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Spectator stresses and CMB observables: The large-scale curvature perturbations induced by spectator anisotropic
stresses are analyzed across the matter-radiation transition. It is assumed
that the anisotropic stress is associated with a plasma component whose energy
density is subdominant both today and prior to photon decoupling. The
enforcement of the momentum constraint and the interplay with the neutrino
anisotropic stress determine the regular initial conditions of the
Einstein-Boltzmann hierarchy. The Cosmic Microwave Background observables have
shapes and phases which differ both from the ones of the conventional adiabatic
mode as well as from their non-adiabatic counterparts. | The X-Ray Zurich Environmental Study (X-ZENS). II. X-ray Observations of
the Diffuse Intragroup Medium in Galaxy Groups: We present the results of a pilot XMM-$Newton$ and $Chandra$ program aimed at
studying the diffuse intragroup medium (DIM) of optically-selected nearby
groups from the Zurinch ENvironmental Study (ZENS) catalog. The groups are in a
narrow mass range about $10^{13}M_\odot$, a mass scale at which the interplay
between the DIM and the group member galaxies is still largely unprobed. X-ray
emission from the DIM is detected in the energy band 0.5--2 keV with flux $\le
10^{-14}$ erg cm$^{-1}$ s$^{-1}$, which is one order of magnitude fainter than
for typical ROSAT groups (RASS). For many groups we set upper limits to the
X-ray luminosity, indicating that the detections are likely probing the upper
envelope of the X-ray emitting groups. We find evidence for our optically
selected groups to be under-luminous with respect to predictions from X-ray
scaling relations. X-ray mass determinations are in best agreement with those
based on the member galaxies bulge luminosity, followed by their total optical
luminosity and velocity dispersion. We measure a stellar mass fraction with a
median value of about 1$\%$, with a contribution from the most massive galaxies
between 30 to 50 \%. Optical and X-ray data give often complementary answers
concerning the dynamical state of the groups, and are essential for a complete
picture of the system. Extending this pilot program to a larger sample of
groups is mandatory to unveil any imprint of interaction between member
galaxies and DIM in halo potentials of key importance for
environmentally-driven galactic evolution. |
Astrometric requirements for strong lensing time-delay cosmography: The time delay between the arrival of photons of multiple images of time
variable sources can be used to constrain absolute distances in the Universe
(Refsdal 1964), and in turn obtain a direct estimate of the Hubble constant and
other cosmological parameters. To convert the time delay into distances, it is
well known that the gravitational potential of the main deflector and the
contribution of the matter along the line-of-sight need to be known to a
sufficient level of precision. In this paper, we discuss a new astrometric
requirement that is becoming important as time-delay cosmography improves in
precision and accuracy with larger samples, and better data and modelling
techniques. We derive an analytic expression for the propagation of astrometric
uncertainties on the multiple image positions into the inference of the Hubble
constant and derive requirements depending on image separation and relative
time delay. We note that this requirement applies equally to the image position
measurements and to the accuracy of the model in reproducing them. To
illustrate the requirement, we discuss some example lensing configurations and
highlight that, especially for time delays of order 10 days or shorter, the
relative astrometric requirement is of order milli-arcseconds, setting a tight
requirement on both measurements and models. With current optical infrared
technology, astrometric uncertainties may be the dominant limitation for strong
lensing cosmography in the small image-separation regime when high-precision
time-delays become accessible. | Anti-truncated stellar light profiles in the outer regions of STAGES
spiral galaxies: bulge or disc related?: We present a comparison of azimuthally averaged radial surface brightness
mu(r) profiles and analytical bulge-disc decompositions (de Vaucouleurs,
r^(1/4) bulge plus exponential disc) for spiral galaxies using Hubble Space
Telescope/Advanced Camera for Surveys V-band imaging from the Space Telescope
A901/2 Galaxy Evolution Survey (STAGES). In the established classification
scheme, antitruncated mu(r) profiles (Type III) have a broken exponential disc
with a shallower region beyond the break radius r_brk. The excess light at
large radii (r > r_brk) can either be caused by an outer exponential disc (Type
III-d) or an extended spheroidal component (Type III-s). Using our comparisons,
we determine the contribution of bulge light at r > r_brk for a large sample of
78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations
(mu_brk > 24 mag arcsec^-2). In the majority of cases (~85 per cent), evidence
indicates that excess light at r > r_brk is related to an outer shallow disc
(Type III-d). Here, the contribution of bulge light at r > r_brk is either
negligible (~70 per cent) or too little to explain the antitruncation (~15 per
cent). However in the latter cases, bulge light can affect the measured disc
properties (e.g. mu_brk, outer scalelength). In the remaining cases (~15 per
cent), light at r > r_brk is dominated by the bulge (Type III-s). Here, for
most cases the bulge profile dominates at all radii and only occasionally (3
galaxies, ~5 per cent) extends beyond that of a dominant disc and explains the
excess light at r > r_brk. We thus conclude that in the vast majority of cases
antitruncated outer discs cannot be explained by bulge light and thus remain a
pure disc phenomenon. |
The SEDs and Host Galaxies of the dustiest GRB afterglows: (Abridged) Until recently the information inferred from gamma-ray burst
follow-up observations was mostly limited to optically bright afterglows,
biasing all demographic studies against sight-lines that contain large amounts
of dust. Here, we present GRB afterglow and host observations for a sample of
bursts that are exemplary of previously missed ones because of high visual
extinction along the sight-line. This facilitates an investigation of the
properties, geometry and location of the absorbing dust of these
poorly-explored host galaxies, and a comparison to hosts from
optically-selected samples. The hosts of the dustiest afterglows are diverse in
their properties, but on average redder, more luminous and massive than the
hosts of optically-bright events. We hence probe a different galaxy population,
suggesting that previous host samples miss most of the massive,
chemically-evolved and metal-rich members. This also indicates that the dust
along the sight-line is often related to host properties, and thus probably
located in the diffuse ISM or interstellar clouds and not in the immediate GRB
environment. Some of the hosts in our sample, are blue, young or of small
stellar mass illustrating that even apparently non-extinguished galaxies
possess very dusty sight-lines due to a patchy dust distribution. The presented
observations establish a population of luminous, massive and correspondingly
chemically-evolved GRB hosts. This suggests that GRBs trace the global
star-formation rate better than studies based on optically-selected host
samples indicate, and the previously-claimed deficiency of high-mass host
galaxies was at least partially a selection effect. | Screenings in Modified Gravity: a perturbative approach: We present a formalism to study screening mechanisms in modified theories of
gravity via perturbative methods in different cosmological scenarios. We
consider Einstein frame posed theories that are recast as Jordan frame
theories, where a known formalism is employed, though the resulting
non-linearities of the Klein-Gordon equation acquire an explicit coupling
between matter and the scalar field, which is not present in Jordan frame
theories. The obtained growth functions are then separated in screening and
non-screened contributions to facilitate its analysis. This allows us to
compare several theoretical models and to recognize patterns which can be used
to differentiate models and their screening mechanisms. In particular, we find
anti-screening features in the Symmetron model. In opposition, chameleon type
theories, both in the Jordan and in the Einstein frame, always present a
screening behaviour. Up to third order in perturbation, we find no
anti-screening behaviour in theories with a Vainshtein mechanism, such as the
DGP and the cubic Galileon. |
Coupled Dark Energy field variation: The variation of the dark energy field is found under the assumption that the
dark energy is parametric and interacts with the cold dark matter. Considering
that the variation of the field could not exceed the Planck mass, we obtain
bounds on the coupling and adiabatic coefficients. Three parameterizations of
the adiabatic coefficients are considered and two coupling terms where the
energy flows from dark energy to dark matter, or the other way around. | Bispectra from two-field inflation using the long-wavelength formalism: We use the long-wavelength formalism to compute the bispectral
non-Gaussianity produced in two-field inflation. We find an exact result that
is used as the basis of numerical studies, and an explicit analytical slow-roll
expression for several classes of potentials that gives insight into the origin
and importance of the various contributions to fNL. We also discuss the
momentum dependence of fNL. Based on these results we find a simple model that
produces a relatively large non-Gaussianity. We show that the long-wavelength
formalism is a viable alternative to the standard delta-N formalism, and can be
preferable to it in certain situations. |
Revisiting Cosmological parameter estimation: Constraining theoretical models with measuring the parameters of those from
cosmic microwave background (CMB) anisotropy data is one of the most active
areas in cosmology. WMAP, Planck and other recent experiments have shown that
the six parameters standard $\Lambda$CDM cosmological model still best fits the
data. Bayesian methods based on Markov-Chain Monte Carlo (MCMC) sampling have
been playing leading role in parameter estimation from CMB data. In one of the
recent studies \cite{2012PhRvD..85l3008P} we have shown that particle swarm
optimization (PSO) which is a population based search procedure can also be
effectively used to find the cosmological parameters which are best fit to the
WMAP seven year data. In the present work we show that PSO not only can find
the best-fit point, it can also sample the parameter space quite effectively,
to the extent that we can use the same analysis pipeline to process PSO sampled
points which is used to process the points sampled by Markov Chains, and get
consistent results. We also present implementations of downhill-simplex Method
of Nelder and Mead and Powell's method of Bound Optimization BY Quadratic
Approximation (BOBYQA) in this work for cosmological parameter estimation, and
compare these methods with PSO. Since PSO has the advantage that it only needs
the search range and does not need covariance-matrix, starting point or any
other quantity which depend on the final results, it can be quite useful for a
blind search of the best fit parameters. Apart from that, PSO is based on a
completely different algorithm so it can supplement MCMC methods. We use PSO to
estimate parameters from the WMAP nine year and Planck data and get consistent
results. | Tomography of Massive Stars from Core Collapse to Supernova Shock
Breakout: Neutrinos and gravitational waves are the only direct probes of the inner
dynamics of a stellar core collapse. They are also the first signals to arrive
from a supernova and, if detected, establish the moment when the shock wave is
formed that unbinds the stellar envelope and later initiates the optical
display upon reaching the stellar surface with a burst of UV and X-ray photons,
the shock breakout (SBO). We discuss how neutrino observations can be used to
trigger searches to detect the elusive SBO event. Observation of the SBO would
provide several important constraints on progenitor structure and the
explosion, including the shock propagation time (the duration between the
neutrino burst and SBO), an observable that is important in distinguishing
progenitor types. Our estimates suggest that next generation neutrino detectors
could exploit the overdensity of nearby SNe to provide several such triggers
per decade, more than an order of magnitude improvement over the present. |
Radio halos in nearby (z < 0.4) clusters of galaxies: The Intra-Cluster Medium is characterized by thermal emission, and by the
presence of large scale magnetic fields. In some clusters of galaxies a diffuse
non-thermal emission is also present, located at the cluster center and named
radio halo. These sources indicate the existence of relativistic particles and
magnetic fields in the cluster volume. In this paper we collect data on all
known nearby cluster radio halos (z < 0.4), to discuss their statistical
properties and to investigate their origin. We searched for published data on
radio halos and reduced new and archive VLA data to increase the number of
known radio halos. We present data on 31 radio halos, 1 new relic source, and 1
giant filament. We note the discovery of a small size diffuse radio emission in
a cluster (A1213) with very low X-ray luminosity. Among statistical results we
confirm the correlation between the average halo radio spectral index and the
cluster temperature. We also discuss the high percentage of clusters where both
a relic and a radio halo is present. The sample of radio halos discussed here
represents the population of radio halos observable with present radio
telescopes. The new telescope generation is necessary for a more detailed
multifrequency study, and to investigate the possible existence of a population
of radio halos with different properties. | Black Hole-Galaxy Correlations without Self-Regulation: Recent models of black hole growth in a cosmological context have forwarded a
paradigm in which the growth is self-regulated by feedback from the black hole
itself. Here we use cosmological zoom simulations of galaxy formation down to z
= 2 to show that such strong self-regulation is required in the popular
spherical Bondi accretion model, but that a plausible alternative model in
which black hole growth is limited by galaxy-scale torques does not require
self-regulation. Instead, this torque-limited accretion model yields black
holes and galaxies evolving on average along the observed scaling relations by
relying only on a fixed, 5% mass retention rate onto the black hole from the
radius at which the accretion flow is fed. Feedback from the black hole may
(and likely does) occur, but does not need to couple to galaxy-scale gas in
order to regulate black hole growth. We show that this result is insensitive to
variations in the initial black hole mass, stellar feedback, or other
implementation details. The torque-limited model allows for high accretion
rates at very early epochs (unlike the Bondi case), which if viable can help
explain the rapid early growth of black holes, while by z = 2 it yields
Eddington factors of 1%-10%. This model also yields a less direct
correspondence between major merger events and rapid phases of black hole
growth. Instead, growth is more closely tied to cosmological disk feeding,
which may help explain observational studies showing that, at least at z > 1,
active galaxies do not preferentially show merger signatures. |
The SRG/eROSITA All-Sky Survey: Dark Energy Survey Year 3 Weak
Gravitational Lensing by eRASS1 selected Galaxy Clusters: Number counts of galaxy clusters across redshift are a powerful cosmological
probe, if a precise and accurate reconstruction of the underlying mass
distribution is performed -- a challenge called mass calibration. With the
advent of wide and deep photometric surveys, weak gravitational lensing by
clusters has become the method of choice to perform this measurement. We
measure and validate the weak gravitational lensing (WL) signature in the shape
of galaxies observed in the first 3 years of the DES Y3 caused by galaxy
clusters selected in the first all-sky survey performed by SRG/eROSITA. These
data are then used to determine the scaling between X-ray photon count rate of
the clusters and their halo mass and redshift. We empirically determine the
degree of cluster member contamination in our background source sample. The
individual cluster shear profiles are then analysed with a Bayesian population
model that self-consistently accounts for the lens sample selection and
contamination, and includes marginalization over a host of instrumental and
astrophysical systematics. To quantify the accuracy of the mass extraction of
that model, we perform mass measurements on mock cluster catalogs with
realistic synthetic shear profiles. This allows us to establish that
hydro-dynamical modelling uncertainties at low lens redshifts ($z<0.6$) are the
dominant systematic limitation. At high lens redshift the uncertainties of the
sources' photometric redshift calibration dominate. With regard to the X-ray
count rate to halo mass relation, we constrain all its parameters. This work
sets the stage for a joint analysis with the number counts of eRASS1 clusters
to constrain a host of cosmological parameters. We demonstrate that WL mass
calibration of galaxy clusters can be performed successfully with source
galaxies whose calibration was performed primarily for cosmic shear
experiments. | The Impact of Nonlinear Structure Formation on the Power Spectrum of
Transverse Momentum Fluctuations and the Kinetic Sunyaev-Zel'dovich Effect: Cosmological transverse momentum fields, whose directions are perpendicular
to Fourier wave vectors, induce temperature anisotropies in the cosmic
microwave background via the kinetic Sunyaev-Zeldovich (kSZ) effect. The
transverse momentum power spectrum contains the four-point function of density
and velocity fields, $\langle\delta\delta v v\rangle$. In the post-reionization
epoch, nonlinear effects dominate in the power spectrum. We use perturbation
theory and cosmological $N$-body simulations to calculate this nonlinearity. We
derive the next-to-leading order expression for the power spectrum with a
particular emphasis on the connected term that has been ignored in the
literature. While the contribution from the connected term on small scales
($k>0.1\,h\,\rm{Mpc}^{-1}$) is subdominant relative to the unconnected term, we
find that its contribution to the kSZ power spectrum at $\ell = 3000$ at $z<6$
can be as large as ten percent of the unconnected term, which would reduce the
allowed contribution from the reionization epoch ($z>6$) by twenty percent. The
power spectrum of transverse momentum on large scales is expected to scale as
$k^2$ as a consequence of momentum conservation. We show that both the leading
and the next-to-leading order terms satisfy this scaling. In particular, we
find that both of the unconnected and connected terms are necessary to
reproduce $k^2$. |
MG-MAMPOSSt: A code to test modifications of gravity with the dynamics
of galaxy clusters: We present an upgraded version of \textsc{MG-MAMPOSSt}, an extension of the
\textsc{MAMPOSSt} algorithm that performs Bayesian fits of models of mass and
velocity anisotropy profiles to the distribution of tracers in projected phase
space, to handle modified gravity models and constrain their parameters. The
new version implements two distinct types of gravity modifications, namely
general chameleon and Vainshtein screening, and is further equipped with a
Monte-Carlo-Markov-Chain module for an efficient parameter space exploration.
The program is complemented by the \textsc{ClusterGEN} code, capable of
producing mock galaxy clusters under the assumption of spherical symmetry,
dynamical equilibrium, and Gaussian local velocity distribution functions as in
\textsc{MAMPOSSt}. We demonstrate the potential of the method by analysing a
set of synthetic, isolated spherically-symmetric dark matter haloes, focusing
on the statistical degeneracies between model parameters. Assuming the
availability of additional lensing-like information, we forecast the
constraints on the modified gravity parameters for the two models presented, as
expected from joint lensing+internal kinematics analyses, in view of upcoming
galaxy cluster surveys. In Vainshtein screening, we forecast the weak lensing
effect through the estimation of the full convergence-shear profile. For
chameleon screening, we constrain the allowed region in the space of the two
free parameters of the model, further focusing on the $f(\mathcal{R})$ subclass
to obtain realistic bounds on the background field $|f_{\mathcal{R}0}|$. Our
analysis demonstrates the complementarity of internal kinematics and lensing
probes for constraining modified gravity theories, and how the bounds on
Vainshtein-screened theories improve through the combination of the two probes. | Properties and observables of massive galaxies in self-interacting dark
matter cosmologies: We use hydrodynamical cosmological simulations to test the differences
between cold and self-interacting dark matter models (CDM and SIDM) in the mass
range of massive galaxies
($10^{12}M_{\odot}h^{-1}<M<10^{13.5}M_{\odot}h^{-1}$). We consider two SIDM
models: one with constant cross section $\sigma/m_{\chi}=1\mathrm{cm^2g^{-1}}$
and one where the cross section is velocity-dependent. We analyse the halo
density profiles and concentrations, comparing the predictions of
dark-matter-only and hydrodynamical simulations in all scenarios. We calculate
the best-fit Einasto profiles and compare the resulting parameters with
previous studies and define the best-fit concentration-mass relations. We find
that the inclusion of baryons reduces the differences between different dark
matter models with respect to the DM-only case. In SIDM hydro runs, deviations
from the CDM density profiles weakly depend on mass: the most massive systems
($M>10^{13}M_{\odot}h^{-1}$) show cored profiles, while the least massive ones
($M<10^{12.5}M_{\odot}h^{-1}$) have cuspier profiles. Finally, we compare the
predictions of our simulations to observational results, by looking at the dark
matter fractions and the distribution of strong lensing Einstein radii. We find
that in SIDM the DM-fractions decrease more rapidly with increasing stellar
mass than in CDM, leading to lower fractions at $M_{*}>10^{11}M_{\odot}$, a
distinctive signature of SIDM. At the same time, the distribution of Einstein
radii, derived from both CDM and SIDM hydro runs, is comparable to observed
samples of strong lenses with $M>10^{13}M_{\odot}h^{-1}$. We conclude that the
interplay between self-interaction and baryons can greatly reduce the expected
differences between CDM and SIDM models at this mass scale, and that techniques
able to separate the dark and luminous mass in the inner regions of galaxies
are needed to constrain self-interactions. |
Galaxy Zoo Morphology and Photometric Redshifts in the Sloan Digital Sky
Survey: It has recently been demonstrated that one can accurately derive galaxy
morphology from particular primary and secondary isophotal shape estimates in
the Sloan Digital Sky Survey imaging catalog. This was accomplished by applying
Machine Learning techniques to the Galaxy Zoo morphology catalog. Using the
broad bandpass photometry of the Sloan Digital Sky Survey in combination with
with precise knowledge of galaxy morphology should help in estimating more
accurate photometric redshifts for galaxies. Using the Galaxy Zoo separation
for spirals and ellipticals in combination with Sloan Digital Sky Survey
photometry we attempt to calculate photometric redshifts. In the best case we
find that the root mean square error for Luminous Red Galaxies classified as
ellipticals is as low as 0.0118. Given these promising results we believe
better photometric redshift estimates for all galaxies in the Sloan Digital Sky
Survey ($\sim$350 million) will be feasible if researchers can also leverage
their derived morphologies via Machine Learning. These initial results look to
be promising for those interested in estimating Weak-Lensing, Baryonic Acoustic
Oscillation, and other fields dependent upon accurate photometric redshifts. | Hubble Parameter and Baryon Acoustic Oscillation Measurement Constraints
on the Hubble Constant, the Deviation from the Spatially-Flat $Λ$cdm
Model, The Deceleration-Acceleration Transition Redshift, and Spatial
Curvature: We compile a complete collection of reliable Hubble parameter $H(z)$ data to
redshift $z \leq 2.36$ and use them with the Gaussian Process method to
determine continuous $H(z)$ functions for various data subsets. From these
continuous $H(z)$'s, summarizing across the data subsets considered, we find
$H_0\sim 67 \pm 4\,\rm km/s/Mpc$, more consistent with the recent lower values
determined using a variety of techniques. In most data subsets, we see a
cosmological deceleration-acceleration transition at 2$\sigma$ significance,
with the data subsets transition redshifts varying over $0.33<z_{\rm da}<1.0$
at 1$\sigma$ significance. We find that the flat-$\Lambda$CDM model is
consistent with the $H(z)$ data to a $z$ of 1.5 to 2.0, depending on data
subset considered, with 2$\sigma$ deviations from flat-$\Lambda$CDM above this
redshift range. Using the continuous $H(z)$ with baryon acoustic oscillation
distance-redshift observations, we constrain the current spatial curvature
density parameter to be $\Omega_{K0}=-0.03\pm0.21$, consistent with a flat
universe, but the large error bar does not rule out small values of spatial
curvature that are now under debate. |
The June 2008 flare of Markarian 421 from optical to TeV energies: We present optical to very-high energy (VHE) gamma-ray observations of Mrk
421 between 2008 May 24 and June 23. A high-energy (HE) gamma-ray signal was
detected by AGILE-GRID during June 9-15, brighter than the average flux
observed by EGRET in Mrk 421 by a factor of approx. 1.5. In 20-60 keV X-rays, a
large-amplitude 5-day flare (June 9-15) was resolved with a maximum flux of
approx. 55 mCrab. SuperAGILE, RXTE/ASM and Swift/BAT data show a clearly
correlated flaring structure between soft and hard X-rays, with a high
flux/amplitude variability in hard X-rays. Hints of the same flaring behavior
is also detected in the simultaneously recorded GASP-WEBT optical data. A
target of opportunity observation by Swift near the flare maximum on June 12-13
revealed the highest 2-10 keV flux ever observed (>100 mCrab) and a peak
synchrotron energy of approx. 3 keV, a large shift from typical values of 0.5-1
keV. Observations at VHE (E>200 GeV) gamma-rays during June 6-8 show the source
flux peaking in a bright state, well correlated with the simultaneous peak in
the X-rays. The gamma-ray flare can be interpreted within the framework of the
Synchrotron Self Compton model in terms of a rapid acceleration of leptons in
the jet. | Bayesian Analysis of a Generalized Starobinsky Model with Reheating
Constraints: We study a generalization of the the Starobinsky model adding a term of the
form $R^{2p}$ to the Einstien-Hilbert action. We take the power $p$ as a
parameter of the model and explore the constraints from CMB plus BAO data
through a Bayesian analysis, thus exploring a range of values for the exponent
parameter. We incorporate a reheating phase to the model through the background
matter content (equation of state) and the duration of this period (number of
$e$-foldings of reheating). We find that incorporating information from
reheating imposes constraints on cosmological quantities, more stringent than
the case of no reheating when tested with the Planck+BAO data. The inferred
value of the exponent parameter is statistically consistent with $p=1$,
favoring the original Starobinsky potential. Moreover, we report tighter
constraints on $p$ and the number of $e$-folds in comparison with previous
works. The obtained values for other inflationary observational parameters,
such as the scalar spectral index $n_s$ and the scalar amplitude of
perturbations $A_s$, are consistent with prior measurements. Finally we present
the alternative use of consistency relations in order to simplify the parameter
space and test the generalized Starobinsky potential even more efficiently. |
Cosmicflows-2: SNIa Calibration and H0: The construction of the Cosmicflows-2 compendium of distances involves the
merging of distance measures contributed by the following methods: (Cepheid)
Period-Luminosity, Tip of the Red Giant Branch (TRGB), Surface Brightness
Fluctuation (SBF), Luminosity-Linewidth (TF), Fundamental Plane (FP), and Type
Ia supernova (SNIa). The method involving SNIa is at the top of an
interconnected ladder, providing accurate distances to well beyond the expected
range of distortions to Hubble flow from peculiar motions. In this paper, the
SNIa scale is anchored by 36 TF spirals with Cepheid or TRGB distances, 56 SNIa
hosts with TF distances, and 61 groups or clusters hosting SNIa with Cepheid,
SBF, TF, or FP distances. With the SNIa scale zero point set, a value of the
Hubble Constant is evaluated over a range of redshifts 0.03 < z < 0.5, assuming
a cosmological model with Omega_m = 0.27 and Omega_Lambda = 0.73. The value
determined for the Hubble Constant is H0 = 75.9 \pm 3.8 km s-1 Mpc-1. | Magnetogenesis from Anisotropic Universe: The existence of large-scale anisotropy can not be ruled out by the cosmic
microwave background (CMB) radiation. Over the years, several models have been
proposed in the context of anisotropic inflation to account for CMB's cold spot
and hemispheric asymmetry. However, any small-scale anisotropy, if exists
during inflation, is not constrained due to its nonlinear evolution in the
subsequent phase. This small-scale anisotropy during inflation can play a
non-trivial role in giving rise to the cosmic magnetic field, which is the
subject of our present study. Assuming a particular phenomenological form of an
anisotropic inflationary universe, we have shown that it can generate a
large-scale magnetic field at $1$-Mpc scale with a magnitude $\sim 4\times
10^{-20}~G$, within the observed bound. Because of the anisotropy, the
conformal flatness property is lost, and the Maxwell field is generated even
without explicit coupling. This immediately resolves the strong coupling
problem in the standard magnetogenesis scenario. In addition, assuming very low
conductivity during the reheating era, we can further observe the evolution of
the electromagnetic field with the equation of state (EoS) $\omega_{eff}$ and
its effects on the present-day magnetic field. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS): spectral
classification through Principal Component Analysis: We develop a Principal Component Analysis aimed at classifying a sub-set of
27,350 spectra of galaxies in the range 0.4 < z < 1.0 collected by the VIMOS
Public Extragalactic Redshift Survey (VIPERS). We apply an iterative algorithm
to simultaneously repair parts of spectra affected by noise and/or sky
residuals, and reconstruct gaps due to rest-frame transformation, and obtain a
set of orthogonal spectral templates that span the diversity of galaxy types.
By taking the three most significant components, we find that we can describe
the whole sample without contamination from noise. We produce a catalogue of
eigen-coefficients and template spectra that will be part of future VIPERS data
releases. Our templates effectively condense the spectral information into two
coefficients that can be related to the age and star formation rate of the
galaxies. We examine the spectrophotometric types in this space and identify
early, intermediate, late and starburst galaxies. | Probing Dark Matter with Future CMB Measurements: Dark Matter (DM) annihilation and decay during the Dark Ages can affect the
cosmic ionization history and leave imprints in the Cosmic Microwave Background
(CMB) anisotropy spectra. CMB polarization anisotropy can be sensitive to such
energy injection at higher redshifts and help reducing degeneracy with
primordial spectral parameters in $\Lambda$CDM and astrophysical ionization
processes during reionization. In light of a number of upcoming CMB
polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory,
Simons Array, SPT-3G, we estimate their prospective sensitivity in probing dark
matter annihilation and decay signals. We find that future missions have 95\%
C.L. projected limits on DM decay and annihilation rates to orders of
$\Gamma_\chi (\tau_{\chi}^{-1}) \sim 10^{-27}{\rm{s}}^{-1}$ and $\left<\sigma v
\right>/m_{\chi} \sim 10^{-29}{\rm{cm^3s^{-1}GeV^{-1}}}$ respectively,
significantly improving the sensitivity to DM from current experimental bounds. |
New probe of magnetic fields in the prereionization epoch. I. Formalism: We propose a method of measuring extremely weak magnetic fields in the
intergalactic medium prior to and during the epoch of cosmic reionization. The
method utilizes the Larmor precession of spin-polarized neutral hydrogen in the
triplet state of the hyperfine transition. This precession leads to a
systematic change in the brightness temperature fluctuations of the 21-cm line
from the high-redshift universe, and thus the statistics of these fluctuations
encode information about the magnetic field the atoms are immersed in. The
method is most suited to probing fields that are coherent on large scales; in
this paper, we consider a homogenous magnetic field over the scale of the 21-cm
fluctuations. Due to the long lifetime of the triplet state of the 21-cm
transition, this technique is naturally sensitive to extremely weak field
strengths, of order $10^{-19}$ G at a reference redshift of $\sim 20$ (or
$10^{-21}$ G if scaled to the present day). Therefore, this might open up the
possibility of probing primordial magnetic fields just prior to reionization.
