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Heating Galaxy Clusters with Interacting Dark Matter: The overcooling of cool core clusters is a persistent puzzle in the
astrophysics of galaxy clusters. We propose that it may naturally be resolved
via interactions between the baryons of the intracluster medium (ICM) and its
dark matter (DM). DM-baryon interactions can inject heat into the ICM to offset
bremmstrahlung cooling, but these interactions are also strongly constrained by
existing experiments and astrophysical observations. We survey existing
constraints and combine these with the energetic needs of an observed sample of
cool core clusters. We find that a robust parameter space exists for baryon-DM
scattering solutions to the cooling flow problem, provided that only a
sub-component of DM interacts strongly with the baryons. Interestingly,
baryon-DM scattering is a thermally stable heating source so long as the baryon
temperature is greater than $1/3-1/2$ the DM temperature, a condition that
seems to be satisfied observationally. | Long term Arecibo monitoring of the water megamaser in MG J0414+0534: We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at
z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible
additional maser components and to measure a potential velocity drift of the
lines. The main maser line profile is complex and can be resolved into a number
of broad features with line widths of 30-160 km/s. A new maser component was
tentatively detected in October 2008 at a velocity of +470 km/s. After
correcting for the estimated lens magnification, we find that the H2O isotropic
luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities,
making this source the most luminous ever discovered. Both the main line peak
and continuum flux densities are surprisingly stable throughout the period of
the observations. An upper limit on the velocity drift of the main peak of the
line has been estimated from our observations and is of the order of 2 km/s per
year. We discuss the results of the monitoring in terms of the possible nature
of the maser emission, associated with an accretion disk or a radio jet. This
is the first time that such a study is performed in a water maser source at
high redshift, potentially allowing us to study the parsec-scale environment
around a powerful radio source at cosmological distances. |
Stellar mass-to-light ratios from galaxy spectra: how accurate can they
be?: Stellar masses play a crucial role in the exploration of galaxy properties
and the evolution of the galaxy population. In this paper, we explore the
minimum possible uncertainties in stellar mass-to-light (M/L) ratios from the
assumed star formation history (SFH) and metallicity distribution, with the
goals of providing a minimum set of requirements for observational studies. We
use a large Monte Carlo library of SFHs to study as a function of galaxy
spectral type and signal-to-noise ratio (S/N) the statistical uncertainties of
M/L values using either absorption-line data or broad band colors. The accuracy
of M/L estimates can be significantly improved by using metal-sensitive indices
in combination with age-sensitive indices, in particular for galaxies with
intermediate-age or young stellar populations. While M/L accuracy clearly
depends on the spectral S/N ratio, there is no significant gain in improving
the S/N much above 50/pix and limiting uncertainties of 0.03 dex are reached.
Assuming that dust is accurately corrected or absent and that the redshift is
known, color-based M/L estimates are only slightly more uncertain than
spectroscopic estimates (at comparable spectroscopic and photometric quality),
but are more easily affected by systematic biases. This is the case in
particular for galaxies with bursty SFHs (high Hdelta at fixed D4000), the M/L
of which cannot be constrained any better than 0.15 dex with any indicators
explored here. Finally, we explore the effects of the assumed prior
distribution in SFHs and metallicity, finding them to be higher for color-based
estimates. | The Best Inflationary Models After Planck: We compute the Bayesian evidence and complexity of 193 slow-roll single-field
models of inflation using the Planck 2013 Cosmic Microwave Background data,
with the aim of establishing which models are favoured from a Bayesian
perspective. Our calculations employ a new numerical pipeline interfacing an
inflationary effective likelihood with the slow-roll library ASPIC and the
nested sampling algorithm MULTINEST. The models considered represent a complete
and systematic scan of the entire landscape of inflationary scenarios proposed
so far. Our analysis singles out the most probable models (from an Occam's
razor point of view) that are compatible with Planck data, while ruling out
with very strong evidence 34% of the models considered. We identify 26% of the
models that are favoured by the Bayesian evidence, corresponding to 15
different potential shapes. If the Bayesian complexity is included in the
analysis, only 9% of the models are preferred, corresponding to only 9
different potential shapes. These shapes are all of the plateau type. |
CMB lensing reconstruction using cut sky polarization maps and pure-$B$
modes: Detailed measurements of the CMB lensing signal are an important scientific
goal of ongoing ground-based CMB polarization experiments, which are mapping
the CMB at high resolution over small patches of the sky. In this work we
simulate CMB polarization lensing reconstruction for the $EE$ and $EB$
quadratic estimators with current-generation noise levels and resolution, and
show that without boundary effects the known and expected zeroth and first
order $N^{(0)}$ and $N^{(1)}$ biases provide an adequate model for non-signal
contributions to the lensing power spectrum estimators. Small sky areas present
a number of additional challenges for polarization lensing reconstruction,
including leakage of $E$ modes into $B$ modes. We show how simple windowed
estimators using filtered pure-$B$ modes can greatly reduce the mask-induced
mean-field lensing signal and reduce variance in the estimators. This provides
a simple method (used with recent observations) that gives an alternative to
more optimal but expensive inverse-variance filtering. | The SRG/eROSITA All-Sky Survey: SRG/eROSITA cross-calibration with
Chandra and XMM-Newton using galaxy cluster gas temperatures: Galaxy cluster gas temperatures ($T$) play a crucial role in many
cosmological and astrophysical studies. However, it has been shown that $T$
measurements can vary between different X-ray telescopes. These $T$ biases can
propagate to several cluster applications for which $T$ can be used. Thus, it
is important to accurately cross-calibrate X-ray instruments to account for
systematic biases. In this work, we present the cross-calibration between
SRG/eROSITA and Chandra/ACIS, and between SRG/eROSITA and XMM-Newton/EPIC,
using for the first time a large sample of galaxy cluster $T$. To do so, we use
the first eROSITA All-Sky Survey data and a large X-ray flux-limited cluster
catalog. We measure X-ray $T$ for 186 independent cluster regions with both
SRG/eROSITA and Chandra/ACIS in a self-consistent way, for three energy bands;
0.7-7 keV (full), 0.5-4 keV (soft), and 1.5-7 keV (hard). We do the same with
SRG/eROSITA and XMM-Newton/EPIC for 71 different cluster regions and all three
bands. We find that SRG/eROSITA measures systematically lower $T$ than the
other two instruments. For the full band, SRG/eROSITA returns 20$\%$ and 14$\%$
lower $T$ than Chandra/ACIS and XMM-Newton/EPIC respectively, when the two
latter instruments measure $k_{\text{B}}T\approx 3$ keV each. The discrepancy
increases to 38\% and 32\% when Chandra/ACIS and XMM-Newton/EPIC measure
$k_{\text{B}}T\approx 10$ keV respectively. For low-$T$ galaxy groups, the
discrepancy becomes milder. The soft band shows a marginally lower discrepancy
than the full band. In the hard band, the cross-calibration of SRG/eROSITA and
the other instruments show stronger differences. We could not identify any
possible systematic biases that significantly alleviated the tension. Finally,
we provide conversion factors between SRG/eROSITA, Chandra/ACIS, and
XMM-Newton/EPIC $T$ which will be beneficial for future cluster studies. |
Correlations between supermassive black holes and hot gas atmospheres in
IllustrisTNG and X-ray observations: Recent X-ray observations have revealed remarkable correlations between the
masses of central supermassive black holes (SMBHs) and the X-ray properties of
the hot atmospheres permeating their host galaxies, thereby indicating the
crucial role of the atmospheric gas in tracing SMBH growth in the high-mass
regime. We examine this topic theoretically using the IllustrisTNG cosmological
simulations and provide insights to the nature of this SMBH -- gaseous halo
connection. By carrying out a mock X-ray analysis for a mass-selected sample of
TNG100 simulated galaxies at $z=0$, we inspect the relationship between the
masses of SMBHs and the hot gas temperatures and luminosities at various
spatial and halo scales -- from galactic ($\sim R_{\rm e}$) to group/cluster
scales ($\sim R_{\rm 500c}$). We find strong SMBH-X-ray correlations mostly in
quenched galaxies and find that the correlations become stronger and tighter at
larger radii. Critically, the X-ray temperature ($k_{\rm B}T_{\rm X}$) at large
radii ($r\gtrsim5R_{\rm e}$) traces the SMBH mass with a remarkably small
scatter ($\sim0.2$ dex). The relations emerging from IllustrisTNG are broadly
consistent with those obtained from recent X-ray observations. Overall, our
analysis suggests that, within the framework of IllustrisTNG, the present-time
$M_{\rm BH}-k_{\rm B}T_{X}$ correlations at the high-mass end ($M_{\rm
BH}\gtrsim 10^8 M_\odot$) are fundamentally a reflection of the SMBH mass --
halo mass relation, which at such high masses is set by the hierarchical
assembly of structures. The exact form, locus, and scatter of those scaling
relations are, however, sensitive to feedback processes such as those driven by
star formation and SMBH activity. | The Peculiar Velocity Correlation Function: We present an analysis of the two-point peculiar velocity correlation
function using data from the CosmicFlows catalogues. The Millennium and
MultiDark Planck 2 N-body simulations are used to estimate cosmic variance and
uncertainties due to measurement errors. We compare the velocity correlation
function to expectations from linear theory to constrain cosmological
parameters. Using the maximum likelihood method, we find values of $\Omega_m=
0.315^{+0.205}_{-0.135}$ and $\sigma_8=0.92^{+0.440}_{-0.295}$, consistent with
the Planck and Wilkinson Microwave Anisotropy Probe CMB derived estimates.
However, we find that the cosmic variance of the correlation function is large
and non-Gaussian distributed, making the peculiar velocity correlation function
less than ideal as a probe of large-scale structure. |
Structural Properties of Central Galaxies in Groups and Clusters: Using a representative sample of 911 central galaxies (CENs) from the SDSS
DR4 group catalogue, we study how the structure of the most massive members in
groups and clusters depend on (1) galaxy stellar mass (Mstar), (2) dark matter
halo mass of the host group (Mhalo), and (3) their halo-centric position. We
establish and thoroughly test a GALFIT-based pipeline to fit 2D Sersic models
to SDSS data. We find that the fitting results are most sensitive to the
background sky level determination and strongly recommend using the SDSS global
value. We find that uncertainties in the background translate into a strong
covariance between the total magnitude, half-light size (r50), and Sersic index
(n), especially for bright/massive galaxies. We find that n depends strongly on
Mstar for CENs, but only weakly or not at all on Mhalo. Less (more) massive
CENs tend to be disk (spheroid)-like over the full Mhalo range. Likewise, there
is a clear r50-Mstar relation for CENs, with separate slopes for disks and
spheroids. When comparing CENs with satellite galaxies (SATs), we find that low
mass (<10e10.75 Msun/h^2) SATs have larger median n than CENs of similar Mstar.
Low mass, late-type SATs have moderately smaller r50 than late-type CENs of the
same Mstar. However, we find no size differences between spheroid-like CENs and
SATs, and no structural differences between CENs and SATs matched in both mass
and colour. The similarity of massive SATs and CENs shows that this distinction
has no significant impact on the structure of spheroids. We conclude that Mstar
is the most fundamental property determining the basic structure of a galaxy.
The lack of a clear n-Mhalo relation rules out a distinct group mass for
producing spheroids, and the responsible morphological transformation processes
must occur at the centres of groups spanning a wide range of masses. (abridged) | The Core-Cusp Problem in Cold Dark Matter Halos and Supernova Feedback:
Effects of Oscillation: This study investigates the dynamical response of dark matter (DM) halos to
recurrent starbursts in forming less-massive galaxies to solve the core-cusp
problem. The gas, which is heated by supernova feedback after a starburst,
expands and the star formation then terminates. This expanding gas loses energy
by radiative cooling and then falls back toward the galactic center.
Subsequently, the starburst is enhanced again. This cycle of expansion and
contraction of the interstellar gas leads to a repetitive change in the
gravitational potential of the gas. The resonance between DM particles and the
density wave excited by the oscillating potential plays a key role in
understanding the physical mechanism of the cusp-core transition of DM halos.
DM halos effectively gain kinetic energy from the baryon potential through the
energy transfer driven by the resonance between the particles and density
waves. We determine that the critical condition for the cusp-core transition is
such that the oscillation period of the gas potential is approximately the same
as the local dynamical time of DM halos. We present the resultant core radius
of a DM halo after the cusp-core transition induced by the resonance by using
the conventional mass density profile predicted by the cold dark matter models.
Moreover, we verify the analytical model by using $N$-body simulations, and the
results validate the resonance model. |
Constraints on a Stochastic Background of Primordial Magnetic Fields
with WMAP and South Pole Telescope data: We constrain a stochastic background of primordial magnetic fields (PMF) by
its contribution to the cosmic microwave background (CMB) anisotropy angular
power spectrum with the combination of WMAP 7 year and South Pole Telescope
(SPT) data. The contamination in the SPT data by unresolved point sources and
by the Sunyaev Zeldovich (SZ) effect due to galaxy clusters has been taken into
account as modelled by the SPT collaboration. With this combination of WMAP 7
yr and SPT data, we constrain the amplitude Gaussian smoothed over 1 Mpc scale
of a stochatic background of non-helical PMF to $B_{\rm 1 Mpc}<3.5$ nG at 95%
confidence level. Our analysis shows that SPT data up to $\ell=3000$ bring an
improvement of almost a factor two with respect to results with previous CMB
high-$\ell$ data. We then discuss the forecasted impact from unresolved points
sources and SZ effect for {\sc Planck} capabilities in constraining PMF. | Super-massive binary black holes and emission lines in active galactic
nuclei: The broad emission spectral lines emitted from AGNs are our main probe of the
geometry and physics of the broad line region (BLR) close to the SMBH. There is
a group of AGNs that emits very broad and complex line profiles, showing two
displaced peaks, one blueshifted and one redshifted from the systemic velocity
defined by the narrow lines, or a single such peak. It has been proposed that
such line shapes could indicate a supermassive binary black hole (SMB) system.
We discuss here how the presence of an SMB will affect the BLRs of AGNs and
what the observational consequences might be.
We review previous claims of SMBs based on broad line profiles and find that
they may have non-SMB explanations as a consequence of a complex BLR structure.
Because of these effects it is very hard to put limits on the number of SMBs
from broad line profiles. It is still possible, however, that unusual broad
line profiles in combination with other observational effects (line ratios,
quasi-periodical oscillations, spectropolarimetry, etc.) could be used for SMBs
detection.
Some narrow lines (e.g., [O\,III]) in some AGNs show a double-peaked profile.
Such profiles can be caused by streams in the Narrow Line Region (NLR), but may
also indicate the presence of a kilo-parsec scale mergers. A few objects
indicated as double-peaked narrow line emitters are confirmed as kpc-scale
margers, but double-peaked narrow line profiles are mostly caused by the
complex NLR geometry.
We briefly discuss the expected line profile of broad Fe K$\alpha$ that
probably originated in the accretion disk(s) around SMBs.
