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Spectral distortions in the cosmic microwave background polarization: We compute the spectral distortions of the Cosmic Microwave Background (CMB)
polarization induced by non-linear effects in the Compton interactions between
CMB photons and cold intergalactic electrons. This signal is of the $y$-type
and is dominated by contributions arising from the reionized era. We stress
that it is not shadowed by the thermal SZ effect which has no equivalent for
polarization. We decompose its angular dependence into $E$- and $B$-modes, and
we calculate the corresponding power spectra, both exactly and using a suitable
Limber approximation that allows a simpler numerical evaluation. We find that
$B$-modes are of the same order of magnitude as $E$-modes. Both spectra are
relatively flat, peaking around $\ell=280$, and their overall amplitude is
directly related to the optical depth to reionization. Moreover, we find this
effect to be one order of magnitude larger than the non-linear kinetic
Sunyaev-Zel'dovich effect in galaxy clusters. Finally, we discuss how to
improve the detectability of our signal by cross-correlating it with other
quantities sourced by the flow of intergalactic electrons. | astro-ph_CO |
Evidence of major dry mergers at M* > 2 x 10^11 Msun from curvature in
early-type galaxy scaling relations?: For early-type galaxies, the correlations between stellar mass and size,
velocity dispersion, surface brightness, color, axis ratio and color-gradient
all indicate that two mass scales, M* = 3 x 10^10 Msun and M* = 2 x 10^11 Msun,
are special. The smaller scale could mark the transition between wet and dry
mergers, or it could be related to the interplay between SN and AGN feedback,
although quantitative measures of this transition may be affected by
morphological contamination. At the more massive scale, mean axis ratios and
color gradients are maximal, and above it, the colors are redder, the sizes
larger and the velocity dispersions smaller than expected based on the scaling
at lower M*. In contrast, the color-sigma relation, and indeed, most scaling
relations with sigma, are not curved: they are well-described by a single power
law, or in some cases, are almost completely flat. When major dry mergers
change masses, sizes, axis ratios and color gradients, they are expected to
change the colors or velocity dispersions much less. Therefore, the fact that
scaling relations at sigma > 150 km/s show no features, whereas the size-M*,
b/a-M*, color-M* and color gradient-M* relations do, suggests that M* = 2 x
10^11 Msun is the scale above which major dry mergers dominate the assembly
histories of early-type galaxies. | astro-ph_CO |
Baryonic effects on weak-lensing two-point statistics and its
cosmological implications: We develop an extension of \textit{the Halo Model} that describes
analytically the corrections to the matter power spectrum due to the physics of
baryons. We extend these corrections to the weak-lensing shear angular power
spectrum. Within each halo, our baryonic model accounts for: 1) a central
galaxy, the major stellar component whose properties are derived from abundance
matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an
adiabatically-contracted dark matter component. This analytic approach allows
us to compare our model to the dark-matter-only case. Our basic assumptions are
tested against the hydrodynamical simulations of Martizzi et. al. (2014), with
which a remarkable agreement is found. Our baryonic model has only one free
parameter, $M_{\rm crit}$, the critical halo mass that marks the transition
between feedback-dominated halos, mostly devoid of gas, and gas rich halos, in
which AGN feedback effects become weaker. We explore the entire cosmological
parameter space, using the angular power spectrum in three redshift bins as the
observable, assuming a Euclid-like survey. We derive the corresponding
constraints on the cosmological parameters, as well as the possible bias
introduced by neglecting the effects of baryonic physics. We find that, up to
$\ell_{max}$=4000, baryonic physics plays very little role in the cosmological
parameters estimation. However, if one goes up to $\ell_{max}$=8000, the
marginalized errors on the cosmological parameters can be significantly
reduced, but neglecting baryonic physics can lead to bias in the recovered
cosmological parameters up to 10$\sigma$. These biases are removed if one takes
into account the main baryonic parameter, $M_{\rm crit}$, which can also be
determined up to 1-2\%, along with the other cosmological parameters. | astro-ph_CO |
Galaxy And Mass Assembly (GAMA): Spectroscopic analysis: The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric
and spectroscopic survey, using the AAOmega spectrograph on the
Anglo-Australian Telescope to obtain spectra for up to ~300000 galaxies over
280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target
galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although
the redshift distribution includes a small number of systems, primarily
quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy
ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signal-to-noise
of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis
pipeline. We present the steps involved in taking the raw two-dimensional
spectroscopic images through to flux-calibrated one-dimensional spectra. The
resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A
at a resolution of R~1300. The final flux calibration is typically accurate to
10-20%, although the reliability is worse at the extreme wavelength ends, and
poorer in the blue than the red. We present details of the measurement of
emission and absorption features in the GAMA spectra. These measurements are
characterised through a variety of quality control analyses detailing the
robustness and reliability of the measurements. We illustrate the quality of
the measurements with a brief exploration of elementary emission line
properties of the galaxies in the GAMA sample. We demonstrate the luminosity
dependence of the Balmer decrement, consistent with previously published
results, and explore further how Balmer decrement varies with galaxy mass and
redshift. We also investigate the mass and redshift dependencies of the
[NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to
discriminate between star forming and nuclear activity in galaxies. | astro-ph_CO |
Some results on the radio-SZ correlation for galaxy cluster radio halos: We present correlation results for the radio halo power in galaxy clusters
with the integrated thermal Sunyaev-Zel'dovich (SZ) effect signal, including
new results obtained at sub-GHz frequencies. The radio data is compiled from
several published works, and the SZ measurements are taken from the Planck ESZ
cluster catalog. The tight correlation between the radio halo power and the SZ
effect demonstrates a clear correspondence between the thermal and non-thermal
electron populations in the intra-cluster medium, as already has been shown in
X-ray based studies. The radio power varies roughly as the square of the global
SZ signal, but when the SZ signal is scaled to within the radio halo radius the
correlation becomes approximately linear, with reduced intrinsic scatter. We do
not find any strong indication of a bi-modal division in the radio halo cluster
population, as has been reported in the literature, which suggests that such
duality could be an artifact of X-ray selection. We compare the SZ signal
dependence of radio halos with simplified predictions from theoretical models,
and discuss some implications and shortcomings of the present work. | astro-ph_CO |
Effective dark matter power spectra in $f(R)$ gravity: Using N-body simulations, we measure the power spectrum of the effective dark
matter density field, which is defined through the modified Poisson equation in
$f(R)$ cosmologies. We find that when compared to the conventional dark matter
power spectrum, the effective power spectrum deviates more significantly from
the $\Lambda$CDM model. For models with $f_{R0}=-10^{-4}$, the deviation can
exceed 150\% while the deviation of the conventional matter power spectrum is
less than 50\%. Even for models with $f_{R0}=-10^{-6}$, for which the
conventional matter power spectrum is very close to the $\Lambda$CDM
prediction, the effective power spectrum shows sizeable deviations. Our results
indicate that traditional analyses based on the dark matter density field may
seriously underestimate the impact of $f(R)$ gravity on galaxy clustering. We
therefore suggest the use of the effective density field in such studies. In
addition, based on our findings, we also discuss several possible methods of
making use of the differences between the conventional and effective dark
matter power spectra in $f(R)$ gravity to discriminate the theory from the
$\Lambda$CDM model. | astro-ph_CO |
Measuring the growth of structure with intensity mapping surveys: Line intensity mapping offers a new avenue for constraining cosmological
parameters in the high redshift Universe. However measurements of the growth of
structure, a sensitive probe of gravity, are affected by a well known
degeneracy with astrophysical parameters, encoded in the mean brightness
temperature of the specific line. In this work we show how to break this
degeneracy, to a level that could allow constraints of the amplitude of
cosmological fluctuations at the percent level, using information in the mildly
non-linear regime of structure formation as described by Lagrangian
Perturbation Theory. We focus on the 21-cm line with forecasts for HIRAX and
the proposed Stage II experiment as illustrations. | astro-ph_CO |
The NGC 404 Nucleus: Star Cluster and Possible Intermediate Mass Black
Hole: We examine the nuclear morphology, kinematics, and stellar populations in
nearby S0 galaxy NGC 404 using a combination of adaptive optics assisted
near-IR integral-field spectroscopy, optical spectroscopy, and HST imaging.
These observations enable study of the NGC 404 nucleus at a level of detail
possible only in the nearest galaxies. The surface brightness profile suggests
the presence of three components, a bulge, a nuclear star cluster, and a
central light excess within the cluster at radii <3 pc. These components have
distinct kinematics with modest rotation seen in the nuclear star cluster and
counter-rotation seen in the central excess. Molecular hydrogen emission traces
a disk with rotation nearly orthogonal to that of the stars. The stellar
populations of the three components are also distinct, with half of the mass of
the nuclear star cluster having ages of ~1 Gyr (perhaps resulting from a galaxy
merger), while the bulge is dominated by much older stars. Dynamical modeling
of the stellar kinematics gives a total nuclear star cluster mass of 1.1x10^7
Msol. Dynamical detection of a possible intermediate mass black hole is
hindered by uncertainties in the central stellar mass profile. Assuming a
constant mass-to-light ratio, the stellar dynamical modeling suggests a black
hole mass of <1x10^5 Msol, while the molecular hydrogen gas kinematics are best
fit by a black hole with mass of 4.5x10^5 Msol. Unresolved and possibly
variable dust emission in the near-infrared and AGN-like molecular hydrogen
emission line ratios do suggest the presence of an accreting black hole in this
nearby LINER galaxy. | astro-ph_CO |
Detecting relic gravitational waves in the CMB: Optimal parameters and
their constraints: The prospect of detecting relic gravitational waves (RGWs), through their
imprint in the cosmic microwave background radiation, provides an excellent
opportunity to study the very early Universe. In simplest viable theoretical
models the RGW background is characterized by two parameters, the
tensor-to-scalar ratio $r$ and the tensor spectral index $n_t$. In this paper,
we analyze the potential joint constraints on these two parameters, $r$ and
$n_t$, using the data from the upcoming cosmic microwave background radiation
experiments. Introducing the notion of the best pivot multipole $\ell_t^*$, we
find that at this pivot multipole the parameters $r$ and $n_t$ are
uncorrelated, and have the smallest variances. We derive the analytical
formulae for the best pivot multipole number $\ell_t^*$, and the variances of
the parameters $r$ and $n_t$. We verify these analytical calculations using
numerical simulation methods, and find agreement to within 20%. The analytical
results provides a simple way to estimate the detection ability for the relic
gravitational waves by the future observations of the cosmic microwave
background radiation. | astro-ph_CO |
Light Primordial Exotic Compact Objects as All Dark Matter: The radiation emitted by horizonless exotic compact objects (ECOs), such as
wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers,
superspinars etc., is expected to be strongly suppressed when compared to the
radiation of black holes. If large primordial curvature fluctuations collapse
into such objects instead of black holes, they do not evaporate or evaporate
much slower than black holes and could thus constitute all of the dark matter
with masses below $M < 10^{-16}M_\odot.$ We reevaluate the relevant
experimental constraints for light ECOs in this mass range and show that very
large new parameter space down to ECO masses $M\sim 10\,{\rm TeV}$ opens up for
light primordial dark matter. A new dedicated experimental program is needed to
test this mass range of primordial dark matter. | astro-ph_CO |
Cosmology and fundamental physics with the ELT-ANDES spectrograph: State-of-the-art 19th century spectroscopy led to the discovery of quantum
mechanics, and 20th century spectroscopy led to the confirmation of quantum
electrodynamics. State-of-the-art 21st century astrophysical spectrographs,
especially ANDES at ESO's ELT, have another opportunity to play a key role in
the search for, and characterization of, the new physics which is known to be
out there, waiting to be discovered. We rely on detailed simulations and
forecast techniques to discuss four important examples of this point: big bang
nucleosynthesis, the evolution of the cosmic microwave background temperature,
tests of the universality of physical laws, and a real-time model-independent
mapping of the expansion history of the universe (also known as the redshift
drift). The last two are among the flagship science drivers for the ELT. We
also highlight what is required for the ESO community to be able to play a
meaningful role in 2030s fundamental cosmology and show that, even if ANDES
only provides null results, such `minimum guaranteed science' will be in the
form of constraints on key cosmological paradigms: these are independent from,
and can be competitive with, those obtained from traditional cosmological
probes. | astro-ph_CO |
The Massive and Distant Clusters of WISE Survey: SZ effect Verification
with the Atacama Compact Array -- Localization and Cluster Analysis: The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides a catalog
of high-redshift ($0.7\lesssim z\lesssim 1.5$) infrared-selected galaxy
clusters. However, the verification of the ionized intracluster medium,
indicative of a collapsed and nearly virialized system, is made challenging by
the high redshifts of the sample members. The main goal of this work is to test
the capabilities of the Atacama Compact Array (ACA; also known as the Morita
Array) Band 3 observations, centered at about 97.5 GHz, to provide robust
validation of cluster detections via the thermal Sunyaev-Zeldovich (SZ) effect.
Using a pilot sample that comprises ten MaDCoWS galaxy clusters, accessible to
ACA and representative of the median sample richness, we infer the masses of
the selected galaxy clusters and respective detection significance by means of
a Bayesian analysis of the interferometric data. Our test of the "Verification
with the ACA - Localization and Cluster Analysis" (VACA LoCA) program
demonstrates that the ACA can robustly confirm the presence of the virialized
intracluster medium in galaxy clusters previously identified in full-sky
surveys. In particular, we obtain a significant detection of the SZ effect for
seven out of the ten VACA LoCA clusters. We note that this result is
independent of the assumed pressure profile. However, the limited angular
dynamic range of the ACA in Band 3 alone, short observational integration
times, and possible contamination from unresolved sources limit the detailed
characterization of the cluster properties and the inference of the cluster
masses within scales appropriate for the robust calibration of mass-richness
scaling relations. | astro-ph_CO |
The SINS survey: modeling the dynamics of z~2 galaxies and the high-z
Tully-Fisher relation: We present the modeling of SINFONI integral field dynamics of 18 star forming
galaxies at z ~ 2 from Halpha line emission. The galaxies are selected from the
larger sample of the SINS survey, based on the prominence of ordered rotational
motions with respect to more complex merger induced dynamics. The quality of
the data allows us to carefully select systems with kinematics dominated by
rotation, and to model the gas dynamics across the whole galaxy using suitable
exponential disk models. We obtain a good correlation between the dynamical
mass and the stellar mass, finding that large gas fractions Mgas~M*) are
required to explain the difference between the two quantities. We use the
derived stellar mass and maximum rotational velocity Vmax from the modeling to
construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2.
