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Hubble distancing: Focusing on distance measurements in cosmology: The Hubble-Lemaitre tension is currently one of the most important questions
in cosmology. Most of the focus so far has been on reconciling the Hubble
constant value inferred from detailed cosmic microwave background measurement
with that from the local distance ladder. This emphasis on one number -- namely
$H_0$ -- misses the fact that the tension fundamentally arises from
disagreements of distance measurements. To be successful, a proposed
cosmological model must accurately fit these distances rather than simply infer
a given value of $H_0$. Using the newly developed likelihood package
`distanceladder', which integrates the local distance ladder into MontePython,
we show that focusing on $H_0$ at the expense of distances can lead to the
spurious detection of new physics in models which change late-time cosmology.
As such, we encourage the observational cosmology community to make their
actual distance measurements broadly available to model builders instead of
simply quoting their derived Hubble constant values. | Galactic structure explained with dissipative mirror dark matter: Dissipative dark matter, such as mirror dark matter and related hidden sector
dark matter candidates, requires an energy source to stabilize dark matter
halos in spiral galaxies. It has been proposed previously that supernovae could
be the source of this energy. Recently, it has been argued that this mechanism
might explain two galactic scaling relations inferred from observations of
spiral galaxies. One of which is that $\rho_0 r_0$ is roughly constant, and
another relates the galactic luminosity to $r_0$. [$\rho_0$ is the dark matter
central density and $r_0$ is the core radius.] Here we derive equations for the
heating of the halo via supernova energy, and the cooling of the halo via
thermal bremsstrahlung. These equations are numerically solved to obtain
constraints on the $\rho_0, \ r_0$ parameters appropriate for spiral galaxies.
These constraints are in remarkable agreement with the aforementioned scaling
relations. |
Horizon Run 3: Topology as a Standard Ruler: We study the Physically Self Bound Cold Dark Matter Halo distribution which
we associate with the massive galaxies within the Horizon Run 3 to estimate the
accuracy in determination of the cosmological distance scale measured by the
topology analysis. We apply the routine "Contour 3D" to 108 Mock Survey of
$\pi$ steradians out to redshift z = 0.6, which effectively correspond to the
SDSS-III BOSS survey, and compare the topology with that of a Gaussian Random
Phase Field. We find that given three separate smoothing lengths $\lambda =$
15, 21, and 34 $h^{-1}{\rm Mpc}$, the least $\chi^2$ fit genus per unit volume
g yields a 1.7 % fractional uncertainty in smoothing length and angular
diameter distance to $z = 0.6$. This is an improvement upon former calibrations
of and presents a competitive error estimate with next BAO scale techniques. We
also present three dimensional graphics of the Horizon Run 3 spherical mock
survey to show a wealth of large-scale structures of the universe that are
predicted in surveys like BOSS. | Cosmic Microwave Background Observables of Small Field Models of
Inflation: We construct a class of single small field models of inflation that can
predict, contrary to popular wisdom, an observable gravitational wave signal in
the cosmic microwave background anisotropies. The spectral index, its running,
the tensor to scalar ratio and the number of e-folds can cover all the
parameter space currently allowed by cosmological observations. A unique
feature of models in this class is their ability to predict a negative spectral
index running in accordance with recent cosmic microwave background
observations. We discuss the new class of models from an effective field theory
perspective and show that if the dimensionless trilinear coupling is small, as
required for consistency, then the observed spectral index running implies a
high scale of inflation and hence an observable gravitational wave signal. All
the models share a distinct prediction of higher power at smaller scales,
making them easy targets for detection. |
Modelling the spectral energy distribution of galaxies: introducing the
artificial neural network: The spectral energy distribution of galaxies is a complex function of the
star formation history and geometrical arrangement of stars and gas in
galaxies. The computation of the radiative transfer of stellar radiation
through the dust distribution is time-consuming. This aspect becomes
unacceptable in particular when dealing with the predictions by semi-analytical
galaxy formation models populating cosmological volumes, to be then compared
with multi-wavelength surveys. Mainly for this aim, we have implemented an
artificial neural network algorithm into the spectro-photometric and radiative
transfer code GRASIL in order to compute the spectral energy distribution of
galaxies in a short computing time. This allows to avoid the adoption of
empirical templates that may have nothing to do with the mock galaxies output
by models. The ANN has been implemented to compute the dust emission spectrum
(the bottleneck of the computation), and separately for the star-forming
molecular clouds and the diffuse dust (due to their different properties and
dependencies). We have defined the input neurons effectively determining their
emission, which means this implementation has a general applicability and is
not linked to a particular galaxy formation model. We have trained the net for
the disc and spherical geometries, and tested its performance to reproduce the
SED of disc and starburst galaxies, as well as for a semi-analytical model for
spheroidal galaxies. We have checked that for this model both the SEDs and the
galaxy counts in the Herschel bands obtained with the ANN approximation are
almost superimposed to the same quantities obtained with the full GRASIL. We
conclude that this method appears robust and advantageous, and will present the
application to a more complex SAM in another paper. | Joint constraints on thermal relic dark matter from strong gravitational
lensing, the Lyman-$α$ forest, and Milky Way satellites: We derive joint constraints on the warm dark matter (WDM) half-mode scale by
combining the analyses of a selection of astrophysical probes: strong
gravitational lensing with extended sources, the Lyman-$\alpha$ forest, and the
number of luminous satellites in the Milky Way. We derive an upper limit of
$\lambda_{\rm hm}=0.089{\rm~Mpc~h^{-1} }$ at the 95 per cent confidence level,
which we show to be stable for a broad range of prior choices. Assuming a
Planck cosmology and that WDM particles are thermal relics, this corresponds to
an upper limit on the half-mode mass of $M_{\rm hm }< 3 \times 10^{7}
{\rm~M_{\odot}~h^{-1}}$, and a lower limit on the particle mass of $m_{\rm th
}> 6.048 {\rm~keV}$, both at the 95 per cent confidence level. We find that
models with $\lambda_{\rm hm}> 0.223 {\rm~Mpc~h^{-1} }$ (corresponding to
$m_{\rm th }> 2.552 {\rm~keV}$ and $M_{\rm hm }< 4.8 \times 10^{8}
{\rm~M_{\odot}~h^{-1}}$) are ruled out with respect to the maximum likelihood
model by a factor $\leq 1/20$. For lepton asymmetries $L_6>10$, we rule out the
$7.1 {\rm~keV}$ sterile neutrino dark matter model, which presents a possible
explanation to the unidentified $3.55 {\rm~keV}$ line in the Milky Way and
clusters of galaxies. The inferred 95 percentiles suggest that we further rule
out the ETHOS-4 model of self-interacting DM. Our results highlight the
importance of extending the current constraints to lower half-mode scales. We
address important sources of systematic errors and provide prospects for how
the constraints of these probes can be improved upon in the future. |
Tully-Fisher analysis of the multiple cluster system Abell 901/902: We derive rotation curves from optical emission lines of 182 disk galaxies
(96 in the cluster and 86 in the field) in the region of Abell 901/902 located
at $z\sim 0.165$. We focus on the analysis of B-band and stellar-mass
Tully-Fisher relations. We examine possible environmental dependencies and
differences between normal spirals and "dusty red" galaxies, i.e. disk galaxies
that have red colors due to relatively low star formation rates. We find no
significant differences between the best-fit TF slope of cluster and field
galaxies. At fixed slope, the field population with high-quality rotation
curves (57 objects) is brighter by $\Delta M_{B}=-0\fm42\pm0\fm15$ than the
cluster population (55 objects). We show that this slight difference is at
least in part an environmental effect. The scatter of the cluster TFR increases
for galaxies closer to the core region, also indicating an environmental
effect. Interestingly, dusty red galaxies become fainter towards the core at
given rotation velocity (i.e. total mass). This indicates that the star
formation in these galaxies is in the process of being quenched. The
luminosities of normal spiral galaxies are slightly higher at fixed rotation
velocity for smaller cluster-centric radii. Probably these galaxies are
gas-rich (compared to the dusty red population) and the onset of ram-pressure
stripping increases their star-formation rates. The results from the TF
analysis are consistent with and complement our previous findings. Dusty red
galaxies might be an intermediate stage in the transformation of infalling
field spiral galaxies into cluster S0s, and this might explain the well-known
increase of the S0 fraction in galaxy clusters with cosmic time. | A highly magnified candidate for a young galaxy seen when the Universe
was 500 Myrs old: The early Universe at redshift z\sim6-11 marks the reionization of the
intergalactic medium, following the formation of the first generation of stars.
However, those young galaxies at a cosmic age of \lesssim 500 million years
(Myr, at z \gtrsim 10) remain largely unexplored as they are at or beyond the
sensitivity limits of current large telescopes. Gravitational lensing by galaxy
clusters enables the detection of high-redshift galaxies that are fainter than
what otherwise could be found in the deepest images of the sky. We report the
discovery of an object found in the multi-band observations of the cluster
MACS1149+22 that has a high probability of being a gravitationally magnified
object from the early universe. The object is firmly detected (12 sigma) in the
two reddest bands of HST/WFC3, and not detected below 1.2 {\mu}m, matching the
characteristics of z\sim9 objects. We derive a robust photometric redshift of z
= 9.6 \pm 0.2, corresponding to a cosmic age of 490 \pm 15Myr (i.e., 3.6% of
the age of the Universe). The large number of bands used to derive the redshift
estimate make it one of the most accurate estimates ever obtained for such a
distant object. The significant magnification by cluster lensing (a factor of
\sim15) allows us to analyze the object's ultra-violet and optical luminosity
in its rest-frame, thus enabling us to constrain on its stellar mass,
star-formation rate and age. If the galaxy is indeed at such a large redshift,
then its age is less than 200 Myr (at the 95% confidence level), implying a
formation redshift of zf \lesssim 14. The object is the first z>9 candidate
that is bright enough for detailed spectroscopic studies with JWST,
demonstrating the unique potential of galaxy cluster fields for finding highly
magnified, intrinsically faint galaxies at the highest redshifts. |
Cosmological constraints on a decomposed Chaplygin gas: Any unified dark matter cosmology can be decomposed into dark matter
interacting with vacuum energy, without introducing any additional degrees of
freedom. We present observational constraints on an interacting vacuum plus
dark energy corresponding to a generalised Chaplygin gas cosmology. We consider
two distinct models for the interaction leading to either a barotropic equation
of state or dark matter that follows geodesics, corresponding to a rest-frame
sound speed equal to the adiabatic sound speed or zero sound speed,
respectively. For the barotropic model, the most stringent constraint on
$\alpha$ comes from the combination of CMB+SNIa+LSS(m) gives
$\alpha<5.66\times10^{-6}$ at the 95% confidence level, which indicates that
the barotropic model must be extremely close to the $\Lambda$CDM cosmology. For
the case where the dark matter follows geodesics, perturbations have zero sound
speed, and CMB+SNIa+gISW then gives the much weaker constraint
$-0.15<\alpha<0.26$ at the 95% confidence level. | Impact of dark matter-baryon relative velocity on the 21cm forest: We study the effect of the relative velocity between the dark matter (DM) and
the baryon on the 21cm forest signals. The DM-baryon relative velocity arises
due to their different evolutions before the baryon-photon decoupling epoch and
it gives an additional anisotropic pressure that can suppress the perturbation
growth. It is intriguing that the scales $k\sim {\cal O}(10\sim
10^3)h/\mathrm{Mpc}$ at which the matter power spectrum is affected by such a
streaming velocity turns out to be the scale at which the 21cm forest signal is
sensitive to. We demonstrate that the 21cm absorption line abundance can
decrease by more than a factor of a few due to the small-scale matter power
spectrum suppression caused by the DM-baryon relative velocity. |
Cosmic shear covariance: The log-normal approximation: [Abridged] We seek approximations to the cosmic shear covariance that are as
easy to use as the common approximations based on normal statistics, but yield
more accurate covariance matrices and parameter errors. We derive expressions
for the cosmic shear covariance under the assumption that the underlying
convergence field follows log-normal statistics. We also derive a simplified
version of this log-normal approximation. We use numerical simulations of weak
lensing to study how well the normal, log-normal, and simplified log-normal
approximations as well as empirical corrections to the normal approximation
proposed in the literature reproduce shear covariances for cosmic shear
surveys. We find that the normal approximation substantially underestimates the
cosmic shear covariances and the inferred parameter confidence regions, in
particular for surveys with small fields of view and large galaxy densities,
but also for very wide surveys. In contrast, the log-normal approximation
yields more realistic covariances and confidence regions, but also requires
evaluating slightly more complicated expressions. However, the simplified
log-normal approximation, although as simple as the normal approximation,
yields confidence regions that are almost as accurate as those obtained from
the log-normal approximation. The empirical corrections to the normal
approximation do not yield more accurate covariances and confidence regions
than the (simplified) log-normal approximation. Moreover, they fail to produce
positive-semidefinite data covariance matrices in certain cases, rendering them
unusable for parameter estimation. The simplified log-normal approximation
should be used in favour of the normal approximation for parameter estimation
and parameter error forecasts. Any approximation to the cosmic shear covariance
should ensure a positive-semidefinite data covariance matrix. | AGN feedback with the Square Kilometer Array (SKA) and implications for
cluster physics and cosmology: AGN feedback is regarded as an important non-gravitational process in galaxy
clusters, providing useful constraints on large-scale structure formation. It
modifies the structure and energetics of the intra-cluster medium (ICM) and
hence its understanding is crucially needed in order to use clusters as high
precision cosmological probes. In this context, particularly keeping in mind
the upcoming high quality radio data expected from radio surveys like SKA with
its higher sensitivity, high spatial and spectral resolutions, we review our
current understanding of AGN feedback, its cosmological implications and the
impact that SKA can have in revolutionizing our understanding of AGN feedback
in large-scale structures. Recent developments regarding the AGN outbursts and
its possible contribution to excess entropy in the hot atmospheres of groups
and clusters, its correlation with the feedback energy in ICM, quenching of
cooling flows and the possible connection between cool core clusters and radio
mini-halos, are discussed. We describe current major issues regarding modeling
of AGN feedback and its impact on the surrounding medium. With regard to the
future of AGN feedback studies, we examine the possible breakthroughs that can
be expected from SKA observations. In the context of cluster cosmology, for
example, we point out the importance of SKA observations for cluster mass
calibration by noting that most of $z>1$ clusters discovered by eROSITA X-ray
mission can be expected to be followed up through a 1000 hour SKA-1 mid
programme. Moreover, approximately $1000$ radio mini halos and $\sim 2500$
radio halos at $z<0.6$ can be potentially detected by SKA1 and SKA2 and used as
tracers of galaxy clusters and determination of cluster selection function. |
Joint analysis of DES Year 3 data and CMB lensing from SPT and Planck I:
Construction of CMB Lensing Maps and Modeling Choices: Joint analyses of cross-correlations between measurements of galaxy
positions, galaxy lensing, and lensing of the cosmic microwave background (CMB)
offer powerful constraints on the large-scale structure of the Universe. In a
forthcoming analysis, we will present cosmological constraints from the
analysis of such cross-correlations measured using Year 3 data from the Dark
Energy Survey (DES), and CMB data from the South Pole Telescope (SPT) and
Planck. Here we present two key ingredients of this analysis: (1) an improved
CMB lensing map in the SPT-SZ survey footprint, and (2) the analysis
methodology that will be used to extract cosmological information from the
cross-correlation measurements. Relative to previous lensing maps made from the
same CMB observations, we have implemented techniques to remove contamination
from the thermal Sunyaev Zel'dovich effect, enabling the extraction of
cosmological information from smaller angular scales of the cross-correlation
measurements than in previous analyses with DES Year 1 data. We describe our
model for the cross-correlations between these maps and DES data, and validate
our modeling choices to demonstrate the robustness of our analysis. We then
forecast the expected cosmological constraints from the galaxy survey-CMB
lensing auto and cross-correlations. We find that the galaxy-CMB lensing and
galaxy shear-CMB lensing correlations will on their own provide a constraint on
$S_8=\sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ at the few percent level, providing a
powerful consistency check for the DES-only constraints. We explore scenarios
where external priors on shear calibration are removed, finding that the joint
analysis of CMB lensing cross-correlations can provide constraints on the shear
calibration amplitude at the 5 to 10% level. | A Computationally Efficient Approach for Calculating Galaxy Two-Point
Correlations: We developed a modification to the calculation of the two-point correlation
function commonly used in the analysis of large scale structure in cosmology.
An estimator of the two-point correlation function is constructed by
contrasting the observed distribution of galaxies with that of a uniformly
populated random catalog. Using the assumption that the distribution of random
galaxies in redshift is independent of angular position allows us to replace
pairwise combinatorics with fast integration over probability maps. The new
method significantly reduces the computation time while simultaneously
increasing the precision of the calculation. It also allows to introduce
cosmological parameters only at the last and least computationally expensive
stage, which is helpful when exploring various choices for these parameters. |
Dark Matter Halo Mergers I: Dependence on Environment & Redshift
Evolution: This paper presents a study of the specific merger rate as a function of
group membership, local environment, and redshift in a very large, $500h^{-1}
Mpc$, cosmological N-body simulation, the \textit{Millennium Simulation}. The
goal is to provide environmental diagnostics of major merger populations in
order to test simulations against observations and provide further constraints
on major merger driven galaxy evolution scenarios. A halo sample is defined
using the maximum circular velocity, which is both well defined for subhalos
and closely correlated with galaxy luminosity. Subhalos, including the
precursors of major mergers, are severely tidally stripped. Major mergers
between subhalos are therefore extremely rare. Tidal stripping also suppresses
dynamical friction, resulting in long major merger time scales when the more
massive halo does not host other subhalos. In contrast, when other subhalos are
present major merger time scales are several times shorter. This enhancement is
likely due to inelastic unbound collisions between subhalos. Following these
results, we predict that major mergers in group environments are dominated by
mergers involving the central galaxy, that the specific merger rate is
suppressed in groups, and that the frequency of fainter companions is enhanced
for mergers and their remnants. We also observe an `assembly bias' in the major
merger rate in that mergers of galaxy-like halos are slightly suppressed in
overdense environments while mergers of group-like halos are slightly enhanced.
A dynamical explanation for this trend is advanced which calls on both tidal
effects and interactions between bound halos beyond the virial radii of locally
dynamically dominant halos. | The puzzles of dark matter searches: Positive results of dark matter searches in DAMA/NaI and DAMA/LIBRA
experiments, being put together with negative results of other groups, can
imply nontrivial particle physics solutions for cosmological dark matter.
Stable particles with charge -2 bind with primordial helium in O-helium "atoms"
(OHe), representing a specific Warmer than Cold nuclear-interacting form of
dark matter. Slowed down in the terrestrial matter, OHe is elusive for direct
methods of underground Dark matter detection like those used in CDMS
experiment, but its reactions with nuclei can lead to annual variations of
energy release in the interval of energy 2-6 keV in DAMA/NaI and DAMA/LIBRA
experiments. Schrodinger equation for system of nucleus and OHe is solved for
spherically symmetrical potential well, formed by the Yukawa tail of nuclear
scalar isoscalar attraction potential, acting on He beyond the nucleus, and
dipole Coulomb repulsion between the nucleus and OHe at distances from the
nuclear surface, smaller than the size of OHe. The window of parameters of this
potential is found, at which the sodium and/or iodine nuclei have a few keV
binding energy with OHe. At nuclear parameters, reproducing DAMA results, the
energy release predicted for detectors with chemical content other than NaI
differ in the most cases from the one in DAMA detector. In particular, it is
shown that in the case of CDMS the energy of OHe-germanium bound state is
beyond the range of 2-6 keV and its formation should not lead to ionization in
the energy interval of DAMA signal. (abridged) |
The correlation structure of dark matter halo properties: We investigate the correlation between nine different dark matter halo
properties using a rank correlation analysis and a Principal Component Analysis
for a sample of haloes spanning five orders of magnitude in mass. We consider
mass and dimensionless measures of concentration, age, relaxedness, sphericity,
triaxiality, substructure, spin, and environment, where the latter is defined
in a way that makes it insensitive to mass. We find that concentration is the
most fundamental property. Except for environment, all parameters are strongly
correlated with concentration. Concentration, age, substructure, mass,
sphericity and relaxedness can be considered a single family of parameters,
albeit with substantial scatter. In contrast, spin, environment, and
triaxiality are more independent, although spin does correlate strongly with
substructure and both spin and triaxiality correlate substantially with
concentration. Although mass sets the scale of a halo, all other properties are
more sensitive to concentration. | CII and HI 21-cm line intensity mapping from the EoR: Impact of the
light-cone effect on auto and cross-power spectra: CII line intensity mapping (LIM) is a potential technique to probe the early
galaxies from the Epoch of Reionization (EoR). Several experiments e.g.
CONCERTO, TIME, CCAT-p are underway to map the CII LIM signal fluctuations from
the EoR, enabling us to estimate the CII power-spectrum and CII$\times$21-cm
cross-power spectrum. Observed LIM signal will have its time evolution embedded
in it along the Line of Sight (LoS) due to the finite travel time of the signal
from its origin to the observer. We have investigated this so-called light-cone
effect on the observed statistics of our semi-numerically simulated CII signal
from the EoR. Using a suit of simulated CII and neutral hydrogen 21-cm maps and
corresponding light-cone boxes, we have shown that the light-cone effect can
impact the CII power spectrum by more than 15% at large scales ($k\sim 0.1\,
\text{Mpc}^{-1}$, at $z=6.8$). We have also observed that the impact of
light-cone effect on the CII power spectrum drops with decreasing redshift
within the redshift range considered here ($7.2 \lesssim z \lesssim 6$). The
CII$\times$21-cm cross-power spectrum is also affected by light-cone, and in
our models where reionization ends before $z=6$, we find that the maximum
impact on cross-power can reach up to 20%. At $z=6.4$, we find comparatively
pronounced variation in the light-cone effect with reionization history on the
cross power. Faster reionization histories have a more drastic light-cone
effect on cross-power. We conclude that we need to incorporate the light-cone
in order to properly model the signal, constrain the EoR-related astrophysical
parameters and reionization history using the CII$\times$21-cm cross-power
spectrum. |
Which Fundamental Constants for CMB and BAO?: We use the three-scale framework of Hu et al. to show how the Cosmic
Microwave Background anisotropy spectrum depends on the fundamental constants.
As expected, the spectrum depends only on \emph{dimensionless} combinations of
the constants, and we emphasize the points that make this generally true for
cosmological observables. Our analysis suggests that the CMB spectrum shape is
mostly determined by $\alpha^2m_e/m_p$ and the proton-CDM-particle mass ratio,
$m_p/\mchi$. The distance to the last-scattering surface depends on
$Gm_p\mchi/\hbar c$, so published CMB observational limits on time variations
of the constants implicitly assume the time-independence of this quantity, as
well as assuming a flat-\lcdm~cosmological model. On the other hand,
low-redshift BAO, $H_0$ and baryon-mass-fraction measurements can be combined
with the \emph{shape} of the CMB spectrum to give information that is largely
independent of these assumptions. In particular we show that the
pre-recombination values of $G\mchi^2/\hbar c$, $m_p/\mchi$ and
$\alpha^2m_e/m_p$ are equal to their present values at a precision of
$\sim15\%$. | Constraining warm dark matter with cosmic shear power spectra: We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV. |
Weak lensing and spectroscopic analysis of the nearby dissociative
merging galaxy cluster Abell 3376: The galaxy cluster Abell~3376 is a nearby (z=0.046) dissociative merging
cluster surrounded by two prominent radio relics and showing an X-ray
comet-like morphology. The merger system is comprised of the subclusters A3376W
& A3376E. Based on new deep multi-wavelength large-field images and published
redshifts, we bring new insights about the history of this merger. Despite the
difficulty of applying the weak lensing technique at such low redshift, we
successfully recovered the mass distribution in the cluster field. Moreover,
with the application of a two-body model, we have addressed the dynamics of
these merging system. We have found the individual masses of
M_{200}^{W}=3.0_{-1.7}^{+1.3}x10^{14} M_{\odot} and
M_{200}^{E}=0.9_{-0.8}^{+0.5}x10^{14} M_{\odot}. The cometary shaped X-ray
distribution shows only one peak spatially coincident with both Eastern BCG and
the A3376E mass peak whereas the gas content of A3376W seems to be stripped
out. Our data allowed us to confirm the existence of a third subcluster located
at the North, 1147+-62 kpc apart from the neighbour subcluster A3376E and
having a mass M_{200}^{N}=1.4_{-1.0}^{+0.7}x10^{14} M_{\odot}. From our
dynamical analysis, we found the merging is taking place very close to the
plane of the sky, with the merger axis just 10 deg +-11 deg from it. The
application of a two-body analysis code showed that the merging cluster is seen
0.9_{-0.3}^{+0.2} Gyr after the pericentric passage and it is currently going
to the point of maximum separation between the subclusters. | Errors in Estimating Omega_Lambda due to the Fluid Approximation: The matter content of the Universe is strongly inhomogeneous on small scales.
