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Stellar Populations of Lyman-alpha Emitters at z=4.86: A Comparison to
$z\sim5$ LBGs: (abridged) We present a study of stellar population of LAEs at z=4.86 in
GOODS-N and its flanking field. With the publicly available IRAC data in
GOODS-N and further IRAC observations in the flanking fields, we select five
LAEs which are not contaminated by neighboring objects in IRAC images and
construct their observed SEDs with I_c, z', IRAC 3.6micron, and 4.5micron band
photometry. The SEDs cover the rest-frame UV to optical wavelengths. We derive
stellar masses, ages, color excesses, and star formation rates of five LAEs
using SED fitting method. Assuming the constant star formation history, we find
that the stellar masses range from 10^8 to $10^{10} Msun with the median value
of 2.5x10^9 Msun. The derived ages range from very young ages (7.4 Myr) to 437
Myr with a median age of 25 Myr. The color excess E(B-V) are between 0.1-0.4
mag. Star formation rates are 55-209 Msun/yr. A comparison of the stellar
populations is made between three LAEs and 88 LBGs selected at the same
redshift, in the same observed field, and down to the same limit of the
rest-frame UV luminosity. These three LAEs are the brightest and reddest
samples among the whole LAE samples at z=4.86. The LAEs distribute at the
relatively faint part of UV-luminosity distribution of LBGs. Deriving the
stellar properties of the LBGs by fitting their SEDs with the same model
ensures that model difference does not affect the comparison. It is found that
the stellar properties of the LAEs lie on distributions of those of LBGs. On
average, the LAEs show less dust extinction, and lower star formation rates
than LBGs, while the stellar mass of LAEs nearly lies in the middle part of the
mass distribution of LBGs. However, the stellar properties of LAEs and LBGs are
similar at the fixed UV or optical luminosity. We also examine the relations
between the output properties from the SED fitting and the rest-frame Lya
equivalent width. | Cosmological perturbations from statistical thermal fluctuations: Cosmological perturbations due to statistical thermal fluctuations in a
single fluid characterized by an arbitrary equation of state are computed.
Formulas to predict the scalar and tensor perturbation spectra and
nongaussianity parameters at a given temperature are derived. These results are
relevant to any cosmological scenario where cosmic structures may have been
seeded thermally instead of originating purely from quantum vacuum
fluctuations. |
Cosmic shear measurement with maximum likelihood and maximum a
posteriori inference: We investigate the problem of noise bias in maximum likelihood and maximum a
posteriori estimators for cosmic shear. We derive the leading and
next-to-leading order biases and compute them in the context of galaxy
ellipticity measurements, extending previous work on maximum likelihood
inference for weak lensing. We show that a large part of the bias on these
point estimators can be removed using information already contained in the
likelihood when a galaxy model is specified, without the need for external
calibration. We test these bias-corrected estimators on simulated galaxy images
similar to those expected from planned space-based weak lensing surveys, with
promising results. We find that the introduction of an intrinsic shape prior
can help with mitigation of noise bias, such that the maximum a posteriori
estimate can be made less biased than the maximum likelihood estimate.
Second-order terms offer a check on the convergence of the estimators, but are
largely sub-dominant. We show how biases propagate to shear estimates,
demonstrating in our simple setup that shear biases can be reduced by orders of
magnitude and potentially to within the requirements of planned space-based
surveys at mild signal-to-noise. We find that second-order terms can exhibit
significant cancellations at low signal-to-noise when Gaussian noise is
assumed, which has implications for inferring the performance of
shear-measurement algorithms from simplified simulations. We discuss the
viability of our point estimators as tools for lensing inference, arguing that
they allow for the robust measurement of ellipticity and shear. | Non-Gaussianity and Gravitational Waves from Quadratic and
Self-interacting Curvaton: In this paper we consider how non-Gaussianity of the primordial density
perturbation and the amplitude of gravitational waves from inflation can be
used to determine parameters of the curvaton scenario for the origin of
structure. We show that in the simplest quadratic model, where the curvaton
evolves as a free scalar field, measurement of the bispectrum relative to the
power spectrum, fNL, and the tensor-to-scalar ratio can determine both the
expectation value of the curvaton field during inflation and its dimensionless
decay rate relative to the curvaton mass. We show how these predictions are
altered by the introduction of self-interactions, in models where higher-order
corrections are determined by a characteristic mass scale and discuss how
additional information about primordial non-Gaussianity and scale dependence
may constrain curvaton interactions. |
Cosmographic constraints on a class of Palatini f(R) gravity: Modified gravity, known as $f(R)$ gravity, has presently been applied to
Cosmology as a realistic alternative to dark energy. For this kind of gravity
the expansion of the Universe may accelerate while containing only baryonic and
cold dark matter. The aim of the present investigation is to place cosmographic
constraints on the class of theories of the form $f(R)=R - \alpha/R^n$ within
the Palatini approach. Although extensively discussed in recent literature and
confronted with several observational data sets, cosmological tests are indeed
inconclusive about the true signal of $n$ in this class of theories. This is
particularly important to define which kind of corrections (infra-red or
high-energy) to general relativity this class of theory indeed represent. We
shed some light on this question by examining the evolution of the deceleration
parameter $q(z)$ for these theories. We find that for a large range of
$\alpha$, models based on $f(R) = R - \alpha/R^{n}$ gravity in the Palatini
approach can only have positive values for $n$, placing thus a broad
restriction on this class of gravity. | Testing Weak Lensing Maps With Redshift Surveys: A Subaru Field: We use a dense redshift survey in the foreground of the Subaru GTO2deg^2 weak
lensing field (centered at $\alpha_{2000}$ = 16$^h04^m44^s$;$\delta_{2000}$
=43^\circ11^{\prime}24^{\prime\prime}$) to assess the completeness and comment
on the purity of massive halo identification in the weak lensing map. The
redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts
measured with the Hectospec on the MMT. Among the weak lensing peaks with a
signal-to-noise greater that 4.25, 2/3 correspond to individual massive
systems; this result is essentially identical to the Geller et al. (2010) test
of the Deep Lens Survey field F2. The Subaru map, based on images in
substantially better seeing than the DLS, enables detection of less massive
halos at fixed redshift as expected. We demonstrate that the procedure adopted
by Miyazaki et al. (2007) for removing some contaminated peaks from the weak
lensing map improves agreement between the lensing map and the redshift survey
in the identification of candidate massive systems. |
Planetary nebulae in the elliptical galaxy NGC 821: kinematics and
distance determination: Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its
FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula
(PN) detections and PN velocity measurements in the flattened elliptical galaxy
NGC 821. A comparison with the detections reported previously by the Planetary
Nebula Spectrograph (PN.S) group indicates that we have confirmed most of their
detections. The velocities measured by the two groups, using different
telescopes, spectrographs and slitless techniques, are in good agreement. We
have built a combined sample of 167 PNs and have confirmed the keplerian
decline of the line-of-sight velocity dispersion reported previously. We also
confirm misaligned rotation from the combined sample. A dark matter halo may
exist around this galaxy, but it is not needed to keep the PN velocities below
the local escape velocity as calculated from the visible mass. We have measured
the m(5007) magnitudes of 145 PNs and produced a statistically complete sample
of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to
estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also
estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a
PNLF distance determination. The PNLF distance modulus is smaller than the
surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic
information permits to rule out the idea that a shorter PNLF distance could be
produced by the contamination of the PNLF by background galaxies with emission
lines redshifted into the on-band filter transmission curve. | Do radio mini-halos and gas heating in cool-core clusters have a common
origin?: In this letter we present a study of the central regions of cool-core
clusters hosting radio mini-halos, which are diffuse synchrotron sources
extended on cluster-scales surrounding the radio-loud brightest cluster galaxy.
We aim to investigate the interplay between the thermal and non-thermal
components in the intra-cluster medium in order to get more insights into these
radio sources, whose nature is still unclear. It has recently been proposed
that turbulence plays a role for heating the gas in cool cores. By assuming
that mini-halos are powered by the same turbulence, we expect that the
integrated radio luminosity of mini-halos, $\nu P_{\nu}$, depends on the
cooling flow power, $P_{\rm CF}$, which in turn constrains the energy available
for the non-thermal components and emission in the cool-core region. We carried
out a homogeneous re-analysis of X-ray Chandra data of the largest sample of
cool-core clusters hosting radio mini-halos currently available ($\sim$ 20
objects), finding a quasi-linear correlation, $\nu P_{\nu} \propto P_{\rm
CF}^{0.8}$. We show that the scenario of a common origin of radio mini-halos
and gas heating in cool-core clusters is energetically viable, provided that
mini-halos trace regions where the magnetic field strength is $B \gg 0.5\,
\mu$G . |
Cosmological searches for the neutrino mass scale and mass ordering: In this thesis, I describe a number of recent important developments in
neutrino cosmology on three fronts. Firstly, focusing on Large-Scale Structure
(LSS) data, I will show that current cosmological probes contain a wealth of
information on the sum of the neutrino masses. I report on the analysis leading
to the currently best upper limit on the sum of the neutrino masses of
$0.12\,{\rm eV}$. I show how cosmological data exhibits a weak preference for
the normal neutrino mass ordering because of parameter space volume effects,
and propose a simple method to quantify this preference. Secondly, I will
discuss how galaxy bias represents a severe limitation towards fully
capitalizing on the neutrino information hidden in LSS data. I propose a method
for calibrating the scale-dependent galaxy bias using CMB lensing-galaxy
cross-correlations. Moreover, in the presence of massive neutrinos, the usual
definition of bias becomes inadequate, as it leads to a scale-dependence on
large scales which has never been accounted for. I show that failure to define
the bias appropriately will be a problem for future LSS surveys, and propose a
simple recipe to account for the effect of massive neutrinos on galaxy bias.
Finally, I discuss implications of correlations between neutrino parameters and
other cosmological parameters. In non-phantom dynamical dark energy models, the
upper limit on the sum of the neutrino masses becomes tighter than the
$\Lambda$CDM limit. Therefore, such models exhibit an even stronger preference
for the normal ordering, and their viability could be jeopardized should
near-future laboratory experiments determine that the mass ordering is
inverted. I then discuss correlations between neutrino and inflationary
parameters. I find that our determination of inflationary parameters is stable
against assumptions about the neutrino sector. (abridged) | Testing Modified Newtonian Dynamics with Rotation Curves of Dwarf and
Low Surface Brightness Galaxies: Dwarf and low surface brightness galaxies are ideal objects to test modified
Newtonian dynamics (MOND), because in most of these galaxies the accelerations
fall below the threshold below where MOND supposedly applies. We have selected
from the literature a sample of 27 dwarf and low surface brightness galaxies.
MOND is successful in explaining the general shape of the observed rotation
curves for roughly three quarters of the galaxies in the sample presented here.
However, for the remaining quarter, MOND does not adequately explain the
observed rotation curves. Considering the uncertainties in distances and
inclinations for the galaxies in our sample, a small fraction of poor MOND
predictions is expected and is not necessarily a problem for MOND. We have also
made fits taking the MOND acceleration constant, a_0, as a free parameter in
order to identify any systematic trends. We find that there appears to be a
correlation between central surface brightness and the best-fit value of a_0,
in the sense that lower surface brightness galaxies tend to have lower a_0.
However, this correlation depends strongly on a small number of galaxies whose
rotation curves might be uncertain due to either bars or warps. Without these
galaxies, there is less evidence of a trend, but the average value we find for
a_0 ~ 0.7*10^-8 cm s^-2 is somewhat lower than derived from previous studies.
Such lower fitted values of a_0 could occur if external gravitational fields
are important. |
A Large Scale Structure at Redshift 1.71 in the Lockman Hole: We previously identified LH146, a diffuse X-ray source in the Lockman Hole,
as a galaxy cluster at redshift 1.753. The redshift was based on one
spectroscopic value, buttressed by seven additional photometric redshifts. We
here confirm the previous spectroscopic redshift and present concordant
spectroscopic redshifts for an additional eight galaxies. The average of these
nine redshifts is 1.714 +/- 0.012 (error on mean). Scrutiny of the galaxy
distribution in redshift and the plane of the sky shows that there are two
concentrations of galaxies near the X-ray source. In addition there are three
diffuse X-ray sources spread along the axis connecting the galaxy
concentrations. LH146 is one of these three and lies approximately at the
center of the two galaxy concentrations and the outer two diffuse X-ray
sources. We thus conclude that LH146 is at the redshift initially reported but
it is not a single virialized galaxy cluster as previously assumed. Rather it
appears to mark the approximate center of a larger region containing more
objects. For brevity we term all these objects and their alignments as large
scale structure. The exact nature of LH146 itself remains unclear. | Parameterizing dark sector perturbations via equations of state: The evolution of perturbations is a crucial part of the phenomenology of the
dark sector cosmology. We advocate parameterizing these perturbations using
equations of state for the entropy perturbation and the anisotropic stress. For
small perturbations, these equations of state will be linear in the density,
velocity and metric perturbations, and in principle these can be related back
to the field content of the underlying model allowing for confrontation with
observations. We illustrate our point by constructing gauge invariant entropy
perturbations for theories where the dark sector Lagrangian is a general
function of a scalar field, its first and second derivatives, and the metric
and its first derivative, ${\cal L}={\cal
L}(\phi,\partial_\mu\phi,\partial_\mu\partial_\nu\phi,g_{\mu\nu},\partial_{\alpha}g_{\mu\nu})$.
As an example, we show how to apply this approach to the case of models of
Kinetic Gravity Braiding. |
Robust Foregrounds Removal for 21-cm Experiments: Direct detection of the Epoch of Reionization via the redshifted 21-cm line
will have unprecedented implications on the study of structure formation in the
early Universe. To fulfill this promise current and future 21-cm experiments
will need to detect the weak 21-cm signal over foregrounds several order of
magnitude greater. This requires accurate modeling of the galactic and
extragalactic emission and of its contaminants due to instrument chromaticity,
ionosphere and imperfect calibration. To solve for this complex modeling, we
propose a new method based on Gaussian Process Regression (GPR) which is able
to cleanly separate the cosmological signal from most of the foregrounds
contaminants. We also propose a new imaging method based on a maximum
likelihood framework which solves for the interferometric equation directly on
the sphere. Using this method, chromatic effects causing the so-called "wedge"
are effectively eliminated (i.e. deconvolved) in the cylindrical ($k_{\perp},
k_{\parallel}$) power spectrum. | Star Formation Properties of Isolated Blue Compact Galaxies: We report H$\alpha$ observations of a sample of very isolated blue compact
galaxies (BCGs) located in the direction of large cosmic voids obtained to
understand their stellar population compositions, the present star formation
(SF) properties, and their star formation histories (SFHs). Our observations
were combined with photometric data from the Sloan Digital Sky Survey (SDSS)
and near-infrared data from the Two Micron All Sky Survey (2MASS), wherever
such data were available. The combined data sets were compared with predictions
of evolutionary synthesis models by Bruzual & Charlot (2003a, 2003b). Current
star formation rates (SFRs) were determined from the H$\alpha$ measurements,
and simplified star formation histories were derived from broad-band and
H$\alpha$ photometry and comparisons with the models. We found that the star
formation rates range within 0.1--1.0 M$_{\odot}$ yr$^{-1}$, with a median rate
of 0.6 M$_{\odot}$ yr$^{-1}$. The observed galaxy colours are better explained
by the combination of a continuous SF process with a recent instantaneous SF
burst, than by a combination of several instantaneous bursts, as has been
suggested previously. We compare our results for the star formation rate of the
sample galaxies with that of samples of dwarf galaxies in the Virgo cluster and
find that the BCGs have significantly stronger SFRs. The BCGs follow the
correlation between H$\alpha$ emission and starlight found for dwarf galaxies
in the Virgo Cluster and for other BCGs. |
PSpectRe: A Pseudo-Spectral Code for (P)reheating: PSpectRe is a C++ program that uses Fourier-space pseudo-spectral methods to
evolve interacting scalar fields in an expanding universe. PSpectRe is
optimized for the analysis of parametric resonance in the post-inflationary
universe, and provides an alternative to finite differencing codes, such as
Defrost and LatticeEasy. PSpectRe has both second- (Velocity-Verlet) and
fourth-order (Runge-Kutta) time integrators. Given the same number of spatial
points and/or momentum modes, PSpectRe is not significantly slower than finite
differencing codes, despite the need for multiple Fourier transforms at each
timestep, and exhibits excellent energy conservation. Further, by computing the
post-resonance equation of state, we show that in some circumstances PSpectRe
obtains reliable results while using substantially fewer points than a finite
differencing code. PSpectRe is designed to be easily extended to other problems
in early-universe cosmology, including the generation of gravitational waves
during phase transitions and pre-inflationary bubble collisions. Specific
applications of this code will be pursued in future work. | Analytic Methods for Cosmological Likelihoods: We present general, analytic methods for Cosmological likelihood analysis and
solve the "many-parameters" problem in Cosmology. Maxima are found by Newton's
Method, while marginalization over nuisance parameters, and parameter errors
and covariances are estimated by analytic marginalization of an arbitrary
likelihood function with flat or Gaussian priors. We show that information
about remaining parameters is preserved by marginalization. Marginalizing over
all parameters, we find an analytic expression for the Bayesian evidence for
model selection. We apply these methods to data described by Gaussian
likelihoods with parameters in the mean and covariance. This method can speed
up conventional likelihood analysis by orders of magnitude when combined with
Monte-Carlo Markov Chain methods, while Bayesian model selection becomes
effectively instantaneous. |
Excess Clustering on Large Scales in the MegaZ DR7 Photometric Redshift
Survey: We observe a large excess of power in the statistical clustering of Luminous
Red Galaxies in the photometric SDSS galaxy sample called MegaZ DR7. This is
seen over the lowest multipoles in the angular power spectra C_{\ell} in four
equally spaced redshift bins between 0.45 < z < 0.65. However, it is most
prominent in the highest redshift band at ~ 4 sigma and it emerges at an
effective scale k ~ 0.01 h Mpc^{-1}. Given that MegaZ DR7 is the largest cosmic
volume galaxy survey to date (3.3 (Gpc h^{-1})^3) this implies an anomaly on
the largest physical scales probed by galaxies. Alternatively, this signature
could be a consequence of it appearing at the most systematically susceptible
redshift. There are several explanations for this excess power that range from
systematics to new physics. This could have important consequences for the next
generation of galaxy surveys or the LCDM model. We test the survey, data and
excess power, as well as possible origins. | Measuring subhalo mass in redMaPPer clusters with CFHT Stripe 82 Survey: We use the shear catalog from the CFHT Stripe-82 Survey to measure the
subhalo masses of satellite galaxies in redMaPPer clusters. Assuming a Chabrier
Initial Mass Function (IMF) and a truncated NFW model for the subhalo mass
distribution, we find that the sub-halo mass to galaxy stellar mass ratio
increases as a function of projected halo-centric radius $r_p$, from $M_{\rm
sub}/M_{\rm star}=4.43^{+ 6.63}_{- 2.23}$ at $r_p \in [0.1,0.3]$ $h^{-1}Mpc$ to
$M_{\rm sub}/M_{\rm star}=75.40^{+ 19.73}_{- 19.09}$ at $r_p \in [0.6,0.9]$
$h^{-1}Mpc$. We also investigate the dependence of subhalo masses on stellar
mass by splitting satellite galaxies into two stellar mass bins:
$10<\log(M_{\rm star}/M_{\rm sun})<10.5$ and $11<\log(M_{\rm star}/M_{\rm
sun})<12$. The best-fit subhalo mass of the more massive satellite galaxy bin
is larger than that of the less massive satellites: $\log(M_{\rm sub}/M_{\rm
sun})=11.14 ^{+ 0.66 }_{- 0.73}$ ($M_{\rm sub}/M_{\rm
star}=19.5^{+19.8}_{-17.9}$) versus $\log(M_{\rm sub}/M_{\rm sun})=12.38 ^{+
0.16 }_{- 0.16}$ ($M_{\rm sub}/M_{\rm star}=21.1^{+7.4}_{-7.7}$). |
Modified Virial Formulae and the Theory of Mass Estimators: We show how to estimate the enclosed mass from the observed motions of an
ensemble of test particles. Traditionally, this problem has been attacked
through virial or projected mass estimators. Here, we examine and extend these
systematically, and show how to construct an optimal estimator for any given
assumption as to the potential. The estimators do not explicitly depend on any
properties of the density of the test objects, which is desirable as in
practice such information is dominated by selection effects. As particular
examples, we also develop estimators tailored for the problem of estimating the
mass of the Hernquist or NFW dark matter haloes from the projected positions
and velocities of stars. | Strong constraints on clustered primordial black holes as dark matter: The idea of dark matter in the form of primordial black holes has seen a
recent revival triggered by the LIGO detection of gravitational waves from
binary black hole mergers. In this context, it has been argued that a large
initial clustering of primordial black holes can help alleviate the strong
constraints on this scenario. In this work, we show that on the contrary, with
large initial clustering the problem is exacerbated and constraints on
primordial black hole dark matter become overwhelmingly strong. |
Emerging spatial curvature can resolve the tension between high-redshift
CMB and low-redshift distance ladder measurements of the Hubble constant: The measurements of the Hubble constant reveal a tension between
high-redshift (CMB) and low-redshift (distance ladder) constraints. So far
neither observational systematics nor new physics has been successfully
implemented to explain this tension away. This paper present a new solution to
the Hubble constant problem. The solution is based on the Simsilun simulation
(relativistic simulation of the large scale structure of the Universe) with the
ray-tracing algorithm implemented. The initial conditions for the Simsilun
simulation were set up as perturbations around the $\Lambda$CDM model. However,
unlike in the Standard Cosmological Model (i.e. $\Lambda$CDM model +
perturbations), within the Simsilun simulation relativistic and nonlinear
evolution of cosmic structures leads to the phenomenon of emerging spatial
curvature, where the mean spatial curvature evolves from spatial flatness of
the early universe towards slightly curved present-day universe. Consqeuently,
the present-day expansion rate is slightly faster compared to the spatially
flat $\Lambda$CDM model. The results of the ray-tracing analysis show that the
universe which starts with initial conditions consistent with the Planck
constraints should have the Hubble constant $H_0 = 72.5 \pm 2.1$ km s$^{-1}$
Mpc$^{-1}$. When the Simsilun simulation was re-run with no inhomogeneities
imposed, the Hubble constant inferred within such a homogeneous simulation was
$H_0 = 68.1 \pm 2.0$ km s$^{-1}$ Mpc$^{-1}$. Thus, the inclusion of nonlinear
relativistic evolution that leads to the emergence of the spatial curvature can
explain why the low-redshift measurements favour higher values compared to
high-redshift constraints and alleviate the tension between the CMB and
distance ladder measurements of the Hubble constant. | Relieving the Tension between Weak Lensing and Cosmic Microwave
Background with Interacting Dark Matter and Dark Energy Models: We constrain interacting dark matter and dark energy (IDMDE) models using a
450-degree-square cosmic shear data from the Kilo Degree Survey (KiDS) and the
angular power spectra from Planck's latest cosmic microwave background
measurements. We revisit the discordance problem in the standard Lambda cold
dark matter ($\Lambda$CDM) model between weak lensing and Planck datasets and
extend the discussion by introducing interacting dark sectors. The IDMDE models
are found to be able to alleviate the discordance between KiDS and Planck as
previously inferred from the $\Lambda$CDM model, and moderately favored by a
combination of the two datasets. |
The extended Baryon Oscillation Spectroscopic Survey (eBOSS): testing a
new approach to measure the evolution of the structure growth: The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is one of the
first of a new generation of galaxy redshift surveys that will cover a large
range in redshift with sufficient resolution to measure the baryon acoustic
oscillations (BAO) signal. For surveys covering a large redshift range we can
no longer ignore cosmological evolution, meaning that either the redshift
shells analysed have to be significantly narrower than the survey, or we have
to allow for the averaging over evolving quantities. Both of these have the
potential to remove signal: analysing small volumes increases the size of the
Fourier window function, reducing the large-scale information, while averaging
over evolving quantities can, if not performed carefully, remove differential
information. It will be important to measure cosmological evolution from these
surveys to explore and discriminate between models. We apply a method to
optimally extract this differential information to mock catalogues designed to
mimic the eBOSS quasar sample. By applying a set of weights to extract redshift
space distortion measurements as a function of redshift, we demonstrate an
analysis that does not invoke the problems discussed above. We show that our
estimator gives unbiased constraints. | Searching for bulk motions in the ICM of massive, merging clusters with
Chandra CCD data: We search for bulk motions in the intracluster medium (ICM) of massive
clusters showing evidence of an ongoing or recent major merger with spatially
resolved spectroscopy in {\sl Chandra} CCD data. We identify a sample of 6
merging clusters with $>$150 ks {\sl Chandra} exposure in the redshift range
$0.1 < z < 0.3$. By performing X-ray spectral analysis of projected ICM regions
selected according to their surface brightness, we obtain the projected
redshift maps for all of these clusters. After performing a robust analysis of
the statistical and systematic uncertainties in the measured X-ray redshift
$z_{\rm X}$, we check whether or not the global $z_{\rm X}$ distribution
differs from that expected when the ICM is at rest. We find evidence of
significant bulk motions at more than 3$\sigma$ in A2142 and A115, and less
than 2$\sigma$ in A2034 and A520. Focusing on single regions, we identify
significant localized velocity differences in all of the merging clusters. We
also perform the same analysis on two relaxed clusters with no signatures of
recent mergers, finding no signs of bulk motions, as expected. Our results
indicate that deep {\sl Chandra} CCD data enable us to identify the presence of
bulk motions at the level of $v_{\rm BM} >$ 1000\ ${\rm km\ s^{-1}}$ in the ICM
of massive merging clusters at $0.1<z<0.3$. Although the CCD spectral
resolution is not sufficient for a detailed analysis of the ICM dynamics, {\sl
Chandra} CCD data constitute a key diagnostic tool complementing X-ray
bolometers on board future X-ray missions. |
Temporal Smearing of Transient Radio Sources by the Intergalactic Medium: The temporal smearing of impulsive radio events at cosmological redshifts
probes the properties of the ionized Inter-Galactic Medium (IGM). We relate the
degree of temporal smearing and the profile of a scattered source to the
evolution of turbulent structure in the IGM as a function of redshift. We
estimate the degree of scattering expected by analysing the contributions to
the Scattering Measure (SM) of the various components of baryonic matter
embedded in the IGM, including the diffuse IGM, intervening galaxies and
intracluster gas. These estimates predict that the amount of temporal smearing
expected at 300\,MHz is typically as low as ~1 ms and suggests that these
bursts may be detectable with low frequency widefield arrays. A generalization
of the DM-SM relation observed for Galactic scattering to the densities and
turbulent conditions relevant to the IGM suggests that scattering measures of
order 10^{-6} kpc m {-20/3} would be expected at z ~ 1. This scattering is
sufficiently low that its effects would, for most lines of sight, not be
manifest in existing observations of the scattering broadening in images of
extragalactic compact sources. The redshift dependence of the temporal smearing
discriminates between scattering that occurs in the host galaxy of the burst
and the IGM, with tau_host \propto (1+z)^{-3} if the scattering probes length
scales below the inner scale of the turbulence or tau_host \propto
(1+z)^{-17/5} if the turbulence follows a Kolmogorov spectrum. This differs
strongly from the expected IGM scaling tau_{IGM} ~ z^2 for z < 1 and
(1+z)^{0.2-0.5} for z >> 1. | CMB constraints on a physical model of reionization: We study constraints on allowed reionization histories by comparing
predictions of a physical semi-numerical model with secondary temperature and
polarization anisotropies of the cosmic microwave background (CMB). Our model
has four free parameters characterizing the evolution of ionizing efficiency
$\zeta$ and the minimum mass $M_{\mathrm{min}}$ of haloes that can produce
ionizing radiation. Comparing the model predictions with the presently
available data of the optical depth $\tau$ and kinematic Sunyaev-Zeldovich
signal, we find that we can already rule out a significant region of the
parameter space. We limit the duration of reionization $\Delta
z=1.30^{+0.19}_{-0.60}$ ($\Delta z < 2.9$ at $99\%$ C.L.), one of the tightest
constraints on the parameter. The constraints mildly favour $M_{\mathrm{min}}
\gtrsim 10^9 \mathrm{M}_{\odot}$ (at $68\%$ C.L.) at $z \sim 8$, thus
indicating the presence of reionization feedback. Our analysis provides an
upper bound on the secondary $B$-mode amplitude $D_{l=200}^{BB}<18$ nK$^2$ at
$99\%$ C.L. We also study how the constraints can be further tightened with
upcoming space and ground-based CMB missions. Our study, which relies solely on
CMB data, has implications not only for upcoming CMB surveys for detecting
primordial gravitational waves but also redshifted 21 cm studies. |
Optimising growth of structure constraints on modified gravity: We use growth of structure data to constrain the effective field theory of
dark energy. Considering as case study Horndeski theories with the speed of
gravitational waves equal to that of light, we show how constraints on the free
parameters and the large-scale structure phenomenological functions can be
improved by two ingredients: firstly by complementing the set of redshift-space
distortions data with the three recent measurements of the growth rate $f$ and
the amplitude of matter fluctuations $\sigma_8$ from the VIPERS and SDSS
collaborations; secondly by applying a local Solar System bound on the
variation of the Newton constant. This analysis allows us to conclude that:
$i)$ despite firmly restricting the predictions of weaker gravity, the
inclusion of the Solar System bound does not prevent suppressed growth relative
to the standard model $\Lambda$CDM at low redshifts; $ii)$ the same bound in
conjunction with the growth of structure data strongly restricts the redshift
evolution of the gravitational slip parameter to be close to unity and the
present value is constrained to one at the $10^{-3}$ level; $iii)$ the growth
of structure data favours a fifth force contribution to the effective
gravitational coupling at low redshifts and at more than one sigma at present
time. | Bars rejuvenating bulges? Evidence from stellar population analysis: We obtained stellar ages and metallicities via spectrum fitting for a sample
of 575 bulges with spectra available from the Sloan Digital Sky Survey. The
structural properties of the galaxies have been studied in detail in Gadotti
(2009b) and the sample contains 251 bulges in galaxies with bars. Using the
whole sample, where galaxy stellar mass distributions for barred and unbarred
galaxies are similar, we find that bulges in barred and unbarred galaxies
occupy similar loci in the age vs. metallicity plane. However, the distribution
of bulge ages in barred galaxies shows an excess of populations younger than ~
4 Gyr, when compared to bulges in unbarred galaxies. Kolmogorov-Smirnov
statistics confirm that the age distributions are different with a significance
of 99.94%. If we select sub-samples for which the bulge stellar mass
distributions are similar for barred and unbarred galaxies, this excess
vanishes for galaxies with bulge mass log M < 10.1 M_Sun while for more massive
galaxies we find a bimodal bulge age distribution for barred galaxies only,
corresponding to two normal distributions with mean ages of 10.4 and 4.7 Gyr.