If the magnetic fields are much stronger, it is still possible to use this
method to infer their direction, and place a lower limit on their strength. In
this paper (Paper I in a series on this effect), we perform detailed
calculations of the microphysics behind this effect, and take into account all
the processes that affect the hyperfine transition, including radiative decays,
collisions, and optical pumping by Lyman-$\alpha$ photons. We conclude with an
analytic formula for the brightness temperature of linear-regime fluctuations
in the presence of a magnetic field, and discuss its limiting behavior for weak
and strong fields. | Mirror Dark Sector Solution of the Hubble Tension with Time-varying
Fine-structure Constant: We explore a model introduced by Cyr-Racine, Ge, and Knox
(arXiv:2107.13000(2)) that resolves the Hubble tension by invoking a ``mirror
world" dark sector with energy density a fixed fraction of the ``ordinary"
sector of Lambda-CDM. Although it reconciles cosmic microwave background and
large-scale structure observations with local measurements of the Hubble
constant, the model requires a value of the primordial Helium mass fraction
that is discrepant with observations and with the predictions of Big Bang
Nucleosynthesis (BBN). We consider a variant of the model with standard Helium
mass fraction but with the value of the electromagnetic fine-structure constant
slightly different during photon decoupling from its present value. If $\alpha$
at that epoch is lower than its current value by $\Delta \alpha \simeq -2\times
10^{-5}$, then we can achieve the same Hubble tension resolution as in
Cyr-Racine, et al. but with consistent Helium abundance. As an example of such
time-evolution, we consider a toy model of an ultra-light scalar field, with
mass $m <4\times 10^{-29}$ eV, coupled to electromagnetism, which evolves after
photon decoupling and that appears to be consistent with late-time constraints
on $\alpha$ variation and the weak equivalence principle. |
Searching for a cosmological preferred direction with 147 rotationally
supported galaxies: It is well known that the Milgrom's MOND (modified Newtonian dynamics)
explains well the mass discrepancy problem in galaxy rotation curves. The MOND
predicts a universal acceleration scale below which the Newtonian dynamics is
invalid yet. The universal acceleration scale we got from the SPARC dataset is
$g_{\dag}=1.02\times10^{-10} \rm m~s^{-2}$. Milgrom suggested that the
acceleration scale may be a fingerprint of cosmology on local dynamics and
related with the Hubble constant $g_{\dag}\sim cH_0$. In this paper, we use the
hemisphere comparison method with the SPARC dataset to investigate the spatial
anisotropy on the acceleration scale. We find that the hemisphere of the
maximum acceleration scale is in the direction $(l,b) =
({175.5^\circ}^{+6^\circ}_{-10^\circ}, {-6.5^\circ}^{+8^\circ}_{-3^\circ})$
with $g_{\dag,max}=1.10\times10^{-10} \rm m~s^{-2}$, while the hemisphere of
the minimum acceleration scale is in the opposite direction $(l,b) =
({355.5^\circ}^{+6^\circ}_{-10^\circ}, {6.5^\circ}^{+3^\circ}_{-8^\circ})$ with
$g_{\dag,min}=0.76\times10^{-10} \rm m~s^{-2}$. The maximum anisotropy level
reaches up to $0.37\pm0.04$. Robust tests present that such a level of
anisotropy can't be reproduced by a statistically isotropic data. In addition,
we show that the spatial anisotropy on the acceleration scale has little
correlation with the non-uniform distribution of the SPARC data points in sky.
We also find that the maximum anisotropy direction is close with other
cosmological preferred directions, especially the direction of the "Australia
dipole" for the fine structure constant. | Curing singularities in cosmological evolution of F(R) gravity: We study $F(R)$ modified gravity models which are capable of driving the
accelerating epoch of the Universe at the present time whilst not destroying
the standard Big Bang and inflationary cosmology. Recent studies have shown
that a weak curvature singularity with $|R|\to\infty$ can arise generically in
viable $F(R)$ models of present dark energy (DE) signaling an internal
incompleteness of these models. In this work we study how this problem is cured
by adding a quadratic correction with a sufficiently small coefficient to the
$F(R)$ function at large curvatures. At the same time, this correction
eliminates two more serious problems of previously constructed viable $F(R)$ DE
models: unboundedness of the mass of a scalar particle (scalaron) arising in
$F(R)$ gravity and the scalaron overabundance problem. Such carefully
constructed models can also yield both an early time inflationary epoch and a
late time de Sitter phase with vastly different values of $R$. The reheating
epoch in these combined models of primordial and present dark energy is
completely different from that of the old $R + R^{2}/6M^{2}$ inflationary
model, mainly due to the fact that values of the effective gravitational
constant at low and intermediate curvatures are different for positive and
negative $R$. This changes the number of e-folds during the observable part of
inflation that results in a different value of the primordial power spectrum
index. |
The Connection between 3.3 μm PAH Emission and AGN Activity: We investigate the connection between starburst and AGN activity by comparing
the 3.3 {\mu}m PAH eimission with AGN properties. Utilizing the slit-less
spectroscopic capability of the AKARI space telescope, we observe
moderate-luminosity Type I AGN at z~0.4 to measure global starburst activity.
The 3.3 {\mu}m PAH emissions are detected for 7 out of 26 target galaxies. We
find no strong correlation between the 3.3 {\mu}m PAH emission and AGN
luminosity in the limted range of the observed AGN luminosity, suggesting that
global star formation may not be tightly related with AGN activity. Combining
our measurements with the previous 3.3 {\mu}m measurements of the low redshift
Type I AGN in the literature, we investigate the connection between nuclear
starburst and AGN activity. In contrast to global star formation, the 3.3
{\mu}m PAH luminosity measured from the central part of galaxies correlates
with AGN luminosity, implying that starburst and AGN activity are directly
connected at the nuclear region. | Observables and unobservables in dark energy cosmologies: The aim of this paper is to answer the following two questions: (1) Given
cosmological observations of the expansion history and linear perturbations in
a range of redshifts and scales as precise as is required, which of the
properties of dark energy could actually be reconstructed without imposing any
parameterization? (2) Are these observables sufficient to rule out not just a
particular dark energy model, but the entire general class of viable models
comprising a single scalar field?
This paper bears both good and bad news. On one hand, we find that the goal
of reconstructing dark energy models is fundamentally limited by the
unobservability of the present values of the matter density Omega_m0, the
perturbation normalization sigma_8 as well as the present matter power
spectrum. On the other, we find that, under certain conditions, cosmological
observations can nonetheless rule out the entire class of the most general
single scalar-field models, i.e. those based on the Horndeski Lagrangian. |
Studying Cosmic Dawn using redshifted HI 21-cm signal: A brief review: In this review article, we briefly outline our current understanding of the
physics associated with the HI 21-cm signal from cosmic dawn. We discuss
different phases of cosmic dawn as the ambient gas and the background
radiations evolve with the redshift. We address the consequences of several
possible heating sources and radiation background on the global 21-cm signal.
We further review our present perspective of other important aspects of the HI
21-cm signal such as the power spectrum and imaging. Finally, we highlight the
future key measurements of the Square Kilometre Array and other
ongoing/upcoming experiments that will enlighten our understanding of the early
Universe. | Probing X-ray irradiation in the nucleus of NGC 1068 with observations
of high-J lines of dense gas tracers: With the incorporation of high-J molecular lines, we aim to constrain the
physical conditions of the dense gas in the central region of the Seyfert 2
galaxy NGC 1068 and to determine signatures of the AGN or the starburst
contribution.
We used the James Clerk Maxwell Telescope to observe the J=4-3 transition of
HCN, HNC, and HCO+, as well as the CN N_J=2_{5/2}-1_{3/2} and
N_J=3_{5/2}-2_{5/2}, in NGC 1068.
We estimate the excitation conditions of HCN, HNC, and CN, based on the line
intensity ratios and radiative transfer models.
We find that the bulk emission of HCN, HNC, CN, and the high-J HCO+ emerge
from dense gas n(H_2)>=10^5 cm^-3). However, the low-J HCO+ lines (dominating
the HCO+ column density) trace less dense (n(H_2)<10^5 cm^-3) and colder
(T_K<=20 K) gas, whereas the high-J HCO+ emerges from warmer (>30 K) gas than
the other molecules.
The HCO+ J=4-3 line intensity, compared with the lower transition lines and
with the HCN J=4-3 line, support the influence of a local XDR environment. The
estimated N(CN)/N(HCN)~1-4 column density ratios are indicative of an XDR/AGN
environment with a possible contribution of grain-surface chemistry induced by
X-rays or shocks. |
Non-Gaussianity from resonant curvaton decay: We calculate curvature perturbations in the scenario in which the curvaton
field decays into another scalar field via parametric resonance. As a result of
a nonlinear stage at the end of the resonance, standard perturbative
calculation techniques fail in this case. Instead, we use lattice field theory
simulations and the separate universe approximation to calculate the curvature
perturbation as a nonlinear function of the curvaton field. For the parameters
tested, the generated perturbations are highly non-Gaussian and not well
approximated by the usual fNL parameterisation. Resonant decay plays an
important role in the curvaton scenario and can have a substantial effect on
the resulting perturbations. | Accurate effective fluid approximation for ultralight axions: Ultralight axions are theoretically interesting and phenomenologically rich
dark sector candidates, but they are difficult to track across cosmological
timescales because of their fast oscillations. We resolve this problem by
developing a novel method to evolve them efficiently and accurately. We first
construct an exact effective fluid which at late times matches the axion but
which evolves in a simple way. We then approximate this evolution with a
carefully chosen equation of state and sound speed. With our scheme we find
that we can obtain subpercent accuracy for the linear theory suppression of
axion density fluctuations relative to that of cold dark matter without
tracking even a single complete oscillation of the axion field. We use our
technique to test other approximation schemes and to provide a fitting formula
for the transfer function for the matter power spectrum in linear theory in
axion models. Implementing our approach in existing cosmological axion codes is
straightforward and will help unleash the potential of high-precision
next-generation experiments. |
Testing the mean field theory of scalar field dark matter: Scalar field dark matter offers an interesting alternative to the traditional
WIMP dark matter picture. Astrophysical and cosmological simulations are useful
to constraining the mass of the dark matter particle in this model. This is
particularly true at low mass where the wavelike nature of the dark matter
particle manifests on astrophysical scales. These simulations typical use a
classical field approximation. In this work, we look at extending these
simulations to include quantum corrections. We look into both the ways in which
large corrections impact the predictions of scalar field dark matter, and the
timescales on which these corrections grow large. Corrections tend to lessen
density fluctuations and increase the effect of "quantum pressure". During
collapse, these corrections grow exponentially, quantum corrections would
become important in about ~30 dynamical times. This implies that the
predictions of classical field simulations may differ from those with quantum
corrections for systems with short dynamical times. | Simulated void galaxies in the standard cold dark matter model: We analyze a (120 h^{-1} Mpc)^3 adaptive mesh refinement hydrodynamic
simulation that contains a higher-resolution 31 x 31 x 35 h^{-3} Mpc subvolume
centered on a ~30 Mpc diameter void. Our detailed ~1 kpc resolution allows us
to identify 1300 galaxies within this void to a limiting halo mass of ~10^{10}
M_sun. Nearly 1000 galaxies are found to be in underdense regions, with 300
galaxies residing in regions less than half the mean density of the simulation
volume. We construct mock observations of the stellar and gas properties of
these systems, and reproduce the range of colors and luminosities observed in
the SDSS for nearby (z < 0.03) galaxies. We find no trends with density for the
most luminous (M_r < -18) galaxies, however our dwarf void galaxies (M_r >
-16), though they are less reliably resolved, typically appear bluer, with
higher rates of star formation and specific star formation and lower mean
stellar ages than galaxies in average density environments. We find a
significant population of low luminosity (M_r ~ -14) dwarf galaxies that is
preferentially located in low density regions and specifically in the void
center. This population may help to reduce, but not remove, the discrepancy
between the predicted and observed number of void galaxies. |
Novel Physics with International Pulsar Timing Array: Axionlike
Particles, Domain Walls and Cosmic Strings: After NANOGrav, the IPTA collaboration also reports a strong evidence of a
stochastic gravitation wave background. This hint has very important
implications for fundamental physics. With the recent IPTA data release two, we
attempt to search signals of light new physics. and give new constraints on the
audible axion, domain walls and cosmic strings models. We find that the best
fit point corresponding to a decay constant $F\approx5\times10^{17}$ GeV and an
axion mass $m_a\approx2\times10^{-13}$ eV from NANOGrav data is ruled out by
IPTA at beyond $2\sigma$ confidence level. Fixing the coupling strength
$\lambda=1$, we obtain a $2\sigma$ lower bound on the breaking scale of $Z_2$
symmetry $\eta>135$ TeV. Interestingly, we give a very strong restriction on
the cosmic-string tension $\mathrm{log}_{10}\,G\mu=-8.93_{-0.06}^{+0.12}$ at
$1\sigma$ confidence level. Employing the rule of Bayes factor, we find that
IPTA data has a moderate, strong and inconclusive preference of an uncorrelated
common power-law (CPL) model over audible axion, domain walls and cosmic
strings, respectively. This means that it is hard to distinguish CPL from
cosmic strings with current observations and more pulsar timing data with high
precision are required to give new clues of underlying physics. | Weak Lensing Science, Surveys, and Systematics: Weak gravitational lensing is one of the key probes of the cosmological
model, dark energy, and dark matter, providing insight into both the cosmic
expansion history and large scale structure growth history. Taking into account
a broad spectrum of physics affecting growth - dynamical dark energy, extended
gravity, neutrino masses, and spatial curvature - we analyze the cosmological
constraints. Similarly we consider the effects of a range of systematic
uncertainties, in shear measurement, photometric redshifts, and the nonlinear
power spectrum, on cosmological parameter extraction. We also investigate, and
provide fitting formulas for, the influence of survey parameters such as
redshift depth, galaxy number densities, and sky area. Finally, we examine the
robustness of results for different fiducial cosmologies. |
Solving the Vlasov equation in two spatial dimensions with the
Schrödinger method: We demonstrate that the Vlasov equation describing collisionless
self-gravitating matter may be solved with the so-called Schr\"odinger method
(ScM). With the ScM, one solves the Schr\"odinger-Poisson system of equations
for a complex wave function in d dimensions, rather than the Vlasov equation
for a 2d-dimensional phase space density. The ScM also allows calculating the
d-dimensional cumulants directly through quasi-local manipulations of the wave
function, avoiding the complexity of 2d-dimensional phase space. We perform for
the first time a quantitive comparison of the ScM and a conventional Vlasov
solver in d=2 dimensions. Our numerical tests were carried out using two types
of cold cosmological initial conditions: the classic collapse of a sine wave
and those of a gaussian random field as commonly used in cosmological cold dark
matter N-body simulations. We compare the first three cumulants, that is, the
density, velocity and velocity dispersion, to those obtained by solving the
Vlasov equation using the publicly available code ColDICE. We find excellent
qualitative and quantitative agreement between these codes, demonstrating the
feasibility and advantages of the ScM as an alternative to N-body simulations.
We discuss, the emergence of effective vorticity in the ScM through the winding
number around the points where the wave function vanishes. As an application we
evaluate the background pressure induced by the non-linearity of large scale
structure formation, thereby estimating the magnitude of cosmological
backreaction. We find that it is negligibly small and has time dependence and
magnitude compatible with expectations from the effective field theory of large
scale structure. | Signatures of large-scale structure of Universe in X-rays: A new sample of 4299 galaxies with X-ray emission was obtained in this work
by cross-correlating 2XMM catalog of X-ray sources with HyperLeda database of
galaxies. We analyzed distributions of optical and X-ray fluxes, redshifts and
X-ray luminosities for this sample. Virgo and Coma galaxy clusters can be
easily detected at redshift-space distribution of X-ray galaxies. X-ray
luminosity function of our galaxies shows the evidences of cosmological
evolution, even at low redshifts. |
Implications of multiple high-redshift galaxy clusters: To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have
been observed, spectroscopically confirmed and are reported in the literature.
These objects should be exceedingly rare in the standard LCDM model. We
conservatively approximate the selection functions of these clusters' parent
surveys, and quantify the tension between the abundances of massive clusters as
predicted by the standard LCDM model and the observed ones. We alleviate the
tension considering non-Gaussian primordial perturbations of the local type,
characterized by the parameter fnl and derive constraints on fnl arising from
the mere existence of these clusters. At the 95% confidence level, fnl>467 with
cosmological parameters fixed to their most likely WMAP5 values, or fnl > 123
(at 95% confidence) if we marginalize over WMAP5 parameters priors. In
combination with fnl constraints from Cosmic Microwave Background and halo
bias, this determination implies a scale-dependence of fnl at approx. 3 sigma.
Given the assumptions made in the analysis, we expect any future improvements
to the modeling of the non-Gaussian mass function, survey volumes, or selection
functions to increase the significance of fnl>0 found here. In order to
reconcile these massive, high-z clusters with an fnl=0, their masses would need
to be systematically lowered by 1.5 sigma or the sigma8 parameter should be
approx. 3 sigma higher than CMB (and large-scale structure) constraints. The
existence of these objects is a puzzle: it either represents a challenge to the
LCDM paradigme or it is an indication that the mass estimates of clusters is
dramatically more uncertain than we think. | Two new tests to the distance duality relation with galaxy clusters: The cosmic distance duality relation is a milestone of cosmology involving
the luminosity and angular diameter distances. Any departure of the relation
points to new physics or systematic errors in the observations, therefore tests
of the relation are extremely important to build a consistent cosmological
framework. Here, two new tests are proposed based on galaxy clusters
observations (angular diameter distance and gas mass fraction) and $H(z)$
measurements. By applying Gaussian Processes, a non-parametric method, we are
able to derive constraints on departures of the relation where no evidence of
deviation is found in both methods, reinforcing the cosmological and
astrophysical hypotheses adopted so far. |
Comments on the paper by E. Gjerlow and O. Elgaroy "Are all modes
created equal ? An analysis of the WMAP 5- and 7-year data without
inflationary prejudice": The amount and characteristics of quantum-mechanically generated relic
gravitational waves and primordial density perturbations is a subject of great
theoretical and observational importance. Unfortunately, this subject is deeply
contaminated by inflationary misunderstandings and incorrect "standard
inflationary results". This note presents comments on a particular paper,
arXiv:1008.4471v1. However, the comments may have a more general significance
and may be of interest to other researchers working in this area of science. | Cosmological information in the redshift-space bispectrum: We use the Fisher-matrix formalism to investigate whether the galaxy
bispectrum in redshift space, $B$, contains additional cosmological information
with respect to the power spectrum, $P$. We focus on a $Euclid$-like survey and
consider cosmological models dominated by dark energy and cold dark matter with
Gaussian primordial perturbations. After discussing the phenomenology of
redshift-space distortions for the bispectrum, we derive an expression for the
cross-covariance between $B$ and $P$ at leading order in perturbation theory.
Our equation generalizes previous results that did not consider binning in the
orientation of wavevector triangles with respect to the line of sight. By
considering Fourier modes with wavenumber $k<0.15 \,h$ Mpc$^{-1}$, we find that
$B$ and $P$ set similar constraints on the cosmological parameters. Generally,
error bars moderately improve when the two probes are combined together. For
instance, the joint 68.3 per cent credible region for the parameters that
describe a dynamical dark-energy equation of state shrinks by a factor of 2.6
with respect to only using the power spectrum. Regrettably, this improvement is
cancelled out when the clustering analysis is combined with priors based on
current studies of the cosmic microwave background. In this case, combining $B$
and $P$ does not give any appreciable benefit other than allowing a precise
determination of galaxy bias. Finally, we discuss how results depend on the
binning strategy for the clustering statistics as well as on the maximum
wavenumber. We also show that only considering the bispectrum monopole leads to
a significant loss of information. |
The core-cusp problem in cold dark matter halos and supernova feedback:
Effects of Mass Loss: The core-cusp problem remains as one of the unsolved discrepancies between
observations and theories predicted by the standard paradigm of cold dark
matter (CDM) cosmology. To solve this problem, we perform N-body simulations to
study the nonlinear response of CDM halos to the variance of the gravitational
potential induced by gas removal from galaxy centers. In this study, we focus
on the timescale of the gas ejection, which is strongly correlated with stellar
activities, and demonstrate that it is one of the key factors in determining
the dynamical response of CDM halos. The results of simulations show that the
power-low index of the mass-density profile of the dark matter halo correlated
with the timescale of the mass loss, and it is flatter when the mass loss
occurs over a short time than when it occurs over a long time. However, it is
still larger than typical observational values; in other words, the central
cusp remains for any mass loss model in the simulations. Moreover, for the slow
mass-loss case, the final density profile of the dark matter halo recovers the
universal density profiles predicted by the CDM cosmology. Therefore, mass loss
driven by stellar feedback may not be an effective mechanism to flatten the
central cusp. | An Unbiased Estimator of Peculiar Velocity with Gaussian Distributed
Errors for Precision Cosmology: We introduce a new estimator of the peculiar velocity of a galaxy or group of
galaxies from redshift and distance estimates. This estimator results in
peculiar velocity estimates which are statistically unbiased and that have
errors that are Gaussian distributed, thus meeting the assumptions of analyses
that rely on individual peculiar velocities. We apply this estimator to the
SFI++ and the Cosmicflows-2 catalogs of galaxy distances and, using the fact
that peculiar velocity estimates of distant galaxies are error dominated,
examine their error distributions, The adoption of the new estimator
significantly improves the accuracy and validity of studies of the large-scale
peculiar velocity field and eliminates potential systematic biases, thus
helping to bring peculiar velocity analysis into the era of precision
cosmology. In addition, our method of examining the distribution of velocity
errors should provide a useful check of the statistics of large peculiar
velocity catalogs, particularly those that are compiled out of data from
multiple sources. |
Double-Disk Dark Matter: Based on observational constraints on large scale structure and halo
structure, dark matter is generally taken to be cold and essentially
collisionless. On the other hand, given the large number of particles and
forces in the visible world, a more complex dark sector could be a reasonable
or even likely possibility. This hypothesis leads to testable consequences,
perhaps portending the discovery of a rich hidden world neighboring our own. We
consider a scenario that readily satisfies current bounds that we call
Partially Interacting Dark Matter (PIDM). This scenario contains
self-interacting dark matter, but it is not the dominant component. Even if
PIDM contains only a fraction of the net dark matter density, comparable to the
baryonic fraction, the subdominant component's interactions can lead to
interesting and potentially observable consequences. Our primary focus will be
the special case of Double-Disk Dark Matter (DDDM), in which self-interactions
allow the dark matter to lose enough energy to lead to dynamics similar to
those in the baryonic sector. We explore a simple model in which DDDM can cool
efficiently and form a disk within galaxies, and we evaluate some of the
possible observational signatures. The most prominent signal of such a scenario
could be an enhanced indirect detection signature with a distinctive spatial
distribution. Even though subdominant, the enhanced density at the center of
the galaxy and possibly throughout the plane of the galaxy can lead to large
boost factors, and could even explain a signature as large as the 130 GeV Fermi
line. Such scenarios also predict additional dark radiation degrees of freedom
that could soon be detectable and would influence the interpretation of future
data, such as that from Planck and from the Gaia satellite. We consider this to
be the first step toward exploring a rich array of new possibilities for dark
matter dynamics. | The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX
II) IV. X-ray Luminosity Function and First Constraints on Cosmological
Parameters: The X-ray luminosity function is an important statistic of the census of
galaxy clusters and an important means to probe the cosmological model of our
Universe. Based on our recently completed REFLEX II cluster sample we construct
the X-ray luminosity function of galaxy clusters for several redshift slices
from $z = 0$ to $z = 0.4$ and discuss its implications. We find no significant
signature of redshift evolution of the luminosity function in the redshift
interval. We provide the results of fits of a parameterized Schechter function
and extensions of it which provide a reasonable characterization of the data.
Using a model for structure formation and galaxy cluster evolution we compare
the observed X-ray luminosity function with predictions for different
cosmological models. For the most interesting constraints for the cosmological
parameters $\Omega_m$ and $\sigma_8$ we obatain $\Omega_m \sim 0.27 \pm 0.03$
and $\sigma_8 \sim 0.80 \pm 0.03$ based on the statistical uncertainty alone.