Motivated by this fact, we consider a model of the Universe that has regularly
spaced discrete masses, rather than a continuous fluid. The optical properties
of such space-times can differ considerably from the continuous fluid case,
even if the 'average' dynamics are the same. We show that these differences
have consequences for cosmological parameter estimation, and that fitting to
recent supernovae observations gives a correction to the inferred value of
Omega_Lambda of ~10%. |
HI intensity mapping with the MIGHTEE survey: power spectrum estimates: Intensity mapping (IM) with neutral hydrogen is a promising avenue to probe
the large scale structure of the Universe. In this paper, we demonstrate that
using the 64-dish MeerKAT radio telescope as a connected interferometer, it is
possible to make a statistical detection of HI in the post-reionization
Universe. With the MIGHTEE (MeerKAT International GHz Tiered Extragalactic
Exploration) survey project observing in the L-band ($856 < \nu < 1712$ MHz, $z
< 0.66$), we can achieve the required sensitivity to measure the HI IM power
spectrum on quasi-linear scales, which will provide an important
complementarity to the single-dish IM MeerKAT observations. We present a
purpose-built simulation pipeline that emulates the MIGHTEE observations and
forecast the constraints that can be achieved on the HI power spectrum at $z =
0.27$ for $k > 0.3$ $\rm{Mpc}^{-1}$ using the foreground avoidance method. We
present the power spectrum estimates with the current simulation on the COSMOS
field that includes contributions from HI, noise and point source models
constructed from the observed MIGHTEE data. The results from our
\textit{visibility} based pipeline are in qualitative agreement to the already
available MIGHTEE data. This paper demonstrates that MeerKAT can achieve very
high sensitivity to detect HI with the full MIGHTEE survey on quasi-linear
scales (signal-to-noise ratio $> 7$ at $k=0.49$ $\rm{Mpc}^{-1}$) which are
instrumental in probing cosmological quantities such as the spectral index of
fluctuation, constraints on warm dark matter, the quasi-linear redshift space
distortions and the measurement of the HI content of the Universe up to $z\sim
0.5$. | Characterizing Structure Formation through Instance Segmentation: Dark matter haloes form from small perturbations to the almost homogeneous
density field of the early universe. Although it is known how large these
initial perturbations must be to form haloes, it is rather poorly understood
how to predict which particles will end up belonging to which halo. However, it
is this process that determines the Lagrangian shape of protohaloes and is
therefore essential to understand their mass, spin and formation history. Here,
we present a machine-learning framework to learn how the protohalo regions of
different haloes emerge from the initial density field. This involves one
neural network to distinguish semantically which particles become part of any
halo and a second neural network that groups these particles by halo membership
into different instances. This instance segmentation is done through the
Weinberger method, in which the network maps particles into a pseudo-space
representation where different instances can be distinguished easily through a
simple clustering algorithm. Our model reliably predicts the masses and
Lagrangian shapes of haloes object-by-object, as well as summary statistics
like the halo-mass function. We find that our model extracts information close
to optimal by comparing it to the degree of agreement between two N-body
simulations with slight differences in their initial conditions. We publish our
model open-source and suggest that it can be used to inform analytical methods
of structure formation by studying the effect of systematic manipulations of
the initial conditions. |
Dark matter scaling relations in intermediate z haloes: We investigate scaling relations between the dark matter (DM) halo model
parameters for a sample of intermediate redshift early - type galaxies (ETGs)
resorting to a combined analysis of Einstein radii and aperture velocity
dispersions. Modeling the dark halo with a Navarro - Frenk - White profile and
assuming a Salpeter initial mass function (IMF) to estimate stellar masses, we
find that the column density ${\cal{S}}$ and the Newtonian acceleration within
the halo characteristic radius $r_s$ and effective radius $R_{eff}$ are not
universal quantities, but correlate with the luminosity $L_V$, the stellar mass
$M_{\star}$ and the halo mass $M_{200}$, contrary to recent claims in the
literature. We finally discuss a tight correlation among the DM mass
$M_{DM}(R_{eff})$ within the effective radius $R_{eff}$, the stellar mass
$M_{\star}(R_{eff})$ and $R_{eff}$ itself. The slopes of the scaling relations
discussed here strongly depend, however, on the DM halo model and the IMF
adopted so that these ingredients have to be better constrained in order to
draw definitive conclusions on the DM scaling relations for ETGs. | Higher-Curvature Corrections and Tensor Modes: Higher-curvature corrections to the effective gravitational action may leave
signatures in the spectrum of primordial tensor perturbations if the
inflationary energy scale is sufficiently high. In this paper we further
investigate the effects of a coupling of the Inflaton field to higher-curvature
tensors in models with a minimal breaking of conformal symmetry. We show that
an observable violation of the tensor consistency relation from
higher-curvature tensors implies also a relatively large running of the tensor
tilt, enhanced even by some order of magnitude with respect to the standard
slow roll case. This may leave signatures in the tensor two-point function that
we could test to recognize higher-curvature effects, above all if they are
translated into a blue tilted spectrum visible by future Gravitational Wave
experiments. Exploiting current cosmic microwave background and gravitational
wave data we also derive constraints on the inflationary parameters, inferring
that large higher-curvature corrections seem to be disfavored. |
Effects of biasing on the galaxy power spectrum at large scales: n this paper we study the effect of biasing on the power spectrum at large
scales. We show that even though non-linear biasing does introduce a white
noise contribution on large scales, the $P(k)\propto k^n$ behavior of the
matter power spectrum on large scales may still be visible and above the white
noise for about one decade. We show, that the Kaiser biasing scheme which leads
to linear bias of the correlation function on {\em large} scales, also
generates a linear bias of the {\rm power spectrum} on rather small scales.
This is a consequence of the divergence on small scales of the pure
Harrison-Zeldovich spectrum. However, biasing becomes k-dependent when we damp
the underlying power spectrum on small scales. We also discuss the effect of
biasing on the baryon acoustic oscillations. | Anisotropies in Scalar-Induced Gravitational-Wave Background from
Inflaton-Curvaton Mixed Scenario with Sound Speed Resonance: We propose a new model to generate large anisotropies in the scalar-induced
gravitational wave (SIGW) background via sound speed resonance in the
inflaton-curvaton mixed scenario. Cosmological curvature perturbations are not
only exponentially amplified at a resonant frequency, but also preserve
significant non-Gaussianity of local type described by $f_{\mathrm{nl}}$.
Besides a significant enhancement of energy-density fraction spectrum, large
anisotropies in SIGWs can be generated, because of super-horizon modulations of
the energy density due to existence of primordial non-Gaussianity. A reduced
angular power spectrum $\tilde{C}_{\ell}$ could reach an amplitude of
$[\ell(\ell+1)\tilde{C}_{\ell}]^{1/2} \sim 10^{-2}$, leading to potential
measurements via planned gravitational-wave detectors such as DECIGO. The large
anisotropies in SIGWs would serve as a powerful probe of the early universe,
shedding new light on the inflationary dynamics, primordial non-Gaussianity,
and primordial black hole dark matter. |
Pantheon+ tomography and Hubble tension: The recently released Type Ia supernovae (SNe Ia) sample, Pantheon+, is an
updated version of Pantheon and has very important cosmological implications.
To explore the origin of the enhanced constraining power and internal
correlations of datasets in different redshifts, we perform a comprehensively
tomographic analysis of the Pantheon+ sample without and with the Cepheid host
distance calibration, respectively. Specifically, we take two binning methods
to analyze the Pantheon+ sample, i.e., equal redshift interval and equal
supernovae number for each bin. For the case of equal redshift interval, after
dividing the sample to 10 bins, the first bin in the redshift range
$z\in[0.00122, \, 0.227235]$ dominates the constraining power of the whole
sample. For the case of equal supernovae number, the first three low redshift
bins prefer a large matter fraction $\Omega_m$ and only the sixth bin gives a
relatively low cosmic expansion rate $H_0$. For both binning methods, we find
no obvious evidence of evolution of $H_0$ and $\Omega_m$ at the $2\,\sigma$
confidence level. The inclusion of the SH0ES calibration can significantly
compress the parameter space of background dynamics of the universe in each
bin. When not considering the calibration, combining the Pantheon+ sample with
cosmic microwave background, baryon acoustic oscillations, cosmic chronometers,
galaxy clustering and weak lensing data, we give the strongest $1\,\sigma$
constraint $H_0=67.88\pm0.42$ km s$^{-1}$ Mpc$^{-1}$. However, the addition of
the calibration leads to a global shift of the parameter space from the
combined constraint and $H_0=68.66\pm0.42$ km s$^{-1}$ Mpc$^{-1}$, which is
inconsistent with the Planck-2018 result at about $2\,\sigma$ confidence level. | Anisotropies in the gravitational wave background as a probe of the
cosmic string network: Pulsar timing arrays are one of the powerful tools to test the existence of
cosmic strings through searching for the gravitational wave background. The
amplitude of the background connects to information on cosmic strings such as
the tension and string network properties. In addition, one may be able to
extract more information on properties of cosmic strings by measuring
anisotropies in the gravitational wave (GW) background. In this paper, we
provide estimates of the level of anisotropy expected in the GW background
generated by cusps on cosmic strings. We find that the anisotropy level
strongly depends on the initial loop size $\alpha$, and thus we may be able to
put constraint on $\alpha$ by measuring the anisotropy of the GW background. We
also find that certain regions of the parameter space can be probed by shifting
the observation frequency of GWs. |
The first (nearly) model-independent constraint on the neutral hydrogen
fraction at z~5--6: Cosmic reionization is expected to be complex, extended and very
inhomogeneous. Existing constraints at z~6 on the volume-averaged neutral
hydrogen fraction, <x_HI>, are highly model-dependent and controversial.
Constraints at z<6, suggesting that the Universe is highly ionized, are also
model-dependent, but more fundamentally are invalid in the context of
inhomogeneous reionization. As such, it has recently been pointed out that
there is no conclusive evidence that reionization has completed by z~5--6, a
fact that has important ramifications on the interpretation of high-redshift
observations and theoretical models. We present the first direct upper limits
on <x_HI> at z~5--6 using the simple and robust statistic of the covering
fraction of dark pixels in the Ly alpha/beta forests of high redshift quasars.
With a sample of 13 Keck ESI spectra we constrain <x_HI> < 0.2 at 5 < z < 5.5,
rising to <x_HI> < 0.8 at z~6.1. We also find tentative evidence for a break in
the redshift evolution of the dark covering fraction at z~5.5. A subsample of
two deep spectra provides a more stringent constraint of <x_HI>(z=6.1) < 0.5
when combined with conservative estimates of cosmic variance. This upper limit
is comparable to existing results at z~6 but is more robust. The results
presented here do not rely on assumptions about the quasar continuum, IGM
density, HII morphology or ionizing background fields, and thus are a good
starting point for future interpretation of high redshift observations. | The effects of lensing by local structures on the dipole of radio source
counts: Our peculiar motion in a homogeneous and isotropic universe imprints a dipole
in the cosmic microwave background (CMB) temperature field and similarly
imprints a dipole in the distribution of extragalactic radio sources on the
sky. Each of these effects have been measured, however each of these
measurements give different results for the velocity of our motion through the
Universe: the radio dipole measurements finds the speed of our motion to be
around three times larger than that of the CMB. Here we show the effects of the
previously unconstrained lensing dipole, whereby necessarily local structures
(required for large angular lensing scales) will distort the distribution of
radio sources on the sky. We find that the inclusion of these effects does not
reduce the tension between the CMB and radio source dipole measurements however
without their inclusion future extragalactic number counts could lead to
incorrect inferences of our peculiar motion. In addition we can constrain the
size of the lensing dipole to be $\kappa < 3 \cdot 10^{-2}$ at the $2 \sigma$
level. |
Cosmic Train Wreck by Massive Black Holes: Discovery of a kpc-Scale
Triple Active Galactic Nucleus: Hierarchical galaxy mergers will lead to the formation of binary and, in the
case of a subsequent merger before a binary coalesce, triple supermassive black
holes (SMBHs), given that most massive galaxies harbor SMBHs. A triple of SMBHs
becomes visible as a triple active galactic nucleus (AGN) when the BHs accrete
large amounts of gas at the same time. Here we report the discovery of a
kpc-scale triple AGN, SDSSJ1027+1749 at z = 0.066, from our systematic search
for hierarchical mergers of AGNs. The galaxy contains three emission-line
nuclei, two of which are offset by ~ 450 and 110 km/s in velocity and by 2.4
and 3.0 kpc in projected separation from the central nucleus. All three nuclei
are classified as obscured AGNs based on optical diagnostic emission line
ratios, with black hole mass estimates M_BH ~> 10^8 M_sun from stellar velocity
dispersions measured in the associated stellar components. Based on dynamical
friction timescale estimates, the three stellar components in SDSSJ1027+1749
will merge in ~ 40 Myr, and their associated SMBHs may evolve into a
gravitationally interacting triple system in ~< 200 Myr. Our result sets a
lower limit of ~ 5 x 10^(-5) for the fraction of kpc-scale triples in optically
selected AGNs at z ~ 0.1. | DEMNUni: comparing nonlinear power spectra prescriptions in the presence
of massive neutrinos and dynamical dark energy: We provide an accurate comparison, against large cosmological $N$-body
simulations, of different prescriptions for modelling nonlinear matter power
spectra in the presence of massive neutrinos and dynamical dark energy. We test
the current most widely used approaches: fitting functions (HALOFIT and
HMcode), the halo-model reaction (ReACT) and emulators (baccoemu and
EuclidEmulator2). Focussing on redshifts $z\leq2$ and scales $k\lesssim 1 \
h/$Mpc (where the simulation mass resolution provides $\sim 1\%$ accuracy), we
find that HMcode and ReACT considerably improve over the HALOFIT prescriptions
of Smith and Takahashi (both combined with the Bird correction), with an
overall agreement of 2\% for all the cosmological scenarios considered.
Concerning emulators, we find that, especially at low redshifts,
EuclidEmulator2 remarkably agrees with the simulated spectra at $\lesssim 1\%$
level in scenarios with dynamical dark energy and massless neutrinos, reaching
a maximum difference of $\sim 2\%$ at $z=2$. baccoemu has a similar behaviour
as EuclidEmulator2, except for a couple of dark energy models. In cosmologies
with massive neutrinos, at $z=0$ all the nonlinear prescriptions improve their
agreement with respect to the massless neutrino case, except for the Bird and
TakaBird models which, however, are not tailored to $w_0$--$w_a$ models. At
$z>0$ we do not find a similar improvement when including massive neutrinos,
probably due to the lower impact of neutrino free-streaming at higher
redshifts; rather at $z=2$ EuclidEmulator2 exceeds $2\%$ agreement for some
dark energy equation of state. When considering ratios between the matter power
spectrum computed in a given cosmological model and its $\Lambda$CDM
counterpart, all the tested prescriptions agree with simulated data, at
sub-percent or percent level, depending on $z$. [ABRIDGED] |
Do we have a Theory of Early Universe Cosmology?: The inflationary scenario has become the paradigm of early universe
cosmology, and - in conjuction with ideas from superstring theory - has led to
speculations about an "inflationary multiverse". From a point of view of
phenomenology, the inflationary universe scenario has been very successful.
However, the scenario suffers from some conceptual problems, and thus it does
not (yet) have the status of a solid theory. There are alternative ideas for
the evolution of the very early universe which do not involve inflation but
which agree with most current cosmological observations as well as inflation
does. In this lecture I will outline the conceptual problems of inflation and
introduce two alternative pictures - the "matter bounce" and "string gas
cosmology", the latter being a realization of the "emergent universe" scenario
based on some key principles of superstring theory. I will demonstrate that
these two alternative pictures lead to the same predictions for the power
spectrum of the observed large-scale structure and for the angular power
spectrum of cosmic microwave background anisotropies as the inflationary
scenario, and I will mention predictions for future observations with which the
three scenarios can be observationally teased apart. | Direct Evidence of Cold Gas in DLA 0812+32B: We present the first direct evidence for cold gas in a high redshift DLA
galaxy. We measured several multiplets of weak neutral carbon (CI) transitions
in order to perform a curve of growth analysis. A delta chi-squared test
constrains the best fit Doppler parameter, b = 0.33_{-0.04}^{+0.05} km/s, and
logN(CI) = 13.30 +- 0.2 cm^-2. This Doppler parameter constrains the kinetic
temperature of the gas to T <= 78 K (T <= 115 K, 2 sigma). We used the
associated CI fine structure lines to constrain the volume density of the gas,
n(HI) ~ 40 - 200 cm^-3 (2 sigma), resulting in a lower limit on the cloud size
of approximately 0.1 - 1 parsec. While it is difficult to determine the
metallicity of the cold component, the absence of Cr II indicates that the cold
cloud suffers a high level of dust depletion. Additionally, the large amount of
Lyman and Werner-band molecular hydrogen absorption (log N(H2)_{total} = 19.88
cm^-2, f_{H_2} >= 0.06) with an excitation temperature of T_{ex} = 46 K as
determined by the rotational J = 0 and J = 1 states, is consistent with the
presence of cold gas. We propose that this cloud may be gravitationally
confined and may represent a transition gas-phase from primarily neutral atomic
gas, to a colder, denser molecular phase that will eventually host star
formation. |
The surprising influence of late charged current weak interactions on
Big Bang Nucleosynthesis: The weak interaction charged current processes ($\nu_e+n\leftrightarrow
p+e^-$, $\bar\nu_e +p\leftrightarrow n+e^+$, $n\leftrightarrow
p+e^-+\bar\nu_e$) interconvert neutrons and protons in the early universe and
have significant influence on Big Bang Nucleosynthesis (BBN) light-element
abundance yields, particulary that for $^{4}{\rm He}$. We demonstrate that the
influence of these processes is still significant even when they operate well
below temperatures $T\sim0.7\,{\rm MeV}$ usually invoked for "weak freeze-out,"
and in fact down nearly into the alpha-particle formation epoch ($T \approx
0.1\,{\rm MeV}$). This physics is correctly captured in commonly used BBN
codes, though this late-time, low-temperature persistent effect of the
isospin-changing weak processes, and the sensitivity of the associated rates to
lepton energy distribution functions and blocking factors are not widely
appreciated. We quantify this late-time influence by analyzing weak interaction
rate dependence on the neutron lifetime, lepton energy distribution functions,
entropy, the proton-neutron mass difference, and Hubble expansion rate. The
effects we point out here render BBN a keen probe of any beyond-standard-model
physics that alters lepton number/energy distributions, even subtly, in epochs
of the early universe all the way down to near $T=100\,{\rm keV}$. | Weighing neutrinos with the halo environment: Nonlinear objects like halos and voids exhibit a scale-dependent bias on
linear scales in massive neutrino cosmologies. The shape of this
scale-dependent bias is a unique signature of the neutrino masses, but the
amplitude of the signal is generally small, of the order of $f_\nu$, the
contribution of neutrinos to the total matter content ($\lesssim 1\%$). In this
paper, we demonstrate for the first time how the strength of this signal can be
substantially enhanced by using information about the halo environment at a
range of scales. This enhancement is achieved by using certain combinations of
the large scale Cold Dark Matter and total matter environments of halos, both
of which are measurable from galaxy clustering and weak lensing surveys. |
KiDS+GAMA: Constraints on Horndeski gravity from combined large-scale
structure probes: We present constraints on Horndeski gravity from a combined analysis of
cosmic shear, galaxy-galaxy lensing and galaxy clustering from
$450\,\mathrm{deg}^2$ of the Kilo-Degree Survey (KiDS) and the Galaxy And Mass
Assembly (GAMA) survey. The Horndeski class of dark energy/modified gravity
models includes the majority of universally coupled extensions to $\Lambda$CDM
with one scalar field in addition to the metric. We study the functions of time
that fully describe the evolution of linear perturbations in Horndeski gravity.
Our results are compatible throughout with a $\Lambda$CDM model. By imposing
gravitational wave constraints, we fix the tensor speed excess to zero and
consider a subset of models including e.g. quintessence and $f(R)$ theories.
Assuming proportionality of the Horndeski functions $\alpha_B$ and $\alpha_M$
(kinetic braiding and the Planck mass run rate, respectively) to the dark
energy density fraction $\Omega_{\mathrm{DE}}(a) = 1 - \Omega_{\mathrm{m}}(a)$,
we find for the proportionality coefficients $\hat{\alpha}_B =
0.20_{-0.33}^{+0.20} \,$ and $\, \hat{\alpha}_M = 0.25_{-0.29}^{+0.19}$. Our
value of $S_8 \equiv \sigma_8 \sqrt{\Omega_{\mathrm{m}}/0.3}$ is in better
agreement with the $Planck$ estimate when measured in the enlarged Horndeski
parameter space than in a pure $\Lambda$CDM scenario. In our joint three-probe
analysis we report a downward shift of the $S_8$ best fit value from the
$Planck$ measurement of $\Delta S_8 = 0.016_{-0.046}^{+0.048}$ in Horndeski
gravity, compared to $\Delta S_8 = 0.059_{-0.039}^{+0.040}$ in $\Lambda$CDM.
Our constraints are robust to the modelling uncertainty of the non-linear
matter power spectrum in Horndeski gravity. Our likelihood code for multi-probe
analysis in both $\Lambda$CDM and Horndeski gravity is publicly available at
http://github.com/alessiospuriomancini/KiDSHorndeski . | An all-sky Atlas of Radio/X-ray Associations: An all-sky comprehensive catalog of calculated radio and X-ray associations
to optical objects is presented. Included are X-ray sources from XMM-Newton,
Chandra and ROSAT catalogs, radio sources from NVSS, FIRST and SUMSS catalogs,
and optical data, identifications and redshifts from the APM, USNO-A, SDSS-DR7
and the extant literature. This "Atlas of Radio/X-ray Associations" inherits
many techniques from the predecessor Quasars.org (2004) catalog, but object
selection is changed and processing tweaked. Optical objects presented are
those which are calculated with >=40% confidence to be associated with
radio/X-ray detections, totalling 602570 objects in all, including 23681 double
radio lobe detections. For each of these optical objects I display the
calculated percentage probabilities of its being a QSO, galaxy, star, or
erroneous radio/X-ray association, plus any identification from the literature.
The catalogue includes 105568 uninvestigated objects listed as 40% to >99%
likely to be a QSO. The catalog is available at http://quasars.org/arxa.htm . |
The road to the red sequence: A detailed view of the formation of a
massive galaxy at z~2: (Abridged) We present here a detailed analysis of the star formation history
(SFH) of FW4871, a massive galaxy at z=1.893+-0.002. We compare rest-frame
optical and NUV slitless grism spectra from the Hubble Space Telescope with a
large set of composite stellar populations to constrain the underlying star
formation history. Even though the morphology features prominent tidal tails,
indicative of a recent merger, there is no sign of on-going star formation
within an aperture encircling one effective radius, which corresponds to a
physical extent of 2.6 kpc. A model assuming truncation of an otherwise
constant SFH gives a formation epoch zF~10, with a truncation after 2.7 Gyr,
giving a mass-weighted age of 1.5 Gyr and a stellar mass of 0.8-3E11Msun,
implying star formation rates of 30-110 Msun/yr. A more complex model including
a recent burst of star formation places the age of the youngest component at
145 Myr, with a mass contribution lower than 20%, and a maximum amount of dust
reddening of E(B-V)<0.4 mag (95% confidence levels). This low level of dust
reddening is consistent with the low emission observed at 24 micron,
corresponding to rest-frame 8 micron, where PAH emission should contribute
significantly if a strong formation episode were present. The colour profile of
FW4871 does not suggest a significant radial trend in the properties of the
stellar populations out to 3Re. We suggest that the recent merger that formed
FW4871 is responsible for the quenching of its star formation. | The quasi-linear nearby Universe: The local Universe provides a unique opportunity for testing cosmology and
theories of structure formation. To facilitate this opportunity we present a
new method for the reconstruction of the quasi-linear matter density and
velocity fields from galaxy peculiar velocities and apply it to the
Cosmicflows-2 data. The method consists of constructing an ensemble of
cosmological simulations, constrained by the standard cosmological model and
the observational data. The quasi-linear density field is the geometric mean
and variance of the fully non-linear density fields of the simulations. The
main nearby clusters (Virgo, Centaurus, Coma), superclusters (Shapley,
Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed.
Galaxies are born biased with respect to the underlying dark matter
distribution. Using our quasi-linear framework we demonstrate that the
luminosity-weighted density field derived from the 2M++ redshift compilations
is non-linearly biased with respect to the matter density field. The bias
diminishes in the linear regime. |
Enhancement of dark matter capture by neutron stars in binary systems: We study the capture of dark matter particles by neutron stars in close
binary systems. By performing a direct numerical simulation, we find that there
is a sizable amplification of the rate of dark matter capture by each of the
companions. In case of the binary pulsar PSR J1906+0746 with the orbital period
of 4 hours the amplification factor is 3.5. This amplification can be
attributed to the energy loss by dark matter particles resulting from their
gravitational scattering off moving companions. | UV-to-FIR analysis of Spitzer/IRAC sources in the Extended Groth Strip
II: Photometric redshifts, Stellar masses and Star formation rates: Based on the ultraviolet to far-infrared photometry already compiled and
presented in a companion paper (Barro et al. 2011a, Paper I), we present a
detailed SED analysis of nearly 80,000 IRAC 3.6+4.5 micron selected galaxies in
the Extended Groth Strip. We estimate photometric redshifts, stellar masses,
and star formation rates separately for each galaxy in this large sample. The
catalog includes 76,936 sources with [3.6] < 23.75 (85% completeness level of
the IRAC survey) over 0.48 square degrees. The typical photometric redshift
accuracy is Delta z/(1+z)=0.034, with a catastrophic outlier fraction of just
2%. We quantify the systematics introduced by the use of different stellar
population synthesis libraries and IMFs in the calculation of stellar masses.