We also find twice as much AGN among barred galaxies, as compared to unbarred
galaxies, for low-mass bulges. By combining a large sample of high quality data
with sophisticated image and spectral analysis, we are able to find evidence
that the presence of bars affect the mean stellar ages of bulges. This lends
strong support to models in which bars trigger star formation activity in the
centers of galaxies. |
Exact Third-Order Density Perturbation and One-Loop Power Spectrum in
General Dark Energy Models: Under the standard perturbation theory (SPT), we obtain the fully consistent
third-order density fluctuation and kernels for the general dark energy models
without using the Einstein-de Sitter (EdS) universe assumption for the first
time. We also show that even though the temporal and spatial components of the
SPT solutions can not be separable, one can find the exact solutions to any
order in general dark energy models. With these exact solutions, we obtain the
less than \% error correction of one-loop matter power spectrum compared to
that obtained from the EdS assumption for $k = 0.1 {\rm h\, Mpc}^{-1}$ mode at
$z = 0$ (1, 1.5). Thus, the EdS assumption works very well at this scale.
However, if one considers the correction for $P_{13}$, the error is about 6 (9,
11) \% for the same mode at $z = 0$ (1, 1.5). One absorbs $P_{13}$ into the
linear power spectrum in the renormalized perturbation theory (RPT) and thus
one should use the exact solution instead of the approximation one. The error
on the resummed propagator $N$ of RPT is about 14 (8, 6) \% at $z =0$ (1, 1.5)
for $k = 0.4 {\rm h\, Mpc}^{-1}$. For $k = 1 {\rm h\, Mpc}^{-1}$, the error
correction of the total matter power spectrum is about 3.6 (4.6, 4.5) \% at $z
= 0$ (1, 1.5). Upcoming observation is required to archive the sub-percent
accuracy to provide the strong constraint on the dark energy and this
consistent solution is prerequisite for the model comparison. | Perturbatively including inhomogeneities in axion inflation: Axion inflation, i.e. an axion-like inflaton coupled to an Abelian gauge
field through a Chern-Simons interaction, comes with a rich and testable
phenomenology. This is particularly true in the strong backreaction regime,
where the gauge field production heavily impacts the axion dynamics. Lattice
simulations have recently demonstrated the importance of accounting for
inhomogeneities of the axion field in this regime. We propose a perturbative
scheme to account for these inhomogeneities while maintaining high
computational efficiency. Our goal is to accurately capture deviations from the
homogeneous axion field approximation within the perturbative regime as well as
self-consistently determine the onset of the non-perturbative regime. |
Searching for the Synchrotron Cosmic Web Again: A replication attempt: We follow up on the surprising recent announcement by Vernstrom et al. (2021)
of the detection of the synchrotron cosmic web. We attempt to reproduce their
detection with new observations with the Phase II, extended configuration of
the Murchison Widefield Array at \SI{118.5}{\mega \hertz}. We reproduce their
detection methodology by stacking pairs of nearby luminous red galaxies (LRGs)
-- used as tracers for clusters and galaxy groups -- contained in our low
frequency radio observations. We show that our observations are significantly
more sensitive than those used in Vernstrom et al., and that our angular
sensitivity is sufficient. And yet, we make no statistically significant
detection of excess radio emission along the bridge spanning the LRG pairs.
This non-detection is true both for the original LRG pair catalogue as used in
Vernstrom et al., as well as for other larger catalogues with modified
selection criteria. Finally, we return to the original data sets used in
Vernstrom et al., and find that whilst we clearly reproduce the excess X-ray
emission from ROSAT, we are not able to reproduce any kind of broad and
extended excess intercluster filamentary emission using the original 118.5 MHz
MWA survey data. In the interests of understanding this result, as part of this
paper we release images of the 14 fields used in this study, the final stacked
images, as well as key components of our stacking and modelling code. | Recoiling Black Holes in Merging Galaxies: Gravitational-wave (GW) recoil of merging supermassive black holes (SMBHs)
may influence the co-evolution of SMBHs and their host galaxies. We examine
this possibility using SPH/N-body simulations of gaseous galaxy mergers in
which the merged BH receives a recoil kick. With our suite of over 200 merger
simulations, we identify systematic trends in the behavior of recoiling BHs.
Our main results are as follows. (1) While BHs kicked at nearly the central
escape speed (vesc) are essentially "lost" to the galaxy, in gas rich mergers,
BHs kicked with up to about 0.7 vesc may be confined to the central few kpc of
the galaxy. (2) The inflow of cold gas during a gas-rich major merger may cause
a rapid increase in central escape speed; in such cases recoil trajectories
will depend on the timing of the BH merger relative to the change in vesc. (3)
Recoil events generally reduce the lifetimes of bright active galactic nuclei
(AGN) but may actually extend AGN lifetimes at lower luminosities. (4)
Recoiling AGN may be observable via kinematic offsets (v > 500 km s^-1) or
spatial offsets (R > 1 kpc) for lifetimes of up to about 10 - 100 Myr. (5)
Rapidly-recoiling BHs may be up to about 5 times less massive than their
stationary counterparts. These mass deficits lower the normalization of the M -
sigma relation and contribute to both intrinsic and overall scatter. (6)
Finally, the displacement of AGN feedback by a recoil event causes higher
central star formation rates in the merger remnant, thereby extending the
starburst phase of the merger and creating a denser, more massive stellar cusp. |
Beauty is Distractive: Particle production during multifield inflation: We consider a two-dimensional model of inflation, where the inflationary
trajectory is "deformed" by a grazing encounter with an Extra Species/Symmetry
Point (ESP) after the observable cosmological scales have left the Hubble
radius. The encounter entails a sudden production of particles, whose
backreaction causes a bending of the trajectory and a temporary decrease in
speed, both of which are sensitive to initial conditions. This "modulated"
effect leads to an additional contribution to the curvature perturbation, which
can be dominant if the encounter is close. We compute associated
non-Gaussianities, the bispectrum and its scale dependence as well as the
trispectrum, which are potentially detectable in many cases. In addition, we
consider a direct modulation of the coupling to the light field at the ESP via
a modulaton field, a mixed scenario whereby the modulaton is identified with a
second inflaton, and an extended Extra Species Locus (ESL); all of these
scenarios lead to similar additional contributions to observables. We conclude
that inflaton interactions throughout inflation are strongly constrained if
primordial non-Gaussianities remain unobserved in current experiments such as
PLANCK. If they are observed, an ESP encounter leaves additional signatures on
smaller scales which may be used to identify the model. | Cosmological evolution in exponential gravity: We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1
(1-e^{- c_2 R})$ ($c_{1, 2} = \mathrm{constant}$). We summarize various
viability conditions and explicitly demonstrate that the late-time cosmic
acceleration following the matter-dominated stage can be realized. We also
study the equation of state for dark energy and confirm that the crossing of
the phantom divide from the phantom phase to the non-phantom (quintessence) one
can occur. Furthermore, we illustrate that the cosmological horizon entropy
globally increases with time. |
Investigating dark energy by electromagnetic frequency shifts II: the
Pantheon+ sample: Following results presented in Spallicci et al. (Eur Phys J Plus 137, 2022)
by the same authors, we investigate the observed red shift $z$, working under
the hypothesis that it might be composed by the expansion red shift $z_{\rm C}$
and an additional frequency shift $z_{\rm S}$, towards the red or the blue, due
to Extended Theories of Electromagnetism (ETE). We have tested this prediction
considering the novel Pantheon+ Catalogue, composed by 1701 light curves
collected by 1550 SNe Ia, and 16 BAO data, for different cosmological models
characterised by the absence of a dark energy component. In particular, we
shall derive which values of $z_{\rm S}$ match the observations, comparing the
new results with the ones obtained considering the older Pantheon Catalogue. We
find interesting differences in the resulting $z_{\rm S}$ distributions,
highlighted in the text. Later, we also add a discussion regarding Extended
Theories of Gravity and how to incorporate them in our methodology. | Big Bang Nucleosynthesis Initial Conditions: Revisiting Wagoner et al.
(1967): We revisit Wagoner et al. (1967), a classic contribution in the development
of Big Bang Nucleosynthesis. We demonstrate that it presents an incorrect
expression for the temperature of the early universe as a function of time in
the high temperature limit, $T \gtrsim 10^{10}$K. As this incorrect expression
has been reproduced elsewhere, we present a corrected form for the initial
conditions required for calculating the formation of the primordial elements in
the Big Bang. |
The Hubble tension and fifth forces: a cosmic screenplay: Fifth forces are ubiquitous in modified theories of gravity. In this paper,
we analyze their effect on the Cepheid-calibrated cosmic distance ladder,
specifically with respect to the inferred value of the Hubble constant ($H_0$).
We consider a variety of effective models where the strength, or amount of
screening, of the fifth force is estimated using proxy fields related to the
large-scale structure of the Universe. For all models considered, the local
distance ladder and the Planck value for $H_0$ agrees with a probability
$\gtrsim 20 \, \%$, relieving the tension compared to the concordance model
with data being excluded at $99 \, \%$ confidence. The alleviated discrepancy
comes partially at the cost of an increased tension between distance estimates
from Cepheids and the tip of the red-giant branch (TRGB). Demanding also that
the consistency between Cepheid and TRGB distance estimates is not impaired,
some fifth force models can still accommodate the data with a probability
$\gtrsim 20 \, \%$. This provides incentive for more detailed investigations of
fundamental theories on which the effective models are based, and their effect
on the Hubble tension. | Sunyaev-Zel'dovich clusters in Millennium Gas simulations: We have exploited the large-volume Millennium Gas cosmological N-body
hydrodynamics simulations to study the SZ cluster population at low and high
redshift, for three models with varying gas physics. We confirm previous
results using smaller samples that the intrinsic (spherical) Y_{500}-M_{500}
relation has very little scatter (sigma_{log_{10}Y}~0.04), is insensitive to
cluster gas physics and evolves to redshift one in accord with self-similar
expectations. Our pre-heating and feedback models predict scaling relations
that are in excellent agreement with the recent analysis from combined Planck
and XMM-Newton data by the Planck Collaboration. This agreement is largely
preserved when r_{500} and M_{500} are derived using the hydrostatic mass
proxy, Y_{X,500}, albeit with significantly reduced scatter
(sigma_{log_{10}Y}~0.02), a result that is due to the tight correlation between
Y_{500} and Y_{X,500}. Interestingly, this assumption also hides any bias in
the relation due to dynamical activity. We also assess the importance of
projection effects from large-scale structure along the line-of-sight, by
extracting cluster Y_{500} values from fifty simulated 5x5 square degree sky
maps. Once the (model-dependent) mean signal is subtracted from the maps we
find that the integrated SZ signal is unbiased with respect to the underlying
clusters, although the scatter in the (cylindrical) Y_{500}-M_{500} relation
increases in the pre-heating case, where a significant amount of energy was
injected into the intergalactic medium at high redshift. Finally, we study the
hot gas pressure profiles to investigate the origin of the SZ signal and find
that the largest contribution comes from radii close to r_{500} in all cases.
The profiles themselves are well described by generalised Navarro, Frenk &
White profiles but there is significant cluster-to-cluster scatter. |
Star formation in galaxy mergers: ISM turbulence, dense gas excess, and
scaling relations for disks and starbusts: Galaxy interactions and mergers play a significant, but still debated and
poorly understood role in the star formation history of galaxies. Numerical and
theoretical models cannot yet explain the main properties of merger-induced
starbursts, including their intensity and their spatial extent. Usually, the
mechanism invoked in merger-induced starbursts is a global inflow of gas
towards the central kpc, resulting in a nuclear starburst. We show here, using
high-resolution AMR simulations and comparing to observations of the gas
component in mergers, that the triggering of starbursts also results from
increased ISM turbulence and velocity dispersions in interacting systems. This
forms cold gas that are denser and more massive than in quiescent disk
galaxies. The fraction of dense cold gas largely increases, modifying the
global density distribution of these systems, and efficient star formation
results. Because the starbursting activity is not just from a global compacting
of the gas to higher average surface densities, but also from higher turbulence
and fragmentation into massive and dense clouds, merging systems can enter a
different regime of star formation compared to quiescent disk galaxies. This is
in quantitative agreement with recent observations suggesting that disk
galaxies and starbursting systems are not the low-activity end and
high-activity end of a single regime, but actually follow different scaling
relations for their star formation. | Consistent use of Type Ia supernovae highly magnified by galaxy clusters
to constrain the cosmological parameters: We discuss how Type Ia supernovae (SNe) strongly magnified by foreground
galaxy clusters should be self-consistently treated when used in samples fitted
for the cosmological parameters. While the cluster lens magnification of a SN
can be well constrained from sets of multiple images of various background
galaxies with measured redshifts, its value is typically dependent on the
fiducial set of cosmological parameters used to construct the mass model to
begin with. In such cases, one should not naively demagnify the observed SN
luminosity by the model magnification into the expected Hubble diagram, which
would then create a bias, but take into account the cosmological parameters
a-priori chosen to construct the mass model. We quantify the effect and find
that a systematic error of typically a few percent, up to a few-dozen percent,
per magnified SN, may be propagated onto a cosmological parameter fit, unless
the cosmology assumed for the mass model is taken into account (the bias can be
even larger if the SN is lying very near the critical curves). We also simulate
how such a bias propagates onto the cosmological parameter fit using the
Union2.1 sample, supplemented with strongly magnified SNe. The resulting bias
on the deduced cosmological parameters is generally at the few percent level,
if only few biased SNe are included, and increasing with the number of lensed
SNe and their redshift. Samples containing magnified Type Ia SNe, e.g. from
ongoing cluster surveys, should readily account for this possible bias. |
Probing Vainsthein-screening gravity with galaxy clusters using internal
kinematics and strong and weak lensing: We use high-precision combined strong/weak lensing and kinematics
measurements of the total mass profiles of the observed galaxy clusters
MACS~J1206.2-0847 and Abell~S1063, to constrain the relativistic sector of the
general DHOST dark energy theories, which exhibit a partial breaking of the so
called Vainsthein screening mechanism, on the linear level of scalar
fluctuations around a cosmological background. In particular, by using the
\textsc{MG-MAMMPOSSt} framework developed in Pizzuti et al. 2021, for the
kinematics analysis of member galaxies in clusters along with lensing mass
profile reconstructions, we provide new constraints on the coupling $Y_2$ which
governs the theory's relativistic contribution to the lensing potential. The
new bound from the combination of kinematics and lensing measurements of MACS
1206, $Y_2=-0.12^{+0.66}_{-0.67}$ at $2\sigma$, provides about a 2-fold
improvement on previous constraints. In the case of Abell~S1063 a $>2\sigma$
tension with the GR expectation arises. We discuss this in some detail, and we
investigate the possible sources of systematics which can explain the tension.
We further discuss why the combination of kinematics of member galaxies with
lensing is capable of providing much tighter bounds compared to kinematics or
lensing alone, and we explain how the number density profile of tracers, as
well as the choice of the velocity anisotropy profile affects the final
results. | Primordial Black Hole Formation in Non-Minimal Curvaton Scenario: In the curvaton scenario, the curvature perturbation is generated after
inflation at the curvaton decay, which may have a prominent non-Gaussian
effect. For a model with a non-trivial kinetic term, an enhanced curvature
perturbation on a small scale can be realized, which can lead to copious
production of primordial black holes (PBHs) and induce secondary gravitational
waves (GWs). Using the probability distribution function (PDF) which takes full
nonlinear effects into account, we calculate the PBH formation. We find that
under the assumption that thus formed PBHs would not overclose the universe,
the non-Gaussianity of the curvature perturbation can be well approximated by
the local quadratic form, which can be used to calculate the induced GWs. In
this model the limit of large non-Gaussianity can be reached when the curvaton
energy fraction $r$ is small at the moment of curvaton decay. We also show that
in the $r\to1$ limit the PDF is similar to that of ultraslow-roll inflation. |
Galaxy downsizing and the redshift evolution of oxygen and nitrogen
abundances: origin of the scatter in the N/H-O/H diagram: The oxygen and nitrogen abundance evolutions with redshift of emission-line
galaxies in the Sloan Digital Sky Survey are considered for four intervals of
galaxy stellar masses, ranging from 10^11.3 M_sun to 10^10.2 M_sun. We have
measured their line fluxes and derived the O and N abundances using recent
calibrations. The evolution of O and N abundances with redshift clearly shows
the galaxy downsizing effect, where enrichment (and hence star formation)
ceases in high-mass galaxies at earlier times and shifts to lower-mass galaxies
at later epochs. The origin of the scatter in the N/H - O/H diagram has been
examined. The most massive galaxies, where O and N enrichment and star
formation has already stopped, occupy a narrow band in the N/H -- O/H diagram,
defining an upper envelope. The less massive galaxies which are still
undergoing star formation at the current epoch are shifted downwards, towards
lower N/H values in the N/H - O/H diagram. This downward shift is caused by the
time delay between N and O enrichment. This time delay together with the
different star formation histories in galaxies is responsible for the large
scatter in the N/H -- O/H diagram. | Probing the azimuthal environment of galaxies around clusters. From
cluster core to cosmic filaments: Galaxy clusters are connected at their peripheries to the large scale
structures by cosmic filaments that funnel accreting material. These
filamentary structures are studied to investigate both environment-driven
galaxy evolution and structure formation and evolution. In the present work, we
probe in a statistical manner the azimuthal distribution of galaxies around
clusters as a function of the cluster-centric distance, the cluster richness,
and the galaxy activity (star-forming or passive).We perform a harmonic
decomposition in large photometric galaxy catalogue around 6400 SDSS clusters
with masses M >1e14 solar masses, in the redshift range of 0.1< z <0.3. The
same analysis is performed on the mock galaxy catalogue from the light-cone of
Magneticum hydrodynamical simulation.
We use the multipole analysis to quantify asymmetries in the 2-D galaxy
distribution. In the inner cluster regions at R <2 R500, we confirm that the
galaxy distribution traces an ellipsoidal shape, which is more pronounced for
richest clusters. In the clusters' outskirts (R= [2-8]R500), filamentary
patterns are detected in harmonic space with a mean angular scale m_mean=
4.2+/-0.1. Massive clusters seem to have a larger number of connected filaments
than low massive ones. We also find that passive galaxies appear to better
trace the filamentary structures around clusters, even if the contribution of
SF ones tend to increase with the cluster-centric distance, suggesting a
gradient of galaxy activity in filaments around clusters. |
Prospects for measuring dark energy with 21 cm intensity mapping
experiments: Using the 21 cm intensity mapping (IM) technique can efficiently perform
large-scale neutral hydrogen surveys, and this method has great potential for
measuring dark-energy parameters. Some 21 cm IM experiments aiming at measuring
dark energy in the redshift range of $0<z<3$ have been proposed and performed,
in which the typical ones using single-dish mode include e.g., BINGO, FAST, and
SKA1-MID, and those using interferometric mode include e.g., HIRAX, CHIME, and
Tianlai. In this work, we make a forecast for these typical 21 cm IM
experiments on their capability of measuring parameters of dark energy. We find
that the interferometers have great advantages in constraining cosmological
parameters. In particular, the Tianlai cylinder array alone can achieve the
standard of precision cosmology for the $\Lambda$CDM model (i.e., the precision
of parameters is better than 1%). However, for constraining dynamical dark
energy, we find that SKA1-MID performs very well. We show that the simulated 21
cm IM data can break the parameter degeneracies inherent in the CMB data, and
CMB+SKA1-MID offers $\sigma(w)=0.013$ in the $w$CDM model, and
$\sigma(w_0)=0.080$ and $\sigma(w_a)=0.25$ in the CPL model. Compared with
CMB+BAO+SN, Tianlai can provide tighter constraints in $\Lambda$CDM and $w$CDM,
but looser constraints (tighter than CMB+BAO) in CPL, and the combination
CMB+BAO+SN+Tianlai gives $\sigma(w)=0.013$, $\sigma(w_0)=0.055$, and
$\sigma(w_a)=0.13$. In addition, it is found that the synergy of FAST
($0<z<0.35$)+SKA1-MID ($0.35<z<0.77$)+Tianlai ($0.77<z<2.55$) offers a very
promising survey strategy. Finally, we find that the residual foreground
contamination amplitude has a considerable impact on constraint results. We
show that in the future 21 cm IM experiments will provide a powerful probe for
exploring the nature of dark energy. | Ion chemistry in the early universe: revisiting the role of HeH+ with
new quantum calculations: The role of HeH+ has been newly assessed with the aid of newly calculated
rates which use entirely ab initio methods, thereby allowing us to compute more
accurately the relevant abundances within the global chemical network of the
early universe. A comparison with the similar role of the ionic molecule LiH+
is also presented. Quantum calculations have been carried out for the gas-phase
reaction of HeH+ with H atoms with our new in-house code, based on the negative
imaginary potential method. Integral cross sections and reactive rate
coefficients obtained under the general conditions of early universe chemistry
are presented and discussed. With the new reaction rate, the abundance of HeH+
in the early universe is more than one order of magnitude larger than in
previous studies. Our more accurate findings further buttress the possibility
to detect cosmological signatures of HeH+. |
A weak lensing perspective on nonlinear structure formation with fuzzy
dark matter: We investigate nonlinear structure formation in the fuzzy dark matter (FDM)
model in comparison to cold dark matter (CDM) models from a weak lensing
perspective using perturbative methods. We use Eulerian perturbation theory
(PT) up to fourth order to compute the tree-level matter trispectrum and the
one-loop matter spectrum and bispectrum from consistently chosen initial
conditions. In addition, we predict the non-linear matter power spectra using
$N$-body simulations with CDM and FDM initial conditions. We go on to derive
the respective lensing spectra, bispectra and trispectra in CDM and FDM in the
context of a Euclid-like weak lensing survey. Finally, we compute the
attainable cumulative signal-to-noise ratios and an estimate of the attainable
$\chi^2$-functionals for distinguishing FDM from CDM at particle masses
$m=10^{-21}$ eV, $m = 10^{-22}$ eV and $m = 10^{-23}$ eV. We find that PT
predictions cannot be used to reliably distinguish the three models in a weak
lensing survey. Assuming that $N$-body simulations overestimate the late-time
small-scale power in the FDM model, future weak lensing survey might be used to
distinguish between the FDM and CDM cases up to a mass of $m = 10^{-23}$ eV.
However, observations probing the local high-$z$ universe are probably more
suited to constrain the FDM mass. | Extreme value statistics of the weak lensing convergence: 1. primordial
non-Gaussianities: The subject of this paper is the investigation of inflationary
non-Gaussianities of the local type with extreme value statistics of the weak
lensing convergence kappa. Specifically, we describe the influence of
inflationary non-Gaussianities parameterised by fnl and gnl on the probability
distribution p(kappa)dkappa of the smoothed convergence field with a
Gram-Charlier series, for which we compute the cumulants kappa_n of the
smoothed convergence field as a configuration space average of the weak
convergence polyspectra. We derive analytical expressions for the extreme value
distribution and show that they correspond very well to direct samples of
extreme values from the Gram-Charlier distribution. We show how the standard
Gumbel distribution for the extreme values is recovered in the limit of large
sample size. We investigate the shape and position of the extreme value
distribution for fnl- and gnl-type non-Gaussianity and quantify the dependence
on the number of available samples, leading to the inference of non-Gaussianity
parameters from observed extreme values. From the observation of single extreme
values in the EUCLID weak lensing survey is is possible to place constraints on
fnl and gnl of the order 10^2 and 10^5, respectively, while tnl can not be
constrained in a meaningful way. |
Exploring the high-redshift PBH-$Λ$CDM Universe: early black hole
seeding, the first stars and cosmic radiation backgrounds: We explore the observational implications of a model in which primordial
black holes (PBHs) with a broad birth mass function ranging in mass from a
fraction of a solar mass to $\sim$10$^6$ M$_{\odot}$, consistent with current
observational limits, constitute the dark matter component in the Universe. The
formation and evolution of dark matter and baryonic matter in this
PBH-\LambdaCDM~Universe are presented. In this picture, PBH DM mini-halos
collapse earlier than in standard \LambdaCDM, baryons cool to form stars at
$z\sim15-20$, and growing PBHs at these early epochs start to accrete through
Bondi capture. The volume emissivity of these sources peaks at $z\sim20$ and
rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a
channel to make early black hole seeds and naturally account for the origin of
an underlying dark matter halo - host galaxy and central black hole connection
that manifests as the $M_{\rm bh}-\sigma$ correlation. To estimate the
luminosity function and contribution to integrated emission power spectrum from
these high-redshift PBH DM halos, we develop a Halo Occupation Distribution
(HOD) model. In addition to tracing the star formation and reionizaton history,
it permits us to evaluate the Cosmic Infrared and X-ray Backgrounds (CIB and
CXB). We find that accretion onto PBHs/AGN successfully accounts for the
detected backgrounds and their cross-correlation, with the inclusion of an
additional IR stellar emission component. Detection of the deep IR source count
distribution by the JWST could reveal the existence of this population of
high-redshift star-forming and accreting PBH DM. | The primordial helium abundance from updated emissivities: Observations of metal-poor extragalactic H II regions allow the determination
of the primordial helium abundance, Y_p. The He I emissivities are the
foundation of the model of the H II region's emission. Porter, Ferland, Storey,
& Detisch (2012) have recently published updated He I emissivities based on
improved photoionization cross-sections. We incorporate these new atomic data
and update our recent Markov Chain Monte Carlo analysis of the dataset
published by Izotov, Thuan, & Stasinska (2007). As before, cuts are made to
promote quality and reliability, and only solutions which fit the data within
95% confidence level are used to determine the primordial He abundance. The
previously qualifying dataset is almost entirely retained and with strong
concordance between the physical parameters. Overall, an upward bias from the
new emissivities leads to a decrease in Y_p. In addition, we find a general
trend to larger uncertainties in individual objects (due to changes in the
emissivities) and an increased variance (due to additional objects included).
From a regression to zero metallicity, we determine Y_p = 0.2465 +/- 0.0097, in
good agreement with the Planck result of Y_p = 0.2485 +/- 0.0002. In the
future, a better understanding of why a large fraction of spectra are not well
fit by the model will be crucial to achieving an increase in the precision of
the primordial helium abundance determination. |
A large population of ultra-compact dwarf galaxies in the Hydra I
cluster: We performed a large spectroscopic survey of compact, unresolved objects in
the core of the Hydra I galaxy cluster (Abell 1060), with the aim of
identifying ultra-compact dwarf galaxies (UCDs), and investigating the
properties of the globular cluster (GC) system around the central cD galaxy NGC
3311. We obtained VIMOS medium resolution spectra of about 1200 candidate
objects with apparent magnitudes 18.5 < V < 24.0 mag, covering both the bright
end of the GC luminosity function and the luminosity range of all known UCDs.
By means of spectroscopic redshift measurements, we identified 118 cluster
members, from which 52 are brighter than M_V = -11.0 mag, and can therefore be
termed UCDs. The brightest UCD in our sample has an absolute magnitude of M_V =
-13.4 mag (corresponding to a mass of > 5 x 10^7 M_sun) and a half-light radius
of 25 pc. This places it among the brightest and most massive UCDs ever
discovered. Most of the GCs/UCDs are both spatially and dynamically associated
to the central cD galaxy. The overall velocity dispersion of the GCs/UCDs is
comparable to what is found for the cluster galaxies. However, when splitting
the sample into a bright and a faint part, we observe a lower velocity
dispersion for the bright UCDs/GCs than for the fainter objects. At a dividing
magnitude of M_V = -10.75 mag, the dispersions differ by more than 200 km/s,
and up to 300 km/s for objects within 5 arcmin around NGC 3311. We interpret
these results in the context of different UCD formation channels, and conclude
that interaction driven formation seems to play an important role in the centre
of Hydra I. | Radio jets and outflows of cold gas: Massive gas outflows are considered a key component in the process of galaxy
formation and evolution. It is, therefore, not surprising that a lot of effort
is going in quantifying their impact via detailed observations. This short
contribution presents recent results obtained from HI and CO observations of
different objects where the AGN - and in particular the radio jet - is likely
playing an important role in producing the gas outflows. These preliminary
results are reinforcing the conclusion that these outflows have a complex and
multiphase structure where cold gas in different phases (atomic and molecular)
is involved and likely represent a major component. These results will also
provide important constraints for establishing how the interaction between
AGN/radio jet and the surrounding ISM occurs and how efficiently the gas should
cool to produce the observed properties of the outflowing gas. HI likely
represents an intermediate phase in this process, while the molecular gas would
be the final stage. Whether the estimated outflow masses match what expected
from simulations of galaxy formation, it is still far from clear. |
The accuracy of the UV continuum as an indicator of the star formation
rate in galaxies: The rest-frame intrinsic UV luminosity is often used as an indicator of the
instantaneous star formation rate (SFR) in a galaxy. While it is in general a
robust indicator of the ongoing star formation activity, the precise value of
the calibration relating the UV luminosity to the SFR ($B_{\nu}$), is sensitive
to various physical properties, such as the recent star formation and metal
enrichment histories, along with the choice of stellar initial mass function.