Finally we consider rare configurations where a SMB system might be
gravitationally lensed by a foreground galaxy, and discuss the expected line
profiles in these systems. |
Search for sterile neutrinos in a universe of vacuum energy interacting
with cold dark matter: We investigate the cosmological constraints on sterile neutrinos in a
universe in which vacuum energy interacts with cold dark matter by using latest
observational data. We focus on two specific interaction models, $Q=\beta
H\rho_{\rm v}$ and $Q=\beta H\rho_{\rm c}$. To overcome the problem of
large-scale instability in the interacting dark energy scenario, we employ the
parametrized post-Friedmann (PPF) approach for interacting dark energy to do
the calculation of perturbation evolution. The observational data sets used in
this work include the Planck 2015 temperature and polarization data, the baryon
acoustic oscillation measurements, the type-Ia supernova data, the Hubble
constant direct measurement, the galaxy weak lensing data, the redshift space
distortion data, and the Planck lensing data. Using the all-data combination,
we obtain $N_{\rm eff}<3.522$ and $m_{\nu,{\rm sterile}}^{\rm eff}<0.576$ eV
for the $Q=\beta H\rho_{\rm v}$ model, and $N_{\rm
eff}=3.204^{+0.049}_{-0.135}$ and $m_{\nu,{\rm sterile}}^{\rm
eff}=0.410^{+0.150}_{-0.330}$ eV for the $Q=\beta H\rho_{\rm c}$ model. The
latter indicates $\Delta N_{\rm eff}>0$ at the 1.17$\sigma$ level and a nonzero
mass of sterile neutrino at the 1.24$\sigma$ level. In addition, for the
$Q=\beta H\rho_{\rm v}$ model, we find that $\beta=0$ is consistent with the
current data, and for the $Q=\beta H\rho_{\rm c}$ model, we find that $\beta>0$
is obtained at more than 1$\sigma$ level. | The Modified Schrodinger Poisson Equation -- Quantum Polytropes: Axions and axion-like particles are a leading model for the dark matter in
the Universe; therefore, dark matter halos may be boson stars in the process of
collapsing. We examine a class of static boson stars with a non-minimal
coupling to gravity. We modify the gravitational density of the boson field to
be proportional to an arbitrary power of the modulus of the field, introducing
a non-standard coupling. We find a class of solutions very similar to Newtonian
polytropic stars that we denote "quantum polytropes." These quantum polytropes
are supported by a non-local quantum pressure and follow an equation very
similar to the Lane-Emden equation for classical polytropes. Furthermore, we
derive a simple condition on the exponent of the non-linear gravitational
coupling, $\alpha>8/3$, beyond which the equilibrium solutions are unstable. |
The $H_0$ and $σ_8$ tensions and the scale invariant spectrum: In a previous communication we showed that a joint analysis of Cosmic
Microwave Background (CMB) data and the current measurement of the local
expansion rate favours a model with a scale invariant spectrum (HZ) over the
minimal $\Lambda$CDM scenario provided that the effective number of
relativistic degrees of freedom, $N_{eff}$, is taken as a free parameter. Such
a result is basically obtained due to the Hubble Space Telescope (HST) value of
the Hubble constant, $H_0 = 73.24 \pm 1.74$ $\rm{km.s^{-1}.Mpc^{-1}}$ (68\%
C.L.), as the CMB data alone discard the HZ+$N_{eff}$ model. Although such a
model is not physically motivated by current scenarios of the early universe,
observations pointing to a scale invariant spectrum may indicate that the
origin of cosmic perturbations lies in an unknown physical process. Here, we
extend the previous results performing a Bayesian analysis using joint CMB,
HST, and Baryon Acoustic Oscillations (BAO) measurements. In order to take into
account the well-known tension on the value of the fluctuation amplitude
parameter, $\sigma_8$, we also consider Cluster Number counts (CN) and Weak
Lensing (WL) data. We use two different samples of BAO data, which are obtained
using two-point spatial (BAO 2PCF) and angular (BAO 2PACF) correlation
functions. Our results show that a joint CMB+HST+BAO 2PCF analysis discards the
HZP$+N_{eff}$ model with respect to the minimal $\Lambda$CDM scenario whereas
the combination CMB+HST+BAO 2PACF favours the former model, even when an
extended dataset with NC and WL is considered. | Gauss-Bonnet Dark Energy and the Speed of Gravitational Waves: Gauss-Bonnet Dark Energy has been a popular model to explain the accelerated
expansion of the Universe. Quite generically it also predicts the speed of
gravitational waves $c_{GW}$ to be different from the speed of light. This fact
alone led some authors to exclude such models in view of the new tight
observational constraints on $c_{GW}$. However, the behaviour of $c_{GW}$
depends on the choice of the Gauss-Bonnet (GB) coupling function. It is
possible to construct models where $c_{GW}$ is always equal to the speed of
light. More generally, $c_{GW}$ is a time dependent function with instances
where both speeds coincide. Nevertheless, we observe that the bound on $c_{GW}$
excludes scenarios where the GB term directly affects the expansion of the
Universe, even if the constraint on the variation of the coupling function does
not appear to be strong. We perform the dynamical systems analysis to see if
the expansion of the Universe could be affected indirectly by modulating the
behaviour of the scalar field, which modulates the GB coupling. It is shown
that either the bounds on $c_{GW}$ are violated by many orders of magnitude, or
it might be very difficult to find models that are consistent with other
cosmological observations. |
Reproducing neutrino effects on the matter power spectrum through a
degenerate Fermi gas approach: Modifications on the predictions about the matter power spectrum based on the
hypothesis of a tiny contribution from a degenerate Fermi gas (DFG) test-fluid
to some dominant cosmological scenario are investigated. Reporting about the
systematic way of accounting for all the cosmological perturbations, through
the Boltzmann equation we obtain the analytical results for density
fluctuation, $\delta$, and fluid velocity divergence, $\theta$, of the DFG.
Small contributions to the matter power spectrum are analytically obtained for
the radiation-dominated background, through an ultra-relativistic
approximation, and for the matter-dominated and $\Lambda$-dominated eras,
through a non-relativistic approximation. The results can be numerically
reproduced and compared with those of considering non-relativistic and
ultra-relativistic neutrinos into the computation of the matter power spectrum.
Lessons concerning the formation of large scale structures of a DFG are
depicted, and consequent deviations from standard $\Lambda$CDM predictions for
the matter power spectrum (with and without neutrinos) are quantified. | Nonlinear Bias of Cosmological Halo Formation in the Early Universe: We present estimates of the nonlinear bias of cosmological halo formation,
spanning a wide range in the halo mass from $\sim 10^{5} M_\odot$ to $\sim
10^{12} M_\odot$, based upon both a suite of high-resolution cosmological
N-body simulations and theoretical predictions. The halo bias is expressed in
terms of the mean bias and stochasticity as a function of local overdensity
($\delta$), under different filtering scales, which is realized as the density
of individual cells in uniform grids. The sampled overdensities span a range
wide enough to provide the fully nonlinear bias effect on the formation of
haloes. A strong correlation between $\delta$ and halo population overdensity
$\delta_h$ is found, along with sizable stochasticity. We find that the
empirical mean halo bias matches, with good accuracy, the prediction by the
peak-background split method based on the excursion set formalism, as long as
the empirical, globally-averaged halo mass function is used. Consequently, this
bias formalism is insensitive to uncertainties caused by varying halo
identification schemes, and can be applied generically. We also find that the
probability distribution function of biased halo numbers has wider distribution
than the pure Poisson shot noise, which is attributed to the sub-cell scale
halo correlation. We explicitly calculate this correlation function and show
that both overdense and underdense regions have positive correlation, leading
to stochasticity larger than the Poisson shot noise in the range of haloes and
halo-collapse epochs we study. |
What it Takes to Measure Reionization with Fast Radio Bursts: Fast Radio Bursts (FRBs) are extra-galactic radio transients which exhibit a
distance-dependent dispersion of their signal, and thus can be used as
cosmological probes. In this article we, for the first time, apply a
model-independent approach to measure reionization from synthetic FRB data
assuming these signals are detected beyond redshift 5. This method allows us to
constrain the full shape of the reionization history as well as the CMB optical
depth $\tau$ while avoiding the problems of commonly used model-based
techniques. 100 localized FRBs, originating from redshifts 5-15, could
constrain (at 68% confidence level) the CMB optical depth to within 11%, and
the midpoint of reionization to 4%, surpassing current state-of-the-art CMB
bounds and quasar limits. Owing to the higher numbers of expected FRBs at lower
redshifts, the $\tau$ constraints are asymmetric (+14%, -7%) providing a much
stronger lower limit. Finally, we show that the independent constraints on
reionization from FRBs will improve limits on other cosmological parameters
such as the amplitude of the power spectrum of primordial fluctuations. | Efficient ILC analysis on polarization maps after EB leakage correction: The Internal Linear Combination (ILC) is widely used to extract the cosmic
microwave background (CMB) signal from multi-frequency observation maps,
especially for Satellite experiments with quasi-full sky coverage. We extend
ILC method to CMB polarization map analysis with a small sky patch which is
especially typical for ground-based experiments, by combing ILC with a template
cleaning method which can give pure $B$ map free from $EB$ leakage caused by
partial sky coverage. The feature of our methods is that we do the ILC analysis
on pseudo-scalar $B$ maps, and the advantage is that it totally avoids the
impact of $EB$ leakage on ILC, so that it can improve the efficiency of
component separation dramatically. We demonstrate our methods with mock data of
a future ground-based experiment with a deep survey on a clean patch in the
northern sky, and the results show that the level of foreground residual can be
well controlled, it biases the tensor to scalar ratio ($r$) at the order of
$10^{-3}$ which is comparable to the statistical error by noise. |
The XMM-Newton/SDSS Galaxy Cluster Survey (PhD thesis): The dissertation has been published at the Potsdam University under the
following URL: http://opus.kobv.de/ubp/volltexte/2014/7122/ | Probing the time variation of the effective Newton's constant with
optimal redshift weights: We propose a new method for probing the time variation of the effective
Newton's constant $G_{\rm eff}$, based on the optimal redshift weighting
scheme, and demonstrate the efficacy using the DESI galaxy spectroscopic
survey. We find that with the optimal redshift weights, the evolution of
$G_{\rm eff}(z)$ can be significantly better measured: the uncertainty of
$G_{\rm eff}(z)$ can be reduced by a factor of $2.2\sim12.8$ using the DESI BGS
sample at $z \lesssim0.45$, and by a factor of $1.3\sim4.4$ using the DESI ELG
sample covering $0.65\lesssim z\lesssim1.65$. |
Constraining primordial black holes as dark matter using the global
21-cm signal with X-ray heating and excess radio background: Using the global 21-cm signal measurement by the EDGES collaboration, we
derive constraints on the fraction of the dark matter that is in the form of
primordial black holes (PBHs) with masses in the range $10^{15}$-$10^{17}\,$g.
Improving upon previous analyses, we consider the effect of the X-ray heating
of the intergalactic medium on these constraints, and also use the full shape
of the 21-cm absorption feature in our inference. In order to account for the
anomalously deep absorption amplitude, we also consider an excess radio
background motivated by LWA1 and ARCADE2 observations. Because the heating rate
induced by PBH evaporation evolves slowly, the data favour a scenario in which
PBH-induced heating is accompanied by X-ray heating. Also, for the same reason,
using the full measurement across the EDGES observation band yields much
stronger constraints on PBHs than just the redshift of absorption. We find that
21-cm observations exclude $f_{\mathrm{PBH}} \gtrsim 10^{-9.7}$ at 95% CL for
$M_{\mathrm{PBH}}=10^{15}\,$g. This limit weakens approximately as
$M_{\mathrm{PBH}}^4$ towards higher masses, thus providing the strongest
constraints on ultralight evaporating PBHs as dark matter over the entire mass
range $10^{15}$-$10^{17}\,$g. Under the assumption of a simple spherical
gravitational collapse based on the Press-Schechter formalism, we also derive
bounds on the curvature power spectrum at extremely small scales ($k\sim
10^{15}\,$Mpc$^{-1}$). This highlights the usefulness of global 21-cm
measurements, including non-detections, across wide frequency bands for probing
exotic physical processes. | Testing standard and non-standard neutrino physics with cosmological
data: Cosmological constraints on the sum of neutrino masses and on the effective
number of neutrino species in standard and non-standard scenarios are computed
using the most recent available cosmological data. Our cosmological data sets
include the measurement of the Baryonic Acoustic Oscillation (BAO) feature in
the Data Release 9 CMASS sample of the Baryon Oscillation Spectroscopic Survey
(BOSS). We study in detail the different degeneracies among the parameters, as
well as the impact of the different data sets used in the analyses. When
considering bounds on the sum of the three active neutrino masses, the
information in the BAO signal from galaxy clustering measurements is
approximately equally powerful as the shape information from the matter power
spectrum. The most stringent bound we find is sum m_nu<0.32 eV at 95 % CL. When
non-standard neutrino scenarios with neff massless or massive neutrino species
are examined, power spectrum shape measurements provide slightly better bounds
than the BAO signal only, due to the breaking of parameter degeneracies. Recent
BOSS data combined with CMB and Hubble Space Telescope measurements give
neff=3.66^{+0.20 +0.73}_{-0.21 -0.69} in the massless neutrino scenario, and
similar results are obtained in the massive case. The evidence for extra
radiation neff>3 often claimed in the literature therefore remains at the 2
sigma level when considering up-to-date cosmological data sets. Measurements
from the Wilkinson Microwave Anisotropy Probe combined with a prior on the
Hubble parameter from the Hubble Space Telescope are very powerful in
constraining either the sum of the three active neutrino masses or the number
of massless neutrino species. If the former two parameters are allowed to
freely vary, however, the bounds from the combination of these two cosmological
probes get worse by an order of magnitude. |
Measuring the modified gravitational waves propagation beyond general
relativity from CMB observations: In modified gravity theories, the gravitational waves propagation are
presented in nonstandard ways. We consider a friction term different from GR
and constrain the modified gravitational waves propagation from observations.
The modified gravitational waves produce anisotropies and polarization which
generate measurable tensor power spectra. We explore the impact of the friction
term on the power spectrum of B-modes and the impact on the constraints on the
other parameters (e.g., $r$ or $A_t$) when $\nu_0$ is allowed to vary in the
Monte Carlo analyses from Planck+BK18 datasets. If we assume the result of the
scalar perturbations is unchanged, the inflation consistency relation alters
with the friction term. In the $\Lambda$CDM+$r$+$\nu_0$ model, the
tensor-to-scalar ratio and the amplitude of tensor spectrum are influenced
obviously. | Effective Theory of Interacting Dark Energy: We present a unifying treatment of dark energy and modified gravity that
allows distinct conformal-disformal couplings of matter species to the
gravitational sector. In this very general approach, we derive the conditions
to avoid ghost and gradient instabilities. We compute the equations of motion
for background quantities and linear perturbations. We illustrate our formalism
with two simple scenarios, where either cold dark matter or a relativistic
fluid is nonminimally coupled. This extends previous studies of coupled dark
energy to a much broader spectrum of gravitational theories. |
Observational constraints on K-inflation models: We extend the ModeCode software of Mortonson, Peiris and Easther to enable
numerical computation of perturbations in K-inflation models, where the scalar
field no longer has a canonical kinetic term. Focussing on models where the
kinetic and potential terms can be separated into a sum, we compute slow-roll
predictions for various models and use these to verify the numerical code. A
Markov chain Monte Carlo analysis is then used to impose constraints from WMAP7
data on the addition of a term quadratic in the kinetic energy to the
Lagrangian of simple chaotic inflation models. For a quadratic potential, the
data do not discriminate against addition of such a term, while for a quartic
(\lambda \phi^4) potential inclusion of such a term is actually favoured.
Overall, constraints on such a term from present data are found to be extremely
weak. | Testing of the dwarf galaxy content and the evolutionary status of
nearby groups of galaxies: We carried out visual and parametric searches for dwarf galaxies in five
loose groups of galaxies. Follow-up spectroscopy with the HET has shown a 50%
success rate of morphological selection. The evolutionary status of the studied
groups differs: while the NGC 6962 group has a partially relaxed core,
surrounded by an infall region, the NGC 5005/5033 group and the IC 65 group,
which consist only of late-type galaxies, are probably still assembling. |
Local gravity test of unified models of inflation and dark energy in
$f(R)$ gravity: We consider $f(R)$ gravity theories which unify $R^n$ inflation and dark
energy models. First, from the final Planck data of the cosmic microwave
background, we obtain a condition, $1.977 < n < 2.003$. Next, under this
constraint, we investigate local-gravity tests for three models. We find that
the $R^n$ term can dominate over the dark energy term even at the Earth's
curvature scale, contrary to intuition; however, the $R^n$ term does not relax
or tighten the constraints on the three models. | Revisiting the effect of lens mass models in cosmological applications
of strong gravitational lensing: Strong gravitational lens system catalogues are typically used to constrain a
combination of cosmological and empirical lens mass model parameters, even
though the simplest singular isothermal sphere (SIS) models yield a $\chi^2$
per degree of freedom $\simeq 2$. To date, this problem has been alleviated by
introducing additional empirical parameters in the extended power law (EPL)
models and constraints from high resolution imagery. The EPL parameters are
taken to vary from lens to lens, rather than defining universal lens profiles.
We investigate these lens models using Bayesian methods through a novel
alternative that treats spatial curvature via the non-FLRW Timescape cosmology.