We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter
of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies,
based on several sets of dust emission templates and SFR indicators. We
evaluate the systematic differences and goodness of the different SFR
estimations using the deep FIDEL 70 micron data available in the EGS. Typical
random uncertainties of the IR-bases SFRs are a factor of two, with
non-negligible systematic effects at z$\gtrsim$1.5 observed when only MIPS 24
micron data is available. All data products (SEDs, postage stamps from imaging
data, and different estimations of the photometric redshifts, stellar masses,
and SFRs of each galaxy) described in this and the companion paper are publicly
available, and they can be accessed through our the web-interface utility
Rainbow-navigator |
Measuring the jet power of flat spectrum radio quasars: We use frequency-dependent position shifts of flat spectrum radio cores to
estimate the kinetic power of AGN jets. We find a correlation between the
derived jet powers and AGN narrow-line luminosity, consistent with the
well-known relation for radio galaxies and steep spectrum quasars. This
technique can be applied to intrinsically weak jets even at high redshift. | AGN-Host Galaxy Connection: Morphology and Colours of X-ray Selected AGN
at z < 2: The connection between AGN and their host galaxies has been widely studied
over recent years, showing it to be of great importance for providing answers
to some fundamental questions related with AGN fueling mechanisms, their
formation and evolution. Using X-ray and one of the deepest broad-band optical
data sets, we studied morphology and colours in relationship with X-ray
properties for sources at redshifts z < 2.0, using a sample of 262 AGN in the
Subaru/XMM-Newton Deep Survey (SXDS). Morphological classification was obtained
using the galSVM code, one of the new methods useful especially when dealing
with high-redshift sources and low-resolution data. Colour-magnitude diagrams
were studied in relationship with redshift, morphology, X-ray obscuration, and
X-ray-to-optical flux ratio. Finally, the significance of different regions was
analysed on colour-magnitude diagrams, relating the observed properties of AGN
populations with some models of their formation and evolution. |
Can background cosmology hold the key for modified gravity tests?: Modified gravity theories are a popular alternative to dark energy as a
possible explanation for the observed accelerating cosmic expansion, and their
cosmological tests are currently an active research field. Studies in recent
years have been increasingly focused on testing these theories in the nonlinear
regime, which is computationally demanding. Here we show that, under certain
circumstances, a whole class of theories can be ruled out by using background
cosmology alone. This is possible because certain classes of models (i) are
fundamentally incapable of producing specific background expansion histories,
and (ii) said histories are incompatible with local gravity tests. As an
example, we demonstrate that a popular class of models, $f(R)$ gravity, would
not be viable if observations suggest even a slight deviation of the background
expansion history from that of the $\Lambda$CDM paradigm. | Generation of rotationally dominated galaxies by mergers of
pressure-supported progenitors: Through the analysis of a set of numerical simulations of major mergers
between initially non-rotating, pressure supported progenitor galaxies with a
range of central mass concentrations, we have shown that: (1) it is possible to
generate elliptical-like galaxies, with v/sigma > 1 outside one effective
radius, as a result of the conversion of orbital- into internal-angular
momentum; (2) the outer regions acquire part of the angular momentum first; (3)
both the baryonic and the dark matter components of the remnant galaxy acquire
part of the angular momentum, the relative fractions depend on the initial
concentration of the merging galaxies. For this conversion to occur the initial
baryonic component must be sufficiently dense and/or the encounter should take
place on a orbit with high angular momentum. Systems with these hybrid
properties have been recently observed through a combination of stellar
absorption lines and planetary nebulae for kinematic studies of early-type
galaxies. Our results are in qualitative agreement with such observations and
demonstrate that even mergers composed of non-rotating, pressure-supported
progenitor galaxies can produce early-type galaxies with significant rotation
at large radii. |
Convolution Lagrangian perturbation theory for biased tracers: We present a new formulation of Lagrangian perturbation theory which allows
accurate predictions of the real- and redshift-space correlation functions of
the mass field and dark matter halos. Our formulation involves a
non-perturbative resummation of Lagrangian perturbation theory and indeed can
be viewed as a partial resummation of the formalism of Matsubara (2008a,b) in
which we keep exponentiated all of the terms which tend to a constant at large
separation. One of the key features of our method is that we naturally recover
the Zel'dovich approximation as the lowest order of our expansion for the
matter correlation function. We compare our results against a suite of N-body
simulations and obtain good agreement for the correlation functions in
real-space and for the monopole correlation function in redshift space. The
agreement becomes worse for higher multipole moments of the redshift-space,
halo correlation function. Our formalism naturally includes non-linear bias and
explains the strong bias-dependence of the multipole moments of the
redshift-space correlation function seen in N-body simulations. | Vacuum dynamics in the Universe versus a rigid $Λ=$const: In this year, in which we celebrate 100 years of the cosmological term,
$\Lambda$, in Einstein's gravitational field equations, we are still facing the
crucial question whether $\Lambda$ is truly a fundamental constant or a mildly
evolving dynamical variable. After many theoretical attempts to understand the
meaning of $\Lambda$, and in view of the enhanced accuracy of the cosmological
observations, it seems now mandatory that this issue should be first settled
empirically before further theoretical speculations on its ultimate nature. In
this work, we summarize the situation of some of these studies. Devoted
analyses made recently show that the $\Lambda=$const. hypothesis, despite being
the simplest, may well not be the most favored one. The overall fit to the
cosmological observables $SNIa+BAO+H(z)+LSS+CMB$ singles out the class RVM of
the "running" vacuum models, in which $\Lambda=\Lambda(H)$ is an affine
power-law function of the Hubble rate. It turns out that the performance of the
RVM as compared to the "concordance" $\Lambda$CDM model (with $\Lambda=$const.)
is much better. The evidence in support of the RVM may reach $\sim 4\sigma$
c.l., and is bolstered with Akaike and Bayesian criteria providing strong
evidence in favor of the RVM option. We also address the implications of this
framework on the tension between the CMB and local measurements of the current
Hubble parameter. |
Cosmic Microwave Background Delensing Revisited: Residual Biases and a
Simple Fix: The delensing procedure is an effective tool for removing lensing-induced
$B$-mode polarization in the Cosmic Microwave Background to allow for deep
searches of primordial $B$-modes. However, the delensing algorithm existing in
the literature breaks down if the target $B$-mode signals overlap significantly
with the lensing $B$-mode ($\sim 300<l<2000$) in multipole-$l$ space. In this
paper, we identify the cause of the breakdown to be correlations between the
input $B$-map and the deflection field estimator ($EB$). The amplitude of this
bias is quantified by numerical simulations and compared to the analytically
derived functional form. We also propose a revised delensing procedure that
circumvents the bias. While the newly identified bias does not affect the
search of degree scale $B$-mode generated by tensor perturbations, the modified
delensing algorithm makes it possible to perform deep searches of high-$l$
$B$-modes such as those generated by patchy reionization, cosmic strings, or
rotation of polarization angles. Finally, we estimate how well future
polarization experiments can do in detecting tensor- and cosmic string-
generated $B$-mode after delensing and comment on different survey strategies. | A fresh look at linear cosmological constraints on a decaying dark
matter component: We consider a cosmological model in which a fraction $f$ of the Dark Matter
(DM) is allowed to decay in an invisible relativistic component, and compute
the resulting constraints on both the decay width (or inverse lifetime)
$\Gamma$ and $f$ from purely gravitational arguments. We report a full
derivation of the Boltzmann hierarchy, correcting a mistake in previous
literature, and compute the impact of the decay --as a function of the
lifetime-- on the CMB and matter power spectra. From CMB only, we obtain that
no more than 3.8 % of the DM could have decayed in the time between
recombination and today (all bounds quoted at 95 % CL). We also comment on the
important application of this bound to the case where primordial black holes
constitute DM, a scenario notoriously difficult to constrain. For lifetimes
longer than the age of the Universe, the bounds can be cast as $f\Gamma <
6.3\times10^{-3}$ Gyr$^{-1}$. For the first time, we also checked that
degeneracies with massive neutrinos are broken when information from the large
scale structure is used. Even secondary effects like CMB lensing suffice to
this purpose. Decaying DM models have been invoked to solve a possible tension
between low redshift astronomical measurements of $\sigma_8$ and $\Omega_{\rm
m}$ and the ones inferred by Planck. We reassess this claim finding that with
the most recent BAO, HST and $\sigma_8$ data extracted from the CFHT survey,
the tension is only slightly reduced despite the two additional free
parameters, loosening the bound to $f\Gamma < 15.9\times10^{-3}$ Gyr$^{-1}$.
The bound however improves to $f\Gamma < 5.9\times10^{-3}$ Gyr$^{-1}$ if only
data consistent with the CMB are included. This highlights the importance of
establishing whether the tension is due to real physical effects or unaccounted
systematics, for settling the reach of achievable constraints on decaying DM. |
NGC3801 caught in the act: A post-merger starforming early-type galaxy
with AGN-jet feedback: In the current models of galaxy formation and evolution, AGN feedback is
crucial to reproduce galaxy luminosity function, colour-magnitude relation and
M-sigma relation. However, if AGN-feedback can indeed expel and heat up
significant amount of cool molecular gas and consequently quench star
formation, is yet to be demonstrated observationally. Only in four cases so far
(Cen A, NGC 3801, NGC 6764 and Mrk 6), X-ray observations have found evidences
of jet-driven shocks heating the ISM. We chose the least-explored galaxy, NGC
3801, and present the first ultraviolet imaging and stellar population
analysisis of this galaxy from GALEX data. We find this merger-remnant
early-type galaxy to have an intriguing spiral-wisp of young star forming
regions (age ranging from 100--500 Myr). Taking clues from dust/PAH, HI and CO
emission images we interpret NGC 3801 to have a kinamatically decoupled core or
an extremely warped gas disk. From the HST data we also show evidence of
ionised gas outflow similar to that observed in HI and molecular gas (CO) data,
which may have caused the decline of star formation leading to the red optical
colour of the galaxy. However, from these panchromatic data we interpret that
the expanding shock shells from the young ($\sim$2.4 million years) radio jets
are yet to reach the outer gaseous regions of the galaxy. It seems, we observe
this galaxy at a rare stage of its evolutionary sequence where post-merger star
formation has already declined and new powerful jet feedback is about to affect
the gaseous star forming outer disk within the next 10 Myr, to further
transform it into a red-and-dead early-type galaxy. | Southern GEMS groups II: HI distribution, mass functions and HI
deficient galaxies: We investigate the neutral hydrogen (HI) content of sixteen groups for which
we have multi-wavelength data including X-ray observations. Wide-field imaging
of the groups was obtained with the 20-cm multibeam system on the 64-m Parkes
telescope. We have detected ten previously uncatalogued HI sources, one of
which has no visible optical counterpart. We examine the HI properties of the
groups, compared to their X-ray characteristics, finding that those groups with
a higher X-ray temperature and luminosity contain less HI per galaxy. The HI
content of a group depends on its morphological make-up, with those groups
dominated by early-type galaxies containing the least total HI. We determined
the expected HI for the spiral galaxies in the groups, and found that a number
of the galaxies were HI deficient. The HI deficient spirals were found both in
groups with and without a hot intra-group medium. The HI deficient galaxies
were not necessarily found at the centre of the groups, however, we did find
that two thirds of HI deficient galaxies were found within about 1 Mpc from the
group centre, indicating that the group environment is affecting the gas-loss
from these galaxies. We determined the HI mass function for a composite sample
of 15 groups, and found that it is significantly flatter than the field HI mass
function. We also find a lack of high HI-mass galaxies in groups. One possible
cause of this effect is the tidal stripping of HI gas from spiral galaxies as
they are pre-processed in groups. |
Precision constraints on radiative neutrino decay with CMB spectral
distortion: We investigate the radiative decay of the cosmic neutrino background, and its
impact on the spectrum of the cosmic microwave background (CMB) that is known
to be a nearly perfect black body. We derive exact formulae for the decay of a
heavier neutrino into a lighter neutrino and a photon, $\nu_j \to \nu_i +
\gamma$, and of absorption as its inverse, $\nu_i + \gamma \to \nu_j$, by
accounting for the precise form of the neutrino momentum distribution. Our
calculations show that if the neutrinos are heavier than $\mathcal O(0.1)$ eV,
the exact formulae give results that differ by $\sim$50%, compared with
approximate ones where neutrinos are assumed to be at rest. We also find that
spectral distortion due to absorption is more important for heavy neutrino
masses (by a factor of $\sim$10 going from a neutrino mass of 0.01 eV to 0.1
eV). By analyzing the CMB spectral data measured with COBE-FIRAS, we obtain
lower limits on the neutrino lifetime of $\tau_{12} \gtrsim 4 \times 10^{21}$ s
(95% C.L.) for the smaller mass splitting and $\tau_{13} \sim \tau_{23} \gtrsim
10^{19}$ s for the larger mass splitting. These represent up to one order of
magnitude improvement over previous CMB constraints. With future CMB
experiments such as PIXIE, these limits will improve by roughly 4 orders of
magnitude. This translates to a projected upper limit on the neutrino magnetic
moment (for certain neutrino masses and decay modes) of $\mu_\nu < 3 \times
10^{-11}\, \mu_B$, where $\mu_B$ is the Bohr magneton. Such constraints would
make future precision CMB measurements competitive with lab-based constraints
on neutrino magnetic moments. | Studying the SN-GRB connection with X-shooter: The GRB 100316D / SN
2010bh case: During the last ten years, observations of long-duration gamma-ray bursts
brought to the conclusion that at least a fraction of them is associated with
bright supernovae of type Ib/c. In this talk, after a short review on the
previously observed GRB-SN connection cases, we present the recent case of GRB
100316/SN 2010bh. In particular, during the observational campaign of SN
2010bh, a pivotal role was played by VLT/X-shooter, sampling with unique high
quality data the spectral energy distribution of the early evolution phases
from the UV to the K band. |
The 2010 M 87 VHE flare and its origin: the multi-wavelength picture: The giant radio galaxy M 87, with its proximity (16 Mpc) and its very massive
black hole ((3 - 6) \times 10^9 M_solar), provides a unique laboratory to
investigate very high energy (E>100 GeV; VHE) gamma-ray emission from active
galactic nuclei and, thereby, probe particle acceleration to relativistic
energies near supermassive black holes (SMBH) and in relativistic jets. M 87
has been established as a VHE gamma-ray emitter since 2005. The VHE gamma-ray
emission displays strong variability on timescales as short as a day. In 2008,
a rise in the 43 GHz Very Long Baseline Array (VLBA) radio emission of the
innermost region (core; extension of < 100 Rs ; Schwarzschild radii) was found
to coincide with a flaring activity at VHE. This had been interpreted as a
strong indication that the VHE emission is produced in the direct vicinity of
the SMBH. In 2010 a flare at VHE was again detected triggering further
multi-wavelength (MWL) observations with the VLBA, Chandra, and other
instruments. At the same time, M 87 was also observed with the Fermi-LAT
telescope at MeV/GeV energies, the European VLBI Network (EVN), and the
Liverpool Telescope (LT). Here, preliminary results from the 2010 campaign will
be reported. | SARCS strong-lensing galaxy groups: II - mass-concentration relation and
strong-lensing bias: Our work is based on the stacked weak-lensing analysis of a sample of 80
strong-lensing galaxy groups. Our main results are the following: (i) the
lensing signal does not allow us to firmly reject a simple singular isothermal
sphere mass distribution compared to the expected NFW mass profile; (ii) we
obtain an average concentration $c_{200}=8.6_{-1.3}^{+2.1}$ that is much higher
than the expected value from numerical simulations for the corresponding
average mass $M_{200}=0.73_{-0.10}^{+0.11}\times10^{14}\mathrm{M_{\odot}}$;
(iii) the combination of our results with those at larger mass scales gives a
mass-concentration relation $c(M)$ over nearly two decades in mass, with a
slope in disagreement with predictions from numerical simulations using
unbiased populations of dark matter haloes; (iv) our combined $c(M)$ relation
matches results from simulations using only haloes with a large strong-lensing
cross section, i.e. elongated with a major axis close to the line of sight; (v)
for the simplest case of prolate haloes, we estimate with a toy model a lower
limit on the minor:major axis ratio $a/c=0.5$ for the average SARCS galaxy
group.
Our analysis based on galaxy groups confirmed the results obtained at larger
mass scales: strong lenses present apparently too large concentrations, which
can be explained by triaxial haloes preferentially oriented with the line of
sight. Because more massive systems already have large lensing cross sections,
they do not require a large elongation along the line of sight, contrary to
less massive galaxy groups. Therefore, it is natural to observe larger lensing
(projected) concentrations for such systems, resulting in an overall
mass-concentration relation steeper than that of non-lensing haloes. |
The clustering of ALFALFA galaxies: dependence on HI mass, relationship
to optical samples & clues on host halo properties: We use a sample of ~6000 galaxies detected by the Arecibo Legacy Fast ALFA
(ALFALFA) 21cm survey, to measure the clustering properties of HI-selected
galaxies. We find no convincing evidence for a dependence of clustering on the
galactic atomic hydrogen (HI) mass, over the range M_HI ~ 10^{8.5} - 10^{10.5}
M_sun. We show that previously reported results of weaker clustering for low-HI
mass galaxies are probably due to finite-volume effects. In addition, we
compare the clustering of ALFALFA galaxies with optically selected samples
drawn from the Sloan Digital Sky Survey (SDSS). We find that HI-selected
galaxies cluster more weakly than even relatively optically faint galaxies,
when no color selection is applied. Conversely, when SDSS galaxies are split
based on their color, we find that the correlation function of blue optical
galaxies is practically indistinguishable from that of HI-selected galaxies. At
the same time, SDSS galaxies with red colors are found to cluster significantly
more than HI-selected galaxies, a fact that is evident in both the projected as
well as the full two-dimensional correlation function. A cross-correlation
analysis further reveals that gas-rich galaxies "avoid" being located within ~3
Mpc of optical galaxies with red colors. Next, we consider the clustering
properties of halo samples selected from the Bolshoi LambdaCDM simulation. A
comparison with the clustering of ALFALFA galaxies suggests that galactic HI
mass is not tightly related to host halo mass, and that a sizable fraction of
subhalos do not host HI galaxies. Lastly, we find that we can recover fairly
well the correlation function of HI galaxies by just excluding halos with low
spin parameter. This finding lends support to the hypothesis that halo spin
plays a key role in determining the gas content of galaxies. | Unifying static analysis of gravitational structures with a
scale-dependent scalar field gravity as an alternative to dark matter: Aims. We investigated the gravitational effects of a scalar field within
scalar-tensor gravity as an alternative to dark matter. Motivated by chameleon,
symmetron and f(R)-gravity models, we studied a phenomenological scenario where
the scalar field has both a mass (i.e. interaction length) and a coupling
constant to the ordinary matter which scale with the local properties of the
considered astrophysical system. Methods. We analysed the feasibility of this
scenario using the modified gravitational potential obtained in its context and
applied it to the galactic and hot gas/stellar dynamics in galaxy clusters and
elliptical/spiral galaxies respectively. This is intended to be a first step in
assessing the viability of this new approach in the context of "alternative
gravity" models. Results. The main results are: 1. the velocity dispersion of
elliptical galaxies can be fitted remarkably well by the suggested scalar
field, with model significance similar to a classical Navarro-Frenk-White dark
halo profile; 2. the analysis of the stellar dynamics and the gas equilibrium
in elliptical galaxies has shown that the scalar field can couple with ordinary
matter with different strengths (different coupling constants) producing and/or
depending on the different clustering state of matter components; 3. elliptical
and spiral galaxies, combined with clusters of galaxies, show evident
correlations among theory parameters which suggest the general validity of our
results at all scales and a way toward a possible unification of the theory for
all types of gravitational systems we considered. All these results demonstrate
that the proposed scalar field scenario can work fairly well as an alternative
to dark matter. |
Compact object coalescence rate estimation from short gamma-ray burst
observations: Recent observational and theoretical results suggest that Short-duration
Gamma-Ray Bursts (SGRBs) are originated by the merger of compact binary systems
of two neutron stars or a neutron star and a black hole. The observation of
SGRBs with known redshifts allows astronomers to infer the merger rate of these
systems in the local universe. We use data from the SWIFT satellite to estimate
this rate to be in the range $\sim 500$-1500 Gpc$^{-3}$yr$^{-1}$. This result
is consistent with earlier published results which were obtained through
alternative approaches. We estimate the number of coincident observations of
gravitational-wave signals with SGRBs in the advanced gravitational-wave
detector era. By assuming that all SGRBs are created by neutron star-neutron
star (neutron star-black hole) mergers, we estimate the expected rate of
coincident observations to be in the range $\simeq 0.2$ to 1 ($\simeq 1$ to 3)
yr$^{-1}$. | Generation of helical magnetic fields from inflation: The generation of helical magnetic fields during single field inflation due
to an axial coupling of the electromagnetic field to the inflaton is discussed.
We find that such a coupling always leads to a blue spectrum of magnetic fields
during slow roll inflation. Though the helical magnetic fields further evolve
during the inverse cascade in the radiation era after inflation, we conclude
that the magnetic fields generated by such an axial coupling can not lead to
observed field strength on cosmologically relevant scales. |
Iterative destriping and photometric calibration for Planck-HFI,
polarized, multi-detector map-making: We present an iterative scheme designed to recover calibrated I, Q, and U
maps from Planck-HFI data using the orbital dipole due to the satellite motion
with respect to the Solar System frame. It combines a map reconstruction, based
on a destriping technique, juxtaposed with an absolute calibration algorithm.
We evaluate systematic and statistical uncertainties incurred during both these
steps with the help of realistic, Planck-like simulations containing CMB,
foreground components and instrumental noise, and assess the accuracy of the
sky map reconstruction by considering the maps of the residuals and their
spectra. In particular, we discuss destriping residuals for polarization
sensitive detectors similar to those of Planck-HFI under different noise
hypotheses and show that these residuals are negligible (for intensity maps) or
smaller than the white noise level (for Q and U Stokes maps), for l > 50. We
also demonstrate that the combined level of residuals of this scheme remains
comparable to those of the destriping-only case except at very low l where
residuals from the calibration appear. For all the considered noise hypotheses,
the relative calibration precision is on the order of a few 10e-4, with a
systematic bias of the same order of magnitude. | HectoMAP: The Complete Redshift Survey (Data Release 2): HectoMAP is a dense redshift survey of 95,403 galaxies based primarily on MMT
spectroscopy with a median redshift $z = 0.345$. The survey covers 54.64 square
degrees in a 1.5$^\circ$ wide strip across the northern sky centered at a
declination of 43.25$^\circ$. We report the redshift, the spectral indicator
D$_{n}$4000, and the stellar mass. The red selected survey is 81\% complete for
55,962 galaxies with $(g-r) > 1$ and $r <20.5$; it is 72\% complete for 32,908
galaxies with $(g-r) > 1$, $(r-i) > 0.5$ and $20.5 < r < 21.3$. Comparison of
the survey basis SDSS photometry with the HSC-SSP photometry demonstrates that
HectoMAP provides complete magnitude limited surveys based on either
photometric system. We update the comparison between the HSC-SSP photometric
redshifts with HectoMAP spectroscopic redshifts; the comparison demonstrates
that the HSC-SSP photometric redshifts have improved between the second and
third data releases. HectoMAP is a foundation for examining the quiescent
galaxy population (63\% of the survey), clusters of galaxies, and the cosmic
web. HectoMAP is completely covered by the HSC-SSP survey, thus enabling a
variety of strong and weak lensing investigations. |
Observational imprints of enhanced scalar power on small scales in ultra
slow roll inflation and associated non-Gaussianities: The discovery of gravitational waves from merging binary black holes has
generated considerable interest in examining whether these black holes could
have a primordial origin. If a significant number of black holes have to be
produced in the early universe, the primordial scalar power spectrum should
have an enhanced amplitude on small scales, when compared to the COBE
normalized values on the larger scales that is strongly constrained by the
anisotropies in the cosmic microwave background. In the inflationary scenario
driven by a single, canonical scalar field, such power spectra can be achieved
in models that permit a brief period of ultra slow roll inflation during which
the first slow roll parameter decreases exponentially. In this review, we shall
consider a handful of such inflationary models as well as a reconstructed
scenario and examine the extent of formation of primordial black holes and the
generation of secondary gravitational waves in these cases. We shall also
discuss the strength and shape of the scalar bispectrum and the associated
non-Gaussianity parameter that arise in such situations. We shall conclude with
an outlook wherein we discuss the wider implications of the increased strengths
of the non-Gaussianities on smaller scales. | 28 -- 40 GHz variability and polarimetry of bright compact sources in
the QUIJOTE cosmological fields: We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological
fields which were brighter than 1 Jy at 30 GHz in the Planck Point Source
Catalogue (version 1), with the Very Large Array at 28 -- 40 GHz, in order to
characterise their high-radio-frequency variability and polarization
properties. We find a roughly log-normal distribution of polarization fractions
with a median of 2%, in agreement with previous studies, and a median rotation
measure (RM) of $\approx$ 1110 rad m$^{-2}$ with one outlier up to $\approx$
64000 rad m$^{-2}$ which is among the highest RMs measured in quasar cores. We
find hints of a correlation between the total intensity flux density and median
polarization fraction. We find 59% of sources are variable in total intensity,
and 100% in polarization at $3\sigma$ level, with no apparent correlation
between total intensity variability and polarization variability. This
indicates that it will be difficult to model these sources without simultaneous
polarimetric monitoring observations and they will need to be masked for
cosmological analysis. |
A needlet ILC analysis of WMAP 7-year data: estimation of CMB
temperature map and power spectrum: The WMAP 7-year temperature maps have been re-analized to extract a CMB map
and CMB power spectrum with reduced contamination by astrophysical foregrounds
and noise. The method used is based on linear combinations of WMAP data and
foreground templates, implemented on a decomposition of the observations onto a
needlet frame. We obtain a clean CMB map with low contamination from
foregrounds and noise, as well as a new estimate of the CMB temperature power
spectrum. The latter is essentially compatible with the power spectrum
published by the WMAP collaboration, although it is slightly but systematically
lower on large scales. The exact origin of this discrepancy is not clear. | The VIMOS Public Extragalactic Redshift Survey (VIPERS). Never mind the
gaps: comparing techniques to restore homogeneous sky coverage: [Abridged] Non-uniform sampling and gaps in sky coverage are common in galaxy
redshift surveys, but these effects can degrade galaxy counts-in-cells and
density estimates. We carry out a comparison of methods that aim to fill the
gaps to correct for the systematic effects. Our study is motivated by the
analysis of the VIMOS Extragalactic Redshift Survey (VIPERS), a flux-limited
survey (i<22.5) based on one-pass observations with VIMOS, with gaps covering
25% of the surveyed area and a mean sampling rate of 35%. Our findings are
applicable to other surveys with similar observing strategies. We compare 1)
two algorithms based on photometric redshift, that assign redshifts to galaxies
based on the spectroscopic redshifts of the nearest neighbours, 2) two Bayesian
methods, the Wiener filter and the Poisson-Lognormal filter. Using galaxy mock
catalogues we quantify the accuracy of the counts-in-cells measurements on
scales of R=5 and 8 Mpc/h after applying each of these methods. We also study
how they perform to account for spectroscopic redshift error and inhomogeneous
and sparse sampling rate. We find that in VIPERS the errors in counts-in-cells
measurements on R<10 Mpc/h scales are dominated by the sparseness of the
sample. All methods underpredict by 20-35% the counts at high densities. This
systematic bias is of the same order as random errors. No method outperforms
the others. Random and systematic errors decrease for larger cells. We show
that it is possible to separate the lowest and highest densities on scales of 5
Mpc/h at redshifts 0.5<z<1.1, over a large volume such as in VIPERS survey.
This is vital for the characterisation of cosmic variance and rare populations
(e.g, brightest galaxies) in environmental studies at these redshifts. |
The XMM Cluster Survey: Testing chameleon gravity using the profiles of
clusters: The chameleon gravity model postulates the existence of a scalar field that
couples with matter to mediate a fifth force. If it exists, this fifth force
would influence the hot X-ray emitting gas filling the potential wells of
galaxy clusters. However, it would not influence the clusters' weak lensing
signal. Therefore, by comparing X-ray and weak lensing profiles, one can place
upper limits on the strength of a fifth force. This technique has been
attempted before using a single, nearby cluster (Coma, $z=0.02$). Here we apply
the technique to the stacked profiles of 58 clusters at higher redshifts
($0.1<z<1.2$), including 12 new to the literature, using X-ray data from the
XMM Cluster Survey (XCS) and weak lensing data from the Canada France Hawaii
Telescope Lensing Survey (CFHTLenS). Using a multi-parameter MCMC analysis, we
constrain the two chameleon gravity parameters ($\beta$ and $\phi_{\infty}$).
Our fits are consistent with general relativity, not requiring a fifth force.
In the special case of $f(R)$ gravity (where $\beta = \sqrt{1/6}$), we set an
upper limit on the background field amplitude today of $|f_{\rm{R0}}| < 6
\times 10^{-5}$ (95% CL). This is one of the strongest constraints to date on
$|f_{\rm{R0}}|$ on cosmological scales. We hope to improve this constraint in
future by extending the study to hundreds of clusters using data from the Dark
Energy Survey. | Bayesian angular power spectrum analysis of interferometric data: We present a Bayesian angular power spectrum and signal map inference engine
which can be adapted to interferometric observations of anisotropies inthe
cosmic microwave background, 21 cm emission line mapping of galactic brightness
fluctuations, or 21 cm absorption line mapping of neutral hydrogen in the dark
ages. The method uses Gibbs sampling to generate a sampled representation of
the angular power spectrum posterior and the posterior of signal maps given a
set of measured visibilities in the uv-plane. We use a mock interferometric CMB
observation to demonstrate the validity of this method in the flat-sky
approximation when adapted to take into account arbitrary coverage of the
uv-plane, mode-mode correlations due to observations on a finite patch, and
heteroschedastic visibility errors. The computational requirements scale as
O(n_p log n_p) where n_p measures the ratio of the size of the detector array
to the inter-detector spacing, meaning that Gibbs sampling is a promising
technique for meeting the data analysis requirements of future cosmology
missions. |
Gravitational waves and pulsar timing: stochastic background, individual
sources and parameter estimation: Massive black holes are key ingredients of the assembly and evolution of
cosmic structures. Pulsar Timing Arrays (PTAs) currently provide the only means
to observe gravitational radiation from massive black hole binary systems with
masses >10^7 solar masses. The whole cosmic population produces a signal
consisting of two components: (i) a stochastic background resulting from the
incoherent superposition of radiation from the all the sources, and (ii) a
handful of individually resolvable signals that raise above the background
level and are produced by sources sufficiently close and/or massive.
Considering a wide range of massive black hole binary assembly scenarios, we
investigate both the level and shape of the background and the statistics of
resolvable sources. We predict a characteristic background amplitude in the
interval h_c(f = 10^-8 Hz)~5*10^-16 - 5*10^-15, within the detection range of
the complete Parkes PTA. We also quantify the capability of PTAs of measuring
the parameters of individual sources, focusing on monochromatic signals
produced by binaries in circular orbit. We investigate how the results depend
on the number and distribution of pulsars in the array, by computing the
variance-covariance matrix of the parameter measurements. For plausible Square
Kilometre Array (SKA) observations (100 pulsars uniformly distributed in the
sky), and assuming a coherent signal-to-noise ratio of 10, the sky position of
massive black hole binaries can be located within a ~40deg^2 error box, opening
promising prospects for detecting a putative electromagnetic counterpart to the
gravitational wave emission. The planned SKA, can plausibly observe these
unique systems, although the number of detections is likely to be small.