Marginalizing over the most important uncertainties, the normalisation and
slope of the $L_X - M$ scaling relation, we find $\Omega_m \sim 0.29 \pm 0.04$
and $\sigma_8 \sim 0.77 \pm 0.07$ ($1\sigma$ confidence limits). We compare our
results with those of the SZ-cluster survey provided by the PLANCK mission and
we find very good agreement with the results using PLANCK clusters as
cosmological probes, but we have some tension with PLANCK cosmological results
from the microwave background anisotropies. We also make a comparison with
other cluster surveys. We find good agreement with these previous results and
show that the REFLEX II survey provides a significant reduction in the
uncertainties compared to earlier measurements. |
A volume-limited sample of X-ray galaxy groups and clusters - I. Radial
entropy and cooling time profiles: We present the first results of our study of a sample of 101 X-ray galaxy
groups and clusters, which is volume-limited in each of three X-ray luminosity
bins. The aim of this work is to study the properties of the innermost ICM in
the cores of our groups and clusters, and to determine the effect of
non-gravitational processes, such as active galactic nucleus (AGN) feedback, on
the ICM. The entropy of the ICM is of special interest, as it bears the imprint
of the thermal history of a cluster, and it also determines a cluster's global
properties. Entropy profiles can therefore be used to examine any deviations
from cluster self-similarity, as well as the effects of feedback on the ICM. We
find that the entropy profiles are well-fitted by a simple powerlaw model, of
the form $K(r) = \alpha\times(r/100 \rm{kpc})^{\beta}$, where $\alpha$ and
$\beta$ are constants. We do not find evidence for the existence of an "entropy
floor", i.e. our entropy profiles do not flatten out at small radii, as
suggested by some previous studies. | Not empty enough: a local void cannot solve the $H_0$ tension: We review arguably the simplest solution for the Hubble tension -- the
possibility that we live in a void. In this scenario, the local Hubble constant
$H_0$ is higher than the global value, thus potentially explaining why $H_0$
measured locally by the distance ladder including Type Ia supernovae (SNIa)
would be larger than the value inferred from the cosmic microwave background
and other cosmological probes. In addition, since the local supernova sample is
sparse and highly inhomogeneous, the error bars in the local Hubble constant
might be larger than previously estimated. These two effects -- local matter
density and sample inhomogeneity -- constitute the sample variance (or the
cosmic variance) of the local Hubble constant measurements. To investigate
these effects explicitly, we have mocked up SNIa observations by exactly
matching their actual spatial distribution in a large N-body simulation. We
have then investigated whether the sample variance is large enough to explain
the Hubble tension. The answer is resoundingly negative: the typical local
variation in $H_0$ is far smaller than what would be required to explain the
Hubble tension; the latter would require a 20-$\sigma$ deviation from the
expected sample variance. Equivalently, the void required to explain the Hubble
tension would need to be so empty ($\delta\approx-0.8$ on a scale 120
$h^{-1}{\rm Mpc}$) that it would be incompatible with the large-scale structure
in a $\Lambda$CDM universe. Therefore, the possibility that we live in a void
does not come close to explaining the Hubble tension. |
The formation of disc galaxies in high resolution moving-mesh
cosmological simulations: We present cosmological hydrodynamical simulations of eight Milky Way-sized
haloes that have been previously studied with dark matter only in the Aquarius
project. For the first time, we employ the moving-mesh code AREPO in zoom
simulations combined with a comprehensive model for galaxy formation physics
designed for large0 cosmological simulations. Our simulations form in most of
the eight haloes strongly disc-dominated systems with realistic rotation
curves, close to exponential surface density profiles, a stellar-mass to
halo-mass ratio that matches expectations from abundance matching techniques,
and galaxy sizes and ages consistent with expectations from large galaxy
surveys in the local Universe. There is no evidence for any dark matter core
formation in our simulations, even so they include repeated baryonic outflows
by supernova-driven winds and black hole quasar feedback. For one of our
haloes, the object studied in the recent `Aquila' code comparison project, we
carried out a resolution study with our techniques, covering a dynamic range of
64 in mass resolution. Without any change in our feedback parameters, the final
galaxy properties are reassuringly similar, in contrast to other modelling
techniques used in the field that are inherently resolution dependent. This
success in producing realistic disc galaxies is reached, in the context of our
interstellar medium treatment, without resorting to a high density threshold
for star formation, a low star formation efficiency, or early stellar feedback,
factors deemed crucial for disc formation by other recent numerical studies. | K-mouflage effects on clusters of galaxies: We investigate the effects of a K-mouflage modification of gravity on the
dynamics of clusters of galaxies. We extend the description of K-mouflage to
situations where the scalar field responsible for the modification of gravity
is coupled to a perfect fluid with pressure. We describe the coupled system at
both the background cosmology and cosmological perturbations levels, focusing
on cases where the pressure emanates from small-scale nonlinear physics. We
derive these properties in both the Einstein and Jordan frames, as these two
frames already differ by a few percents at the background level for K-mouflage
scenarios, and next compute cluster properties in the Jordan frame that is
better suited to these observations. Galaxy clusters are not screened by the
K-mouflage mechanism and therefore feel the modification of gravity in a
maximal way. This implies that the halo mass function deviates from
$\Lambda$-CDM by a factor of order one for masses $M\gtrsim 10^{14} \ h^{-1}
M_\odot$. We then consider the hydrostatic equilibrium of gases embedded in
galaxy clusters and the consequences of K-mouflage on the X-ray cluster
luminosity, the gas temperature, and the Sunyaev-Zel'dovich effect. We find
that the cluster temperature function, and more generally number counts, are
largely affected by K-mouflage, mainly due to the increased cluster abundance
in these models. Other scaling relations such as the mass-temperature and the
temperature-luminosity relations are only modified at the percent level due to
the constraints on K-mouflage from local Solar System tests. |
On the reach of perturbative descriptions for dark matter displacement
fields: We study Lagrangian Perturbation Theory (LPT) and its regularization in the
Effective Field Theory (EFT) approach. We evaluate the LPT displacement with
the same phases as a corresponding $N$-body simulation, which allows us to
compare perturbation theory to the non-linear simulation with significantly
reduced cosmic variance, and provides a more stringent test than simply
comparing power spectra. We reliably detect a non-vanishing leading order EFT
coefficient and a stochastic displacement term, uncorrelated with the LPT
terms. This stochastic term is expected in the EFT framework, and, to the best
of our understanding, is not an artifact of numerical errors or transients in
our simulations. This term constitutes a limit to the accuracy of perturbative
descriptions of the displacement field and its phases, corresponding to a $1\%$
error on the non-linear power spectrum at $k=0.2 h$/Mpc at $z=0$. Predicting
the displacement power spectrum to higher accuracy or larger wavenumbers thus
requires a model for the stochastic displacement. | Cosmic Shear Measurements with DES Science Verification Data: We present measurements of weak gravitational lensing cosmic shear two-point
statistics using Dark Energy Survey Science Verification data. We demonstrate
that our results are robust to the choice of shear measurement pipeline, either
ngmix or im3shape, and robust to the choice of two-point statistic, including
both real and Fourier-space statistics. Our results pass a suite of null tests
including tests for B-mode contamination and direct tests for any dependence of
the two-point functions on a set of 16 observing conditions and galaxy
properties, such as seeing, airmass, galaxy color, galaxy magnitude, etc. We
furthermore use a large suite of simulations to compute the covariance matrix
of the cosmic shear measurements and assign statistical significance to our
null tests. We find that our covariance matrix is consistent with the halo
model prediction, indicating that it has the appropriate level of halo sample
variance. We compare the same jackknife procedure applied to the data and the
simulations in order to search for additional sources of noise not captured by
the simulations. We find no statistically significant extra sources of noise in
the data. The overall detection significance with tomography for our highest
source density catalog is 9.7sigma. Cosmological constraints from the
measurements in this work are presented in a companion paper (DES et al. 2015). |
Type Ia Supernovae as Stellar Endpoints and Cosmological Tools: Empirically, Type Ia supernovae are the most useful, precise, and mature
tools for determining astronomical distances. Acting as calibrated candles they
revealed the presence of dark energy and are being used to measure its
properties. However, the nature of the SN Ia explosion, and the progenitors
involved, have remained elusive, even after seven decades of research. But now
new large surveys are bringing about a paradigm shift --- we can finally
compare samples of hundreds of supernovae to isolate critical variables. As a
result of this, and advances in modeling, breakthroughs in understanding all
aspects of SNe Ia are finally starting to happen. | Towards a self-consistent halo model for the nonlinear large-scale
structure: The halo model is a theoretically and empirically well-motivated framework
for predicting the statistics of the nonlinear matter distribution in the
Universe. However, current incarnations of the halo model suffer from two major
deficiencies: $(i)$ they do not enforce the stress-energy conservation of
matter; $(ii)$ they are not guaranteed to recover exact perturbation theory
results on large scales. Here, we provide a formulation of the halo model
("EHM") that remedies both drawbacks in a consistent way, while attempting to
maintain the predictivity of the approach. In the formulation presented here,
mass and momentum conservation are guaranteed on large scales, and results of
perturbation theory and the effective field theory can in principle be matched
to any desired order on large scales. We find that a key ingredient in the halo
model power spectrum is the halo stochasticity covariance, which has been
studied to a much lesser extent than other ingredients such as mass function,
bias, and profiles of halos. As written here, this approach still does not
describe the transition regime between perturbation theory and halo scales
realistically, which is left as an open problem. We also show explicitly that,
when implemented consistently, halo model predictions do not depend on any
properties of low-mass halos that are smaller than the scales of interest. |
Evolution of fNL to the adiabatic limit: We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL. | Dark Coupling and Gauge Invariance: We study a coupled dark energy-dark matter model in which the energy-momentum
exchange is proportional to the Hubble expansion rate. The inclusion of its
perturbation is required by gauge invariance. We derive the linear perturbation
equations for the gauge invariant energy density contrast and velocity of the
coupled fluids, and we determine the initial conditions. The latter turn out to
be adiabatic for dark energy, when assuming adiabatic initial conditions for
all the standard fluids. We perform a full Monte Carlo Markov Chain likelihood
analysis of the model, using WMAP 7-year data. |
Early Science Result from the Japanese Virtual Observatory: AGN and
Galaxy Clustering at z = 0.3 to 3.0: We present the result of projected cross correlation analysis of AGNs and
galaxies at redshifts from 0.3 to 3.0. The Japanese Virtual Observatory (JVO)
was used to obtain the Subaru Suprime-Cam images and UKIDSS catalog data around
AGNs. We investigated 1,809 AGNs, which is about ten times larger a sample than
that used in previous studies on AGN-galaxy clustering at redshifts larger than
0.6. 90% of the AGN samples are optically-selected AGN from the SDSS and 2dF
catalogs. The galaxy samples at low redshift includes many redder objects from
UKIDSS survey, while at higher redshift they are mainly blue galaxies from
Suprime-Cam. We found significant excess of galaxies around the AGNs at
redshifts from 0.3 to 1.8. For the low redshift samples ($z<0.9$), we obtained
correlation length of $r_{0} = $5--6 $h^{-1}$Mpc ($\gamma = 1.8$), which
indicates that the AGNs at this redshift range reside in a similar environment
around typical local galaxies. We also found that AGNs at higher redshift
ranges reside in a denser environment than lower redshift AGNs; For $z=1.3 \sim
1.8$ AGNs, the cross correlation length was measured as 11$^{+6}_{-3}$
$h^{-1}$Mpc ($\gamma=1.8$). Considering that our galaxies sample is based on
optical observations with Suprime-Cam at the redshift range, it is expected
that blue star-forming galaxies comprise the majority of objects that are
observed to be clustered around the AGNs. It is successfully demonstrated that
the use of the archive through the Virtual Observatory system can provide a
powerful tool for investigating the small scale environment of the intermediate
redshift AGNs. | Signatures of metal-free star formation in Planck 2015 Polarization Data: Standard analyses of the reionization history of the universe from Planck
cosmic microwave background (CMB) polarization measurements consider only the
overall optical depth to electron scattering ($\tau$), and further assume a
step-like reionization history. However, the polarization data contain
information beyond the overall optical depth, and the assumption of a step-like
function may miss high redshift contributions to the optical depth and lead to
biased $\tau$ constraints. Accounting for its full reionization information
content, we reconsider the interpretation of Planck 2015 Low Frequency
Instrument (LFI) polarization data using simple, yet physically-motivated
reionization models. We show that these measurements still, in fact, allow a
non-negligible contribution from metal-free (Pop-III) stars forming in
mini-halos of mass $M \sim 10^5-10^6 M_\odot$ at $z \gtrsim 15$, provided this
mode of star formation is fairly inefficient. Our best fit model includes an
early, self-regulated phase of Pop-III star formation in which the reionization
history has a gradual, plateau feature. In this model, $\sim$20\% of the volume
of the universe is ionized by $z \sim 20$, yet it nevertheless provides a good
match to the Planck LFI measurements. Although preferred when the full
information content of the data is incorporated, this model would spuriously be
disfavored in the standard analysis. This preference is driven mostly by excess
power from E-mode polarization at multipoles of $10 \lesssim \ell \lesssim 20$,
which may reflect remaining systematic errors in the data, a statistical
fluctuation, or signatures of the first stars. Measurements from the Planck
High Frequency Instrument (HFI) should be able to confirm or refute this hint
and future cosmic-variance limited E-mode polarization surveys can provide
substantially more information on these signatures |
X-ray Selected Galaxy Groups in Boötes: We present the X-ray and optical properties of the galaxy groups selected in
the Chandra X-Bo\"otes survey. Our final sample comprises 32 systems at
\textbf{$z<1.75$}, with 14 below $z = 0.35$. For these 14 systems we estimate
velocity dispersions ($\sigma_{gr}$) and perform a virial analysis to obtain
the radii ($R_{200}$ and $R_{500}$) and total masses ($M_{200}$ and $M_{500}$)
for groups with at least five galaxy members. We use the Chandra X-ray
observations to derive the X-ray luminosity ($L_X$). We examine the performance
of the group properties $\sigma_{gr}$, $L_{opt}$ and $L_X$, as proxies for the
group mass. Understanding how well these observables measure the total mass is
important to estimate how precisely the cluster/group mass function is
determined. Exploring the scaling relations built with the X-Bo\"otes sample
and comparing these with samples from the literature, we find a break in the
$L_X$-$M_{500}$ relation at approximately $M_{500} = 5\times10^{13}$ M$_\odot$
(for $M_{500} > 5\times10^{13}$ M$_\odot$, $M_{500} \propto L_X^{0.61\pm0.02}$,
while for $M_{500} \leq 5\times10^{13}$ M$_\odot$, $M_{500} \propto
L_X^{0.44\pm0.05}$). Thus, the mass-luminosity relation for galaxy groups
cannot be described by the same power law as galaxy clusters. A possible
explanation for this break is the dynamical friction, tidal interactions and
projection effects which reduce the velocity dispersion values of the galaxy
groups. By extending the cluster luminosity function to the group regime, we
predict the number of groups that new X-ray surveys, particularly eROSITA, will
detect. Based on our cluster/group luminosity function estimates, eROSITA will
identify $\sim$1800 groups ($L_X = 10^{41}-10^{43}$ ergs s$^{-1}$) within a
distance of 200 Mpc. Since groups lie in large scale filaments, this group
sample will map the large scale structure of the local universe. | Constraining the Black Hole Mass Spectrum with LISA Observations II:
Direct comparison of detailed models: A number of scenarios have been proposed for the origin of the supermassive
black holes (SMBHs) that are found in the centres of most galaxies. Many such
scenarios predict a high-redshift population of massive black holes (MBHs),
with masses in the range 100 to 100000 times that of the Sun. When the Laser
Interferometer Space Antenna (LISA) is finally operational, it is likely that
it will detect on the order of 100 of these MBH binaries as they merge. The
differences between proposed population models produce appreciable effects in
the portion of the population which is detectable by LISA, so it is likely that
the LISA observations will allow us to place constraints on them. However,
gravitational wave detectors such as LISA will not be able to detect all such
mergers nor assign precise black hole parameters to the merger, due to weak
gravitational wave signal strengths. This paper explores LISA's ability to
distinguish between several MBH population models. In this way, we go beyond
predicting a LISA observed population and consider the extent to which LISA
observations could inform astrophysical modellers. The errors in LISA parameter
estimation are applied with a direct method which generates random sample
parameters for each source in a population realisation. We consider how the
distinguishability varies depending on the choice of source parameters (1 or 2
parameters chosen from masses, redshift or spins) used to characterise the
model distributions, with confidence levels determined by 1 and 2-dimensional
tests based on the Kolmogorov-Smirnov test. |
High-precision multi-band measurements of the angular clustering of
X-ray sources: In this paper we present the two-point angular correlation function of the
X-ray source population of 1063 XMM-Newton observations at high Galactic
latitudes, comprising up to ~30000 sources over a sky area of 125.5 sq. deg, in
three energy bands: 0.5-2 (soft), 2-10 (hard), and 4.5-10 (ultrahard) keV. We
have measured the angular clustering of our survey and find significant
positive clustering signals in the soft and hard bands, and a marginal
clustering detection in the ultrahard band. We find dependency of the
clustering strength on the flux limit and no significant differences in the
clustering properties between sources with high hardness ratios and those with
low hardness ratios. Our results show that obscured and unobscured objects
share similar clustering properties and therefore they both reside in similar
environments, in agreement with the unified model of AGN. We deprojected the
angular clustering parameters via Limber's equation to compute their typical
spatial lengths. From that we have inferred the typical mass of the dark matter
haloes in which AGN at redshifts of ~1 are embedded. The short AGN lifetimes
derived suggest that AGN activity might be a transient phase that can be
experienced several times by a large fraction of galaxies throughout their
lives. | Distinguishing models of reionization using future radio observations of
21-cm 1-point statistics: We explore the impact of reionization topology on 21-cm statistics. Four
reionization models are presented which emulate large ionized bubbles around
over-dense regions (21CMFAST/ global-inside- out), small ionized bubbles in
over-dense regions (local-inside-out), large ionized bubbles around under-dense
regions (global-outside-in) and small ionized bubbles around under-dense
regions (local-outside-in). We show that first-generation instruments might
struggle to distinguish global models using the shape of the power spectrum
alone. All instruments considered are capable of breaking this degeneracy with
the variance, which is higher in outside-in models. Global models can also be
distinguished at small scales from a boost in the power spectrum from a
positive correlation between the density and neutral-fraction fields in
outside-in models. Negative skewness is found to be unique to inside-out models
and we find that pre-SKA instruments could detect this feature in maps smoothed
to reduce noise errors. The early, mid and late phases of reionization imprint
signatures in the brightness-temperature moments, we examine their model
dependence and find pre-SKA instruments capable of exploiting these timing
constraints in smoothed maps. The dimensional skewness is introduced and is
shown to have stronger signatures of the early and mid-phase timing if the
inside-out scenario is correct. |
The Current Status of Galaxy Formation: Understanding galaxy formation is one of the most pressing issues in
cosmology. We review the current status of galaxy formation from both an
observational and a theoretical perspective, and summarise the prospects for
future advances. | The Dependence of the $A_V$ Prior for SN\,Ia on Host Mass and Disk
Inclination: Supernovae type Ia (SNIa) are used as "standard candles" for cosmological
distance scales. To fit their light curve shape -- absolute luminosity
relation, one needs to assume an intrinsic color and a likelihood of host
galaxy extinction or a convolution of these, a color distribution prior. The
host galaxy extinction prior is typically assumed to be an exponential drop-off
for the current supernova programs ($P(A_V) \propto e^{-A_V/\tau_0}$). We
explore the validity of this prior using the distribution of extinction values
inferred when two galaxies accidentally overlap (an occulting galaxy pair). We
correct the supernova luminosity distances from the SDSS-III Supernova projects
(SDSS-SN) by matching the host galaxies to one of three templates from
occulting galaxy pairs based on the host galaxy mass and the $A_V$-bias -
prior-scale ($\tau_0$) relation from Jha et al. (2007).
We find that introducing an $A_V$ prior that depends on host mass results in
lowered luminosity distances for the SDSS-SN on average but it does not reduce
the scatter in individual measurements. This points, in our view, to the need
for many more occulting galaxy templates to match to SNIa host galaxies to rule
out this possible source of scatter in the SNIa distance measurements. We match
occulting galaxy templates based on both mass and projected radius and we find
that one should match by stellar mass first with radius as a secondary
consideration. We discuss the caveats of the current approach and our aim is to
convince the reader that a library of occulting galaxy pairs observed with HST
will provide sufficient priors to improve (optical) SNIa measurements to the
next required accuracy in Cosmology. |
Stability analysis and constraints on interacting viscous cosmology: In this work we study the evolution of a spatially flat Universe by
considering a viscous dark matter and perfect fluids for dark energy and
radiation, including an interaction term between dark matter and dark energy.
In the first part, we analyse the general properties of the Universe by
performing a stability analysis and then we constrain the free parameters of
the model using the latest and cosmological-independent measurements of the
Hubble parameter. We find consistency between the viscosity coefficient and the
condition imposed by the second law of the Thermodynamics. The second part is
dedicated to constrain the free parameter of the interacting viscous model
(IVM) for three particular cases: the viscous model (VM), interacting model
(IM), and the perfect fluid case (the concordance model). We report the
deceleration parameter to be $q_0 = -0.54^{+0.06}_{-0.05}$,
$-0.58^{+0.05}_{-0.04}$, $-0.58^{+0.05}_{-0.05}$, $-0.63^{+0.02}_{-0.02}$,
together with the jerk parameter as $j_0 = 0.87^{+0.06}_{-0.09}$,
$0.94^{+0.04}_{-0.06}$, $0.91^{+0.06}_{-0.10}$, $1.0$ for the IVM, VM, IM, and
LCDM respectively, where the uncertainties correspond at 68\% CL. Worth
mentioning that all the particular cases are in good agreement with LCDM, in
some cases producing even better fits, with the advantage of eliminating some
problems that afflicts the standard cosmological model. | On the galactic spin of barred disk galaxies: We present a study of the connection between the galactic spin parameter
$\lambda_{d}$ and the bar fraction in a volume-limited sample of 10,674 disk
galaxies drawn from the Sloan Digital Sky Survey Data Release 7. The galaxies
in our sample are visually classified into galaxies hosting long or short bars,
and non-barred galaxies. We find that the spin distributions of these three
classes are statistically different, with galaxies hosting long bars with the
lowest $\lambda_{d}$ values, followed by non-barred galaxies, while galaxies
with short bars present typically high spin parameters. The bar fraction
presents its maximum at low to intermediate $\lambda_{d}$ values for the case
of long bars, while the maximum for short bars is at high $\lambda_{d}$. This
bi-modality is in good agreement with previous studies finding longer bars
hosted by luminous, massive, red galaxies with low content of cold gas, while
short bars are found in low luminosity, low mass, blue galaxies, usually gas
rich. In addition, the rise and fall of the bar fraction as a function of
$\lambda_{d}$, within the long-bar sample, shown in our results, can be
explained as a result of two competing factors: the self-gravity of the disk
that enhances bar instabilities, and the support by random motions instead of
ordered rotational motion, that prevents the formation/growth of bars. |
Simulating the evolution of disc galaxies in a group environment. I. The
influence of the global tidal field: We present the results of a series of numerical simulations aimed to study
the evolution of a disc galaxy within the global tidal field of a group
environment. Both the disc galaxy and the group are modelled as
multi-component, collision-less, N-body systems, composed by both dark matter
and stars. In our simulations, the evolution of disc galaxies is followed as
their orbits sink towards the group centre, under the effect of dynamical
friction. We explore a broad parameter space, covering several aspects of the
galaxy-group interaction that are potentially relevant to galaxy evolution.
Namely, prograde and retrograde orbits, orbital eccentricities, disc
inclination, role of a central bulge in discs, internal disc kinematics, and
galaxy-to-group mass ratios. We find that significant disc transformations
occur only after the mean density of the group, measured within the orbit of
the galaxy, exceeds ~0.3-1 times the central mean density of the galaxy. The
morphological evolution of discs is found to be strongly dependent on the
initial inclination of the disc with respect to its orbital plane. That is,
discs on face-on and retrograde orbits are shown to retain longer their disc
structures and kinematics, in comparison to prograde discs. This suggests that
after interacting with the global tidal field alone, a significant fraction of
disc galaxies should be found in the central regions of groups. Prominent
central bulges are not produced, and pre-existing bulges are not enhanced in
discs after the interaction with the group. Assuming that most S0 are formed in
group environments, this implies that prominent bulges should be formed mostly
by young stars, created only after a galaxy has been accreted by a group.
Finally, contrary to some current implementations of tidal stripping in
semi-analytical models of galaxy evolution, we find that more massive galaxies
suffer more tidal stripping. | Velocity Structure Diagnostics of Simulated Galaxy Clusters: Gas motions in the hot intracluster medium of galaxy clusters have an
important effect on the mass determination of the clusters through X-ray
observations. The corresponding dynamical pressure has to be accounted for in
addition to the hydrostatic pressure support to achieve a precise mass
measurement. An analysis of the velocity structure of the ICM for simulated
cluster-size haloes, especially focusing on rotational patterns, has been
performed, demonstrating them to be an intermittent phenomenon, strongly
related to the internal dynamics of substructures. We find that the expected
build-up of rotation due to mass assembly gets easily destroyed by passages of
gas-rich substructures close to the central region. Though, if a typical
rotation pattern is established, the corresponding mass contribution is
estimated to be up to ~17% of the total mass in the innermost region, and one
has to account for it. Extending the analysis to a larger sample of simulated
haloes we statistically observe that (i) the distribution of the rotational
component of the gas velocity in the innermost region has typical values of
~200-300 km/s; (ii) except for few outliers, there is no monotonic increase of
the rotational velocity with decreasing redshift, as we would expect from
approaching a relaxed configuration. Therefore, the hypothesis that the
build-up of rotation is strongly influenced by internal dynamics is confirmed,
and minor events like gas-rich substructures passing close to the equatorial
plane can easily destroy any ordered rotational pattern. |
Gravitational Wave Background and Non-Gaussianity as a Probe of the
Curvaton Scenario: We study observational implications of the stochastic gravitational wave
background and a non-Gaussian feature of scalar perturbations on the curvaton
mechanism of the generation of density/curvature fluctuations, and show that
they can determine the properties of the curvaton in a complementary manner to
each other. Therefore even if Planck could not detect any non-Gaussianity,
future space-based laser interferometers such as DECIGO or BBO could
practically exhaust its parameter space. | Weak-lensing observables in relativistic N-body simulations: We present a numerical weak-lensing analysis that is fully relativistic and
non-perturbative for the scalar part of the gravitational potential and
first-order in the vector part, frame dragging. Integrating the photon
geodesics backwards from the observer to the emitters, we solve the Sachs
optical equations and study in detail the weak-lensing convergence, ellipticity
and rotation. For the first time, we apply such an analysis to a
high-resolution relativistic N-body simulation, which consistently includes the
leading-order corrections due to general relativity on both large and small
scales. These are related to the question of gauge choice and to post-Newtonian
corrections, respectively. We present the angular power spectra and one-point
probability distribution functions for the weak-lensing variables, which we
find are broadly in agreement with comparable Newtonian simulations. Our
geometric approach, however, is more robust and flexible, and can therefore be
applied consistently to non-standard cosmologies and modified theories of
gravity. |
Constraints on Earth-mass primordial black holes from OGLE 5-year
microlensing events: We constrain the abundance of primordial black holes (PBH) using 2622
microlensing events obtained from 5-years observations of stars in the Galactic
bulge by the Optical Gravitational Lensing Experiment (OGLE). The majority of
microlensing events display a single or at least continuous population that has
a peak around the light curve timescale $t_{\rm E}\simeq 20~{\rm days}$ and a
wide distribution over the range $t_{\rm E}\simeq [1, 300]~{\rm days}$, while
the data also indicates a second population of 6 ultrashort-timescale events in
$t_{\rm E}\simeq [0.1,0.3]~{\rm days}$, which are advocated to be due to
free-floating planets. We confirm that the main population of OGLE events can
be well modeled by microlensing due to brown dwarfs, main sequence stars and
stellar remnants (white dwarfs and neutron stars) in the standard Galactic
bulge and disk models for their spatial and velocity distributions. Using the
dark matter (DM) model for the Milky Way (MW) halo relative to the Galactic
bulge/disk models, we obtain the tightest upper bound on the PBH abundance in
the mass range $M_{\rm PBH}\simeq[10^{-6},10^{-3}]M_\odot$ (Earth-Jupiter mass
range), if we employ null hypothesis that the OGLE data does not contain any
PBH microlensing event. More interestingly, we also show that Earth-mass PBHs
can well reproduce the 6 ultrashort-timescale events, without the need of
free-floating planets, if the mass fraction of PBH to DM is at a per cent
level, which is consistent with other constraints such as the microlensing
search for Andromeda galaxy (M31) and the longer timescale OGLE events. Our
result gives a hint of PBH existence, and can be confirmed or falsified by
microlensing search for stars in M31, because M31 is towards the MW halo
direction and should therefore contain a much less number of free-floating
planets, even if exist, than the direction to the MW center. | Gravitational Lensing with Three-Dimensional Ray Tracing: High redshift sources suffer from magnification or demagnification due to
weak gravitational lensing by large scale structure. One consequence of this is
that the distance-redshift relation, in wide use for cosmological tests,
suffers lensing-induced scatter which can be quantified by the magnification
probability distribution. Predicting this distribution generally requires a
method for ray-tracing through cosmological N-body simulations. However,
standard methods tend to apply the multiple thin-lens approximation. In an
effort to quantify the accuracy of these methods, we develop an innovative code
that performs ray-tracing without the use of this approximation. The efficiency
and accuracy of this computationally challenging approach can be improved by
careful choices of numerical parameters; therefore, the results are analysed
for the behaviour of the ray-tracing code in the vicinity of Schwarzschild and
Navarro-Frenk-White lenses. Preliminary comparisons are drawn with the multiple
lens-plane ray-bundle method in the context of cosmological mass distributions
for a source redshift of $z_{s}=0.5$. |
The XMM-Newton Wide Angle Survey (XWAS): the X-ray spectrum of type-1
AGN: We discuss the broad band X-ray properties of one of the largest samples of
X-ray selected type-1 AGN to date (487 objects in total), drawn from the
XMM-Newton Wide Angle Survey. The objects cover 2-10 keV luminosities from
~10^{42}-10^{45} erg s^{-1} and are detected up to redshift ~4. We constrain
the overall properties of the broad band continuum, soft excess and X-ray
absorption, along with their dependence on the X-ray luminosity and redshift
and we discuss the implications for models of AGN emission. We constrained the
mean spectral index of the broad band X-ray continuum to <Gamma>=1.96+-0.02
with intrinsic dispersion sigma=0.27_{-0.02}^{+0.01}. The continuum becomes
harder at faint fluxes and at higher redshifts and luminosities. The dependence
of Gamma with flux is likely due to undetected absorption rather than to
spectral variation. We found a strong dependence of the detection efficiency of
objects on the spectral shape which can have a strong impact on the measured
mean continuum shapes of sources at different redshifts and luminosities. We
detected excess absorption in ~3% of our objects, with column densities ~a few
x10^{22} cm^{-2}. The apparent mismatch between the optical classification and
X-ray properties of these objects is a challenge for the standard AGN
unification model. We found that the fraction of objects with detected soft
excess is ~36%. Using a thermal model, we constrained the soft excess mean
temperature and intrinsic dispersion to <kT>~100 eV and sigma~34 eV. The origin
of the soft excess as thermal emission from the accretion disk or Compton
scattered disk emission is ruled out on the basis of the temperatures detected
and the lack of correlation of the measured temperature with the X-ray
luminosity (abridged). | Extended UV Disks and UV-Bright Disks in Low-Mass E/S0 Galaxies: We have identified 15 XUV disks in a largely field sample of 38 E/S0 galaxies
with stellar masses primarily below ~4 x 10^10 M_sun and comparable numbers on
the red and blue sequences. We use a new purely quantitative XUV disk
definition requiring UV extension relative to a UV-defined star formation
threshold radius. The 39(+-9)% XUV-disk frequency for these E/S0s is roughly
twice the ~20% reported for late types, possibly indicating that XUV disks are
associated with galaxies experiencing weak or inefficient star formation.