The relation obtained shows a slope similar to what is observed at lower
redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2
there is an offset in log(M*) for a given rotational velocity of 0.41+-0.11
with respect to the local Universe. This result is consistent with the
predictions of the latest N-body/hydrodynamical simulations of disk formation
and evolution, which invoke gas accretion onto the forming disk in filaments
and cooling flows. This scenario is in agreement with other dynamical evidence
from SINS, where gas accretion from the halo is required to reproduce the
observed properties of a large fraction of the z ~ 2 galaxies. | astro-ph_CO |
On the stability criteria for equatorial circular orbits in Galactic
Dynamics: I.Newtonian Thin Disks: We make a revision of the stability criteria for equatorial circular orbits,
obtained from the epicyclic approximation, which is widely used in Newtonian
models for axisymmetric galaxies. We find that, for the case of thin disk
models, the criteria of vertical stability must be reformulated, due to the
discontinuity in the gravitational field. We show that, for a model
characterized by a surface mass density $\Sigma$, the necessary and sufficient
condition to have vertically stable orbits is that $\Sigma>0$. On the other
hand, the criteria for radial stability is the same as in thick diks, i.e. that
the epicyclic frequency is positive. | astro-ph_CO |
Testing Gravity Using Large-Scale Redshift-Space Distortions: We use Luminous Red Galaxies from the Sloan Digital Sky Survey II to test the
cosmological structure growth in two alternatives to the standard LCDM+GR
cosmological model. We compare observed three-dimensional clustering in SDSS
DR7 with theoretical predictions for the standard vanilla LCDM+GR model,
Unified Dark Matter cosmologies and the normal branch DGP. In computing the
expected correlations in UDM cosmologies, we derive a parameterized formula for
the growth factor in these models. For our analysis we apply the methodology
tested in Raccanelli et al. 2010 and use the measurements of Samushia et al.
2011, that account for survey geometry, non-linear and wide-angle effects and
the distribution of pair orientation. We show that the estimate of the growth
rate is potentially degenerate with wide-angle effects, meaning that extremely
accurate measurements of the growth rate on large scales will need to take such
effects into account. We use measurements of the zeroth and second order
moments of the correlation function from SDSS DR7 data and the Large Suite of
Dark Matter Simulations, and perform a likelihood analysis to constrain the
parameters of the models. Using information on the clustering up to r_max = 120
Mpc/h, and after marginalizing over the bias, we find, for UDM models, a speed
of sound < 6.1e-4, and, for the nDGP model, a cross-over scale r_c > 340 Mpc,
at 95% confidence level. | astro-ph_CO |
Intrinsic colors and ages of extremely red elliptical galaxies at high
redshift: In order to know the formation epoch of the oldest elliptical galaxies as a
function of mass and observed redshift, a statistical analysis for 333
extremely red objects (EROs) classified as old galaxies (OGs) at 0.8<z<2.3 is
carried out. Once we get M_V and (B-V) at rest for each galaxy, we calculate
the average variation of this intrinsic color with redshift and derive the
average age through a synthesis model (the code for the calculation of the age
has been made publicly available). The average gradient of the (B-V) color at
rest of EROs/OGs is 0.07-0.10 Gyr^{-1} for a fixed luminosity. The stars in
these extremely red elliptical galaxies were formed when the Universe was ~2
Gyr old on average. We have not found a significant enough dependence on the
observed redshift and stellar mass: dt_{formation}/dt_{observed}=-0.46+/-0.32,
dt_{formation}/(d log_10 M_*)=-0.81+/-0.98 Gyr. This fits a scenario in which
the stellar formation of the objects that we denominate as EROs-OGs is more
intense at higher redshifts, at which the stellar populations of the most
massive galaxies form earlier than or at the same time as less massive
galaxies. | astro-ph_CO |
Dwarf elliptical galaxies as ancient tidal dwarf galaxies: The formation of tidal dwarf galaxies (TDGs) is triggered by the encounters
of already existing galaxies. Their existence is predicted from numerical
calculations of encountering galaxies and is also well documented with
observations. The numerical calculations on the formation of TDGs furthermore
predict that TDGs cannot contain significant amounts of non-baryonic dark
matter. In this paper, the first exhaustive sample of TDG-candidates from
observations and numerical calculations is gathered from the literature. These
stellar systems are gas-rich at the present, but they will probably evolve into
gas-poor objects that are indistinguishable from old dwarf elliptical galaxies
(dEs) based on their masses and radii. Indeed, known gas-poor TDGs appear as
normal dEs. According to the currently prevailing cosmological paradigm, there
should also be a population of primordial galaxies that formed within haloes of
dark matter in the same mass range. Due to their different composition and
origin, it would be expected that objects belonging to that population would
have a different structure than TDGs and would thus be distinguishable from
them, but such a population cannot be identified from their masses and radii.
Moreover, long-lived TDGs could indeed be numerous enough to account for all
dEs in the Universe. Downsizing, i.e. that less massive galaxies tend to be
younger, would then be a natural consequence of the nature of the dEs. If these
claims can be kept up in the light of future observations, the presently
prevailing understanding of galaxy formation would need to be revised. | astro-ph_CO |
Cosmic Microwave Background temperature and polarization anisotropies
from the large-N limit of global defects: We determine the full C_l spectra and correlation functions of the
temperature and polarization anisotropies in the CMB, generated by a source
modeled by the large N limit of spontaneously broken global O(N)-theories. We
point out a problem in the standard approach of treating the radiation-matter
transition by interpolating the eigenvectors of the unequal-time correlators of
the source energy-momentum tensor. This affects the CMB predictions from all
type of cosmic defects. We propose a method to overcome this difficulty, and
find that in the large-N global model that we study, differences in the final
CMB power spectra amplitudes reach up to 25%, when compared to implementations
of the eigenvector interpolation technique. We discuss as well how to optimally
search for the contribution in the CMB from active sources such as cosmic
defects, in experiments like Planck, COrE and PRISM. | astro-ph_CO |
Using Elliptical Galaxy Kinematics to Compare of the Strength of Gravity
in Cosmological Regions of Differing Gravitational Potential -- A First Look: Various models of modified gravity invoke ``screening'' mechanisms that are
sensitive to the value of the local gravitational potential. This could have
observable consequences for galaxies. These consequences might be seen by
comparing two proxies for galaxy mass -- their luminosity and their internal
kinematics -- as a function of local galaxy density. Motivated by this
prospect, we have compared the observed properties of luminous red galaxies
(LRGs) inside and outside of voids in the cosmic large scale structure. We used
archival measurements of line widths, luminosities, redshifts, colors, and
positions of galaxies in conjunction with recent void catalogs to construct
comparison LRG samples inside and outside of voids. We fitted these two samples
to the well-established fundamental plane of elliptical galaxies to constrain
any differences between the inferred value of the Newtonian gravitational
constant G for the two samples. We obtained a null result, with an upper limit
on any fractional difference in G within and outside of cosmological voids to
be $\alpha =\delta$$ G/G \sim$ 40\%. This upper bound is dominated by the
small-number statistics of our N $\sim $ 100 within-void LRG sample. With the
caveat that environmental effects could influence various parameters such as
star formation, we estimate that a 1\% statistical limit on $\alpha$ could be
attained with data from 10${^5}$ elliptical galaxies within voids. This is
within the reach of future photometric and spectroscopic surveys, both of which
are required to pursue this method. | astro-ph_CO |
The effects of primordial non-Gaussianity on giant-arc statistics: For over a decade, it has been debated whether the concordance LCDM model is
consistent with the observed abundance of giant arcs in clusters. While
previous theoretical studies have focused on properties of the lens and source
populations, as well as cosmological effects such as dark energy, the impact of
initial conditions on the giant-arc abundance is relatively unexplored. Here,
we quantify the impact of non-Gaussian initial conditions with the local
bispectrum shape on the predicted frequency of giant arcs. Using a
path-integral formulation of the excursion set formalism, we extend a
semi-analytic model for calculating halo concentrations to the case of
primordial non-Gaussianity, which may be useful for applications outside of
this work. We find that massive halos tend to collapse earlier in models with
positive f_NL, relative to the Gaussian case, leading to enhanced concentration
parameters. The converse is true for f_NL < 0. In addition to these effects,
which change the lensing cross sections, non-Gaussianity also modifies the
abundance of supercritical clusters available for lensing. These combined
effects work together to either enhance (f_NL > 0) or suppress (f_NL < 0) the
probability of giant-arc formation. Using the best value and 95% confidence
levels currently available from the Wilkinson Microwave Anisotropy Probe, we
find that the giant-arc optical depth for sources at z_s~2 is enhanced by ~20%
and ~45% for f_NL = 32 and 74 respectively. In contrast, we calculate a
suppression of ~5% for f_NL = -10. These differences translate to similar
relative changes in the predicted all-sky number of giant arcs. | astro-ph_CO |
The role of Pop III stars and early black holes in the 21cm signal from
Cosmic Dawn: Modeling the 21cm global signal from the Cosmic Dawn is challenging due to
the many poorly constrained physical processes that come into play. We address
this problem using the semi-analytical code "Cosmic Archaeology Tool" (CAT).
CAT follows the evolution of dark matter halos tracking their merger history
and provides an ab initio description of their baryonic evolution, starting
from the formation of the first (Pop III) stars and black holes (BHs) in
mini-halos at z > 20. The model is anchored to observations of galaxies and AGN
at z < 6 and predicts a reionization history consistent with constraints. In
this work we compute the evolution of the mean global 21cm signal between
$4\leq z \leq 40$ based on the rate of formation and emission properties of
stars and accreting black holes. We obtain an absorption profile with a maximum
depth $\delta {\rm T_b} = -95$ mK at $z \sim 26.5$ (54 MHz). This feature is
quickly suppressed turning into an emission signal at $z = 20$ due to the
contribution of accreting BHs that efficiently heat the IGM at $z < 27$. The
high-$z$ absorption feature is caused by the early coupling between the spin
and kinetic temperature of the IGM induced by Pop III star formation episodes
in mini-halos. Once we account for an additional radio background from early
BHs, we are able to reproduce the timing and the depth of the EDGES signal only
if we consider a smaller X-ray background from accreting BHs, but not the
shape. | astro-ph_CO |
Causality, initial conditions, and inflationary magnetogenesis: The post-inflationary evolution of inflation-produced magnetic fields,
conventional or not, can change dramatically when two fundamental issues are
accounted for. The first is causality, which demands that local physical
processes can never affect superhorizon perturbations. The second is the nature
of the transition from inflation to reheating and then to the radiation era,
which determine the initial conditions at the start of these epochs. Causality
implies that inflationary magnetic fields dot not freeze into the matter until
they have re-entered the causal horizon. The nature of the cosmological
transitions and the associated initial conditions, on the other hand, determine
the large-scale magnetic evolution after inflation. Put together, the two can
slow down the adiabatic magnetic decay on superhorizon scales throughout the
universe's post-inflationary evolution and thus lead to considerably stronger
residual magnetic fields. This is "good news" for both the conventional and the
non-conventional scenarios of cosmic magnetogenesis. Mechanisms operating
outside standard electromagnetism, in particular, do not need to enhance their
fields too much during inflation, in order to produce seeds that can feed the
galactic dynamo today. In fact, even conventionally produced inflationary
magnetic fields might be able to sustain the dynamo. | astro-ph_CO |
Testing Dvali-Gabadadze-Porrati Gravity with Planck: Recently, the Planck collaboration has released the first cosmological papers
providing the highest resolution, full sky, maps of the cosmic microwave
background (CMB) temperature anisotropies. In this paper we study a
phenomenological model which interpolates between the pure $\Lambda$CDM model
and the Dvali-Gabadadze-Porrati (DGP) braneworld model with an additional
parameter $\alpha$. Firstly, we calculate the "distance information" of Planck
data which includes the "shift parameter" $R$, the "acoustic scale" $l_A$, and
the photon decoupling epoch $z_\ast$ in different cosmological models and find
that this information is almost independent on the input models we use. Then,
we compare the constraints on the free parameter $\alpha$ of the DGP model from
the "distance information" of Planck and WMAP data and find that the Planck
data with high precision do not improve the constraint on $\alpha$, but give
the higher median value and the better limit on the current matter density
fraction $\Omega_m$. Then, combining the "distance information" of Planck
measurement, baryon acoustic oscillations (BAO), type Ia supernovae (SNIa) and
the prior on the current Hubble constant (HST), we obtain the tight constraint
on the parameter $\alpha < 0.20$ at $95\%$ confidence level, which implies that
the flat DGP model has been ruled out by the current cosmological data.
Finally, we allow the additional parameter $\alpha < 0$ in our calculations and
interestingly obtain $\alpha=-0.29\pm0.20$ ($68\%$ C.L.), which means the
current data slightly favor the effective equation of state $w_{\rm eff}<-1$.
More importantly, the tension between constraints on $H_0$ from different
observational data has been eased. | astro-ph_CO |
Confronting Models of Dwarf Galaxy Quenching with Observations of the
Local Group: A number of mechanisms have been proposed to connect star-forming dwarf
irregular galaxies with the formation of non-star-forming dwarf spheroidal
galaxies, but distinguishing between these mechanisms has been difficult. We
use the Via Lactea dark matter only cosmological simulations to test two
well-motivated simple hypotheses---transformation of irregulars into dwarf
spheroidal galaxies by tidal stirring and ram pressure stripping following a
close passage to the host galaxy, and transformation via mergers between
dwarfs---and predict the radial distribution and inferred formation times of
the resulting dwarf spheroidal galaxies. We compare this to the observed
distribution in the Local Group and show that 1) the observed dSph distribution
far from the Galaxy or M31 can be matched by the VL halos that have passed near
the host galaxy at least once, though significant halo-to-halo scatter exists,
2) models that require two or more pericenter passages for dSph-formation
cannot account for the dSphs beyond 500 kpc such as Cetus and Tucana, and 3)
mergers predict a flat radial distribution of dSphs and cannot account for the
high dSph fraction near the Galaxy, but are not ruled out at large distances.
The models also suggest that for dSphs found today beyond 500 kpc, mergers tend
to occur significantly earlier than dwarf--host encounters, thus leading to a
potentially observable difference in stellar populations. We argue that tidal
interactions are sufficient to reproduce the observed distribution of dSphs if
and only if a single pericenter passage is sufficient to form a dSph. | astro-ph_CO |
The Copernicus Complexio: a high-resolution view of the small-scale
Universe: We introduce Copernicus Complexio (COCO), a high-resolution cosmological
N-body simulation of structure formation in the $\Lambda{\rm CDM}{}$ model.