(Abridged) | Non-gaussianity and Statistical Anisotropy in Cosmological Inflationary
Models: We study the statistical descriptors for some cosmological inflationary
models that allow us to get large levels of non-gaussianity and violations of
statistical isotropy. Basically, we study two different class of models: a
model that include only scalar field perturbations, specifically a subclass of
small-field slow-roll models of inflation with canonical kinetic terms, and
models that admit both vector and scalar field perturbations. We study the
former to show that it is possible to attain very high, including observable,
values for the levels of non-gaussianity f_{NL} and \tao_{NL} in the bispectrum
B_\zeta and trispectrum T_\zeta of the primordial curvature perturbation \zeta
respectively. Such a result is obtained by taking care of loop corrections in
the spectrum P_\zeta, the bispectrum B_\zeta and the trispectrum T_\zeta .
Sizeable values for f_{NL} and \tao_{NL} arise even if \zeta is generated
during inflation. For the latter we study the spectrum P_\zeta, bispectrum
B_\zeta and trispectrum $T_\zeta of the primordial curvature perturbation when
\zeta is generated by scalar and vector field perturbations. The tree-level and
one-loop contributions from vector field perturbations are worked out
considering the possibility that the one-loop contributions may be dominant
over the tree level terms. The levels of non-gaussianity f_{NL} and \tao_{NL},
are calculated and related to the level of statistical anisotropy in the power
spectrum, g_\zeta . For very small amounts of statistical anisotropy in the
power spectrum, the levels of non-gaussianity may be very high, in some cases
exceeding the current observational limit. |
Quantum to Classical Transition of Inflationary Perturbations -
Continuous Spontaneous Localization as a Possible Mechanism -: The inflationary paradigm provides a mechanism to generate the primordial
perturbations needed to explain the observed large scale structures in the
universe. Inflation traces back all the inhomogeneities to quantum fluctuations
although the structures look classical today. Squeezing of primordial quantum
fluctuations along with the mechanism of decoherence accounts for many aspects
of this quantum to classical transition, although it remains a matter of debate
as to whether this is sufficient to explain the issue of realization of a
single outcome (i.e. the issue of macro-objectification) from a quantum
ensemble given that the universe is a closed system. A similar question of
emergence of classical behavior of macroscopic objects exists also for
laboratory systems and apart from decoherence there have been attempts to
resolve this issue through Continuous Spontaneous Localization (CSL), which is
a stochastic nonlinear modification of the non-relativistic Schr\"{o}dinger
equation. Recently, Martin {\it et al.} have investigated whether a CSL-like
mechanism with a constant strength parameter, when the Mukhanov-Sasaki variable
is taken as the "collapse-operator", can explain how the primordial quantum
perturbations generated during inflation become classical. Within the scope of
their assumptions they essentially come to a negative conclusion. In the
present work, we generalize their analysis by allowing the CSL strength
parameter to depend on physical scales so as to capture the CSL amplification
mechanism. We show that such a generalization provides a mechanism for
macro-objectification (i.e. classicalization) of the inflationary quantum
perturbations, while also preserving scale invariance of the power spectrum and
phase coherence of super-horizon perturbation modes in a particular class of
these models. | Crawling the Cosmic Network: Identifying and Quantifying Filamentary
Structure: We present the Smoothed Hessian Major Axis Filament Finder (SHMAFF), an
algorithm that uses the eigenvectors of the Hessian matrix of the smoothed
galaxy distribution to identify individual filamentary structures. Filaments
are traced along the Hessian eigenvector corresponding to the largest
eigenvalue, and are stopped when the axis orientation changes more rapidly than
a preset threshold. In both N-body simulations and the Sloan Digital Sky Survey
(SDSS) main galaxy redshift survey data, the resulting filament length
distributions are approximately exponential. In the SDSS galaxy distribution,
using smoothing lengths of 10 h^{-1} Mpc and 15 h^{-1} Mpc, we find filament
lengths per unit volume of 1.9x10^{-3} h^2 Mpc^{-2} and 7.6x10^{-4} h^2
Mpc^{-2}, respectively. The filament width distributions, which are much more
sensitive to non-linear growth, are also consistent between the real and mock
galaxy distributions using a standard cosmology. In SDSS, we find mean filament
widths of 5.5 h^{-1} Mpc and 8.4 h^{-1} Mpc on 10 h^{-1} Mpc and 15 h^{-1} Mpc
smoothing scales, with standard deviations of 1.1 h^{-1} Mpc and 1.4 h^{-1}
Mpc, respectively. Finally, the spatial distribution of filamentary structure
in simulations is very similar between z=3 and z=0 on smoothing scales as large
as 15 h^{-1} Mpc, suggesting that the outline of filamentary structure is
already in place at high redshift. |
Dark matter perturbations and viscosity: a causal approach: The inclusion of dissipative effects in cosmic fluids modifies their
clustering properties and could have observable effects on the formation of
large scale structures. We analyse the evolution of density perturbations of
cold dark matter endowed with causal bulk viscosity. The perturbative analysis
is carried out in the Newtonian approximation and the bulk viscosity is
described by the causal Israel-Stewart (IS) theory. In contrast to the
non-causal Eckart theory, we obtain a third order evolution equation for the
density contrast that depends on three free parameters. For certain parameter
values, the density contrast and growth factor in IS mimic their behaviour in
$\Lambda$CDM when $z \geq 1$. Interestingly, and contrary to intuition, certain
sets of parameters lead to an increase of the clustering. | GALEX and Pan-STARRS1 Discovery of SN IIP 2010aq: The First Few Days
After Shock Breakout in a Red Supergiant Star: We present the early UV and optical light curve of Type IIP supernova (SN)
2010aq at z=0.0862, and compare it to analytical models for thermal emission
following SN shock breakout in a red supergiant star. SN 2010aq was discovered
in joint monitoring between the Galaxy Evolution Explorer (GALEX) Time Domain
Survey (TDS) in the NUV and the Pan-STARRS1 Medium Deep Survey (PS1 MDS) in the
g, r, i, and z bands. The GALEX and Pan-STARRS1 observations detect the SN less
than 1 day after shock breakout, measure a diluted blackbody temperature of
31,000 +/- 6,000 K 1 day later, and follow the rise in the UV/optical light
curve over the next 2 days caused by the expansion and cooling of the SN
ejecta. The high signal-to-noise ratio of the simultaneous UV and optical
photometry allows us to fit for a progenitor star radius of 700 +/- 200 R_sun,
the size of a red supergiant star. An excess in UV emission two weeks after
shock breakout compared to SNe well fitted by model atmosphere-code synthetic
spectra with solar metallicity, is best explained by suppressed line blanketing
due to a lower metallicity progenitor star in SN 2010aq. Continued monitoring
of PS1 MDS fields by the GALEX TDS will increase the sample of early UV
detections of Type II SNe by an order of magnitude, and probe the diversity of
SN progenitor star properties. |
Testing foundations of modern cosmology with SKA all-sky surveys: Continuum and HI surveys with the Square Kilometre Array (SKA) will allow us
to probe some of the most fundamental assumptions of modern cosmology,
including the Cosmological Principle. SKA all-sky surveys will map an enormous
slice of space-time and reveal cosmology at superhorizon scales and redshifts
of order unity. We illustrate the potential of these surveys and discuss the
prospects to measure the cosmic radio dipole at high fidelity. We outline
several potentially transformational tests of cosmology to be carried out by
means of SKA all-sky surveys. | On the possibility of the long lifetime of molecular clouds: Arguments are given that at least a fraction of molecular clouds may live
much longer time that it is usually assumed, without the transition into
diffuse atomic gas (HI). We propose that star formation in these clouds may be
strongly delayed and weakened by the magnetic field. |
Contribution to the 2022 Cosmology session of the 56th Rencontres de
Moriond: Moment expansion of polarized dust SED: A new path towards capturing
the CMB $B$-modes with LiteBIRD: Characterizing accurately the polarized dust emission from our Galaxy will be
decisive for the quest for the Cosmic Microwave Background (CMB) primordial
$B$-modes. The incomplete modeling of its potentially complex spectral
properties could lead to biases in the CMB polarization analyses and to a
spurious detection of the tensor-to-scalar ratio $r$. Variations of the dust
properties along and between lines of sight lead to unavoidable distortions of
the spectral energy distribution (SED) that can not be easily anticipated by
standard component separation methods. This issue can be tackled using a moment
expansion of the dust SED, an innovative parametrization method imposing
minimal assumptions on the sky complexity. In the recent work [Vacher \emph{et
al.} (2022)]\cite{Vacher_2022}, we apply this formalism to the $B$-mode
cross-angular power spectra computed from simulated \lb{} polarization data at
frequencies between 100 and 402\,GHz, containing CMB, dust and instrumental
noise. Thanks to the moment expansion, we can measure an unbiased value of the
tensor-to-scalar ratio with a dispersion compatible with the target values
aimed by the instrument. | Survey geometry and the internal consistency of recent cosmic shear
measurements: We explore the impact of an update to the typical approximation for the shape
noise term in the analytic covariance matrix for cosmic shear experiments that
assumes the absence of survey boundary and mask effects. We present an exact
expression for the number of galaxy pairs in this term based on the the survey
mask, which leads to more than a factor of three increase in the shape noise on
the largest measured scales for the Kilo-Degree Survey (KIDS-450) real-space
cosmic shear data. We compare the result of this analytic expression to several
alternative methods for measuring the shape noise from the data and find
excellent agreement. This update to the covariance resolves any internal model
tension evidenced by the previously large cosmological best-fit $\chi^2$ for
the KiDS-450 cosmic shear data. The best-fit $\chi^2$ is reduced from 161 to
121 for 118 degrees of freedom. We also apply a correction to how the
multiplicative shear calibration uncertainty is included in the covariance.
This change, along with a previously known update to the reported effective
angular values of the data vector, jointly shift the inferred amplitude of the
correlation function to higher values. We find that this improves agreement of
the KiDS-450 cosmic shear results with Dark Energy Survey Year 1 and Planck
results. |
Weak lensing analysis of RXC J2248.7-4431: We present a weak lensing analysis of the cluster of galaxies RXC
J2248.7-4431, a massive system at z=0.3475 with prominent strong lensing
features covered by the HST/CLASH survey (Postman et al. 2012). Based on UBVRIZ
imaging from the WFI camera at the MPG/ESO-2.2m telescope, we measure
photometric redshifts and shapes of background galaxies. The cluster is
detected as a mass peak at 5sigma significance. Its density can be parametrised
as an NFW profile (Navarro et al. 1996) with two free parameters, the mass
M_200m=(33.1+9.6-6.8)x10^14Msol and concentration c_200m=2.6+1.5-1.0. We
discover a second cluster inside the field of view at a photometric redshift of
z~0.6, with an NFW mass of M_200m=(4.0+3.7-2.6)x10^14Msol. | AxioNyx: Simulating Mixed Fuzzy and Cold Dark Matter: The distinctive effects of fuzzy dark matter are most visible at non-linear
galactic scales. We present the first simulations of mixed fuzzy and cold dark
matter, obtained with an extended version of the Nyx code. Fuzzy (or
ultralight, or axion-like) dark matter dynamics are governed by the comoving
Schr\"odinger-Poisson equation. This is evolved with a pseudospectral algorithm
on the root grid, and with finite differencing at up to six levels of adaptive
refinement. Cold dark matter is evolved with the existing N-body implementation
in Nyx. We present the first investigations of spherical collapse in mixed dark
matter models, focusing on radial density profiles, velocity spectra and
soliton formation in collapsed halos. We find that the effective granule masses
decrease in proportion to the fraction of fuzzy dark matter which quadratically
suppresses soliton growth, and that a central soliton only forms if the fuzzy
dark matter fraction is greater than 10\%. The Nyx framework supports baryonic
physics and key astrophysical processes such as star formation. Consequently,
AxioNyx will enable increasingly realistic studies of fuzzy dark matter
astrophysics. |
The Spatial Clustering of Primordial Black Holes: The possibility that primordial black holes (PBHs) are the dark matter (or a
fraction thereof) has attracted much attention recently. Their spatial
clustering is a fundamental property which determines, among others, whether
current observational constraints are evaded within a given mass range, whether
merging is significant and whether primordial black holes could generate
cosmological structure. We treat them as discrete objects and clarify the issue
of their spatial clustering, with an emphasis on short-range exclusion and its
impact on their large scale power spectrum. Even if a Poissonian self-pair term
is always present in the zero-lag correlation, this does not necessarily imply
that primordial black holes are initially Poisson distributed. However, while
the initial PBH clustering depends on the detailed shape of the small-scale
power spectrum, we argue that it is not relevant for a narrow spectral feature
and primordial black hole masses still allowed by observations. | Galaxy cluster lensing masses in modified lensing potentials: We determine the concentration-mass relation of 19 X-ray selected galaxy
clusters from the CLASH survey in theories of gravity that directly modify the
lensing potential. We model the clusters as NFW haloes and fit their lensing
signal, in the Cubic Galileon and Nonlocal gravity models, to the lensing
convergence profiles of the clusters. We discuss a number of important issues
that need to be taken into account, associated with the use of nonparametric
and parametric lensing methods, as well as assumptions about the background
cosmology. Our results show that the concentration and mass estimates in the
modified gravity models are, within the errorbars, the same as in $\Lambda$CDM.
This result demonstrates that, for the Nonlocal model, the modifications to
gravity are too weak at the cluster redshifts, and for the Galileon model, the
screening mechanism is very efficient inside the cluster radius. However, at
distances $\sim \left[2-20\right] {\rm Mpc}/h$ from the cluster center, we find
that the surrounding force profiles are enhanced by $\sim20-40\%$ in the Cubic
Galileon model. This has an impact on dynamical mass estimates, which means
that tests of gravity based on comparisons between lensing and dynamical masses
can also be applied to the Cubic Galileon model. |
Constraining spinning primordial black holes with global 21-cm signal: We study the upper projected bounds on the dark matter fraction in the form
of the primordial black holes (PBHs) with a non-zero spin by using the
absorption feature in the global 21-cm signal at redshift z ~ 17. The mass and
spin are fundamental properties of a black hole, and they can substantially
affect the evaporation rate of the black hole. The evaporating black hole can
inject energy into the intergalactic medium and heat the gas. Subsequently, it
can modify the absorption amplitude in the global 21-cm signal. Therefore, the
absorption feature in the 21-cm signal can provide a robust bound on PBHs. We
analyse the projected constraints on the dark matter fraction in the form of
both spinning and non-spinning PBHs. The constraints are more stringent for
spinning PBHs than non-spinning ones. We also compare these bounds with other
observations and find the most stringent lower constraint on PBHs mass, which
is allowed to constitute the entire dark matter to 6.7 x 10^17 g for extremal
spinning PBHs. | A Deep Photometric Look at Two of Andromeda's Dwarf Spheroidals: X and
XVII: We use deep wide-field photometry from the Large Binocular Camera to study
the stellar and structural properties of the recently discovered Andromeda X
and Andromeda XVII (And X and And XVII) dwarf galaxies. Using the mean apparent
magnitude of the horizontal branch (HB), we derive distances of 621 +- 20 kpc
to And X and 734+- 23 kpc to And XVII, closer by >60 kpc than the previous
estimates which were based on red giant branch (RGB) observations. Thus our
results warrant against the use of the RGB tip method for determining distances
to systems with sparsely populated RGBs, and show how crucial HB observations
are in obtaining accurate distances in systems such as these. We find that And
X is a relatively faint (MV = -7.36), highly elongated (e = 0.48) system at a
distance of 174 +- 62 kpc from Andromeda. And XVII is brighter (MV = -8.61)
with an M31-centric distance of 73 kpc which makes it one of the closest
satellites to Andromeda. Both galaxies are metal-poor: we derive <[Fe/H]>=-2.2
for And X, while And XVII shows <[Fe/H]> = -2.0, consistent with the relation
of higher luminosity dwarfs being more metal- rich. Additionally, both galaxies
show considerable intrinsic spreads in metallicity (0.2 and 0.3 dex for And X
and And XVII respectively), consistent with multiple stellar populations. |
Constraining Modified Gravity with Euclid: Future proposed satellite missions as Euclid can offer the opportunity to
test general relativity on cosmic scales through mapping of the galaxy weak
lensing signal. In this paper we forecast the ability of these experiments to
constrain modified gravity scenarios as those predicted by scalar-tensor and
$f(R)$ theories. We found that Euclid will improve constraints expected from
the PLANCK satellite on these modified gravity models by two orders of
magnitude. We discuss parameter degeneracies and the possible biases introduced
by modified gravity. | HeI in the central Giant HII Region of NGC 5253. A 2D observational
approach to collisional and radiative transfer effects: ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios. |
A warm dark matter cosmogony may yield more low-mass galaxy detections
in 21-cm surveys than a cold dark matter one: The 21-cm spectral line widths, $w_{50}$, of galaxies are an approximate
tracer of their dynamical masses, such that the dark matter halo mass function
is imprinted in the number density of galaxies as a function of $w_{50}$.
Correcting observed number counts for survey incompleteness at the level of
accuracy needed to place competitive constraints on warm dark matter (WDM)
cosmological models is very challenging, but forward-modelling the results of
cosmological hydrodynamical galaxy formation simulations into observational
data space is more straightforward. We take this approach to make predictions
for an ALFALFA-like survey from simulations using the EAGLE galaxy formation
model in both cold (CDM) and WDM cosmogonies. We find that for WDM cosmogonies
more galaxies are detected at the low-$w_{50}$ end of the 21-cm velocity width
function than in the CDM cosmogony, contrary to what might na\"ively be
expected from the suppression of power on small scales in such models. This is
because low-mass galaxies form later and retain more gas in WDM cosmogonies
(with EAGLE). While some shortcomings in the treatment of cold gas in the EAGLE
model preclude placing definitive constraints on WDM scenarios, our analysis
illustrates that near-future simulations with more accurate modelling of cold
gas will likely make strong constraints possible, especially in conjunction
with new 21-cm surveys such as WALLABY. | A Universal Luminosity Function for Radio Supernova Remnants: We compile radio supernova remnant (SNR) samples from the literature for 19
nearby galaxies ranging from the SMC to Arp 220, and use this data to constrain
the SNR luminosity function (LF) at 20 cm. We find that radio SNR populations
are strikingly similar across galaxies. The LF can be described as a power law
with constant index and scaling proportional to a galaxy's star formation rate
(SFR). Unlike previous authors, we do not find any dependence of SNR luminosity
on a galaxy's global ISM density. The observed correlation between the
luminosity of a galaxy's brightest SNR and a galaxy's SFR can be completely
explained by statistical effects, wherein galaxies with higher SFR more
thoroughly sample the high-luminosity end of the SNR LF. The LF is well fit by
a model of SNR synchrotron emission which includes diffusive shock acceleration
and magnetic field amplification, if we assume that all remnants are undergoing
adiabatic expansion, the densities of star-forming regions are similar across
galaxies, and the efficiency of CR production is constant. |
Bianchi I meets the Hubble diagram: We improve existing fits of the Bianchi I metric to the Hubble diagram of
supernovae and find an intriguing yet non-significant signal for anisotropy
that should be verified or falsified in the near future by the Large Synoptic
Survey Telescope.
Since the literature contains two different formulas for the apparent
luminosity as a function of time of flight in Bianchi I metrics, we present an
independent derivation confirming the result by Saunders (1969). The present
fit differs from earlier ones by Koivisto & Mota and by Campanelli et al. in
that we use Saunders' formula, a larger sample of supernovae, Union 2 and JLA,
and we use the general Bianchi I metric with three distinct eigenvalues. | What galaxy surveys really measure: In this paper we compute the quantity which is truly measured in a large
galaxy survey. We take into account the effects coming from the fact that we
actually observe galaxy redshifts and sky positions and not true spatial
positions. Our calculations are done within linear perturbation theory for both
the metric and the observer velocities but they can be used for non-linear
matter power spectra. We shall see that the complications due to the fact that
we only observe on our background lightcone and that we do not truly know the
distance of the observed galaxy, but only its redshift is not only an
additional difficulty, but even more a new opportunity for future galaxy
surveys. |
Dynamical Black Hole Masses of BL Lac Objects from the Sloan Digital Sky
Survey: We measure black hole masses for 71 BL Lac objects from the Sloan Digital Sky
Survey with redshifts out to z~0.4. We perform spectral decompositions of their
nuclei from their host galaxies and measure their stellar velocity dispersions.
Black hole masses are then derived from the black hole mass - stellar velocity
dispersion relation. We find BL Lac objects host black holes of similar masses,
~10^{8.5} M_sun, with a dispersion of 0.4 dex, similar to the uncertainties on
each black hole measurement. Therefore, all BL Lac objects in our sample have
the same indistinguishable black hole mass. These 71 BL Lac objects follow the
black hole mass - bulge luminosity relation, and their narrow range of host
galaxy luminosities confirm previous claims that BL Lac host galaxies can be
treated as standard candles. We conclude that the observed diversity in the
shapes of BL Lac object spectral energy distributions is not strongly driven by
black hole mass or host galaxy properties. | Red Spectral Tilt and Observable Gravity Waves in Shifted Hybrid
Inflation: We consider supersymmetric shifted hybrid inflation models with a red tilted
scalar spectral index n_s in agreement with the WMAP 7-yr central value. If
non-minimal supergravity corrections are included, these models can also
support a tensor-to-scalar ratio as large as r = 0.02, which may be observable
by the Planck Satellite. In contrast to the standard supersymmetric hybrid
inflation scenario, topological defects produced via gauge symmetry breaking
are inflated away in the shifted version of the theory. |
Low-Resolution Spectrum of the Extragalactic Background Light with AKARI
InfraRed Camera: The Extragalactic Background Light (EBL) as an integrated light from outside
of our Galaxy includes information of the early universe and the Dark Ages. We
analyzed the spectral data of the astrophysical diffuse emission obtained with
the low-resolution spectroscopy mode on the AKARI Infra-Red Camera (IRC) in
1.8-5.3 um wavelength region. Although the previous EBL observation in this
wavelength region is restricted to the observations by DIRBE and IRTS, this
study adds a new independent result with negligible contamination of Galactic
stars owing to higher sensitivity for point sources. Other two major foreground
components, the zodiacal light (ZL) and the diffuse Galactic light (DGL), were
subtracted by taking correlations with ZL brightness estimated by the DIRBE ZL
model and with the 100 um dust thermal emission, respectively. The isotropic
emission was obtained as EBL, which shows significant excess over integrated
light of galaxies at <4 um. The obtained EBL is consistent with the previous
measurements by IRTS and DIRBE. | Effects of pair freeze-out on photon distributions in BBN epoch: We investigate the evolution of non-extensivity in the photon distribution
during the Big Bang Nucleosynthesis (BBN) epoch using Tsallis statistics.
Assuming a minimal deviation from the Planck distribution, we construct the
perturbed Boltzmann equation for photons, including the collision terms for
pair creation and annihilation processes. We analyze the possibility that these
collisions could cause a slight increase in the number of high-frequency
photons within the BBN era, and consequently, the primordial plasma might be
temporarily placed in a state of chemical non-equilibrium. We also discuss the
restoration of the photon distribution to an equilibrium state as the Universe
enters the matter-dominated era. These findings, which suggest possible changes
in the photon distribution during the epoch between the BBN and the
recombination, offer insights that support the previously proposed ansatz
solution to the primordial lithium problem in arXiv:1812.09472. |
Covariance of the matter power spectrum including the survey window
function effect: N-body simulations vs. fifth-order perturbation theory on
grid: We present a Next-to-next-to-leading (fifth or NNLO) order calculation for
the covariance matrix of the matter power spectrum, taking into account the
effect of survey window functions. Using the grid-based calculation scheme for
the standard perturbation theory, GridSPT, we quickly generate multiple
realizations of the nonlinear density fields to fifth order in perturbation
theory, then estimate the power spectrum and the covariance matrix from the
sample. To the end, we have obtained the non-Gaussian covariance originated
from the one-loop trispectrum without explicitly computing the trispectrum. By
comparing the GridSPT calculations with the N-body results, we show that NNLO
GridSPT result reproduces the N-body results on quasi-linear scales where SPT
accurately models nonlinear matter power spectrum. Incorporating the survey
window function effect to GridSPT is rather straightforward, and the resulting
NNLO covariance matrix also matches well with the N-body results. | SHAMe-SF: Predicting the clustering of star-forming galaxies with an
enhanced abundance matching model: With the advent of several galaxy surveys targeting star-forming galaxies, it
is important to have models capable of interpreting their spatial distribution
in terms of astrophysical and cosmological parameters. To address this need, we
introduce SHAMe-SF, an extension of the subhalo abundance matching (SHAM)
technique designed specifically for analyzing the redshift-space clustering of
star-forming galaxies. Our model directly links a galaxy's star formation rate
to the properties of its host dark-matter halo, with further modulations based
on effective models of feedback and gas stripping. To quantify the accuracy of
our model, we show that it simultaneously reproduces key clustering statistics
such as the projected correlation function, monopole, and quadrupole of
star-forming galaxy samples at various redshifts and number densities. Notably,
these tests were conducted over a wide range of scales $[0.6, 30]\hMpc$, using
samples from both the TNG300 magneto-hydrodynamic simulation and from a
semi-analytical model. SHAMe-SF can also reproduce the clustering of simulated
galaxies that fall within the colour selection criteria employed by DESI for
emission line galaxies. Our model exhibits several potential applications,
including the generation of covariance matrices, exploration of galaxy
formation processes, and even placing constraints on the cosmological
parameters of the Universe. |
The co-planarity of satellite galaxies delivered by randomly aligned
cold mode accretion streams: Recent observations have shown that the majority of the Andromeda galaxy's
satellites are aligned in a thin plane. On the theoretical side it has been
proposed that galaxies acquire their gas via cold streams. In addition,
numerical simulations show that the same streams also deliver gas clumps which
could potentially develop into satellite galaxies. Assuming that cold streams
are a major source of satellite systems around galaxies we calculate the
probabilities in two different models to find a certain fraction of satellites
within a thin plane around the central galaxy of the host halo with and without
having the same sense of rotation. Using simple geometrical considerations and
adopting a random orientation of the streams we demonstrate that the vast thin
disk of satellites detected around Andromeda can naturally be explained within
this framework. In fact, without any satellite scattering, two streams would
lead to too many satellites in the thin plane, compared with the observations.
Three streams reproduce the observations very well. Natural implications from
our model are that all massive galaxies should have a thin plane of satellites
and that the satellites should naturally distribute themselves not only into a
single plane but into several inclined ones. We estimate the effect of
additional satellites accreted from random directions and find it to be of
minor relevance for a mild inflow of satellites from random directions. | GOODS-HERSCHEL: evidence for a UV extinction bump in galaxies at z > 1: Dust attenuation curves in external galaxies are useful to study their dust
properties as well as to interpret their intrinsic spectral energy
distributions. In particular the presence or absence of a UV bump at 2175 A
remains an open issue which has consequences on the interpretation of broad
band colours of distant galaxies. We study the dust attenuation curve in the UV
range at z >1. In particular we search for the presence of a UV bump. We use
deep photometric data of the CDFS obtained with intermediate and broad band
filters by the MUSYC project to sample the UV rest-frame of galaxies with 1<z
<2. Herschel/PACS and Spitzer/MIPS data are used to measure the dust emission.