Consistent with this interpretation, the XUV disks in our sample do not
correlate with enhanced outer-disk star formation as traced by blue optical
outer-disk colors. However, UV-Bright (UV-B) disk galaxies with blue UV colors
outside their optical 50% light radii do display enhanced optical outer-disk
star formation as well as enhanced atomic gas content. UV-B disks occur with a
42(+9/-8)% frequency, and the combined XUV/UV-B frequency is 61(+-9)%. For both
types, UV colors typically imply <1 Gyr ages. XUV disks occur over the full
sample mass range and on both sequences, suggesting an association with galaxy
interactions or another general evolutionary process. In contrast, UV-B disks
favor the blue sequence and may also prefer low masses, perhaps reflecting the
onset of cold-mode accretion or another mass-dependent evolutionary process.
Virtually all blue E/S0s in the gas-rich regime below stellar mass M_t ~ 5 x
10^9 M_sun (the "gas-richness threshold mass") display UV-B disks. [abridged] |
Cosmic Topology: This review aims to cover the central aspects of current research in cosmic
topology from a topological and observational perspective. Beginning with an
overview of the basic concepts of cosmology, it is observed that though a
determinant of local curvature, Einstein's equations of relativity do not
constrain the global properties of space-time. The topological requirements of
a universal space time manifold are discussed, including requirements of
space-time orientability and causality. The basic topological concepts used in
classification of spaces, i.e. the concept of the Fundamental Domain and
Universal covering spaces are discussed briefly. The manifold properties and
symmetry groups for three dimensional manifolds of constant curvature for
negative, positive and zero curvature manifolds are laid out.
Multi-connectedness is explored as a possible explanation for the detected
anomalies in the quadrupole and octopole regions of the power spectrum,
pointing at a possible compactness along one or more directions in space. The
statistical significance of the evidence, however, is also scrutinized and I
discuss briefly the bayesian and frequentist interpretation of the posterior
probabilities of observing the anomalies in a Lambda CDM universe. Some of the
major topologies that have been proposed and investigated as possible
candidates of a universal manifold are the Poincare Dodecahedron and Bianchi
Universes, which are studied in detail. Lastly, the methods that have been
proposed for detecting a multi connected signature are discussed. These include
ingenious observational methods like the circles in the sky method, cosmic
crystallography and Bayesian Analysis which provides the additional advantage
of being free from measurement errors and uses the posterior likelihoods of
models. As of the recent Planck mission, no pressing evidence of a multi
connected topology has been detected. | Radiation pressure confinement - II. Application to the broad line
region in active galactic nuclei: Active galactic nuclei (AGN) are characterized by similar broad emission
lines properties at all luminosities ($10^{39}$-$10^{47}$ erg s$^{-1}$). What
produces this similarity over a vast range of $10^8$ in luminosity?
Photoionization is inevitably associated with momentum transfer to the
photoionized gas. Yet, most of the photoionized gas in the Broad Line Region
(BLR) follows Keplerian orbits, which suggests that the BLR originates from gas
with a large enough column for gravity to dominate. The photoionized surface
layer of the gas must develop a pressure gradient due to the incident radiation
force. We present solutions for the structure of such a hydrostatic
photoionized gas layer in the BLR. The gas is stratified, with a low-density
highly-ionized surface layer, a density rise inwards, and a uniform-density
cooler inner region, where the gas pressure reaches the incident radiation
pressure. This radiation pressure confinement (RPC) of the photoionized layer
leads to a universal ionization parameter $U\sim 0.1$ in the inner photoionized
layer, independent of luminosity and distance. Thus, RPC appears to explain the
universality of the BLR properties in AGN. We present predictions for the BLR
emission per unit covering factor, as a function of distance from the ionizing
source, for a range of ionizing continuum slopes and gas metallicity. The
predicted mean strength of most lines (excluding H$\beta$), and their different
average-emission radii, are consistent with the available observations. |
A fast particle-mesh simulation of non-linear cosmological structure
formation with massive neutrinos: Quasi-N-body simulations, such as FastPM, provide a fast way to simulate
cosmological structure formation, but have yet to adequately include the
effects of massive neutrinos. We present a method to include neutrino particles
in FastPM, enabling computation of the CDM and total matter power spectra to
percent-level accuracy in the non-linear regime. The CDM-neutrino cross-power
can also be computed at a sufficient accuracy to constrain cosmological
observables. To avoid the shot noise that typically plagues neutrino particle
simulations, we employ a quasi-random algorithm to sample the relevant
Fermi-Dirac distribution when setting the initial neutrino thermal velocities.
We additionally develop an effective distribution function to describe a set of
non-degenerate neutrinos as a single particle to speed up non-degenerate
simulations. The simulation is accurate for the full range of physical
interest, $M_\nu \lesssim 0.6$eV, and applicable to redshifts $z\lesssim2$.
Such accuracy can be achieved by initializing particles with the two-fluid
approximation transfer functions (using the REPS package). Convergence can be
reached in $\sim 25$ steps, with a starting redshift of $z=99$. Probing
progressively smaller scales only requires an increase in the number of CDM
particles being simulated, while the number of neutrino particles can remain
fixed at a value less than or similar to the number of CDM particles. In turn,
the percentage increase in runtime-per-step due to neutrino particles is
between $\sim 5-20\%$ for runs with $1024^3$ CDM particles, and decreases as
the number of CDM particles is increased. The code has been made publicly
available, providing an invaluable resource to produce fast predictions for
cosmological surveys and studying reconstruction. | Evolution of the Far-Infrared-Radio Correlation and Infrared SEDs of
Massive Galaxies over z = 0 - 2: We investigate the far-infrared-radio correlation (FRC) of
stellar-mass-selected galaxies in the Extended Chandra Deep Field South using
far-infrared imaging from Spitzer and radio imaging from the Very Large Array
and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe
galaxies below the noise and confusion limits. Radio fluxes are K-corrected
using observed flux ratios, leading to tentative evidence for an evolution in
spectral index. We compare spectral energy distribution (SED) templates of
local galaxies for K-correcting FIR fluxes, and show that the data are best fit
by a quiescent spiral template (M51) rather than a warm starburst (M82) or
ULIRG (Arp220), implying a predominance of cold dust in massive galaxies at
high redshift. In contrast we measure total infrared luminosities that are
consistent with high star-formation rates. We observe that the FRC index (q)
does not evolve significantly over z=0-2 when computed from K-corrected 24 or
160-mum photometry, but that using 70-mum fluxes leads to an apparent decline
in q beyond z~1. This suggests some change in the SED at high redshift, either
a steepening of the spectrum at rest-frame ~25-35mum or a deficiency at ~70mum
leading to a drop in the total infrared/radio ratios. We compare our results to
other work in the literature and find synergies with recent findings on the
high-redshift FRC, high specific star-formation rates of massive galaxies and
the cold dust temperatures in these galaxies. |
Cosmology in the non-linear regime : the small scale miracle: Interest rises to exploit the full shape information of the galaxy power
spectrum, as well as pushing analyses to smaller non-linear scales. Here I use
the halo model to quantify the information content in the tomographic angular
power spectrum of galaxies, for future high resolution surveys : Euclid and
SKA2. I study how this information varies as a function of the scale cut
applied, either with angular cut $\ell_{max}$ or physical cut kmax. For this, I
use analytical covariances with the most complete census of non-Gaussian terms,
which proves critical. I find that the Fisher information on most cosmological
and astrophysical parameters follows a striking behaviour. Beyond the
perturbative regime we first get decreasing returns : the information keeps
rising but the slope slows down until reaching a saturation. The location of
this plateau is a bit beyond the reach of current modeling methods : k $\sim$ 2
Mpc$^{-1}$ and slightly depends on the parameter and redshift bin considered. I
explain the origin of this plateau, which is due to non-linear effects both on
the power spectrum, and more importantly on non-Gaussian covariance terms.
Then, pushing further we see the information rising again in the highly
non-linear regime, with a steep slope. This is the small scale miracle, for
which I give interpretation and discuss the properties. Hints are shown that
this information should be disentanglable from the astrophysical content, and
could improve Dark Energy constraints. Finally, more hints are shown that high
order statistics may yield significant improvements over the power spectrum in
this regime, with the improvements increasing with kmax. Data and notebooks
reproducing all plots and results will be made available at
\url{https://github.com/fabienlacasa/SmallScaleMiracle} | Formation of Relativistic Axion Stars: Axions and axion-like particles are compelling candidates for the missing
dark matter of the universe. As they undergo gravitational collapse, they can
form compact objects such as axion stars or even black holes. In this paper, we
study the formation and distribution of such objects. First, we simulate the
formation of compact axion stars using numerical relativity with aspherical
initial conditions that could represent the final stages of axion dark matter
structure formation. We show that the final states of such collapse closely
follow the known relationship of initial mass and axion decay constant $f_a$.
Second, we demonstrate with a toy model how this information can be used to
scan a model density field to predict the number densities and masses of such
compact objects. In addition to being detectable by the LIGO/VIRGO
gravitational wave interferometer network for axion mass of $10^{-9} < m_a <
10^{-11}$ eV, we show using peak statistics that for $f_a < 0.2M_{pl}$, there
exists a "mass gap" between the masses of axion stars and black holes formed
from collapse. |
Cosmic Birefringence Test of the Hubble Tension: An early dark energy component consisting of a cosmic pseudo Nambu-Goldstone
boson has been recently proposed to resolve the Hubble tension -- the
four-sigma discrepancy between precision measurements of the expansion rate of
the universe. Here we point out that such an axion-like component may be
expected to couple to electromagnetism by a Chern-Simons term, and will thereby
induce an anisotropic cosmic birefringence signal in the polarization of the
cosmic microwave background (CMB). We show that observations of the
rotation-angle power spectrum and cross-correlation with CMB temperature
anisotropy can confirm the presence of this early dark energy component. Future
CMB data as expected from the CMB-S4 experiment will improve sensitivity to
this effect by two orders of magnitude and help in discriminating between
different Hubble tension scenarios. | What can we learn from higher multipole power spectra of galaxy
distribution in redshift space?: We investigate a potential of the higher multipole power spectra of the
galaxy distribution in redshift space as a cosmological probe on halo scales.
Based on the fact that a halo model explains well the multipole power spectra
of the luminous red galaxy (LRG) sample in the Sloan Digital Sky Survey (SDSS),
we focus our investigation on the random motions of the satellite LRGs that
determine the higher multipole spectra at large wavenumbers. We show that our
theoretical model fits the higher multipole spectra at large wave numbers from
N-body numerical simulations and we apply these results for testing the gravity
theory and the velocity structure of galaxies on the halo scales. In this
analysis, we use the multipole spectra P_4(k) and P_6(k) on the small scales of
the range of wavenumber 0.3<k/[h{Mpc}^{-1}]<0.6, which is in contrast to the
usual method of testing gravity by targeting the linear growth rate on very
large scales. We demonstrate that our method could be useful for testing
gravity on the halo scales. |
The evolution of the spatially-resolved metal abundance in galaxy
clusters up to z=1.4: We present the combined analysis of the metal content of 83 objects in the
redshift range 0.09-1.39, and spatially-resolved in the 3 bins (0-0.15,
0.15-0.4, >0.4) R500, as obtained with similar analysis using XMM-Newton data
in Leccardi & Molendi (2008) and Baldi et al. (2012). We use the pseudo-entropy
ratio to separate the Cool-Core (CC) cluster population, where the central gas
density tends to be relatively higher, cooler and more metal rich, from the
Non-Cool-Core systems. The average, redshift-independent, metal abundance
measured in the 3 radial bins decrease moving outwards, with a mean metallicity
in the core that is even 3 (two) times higher than the value of 0.16 times the
solar abundance in Anders & Grevesse (1989) estimated at r>0.4 R500 in CC (NCC)
objects. We find that the values of the emission-weighted metallicity are
well-fitted by the relation $Z(z) = Z_0 (1+z)^{-\gamma}$ at given radius. A
significant scatter, intrinsic to the observed distribution and of the order of
0.05-0.15, is observed below 0.4 R500. The nominal best-fit value of $\gamma$
is significantly different from zero in the inner cluster regions ($\gamma =
1.6 \pm 0.2$) and in CC clusters only. These results are confirmed also with a
bootstrap analysis, which provides a still significant negative evolution in
the core of CC systems (P>99.9 per cent). No redshift-evolution is observed
when regions above the core (r > 0.15 R500) are considered. A reasonable good
fit of both the radial and redshift dependence is provided from the functional
form $Z(r,z)=Z_0 (1+(r/0.15 R500)^2)^{-\beta} (1+z)^{-\gamma}$, with $(Z_0,
\beta, \gamma) = (0.83 \pm 0.13, 0.55 \pm 0.07, 1.7 \pm 0.6)$ in CC clusters
and $(0.39 \pm 0.04, 0.37 \pm 0.15, 0.5 \pm 0.5)$ for NCC systems. Our results
represent the most extensive study of the spatially-resolved metal distribution
in the cluster plasma as function of redshift. | HerMES: A Statistical Measurement of the Redshift Distribution of
Herschel-SPIRE Sources Using the Cross-correlation Technique: The wide-area imaging surveys with the {\it Herschel} Space Observatory at
sub-mm wavelengths have now resulted in catalogs of order one hundred thousand
dusty, star-burst galaxies. We make a statistical estimate of $N(z)$ using a
clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500
$\mu$m from the Herschel Multi-tiered Extragalactic Survey (HerMES) centered on
the Bo\"{o}tes field. We cross-correlate {\it Herschel} galaxies against galaxy
samples at optical and near-IR wavelengths from the Sloan Digital Sky Survey
(SDSS), the NOAO Deep Wide Field Survey (NDWFS) and the Spitzer Deep Wide Field
Survey (SDWFS). We create optical and near-IR galaxy samples based on their
photometric or spectroscopic redshift distributions and test the accuracy of
those redshift distributions with similar galaxy samples defined with catalogs
of the Cosmological Evolution Survey (COSMOS), as the COSMOS field has superior
spectroscopy coverage. We model-fit the clustering auto and cross-correlations
of {\it Herschel} and optical/IR galaxy samples to estimate $N(z)$ and
clustering bias factors. The $S_{350} > 20$ mJy galaxies have a bias factor
varying with redshift as $b(z)=1.0^{+1.0}_{-0.5}(1+z)^{1.2^{+0.3}_{-0.7}}$.
This bias and the redshift dependence is broadly in agreement with galaxies
that occupy dark matter halos of mass in the range of 10$^{12}$ to 10$^{13}$
M$_{\sun}$. We find that the redshift distribution peaks around $z \sim 0.5$ to
1 for galaxies selected at 250 $\mu$m with an average redshift of $< z > = 1.8
\pm 0.2$. For 350 and 500 $\mu$m-selected SPIRE samples the peak shifts to
higher redshift, but the average redshift remains the same with a value of $1.9
\pm 0.2$. |
The X-ray Properties of Optically Selected Clusters of Galaxies: We present the results of Chandra and Suzaku X-ray observations of nine
moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence
Cluster Survey (RCS). Surface brightness profiles are fitted to beta models,
gas masses are determined, integrated spectra are extracted within R2500, and
X-ray temperatures and luminosities are inferred. The Lx-Tx relationship
expected from self-similar evolution is tested by comparing this sample to our
previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically
selected clusters. We find that optically selected clusters are systematically
less luminous than X-ray selected clusters of similar X-ray temperature at both
moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation
with these data, but find it consistent with no evolution, within relatively
large uncertainties. To investigate selection effects, we compare the X-ray
properties of our sample to those of clusters in the representative X-ray
selected REXCESS sample, also determined within R2500. We find that while RCS
cluster X-ray properties span the entire range of those of massive clusters
selected by other methods, their average X-ray properties are most similar to
those of dynamically disturbed X-ray selected clusters. This similarity
suggests that the true cluster distribution might contain a higher fraction of
disturbed objects than are typically detected in X-ray selected surveys. | A Revised SALT2 Surface for Fitting Type Ia Supernova Light Curves: We present a revised SALT2 surface (`SALT2-2021') for fitting the light
curves of Type Ia supernovae (SNe Ia), which incorporates new measurements of
zero-point calibration offsets and Milky Way extinction. The most notable
change in the new surface occurs in the UV region. This new surface alters the
distance measurements of SNe~Ia, which can be used to investigate the nature of
dark energy by probing the expansion history of the Universe. Using the revised
SALT2 surface on public data from the first three years of the Dark Energy
Survey Supernova Program (combined with an external low-$z$ SNe Ia sample) and
combining with cosmic microwave background constraints, we find a change in the
dark energy equation of state parameter, $\Delta w = 0.015 \pm 0.004$. This
result highlights the continued importance of controlling and reducing
systematic uncertainties, particularly with the next generation of supernova
analyses aiming to improve constraints on dark energy properties. |
Combined analysis of galaxy cluster number count, thermal
Sunyaev-Zel'dovich power spectrum, and bispectrum: The Sunyaev-Zel'dovich (SZ) effect is a powerful probe of the evolution of
structures in the universe, and is thus highly sensitive to cosmological
parameters $\sigma_8$ and $\Omega_m$, though its power is hampered by the
current uncertainties on the cluster mass calibration. In this analysis we
revisit constraints on these cosmological parameters as well as the hydrostatic
mass bias, by performing (i) a robust estimation of the tSZ power-spectrum,
(ii) a complete modeling and analysis of the tSZ bispectrum, and (iii) a
combined analysis of galaxy clusters number count, tSZ power spectrum, and tSZ
bispectrum. From this analysis, we derive as final constraints $\sigma_8 = 0.79
\pm 0.02$, $\Omega_{\rm m} = 0.29 \pm 0.02$, and $(1-b) = 0.71 \pm 0.07$. These
results favour a high value for the hydrostatic mass bias compared to numerical
simulations and weak-lensing based estimations. They are furthermore consistent
with both previous tSZ analyses, CMB derived cosmological parameters, and
ancillary estimations of the hydrostatic mass bias. | The effect of selection -- a tale of cluster mass measurement bias
induced by correlation and projection: Cosmology analyses using galaxy clusters by the Dark Energy Survey have
recently uncovered an issue of previously unknown selection effect affecting
weak lensing mass estimates. In this letter, we use the Illustris-TNG
simulation to demonstrate that selecting on galaxy counts induces a selection
effect because of projection and correlation between different observables. We
compute the weak-lensing-like projected mass estimations of dark matter halos
and examine their projected subhalo counts. In the 2-D projected space, halos
that are measured as more massive than truth have higher subhalo counts. Thus,
projection along the line of sight creates cluster observables that are
correlated with cluster mass measurement deviations, which in turn creates a
mass measurement bias when the clusters are selected by this correlated
observable. We demonstrate that the bias is predicted in a forward model using
the observable-mass measurement correlation. |
Observational signatures of modified gravity on ultra-large scales: Extremely large surveys with future experiments like Euclid and the SKA will
soon allow us to access perturbation modes close to the Hubble scale, with
wavenumbers $k \sim \mathcal{H}$. If a modified gravity theory is responsible
for cosmic acceleration, the Hubble scale is a natural regime for deviations
from General Relativity (GR) to become manifest. The majority of studies to
date have concentrated on the consequences of alternative gravity theories for
the subhorizon, quasi-static regime, however. In this paper we investigate how
modifications to the gravitational field equations affect perturbations around
the Hubble scale. We choose functional forms to represent the generic
scale-dependent behaviour of gravity theories that modify GR at long
wavelengths, and study the resulting deviations of ultra large-scale
relativistic observables from their GR behaviour. We find that these are small
unless modifications to the field equations are drastic. The angular dependence
and redshift evolution of the deviations is highly parameterisation- and
survey-dependent, however, and so they are possibly a rich source of modified
gravity phenomenology if they can be measured. | Cosmological Constraints on Interacting Light Particles: Cosmological observations are becoming increasingly sensitive to the effects
of light particles in the form of dark radiation (DR) at the time of
recombination. The conventional observable of effective neutrino number,
$N_{\rm eff}$, is insufficient for probing generic, interacting models of DR.
In this work, we perform likelihood analyses which allow both free-streaming
effective neutrinos (parametrized by $N_{\rm eff}$) and interacting effective
neutrinos (parametrized by $N_{\rm fld}$). We motivate an alternative
parametrization of DR in terms of $N_{\rm tot}$ (total effective number of
neutrinos) and $f_{\rm fs}$ (the fraction of effective neutrinos which are
free-streaming), which is less degenerate than using $N_{\rm eff}$ and $N_{\rm
fld}$. Using the Planck 2015 likelihoods in conjunction with measurements of
baryon acoustic oscillations (BAO), we find constraints on the total amount of
beyond the Standard Model effective neutrinos (both free-streaming and
interacting) of $\Delta N_{\rm tot} < 0.39$ at 2$\sigma$. In addition, we
consider the possibility that this scenario alleviates the tensions between
early-time and late-time cosmological observations, in particular the
measurements of $\sigma_8$ (the amplitude of matter power fluctuations at
8$h^{-1}$ Mpc), finding a mild preference for interactions among light species.
We further forecast the sensitivities of a variety of future experiments,
including Advanced ACTPol (a representative CMB Stage-III experiment), CMB
Stage-IV, and the Euclid satellite. This study is relevant for probing
non-standard neutrino physics as well as a wide variety of new particle physics
models beyond the Standard Model that involve dark radiation. |
Perturbations of ultralight vector field dark matter: We study the dynamics of cosmological perturbations in models of dark matter
based on ultralight coherent vector fields. Very much as for scalar field dark
matter, we find two different regimes in the evolution: for modes with $k^2\ll
{\cal H}ma$, we have a particle-like behaviour indistinguishable from cold dark
matter, whereas for modes with $k^2\gg {\cal H}ma$, we get a wave-like
behaviour in which the sound speed is non-vanishing and of order $c_s^2\simeq
k^2/m^2a^2$. This implies that, also in these models, structure formation could
be suppressed on small scales. However, unlike the scalar case, the fact that
the background evolution contains a non-vanishing homogeneous vector field
implies that, in general, the evolution of the three kinds of perturbations
(scalar, vector and tensor) can no longer be decoupled at the linear level.
More specifically, in the particle regime, the three types of perturbations are
actually decoupled, whereas in the wave regime, the three vector field
perturbations generate one scalar-tensor and two vector-tensor perturbations in
the metric. Also in the wave regime, we find that a non-vanishing anisotropic
stress is present in the perturbed energy-momentum tensor giving rise to a
gravitational slip of order $(\Phi-\Psi)/\Phi\sim c_s^2$. Moreover in this
regime the amplitude of the tensor to scalar ratio of the scalar-tensor modes
is also $h/\Phi\sim c_s^2$. This implies that small-scale density perturbations
are necessarily associated to the presence of gravity waves in this model. We
compare their spectrum with the sensitivity of present and future gravity waves
detectors. | Confirmation of Intervening Filaments of Galaxies at the Redshifts of
$Chandra$ WHIM Absorption Features: We report the $a~posteriori$ confirmation of two large-scale filaments along
the sight-line of the blazar 1ES~1553+113, which correspond to Warm-Hot
Intergalactic Medium (WHIM) absorption features in the X-ray and far
ultraviolet. We use the WISE-SuperCOSMOS photometric catalog to map the
cosmic-web in the direction of the blazar, and find significant filaments at
redshifts of $z=0.23\pm0.02$ and $z=0.31\pm0.02$, which roughly align with the
absorption redshifts. A third X-ray absorption feature at $z_X=0.133$ did not
have any corresponding structures in the photometric catalog. |
Self-Similar Solutions of Triaxial Dark Matter Halos: We investigate the collapse and internal structure of dark matter halos. We
consider halo formation from initially scale-free perturbations, for which
gravitational collapse is self-similar. Fillmore and Goldreich (1984) and
Bertschinger (1985) solved the one dimensional (i.e. spherically symmetric)
case. We generalize their results by formulating the three dimensional
self-similar equations. We solve the equations numerically and analyze the
similarity solutions in detail, focusing on the internal density profiles of
the collapsed halos. By decomposing the total density into subprofiles of
particles that collapse coevally, we identify two effects as the main
determinants of the internal density structure of halos: adiabatic contraction
and the shape of a subprofile shortly after collapse; the latter largely
reflects the triaxiality of the subprofile. We develop a simple model that
describes the results of our 3D simulations. In a companion paper, we apply
this model to more realistic cosmological fluctuations, and thereby explain the
origin of the nearly universal (NFW-like) density profiles found in N-body
simulations. | Revealing local failed supernovae with neutrino telescopes: We study the detectability of neutrino bursts from nearby direct black
hole-forming collapses (failed supernovae) at Megaton detectors. Due to their
high energetics, these bursts could be identified - by the time coincidence of
N >= 2 or N >= 3 events within a ~ 1 s time window - from as far as ~ 4-5 Mpc
away. This distance encloses several supernova-rich galaxies, so that failed
supernova bursts could be detected at a rate of up to one per decade,
comparable to the expected rate of the more common, but less energetic, neutron
star-forming collapses. Thus, the detection of a failed supernova within the
lifetime of a Mt detector is realistic. It might give the first evidence of
direct black hole formation, with important implications on the physics of this
phenomenon. |
A SQUID-based microwave cavity search for dark-matter axions: Axions in the micro eV mass range are a plausible cold dark matter candidate
and may be detected by their conversion into microwave photons in a resonant
cavity immersed in a static magnetic field. The first result from such an axion
search using a superconducting first-stage amplifier (SQUID) is reported. The
SQUID amplifier, replacing a conventional GaAs field-effect transistor
amplifier, successfully reached axion-photon coupling sensitivity in the band
set by present axion models and sets the stage for a definitive axion search
utilizing near quantum-limited SQUID amplifiers. | Separating the memory of reionization from cosmology in the Ly$α$
forest power spectrum at the post-reionization era: It has been recently shown that the astrophysics of reionization can be
extracted from the Ly$\alpha$ forest power spectrum by marginalizing the memory
of reionization over cosmological information. This impact of cosmic
reionization on the Ly$\alpha$ forest power spectrum can survive cosmological
time scales because cosmic reionization, which is inhomogeneous, and subsequent
shocks from denser regions can heat the gas in low-density regions to $\sim
3\times10^4$ K and compress it to mean-density. Current approach of
marginalization over the memory of reionization, however, is not only
model-dependent, based on the assumption of a specific reionization model, but
also computationally expensive. Here we propose a simple analytical template
for the impact of cosmic reionization, thereby treating it as a broadband
systematic to be marginalized over for Bayesian inference of cosmological
information from the Ly$\alpha$ forest in a model-independent manner. This
template performs remarkably well with an error of $\leq 6 \%$ at large scales
$k \approx 0.19$ Mpc$^{-1}$ where the effect of the memory of reionization is
important, and reproduces the broadband effect of the memory of reionization in
the Ly$\alpha$ forest correlation function, as well as the expected bias of
cosmological parameters due to this systematic. The template can successfully
recover the morphology of forecast errors in cosmological parameter space as
expected when assuming a specific reionization model for marginalization
purposes, with a slight overestimation of tens of per cent for the forecast
errors on the cosmological parameters. We further propose a similar template
for this systematic on the Ly$\alpha$ forest 1D power spectrum. |
Can Primordial Black Holes form in the Standard Model ?: We investigate the viability of primordial black hole (PBH) formation in the
Standard Model (SM) in a scenario that does not rely on specific inflationary
features or any exotic physics such as phase transitions or non-minimal
coupling to gravity. If the Brout-Englert-Higgs (BEH) field lies exactly at the
transition between metastability and stability, its potential exhibits an
inflexion point due to radiative corrections. The BEH can act like a stochastic
curvaton field, leading to a non-Gaussian tail of large curvature fluctuations
that later collapse into PBHs when they re-enter inside the horizon. This
scenario would require a precise value of the top-quark mas to ensure the Higgs
stability, which is disfavored but still consistent with the most recent
measurements. However, we also find that large curvature fluctuations are also
generated on cosmological scales that are inconsistent with cosmic microwave
background (CMB) observations. We therefore conclude that the SM cannot have
led to the formation of PBHs based on this mechanism. Nevertheless, a variation
of the scenario based on the Palatini formulation of gravity may have provided
the conditions to produce stellar-mass PBHs with an abundance comparable to
dark matter, without producing too large curvature fluctuations on cosmological
scales. | Linking multipole vectors and pseudoentropies for CMB analysis: Multipole vectors and pseudoentropies provide powerful tools for a
numerically fast and vivid investigation of possible statistically anisotropic,
respectively non-Gaussian signs in CMB temperature fluctuations. After
reviewing and linking these two conceptions we compare their application to
data analysis using the Planck 2015 NILC full sky map. |
Quantifying the global parameter tensions between ACT, SPT and Planck: The overall cosmological parameter tension between the Atacama Cosmology
Telescope 2020 (ACT) and Planck 2018 data within the concordance cosmological
model is quantified using the suspiciousness statistic to be 2.6$\sigma$.