We apply Markov Chain Monte Carlo methods using the catalogue of 161 lens
systems of Chen et al (arXiv:1809.09845) to simulate large mock catalogues for:
(i) the standard $\Lambda$CDM model with zero spatial curvature; and (ii) the
Timescape model. Furthermore, this methodology can be applied to any
cosmological model. In agreement with previous results we find that in
combination with SIS parameters, models with zero FLRW spatial curvature fit
better as the free parameter approaches an unphysical empty universe,
$\Omega_{\rm M0}\to0$. By contrast, the Timescape cosmology is found to prefer
parameter values in which its cosmological parameter, the present void
fraction, is driven to $f_{\rm v0}\to0.73$ matches, close to values found to
best fit independent cosmological data sets: supernovae Ia distances and cosmic
microwave background. This conclusion holds for a large range of seed values
$f_{\rm v0}\to0.73\in\{0.1,0.9\}$, and for Timescape fits to both Timescape and
FLRW mocks. Regardless of cosmology, unphysical estimates of the distance
ratios given from power-law lens models result in poor goodness of fit.
Nonetheless, the results are consistent with non-FLRW spatial curvature
evolution. |
Evolution in the Continuum Morphological Properties of
Lyman-Alpha-Emitting Galaxies from z=3.1 to z=2.1: We present a rest-frame ultraviolet morphological analysis of 108 z=2.1 Lyman
Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and
compare it to a similar sample of 171 LAEs at z=3.1. Using Hubble Space
Telescope (HST) images from the Galaxy Evolution from Morphology and SEDs
survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we
measure size and photometric component distributions, where photometric
components are defined as distinct clumps of UV-continuum emission. At both
redshifts, the majority of LAEs have observed half-light radii <~ 2 kpc, but
the median half-light radius rises from 1.0 kpc at z=3.1 to 1.4 kpc at z=2.1. A
similar evolution is seen in the sizes of individual rest-UV components, but
there is no evidence for evolution in the number of multi-component systems. In
the z=2.1 sample, we see clear correlations between the size of an LAE and
other physical properties derived from its SED. LAEs are found to be larger for
galaxies with higher stellar mass, star formation rate, and dust obscuration,
but there is no evidence for a trend between equivalent width and half-light
radius at either redshift. The presence of these correlations suggests that a
wide range of objects are being selected by LAE surveys at z~2, including a
significant fraction of objects for which a massive and moderately extended
population of old stars underlies the young starburst giving rise to the Lyman
alpha emission. | Comparing weak lensing peak counts in baryonic correction models to
hydrodynamical simulations: Next-generation weak lensing (WL) surveys, such as by the Vera Rubin
Observatory's LSST, the $\textit{Roman}$ Space Telescope, and the
$\textit{Euclid}$ space mission, will supply vast amounts of data probing
small, highly nonlinear scales. Extracting information from these scales
requires higher-order statistics and the controlling of related systematics
such as baryonic effects. To account for baryonic effects in cosmological
analyses at reduced computational cost, semi-analytic baryonic correction
models (BCMs) have been proposed. Here, we study the accuracy of BCMs for WL
peak counts, a well studied, simple, and effective higher-order statistic. We
compare WL peak counts generated from the full hydrodynamical simulation
IllustrisTNG and a baryon-corrected version of the corresponding dark
matter-only simulation IllustrisTNG-Dark. We apply galaxy shape noise expected
at the depths reached by DES, KiDS, HSC, LSST, $\textit{Roman}$, and
$\textit{Euclid}$. We find that peak counts in BCMs are (i) accurate at the
percent level for peaks with $\mathrm{S/N}<4$, (ii) statistically
indistinguishable from IllustrisTNG in most current and ongoing surveys, but
(iii) insufficient for deep future surveys covering the largest solid angles,
such as LSST and $\textit{Euclid}$. We find that BCMs match individual peaks
accurately, but underpredict the amplitude of the highest peaks. We conclude
that existing BCMs are a viable substitute for full hydrodynamical simulations
in cosmological parameter estimation from beyond-Gaussian statistics for
ongoing and future surveys with modest solid angles. For the largest surveys,
BCMs need to be refined to provide a more accurate match, especially to the
highest peaks. |
21 cm cosmology and spin temperature reduction via spin-dependent dark
matter interactions: The EDGES low-band experiment has measured an absorption feature in the
cosmic microwave background radiation (CMB), corresponding to the 21 cm
hyperfine transition of hydrogen at redshift $z \simeq 17$, before the era of
cosmic reionization. The amplitude of this absorption is connected to the ratio
of singlet and triplet hyperfine states in the hydrogen gas, which can be
parametrized by a spin temperature. The EDGES result suggests that the spin
temperature is lower than the expected temperatures of both the CMB and the
hydrogen gas. A variety of mechanisms have been proposed in order to explain
this signal, for example by lowering the kinetic temperature of the hydrogen
gas via dark matter interactions. We introduce an alternative mechanism, by
which a sub-GeV dark matter particle with spin-dependent coupling to nucleons
or electrons can cause hyperfine transitions and lower the spin temperature
directly, with negligible reduction of the kinetic temperature of the hydrogen
gas. We consider a model with an asymmetric dark matter fermion and a light
pseudo-vector mediator. Significant reduction of the spin temperature by this
simple model is excluded, most strongly by coupling constant bounds coming from
stellar cooling. Perhaps an alternative dark sector model, subject to different
sets of constraints, can lower the spin temperature by the same mechanism. | Apparent evidence for Hawking points in the CMB Sky: This paper presents strong observational evidence of numerous previously
unobserved anomalous circular spots, of significantly raised temperature, in
the CMB sky. The spots have angular radii between 0.03 and 0.04 radians (i.e.
angular diameters between about 3 and 4 degrees). There is a clear cut-off at
that size, indicating that each anomalous spot would have originated from a
highly energetic point-like source, located at the end of inflation -- or else
point-like at the conformally expanded Big Bang, if it is considered that there
was no inflationary phase. The significant presence of these anomalous spots,
was initially noticed in the Planck 70 GHz satellite data by comparison with
1000 standard simulations, and then confirmed by extending the comparison to
10000 simulations. Such anomalous points were then found at precisely the same
locations in the WMAP data, their significance confirmed by comparison with
1000 WMAP simulations. Planck and WMAP have very different noise properties and
it seems exceedingly unlikely that the observed presence of anomalous points in
the same directions on both maps may come entirely from the noise.
Subsequently, further confirmation was found in the Planck data by comparison
with 1000 FFP8.1 MC simulations (with $l \leq 1500$). The existence of such
anomalous regions, resulting from point-like sources at the conformally
stretched-out big bang, is a predicted consequence of conformal cyclic
cosmology (CCC), these sources being the Hawking points of the theory,
resulting from the Hawking radiation from supermassive black holes in a cosmic
aeon prior to our own. |
In-in and $δN$ calculations of the bispectrum from non-attractor
single-field inflation: In non-attractor single-field inflation models producing a scale-invariant
power spectrum, the curvature perturbation on super-horizon scales grows as
${\cal R}\propto a^3$. This is so far the only known class of self-consistent
single-field models with a Bunch-Davies initial state that can produce a large
squeezed-limit bispectrum violating Maldacena's consistency relation. Given the
importance of this result, we calculate the bispectrum with three different
methods: using quantum field theory calculations in two different gauges, and
classical calculations (the $\delta N$ formalism). All the results agree,
giving the local-form bispectrum parameter of
$f^{local}_{NL}=5(1+c_s^2)/(4c_s^2)$. This result is valid for arbitrary values
of the speed of sound parameter, $c_s$, for a particular non-attractor model we
consider in this paper. | Indirect Detection of Decaying Dark Matter with High Angular Resolution:
Case for axion search by IRCS at Subaru Telescope: Recent advances in cosmic-ray detectors have provided exceptional
sensitivities of dark matter with high angular resolution. Motivated by this,
we present a comprehensive study of cosmic-ray flux from dark matter decay in
dwarf spheroidal galaxies (dSphs), with a focus on detectors possessing
arcsecond-level field of view and/or angular resolution. We propose to use
differential $D$-factors, which are estimated for various dSphs since such
detectors are sensitive to their dark matter distributions. Our findings reveal
that the resulting signal flux can experience a more than $O$(1-10) enhancement
with different theoretical uncertainty compared to traditional estimations.
Based on this analysis, we find that the Infrared Camera and Spectrograph
(IRCS) installed on the 8.2m Subaru telescope can be a good dark matter
detector for the mass in the eV range, particularly axion-like particles
(ALPs). Observing the Draco or Ursa Major II galaxies with the IRCS for just a
few nights will be sufficient to surpass the stellar cooling bounds for ALP
dark matter with a mass in the range of $1\,{\rm eV} \lesssim m_a \lesssim
2\,\rm eV$. |
Information Gain on Reheating: the One Bit Milestone: We show that the Planck 2015 and BICEP2/KECK measurements of the Cosmic
Microwave Background (CMB) anisotropies provide together an information gain of
0.82 +- 0.13 bits on the reheating history over all slow-roll single-field
models of inflation. This corresponds to a 40% improvement compared to the
Planck 2013 constraints on the reheating. Our method relies on an exhaustive
CMB data analysis performed over nearly 200 models of inflation to derive the
Kullback-Leibler entropy between the prior and the fully marginalized posterior
of the reheating parameter. This number is a weighted average by the Bayesian
evidence of each model to explain the data thereby ensuring its fairness and
robustness. | Fast emulation of cosmological density fields based on dimensionality
reduction and supervised machine-learning: N-body simulations are the most powerful method to study the non-linear
evolution of large-scale structure. However, they require large amounts of
computational resources, making unfeasible their direct adoption in scenarios
that require broad explorations of parameter spaces. In this work, we show that
it is possible to perform fast dark matter density field emulations with
competitive accuracy using simple machine-learning approaches. We build an
emulator based on dimensionality reduction and machine learning regression
combining simple Principal Component Analysis and supervised learning methods.
For the estimations with a single free parameter, we train on the dark matter
density parameter, $\Omega_m$, while for emulations with two free parameters,
we train on a range of $\Omega_m$ and redshift. The method first adopts a
projection of a grid of simulations on a given basis; then, a machine learning
regression is trained on this projected grid. Finally, new density cubes for
different cosmological parameters can be estimated without relying directly on
new N-body simulations by predicting and de-projecting the basis coefficients.
We show that the proposed emulator can generate density cubes at non-linear
cosmological scales with density distributions within a few percent compared to
the corresponding N-body simulations. The method enables gains of three orders
of magnitude in CPU run times compared to performing a full N-body simulation
while reproducing the power spectrum and bispectrum within $\sim 1\%$ and $\sim
3\%$, respectively, for the single free parameter emulation and $\sim 5\%$ and
$\sim 15\%$ for two free parameters. This can significantly accelerate the
generation of density cubes for a wide variety of cosmological models, opening
the doors to previously unfeasible applications, such as parameter and model
inferences at full survey scales as the ESA/NASA Euclid mission. |
Seeding primordial black holes in multifield inflation: The inflationary origin of primordial black holes (PBHs) relies on a large
enhancement of the power spectrum $\Delta_\zeta$ of the curvature fluctuation
$\zeta$ at wavelengths much shorter than those of the cosmic microwave
background anisotropies. This is typically achieved in models where $\zeta$
evolves without interacting significantly with additional (isocurvature) scalar
degrees of freedom. However, quantum gravity inspired models are characterized
by moduli spaces with highly curved geometries and a large number of scalar
fields that could vigorously interact with $\zeta$ (as in the cosmological
collider picture). Here we show that isocurvature fluctuations can mix with
$\zeta$ inducing large enhancements of its amplitude. This occurs whenever the
inflationary trajectory experiences rapid turns in the field space of the model
leading to amplifications that are exponentially sensitive to the total angle
swept by the turn, which induce characteristic observable signatures on
$\Delta_\zeta$. We derive accurate analytical predictions and show that the
large enhancements required for PBHs demand non-canonical kinetic terms in the
action of the multifield system. | Enhanced Preheating after Multi-Field Inflation: On the Importance of
being Special: We discuss preheating after multi-field inflation in the presence of several
preheat matter fields that become light in the vicinity of (but not at) the
inflatons' VEV, at distinct extra-species-points (ESP); this setup is motivated
by inflationary models that include particle production during inflation,
e.g.trapped inflation, grazing ESP encounters or modulated trapping, among
others. While de-phasing of inflatons tends to suppress parametric resonance,
we find two new effects leading to efficient preheating: particle production
during the first in-fall (efficient if many preheat matter fields are present)
and a subsequent (narrow) resonance phase (efficient if an ESP happens to be at
one of several distinct distances from the inflatons' VEV). Particles produced
during the first in-fall are comprised of many species with low occupation
number, while the latter are made up of a few species with high occupation
number.
We provide analytic descriptions of both phases in the absence of
back-reaction, which we test numerically. We further perform lattice
simulations to investigate the effects of back-reaction. We find resonances to
be robust and the most likely cause of inflaton decay in multi-field trapped
inflation if ESP distributions are dense. |
The SDSS Coadd: A Galaxy Photometric Redshift Catalog: We present and describe a catalog of galaxy photometric redshifts (photo-z's)
for the Sloan Digital Sky Survey (SDSS) Coadd Data. We use the Artificial
Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor
Error (NNE) method to estimate photo-z errors for $\sim$ 13 million objects
classified as galaxies in the coadd with $r < 24.5$. The photo-z and photo-z
error estimators are trained and validated on a sample of $\sim 83,000$
galaxies that have SDSS photometry and spectroscopic redshifts measured by the
SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology
Field Galaxy Survey (CNOC2), the Deep Extragalactic Evolutionary Probe Data
Release 3(DEEP2 DR3), the VIsible imaging Multi-Object Spectrograph - Very
Large Telescope Deep Survey (VVDS) and the WiggleZ Dark Energy Survey. For the
best ANN methods we have tried, we find that 68% of the galaxies in the
validation set have a photo-z error smaller than $\sigma_{68} =0.031$. After
presenting our results and quality tests, we provide a short guide for users
accessing the public data. | An Empirical Model for the Star Formation History in Dark Matter Halos: We develop an empirical approach to infer the star formation rate in dark
matter halos from the galaxy stellar mass function (SMF) at different redshifts
and the local cluster galaxy luminosity function (CGLF), which has a steeper
faint end relative to the SMF of local galaxies. As satellites are typically
old galaxies which have been accreted earlier, this feature can cast important
constraint on the formation of low-mass galaxies at high-redshift. The
evolution of the SMFs suggests the star formation in high mass halos
($>10^{12}M_{\odot}h^{-1}$) has to be boosted at high redshift beyond what is
expected from a simple scaling of the dynamical time. The faint end of the CGLF
implies a characteristic redshift $z_c\approx2$ above which the star formation
rate in low mass halos with masses $< 10^{11}M_{\odot}h^{-1}$ must be enhanced
relative to that at lower z. This is not directly expected from the standard
stellar feedback models. Also, this enhancement leads to some interesting
predictions, for instance, a significant old stellar population in present-day
dwarf galaxies with $M_* < 10^8 M_{\odot}h^{-2}$ and steep slopes of high
redshift stellar mass and star formation rate functions. |
Note on galaxy catalogues in UHECR flux modelling: We consider the dependence of ultra-high energy cosmic ray (UHECR) flux
predictions on the choice of galaxy catalogue. We demonstrate that model
predictions by Koers & Tinyakov (2009b), based on the so-called KKKST
catalogue, are in good agreement with predictions based on the XSCz catalogue,
a recently compiled catalogue that contains spectroscopic redshifts for a large
fraction of galaxies. This agreement refutes the claim by Kashti (2009) that
the KKKST catalogue is not suited for studies of UHECR anisotropy due to its
dependence on photometric redshift estimates. In order to quantify the effect
of galaxy catalogues on flux predictions, we develop a measure of anisotropies
associated with model flux maps. This measure offers a general criterion to
study the effect of model parameters and assumptions on the predicted strength
of UHECR anisotropies. | Evolution of the X-ray Profiles of Poor Clusters from the XMM-LSS Survey: A sample consisting of 27 X-ray selected galaxy clusters from the XMM-LSS
survey is used to study the evolution in the X-ray surface brightness profiles
of the hot intracluster plasma. These systems are mostly groups and poor
clusters, with temperatures 0.6-4.8 keV, spanning the redshift range 0.05 to
1.05. Comparing the profiles with a standard beta-model motivated by studies of
low redshift groups, we find 54% of our systems to possess a central excess,
which we identify with a cuspy cool core. Fitting beta-model profiles, allowing
for blurring by the XMM point spread function, we investigate trends with both
temperature and redshift in the outer slope (beta) of the X-ray surface
brightness, and in the incidence of cuspy cores. Fits to individual cluster
profiles and to profiles stacked in bands of redshift and temperature indicate
that the incidence of cuspy cores does not decline at high redshifts, as has
been reported in rich clusters. Rather such cores become more prominent with
increasing redshift. Beta shows a positive correlation with both redshift and
temperature. Given the beta-T trend seen in local systems, we assume that
temperature is the primary driver for this trend. Our results then demonstrate
that this correlation is still present at z~0.3, where most of our clusters
reside. |
Reconstructing the triaxiality of the galaxy cluster Abell 1689: solving
the X-ray and strong lensing mass discrepancy: We present the first determination of the intrinsic triaxial shapes and
tree-dimensional physical parameters of both dark matter (DM) and intra-cluster
medium (ICM) for the galaxy cluster Abell 1689. We exploit the novel method we
recently introduced (Morandi et al. 2010) in order to infer the
tree-dimensional physical properties in triaxial galaxy clusters by combining
jointly X-ray and strong lensing data. We find that Abell 1689 can be modeled
as a triaxial galaxy cluster with DM halo axial ratios 1.24 +/- 0.13 and 2.37
+/- 0.11 on the plane of the sky and along the line of sight, respectively. We
show that accounting for the three-dimensional geometry allows to solve the
discrepancy between the mass determined from X-ray and strong gravitational
lensing observations. We also determined the inner slope of the DM density
profile alpha: we measure alpha = 0.90 +/- 0.05 by accounting explicitly for
the 3D structure for this cluster, a value which is close to the cold dark
matter (CDM) predictions, while the standard spherical modeling leads to the
biased value alpha = 1.16 +/- 0.04. Our findings dispel the potential
inconsistencies arisen in the literature between the predictions of the CDM
scenario and the observations, providing further evidences that support the CDM
scenario. | A low-luminosity type-1 QSO sample - A morphological study of nearby AGN
hosts: There is growing evidence that every galaxy with a considerable spheroidal
component hosts a supermassive black hole (SMBH) at its center. Strong
correlations between the SMBH and the spheroidal component suggest a physical
connection through a coevolutionary scenario. For very massive galaxies a
merger-driven scenario is preferred, resulting in elliptical galaxies. In the
nearby universe, we find many disk galaxies, showing no signs of recent
interaction. Alternative secular evolutionary scenarios for such galaxies
involve internal triggers like bars and spiral arms or minor mergers. We
analyze a sample of 99 nearby galaxies (0.02 < z < 0.06) from the Hamburg/ESO
survey in order to get insight into structural and dynamical properties of the
hosts to trace the origin of the bulge-SMBH correlation. In this work, we first
collect images of sample members to get an impression of the morphological
distribution in the sample. In a second step, we start to analyze sensitive,
high resolution near-infrared images of 20 galaxies, performing aperture
photometry and bulge-disk decomposition with the BUDDA code. We find an
unexpected high fraction of barred galaxies and many other structural
peculiarities. |
Infrared Surface Brightness Fluctuation Distances for MASSIVE and Type
Ia Supernova Host Galaxies: We measured high-quality surface brightness fluctuation (SBF) distances for a
sample of 63 massive early-type galaxies using the WFC3/IR camera on the Hubble
Space Telescope. The median uncertainty on the SBF distance measurements is
0.085 mag, or 3.9% in distance. Achieving this precision at distances of 50 to
100 Mpc required significant improvements to the SBF calibration and data
analysis procedures for WFC3/IR data. Forty-two of the galaxies are from the
MASSIVE Galaxy Survey, a complete sample of massive galaxies within ~100 Mpc;
the SBF distances for these will be used to improve the estimates of the
stellar and central supermassive black hole masses in these galaxies.