30 galaxies were selected with high S/N in all bands. Their SEDs from the UV to
the far-IR are fitted using the CIGALE code and the characteristics of the dust
attenuation curve are obtained. The mean dust attenuation curve we derive
exhibits a UV bump at 2175A whose amplitude corresponds to 35 % (76%) that of
the MW (LMC2 supershell) extinction curve. An analytical expression of the
average attenuation curve is given, it is found slightly steeper than the
Calzetti et al. one, although at a 1 sigma level. Our galaxy sample is used to
study the derivation of the slopes of the UV continuum from broad band colours,
including the GALEX FUV-NUV colour. Systematic errors induced by the presence
of the bump are quantified. We compare dust attenuation factors measured with
CIGALE to the slope of the UV continuum and find that there is a large scatter
around the relation valid for local starbursts (0.7 mag). The uncertainties on
the determination of the UV slope lead to an extra systematic error of the
order of 0.3 to 0.7 mag on dust attenuation when a filter overlaps the UV bump. |
Mid-Infrared Spectral Measures of Star-Formation and AGN Activity in
Normal Galaxies: We investigate the use of MIR PAH bands, continuum and emission lines as
probes of star-formation and AGN activity in a sample of 100 'normal' and local
(z~0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer
Space Telescope Infrared Spectrograph (IRS) as part of the Spitzer-SDSS-GALEX
Spectroscopic Survey (SSGSS) which includes multi-wavelength photometry from
the UV to the FIR and optical spectroscopy. The continuum and features were
extracted using PAHFIT (Smith et al. 2007), a decomposition code which we find
to yield PAH equivalent widths up to ~30 times larger than the commonly used
spline methods. Despite the lack of extreme objects in our sample (such as
strong AGNs, low metallicity galaxies or ULIRGs), we find significant
variations in PAH, continuum and emission line properties and systematic trends
between these MIR properties and optically derived physical properties such as
age, metallicity and radiation field hardness. We revisit the diagnostic
diagram relating PAH equivalent widths and [Ne II]12.8micrometers/[O
IV]25.9micrometers line ratios and find it to be in much better agreement with
the standard optical star-formation/AGN classification than when spline
decompositions are used, while also potentially revealing obscured AGNs. The
luminosity of individual PAH components, of the continuum, and with poorer
statistics, of the neon emission lines and molecular hydrogen lines, are found
to be tightly correlated to the total IR luminosity, making individual MIR
components good gauges of the total dust emission in SF galaxies. Like the
total IR luminosity, these individual components can be used to estimate dust
attenuation in the UV and in Halpha lines based on energy balance arguments. We
also propose average scaling relations between these components and dust
corrected, Halpha derived star-formation rates. | The Odd-Parity CMB Bispectrum: Measurement of the cosmic microwave background (CMB) bispectrum, or
three-point correlation function, has now become one of the principle efforts
in early-Universe cosmology. Here we show that there is a odd-parity component
of the CMB bispectrum that has been hitherto unexplored. We argue that
odd-parity temperature-polarization bispectra can arise, in principle, through
weak lensing of the CMB by chiral gravitational waves or through cosmological
birefringence, although the signals will be small even in the best-case
scenarios. Measurement of these bispectra requires only modest modifications to
the usual data-analysis algorithms. They may be useful as a consistency test in
searches for the usual bispectrum and to search for surprises in the data. |
MGCAMB with massive neutrinos and dynamical dark energy: We present a major upgrade of MGCAMB, a patch for the Einstein-Boltzmann
solver CAMB used for phenomenological tests of general relativity against
cosmological datasets. This new version is compatible with the latest CosmoMC
code and includes a consistent implementation of massive neutrinos and
dynamical dark energy. The code has been restructured to make it easier to
modify to fit the custom needs of specific users. To illustrate the
capabilities of the code, we present joint constraints on the modified growth,
massive neutrinos and the dark energy equation of state from the latest
cosmological observations, including the recent galaxy counts and weak lensing
measurements from the Dark Energy Survey, and find a good consistency with the
{\Lambda}CDM model. | Dark Stars: A New Study of the FIrst Stars in the Universe: We have proposed that the first phase of stellar evolution in the history of
the Universe may be Dark Stars (DS), powered by dark matter heating rather than
by nuclear fusion. Weakly Interacting Massive Particles, which may be their own
antipartners, collect inside the first stars and annihilate to produce a heat
source that can power the stars. A new stellar phase results, a Dark Star,
powered by dark matter annihilation as long as there is dark matter fuel, with
lifetimes from millions to billions of years. We find that the first stars are
very bright ($\sim 10^6 L_\odot$) and cool ($T_{surf} < 10,000$K) during the DS
phase, and grow to be very massive (500-1000 times as massive as the Sun).
These results differ markedly from the standard picture in the absence of DM
heating, in which the maximum mass is about 140$M_\odot$ and the temperatures
are much hotter ($T_{surf} > 50,000$K); hence DS should be observationally
distinct from standard Pop III stars. Once the dark matter fuel is exhausted,
the DS becomes a heavy main sequence star; these stars eventually collapse to
form massive black holes that may provide seeds for supermassive black holes
observed at early times as well as explanations for recent ARCADE data and for
intermediate black holes. |
Self-Consistent Solution of Cosmological Radiation-Hydrodynamics and
Chemical Ionization: We consider a PDE system comprising compressible hydrodynamics, flux-limited
diffusion radiation transport and chemical ionization kinetics in a
cosmologically-expanding universe. Under an operator-split framework, the
cosmological hydrodynamics equations are solved through the Piecewise Parabolic
Method, as implemented in the Enzo community hydrodynamics code. The remainder
of the model, including radiation transport, chemical ionization kinetics, and
gas energy feedback, form a stiff coupled PDE system, which we solve using a
fully-implicit inexact Newton approach, and which forms the crux of this paper.
The inner linear Newton systems are solved using a Schur complement
formulation, and employ a multigrid-preconditioned conjugate gradient solver
for the inner Schur systems. We describe this approach and provide results on a
suite of test problems, demonstrating its accuracy, robustness, and scalability
to very large problems. | Implications of Pulsar Timing Array Data for Scalar-Induced
Gravitational Waves and Primordial Black Holes: Primordial Non-Gaussianity
$f_{\mathrm{NL}}$ Considered: Multiple pulsar-timing-array collaborations have reported strong evidence for
the existence of a gravitational-wave background. We study physical
implications of this signal for cosmology, assuming that it is attributed to
scalar-induced gravitational waves. By incorporating primordial non-Gaussianity
$f_{\mathrm{NL}}$, we specifically examine the nature of primordial curvature
perturbations and primordial black holes. We find that the signal allows for a
primordial non-Gaussianity $f_{\mathrm{NL}}$ in the range of $-4.1\lesssim
f_{\mathrm{NL}} \lesssim 4.1$ (68\% confidence intervals) and a mass range for
primordial black holes $m_{\mathrm{pbh}}$ spanning from $\sim10^{-5}M_{\odot}$
to $\sim10^{-2}M_{\odot}$. Furthermore, we find that the signal favors a
negative non-Gaussianity, which can suppress the abundance of primordial black
holes. We also demonstrate that the anisotropies of scalar-induced
gravitational waves serve as a powerful tool to probe the non-Gaussianity
$f_{\mathrm{NL}}$. We conduct a comprehensive analysis of the angular power
spectrum within the nano-Hertz band. Looking ahead, we anticipate that future
projects, such as the Square Kilometre Array, will have the potential to
measure these anisotropies and provide further insights into the primordial
universe. |
The halo masses and galaxy environments of hyperluminous QSOs at z~2.7
in the Keck Baryonic Structure Survey: We present an analysis of the galaxy distribution surrounding 15 of the most
luminous (>10^{14} L_sun; M_1450 ~ -30) QSOs in the sky with z~2.7. Our data
are drawn from the Keck Baryonic Structure Survey (KBSS). In this work, we use
the positions and spectroscopic redshifts of 1558 galaxies that lie within ~3',
(4.2 h^{-1} comoving Mpc; cMpc) of the hyperluminous QSO (HLQSO) sightline in
one of 15 independent survey fields, together with new measurements of the
HLQSO systemic redshifts. We measure the galaxy-HLQSO cross-correlation
function, the galaxy-galaxy autocorrelation function, and the characteristic
scale of galaxy overdensities surrounding the sites of exceedingly rare,
extremely rapid, black hole accretion. On average, the HLQSOs lie within
significant galaxy overdensities, characterized by a velocity dispersion
sigma_v ~ 200 km s^{-1} and a transverse angular scale of ~25", (~200 physical
kpc). We argue that such scales are expected for small groups with
log(M_h/M_sun)~13. The galaxy-HLQSO cross-correlation function has a best-fit
correlation length r_0_GQ = (7.3 \pm 1.3) h^{-1} cMpc, while the galaxy
autocorrelation measured from the spectroscopic galaxy sample in the same
fields has r_0_GG = (6.0 \pm 0.5) h^{-1} cMpc. Based on a comparison with
simulations evaluated at z ~ 2.6, these values imply that a typical galaxy
lives in a host halo with log(M_h/M_sun) = 11.9\pm0.1, while HLQSOs inhabit
host halos of log(M_h/M_sun) = 12.3\pm0.5. In spite of the extremely large
black hole masses implied by their observed luminosities [log(M_BH/M_sun) >
9.7], it appears that HLQSOs do not require environments very different from
their much less luminous QSO counterparts. Evidently, the exceedingly low space
density of HLQSOs (< 10^{-9} cMpc^{-3}) results from a one-in-a-million event
on scales << 1 Mpc, and not from being hosted by rare dark matter halos. | The clustering of luminous red galaxies at z $\sim$ 0.7 from eBOSS and
BOSS data: We present the first scientific results from the luminous red galaxy sample
(LRG) of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). We
measure the small and intermediate scale clustering from a sample of more than
61,000 galaxies in the redshift range $0.6 < z < 0.9$. We interpret these
measurements in the framework of the Halo Occupation Distribution. The bias of
eBOSS LRGs is $2.30 \pm 0.03$, with a satellite fraction of $13\pm3$\% and a
mean halo mass of $2.5\times10^{13}h^{-1}M_{\odot}$. These results are
consistent with expectations, demonstrating that eBOSS galaxies will be
reliable tracers of large scale structure at $z\sim 0.7$. The eBOSS galaxy bias
implies a scatter of luminosity at fixed halo mass, $\sigma_{\log L}$, of 0.19
dex. Using the clustering of massive galaxies from BOSS-CMASS, BOSS-LOWZ, and
SDSS, we find that $\sigma_{\log L}=0.19$ is consistent with observations over
the full redshift range that these samples cover. The addition of eBOSS to
previous surveys allows investigation of the evolution of massive galaxies over
the past $\sim 7$ Gyr. |
Constraining R$_V$ Variation Using Highly Reddened Type Ia Supernovae
from the Pantheon+ Sample: Type Ia supernovae (SNe Ia) are powerful tools for measuring the expansion
history of the universe, but the impact of dust around SNe Ia remains unknown
and is a critical systematic uncertainty. One way to improve our empirical
description of dust is to analyse highly reddened SNe Ia ($E(B-V)>0.4$, roughly
equivalent to the fitted SALT2 light-curve parameter $c>0.3$). With the
recently released Pantheon+ sample, there are 57 SNe Ia that were removed
because of their high colour alone (with colours up to $c=1.61$), which can
provide enormous leverage on understanding line-of-sight $R_V$. Previous
studies have claimed that $R_V$ decreases with redder colour, though it is
unclear if this is due to limited statistics, selection effects, or an
alternative explanation. To test this claim, we fit two separate
colour-luminosity relationships, one for the main cosmological sample ($c<0.3$)
and one for highly reddened ($c>0.3$) SNe Ia. We find the change in the
colour-luminosity coefficient to be consistent with zero. Additionally, we
compare the data to simulations with different colour models, and find that the
data prefers a model with a flat dependence of $R_V$ on colour over a declining
dependence. Finally, our results strongly support that line-of-sight $R_V$ to
SNe Ia is not a single value, but forms a distribution. | Torsion, an alternative to the cosmological constant?: We confront Einstein-Cartan's theory with the Hubble diagram and obtain a
negative answer to the question in the title. Contrary findings in the
literature seem to stem from an error in the field equations. |
Large scale environmental bias of the QSO line of sight proximity effect: We analyse the proximity zone of the intergalactic matter around
high-redshift quasars in a cosmological environment. In a box of 64 h-1 Mpc
base length we employ dark matter only simulations. For estimating the hydrogen
temperature and density distribution we use the effective equation of state.
Hydrogen is assumed to be in photoionisation equilibrium with a model
background flux which is fit to recent observations of the mean optical depth
and transmission flux statistics. At redshifts z = 3, 4, and 4.8, we select
model quasar positions at the centre of the 20 most massive halos and 100 less
massive halos identified in the simulation. From each assumed quasar position
we cast 100 random lines of sight for two box length including the changes in
the ionisation fractions by the QSO flux field and derive mock Ly{\alpha}
spectra. The proximity effect describes the dependence of the mean normalised
optical depth {\xi} = {\tau}eff, QSO/{\tau}eff, Ly{\alpha} as a function of the
ratio of the ionisation rate by the QSO and the background field, {\omega} =
{\Gamma}QSO/{\Gamma}UVB, i.e. the profile {\xi} = (1 + {\omega}/a)-0.5, where a
strength parameter a is introduced. The strength parameter measures the
deviation from the theoretical background model and is used to quantify any
influence of the environmental density field. We reproduce an unbiased
measurement of the proximity effect which is not affected by the host halo
mass. The scatter between different lines of sight and different quasar host
positions increases with decreasing redshift. Around the host halos, we find
only a slight average overdensity in the proximity zone at comoving radii of 1
< rc < 10h-1 Mpc. However, a clear power-law correlation of the strength
parameter with the average overdensity in rc is found, showing an
overestimation of the ionising background in overdense regions and an
underestimation in underdense regions. | An Accurate Reconstruction of CMB E Mode Signal over Large Angular
Scales using Prior Information of CMB Covariance Matrix in ILC Algorithm: In the recent years, the internal-linear-combination (ILC) method was
investigated extensively in the context of reconstruction of Cosmic Microwave
Background (CMB) temperature anisotropy signal using observations obtained by
WMAP and Planck satellite missions. In this article, we, for the first time,
apply the ILC method to reconstruct the large scale CMB E mode polarization
signal, which serves as the unique probe of ionization history of the Universe,
using simulated observations of 15 frequency CMB polarization maps of future
generation COrE satellite mission. We find that usual ILC cleaned E mode map is
highly erroneous due to presence of a chance-correlation between CMB and
astrophysical foreground components in the empirical covariance matrix which is
used to estimate the weight factors. The cleaned angular power spectrum for E
mode is strongly biased and erroneous due to these chance correlation factors.
In order to address the issues of bias and errors we extend and improve the
usual ILC method for CMB E mode reconstruction by incorporating prior
information of theoretical E mode angular power spectrum while estimating the
weights for linear combination of input maps. Using the E mode covariance
matrix effectively suppresses the CMB-foreground chance correlation power
leading to an accurate reconstruction of cleaned CMB E mode map and its angular
power spectrum. We provide a comparative study of the performance of the usual
ILC and the new method over large angular scales of the sky and show that the
later produces significantly statistically improved results than the former.
The new E mode CMB angular power spectrum contains neither any significant
negative bias at the low multipoles nor any positive foreground bias at
relatively higher mutlipoles. The error estimates of the cleaned spectrum agree
very well with the cosmic variance induced error. |
Resonant bar detector constraints on macro dark matter: The current standard model of cosmology, $\Lambda$CDM, requires dark matter
to make up around $25\%$ of the total energy budget of the Universe. Yet, quite
puzzlingly, there appears to be no candidate particle in the current Standard
Model of particle physics. Assuming the validity of the cold dark matter (CDM)
paradigm, dark matter has evaded detection thus far either because it is
intrinsically a weakly interacting substance or because its interactions are
suppressed by its high constituent mass and low number density. Most approaches
to explain dark matter to date assume the former and therefore require
beyond-the-Standard-Model particles that have yet to be observed directly or
indirectly. Given the dearth of evidence for this class of candidates it is
timely to consider the latter possibility, which allows for candidates that may
or may not arise from the Standard Model. In this work we extend a recent study
of this general class of so-called macro dark matter--candidates with
characteristic masses of grams and geometric cross sections of cm$^2$. We
consider new bounds that can be set using existing data from the resonant bar
gravitational wave detectors NAUTILUS and EXPLORER. | A new view on the ISM of galaxies: far-infrared and submillimetre
spectroscopy with Herschel: The FIR/submm window is amongst the least explored spectral regions of the
electromagnetic spectrum. It is, however, a key to study the general properties
of the interstellar medium of galaxies, as it contains important spectral line
diagnostics from the neutral, ionized and molecular ISM. The Herschel Space
Observatory, successfully launched on 14 May 2009, is the first observatory to
cover the entire FIR/submm range between 57 and 672 mum. We discuss the main
results from the ISO era on FIR spectroscopy of galaxies and the enormous
science potential of the Herschel mission through a presentation of its
spectroscopic extragalactic key programs. |
The Angular Momentum Problem in Cosmological Simulations of Disk Galaxy
Formation: We conduct a systematic study of the angular momentum problem in numerical
simulations of disk galaxy formation. We investigate the role of numerical
resolution using a semi-cosmological setup which combines an efficient use of
the number of particles in an isolated halo while preserving the hierarchical
build-up of the disk through the merging of clumps. We perform the same
simulation varying the resolution over 4 orders of magnitude. Independent on
the level of resolution, the loss of angular momentum stays the same and can be
tied to dynamical friction during the build-up phase. This is confirmed in a
cosmological simulation. We also perform simulations including star formation
and star formation and supernova feedback. While the former has no influence on
the angular momentum problem, the latter reduces the loss to a level
potentially in agreement with observations. This is achieved through a
suppression of early star formation and therefore the formation of a large,
slowly rotating bulge. We conclude that feedback is a critical component to
achieve realistic disk galaxies in cosmological simulations. Numerical
resolution is important, but by itself not capable of solving the angular
momentum problem. | MADmap: A Massively Parallel Maximum-Likelihood Cosmic Microwave
Background Map-Maker: MADmap is a software application used to produce maximum-likelihood images of
the sky from time-ordered data which include correlated noise, such as those
gathered by Cosmic Microwave Background (CMB) experiments. It works efficiently
on platforms ranging from small workstations to the most massively parallel
supercomputers. Map-making is a critical step in the analysis of all CMB data
sets, and the maximum-likelihood approach is the most accurate and widely
applicable algorithm; however, it is a computationally challenging task. This
challenge will only increase with the next generation of ground-based,
balloon-borne and satellite CMB polarization experiments. The faintness of the
B-mode signal that these experiments seek to measure requires them to gather
enormous data sets. MADmap is already being run on up to $O(10^{11})$ time
samples, $O(10^8)$ pixels and $O(10^4)$ cores, with ongoing work to scale to
the next generation of data sets and supercomputers. We describe MADmap's
algorithm based around a preconditioned conjugate gradient solver, fast Fourier
transforms and sparse matrix operations. We highlight MADmap's ability to
address problems typically encountered in the analysis of realistic CMB data
sets and describe its application to simulations of the Planck and EBEX
experiments. The massively parallel and distributed implementation is detailed
and scaling complexities are given for the resources required. MADmap is
capable of analysing the largest data sets now being collected on computing
resources currently available, and we argue that, given Moore's Law, MADmap
will be capable of reducing the most massive projected data sets. |
Primordial Black Hole Clusters and their Evolution: A possibility of pregalactic seeds of the Active Galactic Nuclei can be a
nontrivial cosmological consequence of particle theory. Such seeds can appear
as Primordial Black Hole (PBH) clusters, formed in the succession of phase
transitions with spontaneous and then manifest breaking of the global U(1)
symmetry. If the first phase transition takes place at the inflationary stage,
a set of massive closed walls may be formed at the second phase transition and
the collapse of these closed walls can result in formation of PBH clusters. We
present the results of our studies of the evolution of such PBH Clusters. | A data-driven model for spectra: Finding double redshifts in the Sloan
Digital Sky Survey: We present a data-driven method - heteroscedastic matrix factorization, a
kind of probabilistic factor analysis - for modeling or performing
dimensionality reduction on observed spectra or other high-dimensional data
with known but non-uniform observational uncertainties. The method uses an
iterative inverse-variance-weighted least-squares minimization procedure to
generate a best set of basis functions. The method is similar to principal
components analysis, but with the substantial advantage that it uses
measurement uncertainties in a responsible way and accounts naturally for
poorly measured and missing data; it models the variance in the
noise-deconvolved data space. A regularization can be applied, in the form of a
smoothness prior (inspired by Gaussian processes) or a non-negative constraint,
without making the method prohibitively slow. Because the method optimizes a
justified scalar (related to the likelihood), the basis provides a better fit
to the data in a probabilistic sense than any PCA basis. We test the method on
SDSS spectra, concentrating on spectra known to contain two redshift
components: These are spectra of gravitational lens candidates and massive
black-hole binaries. We apply a hypothesis test to compare one-redshift and
two-redshift models for these spectra, utilizing the data-driven model trained
on a random subset of all SDSS spectra. This test confirms 129 of the 131 lens
candidates in our sample and all of the known binary candidates, and turns up
very few false positives. |
The warm absorber and X-ray variability of the Seyfert 1 galaxy NGC 3516
as seen by the XMM-Newton RGS: We present a new analysis of the soft and medium energy X-ray spectrum of the
Seyfert 1 galaxy NGC 3516 taken with the Reflection Grating Spectrometer (RGS)
and European Photon Imaging Camera (EPIC) on board the XMM-Newton observatory.
We examine four observations made in October 2006. We investigate whether the
observed variability is due to absorption by the warm absorber and/or is
intrinsic to the source emission. We analyse in detail the EPIC-pn and RGS
spectra of each observation separately. The warm absorber in NGC 3516 is found
to consist of three phases of ionisation, two of which have outflow velocities
of more than 1000 km/s. The third phase (the least ionised one) is much slower
at 100 km/s. One of the high ionisation phases, with log xi of 2.4, is found to
have a partial covering fraction of about 60%. It has previously been suggested
that the passage of a cloud, part of a disk wind, in front of the source
(producing a change in the covering fraction) was the cause of a significant
dip in the lightcurve during one of the observations. From our modelling of the
EPIC-pn and RGS spectra, we find that variation in the covering fraction cannot
be solely responsible for this. We show that intrinsic change in the source
continuum plays a much more significant role in explaining the observed flux
and spectral variability than originally thought. | On the relative bias of void tracers in the Dark Energy Survey: Luminous tracers of large-scale structure are not entirely representative of
the distribution of mass in our Universe. As they arise from the highest peaks
in the matter density field, the spatial distribution of luminous objects is
biased towards those peaks. On large scales, where density fluctuations are
mild, this bias simply amounts to a constant offset in the clustering amplitude
of the tracer, known as linear bias. In this work we focus on the relative bias
between galaxies and galaxy clusters that are located inside and in the
vicinity of cosmic voids, extended regions of relatively low density in the
large-scale structure of the Universe. With the help of hydro-dynamical
simulations we verify that the relation between galaxy and cluster overdensity
around voids remains linear. Hence, the void-centric density profiles of
different tracers can be linked by a single multiplicative constant. This
amounts to the same value as the relative linear bias between tracers for the
largest voids in the sample. For voids of small sizes, which typically arise in
higher density regions, this constant has a higher value, possibly showing an
environmental dependence similar to that observed for the linear bias itself.
We confirm our findings by analysing mocks and data obtained during the first
year of observations by the Dark Energy Survey. As a side product, we present
the first catalogue of three-dimensional voids extracted from a photometric
survey with a controlled photo-z uncertainty. Our results will be relevant in
forthcoming analyses that attempt to use voids as cosmological probes. |
CMB Polarization Systematics Due to Beam Asymmetry: Impact on
Cosmological Birefringence: The standard cosmological model is assumed to respect parity symmetry. Under
this assumption the cross-correlations of the CMB's temperature anisotropy and
`gradient'-like polarization, with the `curl'-like polarization identically
vanish over the full sky. However, extensions of the standard model which allow
for light scalar field or axion coupling to the electromagnetic field, or
coupling to the Riemann gravitational field-strength, as well as other
modifications of field theories, may induce a rotation of the CMB polarization
plane on cosmological scales and manifest itself as nonvanishing TB and EB
cross-correlations. Recently, the degree of parity violation (reflected in
polarization rotation) was constrained using data from BOOMERANG, WMAP and
QUAD. Forecasts have been made for near-future experiments (e.g. PLANCK) to
further constrain parity- and Lorentz-violating terms in the fundamental
interactions of nature. Here we consider a real-world effect induced by a class
of telescope beam systematics which can mimic the rotation of polarization
plane or otherwise induce nonvanishing TB and EB correlations. In particular,
adopting the viewpoint that the primary target of future experiments will be
the inflationary B-mode signal, we assume the beam-systematics of the upcoming
PLANCK and POLARBEAR experiments are optimized towards this goal, and explore
the implications of the allowed levels of beam systematics on the resulting
precision of polarization-rotation measurements. | Unexpected LIGO events and the Mirror World: We consider the possibility that LIGO events GW190521, GW190425 and GW190814
may have emerged from the mirror world binaries. Theories of star evolution
predict so called upper and lower mass gaps and masses of these merger
components lie in that gaps. In order to explain these challenging events very
specific assumptions are required and we argue that such scenarios are order of
magnitude more probable in mirror world, where star formation begins earlier
and matter density can exceed 5 times the ordinary matter density. |
Do Cosmological Perturbations Have Zero Mean?: A central assumption in our analysis of cosmic structure is that cosmological
perturbations have zero ensemble mean. This property is one of the consequences
of statistically homogeneity, the invariance of correlation functions under
spatial translations. In this article we explore whether cosmological
perturbations indeed have zero mean, and thus test one aspect of statistical
homogeneity. We carry out a classical test of the zero mean hypothesis against
a class of alternatives in which perturbations have non-vanishing means, but
homogeneous and isotropic covariances. Apart from Gaussianity, our test does
not make any additional assumptions about the nature of the perturbations and
is thus rather generic and model-independent. The test statistic we employ is
essentially Student's t statistic, applied to appropriately masked,
foreground-cleaned cosmic microwave background anisotropy maps produced by the
WMAP mission. We find evidence for a non-zero mean in a particular range of
multipoles, but the evidence against the zero mean hypothesis goes away when we
correct for multiple testing. We also place constraints on the mean of the
temperature multipoles as a function of angular scale. On angular scales
smaller than four degrees, a non-zero mean has to be at least an order of
magnitude smaller than the standard deviation of the temperature anisotropies. | Evolution of BCGs structural parameters in the last $\sim$6 Gyr:
feedback processes versus merger events: We present results on the evolution in the last 6 Gyr of the structural
parameters of two samples of brightest cluster galaxies (BCGs). The nearby
sample of BCGs consist on 69 galaxies from the WINGS survey spanning a redshift
range of 0.04$<$z$<$0.07. The intermediate redshift (0.3$<$z$<$0.6) sample is
formed by 20 BCGs extracted from the Hubble Space Telescope archive. Both
samples have similar spatial resolution and their host clusters have similar
X-ray luminosities. We report an increase in the size of the BCGs from
intermediate to local redshift. However, we do not detect any variation in the
S\'ersic shape parameter in both samples. These results are proved to be robust
since the observed tendencies are model independent. We also obtain significant
correlations between some of the BCGs parameters and the main properties of the
host clusters. More luminous, larger and centrally located BCGs are located in
more massive and dominant galaxy clusters. These facts indicate that the host
galaxy cluster has played an important role in the formation of their BCGs. We
discuss the possible mechanisms that can explain the observed evolution of the
structural parameters of the BCGs. We conclude that the main mechanisms that
can explain the increase in size and the non-evolution in the S\'ersic shape
parameter of the BCGs in the last 6 Gyr are feedback processes. This result
disagrees with semi-analytical simulation results supporting that merging
processes are the main responsible for the evolution of the BCGs until the
present epoch. |
Constraints on parity violation from ACTpol and forecasts for
forthcoming CMB experiments: We use the ACTpol published cosmic microwave background (CMB) polarization
data to constrain cosmological birefringence, a tracer of parity violation
beyond the standard model of particle physics. To this purpose, we employ all
the polarized ACTpol spectra, including the cross-correlations between
temperature anisotropy and B mode polarization (TB) and between E mode and B
mode (EB), which are most sensitive to the effect. We build specific, so-called
D-estimators for birefringence and assess their performances and error budgets
by using realistic Monte Carlo simulations based on the experimental
characteristics provided by the ACTpol collaboration. We determine the optimal
multipole range for our analysis to be $250 < \ell < 3025$ over which we find a
null result for the uniform birefringence angle $\alpha = 0.29^\circ \pm
0.28^\circ$ (stat.) $\pm 0.5^\circ$ (syst.), the latter uncertainty being the
estimate published by the ACTpol team on their global systematic error budget.
