between gas and stars seems universal. The
relation between LIR and L'CO for distant cluster galaxies extends the relation
of nearby galaxies to higher IR luminosities. Nevertheless, the intermediate
redshift galaxies fall well within the dispersion of the trend defined by local
systems. Considering that L'CO is generally derived from the CO(1-0) line and
sensitive to the vast majority of the molecular gas in the cold interstellar
medium of galaxies, but less to the part which will actually be used to form
stars, we suggest that molecular gas can be stripped before the star formation
rate is affected. Combining the sample of Geach et al. (2009, 2011) and ours,
we find evidence for a decrease in CO towards the cluster centers. This is the
first hint of an environmental impact on cold gas at intermediate redshift. |
Resolving the Far-IR Line Deficit: Photoelectric Heating and Far-IR Line
Cooling in NGC 1097 and NGC 4559: The physical state of interstellar gas and dust is dependent on the processes
which heat and cool this medium. To probe heating and cooling of the ISM over a
large range of infrared surface brightness, on sub-kiloparsec scales, we employ
line maps of [C \ii] 158 $\mu$m, [O \one] 63 $\mu$m, and [N \ii] 122 $\mu$m in
NGC 1097 and NGC 4559, obtained with the PACS spectrometer onboard {\it
Herschel}. We matched new observations to existing Spitzer-IRS data that trace
the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at
small scales in these galaxies that the canonical measure of photoelectric
heating efficiency, ([C \ii] + [O \one])/TIR, decreases as the far-infrared
color, $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100 $\mu$m), increases. In contrast,
the ratio of far-infrared (far-IR) cooling to total PAH emission, ([C \ii] + [O
\one])/PAH, is a near constant $\sim$6% over a wide range of far-infrared
color, 0.5 \textless\ $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100 $\mu$m) $\lesssim$
0.95. In the warmest regions, where $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100
$\mu$m) $\gtrsim$ 0.95, the ratio ([C \ii] + [O \one])/PAH drops rapidly to 4%.
We derived representative values of the local UV radiation density, $G_0$, and
the gas density, $n_H$, by comparing our observations to models of
photodissociation regions. The ratio $G_0/n_H$, derived from fine-structure
lines, is found to correlate with the mean dust-weighted starlight intensity,
$<U>$ derived from models of the IR SED. Emission from regions that exhibit a
line deficit is characterized by an intense radiation field, indicating that
small grains are susceptible to ionization effects. We note that there is a
shift in the 7.7 / 11.3 $\mu$m PAH ratio in regions that exhibit a deficit in
([C \ii] + [O \one])/PAH, suggesting that small grains are ionized in these
environments. | Far-infrared Fine-Structure Line Diagnostics of Ultraluminous Infrared
Galaxies: We present Herschel observations of six fine-structure lines in 25
Ultraluminous Infrared Galaxies at z<0.27. The lines, [O III]52, [N III]57, [O
I]63, [N II]122, [O I]145, and [C II]158, are mostly single gaussians with
widths <600 km s-1 and luminosities of 10^7 - 10^9 Solar. There are deficits in
the [O I]63/L_IR, [N II]/L_IR, [O I]145/L_IR, and [C II]/L_IR ratios compared
to lower luminosity systems. The majority of the line deficits are consistent
with dustier H II regions, but part of the [C II] deficit may arise from an
additional mechanism, plausibly charged dust grains. This is consistent with
some of the [C II] originating from PDRs or the ISM. We derive relations
between far-IR line luminosities and both IR luminosity and star formation
rate. We find that [N II] and both [O I] lines are good tracers of IR
luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR
luminosity and star formation rate, and does not improve as a tracer of either
quantity if the [C II] deficit is accounted for. The continuum luminosity
densities also correlate with IR luminosity and star formation rate. We derive
ranges for the gas density and ultraviolet radiation intensity of 10^1 < n <
10^2.5 and 10^2.2 < G_0 < 10^3.6, respectively. These ranges depend on optical
type, the importance of star formation, and merger stage. We do not find
relationships between far-IR line properties and several other parameters; AGN
activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that
these far-IR lines arise from gas heated by starlight, and that they are not
strongly influenced by AGN activity. |
The clustering of massive Primordial Black Holes as Dark Matter:
measuring their mass distribution with Advanced LIGO: The recent detection by Advanced LIGO of gravitational waves (GW) from the
merging of a binary black hole system sets new limits on the merging rates of
massive primordial black holes (PBH) that could be a significant fraction or
even the totality of the dark matter in the Universe. aLIGO opens the way to
the determination of the distribution and clustering of such massive PBH. If
PBH clusters have a similar density to the one observed in ultra-faint dwarf
galaxies, we find merging rates comparable to aLIGO expectations. Massive PBH
dark matter predicts the existence of thousands of those dwarf galaxies where
star formation is unlikely because of gas accretion onto PBH, which would
possibly provide a solution to the missing satellite and too-big-to-fail
problems. Finally, we study the possibility of using aLIGO and future GW
antennas to measure the abundance and mass distribution of PBH in the range [5
- 200] Msun to 10\% accuracy. | FIR/submm spectroscopy with Herschel: first results from the VNGS and