Twenty-four of the galaxies are Type Ia supernova hosts, useful for calibrating
SN Ia distances for early-type galaxies and exploring possible systematic
trends in the peak luminosities. Our results demonstrate that the SBF method is
a powerful and versatile technique for measuring distances to galaxies with
evolved stellar populations out to 100 Mpc and constraining the local value of
the Hubble constant. | Uncovering delayed patterns in noisy and irregularly sampled time
series: an astronomy application: We study the problem of estimating the time delay between two signals
representing delayed, irregularly sampled and noisy versions of the same
underlying pattern. We propose and demonstrate an evolutionary algorithm for
the (hyper)parameter estimation of a kernel-based technique in the context of
an astronomical problem, namely estimating the time delay between two
gravitationally lensed signals from a distant quasar. Mixed types (integer and
real) are used to represent variables within the evolutionary algorithm. We
test the algorithm on several artificial data sets, and also on real
astronomical observations of quasar Q0957+561. By carrying out a statistical
analysis of the results we present a detailed comparison of our method with the
most popular methods for time delay estimation in astrophysics. Our method
yields more accurate and more stable time delay estimates: for Q0957+561, we
obtain 419.6 days for the time delay between images A and B. Our methodology
can be readily applied to current state-of-the-art optical monitoring data in
astronomy, but can also be applied in other disciplines involving similar time
series data. |
WIMP astronomy and particle physics with liquid-noble and cryogenic
direct-detection experiments: Once weakly-interacting massive particles (WIMPs) are unambiguously detected
in direct-detection experiments, the challenge will be to determine what one
may infer from the data. Here, I examine the prospects for reconstructing the
local speed distribution of WIMPs in addition to WIMP particle-physics
properties (mass, cross sections) from next-generation cryogenic and
liquid-noble direct-detection experiments. I find that the common method of
fixing the form of the velocity distribution when estimating constraints on
WIMP mass and cross sections means losing out on the information on the speed
distribution contained in the data and may lead to biases in the inferred
values of the particle-physics parameters. I show that using a more general,
empirical form of the speed distribution can lead to good constraints on the
speed distribution. Moreover, one can use Bayesian model-selection criteria to
determine if a theoretically-inspired functional form for the speed
distribution (such as a Maxwell-Boltzmann distribution) fits better than an
empirical model. The shape of the degeneracy between WIMP mass and cross
sections and their offset from the true values of those parameters depends on
the hypothesis for the speed distribution, which has significant implications
for consistency checks between direct-detection and collider data. In addition,
I find that the uncertainties on theoretical parameters depends sensitively on
the upper end of the energy range used for WIMP searches. Better constraints on
the WIMP particle-physics parameters and speed distribution are obtained if the
WIMP search is extended to higher energy (~ 1 MeV). | Primordial Spikes from Wrapped Brane Inflation: Cosmic inflation driven by branes wrapping the extra dimensions involves
Kaluza-Klein (KK) degrees of freedom in addition to the zero-mode position of
the brane which plays the role of the inflaton. As the wrapped brane passes by
localized sources or features along its inflationary trajectory in the extra
dimensional space, the KK modes along the wrapped direction are excited and
start to oscillate during inflation. We show that the oscillating KK modes
induce parametric resonance for the curvature perturbations, generating sharp
signals in the perturbation spectrum. The effective four dimensional picture is
a theory where the inflaton couples to the heavy KK modes. The Nambu-Goto
action of the brane sources couplings between the inflaton kinetic terms and
the KK modes, which trigger significant resonant amplification of the curvature
perturbations. We find that the strong resonant effects are localized to narrow
wave number ranges, producing spikes in the perturbation spectrum.
Investigation of such resonant signals opens up the possibility of probing the
extra dimensional space through cosmological observations. |
Cosmic voids and the kinetic analysis. III. Hubble tension and structure
formation in the late Universe: We study structure formation in the late Universe within the Vlasov kinetic
self-consistent field approach. Our work is principally focused on the use of
the modified gravitational potential with a repulsive term of the cosmological
constant, which is directly linked to observations that enable
characterizations of the Hubble tension as the result of local and global
flows. We formulate the criteria for the formation of the semi-periodic
gravitating structures, along with the predictions of their quantitative scales
associated with observable parameters. Our principal conclusion is that
filament formation in the Local (late) Universe can proceed as a deterministic
process that is distinct from the structures at larger scales that result from
the essentially stochastic dynamics of density perturbations. | Measuring patchy reionisation with kSZ$^2$-21 cm correlations: We study cross-correlations of the kinetic Sunyaev-Zel'dovich effect (kSZ)
and 21 cm signals during the epoch of reionisation (EoR) to measure the effects
of patchy reionisation. Since the kSZ effect is proportional to the
line-of-sight velocity, the kSZ-21 cm cross correlation suffers from
cancellation at small angular scales. We thus focus on the correlation between
the kSZ-squared field (kSZ$^2$) and 21 cm signals. When the global ionisation
fraction is low ($x_e\lesssim 0.7$), the kSZ$^2$ fluctuation is dominated by
rare ionised bubbles which leads to an anti-correlation with the 21 cm signal.
When $0.8\lesssim x_e<1$, the correlation is dominated by small pockets of
neutral regions, leading to a positive correlation. However, at very high
redshifts when $x_e<0.15$, the spin temperature fluctuations change the sign of
the correlation from negative to positive, as weakly ionised regions can have
strong 21 cm signals in this case. To extract this correlation, we find that
Wiener filtering is effective in removing large signals from the primary CMB
anisotropy. The expected signal-to-noise ratios for a $\sim$10-hour integration
of upcoming Square Kilometer Array data cross-correlated with maps from the
current generation of CMB observatories with 3.4~$\mu$K arcmin noise and
1.7~arcmin beam over 100~deg$^2$ are 51, 60, and 37 for $x_e=0.2$, 0.5, and
0.9, respectively. |
Non-linear damping of superimposed primordial oscillations on the matter
power spectrum in galaxy surveys: Galaxy surveys are an important probe for superimposed oscillations on the
primordial power spectrum of curvature perturbations, which are predicted in
several theoretical models of inflation and its alternatives. In order to
exploit the full cosmological information in galaxy surveys it is necessary to
study the matter power spectrum to fully non-linear scales. We therefore study
the non-linear clustering in models with superimposed linear and logarithmic
oscillations to the primordial power spectrum by running high-resolution
dark-matter-only N-body simulations. We fit a Gaussian envelope for the
non-linear damping of superimposed oscillations in the matter power spectrum to
the results of the N-body simulations for $k \lesssim 0.6\ h/$Mpc at $0 \leq z
\leq 5$ with an accuracy below the percent. We finally use this fitting formula
to forecast the capabilities of future galaxy surveys, such as Euclid and
Subaru, to probe primordial oscillation down to non-linear scales alone and in
combination with the information contained in CMB anisotropies. | Study of the structure and kinematics of the NGC 7465/64/63 triplet
galaxies: This paper is devoted to the analysis of new observational data for the group
of galaxies NGC 7465/64/63, which were obtained at the 6-m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS)
with the multimode instrument SCORPIO and the Multi Pupil Fiber Spectrograph.
For one of group members (NGC 7465) the presence of a polar ring was suspected.
Large-scale brightness distributions, velocity and velocity dispersion fields
of the ionized gas for all three galaxies as well as line-of-sight velocity
curves on the basis of emission and absorption lines and a stellar velocity
field in the central region for NGC 7465 were constructed. As a result of the
analysis of the obtained information, we revealed an inner stellar disk (r ~
0.5 kpc) and a warped gaseous disk in addition to the main stellar disk, in NGC
7465. On the basis of the joint study of photometric and spectral data it was
ascertained that NGC 7464 is the irregular galaxy of the IrrI type, whose
structural and kinematic peculiarities resulted most likely from the
gravitational interaction with NGC 7465. The velocity field of the ionized gas
of NGC 7463 turned out typical for spiral galaxies with a bar, and the bending
of outer parts of its disk could arise owing to the close encounter with one of
galaxies of the environment. |
Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon
Escape Fraction: We explore scenarios for reionizing the intergalactic medium with low galaxy
ionizing photon escape fractions. We combine simulation-based halo-mass
dependent escape fractions with an extrapolation of the observed galaxy
rest-ultraviolet luminosity functions to solve for the reionization history
from z=20 to z=4. We explore the posterior distributions for key unknown
quantities, including the limiting halo mass for star-formation, the ionizing
photon production efficiency, and a potential contribution from active galactic
nuclei (AGN). We marginalize over the allowable parameter space using a Markov
Chain Monte Carlo method, finding a solution which satisfies the most
model-independent constraints on reionization. Our fiducial model can match
observational constraints with an average escape fraction of <5% throughout the
bulk of the epoch of reionization if: i) galaxies form stars down to the atomic
cooling limit before reionization and a photosuppression mass of
log(M_h/Msol)~9 during/after reionization (-13<M_UV,lim<-11); ii) galaxies
become more efficient producers of ionizing photons at higher redshifts and
fainter magnitudes, and iii) there is a significant, but sub-dominant,
contribution by AGN at z < 7. In this model the faintest galaxies (M_UV>-15)
dominate the ionizing emissivity, leading to an earlier start to reionization
and a smoother evolution of the ionized volume filling fraction than models
which assume a single escape fraction at all redshifts and luminosities. The
ionizing emissivity from this model is consistent with observations at z=4-5
(and below, when extrapolated), in contrast to some models which assume a
single escape fraction. Our predicted ionized volume filling fraction at z=7 of
Q_HII=78% (+\- 8%) is in ~1-2 sigma tension with observations of Lya emitters
at z~7 and the damping wing analyses of the two known z>7 quasars, which prefer
Q_HII,z=7~40-50%. | Lensed Type Ia Supernovae as Probes of Cluster Mass Models: Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH
clusters, we perform a first pilot study to see whether standardizable candles
can be used to calibrate cluster mass maps created from strong lensing
observations. Such calibrations will be crucial when next generation HST
cluster surveys (e.g. FRONTIER) provide magnification maps that will, in turn,
form the basis for the exploration of the high redshift Universe. We classify
SNe using combined photometric and spectroscopic observations, finding two of
the three to be clearly of type SN Ia and the third probable. The SNe exhibit
significant amplification, up to a factor of 1.7 at $\sim5\sigma$ significance
(SN-L2). We conducted this as a blind study to avoid fine tuning of parameters,
finding a mean amplification difference between SNe and the cluster lensing
models of $0.09 \pm 0.09^{stat} \pm 0.05^{sys}$ mag. This impressive agreement
suggests no tension between cluster mass models and high redshift standardized
SNe Ia. However, the measured statistical dispersion of $\sigma_{\mu}=0.21$ mag
appeared large compared to the dispersion expected based on statistical
uncertainties ($0.14$). Further work with the supernova and cluster lensing
models, post unblinding, reduced the measured dispersion to
$\sigma_{\mu}=0.12$. An explicit choice should thus be made as to whether SNe
are used unblinded to improve the model, or blinded to test the model. As the
lensed SN samples grow larger, this technique will allow improved constraints
on assumptions regarding e.g. the structure of the dark matter halo. |
On the origin and acceleration of cosmic rays: Cooling flow clusters and
AGN hosts: We are looking for radio `relics' and `halos' in an X-ray selected sample of
clusters of galaxies. These radio features are not a product of the Active
Galactic Nuclei (AGN)-mechanism, but more likely are associated with past
cluster merger events. AGN hosts of cooling flow clusters contain particle
bubbles that show non-thermal radio emission. These bubbles could explain the
presence of radio relics and halos if they can restrict cosmic rays
efficiently. Intracluster magnetic fields and cluster environments can reveal
the acceleration mechanisms of cosmic rays. Using radio/X-ray data and
analytical methods we examine three AGN hosts out of our 70 clusters, namely
Hercules A, 3C310 and 3C388. We found that none of these clusters contain
relics and/or halos. | Cross-correlation between Subaru Hyper Suprime-Cam Galaxy Weak Lensing
and Planck Cosmic Microwave Background Lensing: Cross-correlations between galaxy weak lensing (WL) and Cosmic Microwave
Background (CMB) lensing are a powerful tool to probe matter fluctuations at
intermediate redshifts and to detect residual systematics in either probe. In
this paper, we study the cross-correlation of galaxy WL from the Hyper
Suprime-Cam Subaru Strategic Program (HSC) first data release and CMB lensing
from the final Planck data release, for HSC source galaxies at 0.3< z < 1.5.
HSC is the deepest Stage-III galaxy WL survey, and provides both a great
opportunity to study the high-redshift universe and new challenges related to
its exceptionally high source density, such as source blending. The
cross-correlation signal is measured at a significance level of 3.1$\sigma$.