We show that this result holds consistently when other multipole ranges are
considered. Finally, we forecast the capability of several forthcoming ground
based, balloon and space borne CMB experiments to constrain the birefringence
angle, showing, e.g., that the proposed post-Planck COrE satellite mission
could in principle constrain $\alpha$ at a level of 10 arcsec, provided that
all systematics are under control. Under the same circumstances, we find the
COrE constraints to be at least 2 or 3 times better than what could ideally be
achieved by the other experiments considered. | Reverberation Mapping of the Intermediate Mass Nuclear Black Hole in
SDSS J114008.71+030711.4: We present the results of a reverberation mapping (RM) campaign on the black
hole (BH) associated with the active galactic nucleus (AGN) in SDSS
J114008.71+030711.4 (hereafter GH08). This object is selected from a sample of
19 candidate intermediate mass BHs (M_{BH} < 10^{6} Msun) found by Greene & Ho
2004 in the Sloan Digital Sky Survey (SDSS). We used the Hobby-Eberly Telescope
to obtain 30 spectra over a period of 178 days in an attempt to resolve the
reverberation time lag (tau) between the continuum source and the broad line
region (BLR) in order to determine the radius of the BLR (R_{BLR}) in GH08. We
measure tau to be 2 days with an upper limit of 6 days. We estimate the AGN
luminosity at 5100 Angstroms to be approximately 1.1 x 10^{43} erg s^{-1} after
deconvolution from the host galaxy. The most well calibrated R_{BLR}-L relation
predicts a time lag which is 4 times larger than what we measure. Using the
measured H\beta\ full-width-at-half-maximum of 703 (+/-) 110 km s^{-1} and an
upper limit for R_{BLR} = 6 light days, we find M_{BH} < 5.8 x 10^{5} Msun as
an upper limit to the BH virial mass in GH08, which implies super-Eddington
accretion. Based on our measured M_{BH} we propose that GH08 may be another
candidate to add to the very short list of AGNs with M_{BH} < 10^{6} Msun
determined using RM. |
Bayesian model-independent evaluation of expansion rates of the universe: Marginal likelihoods for the cosmic expansion rates are evaluated using the
`Constitution' data of 397 supernovas, thereby updating the results in some
previous works. Even when beginning with a very strong prior probability that
favors an accelerated expansion, we obtain a marginal likelihood for the
deceleration parameter $q_0$ peaked around zero in the spatially flat case. It
is also found that the new data significantly constrains the cosmographic
expansion rates, when compared to the previous analyses. These results may
strongly depend on the Gaussian prior probability distribution chosen for the
Hubble parameter represented by $h$, with $h=0.68\pm 0.06$. This and similar
priors for other expansion rates were deduced from previous data. Here again we
perform the Bayesian model-independent analysis in which the scale factor is
expanded into a Taylor series in time about the present epoch. Unlike such
Taylor expansions in terms of redshift, this approach has no convergence
problem. | Hubble Constant from LSST Strong lens time delays with microlensing
systematics: Strong lens time delays have been widely used in cosmological studies,
especially to infer $H_0$. The upcoming LSST will provide several hundred well
measured time delays from the light curves of lensed quasars. However, due to
the inclination of the finite AGN accretion disc and the differential
magnification of the coherent temperature fluctuations, the microlensing by the
stars can lead to changes in the actual time delay on the light-crossing time
scale of the emission region $\sim days$. We first study how this would change
the uncertainty of $H_0$ in the LSST era, assuming the microlensing time delays
can be well estimated. We adopt 1/3, 1 and 3 days respectively as the typical
microlensing time delay uncertainties. The relative uncertainty of $H_0$ will
be enlarged to $0.47\%$, $0.51\%$, $0.76\%$, respectively from the one without
microlensing impact $0.45\%$. Then, due to the lack of understandings on the
quasar models and microlensing patterns, we also test the reliability of the
results if one neglects this effect in the analysis. The biases of $H_0$ will
be $0.12\%$, $0.22\%$ and $0.70\%$, respectively, suggesting that 1 day is the
cut-off for a robust $H_0$ estimate. |
Reconstructing the stellar mass distributions of galaxies using S4G IRAC
3.6 and 4.5 micron images: I. Correcting for contamination by PAH, hot dust,
and intermediate age stars: With the aim of constructing accurate 2D maps of the stellar mass
distribution in nearby galaxies from S4G 3.6 and 4.5 micron images, we report
on the separation of the light from old stars from the emission contributed by
contaminants (e.g. hot dust and the 3.3 micron PAH feature). Results for a
small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC
4321, and NGC 5194) with a range of morphological properties, dust contents and
star formation histories are presented to demonstrate our approach. We use an
Independent Component Analysis (ICA) technique designed to separate
statistically independent source distributions, maximizing the distinction in
the [3.6]-[4.5] colors of the sources. The technique also removes emission from
intermediate-age evolved red objects with a low mass-to-light ratio, such as
asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of
the underlying old distribution of light with [3.6]-[4.5] colors consistent
with the colors of K and M giants. Contaminants are identified via comparison
to the non-stellar emission imaged at 8 microns, which is dominated by the
broad PAH feature. Using the measured 3.6/8 micron ratio to select the
individual contaminants, we find that hot dust and PAH together contribute
between ~5-15% to the integrated light at 3.6 microns, while light from regions
dominated by intermediate-age stars accounts for only 1-5%. Locally, however,
the contribution from either contaminant can reach much higher levels; dust
contributes on average 22% to the emission in star-forming regions throughout
the sample, while intermediate age-stars contribute upwards of 50% in localized
knots. The removal of these contaminants with ICA leaves maps of the old
stellar disk that retain a high degree of structural information and are
ideally suited for tracing the stellar mass, as will be the focus in a
companion paper. | Modeling The Large Scale Bias of Neutral Hydrogen: We present new analytical estimates of the large scale bias of neutral
hydrogen (HI). We use a simple, non-parametric model which monotonically
relates the total mass of a halo M_tot with its HI mass M_HI at zero redshift;
for earlier times we assume limiting models for the HI density evolution
consistent with the data presently available, as well as two main scenarios for
the evolution of our M_HI - M_tot relation. We find that both the linear and
the first nonlinear bias terms exhibit a strong evolution with redshift,
regardless of the specific limiting model assumed for the H I density over
time. These analytical predictions are then shown to be consistent with
measurements performed on the Millennium Simulation. Additionally, we show that
this strong bias evolution does not sensibly affect the measurement of the HI
power spectrum. |
Isocurvature Constraints on Portal Couplings: We consider portal models which are ultraweakly coupled with the Standard
Model, and confront them with observational constraints on dark matter
abundance and isocurvature perturbations. We assume the hidden sector to
contain a real singlet scalar $s$ and a sterile neutrino $\psi$ coupled to $s$
via a pseudoscalar Yukawa term. During inflation, a primordial condensate
consisting of the singlet scalar $s$ is generated, and its contribution to the
isocurvature perturbations is imprinted onto the dark matter abundance. We
compute the total dark matter abundance including the contributions from
condensate decay and nonthermal production from the Standard Model sector. We
then use the Planck limit on isocurvature perturbations to derive a novel
constraint connecting dark matter mass and the singlet self coupling with the
scale of inflation: $m_{\rm DM}/{\rm GeV}\lesssim 0.2\lambda_{\rm
s}^{\scriptscriptstyle 3/8} \left(H_*/10^{\scriptscriptstyle 11}{\rm
GeV}\right)^{\scriptscriptstyle -3/2}$. This constraint is relevant in most
portal models ultraweakly coupled with the Standard Model and containing light
singlet scalar fields. | The merger history of massive spheroids since z~1 is size independent: Using a compilation of 379 massive (stellar mass M > 10^{11} M_Sun)
spheroid-like galaxies from the near-infrared Palomar/DEEP-2 survey, we have
probed, up to z~1, whether the presence of companions depends on the size of
the host galaxies. We have explored the presence of companions with mass ratios
down to 1:10 and 1:100, with respect to the central massive galaxy, and within
a projected distance of 30, 50 and 100 kpc of these objects. We find evidence
for these companions being equally distributed around both compact and extended
massive spheroids. This finding suggests that, at least since z~1, the merger
activity in these objects is rather homogeneous across the whole population and
its merger history is not affected for the size of the host galaxy. Our result
could indicate that both compact and extended massive spheroid-like galaxies
are growing in size at the same rate. |
A photometric study of the field around the candidate recoiling/binary
black hole SDSS J092712.65+294344.0: We present a photometric FUV to Ks-band study of the field around quasar SDSS
J092712.65+294344.0. The SDSS spectrum of this object shows various emission
lines with two distinct redshifts, at z=0.699 and z=0.712. Because of this
peculiar spectroscopic feature this source has been proposed as a candidate
recoiling or binary black hole. A third alternative model involves two galaxies
moving in the centre of a rich galaxy cluster. Here we present a study
addressing the possible presence of such a rich cluster of galaxies in the SDSS
J092712.65+294344.0 field. We observed the 3.6x2.6 square arcmin field in the
Ks-band and matched the NIR data with the FUV and NUV images in the GALEX
archive and the ugriz observations in the SDSS. From various colour-colour
diagrams we were able to classify the nature of 32 sources, only 6-11 of which
have colours consistent with galaxies at z~0.7. We compare these numbers with
the surface density of galaxies, stars & quasars, and the expectations for
typical galaxy clusters both at low and high redshift. Our study shows that the
galaxy cluster scenario is in clear disagreement with the new observations. | Spoon or slide? The non-linear matter power spectrum in the presence of
massive neutrinos: Numerical simulations of massive neutrino cosmologies consistently find a
spoon-like feature in the non-linear matter power spectrum ratios of
cosmological models that differ only in the neutrino mass fraction f_N.
Typically, the ratio approaches unity at low wave numbers k, decreases by ~ 10
f_N at k ~ 1 h/Mpc, and turns up again at large k. Using the halo model of
large-scale structure, we show that this spoon feature originates in the
transition from the two-halo power spectrum to the one-halo power spectrum. The
former's sensitivity to f_N rises with k, while that of the latter decreases
with k. The presence of this spoon feature is robust with respect to different
choices of the halo mass function and the halo density profile, and does not
require any parameter tuning within the halo model. We demonstrate that a
standard halo model calculation is already able to predict the depth, width,
and position of this spoon as well as its evolution with redshift z with
remarkable accuracy. Predictions at z >= 1 can be further improved using
non-linear perturbative inputs. |
The impact of supernovae driven winds on stream-fed protogalaxies: SNe driven winds are widely thought to be very influential in the
high-redshift Universe, shaping the properties of the circum-galactic medium,
enriching the IGM with metals and driving the evolution of low-mass galaxies.
However, it is not yet fully understood how SNe driven winds interact with
their surroundings in a cosmological context, nor is it clear whether they are
able to significantly impact the evolution of low-mass galaxies from which they
originate by altering the amount of cold material these accrete from the cosmic
web. We implement a standard Taylor-Sedov type solution, widely used in the
community to depict the combined action of many SN explosions, in a
cosmological resimulation of a low mass galaxy at z =9 from the 'Nut' suite.
However, in contrast with previous work, we achieve a resolution high enough to
capture individual SN remnants in the Taylor-Sedov phase, for which the
solution provides an accurate description of the expansion. We report the
development of a high-velocity, far-reaching galactic wind produced by the
combined action of SNe in the main galaxy and its satellites, which are located
in the same or a neighbouring dark matter halo. Despite this, we find that (i)
this wind carries out very little mass (the measured outflow is of the order of
a tenth of the inflow/star formation rate) and (ii) the cold gas inflow rate
remains essentially unchanged from the run without SNe feedback. Moreover,
there are epochs during which star formation is enhanced in the feedback run
relative to its radiative cooling only counterpart. We attribute this
'positive' feedback to the metal enrichment that is present only in the former.
We conclude that at very high redshift, efficient SNe feedback can drive
large-scale galactic winds but does not prevent massive cold gas inflow from
fuelling galaxies, resulting in long-lived episodes of intense star
formation.(abridged) | Looking for ultralight dark matter near supermassive black holes: Measurements of the dynamical environment of supermassive black holes (SMBHs)
are becoming abundant and precise. We use such measurements to look for
ultralight dark matter (ULDM), which is predicted to form dense cores
("solitons") in the centre of galactic halos. We search for the gravitational
imprint of an ULDM soliton on stellar orbits near Sgr A* and by combining
stellar velocity measurements with Event Horizon Telescope imaging of M87*.
Finding no positive evidence, we set limits on the soliton mass for different
values of the ULDM particle mass $m$. The constraints we derive exclude the
solitons predicted by a naive extrapolation of the soliton-halo relation, found
in DM-only numerical simulations, for $2\times10^{-20}~{\rm eV}\lesssim
m\lesssim8\times10^{-19}~{\rm eV}$ (from Sgr A*) and
$m\lesssim4\times10^{-22}~{\rm eV}$ (from M87*). However, we present
theoretical arguments suggesting that an extrapolation of the soliton-halo
relation may not be adequate: in some regions of the parameter space, the
dynamical effect of the SMBH could cause this extrapolation to over-predict the
soliton mass by orders of magnitude. |
Resurrecting power law inflation in the light of Planck results: It is well known that a canonical scalar field with an exponential potential
can drive power law inflation (PLI). However, the tensor-to-scalar ratio in
such models turns out to be larger than the stringent limit set by recent
Planck results. We propose a new model of power law inflation for which the
scalar spectra index, the tensor-to-scalar ratio and the non-gaussianity
parameter $f_{_{\mathbf{NL}}}^{\mathrm{equil}}$ are in excellent agreement with
Planck results. Inflation, in this model, is driven by a non-canonical scalar
field with an inverse power law potential. The Lagrangian for our model is
structurally similar to that of a canonical scalar field and has a power law
form for the kinetic term. A simple extension of our model resolves the
graceful exit problem which usually afflicts models of power law inflation. | Observational tests for Λ(t)CDM cosmology: We investigate the observational viability of a class of cosmological models
in which the vacuum energy density decays linearly with the Hubble parameter,
resulting in a production of cold dark matter particles at late times.
Similarly to the flat \Lambda CDM case, there is only one free parameter to be
adjusted by the data in this class of \Lambda(t)CDM scenarios, namely, the
matter density parameter. To perform our analysis we use three of the most
recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the
current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and
the position of the first acoustic peak of the CMB power spectrum. We show that
in terms of $\chi^2$ statistics both models provide good fits to the data and
similar results. A quantitative analysis discussing the differences in
parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2)
is studied using the current SDSS and Constitution SNe Ia compilations. A
matter power spectrum analysis using the 2dFGRS is also performed, providing a
very good concordance with the constraints from the SDSS and Constitution
MLCS2k2 data. |
Strong lensing in UNIONS: Toward a pipeline from discovery to modeling: We present a search for galaxy-scale strong gravitational lenses in the
initial 2 500 square degrees of the Canada-France Imaging Survey (CFIS). We
designed a convolutional neural network (CNN) committee that we applied to a
selection of 2 344 002 exquisite-seeing $r$-band images of color-selected
luminous red galaxies (LRGs). Our classification uses a realistic training set
where the lensing galaxies and the lensed sources are both taken from real
data, namely the CFIS $r$-band images themselves and the Hubble Space Telescope
(HST). A total of 9 460 candidates obtain a score above 0.5 with the CNN
committee. After a visual inspection of the candidates, we find a total of 133
lens candidates, of which 104 are completely new. The set of false positives
mainly contains ring, spiral, and merger galaxies, and to a lesser extent
galaxies with nearby companions. We classify 32 of the lens candidates as
secure lenses and 101 as maybe lenses. For the 32 highest quality lenses, we
also fit a singular isothermal ellipsoid mass profile with external shear along
with an elliptical Sersic profile for the lens and source light. This automated
modeling step provides distributions of properties for both sources and lenses
that have Einstein radii in the range $0.5\arcsec<\theta_E<2.5\arcsec$.
Finally, we introduce a new lens and/or source single-band deblending algorithm
based on auto-encoder representation of our candidates. This is the first time
an end-to-end lens-finding and modeling pipeline is assembled together, in view
of future lens searches in a single band, as will be possible with Euclid. | Galactic chemical evolution in hierarchical formation models - II. The
Intracluster Medium: We use the cosmological semi-analytic model (SAM) for galaxy formation
presented in Paper I to study the metallicities and abundance ratios of the
intracluster medium (ICM) within the hierarchical structure formation paradigm.
By requiring a slightly flat IMF (x=1.15) and a two-population
delay-time-distribution (DTD) for SN Ia explosions we found previously that
this model is able to reproduce the abundance ratios and supernova rates of
early-type galaxies in the local Universe. Predictions for elemental abundances
in the ICM pose a further test of the model. We find that with the fiducial
model from Paper I the overall metal content of the ICM is too low, although
the abundance ratios are in good agreement with the data. However, we find that
allowing a fraction of the metal-enriched material ejected by stars to be
deposited directly into the hot ICM, instead of being deposited into the cold
ISM, appears to be a plausible and physically-motivated solution. |
Extra-tensor-induced origin for the PTA signal: No primordial black hole
production: Recently, pulsar timing array (PTA) collaborations announced evidence for an
isotropic stochastic gravitational wave (GW) background. The origin of the PTA
signal can be astrophysical or cosmological. In the latter case, the so-called
secondary scalar-induced GW scenario is one of the viable explanations, but it
has a potentially serious issue of the overproduction of primordial black holes
(PBHs) due to the enhanced curvature perturbation. In this letter, we present a
new interpretation of the PTA signal. Namely, it is originated from an extra
spectator tensor field that exists on top of the metric tensor perturbation. As
the energy density of the extra tensor field is always subdominant, it cannot
lead to the formation of PBHs. Thus our primordial-tensor-induced scenario is
free from the PBH overproduction issue. | A Large Mass Hierarchy from a Small Non-minimal Coupling: We propose a simple but novel cosmological scenario where both the Planck
mass and the dark energy scale emerge from the same super-Hubble quantum
fluctuations of a non-minimally coupled ultra-light scalar field during
primordial inflation. The current cosmic and solar-system observations
constrain the non-minimal coupling to be small. |
Shape, shear & flexion: An analytic flexion formalism for realistic mass
profiles: Flexion is a non-linear gravitational lensing effect that arises from
gradients in the convergence and shear across an image. We derive a formalism
that describes non-linear gravitational lensing by a circularly symmetric lens
in the thin-lens approximation. This provides us with relatively simple
expressions for first- and second-flexion in terms of only the surface density
and projected mass distribution of the lens. We give details of exact lens
models, in particular providing flexion calculations for a Sersic-law profile,
which has become increasingly popular over recent years. We further provide a
single resource for the analytic forms of convergence, shear, first- and
second-flexion for the following mass distributions: a point mass, singular
isothermal sphere (SIS); Navarro-Frenk-White (NFW) profile; Sersic-law profile.
We quantitatively compare these mass distributions and show that the
convergence and first-flexion are better indicators of the Sersic shape
parameter, while for the concentration of NFW profiles the shear and
second-flexion terms are preferred. | Metallicity of the polar disk in NGC4650A: constraints for cold
accretion scenario: We used high resolution spectra in the optical and near-infrared wavelength
range to study the abundance ratios and metallicities of the HII regions
associated with the polar disk in NGC4650A, in order to put constraints on the
formation of the polar disk through cold gas accretion along a filament; this
might be the most realistic way by which galaxies get their gas. We have
compared the measured metallicities for the polar structure in NGC4650A with
those of different morphological types and we have found that they are similar
to those of late-type galaxies: such results is consistent with a polar disk
formed by accretion from cosmic web filaments of external cold gas. |
Tests and problems of the standard model in Cosmology: The main foundations of the standard $\Lambda $CDM model of cosmology are
that: 1) The redshifts of the galaxies are due to the expansion of the Universe
plus peculiar motions; 2) The cosmic microwave background radiation and its
anisotropies derive from the high energy primordial Universe when matter and
radiation became decoupled; 3) The abundance pattern of the light elements is
explained in terms of primordial nucleosynthesis; and 4) The formation and
evolution of galaxies can be explained only in terms of gravitation within a
inflation+dark matter+dark energy scenario. Numerous tests have been carried
out on these ideas and, although the standard model works pretty well in
fitting many observations, there are also many data that present apparent
caveats to be understood with it. In this paper, I offer a review of these
tests and problems, as well as some examples of alternative models. | Last scattering, relic gravitons and the circular polarization of the
CMB: The tensor contribution to the $V$-mode polarization induced by a magnetized
plasma at last scattering vanishes exactly. Conversely a polarized background
of relic gravitons cannot generate a $V$-mode polarization. The reported
results suggest that, in the magnetized $\Lambda$CDM paradigm, the dominant
source of circular dichroism stems from the large-scale fluctuations of the
spatial curvature. |
Probing primordial non-Gaussianity via iSW measurements with SKA
continuum surveys: The Planck CMB experiment has delivered the best constraints so far on
primordial non-Gaussianity, ruling out early-Universe models of inflation that
generate large non-Gaussianity. Although small improvements in the CMB
constraints are expected, the next frontier of precision will come from future
large-scale surveys of the galaxy distribution. The advantage of such surveys
is that they can measure many more modes than the CMB -- in particular,
forthcoming radio surveys with the SKA will cover huge volumes. Radio continuum
surveys deliver the largest volumes, but with the disadvantage of no redshift
information. In order to mitigate this, we use two additional observables.
First, the integrated Sachs-Wolfe effect -- the cross-correlation of the radio
number counts with the CMB temperature anisotropies -- helps to reduce
systematics on the large scales that are sensitive to non-Gaussianity. Second,
optical data allows for cross-identification in order to gain some redshift
information. We show that, while the single redshift bin case can provide a
sigma(fNL) ~ 20, and is therefore not competitive with current and future
constraints on non-Gaussianity, a tomographic analysis could improve the
constraints by an order of magnitude, even with only two redshift bins. A huge
improvement is provided by the addition of high-redshift sources, so having
cross-ID for high-z galaxies and an even higher-z radio tail is key to enabling
very precise measurements of fNL. Our results show that SKA continuum surveys
could provide constraints competitive with CMB and forthcoming optical surveys,
potentially allowing a measurement of sigma(fNL) ~ 1 to be made. Moreover,
these measurements would act as a useful check of results obtained with other
probes at other redshift ranges with other methods. | The bispectrum of polarized galactic foregrounds: Understanding the properties of the galactic emission at millimetre
wavelengths is important for studies of the cosmic microwave background (CMB).
In this work we explore the bispectrum, the harmonic equivalent of the three
point function, from galactic dust and synchrotron emission. We investigate
these effects across a broad range of frequencies using the synchrotron
dominated S-band Polarization All Sky Survey (SPASS) maps at 2.3 GHz, the
Planck satellite maps (30-857 GHz) and dust dominated Infrared Astronomical
Satellite (IRAS) maps at 3 THz. We measure bispectra of total intensity fields,
T, as well as the gradient, E, and curl modes, B, of the polarization field. We
find that the synchrotron and galactic dust have strong temperature bispectra
with significant contributions in the squeezed limit, which probes the
correlations between two small scale modes with a large scale mode.
Additionally, we find that the dust also has strong polarised bispectra that
also peak in the squeezed configuration. We explore parity odd bispectra, such
as BTT bispectra, and find strong parity odd bispectra for the galactic dust
notably in BTT, BTE and BEE configurations. After masking bright sources, we
find no evidence for polarised synchrotron bispectra and no evidence for cross
bispectra between the dust and synchrotron emission. The strong foreground
bispectra discussed here need to be carefully controlled to avoid biasing
measurements of primordial non-Gaussianity. Finally we use these bispectra
tools to test for residual foregrounds in the component separated Planck maps
and find no evidence of residual foregrounds. These tools will be useful for
characterizing residual foregrounds in component separated maps, particularly
for experiments with less frequency coverage than the Planck satellite. |
f(R) gravity constraints from gravitational waves: The recent LIGO observation sparked interest in the field of gravity wave
signals. Besides the gravity wave observation the LIGO collaboration used the
inspiraling black hole pair to constrain the graviton mass. Unlike general
relativity, $f(R)$ theories have a characteristic non-zero mass graviton. We
apply the constraint on the graviton mass to viable $f(R)$ models to find the
effects on model parameters. We find it possible to constrain the parameter
space with the gravity wave based observations. We make a case study for the
popular Hu-Sawicki model and find a parameter bracket. The result generalizes
to other $f(R)$ theories and can be used to contain the parameter space. | Beta-Skeleton Analysis of the Cosmic Web: The $\beta$-skeleton is a mathematical method to construct graphs from a set
of points that has been widely applied in the areas of image analysis, machine
learning, visual perception, and pattern recognition. In this work, we apply
the $\beta$-skeleton to study the cosmic web. We use this tool on observed and
simulated data to identify the filamentary structures and characterize the
statistical properties of the skeleton. In particular, we compare the
$\beta$-skeletons built from SDSS-III galaxies to those obtained from MD-PATCHY
mocks, and also to mocks directly built from the Big MultiDark $N$-body
simulation. We find that the $\beta$-skeleton is able to reveal the underlying
structures in observed and simulated samples without any parameter fine-tuning.
A different degree of sparseness can be obtained by adjusting the value of
$\beta$; in addition, the statistical properties of the length and direction of
the skeleton connections show a clear dependence on redshift space distortions
(RSDs), cosmological effects and galaxy bias. We also find that the $N$-body
simulation accurately reproduces the RSD effect in the data, while the
MD-PATCHY mocks appear to underestimate its magnitude. Our proof-of-concept
study shows that the statistical properties of the $\beta$-skeleton can be used
to probe cosmological parameters and galaxy evolution. |
Studies on dark energy evolution: In this work we explore signatures of evolution for the dark energy density
$X(z)=\rho_{de}(z)/\rho_{de}(0)$ using latest observations on SNIa and H(z).