The distribution of these properties for the star-forming galaxy population
then suggests that the adoption of a single calibration is not appropriate
unless properly qualified with the uncertainties on the calibration. We
investigate, with the aid of the {\sc galform} semi-analytic model of galaxy
formation, the distribution of UV-SFR calibrations obtained using realistic
star formation and metal enrichment histories. At $z=0$, we find that when the
initial mass function is fixed (to the Kennicutt IMF), the median calibration
is $B_{\rm fuv}=0.9$ where ${\rm SFR}/[{\rm M_{\odot}\,yr^{-1}}]=B_{\nu}\times
10^{-28}\times L_{\nu}/[{\rm ergs\,s^{-1}\,Hz^{-1}}]$. However, the width of
the distribution $B_{\rm fuv}$ suggests that for a single object there is
around a 20% {\em intrinsic} uncertainty (at $z=0$, rising to $\simeq 30%$ at
$z=6$) on the star formation rate inferred from the FUV luminosity without
additional constraints on the star formation history or metallicity. We also
find that the median value of the calibration $B_{\rm fuv}$ is correlated with
the star formation rate and redshift (at $z>3$) raising implications for the
correct determination of the star formation rate from the UV. | Cosmic Microwave Background Dipole Asymmetry could be explained by Axion
Monodromy Cosmic Strings: Observations by the Wilkinson Microwave Anisotropy Probe and the Planck
mission suggest a hemispherical power amplitude asymmetry in the cosmic
microwave background, with a correlation length on the order of the size of the
observable Universe. We find that this anomaly can be naturally explained by an
axion-like particle (ALP) cosmic string formed near our visible Universe. The
field variation associated to this cosmic string creates particle density
fluctuations after inflation, which consequently decay into radiation before
the Big Bang Nucleosynthesis (BBN) era and resulted in the observed power
asymmetry. We find in this scenario that the hemispherical power amplitude
asymmetry is strongly scale dependent: $A(k)\propto {\rm exp}(-kl)/k$.
Admittedly, typical inflation models predict a relic number density of
topological defects of order one per observable Universe and so in our model
the cosmic string must be tuned to have an impact factor of order $1/H_0$.
Interestingly, the constraints based on purely cosmological considerations also
give rise to a Peccei-Quinn scale $F_a$ of order $10^3$ larger then the Hubble
scale of inflation $H_I$. Assuming $H_I\sim 10^{13}$GeV, we then have an ALP
with $F_a\sim 10^{16}$GeV, which coincides with the presumed scale of grand
unification. As we require ALP decays occur before the BBN era, which implies a
relatively heavy mass or strong self-coupling, and considering that the
associated potential should break the shift symmetry softly in order to protect
the system from radiative corrections, we also conclude that the required ALP
potential should be monodromic in nature. |
Halo Occupation Distribution Modeling of Green Valley Galaxies: We present a clustering analysis of near ultraviolet (NUV) - optical color
selected luminosity bin samples of green valley galaxies. These galaxy samples
are constructed by matching the Sloan Digital Sky Survey Data Release 7 with
the latest Galaxy Evolution Explorer source catalog which provides NUV
photometry. We present cross-correlation function measurements and determine
the halo occupation distribution of these transitional galaxies using a new
multiple tracer analysis technique.
We extend the halo-occupation formalism to model the cross-correlation
function between a galaxy sample of interest and multiple tracer populations
simultaneously. This method can be applied to commonly used luminosity
threshold samples as well as to color and luminosity bin selected galaxy
samples, and improves the accuracy of clustering analyses for sparse galaxy
populations.
We confirm the previously observed trend that red galaxies reside in more
massive halos and are more likely to be satellite galaxies than average
galaxies of similar luminosity. While the change in central galaxy host mass as
a function of color is only weakly constrained, the satellite fraction and
characteristic halo masses of green satellite galaxies are found to be
intermediate between those of blue and red satellite galaxies. | The UVES Large Program for Testing Fundamental Physics: I Bounds on a
change in alpha towards quasar HE 2217-2818: Absorption line systems detected in quasar spectra can be used to compare the
value of the fine-structure constant, {\alpha}, measured today on Earth with
its value in distant galaxies. In recent years, some evidence has emerged of
small temporal and also spatial variations of {\alpha} on cosmological scales
which may reach a fractional level of ~ 10 ppm (parts per million). To test
these claims we are conducting a Large Program with the VLT UVES . We are
obtaining high-resolution (R ~ 60000 and high signal-to-noise ratio (S/N ~ 100)
UVES spectra calibrated specifically for this purpose. Here we analyse the
first complete quasar spectrum from this Program, that of HE 2217-2818. We
apply the Many Multiplet method to measure {\alpha} in 5 absorption systems
towards this quasar: zabs = 0.7866, 0.9424, 1.5558, 1.6279 and 1.6919. The most
precise result is obtained for the absorber at zabs = 1.6919 where 3 Fe II
transitions and Al II {\lambda}1670 have high S/N and provide a wide range of
sensitivities to {\alpha}. The absorption profile is complex, with several very
narrow features, and requires 32 velocity components to be fitted to the data.
Our final result for the relative variation in {\alpha} in this system is
Delta{\alpha}/{\alpha} = +1.3 +/- 2.4stat +/- 1.0sys ppm. This is one of the
tightest current bounds on {\alpha} variation from an individual absorber. The
absorbers towards quasar HE 2217-2818 reveal no evidence for variation in
{\alpha} at the 3 ppm precision level (1{\sigma} confidence). If the recently
reported 10 ppm dipolar variation of {\alpha} across the sky were correct, the
expectation at this sky position is (3.2-5.4) +/-1.7 ppm depending on dipole
model used . Our constraint of Delta{\alpha}/{\alpha}=+1.3+/-2.4stat +/-1.0sys
ppm is not inconsistent with this expectation. |
E pur si muove: Galiliean-invariant cosmological hydrodynamical
simulations on a moving mesh: Hydrodynamic cosmological simulations at present usually employ either the
Lagrangian SPH technique, or Eulerian hydrodynamics on a Cartesian mesh with
adaptive mesh refinement. Both of these methods have disadvantages that
negatively impact their accuracy in certain situations. We here propose a novel
scheme which largely eliminates these weaknesses. It is based on a moving
unstructured mesh defined by the Voronoi tessellation of a set of discrete
points. The mesh is used to solve the hyperbolic conservation laws of ideal
hydrodynamics with a finite volume approach, based on a second-order unsplit
Godunov scheme with an exact Riemann solver. The mesh-generating points can in
principle be moved arbitrarily. If they are chosen to be stationary, the scheme
is equivalent to an ordinary Eulerian method with second order accuracy. If
they instead move with the velocity of the local flow, one obtains a Lagrangian
formulation of hydrodynamics that does not suffer from the mesh distortion
limitations inherent in other mesh-based Lagrangian schemes. In this mode, our
new method is fully Galilean-invariant, unlike ordinary Eulerian codes, a
property that is of significant importance for cosmological simulations. In
addition, the new scheme can adjust its spatial resolution automatically and
continuously, and hence inherits the principal advantage of SPH for simulations
of cosmological structure growth. The high accuracy of Eulerian methods in the
treatment of shocks is retained, while the treatment of contact discontinuities
improves. We discuss how this approach is implemented in our new parallel code
AREPO, both in 2D and 3D. We use a suite of test problems to examine the
performance of the new code and argue that it provides an attractive and
competitive alternative to current SPH and Eulerian techniques. (abridged) | Equivalent Neutrinos, Light WIMPs, and the Chimera of Dark Radiation: According to conventional wisdom, in the standard model (SM) of particle
physics and cosmology the effective number of neutrinos is Neff=3 (more
precisely, 3.046). In extensions of the standard model allowing for the
presence of DeltaNnu equivalent neutrinos (or dark radiation), Neff is
generally >3. The canonical results are reconsidered here, revealing that a
measurement of Neff>3 can be consistent with DeltaNnu=0 (dark radiation without
dark radiation). Conversely, a measurement consistent with Neff=3 is not
inconsistent with the presence of dark radiation (DeltaNnu>0). In particular,
if there is a light WIMP that annihilates to photons after the SM neutrinos
have decoupled, the photons are heated beyond their usual heating from e+-
annihilation, reducing the late time ratio of neutrino and photon temperatures
(and number densities), leading to Neff<3. This opens the window for one or
more equivalent neutrinos, including sterile neutrinos, to be consistent with
Neff=3. By reducing the neutrino number density at present, this allows for
more massive neutrinos, relaxing the current constraints on the sum of the
neutrino masses. In contrast, if the light WIMP only couples to the SM
neutrinos and not to the photons, its late time annihilation heats the
neutrinos but not the photons, resulting in Neff>3 even in the absence of
equivalent neutrinos or dark radiation. A measurement of Neff>3 is thus no
guarantee of the presence of equivalent neutrinos or dark radiation. In the
presence of light WIMPs and/or equivalent neutrinos there are degeneracies
among the light WIMP mass and its nature (fermion or boson, as well as its
couplings to neutrinos or photons), the number and nature (fermion or boson) of
the equivalent neutrinos, and their decoupling temperature (the strength of
their interactions with the SM particles). There's more to a measurement of
Neff than meets the eye. |
The mass-to-light ratio of rich star clusters: We point out a strong time-evolution of the mass-to-light conversion factor
eta commonly used to estimate masses of unresolved star clusters from observed
cluster spectro-photometric measures. We present a series of gas-dynamical
models coupled with the Cambridge stellar evolution tracks to compute
line-of-sight velocity dispersions and half-light radii weighted by the
luminosity. We explore a range of initial conditions, varying in turn the
cluster mass and/or density, and the stellar population's IMF. We find that
eta, and hence the estimated cluster mass, may increase by factors as large as
3 over time-scales of 50 million years. We apply these results to an hypothetic
cluster mass distribution function (d.f.) and show that the d.f. shape may be
strongly affected at the low-mass end by this effect. Fitting truncated
isothermal (Michie-King) models to the projected light profile leads to
over-estimates of the concentration parameter c of delta c ~ 0.3 compared to
the same functional fit applied to the projected mass density. | Decaying Dark Atom constituents and cosmic positron excess: We present a scenario where dark matter is in the form of dark atoms that can
accomodate the experimentally observed excess of positrons in PAMELA and AMS-02
while being compatible with the constraints imposed on the gamma-ray flux from
Fermi/LAT. This scenario assumes that the dominant component of dark matter is
in the form of a bound state between a helium nucleus and a $-2$ particle and a
small component is in the form of a WIMP-like dark atom compatible with direct
searches in underground detectors. One of the constituents of this WIMP-like
state is a $+2$ metastable particle with a mass of 1 TeV or slightly below that
by decaying to $e^+e^+$, $\mu^+ \mu^+$ and $\tau^+ \tau^+$ produces the
observed positron excess. These decays can naturally take place via GUT
interactions. If it exists, such a metastable particle can be found in the next
run of LHC. The model predicts also the ratio of leptons over baryons in the
Universe to be close to -3. |
Density perturbations in general modified gravitational theories: We derive the equations of linear cosmological perturbations for the general
Lagrangian density $f (R,\phi, X)/2+L_c$, where $R$ is a Ricci scalar, $\phi$
is a scalar field, and $X=-(\nabla \phi)^2/2$ is a field kinetic energy. We
take into account a nonlinear self-interaction term $L_c$ recently studied in
the context of "Galileon" cosmology, which keeps the field equations at second
order. Taking into account a scalar-field mass explicitly, the equations of
matter density perturbations and gravitational potentials are obtained under a
quasi-static approximation on sub-horizon scales. We also derive conditions for
the avoidance of ghosts and Laplacian instabilities associated with propagation
speeds. Our analysis includes most of modified gravity models of dark energy
proposed in literature and thus it is convenient to test the viability of such
models from both theoretical and observational points of view. | Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the
Properties of Milky Way Satellites: Sterile neutrinos produced through a resonant Shi-Fuller mechanism are
arguably the simplest model for a dark matter interpretation origin of the
recent unidentified X-ray line seen toward a number of objects harboring dark
matter. Here, I calculate the exact parameters required in this mechanism to
produce the signal. The suppression of small scale structure predicted by these
models is consistent with Local Group and high-$z$ galaxy count constraints.
Very significantly, the parameters necessary in these models to produce the
full dark matter density fulfill previously determined requirements to
successfully match the Milky Way Galaxy's total satellite abundance, the
satellites' radial distribution and their mass density profile, or "too big to
fail problem." I also discuss how further precision determinations of the
detailed properties of the candidate sterile neutrino dark matter can probe the
nature of the quark-hadron transition, which takes place during the dark matter
production. |
Misalignment mechanism for a mass-varying vector boson: A coherent field over the entire universe is an attractive picture in
studying the dark sector of the universe. The misalignment mechanism, which
relies on inflation to achieve homogeneousness of the field, is a popular
mechanism for producing such a coherent dark matter. Nevertheless, unlike a
scalar field case, a vector boson field suffers because its energy density is
exponentially suppressed by the scale factor during the cosmic expansion. We
show that if the vector field gets a mass from a scalar field, whose value
increases by orders of magnitude, the suppression can be compensated, and the
misalignment can produce the coherent vector boson that has a sizable amount of
energy density in the present universe. Quintessence can be such a scalar
field. | Analytic gas orbits in an arbitrary rotating galactic potential using
the linear epicyclic approximation: A code, Epic5, has been developed which computes, in the two-dimensional
case, the initially circular orbits of guiding centra in an arbitrary
axisymmetric potential with an arbitrary, weak perturbing potential in solid
body rotation. This perturbing potential is given by its Fourier expansion. The
analytic solution solves the linear epicyclic approximation of the equations of
motion. To simulate the motion of interstellar matter and to damp the Lindblad
resonances, we have in these equations introduced a friction which is
proportional to the deviation from circular velocity. The corotation resonance
is also damped by a special parameter. The program produces, in just a few
seconds, orbital and density maps, as well as line of sight velocity maps for a
chosen orientation of the galaxy.
We test Epic5 by comparing its results with previous simulations and
observations from the literature, which gives satisfactory agreement. The aim
is that this program should be a useful complement to elaborate numerical
simulations. Particularly so are its abilities to quickly explore the parameter
space, to construct artificial galaxies, and to isolate various single agents
important for developing structure of interstellar matter in disc galaxies. |
LoCuSS: Hydrostatic Mass Measurements of the High-$L_X$ Cluster Sample
-- Cross-calibration of Chandra and XMM-Newton: We present a consistent analysis of Chandra and XMM-Newton observations of an
approximately mass-selected sample of 50 galaxy clusters at $0.15<z<0.3$ -- the
"LoCuSS High-$L_X$ Sample". We apply the same analysis methods to data from
both satellites, including newly developed analytic background models that
predict the spatial variation of the Chandra and XMM-Newton backgrounds to
$<2\%$ and $<5\%$ precision respectively. To verify the cross-calibration of
Chandra and XMM-Newton-based cluster mass measurements, we derive the mass
profiles of the 21 clusters that have been observed with both satellites,
extracting surface brightness and temperature profiles from identical regions
of the respective datasets. We obtain consistent results for the gas and total
hydrostatic cluster masses: the average ratio of Chandra- to XMM-Newton-based
measurements of $M_{\rm gas}$ and $M_X$ at $r_{500}$ are $0.99\pm0.02$ and
$1.02\pm0.05$, respectively with an intrinsic scatter of $\sim3\%$ for gas
masses and $\sim8\%$ for hydrostatic masses. Comparison of our hydrostatic mass
measurements at $r_{500}$ with the latest LoCuSS weak-lensing results indicate
that the data are consistent with non-thermal pressure support at this radius
of $\sim7\%$. We also investigate the scaling relation between our hydrostatic
cluster masses and published integrated Compton parameter $Y_{sph}$
measurements from the Sunyaev-Zel'dovich Array. We measure a scatter in mass at
fixed $Y_{sph}$ of $\sim16\%$ at $\Delta=500$, which is consistent with
theoretical predictions of $\sim10-15\%$ scatter. | Primordial black holes in peak theory with a non-Gaussian tail: In this paper, we update the peak theory for the estimation of the primordial
black hole (PBH) abundance, particularly by implementing the critical behavior
in the estimation of the PBH mass and employing the averaged compaction
function for the PBH formation criterion to relax the profile dependence. We
apply our peak theory to a specific non-Gaussian feature called the exponential
tail, which is characteristic in ultra slow-roll models of inflation. With this
type of non-Gaussianity, the probability of a large perturbation is not
suppressed by the Gaussian factor but decays only exponentially, so the PBH
abundance is expected to be much enhanced. Not only do we confirm this
enhancement even compared to the case of the corresponding nonlinearity
parameter $f_\mathrm{NL}=5/2$, but also we find that the resultant PBH mass
spectrum has a characteristic maximal mass which is not seen in the simple
Press--Schechter approach. |
Peaks in the CMBR power spectrum. II. Physical interpretation for any
cosmological scenario: In a previous paper (part I), the mathematical properties of the cosmic
microwave background radiation power spectrum which presents oscillations were
discussed. Here, we discuss the physical interpretation: a power spectrum with
oscillations is a rather normal characteristic expected from any fluid with
clouds of overdensities that emits/absorb radiation or interact gravitationally
with the photons, and with a finite range of sizes and distances for those
clouds. The standard cosmological interpretation of "acoustic" peaks is just a
particular case; peaks in the power spectrum might be generated in scenarios
within some alternative cosmological model that have nothing to do with
oscillations due to gravitational compression in a fluid.
We also calculate the angular correlation function of the anisotropies from
the WMAP-7yr and ACT data, in an attempt to derive the minimum number of
parameters a polynomial function should have to fit it: a set of polynomial
functions with a total of six free parameters, apart from the amplitude, is
enough to reproduce the first two peaks. However, the standard model with six
tunable free parameters also reproduces higher order peaks, giving the standard
model a higher confidence. At present, while no simple function with six free
parameters is found to give a fit as good as the one given by the standard
cosmological model, we may consider the predictive power of the standard model
beyond an instrumentalist approach (such as the Ptolemaic astronomy model of
the orbits of the planets). | Signals of primordial black holes at gravitational wave interferometers: Primordial black holes (PBHs) can form as a result of primordial scalar
perturbations at small scales. This PBH formation scenario has associated
gravitational wave (GW) signatures from second-order GWs induced by the
primordial curvature perturbation, and from GWs produced during an early PBH
dominated era. We investigate the ability of next generation GW experiments,
including BBO, LISA, and CE, to probe this PBH formation scenario in a wide
mass range. Measuring the stochastic GW background with GW observatories can
constrain the allowed parameter space of PBHs for masses 1e9 - 1e27 g. We also
discuss possible GW sources from an unconstrained region where light PBHs (<
1e9 g) temporarily dominate the energy density of the universe before
evaporating. We show how PBH formation impacts the reach of GW observatories to
the primordial power spectrum and provide constraints implied by existing PBH
bounds. |
The $m$-$z$ relation for type Ia supernovae, locally inhomogeneous
cosmological models, and the nature of dark matter: The $m$-$z$ relation for type Ia supernovae is one of the key pieces of
evidence supporting the cosmological `concordance model' with $\lambda_0
\approx 0.7$ and $\Omega_0 \approx 0.3$. However, it is well known that the
$m$-$z$ relation depends not only on $\lambda_0$ and $\Omega_0$ (with $H_0$ as
a scale factor) but also on the density of matter along the line of sight,
which is not necessarily the same as the large-scale density. I investigate to
what extent the measurement of $\lambda_0$ and $\Omega_0$ depends on this
density when it is characterized by the parameter $\eta$ ($0 \le \eta \le 1$),
which describes the ratio of density along the line of sight to the overall
density. I also discuss what constraints can be placed on $\eta$, both with and
without constraints on $\lambda_0$ and $\Omega_0$ in addition to those from the
$m$-$z$ relation for type~Ia supernovae. | How early is early dark energy?: We investigate constraints on early dark energy (EDE) from the Cosmic
Microwave Background (CMB) anisotropy, taking into account data from WMAP9
combined with latest small scale measurements from the South Pole Telescope
(SPT). For a constant EDE fraction we propose a new parametrization with one
less parameter but still enough to provide similar results to the ones
previously studied in literature. The main emphasis of our analysis, however,
compares a new set of different EDE parametrizations that reveal how CMB
constraints depend on the redshift epoch at which Dark Energy was non
negligible. We find that bounds on EDE get substantially weaker if dark energy
starts to be non-negligible later, with early dark energy fraction Omega_e free
to go up to about 5% at 2 sigma if the onset of EDE happens at z < 100. Tight
bounds around 1-2% are obtained whenever dark energy is present at last
scattering, even if its effects switch off afterwards. We show that the CMB
mainly constrains the presence of Dark Energy at the time of its emission,
while EDE-modifications of the subsequent growth of structure are less
important. |
New Observations of the Very Luminous Supernova 2006gy: Evidence for
Echoes: Supernova (SN) 2006gy was a hydrogen-rich core-collapse SN that remains one
of the most luminous optical supernovae ever observed. The total energy budget
(> 2 x 10^51 erg radiated in the optical alone) poses many challenges for
standard SN theory. We present new ground-based near-infrared (NIR)
observations of SN 2006gy, as well as a single epoch of Hubble Space Telescope
(HST) imaging obtained more than two years after the explosion. Our NIR data
taken around peak optical emission show an evolution that is largely consistent
with a cooling blackbody, with tentative evidence for a growing NIR excess
starting at day ~100. Our late-time Keck adaptive optics (AO) NIR image, taken
on day 723, shows little change from previous NIR observations taken around day
400. Furthermore, the optical HST observations show a reduced decline rate
after day 400, and the SN is bluer on day 810 than it was at peak. This
late-time decline is inconsistent with Co56 decay, and thus is problematic for
the various pair-instability SN models used to explain the nature of SN 2006gy.
The slow decline of the NIR emission can be explained with a light echo, and we
confirm that the late-time NIR excess is the result of a massive (>10 Msun)
dusty shell heated by the SN peak luminosity. The late-time optical
observations require the existence of a scattered light echo, which may be
generated by the same dust that contributes to the NIR echo. Both the NIR and
optical echoes originate in the proximity of the progenitor, ~10^18 cm for the
NIR echo and <~10-40 pc for the optical echo, which provides further evidence
that the progenitor of SN 2006gy was a very massive star. | The Cosmic Mach Number: Comparison from Observations, Numerical
Simulations and Nonlinear Predictions: We calculate the cosmic Mach number M - the ratio of the bulk flow of the
velocity field on scale R to the velocity dispersion within regions of scale R.
M is effectively a measure of the ratio of large-scale to small-scale power and
can be a useful tool to constrain the cosmological parameter space. Using a
compilation of existing peculiar velocity surveys, we calculate M and compare
it to that estimated from mock catalogues extracted from the LasDamas (a LCDM
cosmology) numerical simulations. We find agreement with expectations for the
LasDamas cosmology at ~ 1.5 sigma CL. We also show that our Mach estimates for
the mocks are not biased by selection function effects. To achieve this, we
extract dense and nearly-isotropic distributions using Gaussian selection
functions with the same width as the characteristic depth of the real surveys,
and show that the Mach numbers estimated from the mocks are very similar to the
values based on Gaussian profiles of the corresponding widths. We discuss the
importance of the survey window functions in estimating their effective depths.
We investigate the nonlinear matter power spectrum interpolator PkANN as an
alternative to numerical simulations, in the study of Mach number. |
A first comparison of Kinetic Field Theory with Eulerian Standard
Perturbation Theory: We present a detailed comparison of the newly developed particle-based
Kinetic Field Theory framework for cosmic large-scale structure formation with
the established formalism of Eulerian Standard Perturbation Theory. We
highlight the qualitative differences of both approaches by a comparative
analysis of the respective equations of motion and implementation of initial
conditions. A natural starting point for a first quantitative comparison is
given by the non-interacting regime of free-streaming kinematics. Our results
suggest that Kinetic Field Theory contains a complete resummation of Standard
Perturbation Theory in this regime. We further show that the exact
free-streaming solution of Kinetic Field Theory can not be recovered in any
finite order of Standard Perturbation Theory. Kinetic Field Theory should
therefore provide a better starting point for perturbative treatments of
non-linear structure formation. | Cold gas dynamics in Hydra-A: evidence for a rotating disk: We present multi-frequency observations of the radio galaxy Hydra-A (3C218)
located in the core of a massive, X-ray luminous galaxy cluster. IFU
spectroscopy is used to trace the kinematics of the ionised and warm molecular
hydrogen which are consistent with a ~ 5 kpc rotating disc. Broad,
double-peaked lines of CO(2-1), [CII]157 $\mu$m and [OI]63 $\mu$m are detected.
We estimate the mass of the cold gas within the disc to be M$_{gas}$ = 2.3
$\pm$ 0.3 x 10$^9$ M$_{\odot}$. These observations demonstrate that the complex
line profiles found in the cold atomic and molecular gas are related to the
rotating disc or ring of gas. Finally, an HST image of the galaxy shows that
this gas disc contains a substantial mass of dust. The large gas mass, SFR and
kinematics are consistent with the levels of gas cooling from the ICM. We
conclude that the cold gas originates from the continual quiescent accumulation
of cooled ICM gas. The rotation is in a plane perpendicular to the projected
orientation of the radio jets and ICM cavities hinting at a possible connection
between the kpc-scale cooling gas and the accretion of material onto the black
hole. We discuss the implications of these observations for models of cold
accretion, AGN feedback and cooling flows. |
The BACCO Simulation Project: Exploiting the full power of large-scale
structure for cosmology: We present the BACCO project, a simulation framework specially designed to
provide highly-accurate predictions for the distribution of mass, galaxies, and
gas as a function of cosmological parameters. In this paper, we describe our
main suite of simulations (L $\sim2$ Gpc and $4320^3$ particles) and present
various validation tests. Using a cosmology-rescaling technique, we predict the
nonlinear mass power spectrum over the redshift range $0<z<1.5$ and over scales
$10^{-2} < k/(h Mpc^{-1} ) < 5$ for 800 points in an 8-dimensional cosmological
parameter space. For an efficient interpolation of the results, we build an
emulator and compare its predictions against several widely-used methods. Over
the whole range of scales considered, we expect our predictions to be accurate
at the 2\% level for parameters in the minimal $\Lambda$ CDM model and to 3\%
when extended to dynamical dark energy and massive neutrinos. We make our
emulator publicly available under http://www.dipc.org/bacco | Exploring Mirror Twin Higgs Cosmology with Present and Future Weak
Lensing Surveys: We explore the potential of precision cosmological data to study non-minimal
dark sectors by updating the cosmological constraint on the mirror twin Higgs
model (MTH). The MTH model addresses the Higgs little hierarchy problem by
introducing dark sector particles. In this work, we perform a Bayesian global
analysis that includes the latest cosmic shear measurement from the DES
three-year survey and the Planck CMB and BAO data. In the early Universe, the
mirror baryon and mirror radiation behave as dark matter and dark radiation,
and their presence modifies the Universe's expansion history. Additionally, the
scattering between mirror baryon and photon generates the dark acoustic
oscillation process, suppressing the matter power spectrum from the cosmic
shear measurement. We demonstrate how current data constrain these corrections
to the $\Lambda$CDM cosmology and find that for a viable solution to the little
hierarchy problem, the proportion of MTH dark matter cannot exceed about $30\%$
of the total dark matter density, unless the temperature of twin photon is less
than $30\%$ of that of the standard model photon. While the MTH model is
presently not a superior solution to the observed $H_0$ tension compared to the
$\Lambda$CDM+$\Delta N_{\rm eff}$ model, we demonstrate that it has the
potential to alleviate both the $H_0$ and $S_8$ tensions, especially if the
$S_8$ tension persists in the future and approaches the result reported by the
Planck SZ (2013) analysis. In this case, the MTH model can relax the tensions
while satisfying the DES power spectrum constraint up to $k \lesssim 10~h\rm
{Mpc}^{-1}$. If the MTH model is indeed accountable for the $S_8$ and $H_0$
tensions, we show that the future China Space Station Telescope (CSST) can
determine the twin baryon abundance with a $10\%$ level precision. |
A thermodynamic point of view on dark energy models: We present a conjugate analysis of two different dark energy models
investigating both their agreement with recent data and their thermodynamical
properties. The successful match with the data allows to both constrain the
model parameters and characterize their kinematical properties. As a novel
step, we exploit the strong connection between gravity and thermodynamics to
further check models viability by investigating their thermodynamical
quantities. In particular, we study whether the cosmological scenario fulfills
the generalized second law of thermodynamics and, moreover, we contrast the two
model asking whether the evolution of the total entropy is in agreement with
the expectation for a closed system. As a general result, we discuss whether
thermodynamic constraints can be a valid complementary way to both constrain
dark energy models and differentiate among rival scenarios. | Teasing bits of information out of the CMB energy spectrum: Departures of the Cosmic Microwave Background (CMB) frequency spectrum from a
blackbody - commonly referred to as spectral distortions - encode information
about the thermal history of the early Universe (redshift z < few x 10^6).