COCO follows an approximately spherical region of radius $\sim 17.4h^{-1}\,{\rm
Mpc}$ embedded in a much larger periodic cube that is followed at lower
resolution. The high resolution volume has a particle mass of
$1.135\times10^5h^{-1}{\rm M}_{\odot}$ (60 times higher than the Millennium-II
simulation). COCO gives the dark matter halo mass function over eight orders of
magnitude in halo mass; it forms $\sim 60$ haloes of galactic size, each
resolved with about 10 million particles. We confirm the power-law character of
the subhalo mass function, $\bar{N}(>\mu)\propto\mu^{-s}$, down to a reduced
subhalo mass $M_{sub}/M_{200}\equiv\mu=10^{-6}$, with a best-fit power-law
index, $s=0.94$, for hosts of mass $\langle M_{200}\rangle=10^{12}h^{-1}{\rm
M}_{\odot}$. The concentration-mass relation of COCO haloes deviates from a
single power law for masses $M_{200}<\textrm{a few}\times 10^{8}h^{-1}{\rm
M}_{\odot}$, where it flattens, in agreement with results by Sanchez-Conde et
al. The host mass invariance of the reduced maximum circular velocity function
of subhaloes, $\nu\equiv V_{max}/V_{200}$, hinted at in previous simulations,
is clearly demonstrated over five orders of magnitude in host mass. Similarly,
we find that the average, normalised radial distribution of subhaloes is
approximately universal (i.e. independent of subhalo mass), as previously
suggested by the Aquarius simulations of individual haloes. Finally, we find
that at fixed physical subhalo size, subhaloes in lower mass hosts typically
have lower central densities than those in higher mass hosts. | astro-ph_CO |
KiDS-450: Cosmological Constraints from Weak Lensing Peak Statistics -
II: Inference from Shear Peaks using N-body Simulations: We study the statistics of peaks in a weak lensing reconstructed mass map of
the first 450 square degrees of the Kilo Degree Survey. The map is computed
with aperture masses directly applied to the shear field with an NFW-like
compensated filter. We compare the peak statistics in the observations with
that of simulations for various cosmologies to constrain the cosmological
parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$, which probes the
($\Omega_{\rm m}, \sigma_8$) plane perpendicularly to its main degeneracy. We
estimate $S_8=0.750\pm0.059$, using peaks in the signal-to-noise range $0 \leq
{\rm S/N} \leq 4$, and accounting for various systematics, such as
multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic
alignment, and shear-position coupling. These constraints are $\sim25\%$
tighter than the constraints from the high significance peaks alone ($3 \leq
{\rm S/N} \leq 4$) which typically trace single-massive halos. This
demonstrates the gain of information from low-S/N peaks. However we find that
including ${\rm S/N} < 0$ peaks does not add further information. Our results
are in good agreement with the tomographic shear two-point correlation function
measurement in KiDS-450. Combining shear peaks with non-tomographic
measurements of the shear two-point correlation functions yields a $\sim20\%$
improvement in the uncertainty on $S_8$ compared to the shear two-point
correlation functions alone, highlighting the great potential of peaks as a
cosmological probe. | astro-ph_CO |
Curvature Perturbations Protected Against One Loop: We examine one-loop corrections from small-scale curvature perturbations to
the superhorizon-limit ones in single-field inflation models, which have
recently caused controversy. We consider the case where the Universe
experiences transitions of slow-roll (SR) $\to$ intermediate period $\to$ SR.
The intermediate period can be an ultra-slow-roll period or a resonant
amplification period, either of which enhances small-scale curvature
perturbations. We assume that the superhorizon curvature perturbations are
conserved at least during each of the SR periods. Within this framework, we
show that the superhorizon curvature perturbations during the first and the
second SR periods coincide at one-loop level in the slow-roll limit. | astro-ph_CO |
The extraordinary mid-infrared spectral properties of FeLoBAL Quasars: We present mid-infrared spectra of six FeLoBAL QSOs at 1<z<1.8, taken with
the Spitzer space telescope. The spectra span a range of shapes, from hot dust
dominated AGN with silicate emission at 9.7 microns, to moderately obscured
starbursts with strong Polycyclic Aromatic Hydrocarbon (PAH) emission. The
spectrum of one object, SDSS 1214-0001, shows the most prominent PAHs yet seen
in any QSO at any redshift, implying that the starburst dominates the mid-IR
emission with an associated star formation rate of order 2700 solar masses per
year. With the caveats that our sample is small and not robustly selected, we
combine our mid-IR spectral diagnostics with previous observations to propose
that FeLoBAL QSOs are at least largely comprised of systems in which (a) a
merger driven starburst is ending, (b) a luminous AGN is in the last stages of
burning through its surrounding dust, and (c) which we may be viewing over a
restricted line of sight range. | astro-ph_CO |
Cosmology at the boundary of de Sitter using the dS/QFT correspondence: Using the dS/QFT correspondence in the context of inflation allows for the
study of interesting, otherwise inaccessible physics. In particular, by
studying inflation via its dual field theory at the boundary of the de Sitter
space, it may be possible to study a regime of strongly coupled gravity at
early times. The purpose of this work is to completely express cosmological
observables in terms of the free parameters of a dual field theory and to
compare them with CMB data. In this way, constraints on the observational
parameters constrains the validity of the strongly coupled inflation picture by
imposing limits on the parameters of the field theory. The fit with data
defines a limit for the consistency and validity of the approach taken and
shows that, within this limit, the model is almost unconstrained, but quite
predictive, producing power spectra of density perturbations extremely near
scale invariance. | astro-ph_CO |
Inhomogeneities in the universe: Standard models of galaxy formation predict that matter distribution is
statistically homogeneous and isotropic and characterized by (i) spatial
homogeneity for r<10 Mpc/h, (ii) small-amplitude structures of relatively
limited size (i.e., r<100) Mpc/h and (iii) anti-correlations for r > r_c ~ 150
Mpc/h (i.e., no structures of size larger than r_c). Whether or not the
observed galaxy distribution is interpreted to be compatible with these
predictions depend on the a-priori assumptions encoded in the statistical
methods employed to characterize the data and on the a-posteriori hypotheses
made to interpret the results. We present strategies to test the most common
assumptions and we find evidences that, in the available samples, galaxy
distribution is spatially inhomogeneous for r<100 Mpc/h but statistically
homogeneous and isotropic. We conclude that the observed inhomogeneities pose a
fundamental challenge to the standard picture of cosmology but they also
represent an important opportunity which may open new directions for many
cosmological puzzles. | astro-ph_CO |
A survey of molecular gas in luminous sub-millimetre galaxies: We present the results from a survey for 12CO emission in 40 luminous
sub-millimetre galaxies (SMGs), with 850um fluxes of S850 = 4 - 20 mJy,
conducted with the Plateau de Bure Interferometer. We detect 12CO emission in
32 SMGs at z~1.2 - 4.1, including 16 SMGs not previously published. Using
multiple 12CO line (J_up =2 - 7) observations, we derive a median spectral line
energy distribution for luminous SMGs and use this to estimate a mean gas mass
of (5.3 +/- 1.0) \times 10^10 Msun. We report the discovery of a fundamental
relationship between 12CO FWHM and 12CO line luminosity in high-redshift
starbursts, which we interpret as a natural consequence of the baryon-dominated
dynamics within the regions probed by our observations. We use far-infrared
luminosities to assess the star-formation efficiency in our SMGs, finding a
steepening of the L'CO-LFIR relation as a function of increasing 12CO J_up
transition. We derive dynamical masses and molecular gas masses, and use these
to determine the redshift evolution of the gas content of SMGs, finding that
they do not appear to be significantly more gas rich than less vigorously
star-forming galaxies at high redshifts. Finally, we collate X-ray
observations, and study the interdependence of gas and dynamical properties of
SMGs with their AGN activity and supermassive black hole masses (MBH), finding
that SMGs lie significantly below the local M_BH-sigma relation. We conclude
that SMGs represent a class of massive, gas-rich ultraluminous galaxies with
somewhat heterogeneous properties, ranging from starbursting disc-like systems
with L~10^12 L_sun, to the most highly star-forming mergers in the Universe. | astro-ph_CO |
Massive and Newly Dead: Discovery of a Significant Population of
Galaxies with High Velocity Dispersions and Strong Balmer Lines at z~1.5 from
Deep Keck Spectra and HST/WFC3 Imaging: We present deep Keck/LRIS spectroscopy and HST/WFC3 imaging in the rest-frame
optical for a sample of eight galaxies at z~1.5 with high
photometrically-determined stellar masses. The data are combined with
VLT/XShooter spectra of five galaxies from van de Sande et al. (2011, 2012 to
be submitted). We find that these thirteen galaxies have high velocity
dispersions, with a median of sigma=301 km s^{-1}. This high value is
consistent with their relatively high stellar masses and compact sizes. We
study their stellar populations using the strength of Balmer absorption lines,
which are not sensitive to dust absorption. We find a large range in Balmer
absorption strength, with many galaxies showing very strong lines indicating
young ages. The median Hdelta_A equivalent width, determined directly or
inferred from the H10 line, is 5.4 Angstroms, indicating a luminosity-weighted
age of ~1 Gyr. Although this value may be biased towards higher values because
of selection effects,high-dispersion galaxies with such young ages are
extremely rare in the local Universe. Interestingly we do not find a simple
correlation with rest-frame U-V color: some of the reddest galaxies have very
strong Balmer absorption lines. These results demonstrate that many
high-dispersion galaxies at z~1.5 were quenched recently. This implies that
there must be a population of star-forming progenitors at z~2 with high
velocity dispersions or linewidths, which are notoriously absent from CO/Halpha
selected surveys. | astro-ph_CO |
Multiphase Signatures of AGN Feedback in Abell 2597: We present new Chandra X-ray observations of the brightest cluster galaxy
(BCG) in the cool core cluster Abell 2597. The data reveal an extensive
kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas
exhibiting strong spatial correlation with archival VLA radio data. In addition
to several possible scenarios, multiwavelength evidence may suggest that the
filament is associated with multiphase (10^3 - 10^7 K) gas that has been
entrained and dredged-up by the propagating radio source. Stemming from a full
spectral analysis, we also present profiles and 2D spectral maps of modeled
X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an
arc of hot gas which in projection borders the inner edge of a large X-ray
cavity. Although limited by strong caveats, we suggest that the hot arc may be
(a) due to a compressed rim of cold gas pushed outward by the radio bubble or
(b) morphologically and energetically consistent with cavity-driven active
galactic nucleus (AGN) heating models invoked to quench cooling flows, in which
the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas
rushes to refill its wake. If confirmed, this would be the first observational
evidence for this model. | astro-ph_CO |
Virial halo mass function in the ${\it Planck}$ cosmology: We study halo mass functions with high-resolution $N$-body simulations under
a $\Lambda$CDM cosmology. Our simulations adopt the cosmological model that is
consistent with recent measurements of the cosmic microwave backgrounds with
the ${\it Planck}$ satellite. We calibrate the halo mass functions for
$10^{8.5} \lower.5ex\hbox{$\; \buildrel < \over \sim \;$} M_\mathrm{vir} /
(h^{-1}M_\odot) \lower.5ex\hbox{$\; \buildrel < \over \sim \;$} 10^{15.0 - 0.45
\, z}$, where $M_\mathrm{vir}$ is the virial spherical overdensity mass and
redshift $z$ ranges from $0$ to $7$. The halo mass function in our simulations
can be fitted by a four-parameter model over a wide range of halo masses and
redshifts, while we require some redshift evolution of the fitting parameters.
Our new fitting formula of the mass function has a 5\%-level precision except
for the highest masses at $z\le 7$. Our model predicts that the analytic
prediction in Sheth $\&$ Tormen would overestimate the halo abundance at $z=6$
with $M_\mathrm{vir} = 10^{8.5-10}\, h^{-1}M_\odot$ by $20-30\%$. Our
calibrated halo mass function provides a baseline model to constrain warm dark
matter (WDM) by high-$z$ galaxy number counts. We compare a cumulative
luminosity function of galaxies at $z=6$ with the total halo abundance based on
our model and a recently proposed WDM correction. We find that WDM with its
mass lighter than $2.71\, \mathrm{keV}$ is incompatible with the observed
galaxy number density at a $2\sigma$ confidence level. | astro-ph_CO |
A New Probe of the High-z BAO scale: BAO tomography With CMB $\times$
LIM-Nulling Convergence: Standard rulers such as the baryon acoustic oscillation (BAO) scale serve as
workhorses for precision tests of cosmology, enabling distance measurements
that probe the geometry and expansion history of our Universe. Aside from BAO
measurements from the cosmic microwave background (CMB), most standard ruler
techniques operate at relatively low redshifts and depend on biased tracers of
the matter density field. In a companion paper, we explored the scientific
reach of nulling estimators, where CMB lensing convergence maps are
cross-correlated with linear combinations of similar maps from line intensity
mapping (LIM) to precisely null out the low-redshift contributions to CMB
lensing. We showed that nulling estimators can be used to constrain the high
redshift matter power spectrum and showed that this spectrum exhibits
discernible BAO features. Here we propose using these features as a standard
ruler at high redshifts that does not rely on biased tracers. Forecasting such
a measurement at $z \sim 5$, we find that next-generation instruments will be
able to constrain the BAO scale to percent-level precision at $7.2 \%$, while
our futuristic observing scenario can constrain the BAO scale to $4\%$
precision. This constitutes a fundamentally new kind of BAO measurement during
early epochs in our cosmic history. | astro-ph_CO |
The Trispectrum in the Effective Theory of Inflation with Galilean
symmetry: We calculate the trispectrum of curvature perturbations for a model of
inflation endowed with Galilean symmetry at the level of the fluctuations
around an FRW background. Such a model has been shown to posses desirable
properties such as unitarity (up to a certain scale) and non-renormalization of
the leading operators, all of which point towards the reasonable assumption
that a full theory whose fluctuations reproduce the one here might exist as
well as be stable and predictive. The cubic curvature fluctuations of this
model produce quite distinct signatures at the level of the bispectrum. Our
analysis shows how this holds true at higher order in perturbations. We provide
a detailed study of the trispectrum shape-functions in different configurations
and a comparison with existent literature. Most notably, predictions markedly
differ from their P(X,\phi) counterpart in the so called equilateral
trispectrum configuration. The zoo of inflationary models characterized by
somewhat distinctive predictions for higher order correlators is already quite
populated; what makes this model more compelling resides in the above mentioned
stability properties. | astro-ph_CO |
Bridging the gap: spectral distortions meet gravitational waves: Gravitational waves (GWs) have the potential to probe the entirety of
cosmological history due to their nearly perfect decoupling from the thermal
bath and any intervening matter after emission. In recent years, GW cosmology
has evolved from merely being an exciting prospect to an actively pursued
avenue for discovery, and the early results are very promising. As we highlight
in this paper, spectral distortions (SDs) of the cosmic microwave background
(CMB) uniquely probe GWs over six decades in frequency, bridging the gap
between astrophysical high- and cosmological low-frequency measurements. This
means SDs will not only complement other GW observations, but will be the sole
probe of physical processes at certain scales. To illustrate this point, we
explore the constraining power of various proposed SD missions on a number of
phenomenological scenarios: early-universe phase transitions (PTs), GW
production via the dynamics of SU(2) and ultra-light U(1) axions, and cosmic
string (CS) network collapse. We highlight how some regions of parameter space
were already excluded with data from COBE/FIRAS, taken over two decades ago. To
facilitate the implementation of SD constraints in arbitrary models we provide
GW2SD. This tool calculates the window function, which easily maps a GW
spectrum to a SD amplitude, thus opening another portal for GW cosmology with
SDs, with wide reaching implications for particle physics phenomenology. | astro-ph_CO |
Accurate AGN black hole masses and the scatter in the M_{bh} - L_{bulge}
relationship: A new empirical formulae is given for estimating the masses of black holes in
AGNs from the H beta velocity dispersion and the continuum luminosity at 5100
Angstroms. It is calibrated to reverberation-mapping and stellar-dynamical
estimates of black hole masses. The resulting mass estimates are as accurate as
reverberation-mapping and stellar-dynamical estimates. The new mass estimates
show that there is very little scatter in the M_{bh} - L_{bulge} relationship
for high-luminosity galaxies, and that the scatter increases substantially in
lower-mass galaxies. | astro-ph_CO |
H0LiCOW I. $H_0$ Lenses in COSMOGRAIL's Wellspring: Program Overview: Strong gravitational lens systems with time delays between the multiple
images allow measurements of time-delay distances, which are primarily
sensitive to the Hubble constant that is key to probing dark energy, neutrino
physics, and the spatial curvature of the Universe, as well as discovering new
physics. We present H0LiCOW ($H_0$ Lenses in COSMOGRAIL's Wellspring), a
program that aims to measure $H_0$ with $<3.5\%$ uncertainty from five lens
systems (B1608+656, RXJ1131-1231, HE0435-1223, WFI2033-4723 and HE1104-1805).