The amplitude of our best-fit model with respect to the best-fit 2018 Planck
cosmology is $A = 0.81\pm 0.25$, consistent with $A=1$. Our result is also
consistent with previous CMB lensing and galaxy WL cross-correlation studies
using different surveys. We perform tests with respect to the WL $B$-modes, the
point-spread-function, photometric redshift errors, and thermal
Sunyaev-Zel'dovich leakage, and find no significant evidence of residual
systematics. |
Extraplanar Dust in Spiral Galaxies: Tracing Outflows in the Disk-Halo
Interface: There is now ample evidence that the interstellar thick disks of spiral
galaxies are dusty. Although the majority of extraplanar gas in the first few
kiloparsecs above the plane of a spiral galaxy is matter that has been expelled
from the thin disk, the feedback-driven expulsion does not destroy dust grains
altogether (and there is not yet any good measure suggesting it changes the
dust-to-gas mass ratio). Direct optical imaging of a majority of edge-on spiral
galaxies shows large numbers of dusty clouds populating the thick disk to
heights z~2 kpc. These observations are likely revealing a cold, dense phase of
the thick disk interstellar medium. New observations in the mid-infrared show
emission from traditional grains and polycyclic aromatic hydrocarbons (PAHs) in
the thick disks of spiral galaxies. PAHs are found to have large scale heights
and to arise both in the dense dusty clouds traced through direct optical
imaging and in the diffuse ionized gas. In this contribution, we briefly
summarize these probes of dust in the thick disks of spiral galaxies. We also
argue that not only can dust can be used to trace extraplanar material that has
come from within the thick disk, but that its absence can be a marker for newly
accreted matter from the circumgalactic or intergalactic medium. Thus,
observations of dust can perhaps provide a quantitative measure of the
importance of "outflow versus infall" in spiral galaxies. | Exploring neutrino mass and mass hierarchy in interacting dark energy
models: We investigate how the dark energy properties impact the constraints on the
total neutrino mass in interacting dark energy (IDE) models. In this study, we
focus on two typical interacting dynamical dark energy models, i.e., the
interacting $w$ cold dark matter (I$w$CDM) model and the interacting
holographic dark energy (IHDE) model. To avoid the large-scale instability
problem in IDE models, we apply the parameterized post-Friedmann approach to
calculate the perturbation of dark energy. We employ the Planck 2015 cosmic
microwave background temperature and polarization data, combined with
low-redshift measurements on baryon acoustic oscillation distance scales, type
Ia supernovae, and the Hubble constant, to constrain the cosmological
parameters. We find that the dark energy properties could influence the
constraint limits on the total neutrino mass. Once dynamical dark energy is
considered in the IDE models, the upper bounds of $\sum m_\nu$ will be changed.
By considering the values of $\chi^2_{\rm min}$, we find that in these IDE
models the normal hierarchy case is slightly preferred over the inverted
hierarchy case; for example, $\Delta\chi^2=2.720$ is given in the IHDE+$\sum
m_\nu$ model. In addition, we also find that in the I$w$CDM+$\sum m_\nu$ model
$\beta=0$ is consistent with current observational data inside the 1$\sigma$
range, and in the IHDE+$\sum m_\nu$ model $\beta>0$ is favored at more than
2$\sigma$ level. |
The Dark Side of Using Dark Sirens to Constrain the Hubble-Lemaître
Constant: Dark sirens, i.e., gravitational-wave (GW) sources without electromagnetic
counterparts, are new probes of the expansion of the universe. The efficacy of
this method relies on correctly localizing the host galaxies. However, recent
theoretical studies have shown that astrophysical environments could mislead
the spatial localization by distorting the GW signals. It is unclear whether
and to what degree the incorrect spatial localizations of dark sirens would
impair the accuracy of the measurement of the cosmological parameters. To
address this issue, we consider the future observations of dark sirens using
the Cosmic Explorer and the Einstein Telescope, and we design a Bayesian
framework to access the precision of measuring the Hubble-Lema\^itre constant
$H_0$. Interestingly, we find that the precision is not compromised when the
number of well-localized dark sirens is significantly below $300$, even in the
extreme scenario that all the dark sirens are localized incorrectly. As the
number exceeds $300$, the incorrect spatial localizations start to produce
statistically noticeable effects, such as a slow convergence of the posterior
distribution of $H_0$. We propose several tests that can be used in future
observations to verify the spatial localizations of dark sirens. Simulations of
these tests suggest that incorrect spatial localizations will dominate a
systematic error of $H_0$ if as much as $10\%$ of a sample of $300$
well-localized dark sirens are affected by their environments. Our results have
important implications for the long-term goal of measuring $H_0$ to a precision
of $<1\%$ using dark sirens. | The art of building a smooth cosmic distance ladder in a perturbed
universe: How does a smooth cosmic distance ladder emerge from observations made from a
single location in a lumpy Universe? Distances to Type Ia supernovae in the
Hubble flow are anchored on local distance measurements to sources that are
very nearby. We described how this configuration could be built in a perturbed
universe where lumpiness is described as small perturbations on top of a flat
Friedmann-Lema{\i}tre Robertson-Walker spacetime. We show that there is a
non-negligible modification (about 11\%) to the background
Friedmann-Lema{\i}tre Robertson-Walker area distance due to the presence of
inhomogeneities in the immediate neighbourhood of an observer. We find that the
modification is sourced by the electric part of the Weyl tensor indicating a
tidal deformation of the local spacetime of the observer. We show in detail how
it could impact the calibration of the Type Ia supernova absolute magnitude in
the Hubble flow. We show that it could potentially resolve the Type Ia
supernova absolute magnitude and Hubble tensions simultaneously without the
need for early or late dark energy. |
Measuring cosmological parameters with a luminosity-time correlation of
gamma-ray bursts: Gamma-ray bursts (GRBs), as a possible probe to extend the Hubble diagram to
high redshifts, have attracted much attention recently. In this paper, we
select two samples of GRBs that have a plateau phase in X-ray afterglow. One is
short GRBs with plateau phases dominated by magnetic dipole (MD) radiations.
The other is long GRBs with gravitational-wave (GW) dominated plateau phases.
These GRBs can be well standardized using the correlation between the plateau
luminosity $L_0$ and the end time of plateau $t_b$. The so-called circularity
problem is mitigated by using the observational Hubble parameter data and
Gaussian process method. The calibrated \ltb ~correlations are also used to
constrain $\Lambda$CDM and $w(z)$ = $w_{0}$ models. Combining the MD-LGRBs
sample from Wang et al. (2021) and the MD-SGRBs sample, we find $\Omega_{m} =
0.33_{-0.09}^{+0.06}$ and $\Omega_{\Lambda}$ = $1.06_{-0.34}^{+0.15}$ excluding
systematic uncertainties in the nonflat $\Lambda$CDM model. Adding type Ia
supernovae from Pantheon sample, the best-fitting results are $w_{0}$ =
$-1.11_{-0.15}^{+0.11}$ and $\Omega_{m}$ = $0.34_{-0.04}^{+0.05}$ in the
$w=w_0$ model. These results are in agreement with the $\Lambda$CDM model. Our
result supports that selection of GRBs from the same physical mechanism is
crucial for cosmological purposes. | On the nature of sub-millimetre galaxies: I discuss our current understanding of the nature of high-redshift (z > 2)
(sub)-millimetre-selected galaxies, with a particular focus on whether their
properties are representative of, or dramatically different from those
displayed by the general star-forming galaxy population at these epochs. As a
specific case study, I present some new results on the one sub-millimetre
galaxy which happens to lie within the Hubble Ultra Deep Field and thus
benefits from the very best available ultra-deep optical-infrared Hubble Space
Telescope and Spitzer Space Telescope imaging. I then consider what these and
other recent results from optical-infrared studies of sub-millimetre and
millimetre selected galaxies imply about their typical masses, sizes and
specific star-formation rates, and how these compare with those of other
star-forming galaxies selected at similar redshifts. I conclude with a brief
discussion of the continued importance and promise of SCUBA2 in the era of
Herschel. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS): A quiescent
formation of massive red-sequence galaxies over the past 9 Gyr: We explore the evolution of the Colour-Magnitude Relation (CMR) and
Luminosity Function (LF) at 0.4<z<1.3 from the VIMOS Public Extragalactic
Redshift Survey (VIPERS) using ~45,000 galaxies with precise spectroscopic
redshifts down to i'_AB<22.5 over ~10.32 deg^2 in two fields. From z=0.5 to
z=1.3 the LF and CMR are well defined for different galaxy populations and
M^*_B evolves by ~1.04(1.09)+/-0.06(0.10) mag for the total (red) galaxy
sample. We compare different criteria for selecting early-type galaxies (ETGs):
(1) fixed cut in rest-frame (U-V) colours, (2) evolving cut in (U-V) colours,
(3) rest-frame (NUV-r')-(r'-K) colour selection, and (4) SED classification.
Regardless of the method we measure a consistent evolution of the red-sequence
(RS). Between 0.4<z<1.3 we find a moderate evolution of the RS intercept of
Delta(U-V)=0.28+/-0.14 mag, favouring exponentially declining star formation
(SF) histories with SF truncation at 1.7<=z<=2.3. Together with the rise in the
ETG number density by 0.64 dex since z=1, this suggests a rapid build-up of
massive galaxies (M>10^11 M_sun) and expeditious RS formation over a short
period of ~1.5 Gyr starting before z=1. This is supported by the detection of
ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar
populations of ETGs at 0.5<z<0.6. There is an increase in the observed CMR
scatter with redshift, two times larger than in galaxy clusters and at variance
with theoretical models. We discuss possible physical mechanisms that support
the observed evolution of the red galaxy population. Our findings point out
that massive galaxies have experienced a sharp SF quenching at z~1 with only
limited additional merging. In contrast, less-massive galaxies experience a mix
of SF truncation and minor mergers which build-up the low- and
intermediate-mass end of the CMR. | Testing General Relativity using the Environmental Dependence of Dark
Matter Halos: In this Letter, we investigate the environmental dependence of dark matter
halos in theories that attempt to explain the accelerated expansion of the
Universe by modifying general relativity (GR). Using high-resolution N-body
simulations in f(R) gravity models which recover GR in dense environments by
virtue of the chameleon mechanism, we find a strong environmentally-dependent
difference between the lensing mass and dynamical mass estimates of dark matter
halos. This environmental dependence of the halo properties can be used as a
smoking gun to test GR observationally. |
Time variable cosmological constant of holographic origin with
interaction in Brans-Dicke theory: Time variable cosmological constant (TVCC) of holographic origin with
interaction in Brans-Dicke theory is discussed in this paper. We investigate
some characters for this model, and show the evolutions of deceleration
parameter and equation of state (EOS) for dark energy. It is shown that in this
scenario an accelerating universe can be obtained and the evolution of EOS for
dark energy can cross over the boundary of phantom divide. In addition, a
geometrical diagnostic method, jerk parameter is applied to this model to
distinguish it with cosmological constant. | Field-level inference of galaxy intrinsic alignment from the SDSS-III
BOSS survey: As a large-scale overdensity collapses, it affects the orientation and shape
of galaxies that form, by exerting tidal shear along their axes. Therefore, the
shapes of elliptical galaxies align with the tidal field of cosmic structures.
This intrinsic alignment provides insights into galaxy formation and the
primordial universe, complements late-time cosmological probes and constitutes
a significant systematic effect for weak gravitational lensing observations. In
the present study, we provide constraints on the linear alignment model using a
fully Bayesian field-level approach, using galaxy shape measurements from the
SDSS-III BOSS LOWZ sample and three-dimensional tidal fields constrained with
the LOWZ and CMASS galaxy samples of the SDSS-III BOSS survey. We find
4$\sigma$ evidence of intrinsic alignment, with an amplitude of $A_I=2.9 \pm
0.7$ at 20$h^{-1}\;\mathrm{Mpc}$. |
Discovery of a supercluster candidate at $z \sim 1.1$: We report a promising candidate for a distant supercluster at z $\sim 1.1$ in
the Dark Energy Survey Science Verification data. We examine smoothed semi-3D
galaxy density maps in various photo-z slices. Among several overdense regions,
in this work we report the most significant one as having a $3\sigma$
overdensity at a redshift of $\sim1.1$, over a $\sim160$ Mpc scale, much larger
than the regular cluster scale (several Mpc). The shape of the supercluster is
not circular in the sky projection. Therefore, we regard the point of maximum
overdensity as the center for quantitative measurements. Two different
estimates suggest the mass of the supercluster to be $1.37\substack{+1.31 \\
-0.79} \times 10^{17} M_{\odot}$, more than one order more massive than regular
galaxy clusters. Except for protosuperclusters found with emission-line
galaxies, this could be the most distant supercluster to date defined by
regular galaxies. A spectroscopic confirmation would make this a very
interesting object for cosmology. We discuss the possible implications of such
a massive structure for $\Lambda$CDM cosmology. | Molecular Gas Properties of the Giant Molecular Cloud Complexes in the
Arms and Inter-arms of the Spiral Galaxy NGC 6946: Combining observations of multiple CO lines with radiative transfer modeling
is a very powerful tool to investigate the physical properties of the molecular
gas in galaxies. Using new observations as well as literature data, we provide
the most complete CO ladders ever generated for eight star-forming regions in
the spiral arms and inter-arms of the spiral galaxy NGC 6946, with observations
of the CO(1-0), CO(2-1), CO(3-2), CO(4-3), CO(6-5), 13CO(1-0) and 13CO(2-1)
transitions. For each region, we use the large velocity gradient assumption to
derive beam-averaged molecular gas physical properties, namely the gas kinetic
temperature (T_K), H2 number volume density n(H2) and CO number column density
N(CO). Two complementary approaches are used to compare the observations with
the model predictions: chi-square minimisation and likelihood. The physical
conditions derived vary greatly from one region to the next: T_K=10-250 K,
n(H2)=10^2.3-10^7.0 cm^-3 and N(CO)=10^15.0-10^19.3 cm^-2. The spectral line
energy distribution (SLED) of some of these extranuclear regions indicates a
star-formation activity that is more intense than that at the centre of our own
Milky Way. The molecular gas in regions with a large SLED turnover transition
(J_max>4) is hot but tenuous with a high CO column density, while that in
regions with a low SLED turnover transition (J_max<=4) is cold but dense with a
low CO column density. We finally discuss and find some correlations between
the physical properties of the molecular gas in each region and the presence of
young stellar population indicators (supernova remnants, HII regions, HI holes,
etc.) |
Monitoring Quasar Colour Variability in Stripe 82: Broad Absorption Line (BAL) trough variability is predominantly due to cloud
motion transverse to our line of sight. The rate at which the variability
occurs indicates the velocity of the cloud, which can provide constraints on
the cloud's distance from the central source. This requires detailed
spectroscopy during a variability event. Such spectra have proven elusive,
suggesting either the timescale of variability is too short to be caught, or
too long to notice until a sufficient amount of time has passed. Photometric
monitoring of BAL quasar colours may potentially be used as an early warning
system to trigger time resolved spectroscopic monitoring of BAL variability.