While the signal is usually characterized as mu- and y-type distortion, a
smaller residual (non-y/non-mu) distortion can also be created at intermediate
redshifts 10^4 < z < 3 x 10^5. Here, we construct a new set of observables,
mu_k, that describes the principal components of this residual distortion. The
principal components are orthogonal to temperature shift, y- and mu-type
distortion, and ranked by their detectability, thereby delivering a compression
of all valuable information offered by the CMB spectrum. This method provides
an efficient way of analyzing the spectral distortion for given experimental
settings, and can be applied to a wide range of energy-release scenarios. As an
illustration, we discuss the analysis of the spectral distortion signatures
caused by dissipation of small-scale acoustic waves and decaying/annihilating
particles for a PIXIE-type experiments. We provide forecasts for the expected
measurement uncertainties of model parameters and detections limits in each
case. We furthermore show that a PIXIE-type experiments can in principle
distinguish dissipative energy release from particle decays for a nearly
scale-invariant primordial power spectrum with small running. Future CMB
spectroscopy thus offers a unique probe of physical processes in the primordial
Universe. |
WIMP annihilation effects on primordial star formation: We study the effects of WIMP dark matter (DM) annihilations on the thermal
and chemical evolution of the gaseous clouds where the first generation of
stars in the Universe is formed. We follow the collapse of the gas inside a
typical halo virializing at very high redshift, from well before virialization
until a stage where the heating from DM annihilations exceeds the gas cooling
rate. The DM energy input is estimated by inserting the energy released by DM
annihilations (as predicted by an adiabatic contraction of the original DM
profile) in a spherically symmetric radiative transfer scheme. In addition to
the heating effects of the energy absorbed, we include its feedback upon the
chemical properties of the gas, which is critical to determine the cooling rate
in the halo, and hence the fragmentation scale and Jeans mass of the first
stars. We find that DM annihilation does alter the free electron and especially
the H2 fraction when the gas density is n>~ 10^4 cm^-3, for our fiducial
parameter values. However, even if the change in the H2 abundance and the
cooling efficiency of the gas is large (sometimes exceeding a factor 100), the
effects on the temperature of the collapsing gas are far smaller (a reduction
by a factor <~1.5), since the gas cooling rate depends very strongly on
temperature: then, the fragmentation mass scale is reduced only slightly,
hinting towards no dramatic change in the initial mass function of the first
stars. | Inverse-Compton Scattering of the Cosmic Infrared Background: The thermal Sunyaev-Zel'dovich (tSZ) effect is the distortion generated in
the cosmic microwave background (CMB) spectrum by the inverse-Compton
scattering of CMB photons off free, energetic electrons, primarily located in
the intracluster medium (ICM). Cosmic infrared background (CIB) photons from
thermal dust emission in star-forming galaxies are expected to undergo the same
process. In this work, we perform the first calculation of the resulting
tSZ-like distortion in the CIB. Focusing on the CIB monopole, we use a halo
model approach to calculate both the CIB signal and the Compton-$y$ field that
generates the distortion. We self-consistently account for the redshift
co-evolution of the CIB and Compton-$y$ fields: they are (partially) sourced by
the same dark matter halos, which introduces new aspects to the calculation as
compared to the CMB case. We find that the inverse-Compton distortion to the
CIB monopole spectrum has a positive (negative) peak amplitude of $\approx 4$
Jy/sr ($\approx -5$ Jy/sr) at 2260 GHz (940 GHz). In contrast to the usual tSZ
effect, the distortion to the CIB spectrum has two null frequencies, at
approximately 196 GHz and 1490 GHz. We perform a Fisher matrix calculation to
forecast the detectability of this new distortion signal by future experiments.
$\textit{PIXIE}$ would have sufficient instrumental sensitivity to detect the
signal at $4\sigma$, but foreground contamination reduces the projected
signal-to-noise by a factor of $\approx 70$. A future ESA Voyage 2050
spectrometer could detect the CIB distortion at $\approx 5\sigma$ significance,
even after marginalizing over foregrounds. A measurement of this signal would
provide new information on the star formation history of the Universe, and the
distortion anisotropies may be accessible by near-future ground-based
experiments. |
Constraining a possible variation of G with Type Ia supernovae: Astrophysical cosmology constrains the variation of Newton's Constant in a
manner complementary to laboratory experiments, such as the celebrated lunar
laser ranging campaign. Supernova cosmology is an example of the former and has
attained campaign status, following planning by a Dark Energy Task Force in
2005. In this paper we employ the full SNIa dataset to the end of 2013 to set a
limit on G variation. In our approach we adopt the standard candle delineation
of the redshift distance relation. We set an upper limit on its rate of change
|G dot / G| of 0.1 parts per billion per year over 9 Gyrs. By contrast lunar
laser ranging tests variation of G over the last few decades. Conversely, one
may adopt the laboratory result as a prior and constrain the effect of variable
G in dark energy equation of state experiments to delta w < 0.02. We also
examine the parameterization G ~ 1 + z. Its short expansion age conflicts with
the measured values of the expansion rate and the density in a flat Universe.
In conclusion, supernova cosmology complements other experiments in limiting G
variation. An important caveat is that it rests on the assumption that the same
mass of 56Ni is burned to create the standard candle regardless of redshift.
These two quantities, f and G, where f is the Chandrasekhar mass fraction
burned, are degenerate. Constraining f variation alone requires more
understanding of the SNIa mechanism. | Starburst or AGN Dominance in Submillimetre-Luminous Candidate AGN?: It is widely believed that ultraluminous infrared (IR) galaxies and active
galactic nuclei (AGN) activity are triggered by galaxy interactions and
merging, with the peak of activity occurring at z~2, where submillimetre
galaxies are thousands of times more numerous than local ULIRGs. In this
evolutionary picture, submillimetre galaxies (SMGs) would host an AGN, which
would eventually grow a black hole (BH) strong enough to blow off all of the
gas and dust leaving an optically luminous QSO. To probe this evolutionary
sequence we have focussed on the 'missing link' sources, which demonstrate both
strong starburst (SB) and AGN signatures, in order to determine if the SB is
the main power source even in SMGs when we have evidence that an AGN is present
from their IRAC colours. The best way to determine if a dominant AGN is present
is to look for their signatures in the mid-infrared with the Spitzer IRS, since
often even deep X-ray observations miss identifying the presence of AGN in
heavily dust-obscured SMGs. We present the results of our audit of the energy
balance between star-formation and AGN within this special sub-population of
SMGs -- where the BH has grown appreciably to begin heating the dust emission. |
Joint Analysis of Gravitational Lensing, Clustering and Abundance:
Toward the Unification of Large-Scale Structure Analysis: We explore three different methods based on weak lensing to extract
cosmological constraints from the large-scale structure. In the first approach
(method I), small-scale galaxy lensing measurements of their halo mass provide
a constraint on the halo bias, which can be combined with the large-scale
galaxy clustering to measure the dark matter clustering. In the second approach
(method II), large-scale galaxy clustering and large-scale galaxy-galaxy
lensing can be combined into a direct measurement of the dark matter
clustering. These two methods can be combined into one method I+II to make use
of lensing measurements on all scales. In the third approach (method III), we
add abundance information to the method I. We explore the statistical power of
these three approaches as a function of galaxy luminosity to investigate the
optimal mass range for each method and their cosmological constraining power.
In the case of the SDSS, we find that the three methods give comparable
constraints, but not in the same mass range: the method II works best for halos
of M~10^13 Msun, and the methods I and III work best for halos of M~10^14 Msun.
We discuss the robustness of each method against various systematics.
Furthermore, we extend the analysis to the future large-scale galaxy surveys
and find that the cluster abundance method is not superior to the combined
method I+II, both in terms of statistical power and robustness against
systematic errors. The cosmic shear-shear correlation analysis in the future
surveys yields constraints as strong as the combined method, but suffer from
additional systematic effects. We thus advocate the combined analysis of
clustering and lensing (method I+II) as a powerful alternative to other
large-scale probes. Our analysis provides a guidance to observers planning
large-scale galaxy surveys such as the DES, Euclid, and the LSST. | On the Rates of Type Ia Supernovae in Dwarf and Giant Hosts with
ROTSE-IIIb: We present a sample of 23 spectroscopically confirmed Type Ia supernovae that
were discovered in the background of galaxy clusters targeted by ROTSE-IIIb and
use up to 18 of these to determine the local (z = 0.05) volumetric rate. Since
our survey is flux limited and thus biased against fainter objects, the
pseudo-absolute magnitude distribution (pAMD) of SNeIa in a given volume is an
important concern, especially the relative frequency of high to low-luminosity
SNeIa. We find that the pAMD derived from the volume limited Lick Observatory
Supernova Search (LOSS) sample is incompatible with the distribution of SNeIa
in a volume limited (z<0.12) sub sample of the SDSS-II. The LOSS sample
requires far more low-luminosity SNeIa than the SDSS-II can accommodate. Even
though LOSS and SDSS-II have sampled different SNeIa populations, their
volumetric rates are surprisingly similar. Using the same model pAMD adopted in
the SDSS-II SNeIa rate calculation and excluding two high-luminosity SNeIa from
our sample, we derive a rate that is marginally higher than previous
low-redshift determinations. With our full sample and the LOSS pAMD our rate is
more than double the canonical value. We also find that 5 of our 18 SNeIa are
hosted by very low-luminosity (M_B > -16) galaxies, whereas only 1 out 79
nearby SDSS-II SNeIa have such faint hosts. It is possible that previous works
have under-counted either low luminosity SNeIa, SNeIa in low luminosity hosts,
or peculiar SNeIa (sometimes explicitly), and the total SNeIa rate may be
higher than the canonical value. |
Dark Matter in the Milky Way's Dwarf Spheroidal Satellites: The Milky Way's dwarf spheroidal satellites include the nearest, smallest and
least luminous galaxies known. They also exhibit the largest discrepancies
between dynamical and luminous masses. This article reviews the development of
empirical constraints on the structure and kinematics of dSph stellar
populations and discusses how this phenomenology translates into constraints on
the amount and distribution of dark matter within dSphs. Some implications for
cosmology and the particle nature of dark matter are discussed, and some
topics/questions for future study are identified. | Extending light WIMP searches to single scintillation photons in LUX: We present a novel analysis technique for liquid xenon time projection
chambers that allows for a lower threshold by relying on events with a prompt
scintillation signal consisting of single detected photons. The energy
threshold of the LUX dark matter experiment is primarily determined by the
smallest scintillation response detectable, which previously required a 2-fold
coincidence signal in its photomultiplier arrays, enforced in data analysis.
The technique presented here exploits the double photoelectron emission effect
observed in some photomultiplier models at vacuum ultraviolet wavelengths. We
demonstrate this analysis using an electron recoil calibration dataset and
place new constraints on the spin-independent scattering cross section of
weakly interacting massive particles (WIMPs) down to 2.5 GeV/c$^2$ WIMP mass
using the 2013 LUX dataset. This new technique is promising to enhance light
WIMP and astrophysical neutrino searches in next-generation liquid xenon
experiments. |
A derivation of masses and total luminosities of galaxy groups and
clusters in the maxBCG catalogue: We report the results of a multi-waveband analysis of the masses and
luminosities of $\sim$600 galaxy groups and clusters identified in the maxBCG
catalogue. These data are intended to form the basis of future work on the
formation of the "$m_{12}$ gap" in galaxy groups and clusters. We use SDSS
spectroscopy and $g$, $r$ and $i$ band photometry to estimate galaxy
group/cluster virial radii, masses and total luminosities. In order to
establish the robustness of our results, we compare them with literature
studies that utilize a variety of mass determinations techniques (dynamical,
X-ray, weak lensing) and total luminosities estimated in the $B$, $r$, $i$, and
$K$ wavebands. We also compare our results to predictions derived from the
Millennium Simulation. We find that, once selection effects are properly
accounted for, excellent agreement exists between our results and the
literature with the exception of a single observational study. We also find
that the Millennium Simulation does an excellent job of predicting the effects
of our selection criteria. Our results show that, over the mass range
$\sim10^{13}-10^{15}$ M$_{\odot}$, variations in the slope of the
mass-luminosity scaling relation with mass detected in this and many other
literature studies is in part the result of selection effects. We show that
this can have serious ramifications on attempts to determine how the
mass-to-light ratio of galaxy groups and cluster varies with mass. | Cosmological Structure Formation in Decaying Dark Matter Models: The standard cold dark matter (CDM) model predicts too many and too dense
small structures. We consider an alternative model that the dark matter
undergoes two-body decays with cosmological lifetime $\tau$ into only one type
of massive daughters with non-relativistic recoil velocity $V_k$. This decaying
dark matter model (DDM) can suppress the structure formation below its
free-streaming scale at time scale comparable to $\tau$. Comparing with warm
dark matter (WDM), DDM can better reduce the small structures while being
consistent with high redshfit observations. We study the cosmological structure
formation in DDM by performing self-consistent N-body simulations and point out
that cosmological simulations are necessary to understand the DDM structures
especially on non-linear scales. We propose empirical fitting functions for the
DDM suppression of the mass function and the mass-concentration relation, which
depend on the decay parameters lifetime $\tau$ and recoil velocity $V_k$, and
redshift. The fitting functions lead to accurate reconstruction of the the
non-linear power transfer function of DDM to CDM in the framework of halo
model. Using these results, we set constraints on the DDM parameter space by
demanding that DDM does not induce larger suppression than the Lyman-$\alpha$
constrained WDM models. We further generalize and constrain the DDM models to
initial conditions with non-trivial mother fractions and show that the halo
model predictions are still valid after considering a global decayed fraction.
Finally, we point out that the DDM is unlikely to resolve the disagreement on
cluster numbers between the Planck primary CMB prediction and the
Sunyaev-Zeldovich (SZ) effect number count for $\tau \sim H_{0}^{-1}$. |
The Effect of Anisotropic Viscosity on Cold Fronts in Galaxy Clusters: Cold fronts -- contact discontinuities in the intracluster medium (ICM) of
galaxy clusters -- should be disrupted by Kelvin-Helmholtz (K-H) instabilities
due to the associated shear velocity. However, many observed cold fronts appear
stable. This opens the possibility to place constraints on microphysical
mechanisms that stabilize them, such as the ICM viscosity and/or magnetic
fields. We performed exploratory high-resolution simulations of cold fronts
arising from subsonic gas sloshing in cluster cores using the grid-based Athena
MHD code, comparing the effects of isotropic Spitzer and anisotropic Braginskii
viscosity (expected in a magnetized plasma). Magnetized simulations with full
Braginskii viscosity or isotropic Spitzer viscosity reduced by a factor f ~ 0.1
are both in qualitative agreement with observations in terms of suppressing K-H
instabilities. The RMS velocity of turbulence within the sloshing region is
only modestly reduced by Braginskii viscosity. We also performed unmagnetized
simulations with and without viscosity and find that magnetic fields have a
substantial effect on the appearance of the cold fronts, even if the initial
field is weak and the viscosity is the same. This suggests that determining the
dominant suppression mechanism of a given cold front from X-ray observations
(e.g. viscosity or magnetic fields) by comparison with simulations is not
straightforward. Finally, we performed simulations including anisotropic
thermal conduction, and find that including Braginskii viscosity in these
simulations does not significant affect the evolution of cold fronts; they are
rapidly smeared out by thermal conduction, as in the inviscid case. | The full squeezed CMB bispectrum from inflation: The small-scale CMB temperature we observe on the sky is modulated by
perturbations that were super-horizon at recombination, giving differential
focussing and lensing that generate a non-zero bispectrum even for single-field
inflation where local physics is identical. Understanding this signal is
important for primordial non-Gaussianity studies and also parameter constraints
from the CMB lensing bispectrum signal. Because of cancellations individual
effects can appear larger or smaller than they are in total, so a full analysis
may be required to avoid biases. I relate angular scales on the sky to physical
scales at recombination using the optical equations, and give full-sky results
for the large-scale adiabatic temperature bispectrum from Ricci focussing
(expansion of the ray bundle), Weyl lensing (convergence and shear), and
temperature redshift modulations of small-scale power. The delta N expansion of
the beam is described by the constant temperature 3-curvature, and gives a
nearly-observable version of the consistency relation prediction from
single-field inflation. I give approximate arguments to quantify the likely
importance of dynamical effects, and argue that they can be neglected for
modulation scales l <~ 100, which is sufficient for lensing studies and also
allows robust tests of local primordial non-Gaussianity using only the
large-scale modulation modes. For accurate numerical results early and
late-time ISW effects must be accounted for, though I confirm that the
late-time non-linear Rees-Sciama contribution is negligible compared to other
more important complications. The total corresponds to f_NL ~ 7 for Planck-like
temperature constraints and f_NL ~ 11 for cosmic-variance limited data to
lmax=2000. Temperature lensing bispectrum estimates are affected at the 0.2
sigma level by Ricci focussing, and up to 0.5 sigma with polarization. |
Cosmological constraints on non-standard inflationary quantum collapse
models: We briefly review an important shortcoming --unearthed in previous works-- of
the standard version of the inflationary model for the emergence of the seeds
of cosmic structure. We consider here some consequences emerging from a
proposal inspired on ideas of Penrose and Di\'osi about a quantum-gravity
induced reduction of the wave function, which has been put forward to address
the shortcomings, arguing that its effect on the inflaton field is what can
lead to the emergence of the seeds of cosmic structure. The proposal leads to a
deviation of the primordial spectrum from the scale-invariant
Harrison-Zel'dovich one, and consequently, to a different CMB power spectrum.
We perform statistical analyses to test two quantum collapse schemes with
recent data from the CMB, including the 7-yr release of WMAP and the matter
power spectrum measured using LRGs by the Sloan Digital Sky Survey. Results
from the statistical analyses indicate that several collapse models are
compatible with CMB and LRG data, and establish constraints on the free
parameters of the models. The data put no restriction on the timescale for the
collapse of the scalar field modes. | Observational constraints on unified dark matter including Hubble
parameter data: We constrain a unified dark matter (UDM) model from the latest observational
data. This model assumes that the dark sector is degenerate. Dark energy and
dark matter are the same component. It can be described by an affine equation
of state $P_X= p_0 +\alpha \rho_X$. Our data set contains the newly revised
$H(z)$ data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic
oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey
(SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave
background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy
Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we
obtain the results in a flat universe:
$\Omega_\Lambda$=$0.719_{-0.0305}^{+0.0264}(1\sigma)_{-0.0458}^{+0.0380}(2\sigma)$,
$\alpha$=$1.72_{-4.79}^{+3.92}(1\sigma)_{-7.30}^{+5.47}(2\sigma)(\times10^{-3})$,
$\Omega_bh^2$=$0.0226_{-0.0011}^{+0.0011}(1\sigma)_{-0.0015}^{+0.0016}(2\sigma)$.
Moreover, when considering a non-flat universe,
$\Omega_\Lambda$=$0.722_{-0.0447}^{+0.0362}(1\sigma)_{-0.0634}^{+0.0479}(2\sigma)$,
$\alpha$=$0.242_{-0.775}^{+0.787}(1\sigma)_{-1.03}^{+1.10}(2\sigma)(\times10^{-2})$,
$\Omega_bh^2$=$0.0227_{-0.0014}^{+0.0015}(1\sigma)_{-0.0018}^{+0.0021}(2\sigma)$,
$\Omega_k$=$-0.194_{-1.85}^{+2.02}(1\sigma)_{-2.57}^{+2.75}(2\sigma)(\times10^{-2})$.
These give a more stringent results than before. We also give the results from
other combinations of these data for comparison. The observational Hubble
parameter data can give a more stringent constraint than SNe Ia. From the
constraint results, we can see the parameters $\alpha$ and $\Omega_k$ are very
close to zero, which means a flat universe is strongly supported and the speed
of sound of the dark sector seems to be zero. |
A Study of Catalogued Nearby Galaxy Clusters in the SDSS-DR4. II.
Cluster Substructure: According to the current cosmological paradigm, large scale structures form
hierarchically in the Universe. Clusters of galaxies grow through a continuous
accretion of mass. Nevertheless, the rate and manner of mass accretion events
are still matters of debate. We have analysed the presence of substructures in
one of the largest sample of nearby cluster galaxies available in the
literature. We have determined the fraction of clusters with substructure and
the properties of the galaxies located in such substructures. Substructure in
the galaxy clusters was studied using the Dressler--Shectman test, which was
calibrated through extensive Monte Carlo simulations of galaxy clusters similar
to real ones. In order to avoid possible biases in the results due to differing
incompleteness among clusters, we selected two galaxy populations: a) galaxies
brighter than M$_{r} = $-20 located in clusters at $z < 0.1$ (EC1); and b)
galaxies of brightness $M_{r} < -19$ located at $z<0.07$ (EC2). In the inner
cluster regions ($r < r_{200}$) 11$\%$ and 33$\%$ of the clusters of EC1 and
EC2 respectively show substructure. This fraction is larger in the outer
cluster regions ($\approx 55\%$) for EC1 and EC2 samples. Cluster global
properties, such as $\sigma_{c}$, $f_{b}$ or $\Delta m_{12}$ do not depend on
the amount of cluster substructure. We have studied the properties of
individual galaxies located in substructures in the EC1 and EC2 galaxy
populations. The fraction of galaxies within substructures is larger in the
outer cluster regions when fainter galaxies are included. The distribution of
relative velocities of galaxies within substructures suggest that they consist
of an infalling population mixed with backsplash galaxies. We can not rule out
that the infalling galaxy population located in substructures are genuine field
ones. | Cosmological constraints on parameters of one-brane models with extra
dimension: We study some aspects of cosmologies in 5D models with one infinite extra
dimension. Matter is confined to the brane, gravity extends to the bulk. Models
with positive and negative tension of the brane are considered. Cosmological
evolution of the 4D world is described by warped solutions of the generalized
Friedmann equation. Cosmological solutions on the brane are obtained with the
input of the present-time observational cosmological parameters. We estimate
the age of the Universe and abundance of ${}^4 He$ produced in primordial
nucleosynthesis in different models. Using these estimates we find constraints
on dimensionless combinations of the 5D gravitational scale, scale of the warp
factor and coupling at the 4D curvature term in the action. |
Imprint of entanglement entropy in the power spectrum of inflationary
fluctuations: If the inflaton couples to other degrees of freedom that populate the
post-inflationary stage, such coupling modifies the dynamics of the inflaton
\emph{during} inflation. We consider light fermions Yukawa coupled to the
inflaton as "unobserved" degrees of freedom integrated out of the total density
matrix. Tracing out these degrees of freedom yields a \emph{mixed} density
matrix whose time evolution is described by an effective field theory. We show
that the coupling leads to profuse fermion pair production for super-Hubble
inflaton fluctuations which lead to the \emph{growth of entanglement entropy
during inflation}. The power spectrum of inflaton fluctuations features scale
invariance violations $\mathcal{P}(k) = \mathcal{P}_0(k)\,\,\exp\{8\,\xi_k\}$
with corrections to the \emph{index and its running directly correlated with
the entanglement entropy}: $S_{vN} = - \sum_{k} \Big[ \ln(1-\xi_k) +
\frac{\xi_k\,\ln(\xi_k)}{1-\xi_k} \Big]$. For super-Hubble fluctuations we find
$\xi_k = -\frac{Y^2}{48\pi^2}\Big\{2\,N_T\,\ln(k/k_f) + \ln^2(k/k_f)\Big\}$
with $Y$ the Yukawa coupling, $N_T$ the total number of e-folds during
inflation, and $k_f$ a "pivot" scale corresponding to the mode that crosses the
Hubble radius at the end of inflation. | On the detection of a cosmic dawn signal in the radio background: The astrophysics of cosmic dawn, when star formation commenced in the first
collapsed objects, is predicted to be revealed as spectral and spatial
signatures in the cosmic radio background at long wavelengths. The sky-averaged
redshifted 21-cm absorption line of neutral hydrogen is a probe of cosmic dawn.
The line profile is determined by the evolving thermal state of the gas,
radiation background, Lyman-$\alpha$ radiation from stars scattering off cold
primordial gas and the relative populations of the hyperfine spin levels in
neutral hydrogen atoms. We report a radiometer measurement of the spectrum of
the radio sky in the 55--85~MHz band, which shows that the profile found by
Bowman et al. in data taken with the Experiment to Detect the Global Epoch of
Reionization Signature (EDGES) low-band instrument is not of astrophysical
origin; their best-fitting profile is rejected with 95.3\% confidence. The
profile was interpreted to be a signature of cosmic dawn; however, its
amplitude was substantially higher than that predicted by standard cosmological
models. Explanations for the amplitude of the profile included non-standard
cosmology, additional mechanisms for cooling the baryons, perhaps via
interactions with millicharged dark matter and an excess radio background at
redshifts beyond 17. Our non-detection bears out earlier concerns and suggests
that the profile found by Bowman et al. is not evidence for new astrophysics or
non-standard cosmology. |
A nearby GRB host galaxy: VLT/X-shooter observations of HG 031203: (abridged) Long-duration gamma-ray bursts (LGRBs) occur in galaxies of
generally low metallicity. We aim at a spectroscopic analysis of HG 031203, the
host galaxy of a LRGB burst, to obtain its properties. Based on VLT/X-shooter
spectroscopic observations in the wavelength range 3200-24000A, we use standard
direct methods to evaluate physical conditions and element abundances. The
resolving power of the instrument also allowed us to trace the kinematics of
the ionised gas. We derive an interstellar oxygen abundance of
12+logO/H=8.20+/-0.03. The observed fluxes of hydrogen lines correspond to the
theoretical recombination values after correction for extinction with a single
value C(Hbeta)=1.67. We produce the CLOUDY photoionisation HII region model
that reproduces observed emission-line fluxes of different ions in the optical
range. This model also predicts emission-line fluxes in the near-infrared (NIR)
and mid-infrared (MIR) ranges that agree well with the observed ones. This
implies that the star-forming region observed in the optical range is the only
source of ionisation and there is no additional source of ionisation seen in
the NIR and MIR ranges that is hidden in the optical range.We find that the
heavy element abundances, Halpha luminosity, stellar mass, star-formation rate
and specific star-formation rate of HG 031203 are in the range that is covered
by the luminous compact galaxies (LCGs).This implies that the LCGs with extreme
star-formation that also comprise green pea galaxies as a subclass may harbour
LGRBs. | Populations behind the source-subtracted cosmic infrared background
anisotropies: While the upcoming telescopes will reveal correspondingly fainter, more
distant galaxies, a question will persist: what more is there that these
telescopes cannot see? One answer is the source-subtracted Cosmic Infrared
Background (CIB). The CIB is comprised of the collective light from all sources
remaining after known, resolved sources are accounted for. Ever-more-sensitive
surveys will identify the brightest of these, allowing them to be removed, and
- like peeling layers off an onion - reveal deeper layers of the CIB. In this
way it is possible to measure the contributions from populations not accessible
to direct telescopic observation. Measurement of fluctuations in the
source-subtracted CIB, i.e., the spatial power spectrum of the CIB after
subtracting resolved sources, provides a robust means of characterizing its
faint, and potentially new, populations. Studies over the past 15 years have
revealed source-subtracted CIB fluctuations on scales out to ~100' which cannot
be explained by extrapolating from known galaxy populations. Moreover, they
appear highly coherent with the unresolved Cosmic X-ray Background, hinting at
a significant population of accreting black holes among the CIB sources.