We have been acquiring (1) time delays through COSMOGRAIL and Very Large Array
monitoring, (2) high-resolution Hubble Space Telescope imaging for the lens
mass modeling, (3) wide-field imaging and spectroscopy to characterize the lens
environment, and (4) moderate-resolution spectroscopy to obtain the stellar
velocity dispersion of the lenses for mass modeling. In cosmological models
with one-parameter extension to flat $\Lambda$CDM, we expect to measure $H_0$
to $<3.5\%$ in most models, spatial curvature $\Omega_{\rm k}$ to 0.004, $w$ to
0.14, and the effective number of neutrino species to 0.2 (1$\sigma$
uncertainties) when combined with current CMB experiments. These are,
respectively, a factor of $\sim15$, $\sim2$, and $\sim1.5$ tighter than CMB
alone. Our data set will further enable us to study the stellar initial mass
function of the lens galaxies, and the co-evolution of supermassive black holes
and their host galaxies. This program will provide a foundation for extracting
cosmological distances from the hundreds of time-delay lenses that are expected
to be discovered in current and future surveys. | astro-ph_CO |
The effect of massive neutrinos on the BAO peak: We study the impact of neutrino masses on the shape and height of the BAO
peak of the matter correlation function, both in real and redshift space. In
order to describe the nonlinear evolution of the BAO peak we run N-body
simulations and compare them with simple analytic formulae. We show that the
evolution with redshift of the correlation function and its dependence on the
neutrino masses is well reproduced in a simplified version of the Zel'dovich
approximation, in which the mode-coupling contribution to the power spectrum is
neglected. While in linear theory the BAO peak decreases for increasing
neutrino masses, the effect of nonlinear structure formation goes in the
opposite direction, since the peak broadening by large scale flows is less
effective. As a result of this combined effect, the peak decreases by $\sim 0.6
\%$ for $ \sum m_\nu = 0.15$ eV and increases by $\sim1.2 \%$ for $ \sum m_\nu
= 0.3$ eV, with respect to a massless neutrino cosmology with equal value of
the other cosmological parameters. We extend our analysis to redshift space and
to halos, and confirm the agreement between simulations and the analytic
formulae. We argue that all analytical approaches having the Zel'dovich
propagator in their lowest order approximation should give comparable
performances, irrespectively to their formulation in Lagrangian or in Eulerian
space. | astro-ph_CO |
Intrinsic brightness of SDSS objects is similar at all redshifts in de
Sitter space: The redshift-luminosity distributions for well-defined galaxies and quasars
in the Sloan Digital Sky Survey (SDSS) are compared for the two
redshift-distance relations of a Hubble redshift and a de Sitter redshift.
Assuming a Hubble redshift, SDSS data can be interpreted as luminosity
evolution following the Big Bang. In contrast, given a de Sitter redshift, the
intrinsic brightness of objects at all redshifts is roughly the same. In a de
Sitter universe, 95 per cent of SDSS galaxies and quasars fall into a magnitude
range of only 2.8, and 99.7 per cent are within 5.4 mag. The comparable Hubble
luminosity ranges are much larger: 95 per cent within 6.9, and 99.7 per cent
within 11.5 mag. De Sitter space is now widely discussed, but the de Sitter
redshift is hardly mentioned. | astro-ph_CO |
Observational constraints on the tilted spatially-flat and the untilted
nonflat $φ$CDM dynamical dark energy inflation models: We constrain spatially-flat tilted and nonflat untilted scalar field ($\phi$)
dynamical dark energy inflation ($\phi$CDM) models by using Planck 2015 cosmic
microwave background (CMB) anisotropy measurements and recent baryonic acoustic
oscillation distance observations, Type Ia supernovae apparent magnitude data,
Hubble parameter measurements, and growth rate data. We assume an inverse
power-law scalar field potential energy density $V(\phi)=V_0 \phi^{-\alpha}$.
We find that the combination of the CMB data with the four non-CMB data sets
significantly improves parameter constraints and strengthens the evidence for
nonflatness in the nonflat untilted $\phi$CDM case from $1.8\sigma$ for the CMB
measurements only to more than $3.1\sigma$ for the combined data. In the
nonflat untilted $\phi$CDM model current observations favor a spatially closed
universe with spatial curvature contributing about two-thirds of a percent of
the present cosmological energy budget. The flat tilted $\phi$CDM model is a
0.4$\sigma$ better fit to the data than is the standard flat tilted
$\Lambda$CDM model: current data allow for the possibility that dark energy is
dynamical. The nonflat tilted $\phi$CDM model is in better accord with the Dark
Energy Survey bounds on the rms amplitude of mass fluctuations now ($\sigma_8$)
as a function of the nonrelativistic matter density parameter now ($\Omega_m$)
but it does not provide as good a fit to the larger-multipole Planck 2015 CMB
anisotropy data as does the standard flat tilted $\Lambda$CDM model. A few
cosmological parameter value measurements differ significantly when determined
using the tilted flat and the untilted nonflat $\phi$CDM models, including the
cold dark matter density parameter and the reionization optical depth. | astro-ph_CO |
Cosmic transparency and acceleration: In this paper, by considering an absorption probability independent of photon
wavelength, we show that current type Ia supernovae (SNe Ia) and gamma ray
burst (GRBs) observations plus high-redshift measurements of the cosmic
microwave background (CMB) radiation temperature support cosmic acceleration
regardless of the transparent-universe assumption. Two flat scenarios are
considered in our analyses: the $\Lambda$CDM model and a kinematic model. We
consider $\tau(z)=2\ln(1+z)^{\varepsilon}$, where $\tau(z)$ denotes the opacity
between an observer at $z=0$ and a source at $z$. This choice is equivalent to
deforming the cosmic distance duality relation as $D_LD^{-1}_A = (1 +
z)^{2+\varepsilon}$ and, if the absorption probability is independent of photon
wavelength, the CMB temperature evolution law is
$T_{CMB}(z)=T_0(1+z)^{1+2\varepsilon/3 }$. By marginalizing on the
$\varepsilon$ parameter, our analyses rule out a decelerating universe at 99.99
\% c.l. for all scenarios considered. Interestingly, by considering only SNe Ia
and GRBs observations, we obtain that a decelerated universe indicated by
$\Omega_{\Lambda} \leq 0.33$ and $q_0 > 0$ is ruled out around 1.5$\sigma$ c.l.
and 2$\sigma$ c.l., respectively, regardless of the transparent-universe
assumption. | astro-ph_CO |
Swift BAT, Fermi LAT, and the Blazar Sequence: Using public \fermi LAT and \swift BAT observations, we constructed the first
sample of blazars selected at both hard X-rays and gamma-rays. Studying its
spectral properties, we find a luminosity dependence of the spectral slopes at
both energies. Specifically, luminous blazars, generally classified as FSRQs,
have {\it hard} continua in the medium-hard X-ray range but {\it soft} continua
in the LAT gamma-ray range (photon indices $\Gamma_X$ \ltsima 2 and $\Gamma_G$
\gtsima 2), while lower luminosity blazars, classified as BL Lacs, have
opposite behavior, i.e., {\it soft} X-ray and {\it hard} gamma-ray continua
($\Gamma_X$ \gtsima 2.4 and $\Gamma_G < 2$). The trends are confirmed by
detailed Monte Carlo simulations explicitly taking into account the
observational biases of both instruments. Our results support the so-called
``blazar sequence'' which was originally based on radio samples of blazars and
radio luminosities. We also argue that the X-ray-to-gamma-ray continua of
blazars may provide independent insights into the physical conditions around
the jet, complementing/superseding the ambiguities of the traditional
classification based on optical properties. | astro-ph_CO |
B-mode in CMB polarization. What's that and why it is interesting: Generation of the B-mode of CMB polarization by background of relic
gravitational wave is discussed in connection with the BICEP2 measurements.
Description of the polarization maps in terms of the eigenvectors of the
polarization matrix is considered. | astro-ph_CO |
Post-Planck Dark Energy Constraints: We constrain plausible dark energy models, parametrized by multiple candidate
equation of state, using the recently published Cosmic Microwave Background
(CMB) temperature anisotropy data from Planck together with the WMAP-9
low-$\ell$ polarization data and data from low redshift surveys. To circumvent
the limitations of any particular equation of state towards describing all
existing dark energy models, we work with three different equation of state
covering a broader class of dark energy models and, hence, provide more robust
and generic constraints on the dark energy properties. We show that a clear
tension exists between dark energy constraints from CMB and non-CMB
observations when one allows for dark energy models having both phantom and
non-phantom behavior; while CMB is more favorable to phantom models, the low-z
data prefers model with behavior close to a Cosmological Constant. Further, we
reconstruct the equation of state of dark energy as a function of redshift
using the results from combined CMB and non-CMB data and find that Cosmological
Constant lies outside the 1$\sigma$ band for multiple dark energy models
allowing phantom behavior. A considerable fine tuning is needed to keep models
with strict non-phantom history inside 2$\sigma$ allowed range. This result
might motivate one to construct phantom models of dark energy,which is
achievable in the presence of higher derivative operators as in string theory.
However, disallowing phantom behavior, based only on strong theoretical prior,
leads to both CMB and non-CMB datasets agree on the nature of dark energy, with
the mean equation of state being very close to the Cosmological Constant.
Finally, to illustrate the impact of additional dark energy parameters on other
cosmological parameters, we provide the cosmological parameter constraints for
different dark energy models. | astro-ph_CO |
Gravitational waves, dark energy and inflation: In this paper we first present a complete classification of gravitational
waves according to their frequencies: (i) Ultra high frequency band (above 1
THz); (ii) Very high frequency band (100 kHz - 1 THz); (iii) High frequency
band (10 Hz - 100 kHz); (iv) Middle frequency band (0.1 Hz - 10 Hz); (v) Low
frequency band (100 nHz - 0.1 Hz); (vi) Very low frequency band (300 pHz - 100
nHz); (vii) Ultra low frequency band (10 fHz - 300 pHz); (viii) Hubble
(extremely low) frequency band (1 aHz - 10 fHz); (ix) Infra-Hubble frequency
band (below 1 aHz). After briefly discussing the method of detection for
different frequency bands, we review the concept and status of space
gravitational-wave missions --- LISA, ASTROD, ASTROD-GW, Super-ASTROD, DECIGO
and Big Bang Observer. We then address to the determination of dark energy
equation, and probing the inflationary physics using space gravitational wave
detectors. | astro-ph_CO |
Testing flatness of the universe with probes of cosmic distances and
growth: When using distance measurements to probe spatial curvature, the geometric
degeneracy between curvature and dark energy in the distance-redshift relation
typically requires either making strong assumptions about the dark energy
evolution or sacrificing precision in a more model-independent approach.
Measurements of the redshift evolution of the linear growth of perturbations
can break the geometric degeneracy, providing curvature constraints that are
both precise and model-independent. Future supernova, CMB, and cluster data
have the potential to measure the curvature with an accuracy of
sigma(Omega_K)=0.002, without specifying a particular dark energy
phenomenology. In combination with distance measurements, the evolution of the
growth function at low redshifts provides the strongest curvature constraint if
the high-redshift universe is well approximated as being purely matter
dominated. However, in the presence of early dark energy or massive neutrinos,
the precision in curvature is reduced due to additional degeneracies, and
precise normalization of the growth function relative to recombination is
important for obtaining accurate constraints. Curvature limits from distances
and growth compare favorably to other approaches to curvature estimation
proposed in the literature, providing either greater accuracy or greater
freedom from dark energy modeling assumptions, and are complementary due to the
use of independent data sets. Model-independent estimates of curvature are
critical for both testing inflation and obtaining unbiased constraints on dark
energy parameters. | astro-ph_CO |
Effects of a Late Gravitational Transition on Gravitational Waves and
Anticipated Constraints: We investigate the evolution of gravitational waves through discontinuous
evolution (transition) of the Hubble expansion rate $H(z)$ at a sudden
cosmological singularity, which may be due to a transition of the value of the
gravitational constant. We find the evolution of the scale factor and the
gravitational wave waveform through the singularity by imposing the proper
boundary conditions. We also use existing cosmological data and mock data of
future gravitational wave experiments (the ET) to impose current and
anticipated constraints on the magnitude of such a transition. We show that
mock data of the Einstein Telescope can reduce the uncertainties by up to a
factor of three depending on the cosmological parameter considered. | astro-ph_CO |
Cosmic string loop shapes: We analyze the shapes of cosmic string loops found in large-scale simulations
of an expanding-universe string network. The simulation does not include
gravitational back reaction, but we model that process by smoothing the loop
using Lorentzian convolution. We find that loops at formation consist of
generally straight segments separated by kinks. We do not see cusps or any
cusp-like structure at the scale of the entire loop, although we do see very
small regions of string that move with large Lorentz boosts. However, smoothing
of the string almost always introduces two cusps on each loop. The smoothing
process does not lead to any significant fragmentation of loops that were in
non-self-intersecting trajectories before smoothing. | astro-ph_CO |
The sub-mJy radio population of the E-CDFS: optical and infrared
counterpart identification: We study a sample of 883 sources detected in a deep Very Large Array survey
at 1.4 GHz in the Extended Chandra Deep Field South. The paper focuses on the
identification of their optical and infrared (IR) counterparts. We use a
likelihood ratio technique that is particularly useful when dealing with deep
optical images to minimize the number of spurious associations. We find a
reliable counterpart for 95% of our radio sources. Most of the counterparts
(74%) are detected at optical wavelengths, but there is a significant fraction
(21%) only detectable in the IR. Combining newly acquired optical spectra with
data from the literature we are able to assign a redshift to 81% of the
identified radio sources (37% spectroscopic). We also investigate the X-ray
properties of the radio sources using the Chandra 4 Ms and 250 ks observations.