Towards this end, we are analyzing both BAL and non-BAL colour variability
using time series photometry from Stripe 82 in the Sloan Digital Sky Survey. | Consistency of cosmic shear analyses in harmonic and real space: Recent cosmic shear studies have reported discrepancies of up to $1\sigma$ on
the parameter ${S_{8}=\sigma_{8}\sqrt{\Omega_{\rm m}/0.3}}$ between the
analysis of shear power spectra and two-point correlation functions, derived
from the same shear catalogs. It is not a priori clear whether the measured
discrepancies are consistent with statistical fluctuations. In this paper, we
investigate this issue in the context of the forthcoming analyses from the
third year data of the Dark Energy Survey (DES-Y3). We analyze DES-Y3 mock
catalogs from Gaussian simulations with a fast and accurate importance sampling
pipeline. We show that the methodology for determining matching scale cuts in
harmonic and real space is the key factor that contributes to the scatter
between constraints derived from the two statistics. We compare the published
scales cuts of the KiDS, Subaru-HSC and DES surveys, and find that the
correlation coefficients of posterior means range from over 80% for our
proposed cuts, down to 10% for cuts used in the literature. We then study the
interaction between scale cuts and systematic uncertainties arising from
multiple sources: non-linear power spectrum, baryonic feedback, intrinsic
alignments, uncertainties in the point-spread function, and redshift
distributions. We find that, given DES-Y3 characteristics and proposed cuts,
these uncertainties affect the two statistics similarly; the differential
biases are below a third of the statistical uncertainty, with the largest
biases arising from intrinsic alignment and baryonic feedback. While this work
is aimed at DES-Y3, the tools developed can be applied to Stage-IV surveys
where statistical errors will be much smaller. |
A multifrequency study of the large radio galaxies 3C46 and 3C452: We present low-frequency observations starting from ~150 MHz with the Giant
Metrewave Radio Telescope (GMRT), and high-frequency observations with the Very
Large Array (VLA) of two large radio galaxies 3C46 and 3C452. These
observations were made with the objectives of estimating their spectral ages
and examining any evidence of diffuse extended emission at low radio
frequencies due to an earlier cycle of activity. While no evidence of extended
emission due to an earlier cycle of activity has been found, the spectral ages
have been estimated to be ~15 and 27 Myr for the oldest relativistic plasma
seen in the regions close to the cores for 3C46 and 3C452 respectively. The
spectra in the vicinity of the hotspots are consistent with a straight spectrum
with injection spectral indices of ~1.0 and 0.78 respectively, somewhat steeper
than theoretical expectations. | Observational constraints on the energy scale of inflation: Determining the energy scale of inflation is crucial to understand the nature
of inflation in the early Universe. We place observational constraints on the
energy scale of the observable part of the inflaton potential by combining the
7-year Wilkinson Microwave Anisotropy Probe data with distance measurements
from the baryon acoustic oscillations in the distribution of galaxies and the
Hubble constant measurement. Our analysis provides an upper limit on this
energy scale, 2.3 \times 10^{16} GeV at 95% confidence level. Moreover, we
forecast the sensitivity and constraints achievable by the Planck experiment by
performing Monte Carlo studies on simulated data. Planck could significantly
improve the constraints on the energy scale of inflation and on the shape of
the inflaton potential. |
The ecology of dark matter haloes I: The rates and types of halo
interactions: Interactions such as mergers and flybys play a fundamental role in shaping
galaxy morphology. Using the Horizon Run 4 cosmological N-body simulation, we
studied the frequency and type of halo interactions, and their redshift
evolution as a function of the environment defined by the large-scale density,
pair separation, mass ratio, and target halo mass. Most interactions happen at
large-scale density contrast $\delta \approx 20$, regardless of the redshift,
corresponding to groups and relatively dense part of filaments. However, the
fraction of interacting target is maximum at $\delta \approx 1000$. We provide
a new empirical fitting form for the interaction rate as a function of the halo
mass, large-scale density, and redshift. We also report the existence of two
modes of interactions from the distributions of mass ratio and relative
distance, implying two different physical origins of the interaction. Satellite
targets lose their mass as they proceed deeper into the host halo. The relative
importance of these two trends strongly depends on the large-scale density,
target mass, and redshift. | Cosmological model-independent constraints on the baryon fraction in the
IGM from fast radio bursts and supernovae data: Fast Radio Bursts (FRBs) are millisecond-duration radio transients with an
observed dispersion measure ($DM$) greater than the expected Milky Way
contribution, which suggests that such events are of extragalactic origin.
Although some models have been proposed to explain the physics of the pulse,
the mechanism behind the FRBs emission is still unknown. From FRBs data with
known host galaxies, the redshift is directly measured and can be combined with
estimates of the $DM$ to constrain the cosmological parameters, such as the
baryon number density and the Hubble constant. However, the poor knowledge of
the fraction of baryonic mass in the intergalactic medium ($f_{IGM}$) and its
degeneracy with the cosmological parameters impose limits on the cosmological
application of FRBs. In this work we present a cosmological model-independent
method to determine the evolution of $f_{IGM}$ combining the latest FRBs
observations with localized host galaxy and current supernovae data. We
consider constant and time-dependent $f_{IGM}$ parameterizations and show,
through a Bayesian model selection analysis, that a conclusive answer about the
time-evolution of $f_{IGM}$ depend strongly on the $DM$ fluctuations due to the
spatial variation in cosmic electron density ($\delta$). In particular, our
analysis show that the evidence varies from strong (in favor of a growing
evolution of $f_{IGM}$ with redshift) to inconclusive, as larger values of
$\delta$ are considered. |
Fingerprints of Anomalous Primordial Universe on the Abundance of Large
Scale Structures: We study the predictions of anomalous inflationary models on the abundance of
structures in large scale structure observations. The anomalous features
encoded in primordial curvature perturbation power spectrum are (a): localized
feature in momentum space, (b): hemispherical asymmetry and (c): statistical
anisotropies. We present a model-independent expression relating the number
density of structures to the changes in the matter density variance. Models
with localized feature can alleviate the tension between observations and
numerical simulations of cold dark matter structures on galactic scales as a
possible solution to the missing satellite problem. In models with
hemispherical asymmetry we show that the abundance of structures becomes
asymmetric depending on the direction of observation to sky. In addition, we
study the effects of scale-dependent dipole amplitude on the abundance of
structures and, using the quasars data, we find the upper bound $n_A<0.6$ for
the spectral index of the dipole asymmetry. In all cases there is a critical
mass scale $M_c$ in which for $M<M_c (M> M_c)$ the enhancement in variance
induced from anomalous feature decreases (increases) the abundance of dark
matter structures in Universe. | Radio to infrared spectra of late-type galaxies with Planck and WMAP
data: We use the Planck Early Release Compact Source Catalogue combined with WMAP
and other archival measurements to construct continuum spectra of three nearby
dusty star-forming galaxies: Messier 82, NGC 253 and NGC 4945. We carry out a
least-squares fit to the spectra using a combination of simple synchrotron,
free-free and thermal dust models, and look for evidence of anomalous microwave
emission (AME). We find that the radio spectra of all three galaxies are
consistent with steep spectrum synchrotron emission, with a significant amount
of free-free emission required to explain the Planck and WMAP data points in
the frequency range 30-150 GHz. This brings the star-formation rate based on
free-free emission into better agreement with that from the non-thermal
emission. We place limits on the presence of AME in these galaxies, finding
that it is lower than expectations based on the ratio of far infrared to AME
from the Galaxy. Nevertheless, the shape of the spectrum of NGC 4945 hints at
the presence of AME with a peak around 30 GHz. Future Planck data will let us
look more closely at these galaxies, as well as to extend the analysis to many
more galaxies. |
Star Formation History of Dwarf Galaxies in Cosmological Hydrodynamic
Simulations: We examine the past and current work on the star formation (SF) histories of
dwarf galaxies in cosmological hydrodynamic simulations. The results obtained
from different numerical methods are still somewhat mixed, but the differences
are understandable if we consider the numerical and resolution effects. It
remains a challenge to simulate the episodic nature of SF history in dwarf
galaxies at late times within the cosmological context of a cold dark matter
model. More work is needed to solve the mysteries of SF history of dwarf
galaxies employing large-scale hydrodynamic simulations on the next generation
of supercomputers. | Can dark matter induce cosmological evolution of the fundamental
constants of Nature?: We demonstrate that massive fields, such as dark matter, can directly produce
a cosmological evolution of the fundamental constants of Nature. We show that a
scalar or pseudoscalar (axion-like) dark matter field $\phi$, which forms a
coherently oscillating classical field and interacts with Standard Model
particles via quadratic couplings in $\phi$, produces `slow' cosmological
evolution and oscillating variations of the fundamental constants. We derive
limits on the quadratic interactions of $\phi$ with the photon, electron and
light quarks from measurements of the primordial $^4$He abundance produced
during Big Bang nucleosynthesis and recent atomic dysprosium spectroscopy
measurements. These limits improve on existing constraints by up to 15 orders
of magnitude. We also derive limits on the previously unconstrained linear and
quadratic interactions of $\phi$ with the massive vector bosons from
measurements of the primordial $^4$He abundance. |
Mortality and dust expulsion in early phases of stellar clusters.
Evidence from NIR photometry of nearby, spiral galaxies: It is often argued that young stellar clusters suffer a significant infant
mortality that is partly related to the expulsion of dust and gas in their
early phases caused by radiation pressure from hot stars and supernovae.
Near-infrared (J-K)-Mk diagrams of young stellar clusters in nearby spiral
galaxies show a bi-modal distribution that is consistent with a fast decline of
their intrinsic extinction at an early epoch.
The distinct features in the color-magnitude diagrams (CMD) and the fast
change of colors for the youngest clusters allow us to place constraints on
their early evolutionary phases, including the time scale for the decreasing
extinction caused for instance by gas and dust expulsion.
Monte Carlo simulations of cluster populations were performed using the
power-law distribution function g(M, t) ~ M^a t^gam. Integrated colors were
computed from Starburst99 models. The simulated near-infrared CMD were compared
with those observed for six grand-design, spiral galaxies using statistical
goodness-of-fit tests.
The CMDs indicate a significant mortality of young, massive clusters with gam
= -1.4 +-0.5. High initial extinction Av = 8-11m and strong nebular emission
are required to reproduce the bi-modal color distributions of the clusters. An
extended star formation phase of longer than 5 Myr is suggested. The reduction
of the internal extinction of the clusters starts during their active star
formation and lasts for a period of 5-10 Myr. | Gravitational wave constraints on dark sector models: We explore the constraints on dark sector models imposed by the recent
observation of coincident gravitational waves and gamma rays from a binary
neutron star merger, GW170817. Rather than focusing on specific models as has
been considered by other authors, we explore this in the context of the
equation of state approach of which the specific models are special cases.
After confirming the strong constraints found by others for Horndeski,
Einstein-Aether and massive gravity models, we discuss how it is possible to
construct models which might evade the constraints from GW170817 but still
leading to cosmologically interesting modifications to gravity. Possible
examples are ``miracle cancellations" such as in $f(R)$ models, nonlocal models
and higher-order derivatives. The latter two rely on the dimensionless ratio of
the wave number of the observed gravitational waves to the Hubble expansion
rate being very large ($\sim10^{19}$) which is used to suppress modifications
to the speed of gravitational waves. |
A novel approach in the WIMP quest: Cross-Correlation of Gamma-Ray
Anisotropies and Cosmic Shear: Both cosmic shear and cosmological gamma-ray emission stem from the presence
of Dark Matter (DM) in the Universe: DM structures are responsible for the
bending of light in the weak lensing regime and those same objects can emit
gamma-rays, either because they host astrophysical sources (active galactic
nuclei or star-forming galaxies) or directly by DM annihilations (or decays,
depending on the properties of the DM particle). Such gamma-rays should
therefore exhibit strong correlation with the cosmic shear signal. In this
Letter, we compute the cross-correlation angular power spectrum of cosmic shear
and gamma-rays produced by the annihilation/decay of Weakly Interacting Massive
Particle (WIMP) DM, as well as from astrophysical sources. We show that this
observable provides novel information on the composition of the Extra-galactic
Gamma-ray Background (EGB), since the amplitude and shape of the
cross-correlation signal strongly depends on which class of source is
responsible for the gamma-ray emission. If the DM contribution to the EGB is
significant (at least in a definite energy range), although compatible with
current observational bounds, its strong correlation with the cosmic shear
makes such signal potentially detectable by combining Fermi-LAT data with
forthcoming galaxy surveys, like Dark Energy Survey and Euclid. At the same
time, the same signal would demonstrate that the weak lensing observables are
indeed due to particle DM matter and not to possible modifications of General
Relativity. | Constraining Dark Matter properties with the first generation of stars: Dark Matter (DM) can be trapped by the gravitational field of any star, since
collisions with nuclei in dense environments can slow down the DM particle
below the escape velocity ($v_{esc}$) at the surface of the star. If captured,
the DM particles can self-annihilate, and, therefore, provide a new source of
energy for the star. We investigate this phenomenon for capture of DM particles
by the first generation of stars [Population III (Pop III) stars], by using the
multiscatter capture formalism. Pop III stars are particularly good DM captors,
since they form in DM-rich environments, at the center of$~\sim 10^6 M_\odot$
DM minihalos, at redshifts $z\sim 15$. Assuming a DM-proton scattering cross
section ($\sigma)$ at the current deepest exclusion limits provided by the
XENON1T experiment, we find that captured DM annihilations at the core of Pop
III stars can lead, via the Eddington limit, to upper bounds in stellar masses
that can be as low as a few $M_\odot$ if the ambient DM density ($\rho_X$) at
the location of the Pop III star is sufficiently high. Conversely, when Pop III
stars are identified, one can use their observed mass ($M_\star$) to place
bounds on $\rho_X\sigma$. Using adiabatic contraction to estimate the ambient
DM density in the environment surrounding Pop III stars, we place projected
upper limits on $\sigma$, for $M_\star$ in the $100-1000~M_\odot$ range, and
find bounds that are competitive with, or deeper than, those provided by the
most sensitive current direct detection experiments for both spin independent
and spin dependent interactions, for a wide range of DM masses. Most
intriguingly, we find that Pop III stars with mass $M_\star \gtrsim 300
M_\odot$ could be used to probe the SD proton-DM cross section below the
"neutrino floor," i.e. the region of parameter space where DM direct detection
experiments will soon become overwhelmed by neutrino backgrounds. |
A minor-merger origin for inner disks and rings in early-type galaxies: Nuclear disks and rings are frequent galaxy substructures, for a wide range
of morphological types (from S0 to Sc). We have investigated the possible
minor-merger origin of inner disks and rings in spiral galaxies through
collisionless N-body simulations. The models confirm that minor mergers can
drive the formation of thin, kinematically-cold structures in the center of
galaxies out of satellite material, without requiring the previous formation of
a bar. Satellite core particles tend to be deposited in circular orbits in the
central potential, due to the strong circularization experienced by the
satellite orbit through dynamical friction. The material of the satellite core
reaches the remnant center if satellites are dense or massive, building up a
thin inner disk; whereas it is fully disrupted before reaching the center in
the case of low-mass satellites, creating an inner ring instead. | Gas entropy in a representative sample of nearby X-ray galaxy clusters
(REXCESS): relationship to gas mass fraction: (Abridged) We examine the radial entropy distribution and its scaling using
31 nearby galaxy clusters from the Representative XMM-Newton Cluster Structure
Survey (REXCESS). The entropy profiles are robustly measured at least out to
R_1000 in all systems and out to R_500 in 13 systems. Compared to theoretical
expectations, the observed distributions show a radial and mass-dependent
excess entropy that is greater and extends to larger radii in lower mass
systems. At R_500, the mass dependence and entropy excess are both negligible
within the uncertainties. Mirroring this behaviour, the scaling of gas entropy
is shallower than self-similar in the inner regions, but steepens with radius,
becoming consistent with self-similar at R_500. The dispersion in scaled
entropy in the inner regions is linked to the presence of cool cores and
dynamical activity; at larger radii the dispersion decreases by a factor of two
and the dichotomy between subsamples disappears. Parameterising the profiles
with a power law plus constant model, there are two peaks in central entropy
K_0; however, we cannot distinguish between a bimodal or a left-skewed
distribution. The outer slopes are correlated with system temperature; their
distribution is unimodal with a median value of 0.98. Renormalising the
dimensionless entropy profiles by the gas mass fraction profile f_gas(< R),
leads to a remarkable reduction in the scatter, implying that gas mass fraction
variations with radius and mass are the cause of the observed entropy
properties. We discuss a tentative scenario to explain the behaviour of the
entropy and gas mass fraction in the REXCESS sample, in which extra heating and
merger mixing maintains an elevated central entropy level in the majority of
the population, and a smaller fraction of systems develops a cool core. |
Inflationary predictions in scalar-tensor DBI inflation: The scalar-tensor Dirac-Born-Infeld (DBI) inflation scenario provides a
simple mechanism to reduce the large values of the boost factor associated with
single field models with DBI action, whilst still being able to drive 60 efolds
of inflation. Using a slow-roll approach, we obtain an analytical expression
for the spectral index of the perturbations and, moreover, determine
numerically the regions of the parameter space of the model capable of giving
rise to a power spectrum with amplitude and spectral index within the observed
bounds. We find that regions that exhibit significant DBI effects throughout
the inflationary period can be discarded by virtue of a blue-tilted spectral
index, however, there are a number of viable cases --- associated with a more
red-tilted spectral index --- for which the boost factor is initially
suppressed by the effect of the coupling between the fields, but increases
later to moderate values. | Resolving Cosmic Neutrino Structure: A Hybrid Neutrino N-body Scheme: We present the first simulation capable of resolving the structure of
neutrino clustering on Mpc scales. The method combines grid- and particle-based
methods and achieves very good accuracy on both small and large scales, while
keeping CPU consumption under control. Such simulations are not only ideal for
calculating the non-linear matter power spectrum but also particularly relevant
for studies of how neutrinos cluster in galaxy- or cluster-sized halos. We
perform the largest neutrino N-body simulation to date, effectively containing
10 different neutrino hot dark matter components with different thermal
properties. |
Galaxy distribution and extreme value statistics: We consider the conditional galaxy density around each galaxy, and study its
fluctuations in the newest samples of the Sloan Digital Sky Survey Data Release
7. Over a large range of scales, both the average conditional density and its
variance show a nontrivial scaling behavior, which resembles to criticality.