Characterizing the source-subtracted CIB with high accuracy, and thereby
constraining the nature of the new populations, is feasible with upcoming
instruments and would produce critically important cosmological information in
the next decade. New coextensive deep and wide-area near-infrared, X-ray, and
microwave surveys will bring decisive opportunities to examine, with high
fidelity, the spatial spectrum and origin of the CIB fluctuations and their
cross-correlations with cosmic microwave and X-ray backgrounds, and determine
the formation epochs and the nature of the new sources (stellar nucleosynthetic
or accreting black holes). |
The Sherwood-Relics simulations: overview and impact of patchy
reionization and pressure smoothing on the intergalactic medium: We present the Sherwood-Relics simulations, a new suite of large cosmological
hydrodynamical simulations aimed at modelling the intergalactic medium (IGM)
during and after the cosmic reionization of hydrogen. The suite consists of
over 200 simulations that cover a wide range of astrophysical and cosmological
parameters. It also includes simulations that use a new lightweight hybrid
scheme for treating radiative transfer effects. This scheme follows the spatial
variations in the ionizing radiation field, as well as the associated
fluctuations in IGM temperature and pressure smoothing. It is computationally
much cheaper than full radiation hydrodynamics simulations and circumvents the
difficult task of calibrating a galaxy formation model to observational
constraints on cosmic reionization. Using this hybrid technique, we study the
spatial fluctuations in IGM properties that are seeded by patchy cosmic
reionization. We investigate the relevant physical processes and assess their
impact on the z > 4 Lyman-alpha forest. Our main findings are: (i) Consistent
with previous studies patchy reionization causes large scale temperature
fluctuations that persist well after the end of reionization, (ii) these
increase the Lyman-alpha forest flux power spectrum on large scales, and (iii)
result in a spatially varying pressure smoothing that correlates well with the
local reionization redshift. (iv) Structures evaporated or puffed up by
photoheating cause notable features in the Lyman-alpha forest, such as
flat-bottom or double-dip absorption profiles. | Exploring delaying and heating effects on the 21-cm signature of fuzzy
dark matter: In the fuzzy dark matter (FDM) model, dark matter is composed of ultra-light
particles with a de Broglie wavelength of $\sim$kpc, above which it behaves
like cold dark matter (CDM). Due to this, FDM suppresses the growth of
structure on small scales, which delays the onset of the cosmic dawn (CD) and
the subsequent epoch of reionization (EoR). This leaves potential signatures in
the sky averaged 21-cm signal (global), as well as in the 21-cm fluctuations,
which can be sought for with ongoing and future 21-cm global and intensity
mapping experiments. To do so reliably, it is crucial to include effects such
as the dark-matter/baryon relative velocity and Lyman-Werner star-formation
feedback, which also act as delaying mechanisms, as well as CMB and \lya
heating effects, which can significantly change the amplitude and timing of the
signal, depending on the strength of X-ray heating sourced by the remnants of
the first stars. Here we model the 21-cm signal in FDM cosmologies across CD
and EoR using a modified version of the public code 21cmvFAST that accounts for
all these additional effects, and is directly interfaced with the Boltzmann
code CLASS so that degeneracies between cosmological and astrophysical
parameters can be fully explored. We examine the prospects to distinguish
between the CDM and FDM models and forecast joint astrophysical, cosmological
and FDM parameter constraints achievable with intensity mapping experiments
such as HERA and global signal experiments like EDGES. We find that HERA will
be able to detect FDM particle masses up to $m_{\rm FDM}\! \sim
\!10^{-19}\,{\rm eV}\!-\!10^{-18}\,{\rm eV}$, depending on foreground
assumptions, despite the mitigating effect of the delaying and heating
mechanisms included in the analysis. |
The nonlinear evolution of large scale structures in Growing Neutrino
cosmologies: We present the results of the first N-body simulations of the Growing
Neutrino scenario, as recently discussed in Baldi et al. (2011). Our results
have shown for the first time how neutrino lumps forming in the context of
Growing Neutrino cosmologies are expected to pulsate as a consequence of the
rapid oscillations of the dark energy scalar field. We have also computed for
the first time a realistic statistical distribution of neutrino halos and
determined their impact on the underlying Cold Dark Matter structures. | The Connection Between Diffuse Light and Intracluster Planetary Nebulae
in the Virgo Cluster: We compare the distribution of diffuse intracluster light detected in the
Virgo Cluster via broadband imaging with that inferred from searches for
intracluster planetary nebulae (IPNe). We find a rough correspondence on large
scales (~ 100 kpc) between the two, but with very large scatter (~ 1.3
mag/arcsec^2). On smaller scales (1 -- 10 kpc), the presence or absence of
correlation is clearly dependent on the underlying surface brightness. On these
scales, we find a correlation in regions of higher surface brightness (mu_V <
~27) which are dominated by the halos of large galaxies such as M87, M86, and
M84. In those cases, we are likely tracing PNe associated with galaxies rather
than true IPNe. In true intracluster fields, at lower surface brightness, the
correlation between luminosity and IPN candidates is much weaker. While a
correlation between broadband light and IPNe is expected based on stellar
populations, a variety of statistical, physical, and methodological effects can
act to wash out this correlation and explain the lack of a strong correlation
at lower surface brightness found here. [abridged] |
Multi-wavelength properties of Spitzer-selected starbursts at z~2: A complete sample of 33 sources believed to be starbursts
("5.8micron-peakers") was selected in the (0.5 sq. deg.) J1046+56 field with
selection criteria F_(24micron)>400muJy, the presence of a redshifted stellar
emission peak at 5.8um, and r'(Vega)>23. The field, part of the SWIRE Lockman
Hole field, benefits from very deep VLA/GMRT 20cm, 50cm, and 90cm radio data
(all 33 sources are detected at 50cm), and deep 160micron and 70micron Spitzer
data. The 33 sources, with photometric redshifts ~1.5-2.5, were observed at
1.2mm with IRAM-30m/MAMBO to an rms ~0.7-0.8mJy in most cases. Their
millimeter, radio, 7-band Spitzer, and near-IR properties were jointly
analyzed. The entire sample of 33 sources has an average 1.2mm flux density of
1.56+/-0.22mJy and a median of 1.61mJy, so the majority of the sources can be
considered SMGs. Four sources have confirmed 4sigma detections, and nine were
tentatively detected at the 3sigma level. Because of its 24micron selection,
our sample shows systematically lower F_(1.2mm)/F_(24micron) flux ratios than
classical SMGs, probably because of enhanced PAH emission. A median FIR SED was
built by stacking images at the positions of 21 sources in the region of
deepest Spitzer coverage. Its parameters are T_(dust)=37+/-8K,
L_(FIR)=2.5x10^{12}Lo, and SFR=450Mo/yr. The FIR-radio correlation provides
another estimate of L_(FIR) for each source, with an average value of
4.1x10^{12}Lo; however, this value may be overestimated because of some AGN
contribution. Most of our targets are also luminous star-forming BzK galaxies
which constitute a significant fraction of weak SMGs at 1.7<z<2.3. | The Halo Boltzmann Equation: Dark matter halos are the building blocks of the universe as they host
galaxies and clusters. The knowledge of the clustering properties of halos is
therefore essential for the understanding of the galaxy statistical properties.
We derive an effective halo Boltzmann equation which can be used to describe
the halo clustering statistics. In particular, we show how the halo Boltzmann
equation encodes a statistically biased gravitational force which generates a
bias in the peculiar velocities of virialized halos with respect to the
underlying dark matter, as recently observed in N-body simulations. |
Dark Matter in Cosmology: In this paper we review the main theoretical and experimental achievements in
the field of Dark Matter from the Cosmological and Astrophysical point of view.
We revisit it from the very first surveys of local astrophysical matter, up to
the stringent constraints on matter properties, coming from the last release of
data on cosmological scales. To bring closer and justify the idea of dark
matter, we will go across methods and tools for measuring dark matter
characteristics, and in some cases a combination of methods that provide one of
the greatest direct proofs for dark matter, such as Bullet cluster. | Full-sky CMB lensing reconstruction in presence of sky-cuts: We consider the reconstruction of the CMB lensing potential and its power
spectrum of the full sphere in presence of sky-cuts due to point sources and
Galactic contaminations. Those two effects are treated separately. Small
regions contaminated by point sources are filled in using Gaussian constrained
realizations. The Galactic plane is simply masked using an apodized mask before
lensing reconstruction. This algorithm recovers the power spectrum of the
lensing potential with no significant bias. |
Primordial non-Gaussianity from mixed inflaton-curvaton perturbations: We characterise the primordial perturbations produced due to both inflaton
and curvaton fluctuations in models where the curvaton has a quadratic, cosine
or hyperbolic potential, and the inflaton potential is characterised by the
usual slow-roll parameters. Isocurvature curvaton field perturbations can
produce significant non-Gaussianity in the primordial density field, in
contrast with adiabatic inflaton field perturbations which produce negligible
non-Gaussianity for canonical scalar fields. A non-self-interacting curvaton
with quadratic potential produces a local-type non-Gaussianity that is well
described by the non-linearity parameter fNL, which may be scale-dependent when
the inflaton perturbations dominate the power spectrum. We show how
observational bounds on non-linearity parameters and the tensor-scalar ratio
can be used to constrain curvaton and inflaton parameters. We find a
consistency relation between the bispectrum and trispectrum parameters in a
mixed inflaton-curvaton model for a quadratic curvaton potential.
Self-interaction terms in the curvaton potential can lead to both a large
trispectrum parameter, gNL, and scale-dependence of the non-linearity
parameters. | Dark energy as stimulated emission of gravitons from a background brane: The idea that dark energy is gravitational waves may explain its strength and
its time-evolution provided that the additional energy comes from a background.
A possible concept is that dark energy is the ensemble of coherent bursts
(solitons) of gravitational waves originally produced by stimulated emission
when the first generation of super-massive black holes was formed. These
solitons get their initial energy as well as keep up their energy density
throughout the evolution of the universe by stimulating emission from a
background brane. We model this process by working out this energy transfer in
a Boltzmann equation approach. The transit of these gravitational wave solitons
may be detectable. Key tests include pulsar timing, clock jitter and the radio
and neutrino backgrounds. |
The CoNFIG Catalogue - II. Comparison of Space Densities in the FR
Dichotomy: This paper focuses on a comparison of the space densities of FRI and FRII
sources at different epochs, with a particular focus on FRI sources. First, we
present the concluding steps in constructing the Combined NVSS-FIRST Galaxy
catalogue (CoNFIG), including new VLA observations, optical identifications and
redshift estimates. The final catalogue consists of 859 sources over 4 samples
(CoNFIG-1, 2, 3 and 4 with flux density limits of S_1.4GHz = 1.3, 0.8, 0.2 and
0.05 Jy respectively). It is 95.7% complete in radio morphology classification
and 74.3% of the sources have redshift data. Combining CoNFIG with
complementary samples, the distribution and evolution of FRI and FRII sources
are investigated. We find that FRI sources undergo mild evolution and that, at
the same radio luminosity, FRI and FRII sources show similar space density
enhancements in various redshift ranges, possibly implying a common evolution. | The Planetary Nebula Spectrograph survey of S0 galaxy kinematics. Data
and Overview: The origins of S0 galaxies remain obscure, with various mechanisms proposed
for their formation, likely depending on environment. These mechanisms would
imprint different signatures in the galaxies' stellar kinematics out to large
radii, offering a method for distinguishing between them. We aim to study a
sample of six S0 galaxies from a range of environments, and use planetary
nebulae (PNe) as tracers of their stellar populations out to very large radii,
to determine their kinematics in order to understand their origins. Using a
special-purpose instrument, the Planetary Nebula Spectrograph, we observe and
extract PNe catalogues for these six systems*. We show that the PNe have the
same spatial distribution as the starlight, that the numbers of them are
consistent with what would be expected in a comparable old stellar population
in elliptical galaxies, and that their kinematics join smoothly onto those
derived at smaller radii from conventional spectroscopy. The high-quality
kinematic observations presented here form an excellent set for studying the
detailed kinematics of S0 galaxies, in order to unravel their formation
histories. We find that PNe are good tracers of stellar kinematics in these
systems. We show that the recovered kinematics are largely dominated by
rotational motion, although with significant random velocities in most cases. |
The Scale Dependence of the Molecular Gas Depletion Time in M33: We study the Local Group spiral galaxy M33 to investigate how the observed
scaling between the (kpc-averaged) surface density of molecular gas (\Sigma_H2)
and recent star formation rate (\Sigma_SFR) relates to individual star-forming
regions. To do this, we measure the ratio of CO emission to
extinction-corrected Halpha emission in apertures of varying sizes centered
both on peaks of CO and Halpha emission. We parameterize this ratio as a
molecular gas (H_2) depletion time (\tau_dep). On large (kpc) scales, our
results are consistent with a molecular star formation law (Sigma_SFR \sim
Sigma_H2^b) with b \sim 1.1 - 1.5 and a median \tau_dep \sim 1 Gyr, with no
dependence on type of region targeted. Below these scales, \tau_dep is a strong
function of adopted angular scale and the type of region that is targeted.
Small (\lesssim 300pc) apertures centered on CO peaks have very long \tau_dep
(i.e., high CO-to-Halpha flux ratio) and small apertures targeted toward Halpha
peaks have very short \tau_dep. This implies that the star formation law
observed on kpc scales breaks down once one reaches aperture sizes of \lesssim
300pc. For our smallest apertures (75pc), the difference in \tau_dep between
the two types of regions is more than one order of magnitude. This scale
behavior emerges from averaging over star-forming regions with a wide range of
CO-to-Halpha ratios with the natural consequence that the breakdown in the star
formation law is a function of the surface density of the regions studied. We
consider the evolution of individual regions the most likely driver for
region-to-region differences in \tau_dep (and thus the CO-to-Halpha ratio). | Photon Number Conserving Models of H II Bubbles during Reionization: Traditional excursion set based models of H II bubble growth during the epoch
of reionization are known to violate photon number conservation, in the sense
that the mass fraction in ionized bubbles in these models does not equal the
ratio of the number of ionizing photons produced by sources and the number of
hydrogen atoms in the intergalactic medium. E.g., for a Planck13 cosmology with
electron scattering optical depth $\tau\simeq0.066$, the discrepancy is
$\sim15$ per cent for $x_{\rm HII}=0.1$ and $\sim5$ per cent for $x_{\rm
HII}=0.5$. We demonstrate that this problem arises from a fundamental
conceptual shortcoming of the excursion set approach (already recognised in the
literature on this formalism) which only tracks average mass fractions instead
of the exact, stochastic source counts. With this insight, we build an
approximately photon number conserving Monte Carlo model of bubble growth based
on partitioning regions of dark matter into halos. Our model, which is formally
valid for white noise initial conditions (ICs), shows dramatic improvements in
photon number conservation, as well as substantial differences in the bubble
size distribution, as compared to traditional models. We explore the trends
obtained on applying our algorithm to more realistic ICs, finding that these
improvements are robust to changes in the ICs. Since currently popular
semi-numerical schemes of bubble growth also violate photon number
conservation, we argue that it will be worthwhile to pursue new, explicitly
photon number conserving approaches. Along the way, we clarify some
misconceptions regarding this problem that have appeared in the literature. |
Effective Field Theory for Large Scale Structure: This chapter is a non-expert introduction to the effective field theory of
large scale structure. First, we give a detailed pedagogical explanation of why
previous attempts to build non-linear cosmological perturbation theory failed.
After that we introduce the description of dark matter as an effective
non-ideal fluid and show how it corrects the shortcomings of the previous
approaches. Finally, we develop a formulation of the effective field theory of
large-scale structure from a nonequilibrium field theory perspective, called
time-sliced perturbation theory. We show how this framework can be used for a
consistent renormalization of cosmological correlation functions and a
systematic resummation of large infrared effects relevant for the baryon
acoustic oscillations. | Physics Beyond The Standard Model with Circular Polarization in the CMB
and CMB-21cm Cross-Correlation: Circular polarization is a relatively unexplored realm of CMB physics. Given
the substantial community effort towards building next generation CMB
polarization experiments, including those which will be sensitive to circular
polarization, it behooves theorists to understand the possible sources and
relevant physics of circular polarization, as encoded in the Stokes V
parameter. In this work we develop and derive the requisite formalism, namely
the Boltzmann hierarchy for V-mode scalar, vector, and tensor, anisotropies. We
derive the V-mode anisotropies induced by a general source term, and
demonstrate how existing proposals for the generation of V can be incorporated
as source terms in the Boltzmann hierarchy. A subset of these effects may be
correlated with 21cm intensity; we provide a worked example and derive an
estimator to extract this information from observations. We conclude by
computing the CMB TV cross-correlation generated by axions, and find a relation
between TV and VV spectra in axion models. |
X-ray Spectral Constraints for z~2 Massive Galaxies: The Identification
of Reflection-Dominated Active Galactic Nuclei: We use the 4Ms CDF-S survey to place direct X-ray constraints on the ubiquity
of z~2 heavily obscured AGNs in K<22 BzK galaxies. Forty seven of the 222 BzK
galaxies in the central region of the CDF-S are detected at X-ray energies, 11
of which have hard X-ray spectral slopes (Gamma<1) indicating the presence of
heavily obscured AGN activity. The other 36 X-ray detected BzK galaxies appear
to be relatively unobscured AGNs and starburst galaxies; we use X-ray
variability analyses over a rest-frame baseline of ~3 years to further confirm
the presence of AGN activity in many of these systems. The majority (7 out of
11) of the heavily obscured AGNs have excess IR emission over that expected
from star formation (termed "IR-excess galaxies"). However, we find that X-ray
detected heavily obscured AGNs only comprise ~25% of the IR-excess galaxy
population, which is otherwise composed of relatively unobscured AGNs and
starburst galaxies. We find that the typical X-ray spectrum of the heavily
obscured AGNs is better characterized by a pure reflection model than an
absorbed power-law model, suggesting extreme Compton-thick absorption in some
systems. We verify this result by producing a composite rest-frame 2-20 keV
spectrum, which has a similar shape as a reflection-dominated X-ray spectrum
and reveals an emission feature at rest-frame energy ~6.4 keV, likely to be due
to Fe K. These heavily obscured AGNs are likely to be the distant analogs of
the reflection-dominated AGNs recently identified at z~0 with >10 keV
observatories. On the basis of these analyses we estimate the space density for
typical (intrinsic X-ray luminosities of L_X>1E43 erg/s) heavily obscured and
Compton-thick AGNs at z~2. Our space-density constraints are conservative lower
limits but they are already consistent with the range of predictions from X-ray
background models. | Interpreting measurements of the anisotropic galaxy power spectrum: The most commonly used estimators of the anisotropic galaxy power spectrum
employ Fast Fourier transforms, and rely on a specific choice of the
line-of-sight that breaks the symmetry between the galaxy pair. This leads to
wide-angle effects, including the presence of odd power spectrum multipoles
like the dipole ($\ell = 1$) and octopole ($\ell = 3$). In Fourier-space these
wide-angle effects also couple to the survey window function. We present a
self-consistent framework extending the commonly used window function treatment
to include the wide-angle effects. We show that our framework can successfully
model the wide-angle effects in the BOSS DR12 dataset. We present estimators
for the odd power spectrum multipoles and, detect these multipoles in BOSS DR12
with high significance. Understanding the impact of the wide-angle effects on
the power spectrum multipoles is essential for many cosmological observables
like primordial non-Gaussianity and the detection of General Relativistic
effects and represents a potential systematic for measurements of Baryon
Acoustic Oscillations and redshift-space distortions. |
Can Early Dark Energy Explain EDGES?: The Experiment to Detect the Global Epoch of Reionization Signature (EDGES)
collaboration has reported the detection of an absorption feature in the
sky-averaged spectrum at $\approx 78$ MHz. This signal has been interpreted as
the absorption of cosmic microwave background (CMB) photons at redshifts $15
\lesssim z \lesssim 20$ by the 21cm hyperfine transition of neutral hydrogen,
whose temperature is expected to be coupled to the gas temperature by the
Wouthuysen-Field effect during this epoch. Because the gas is colder than the
CMB, the 21cm signal is seen in absorption. However, the absorption depth
reported by EDGES is more than twice the maximal value expected in the standard
cosmological model, at $\approx 3.8\sigma$ significance. Here, we propose an
explanation for this depth based on "early dark energy" (EDE), a scenario in
which an additional component with equation of state $w=-1$ contributes to the
cosmological energy density at early times, before decaying rapidly at a
critical redshift, $z_c$. For $20 \lesssim z_c \lesssim 1000$, the accelerated
expansion due to the EDE can produce an earlier decoupling of the gas
temperature from the radiation temperature than that in the standard model,
giving the gas additional time to cool adiabatically before the first luminous
sources form. We show that the EDE scenario can successfully explain the large
amplitude of the EDGES signal. However, such models are strongly ruled out by
observations of the CMB temperature power spectrum. Moreover, the EDE models
needed to explain the EDGES signal exacerbate the current tension in low- and
high-redshift measurements of the Hubble constant. We conclude that
non-finely-tuned modifications of the background cosmology are unlikely to
explain the EDGES signal while remaining consistent with other cosmological
observations. | The shape of the CMB lensing bispectrum: Lensing of the CMB generates a significant bispectrum, which should be
detected by the Planck satellite at the 5-sigma level and is potentially a
non-negligible source of bias for f_NL estimators of local non-Gaussianity. We
extend current understanding of the lensing bispectrum in several directions:
(1) we perform a non-perturbative calculation of the lensing bispectrum which
is ~10% more accurate than previous, first-order calculations; (2) we
demonstrate how to incorporate the signal variance of the lensing bispectrum
into estimates of its amplitude, providing a good analytical explanation for
previous Monte-Carlo results; and (3) we discover the existence of a
significant lensing bispectrum in polarization, due to a previously-unnoticed
correlation between the lensing potential and E-polarization as large as 30% at
low multipoles. We use this improved understanding of the lensing bispectra to
re-evaluate Fisher-matrix predictions, both for Planck and cosmic variance
limited data. We confirm that the non-negligible lensing-induced bias for
estimation of local non-Gaussianity should be robustly treatable, and will only
inflate f_NL error bars by a few percent over predictions where lensing effects
are completely ignored (but note that lensing must still be accounted for to
obtain unbiased constraints). We also show that the detection significance for
the lensing bispectrum itself is ultimately limited to 9 sigma by cosmic
variance. The tools that we develop for non-perturbative calculation of the
lensing bispectrum are directly relevant to other calculations, and we give an
explicit construction of a simple non-perturbative quadratic estimator for the
lensing potential and relate its cross-correlation power spectrum to the
bispectrum. Our numerical codes are publicly available as part of CAMB and
LensPix. |
A Monte Carlo Approach to Evolution of the Far-Infrared Luminosity
Function with BLAST: We constrain the evolution of the rest-frame far-infrared (FIR) luminosity
function out to high redshift, by combining several pieces of complementary
information provided by the deep Balloon-borne Large-Aperture Submillimeter
Telescope surveys at 250, 350 and 500 micron, as well as other FIR and
millimetre data. Unlike most other phenomenological models, we characterise the
uncertainties in our fitted parameters using Monte Carlo Markov Chains. We use
a bivariate local luminosity function that depends only on FIR luminosity and
60-to-100 micron colour, along with a single library of galaxy spectral energy
distributions indexed by colour, and apply simple luminosity and density
evolution. We use the surface density of sources, Cosmic Infrared Background
(CIB) measurements and redshift distributions of bright sources, for which
identifications have been made, to constrain this model. The precise evolution
of the FIR luminosity function across this crucial range has eluded studies at
longer wavelengths (e.g., using SCUBA and MAMBO) and at shorter wavelengths
(e.g., Spitzer), and should provide a key piece of information required for the
study of galaxy evolution. Our adoption of Monte Carlo methods enables us not
only to find the best-fit evolution model, but also to explore correlations
between the fitted parameters. Our model-fitting approach allows us to focus on
sources of tension coming from the combination of data-sets. We specifically
find that our choice of parameterisation has difficulty fitting the combination
of CIB measurements and redshift distribution of sources near 1 mm. Existing
and future data sets will be able to dramatically improve the fits, as well as
break strong degeneracies among the models. [abridged] | The discovery of diffuse steep spectrum sources in Abell 2256: Context: Hierarchical galaxy formation models indicate that during their
lifetime galaxy clusters undergo several mergers. Here we report on the
discovery of three diffuse radio sources in the periphery of Abell 2256, using
the GMRT.
Aims: The aim of the observations was to search for diffuse ultra-steep
spectrum radio sources within the galaxy cluster Abell 2256.
Methods: We have carried out GMRT 325 MHz radio continuum observations of
Abell 2256. V, R and I band images of the cluster were taken with the 4.2m WHT.
Results: We have discovered three diffuse elongated radio sources located
about 1 Mpc from the cluster center. Two are located to the west of the cluster
center, and one to the southeast. The sources have a measured physical extent
of 170, 140 and 240 kpc, respectively. The two western sources are also visible
in deep low-resolution 115-165 MHz WSRT images, although they are blended into
a single source. For the combined emission of the blended source we find an
extreme spectral index of -2.05\pm 0.14 between 140 and 351 MHz. The extremely
steep spectral index suggests these two sources are most likely the result of
adiabatic compression of fossil radio plasma due to merger shocks.
Conclusions: The discovery of the steep spectrum sources implies the
existence of a population of faint diffuse radio sources in (merging) clusters
with such steep spectra that they have gone unnoticed in higher frequency
(\gtrsim 1 GHz) observations. An exciting possibility therefore is that such
sources will determine the general appearance of clusters in low-frequency high
resolution radio maps as will be produced by for example LOFAR or LWA. |
A Search for Moderate-Redshift Survivors from the Population of Luminous
Compact Passive Galaxies at High Redshift: From a search of a ~ 2400 square degree region covered by both the SDSS and
UKIDSS databases, we have attempted to identify galaxies at z ~ 0.5 that are
consistent with their being essentially unmodified examples of the luminous
passive compact galaxies found at z ~ 2.5. After isolating good candidates via
deeper imaging, we further refine the sample with Keck moderate-resolution
spectroscopy and laser-guide-star adaptive-optics imaging. For 4 of the 5
galaxies that so far remain after passing through this sieve, we analyze
plausible star-formation histories based on our spectra in order to identify
galaxies that may have survived with little modification from the population
formed at high redshift. We find 2 galaxies that are consistent with having
formed > 95% of their mass at z > 5. We attempt to estimate masses both from
our stellar population determinations and from velocity dispersions. Given the
high frequency of small axial ratios, both in our small sample and among
samples found at high redshifts, we tentatively suggest that some of the more
extreme examples of passive compact galaxies may have prolate morphologies. | Lens modelling of the strongly lensed Type Ia supernova iPTF16geu: In 2016, the first strongly lensed Type Ia supernova, iPTF16geu at redshift
$z=0.409$ with four resolved images arranged symmetrically around the lens
galaxy at $z=0.2163$, was discovered. Here, refined observations of iPTF16geu,
including the time delay between images, are used to decrease uncertainties in
the lens model, including the the slope of the projected surface density of the
lens galaxy, $\Sigma\propto r^{1-\eta}$, and to constrain the universal
expansion rate $H_0$. Imaging with HST provides an upper limit on the slope
$\eta$, in slight tension with the steeper density profiles indicated by
imaging with Keck after iPTF16geu had faded, potentially due to dust extinction
not corrected for in host galaxy imaging. Since smaller $\eta$ implies larger
magnifications, we take advantage of the standard candle nature of Type Ia
supernovae constraining the image magnifications, to obtain an independent
constraint of the slope. We find that a smooth lens density fails to explain
the iPTF16geu fluxes, regardless of the slope, and additional sub-structure
lensing is needed. The total probability for the smooth halo model combined
with star microlensing to explain the iPTF16geu image fluxes is maximized at
$12\,\%$ for $\eta\sim 1.8$, in excellent agreement with Keck high spatial
resolution data, and flatter than an isothermal halo. It also agrees perfectly
with independent constraints on the slope from lens velocity dispersion
measurements. Combining with the observed time delays between the images, we
infer a lower bound on the Hubble constant, $H_0 \gtrsim 40\,{\rm km \ s^{-1}
Mpc^{-1}}$ at $68.3\,\%$ confidence level. |
Limits of Quasi-Static Approximation in Modified-Gravity Cosmologies: We investigate the limits of applicability of the quasi-static approximation
in cosmologies featuring general models of dark energy or modified gravity. We
show that, at best, the quasi-static approximation breaks down outside of the
sound horizon of the dark-energy, rather than the cosmological horizon as is
frequently assumed. When the sound speed of dark energy is significantly below
that of light, the quasi-static limit is only valid in a limited range of
observable scales and this must be taken into account when computing effects on
observations in such models. As an order of magnitude estimate, in the analysis
of data from today's weak-lensing and peculiar-velocity surveys, dark energy
can be modelled as quasi-static only if the sound speed is larger than order 1%
of that of light. In upcoming surveys, such as Euclid, it should only be used
when the sound speed exceeds around 10% of the speed of light. In the analysis
of the cosmic microwave background, the quasi-static limit should never be used
for the integrated Sachs-Wolf effect and for lensing only when the sound speed
exceeds 10% of the speed of light. | Cosmic metal invaders: Intergalactic OVII as a tracer of the warm-hot
intergalactic medium within cosmic filaments in the EAGLE simulation: The current observational status of the hot (log T(K) > 5.5) warm-hot
intergalactic medium (WHIM) remains incomplete. While recent observations from
stacking large numbers of Cosmic Web filaments have yielded statistically
significant detections, direct measurements of single objects remain scarce.
The lack of such a sample currently prevents a robust analysis of the cosmic
baryon content composed of the hot WHIM, which could help solve the
cosmological missing baryons problem. To improve the search for the missing
baryons, we used the EAGLE simulation. Our aim is to understand the metal
enrichment and distribution of highly ionised metals in the Cosmic Web. We
detected the filaments by applying the Bisous formalism to the simulated
galaxies, and characterised the spatial distributions as well as mass and
volume fractions of the filamentary oxygen and OVII. We then constructed OVII
column density maps and determined their detectability with Athena X-IFU.
However, the oxygen and OVII number densities drop fast beyond the virial radii
of haloes, falling below detectable levels at 700 kpc. Thus, only ~1% of the
filament volumes are filled with OVII at detectable densities. This
non-homogeneous distribution of the OVII complicates its usage for tracing the
missing baryons. Instead, OVII forms narrow envelopes around haloes. This
localised nature results in a low chance (10-20% per sight line) of detecting
intergalactic OVII with Athena X-IFU within the SDSS catalogue of filaments.