In particular, we use a stacking technique to derive the average properties of
radio objects undetected in the Chandra images. The results of our analysis are
collected in a new catalog containing the position of the optical/IR
counterpart, the redshift information and the X-ray fluxes. It is the deepest
multi-wavelength catalog of radio sources, which will be used for future study
of this galaxy population. | astro-ph_CO |
Calibrated Ultra Fast Image Simulations for the Dark Energy Survey: Weak lensing by large-scale structure is a powerful technique to probe the
dark components of the universe. To understand the measurement process of weak
lensing and the associated systematic effects, image simulations are becoming
increasingly important. For this purpose we present a first implementation of
the $\textit{Monte Carlo Control Loops}$ ($\textit{MCCL}$; Refregier & Amara
2014), a coherent framework for studying systematic effects in weak lensing. It
allows us to model and calibrate the shear measurement process using image
simulations from the Ultra Fast Image Generator (UFig; Berge et al. 2013). We
apply this framework to a subset of the data taken during the Science
Verification period (SV) of the Dark Energy Survey (DES). We calibrate the UFig
simulations to be statistically consistent with DES images. We then perform
tolerance analyses by perturbing the simulation parameters and study their
impact on the shear measurement at the one-point level. This allows us to
determine the relative importance of different input parameters to the
simulations. For spatially constant systematic errors and six simulation
parameters, the calibration of the simulation reaches the weak lensing
precision needed for the DES SV survey area. Furthermore, we find a sensitivity
of the shear measurement to the intrinsic ellipticity distribution, and an
interplay between the magnitude-size and the pixel value diagnostics in
constraining the noise model. This work is the first application of the
$\textit{MCCL}$ framework to data and shows how it can be used to methodically
study the impact of systematics on the cosmic shear measurement. | astro-ph_CO |
Metals and ionizing photons from dwarf galaxies: We estimate the potential contribution of M < 10^9 Msun dwarf galaxies to the
reionization and early metal-enrichment of the Milky Way environment, or
circum-Galactic Medium. Our approach is to use the observed properties of
ancient stars (> 12 Gyr old) measured in nearby dwarf galaxies to characterize
the star-formation at high-z. We use a merger-tree model for the build-up of
the Milky Way, which self-consistently accounts for feedback processes, and
which is calibrated to match the present-day properties of the Galaxy and its
dwarf satellites. We show that the high-z analogues of nearby dwarf galaxies
can produce the bulk of ionizing radiation (>80%) required to reionize the
Milky Way environment. Our fiducial model shows that the gaseous environment
can be 50% reionized at z ~ 8 by galaxies with 10^7 Msun < M < 10^8 Msun. At
later times, radiative feedback stops the star-formation in these small
systems, and reionization is completed by more massive dwarf galaxies by z_rei
= 6.4\pm 0.5. The metals ejected by supernova-driven outflows from M < 10^9
Msun dwarf galaxies almost uniformly fill the Milky Way environment by z ~ 5,
enriching it to Z ~ 2 10^-2 Zsun. At z ~ 2 these early metals are still found
to represent ~ 50% of the total mass of heavy elements in the circum-Galactic
Medium. | astro-ph_CO |
The Evolution and Eddington Ratio Distribution of Compton Thick Active
Galactic Nuclei: Previous studies of the active galactic nuclei (AGN) contribution to the
cosmic X-ray background (CXB) consider only observable parameters such as
luminosity and absorbing column. Here, for the first time, we extend the study
of the CXB to physical parameters including the Eddington ratio of the sources
and the black hole mass. In order to calculate the contribution to the CXB of
AGN accreting at various Eddington ratios, an evolving Eddington ratio space
density model is calculated. In particular, Compton thick (CT) AGN are modeled
as accreting at specific, physically motivated Eddington ratios instead of as a
simple extension of the Compton thin type 2 AGN population. Comparing against
the observed CT AGN space densities and log N-log S relation indicates that CT
AGN are likely a composite population of AGN made up of sources accreting
either at >90% or <1% of their Eddington rate. | astro-ph_CO |
Environmental Effects on the Star Formation Activity in Galaxies at
z=1.2 in the COSMOS Field: We investigate the relation between the star-formation activity in galaxies
and environment at z=1.2 in the COSMOS field, using the fraction of [OII]
emitters and the local galaxy density. The fraction of [OII] emitters appears
to be almost constant over the surface density of galaxies between 0.2 and 10
Mpc^-2. This trend is different from that seen in the local universe where the
star-formation activity is weaker in higher density regions. To understand this
difference between z~1 and z~0, we study the fraction of non-isolated galaxies
as a function of local galaxy density. We find that the fraction of
non-isolated galaxies increases with increasing density. Our results suggest
that the star formation in galaxies at z~1 is triggered by galaxy interaction
and/or mergers. | astro-ph_CO |
Light Fields during Inflation from BOSS and Future Galaxy Surveys: Primordial non-Gaussianity generated by additional fields present during
inflation offers a compelling observational target for galaxy surveys. These
fields are of significant theoretical interest since they offer a window into
particle physics in the inflaton sector. They also violate the single-field
consistency conditions and induce a scale-dependent bias in the galaxy power
spectrum. In this paper, we explore this particular signal for light scalar
fields and study the prospects for measuring it with galaxy surveys. We find
that the sensitivities of current and future surveys are remarkably stable for
different configurations, including between spectroscopic and photometric
redshift measurements. This is even the case at non-zero masses where the
signal is not obviously localized on large scales. For realistic galaxy number
densities, we demonstrate that the redshift range and galaxy bias of the sample
have the largest impact on the sensitivity in the power spectrum. These results
additionally motivated us to explore the potentially enhanced sensitivity of
Vera Rubin Observatory's LSST through multi-tracer analyses. Finally, we apply
this understanding to current data from the last data release of the Baryon
Oscillation Spectroscopic Survey (BOSS DR12) and place new constraints on light
fields coupled to the inflaton. | astro-ph_CO |
Multiband Comparative Study of Optical Microvariability in RL vs. RQ
Quasars: We present the results of an optical multi-band (BVR) photometric monitoring
program of 22 core-dominated radio-loud quasars (CRLQs) and 22 radio-quiet
quasars (RQQs). The aim was to compare the properties of microvariability in
both types of quasars. We detected optical microvariability in 5 RQQs and 4
CRLQs. Our results confirm that microvariability in RQQs may be as frequent as
in CRLQs. In addition we compare microvariability duty cycles in different
bands. Finally, the implications for the origin of the microvariations are
briefly discussed. | astro-ph_CO |
Connecting massive galaxies to dark matter halos in BOSS - I. Is galaxy
color a stochastic process in high-mass halos?: We use subhalo abundance matching (SHAM) to model the stellar mass function
(SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS)
"CMASS" sample at $z\sim0.5$. We introduce a novel method which accounts for
the stellar mass incompleteness of CMASS as a function of redshift, and produce
CMASS mock catalogs which include selection effects, reproduce the overall SMF,
the projected two-point correlation function $w_{\rm p}$, the CMASS $dn/dz$,
and are made publicly available. We study the effects of assembly bias above
collapse mass in the context of "age matching" and show that these effects are
markedly different compared to the ones explored by Hearin et al. (2013) at
lower stellar masses. We construct two models, one in which galaxy color is
stochastic ("AbM" model) as well as a model which contains assembly bias
effects ("AgM" model). By confronting the redshift dependent clustering of
CMASS with the predictions from our model, we argue that that galaxy colors are
not a stochastic process in high-mass halos. Our results suggest that the
colors of galaxies in high-mass halos are determined by other halo properties
besides halo peak velocity and that assembly bias effects play an important
role in determining the clustering properties of this sample. | astro-ph_CO |
X-ray observations of the merging cluster CIZA J2242.8+5301: Multiwavelength studies of radio relics at merger shocks set powerful
constraints on the relics origin and formation mechanism. However, for X-ray
observations, a main difficulty is represented by the low X-ray surface
brightness far out in the cluster outskirts, where relics are typically found.
Here, we present XMM-Newton results from a 130-ks observation of CIZA
J2242.8+5301, a cluster at z=0.19 that hosts a double radio relic. We focus on
the well-defined northern relic. There is a difference of ~55% between the
temperature we measure behind the relic, and the temperature measured with
Suzaku. We analyse the reasons for this large discrepancy, and discuss the
possibility of reliably measuring the temperature beyond the northern relic. | astro-ph_CO |
Detectability of the cross-correlation between CMB lensing and
stochastic GW background from compact object mergers: The anisotropies of the Stochastic Gravitational-Wave Background (SGWB)
produced by merging compact binaries constitute a possible new probe of the
Large-Scale Structure (LSS). However, the significant shot noise contribution
caused by the discreteness of the GW sources and the poor angular resolution of
the instruments hamper the detection of the intrinsic anisotropies induced by
the LSS. In this work, we investigate the potential of cross-correlating
forthcoming high precision measurements of the SGWB energy density and the
Cosmic Microwave Background (CMB) lensing convergence to mitigate the effect of
shot noise. Combining a detailed model of stellar and galactic astrophysics
with a novel framework to distribute the GW emitters in the sky, we compute the
auto- and cross-correlation power spectra for the two cosmic fields, evaluate
the shot noise contribution and predict the signal-to-noise ratio. The results
of our analysis show that the SGWB energy density correlates significantly with
the CMB lensing convergence and that the cross-correlation between these two
cosmic fields reduces the impact of instrumental and shot noise. Unfortunately,
the S/N is not high enough to detect the intrinsic SGWB anisotropies.
Nevertheless, a network composed of both present and future generation GW
interferometers, operating for at least 10 yrs, should be able to measure the
shot noise contribution. | astro-ph_CO |
A unique isolated dwarf spheroidal galaxy at D=1.9 Mpc: We present a photometric and spectroscopic study of the unique isolated
nearby dSph galaxy KKR25. The galaxy was resolved into stars with HST/WFPC2
including old red giant branch and red clump. We have constructed a model of
the resolved stellar populations and measured the star formation rate and
metallicity as function of time. The main star formation activity period
occurred about 12.6 to 13.7 Gyr ago. These stars are mostly metal-poor, with a
mean metallicity [Fe/H]\sim -1 to -1.6 dex. About 60 per cent of the total
stellar mass was formed during this event. There are indications of
intermediate age star formation in KKR25 between 1 and 4 Gyr with no
significant signs of metal enrichment for these stars. Long-slit spectroscopy
was carried out using the Russian 6-m telescope of the integrated starlight and
bright individual objects in the galaxy. We have discovered a planetary nebula
(PN) in KKR25. This is the first known PN in a dwarf spheroidal galaxy outside
the Local Group. We have measured its oxygen abundance 12+log(O/H)=7.60+-0.07
dex and a radial velocity Vh=-79 km/s. We have analysed the stellar density
distribution in the galaxy body. The galaxy has an exponential surface
brightness profile with a central light depression. We discuss the evolutionary
status of KKR25, which belongs to a rare class of very isolated dwarf galaxies
with spheroidal morphology. | astro-ph_CO |
Cross-Correlation of Diffuse Synchrotron and Large-Scale Structures: We explore for the first time the method of cross-correlation of radio
synchrotron emission and tracers of large-scale structure in order to detect
the diffuse IGM/WHIM. We performed a cross-correlation of a 34 x 34 degree area
of 2MASS galaxies for two redshift slices (0.03 < z < 0.04 and 0.06 < z < 0.07)
with the corresponding region of the 1.4 GHz Bonn survey. For this analysis, we
assumed that the synchrotron surface brightness is linearly proportional to
surface density of galaxies. We also sampled the cross-correlation function
using 24 distant fields of the same size from the Bonn survey, to better assess
the noise properties. Though we obtained a null result, we found that by adding
a signal weighted by the 2MASS image with a filament (peak) surface brightness
of 1 (7) mK and 7 (49) mK would produce a 3 sigma positive correlation for the
0.03 < z < 0.04 and 0.06 < z < 0.07 redshift slices respectively. These
detection thresholds correspond to minimum energy magnetic fields as low as 0.2
microG, close to some theoretical expectations for filament field values. This
injected signal is also below the rms noise of the Bonn survey, and
demonstrates the power of this technique and its utility for upcoming sensitive
continuum surveys such as GALFACTS at Arecibo and those planned with the
Murchison Widefield Array (MWA). | astro-ph_CO |
The Brightest of Reionizing Galaxies (BoRG) survey: Until now, investigating the early stages of galaxy formation has been
primarily the realm of theoretical modeling and computer simulations, which
require many physical ingredients and are challenging to test observationally.
However, the latest Hubble Space Telescope observations in the near infrared
are shedding new light on the properties of galaxies within the first billion
years after the Big Bang, including our recent discovery of the most distant
proto-cluster of galaxies at redshift z~8. Here, I compare predictions from
models of primordial and metal-enriched star formation during the dark ages
with the latest Hubble observations of galaxies during the epoch of
reionization. I focus in particular on the luminosity function and on galaxy
clustering as measured from our Hubble Space Telescope Brightest of Reionizing
Galaxies (BoRG) survey. BoRG has the largest area coverage to find luminous and
rare z~8 sources that are among the first galaxies to have formed in the
Universe. | astro-ph_CO |
Episodic Star Formation Coupled to Reignition of Radio Activity in 3C
236: We present Hubble Space Telescope UV and optical imaging of the radio galaxy
3C 236, whose relic 4 Mpc radio jet lobes and inner 2 kpc CSS radio source are
evidence of multiple epochs of AGN activity. Our data confirm the presence of
four bright knots of FUV emission in an arc along the edge of the inner
circumnuclear dust disk in the galaxy's nucleus, as well as FUV emission
cospatial with the nucleus itself. We interpret these to be sites of recent or
ongoing star formation. We present photometry of these knots, as well as an
estimate for the internal extinction in the source using the Balmer decrement
from SDSS spectroscopy. We estimate the ages of the knots by comparing our
extinction-corrected photometry with stellar population synthesis models. We
find the four knots cospatial with the dusty disk to be young, of order 10^7 yr
old. The FUV emission in the nucleus is likely due to an episode of star
formation triggered ~10^9 yr ago. We argue that the young 10^7 yr old knots
stem from an episode of star formation that was roughly coeval with the event
resulting in reignition of radio activity, creating the CSS source. The 10^9 yr
old stars in the nucleus may be associated with the previous epoch of activity
that generated the 4 Mpc relic source, before it was cut off by exhaustion or
interruption. The ages of the knots, considered in context with the disturbed
morphology of the nuclear dust and the double-double morphology of the "old"
and "young" radio sources, present evidence for an episodic AGN/starburst
connection. We suggest that the AGN fuel supply was interrupted for ~10^7 yr
due to a minor merger event and has now been restored, and the resultant
non-steady flow of gas toward the nucleus is likely responsible for both the
new episode of infall-induced star formation and also the multiple epochs of
radio activity. | astro-ph_CO |
Cosmological constraints from multiple tracers in spectroscopic surveys: We use the Fisher matrix formalism to study the expansion and growth history
of the Universe using galaxy clustering with 2D angular cross-correlation
tomography in spectroscopic or high resolution photometric redshift surveys.