Between ACT and the South Pole Telescope (SPT) we find a tension of
2.4$\sigma$, and 2.8$\sigma$ between ACT and Planck+SPT combined. While it is
unclear whether the tension is caused by statistical fluctuations, systematic
effects or new physics, caution should be exercised in combining these cosmic
microwave background datasets in the context of the $\Lambda$CDM standard model
of the universe. | The dust emission SED of X-ray emitting regions in Stephan's Quintet: We analysed the Spitzer maps of Stephan's Quintet in order to investigate the
nature of the dust emission associated with the X-ray emitting regions of the
large scale intergalactic shock and of the group halo. This emission can in
principle be powered by dust-gas particle collisions, thus providing efficient
cooling of the hot gas. However the results of our analysis suggest that the
dust emission from those regions is mostly powered by photons. Nonetheless dust
collisional heating could be important in determining the cooling of the IGM
gas and the large scale star formation morphology observed in SQ. |
Modelling neutral hydrogen in galaxies using cosmological hydrodynamical
simulations: The characterisation of the atomic and molecular hydrogen content of
high-redshift galaxies is a major observational challenge that will be
addressed over the coming years with a new generation of radio telescopes. We
investigate this important issue by considering the states of hydrogen across a
range of structures within high-resolution cosmological hydrodynamical
simulations. Additionally, our simulations allow us to investigate the
sensitivity of our results to numerical resolution and to sub-grid baryonic
physics (especially feedback from supernovae and active galactic nuclei). We
find that the most significant uncertainty in modelling the neutral hydrogen
distribution arises from our need to model a self-shielding correction in
moderate density regions. Future simulations incorporating radiative transfer
schemes will be vital to improve on our empirical self-shielding threshold.
Irrespective of the exact nature of the threshold we find that while the atomic
hydrogen mass function evolves only mildly from redshift two to zero, the
molecular hydrogen mass function increases with increasing redshift, especially
at the high-mass end. Interestingly, the weak evolution of the neutral hydrogen
mass function is insensitive to the feedback scheme utilised, but the opposite
is true for the molecular gas, which is more closely associated with the star
formation in the simulations. | The Effect of Host Galaxies on Type Ia Supernovae in the SDSS-II
Supernova Survey: We present an analysis of the host galaxy dependencies of Type Ia Supernovae
(SNe Ia) from the full three year sample of the SDSS-II Supernova Survey. We
rediscover, to high significance, the strong correlation between host galaxy
typeand the width of the observed SN light curve, i.e., fainter, quickly
declining SNe Ia favor passive host galaxies, while brighter, slowly declining
Ia's favor star-forming galaxies. We also find evidence (at between 2 to 3
sigma) that SNe Ia are ~0.1 magnitudes brighter in passive host galaxies, than
in star-forming hosts, after the SN Ia light curves have been standardized
using the light curve shape and color variations: This difference in brightness
is present in both the SALT2 and MCLS2k2 light curve fitting methodologies. We
see evidence for differences in the SN Ia color relationship between passive
and star-forming host galaxies, e.g., for the MLCS2k2 technique, we see that
SNe Ia in passive hosts favor a dust law of R_V ~1, while SNe Ia in
star-forming hosts require R_V ~2. The significance of these trends depends on
the range of SN colors considered. We demonstrate that these effects can be
parameterized using the stellar mass of the host galaxy (with a confidence of
>4 sigma) and including this extra parameter provides a better statistical fit
to our data. Our results suggest that future cosmological analyses of SN Ia
samples should include host galaxy information. |
Power spectrum in stochastic inflation: We compute the power spectrum of curvature perturbations in stochastic
inflation. This combines the distribution of first crossing times through the
end-of-inflation surface, which has been previously studied, with the
distribution of the fields value at the time when a given scale crosses out the
Hubble radius during inflation, which we show how to compute. This allows the
stochastic-$\delta N$ formalism to make concrete contact with observations. As
an application, we study how quantum diffusion at small scales (arising e.g. in
models leading to primordial black holes) affects the large-scale perturbations
observed in the cosmic microwave background. We find that even if those sets of
scales are well separated, large effects can arise from the distortion of the
classical relationship between field values and wavenumbers brought about by
quantum diffusion near the end of inflation. This shows that cosmic microwave
background measurements can set explicit constraints on the entire inflationary
potential down to the end of inflation. | Delayed Reheating and the Breakdown of Coherent Oscillations: We analyze the evolution of the perturbations in the inflaton field and
metric following the end of inflation. We present accurate analytic
approximations for the perturbations, showing that the coherent oscillations of
the post-inflationary condensate necessarily break down long before any current
phenomenological constraints require the universe to become radiation
dominated. Further, the breakdown occurs on length-scales equivalent to the
comoving post-inflationary horizon size. This work has implications for both
the inflationary "matching" problem, and the possible generation of a
stochastic gravitational wave background in the post-inflationary universe. |
Discovery of a Large Population of Ultraluminous X-ray Sources in the
Bulge-less Galaxies NGC 337 and ESO 501-23: We have used Chandra observations of eight bulge-less disk galaxies to
identify new ultraluminous X-ray source (ULX) candidates, study their high mass
X-ray binary (HMXB) population, and search for low-luminosity active galactic
nuclei (AGN). We report the discovery of 16 new ULX candidates in our sample of
galaxies. Eight of these are found in the star forming galaxy NGC 337, none of
which are expected to be background contaminants. The HMXB luminosity function
of NGC 337 implies a star formation rate (SFR) of 6.8$^{+4.4}_{-3.5}$ \msun\
yr$^{-1}$, consistent at 1.5$\sigma$ with a recent state of the art SFR
determination. We also report the discovery of a bright ULX candidate (X-1) in
ESO 501-23. X-1's spectrum is well fit by an absorbed power law with $\Gamma =
1.18^{+0.19}_{-0.11}$ and N$\rm{_H}$ = 1.13$^{+7.07}_{-1.13} \times 10^{20}$
cm$^{-2}$, implying a 0.3-8 keV flux of $1.08^{+0.05}_{-0.07} \times 10^{-12}$
\esc. Its X-ray luminosity (L$_X$) is poorly constrained due to uncertainties
in the host galaxy's distance, but we argue that its spectrum implies L$_X >
10^{40}$ \es. An optical counterpart to this object may be present in HST
imaging. We also identify ULX candidates in IC 1291, PGC 3853, NGC 5964 and NGC
2805. We find no evidence of nuclear activity in the galaxies in our sample,
placing a flux upper limit of $4 \times 10^{-15}$ \esc\ on putative AGN.
Additionally, the type II-P supernova SN 2011DQ in NGC 337, which exploded 2
months before our X-ray observation, is undetected. | Early Growth in a Perturbed Universe: Exploring Dark Matter Halo
Populations in 2LPT and ZA Simulations: We study the structure and evolution of dark matter halos from z = 300 to z =
6 for two cosmological N-body simulation initialization techniques. While the
second order Lagrangian perturbation theory (2LPT) and the Zel'dovich
approximation (ZA) both produce accurate present day halo mass functions,
earlier collapse of dense regions in 2LPT can result in larger mass halos at
high redshift. We explore the differences in dark matter halo mass and
concentration due to initialization method through three 2LPT and three ZA
initialized cosmological simulations. We find that 2LPT induces more rapid halo
growth, resulting in more massive halos compared to ZA. This effect is most
pronounced for high mass halos and at high redshift. Halo concentration is, on
average, largely similar between 2LPT and ZA, but retains differences when
viewed as a function of halo mass. For both mass and concentration, the
difference between typical individual halos can be very large, highlighting the
shortcomings of ZA-initialized simulations for high-z halo population studies. |
Cosmological Magnetic Fields: Magnetic fields are observed on nearly all scales in the universe, from stars
and galaxies upto galaxy clusters and even beyond. The origin of cosmic
magnetic fields is still an open question, however a large class of models puts
its origin in the very early universe. A magnetic dynamo amplifying an initial
seed magnetic field could explain the present day strength of the galactic
magnetic field. However, it is still an open problem how and when this initial
magnetic field was created. Observations of the cosmic microwave background
(CMB) provide a window to the early universe and might therefore be able to
tell us whether cosmic magnetic fields are of primordial, cosmological origin
and at the same time constrain its parameters. We will give an overview of the
observational evidence of large scale magnetic fields, describe generation
mechanisms of primordial magnetic fields and possible imprints in the CMB. | Impacts of Source Properties on Strong Lensing by Rich Galaxy Clusters: We use a high-resolution $N$-body simulation to investigate the influence of
background galaxy properties, including redshift, size, shape and clustering,
on the efficiency of forming giant arcs by gravitational lensing of rich galaxy
clusters. Two large sets of ray-tracing simulations are carried out for 10
massive clusters at two redshifts, i.e. $z_{\rm l} \sim 0.2$ and 0.3. The
virial mass ($M_{\rm vir}$) of the simulated lens clusters at $z\sim0.2$ ranges
from $6.8\times10^{14} h^{-1} {M_{\odot}}$ to $1.1\times 10^{15} h^{-1}
M_{\odot}$. The information of background galaxies brighter than 25 magnitude
in the $I$-band is taken from Cosmological Evolution Survey (COSMOS) imaging
data. Around $1.7\times 10^5$ strong lensing realizations with these images as
background galaxies have been performed for each set. We find that the
efficiency for forming giant arcs for $z_{\rm l}=0.2$ clusters is broadly
consistent with observations. The efficiency of producing giant arcs by rich
clusters is weakly dependent on the source size and clustering. Our principal
finding is that a small proportion ($\sim 1/3$) of galaxies with elongated
shapes (e.g. ellipticity $\epsilon=1-b/a>0.5$) can boost the number of giant
arcs substantially. Compared with recent studies where a uniform ellipticity
distribution from 0 to 0.5 is used for the sources, the adoption of directly
observed shape distribution increases the number of giant arcs by a factor of
$\sim2$. Our results indicate that it is necessary to account for source
information and survey parameters (such as point-spread-function, seeing) to
make correct predictions of giant arcs and further to constrain the
cosmological parameters.(abridged) |
The CMB Dipole: Eppur Si Muove: The largest temperature anisotropy in the cosmic microwave background (CMB)
is the dipole. The simplest interpretation of the dipole is that it is due to
our motion with respect to the rest frame of the CMB. As well as creating the
$\ell$=1 mode of the CMB sky, this motion affects all astrophysical
observations by modulating and aberrating sources across the sky. It can be
seen in galaxy clustering, and in principle its time derivative through a
dipole-shaped acceleration pattern in quasar positions. Additionally, the
dipole modulates the CMB temperature anisotropies with the same frequency
dependence as the thermal Sunyaev-Zeldovich (tSZ) effect and so these modulated
CMB anisotropies can be extracted from the tSZ maps produced by Planck.
Unfortunately, this measurement cannot determine if the dipole is due to our
motion, but it does provide an independent measure of the dipole and a
validation of the y maps. This measurement, and a description of the
first-order terms of the CMB dipole, are outlined here. | Interpreting the Transmission Windows of Distant Quasars: We propose the Apparent Shrinking Criterion (ASC) to interpret the spatial
extent, R_w, of transmitted flux windows in the absorption spectra of high-z
quasars. The ASC can discriminate between the two regimes in which R_w
corresponds either to the physical size, R_HII, of the quasar HII region, or to
the distance, R^{max}_w, at which the transmitted flux drops to =0.1 and a
Gunn-Peterson (GP) trough appears. In the first case (HR regime), one can
determine the IGM mean HI fraction, x_HI; in the second (PR regime), the value
of R_w allows to measure the local photoionization rate and the local
enhancement of the photoionization rate, Gamma_G, due to nearby/intervening
galaxies. The ASC has been tested against radiative transfer+SPH numerical
simulations, and applied to 15 high-z (z>5.8) quasars sample from Fan et al.
(2006). All sample quasars are found to be in the PR regime; hence, their
observed spectral properties (inner flux profile, extent of transmission
window) cannot reliably constrain the value of x_HI. Four sample quasars show
evidence for a local enhancement (up to 50%) in the local photoionization rate
possibly produced by a galaxy overdensity. We discuss the possible
interpretations and uncertainties of this result. |
Scalar Induced Gravitational Waves from Finslerian Inflation and Pulsar
Timing Arrays Observations: The recent data from NANOGrav provide strong evidence of the existence of the
\acp{SGWB}. We investigate \acp{SIGW} from Finslerian inflation as a potential
source of stochastic gravitational wave background. Small-scale ($\lesssim$1
Mpc) statistically anisotropic primordial scalar perturbations can be generated
in Finslerian inflation. The second order \acp{SIGW} from Finslerian inflation
are also anisotropic on small scales. After spatially averaging the small-scale
anisotropic \acp{SIGW}, we obtain the large-scale isotropic \acp{SGWB}. We find
that the parameters of small-scale anisotropic primordial power spectrum
generated by Finslerian inflation affect the \acp{PTA} observations of
large-scale isotropic gravitational wave background. | The GW190521 Mass Gap Event and the Primordial Black Hole Scenario: The LIGO/Virgo Collaboration has recently observed GW190521, the first binary
black hole merger with at least the primary component mass in the mass gap
predicted by the pair-instability supernova theory. This observation disfavors
the standard stellar-origin formation scenario for the heavier black hole,
motivating alternative hypotheses. We show that GW190521 cannot be explained
within the Primordial Black Hole (PBH) scenario if PBHs do not accrete during
their cosmological evolution, since this would require an abundance which is
already in tension with current constraints. On the other hand, GW190521 may
have a primordial origin if PBHs accrete efficiently before the reionization
epoch. |
First results from the CRESST-III low-mass dark matter program: The CRESST experiment is a direct dark matter search which aims to measure
interactions of potential dark matter particles in an earth-bound detector.
With the current stage, CRESST-III, we focus on a low energy threshold for
increased sensitivity towards light dark matter particles. In this manuscript
we describe the analysis of one detector operated in the first run of
CRESST-III (05/2016-02/2018) achieving a nuclear recoil threshold of 30.1eV.
This result was obtained with a 23.6g CaWO$_4$ crystal operated as a cryogenic
scintillating calorimeter in the CRESST setup at the Laboratori Nazionali del
Gran Sasso (LNGS). Both the primary phonon/heat signal and the simultaneously
emitted scintillation light, which is absorbed in a separate
silicon-on-sapphire light absorber, are measured with highly sensitive
transition edge sensors operated at ~15mK. The unique combination of these
sensors with the light element oxygen present in our target yields sensitivity
to dark matter particle masses as low as 160MeV/c$^2$. | Towards to $H_0$ Tension by the Theoretical Hubble Parameter in the
Infinite Future: There exists a constant value of $H(z)$ at $z=-1$ when in $\omega$CDM
universe with $\omega > -1$, which is independent on other cosmological
parameters. We first combine this theoretical $H(z)$ value with the latest 43
observational $H(z)$ data (OHD) to perform the model-independent Gaussian
Processes (GP) and constrain the Hubble constant. We obtain
$H_0$=67.67$\pm3.03\ {\rm km\ s^{-1} Mpc^{-1}}$, which is in agreement with
$H_0$ values from Plank Collaboration (2015) ($0.24 \sigma $ tension) but a
larger deviation from Riess et al. (2016) ($1.60 \sigma $ tension), while
$H_0$=71.09\ $\pm3.71\ {\rm km\ s^{-1} Mpc^{-1}}$ $ (0.64 \sigma $ tension) by
only using latest 43 OHD. Using this $H_0$ value, we perform $\chi^2$
statistics with Markov Chain Monte Carlo (MCMC) method to constrain
cosmological parameters. We obtain $\Omega_M=0.26 \pm 0.02$ and $\omega=-0.85
\pm 0.06$ in flat $\omega CDM$ model, and $\Omega_M=0.27\pm 0.04 ,
\Omega_\Lambda=0.80 \pm 0.12$ and $\omega=-0.82 \pm 0.07$ in non-flat $\omega
CDM$ model, which are larger than those not using the theoretical $H(z)$ value. |
On the Effective Field Theory for Quasi-Single Field Inflation: We study the effective field theory (EFT) description of the virtual particle
effects in quasi-single field inflation, which unifies the previous results on
large mass and large mixing cases. By using a horizon crossing approximation
and matching with known limits, approximate expressions for the power spectrum
and the spectral index are obtained. The error of the approximate solution is
within 10% in dominate parts of the parameter space, which corresponds to
less-than-0.1% error in the $n_s$-$r$ diagram. The quasi-single field
corrections on the $n_s$-$r$ diagram are plotted for a few inflation models.
Especially, the quasi-single field correction drives $m^2\phi^2$ inflation to
the best fit region on the $n_s$-$r$ diagram, with an amount of equilateral
non-Gaussianity which can be tested in future experiments. | What does a cosmological experiment really measure? Covariant posterior
decomposition with normalizing flows: We present methods to rigorously extract parameter combinations that are
constrained by data from posterior distributions. The standard approach uses
linear methods that apply to Gaussian distributions. We show the limitations of
the linear methods for current surveys, and develop non-linear methods that can
be used with non-Gaussian distributions, and are independent of the parameter
basis. These are made possible by the use of machine-learning models,
normalizing flows, to learn posterior distributions from their samples. These
models allow us to obtain the local covariance of the posterior at all
positions in parameter space and use its inverse, the Fisher matrix, as a local
metric over parameter space. The posterior distribution can then be
non-linearly decomposed into the leading constrained parameter combinations via
parallel transport in the metric space. We test our methods on two
non-Gaussian, benchmark examples, and then apply them to the parameter
posteriors of the Dark Energy Survey and Planck CMB lensing. We illustrate how
our method automatically learns the survey-specific, best constrained effective
amplitude parameter $S_8$ for cosmic shear alone, cosmic shear and galaxy
clustering, and CMB lensing. We also identify constrained parameter
combinations in the full parameter space, and as an application we estimate the
Hubble constant, $H_0$, from large-structure data alone. |
The Discovery of Vibrationally-Excited H_2 in the Molecular Cloud near
GRB 080607: GRB 080607 has provided the first strong observational signatures of
molecular absorption bands toward any galaxy hosting a gamma-ray burst. Despite
the identification of dozens of features as belonging to various atomic and
molecular (H_2 and CO) carriers, many more absorption features remained
unidentified. Here we report on a search among these features for absorption
from vibrationally-excited H_2, a species that was predicted to be produced by
the UV flash of a GRB impinging on a molecular cloud. Following a detailed
comparison between our spectroscopy and static, as well as dynamic, models of
H_2* absorption, we conclude that a column density of 10^{17.5+-0.2} cm^{-2} of
H_2* was produced along the line of sight toward GRB 080607. Depending on the
assumed amount of dust extinction between the molecular cloud and the GRB, the
model distance between the two is found to be in the range 230--940 pc. Such a
range is consistent with a conservative lower limit of 100 pc estimated from
the presence of Mg I in the same data. These distances show that substantial
molecular material is found within hundreds of pc from GRB 080607, part of the
distribution of clouds within the GRB host galaxy. | The Swift BAT Perspective on Non-thermal Emission in HIFLUGCS Galaxy
Clusters: The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy
clusters at hard X-ray energies has been underway for many years, with most
detections being either of low significance or controversial. In this work, we
investigate 14-195 keV spectra from the Swift Burst Alert Telescope (BAT)
all-sky survey for evidence of non-thermal excess emission above the
exponentially decreasing tail of thermal emission in the flux-limited HIFLUGCS
sample. To account for the thermal contribution at BAT energies, XMM-Newton
EPIC spectra are extracted from coincident spatial regions so that both thermal
and non-thermal spectral components can be determined simultaneously. We find
marginally significant IC components in six clusters, though after closer
inspection and consideration of systematic errors we are unable to claim a
clear detection in any of them. The spectra of all clusters are also summed to
enhance a cumulative non-thermal signal not quite detectable in individual
clusters. After constructing a model based on single-temperature fits to the
XMM-Newton data alone, we see no significant excess emission above that
predicted by the thermal model determined at soft energies. This result also
holds for the summed spectra of various subgroups, except for the subsample of
clusters with diffuse radio emission. For clusters hosting a diffuse radio
halo, a relic, or a mini-halo, non-thermal emission is initially detected at
the \sim5-sigma confidence level - driven by clusters with mini-halos - but
modeling and systematic uncertainties ultimately degrade this significance. In
individual clusters, the non-thermal pressure of relativistic electrons is
limited to \sim10% of the thermal electron pressure, with stricter limits for
the more massive clusters, indicating that these electrons are likely not
dynamically important in the central regions of clusters. |
Cosmic Tides: We apply CMB lensing techniques to large scale structure and solve for the
3-D cosmic tidal field. We use small scale filamentary structures to solve for
the large scale tidal shear and gravitational potential. By comparing this to
the redshift space density field, one can measure the gravitational growth
factor on large scales without cosmic variance. This potentially enables
accurate measurements of neutrino masses and reconstruction of radial modes
lost in 21 cm intensity mapping, which are essential for CMB and other cross
correlations. We relate the tidal fields to the squeezed limit bispectrum, and
present initial results from simulations and data from the SDSS. | Euclid: constraining dark energy coupled to electromagnetism using
astrophysical and laboratory data: In physically realistic scalar-field based dynamical dark energy models
(including, e.g., quintessence) one naturally expects the scalar field to
couple to the rest of the model's degrees of freedom. In particular, a coupling
to the electromagnetic sector leads to a time (redshift) dependence of the
fine-structure constant and a violation of the Weak Equivalence Principle. Here
we extend the previous Euclid forecast constraints on dark energy models to
this enlarged (but physically more realistic) parameter space, and forecast how
well Euclid, together with high-resolution spectroscopic data and local
experiments, can constrain these models. Our analysis combines simulated Euclid
data products with astrophysical measurements of the fine-structure constant,
$\alpha$, and local experimental constraints, and includes both parametric and
non-parametric methods. For the astrophysical measurements of $\alpha$ we
consider both the currently available data and a simulated dataset
representative of Extremely Large Telescope measurements and expected to be
available in the 2030s. Our parametric analysis shows that in the latter case
the inclusion of astrophysical and local data improves the Euclid dark energy
figure of merit by between $8\%$ and $26\%$, depending on the correct fiducial
model, with the improvements being larger in the null case where the fiducial
coupling to the electromagnetic sector is vanishing. These improvements would
be smaller with the current astrophysical data. Moreover, we illustrate how a
genetic algorithms based reconstruction provides a null test for the presence
of the coupling. Our results highlight the importance of complementing surveys
like Euclid with external data products, in order to accurately test the wider
parameter spaces of physically motivated paradigms. |
Cosmic growth rate measurements from Tully-Fisher peculiar velocities: Peculiar velocities are an important probe of the growth rate of structure in
the Universe, directly measuring the effects of gravity on the largest scales
and thereby providing a test for theories of gravity. Complete peculiar
velocity datasets comprise both galaxy redshifts and redshift-independent
distance measures, estimated by methods such as the Tully-Fisher relation.
Traditionally, the Tully-Fisher relation is first calibrated using distance
indicators such as Cepheid variables in a small sample of galaxies; the
calibrated relation is then used to determine peculiar velocities. In this
analysis, we employ a one-step Bayesian method to simultaneously determine the
parameters of the Tully-Fisher relation and the peculiar velocity field. We
have also generalised the Tully-Fisher relation by allowing for a curvature at
the bright end. We design a mock survey to emulate the Cosmicflows-4 (CF4)
peculiar velocity dataset. We then apply our method to the CF4 data to obtain
new constraints for the growth rate of structure parameter
($\beta=0.40\pm0.07$), the residual bulk flow ($\mathbf{V}_{\textrm{ext}}
=$[69$\pm$15,$-$158$\pm$9,14$\pm$7]\,km$~s^{-1}$ in Supergalactic coordinates),
and the parameters for a Tully-Fisher relation with curvature. We obtain an
estimate for the product of the growth rate and mass fluctuation amplitude
$f\sigma_{8}=0.40\pm0.07$. We combine this measurement of $f\sigma_{8}$ with
those of other galaxy redshift surveys to fit the growth index $\gamma$.
Assuming cosmological parameters from the latest Planck CMB results, we find
that $\gamma>6/11$ is favoured. We plan to use this improved method for
recovering peculiar velocities on the large new samples of Tully-Fisher data
from surveys such as WALLABY, resulting in more precise growth rate
measurements at low redshifts. | The MUSIC of CLASH: predictions on the concentration-mass relation: We present the results of a numerical study based on the analysis of the
MUSIC-2 simulations, aimed at estimating the expected concentration-mass
relation for the CLASH cluster sample. We study nearly 1400 halos simulated at
high spatial and mass resolution, which were projected along many
lines-of-sight each. We study the shape of both their density and
surface-density profiles and fit them with a variety of radial functions,
including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the
Einasto density profiles. We derive concentrations and masses from these fits
and investigate their distributions as a function of redshift and halo
relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra
observations of the halos and we use them to identify objects resembling the
X-ray morphologies and masses of the clusters in the CLASH X-ray selected
sample. We also derive a concentration-mass relation for strong-lensing
clusters. We find that the sample of simulated halos which resemble the X-ray
morphology of the CLASH clusters is composed mainly by relaxed halos, but it
also contains a significant fraction of un-relaxed systems. For such a sample
we measure an average 2D concentration which is ~11% higher than found for the
full sample of simulated halos. After accounting for projection and selection
effects, the average NFW concentrations of CLASH clusters are expected to be
intermediate between those predicted in 3D for relaxed and super-relaxed halos.
Matching the simulations to the individual CLASH clusters on the basis of the
X-ray morphology, we expect that the NFW concentrations recovered from the
lensing analysis of the CLASH clusters are in the range [3-6], with an average
value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray
morphologies similar to those of the CLASH clusters are affected by a modest
orientation bias. |
Suppression of Star Formation in Low-Mass Galaxies Caused by the
Reionization of their Local Neighborhood: Photoheating associated with reionization suppressed star formation in
low-mass galaxies. Reionization was inhomogeneous, however, affecting different
regions at different times. To establish the causal connection between
reionization and suppression, we must take this local variation into account.