With future filament samples from the 4MOST survey, the chances increase up to
a level of ~50%. Nonetheless, based on EAGLE results, this would not be enough
to conclusively solve the missing baryon problem, as it would be limited to a
few times the virial radii of haloes. Fortunately, the volumes around haloes
are dense in hot WHIM, and tracing it could reduce the content of baryons still
missing by ~25%. |
Why weak lensing cluster shapes are insensitive to self-interacting dark
matter: We investigate whether the shapes of galaxy clusters inferred from weak
gravitational lensing can be used as a test of the nature of dark matter. We
analyse mock weak lensing data, with gravitational lenses extracted from
cosmological simulations run with two different dark matter models (CDM and
SIDM). We fit elliptical NFW profiles to the shear fields of the simulated
clusters. Despite large differences in the distribution of 3D shapes between
CDM and SIDM, we find that the distributions of weak-lensing-inferred cluster
shapes are almost indistinguishable. We trace this information loss to two
causes. Firstly, weak lensing measures the shape of the projected mass
distribution, not the underlying 3D shape, and projection effects wash out some
of the difference. Secondly, weak lensing is most sensitive to the projected
shape of clusters, on a scale approaching the virial radius (~ 1.5 Mpc),
whereas SIDM shapes differ most from CDM in the inner halo. We introduce a
model for the mass distribution of galaxy clusters where the ellipticity of the
mass distribution can vary with distance to the centre of the cluster. While
this mass distribution does not enable weak lensing data to distinguish between
CDM and SIDM with cluster shapes (the ellipticity at small radii is poorly
constrained by weak lensing), it could be useful when modelling combined strong
and weak gravitational lensing of clusters. | Large Covariance Matrices: Smooth Models from the 2-Point Correlation
Function: We introduce a new method for estimating the covariance matrix for the galaxy
correlation function in surveys of large-scale structure. Our method combines
simple theoretical results with a realistic characterization of the survey to
dramatically reduce noise in the covariance matrix. For example, with an
investment of only ~1,000 CPU hours we can produce a model covariance matrix
with noise levels that would otherwise require ~35,000 mocks. Non-Gaussian
contributions to the model are calibrated against mock catalogs, after which
the model covariance is found to be in impressive agreement with the mock
covariance matrix. Since calibration of this method requires fewer mocks than
brute force approaches, we believe that it could dramatically reduce the number
of mocks required to analyse future surveys. |
The Mass-Metallicity-SFR Relation at z >~ 2 with 3D-HST: We present new accurate measurements of the physical properties of a
statistically significant sample of 103 galaxies at z~2 using near-infrared
spectroscopy taken as part of the 3D-HST survey. We derive redshifts,
metallicities and star formation rates (SFRs) from the [OII], [OIII] and Hbeta
nebular emission lines and exploit the multi-wavelength photometry available in
CANDELS to measure stellar masses. We find the mass-metallicity relation (MZR)
derived from our data to have the same trend as previous determinations in the
range 0<z<3, with lower mass galaxies having lower metallicities. However we
find an offset in the relation compared to the previous determination of the
z~2 MZR by Erb et al. 2006b, who measure metallicities using the [NII]/Halpha
ratio, with metallicities lower at a given mass. Incorporating our SFR
information we find that our galaxies are offset from the Fundamental
Metallicity Relation (FMR) by ~0.3 dex. We investigate the photoionization
conditions and find that our galaxies are consistent with the elevated
ionization parameter previously reported in high-redshift galaxies. Using the
BPT diagram we argue that, if this is the case, metallicity indicators based on
[NII] and Halpha may not be consistent with the ones obtained via oxygen lines
and Hbeta. Using a recent determination of the theoretical evolution of the
star forming sequence in the BPT diagram we convert our measured [OIII]/Hbeta
line ratios to [NII]/Halpha ratios. From the [NII]/Halpha ratio we infer
systematically higher metallicities in better agreement with the FMR. Our
results thus suggest the evolution of the FMR previously reported at z~2-3 may
be an artifact of the differential evolution in metallicity indicators, and
caution against using locally calibrated metallicity relations at high redshift
which do not account for evolution in the physical conditions of star-forming
regions. | A study of the sensitivity of shape measurements to the input parameters
of weak lensing image simulations: Improvements in the accuracy of shape measurements are essential to exploit
the statistical power of planned imaging surveys that aim to constrain
cosmological parameters using weak lensing by large-scale structure. Although a
range of tests can be performed using the measurements, the performance of the
algorithm can only be quantified using simulated images. This yields, however,
only meaningful results if the simulated images resemble the real observations
sufficiently well. In this paper we explore the sensitivity of the
multiplicative bias to the input parameters of Euclid-like image simulations.We
find that algorithms will need to account for the local density of sources. In
particular the impact of galaxies below the detection limit warrants further
study, because magnification changes their number density, resulting in
correlations between the lensing signal and multiplicative bias. Although
achieving sub-percent accuracy will require further study, we estimate that
sufficient archival Hubble Space Telescope data are available to create
realistic populations of galaxies. |
Cosmology with all-sky surveys: Various aspects of cosmology require comprehensive all-sky mapping of the
cosmic web to considerable depths. In order to probe the whole extragalactic
sky beyond 100 Mpc, one must draw on multiwavelength datasets and
state-of-the-art photometric redshift techniques. Here I summarize our
dedicated program that employs the largest photometric all-sky surveys --
2MASS, WISE and SuperCOSMOS -- to obtain accurate redshift estimates of
millions of galaxies. The first outcome of these efforts -- the 2MASS
Photometric Redshift catalog (2MPZ) -- was publicly released in 2013 and
includes almost 1 million galaxies with a median redshift of z~0.1. I discuss
how this catalog was constructed and how it is being used for various
cosmological tests. I also present how combining the WISE mid-infrared survey
with SuperCOSMOS optical data allowed us to push to depths over 1 Gpc on
unprecedented angular scales. These photometric redshift samples, with about 20
million sources in total, provide access to volumes large enough to study
observationally the Copernican Principle of universal homogeneity and isotropy,
as well as to probe various aspects of dark energy and dark matter through
cross-correlations with other data such as the cosmic microwave or gamma-ray
backgrounds. Last but not least, they constitute a test-bed for forthcoming
wide-angle multi-million galaxy samples expected from such instruments as the
SKA, Euclid, or LSST. | The biasing of baryons on the cluster mass function and cosmological
parameter estimation: We study the effect of baryonic processes on the halo mass function in the
galaxy cluster mass range using a catalogue of 153 high resolution cosmological
hydrodynamical simulations performed with the AMR code ramses. We use the
results of our simulations within a simple analytical model to gauge the
effects of baryon physics on the halo mass function. Neglect of AGN feedback
leads to a significant boost in the cluster mass function similar to that
reported by other authors. However, including AGN feedback not only gives rise
to systems that are similar to observed galaxy clusters, but they also reverse
the global baryonic effects on the clusters. The resulting mass function is
closer to the unmodified dark matter halo mass function but still contains a
mass dependent bias at the 5-10% level. These effects bias measurements of the
cosmological parameters, such as $\sigma_8$ and $\Omega_m$. For current cluster
surveys baryonic effects are within the noise for current survey volumes, but
forthcoming and planned large SZ, X-ray and multi-wavelength surveys will be
biased at the percent level by these processes. The predictions for the halo
mass function including baryonic effects need to be carefully studied with
larger and improved simulations. However, simulations of full cosmological
boxes with the resolution we achieve and including AGN feedback are still
computationally challenging. |
Constraints on the CMB temperature redshift dependence from SZ and
distance measurements: The relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)$
is a key prediction of standard cosmology, but is violated in many non-standard
models. Constraining possible deviations to this law is an effective way to
test the $\Lambda$CDM paradigm and search for hints of new physics. We present
state-of-the-art constraints, using both direct and indirect measurements. In
particular, we point out that in models where photons can be created or
destroyed, not only does the temperature-redshift relation change, but so does
the distance duality relation, and these departures from the standard behaviour
are related, providing us with an opportunity to improve constraints. We show
that current datasets limit possible deviations of the form
$T_{CMB}(z)=T_0(1+z)^{1-\beta}$ to be $\beta=0.004\pm0.016$ up to a redshift
$z\sim 3$. We also discuss how, with the next generation of space and
ground-based experiments, these constraints can be improved by more than one
order of magnitude. | Bayesian non-linear large scale structure inference of the Sloan Digital
Sky Survey data release 7: In this work we present the first non-linear, non-Gaussian full Bayesian
large scale structure analysis of the cosmic density field conducted so far.
The density inference is based on the Sloan Digital Sky Survey data release 7,
which covers the northern galactic cap. We employ a novel Bayesian sampling
algorithm, which enables us to explore the extremely high dimensional
non-Gaussian, non-linear log-normal Poissonian posterior of the three
dimensional density field conditional on the data. These techniques are
efficiently implemented in the HADES computer algorithm and permit the precise
recovery of poorly sampled objects and non-linear density fields. The
non-linear density inference is performed on a 750 Mpc cube with roughly 3 Mpc
grid-resolution, while accounting for systematic effects, introduced by survey
geometry and selection function of the SDSS, and the correct treatment of a
Poissonian shot noise contribution. Our high resolution results represent
remarkably well the cosmic web structure of the cosmic density field.
Filaments, voids and clusters are clearly visible. Further, we also conduct a
dynamical web classification, and estimated the web type posterior distribution
conditional on the SDSS data. |
Clusternets: A deep learning approach to probe clustering dark energy: Machine Learning (ML) algorithms are becoming popular in cosmology for
extracting valuable information from cosmological data. In this paper, we
evaluate the performance of a Convolutional Neural Network (CNN) trained on
matter density snapshots to distinguish clustering Dark Energy (DE) from the
cosmological constant scenario and to detect the speed of sound ($c_s$)
associated with clustering DE. We compare the CNN results with those from a
Random Forest (RF) algorithm trained on power spectra. Varying the dark energy
equation of state parameter $w_{\rm{DE}}$ within the range of -0.7 to -0.99,
while keeping $c_s^2 = 1$, we find that the CNN approach results in a
significant improvement in accuracy over the RF algorithm. The improvement in
classification accuracy can be as high as $40\%$ depending on the physical
scales involved. We also investigate the ML algorithms' ability to detect the
impact of the speed of sound by choosing $c_s^2$ from the set $\{1, 10^{-2},
10^{-4}, 10^{-7}\}$ while maintaining a constant $w_{\rm DE}$ for three
different cases: $w_{\rm DE} \in \{-0.7, -0.8, -0.9\}$. Our results suggest
that distinguishing between various values of $c_s^2$ and the case where
$c_s^2=1$ is challenging, particularly at small scales and when
$w_{\rm{DE}}\approx -1$. However, as we consider larger scales, the accuracy of
$c_s^2$ detection improves. Notably, the CNN algorithm consistently outperforms
the RF algorithm, leading to an approximate $20\%$ enhancement in $c_s^2$
detection accuracy in some cases. | Dissecting the Compton scattering kernel I: Isotropic media: Compton scattering between electrons and photons plays a crucial role in
astrophysical plasmas. Many important aspects of this process can be captured
by using the so-called Compton scattering kernel. For isotropic media, exact
analytic expressions (valid at all electron and photon energies) do exist but
are hampered by numerical issues and often are presented in complicated ways.
In this paper, we summarize, simplify and improve existing analytic expressions
for the Compton scattering kernel, with an eye on clarity and physical
understanding. We provide a detailed overview of important properties of the
kernel covering a wide range of energies and highlighting aspects that have not
been appreciated as much previously. We discuss analytic expressions for the
moments of the kernel, comparing various approximations and demonstrating their
precision. We also illustrate the properties of the scattering kernel for
thermal electrons at various temperatures and photon energies, introducing new
analytic approximations valid to high temperatures. The obtained improved
formulae for the kernel and its moments should prove useful in many
astrophysical computations, one of them being the evolution of spectral
distortions of the cosmic microwave background in the early Universe. A novel
code, CSpack, for efficient computations of the Compton scattering kernel and
its properties (in the future also including anisotropies in the initial
electron and photon distributions) is being developed in a series of papers and
will be available within one month. |
Bayesian model selection without evidences: application to the dark
energy equation-of-state: A method is presented for Bayesian model selection without explicitly
computing evidences, by using a combined likelihood and introducing an integer
model selection parameter $n$ so that Bayes factors, or more generally
posterior odds ratios, may be read off directly from the posterior of $n$. If
the total number of models under consideration is specified a priori, the full
joint parameter space $(\theta, n)$ of the models is of fixed dimensionality
and can be explored using standard Markov chain Monte Carlo (MCMC) or nested
sampling methods, without the need for reversible jump MCMC techniques. The
posterior on $n$ is then obtained by straightforward marginalisation. We
demonstrate the efficacy of our approach by application to several toy models.
We then apply it to constraining the dark energy equation-of-state using a
free-form reconstruction technique. We show that $\Lambda$CDM is significantly
favoured over all extensions, including the simple $w(z){=}{\rm constant}$
model. | Discovering bright quasars at intermediate redshifts based on the
optical/near-IR colors: Identifications of quasars at intermediate redshifts (2.2<z<3.5) are
inefficient in most previous quasar surveys as their optical colors are similar
to those of stars. The near-IR K-band excess technique has been suggested to
overcome this difficulty. Our study also proposed to use optical/near-IR colors
for selecting z<4 quasars. To this method, we selected 105 unidentified bright
targets with i<18.5 from the quasar candidates of SDSS DR6 with both SDSS ugriz
optical and UKIDSS YJHK near-IR photometric data, which satisfy our proposed
Y-K/g-z criterion and have photometric redshifts between 2.2 and 3.5 estimated
from the 9-band SDSS-UKIDSS data. 43 of them were observed with the 2.16m
telescope of NAOC in 2012. 36 of them were identified as quasars at 2.1<z<3.4.
High success rate of discovering these quasars in the SDSS spectroscopic
surveyed area demonstrates the robustness of both the Y-K/g-z selection
criterion and the photometric redshift estimation technique. We also used the
above criterion to investigate the possible star contamination rate to the
quasar candidates of SDSS DR6, and found that it is much higher in selecting
3<z<3.5 quasar candidates than selecting lower redshift ones (z<2.2). The
significant improvement in the photometric redshift estimation by using the
9-band SDSS-UKIDSS data than using the 5-band SDSS data is demonstrated and a
catalog of 7,727 unidentified quasar candidates with photometric redshifts
between 2.2 and 3.5 is provided. We also tested the Y-K/g-z selection criterion
with the SDSS-III/DR9 quasar catalog, and found 96.2% of 17,999 DR9 quasars
with UKIDSS Y and K-band data satisfy our criterion. With some samples of red
and type II quasars, we found that 88% and 96.5% of them can be selected by the
Y-K/g-z criterion respectively, which supports that using the Y-K/g-z criterion
we can efficiently select both unobscured and obscured quasars. (abridged) |
Isocurvature Constraints and Gravitational Ward Identity: Axions and WIMPZILLAs are well-motivated dark matter candidates with
interesting cos- mological implications, such as isocurvature perturbations and
non-Gaussianities. How- ever, these predicted implications in the literature
are based on the assumption that the cross-correlation between curvature and
CDM isocurvature is negligible. This contribution discusses the
cross-correlation in the axion and the WIMPZILLA scenarios. Particularly, it is
shown that the gravitational Ward identity associated with diffeomorphism
invariance plays an important role in this cross-correlation calculation
confirming the assumption. | The slope of the Baryonic Tully-Fisher relation: We present the results of a baryonic Tully-Fisher relation (BTFR) study for a
local sample of relatively isolated disk galaxies. We derive a BTFR with a
slope near 3 measured over about 4 dex in baryon mass for our combined
\textrm{H\,\scriptsize{I}} and bright spiral disk samples. This BTFR is
significantly flatter and has less scatter than the TFR (stellar mass only)
with its slope near 4 reported for other samples and studies. A BTFR slope near
3 is in better agreement with the expected slope from simple $\Lambda$CDM
cosmological simulations that include both stellar and gas baryons. The scatter
in the TFR/BTFR appears to depend on $W_{20}$: galaxies that rotate slower have
more scatter. The atomic gas--to--stars ratio shows a break near $W_{20} = 250$
\kms\, probably associated with a change in star formation efficiency. In
contrast the absence of such a break in the BTFR suggests that this relation
was probably set at the main epoch of baryon dissipation rather than as a
product of later galactic evolution. |
The Cosmically Depressed: Life, Sociology and Identity of Voids: We review and discuss aspects of Cosmic Voids that form the background for
our Void Galaxy Survey (see accompanying paper by Stanonik et al.). Following a
sketch of the general characteristics of void formation and evolution, we
describe the influence of the environment on their development and structure
and the characteristic hierarchical buildup of the cosmic void population. In
order to be able to study the resulting tenuous void substructure and the
galaxies populating the interior of voids, we subsequently set out to describe
our parameter free tessellation-based watershed void finding technique. It
allows us to trace the outline, shape and size of voids in galaxy redshift
surveys. The application of this technique enables us to find galaxies in the
deepest troughs of the cosmic galaxy distribution, and has formed the basis of
our void galaxy program. | The escape of ionizing photons from supernova-dominated primordial
galaxies: In order to assess the contribution of Lyman break galaxies (LBGs) and Lyman
alpha emitters (LAEs) at redshifts 3<z<7 to the ionization of intergalactic
medium (IGM), we investigate the escape fractions of ionizing photons from
supernova-dominated primordial galaxies by solving the three-dimensional
radiative transfer. The model galaxy is employed from an ultra-high-resolution
chemodynamic simulation of a primordial galaxy by Mori & Umemura (2006),which
well reproduces the observed properties of LAEs and LBGs. The total mass of
model galaxy is 10^{11}M_sun. We solve not only photo-ionization but also
collisional ionization by shocks. In addition, according to the chemical
enrichment, we incorporate the effect of dust extinction, taking the size
distributions of dust into account. As a result, we find that dust extinction
reduces the escape fractions by a factor 1.5-8.5 in the LAE phase and by a
factor 2.5-11 in the LBG phase, while the collisional ionization by shocks
increases the escape fractions by a factor ~ 2. The resultant escape fractions
are 0.07-0.47 in the LAE phase and 0.06-0.17 in the LBG phase. These results
are well concordant with the recent estimations derived from the flux ratio at
1500 angstrom to 900 angstrom of LAEs and LBGs. Combining the resultant escape
fractions with the luminosity functions of LAEs and LBGs, we find that high-z
LAEs and LBGs can ionize the IGM at z=3-5. However, ionizing radiation from
LAEs as well as LBGs falls short to ionize the IGM at z>6. That implies that
additional ionization sources may required at z>6. |
HOLISMOKES -- I. Highly Optimised Lensing Investigations of Supernovae,
Microlensing Objects, and Kinematics of Ellipticals and Spirals: We present the HOLISMOKES programme on strong gravitational lensing of
supernovae as a probe of supernova (SN) physics and cosmology. We investigate
the effects of microlensing on early-phase SN Ia spectra using four different
SN explosion models, and find that within 10 rest-frame days after SN
explosion, distortions of SN Ia spectra due to microlensing are typically
negligible ($<$1% distortion within the 1$\sigma$ spread, and $\lesssim$10%
distortion within the 2$\sigma$ spread). This shows great prospects of using
lensed SNe Ia to obtain intrinsic early-phase SN spectra for deciphering SN Ia
progenitors. As a demonstration of the usefulness of lensed SNe Ia for
cosmology, we simulate a sample of mock lensed SN Ia systems that are expected
to have accurate and precise time-delay measurements in the era of the Rubin
Observatory Legacy Survey of Space and Time (LSST). Adopting realistic yet
conservative uncertainties on their time-delay distances and lens angular
diameter distances (of 6.6% and 5%, respectively), we find that a sample of 20
lensed SNe Ia would allow a constraint on the Hubble constant ($H_0$) with 1.3%
uncertainty in the flat $\Lambda$CDM cosmology. We find a similar constraint on
$H_0$ in an open $\Lambda$CDM cosmology, while the constraint degrades to $3\%$
in a flat $w$CDM cosmology. We anticipate lensed SNe to be an independent and
powerful probe of SN physics and cosmology in the upcoming LSST era. | Scatter and bias in weak lensing selected clusters: We examine scatter and bias in weak lensing selected clusters, employing both
an analytic model of dark matter haloes and numerical mock data of weak lensing
cluster surveys. We pay special attention to effects of the diversity of dark
matter distributions within clusters. We find that peak heights of the lensing
convergence map correlates rather poorly with the virial mass of haloes. The
correlation is tighter for the spherical overdensity mass with a higher mean
interior density. We examine the dependence of the halo shape on the peak
heights, and find that the rms scatter caused by the halo diversity scales
linearly with the peak heights with the proportionality factor of 0.1-0.2. The
noise originated from the halo shape is found to be comparable to the source
galaxy shape noise and the cosmic shear noise. We find the significant halo
orientation bias, i.e., weak lensing selected clusters on average have their
major axes aligned with the line-of-sight direction. We compute the orientation
bias using an analytic triaxial halo model and obtain results quite consistent
with the ray-tracing results. We develop a prescription to analytically compute
the number count of weak lensing peaks taking into account all the main sources
of scatters in peak heights. We find that the improved analytic predictions
agree well with the simulation results for high S/N peaks. We also compare the
expected number count with our weak lensing analysis results for 4 sq deg of
Subaru/Suprime-Cam observations and find a good agreement. |
Narrow-Line AGNs: confirming the relationship between metallicity and
accretion rate: We have selected a sample of 292 SDSS Narrow-Emission-Line galaxies known to
have formed and evolved in relative isolation to study the nature and origin of
the AGN phenomenon. The galaxies in our sample have line fluxes with S/N>3 and
were separated using a standard diagnostic diagram into Star Forming Galaxies
(SFGs; 36.0%), Transition type Objects (TOs; 28.4%) and Narrow-Line AGNs
(NLAGNs; 35.6%). Having found a strong correlation between the bulge mass and
the NLAGN phenomenon, we have applied the same relation as for the Broad-Line
AGNs to estimate their black hole (BH) masses. The BH in the NLAGNs are 2 to 3
orders lower in mass than the BHs found in BLAGNs, but are comparable to those
observed in Narrow-Line Seyfert~1, although none of our objects can be
classified as such. To determine the metallicities, [O/H], of the NLAGNs we
calibrated the standard diagnostic diagram [OIII]/Hb vs. [NII]/Ha using similar
relation as for the SFGs, which reproduce the values obtained with CLOUDY
simulations developed for Bennert et al. [3]. For some individual objects we
compared our line ratios with other CLOUDY similations by different authors.
This suggests we achieve a typical uncertainty of 0.2 dex on [O/H], increasing
to 0.3-0.5 in the Seyfert~2 (S2). This calibration suggests the metallicities
of the NLAGNs are subsolar, varying between 1 and 0.3 $Z_\odot$. We find two
statistically significant positive correlations: for [O/H] with the BH mass and
for [O/H] with the luminosity at 5100\AA, $\lambda L(5100$\AA$)$. No
correlation is found between [O/H] and the accretion rate, L_bol/L_Edd.
However, comparisons with the BLAGNs suggest the NLAGNs extend the
metallicity-accretion rate relationship [24] to the low metallicity regime.
Although the NLS1 have similar BH masses as the NLAGNs they show higher
accretion rates, which is consistent with their higher metallicities. | Quantifying the collisionless nature of dark matter and galaxies in
A1689: We use extensive measurements of the cluster A1689 to assess the expected
similarity in the dynamics of galaxies and dark matter (DM) in their motion as
collisionless `particles' in the cluster gravitational potential. To do so we
derive the radial profile of the specific kinetic energy of the cluster
galaxies from the Jeans equation and observational data. Assuming that the
specific kinetic energies of galaxies and DM are roughly equal, we obtain the
mean value of the DM velocity anisotropy parameter, and the DM density profile.
Since this deduced profile has a scale radius that is higher than inferred from
lensing observations, we tested the validity of the assumption by repeating the
analysis using results of simulations for the profile of the DM velocity
anisotropy. Results of both analyses indicate a significant difference between
the kinematics of galaxies and DM within $r \lesssim 0.3r_{\rm vir}$. This
finding is reflected also in the shape of the galaxy number density profile,
which flattens markedly with respect to the steadily rising DM profile at small
radii. Thus, $r \sim 0.3r_{\rm vir}$ seems to be a transition region interior
to which collisional effects significantly modify the dynamical properties of
the galaxy population with respect to those of DM in A1689 |
When tension is just a fluctuation: How noisy data affect model
comparison: Summary statistics of the likelihood, such as the Bayesian evidence, offer a
principled way of comparing models and assessing tension between, or within,
the results of physical experiments. Noisy realisations of the data induce
scatter in these model comparison statistics. For a realistic case of
cosmological inference from large-scale structure we show that the logarithm of
the Bayes factor attains scatter of order unity, increasing significantly with
stronger tension between the models under comparison. We develop an approximate
procedure that quantifies the sampling distribution of the evidence at small
additional computational cost and apply it to real data to demonstrate the
impact of the scatter, which acts to reduce the significance of any model
discrepancies. Data compression is highlighted as a potential avenue to
suppressing noise in the evidence to negligible levels, with a proof of concept
on Planck cosmic microwave background data. | Small scale structures in coupled scalar field dark matter: We investigate structure formation for ultralight scalar field dark matter
coupled to quintessence, in particular the cosmon-bolon system. The linear
power spectrum is computed by a numerical solution of the coupled field
equations. We infer the substructure abundance within a Milky Way-like halo.
Estimates of dark halo abundances from recent galaxy surveys imply a lower
bound on the bolon mass of about $9 \times 10^{-22}$ eV. This seems to exclude
a possible detection of scalar field dark matter through time variation in
pulsar timing signals in the near future. |
Precision Calibration of Radio Interferometers for 21 cm Cosmology with
No Redundancy and Little Knowledge of Antenna Beams and the Radio Sky: We introduce CALAMITY, a precision bandpass calibration method for radio
interferometry. CALAMITY can solve for direction independent gains with
arbitrary frequency structure to the high precision required for 21 cm
cosmology with minimal knowledge of foregrounds or antenna beams and does not
require any degree of redundancy (repeated identical measurements of the same
baseline).
We have achieved this through two key innovations. Firstly, we model the
foregrounds on each baseline independently using a flexible and highly
efficient set of basis functions that have minimal overlap with 21 cm modes and
enforce spectral smoothness in the calibrated foregrounds. Secondly, we use an
off-the-shelf GPU accelerated API (TENSORFLOW) to solve for per-baseline
foregrounds simultaneously with per-frequency antenna gains in a single
optimization loop. GPU acceleration is critical for our technique to be able to
solve for the large numbers of foreground and gain parameters simultaneously
across all frequencies for an interferometer with $\gtrsim 10$ antennas in a
reasonable amount of time. In this paper, we give an overview of our technique
and using realistic simulations and demonstrate its performance in solving for
and removing pathological gain structures to the level necessary to measure
fluctuations in the 21 cm emission field from Hydrogen gas during the Cosmic
Dawn and Reionization. If you want to start using CALAMITY now, you can find a
tutorial notebook at
https://github.com/aewallwi/calamity/blob/main/examples/Calamity_Tutorial.ipynb . | PHAT: PHoto-z Accuracy Testing: Here we introduce PHAT, the PHoto-z Accuracy Testing programme, an
international initiative to test and compare different methods of photo-z
estimation. Two different test environments are set up, one (PHAT0) based on
simulations to test the basic functionality of the different photo-z codes, and
another one (PHAT1) based on data from the GOODS survey. The accuracy of the
different methods is expressed and ranked by the global photo-z bias, scatter,
and outlier rates. Most methods agree well on PHAT0 but produce photo-z
scatters that can differ by up to a factor of two even in this idealised case.
A larger spread in accuracy is found for PHAT1. Few methods benefit from the
addition of mid-IR photometry. Remaining biases and systematic effects can be
explained by shortcomings in the different template sets and the use of priors
on the one hand and an insufficient training set on the other hand. Scatters of
4-8% in Delta_z/(1+z) were obtained, consistent with other studies. However,
somewhat larger outlier rates (>7.5% with Delta_z/(1+z)>0.15; >4.5% after
cleaning) are found for all codes. There is a general trend that empirical
codes produce smaller biases than template-based codes. The systematic,
quantitative comparison of different photo-z codes presented here is a snapshot
of the current state-of-the-art of photo-z estimation and sets a standard for
the assessment of photo-z accuracy in the future. The rather large outlier
rates reported here for PHAT1 on real data should be investigated further since
they are most probably also present (and possibly hidden) in many other
studies. The test data sets are publicly available and can be used to compare
new methods to established ones and help in guiding future photo-z method
development. (abridged) |
Snowmass2021 CMB-HD White Paper: CMB-HD is a proposed millimeter-wave survey over half the sky that would be
ultra-deep (0.5 uK-arcmin) and have unprecedented resolution (15 arcseconds at
150 GHz). Such a survey would answer many outstanding questions about the
fundamental physics of the Universe. Major advances would be 1.) the use of
gravitational lensing of the primordial microwave background to map the
distribution of matter on small scales (k~10 h Mpc^(-1)), which probes dark
matter particle properties. It will also allow 2.) measurements of the thermal
and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density
and velocity, another probe of cosmic structure. In addition, CMB-HD would
allow us to cross critical thresholds: 3.) ruling out or detecting any new,
light (< 0.1 eV) particles that were in thermal equilibrium with known
particles in the early Universe, 4.) testing a wide class of multi-field models
that could explain an epoch of inflation in the early Universe, and 5.) ruling
out or detecting inflationary magnetic fields. CMB-HD would also provide
world-leading constraints on 6.) axion-like particles, 7.) cosmic
birefringence, 8.) the sum of the neutrino masses, and 9.) the dark energy
equation of state. The CMB-HD survey would be delivered in 7.5 years of
observing 20,000 square degrees of sky, using two new 30-meter-class off-axis
crossed Dragone telescopes to be located at Cerro Toco in the Atacama Desert.