The density depends, for 10 < r < 80 Mpc/h, only weakly (logarithmically) on
the system size. Correspondingly, we find that the density fluctuations follow
the Gumbel distribution of extreme value statistics. This distribution is
clearly distinguishable from a Gaussian distribution, which would arise for a
homogeneous spatial galaxy configuration. We also point out similarities
between the galaxy distribution and critical systems of statistical physics. | Growth of perturbations in nonlocal gravity with non-$Λ$CDM
background: We re-analyze the nonlocal gravity model of Deser and Woodard which was
proposed to account for the current phase of cosmic acceleration. We show that
the growth of perturbations predicted by this nonlocal gravity model when its
background evolution is fixed by some particular non-$\Lambda$CDM models can be
substantially lower than when its background is fixed by $\Lambda$CDM. This can
be seen when we consider the background expansion by a dark energy model with a
slightly less negative equation of state with respect to cosmological constant.
Our results hints towards a fact that the choice of the background expansion
can play a crucial role how this nonlocal gravity model can fit the growth
history data. While the growth data might show better consistency to GR models
(among the background models we studied so far), it seems the nonlocal gravity
model studied in this work is able to show comparable consistency to the growth
data as well. Showing this consistency can be considered as a significant
result since this model can stand as a distinguishable alternative to the
standard model of cosmology. |
Bayesian evidence of the post-Planck curvaton: We perform a Bayesian model comparison for scenarios within the quadratic
curvaton model, determining the degree to which both are disfavoured with
respect to the $\Lambda$CDM concordance model and single-field quadratic
inflation, using the recent \emph{Planck} data release. Despite having three
additional model parameters, the simplest curvaton scenario is not disfavoured
relative to single-field quadratic inflation, and it becomes favoured against
this single-field model when we include the joint BICEP/Keck/\emph{Planck}
analysis. In all cases we assume an instantaneous inflaton decay and no
surviving isocurvature perturbations. Despite the success of \emph{Planck}
reaching its forecast measurement accuracy, we show that the current
constraints on local non-Gaussianity are insufficiently precise to have any
significant impact on the evidence ratios so far. We also determine the
precision $\sigma(f_{\mathrm{NL}})$ required by future measurements assuming a
fiducial value of $f_{\mathrm{NL}}=-5/4$ or $10.8$ to no longer disfavour the
curvaton against the $\Lambda$CDM parametrisation, and we discuss the effect
that the predicted increase in precision from future measurements on
$f_{\mathrm{NL}}$ may have. We show that our results are not very sensitive to
our choice of priors. | The Diverse Nature of Optical Emission Lines in Brightest Cluster
Galaxies: IFU Observations of the Central Kiloparsecs: We present integral field spectroscopy of the nebular line emission in a
sample of 9 brightest cluster galaxies (BCGs). The sample was chosen to probe
both cooling flow and non-cooling flow clusters, as well as a range of cluster
X-ray luminosities. The line emission morphology and velocity gradients suggest
a great diversity in the properties of the line emitting gas. While some BGCs
show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and
MKW3s), others have extended emission (Abell 1204, Abell 2199), while still
others have centrally concentrated emission (Abell 2052). We examine diagnostic
line ratios to determine the dominant ionization mechanisms in each galaxy.
Most of the galaxies show regions with AGN-like spectra, however for two BCGs,
Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which
can be described by the emission from young stellar populations. The diversity
of emission line properties in our sample of BCGs suggests that the emission
mechanism is not universal, with different ionization processes dominating
different systems. Given this diversity, there is no evidence for a clear
distinction of the emission line properties between cooling flow and
non-cooling flow BCGs. It is not always cooling flow BCGs which show emission
(or young stellar populations), and non-cooling flow BCGs which do not. |
Contribution of the hybrid inflation waterfall to the primordial
curvature perturbation: A contribution $\zeta_\chi$ to the curvature perturbation will be generated
during the waterfall that ends hybrid inflation, that may be significant on
small scales. In particular, it may lead to excessive black hole formation. We
here consider standard hybrid inflation, where the tachyonic mass of the
waterfall field is much bigger than the Hubble parameter. We calculate
$\zeta_\chi$ in the simplest case, and see why earlier calculations of
$\zeta_\chi$ are incorrect. | Nonlinear stochastic growth rates and redshift space distortions: The linear growth rate is commonly defined through a simple deterministic
relation between the velocity divergence and the matter overdensity in the
linear regime. We introduce a formalism that extends this to a nonlinear,
stochastic relation between $\theta = \nabla \cdot v({\bf x},t)/aH$ and
$\delta$. This provides a new phenomenological approach that examines the
conditional mean $< \theta|\delta>$, together with the fluctuations of $\theta$
around this mean. We measure these stochastic components using N-body
simulations and find they are non-negative and increase with decreasing scale
from $\sim$10% at $k<0.2 h $Mpc$^{-1}$ to 25% at $k\sim0.45h$Mpc$^{-1}$ at $z =
0$. Both the stochastic relation and nonlinearity are more pronounced for
halos, $M \le 5 \times 10^{12}M_\odot h^{-1}$, compared to the dark matter at
$z=0$ and $1$. Nonlinear growth effects manifest themselves as a rotation of
the mean $< \theta|\delta>$ away from the linear theory prediction $-f_{\tiny
\rm LT}\delta$, where $f_{\tiny \rm LT}$ is the linear growth rate. This
rotation increases with wavenumber, $k$, and we show that it can be
well-described by second order Lagrangian perturbation theory (2LPT) for $k <
0.1 h$Mpc$^{-1}$. The stochasticity in the $\theta$ -- $\delta$ relation is not
so simply described by 2LPT, and we discuss its impact on measurements of
$f_{\tiny \rm LT}$ from two point statistics in redshift space. Given that the
relationship between $\delta$ and $\theta$ is stochastic and nonlinear, this
will have implications for the interpretation and precision of $f_{\tiny \rm
LT}$ extracted using models which assume a linear, deterministic expression. |
Abundances, masses, and weak-lensing mass profiles of galaxy clusters as
a function of richness and luminosity in LambdaCDM cosmologies: We test the concordance LCDM cosmology by comparing predictions for the mean
properties of galaxy clusters to observations. We use high-resolution N-body
simulations of cosmic structure formation and semi-analytic models of galaxy
formation to compute the abundance, mean density profile, and mass of galaxy
clusters as a function of richness and luminosity, and we compare these
predictions to observations of clusters in the Sloan Digital Sky Survey (SDSS)
maxBCG catalogue. We discuss the scatter in the mass-richness relation, the
reconstruction of the cluster mass function from the mass-richness relation,
and fits to the weak-lensing cluster mass profiles. The impact of cosmological
parameters on the predictions is investigated by comparing results from galaxy
models based on the Millennium Simulation (MS) and another WMAP1 simulation to
those from a WMAP3 simulation. We find that the simulated weak-lensing mass
profiles and the observed profiles of the SDSS maxBCG clusters agree well in
shape and amplitude. The mass-richness relations in the simulations are close
to the observed relation, with differences lesssim 30%. The MS and WMAP1
simulations yield cluster abundances similar to those observed, whereas
abundances in the WMAP3 simulation are 2-3 times lower. The differences in
cluster abundance, mass, and density amplitude between the simulations and the
observations can be attributed to differences in the underlying cosmological
parameters, in particular the power spectrum normalisation sigma_8. Better
agreement between predictions and observations should be reached with a
normalisation $0.722<sigma_8<0.9$ (probably closer to the upper value), i.e.
between the values underlying the two simulation sets. | More on QCD Ghost Dark Energy: The difference between vacuum energy of quantum fields in Minkowski space and
in Friedmann-Robterson-Walker universe might be related to the observed dark
energy. The vacuum energy of the Veneziano ghost field introduced to solve the
$U(1)_A$ problem in QCD is of the form, $ H+ {\cal O}(H^2)$. Based on this, we
study the dynamical evolution of a phenomenological dark energy model whose
energy density is of the form $\alpha H+\beta H^2$. In this model, the universe
approaches to a de Sitter phase at late times. We fit the model with current
observational data including SnIa, BAO, CMB, BBN, Hubble parameter and growth
rate of matter perturbation. It shows that the universe begins to accelerate at
redshift $z\sim 0.75$ and this model is consistent with current data. In
particular, this model fits the data of growth factor well as the $\Lambda CDM$
model. |
Superheavy scalar dark matter from gravitational particle production in
$α$-attractor models of inflation: We study the phenomenon of gravitational particle production as applied to a
scalar spectator field in the context of $\alpha$-attractor inflation. Assuming
that the scalar has a minimal coupling to gravity, we calculate the abundance
of gravitationally-produced particles as a function of the spectator's mass
$m_\chi$ and the inflaton's $\alpha$ parameter. If the spectator is stable and
sufficiently weakly coupled, such that it does not thermalize after reheating,
then a population of spin-0 particles is predicted to survive in the universe
today, providing a candidate for dark matter. Inhomogeneities in the spatial
distribution of dark matter correspond to an isocurvature component, which can
be probed by measurements of the cosmic microwave background anisotropies. We
calculate the dark matter-photon isocurvature power spectrum and by comparing
with upper limits from Planck, we infer constraints on $m_\chi$ and $\alpha$.
If the scalar spectator makes up all of the dark matter today, then for $\alpha
= 10$ and $T_\text{RH} = 10^4 \ \mathrm{GeV}$ we obtain $m_\chi > 1.8 \times
10^{13} \ \mathrm{GeV} \approx 1.2 \, m_\phi$, where $m_\phi$ is the inflaton's
mass. | Imaging Atomic and Highly Excited Molecular Gas in a z=6.42 Quasar Host
Galaxy: Copious Fuel for an Eddington-Limited Starburst at the End of Cosmic
Reionization: We have imaged CO(J=7-6) and CI(3P2-3P1) emission in the host galaxy of the
z=6.42 quasar SDSS J114816.64+525150.3 (hereafter: J1148+5251) through
observations with the Plateau de Bure Interferometer. The region showing
CO(J=7-6) emission is spatially resolved, and its size of 5 kpc is in good
agreement with earlier CO(J=3-2) observations. In combination with a revised
model of the collisional line excitation in this source, this indicates that
the highly excited molecular gas traced by the CO J=7-6 line is subthermally
excited (showing only 58+/-8% of the CO J=3-2 luminosity), but not more
centrally concentrated. We also detect CI(3P2-3P1) emission in the host galaxy
of J1148+5251, but the line is too faint to enable a reliable size measurement.
From the CI(3P2-3P1) line flux, we derive a total atomic carbon mass of
M_CI=1.1x10^7 M_sun, which corresponds to ~5x10^-4 times the total molecular
gas mass. We also searched for H2O(J_KaKc=2_12-1_01) emission, and obtained a
sensitive line luminosity limit of L'_H2O<4.4x10^9 K kms pc^2, i.e., <15% of
the CO(J=3-2) luminosity. The warm, highly excited molecular gas, atomic gas
and dust in this quasar host at the end of cosmic reionization maintain an
intense starburst that reaches surface densities as high as predicted by (dust
opacity) Eddington limited star formation over kiloparsec scales. |
A study of the environments of large radio galaxies using SDSS: The distributions of galaxies in the environments of 16 large radio sources
have been examined using the Sloan Digital Sky Survey. In the giant radio
galaxy J1552+2005 (3C326) which has the highest arm-length ratio, the shorter
arm is found to interact with a group of galaxies which forms part of a
filamentary structure. Although most large sources occur in regions of low
galaxy density, the shorter arm is brighter in most cases suggesting
asymmetries in the intergalactic medium which may not be apparent in the
distribution of galaxies. In two cases with strong and variable cores,
J0313+4120 and J1147+3501, the large flux density asymmetries are possibly also
caused by the effects of relativistic motion. | Forecast constraints on cosmic strings from future CMB, pulsar timing
and gravitational wave direct detection experiments: We study future observational constraints on cosmic string parameters from
various types of next-generation experiments: direct detection of gravitational
waves (GWs), pulsar timing array, and the cosmic microwave background (CMB). We
consider both GW burst and stochastic GW background searches by ground- and
space-based interferometers as well as GW background detection in pulsar timing
experiments. We also consider cosmic string contributions to the CMB
temperature and polarization anisotropies. These different types of
observations offer independent probes of cosmic strings and may enable us to
investigate cosmic string properties if the signature is detected. In this
paper, we evaluate the power of future experiments to constrain cosmic string
parameters, such as the string tension Gmu, the initial loop size alpha, and
the reconnection probability p, by performing Fisher information matrix
calculations. We find that combining the information from the different types
of observations breaks parameter degeneracies and provides more stringent
constraints on the parameters. We also find future space-borne interferometers
independently provide a highly precise determination of the parameters. |
The importance of local measurements for cosmology: We explore how local, cosmology-independent measurements of the Hubble
constant and the age of the Universe help to provide a powerful consistency
check of the currently favored cosmological model (flat LambdaCDM) and
model-independent constraints on cosmology. We use cosmic microwave background
(CMB) data to define the model-dependent cosmological parameters, and add local
measurements to assess consistency and determine whether extensions to the
model are justified. At current precision, there is no significant tension
between the locally measured Hubble constant and age of the Universe (with
errors of 3% and 5% respectively) and the corresponding parameters derived from
the CMB. However, if errors on the local measurements could be decreased by a
factor of two, one could decisively conclude if there is tension or not. We
also compare the local and CMB data assuming simple extensions of the flat,
$\Lambda$CDM model (including curvature, dark energy with a constant equation
of state parameter not equal to -1, non-zero neutrino masses and a non-standard
number of neutrino families) and find no need for these extra parameters; in
particular, we constrain the effective number of neutrino species to be Neff <
4 at 95% confidence. We show that local measurements provide constraints on the
curvature and equation of state of dark energy nearly orthogonal to those of
the CMB. We argue that cosmology-independent measurements of local quantities
at the percent level would be very useful to explore cosmology in a
model-independent way. | Photometric observations of selected, optically bright quasars for Space
Interferometry Mission and other future celestial reference frames: Photometric observations of 235 extragalactic objects that are potential
targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R,
I magnitudes at the 5% level are obtained at 1 - 4 epochs between 2005 and 2007
using the 1-m telescopes at Cerro Tololo Inter-American Observatory and Naval
Observatory Flagstaff Station. Of the 134 sources which have V magnitudes in
the Veron & Veron-Cetty catalog a difference of over 1.0 mag is found for the
observed-catalog magnitudes for about 36% of the common sources, and 10 sources
show over 3 mag difference. Our first set of observations presented here form
the basis of a long-term photometric variability study of the selected
reference frame sources to assist in mission target selection and to support in
general QSO multi-color photometric variability studies. |
Large-Scale Magnetic Fields, Dark Energy and QCD: Cosmological magnetic fields are being observed with ever increasing
correlation lengths, possibly reaching the size of superclusters, therefore
disfavouring the conventional picture of generation through primordial seeds
later amplified by galaxy-bound dynamo mechanisms. In this paper we put forward
a fundamentally different approach that links such large-scale magnetic fields
to the cosmological vacuum energy. In our scenario the dark energy is due to
the Veneziano ghost (which solves the $U(1)_A$ problem in QCD). The Veneziano
ghost couples through the triangle anomaly to the electromagnetic field with a
constant which is unambiguously fixed in the standard model. While this
interaction does not produce any physical effects in Minkowski space, it
triggers the generation of a magnetic field in an expanding universe at every
epoch. The induced energy of the magnetic field is thus proportional to
cosmological vacuum energy: $\rho_{EM}\simeq B^2 \simeq (\frac{\alpha}{4\pi})^2
\rho_{DE}$, $\rho_{DE}$ hence acting as a source for the magnetic energy
$\rho_{EM}$. The corresponding numerical estimate leads to a magnitude in the
nG range. There are two unique and distinctive predictions of our proposal: an
uninterrupted active generation of Hubble size correlated magnetic fields
throughout the evolution of the universe; the presence of parity violation on
the enormous scales $1/H$, which apparently has been already observed in CMB.