We analyze the results of CoDa (`Cosmic Dawn') I, the first fully-coupled
radiation-hydrodynamical simulation of reionization and galaxy formation in the
Local Universe, in a volume large enough to model reionization globally but
with enough resolving power to follow all atomic-cooling galactic halos in that
volume. For every halo identified at a given time, we find the redshift at
which the surrounding IGM reionized, along with its instantaneous star
formation rate (`SFR') and baryonic gas-to-dark matter ratio
($M_\text{gas}/M_\text{DM}$). The average SFR per halo with $M < 10^9 \text{
M}_\odot$ was steady in regions not yet reionized, but declined sharply
following local reionization. For $M > 10^{10} \text{ M}_\odot$, this SFR
continued through local reionization, increasing with time, instead. For $10^9
< M < 10^{10} \text{ M}_\odot$, the SFR generally increased modestly through
reionization, followed by a modest decline. In general, halo SFRs were higher
for regions that reionized earlier. A similar pattern was found for
$M_\text{gas}/M_\text{DM}$, which declined sharply following local reionization
for $M < 10^9 \text{ M}_\odot$. Local reionization time correlates with local
matter overdensity, which determines the local rates of structure formation and
ionizing photon consumption. The earliest patches to develop structure and
reionize ultimately produced more stars than they needed to finish and maintain
their own reionization, exporting their `surplus' starlight to help reionize
regions that developed structure later. | LoCuSS: Testing hydrostatic equilibrium in galaxy clusters: We test the assumption of hydrostatic equilibrium in an X-ray luminosity
selected sample of 50 galaxy clusters at $0.15<z<0.3$ from the Local Cluster
Substructure Survey (LoCuSS). Our weak-lensing measurements of $M_{500}$
control systematic biases to sub-4 per cent, and our hydrostatic measurements
of the same achieve excellent agreement between XMM-Newton and Chandra. The
mean ratio of X-ray to lensing mass for these 50 clusters is $\beta_{\rm
X}=0.95\pm0.05$, and for the 44 clusters also detected by Planck, the mean
ratio of Planck mass estimate to LoCuSS lensing mass is $\beta_{\rm
P}=0.95\pm0.04$. Based on a careful like-for-like analysis, we find that
LoCuSS, the Canadian Cluster Comparison Project (CCCP), and Weighing the Giants
(WtG) agree on $\beta_{\rm P}\simeq0.9-0.95$ at $0.15<z<0.3$. This small level
of hydrostatic bias disagrees at $\sim5\sigma$ with the level required to
reconcile Planck cosmology results from the cosmic microwave background and
galaxy cluster counts. |
Expected constraints on models of the epoch of reionization with the
variance and skewness in redshifted 21cm-line fluctuations: Redshifted 21cm-line signal from neutral hydrogens in the intergalactic
medium (IGM) gives a direct probe of the epoch of reionization (EoR). In this
paper, we investigate the potential of the variance and skewness of the
probability distribution function of the 21cm brightness temperature for
constraining EoR models. These statistical quantities are simple, easy to
calculate from the observed visibility and thus suitable for the early
exploration of the EoR with ongoing telescopes such as the Murchison Widefield
Array (MWA) and LOw Frequency ARray (LOFAR). We show, by performing Fisher
analysis, that the variance and skewness at $z=7-9$ are complementary to each
other to constrain the EoR model parameters such as the minimum virial
temperature of halos which host luminous objects, ionizing efficiency and mean
free path of ionizing photons in the IGM. Quantitatively, the constraining
power highly depends on the quality of the foreground subtraction and
calibration. We give a best case estimate of the constraints on the parameters,
neglecting the systematics other than the thermal noise. | The evolution of the scatter of the cosmic average color-magnitude
relation: Demonstrating consistency with the ongoing formation of elliptical
galaxies: We present first measurements of the evolution of the scatter of the cosmic
average early-type galaxy color-magnitude relation (CMR) from z=1 to the
present day, finding that it is consistent with models in which galaxies are
constantly being added to the red sequence through truncation of star formation
in blue cloud galaxies. We used a sample of over 700 red sequence,
structurally-selected early-type galaxies (defined to have Sersic index >2.5)
with redshifts 0<z<1 taken from the Extended Chandra Deep Field South (173
galaxies) and the Sloan Digital Sky Survey (550 galaxies), constructing
rest-frame U-V colors accurate to <0.04mag. We find that the scatter of the CMR
of cosmic average early-type galaxies is ~0.1mag in rest-frame U-V color at
0.05<z<0.75, and somewhat higher at z=1. We compared these observations with a
model in which new red sequence galaxies are being constantly added at the rate
required to match the observed number density evolution, and found that this
model predicts the correct CMR scatter and its evolution. Furthermore, this
model predicts approximately the correct number density of `blue spheroids' -
structurally early-type galaxies with blue colors - albeit with considerable
model dependence. Thus, we conclude that both the evolution of the number
density and colors of the early-type galaxy population paint a consistent
picture in which the early-type galaxy population grows significantly between
z=1 and the present day through the quenching of star formation in blue cloud
galaxies. |
A Stochastic Theory of the Hierarchical Clustering III. The
Non-universality and Non-stationarity of the Halo Mass Function: In the framework of the stochastic theory for hierarchical clustering, we
investigate the time-dependent solutions of the Fokker-Planck equation
describing the statistics of dark matter halos, and discuss the typical
timescales needed for these to converge toward stationary states, far away
enough from initial conditions. Although we show that the stationary solutions
can reproduce the outcomes of state-of-the-art $N-$body simulations at
$z\approx 0$ to a great accuracy, one needs to go beyond to fully account for
the cosmic evolution of the simulated halo mass function toward high-redshift.
Specifically, we demonstrate that the time-dependent solutions of the
Fokker-Planck equation can describe, for reasonable initial conditions, the
non-universal evolution of the simulated halo mass functions. Compared to
standard theoretical estimates, our stochastic theory predicts a halo number
density higher by factor of several toward $z\gtrsim 10$, an outcome which can
be helpful in elucidating early and upcoming data from JWST. Finally, we point
out the relevance of our approach in designing, interpreting and emulating
present and future $N-$body experiments. | Probing dark radiation with inflationary gravitational waves: Recent cosmological observations indicate the existence of extra light
species, i.e., dark radiation. In this paper we show that signatures of the
dark radiation are imprinted in the spectrum of inflationary gravitational
waves. If the dark radiation is produced by the decay of a massive particle,
high frequency mode of the gravitational waves are suppressed. In addition, due
to the effect of the anisotropic stress caused by the dark radiation, a dip in
the gravitational wave spectrum may show up at the frequency which enters the
horizon at the time of the dark radiation production. Once the gravitational
wave spectrum is experimentally studied in detail, we can infer the information
on how and when the dark radiation was produced in the Universe. |
Discovery of a radio halo (and relic) in a $M_{500} < 2 \times 10^{14}$
M$_\odot$ cluster: Radio halos are diffuse synchrotron sources observed in dynamically unrelaxed
galaxy clusters. Current observations and models suggest that halos trace
turbulent regions in the intra-cluster medium where mildly relativistic
particles are re-accelerated during cluster mergers. Due to the higher
luminosities and detection rates with increasing cluster mass, radio halos have
been mainly observed in massive systems ($M_{500} \gtrsim 5 \times10^{14}$
M$_\odot$). Here, we report the discovery of a radio halo with a largest linear
scale of $\simeq$750 kpc in PSZ2G145.92-12.53 ($z=0.03$) using LOFAR
observations at 120$-$168 MHz. With a mass of $M_{500} = (1.9\pm0.2) \times
10^{14}$ M$_\odot$ and a radio power at 150 MHz of $P_{150} = (3.5 \pm 0.7)
\times 10^{23}$ W/Hz, this is the least powerful radio halo in the least
massive cluster discovered to date. Additionally, we discover a radio relic
with a mildly convex morphology at $\sim$1.7 Mpc from the cluster center. Our
results demonstrate that LOFAR has the potential to detect radio halos even in
low-mass clusters, where the expectation to form them is very low ($\sim$5%)
based on turbulent re-acceleration models. Together with the observation of
large samples of clusters, this opens the possibility to constrain the low end
of the power-mass relation of radio halos. | Decaying dark matter: the case for a deep X-ray observation of Draco: Recent studies of M31, the Galactic centre, and galaxy clusters have made
tentative detections of an X-ray line at ~3.5 keV that could be produced by
decaying dark matter. We use high resolution simulations of the Aquarius
project to predict the likely amplitude of the X-ray decay flux observed in the
GC relative to that observed in M31, and also of the GC relative to other parts
of the Milky Way halo and to dwarf spheroidal galaxies. We show that the
reported detections from M31 and Andromeda are compatible with each other, and
with upper limits arising from high galactic latitude observations, and imply a
decay time {\tau} ~10^28 seconds. We argue that this interpretation can be
tested with deep observations of dwarf spheroidal galaxies: in 95 per cent of
our mock observations, a 1.3 Msec pointed observation of Draco with XMM-Newton
will enable us to discover or rule out at the 3{\sigma} level an X-ray feature
from dark matter decay at 3.5 keV, for decay times {\tau} < 0.8x10^28 sec. |
Gravitational Wave Detection Using Redshifted 21-cm Observations: A gravitational wave traversing the line of sight to a distant source
produces a frequency shift which contributes to redshift space distortion. As a
consequence, gravitational waves are imprinted as density fluctuations in
redshift space. The gravitational wave contribution to the redshift space power
spectrum. has a different \mu dependence as compared to the dominant
contribution from peculiar velocities. This allows the two signals to be
separated. The prospect of a detection is most favourable at the highest
observable redshift z. Observations of redshifted 21-cm radiation from neutral
hydrogen (HI) hold the possibility of probing very high redshifts. We consider
the possibility of detecting primordial gravitational waves using the redshift
space HI power spectrum. However, we find that the gravitational wave signal,
though present, will not be detectable on super-horizon scales because of
cosmic variance and on sub-horizon scales where the signal is highly
suppressed. | Infrared Narrow-Band Tomography of the Local Starburst NGC 1569 with
LBT/LUCIFER: We used the near-IR imager/spectrograph LUCIFER mounted on the Large
Binocular Telescope (LBT) to image, with sub-arcsec seeing, the local dwarf
starburst NGC 1569 in the JHK bands and HeI 1.08 micron, [FeII] 1.64 micron and
Brgamma narrow-band filters. We obtained high-quality spatial maps of HeI,
[FeII] and Brgamma emission across the galaxy, and used them together with
HST/ACS images of NGC 1569 in the Halpha filter to derive the two-dimensional
spatial map of the dust extinction and surface star formation rate density. We
show that dust extinction is rather patchy and, on average, higher in the
North-West (NW) portion of the galaxy [E_g(B-V) = 0.71 mag] than in the
South-East [E_g(B-V) = 0.57 mag]. Similarly, the surface density of star
formation rate peaks in the NW region of NGC 1569, reaching a value of about 4
x 10^-6 M_sun yr^-1 pc^-2. The total star formation rate as estimated from the
integrated, dereddened Halpha luminosity is about 0.4 M_sun yr^-1, and the
total supernova rate from the integrated, dereddened [FeII] luminosity is about
0.005 yr^-1 (assuming a distance of 3.36 Mpc). The azimuthally averaged
[FeII]/Brgamma flux ratio is larger at the edges of the central, gas-deficient
cavities (encompassing the super star clusters A and B) and in the galaxy
outskirts. If we interpret this line ratio as the ratio between the average
past star formation (as traced by supernovae) and on-going activity
(represented by OB stars able to ionize the interstellar medium), it would then
indicate that star formation has been quenched within the central cavities and
lately triggered in a ring around them. The number of ionizing hydrogen and
helium photons as computed from the integrated, dereddened Halpha and HeI
luminosities suggests that the latest burst of star formation occurred about 4
Myr ago and produced new stars with a total mass of ~1.8 x 10^6 M_sun.
[Abridged] |
Environment and self-regulation in galaxy formation: The environment is known to affect the formation and evolution of galaxies
considerably best visible through the well-known morphology-density
relationship. In this paper we study the effect of environment on the evolution
of early-type galaxies by analysing the stellar population properties of 3,360
galaxies morphologically selected by visual inspection from the SDSS in the
redshift range 0.05<z<0.06. We find that the distribution of ages is bimodal
with a strong peak at old ages and a secondary peak at young ages around ~
2.5Gyr containing about 10 per cent of the objects. This is analogue to 'red
sequence' and 'blue cloud' identified in galaxy populations usually containing
both early and late type galaxies. The fraction of the young, rejuvenated
galaxies increases with both decreasing galaxy mass and decreasing
environmental density up to about 45 per cent. The rejuvenated galaxies have
lower alpha/Fe ratios than the average and most of them show signs of ongoing
star formation through their emission line spectra. All objects that host AGN
in their centres without star formation are part of the red sequence
population. We confirm and statistically strengthen earlier results that
luminosity weighted ages, metallicities, and alpha/Fe element ratios of the red
sequence population correlate well with velocity dispersion and galaxy mass.
Most interestingly, however, these scaling relations are not sensitive to
environmental densities and are only driven by galaxy mass. We infer that
early-type galaxy formation has undergone a phase transition a few billion
years ago around z~0.2. A self-regulated formation phase without environmental
dependence has recently been superseded by a rejuvenation phase, in which the
environment plays a decisive role possibly through galaxy interactions. | The multi-frequency angular power spectrum in parameter studies of the
cosmic 21-cm signal: The light-cone effect breaks the periodicity and statistical homogeneity
(ergodicity) along the line-of-sight direction of cosmological
emission/absorption line surveys. The spherically averaged power spectrum
(SAPS), which by definition assumes ergodicity and periodicity in all
directions, can only quantify some of the second-order statistical information
in the 3D light-cone signals and therefore gives a biased estimate of the true
statistics. The multi-frequency angular power spectrum (MAPS), by extracting
more information from the data, does not rely on these assumptions. It is
therefore better aligned with the properties of the signal. We have compared
the performance of the MAPS and SAPS metrics for parameter estimation for a
mock 3D light-cone observation of the 21-cm signal from the Epoch of
Reionization. Our investigation is based on a simplified 3-parameter 21cmFAST
model. We find that the MAPS produces parameter constraints which are a factor
of $\sim 2$ more stringent than when the SAPS is used. The significance of this
result does not change much even in the presence of instrumental noise expected
for 128 hours of SKA-Low observations. Our results therefore suggest that a
parameter estimation framework based on the MAPS metric would yield superior
results over one using the SAPS metric. |
The Dark Matter distribution function and Halo Thermalization from the
Eddington equation in Galaxies: We find the distribution function f(E) for dark matter (DM) halos in galaxies
and the corresponding equation of state from the (empirical) DM density
profiles derived from observations. We solve for DM in galaxies the analogous
of the Eddington equation originally used for the gas of stars in globular
clusters. The observed density profiles are a good realistic starting point and
the distribution functions derived from them are realistic. We do not make any
assumption about the DM nature, the methods developed here apply to any DM
kind, though all results are consistent with Warm DM. With these methods we
find: (i) Cored density profiles behaving quadratically for small distances
rho(r) r -> 0 = rho(0) - K r^2 produce distribution functions which are finite
and positive at the halo center while cusped density profiles always produce
divergent distribution functions at the center. (ii) Cored density profiles
produce approximate thermal Boltzmann distribution functions for r < 3 r_h
where r_h is the halo radius. (iii) Analytic expressions for the dispersion
velocity and the pressure are derived yielding an ideal DM gas equation of
state with local temperature T(r) = m v^2(r)/3. T(r) turns to be constant in
the same region where the distribution function is thermal and exhibits the
same temperature within the percent. The self-gravitating DM gas can thermalize
despite being collisionless because it is an ergodic system. (iv) The DM halo
can be consistently considered at local thermal equilibrium with: (a) a
constant temperature T(r) = T_0 for r < 3 \; r_h, (b) a space dependent
temperature T(r) for 3 r_h < r < R_{virial}, which slowly decreases with r.
That is, the DM halo is realistically a collisionless self-gravitating thermal
gas for r < R_{virial}. (v) T(r) outside the halo radius nicely follows the
decrease of the circular velocity squared. | 21cmFAST: A Fast, Semi-Numerical Simulation of the High-Redshift 21-cm
Signal: We introduce a powerful semi-numeric modeling tool, 21cmFAST, designed to
efficiently simulate the cosmological 21-cm signal. Our code generates 3D
realizations of evolved density, ionization, peculiar velocity, and spin
temperature fields, which it then combines to compute the 21-cm brightness
temperature. Although the physical processes are treated with approximate
methods, we compare our results to a state-of-the-art large-scale hydrodynamic
simulation, and find good agreement on scales pertinent to the upcoming
observations (>~ 1 Mpc). The power spectra from 21cmFAST agree with those
generated from the numerical simulation to within 10s of percent, down to the
Nyquist frequency. We show results from a 1 Gpc simulation which tracks the
cosmic 21-cm signal down from z=250, highlighting the various interesting
epochs. Depending on the desired resolution, 21cmFAST can compute a redshift
realization on a single processor in just a few minutes. Our code is fast,
efficient, customizable and publicly available, making it a useful tool for
21-cm parameter studies. |
Systematic error mitigation for the PIXIE Fourier transform spectrometer: The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission
concept to measure the spectrum and polarization of the cosmic microwave
background. Cosmological signals are small compared to the instantaneous
instrument noise, requiring strict control of instrumental signals. The
instrument design provides multiple levels of null operation, signal
modulation, and signal differences, with only few-percent systematic error
suppression required at each level. Jackknife tests based on discrete
instrument symmetries provide an independent means to identify, model, and
remove remaining instrumental signals. We use detailed time-ordered
simulations, including realistic performance and tolerance parameters, to
evaluate the instrument response to broad classes of systematic errors for both
spectral distortions and polarization. The largest systematic errors contribute
additional white noise at the few-percent level compared to the dominant photon
noise. Coherent instrumental effects which do not integrate down are smaller
still, and remain several orders of magnitude below the targeted cosmological
signals. | Dark matter distribution in galaxy groups from combined strong lensing
and dynamics analysis: Using a combined analysis of strong lensing and galaxy dynamics, we
characterize the mass distributions and M/L ratios of galaxy groups, which form
an important transition regime in Lambda-CDM cosmology. By mapping the
underlying mass distribution, we test whether groups are dark matter dominated
as hypothesized by the standard cosmogony, or isothermal as observed in baryon
rich field galaxies. We present our lensing + galaxy dynamics formalism built
around the dark matter dominant NFW and Hernquist distributions, compared
against the Isothermal Sphere observed in galaxy scale objects. We show that
mass measurement in the core of the group (r ~ 0.2 r_{vir}), determined jointly
from a lens model and from differential velocity dispersion estimates, may
effectively distinguish between these density distributions. We apply our
method to MOS observations of two groups, SL2SJ1430+5546 and SL2SJ1431+5533,
drawn from our CFHTLS lens catalog. With the measured lensing and dynamical
masses, combined with a maximum likelihood estimator built around our model, we
estimate the concentration index characterizing each density distribution and
the corresponding virial mass of each group. Our results indicate that both
groups are dark matter dominant, and reject the Isothermal distribution at >>3
sigma level. For both groups, the estimated i-band M/L ratios of ~260
Msun/Lsun, are similar to other published values for groups. The Gaussian
distributions of the velocities of their member galaxies support a high degree
of virialization. The differences in their virial masses, 2.8 and 1.6 x 10^14
Msun, and velocity dispersions, 720 and 560 km/s respectively, may indicate
however that each group is at a different stage of transition to a cluster. We
aim to populate this important transition regime with additional results from
ongoing observations of the remaining lensing groups in our catalog. |
Metallicity-Dependent quenching of Star Formation at High Redshift in
Small Galaxies: [abridged] The star formation rates (SFR) of low-metallicity galaxies depend
sensitively on the gas metallicity, because metals are crucial to mediating the
transition from intermediate-temperature atomic gas to cold molecular gas, a
necessary precursor to star formation. We study the impact of this effect on
the star formation history of galaxies. We incorporate metallicity-dependent
star formation and metal enrichment in a simple model that follows the
evolution of a halo main progenitor. Our model shows that including the effect
of metallicity leads to suppression of star formation at redshift z>2 in dark
halos with masses <~ 10^11 Msun, with the suppression becoming near total for
halos below ~10^9.5-10 Msun. We find that at high redshift the SFR cannot catch
up with the gas inflow rate (IR), because the SFR is limited by the free-fall
time, and because it is suppressed further by a lack of metals. As a result, in
each galaxy the SFR is growing in time faster than the IR, and the integrated
cosmic SFR density is rising with time. The suppressed in situ SFR at high z
makes the growth of stellar mass dominated by ex situ SFR which implies that
the specific SFR (sSFR) remains constant with time. The intensely accreted gas
at high z is accumulating as an atomic gas reservoir. This provides additional
fuel for star formation in 10^10 - 10^12 Msun halos at z ~ 1-3, which allows
the SFR to exceed the instantaneous IR, and may enable an even higher outflow
rate. At z<1, following the natural decline in IR with time due to the
universal expansion, the SFR and sSFR are expected to drop. We specify the
expected dependence of sSFR and metallicity on stellar mass and redshift. At a
given z, and below a critical mass, these relations are predicted to be flat
and rising respectively. Our model predictions qualitatively match some of the
puzzling features in the observed star formation history. | Reconstruction of A Scale-Dependent Gravitational Phase Transition: In this work we extend our earlier phenomenological model for a gravitational
phase transition (GPT) and its generalization to early times by letting the
modifications in the linearly-perturbed Einstein equations be scale-dependent.
These modifications are characterized as deviations of the parameters
$\mu(z,k)$ and $\gamma(z,k)$ from their values in general relativity (GR). The
scale-dependent amplitudes of modified $\mu(z,k)$ and $\gamma(z,k)$ and the
parameters defining the phase transition, along with the standard cosmological
parameters, are measured by various data combinations. Out of the perturbation
parameters, we construct gravity eigenmodes which represent patterns of
perturbations best detectable by data. We detect no significant deviation from
GR in these parameters. However, the larger parameter space produced due to the
new degrees of freedom allows for the reconciliation of various datasets which
are in tension in $\Lambda$CDM. In particular, we find $H_0=71.9\pm 9.2$ from
anisotropies of the Cosmic Microwave Background as measured by Planck and
various measurements of the Baryonic Acoustic Oscillations, in agreement with
local Hubble measurements. We also find that the $\sigma_8$ tension between the
measurements of Dark Energy Survey and Planck is reduced to less than
$1\sigma$. |
Planck intermediate results. XLVI. Reduction of large-scale systematic
effects in HFI polarization maps and estimation of the reionization optical
depth: This paper describes the identification, modelling, and removal of previously
unexplained systematic effects in the polarization data of the Planck High
Frequency Instrument (HFI) on large angular scales, including new mapmaking and
calibration procedures, new and more complete end-to-end simulations, and a set
of robust internal consistency checks on the resulting maps. These maps, at
100, 143, 217, and 353 GHz, are early versions of those that will be released
in final form later in 2016.
The improvements allow us to determine the cosmic reionization optical depth
$\tau$ using, for the first time, the low-multipole $EE$ data from HFI,
reducing significantly the central value and uncertainty, and hence the upper
limit. Two different likelihood procedures are used to constrain $\tau$ from
two estimators of the CMB $E$- and $B$-mode angular power spectra at 100 and
143 GHz, after debiasing the spectra from a small remaining systematic
contamination. These all give fully consistent results.
A further consistency test is performed using cross-correlations derived from
the Low Frequency Instrument maps of the Planck 2015 data release and the new
HFI data. For this purpose, end-to-end analyses of systematic effects from the
two instruments are used to demonstrate the near independence of their dominant
systematic error residuals.
The tightest result comes from the HFI-based $\tau$ posterior distribution
using the maximum likelihood power spectrum estimator from $EE$ data only,
giving a value $0.055\pm 0.009$. In a companion paper these results are
discussed in the context of the best-fit Planck $\Lambda$CDM cosmological model
and recent models of reionization. | Cosmological Measurements with General Relativistic Galaxy Correlations: We investigate the cosmological dependence and the constraining power of
large-scale galaxy correlations, including all redshift-distortions,
wide-angle, lensing and gravitational potential effects on linear scales. We
analyze the cosmological information present in the lensing convergence and in
the gravitational potential terms describing the so-called "relativistic
effects," and we find that, while smaller than the information contained in
intrinsic galaxy clustering, it is not negligible. We investigate how
neglecting them does bias cosmological measurements performed by future
spectroscopic and photometric large-scale surveys such as SKA and Euclid. We
perform a Fisher analysis using the CLASS code, modified to include
scale-dependent galaxy bias and redshift-dependent magnification and evolution
bias. Our results show that neglecting relativistic terms introduces an error
in the forecasted precision in measuring cosmological parameters of the order
of a few tens of percent, in particular when measuring the matter content of
the Universe and primordial non-Gaussianity parameters. Therefore, we argue
that radial correlations and integrated relativistic terms need to be taken
into account when forecasting the constraining power of future large-scale
number counts of galaxy surveys. |
A fourth HI 21-cm absorption system in the sight-line of MG J0414+0534:
a record for intervening absorbers: We report the detection of a strong HI 21-cm absorption system at z=0.5344,
as well as a candidate system at z=0.3389, in the sight-line towards the z=2.64
quasar MG J0414+0534. This, in addition to the absorption at the host redshift
and the other two intervening absorbers, takes the total to four (possibly
five). The previous maximum number of 21-cm absorbers detected along a single
sight-line is two and so we suspect that this number of gas-rich absorbers is
in some way related to the very red colour of the background source. Despite
this, no molecular gas (through OH absorption) has yet been detected at any of
the 21-cm redshifts, although, from the population of 21-cm absorbers as a
whole, there is evidence for a weak correlation between the atomic line
strength and the optical--near-infrared colour. In either case, the fact that
so many gas-rich galaxies (likely to be damped Lyman-alpha absorption systems)
have been found along a single sight-line towards a highly obscured source may
have far reaching implications for the population of faint galaxies not
detected in optical surveys, a possibility which could be addressed through
future wide-field absorption line surveys with the Square Kilometre Array. | The Lyman-$α$ power spectrum - CMB lensing convergence
cross-correlation: We investigate the three-point correlation between the Lyman-$\alpha$ forest
and the CMB weak lensing ($\delta_F \delta_F \kappa$) expressed as the
cross-correlation between the CMB weak lensing field and local variations in
the forest power spectrum. In addition to the standard gravitational bispectrum
term, we note the existence of a non-standard systematic term coming from
mis-estimation of the mean flux over the finite length of Lyman-$\alpha$
skewers. We numerically calculate the angular cross-power spectrum and discuss
its features. We integrate it into zero-lag correlation function and compare
our predictions with recent results by Doux et al.. We find that our
predictions are statistically consistent with the measurement, and including
the systematic term improves the agreement with the measurement. We comment on
the implication of the response of the Lyman-$\alpha$ forest power spectrum to
the long-wavelength density perturbations. |
A Census of Stellar Mass in 10 Massive Haloes at z~1 from the GCLASS
Survey: We study the stellar mass content of massive haloes in the redshift range
0.86<z<1.34, by measuring: (1) The stellar mass in the central galaxy versus
total dynamical halo mass. (2) The total stellar mass (including satellites)
versus total halo mass. (3) The radial stellar mass and number density profiles
for the ensemble halo. We use a Ks-band selected catalogue for the 10 clusters
in the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), with
photometric redshifts and stellar masses measured from 11-band SED fitting.
Combining the photometric catalogues with the deep spectroscopic component of
GCLASS, we correct the cluster galaxy sample for interlopers. We also perform a
dynamical analysis of the cluster galaxies to estimate the halo mass M200 for
each cluster based on a measurement of its velocity dispersion. (1) We find
that the central galaxy stellar mass fraction decreases with total halo mass,
and that this is in reasonable quantitative agreement with measurements from
abundance matching studies at z~1. (2) The total stellar mass fractions of
these systems decrease with halo mass, indicating that lower mass systems are
more efficient at transforming baryons into stars. We find the total stellar
mass to be a good proxy for total halo mass, with a small intrinsic scatter.