Each telescope would field 800,000 detectors (200,000 pixels), for a total of
1.6 million detectors. | Averaging in cosmological models: The averaging problem in cosmology is of considerable importance for the
correct interpretation of cosmological data. We review cosmological
observations and discuss some of the issues regarding averaging. We present a
precise definition of a cosmological model and a rigorous mathematical
definition of averaging, based entirely in terms of scalar invariants. |
A Strong Blend in the Morning: Studying the Circumgalactic Medium Before
Cosmic Noon with Strong, Blended Lyman-$α$ Forest Systems: We study of the properties of a new class of circumgalactic medium absorbers
identified in the Lyman-$\alpha$ forest: "Strong, Blended Lyman-$\alpha$" (or
SBLA) absorption systems. We study SBLAs at $2.4<z<3.1$ in SDSS-IV/eBOSS
spectra by their strong extended Lyman-$\alpha$ absorption complexes covering
138 km/s with an integrated $\log (N_{HI}/$cm$^{-2}) =16.04^{+0.05}_{-0.06}$
and Doppler parameter $b=18.1^{+0.7}_{-0.4}$ km/s.
Clustering with the Lyman-$\alpha$ forest provides a large-scale structure
bias of $b = 2.34\pm0.06$ and halo mass estimate of $M_h \approx 10^{12}{\rm
h^{-1}M_{sol}}$ for our SBLA sample. We measure the ensemble mean column
densities of 22 metal features in the SBLA composite spectrum and find that no
single-population multiphase model for them is viable. We therefore explore the
underlying SBLA population by forward modelling the SBLA absorption
distribution. Based on covariance measurements and favoured populations we find
that $\approx 25$% of our SBLAs have stronger metals. Using silicon only we
find that our strong metal SBLAs trace gas with a $\log(n_H / $cm$^{-3}) >
-2.45$ for $T=10^{3.5}$K and show gas clumping on $<255$ parsec scales. We fit
multiphase models to this strong sub-population and find a low ionization phase
with $n_H=1$cm$^{-3}$, $T=10^{3.5}$K and $[X/H]=0.8$, an intermediate
ionization phase with $\log(n_H / $cm$^{-3}) = -3.35$, $T=10^{3.5}$K and
$[X/H]=-1.1$, and a poorly constrained higher ionization phase. We find that
the low ionization phase traces cold, dense super-solar metallicity gas with a
clumping scale of just 0.009 parsecs. | A Model for the Squeezed Bispectrum in the Non-Linear Regime: We present a model for the squeezed dark matter bispectrum, where the short
modes are deep in the non-linear regime. We exploit the consistency relations
for large-scale structures combined with a response function approach to write
the squeezed bispectrum in terms of a few unknown functions of the short modes.
We provide an ansatz for a fitting function for these response functions,
checking that the resulting model is reliable when compared to the one-loop
squeezed bispectrum. We then test the model against measured bispectra from
numerical simulations for short modes ranging between $k \sim 0.1 \, h/$Mpc,
and $k \sim 0.7 \, h/$Mpc at redshift $z=0$. To evaluate the goodness of the
fit of our model we implement a non-Gaussian covariance and find agreement
within $1$-$\sigma$ standard deviation of the simulated data. |
A Measurement of the CMB Temperature Power Spectrum and Constraints on
Cosmology from the SPT-3G 2018 TT/TE/EE Data Set: We present a sample-variance-limited measurement of the temperature power
spectrum ($TT$) of the cosmic microwave background (CMB) using observations of
a $\sim\! 1500 \,\mathrm{deg}^2$ field made by SPT-3G in 2018. We report
multifrequency power spectrum measurements at 95, 150, and 220GHz covering the
angular multipole range $750 \leq \ell < 3000$. We combine this $TT$
measurement with the published polarization power spectrum measurements from
the 2018 observing season and update their associated covariance matrix to
complete the SPT-3G 2018 $TT/TE/EE$ data set. This is the first analysis to
present cosmological constraints from SPT $TT$, $TE$, and $EE$ power spectrum
measurements jointly. We blind the cosmological results and subject the data
set to a series of consistency tests at the power spectrum and parameter level.
We find excellent agreement between frequencies and spectrum types and our
results are robust to the modeling of astrophysical foregrounds. We report
results for $\Lambda$CDM and a series of extensions, drawing on the following
parameters: the amplitude of the gravitational lensing effect on primary power
spectra $A_\mathrm{L}$, the effective number of neutrino species
$N_{\mathrm{eff}}$, the primordial helium abundance $Y_{\mathrm{P}}$, and the
baryon clumping factor due to primordial magnetic fields $b$. We find that the
SPT-3G 2018 $T/TE/EE$ data are well fit by $\Lambda$CDM with a
probability-to-exceed of $15\%$. For $\Lambda$CDM, we constrain the expansion
rate today to $H_0 = 68.3 \pm 1.5\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$ and the
combined structure growth parameter to $S_8 = 0.797 \pm 0.042$. The SPT-based
results are effectively independent of Planck, and the cosmological parameter
constraints from either data set are within $<1\,\sigma$ of each other.
(abridged) | Dark matter-radiation interactions: the impact on dark matter haloes: Interactions between dark matter (DM) and radiation (photons or neutrinos) in
the early Universe suppress density fluctuations on small mass scales. Here we
perform a thorough analysis of structure formation in the fully non-linear
regime using N-body simulations for models with DM-radiation interactions and
compare the results to a traditional calculation in which DM only interacts
gravitationally. Significant differences arise due to the presence of
interactions, in terms of the number of low-mass DM haloes and their
properties, such as their spin and density profile. These differences are
clearly seen even for haloes more massive than the scale on which density
fluctuations are suppressed. We also show that semi-analytical descriptions of
the matter distribution in the non-linear regime fail to reproduce our
numerical results, emphasizing the challenge of predicting structure formation
in models with physics beyond collisionless DM. |
Planck 2015 constraints on the non-flat $φ$CDM inflation model: We perform Markov chain Monte Carlo analyses to put constraints on the
non-flat $\phi$CDM inflation model using Planck 2015 cosmic microwave
background (CMB) anisotropy data and baryon acoustic oscillation distance
measurements. The $\phi$CDM model is a consistent dynamical dark energy model
in which the currently accelerating cosmological expansion is powered by a
scalar field $\phi$ slowly rolling down an inverse power-law potential energy
density. We also use a physically consistent power spectrum for energy density
inhomogeneities in this non-flat model. We find that, like the
closed-$\Lambda$CDM and closed-XCDM models, the closed-$\phi$CDM model provides
a better fit to the lower multipole region of the CMB temperature anisotropy
data compared to that provided by the tilted flat-$\Lambda$CDM model. Also,
like the other closed models, this model reduces the tension between the Planck
and the weak lensing $\sigma_8$ constraints. However, the higher multipole
region of the CMB temperature anisotropy data are better fit by the tilted
flat-$\Lambda$CDM model than by the closed models. | Cross-Correlating Probes of Primordial Gravitational Waves: One of the most promising ways of detecting primordial gravitational waves
generated during inflation is to observe B-modes of polarization, generated by
Thomson scattering after reionization, in the cosmic microwave background
(CMB). Large scale foregrounds though are expected to be a major systematic
issue, so -- in the event of a tentative detection -- an independent
confirmation of large scale gravitational waves would be most welcome. Previous
authors have suggested searching for the analogous mode of cosmic shear in weak
lensing surveys but have shown that the signal to noise of this mode is
marginal at best. This argument is reconsidered here, accounting for the
cross-correlations of the polarization and lensing B-modes. A lensing survey
can potentially strengthen the argument for a detection of primordial
gravitational waves, although it is unlikely to help constrain the amplitude of
the signal. |
Measuring the Hubble Constant with cosmic chronometers: a machine
learning approach: Local measurements of the Hubble constant ($H_0$) based on Cepheids e Type Ia
supernova differ by $\approx 5 \sigma$ from the estimated value of $H_0$ from
Planck CMB observations under $\Lambda$CDM assumptions. In order to better
understand this $H_0$ tension, the comparison of different methods of analysis
will be fundamental to interpret the data sets provided by the next generation
of surveys. In this paper, we deploy machine learning algorithms to measure the
$H_0$ through a regression analysis on synthetic data of the expansion rate
assuming different values of redshift and different levels of uncertainty. We
compare the performance of different regression algorithms as Extra-Trees,
Artificial Neural Network, Gradient Boosting, Support Vector Machines, and we
find that the Support Vector Machine exhibits the best performance in terms of
bias-variance tradeoff in most cases, showing itself a competitive cross-check
to non-supervised regression methods such as Gaussian Processes. | A simple Hubble-like law in lieu of dark energy: Within the frame of the $\Lambda$ cold dark matter paradigm, a dark energy
component of unknown origin is expected to represent nearly 70% of the energy
of the Universe. Herein, a non-standard form of the Hubble law is advocated,
with the aim of providing safe grounds on which alternative cosmologies could
be developed. Noteworthy, it yields an age-redshift relationship which is
consistent with available data. Together with a straightforward analysis of
gamma-ray burst counts, it further suggests that the observable Universe has
been euclidean and static over the last 12 Gyr. Although a non-standard
distance-duality relation is then required for interpreting luminosity
distances, the magnitude-redshift relationship obtained is compatible with type
Ia supernovae data. |
Revisiting The First Galaxies: The epoch of Population III stars: We investigate the transition from primordial Population III (Pop III) star
formation to normal Pop II star formation in the first galaxies using new
cosmological hydrodynamic simulations. We find that while the first stars seed
their host galaxies with metals, they cannot sustain significant outflows to
enrich the intergalactic medium, even assuming a top-heavy initial mass
function. This means that Pop III star formation could potentially continue
until z~6 in different unenriched regions of the universe, before being
ultimately shut off by cosmic reionization. Within an individual galaxy, the
metal production and stellar feedback from Pop II stars overtake Pop III stars
in 20-200 Myr, depending on galaxy mass. | The Origin of the Microlensing Events Observed Towards the LMC and the
Stellar Counterpart of the Magellanic Stream: We introduce a novel theoretical model to explain the long-standing puzzle of
the nature of the microlensing events reported towards the Large Magellanic
Cloud (LMC) by the MACHO and OGLE collaborations. We propose that a population
of tidally stripped stars from the Small Magellanic Cloud (SMC) located ~4-10
kpc behind a lensing population of LMC disk stars can naturally explain the
observed event durations (17-71 days), event frequencies and spatial
distribution of the reported events. Differences in the event frequencies
reported by the OGLE (~0.33 /yr) and MACHO (~1.75 /yr) surveys appear to be
naturally accounted for by their different detection efficiencies and
sensitivity to faint sources. The presented models of the Magellanic System
were constructed without prior consideration of the microlensing implications.
These results favor a scenario for the interaction history of the Magellanic
Clouds, wherein the Clouds are on their first infall towards the Milky Way and
the SMC has recently collided with the LMC 100-300 Myr ago, leading to a large
number of faint sources distributed non-uniformly behind the LMC disk. In
contrast to self-lensing models, microlensing events are also expected to occur
in fields off the LMC's stellar bar since the stellar debris is not expected to
be concentrated in the bar region. This scenario leads to a number of
observational tests: the sources are low-metallicity SMC stars, they exhibit
high velocities relative to LMC disk stars that may be detectable via proper
motion studies, and, most notably, there should exist a stellar counterpart to
the gaseous Magellanic Stream and Bridge with a V-band surface brightness of >
32 mag/arcsec^2. In particular, the stellar Bridge should contain enough RR
Lyrae stars to be detected by the ongoing OGLE survey of this region. |
Grigori Kuzmin and Stellar Dynamics: Grigori Kuzmin was a very gifted dynamicist and one of the towering figures
in the distinguished history of the Tartu Observatory. He obtained a number of
important results in relative isolation which were later rediscovered in the
West. This work laid the foundation for further advances in the theory of
stellar systems in dynamical equilibrium, thereby substantially increasing our
understanding of galaxy dynamics. | Magnetic field back reaction on the matter power spectrum: At lowest order comoving magnetic fields which are frozen-into the expanding
cosmic fluid do not evolve in time. At next-to-leading order the induction
equation is sourced by the interaction term between the baryon velocity and the
magnetic field amplitude which leads to a non-trivial evolution of the comoving
magnetic field. Moreover, it induces non-trivial cross correlations between the
adiabatic curvature mode and the magnetic mode. This cross correlation together
with the evolution of the induced matter perturbation leads to interesting
effects on the total matter power spectrum at small scales. |
Easing cosmic tensions with an open and hotter universe: Despite the great observational success of the standard cosmological model
some discrepancies in the inferred parameter constraints have manifested among
a number of cosmological data sets. These include a tension between the
expansion rate of our Cosmos as inferred from the cosmic microwave background
(CMB) and as found from local measurements, the preference for an enhanced
amplitude of CMB lensing, a somewhat low quadrupole moment of the CMB
fluctuations as well as a preference for a lower amplitude of matter
fluctuations in large-scale structure surveys than inferred from the CMB. We
analyse these observational tensions under the addition of spatial curvature
and a free CMB background temperature that may deviate from its locally
measured value. With inclusion of these parameters, we observe a trend in the
parameter constraints from CMB and baryon acoustic oscillation data towards an
open and hotter universe with larger current expansion rate, standard CMB
lensing amplitudes, lower amplitude of matter fluctuations, and marginally
lower CMB quadrupole moment, consistently reducing the individual tensions
among the cosmological data sets. Combining this data with local distance
measurements, we find a preference for an open and hotter universe beyond the
99.7% confidence level. Finally, we briefly discuss a local void as a possible
source for a deviation of the locally measured CMB temperature from its
background value and as mimic of negative spatial curvature for CMB photons.
This interpretation implies a $\sim$20% underdensity in our local neighbourhood
of $\sim$10-100 Mpc in diameter, which is well within cosmic variance. | Estimating the impact of recombination uncertainties on the cosmological
parameter constraints from cosmic microwave background experiments: [Abridged] We use our most recent training set for the RICO code to estimate
the impact of recombination uncertainties on the posterior probability
distributions which will be obtained from future CMB experiments, and in
particular the Planck satellite. Using a MCMC analysis to sample the posterior
distribution of the cosmological parameters, we find that Planck will have
biases of -0.7, -0.3 and -0.4 sigmas for n_S, Omega_b h2 and log(As),
respectively, in the minimal 6-parameter LCDM model, if the description of the
recombination history given by RICO is not used. The remaining parameters are
not significantly affected. We also show, that the cosmology dependence of the
corrections to the recombination history modeled with RICO has a negligible
impact on the posterior distributions obtained for the case of the Planck
satellite. In practice, this implies that the inclusion of additional
corrections to existing recombination codes can be achieved using simple
cosmology-independent `fudge functions'. Finally, we also investigated the
impact of some recent improvements in the treatment of hydrogen recombination
which are still not included in the current version of our training set for
Rico, by assuming that the cosmology dependence of those corrections can be
neglected. In summary, with our current understanding of the complete
recombination process, the expected biases in the cosmological parameters
inferred from Planck might be as large as -2.3, -1.7 and -1 sigmas for n_S,
Omega_b h2 and log(As) respectively, if all those corrections are not taken
into account. We note that although the list of physical processes that could
be of importance for Planck seems to be nearly complete, still some effort has
to be put in the validation of the results obtained by the different groups. |
DESI luminous red galaxy samples for cross-correlations: We present two galaxy samples, selected from DESI Legacy Imaging Surveys (LS)
DR9, with approximately 20,000 square degrees of coverage and spectroscopic
redshift distributions designed for cross-correlations such as with CMB
lensing, galaxy lensing, and the Sunyaev-Zel'dovich effect. The first sample is
identical to the DESI Luminous Red Galaxy (LRG) sample, and the second sample
is an extended LRG sample with 2-3 times the DESI LRG density. We present the
improved photometric redshifts, tomographic binning and their spectroscopic
redshift distributions and imaging systematics weights, and magnification bias
coefficients. The catalogs and related data products will be made publicly
available. The cosmological constraints using this sample and Planck lensing
maps are presented in a companion paper. We also make public the new set of
general-purpose photometric redshifts trained using DESI spectroscopic
redshifts, which are used in this work, for all galaxies in LS DR9. | ALMA Submillimeter Continuum Imaging of the Host Galaxies of GRB021004
and GRB080607: We report 345 GHz continuum observations of the host galaxies of gamma-ray
bursts (GRBs) 021004 and 080607 at z>2 using the Atacama Large
Millimeter/Submillimeter Array (ALMA) in Cycle 0. Of the two bursts, GRB021004
is one of the few GRBs that originates in a Lyman limit host, while GRB080607
is classified as a "dark burst" and its host galaxy is a candidate of dusty
star forming galaxy at z~3. With an order of magnitude improvement in the
sensitivities of the new imaging searches, we detect the host galaxy of
GRB080607 with a flux of S_{345} = 0.31+/-0.09 mJy and a corresponding infrared
luminosity of L_{IR}=(2.4-4.5)x10^{11} L_sun. However, the host galaxy of
GRB021004 remains undetected and the ALMA observations allow us to place a
3-sigma upper limit of L_{IR}<3.1x10^{11} L_sun for the host galaxy. The
continuum imaging observations show that the two galaxies are not ultraluminous
infrared galaxies but are at the faintest end of the dusty galaxy population
that gives rise to the submillimeter extragalactic background light. The
derived star formation rates of the two GRB host galaxies are less than 100
M_sun yr^{-1}, which are broadly consistent with optical measurements. The
result suggests that the large extinction (A_V~3) in the afterglow of GRB080607
is confined along its particularly dusty sightline, and not representative of
the global properties of the host galaxy. |
Detecting strongly-lensed type Ia supernovae with LSST: Strongly-lensed supernovae are rare and valuable probes of cosmology and
astrophysics. Upcoming wide-field time-domain surveys, such as the Vera C.
Rubin Observatory's Legacy Survey of Space and Time (LSST), are expected to
discover an order-of-magnitude more lensed supernovae than have previously been
observed. In this work, we investigate the cosmological prospects of lensed
type Ia supernovae (SNIa) in LSST by quantifying the expected annual number of
detections, the impact of stellar microlensing, follow-up feasibility, and how
to best separate lensed and unlensed SNIa. We simulate SNIa lensed by galaxies,
using the current LSST baseline v3.0 cadence, and find an expected number of 44
lensed SNIa detections per year. Microlensing effects by stars in the lens
galaxy are predicted to lower the lensed SNIa detections by $\sim 8 \%$. The
lensed events can be separated from the unlensed ones by jointly considering
their colours and peak magnitudes. We define a `gold sample' of $\sim 10$
lensed SNIa per year with time delay $> 10$ days, $> 5$ detections before
light-curve peak, and sufficiently bright ($m_i < 22.5$ mag) for follow-up
observations. In three years of LSST operations, such a sample is expected to
yield a $1.5\%$ measurement of the Hubble constant. | Recent star formation history of the Large and Small Magellanic Clouds: We traced the age of the last star formation event (LSFE) in the inner Large
& Small Magellanic Cloud (L&SMC) using the photometric data from the Optical
Gravitational Lensing Experiment (OGLE-III) and the Magellanic Cloud
Photometric Survey (MCPS). The LSFE is estimated from the main-sequence turn
off point in the color-magnitude diagram (CMD) of a region. Extinction
corrected turn off magnitude is converted to age, which represents the LSFE in
a region. The spatial map of the LSFE age shows that the star formation has
shrunk to the central regions in the last 100Myr in both the galaxies. The
location and age of LSFE is found to correlate well with those of the star
cluster in both the Clouds. The SMC map shows two separate concentrations of
young star formation. We detect peaks of star formation at 0-10, 90-100Myr in
the LMC, and 0-10, 50- 60Myr in the SMC. The quenching of star formation in the
LMC is found to be asymmetric with respect to the optical center such that most
of the young star forming regions are located to the north and east. On
deprojecting the data on the LMC plane, the recent star formation appears to be
stretched in the north-east direction and the HI gas is found to be distributed
preferentially in the North. The centroid is found to shift to north in
200-40Myr, and to north-east in the last 40Myr. In the SMC, we detect a shift
in centroid of population of 500-40Myr in the direction of the LMC. We propose
that the HI gas in the LMC is pulled to the north of the LMC in the last 200Myr
due to the gravitational attraction of our Galaxy at the time of perigalactic
passage. The shifted HI gas is preferentially compressed in the north during
200-40Myr and in the north-east in the last 40Myr, due to the motion of the LMC
in the Galactic halo. The recent star formation in the SMC is due to the
combined gravitational effect of the LMC and the perigalactic passage. |
JWST Observations Reject Unrecognized Crowding of Cepheid Photometry as
an Explanation for the Hubble Tension at 8 sigma Confidence: We present high-definition observations with the James Webb Space Telescope
of >1000 Cepheids in a geometric anchor of the distance ladder, NGC4258, and in
5 hosts of 8 SNe~Ia, a far greater sample than previous studies with JWST.
These galaxies individually contain the largest samples of Cepheids, an average
of >150 each, producing the strongest statistical comparison to those
previously measured with the Hubble Space Telescope in the NIR. They also span
the distance range of those used to determine the Hubble constant with HST,
allowing us to search for a distance-dependent bias in HST measurements. The
superior resolution of JWST negates crowding noise, the largest source of
variance in the NIR Cepheid Period-Luminosity relations (Leavitt laws) measured
with HST. Together with the use of two-epochs to constrain Cepheid phases and
three filters to remove reddening, we reduce the dispersion in the Cepheid PL
relations by a factor of 2.5. We find no significant difference in the mean
distance measurements determined from HST and JWST, with a formal difference of
-0.01+/-0.03 mag. This result is independent of zeropoints and analysis
variants including metallicity dependence, local crowding, choice of filters,
and relation slope. We can reject the hypothesis of unrecognized crowding of
Cepheid photometry from HST that grows with distance as the cause of the
``Hubble Tension'' at 8.2 sigma, i.e., greater confidence than that of the
Hubble Tension itself. We conclude that errors in photometric measurements of
Cepheids across the distance ladder do not significantly contribute to the
Tension. | Formation Criteria and the Mass of Secondary Population III Stars: We explore the formation of secondary Population III (Pop III) stars under
radiation hydrodynamic (RHD) feedback by a preformed massive star. To properly
treat RHD feedback, we perform three-dimensional RHD simulations incorporating
the radiative transfer of ionizing photons as well as H_2 dissociating photons
from a preformed star. A collapsing gas cloud is settled at a given distance
from a 120Msun Pop III star, and the evolution of the cloud is pursued
including RHD feedback. We derive the threshold density depending on the
distance, above which the cloud can keep collapsing owing to the shielding of
H_2 dissociating radiation. We find that an H_2 shell formed ahead of an
ionizing front works effectively to shield the H_2 dissociating radiation,
leading to the positive feedback for the secondary Pop III star formation.
Also, near the threshold density, the envelope of gas cloud is stripped
significantly by a shock associated with an ionizing front. By comparing the
mass accretion timescale with the Kelvin-Helmholtz timescale, we estimate the
mass of secondary Pop III stars. It turns out that the stripping by a shock can
reduce the mass of secondary Pop III stars down to \approx 20Msum. |
Cosmic Reionization History and Dark Matter Scenarios: We perform an analysis of the cosmic reionization in the standard cold dark
matter (CDM) paradigm and in alternative dark matter scenarios. Building upon
the work of Corasaniti et al. (2017), we predict the reionization history for
CDM, for warm dark matter (WDM), late-forming dark matter (LFDM) and
ultra-light axion dark matter (ADM) models which reproduce state-of-art
measurements of the galaxy luminosity function at very high-redshifts $6\le
z\le 10$. To this purpose we adopt a reionization model parametrized in terms
of the limiting UV-magnitude of galaxies contributing to the reionization
$M_{\rm lim}$ and the average effective escape fraction of UV photons reaching
the intergalactic medium $\tilde{f}$. For each DM model we compute the redshift
evolution of the Thomson scattering optical depth $\tau_e(z)$ and the comoving
ionization fraction $Q_{\rm HII}(z)$. We find the different DM models to have
similar reionization histories. Differences with respect to the CDM case
increase at fainter limiting UV-magnitudes and are degenerate with the effect
of varying the reionization model parameters. Using Planck's determination of
the integrated optical depth in combination with measurements of the neutral
hydrogen fraction at different redshifts, we infer constraints on $\tilde{f}$
and $M_{\rm lim}$. The results are largely independent of the assumed DM
scenario, in particular for $M_{\rm lim}\gtrsim -13$ we obtain that the
effective escape fraction lies in the range $0.07\lesssim \tilde{f}\lesssim
0.15$ at $2\sigma$. | $5 σ$ tension between Planck cosmic microwave background and eBOSS
Lyman-alpha forest and constraints on physics beyond $Λ$CDM: We find that combined Planck cosmic microwave background, baryon acoustic
oscillations and supernovae data analyzed under $\Lambda$CDM are in 4.9$\sigma$
tension with eBOSS Ly$\alpha$ forest in inference of the linear matter power
spectrum at wavenumber $\sim 1 h\,\mathrm{Mpc}^{-1}$ and redshift = 3. Model
extensions can alleviate this tension: running in the tilt of the primordial
power spectrum ($\alpha_\mathrm{s} \sim -0.01$); a fraction $\sim (1 - 5)\%$ of
ultra-light axion dark matter (DM) with particle mass $\sim 10^{-25}$ eV or
warm DM with mass $\sim 90$ eV. The new DESI survey, coupled with high-accuracy
modeling, will help distinguish the source of this discrepancy. |
The redshift distribution of cosmological samples: a forward modeling
approach: Determining the redshift distribution $n(z)$ of galaxy samples is essential
for several cosmological probes including weak lensing. For imaging surveys,
this is usually done using photometric redshifts estimated on an
object-by-object basis. We present a new approach for directly measuring the
global $n(z)$ of cosmological galaxy samples, including uncertainties, using
forward modeling. Our method relies on image simulations produced using UFig
(Ultra Fast Image Generator) and on ABC (Approximate Bayesian Computation)
within the $MCCL$ (Monte-Carlo Control Loops) framework. The galaxy population
is modeled using parametric forms for the luminosity functions, spectral energy
distributions, sizes and radial profiles of both blue and red galaxies. We
apply exactly the same analysis to the real data and to the simulated images,
which also include instrumental and observational effects. By adjusting the
parameters of the simulations, we derive a set of acceptable models that are
statistically consistent with the data. We then apply the same cuts to the
simulations that were used to construct the target galaxy sample in the real
data. The redshifts of the galaxies in the resulting simulated samples yield a
set of $n(z)$ distributions for the acceptable models. We demonstrate the
method by determining $n(z)$ for a cosmic shear like galaxy sample from the
4-band Subaru Suprime-Cam data in the COSMOS field. We also complement this
imaging data with a spectroscopic calibration sample from the VVDS survey. We
compare our resulting posterior $n(z)$ distributions to the one derived from
photometric redshifts estimated using 36 photometric bands in COSMOS and find
good agreement. This offers good prospects for applying our approach to current
and future large imaging surveys. | A lower limit of dz > 0.06 for the duration of the reionization epoch: Observations of the 21-centimetre line of atomic hydrogen in the early
Universe directly probe the history of the reionization of the gas between
galaxies. The observations are challenging, though, because of the low expected
signal strength (~10 mK), and contamination by strong (>100 K) foreground
synchrotron emission in the Milky Way and extragalactic continuum sources2. If
reionization happened rapidly, there should be a characteristic signature
visible against the smooth foreground in an all-sky spectrum. Here we report an
all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6
< z < 13 for the 21-centimetre line. The data exclude a rapid reionization
timescale of dz < 0.06 at the 95% confidence level. |
Numerical evaluation of inflationary 3-point functions on curved field
space: We extend the public CppTransport code to calculate the statistical
properties of fluctuations in multiple-field inflationary models with curved
field space. Our implementation accounts for all physical effects at tree-level
in the 'in-in' diagrammatic expansion. This includes particle production due to
time-varying masses, but excludes scenarios where the curvature perturbation is
generated by averaging over the decay of more than one particle. We test our
implementation by comparing results in Cartesian and polar field-space
coordinates, showing excellent numerical agreement and only minor degradation
in compute time. We compare our results with the PyTransport 2.0 code, which
uses the same computational approach but a different numerical implementation,
finding good agreement. Finally, we use our tools to study a class of
gelaton-like models which could produce an enhanced non-Gaussian signal on
equilateral configurations of the Fourier bispectrum. We show this is difficult
to achieve using hyperbolic field-space manifolds and simple inflationary
potentials. | Multiwavelength observation from radio through very-high-energy
Gamma-ray of OJ 287 during the 12-year cycle flare in 2007: We performed simultaneous multiwavelength observations of OJ 287 with the
Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope
for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very
high energy (VHE) gamma-ray in 2007. The observations were conducted for a
quiescent state in April and in a flaring state in November-December. We
clearly observed increase of fluxes from radio to X-ray bands during the
flaring state while MAGIC could not detect significant VHE gamma-ray emission
from the source. We could derive an upper limit (95% confidence level) of 1.7%
of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC
observation. A simple SSC model suggests that the observed flaring activity
could be caused by evolutions in the distribution of the electron population
rather than changes of the magnetic field strength or Doppler beaming factor in
the jet. |
Una revisión a la teoría básica del CMB (A review of the basic
theory of CMB): Spanish: La Cosmolog\'ia esta progresando a pasos agigantados gracias a la
cantidad espectacular de datos observacionales que se obtienen tanto de los
experimentos en tierra como sat\'elites. Un papel fundamental es desempe\~ndo
por las observaciones del Fondo C\'osmico de Microondas (CMB por sus siglas en
ingl\'e, Cosmic Microwave Background), la cual nos proporciona la prueba
observacional m\'as directa de los inicios del Universo. Las observaciones de
la temperatura y las anisotrop\'ias en el CMB han jugado un papel fundamental
en la definici\'on del modelo cosmol\'ogico. Esta contribuci\'on tiene como
objetivo resumir algunos de los conceptos b\'asicos que hay detr\'as de la
f\'isica del CMB. La mayor parte de los ingredientes del modelo cosmol\'ogico
est\'andar son poco conocidos en t\'erminos de la f\'isica fundamental, por
efemplo, la materia oscura y la energ\'ia oscura. Se discute c\'omo las
observaciones actuales abordan algunas de estas cuestiones.