The radial information is contained in the cross correlations between narrow
redshift bins. We show how multiple tracers with redshift space distortions
cancel sample variance and arbitrarily improve the constraints on the dark
energy equation of state $\omega(z)$ and the growth parameter $\gamma$ in the
noiseless limit. The improvement for multiple tracers quickly increases with
the bias difference between the tracers, up to a factor $\sim4$ in
$\text{FoM}_{\gamma\omega}$. We model a magnitude limited survey with realistic
density and bias using a conditional luminosity function, finding a factor
1.3-9.0 improvement in $\text{FoM}_{\gamma\omega}$ -- depending on global
density -- with a split in a halo mass proxy. Partly overlapping redshift bins
improve the constraints in multiple tracer surveys a factor $\sim1.3$ in
$\text{FoM}_{\gamma\omega}$. This findings also apply to photometric surveys,
where the effect of using multiple tracers is magnified. We also show large
improvement on the FoM with increasing density, which could be used as a
trade-off to compensate some possible loss with radial resolution. | astro-ph_CO |
The early-type dwarf galaxy population of the Centaurus cluster: We present a photometric study of the early-type dwarf galaxy population of
the Centaurus cluster, aiming at investigating the galaxy luminosity function
(LF) and galaxy scaling relations down to the regime of galaxies with M_V~-10
mag. On deep VLT/FORS1 V- and I-band images of the central part of the cluster,
we identify cluster dwarf-galaxy candidates using both morphological and
surface brightness selection criteria. Photometric and structural parameters of
the candidates are derived from analysis of their surface brightness profiles.
Fundamental scaling relations, such as the colour-magnitude and the
magnitude-surface brightness relation, are used to distinguish the cluster from
the background. We find a flat LF with a slope of \alpha = -1.14 \pm 0.12 for
M_V>-14 mag, when fitting a power law to the completeness-corrected galaxy
number counts. When plotting the central surface brightness of a Sersic model
vs. the galaxy magnitude, we find a continuous relation for magnitudes
-20<M_V<-10 mag, with only the brightest core galaxies deviating from this
relation, in agreement with previous studies of other clusters. In a
size-luminosity diagram of early-type galaxies from a range of environments, we
observe that R_eff slowly decreases with decreasing luminosity for -21<M_V<-13
mag and decreases more rapidly at fainter magnitudes. This trend continues to
the ultra-faint Local Group dwarf galaxies (M_V~-4 mag). The continuous central
surface brightness vs. absolute magnitude relation and the smooth relation in
the size-luminosity diagram over a wide range of magnitudes are consistent with
the interpretation of dwarf galaxies and more massive elliptical galaxies being
one family of objects with gradually changing structural properties. The most
massive core galaxies and the rare cE galaxies are the only exceptions. | astro-ph_CO |
Sunyaev Zel'dovich effect in galaxy clusters cavities: thermal or
non-thermal origin?: Several galaxy clusters host X-ray cavities, often filled with relativistic
electrons emitting in the radio band. In the cluster MS 0735.6+7421 the
cavities have been detected through the Sunyaev Zel'dovich (SZ) effect, but it
has not been possible to determine if this effect is thermal (produced by a
very high temperature gas filling the cavity) or non-thermal (produced by the
relativistic electrons that produce the diffuse radio emission detected in the
cavity). In this paper we discuss the role of the density of the high
temperature gas inside the cavities in determining whether the dominant SZ
effect is the thermal or the non-thermal one, and how it can be possible to
distinguish between the two possibilities, discussing the role of observations
at higher energy bands. | astro-ph_CO |
Calibrating Gamma-Ray Bursts by Using a Gaussian Process with Type Ia
Supernovae: In this paper, we calibrate the Amati relation (the $E_{\rm p}$-${E}_{\rm
iso}$ correlation) of gamma-ray bursts (GRBs) in a cosmology-independent way.
By using Gaussian process to reconstruct the smoothed luminosity distance from
the Pantheon type Ia supernovae (SNe Ia) sample, we utilize the reconstructed
results to calibrate the $E_{\rm p}$-${E}_{\rm iso}$ correlation with the
Markov Chain Monte Carlo method and construct a Hubble diagram with the A220
GRB data, in which there are A118 GRB data with the higher qualities
appropriate for cosmological purposes. With 98 GRBs at $1.4<z\leq8.2$ in the
A118 sample and the observed Hubble data, we obtain $\Omega_{\rm
m}$=$0.346^{+0.048}_{-0.069}$, $h$=$0.677^{+0.029}_{-0.029}$ for the flat
$\Lambda$CDM model, and $\Omega_{\rm m}$=$0.314^{+0.072}_{-0.055}$,
$h$=$0.705^{+0.055}_{-0.069}$, $w$=$-1.23^{+0.33}_{-0.64}$ for the flat $w$CDM
model, which are consistent with those from fitting the coefficients of the
Amati relation and the cosmological parameters simultaneously. | astro-ph_CO |
A Spectroscopic Model of the Type Ia Supernova--Host Galaxy Mass
Correlation from SALT3: The unknown cause of the correlation between Type Ia supernova (SN Ia) Hubble
residuals and their host-galaxy masses (the "mass step") may bias cosmological
parameter measurements. To better understand the mass step, we develop a SALT3
light-curve model for SN cosmology that uses the host-galaxy masses of 296
low-redshift SNe Ia to derive a spectral-energy distribution--host-galaxy mass
relationship. The resulting model has larger Ca II H&K, Ca II near-infrared
triplet, and Si II equivalent widths for SNe in low-mass host galaxies at
2.2-2.7$\sigma$ significance; this indicates higher explosion energies per unit
mass in low-mass-hosted SNe. The model has phase-dependent changes in SN Ia
colors as a function of host mass, indicating intrinsic differences in mean
broadband light curves. Although the model provides a better fit to the SN data
overall, it does not substantially reduce data--model residuals for a typical
light curve in our sample nor does it significantly reduce Hubble residual
dispersion. This is because we find that previous SALT models parameterized
most host-galaxy dependencies with their first principal component, although
they failed to model some significant spectral variations. Our new model is
luminosity and cosmology independent, and applying it to data reduces the mass
step by $0.021\pm0.002$ mag (uncertainty accounts for correlated data sets);
these results indicate that $\sim$35% of the mass step can be attributed to
luminosity-independent effects. This SALT model version could be trained using
alternative host-galaxy properties and at different redshifts, and therefore
will be a tool for understanding redshift-dependent correlations between SNe Ia
and their host properties as well as their impact on cosmological parameter
measurements. | astro-ph_CO |
The last breath of the young gigahertz-peaked spectrum radio source PKS
1518+047: We present the results from multi-frequency VLBA observations from 327 MHz to
8.4 GHz of the gigahertz-peaked spectrum radio source PKS 1518+047 (4C 04.51)
aimed at studying the spectral index distribution across the source. Further
multi-frequency archival VLA data were analysed to constrain the spectral shape
of the whole source. The pc-scale resolution provided by the VLBA data allows
us to resolve the source structure in several sub-components. The analysis of
their synchrotron spectra showed that the source components have steep spectral
indices, suggesting that no supply/re-acceleration of fresh particles is
currently taking place in any region of the source. By assuming the
equipartition magnetic field of 4 mG, we found that only electrons with
$\gamma$ < 600, are still contributing to the radio spectrum, while electrons
with higher energies have been almost completed depleted. The source radiative
lifetime we derived is 2700+/-600 years. Considering the best fit to the
overall spectrum, we find that the time in which the nucleus has not been
active represents almost 20% of the whole source lifetime, indicating that the
source was 2150+/-500 years old when the radio emission switched off. | astro-ph_CO |
Caustic and hydrostatic mass bias: Implications for modified gravity: We propose and perform a joint analysis of the two different mass estimates
of galaxy clusters, namely the hydrostatic and caustic techniques. Firstly, we
show comprehensively that the mass bias between these two techniques can be
possibly alleviated when cluster-specific assumptions constrained using the
hydrostatic technique are utilized within the caustic technique. While at face
value this demotes the caustic technique from a completely independent method,
this allows one to further tighten the constraints on the cluster mass and
subsequently, allow us to test modifications to gravity. Implementing the
aforementioned formalism for two well-observed massive galaxy clusters, A2029
and A2142, we highlight the proof of concept. In the current implementation, we
use this method to constrain the Chameleon screening and Vainshtein screening.
As anticipated, we show that the joint analysis can help improve the
constraints on these modified gravity scenarios. | astro-ph_CO |
Large-scale asymmetry in the distribution of galaxy spin directions --
analysis and reproduction: Recent independent observations using several different telescope systems an
analysis methods have provided evidence of parity violation between the number
of galaxies that spin in opposite directions. On the other hand, other studies
argued that no parity violation can be identified. This paper provides detailed
analysis, statistical inference, and reproduction of previous reports that show
no preferred spin direction. Code and data used for the reproduction are
publicly available. The results show that the data used in all of these studies
agrees with the observation of a preferred direction as observed from Earth. In
some of these studies the datasets were too small, or the statistical analysis
was incomplete. In other papers the results were impacted by experimental
design decisions that lead directly to show non-preferred direction. In some of
these cases these decisions are not stated in the papers, but were revealed
after further investigation in cases where the reproduction of the work did not
match the results reported in the papers. These results show that the data used
in all of these previous studies in fact agree with the contention that
galaxies as observed from Earth have a preferred spin direction, and the
distribution of galaxy spin directions as observed from Earth form a
cosmological-scale dipole axis. This study also shows that the reason for the
observations is not necessarily an anomaly in the large-scale structure, and
can also be related to internal structure of galaxies. | astro-ph_CO |
An influence of the matter distribution on the positional accuracy of
reference sources: We consider an influence of a non-stationary gravitational field of the
Galaxy on the visible positions of extragalactic sources. A contribution of the
baryonic component of the galactic matter as well as of the hidden matter
(including a population of brown dwarfs) were took into account. The observed
variations of the deflection angle of light rays in a gravitational field of
randomly moving point-like masses can be considered as a stochastic process.
Using such an approach we constructed an autocorrelation function of studied
stochastic process and found that its relative changes are about 15% for one
year and about 35% for ten years. | astro-ph_CO |
X-ray emission around the z=4.1 radio galaxy TNJ1338-1942 and the
potential role of far-infrared photons in AGN Feedback: We report the discovery in an 80-ks observation of spatially-extended X-ray
emission around the high-redshift radio galaxy TNJ1388-1942 (z=4.11) with the
Chandra X-ray Observatory. The X-ray emission extends over a ~30-kpc diameter
region and although it is less extended than the GHz-radio lobes, it is roughly
aligned with them. We suggest that the X-ray emission arises from Inverse
Compton (IC) scattering of photons by relativistic electrons around the radio
galaxy. At z=4.11 this is the highest redshift detection of IC emission around
a radio galaxy. We investigate the hypothesis that in this compact source, the
Cosmic Microwave Background (CMB), which is ~700x more intense than at z~0 is
nonetheless not the relevant seed photon field for the bulk of the IC emission.
Instead, we find a tentative correlation between the IC emission and
far-infrared luminosities of compact, far-infrared luminous high-redshift radio
galaxies (those with lobe lengths of <100kpc). Based on these results we
suggest that in the earliest phases of the evolution of radio-loud AGN at very
high redshift, the far-infrared photons from the co-eval dusty starbursts
occuring within these systems may make a significant contribution to their IC
X-ray emission and so contribute to the feedback in these massive high-redshift
galaxies. | astro-ph_CO |
Deblending Galaxies with Generative Adversarial Networks: Deep generative models including generative adversarial networks (GANs) are
powerful unsupervised tools in learning the distributions of data sets.
Building a simple GAN architecture in PyTorch and training on the CANDELS data
set, we generate galaxy images with the Hubble Space Telescope resolution
starting from a noise vector. We proceed by modifying the GAN architecture to
improve the Subaru Hyper Suprime-Cam ground-based images by increasing their
resolution to the HST resolution. We use the super resolution GAN on a large
sample of blended galaxies which we create using CANDELS cutouts. In our
simulated blend sample, $\sim 20 \%$ would unrecognizably be blended even in
the HST resolution cutouts. In the HSC-like cutouts this fraction rises to
$\sim 90\%$. With our modified GAN we can lower this value to $\sim 50\%$. We
quantify the blending fraction in the high, low and GAN resolutions over the
whole manifold of angular separation, flux ratios, sizes and redshift
difference between the two blended objects. The two peaks found by the GAN
deblender result in ten times improvement in the photometry measurement of the
blended objects. Modifying the architecture of the GAN, we also train a
Multi-wavelength GAN with seven band optical+NIR HST cutouts. This
multi-wavelength GAN improves the fraction of detected blends by another $\sim
10\%$ compared to the single-band GAN. This is most beneficial to the current
and future precision cosmology experiments (e.g., LSST, SPHEREx, Euclid,
Roman), specifically those relying on weak gravitational lensing, where
blending is a major source of systematic error. | astro-ph_CO |
Stellar population and the origin of intra-cluster stars around
brightest cluster galaxies: the case of NGC 3311: Context. We investigate the stellar population and the origin of diffuse
light around brightest cluster galaxies.
Aims. We study the stellar population of the dynamically hot stellar halo of
NGC 3311, the brightest galaxy in the Hydra I cluster, and that of photometric
substructures in the diffuse light to constrain the origin of these components.
Methods. We analyze absorption lines in medium-resolution, long-slit spectra
in the wavelength range 4800-5800 angstrom obtained with FORS2 at the Very
Large Telescope. We measure the equivalent width of Lick indices out to 20 kpc
from the center of NGC 3311 and fit them with stellar population models that
account for the [alpha/Fe] overabundance.
Results. Stars in the dynamically hot halo of NGC 3311 are old (age > 13
Gyr), metal-poor ([Z/H] ~ -0.35), and alpha-enhanced ([alpha/Fe] ~ 0.48).
Together with the high velocity dispersion, these measurements indicate that
the stars in the halo were accreted from the outskirts of other early-type
galaxies, with a possible contribution from dwarf galaxies. We identify a
region in the halo of NGC 3311 associated with a photometric substructure where
the stellar population is even more metal-poor ([Z/H] ~ -0.73). In this region,
our measurements are consistent with a composite stellar population superposed
along the line of sight, consisting of stars from the dynamically hot halo of
NGC 3311 and stars stripped from dwarf galaxies. The latter component
contributes < 28% to the local surface brightness.