H-ATLAS surveys: The FIR/submm window is one of the least-studied regions of the
electromagnetic spectrum, yet this wavelength range is absolutely crucial for
understanding the physical processes and properties of the ISM in galaxies. The
advent of the Herschel Space Observatory has opened up the entire FIR/submm
window for spectroscopic studies. We present the first FIR/submm spectroscopic
results on both nearby and distant galaxies obtained in the frame of two
Herschel key programs: the Very Nearby Galaxies Survey and the Herschel ATLAS. |
Lyman-alpha Emission From Cosmic Structure I: Fluorescence: We present predictions for the fluorescent Lyman-alpha emission signature
arising from photoionized, optically thick structures in Smoothed Particle
Hydrodynamic (SPH) cosmological simulations of a Lambda-CDM universe using a
Monte Carlo Lyman-alpha radiative transfer code. We calculate the expected
Lyman-alpha image and 2-dimensional spectra for gas exposed to a uniform
ultraviolet ionizing background as well as gas exposed additionally to the
photoionizing radiation from a local quasar, after correcting for the
self-shielding of hydrogen. As a test of our numerical methods and for
application to current observations, we examine simplified analytic structures
that are uniformly or anisotropically illuminated. We compare these results
with recent observations. We discuss future observing campaigns on large
telescopes and realistic strategies for detecting fluorescence owing to the
ambient metagalactic ionization and in regions close to bright quasars. While
it will take hundreds of hours on the current generation of telescopes to
detect fluorescence caused by the ultraviolet background (UVB) alone, our
calculations suggest that of order ten sources of quasar-induced fluorescent
Lyman-alpha emission should be detectable after a 10 hour exposure in a 10
arcmin^2 field around a bright quasar. These observations will help probe the
physical conditions in the densest regions of the intergalactic medium as well
as the temporal light curves and isotropy of quasar radiation. | The ages of stellar populations in a warm dark matter universe: By means of a semi-analytic model of galaxy formation, we show how the local
observed relation between age and galactic stellar mass is affected by assuming
a DM power spectrum with a small-scale cutoff. We compare results obtained by
means of both a Lambda-cold dark matter (LambdaCDM) and a Lambda-warm dark
matter (LambdaWDM) power spectrum - suppressed with respect to the LambdaCDM at
scales below ~ 1 Mpc. We show that, within a LWDM cosmology with a thermal
relic particle mass of 0.75 keV, both the mass-weighted and the
luminosity-weighted age-mass relations are steeper than those obtained within a
LambdaCDM universe, in better agreement with the observed relations. Moreover,
both the observed differential and cumulative age distributions are better
reproduced within a LambdaWDM cosmology. In such a scenario, star formation
appears globally delayed with respect to the LambdaCDM, in particular in
low-mass galaxies. The difficulty of obtaining a full agreement between model
results and observations is to be ascribed to our present poor understanding of
baryonic physics. |
Detection of the Missing Baryons toward the Sightline of H1821+643: Based on constraints from Big Bang nucleosynthesis and the cosmic microwave
background, the baryon content of the high-redshift Universe can be precisely
determined. However, at low redshift, about one-third of the baryons remain
unaccounted for, which poses the long-standing missing baryon problem. The
missing baryons are believed to reside in large-scale filaments in the form of
warm-hot intergalactic medium (WHIM). In this work, we employ a novel stacking
approach to explore the hot phases of the WHIM. Specifically, we utilize the
470 ks Chandra LETG data of the luminous quasar, H1821+643, along with previous
measurements of UV absorption line systems and spectroscopic redshift
measurements of galaxies toward the quasar's sightline. We repeatedly blueshift
and stack the X-ray spectrum of the quasar corresponding to the redshifts of
the 17 absorption line systems. Thus, we obtain a stacked spectrum with $8.0$
Ms total exposure, which allows us to probe X-ray absorption lines with
unparalleled sensitivity. Based on the stacked data, we detect an OVII
absorption line that exhibits a Gaussian line profile and is statistically
significant at the $3.3 \sigma$ level. Since the redshifts of the UV absorption
line systems were known a priori, this is the first definitive detection of an
X-ray absorption line originating from the WHIM. The equivalent width of the
OVII line is $(4.1\pm1.3) \ \mathrm{m\AA}$, which corresponds to an OVII column
density of $(1.4\pm0.4)\times10^{15} \ \mathrm{cm^{-2}}$. We constrain the
absorbing gas to have a density of $n_{\rm H} = (1-2)\times10^{-6} \
\rm{cm^{-3}}$ for a single WHIM filament. We derive $\Omega_{\rm b} \rm(O\,VII)
= (0.0023 \pm 0.0007) \, \left[ f_{O\,VII} \, {Z/Z_{\odot}} \right]^{-1}$ for
the cosmological mass density of OVII, assuming that all 17 systems contribute
equally. | Detecting relic gravitational waves in the CMB: Comparison of different
methods: In this paper, we discuss the constraint on the relic gravitational waves by
both temperature and polarization anisotropies power spectra of cosmic
microwave background radiation. Taking into account the instrumental noises of
Planck satellite, we calculate the signal-to-noise ratio $S/N$ by the
simulation and the analytic approximation methods. We find that, comparing with