English: The cosmic microwave background (CMB) provides the most direct
observational test of the early universe. The observations of the temperature
anisotropies in the CMB have played a key role in defining the cosmological
model. This contribution aims to summarize some of the basic concepts behind
the physics of the CMB. Most of the ingredients of the standard cosmological
model are poorly understood in terms of fundamental physics, for instance, dark
matter and dark energy. We discuss how current observations addressed some of
these issues. | IWDM: The fate of an interacting non-cold dark matter $-$ vacuum
scenario: In most cosmological models, the equation of state of the dark matter is
assumed to be zero, which means that the dark matter is pressure-less or cold.
While this hypothesis is based on the abundance of cold dark matter in the
universe, however, there is no compelling reason to assume that the equation of
state of dark matter is exactly zero. A more general approach would be to allow
for a range of values for the dark matter equation of state and use the
observational data to determine which values are most likely. With the
increasing accuracy of experimental data, we have chosen to explore the
possibility of interacting non-cold dark matter $-$ vacuum scenario, where the
equation of state of the dark matter is constant but can take different values
within a specific range. Using the Cosmic Microwave Background (CMB)
anisotropies and the CMB lensing reconstruction from the Planck legacy release,
plus other non-CMB measurements, namely, the baryon acoustic oscillations
distance measurements, and the Pantheon catalogue from Type Ia Supernovae, we
have analyzed this scenario and found that a non-zero value for the dark matter
equation of state is preferred with a confidence level of over 68\%. While this
is not significant by itself, however, it does suggest that investigating the
possibility of non-cold dark matter in the universe is worth exploring further
to gain a better understanding of the nature of dark matter. |
Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT
observations: Foreground removal is a major challenge for detecting the redshifted 21-cm
neutral hydrogen (HI) signal from the Epoch of Reionization (EoR). We have used
150 MHz GMRT observations to characterize the statistical properties of the
foregrounds in four different fields of view. The measured multi-frequency
angular power spectrum C_l(Delta nu) is found to have values in the range 10^4
mK^2 to 2 x 10^4 mK^2 across 700 <= l <= 2 x 10^4 and Delta nu <= 2.5 MHz,
which is consistent with model predictions where point sources are the most
dominant foreground component. The measured C_l(Delta nu) does not show a
smooth Delta nu dependence, which poses a severe difficulty for foreground
removal using polynomial fitting.
The observational data was used to assess point source subtraction.
Considering the brightest source (~ 1 Jy) in each field, we find that the
residual artifacts are less than 1.5% in the most sensitive field (FIELD I). We
have used FIELD I, which has a rms noise of 1.3 mJy/Beam, to study the
properties of the radio source population to a limiting flux of 9 mJy. The
differential source count is well fitted with a single power law of slope -1.6.
We find there is no evidence for flattening of the source counts towards lower
flux densities which suggests that source population is dominated by the
classical radio-loud Active Galactic Nucleus (AGN).
The diffuse Galactic emission is revealed after the point sources are
subtracted out from FIELD I . We find C_l \propto l^{-2.34} for 253 <= l <= 800
which is characteristic of the Galactic synchrotron radiation measured at
higher frequencies and larger angular scales. We estimate the fluctuations in
the Galactic synchrotron emission to be sqrt{l(l+1)C_l/2 pi} ~ 10 K at l=800
(theta > 10'). The measured C_l is dominated by the residual point sources and
artifacts at smaller angular scales where C_l ~ 10^3 mK^2 for l > 800. | The WIRCam Deep Survey I: Counts, colours and mass-functions derived
from near-infrared imaging in the CFHTLS deep fields: We present a new near-infrared imaging survey in the four CFHTLS deep fields:
the WIRCam Deep Survey (WIRDS). WIRDS comprises extremely deep, high quality
(FWHM ~0.6") J, H and K imaging covering a total effective area of 2.1 deg^2
and reaching AB 50% completeness limits of ~24.5. We combine our images with
the CFHTLS to create a unique eight-band ugrizJHK photometric catalogues in the
CFHTLS deep fields; these four separate fields allow us to make a robust
estimate of the effect of cosmic variance for all our measurements. We use
these catalogues to estimate precise photometric redshifts, galaxy types and
stellar masses for a unique sample of ~1.8 million galaxies. Our JHK number
counts are consistent with previous studies. We apply the BzK selection to our
gzK filter set and find that the star forming BzK selection successfully
selects 76% of star-forming galaxies in the redshift range 1.4<z<2.5 in our
photometric catalogue. The passive BzK selection returns 52% of the passive
1.4<z<2.5 population identified in the photometric catalogue. We present the
galaxy stellar mass function as a function of redshift up to z=2 and present
fits using double Schechter functions. A mass-dependent evolution of the mass
function is seen with the numbers of galaxies with masses of log(M)<10.75 still
evolving at z<1, but galaxies of higher mass reaching their present day numbers
by z~0.8-1. This is consistent with the present picture of downsizing in galaxy
evolution. We compare our results with the predictions of the GALFORM
semi-analytical galaxy formation model and find that the simulations provide a
relatively successful fit to the observed mass functions at intermediate masses
(i.e. 10<log(M)<11). However, the GALFORM results under-predict the mass
function at low masses, whilst the fit as a whole degrades beyond redshifts of
z~1.2. |
Properties and short-time evolution of nearby galaxies: We analyze the results of processing of data of observations which had been
carried out with the VLBA during 10 last years. All the data have been
retrieved from archive of the National Radio Astronomy Observatory (USA NRAO,
Socorro, New Mexico). Particularly, we examine data of VLBA observational
sessions titled BK068, BL111, BL137, BL149, and BD086. Objects of our interest
are near galaxies with z < 0.02. The radio maps of compact structure around the
active galactic nuclei (AGN) reconstructed for two such galaxies (NGC315 and
3C274) in U frequency band (15 GHz) are presented. Some parameters of these
sources are shown in Table 1. We have to perform the careful amplitude and
phase calibration for all the data. Particularly, a correction of the delay
caused by the Earth atmosphere has been made because it is necessary in this
frequency range. Bright quasars close to the target sources (for instance,
J0136+4751 and 3C279 correspondingly) are used as atmosphere calibrators.
Secondly, the Multi Frequency Synthesis (MFS) method is used for final maps
reconstruction as well as for estimation of spectral index values of core and
jet of AGN of both objects. As a result, we can make some conclusions about the
milliarcsecond structure of central regions of sources thanks to the using of
these two methods of the VLBA data processing. Moreover, we can reveal some
changes of this structure in 1999 - 2009, and estimate roughly the velocities
and acceleration/deceleration values for brightest components of the nuclei of
NGC315 and 3C274. Any polarization phenomena are not taken into account. We
present results of processing of data of LL polarization for all the
observational sessions. | Tracing low-mass galaxy clusters with radio relics: the discovery of
Abell 3527-bis: Galaxy clusters undergo mergers that can generate extended radio sources
called radio relics. Radio relics are the consequence of merger-induced shocks
that propagate in the intra cluster medium (ICM). In this paper we analyse the
radio, optical and X-ray data from a candidate galaxy cluster that has been
selected from the radio emission coming from a candidate radio relic detected
in NRAO VLA Sky Survey (NVSS). Our aim is to clarify the nature of this source
and prove that under certain conditions radio emission from radio relics can be
used to trace relatively low-mass galaxy clusters. We have observed the
candidate galaxy cluster with the Giant Meterwave Radio Telescope (GMRT) at
three different frequencies. These datasets have been analysed together with
archival data from ROSAT in the X-ray and with archival data from the Gamma-Ray
Burst Optical/Near-Infrared Detector (GROND) telescope in four different
optical bands. We confirm the presence of a 1 Mpc long radio relic located in
the outskirts of a previously unknown galaxy cluster. We confirm the presence
of the galaxy cluster through dedicated optical observations and using archival
X-ray data. Due to its proximity and similar redshift to a known Abell cluster,
we named it: Abell 3527-bis. The galaxy cluster is among the least massive
cluster known to host a radio relic. We showed that radio relics can be
effectively used to trace a subset of relatively low-mass galaxy clusters that
might have gone undetected in X-ray or Sunyaev-Zel'dovich (SZ) surveys. This
technique might be used in future deep, low-frequency surveys as those carried
on by LOFAR, uGMRT and, ultimately, SKA. |
Cosmic birefringence tomography and calibration-independence with
reionization signals in the CMB: The search for cosmic polarization rotation or birefringence in the CMB is
well-motivated because it can provide powerful constraints on parity-violating
new physics, such as axion-like particles. In this paper we point out that
since the CMB polarization is produced at two very different redshifts - it is
generated at both reionization and recombination - new parity-violating physics
can generically rotate the polarization signals from these different sources by
different amounts. We explore two implications of this. First, measurements of
CMB birefringence are challenging because the effect is degenerate with a
miscalibration of CMB polarization angles; however, by taking the difference of
the reionization and recombination birefringence angles (measured from
different CMB angular scales), we can obtain a cosmological signal that is
immune to instrumental angle miscalibration. Second, we note that the
combination with other methods for probing birefringence can give tomographic
information, constraining the redshift origin of any physics producing
birefringence. We forecast that the difference of the reionization and
recombination birefringence angles can be competitively determined to within
~0.05 degrees for future CMB satellites such as LiteBIRD. Although much further
work is needed, we argue that foreground mitigation for this measurement should
be less challenging than for inflationary B-mode searches on similar scales due
to larger signals and lower foregrounds. | Interacting Dark Matter as an Alternative to Dark Energy: We investigate the global dynamics of the universe within the framework of
the Interacting Dark Matter (IDM) scenario. Considering that the dark matter
obeys the collisional Boltzmann equation, we can obtain analytical solutions of
the global density evolution, which can accommodate an accelerated expansion,
equivalent to either the {\em quintessence} or the standard $\Lambda$ models.
This is possible if there is a disequilibrium between the DM particle creation
and annihilation processes with the former process dominating, which creates an
effective source term with negative pressure. Comparing the predicted Hubble
expansion of one of the IDM models (the simplest) with observational data, we
find that the effective annihilation term is quite small, as suggested by
various experiments. |
Application of beyond $δN$ formalism -- Varying sound speed: We focus on the evolution of curvature perturbation on superhorizon scales by
adopting the spatial gradient expansion and show that the nonlinear theory,
called the beyond $\delta N$-formalism as the next-leading order in the
expansion. As one application of our formalism for a single scalar field, we
investigate the case of varying sound speed. In our formalism, we can deal with
the time evolution in contrast to $\delta N$-formalism, where curvature
perturbations remain just constant, and nonlinear curvature perturbation
follows the simple master equation whose form is similar as one in linear
theory. So the calculation of bispectrum can be done in the next-leading order
in the expansion as similar as the case of deriving the power spectrum. We
discuss localized features of both primordial power and bispectrum generated by
the effect of varying sound speed with a finite duration time. We can see a
local feature like a bump in the equilateral bispectrum. | Beyond the traditional Line-of-Sight approach of cosmological angular
statistics: We present a new efficient method to compute the angular power spectra of
large-scale structure observables that circumvents the numerical integration
over Bessel functions, expanding on a recently proposed algorithm based on
FFTlog. This new approach has better convergence properties. The method is
explicitly implemented in the CLASS code for the case of number count
$C_\ell$'s (including redshift-space distortions, weak lensing, and all other
relativistic corrections) and cosmic shear $C_\ell$'s. In both cases our
approach speeds up the calculation of the exact $C_\ell$'s (without the Limber
approximation) by a factor of order 400 at a fixed precision target of 0.1%. |
Evolution of the cosmological mass density of neutral gas from Sloan
Digital Sky Survey II - Data Release 7: We present the results of a search for damped Lyman-alpha (DLA) systems in
the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully
automatic procedure to identify DLAs and derive their column densities. The
procedure is checked against the results of previous searches for DLAs in SDSS.
We discuss the agreements and differences and show the robustness of our
procedure. For each system, we obtain an accurate measurement of the absorber's
redshift, the HI column density and the equivalent width of associated metal
absorption lines, without any human intervention. We find 1426 absorbers with
2.15 < z < 5.2 with log N(HI)>=20, out of which 937 systems have log N(HI)>=
20.3. This is the largest DLA sample ever built, made available to the
scientific community through the electronic version of this paper. In the
course of the survey, we discovered the intervening DLA with highest HI column
density known to date with log N(HI)=22.0+/-0.1. This single system provides a
strong constraint on the high-end of the N(HI) frequency distribution now
measured with high accuracy. We show that the presence of a DLA at the blue end
of a QSO spectrum can lead to important systematic errors and propose a method
to avoid them. This has important consequences for the measurement of the
cosmological mass density of neutral gas at z~2.2 and therefore on our
understanding of galaxy evolution over the past 10 billion years. [truncated] | On the Cluster Physics of Sunyaev-Zel'dovich and X-ray Surveys III:
Measurement Biases and Cosmological Evolution of Gas and Stellar Mass
Fractions: Gas masses tightly correlate with the virial masses of galaxy clusters,
allowing for a precise determination of cosmological parameters by means of
large-scale X-ray surveys. However, according to recent Suzaku X-ray
measurements, gas mass fractions, f_gas, appear to be considerably larger than
the cosmic mean at the virial radius, R_200, questioning the accuracy of the
cosmological parameter estimations. Here, we use a large suite of cosmological
hydrodynamical simulations to study measurement biases of f_gas. We employ
different variants of simulated physics, including radiative gas physics, star
formation, and thermal feedback by active galactic nuclei. Computing the mass
profiles in 48 angular cones, whose footprints partition the sphere, we find
anisotropic gas and total mass distributions that imply an angular variance of
f_gas at the level of 30%. This anisotropic distribution originates from the
recent formation epoch of clusters and from the strong internal
baryon-to-dark-matter density bias. In the most extreme cones, f_gas can be
biased high by a factor of two at R_200 in massive clusters, thereby providing
a potential explanation for high f_gas measurements by Suzaku. While projection
lowers this factor, there are other measurement biases that may (partially)
compensate. We find that at R_200, f_gas is biased high by 20% when assuming
hydrostatic equilibrium masses, i.e., neglecting the kinetic pressure, and by
another ~10-20% due to the presence of density clumping. At larger radii, both
measurement biases increase dramatically. While the cluster sample variance of
the true f_gas decreases to a level of 5% at R_200, the sample variance that
includes both measurement biases remains fairly constant at the level of
10-20%. The constant redshift evolution of f_gas within R_500 for massive
clusters is encouraging for using gas masses to derive cosmological parameters. |
Halo abundances in the f_{nl} model: We show how the excursion set moving barrier model for halo abundances may be
generalized to the local non-Gaussian f_{nl} model. Our estimate assumes that
the distribution of step sizes depends on f_{nl}, but that they are otherwise
uncorrelated. Our analysis is consistent with previous results for the case of
a constant barrier, and highlights some implicit assumptions. It also clarifies
the basis of an approximate analytic solution to the moving barrier problem in
the Gaussian case, and shows how it might be improved. | Cosmology with the Laser Interferometer Space Antenna: The Laser Interferometer Space Antenna (LISA) has two scientific objectives
of cosmological focus: to probe the expansion rate of the universe, and to
understand stochastic gravitational-wave backgrounds and their implications for
early universe and particle physics, from the MeV to the Planck scale. However,
the range of potential cosmological applications of gravitational wave
observations extends well beyond these two objectives. This publication
presents a summary of the state of the art in LISA cosmology, theory and
methods, and identifies new opportunities to use gravitational wave
observations by LISA to probe the universe. |
Late-transition vs smooth $H(z)$ deformation models for the resolution
of the Hubble crisis: Gravitational transitions at low redshifts ($z_t<0.1$) have been recently
proposed as a solution to the Hubble and growth tensions. Such transitions
would naturally lead to a transition in the absolute magnitude $M$ of type Ia
supernovae (SnIa) at $z_t$ (Late $M$ Transitions - $LMT$) and possibly in the
dark energy equation of state parameter $w$ (Late $w-M$ Transitions - $LwMT$).
Here, we compare the quality of fit to cosmological data of this class of
models, with the corresponding quality of fit of the cosmological constant
model ($\Lambda$CDM) and some of the best smooth $H(z)$ deformation models
($w$CDM, CPL, PEDE). We also perform model selection via the Akaike Information
Criterion and the Bayes factor. We use the full CMB temperature anisotropy
spectrum data, the baryon acoustic oscillations (BAO) data, the Pantheon SnIa
data, the SnIa absolute magnitude $M$ as determined by Cepheid calibrators and
the value of the Hubble constant $H_0$ as determined by local SnIa calibrated
using Cepheids. We find that smooth $H(z)$ deformation models perform worse
than transition models for the following reasons: 1) They have a worse fit to
low-$z$ geometric probes (BAO and SnIa data); 2) They favor values of the SnIa
absolute magnitude $M$ that are lower as compared to the value $M_c$ obtained
with local Cepheid calibrators at $z<0.01$; 3) They tend to worsen the
$\Omega_\mathrm{m,0}-\sigma_\mathrm{8,0}$ growth tension. We also find that the
$w-M$ transition model ($LwMT$) does not provide a better quality of fit to
cosmological data than a pure $M$ transition model ($LMT$) where $w$ is fixed
to the \lcdm value $w=-1$ at all redshifts. We conclude that the $LMT$ model
has significant statistical advantages over smooth late-time $H(z)$ deformation
models in addressing the Hubble crisis. | Is there really a Hubble tension?: The heliocentric redshifts ($z_\mathrm{hel}$) reported for 150 Type Ia
supernovae in the Pantheon compilation are significantly discrepant from their
corresponding values in the JLA compilation. Both catalogues include
corrections to the redshifts and magnitudes of the supernovae to account for
the motion of the heliocentric frame relative to the `CMB rest frame', as well
as corrections for the directionally coherent bulk motion of local galaxies
with respect to this frame. The latter is done employing modelling of peculiar
velocities which assume the $\Lambda$CDM cosmological model but nevertheless
provide evidence for residual bulk flows which are discordant with this model
(implying that the observed Universe is in fact anisotropic). Until recently
such peculiar velocity corrections in the Pantheon catalogue were made at
redshifts exceeding 0.2 although there is no data on which to base such
corrections. We study the impact of these vexed issues on the 4.4 $\sigma$
discrepancy between the Hubble constant of $H_0 = 67.4 \pm 0.5$ km/s/Mpc
inferred from observations of CMB anisotropies by Planck assuming $\Lambda$CDM,
and the measurement of $H_0 = 73.5 \pm 1.4$ km/s/Mpc by the SH0ES project which
extended the local distance ladder using Type Ia supernovae. Using the same
methodology as the latter study we find that for supernovae whose redshifts are
discrepant between Pantheon and JLA with $\Delta z_\mathrm{hel} > 0.0025$, the
Pantheon redshifts favour $H_0 \simeq 72$ km/s/Mpc, while the JLA redshifts
favour $H_0 \simeq 68$ km/s/Mpc. Thus the discrepancies between SNe Ia datasets
are sufficient to undermine the claimed `Hubble tension'. We further note the
systematic variation of $H_0$ by $\sim$ 6-9 km/s/Mpc across the sky seen in
multiple datasets, implying that it cannot be measured locally to better than
$\sim$ 10% in a model-independent manner. |
Turbulence in the Intergalactic Medium: We study supernova-driven galactic outflows as a mechanism for injecting
turbulence in the intergalactic medium (IGM) far from galaxies. To this aim we
follow the evolution of a 10^13 Msun galaxy along its merger tree, with
carefully calibrated prescriptions for star formation and wind efficiencies. At
z~3 the majority of the bubbles around galaxies are old (ages >1Gyr), i.e. they
contain metals expelled by their progenitors at earlier times; their filling
factor increases with time reaching about 10% at z<2. The energy deposited by
these expanding shocks in the IGM is predominantly in kinetic form (mean energy
density of 1 \mu eV cm^-3, about 2-3 x the thermal one), which is rapidly
converted in disordered motions by instabilities, finally resulting in a fully
developed turbulent spectrum whose evolution is followed through a spectral
transfer function approach. The derived mean IGM turbulent Doppler parameter,
b_t, peaks at z~1 at about 1.5 km/s with maximum b_t = 25 km/s. The shape of
the b_t distribution does not significantly evolve with redshift but undergoes
a continuous shift towards lower b_t values with time, as a result of bubble
aging. We find also a clear trend of decreasing b_t with N_HI and a more
complex dependence on R_s resulting from the age spread of the bubbles. We have
attempted a preliminary comparison with the data, hampered by the scarcity of
the latter and by the challenge provided by the subtraction of peculiar and
thermal motions. Finally we comment on the implications of turbulence for
various cosmological studies. | CMB distortion from circumgalactic gas: We study the Sunyaev-Zel'dovich (SZ) distortion of the cosmic microwave
background radiation (CMBR) from extensive circumgalactic gas (CGM) in massive
galactic halos. Recent observations have shown that galactic halos contain a
large amount of X-ray emitting gas at the virial temperature, as well as a
significant amount of warm OVI absorbing gas. We consider the SZ distortion
from the hot gas in those galactic halos in which the gas cooling time is
longer than the halo destruction time scale. We show that the SZ distortion
signal from the hot gas in these galactic halos at redshifts $z\approx
1\hbox{--}8$ can be significant at small angular scales ($\ell\sim 10^4$), and
dominate over the signal from galaxy clusters. The estimated SZ signal for most
massive galaxies (halo mass $\ge 10^{12.5}$ M$_\odot$) is consistent with the
marginal detection by {\it Planck} at these mass scales. We also consider the
SZ effect from warm circumgalactic gas. The integrated Compton distortion from
the warm OVI absorbing gas is estimated to be $y\sim 10^{-8}$, which could
potentially be detected by experiments planned for the near future. Finally, we
study the detectability of the SZ signal from circumgalactic gas in two types
of surveys, a simple extension of the SPT survey and a more futuristic cosmic
variance-limited survey. We find that these surveys can easily detect the kSZ
signal from CGM. With the help of a Fisher Matrix analysis, we find that it
will be possible for these surveys to constrain the gas fraction in CGM, after
marginalizing over cosmological parameters, to $\le 33$\%, in case of no
redshift evolution of the gas fraction. |
SDSS DR7 superclusters. The catalogues: We have constructed a set of supercluster catalogues for the galaxies from
the SDSS survey main and luminous red galaxy (LRG) flux-limited samples. To
delineate superclusters, we calculated luminosity density fields using the
B3-spline kernel of the radius of 8 Mpc/h for the main sample and 16 Mpc/h for
the LRG sample and define regions with densities over a selected threshold as
superclusters, while utilising almost the whole volume of both samples. We
created two types of catalogues, one with an adaptive local threshold and a set
of catalogues with different global thresholds. We describe the supercluster
catalogues and their general properties. Using smoothed bootstrap, we find
uncertainty estimates for the density field and use these to attribute
confidence levels to the catalogue objects. We have also created a test
catalogue for the galaxies from the Millennium simulation to compare the
simulated and observed superclusters and to clarify the methods we use. We find
that the superclusters are well-defined systems, and the properties of the
superclusters of the main and LRG samples are similar. We also show that with
adaptive local thresholds we get a sample of superclusters, the properties of
which do not depend on their distance from the observer. The Millennium galaxy
catalogue superclusters are similar to those observed. | Specific star-formation and the relation to stellar mass from 0<z<2 as
seen in the far-infrared at 70 and 160mu: We use the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) to
explore the specific star-formation activity of galaxies and their evolution
near the peak of the cosmic far-infrared (FIR) background at 70 and 160um. We
use a stacking analysis to determine the mean FIR properties of well defined
subsets of galaxies at flux levels well below the FIR catalogue detection
limits of SWIRE and other Spitzer surveys. We tabulate the contribution of
different subsets of galaxies to the FIR background at 70um and 160um. These
long wavelengths provide a good constraint on the bolometric, obscured
emission. The large area provides good constraints at low z and in finer
redshift bins than previous work. At all redshifts we find that the specific
FIR Luminosity (sLFIR) decreases with increasing mass, following a trend
L_FIR/M* propto M_* ^beta with beta =-0.38\pm0.14. This is a more continuous
change than expected from the {Delucia2007} semi-analytic model suggesting
modifications to the feedback prescriptions. We see an increase in the sLFIR by
about a factor of ~100 from 0<z<2 and find that the sLFIR evolves as
(1+z)^alpha with alpha=4.4\pm0.3 for galaxies with 10.5 < log M*/Msun < 12.
This is considerably steeper than the {Delucia2007} semi-analytic model (alpha
\sim 2.5). When separating galaxies into early and late types on the basis of
the optical/IR spectral energy distributions we find that the decrease in sLFIR
with stellar mass is stronger in early type galaxies (beta ~ -0.46), while late
type galaxies exhibit a flatter trend (beta \sim -0.15). The evolution is
strong for both classes but stronger for the early type galaxies. The early
types show a trend of decreasing strength of evolution as we move from lower to
higher masses while the evolution of the late type galaxies has little
dependence on stellar mass. We suggest that in late-type galaxies we are seeing
a consistently declining sSFR.. |
Dust grain growth in the interstellar medium of 5<z<6.5 quasars: We investigate whether stellar dust sources i.e. asymptotic giant branch
(AGB) stars and supernovae (SNe) can account for dust detected in 5<z<6.5
quasars (QSOs). We calculate the required dust yields per AGB star and per SN
using the dust masses of QSOs inferred from their millimeter emission and
stellar masses approximated as the difference between the dynamical and the H_2
gas masses of these objects. We find that AGB stars are not efficient enough to
form dust in the majority of the z>5 QSOs, whereas SNe may be able to account
for dust in some QSOs. However, they require very high dust yields even for a
top-heavy initial mass function. This suggests additional non-stellar dust
formation mechanism e.g. significant dust grain growth in the interstellar
medium of at least three out of nine z>5 QSOs. SNe (but not AGB stars) may
deliver enough heavy elements to fuel this growth. | A Dynamical Analysis of the Corona Borealis Supercluster: Using data from the Sloan Digital Sky Survey we assess the current dynamical
state of the Corona Borealis Supercluster (CSC), a highly dense and compact
supercluster at z = 0.07. The Fundamental Plane relation is used to determine
redshift independent distances to six clusters in the densest region of the
supercluster, with mean accuracy in the relative distance estimates of 4 per
cent. Peculiar velocities determined from these distance estimates indicate
that the clusters have broken from the Hubble Flow, suggesting that the CSC
likely contains two regions that have reached turnaround and are currently
undergoing gravitational collapse. These results provide the strongest
observational evidence to date that the CSC is a bound system similar to the
much more extensive Shapley Supercluster, which is the most extensive confirmed
bound supercluster yet identified in the Universe. When compared with
simulations of the CSC our results require substantially more mass than is
contained within the clusters, possibly indicating a significant inter-cluster
dark matter component. In order to facilitate comparison with studies for which
spectroscopic data are not available, an alternative analysis of the dynamics
is made using the Kormendy relation as a distance indicator. The results are
generally consistent with those of the Fundamental Plane and suggest similar
global dynamics, but we find that the relatively sparse sampling of the
clusters makes the Kormendy relation less reliable overall and more susceptible
to small systematic differences between the cluster samples. |
Simultaneous determination of the cosmic birefringence and miscalibrated
polarization angles II: Including cross frequency spectra: We develop a strategy to determine the cosmic birefringence and miscalibrated
polarization angles simultaneously using the observed $EB$ polarization power
spectra of the cosmic microwave background and the Galactic foreground
emission. We extend the methodology of Y. Minami et al. (Prog. Theor. Exp.
Phys. $\mathbf{2019}$, 083E02, 2019), which was developed for auto frequency
power spectra, by including cross frequency spectra. By fitting one global
birefringence angle and independent miscalibration angles at different
frequency bands, we determine both angles with significantly smaller
uncertainties (by more than a factor of two) compared to the auto spectra. | Nebular Attenuation in Hα-selected Star-forming Galaxies at z=0.8
from the NewHα Survey: We present measurements of the dust attenuation of H\alpha-selected
emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The
analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which
captures the strong rest-frame optical emission lines from [OII] \lambda 3727
to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists
of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction
using diagnostics which can be applied at intermediate redshift. We find that
at least 5% of the objects in our spectroscopic sample can be classified as AGN
and 2% are composite, i.e. powered by a combination of star-formation and AGN
activity. We measure the dust attenuation for individual objects from the
ratios of the higher order Balmer lines. The H\beta\ and H\gamma\ pair of lines
is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\
pair is detected in 50 individual objects. We also create stacked spectra to
probe the attenuation in objects without individual detections. The median
attenuation at H\alpha\ based on the objects with individually detected lines
is A(H\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found
in local samples of star-forming galaxies. We find that the z=0.8 galaxies
occupy a similar locus of attenuation as a function of magnitude, mass and SFR
as a comparison sample drawn from the SDSS DR4. Both the results from the
individual z=0.8 galaxies and from the stacked spectra show consistency with
the mass -- attenuation and SFR -- attenuation relations found in the local
Universe, indicating that these relations are also applicable at intermediate
redshift. |
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