Conclusions. The build-up of diffuse light around NGC 3311 is on-going. Based
on the observed stellar population properties, the dominant part of these stars
may have come from the outskirts of bright early-type galaxies, while stars
from stripped dwarf galaxies are presently being added. | astro-ph_CO |
Big Bang Nucleosynthesis: As the early universe expands and cools the rates of the weak interactions
that keep neutrinos in thermal equilibrium with the matter and the related
rates of the reactions that inter-convert neutrons and protons decrease.
Eventually, these rates fall below the expansion rate -- they freeze out.
Likewise, the rates of the strong and electromagnetic nuclear reactions that
build up and tear down nuclei, though fast enough to maintain equilibrium early
on, slow down and ultimately lead to freeze out. Together these freeze out
processes comprise the epoch of Big Bang Nucleosynthesis (BBN). The relics
emerging from this early time include the light element abundances, for example
of helium and deuterium, and a background of decoupled neutrinos, a "C$\nu$B" ,
roughly analogous to the Cosmic Microwave Background, the CMB. These fossil
relics encode the history of the physics operating in the early universe.
Consequently, BBN has emerged as a key tool for constraining new,
beyond-standard-model (BSM) physics. BBN may become an even finer probe of BSM
physics, given the anticipated higher precision in measurements of the
primordial abundances of deuterium and helium afforded by the advent of large
optical telescopes and Stage-4 CMB experiments. The latter experiments will
also provide higher precision determinations of $N_{\rm eff}$, a measure of the
relativistic energy density at the photon decoupling epoch and, hence, an
important probe of the C$\nu$B. | astro-ph_CO |
First results on the search for dark matter in the Sun with the ANTARES
neutrino telescope: The ANTARES collaboration is currently operating the largest neutrino
detector in the Northern Hemisphere. One of the goals of ANTARES is the search
for dark matter in the universe. In this paper, the first results on the search
for dark matter in the Sun with ANTARES in its 5 line configuration, as well as
sensitivity studies on the dark matter search with the full ANTARES detector
and the future cubic-kilometer neutrino telescope studied by the KM3NeT
consortium are presented. | astro-ph_CO |
Detecting patchy reionization in the CMB: Upcoming cosmic microwave background (CMB) experiments will measure
temperature fluctuations on small angular scales with unprecedented precision.
Small-scale CMB fluctuations are a mixture of late-time effects: gravitational
lensing, Doppler shifting of CMB photons by moving electrons (the kSZ effect),
and residual foregrounds. We propose a new statistic which separates the kSZ
signal from the others, and also allows the kSZ signal to be decomposed in
redshift bins. The decomposition extends to high redshift, and does not require
external datasets such as galaxy surveys. In particular, the high-redshift
signal from patchy reionization can be cleanly isolated, enabling future CMB
experiments to make high-significance and qualitatively new measurements of the
reionization era. | astro-ph_CO |
Viscosity, pressure, and support of the gas in simulations of merging
cool-core clusters: Major mergers are considered to be a significant source of turbulence in
clusters. We performed a numerical simulation of a major merger event using
nested-grid initial conditions, adaptive mesh refinement, radiative cooling of
primordial gas, and a homogeneous ultraviolet background. By calculating the
microscopic viscosity on the basis of various theoretical assumptions and
estimating the Kolmogorov length from the turbulent dissipation rate computed
with a subgrid-scale model, we are able to demonstrate that most of the
warm-hot intergalactic medium can sustain a fully turbulent state only if the
magnetic suppression of the viscosity is considerable. Accepting this as
premise, it turns out that ratios of turbulent and thermal quantities change
only little in the course of the merger. This confirms the tight correlations
between the mean thermal and non-thermal energy content for large samples of
clusters in earlier studies, which can be interpreted as second self-similarity
on top of the self-similarity for different halo masses. Another long-standing
question is how and to which extent turbulence contributes to the support of
the gas against gravity. From a global perspective, the ratio of turbulent and
thermal pressures is significant for the clusters in our simulation. On the
other hand, a local measure is provided by the compression rate, i.e. the
growth rate of the divergence of the flow. Particularly for the intracluster
medium, we find that the dominant contribution against gravity comes from
thermal pressure, while compressible turbulence effectively counteracts the
support. For this reason it appears to be too simplistic to consider turbulence
merely as an effective enhancement of thermal energy. | astro-ph_CO |
Thermal SZ effect in a magnetized IGM dominated by interacting DM
decay/annihilation during dark ages: During cosmic dawn, the thermal history of the universe is well studied, and
a study of this era can give us some of the most useful insight into the
universe before the recombination epoch. Its precise modeling and future
high-precision measurements will be a valuable tool for determining the thermal
history of the universe. In the present work, we study the thermal and
ionization history of IGM in the presence of decaying magnetic fields via
ambipolar and turbulent decay, Baryon-Dark matter (BDM) interaction, including
the DM decay/annihilation. The BDM interaction cross-sections considered are of
the form $\sigma=\sigma_0 v^{n}$, where $n=-2$ and $n=-4$. In this work, we
show that in the current scenario, the decay/annihilation of the DM particles
have a considerable impact on the temperature and ionization histories at low
redshift. With the addition of the concept of fractional interaction, which
states that if a fraction of the DM particles interacts with the baryons, the
temperature and ionization fraction of the baryons show a strong dependence on
the percentage of DM particles interacting with the baryons. We have also
studied the interesting consequences of the present scenario on the thermal
Sunyaev-Zeldovich (tSZ) effect. We show that the highest value of the absolute
value of the mean $y-$parameter in the current DM decay/annihilation scenario
is well within the values derived from experimental data such as PLANCK, FIRAS,
and PIXIE. Later we calculate the bound on the ordinary magnetic fields
originating from the Dark photons. | astro-ph_CO |
Athena X-IFU synthetic observations of galaxy clusters to probe the
chemical enrichment of the Universe: Answers to the metal production of the Universe can be found in galaxy
clusters, notably within their Intra-Cluster Medium (ICM). The X-ray Integral
Field Unit (X-IFU) on board the next-generation European X-ray observatory
Athena (2030s) will provide the necessary leap forward in spatially-resolved
spectroscopy required to disentangle the intricate mechanisms responsible for
this chemical enrichment. In this paper, we investigate the future capabilities
of the X-IFU in probing the hot gas within galaxy clusters. From a test sample
of four clusters extracted from cosmological hydrodynamical simulations, we
present comprehensive synthetic observations of these clusters at different
redshifts (up to z = 2) and within the scaled radius R500 performed using the
instrument simulator SIXTE. Through 100 ks exposures, we demonstrate that the
X-IFU will provide spatially-resolved mapping of the ICM physical properties
with little to no biases (<5%) and well within statistical uncertainties. The
detailed study of abundance profiles and abundance ratios within R500 also
highlights the power of the X-IFU in providing constraints on the various
enrichment models. From synthetic observations out to z = 2, we also quantify
its ability to track the chemical elements across cosmic time with excellent
accuracy, and thereby to investigate the evolution of metal production
mechanisms as well as the link to the stellar initial mass-function. Our study
demonstrates the unprecedented capabilities of the X-IFU in unveiling the
properties of the ICM but also stresses the data analysis challenges faced by
future high-resolution X-ray missions such as Athena. | astro-ph_CO |
The ~0.9 mJy sample: A mid-infrared spectroscopic catalog of 150
infrared-luminous, 24 micron selected galaxies at 0.3<z<3.5: We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR)
luminous galaxies in the Spitzer extragalactic first look survey obtained with
IRS on board Spitzer. The sample is selected to be brighter than ~0.9 mJy at 24
micron and it has a z distribution in the range [0.3,3.5] with a peak at z=1.
It primarily comprises ultraluminous IR galaxies at z>1 and luminous IR
galaxies at z<1, as estimated from their monochromatic 14 micron luminosities.
The number of sources with spectra that are dominated by an active galactic
nucleus (AGN) continuum is 49, while 39 sources have strong, star-formation
related features. For this classification, we used the equivalent width (EW) of
the 11.3 micron polycyclic aromatic hydrocarbon (PAH) feature. Several
intermediate/high z starbursts have higher PAH EW than local ULIRGs. An
increase in the AGN activity is observed with increasing z and luminosity,
based on the decreasing EW of PAHs and the increasing [NeIII]/[NeII] ratio.
Spectral stacking leads to the detection of the 3.3 micron PAH, the H2 0-0 S(1)
and S(3) lines, and the [NeV] line. We observe differences in the flux ratios
of PAHs in the stacked spectra of IR-luminous galaxies with z or luminosity,
which are not due to extinction effects. When placing the observed galaxies on
IR color-color diagrams, we find that the wedge defining AGN comprises most
sources with continuum-dominated spectra, but also contains many starbursts.
The comparison of the 11.3 micron PAH EW and the H-band effective radius,
measured from HST data, indicates that sources with EW>2 micron, are typically
more extended than ~3 kpc. However, there is no strong correlation between the
MIR spectral type and the near-IR extent of the sources. [Abridged]. | astro-ph_CO |
Probing general relativistic effects during AGN X-ray eclipses: Long X-ray observations of bright Active Galactic Nuclei show that X-ray
eclipses, with durations from a few hours to a few days, are rather common.
This opens up a new window of opportunity in the search for signatures of
relativistic effects in AGNs: an obscuring cloud covers/uncovers different
parts of the accretion disc at different times, allowing a direct check of the
expected pattern of disc emission. In particular, the combination of
gravitational redshift and relativistic Doppler boosting should imply strong
differences between the receding and approaching parts of an inclined thin
disc. At present, these effects may be already detectable with a "lucky"
XMM-Newton or Suzaku observation of a complete eclipse by a Compton-thick cloud
(a rare, but not impossible-to-see event). In the future, higher sensitivity
observatories will be able to perform these tests easily on tens of AGNs. This
will provide a powerful and direct way to test extreme gravity, and to probe
the structure of AGNs in the close vicinity of the central black holes. | astro-ph_CO |
The Effects of Calibration on the Bias of Shear Measurements: Forthcoming large-scale surveys will soon attempt to measure cosmic shear to
an unprecedented level of accuracy, requiring a similarly high level of
accuracy in the shear measurements of galaxies. Factors such as pixelisation,
imperfect point-spread function (PSF) correction, and pixel noise can all
directly or indirectly lead to biases in shear measurements, and so it can be
necessary for shear measurement methods to be calibrated against internal,
external, or simulated data to minimize bias. It is thus important to
understand the nature of this calibration. In this paper, we show that a
typical calibration procedure will on average leave no residual additive bias,
but will leave a residual multiplicative bias. Additionally, the errors on the
post-calibration bias parameters will be changed, and on average increased,
from the errors on the pre-calibration measurements of these parameters, but
that this is generally worth the benefit in decreasing the expected value of
the multiplicative bias. We find that in most typical cases, it is worthwhile
to apply a first-order bias correction, while a higher-order bias correction is
only worthwhile for methods with intrinsically high multiplicative bias ($>10$
per cent) or when the simulation size is very small ($<10^6$ simulated
galaxies). | astro-ph_CO |
Post-reionization HI 21-cm signal: A probe of negative cosmological
constant: In this study, we investigate a cosmological model involving a negative
cosmological constant (AdS vacua in the dark energy sector). We consider a
quintessence field on top of a negative cosmological constant and study its
impact on cosmological evolution and structure formation. We use the power
spectrum of the redshifted HI 21 cm brightness temperature maps from the
post-reionization epoch as a cosmological probe. The signature of baryon
acoustic oscillations (BAO) on the multipoles of the power spectrum is used to
extract measurements of the angular diameter distance $D_A(z)$ and the Hubble
parameter $H(z)$. The projected errors on these are then subsequently employed
to forecast the constraints on the model parameters ($\Omega_\Lambda, w_0,
w_a$) using Markov Chain Monte Carlo techniques. We find that a negative
cosmological constant with a phantom dark energy equation of state (EoS) and a
higher value of $H_0$ is viable from BAO distance measurements data derived
from galaxy samples. We also find that BAO imprints on the 21cm power spectrum
obtained from a futuristic SKA-mid like experiment yield a $1-\sigma$ error on
a negative cosmological constant and the quintessence dark energy EoS
parameters to be $\Omega_\Lambda=-1.030^{0.589}_{-1.712}$ and
$w_0=-1.023^{0.043}_{-0.060}$, $w_a=-0.141^{0.478}_{-0.409}$ respectively. | astro-ph_CO |
Lyalpha versus X-ray heating in the high-z IGM: In this paper we examine the effect of X-ray and Lyalpha photons on the
intergalactic medium temperature. We calculate the photon production from a
population of stars and micro-quasars in a set of cosmological hydrodynamic
simulations which self-consistently follow the dark matter dynamics, radiative
processes as well as star formation, black hole growth and associated feedback
processes. We find that, (i) IGM heating is always dominated by X-rays unless
the Lyalpha photon contribution from stars in objects with mass M<10^8 Msun
becomes significantly enhanced with respect to the X-ray contribution from BHs
in the same halo (which we do not directly model). (ii) Without overproducing
the unresolved X-ray background, the gas temperature becomes larger than the
CMB temperature, and thus an associated 21 cm signal should be expected in
emission, at z<11.5. We discuss how in such a scenario the transition redshift
between a 21 cm signal in absorption and in emission could be used to
constraint BHs accretion and associated feedback processes. | astro-ph_CO |
Unsupervised Searches for Cosmological Parity-Violation: An
Investigation with Convolutional Neural Networks: Recent measurements of the $4$-point correlation functions (4PCF) from
spectroscopic surveys provide evidence for parity-violations in the large-scale
structure of the Universe. If physical in origin, this could point to exotic
physics during the epoch of inflation. However, searching for parity-violations
in the 4PCF signal relies on a large suite of simulations to perform a rank
test, or an accurate model of the 4PCF covariance to claim a detection, and
this approach is incapable of extracting parity information from the
higher-order $N$-point functions. In this work we present an unsupervised
method which overcomes these issues, before demonstrating the approach is
capable of detecting parity-violations in a few toy models using convolutional
neural networks. This technique is complementary to the 4-point method and
could be used to discover parity-violations in several upcoming surveys
including DESI, Euclid and Roman. | astro-ph_CO |
Lower Bounds on Intergalactic Magnetic Fields from Simultaneously
Observed GeV-TeV Light Curves of the Blazar Mrk 501: We derive lower bounds on intergalactic magnetic fields (IGMFs) from upper
limits on the pair echo emission from the blazar Mrk 501, that is, delayed GeV
emission from secondary $e^{-}e^{+}$ pairs produced via interactions of primary
TeV gamma rays with the cosmic infrared background. Utilizing only simultaneous
GeV-TeV light curves observed by VERITAS, MAGIC and {\it Fermi}-LAT during a
multiwavelength campaign in 2009 that included a TeV flare, bounds are deduced
on the IGMF strength of $B \gtrsim 10^{-20} {\rm G}$ at 90% confidence level
for a field coherence length of 1 kpc. Since our analysis is based firmly on
the observational data alone and nearly free of assumptions concerning the
primary TeV flux in unobserved periods or spectral bands, our evaluation of the
pair echo flux is conservative and the evidence for a non-zero IGMF is more
robust compared to previous studies. | astro-ph_CO |
The Case Against Warm or Self-Interacting Dark Matter as Explanations
for Cores in Low Surface Brightness Galaxies: Warm dark matter (WDM) and self-interacting dark matter (SIDM) are often
motivated by the inferred cores in the dark matter halos of low surface
brightness (LSB) galaxies. We test thermal WDM, non-thermal WDM, and SIDM using
high-resolution rotation curves of nine LSB galaxies. We fit these dark matter
models to the data and determine the halo core radii and central densities.