When we compare these results with literature measurements, we find that the
stellar mass fraction at fixed halo mass shows no significant evolution in the
range 0<z<1. (3) We measure a relatively high NFW concentration parameter c ~ 7
for the stellar mass distribution in these clusters. A simple model shows that
the stellar mass content of GCLASS can evolve in typical distributions observed
at lower redshifts if the clusters primarily accrete stellar mass onto the
outskirts. [Abridged] | Probing the Cosmological Principle with the CSST Photometric Survey: The cosmological principle states that our Universe is statistically
homogeneous and isotropic at large scales. However, due to the relative motion
of the Solar System, an additional kinematic dipole can be detected in the
distribution of galaxies, which should be consistent with the dipole observed
in the cosmic microwave background temperature. In this paper, we forecast the
mock number count maps from the China Space Station Telescope photometric
survey to reconstruct the kinematic dipole. Using the whole photometric mock
data, we obtain a positive evidence for the dipole signal detection at 3 sigma
confidence level, and the significance would be increased to 4 sigma when we
only use the high-redshift samples with z = 1.8 to 4. This result can provide a
good consistency check between the kinematic dipoles measured in the CMB and
that from the large scale structure, which can help us to verify the basic
cosmological principle. |
High-n Hydrogen Recombination Lines from the First Galaxies: We investigate the prospects of blind and targeted searches in the radio
domain (10 MHz to 1 THz) for high-n hydrogen recombination lines from the first
generation of galaxies, at z < 10. The expected optically thin spontaneous
alpha-line luminosities are calculated as a function of the absolute AB
magnitude of a galaxy at 1500 angstrom. For a blind search, semi-empirical
luminosity functions are used to calculate the number of galaxies whose
expected flux densities exceed an assumed detectability threshold. Plots of the
minimum sky area, within which at least one detectable galaxy is expected at a
given observing frequency, in the fiducial instantaneous passband of 10^4 km/s,
allow to assess the blind search time necessary for detection by a given
facility. We show that the chances for detection are the highest in the mm and
submm domains, but finding spontaneous emission in a blind search, especially
from redshifts z >> 1, is a challenge even with powerful facilities, such as
ALMA and SKA. The probability of success is higher for a targeted search of
lines with principal quantum number n ~ 10 in Lyman-break galaxies amplified by
gravitational lensing. Detection of more than one hydrogen line in such a
galaxy will allow for line identification and a precise determination of the
galaxy's redshift. | Cosmic dichotomy in the hosts of rapidly star-forming systems at low and
high redshifts: This paper presents a compilation of clustering results taken from the
literature for galaxies with highly enhanced (SFR [30-10^3] Msun/yr) star
formation activity observed in the redshift range z=[0-3]. We show that,
irrespective of the selection technique and only very mildly depending on the
star forming rate, the clustering lengths of these objects present a sharp
increase of about a factor 3 between z~1 and z~2, going from values of ~5 Mpc
to about 15 Mpc and higher. This behaviour is reflected in the trend of the
masses of the dark matter hosts of star-forming galaxies which increase from
~10^11.5 Msun to ~10^13.5 Msun between z~1 and z~2. Our analysis shows that
galaxies which actively form stars at high redshifts are not the same
population of sources we observe in the more local universe. In fact, vigorous
star formation in the early universe is hosted by very massive structures,
while for z~1 a comparable activity is encountered in much smaller systems,
consistent with the down-sizing scenario. The available clustering data can
hardly be reconciled with merging as the main trigger for intense star
formation activity at high redshifts.
We further argue that, after a characteristic time-scale of ~1 Gyr, massive
star-forming galaxies at z>~2 evolve into z<~1.5 passive galaxies with large
(Mstellar=[10^11 - 10^12] Msun) stellar masses. |
Conformal model for gravitational waves and dark matter: A status update: We present an updated analysis of the first-order phase transition associated
with symmetry breaking in the early Universe in a classically scale-invariant
model extended with a new SU(2) gauge group. Including recent developments in
understanding supercooled phase transitions, we compute all of its
characteristics and significantly constrain the parameter space. We then
predict gravitational wave spectra generated during this phase transition and
by computing the signal-to-noise ratio we conclude that this model is well
testable (and falsifiable) with LISA. We also provide predictions for the relic
dark matter abundance. It is consistent with observations in a rather narrow
part of the parameter space, since we exclude the so-called supercool dark
matter scenario based on an improved description of percolation and reheating
after the phase transition as well as inclusion of the running of couplings.
Finally, we devote attention to renormalisation-scale dependence of the
results. Even though our main results are obtained with the use of
renormalisation-group improved effective potential, we also perform a
fixed-scale analysis which proves that the dependence on the scale is not only
qualitative but also quantitative. | Elementary analysis of galaxy clusters: similarity criteria,
Tully-Fischer, and approximate invariants: At observations of galaxy clusters luminosity L, size R, mass M, temperature
T$_e$, sometimes velocities are usually measured. These four quantities and the
gravity constant G are determined by three measurements units: mass M, length L
and time T. Therefore one can form two non-dimensional similarity criteria:
$\Pi_1$ and $\Pi_2$. Any chosen observable can be formed as a function of the
other three ones. The author has at hand the data by Vikhlinin (2002) and
Vikhlinin et al. (2006), rather more complete than any other. This material
consists of more than thirty clusters at 0.4 $\le$ z < 1.26 and z $\le$ 0. This
material gives a possibility to test the derived dimensional relationships and
to determine the dimensionless numerical coefficients at them. These
coefficients are found with a scatter less than 30 per cent in the data above
and could be considered as other similarity criteria but functions of $\Pi_1$
and $\Pi_2$. With this scatter they may be called approximate invariants. The
luminosity L and universal constant G are forming the dynamical velocity scale
U$_d$, which immediately explains the empirical Tully-Fisher law. The
temperature T$_e$ determines the thermal velocity of the gas plasma particles
U$_T$. The ratio U$_d$/ U$_T$= $\Pi_1$ is used here as a new similarity
criterium which is found to be constant within six per cent for nearly 30
objects cited above: $\Pi_1$=0.163$\pm$0.009 and may be interpreted as the Mach
number. The other criterium $\Pi_2 is the virial one. It is found to be a
function of the cluster age. At z>0.5 the mean cluster mass is five times less,
that at small z $\le$0.2. It is demanding to expand these results to other
clusters and different objects: singular galaxies, stars and their clouds, etc. |
The lensing and temperature imprints of voids on the Cosmic Microwave
Background: We have searched for the signature of cosmic voids in the CMB, in both the
Planck temperature and lensing-convergence maps; voids should give decrements
in both. We use zobov voids from the DR12 SDSS CMASS galaxy sample. We base our
analysis on N-body simulations, to avoid a posteriori bias. For the first time,
we detect the signature of voids in CMB lensing: the significance is
$3.2\sigma$, close to $\Lambda$CDM in both amplitude and projected
density-profile shape. A temperature dip is also seen, at modest significance
($2.3\sigma$), with amplitude about 6 times the prediction. This temperature
signal is induced mostly by voids with radius between 100 and 150 Mpc/h, while
the lensing signal is mostly contributed by smaller voids -- as expected;
lensing relates directly to density, while ISW depends on gravitational
potential. The void abundance in observations and simulations agree, as well.
We also repeated the analysis excluding lower-significance voids: no lensing
signal is detected, with an upper limit of about twice the $\Lambda$CDM
prediction. But the mean temperature decrement now becomes non-zero at the
$3.7\sigma$ level (similar to that found by Granett et al.), with amplitude
about 20 times the prediction. However, the observed dependence of temperature
on void size is in poor agreement with simulations, whereas the lensing results
are consistent with $\Lambda$CDM theory. Thus, the overall tension between
theory and observations does not favour non-standard theories of gravity,
despite the hints of an enhanced amplitude for the ISW effect from voids. | The Universe acceleration from the Unimodular gravity view point:
Background and linear perturbations: With the goal of studying the cosmological constant (CC) problem, we present
an exhaustive analysis of unimodular gravity as a possible candidate to resolve
the CC origin and with this, the current Universe acceleration. In this theory,
a correction constant (CC-like) in the field equations sources the late cosmic
acceleration. This constant is related to a new parameter, $z_{ini}$, which is
interpreted as the redshift of CC-like emergence. By comparing with the CC
value obtained from Planck and Supernovaes measurements, it is possible to
estimate $z_{ini}=11.15^{+0.01}_{-0.02}$ and $z_{ini}=11.43^{+0.03}_{-0.06}$
respectively, which is close to the reionization epoch. Moreover, we use the
observational Hubble data (OHD), Type Ia Supernovae (SnIa), Baryon Acoustic
Oscillations (BAO) and the Cosmic Microwave Background Radiation (CMB) distance
data to constrain the UG cosmological parameters. A Joint analysis
(OHD+SnIa+BAO+CMB), results in $z_{ini}=11.47^{+0.074}_{-0.073}$ within
$1\sigma$ confidence level consistent with our estimation from Planck and
Supernovae measurements. We also include linear perturbations, starting with
scalar and tensor perturbations and complementing with the perturbed Boltzmann
equation for photons. We show that the $00$ term in the UG field equations and
the Boltzmann equation for photons contains corrections, meanwhile the other
equations are similar as those obtained in standard cosmology. |
Lecture notes on the physics of cosmic microwave background anisotropies: We review the theory of the temperature anisotropy and polarization of the
cosmic microwave background (CMB) radiation, and describe what we have learned
from current CMB observations. In particular, we discuss how the CMB is being
used to provide precise measurements of the composition and geometry of the
observable universe, and to constrain the physics of the early universe. We
also briefly review the physics of the small-scale CMB fluctuations generated
during and after the epoch of reionization, and which are the target of a new
breed of arcminute-resolution instruments. | Herschel-PACS observations of [OI]63um towards submillimetre galaxies at
z~1: We present Herschel-PACS spectroscopy of the [OI]63um far-infrared cooling
line from a sample of six unlensed and spectroscopically-confirmed
870um-selected submillimetre (submm) galaxies (SMGs) at 1.1<z<1.6 from the
LABOCA Extended Chandra Deep Field South (ECDFS) Submm Survey (LESS). This is
the first survey of [OI]63um, one of the main photodissociation region (PDR)
cooling lines, in SMGs. New high-resolution ALMA interferometric 870um
continuum imaging confirms that these six Herschel-targeted SMG counterparts
are bona fide sources of submm emission. We detect [OI]63um in two SMGs with a
SNR >3, tentatively detect [OI]63um in one SMG, and constrain the line flux for
the non-detections. We also exploit the combination of submm continuum
photometry from 250-870um and our new PACS continuum measurements to constrain
the far-infrared (FIR) luminosity, L_FIR, in these SMGs to < 30%. We find that
SMGs do not show a deficit in their [OI]63um-to-far-infrared continuum
luminosity ratios (with ratios ranging from ~0.5-1.5%), similar to what was
seen previously for the [CII]158um-to-FIR ratios in SMGs. These observed ratios
are about an order of magnitude higher than what is seen typically for local
ultra luminous infrared galaxies (ULIRGs), which adds to the growing body of
evidence that SMGs are not simply `scaled up' versions of local ULIRGs. Rather,
the PDR line-to-L_FIR ratios suggest that the star formation modes of SMGs are
likely more akin to that of local normal (lower-luminosity) star-forming
galaxies, with the bulk of the star formation occurring in extended regions,
galaxy-scale (~kpc) in size. These observations represent the first step
towards a census of the major PDR cooling lines in typical SMGs that will be
attainable with ALMA, enabling detailed modelling to probe the global
properties of the star formation and the evolutionary status of SMGs. |
Mildly mixed coupled models vs. WMAP7 data: Mildly mixed coupled models include massive neutrinos and CDM--DE coupling.
We present new tests of their likelihood vs. recent data including WMAP7,
confirming it to exceed LCDM, although at ~2\sigma's. We then show the impact
on the physics of the dark components of neutrino mass detection in tritium
beta decay or neutrinoless double beta decay experiments. | Probing neutrino interactions and dark radiation with gravitational
waves: After their generation, cosmological backgrounds of gravitational waves
propagate nearly freely but for the expansion of the Universe and the
anisotropic stress of free-streaming particles. Primordial signals -- both that
from inflation and the infrared spectrum associated to subhorizon production
mechanisms -- would carry clean information about the cosmological history of
these effects. We study the modulation of the standard damping of gravitational
waves by free-streaming radiation due to the decoupling (or recoupling) of
interactions. We focus on nonstandard neutrino interactions in effect after the
decoupling of weak interactions as well as more general scenarios in the early
Universe involving other light relics. We develop semianalytic results in fully
free-streaming scenarios to provide intuition for numerical results that
incorporate interaction rates with a variety of temerpature dependencies.
Finally, we compute the imprint of neutrino interactions on the $B$-mode
polarization of the cosmic microwave background, and we comment on other means
to infer the presence of such effects at higher frequencies. |
Mg II Absorption Characteristics of a Volume-Limited Sample of Galaxies
at z ~ 0.1: We present an initial survey of Mg II absorption characteristics in the halos
of a carefully constructed, volume-limited subsample of galaxies embedded in
the spectroscopic part of the Sloan Digital Sky Survey. We observed quasars
near sightlines to 20 low-redshift (z ~ 0.1), luminous M_r <= -20.5 galaxies in
SDSS DR4 and DR6 with the LRIS-B spectrograph on the Keck I telescope. The
primary systematic criteria for the targeted galaxies are a redshift z >~ 0.1
and the presence of an appropriate bright background quasar within a projected
75 kpc/h of its center, although we preferentially sample galaxies with lower
impact parameters and slightly more star formation within this range. Of the
observed systems, six exhibit strong [EW(2796) >= 0.3 Ang.] Mg II absorption at
the galaxy's redshift, six systems have upper limits which preclude strong Mg
II absorption, while the remaining observations rule out very strong [EW(2796)
>= 1-2 Ang] absorption. The absorbers fall at higher impact parameters than
many non-absorber sightlines, indicating a covering fraction f_c <~ 0.4 for >=
0.3-Angstrom absorbers at z ~ 0.1, even at impact parameters <= 35 kpc/h (f_c ~
0.25). The data are consistent with a possible dependence of covering fraction
and/or absorption halo size on the environment or star-forming properties of
the central galaxy. | Galaxy-group (halo) alignments from SDSS DR7 and the ELUCID simulation: Based on galaxies from the Sloan Digital Sky Survey (SDSS) and subhalos in
the corresponding reconstructed region from the constrained simulation of
ELUCID, we study the alignment of central galaxies relative to their host
groups in the group catalog, as well as the alignment relative to the
corresponding subhalos in the ELUCID simulation. Galaxies in observation are
matched to dark matter subhalos in the ELUCID simulation using a novel
neighborhood abundance matching method. In observation, the major axes of
galaxies are found to be preferentially aligned to the major axes of their host
groups. There is a color dependence of galaxy-group alignment that red centrals
have a stronger alignment along the major axes of their host groups than blue
centrals. Combining galaxies in observation and subhalos in the ELUCID
simulation, we also find that central galaxies have their major axes to be
aligned to the major axes of their corresponding subhalos in the ELUCID
simulation. We find that the galaxy-group and galaxy-subhalo alignment signals
are stronger for galaxies in more massive halos. We find that the alignments
between main subhalos and the SDSS matched subhalo systems in simulation are
slightly stronger than the galaxy-group alignments in observation. |
The WiggleZ Dark Energy Survey: Survey Design and First Data Release: The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies
in the distant universe, measured with the AAOmega spectrograph on the 3.9-m
Anglo-Australian Telescope (AAT). The target galaxies are selected using
ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8
mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The
primary aim of the survey is to precisely measure the scale of baryon acoustic
oscillations (BAO) imprinted on the spatial distribution of these galaxies at
look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will
measure the BAO scale to better than 2% and the tangential and radial acoustic
wave scales to approximately 3% and 5%, respectively.
This paper provides a detailed description of the survey and its design, as
well as the spectroscopic observations, data reduction, and redshift
measurement techniques employed. It also presents an analysis of the properties
of the target galaxies, including emission line diagnostics which show that
they are mostly extreme starburst galaxies, and Hubble Space Telescope images,
which show they contain a high fraction of interacting or distorted systems. In
conjunction with this paper, we make a public data release of data for the
first 100,000 galaxies measured for the project. | Quantum Generation of Dark Energy: We present a type of dark energy models where the particles of dark energy
phi are dynamically produced via a quantum transition at very low energies. The
scale where the transition takes places depends on the strength g of the
interaction between phi and a relativistic field varphi. We show that a g
\simeq 10^{-12} gives a generation scale E_gen simeq eV with a cross section
sigma simeq 1 pb close to the WIMPs cross section sigma_w simeq pb at
decoupling. The number density n_phi of the \phi particles are a source term in
the eq. of motion of phi and it generates the scalar potential v(phi)
responsible for the late time acceleration of our universe. Since the
appearance of phi may be at very low scales, close to present time, the
cosmological coincidence problem can be explained simply due to the size of the
coupling constant. We unify dark energy with inflation in terms of a single
scalar field phi, and we use the same potential v for inflation and dark
energy. However, after inflation phi decays completely and reheats the universe
at a scale E_RH propto h^2 m_Pl, where h is the coupling between the SM
particles and varphi. The field phi disappears from the spectrum during, from
reheating until its re-generation, and therefore it does not interfere with the
standard decelerating radiation/matter cosmological model allowing for a
successful unification scheme. The same interaction term that gives rise to the
inflaton decay accounts for the late time re-generation of phi. We present a
simple model where the strength of the g and h couplings are set by the
inflation scale E_I with g=h^2 propto E_I/m_Pl giving a reheating scale E_RH
propto E_I=100TeV and phi-generation scale E_gen propto E_I^2/m_pl=eV << E_RH. |
Radial profiles of Fe abundance in the intracluster medium of nearby
clusters observed with XMM-Newton: Aims.The abundances of Fe in the intracluster medium of nearby (z<0.08)
clusters were measured up to 0.3$\sim$ 0.5r$_{180}$. Methods.We analyzed 28
clusters of galaxies observed with XMM-Newton. We derived Fe abundances from
the flux ratios of Fe lines to the continuum within an energy range of 3.5--6
keV to minimize and evaluate systematic uncertainties. Results.The radial
profiles of the Fe abundances of relaxed clusters with a cD galaxy at their
X-ray peak have similar slopes. These clusters show similar enhancements in the
Fe abundance within 0.1$r_{180}$, and at 0.1--0.3$r_{180}$, they have flatter
Fe abundance profiles at 0.4$\sim$0.5 solar, with a small scatter. Most other
clusters, including merging clusters, also have similar Fe abundance profiles
beyond 0.1$r_{180}$. These clusters may have universal metal enrichment
histories,and a significant amount of Fe was synthesized at a very early stage
in cluster formation. Mergers of clusters can destroy the central Fe peak. | Multiband lightcurves of tidal disruption events: Unambiguous detection of the tidal disruption of a star would allow an
assessment of the presence and masses of supermassive black holes in quiescent
galaxies. It would also provide invaluable information on bulge scale stellar
processes (such as two-body relaxation) via the rate at which stars are
injected into the tidal sphere of influence of the black holes. This rate, in
turn, is essential to predict gravitational radiation emission by compact
object inspirals. The signature of a tidal disruption event is thought to be a
fallback rate for the stellar debris onto the black hole that decreases as
$t^{-5/3}$. This mass flux is often assumed to yield a luminous signal that
decreases in time at the same rate. In this paper, we calculate the
monochromatic lightcurves arising from such an accretion event. Differently
from previous studies, we adopt a more realistic description of the fallback
rate and of the super-Eddigton accretion physics. We also provide simultaneous
lightcurves in optical, UV and X-rays. We show that, after a few months,
optical and UV lightcurves scale as $t^{-5/12}$, and are thus substantially
flatter than the $t^{-5/3}$ behaviour, which is a prerogative of the bolometric
lightcurve, only. At earlier times and for black hole masses $< 10^7 M_{\sun}$,
the wind emission dominates: after reaching a peak of $10^{41}-10^{43}$ erg/s
at roughly a month, the lightcurve decreases steeply as $\sim t^{-2.6}$, until
the disc contribution takes over. The X-ray band, instead, is the best place to
detect the $t^{-5/3}$ "smoking gun" behaviour, although it is displayed only
for roughly a year, before the emission steepens exponentially. |
Spatially resolved properties of the grand-design spiral galaxy UGC
9837: a case for high-redshift 2D observations: Context. We carry out a detailed 2D study of the ionised gas in the local
universe galaxy UGC9837. In nearby galaxies, like the galaxy in question here,
the spatial distribution of the physical properties can be studied in detail,
providing benchmarks for galaxy formation models.
Aims. Our aim is to derive detailed and spatially resolved physical
properties of the ionised gas of UGC 9837. In addition, we derive an integrated
spectrum of the galaxy and study how varying spatial coverage affects the
derived integrated properties. We also study how the same properties would be
seen if the galaxy was placed at a higher redshift and observed as part of one
of the high-z surveys.
Methods. UGC9837 was observed using the PMAS PPAK integral field unit. The
spectra are reduced and calibrated and the stellar and ionised components
separated. Using strong emission line ratios of the ionised gas, the source of
ionisation, the dust extinction, the star formation rate, the electron density
and the oxygen abundance derived from a total integrated spectrum, central
integrated spectrum and individual fibre spectra are studied. Finally, the same
properties are studied in a spectrum whose spatial resolution is degraded to
simulate high-z observations.
Results. The spatial distribution of the ionised gas properties is consistent
with inside-out growing scenario of galaxies. We also find that lack of spatial
coverage would bias the results derived from the integrated spectrum leading,
e.g., to an under-estimation of ionisation and over-estimation of metallicity,
if only the centre of the galaxy was covered by the spectrum. Our simulation of
high-z observations shows that part of the spatial information, such as dust
and SFR distribution would be lost while shallower gradients in metallicity and
ionisation strength would be detected. | Anisotropic power spectrum and the observed low-l power in PLANCK CMB
data: In this work, we study a direction dependent power spectrum in anisotropic
Finsler space-time. We use this direction dependent power spectrum to address
the low-l power observed in WMAP and PLANCK data. The angular power spectrum of
the temperature fluctuations has a lower amplitude in comparison to the
$\Lambda$CDM model in the multipole range l = 2-40. Our theoretical model gives
a correction to the isotropic angular power spectrum $C^{TT}_l$ due to the
breaking of the rotational invariance of the primordial power spectrum. We
estimate best-fit model parameters along with the six $\Lambda$CDM cosmological
parameters using PLANCK likelihood code in CosmoMC software. We see that this
modified angular power spectrum fits the CMB temperature data in the multipole
range l=2-10 to a good extent but fails for the whole multipole range l = 2-40. |
Alternatives to $Λ$: Torsion, Generalized Couplings, and Scale
Invariance: We present a comparative analysis of current observational constraints on
three recently discussed alternative models for explaining the low-redshift
acceleration of the universe: the so-called steady-state torsion model, the
generalized coupling model, and the scale invariant model by Maeder (an example
of a broader class which we also briefly study) These are compared to the
traditional parameterization of Chevallier, Polarski and Linder. Each of the
candidate models is studied under two different assumptions: as genuine
alternatives to $\Lambda$CDM (where a new degree of freedom would be expected
to explain the recent acceleration of the universe without any cosmological
constant) and as parametric extensions of $\Lambda$CDM (where both a
cosmological constant and the new mechanism can coexist, and the relative
contributions of both are determined by the data). Our comparative analysis
suggests that, from a phenomenological point of view, all such models neatly
divide into two classes, with different observational consequences. | A common origin for baryons and dark matter: The origin of the baryon asymmetry of the Universe (BAU) and the nature of
dark matter are two of the most challenging problems in cosmology. We propose a
scenario in which the gravitational collapse of large inhomogeneities at the
quark-hadron epoch generates both the baryon asymmetry and dark matter in the
form of primordial black holes (PBHs). This is due to the sudden drop in
radiation pressure during the transition from a quark-gluon plasma to
non-relativistic hadrons. The collapse to a PBH is induced by fluctuations of a
light spectator scalar field in rare regions and is accompanied by the violent
expulsion of surrounding material, which might be regarded as a sort of
"primordial supernova" . The acceleration of protons to relativistic speeds
provides the ingredients for efficient baryogenesis around the collapsing
regions and its subsequent propagation to the rest of the Universe. This
scenario naturally explains why the observed BAU is of order the PBH collapse
fraction and why the baryons and dark matter have comparable densities. The
predicted PBH mass distribution ranges from sub-solar to several hundred solar
masses. This is compatible with current observational constraints and could
explain the rate, mass and low spin of the black hole mergers detected by
LIGO-Virgo. Future observations will soon be able to test this scenario. |
k-cut Cosmic Shear: Tunable Power Spectrum Sensitivity to Test Gravity: If left unchecked modeling uncertainties at small scales, due to poorly
understood baryonic physics and non-linear structure formation, will
significantly bias Stage IV cosmic shear two-point statistic parameter
constraints. While it is perhaps possible to run N-body or hydrodynamical
simulations to determine the impact of these effects this approach is
computationally expensive; especially to test a large number of theories of
gravity. Instead we propose directly removing sensitivity to small-scale
structure from the lensing spectrum, creating a statistic that is robust to
these uncertainties. We do this by taking a redshift-dependent l-cut after
applying the Bernardeau-Nishimichi-Taruya (BNT) nulling scheme. This
reorganizes the information in the lensing spectrum to make the relationship
between the angular scale, l, and the structure scale, k, much clearer compared
to standard cosmic shear power spectra -- for which no direct relationship
exists. We quantify the effectiveness of this method at removing sensitivity to
small scales and compute the predicted Fisher error on the dark energy equation
of state, w0, for different k-cuts in the matter power spectrum. | Astro2020 Science White Paper: A proposal to exploit galaxy-21cm
synergies to shed light on the Epoch of Reionization: This white paper highlights the crucial and urgent synergies required between
WFIRST, Subaru Hyper Suprime-Cam or other >25m-class telescopes galaxy
observations and SKA 21cm measurements to constrain the nature of reionization
(ionization history and topology) and its sources. |
Optimal strategies for identifying quasars in DESI: As spectroscopic surveys continue to grow in size, the problem of classifying
spectra targeted as quasars (QSOs) will need to move beyond its historical
reliance on human experts. Instead, automatic classifiers will increasingly
become the dominant classification method, leaving only small fractions of
spectra to be visually inspected in ambiguous cases. In order to maximise
classification accuracy, making best use of available classifiers will be of
great importance, particularly when looking to identify and eliminate
distinctive failure modes. In this work, we demonstrate that the machine
learning-based classifier QuasarNET will be of use for future surveys such as
the Dark Energy Spectroscopic Instrument (DESI), comparing its performance to
the DESI pipeline classifier redrock. During the first of four passes across
its footprint DESI will need to select high-$z$ ($z\geq2.1$) QSOs for
reobservation, and so we first assess the classifiers' performance at
identifying high-$z$ QSOs from single-exposure spectra. We then quantify the
classifiers' abilities to construct QSO catalogues in both low- and high-$z$
bins, using coadded spectra to simulate end-of-survey data. For such tasks,
QuasarNET is able to outperform redrock in its current form, identifying
approximately 99% of high-$z$ QSOs from single exposures and producing QSO
catalogues with sub-percent levels of contamination. By combining QuasarNET and
redrock's outputs, we can further improve the classification strategies to
identify up to 99.5% of high-$z$ QSOs from single exposures and reduce final
QSO catalogue contamination to below 0.5%. These combined strategies address
DESI's QSO classification needs effectively. | The evolution of the large-scale structure of the universe: beyond the
linear regime: These lecture notes introduce analytical tools, methods and results
describing the growth of cosmological structure beyond the linear regime. The
presentation is focused on the single flow regime of the Vlasov-Poisson
equation describing the development of gravitational instabilities in a
pressureless fluid. These notes include the introduction of diagrammatic
representations of the standard perturbation theory with applications to the
calculation of the so-called loop contributions to the power spectra. A large
part of these notes is devoted to the exploration of the convergence properties
of these terms from the contribution of both the long-wave modes and the
short-wave modes. The resulting performances of the two-loop corrections of the
power spectra are then presented. Finally other avenues that use different
methods are explored. In particular it is shown how joint density and profile
probability distribution functions can be constructed out of the
multiple-variable cumulant generating functions computed at tree order. |
HST Observations of the Double-Peaked Emission Lines in the Seyfert
Galaxy Markarian 78: Mass Outflows from a Single AGN: Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a
double set of emission lines, similar to those seen in several AGN from recent
surveys. Are the double lines due to two AGN with different radial velocities
in the same galaxy, or are they due to mass outflows from a single AGN?We
present a study of the outflowing ionized gas in the resolved narrow-line
region (NLR) of Mrk 78 using observations from Space Telescope Imaging
Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space
Telescope(HST) as part of an ongoing project to determine the kinematics and
geometries of active galactic nuclei (AGN) outflows. From the spectroscopic
information, we deter- mined the fundamental geometry of the outflow via our
kinematics modeling program by recreating radial velocities to fit those seen
in four different STIS slit positions. We determined that the double emission
lines seen in ground-based spectra are due to an asymmetric distribution of
outflowing gas in the NLR. By successfully fitting a model for a single AGN to
Mrk 78, we show that it is possible to explain double emission lines with
radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual
supermassive black holes. | The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: cosmological implications of the large-scale two-point
correlation function: We obtain constraints on cosmological parameters from the spherically
averaged redshift-space correlation function of the CMASS Data Release 9 (DR9)
sample of the Baryonic Oscillation Spectroscopic Survey (BOSS). We combine this
information with additional data from recent CMB, SN and BAO measurements. Our
results show no significant evidence of deviations from the standard
flat-Lambda CDM model, whose basic parameters can be specified by Omega_m =
0.285 +- 0.009, 100 Omega_b = 4.59 +- 0.09, n_s = 0.96 +- 0.009, H_0 = 69.4 +-
0.8 km/s/Mpc and sigma_8 = 0.80 +- 0.02. The CMB+CMASS combination sets tight
constraints on the curvature of the Universe, with Omega_k = -0.0043 +- 0.0049,
and the tensor-to-scalar amplitude ratio, for which we find r < 0.16 at the 95
per cent confidence level (CL). These data show a clear signature of a
deviation from scale-invariance also in the presence of tensor modes, with n_s
<1 at the 99.7 per cent CL. We derive constraints on the fraction of massive
neutrinos of f_nu < 0.049 (95 per cent CL), implying a limit of sum m_nu < 0.51
eV. We find no signature of a deviation from a cosmological constant from the
combination of all datasets, with a constraint of w_DE = -1.033 +- 0.073 when
this parameter is assumed time-independent, and no evidence of a departure from
this value when it is allowed to evolve as w_DE(a) = w_0 + w_a (1 - a). The
achieved accuracy on our cosmological constraints is a clear demonstration of
the constraining power of current cosmological observations. |
Cosmological-model-independent tests for the distance-duality relation
from Galaxy Clusters and Type Ia Supernova: We perform a cosmological-model-independent test for the distance-duality
(DD) relation $\eta(z)=D_L(z)(1+z)^{-2}/D_A(z)$, where $D_L$ and $D_A$ are the
luminosity distance and angular diameter distance respectively, with a
combination of observational data for $D_L$ taken from the latest Union2 SNe Ia
and that for $D_A$ provided by two galaxy clusters samples compiled by De
Filippis {\it et al.} and Bonamente {\it et al.}. Two parameterizations for
$\eta(z)$, i.e., $\eta(z)=1+\eta_0z$ and $\eta(z)=1+\eta_0z/(1+z)$, are used.