the $BB$ channel, the value of $S/N$ is much improved in the case where all the
power spectra, $TT$, $TE$, $EE$ and $BB$, are considered. If the noise power
spectra of Planck satellite increase for some reasons, the value of $S/N$ in
$BB$ channel is much reduced. However, in the latter case where all the power
spectra of cosmic microwave background radiation are considered, the value of
$S/N$ is less influenced. We also find that the free parameters $A_s$, $n_s$
and $n_t$ have little influence on the value of $S/N$ in both cases. |
Radius-Dependent Spin Transition of Dark Matter Halos: A numerical detection of the radius-dependent spin transition of dark matter
halos is reported. Analyzing the data from the IllustrisTNG simulations, we
measure the halo spin vectors at several inner radii within the virial
boundaries and investigate their orientations in the principal frames of the
tidal and velocity shear fields, called the Tweb and Vweb, respectively. The
halo spin vectors in the high-mass section exhibit a transition from the Tweb
intermediate to major principal axes as they are measured at more inner radii,
which holds for both of the dark matter and baryonic components. The radius
threshold at which the transition occurs depends on the smoothing scale,
$R_{f}$, becoming larger as $R_{f}$ decreases. For the case of the Vweb, the
occurrence of the radius-dependent spin transition is witnessed only when
$R_{f}\ge 1\, h^{-1}$Mpc. Repeating the same analysis but with the vorticity
vectors, we reveal a critical difference from the spins. The vorticity vectors
are always perpendicular to the Tweb (Vweb) major principal axes, regardless of
$R_{f}$, which indicates that the halo inner spins are not strongly affected by
the generation of vorticity. It is also shown that the halo spins, as well as
the Tweb (Vweb) principal axes, have more directional coherence over a wide
range of radial distances in the regions where the vorticity vectors have
higher magnitudes. The physical interpretations and implications of our results
are discussed. | First detection of a virial shock with SZ data: implication for the mass
accretion rate of Abell 2319: Shocks produced by the accretion of infalling gas in the outskirt of galaxy
clusters are expected in the hierarchical structure formation scenario, as
found in cosmological hydrodynamical simulations. Here, we report the detection
of a shock front at a large radius in the pressure profile of the galaxy
cluster A2319 at a significance of $8.6\sigma$, using Planck thermal
Sunyaev-Zel'dovich data. The shock is located at $(2.93 \pm 0.05) \times
R_{500}$ and is not dominated by any preferential radial direction. Using a
parametric model of the pressure profile, we derive a lower limit on the Mach
number of the infalling gas, $\mathcal{M} > 3.25$ at 95\% confidence level.
These results are consistent with expectations derived from hydrodynamical
simulations. Finally, we use the shock location to constrain the accretion rate
of A2319 to $\dot{M} \simeq (1.4 \pm 0.4) \times 10^{14}$ M$_\odot$ Gyr$^{-1}$,
for a total mass, $M_{200} \simeq 10^{15}$ M$_\odot$. |
Neural networks and standard cosmography with newly calibrated high
redshift GRB observations: Gamma-ray bursts (GRBs) detected at high redshift can be used to trace the
cosmic expansion history. However, the calibration of their luminosity
distances is not an easy task in comparison to Type Ia Supernovae (SNeIa). To
calibrate these data, correlations between their luminosity and other observed
properties of GRBs need to be identified, and we must consider the validity of
our assumptions about these correlations over their entire observed redshift
range. In this work, we propose a new method to calibrate GRBs as cosmological
distance indicators using SNeIa observations with a machine learning
architecture. As well we include a new data GRB calibrated sample using
extended cosmography in a redshift range above $z>3.6$. An overview of this
machine learning technique was developed in [1] to study the evolution of dark
energy models at high redshift. The aim of the method developed in this work is
to combine two networks: a Recurrent Neural Network (RNN) and a Bayesian Neural
Network (BNN). Using this computational approach, denoted RNN+BNN, we extend
the network's efficacy by adding the computation of covariance matrices to the
Bayesian process. Once this is done, the SNeIa distance-redshift relation can
be tested on the full GRB sample and therefore used to implement a cosmographic
reconstruction of the distance-redshift relation in different regimes. Thus,
our newly-trained neural network is used to constrain the parameters describing
the kinematical state of the Universe via a cosmographic approach at high
redshifts (up to $z\approx 10$), wherein we require a very minimal set of
assumptions on the deep learning architecture itself that do not rely on
dynamical equations for any specific theory of gravity. | Exploring Evaporating Primordial Black Holes with Gravitational Waves: Primordial black holes (PBHs) from the early Universe have been connected
with the nature of dark matter and can significantly affect cosmological
history. We show that coincidence dark radiation and density fluctuation
gravitational wave signatures associated with evaporation of $\lesssim10^9$ g
PBHs can be used to explore and obtain important hints about the formation
mechanisms of spinning and non-spinning PBHs spanning orders of magnitude in
mass-range, which is challenging to do otherwise. |
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