While the minimum core size in WDM models is predicted to decrease with halo
mass, we find that the inferred core radii increase with halo mass and also
cannot be explained with a single value of the primordial phase space density.
Moreover, if the core size is set by WDM particle properties, then even the
smallest cores we infer would require primordial phase space density values
that are orders of magnitude smaller than lower limits obtained from the Lyman
alpha forest power spectra. We also find that the dark matter halo core
densities vary by a factor of about 30 from system to system while showing no
systematic trend with the maximum rotation velocity of the galaxy. This
strongly argues against the core size being directly set by large
self-interactions (scattering or annihilation) of dark matter. We therefore
conclude that the inferred cores do not provide motivation to prefer WDM or
SIDM over other dark matter models. | astro-ph_CO |
Astrophysical information from the Rayleigh-Jeans Tail of the CMB: One of the explanations for the recent EDGES-LOW band 21-cm measurements of a
strong absorption signal around 80~MHz is the presence of an excess radio
background to the Cosmic Microwave Background (CMB). Such excess can be
produced by the decay of unstable particles into small mass dark photons which
have a non-zero mixing angle with electromagnetism. We use the EDGES-LOW band
measurements to derive joint constraints on the properties of the early
galaxies and the parameters of such a particle physics model for the excess
radio background. A Bayesian analysis shows that a high star formation
efficiency and X-ray emission of $4-7 \times 10^{48} ~\rm erg$ per solar mass
in stars are required along with a suppression of star formation in halos with
virial temperatures $\lesssim 2\times 10^4$ K. The same analysis also suggests
a 68 percent credible intervals for the mass of the decaying dark matter
particles, it's lifetime, dark photon mass and the mixing angle of the dark and
ordinary photon oscillation of $[10^{-3.5}, 10^{-2.4}]$ eV, $[10^{1.1},
10^{2.7}]\times 13.8 ~\rm Gyr$, $[10^{-12.2}, 10^{-10}]$ eV and $[10^{-7},
10^{-5.6}]$ respectively. This implies an excess radio background which is
$\approx 5.7$ times stronger than the CMB around 80~MHz. This value is a factor
$\sim 3$ higher than the previous predictions which used a simplified model for
the 21-cm signal. | astro-ph_CO |
Inflation in a closed universe: To derive a power spectrum for energy density inhomogeneities in a closed
universe, we study a spatially-closed inflation-modified hot big bang model
whose evolutionary history is divided into three epochs: an early
slowly-rolling scalar field inflation epoch and the usual radiation and
non-relativistic matter epochs. (For our purposes it is not necessary to
consider a final dark energy dominated epoch.) We derive general solutions of
the relativistic linear perturbation equations in each epoch. The constants of
integration in the inflation epoch solutions are determined from de Sitter
invariant quantum-mechanical initial conditions in the Lorentzian section of
the inflating closed de Sitter space derived from Hawking's prescription that
the quantum state of the universe only include field configurations that are
regular on the Euclidean (de Sitter) sphere section. The constants of
integration in the radiation and matter epoch solutions are determined from
joining conditions derived by requiring that the linear perturbation equations
remain nonsingular at the transitions between epochs. The matter epoch power
spectrum of gauge-invariant energy density inhomogeneities is not a power law,
and depends on spatial wavenumber in the way expected for a generalization to
the closed model of the standard flat-space scale-invariant power spectrum. The
power spectrum we derive appears to differ from a number of other closed
inflation model power spectra derived assuming different (presumably non de
Sitter invariant) initial conditions. | astro-ph_CO |
On the nature of sodium excess objects. I. Data and observed trends: Several studies have reported the presence of sodium excess objects that have
neutral atomic absorption lines at 5895A (NaD) and 8190A that are deeper than
expected based on stellar population models. van Dokkum & Conroy proposed that
low-mass stars are more prevalent in massive early-type galaxies, which may
lead to a strong NaI8190 line strength. It is, however, necessary to test this
prediction against other prominent line indices in optical wavelengths. We
newly identified roughly a thousand NaD excess objects (NEOs) based on the NaD
line strength in the redshift range 0.00<z<0.08 from the SDSS DR7. The novelty
of this work is that galaxies were carefully identified through direct visual
inspection of SDSS images, and we systematically compared the properties of
NEOs and those of a control sample of normal galaxies. Note that the majority
of galaxies with high velocity dispersion (>250km/s) show NaD excess. Most
late-type NEOs have strong Hb line strengths and significant emission lines.
This implies that the presence of ISM and/or dust contributes to the increase
in NaD line strengths observed for these galaxies. In contrast, the majority of
early-type NEOs are predominantly luminous and massive systems. However, we
find that models used to reproduce the NaI8190 line strengths that adopt a
bottom-heavy IMF are not able to reproduce the observed NaD line strengths. By
comparing the observed NaD, Mgb and Fe5270 line strengths with those of the
models, we identify a plausible range of parameters. In these models, the
majority of early-type NEOs are alpha-enhanced ([a/Fe]~0.3), metal-rich
([Z/H]~0.3) and especially Na-enhanced ([Na/Fe]~0.3). Enhanced Na abundance is
a particularly compelling hypothesis for the increase in the strength of the
NaD line index in our early-type NEOs that appear devoid of dust, both in their
SDSS images and spectra. | astro-ph_CO |
The VLA-COSMOS Perspective on the IR-Radio Relation. I. New Constraints
on Selection Biases and the Non-Evolution of the IR/Radio Properties of Star
Forming and AGN Galaxies at Intermediate and High Redshift: VLA 1.4 GHz (rms noise ~0.012 mJy) and MIPS 24 and 70 micron (rms noise ~0.02
and ~1.7 mJy, respectively) observations covering the 2 square degree COSMOS
field are combined with an extensive multi-wavelength data set to study the
evolution of the IR-radio relation at intermediate and high redshift. With
~4500 sources -- of which ~30% have spectroscopic redshifts -- the current
sample is significantly larger than previous ones used for the same purpose.
Both monochromatic IR/radio flux ratios (q24 & q70), as well as the ratio of
the total IR and the 1.4 GHz luminosity (qTIR) are used as indicators for the
IR/radio properties of star forming galaxies and AGN.
Using a sample jointly selected at IR and radio wavelengths in order to
reduce selection biases, we provide firm support for previous findings that the
IR-radio relation remains unchanged out to at least z~1.4. Moreover, based on
data from ~150 objects we also find that the local relation likely still holds
at 2.5<z<5. At redshift z<1.4 we observe that radio-quiet AGN populate the
locus of the IR-radio relation in similar numbers as star forming sources. In
our analysis we employ the methods of survival analysis in order to ensure a
statistically sound treatment of flux limits arising from non-detections. We
determine the observed shift in average IR/radio properties of IR- and radio-
selected populations and show that it can reconcile apparently discrepant
measurements presented in the literature. Finally, we also investigate
variations of the IR/radio ratio with IR and radio luminosity and find that it
hardly varies with IR luminosity but is a decreasing function of radio
luminosity. | astro-ph_CO |
Conserved Quantities in Lemaitre-Tolman-Bondi Cosmology: We study linear perturbations to a Lema{\^\i}tre-Tolman-Bondi (LTB)
background spacetime. Studying the transformation behaviour of the
perturbations under gauge transformations, we construct gauge invariant
quantities. We show, using the perturbed energy conservation equation, that
there are conserved quantities in LTB, in particular a spatial metric trace
perturbation, \zeta_{SMTP}, which is conserved on all scales. We then briefly
extend our discussion to the Lema{\^\i}tre spacetime, and construct
gauge-invariant perturbations in this extension of LTB spacetime. | astro-ph_CO |
How to Falsify the GR+LambdaCDM Model with Galaxy Redshift Surveys: A wide range of models describing modifications to General Relativity have
been proposed, but no fundamental parameter set exists to describe them.
Similarly, no fundamental theory exists for dark energy to parameterize its
potential deviation from a cosmological constant. This motivates a
model-independent search for deviations from the concordance GR+LambdaCDM
cosmological model in large galaxy redshift surveys. We describe two
model-independent tests of the growth of cosmological structure, in the form of
quantities that must equal one if GR+LambdaCDM is correct. The first, epsilon,
was introduced previously as a scale-independent consistency check between the
expansion history and structure growth. The second, upsilon, is introduced here
as a test of scale-dependence in the linear evolution of matter density
perturbations. We show that the ongoing and near-future galaxy redshift surveys
WiggleZ, BOSS, and HETDEX will constrain these quantities at the 5-10% level,
representing a stringent test of concordance cosmology at different redshifts.
When redshift space distortions are used to probe the growth of cosmological
structure, galaxies at higher redshift with lower bias are found to be most
powerful in detecting deviations from the GR+LambdaCDM model. | astro-ph_CO |
Gravitational Waves in Cold Dark Matter: We study the effects of cold dark matter on the propagation of gravitational
waves of astrophysical and primordial origin. We show that the dominant effect
of cold dark matter on gravitational waves from astrophysical sources is a
small frequency dependent modification of the propagation speed of
gravitational waves. However, the magnitude of the effect is too small to be
detected in the near future. We furthermore show that the spectrum of
primordial gravitational waves in principle contains detailed information about
the properties of dark matter. However, depending on the wavelength, the
effects are either suppressed because the dark matter is highly
non-relativistic or because it contributes a small fraction of the energy
density of the universe. As a consequence, the effects of cold dark matter on
primordial gravitational waves in practice also appear too small to be
detectable. | astro-ph_CO |
The effects of non-linearity on the growth rate constraint from velocity
correlation functions: The two-point statistics of the cosmic velocity field, measured from galaxy
peculiar velocity (PV) surveys, can be used as a dynamical probe to constrain
the growth rate of large-scale structures in the universe. Most works use the
statistics on scales down to a few tens of Megaparsecs, while using a
theoretical template based on the linear theory. In addition, while the cosmic
velocity is volume-weighted, the observable line-of-sight velocity two-point
correlation is density-weighted, as sampled by galaxies, and therefore the
density-velocity correlation term also contributes, which has often been
neglected. These effects are fourth order in powers of the linear density
fluctuation $\delta_{\rm L}^4$, compared to $\delta_{\rm L}^2$ of the linear
velocity correlation function, and have the opposite sign. We present these
terms up to $\delta_{\rm L}^4$ in real space based on the standard perturbation
theory, and investigate the effect of non-linearity and the density-velocity
contribution on the inferred growth rate $f\sigma_8$, using $N$-body
simulations. We find that for a next-generation PV survey of volume $\sim {\cal
O}(500 \, h^{-1} \, {\rm Mpc})^3$, these effects amount to a shift of
$f\sigma_8$ by $\sim 10$ per cent and is comparable to the forecasted
statistical error when the minimum scale used for parameter estimation is
$r_{\rm min} = 20 \, h^{-1} \, {\rm Mpc}$. | astro-ph_CO |
A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to
Damped Lyman-alpha Systems - V. Neutral and Ionised Phase Metallicities: The gas-phase and stellar metallicities have proven to be important
parameters to constrain the star formation history of galaxies. However, HII
regions associated with recent star-formation may not have abundances typical
for the galaxy as a whole and it is believed that the bulk of the metals may be
contained in the neutral gas. It is therefore important to directly probe the
metal abundances in the neutral gas, which can be done by using absorption
lines imprinted on a background quasar. Recently, we have presented studies of
the stellar content of a small sample of such quasar absorbers with HI column
densities measured to be in the sub-Damped Lyman-alpha to Damped Lyman-alpha
range. Here, we present observations covering 300 nm to 2.5 microns of emission
line spectra of three of these absorbing-galaxies using the long-slit
spectrograph X-Shooter on the VLT. This allows us to compare the neutral and
ionised phase metallicities in the same objects and relates these measures to
possible signature of low-metallicity gas accretion or outflows of gas enriched
by star formation. Our results suggest that the abundances derived in
absorption along the line-of-sight to background quasars are reliable measures
of the overall galaxy metallicities. In addition to a comparison of abundances
in different phases of the gas, a potential observational consequence of
differences in fueling mechanisms for disc galaxies is the internal
distribution of their chemical abundances. We present some evidence for small
negative metallicity gradients in the three systems. The flat slopes are in
line with the differences observed between the two phases of the gas. These
results suggest that a comparison of the HI and HII metallicities is a robust
indicator of abundance gradients in high-redshift galaxies and do not favour
the presence of infall of fresh gas in these objects. | astro-ph_CO |
Big Bang Nucleosynthesis with an Inhomogeneous Primordial Magnetic Field
Strength: We investigate the effect on the Big Bang Nucleosynthesis (BBN) from the
presence of a stochastic primordial magnetic field (PMF) whose strength is
spatially inhomogeneous. We assume a uniform total energy density and a
gaussian distribution of field strength. In this case, domains of different
temperatures exist in the BBN epoch due to variations in the local PMF. We show
that in such case, the effective distribution function of particle velocities
averaged over domains of different temperatures deviates from the
Maxwell-Boltzmann distribution. This deviation is related to the scale
invariant strength of the PMF energy density $\rho_{\rm Bc}$ and the
fluctuation parameter $\sigma_{\rm B}$. We perform BBN network calculations
taking into account the PMF strength distribution, and deduce the element
abundances as functions of the baryon-to-photon ratio $\eta$, $\rho_{\rm Bc}$,
and $\sigma_{\rm B}$. We find that the fluctuations of the PMF reduces the
$^7$Be production and enhances D production. We analyze the averaged
thermonuclear reaction rates compared with those of a single temperature, and
find that the averaged charged-particle reaction rates are very different.
Finally, we constrain the parameters $\rho_{\rm Bc}$ and $\sigma_{\rm B}$ from
observed abundances of $^4$He and D, and find that the $^7$Li abundance is
significantly reduced. We also find that if the $\eta$ value during BBN was
larger than the present-day value due to a dissipation of the PMF or a
radiative decay of exotic particles after BBN or if the stellar depletion of
$^7$Li occurred, abundances of all light elements can be consistent with
observational constraints. | astro-ph_CO |
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