The models consist of parametrizations of the dark energy density and
consequently a reconstruction for the EoS parameter w(z) as a function of
redshift. Both parametrization methods using the SH0Es prior results in a small
deviation from LCDM at 1$\sigma$ for $X(z)$. Extending the analysis up to
2$\sigma$, the evidence for evolution of $X(z)$ dilute in both cases. We have
also studied an interacting dark model where this trend is also found. | Limits on Spacetime Foam: Plausibly spacetime is "foamy" on small distance scales, due to quantum
fluctuations. We elaborate on the proposal to detect spacetime foam by looking
for seeing disks in the images of distant quasars and AGNs. This is a null test
in the sense that the continued presence of unresolved "point" sources at the
milli-arc second level in samples of distant compact sources puts severe
constraints on theories of quantized spacetime foam at the Planckian level. We
discuss the geometry of foamy spacetime, and the appropriate distance measure
for calculating the expected angular broadening. We then deal with recent data
and the constraints they put on spacetime foam models. While time lags from
distant pulsed sources such as GRBs have been posited as a possible test of
spacetime foam models, we demonstrate that the time-lag effect is rather
smaller than has been calculated, due to the equal probability of positive and
negative fluctuations in the speed of light inherent in such models. Thus far,
images of high-redshift quasars from the Hubble Ultra-Deep Field (UDF) provide
the most stringent test of spacetime foam theories. While random walk models
($\alpha = 1/2$) have already been ruled out, the holographic ($\alpha=2/3$)
model remains viable. Here $\alpha \sim 1$ parametrizes the different spacetime
foam models according to which the fluctuation of a distance $l$ is given by
$\sim l^{1 - \alpha} l_P^{\alpha}$ with $l_P$ being the Planck length. Indeed,
we see a slight wavelength-dependent blurring in the UDF images selected for
this study. Using existing data in the {\it Hubble Space Telescope (HST)}
archive we find it is impossible to rule out the $\alpha=2/3$ model, but
exclude all models with $\alpha<0.65$. By comparison, current GRB time lag
observations only exclude models with $\alpha<0.3$. |
Comparison of results on $N_\mathrm{eff}$ from various Planck
likelihoods: In this paper, we study the estimation of the effective number of
relativistic species from a combination of CMB and BAO data. We vary different
ingredients of the analysis: the Planck high-$\ell$ likelihoods, the Boltzmann
solvers, and the statistical approaches. The variation of the inferred values
gives an indication of an additional systematic uncertainty, which is of the
same order of magnitude as the error derived from each individual likelihood.
We show that this systematic is essentially associated to the assumptions made
in the high-$\ell$ likelihoods implementations, in particular for the
foreground residuals modellings. We also compare a subset of likelihoods using
only the TE power spectra, expected to be less sensitive to foreground
residuals. | The SINS/zC-SINF Survey of z~2 Galaxy Kinematics: The Nature of
Dispersion Dominated Galaxies: We analyze the spectra, spatial distributions and kinematics of Ha, [NII] and
[SII] emission in a sample of 42, z~2.2 UV/optically selected star forming
galaxies (SFGs) from the SINS & zC-SINF surveys, 35 of which were observed in
the adaptive optics mode of SINFONI. This is supplemented by kinematic data
from 48 z~1-2.5 galaxies from the literature. We find that the kinematic
classification of the high-z SFGs as `dispersion dominated' or `rotation
dominated' correlates most strongly with their intrinsic sizes. Smaller
galaxies are more likely `dispersion-dominated' for two main reasons: 1) The
rotation velocity scales linearly with galaxy size but intrinsic velocity
dispersion does not depend on size, and as such, their ratio is systematically
lower for smaller galaxies, and 2) Beam smearing strongly decreases large-scale
velocity gradients and increases observed dispersion much more for galaxies
with sizes at or below the resolution. Dispersion dominated SFGs may thus have
intrinsic properties similar to `rotation dominated' SFGs, but are primarily
more compact, lower mass, less metal enriched and may have higher gas
fractions, plausibly because they represent an earlier evolutionary state. |
Extending the Eigenvector 1 Space to the Optical Variability of Quasars: We introduce a new physical parameter, the optical variability amplitude, to
the well-established Eigenvector 1 space of quasars and test a sample of
long-term B-band light curves of 42 PG quasars monitored by Giveon et al.
(1999). We find that the optical variability amplitude strongly correlates with
the intensity ratio of Fe II to H$\beta$, H$\beta$ width and peak luminosity at
5007$\rm{\AA}$. We briefly discuss the physical meaning of our findings and
suggest that the Eddington ratio may be a key factor in determining a quasar's
variability. | CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey
presentation: We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey,
which has been designed to provide a first step in this direction.We summarize
the survey goals and design, including sample selection and observational
strategy.We also showcase the data taken during the first observing runs
(June/July 2010) and outline the reduction pipeline, quality control schemes
and general characteristics of the reduced data. This survey is obtaining
spatially resolved spectroscopic information of a diameter selected sample of
$\sim600$ galaxies in the Local Universe (0.005< z <0.03). CALIFA has been
designed to allow the building of two-dimensional maps of the following
quantities: (a) stellar populations: ages and metallicities; (b) ionized gas:
distribution, excitation mechanism and chemical abundances; and (c) kinematic
properties: both from stellar and ionized gas components. CALIFA uses the PPAK
Integral Field Unit (IFU), with a hexagonal field-of-view of
$\sim1.3\sq\arcmin'$, with a 100% covering factor by adopting a three-pointing
dithering scheme. The optical wavelength range is covered from 3700 to 7000
{\AA}, using two overlapping setups (V500 and V1200), with different
resolutions: R\sim850 and R\sim1650, respectively. CALIFA is a legacy survey,
intended for the community. The reduced data will be released, once the quality
has been guaranteed. The analyzed data fulfill the expectations of the original
observing proposal, on the basis of a set of quality checks and exploratory
analysis.
We conclude from this first look at the data that CALIFA will be an important
resource for archaeological studies of galaxies in the Local Universe. |
Searching for dilaton fields in the Ly$α$ forest: Dilatons (and moduli) couple to the masses and coupling constants of ordinary
matter, and these quantities are fixed by the local value of the dilaton field.
If, in addition, the dilaton with mass $m_\phi$ contributes to the cosmic dark
matter density, then such quantities oscillate in time at the dilaton Compton
frequency. We show how these oscillations lead to broadening and shifting of
the Voigt profile of the Ly$\alpha$ forest, in a manner that is correlated with
the local dark matter density. We further show how tomographic methods allow
the effect to be reconstructed by observing the Ly$\alpha$ forest spectrum of
distant quasars. We then simulate a large number of quasar lines of sight using
the lognormal density field, and forecast the ability of future astronomical
surveys to measure this effect. We find that in the ultra low mass range
$10^{-32}\text{ eV}\leq m_\phi\leq 10^{-28}\text{ eV}$ upcoming observations
can improve over existing limits to the dilaton electron mass and fine
structure constant couplings set by fifth force searches by up to five orders
of magnitude. Our projected limits apply assuming that the ultralight dilaton
makes up a few percent of the dark matter density, consistent with upper limits
set by the cosmic microwave background anisotropies. | A weak lensing detection of a deviation from General Relativity on
cosmic scales: We consider evidence for deviations from General Relativity (GR) in the
growth of large scale structure, using two parameters, $\gamma$ and $\eta$, to
quantify the modification. We consider the Integrated Sachs-Wolfe effect (ISW)
in the WMAP Cosmic Microwave Background data, the cross-correlation between the
ISW and galaxy distributions from 2MASS and SDSS surveys, and the weak lensing
shear field from the Hubble Space Telescope's COSMOS survey along with
measurements of the cosmic expansion history. We find current data, driven by
the COSMOS weak lensing measurements, disfavors GR on cosmic scales, preferring
$\eta<1$ at $1<z<2$ at the 98% significance level. |
Results on photon-mediated dark matter-nucleus interactions from the
PICO-60 C$_{3}$F$_{8}$ bubble chamber: Many compelling models predict dark matter coupling to the electromagnetic
current through higher multipole interactions, while remaining electrically
neutral. Different multipole couplings have been studied, among them anapole
moment, electric and magnetic dipole moments, and millicharge. This study sets
limits on the couplings for these photon-mediated interactions using
non-relativistic contact operators in an effective field theory framework.
Using data from the PICO-60 bubble chamber leading limits for dark matter
masses between 2.7 GeV/c$^2$ and 24 GeV/c$^2$ are reported for the coupling of
these photon-mediated dark matter-nucleus interactions. The detector was filled
with 52 kg of C$_3$F$_8$ operating at thermodynamic thresholds of 2.45 keV and
3.29 keV, reaching exposures of 1404 kg-day and 1167 kg-day, respectively. | The impact of point source subtraction residuals on 21 cm Epoch of
Reionization estimation: Precise subtraction of foreground sources is crucial for detecting and
estimating 21cm HI signals from the Epoch of Reionization (EoR). We quantify
how imperfect point source subtraction due to limitations of the measurement
dataset yields structured residual signal in the dataset. We use the Cramer-Rao
lower bound, as a metric for quantifying the precision with which a parameter
may be measured, to estimate the residual signal in a visibility dataset due to
imperfect point source subtraction. We then propagate these residuals into two
metrics of interest for 21cm EoR experiments - the angular and two-dimensional
power spectrum - using a combination of full analytic covariant derivation,
analytic variant derivation, and covariant Monte Carlo simulations. This
methodology differs from previous work in two ways: (1) it uses information
theory to set the point source position error, rather than assuming a global
root-mean-square error, and (2) it describes a method for propagating the
errors analytically, thereby obtaining the full correlation structure of the
power spectra. The methods are applied to two upcoming low-frequency
instruments: the Murchison Widefield Array and the Precision Array for Probing
the Epoch of Reionization. In addition to the actual antenna configurations, we
apply the methods to minimally-redundant and maximally-redundant
configurations. We find that for peeling sources above 1 Jy, the amplitude of
the residual signal, and its variance, will be smaller than the contribution
from thermal noise for the observing parameters proposed for upcoming EoR
experiments, and that optimal subtraction of bright point sources will not be a
limiting factor for EoR parameter estimation. We then use the formalism to
provide an ab initio analytic derivation motivating the 'wedge' feature in the
two-dimensional power spectrum, complementing previous discussion in the
literature. |
Discovery of the most metal-poor damped Lyman-alpha system: We report the discovery and analysis of the most metal-poor damped
Lyman-alpha (DLA) system currently known, based on observations made with the
Keck HIRES spectrograph. The metal paucity of this system has only permitted
the determination of three element abundances: [C/H] = -3.43 +/- 0.06, [O/H] =
-3.05 +/- 0.05, and [Si/H] = -3.21 +/- 0.05, as well as an upper limit on the
abundance of iron: [Fe/H] < -2.81. This DLA is among the most carbon-poor
environment currently known with detectable metals. By comparing the abundance
pattern of this DLA to detailed models of metal-free nucleosynthesis, we find
that the chemistry of the gas is consistent with the yields of a 20.5 M_sun
metal-free star that ended its life as a core-collapse supernova; the
abundances we measure are inconsistent with the yields of pair-instability
supernovae. Such a tight constraint on the mass of the progenitor Population
III star is afforded by the well-determined C/O ratio, which we show depends
almost monotonically on the progenitor mass when the kinetic energy of the
supernova explosion is E_exp > 1.5x10^51 erg. We find that the DLA presented
here has just crossed the critical 'transition discriminant' threshold,
rendering the DLA gas now suitable for low mass star formation. We also discuss
the chemistry of this system in the context of recent models that suggest some
of the most metal-poor DLAs are the precursors of the 'first galaxies', and are
the antecedents of the ultra-faint dwarf galaxies. | Optical and near-infrared velocity dispersions of early-type galaxies: We have carried out a systematic, homogeneous comparison of optical and
near-infrared dispersions. Our magnitude-limited sample of early-type galaxies
in the Fornax cluster comprises 11 elliptical and 11 lenticular galaxies more
luminous than MB = -17. We were able to determine the central dispersions based
on the near-infrared CO absorption band head for 19 of those galaxies. The
velocity dispersions range from less than 70 km/s to over 400 km/s. We compare
our near-infrared velocity dispersions to the optical dispersions measured by
Kuntschner (2000). Contrary to previous studies, we find a one-to-one
correspondence with a median fractional difference of 6.4%. We examine the
correlation between the relative dust mass and the fractional difference of the
velocity dispersions, but find no significant trend. Our results suggest that
early-type galaxies are largely optically thin, which is consistent with recent
Herschel observations. |
Stabilising the Planck mass shortly after inflation: We consider a model of the early universe which consists of two scalar
fields: the inflaton, and a second field which drives the stabilisation of the
Planck mass (or gravitational constant). We show that the non-minimal coupling
of this second field to the Ricci scalar sources a non-adiabatic pressure
perturbation. By performing a fully numerical calculation we find, in turn,
that this boosts the amplitude of the primordial power spectrum after
inflation. | Self-Interacting Dark Matter Scattering Rates Through Cosmic Time: We estimate the rate of dark matter scattering in collapsed structures
throughout the history of the Universe. If the scattering cross-section is
velocity-independent, then the canonical picture is correct that scatterings
occur mainly at late times. The scattering rate peaks slightly at redshift z~6,
and remains significant today. Half the scatterings occur after z~1, in
structures more massive than 10^12 M_sun. Within a factor of two, these numbers
are robust to changes in the assumed astrophysics, and the scatterings would be
captured in cosmological simulations. However, for particle physics models with
a velocity-dependent cross-section (as for Yukawa potential interactions via a
massive mediator), the scattering rate peaks before z~20, in objects with mass
less than 10^4 M_sun. These precise values are sensitive to the
redshift-dependent mass-concentration relation and the small-scale cutoff in
the matter power spectrum. In extreme cases, the qualitative effect of early
interactions may be reminiscent of warm dark matter and strongly affect the
subsequent growth of structure. However, these scatterings are being missed in
existing cosmological simulations with limited mass resolution. |
The Westerbork SINGS survey III. Global magnetic field topology: A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS)
galaxies was recently observed with the Westerbork Synthesis Radio Telescope
(WSRT) at 1300-1760 MHz. In Paper II of this series, we described sensitive
observations of the linearly polarized radio continuum emission in this
WSRT-SINGS galaxy sample. Here we explore the systematic patterns of azimuthal
modulation of both the Faraday depth and the polarized intensity and their
variation with galaxy inclination. A self-consistent and fully general model
for both the locations of net polarized emissivity at 1-2 GHz frequencies and
the global magnetic field topology of nearby galaxies emerges. Net polarized
emissivity is concentrated into two zones located above and below the galaxy
mid-plane, with the back-side zone suffering substantial depolarization (by a
factor of 4-5) relative to the front-side zone in its propagation through the
turbulent mid-plane. The field topology, which characterizes the thick-disk
emission zone is in all cases an axisymmetric spiral with a quadrupole
dependence on height above the mid-plane. The front-side emission is affected
by only mild dispersion (10's of rad/m2) from the thermal plasma in the galaxy
halo, while the back-side emission is affected by additional strong dispersion
(100's of rad/m2) from an axisymmetric spiral field in the galaxy mid-plane.
The field topology in the upper halo of galaxies is a mix of two distinct
types: a simple extension of the axisymmetric spiral quadrupole field of the
thick disk and a radially directed dipole field. The dipole component might be
a manifestation of (1) a circumnuclear, bipolar outflow, (2) an in situ
generated dipole field, or (3) evidence of a non-stationary global halo. | A non-linear approximation for perturbations in ΛCDM: We describe inhomogeneities in a {\Lambda}CDM universe with a gradient series
expansion and show that it describes the gravitational evolution far into the
non-linear regime and beyond the capacity of standard perturbation theory at
any order. We compare the gradient expansion with exact inhomogeneous
{\Lambda}LTB solutions (Lema\^itre-Tolman-Bondi metric with the inclusion of a
cosmological constant) describing growing structure in a {\Lambda}CDM universe
and find that the expansion approximates the exact solution well, following the
collapse of an over-density all the way into a singularity. |
The Primordial Black Hole Abundance: The Broader, the Better: We show that the abundance of primordial black holes, if formed through the
collapse of large fluctuations generated during inflation and unless the power
spectrum of the curvature perturbation is very peaked, is always dominated by
the broadest profile of the compaction function, even though statistically it
is not the most frequent. The corresponding threshold is therefore 2/5. This
result exacerbates the tension when combining the primordial black hole
abundance with the signal seen by pulsar timing arrays and originated from
gravitational waves induced by the same large primordial perturbations. | A Deep 1.2 mm Map of the Lockman Hole North Field: We present deep 1.2 mm continuum mapping of a 566 arcmin^2 area within the
Lockman Hole North field, previously a target of the Spitzer Wide-area Infrared
Extragalactic (SWIRE) survey and extremely deep 20 cm mapping with the Very
Large Array, which we have obtained using the Max-Planck millimeter bolometer
(MAMBO) array on the IRAM 30 m telescope. After filtering, our full map has an
RMS sensitivity ranging from 0.45 to 1.5 mJy/beam, with an average of 0.75
mJy/beam. Using the pixel flux distribution in a map made from our best data,
we determine the shape, normalization, and approximate flux density cutoff for
1.2 mm number counts well below our nominal sensitivity and confusion limits.
After validating our full dataset through comparison with this map, we
successfully detect 41 1.2 mm sources with S/N > 4.0 and S(1.2 mm)\simeq 2-5
mJy. We use the most significant of these detections to directly determine the
integral number counts down to 1.8 mJy, which are consistent with the results
of the pixel flux distribution analysis. 93% of our 41 individual detections
have 20 cm counterparts, 49% have Spitzer/MIPS 24 micron counterparts, and one
may have a significant Chandra X-ray counterpart. We resolve \simeq 3% of the
cosmic infrared background (CIB) at 1.2 mm into significant detections, and
directly estimate a 0.05 mJy faint-end cutoff for the counts that is consistent
with the full intensity of the 1.2 mm CIB. The median redshift of our 17
detections with spectroscopic or robust photometric redshifts is z(median)=2.3,
and rises to z(median)=2.9 when we include redshifts estimated from the
radio/far-infrared spectral index. By using a nearest neighbor and angular
correlation function analysis, we find evidence that our S/N>4.0 detections are
clustered at the 95% confidence level. |
The COpernicus COmplexio: Statistical Properties of Warm Dark Matter
Haloes: The recent detection of a 3.5 keV X-ray line from the centres of galaxies and
clusters by Bulbul et al. (2014a) and Boyarsky et al. (2014a) has been
interpreted as emission from the decay of 7 keV sterile neutrinos which could
make up the (warm) dark matter (WDM). As part of the COpernicus COmplexio
(COCO) programme, we investigate the properties of dark matter haloes formed in
a high-resolution cosmological $N$-body simulation from initial conditions
similar to those expected in a universe in which the dark matter consists of 7
keV sterile neutrinos. This simulation and its cold dark matter (CDM)
counterpart have $\sim13.4$bn particles, each of mass $\sim 10^5\, h^{-1}
M_\odot$, providing detailed information about halo structure and evolution
down to dwarf galaxy mass scales. Non-linear structure formation on small
scales ($M_{200}\, \leq\, 2 \times 10^9\,h^{-1}\,M_\odot$) begins slightly
later in COCO-Warm than in COCO-Cold. The halo mass function at the present day
in the WDM model begins to drop below its CDM counterpart at a mass $\sim 2
\times 10^{9}\,h^{-1}\,M_\odot$ and declines very rapidly towards lower masses
so that there are five times fewer haloes of mass $M_{200}=
10^{8}\,h^{-1}\,M_\odot$ in COCO-Warm than in COCO-Cold. Halo concentrations on
dwarf galaxy scales are correspondingly smaller in COCO-Warm, and we provide a
simple functional form that describes its evolution with redshift. The shapes
of haloes are similar in the two cases, but the smallest haloes in COCO-Warm
rotate slightly more slowly than their CDM counterparts. | The trouble with $H_0$: We perform a comprehensive cosmological study of the $H_0$ tension between
the direct local measurement and the model-dependent value inferred from the
Cosmic Microwave Background. With the recent measurement of $H_0$ this tension
has raised to more than $3\sigma$. We consider changes in the early time
physics without modifying the late time cosmology. We also reconstruct the late
time expansion history in a model independent way with minimal assumptions
using distances measures from Baryon Acoustic Oscillations and Type Ia
Supernovae, finding that at $z<0.6$ the recovered shape of the expansion
history is less than 5 % different than that of a standard LCDM model. These
probes also provide a model insensitive constraint on the low-redshift standard
ruler, measuring directly the combination $r_s h$ where $H_0=h \times 100$
km/s/Mpc and $r_s$ is the sound horizon at radiation drag (the standard ruler),
traditionally constrained by CMB observations. Thus $r_s$ and $H_0$ provide
absolute scales for distance measurements (anchors) at opposite ends of the
observable Universe. We calibrate the cosmic distance ladder and obtain a
model-independent determination of the standard ruler for acoustic scale,
$r_s$. The tension in $H_0$ reflects a mismatch between our determination of
$r_s$ and its standard, CMB-inferred value. Without including high-l Planck CMB
polarization data (i.e., only considering the "recommended baseline" low-l
polarisation and temperature and the high l temperature data), a modification
of the early-time physics to include a component of dark radiation with an
effective number of species around 0.4 would reconcile the CMB-inferred
constraints, and the local $H_0$ and standard ruler determinations. The
inclusion of the "preliminary" high-l Planck CMB polarisation data disfavours
this solution. |
A Constrained NILC method for CMB B mode observations: The Internal Linear Combination (ILC) method is commonly employed to extract
the cosmic microwave background (CMB) signal from multi-frequency observation
maps. However, the performance of the ILC method tends to degrade when the
signal-to-noise ratio (SNR) is relatively low, especially when measuring the
primordial $B$-modes for detecting the primordial gravitational waves. To
address this issue, an enhanced version of the ILC method on the $B$ map,
called constrained ILC, is suggested in the literature. This method is designed
to be more suitable for situations with low signal-to-noise ratio (SNR) by
incorporating additional prior foreground information. In our study, we have
made modifications to the constraint Needlet ILC method and have successfully
enhanced its performance. We illustrate our methods using mock data generated
from the combination of WMAP, Planck and a ground-based experiment in the
northern hemisphere, and the chosen noise level for the ground-based experiment
are very conservative which can be easily achieved in the very near future. The
results show that the level of foreground residual can be well controlled. In
comparison to the standard NILC method, which introduces a bias to the
tensor-to-scalar ratio ($r$) of approximately $0.05$, the constrained NILC
method exhibits a significantly reduced bias of only around $5\times10^{-3}$
towards $r$ which is much smaller than the statistical error. | Non-gaussianity from the trispectrum and vector field perturbations: We use the \delta N formalism to study the trispectrum T_\zeta of the
primordial curvature perturbation \zeta when the latter is generated by vector
field perturbations, considering the tree-level and one-loop contributions. The
order of magnitude of the level of non-gaussianity in the trispectrum,
\tau_{NL}, is calculated in this scenario and related to the order of magnitude
of the level of non-gaussianity in the bispectrum, f_{NL}, and the level of
statistical anisotropy in the power spectrum, g_\zeta. Such consistency
relations will put under test this scenario against future observations.
Comparison with the expected observational bound on \tau_{NL} from WMAP, for
generic inflationary models, is done. |
The Early-Time Evolution of the Cosmological Perturbations in f(R)
Gravity: We investigate the evolution of the linear cosmological perturbations in f(R)
gravity, an alternative to dark energy for explaining the late-time cosmic
acceleration. We numerically calculate the early-time evolution with an
approximation we contrive to solve a problem that commonly appears when one
solves the full evolution equations. With the approximate evolution equations
we can fairly assess the effect of the gravity modification on the early-time
evolution, thereby examining the validity of the general-relativity (GR)
approximation that is widely used for the early universe. In particular, we
compare the CMB photon density perturbation and the matter density perturbation
obtained respectively by our approximation and the conventional GR
approximation. We find that the effect of the gravity modification at early
times in f(R) gravity may not be negligible. We conclude that to be
self-consistent, in the f(R) theory one should employ the approximation
presented in this paper instead of that of GR in the treatment of the
early-time evolution. | Formaldehyde Densitometry of Starburst Galaxies: Density-Independent
Global Star Formation: Accurate techniques which allow for the derivation of the spatial density in
star formation regions are rare. A technique which has found application for
the derivation of spatial densities in Galactic star formation regions utilizes
the density-sensitive properties of the K-doublet transitions of formaldehyde
(H2CO). In this paper, we present an extension of our survey of the
formaldehyde 1(10)-1(11) (lambda = 6.2 cm) and 2(11)-2(12) (lambda = 2.1 cm)
K-doublet transitions of H2CO in a sample of 56 starburst systems (Mangum etal.
2008). We have extended the number of galaxies in which both transitions have
been detected from 5 to 13. We have improved our spatial density measurements
by incorporating kinetic temperatures based upon NH3 measurements of 11 of the
galaxies with a total of 14 velocity components in our sample (Mangum etal.
2013). Our spatial density measurements lie in a relatively narrow range of
from 10^(4.5) to 10^(5.5) cm^(-3). This implies that the Schmidt-Kennicutt
relation between L_(IR) and M_(dense): (1) Is an indication of the dense gas
mass reservoir available to form stars, and (2) Is not directly dependent upon
a higher average density driving the star formation process in the most
luminous starburst galaxies. We have also used our H2CO measurements to derive
two separate measures of the dense gas mass which are generally smaller, in
many cases by a factor of 10^2-10^3, than those derived using HCN. This
disparity suggests that H2CO traces a denser, more compact, component of the
giant molecular clouds in our starburst galaxy sample.
We also report measurements of the rotationally-excited lambda = 6.3 cm
2P_(1/2) J=1/2 state of OH and the H111alpha radio recombination line taken
concurrently with our H2CO 1(10)-1(11) measurements. |
Probing the inflationary background of gravitational waves from large to
small scales: The detection of Primordial Gravitational Waves (PGWs) is one of the most
important goals of modern cosmology since PGWs can both provide substantial
evidence for primordial inflation and shed light on its physical nature. Small
scale experiments on gravitational waves such as LIGO/VIRGO and, in future,
LISA and Einstein Telescope (ET), being sensitive to the stochastic background
of gravitational waves, can be used together with the CMB data to constrain the
inflationary parameters. In performing these analyses the primordial tensor
spectrum is usually parametrized with a power law that includes only the
amplitude and a scale independent tilt. In this paper, we investigate the
robustness of assuming the tensor tilt as scale independent. We show that due
to the huge difference in the scales probed by CMB and GWs data, even a small
scale dependence can remarkably affect the shape of the primordial spectrum
possibly breaking the power-law assumption. When the non-linear corrections are
considered the final constraints can be significantly changed. We also study
the scale dependence in two different physical models of inflation providing an
example of negligible scale dependence and an example of non-negligible scale
dependence. | Estimating the redshift error in supernova data analysis: Recent works have shown that small shifts in redshift -- gravitational
redshift or systematic errors -- could potentially cause a significant bias in
the estimation of cosmological parameters. I aim to verify whether a
theoretical correction on redshift is sufficient to ease the tension between
the estimates of cosmological parameters from SNe 1a dataset and Planck 2015
results. A free parameter for redshift shift($\Delta z$) is implemented in the
Maximum Likelihood Estimator. Redshift error was estimated from the Joint
Light-curve Analysis(JLA) dataset and results from the Planck 2015 survey. The
estimation from JLA dataset alone gives a best fit value of $\Omega_m = 0.272$,
$\Omega_{\Lambda} = 0.390$, and $\Delta z = 3.77 \times 10^{-4}$. The best fit
values of both $\Omega_m$ and $\Omega_{\Lambda}$ disagrees heavily with results
from other observations. Information criteria and observed density contrasts
suggest that the current data from SNe 1a is not accurate enough to give a
proper estimate of $\Delta z$. A joint analysis with Planck results seems to
give a more plausible value of the redshift error, and can potentially be used
as a probe to measure our local gravitational environment. |
Dipole of the Epoch of Reionization 21-cm signal: The motion of the solar system with respect to the cosmic rest frame
modulates the monopole of the Epoch of Reionization 21-cm signal into a dipole.