We find that the DD relation can be accommodated at $1\sigma$ confidence level
(CL) for the De Filippis {\it et al.} sample and at $3\sigma$ CL for the
Bonamente {\it et al.} sample. We also examine the DD relation by postulating
two more general parameterizations: $\eta(z)=\eta_0+\eta_1z$ and
$\eta(z)=\eta_0+\eta_1z/(1+z)$, and find that the DD relation is compatible
with the results from the De Filippis {\it et al.} and the Bonamente {\it et
al.} samples at $1\sigma$ and $2\sigma$ CLs, respectively. Thus, we conclude
that the DD relation is compatible with present observations. | A search for low-mass WIMPs with EDELWEISS-II heat-and-ionization
detectors: We report on a search for low-energy (E < 20 keV) WIMP-induced nuclear
recoils using data collected in 2009 - 2010 by EDELWEISS from four germanium
detectors equipped with thermal sensors and an electrode design (ID) which
allows to efficiently reject several sources of background. The data indicate
no evidence for an exponential distribution of low-energy nuclear recoils that
could be attributed to WIMP elastic scattering after an exposure of 113 kg.d.
For WIMPs of mass 10 GeV, the observation of one event in the WIMP search
region results in a 90% CL limit of 1.0x10^-5 pb on the spin-independent
WIMP-nucleon scattering cross-section, which constrains the parameter space
associated with the findings reported by the CoGeNT, DAMA and CRESST
experiments. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Galaxy
clustering and redshift-space distortions at z=0.8 in the first data release: We present in this paper the general real- and redshift-space clustering
properties of galaxies as measured in the first data release of the VIPERS
survey. VIPERS is a large redshift survey designed to probe the distant
Universe and its large-scale structure at 0.5 < z < 1.2. We describe in this
analysis the global properties of the sample and discuss the survey
completeness and associated corrections. This sample allows us to measure the
galaxy clustering with an unprecedented accuracy at these redshifts. From the
redshift-space distortions observed in the galaxy clustering pattern we provide
a first measurement of the growth rate of structure at z = 0.8: f\sigma_8 =
0.47 +/- 0.08. This is completely consistent with the predictions of standard
cosmological models based on Einstein gravity, although this measurement alone
does not discriminate between different gravity models. | Three newly discovered globular clusters in NGC 6822: We present three newly discovered globular clusters (GCs) in the Local Group
dwarf irregular NGC 6822. Two are luminous and compact, while the third is a
very low luminosity diffuse cluster. We report the integrated optical
photometry of the clusters, drawing on archival CFHT/Megacam data. The spatial
positions of the new GCs are consistent with the linear alignment of the
already-known clusters. The most luminous of the new GCs is also highly
elliptical, which we speculate may be due to the low tidal field in its
environment. |
Reionization in the dark and the light from Cosmic Microwave Background: We explore the constraints on the history of reionization from Planck 2015
Cosmic Microwave Background (CMB) data and we derive the forecasts for future
CMB observations. We consider a class of monotonic histories of reionization as
parametrized by two additional extra parameters with respect to the average
optical depth used in the instantaneous reionization modeling. We investigate
the degeneracies between the history of reionization and selected extensions of
the standard cosmological model. In particular, we consider the degeneracies
with the total mass of the neutrino sector and we discuss the possible
correlation between the dark matter annihilation and the duration of
reionization in the CMB. We use an extension to poly-reion model that was
proposed in Hazra and Smoot, JCAP 1711, 028 (2017). We compare the constraints
from Planck 2015 data with the predicted constraints from possible future CMB
mission as LiteBIRD, and we also use the proposed CORE-like specifications as
an example of what higher resolution can bring in addition. We find that the
degeneracy between the average optical depth and the duration of reionization
will be substantially removed by both concepts. Degeneracies between the
reionization history and either the total neutrino mass and properties of dark
matter annihilation will also be improved by future surveys. We find only
marginal improvement in the constraints on reionization history for the higher
resolution in the case of long duration of reionization. | Galaxy And Mass Assembly: Estimating galaxy group masses via caustic
analysis: We have generated complementary halo mass estimates for all groups in the
Galaxy And Mass Assembly Galaxy Group Catalogue (GAMA G3Cv1) using a modified
caustic mass estimation algorithm, originally developed by Diaferio & Geller
(1997). We calibrate the algorithm by applying it on a series of 9 GAMA mock
galaxy light cones and investigate the effects of using different definitions
for group centre and size. We select the set of parameters that provide
median-unbiased mass estimates when tested on mocks, and generate mass
estimates for the real group catalogue. We find that on average, the caustic
mass estimates agree with dynamical mass estimates within a factor of 2 in 90.8
+/- 6.1% groups and compares equally well to velocity dispersion based mass
estimates for both high and low multiplicity groups over the full range of
masses probed by the G3Cv1. |
Impact of the reduced speed of light approximation on the post-overlap
neutral hydrogen fraction in numerical simulations of the epoch of
reionization: The reduced speed of light approximation is used in a variety of simulations
of the epoch of reionization and galaxy formation. Its popularity stems from
its ability to drastically reduce the computing cost of a simulation, by
allowing the use of larger, and therefore fewer timesteps to reach a solution.
It is physically motivated by the fact that ionization fronts rarely propagate
faster than some fraction of the speed of light. However, no global proof of
the physical validity of this approach is available, and possible artefacts
resulting from this approximation therefore need to be identifited and
characterized to allow its proper use. In this paper we investigate the impact
of the reduced speed of light approximation on the predicted properties of the
intergalactic medium. To this end we use fully coupled radiation-hydrodynamics
RAMSES-CUDATON simulations of the epoch of reionization. We find that reducing
the speed of light by a factor 5 (20, 100) leads to overestimating the
post-reionization volume-weighted $x_{HI}$ by a similar factor ~5 (20, 100)
with respect to full speed of light simulations. We show that the error is
driven by the hydrogen - photon chemistry. In photo-ionization equilibrium,
reducing the speed of light has the same effect as artificially reducing the
photon density or the reaction cross-section and leads to an underestimated
ionizing flux. We confirm this interpretation by running additional simulations
using a reduced speed of light in the photon propagation module, but keeping
this time the full speed of light in the chemistry module. With this setup, the
post-reionization neutral hydrogen fractions converge to the full speed of
light value, which validates our explanation. Increasing spatial resolution
beyond a cell size of 1 kpc physical, so as to better resolve Lyman-limit
systems, does not significantly affect our conclusions. | Properties and environment of Radio Emitting Galaxies in the VLA-zCOSMOS
survey: We investigate the properties and the environment of radio sources with
optical counterpart from the combined VLA-COSMOS and zCOSMOS samples. The
advantage of this sample is the availability of optical spectroscopic
information, high quality redshifts, and accurate density determination.
By comparing the star formation rates estimated from the optical spectral
energy distribution with those based on the radio luminosity, we divide the
radio sources in three families, passive AGN, non-passive AGN and star forming
galaxies. These families occupy specific regions of the 8.0-4.5 $\mu$m infrared
color--specific star formation plane, from which we extract the corresponding
control samples.
Only the passive AGN have a significantly different environment distribution
from their control sample. The fraction of radio-loud passive AGN increases
from ~2% in underdense regions to ~15% for overdensities (1+delta) greater than
10. This trend is also present as a function of richness of the groups hosting
the radio sources. Passive AGN in overdensities tend to have higher radio
luminosities than those in lower density environments. Since the black hole
mass distribution is similar in both environments, we speculate that, for low
radio luminosities, the radio emission is controlled (through fuel
disponibility or confinement of radio jet by local gas pressure) by the
interstellar medium of the host galaxy, while in other cases it is determined
by the structure (group or cluster) in which the galaxy resides. |
Optimistic estimation on probing primordial gravitational waves with CMB
B-mode polarization: In the measurements of cosmic microwave background polarizations, three
frequency channels are necessary for discriminating the primordial B-modes from
the polarized dust and the synchrotron emission. We carry out an optimistic
estimate on the sensitivity to the detection of primordial gravitational waves
using the cosmic microwave background B-modes only, and explore how to reach
the thresholds for the tensor-to-scalar ratio $r$ in the theoretically
well-motivated inflation models. For example, Lyth bound implies $r \simeq
2\times10^{-3}$, a corrected Lyth bound shows $r \simeq 7\times10^{-4}$, and
some typical inflation models gives $r\simeq4\times10^{-5}$. Taking into
account the up-to-date constraints on $r$, i.e. $r_{0.05}<0.07$ at $95\%$
confidence, we find that the consistency relation $n_t=-r/8$ in the canonical
single-field slow-roll inflation cannot be distinguished from the scale
invariance, due to the cosmic variance in the power spectrum of cosmic
microwave background B-modes. The cosmic variance places an inevitable limit on
the measurements of the tensor spectral index, i.e. $\sigma_{n_t}\simeq0.01$
for $2\leqslant\ell\leqslant \ell_\text{max}=300$. | On the dust abundance gradients in late-type galaxies: II. Analytical
models as evidence for massive interstellar dust growth in SINGS galaxies: We use simple analytical models of the build up of the dust component and
compare these with radial dust distributions derived from observations of SINGS
galaxies. The observations show that dust gradients are indeed typically
steeper than the corresponding metallicity gradients and our models indicate
very little dust destruction, but significant dust growth in the ISM for most
of these galaxies. Hence, we conclude that there is evidence for significant
non-stellar dust production, and little evidence for dust destruction due to
SNe shock waves. We find that dust is reprocessed rather than destroyed by
shocks from SNe. Finally, we argue that dust abundances derived using standard
methods may be overestimated, since even very 'generous' estimates of the
metallicity results in dust-to-metals ratios above unity in several cases, if
the dust abundances given in the literature are taken at face value. |
Nonlinear evolution of dark matter subhalos and applications to warm
dark matter: We describe the methodology to include nonlinear evolution, including tidal
effects, in the computation of subhalo distribution properties in both cold
(CDM) and warm (WDM) dark matter universes. Using semi-analytic modeling, we
include effects from dynamical friction, tidal stripping, and tidal heating,
allowing us to dynamically evolve the subhalo distribution. We calibrate our
nonlinear evolution scheme to the CDM subhalo mass function in the Aquarius
N-body simulation, producing a subhalo mass function within the range of
simulations. We find tidal effects to be the dominant mechanism of nonlinear
evolution in the subhalo population. Finally, we compute the subhalo mass
function for $m_\chi=1.5$ keV WDM including the effects of nonlinear evolution,
and compare radial number densities and mass density profiles of subhalos in
CDM and WDM models. We show that all three signatures differ between the two
dark matter models, suggesting that probes of substructure may be able to
differentiate between them. | Limits on Self-Interacting Dark Matter: We impose new severe constraints on the self-interactions of fermionic
asymmetric dark matter based on observations of nearby old neutron stars. WIMP
self-interactions mediated by Yukawa- type interactions can lower significantly
the number of WIMPs necessary for gravitational collapse of the WIMP population
accumulated in a neutron star. Even nearby neutron stars located at regions of
low dark matter density can accrete sufficient number of WIMPs that can
potentially collapse, form a mini black hole, and destroy the host star. Based
on this, we derive constraints on the WIMP self-interactions which in some
cases are by several orders of magnitude stricter than the ones from the bullet
cluster (which are currently considered the most stringent). |
Measurement of $H(z)$ and $D_A(z)$ from the two-dimensional power
spectrum of Sloan Digital Sky Survey luminous red galaxies: We present a method to measure the Hubble parameter $H(z)$ and the angular
diameter distance $D_A(z)$ simultaneously from the two-dimensional matter power
spectrum from galaxy surveys with broad sky coverage. We validate this method
by applying it to the LasDamas mock galaxy catalogs. Then we apply this method
to Sloan Digital Sky Survey (SDSS) Data Release 7 and obtain measurements of
$\Omega_mh^2=0.1268 \pm 0.0085$, $H(z=0.35)=81.3\pm 3.8$km/s/Mpc, $D_A(z=0.35)
= 1037\pm44$Mpc, without assuming a dark energy model or a flat universe. We
also find that the derived parameters $H(0.35)r_s(z_d)/c=0.0431 \pm 0.0018$ and
$D_A(0.35)/r_s(z_d)=6.48 \pm 0.25$. These are in excellent agreement with
similar measurements from the two-dimensional correlation function of the same
data. | Detection of the kinematic Sunyaev-Zel'dovich effect with DES Year 1 and
SPT: We detect the kinematic Sunyaev-Zel'dovich (kSZ) effect with a statistical
significance of $4.2 \sigma$ by combining a cluster catalogue derived from the
first year data of the Dark Energy Survey (DES) with CMB temperature maps from
the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) Survey. This measurement
is performed with a differential statistic that isolates the pairwise kSZ
signal, providing the first detection of the large-scale, pairwise motion of
clusters using redshifts derived from photometric data. By fitting the pairwise
kSZ signal to a theoretical template we measure the average central optical
depth of the cluster sample, $\bar{\tau}_e = (3.75 \pm 0.89)\cdot 10^{-3}$. We
compare the extracted signal to realistic simulations and find good agreement
with respect to the signal-to-noise, the constraint on $\bar{\tau}_e$, and the
corresponding gas fraction. High-precision measurements of the pairwise kSZ
signal with future data will be able to place constraints on the baryonic
physics of galaxy clusters, and could be used to probe gravity on scales $
\gtrsim 100$ Mpc. |
Accretion processes in the galaxy cluster Hydra A/Abell 780: Clusters of galaxies evolve and accrete mass, mostly from small galaxy
systems. Our aim is to study the velocity field of the galaxy cluster Abell
780, which is known for the powerful radio source Hydra A at its center and
where a spectacular X-ray tail associated with the galaxy LEDA 87445 has been
discovered. Our analysis is based on the new spectroscopic data for hundreds of
galaxies obtained with the Italian Telescopio Nazionale {\em Galileo} and the
Very Large Telescope. We have constructed a redshift catalog of 623 galaxies
and selected a sample of 126 cluster members. We analyze the internal structure
of the cluster using a number of techniques. We estimate the mean redshift
z=0.0545, the line-of-sight velocity dispersion sigmav about 800 km/s, and the
dynamical mass M200 about 5.4 10E14 solar masses. The global properties of
Abell 780 are typical of relaxed clusters. On a smaller scale, we can detect
the presence of a galaxy group associated with LEDA 87445 in projected phase
space. The mean velocity and position of the center of the group agree well
with the velocity and position of LEDA 87445. We estimate the following
parameters of the collision. The group is characterized by a higher velocity
relative to the main system. It is infalling at a rest frame velocity of
Vrf=+870 km/s and lies at a projected distance D=1.1 Mpc to the south, slightly
southeast of the cluster center. The mass ratio between the group and the
cluster is about 1:5. We also find evidence of an asymmetry in the velocity
distribution of galaxies in the inner cluster region, which might be related to
a small low-velocity group detected as a substructure at Vrf=-750 km/s. We
conclude that A780, although dynamically relaxed at first sight, contains small
substructures that may have some impact on the energetics of the core region. | What is the redshift of the gamma- ray BL Lac source S4 0954+65?: High signal-to-noise ratio spectroscopic observations of the BL Lac object S4
0954+65 at the alleged redshift z = 0.367 are presented. This source was
detected at gamma frequencies by MAGIC (TeV) and FERMI (GeV) telescopes during
a remarkable outburst that occurred in February 2015, making the determination
of its distance particularly relevant for our understanding of the properties
of the Extragalactic Background Light. Contrary to previous reports on the
redshift, we found that the optical spectrum is featureless at an equivalent
width limit of \sim 0.1 Ang. A critical analysis of the existing observations
indicates that the redshift is still unknown. Based on the new data we estimate
a lower limit to the redshift at z \geq 0.45. |
Carbon ionization states and the cosmic far-UV background with HeII
absorption: We constrain the spectrum of the cosmic ultraviolet background radiation by
fitting the observed abundance ratios carbon ions at $z\sim 2\hbox{--}3$ with
those expected from different models of the background radiation. We use the
recently calculated modulation of the background radiation between 3 and 4 Ryd
due to resonant line absorption by intergalactic HeII, and determine the ratios
of CIII to CIV expected at these redshifts, as functions of metallicity, gas
density and temperature. Our analysis of the observed ratios shows that
'delayed reionization' models, which assume a large fraction of HeII at
$z\sim3$, is not favored by data. Our results suggest that HeII reionization
was inhomogeneous, consistent with the predictions from recent simulations. | Substructure of fuzzy dark matter haloes: We derive the halo mass function (HMF) for fuzzy dark matter (FDM) by solving
the excursion set problem explicitly with a mass-dependent barrier function,
which has not been done before. We find that compared to the naive approach of
the Sheth--Tormen HMF for FDM, our approach has a higher cut off mass and the
cut off mass changes less strongly with redshifts. Using merger trees
constructed with a modified version of the Lacey & Cole formalism that accounts
for suppressed small scale power and the scale-dependent growth of FDM haloes
and the semi-analytic GALACTICUS code, we study the statistics of halo
substructure including the effects from dynamical friction and tidal stripping.
We find that if the dark matter is a mixture of cold dark matter (CDM) and FDM,
there will be a suppression on the halo substructure on small scales which may
be able to solve the Missing Satellites Problem faced by the pure CDM model.
The suppression becomes stronger with increasing FDM fraction or decreasing FDM
mass. Thus, it may be used to constrain the FDM model. |
Observations of Feedback from Radio-Quiet Quasars - II. Kinematics of
Ionized Gas Nebulae: The prevalence and energetics of quasar feedback is a major unresolved
problem in galaxy formation theory. In this paper, we present Gemini Integral
Field Unit observations of ionized gas around eleven luminous, obscured,
radio-quiet quasars at z~0.5 out to ~15 kpc from the quasar; specifically, we
measure the kinematics and morphology of [O III]5007 emission. The round
morphologies of the nebulae and the large line-of-sight velocity widths (with
velocities containing 80% of the emission as high as 1000 km/s combined with
relatively small velocity difference across them (from 90 to 520 km/s) point
toward wide-angle quasi-spherical outflows. We use the observed velocity widths
to estimate a median outflow velocity of 760 km/s, similar to or above the
escape velocities from the host galaxies. The line-of-sight velocity dispersion
declines slightly toward outer parts of the nebulae (by 3% per kpc on average).
The majority of nebulae show blueshifted excesses in their line profiles across
most of their extents, signifying gas outflows. For the median outflow
velocity, we find a kinetic energy flow between 4x10^{44} and 3x10^{45} erg/s
and mass outflow rate between 2000 and 20000 Msun/yr. These values are large
enough for the observed quasar winds to have a significant impact on their host
galaxies. The median rate of converting bolometric luminosity to kinetic energy
of ionized gas clouds is ~2%. We report four new candidates for "super-bubbles"
-- outflows that may have broken out of the denser regions of the host galaxy. | Physical modelling of galaxy clusters detected by Planck: We present a comparison of mass estimates for $54$ galaxy cluster candidates
from the second Planck catalogue (PSZ2) of Sunyaev-Zel'dovich sources. We
compare the mass values obtained with data taken from the Arcminute Microkelvin
Imager (AMI) radio interferometer system and from the Planck satellite. The
former of these uses a Bayesian analysis pipeline that parameterises a cluster
in terms of its physical quantities, and models the dark matter & baryonic
components of a cluster using NFW and GNFW profiles respectively. Our mass
estimates derived from Planck data are obtained from the results of the
Bayesian detection algorithm PowellSnakes (PwS), are based on the methodology
detailed in the PSZ2 paper, and produce two sets of mass estimates; one
estimate is calculated directly from the angular radius $\theta$ - integrated
Comptonisation parameter $Y$ posterior distributions, and the other uses a
`slicing function' to provide information on $\theta$ based on X-ray
measurements and previous Planck mission samples. We find that for $37$ of the
clusters, the AMI mass estimates are lower than both values obtained from
Planck data. However the AMI and slicing function estimates are within one
combined standard deviation of each other for $31$ clusters. We also generate
cluster simulations based on the slicing-function mass estimates, and analyse
them in the same way as we did the real AMI data. We find that inclusion in the
simulations of radio-source confusion & CMB noise and measurable radio-sources
causes AMI mass estimates to be systematically low. |
Nonminimally coupled ultralight axions as cold dark matter: We consider a nonminimally coupled scalar field as a potential cold dark
matter candidate. These models are natural extensions of the ultralight axion
models which are based on minimally coupled scalar fields. Such ultralight
scalar fields are motivated by string theory and, in particular, have been
studied in the context of the axiverse scenario. For a nonminimally coupled
field, the scalar-field energy density behaves as radiation at early times,
which yields a bound on the coupling constant, $\xi \lesssim 10$, from the
primordial nucleosynthesis theory. The first-order perturbations of the
nonminimally coupled field with adiabatic initial conditions cause the
gravitational potential to decay on large scales. A comparison of the
cosmological data with the theoretical matter power spectrum yields the
following constraint on the coupling constant: $\xi \lesssim 0.01$. We also
consider isocurvature modes in our analysis. We argue that a mix of adiabatic
and isocurvature initial conditions for a nonminimally coupled scalar field
might allow one to obtain the usual adiabatic CDM power spectrum. | The CMB Bispectrum: We use a separable mode expansion estimator with WMAP data to estimate the
bispectrum for all the primary families of non-Gaussian models. We review the
late-time mode expansion estimator methodology which can be applied to any
non-separable primordial and CMB bispectrum model, and we demonstrate how the
method can be used to reconstruct the CMB bispectrum from an observational map.
We extend the previous validation of the general estimator using local map
simulations. We apply the estimator to the coadded WMAP 5-year data,
reconstructing the WMAP bispectrum using $l<500$ multipoles and $n=31$
orthonormal 3D eigenmodes. We constrain all popular nearly scale-invariant
models, ensuring that the theoretical bispectrum is well-described by a
convergent mode expansion. Constraints from the local model $ \fnl=54.4\pm
29.4$ and the equilateral model $\fnl=143.5\pm 151.2$ ($\Fnl = 25.1\pm 26.4$)
are consistent with previously published results. (Here, we use a nonlinearity
parameter $\Fnl$ normalised to the local case, to allow more direct comparison
between different models.) Notable new constraints from our method include
those for the constant model $\Fnl = 35.1 \pm 27.4 $, the flattened model $\Fnl
= 35.4\pm 29.2$, and warm inflation $\Fnl = 10.3\pm 27.2$. We investigate
feature models surveying a wide parameter range in both the scale and phase,
and we find no significant evidence of non-Gaussianity in the models surveyed.
We propose a measure $\barFnl$ for the total integrated bispectrum and find
that the measured value is consistent with the null hypothesis that CMB
anisotropies obey Gaussian statistics. We argue that this general bispectrum
survey with the WMAP data represents the best evidence for Gaussianity to date
and we discuss future prospects, notably from the Planck satellite. |
Dust Attenuation in UV-selected Starbursts at High Redshift and their
Local Counterparts: Implications for the Cosmic Star Formation Rate Density: We present a new analysis of the dust obscuration in starburst galaxies at
low and high redshift. This study is motivated by our unique sample of the most
extreme UV-selected starburst galaxies in the nearby universe (z<0.3), found to
be good analogs of high-redshift Lyman Break Galaxies (LBGs) in most of their
physical properties. We find that the dust properties of the Lyman Break
Analogs (LBAs) are consistent with the relation derived previously by Meurer et
al. (M99) that is commonly used to dust-correct star formation rate
measurements at a very wide range of redshifts. We directly compare our results
with high redshift samples (LBGs, BzK, and sub-mm galaxies at z=2-3) having IR
data either from Spitzer or Herschel. The attenuation in typical LBGs at z=2-3
and LBAs is very similar. Because LBAs are much better analogs to LBGs compared
to previous local star-forming samples, including M99, the practice of
dust-correcting the SFRs of high redshift galaxies based on the local
calibration is now placed on a much more solid ground. We illustrate the
importance of this result by showing how the locally calibrated relation
between UV measurements and extinction is used to estimate the integrated,
dust-corrected star formation rate density at z=2-6. | An Estimate of the Primordial Non-Gaussianity Parameter f_NL Using the
Needlet Bispectrum from WMAP: We use the full bispectrum of spherical needlets applied to the WMAP data of
the cosmic microwave background as an estimator for the primordial
non-Gaussianity parameter f_NL. We use needlet scales up to l_max=1000 and the
KQ75 galactic cut and find f_NL=84 +/- 40 corrected for point source bias. We
also introduce a set of consistency tests to validate our results against the
possible influence of foreground residuals or systematic errors. In particular,
fluctuations in the value of f_NL obtained from different frequency channels,
different masks and different multipoles are tested against simulated maps. All
variations in f_NL estimates are found statistically consistent with
simulations. |
Inferring dark matter substructure with astrometric lensing beyond the
power spectrum: Astrometry -- the precise measurement of positions and motions of celestial
objects -- has emerged as a promising avenue for characterizing the dark matter
population in our Galaxy. By leveraging recent advances in simulation-based
inference and neural network architectures, we introduce a novel method to
search for global dark matter-induced gravitational lensing signatures in
astrometric datasets. Our method based on neural likelihood-ratio estimation
shows significantly enhanced sensitivity to a cold dark matter population and
more favorable scaling with measurement noise compared to existing approaches
based on two-point correlation statistics. We demonstrate the real-world
viability of our method by showing it to be robust to non-trivial modeled as
well as unmodeled noise features expected in astrometric measurements. This
establishes machine learning as a powerful tool for characterizing dark matter
using astrometric data. | A comparison between axion-like and power law potentials in cosmological
background: In this paper, we compare the scalar field dynamics in axion-like and power
law potentials for both positive and negative values of the exponents. We find
that, for positive exponents, both the potentials exhibit similar scalar field
dynamics and it can be difficult to distinguish them at least at the background
level. Even though the potentials are oscillatory in nature for positive
exponents scaling solutions can be achieved for larger values of the exponent
for which the dynamics can be different during early times. Because of the
presence of this scaling nature there is a turnaround in the values of the
scalar field equation of state as we increase the values of the exponent in
both the potentials. This indicates the deviation from the oscillatory
behaviour for the larger values of the exponent. For negative values of the
exponent, the dynamics of the scalar field is distinguishable and axion-like
potential can give rise to cosmologically viable tracker solutions unlike the
power law potentials. So, while for positive exponents we may not distinguish
the two potentials for negative exponents the dynamics of the scalar field is
distinguishable. |
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