This dipole has a characteristic frequency dependence that is dominated by the
frequency derivative of the monopole signal. We argue that although the signal
is weaker by a factor of $\sim100$, there are significant benefits in measuring
the dipole. Most importantly, the direction of the cosmic velocity vector is
known exquisitely well from the cosmic microwave background and is not aligned
with the galaxy velocity vector that modulates the foreground monopole.
Moreover, an experiment designed to measure a dipole can rely on differencing
patches of the sky rather than making an absolute signal measurement, which
helps with some systematic effects. | The Epoch of Reionization: The Universe's dark ages end with the formation of the first generation of
galaxies. These objects start emitting ultraviolet radiation that carves out
ionized regions around them. After a sufficient number of ionizing sources have
formed, the ionized fraction of the gas in the Universe rapidly increases until
hydrogen becomes fully ionized. This period, during which the cosmic gas went
from neutral to ionized, is known as the Universe's Epoch of Reionization . The
Epoch of Reionization is related to many fundamental questions in cosmology,
such as properties of the first galaxies, physics of (mini-)quasars, formation
of very metal-poor stars and a slew of other important research topics in
astrophysics. Hence uncovering it will have far reaching implications on the
study of structure formation in the early Universe. This chapter reviews the
current observational evidence for the occurrence of this epoch, its key
theoretical aspects and main characteristics, and finally the various
observational probes that promise to uncover it. A special emphasis is put on
the redshifted 21 cm probe, the various experiments that are currently being
either built or designed, and what we can learn from them about the Epoch of
Reionization. |
Clustering of Extragalactic Sources from 151 MHz to 232 MHz:
Implications for Cosmological 21-cm Observations: In order to construct accurate point sources simulations at the frequencies
relevant to 21-cm experiments, the angular correlation of radio sources must be
taken into account. This paper presents a measurement of angular two-point
correlation function, w(\theta), at 232 MHz from the MIYUN survey - tentative
measurements of w(\theta) are also performed at 151 MHz. It is found that
double power law with shape w(\theta) = A \theta^{-\gamma} fits the 232 MHz
data well. For the angular lenght of 0.2 degrees < \theta < 0.6 degrees, \gamma
~ -1.12, and this value of slope is independent of the flux-density threshold;
while for angular lenghts much greater than 0.6 degrees, \gamma has a shallower
value of about -0.16. By comparing the results of this paper with previous
measurements of w(\theta), it is discussed how w(\theta) changes with the
change of frequency and completness limit. | Rich structure of non-thermal relativistic CMB spectral distortions from
high energy particle cascades at redshifts $z\lesssim 2\times 10^5$: It is generally assumed that for energy injection before recombination, all
of the injected energy is dissipated as heat in the baryon-photon plasma,
giving rise to the $y$-type, $i$-type, and $\mu$-type distortions in the CMB
spectrum. We show that this assumption is incorrect when the energy is injected
in the form of energetic (i.e. energy much greater than the background CMB
temperature) particles. We evolve the electromagnetic cascades, from the
injection of high energy particles, in the expanding Universe and follow the
non-thermal component of CMB spectral distortions resulting from the
interaction of the electromagnetic shower with the background photons,
electrons, and ions. The electromagnetic shower loses a substantial fraction of
its energy to the CMB spectral distortions before the energy of the particles
in the shower has degraded to low enough energies that they can thermalize with
the background plasma. This spectral distortion is the result of the
interaction of non-thermal energetic electrons in the shower with the CMB and
thus has a shape that is substantially different from the $y$-type or $i$-type
distortions. The shape of the final \emph{non-thermal relativistic}
($ntr$-type) CMB spectral distortion depends upon the initial energy spectrum
of the injected electrons, positrons, and photons and thus has information
about the energy injection mechanism e.g. the decay or annihilation channel of
the decaying or annihilating dark matter particles. The shape of the spectral
distortion is also sensitive to the redshift of energy injection. Our
calculations open up a new window into the energy injection at $z\lesssim
2\times 10^5$ which is not degenerate with, and can be distinguished from the
low redshift thermal $y$-type distortions. |
Some properties of galaxy structures: We analysed some properties of galaxies structures based on PF Catalogue of
galaxy structures (Panko & Flin 2006) and Tully NBG Catalog (Tully 1988) At
first, we analyzed the orientation of galaxies in the 247 optically selected
rich Abell clusters, having in the area considered as cluster at least 100
members. The distribution of the position angles of the galaxy as well as two
angles describing the spatial orientation of galaxy plane were tested for
isotropy, applying three statistical tests. We found that anisotropy increases
with the number of member galaxies, which means there exists the relation
between anisotropy and cluster richness. We do not find connection of galaxy
alignment and Bautz - Morgan morphological type of parent cluster. The
statistically marginal relation between velocity dispersion and cluster
richness was observed. However it was found that velocity dispersion decreases
with Bautz - Morgan type at almost $3 \sigma$ level. Separately we analyzed
ellipticities for 6188 low redshift ($z < 0.18$) poor and rich galaxy
structures which have been examined along with their evolution. Finally we
analysed the Binggeli effect. The orientation of galaxy groups in the Local
Supercluster (LSC), is strongly correlated with the distribution of
neighbouring groups in the scale till about 20 Mpc. During analyses of galaxy
structures from PF catalogue the situation was quite different. The efect is
observed only for more elongated structures ($e \le 0.3$). The range of the
distance in which the effect was observed, was estimated as about $60 h^{-1}
MPc$. | K-Oscillons: Oscillons with Non-Canonical Kinetic Terms: Oscillons are long-lived, localized, oscillatory scalar field configurations.
In this work we derive a condition for the existence of small-amplitude
oscillons (and provide solutions) in scalar field theories with non-canonical
kinetic terms. While oscillons have been studied extensively in the canonical
case, this is the first example of oscillons in scalar field theories with
non-canonical kinetic terms. In particular, we demonstrate the existence of
oscillons supported solely by the non-canonical kinetic terms, without any need
for nonlinear terms in the potential. In the small-amplitude limit, we provide
an explicit condition for their stability in d+1 dimensions against
long-wavelength perturbations. We show that for d > 2, there exists a
long-wavelength instability which can lead to radial collapse of
small-amplitude oscillons. |
Tensor Spectra Templates for Axion-Gauge Fields Dynamics during
Inflation: $SU(2)$ gauge fields can generate large gravitational waves during inflation,
if they are coupled to an axion which can be either the inflaton or a spectator
field. The shape of the produced tensor power spectrum $\mathcal{P}_h$ depends
on the form of the axion potential. We derive analytic expressions and provide
general templates for $\mathcal{P}_h$ for various types of the spectator axion
potential. Furthermore, we explore the detectability of the oscillatory
feature, which is present in $\mathcal{P}_h$ in the case of an axion monodromy
model, by possible future CMB B-mode polarization observations. | The coevolution of the velocity and mass functions of galaxies and dark
haloes: We employ a bias-corrected abundance matching technique to investigate the
coevolution of the LCDM dark halo mass function (HMF), the observationally
derived velocity dispersion and stellar mass functions (VDF, SMF) of galaxies
between z=1 and 0. We use for the first time the evolution of the VDF
constrained through strong lensing statistics by Chae (2010) for galaxy-halo
abundance matching studies. As a local benchmark we use a couple of z ~ 0 VDFs
(a Monte-Carlo realised VDF based on SDSS DR5 and a directly measured VDF based
on SDSS DR6). We then focus on connecting the VDF evolution to the HMF
evolution predicted by N-body simulations and the SMF evolution constrained by
galaxy surveys. On the VDF-HMF connection, we find that the local dark halo
virial mass-central stellar velocity dispersion (Mvir-sigma) relation is in
good agreement with the individual properties of well-studied low-redshift dark
haloes, and the VDF evolution closely parallels the HMF evolution meaning
little evolution in the Mvir-sigma relation. On the VDF-SMF connection, it is
also likely that the stellar mass-stellar velocity dispersion (Mstar-sigma)
relation evolves little taking the abundance matching results together with
other independent observational results and hydrodynamic simulation results.
Our results support the simple picture that as the halo grows hierarchically,
the stellar mass and the central stellar velocity dispersion grow in parallel.
We discuss possible implications of this parallel coevolution for galaxy
formation and evolution under the LCDM paradigm. |
The dust SED of dwarf galaxies I. The case of NGC 4214: The goal of the present study is to establish the physical origin of dust
heating and emission based on radiation transfer models, which
self-consistently connect the emission components from diffuse dust and the
dust in massive star forming regions. NGC 4214 is a nearby dwarf galaxy with a
large set of ancillary data, ranging from the ultraviolet (UV) to radio,
including maps from SPITZER, HERSCHEL and detections from PLANCK. We mapped
this galaxy with MAMBO at 1.2 mm at the IRAM 30 m telescope. We extract
separate dust emission components for the HII regions (plus their associated
PDRs on pc scales) and for the diffuse dust (on kpc scales). We analyse the
full UV to FIR/submm SED of the galaxy using a radiation transfer model which
self-consistently treats the dust emission from diffuse and SF complexes
components, considering the illumination of diffuse dust both by the
distributed stellar populations, and by escaping light from the HII regions.
While maintaining consistency with the framework of this model we additionally
use a model that provides a detailed description of the dust emission from the
HII regions and their surrounding PDRs on pc scales. Due to the large amount of
available data and previous studies for NGC 4214 very few free parameters
remained in the model fitting process. We achieve a satisfactory fit for the
emission from HII+PDR regions on pc scales, with the exception of the emission
at 8\mi, which is underpredicted by the model. For the diffuse emission we
achieve a good fit if we assume that about 30-70% of the emission escaping the
HII+PDR regions is able to leave the galaxy without passing through a diffuse
ISM, which is not an unlikely scenario for a dwarf galaxy which has recently
undergone a nuclear starburst. We determine a dust-to-gas mass ratio of 350-390
which is close to the expected value based on the metallicity. | Multi-wavelength consensus of large-scale linear bias: We model the large-scale linear galaxy bias $b_g(x,z)$ as a function of
redshift $z$ and observed absolute magnitude threshold $x$ for broadband
continuum emission from the far infrared to ultra-violet, as well as for
prominent emission lines, such as the H$\alpha$, H$\beta$, Lya and [OII] lines.
The modelling relies on the semi-analytic galaxy formation model GALFORM, run
on the state-of-the-art $N$-body simulation SURFS with the Planck 2015
cosmology. We find that both the differential bias at observed absolute
magnitude $x$ and the cumulative bias for magnitudes brighter than $x$ can be
fitted with a five-parameter model: $b_g(x,z)=a + b(1+z)^e(1 +
\exp{[(x-c)d]})$. We also find that the bias for the continuum bands follows a
very similar form regardless of wavelength due to the mixing of star-forming
and quiescent galaxies in a magnitude limited survey. Differences in bias only
become apparent when an additional colour separation is included, which suggest
extensions to this work could look at different colours at fixed magnitude
limits. We test our fitting formula against observations, finding reasonable
agreement with some measurements within $1\sigma$ statistical uncertainties,
and highlighting areas of improvement. We provide the fitting parameters for
various continuum bands, emission lines and intrinsic galaxy properties,
enabling a quick estimation of the linear bias in any typical survey of
large-scale structure. |
Statistical distribution of HI 21cm intervening absorbers as potential
cosmic acceleration probes: Damped Lyman-$\alpha$ Absorber (DLA), or HI 21cm Absorber (H21A), is an
important probe to model-independently measure the acceleration of
spectroscopic velocity ($v_\mathrm{S}$) via the Sandage-Loeb (SL) effect.
Confined by the shortage of DLAs and Background Radio Sources (BRSs) with
adequate information, the detectable amount of DLAs is ambiguous in the bulk of
previous work. After differing the acceleration of scale factor ($\ddot{a}$)
from the first order time derivative of spectroscopic velocity
($\dot{v}_\mathrm{S}$), we make a statistical investigation of the amount of
potential DLAs in the most of this paper. Using Kernel Density Estimation (KDE)
to depict general redshift distributions of BRSs, observed DLAs and a DLA
detection rate with different limitations (1.4GHz flux, HI column density and
spin temperature), we provide fitted multi-Gaussian expressions of the three
components and their 1$\sigma$ regions by bootstrap, with a proportional
constant of H21As in detected DLAs, leading to the measurable number
predictions of H21As for FAST, ASKAP and SKA1-Mid in HI absorption blind
survey. In our most optimistic condition ($F_\mathrm{1.4GHz}$>10mJy,
$N_\mathrm{HI}>2\times10^{20}\mathrm{cm^{-2}}$ and $T_\mathrm{S}$>500K), the
FAST, AKSAP and SKA1-Mid would probe about 80, 500 and 600 H21As respectively. | Primordial black hole formation during slow-reheating: A review: In this paper we review the possible mechanisms for the production of
primordial black holes (PBHs) during a slow-reheating period {in which the
energy transfer of the inflaton field to standard model particles becomes
effective at slow temperatures}, offering a comprehensive examination of the
theoretical foundations and conditions required for each of formation channel.
In particular, we focus on post-inflationary scenarios where there are no
self-resonances and the reheating epoch can be described {by the inflaton
evolving in} a quadratic-like potential. In the hydrodynamical interpretation
of this field during the slow-reheating epoch, the gravitational collapse of
primordial fluctuations is subject to conditions on their sphericity, limits on
their spin, as well as a maximum velocity dispersion. We show how to account
for all conditions and show that PBHs form with different masses depending on
the collapse mechanism. Finally we show, through an example, how PBH production
serves to probe both the physics after primordial inflation, as well as the
primordial powerspectrum at the smallest scales. |
On Dark Gravitational Wave Standard Sirens as Cosmological Inference and
Forecasting the Constraint on Hubble Constant using Binary Black Holes
Detected by Deci-hertz Observatory: Gravitational wave (GW) signals from compact binary coalescences can be used
as standard sirens to constrain cosmological parameters if their redshift can
be measured independently. However, mergers of stellar binary black holes
(BBHs) may not have electromagnetic counterparts and thus have no direct
redshift measurements. These dark sirens may be still used to statistically
constrain cosmological parameters by combining their GW measured luminosity
distances and localization with deep redshift surveys of galaxies around it. We
investigate this dark siren method in detail by using mock BBH and galaxy
samples. We find that the Hubble constant can be constrained well with an
accuracy $\lesssim1\%$ with a few tens or more of BBH mergers at redshift up to
$1$ if GW observations can provide accurate estimates of their luminosity
distance (with relative error of $\lesssim0.01$) and localization
($\lesssim0.1~\rm{deg}^2$), though the constraint may be significantly biased
if the luminosity distance and localization errors are larger. We also
introduce a simple method to correct this bias and find it is valid when the
luminosity distance and localization errors are modestly large. We further
generate mock BBH samples, according to current constraints on BBH merger rate
and the distributions of BBH properties, and find that the Deci-hertz
Observatory (DO) in a half year observation period may detect about one hundred
BBHs with signal-to-noise ratio $\varrho\gtrsim30$, relative luminosity
distance error $\lesssim0.02$, and localization error $\lesssim0.01\rm{deg}^2$.
By applying the dark standard siren method, we find that the Hubble constant
can be constrained to the $\sim0.1-1\%$ level using these DO BBHs, an accuracy
comparable to the constraints obtained by using electromagnetic observations in
the near future, thus it may provide insight into the Hubble tension. | The Kullback-Leibler Divergence as an Estimator of the Statistical
Properties of CMB Maps: The identification of unsubtracted foreground residuals in the cosmic
microwave background maps on large scales is of crucial importance for the
analysis of polarization signals. These residuals add a non-Gaussian
contribution to the data. We propose the Kullback-Leibler (KL) divergence as an
effective, non-parametric test on the one-point probability distribution
function of the data. With motivation in information theory, the KL divergence
takes into account the entire range of the distribution and is highly
non-local. We demonstrate its use by analyzing the large scales of the Planck
2013 SMICA temperature fluctuation map and find it consistent with the expected
distribution at a level of 6%. Comparing the results to those obtained using
the more popular Kolmogorov-Smirnov test, we find the two methods to be in
general agreement. |
On the Anisotropy of the Stochastic Gravitational Wave Background from
Sub-Horizon-Collapsed Primordial Black Hole Mergers: We study the properties of the stochastic gravitational wave background
(SGWB) resulting from the mergers of primordial black holes (PBH) that formed
from the collapse of sub-horizon regions in the early universe. We adopt a
model-independent approach, where we parameterize the fraction $f_H$ of the
wavelength of the perturbation mode in units of the horizon radius when the
patch starts to gravitationally collapse. Assuming a monochromatic spectrum of
isocurvature perturbations and spherically-symmetric density perturbations, we
investigate the isotropic SGWB energy density and angular power spectrum at
various frequencies, PBH masses, and horizon size fractions. The key effect of
sub-horizon formation is a change in the PBH mass function and formation
redshift, which, in turn, affects gravitational wave (GW) observables. We find
that sub-horizon PBH formation in general enhances the isotropic SGWB energy
density and the absolute angular power spectrum. However, the quasi-monotonic
increases in both quantities as $f_H$ decreases cease when the chirp mass of
the binary PBHs reaches a mass threshold determined by the frequency of
observation; the isotropic SGWB energy density spectrum significantly drops
above the corresponding cutoff frequency. | On the driver of relativistic effects strength in Seyfert galaxies: Spectroscopy of X-ray emission lines emitted in accretion discs around
supermassive black holes is one of the most powerful probes of the accretion
flow physics and geometry, while also providing in principle observational
constraints on the black hole spin.[...] We aim at determining the ultimate
physical driver of the strength of this relativistic reprocessing feature. We
first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so
far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column
density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties
depends on the AGN optical classification, as expected from the Seyfert
unification scenarios. There is also no correlation between the accretion disc
inclination, as derived from formal fits of the line profiles, and the optical
type or host galaxy aspect angle, suggesting that the innermost regions of the
accretion disc and the host galaxy plane are not aligned. [...]. Data are not
sensitive enough to the detailed ionisation state of the line-emitting disc.
However, the lack of dependency of the line EW on either the luminosity or the
rest-frame centroid energy rules out that disc ionisation plays an important
role on the EW dynamical range in Seyferts. The dynamical range of the
relativistically broadened K-alpha iron line EW in nearby Seyferts appears to
be mainly determined by the properties of the innermost accretion flow. We
discuss several mechanisms (disc ionisation, disc truncation, aberration due to
a mildly relativistic outflowing corona) which can explain this. [...]
Observational data are still not in contradiction with scenarios invoking
different mechanisms for the spectral complexity around the iron line, most
notably the "partial covering" absorption scenario. (abridged). |
Challenges in Cosmology from the Big Bang to Dark Energy, Dark Matter
and Galaxy Formation: I review the current status of Big Bang Cosmology, with emphasis on current
issues in dark matter, dark energy, and galaxy formation. These topics motivate
many of the current goals of experimental cosmology which range from targeting
the nature of dark energy and dark matter to probing the epoch of the first
stars and galaxies. | Cosmic Reionization On Computers: Reionization Histories of Present-day
Galaxies: We examine the reionization history of present-day galaxies by explicitly
tracing the building blocks of halos from the Cosmic Reionization On Computers
project. We track dark matter particles that belong to $z=0$ halos to trace the
neutral fractions at corresponding positions during rapid global reionization.
The resulting particle reionization histories allow us to explore different
definitions of a halo's reionization redshift and to account for the neutral
content of the interstellar medium. Consistent with previous work, we find a
systematic trend of reionization redshift with mass - present day halos with
higher masses have earlier reionization times. Finally, we quantify the spread
of reionization times within each halo, which also has a mass dependence. |
Confronting the primordial black hole scenario with the
gravitational-wave events detected by LIGO-Virgo: Adopting a binned method, we model-independently reconstruct the mass
function of primordial black holes (PBHs) from GWTC-3 and find that such a PBH
mass function can be explained by a broad red-tilted power spectrum of
curvature perturbations. Even though GW190521 with component masses in upper
mass gap $(m>65M_\odot)$ can be naturally interpreted in the PBH scenario, the
events (including GW190814, GW190425, GW200105, and GW200115) with component
masses in the light mass range $(m<3M_\odot)$ are quite unlikely to be
explained by binary PBHs although there are no electromagnetic counterparts
because the corresponding PBH merger rates are much smaller than those given by
LIGO-Virgo. Furthermore, we predict that both the gravitational-wave (GW)
background generated by the binary PBHs and the scalar-induced GWs accompanying
the formation of PBHs should be detected by the ground-based and space-borne GW
detectors and pulsar timing arrays in the future. | Shock and Splash: Gas and Dark Matter Halo Boundaries around LambdaCDM
Galaxy Clusters: Recent advances in simulations and observations of galaxy clusters suggest
that there exists a physical outer boundary of massive cluster-size dark matter
haloes. In this work, we investigate the locations of the outer boundaries of
dark matter and gas around cluster-size dark matter haloes, by analyzing a
sample of 65 massive dark matter halos extracted from the Omega500 zoom-in
hydrodynamical cosmological simulations. We show that the location of accretion
shock is offset from that of the dark matter splashback radius, contrary to the
prediction of the self-similar models. The accretion shock radius is larger
than all definitions of the splashback radius in the literature by 20-100%. The
accretion shock radius defined using the steepest drop in the entropy pressure
profiles is approximately 2 times larger than the splashback radius defined by
the steepest slope in the dark matter density profile, and it is ~1.2 times
larger than the edge of the dark matter phase-space structure. We discuss
implications of our results for multi-wavelength studies of galaxy clusters. |
Numerical evaluation of the three-point scalar-tensor cross-correlations
and the tensor bi-spectrum: Utilizing the Maldacena formalism and extending the earlier efforts to
compute the scalar bi-spectrum, we construct a numerical procedure to evaluate
the three-point scalar-tensor cross-correlations as well as the tensor
bi-spectrum in single field inflationary models involving the canonical scalar
field. We illustrate the accuracy of the adopted procedure by comparing the
numerical results with the analytical results that can be obtained in the
simpler cases of power law and slow roll inflation. We also carry out such a
comparison in the case of the Starobinsky model described by a linear potential
with a sudden change in the slope, which provides a non-trivial and interesting
(but, nevertheless, analytically tractable) scenario involving a brief period
of deviation from slow roll. We then utilize the code we have developed to
evaluate the three-point correlation functions of interest (and the
corresponding non-Gaussianity parameters that we introduce) for an arbitrary
triangular configuration of the wavenumbers in three different classes of
inflationary models which lead to features in the scalar power spectrum, as
have been recently considered by the Planck team. We also discuss the
contributions to the three-point functions during preheating in inflationary
models with a quadratic minimum. We conclude with a summary of the main results
we have obtained. | Self consistent model for the evolution of eccentric massive black hole
binaries in stellar environments: implications for gravitational wave
observations: We construct evolutionary tracks for massive black hole binaries (MBHBs)
embedded in a surrounding distribution of stars. The dynamics of the binary is
evolved by taking into account the erosion of the central stellar cusp bound to
the massive black holes, the scattering of unbound stars feeding the binary
loss cone, and the emission of gravitational waves (GWs). Stellar dynamics is
treated in a hybrid fashion by coupling the results of numerical 3-body
scattering experiments of bound and unbound stars to an analytical framework
for the evolution of the stellar density distribution and for the efficiency of
the binary loss cone refilling. Our main focus is on the behaviour of the
binary eccentricity, in the attempt of addressing its importance in the merger
process and its possible impact for GW detection with the planned Laser
Interferometer Space Antenna ({\it LISA}), and ongoing and forthcoming pulsar
timing array (PTA) campaigns. We produce a family of evolutionary tracks
extensively sampling the relevant parameters of the system which are the binary
mass, mass ratio and initial eccentricity, the slope of the stellar density
distribution, its normalization and the efficiency of loss cone refilling. We
find that, in general, stellar dynamics causes a dramatic increase of the MBHB
eccentricity, especially for initially already mildly eccentric and/or unequal
mass binaries. When applied to standard MBHB population models, our results
predict eccentricities in the ranges $10^{-3}-0.2$ and $0.03-0.3$ for sources
detectable by {\it LISA} and PTA respectively. Such figures may have a
significant impact on the signal modelling, on source detection, and on the
development of parameter estimation algorithms. |
Probing Cosmological Reionization through Radio-interferometric
Observations of Neutral Hydrogen: The epoch of reionization is one of the least known chapters in the
evolutionary history of the Universe. This thesis investigates two major
approaches to unveil the reionization history of the Universe using HI 21-cm
maps.The most discussed approach has been to study the global statistical
properties of the reionization HI 21-cm. We develop the formalism to calculate
the Multi-frequency Angular Power Spectrum (MAPS) and quantify the statistics
of the HI signal as a joint function of the angular multipole l and frequency
separation \Delta\nu. We adopt a simple model for the HI distribution which
incorporates patchy reionization and use it to study the signatures of ionized
bubbles on MAPS. We also study the implications of the foreground subtraction.
A major part of the thesis investigates the possibility of detecting ionized
bubbles around individual sources in 21-cm maps. We present a visibility based
matched filter technique to optimally combine the signal from an ionized bubble
and minimize the noise and foreground contributions. The formalism makes
definite predictions on the ability to detect an ionized bubble or conclusively
rule out its presence within a radio map. Results are presented for the GMRT
and the MWA. Using simulated HI maps we analyzed the impact of HI fluctuations
outside the bubble on its detectability. Various other issues such as (i)
bubble size determination (ii) blind search for bubbles, (iii) optimum redshift
for bubble detection are also discussed. | Measuring galaxy-galaxy-galaxy-lensing with higher precision and
accuracy: Galaxy-galaxy-galaxy lensing (G3L) is a powerful tool for constraining the
three-point correlation between the galaxy and matter distribution and thereby
models of galaxy evolution. We propose three improvements to current
measurements of G3L: (i) a weighting of lens galaxies according to their
redshift difference, (ii) adaptive binning of the three-point correlation
function, and (iii) accounting for the effect of lens magnification by the
cosmic large-scale structure. Improvement (i) is designed to improve the
precision of the G3L measurement, whereas improvements (ii) and (iii) remove
biases of the estimator. We further show how the G3L signal can be converted
from angular into physical scales. The improvements were tested on simple mock
data and simulated data based on the Millennium Run with an implemented
semi-analytic galaxy model. Our improvements increase the signal-to-noise ratio
by 35 % on average at angular scales between 0.1 arcmin and 10 arcmin and
physical scales between $0.02$ and $2 \, h^{-1}\, \textrm{Mpc}$. They also
remove the bias of the G3L estimator at angular scales below 1 arcmin, which
was originally up to 40 %. The signal due to lens magnification is
approximately 10 % of the total signal. |
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