These predictions are entirely rooted into the standard model of particle
physics. | Can HI 21 cm line trace the Missing Baryons in the Filamentary
Structures?: A large fraction of baryons predicted from the standard cosmology has been
missing observationally. Although previous numerical simulations have indicated
that most of the missing baryons reside in large-scale filaments in the form of
Warm Hot Intergalactic Medium (WHIM), it is generally very difficult to detect
signatures from such a diffuse gas. In this work, we focus on the hyperfine
transition of neutral hydrogen (HI) called 21-cm line as a tool to trace the
WHIM. For the purpose, we first construct the map of the 21-cm signals by using
the data provided by the state-of-the-art cosmological hydrodynamics simulation
project, Illustris, in which detailed processes affecting the dynamical and
thermal evolution of the WHIM are implemented. From the comparison with the
constructed 21-cm signal map with the expected noise level of the Square
Kilometre Array phase 1 mid-frequency instrument (SKA1-mid), we find that the
21-cm signals from the filamentary structures at redshifts z=0.5-3 are
detectable with the SKA1-mid if we assume the angular resolution of
\Delta\theta > 10 arcmin and the observing time of t_obs > 100 hours. However,
it also turns out that the signals mainly come from galaxies residing in the
filamentary structures and the contribution from the WHIM is too small to
detect with the SKA1-mid. Our results suggest that about 10 times higher
sensitivity than the SKA1-mid is possibly enough to detect the WHIM at z=0.5-3. |
New Developments in Cosmology: In this Thesis I discuss several recent results obtained using the CMB
spectra measured by Planck and several other cosmological probes. Extensions of
the $\Lambda$CDM model are studied, including the presence of an additional
sterile neutrino (motivated by the short-baseline oscillation anomalies) and of
a thermal axion. The degeneracies of the cosmological effects of these
particles with the power spectrum of primordial perturbations are tested. We
also show that the power spectrum of initial scalar perturbations can be
degenerate with the presence of primordial non-Gaussianities, thus affecting
the constraints on the non-Gaussianity parameter $f_{NL}$. Finally, an
effective interaction between dark energy and dark matter is studied. | Planck 2013 results. I. Overview of products and scientific results: The ESA's Planck satellite, dedicated to studying the early Universe and its
subsequent evolution, was launched 14 May 2009 and has been scanning the
microwave and submillimetre sky continuously since 12 August 2009. This paper
gives an overview of the mission and its performance, the processing, analysis,
and characteristics of the data, the scientific results, and the science data
products and papers in the release. The science products include maps of the
CMB and diffuse extragalactic foregrounds, a catalogue of compact Galactic and
extragalactic sources, and a list of sources detected through the SZ effect.
The likelihood code used to assess cosmological models against the Planck data
and a lensing likelihood are described. Scientific results include robust
support for the standard six-parameter LCDM model of cosmology and improved
measurements of its parameters, including a highly significant deviation from
scale invariance of the primordial power spectrum. The Planck values for these
parameters and others derived from them are significantly different from those
previously determined. Several large-scale anomalies in the temperature
distribution of the CMB, first detected by WMAP, are confirmed with higher
confidence. Planck sets new limits on the number and mass of neutrinos, and has
measured gravitational lensing of CMB anisotropies at greater than 25 sigma.
Planck finds no evidence for non-Gaussianity in the CMB. Planck's results agree
well with results from the measurements of baryon acoustic oscillations. Planck
finds a lower Hubble constant than found in some more local measures. Some
tension is also present between the amplitude of matter fluctuations derived
from CMB data and that derived from SZ data. The Planck and WMAP power spectra
are offset from each other by an average level of about 2% around the first
acoustic peak. |
Non-Gaussianity in inflationary scenarios for primordial black holes: Working in an idealised framework in which a series of phases of evolution
defined by the second slow-roll parameter $\eta$ are matched together, we
calculate the reduced bispectrum, $f_{\rm NL}$, for models of inflation with a
large peak in their primordial power spectra. We find $f_{\rm NL}$ is typically
approximately constant over scales at which the peak is located, and provide an
analytic approximation for this value. This allows us to identify the
conditions under which $f_{\rm NL}$ is large enough to have a significant
impact on the resulting production of primordial black holes (PBHs) and scalar
induced gravitational waves (SIGWs). Together with analytic formulae for the
gradient of the rise and fall in the power spectrum, this provides a toolkit
for designing or quickly analysing inflationary models that produce PBHs and
SIGWs. | Exploring extra dimensions through observational tests of dark energy
and varying Newton's constant: We recently presented a series of dark energy theorems that place constraints
on the equation of state of dark energy ($\wdark$), the ime-variation of
Newton's constant ($\dot G$), and the violation of energy conditions in
theories with extra dimensions. In this paper, we explore how current and
future measurements of $\wdark$ and $\dot G$ can be used to place tight limits
on large classes of these theories (including some of the most well-motivated
examples) independent of the size of the extra dimensions. As an example, we
show that models with conformally Ricci-flat metrics obeying the null energy
condition (a common ansatz for Kaluza-Klein and string constructions) are
highly constrained by current ata and may be ruled out entirely by future dark
energy and pulsar observations. |
Late time cosmology with LISA: probing the cosmic expansion with massive
black hole binary mergers as standard sirens: This paper summarises the potential of the LISA mission to constrain the
expansion history of the universe using massive black hole binary mergers as
gravitational wave standard sirens. After briefly reviewing the concept of
standard siren, the analysis and methodologies of Ref. [1] are briefly outlined
to show how LISA can be used as a cosmological probe, while a selection of
results taken from Refs. [1,2] is presented in order to estimate the power of
LISA in constraining cosmological parameters. | A Stellar Mass Threshold for Quenching of Field Galaxies: We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no
active star formation are extremely rare (<0.06%) in the field. Our sample is
based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky
Survey Data Release 8. We examine the relative number of quenched versus star
forming dwarf galaxies, defining quenched galaxies as having no Halpha emission
(EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf
galaxies decreases rapidly with increasing distance from a massive host,
leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of
a massive host galaxy to be in the field. We demonstrate that there is a
stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched
galaxies do not exist in the field. Below this threshold, we find that none of
the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show
evidence for recent star formation. Correcting for volume effects, this
corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more
dense environments, quenched galaxies account for 23% of the dwarf population
over the same stellar mass range. The majority of quenched dwarf galaxies
(often classified as dwarf elliptical galaxies) are within 2 virial radii of a
massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond
4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun,
ending star-formation requires the presence of a more massive neighbor,
providing a stringent constraint on models of star formation feedback. |
History of Star Formation of Early Type Galaxies from Integrated Light:
Clues from Stellar Ages and Abundances: I briefly review what has been recently learned from determinations of mean
stellar ages and abundances from integrated light studies of early-type
galaxies, and discuss some new questions posed by recent data. A short
discussion of spectroscopic ages is presented, but the main focus of this
review is on the abundances of Fe, Mg, Ca, N, and C, obtained from comparisons
of measurements taken in integrated spectra of galaxies with predictions from
stellar population synthesis models. | Constraining dark matter sub-structure with the dynamics of
astrophysical systems: The accuracy of the measurements of some astrophysical dynamical systems
allows to constrain the existence of incredibly small gravitational
perturbations. In particular, the internal Solar System dynamics (planets,
Earth-Moon) opens up the possibility, for the first time, to prove the
abundance, mass and size, of dark sub-structures at the Earth vicinity. We find
that adopting the standard dark matter density, its local distribution can be
composed by sub-solar mass halos with no currently measurable dynamical
consequences, regardless of the mini-halo fraction. On the other hand, it is
possible to exclude the presence of dark streams with linear mass densities
higher than $\lambda_{\rm st}> 10^{-10} \Msun/\AU$ (about the Earth mass spread
along the diameter of the SS up to the Kuiper belt). In addition, we review the
dynamics of wide binaries inside the dwarf spheroidal galaxies in the MW. The
dynamics of such kind of binaries seem to be compatible with the presence of a
huge fraction of dark sub-structure, thus their existence is not a sharp
discriminant of the dark matter hypothesis as been claimed before. However,
there are regimes where the constraints from different astrophysical systems
may reveal the sub-structure mass function cut-off scale. |
Estimating major merger rates and spin parameters ab initio via the
clustering of critical events: We build a model to predict from first principles the properties of major
mergers. We predict these from the coalescence of peaks and saddle points in
the vicinity of a given larger peak, as one increases the smoothing scale in
the initial linear density field as a proxy for cosmic time. To refine our
results, we also ensure, using a suite of $\sim 400$ power-law Gaussian random
fields smoothed at $\sim 30$ different scales, that the relevant peaks and
saddles are topologically connected: they should belong to a persistent pair
before coalescence. Our model allows us to (a) compute the probability
distribution function of the satellite-merger separation in Lagrangian space:
they peak at three times the smoothing scale; (b) predict the distribution of
the number of mergers as a function of peak rarity: halos typically undergo two
major mergers ($>$1:10) per decade of mass growth; (c) recover that the typical
spin brought by mergers: it is of the order of a few tens of per cent. | Revisiting Chaplygin gas cosmologies with the recent observations of
high-redshfit quasars: In this paper, we use the latest observations of quasars covering the
redshift range of $0.04<z<5.1$ to investigate a series of Chaplygin gas models
as candidates for unified dark matter and dark energy. Based on different
combinations of available standard candle and standard ruler data, we put
constraints on the generalized Chaplygin gas (GCG), modified Chaplygin gas
(MCG), new generalized Chaplygin gas (NGCG) and viscous generalized Chaplygin
gas (VGCG) models. Moreover, we apply Jensen-Shannon divergence (JSD),
statefinder diagnostics, and the deviance information criterion (DIC) to
distinguish these CG models, based on the statistical results derived from
Markov chain Monte Carlo method. The results show that (1) The standard ruler
data could provide more stringent constraints on the cosmological parameters of
different CG models considered in this analysis. Interestingly, the matter
density parameter $\Omega_{m}$ and Hubble constant $H_{0}$ derived from the
available data are well consistent with those from the Planck 2018 results; (2)
Based on the statistical criteria JSD, our findings demonstrate the well
consistency between Chaplygin gas and the concordance $\Lambda$CDM model.
However, in the framework of statefinder diagnostics, the GCG and NGCG models
cannot be distinguished from $\Lambda$CDM, while MCG and VGCG models show
significant deviation from $\Lambda$CDM in the present epoch; (3) According to
the the statistical criteria DIC, we show that the MCG and VGCG models have
substantial observational support from high-redshfit quasars, whereas the GCG
and NGCG models miss out on the less observational support category but can not
be ruled out. |
Testing distance duality with CMB anisotropies: We constrain deviations of the form $T\propto (1+z)^{1+\epsilon}$ from the
standard redshift-temperature relation, corresponding to modifying distance
duality as $D_L=(1+z)^{2(1+\epsilon)} D_A$. We consider a consistent model, in
which both the background and perturbation equations are changed. For this
purpose, we introduce a species of dark radiation particles to which photon
energy density is transferred, and assume $\epsilon\ge0$. The Planck 2015
release high multipole temperature plus low multipole data give the limit
$\epsilon<4.5\times 10^{-3}$ at 95% C.L. The main obstacle to improving this
CMB-only result is strong degeneracy between $\epsilon$ and the physical matter
densities $\omega_{\rm b}$ and $\omega_{\rm c}$. A constraint on deuterium
abundance improves the limit to $\epsilon<1.8\times 10^{-3}$. Adding the Planck
high-multipole CMB polarisation and BAO data leads to a small improvement; with
this maximal dataset we obtain $\epsilon<1.3\times 10^{-3}$. This dataset
constrains the present dark radiation energy density to at most 12% of the
total photon plus dark radiation density. Finally, we discuss the degeneracy
between dark radiation and the effective number of relativistic species $N_{\rm
eff}$, and consider the impact of dark radiation perturbations and allowing
$\epsilon<0$ on the results. | The Dust Extinction Curves of Gamma-Ray Burst Host Galaxies: The composition and amount of interstellar dust within gamma-ray burst (GRB)
host galaxies is of key importance when addressing selection effects in the GRB
redshift distribution, and when studying the properties of their host galaxies.
As well as the implications for GRB research, probing the dust within the
high-z hosts of GRBs also contributes to our understanding of the conditions of
the interstellar medium and star-formation in the distant Universe.
Nevertheless, the physical properties of dust within GRB host galaxies
continues to be a highly contended issue. In this paper we explore the mean
extinction properties of dust within the host galaxies of a sample of 17 GRBs
with total host galaxy visual extinction Av<1 (<Av>=0.4), covering a redshift
range z=0.7-3.1. We find the average host extinction curve to have an
ultraviolet slope comparable to that of the LMC, but with little evidence of a
2175Angs dust extinction feature as observed along Milky Way and LMC
sightlines. We cannot at present rule out the presence of a 2175Angs feature,
and both the standard SMC and LMC extinction curves also provide good fits to
our data. However, we can reject an extinction curve that has a UV slope as
flat as the mean Milky Way extinction curve, whilst also having a 2175Angs
feature as prominent as seen in the mean Milky Way extinction curve. This is in
contrast to the clear detection of a 2175Angs bump and the flatter extinction
curves of some more heavily extinguished GRBs (Av>1), which may be indicative
of there being a dependence between dust abundance and the wavelength
dependence of dust extinction, as has been previously speculated. |
Cosmological constraints on scalar-tensor gravity and the variation of
the gravitational constant: We present cosmological constraints on the scalar-tensor theory of gravity by
analyzing the angular power spectrum data of the cosmic microwave background
obtained from the Planck 2015 results together with the baryon acoustic
oscillations (BAO) data. We find that the inclusion of the BAO data improves
the constraints on the time variation of the effective gravitational constant
by more than $10\%$, that is, the time variation of the effective gravitational
constant between the recombination and the present epochs is constrained as
$G_{\rm rec}/G_0-1 <1.9\times 10^{-3}\ (95.45\%\ {\rm C.L.})$ and $G_{\rm
rec}/G_0-1 <5.5\times 10^{-3}\ (99.99 \%\ {\rm C.L.})$. We also discuss the
dependence of the constraints on the choice of the prior. | Limits for primordial magnetic fields: A possible explanation for the origin of the magnetic fields observed today
in matter structures is that they were generated in the primordial universe.
After briefly revising the model of a primordial stochastic magnetic field and
sketching the main features of its time evolution in the primordial plasma, we
illustrate the current upper bounds on the magnetic field amplitude and
spectral index from Cosmic Microwave Background observations and gravitational
wave production. We conclude that a primordial magnetic field generated by a
non-causal process such as inflation with a red spectrum seems to be favoured
as a seed for the magnetic fields observed today in structures. |
Spatially resolved star formation histories of nearby galaxies: evidence
for episodic star formation in discs: We use long-slit spectroscopy from Moran et al. to study the radial
dependence of the recent star formation histories of nearby galaxies with
stellar masses greater than 10^10M_sun. We fit stellar population models to the
combination of SSFR, D4000 and Hdelta_A and show that many galaxies have Balmer
absorption line equivalent widths that require recent short-lived episodes or
bursts of star formation. The fraction of galaxies that have experienced
episodic rather than continuous star formation is highest for late-type
galaxies with low stellar masses. In these systems, bursts occur both in the
inner and outer regions of the galaxy. The fraction of stars formed in a single
burst episode is typically around 15% of the total stellar mass in the inner
regions of the galaxy and around 5% of the mass in the outer regions. When we
average over the population, we find that such bursts contribute around a half
of the total mass in stars formed in the last 2 Gyr. In massive galaxies,
bursts occur predominantly in the outer disk. Around a third of all massive,
bulge-dominated galaxies have experienced recent star formation episodes that
are fully confined to their outer (R > 0.7R_90) regions. The fraction of stars
formed in a single episode is only 2 - 3 % of the underlying stellar mass, but
such bursts contribute nearly all the stellar mass formed in the last 2 Gyr.
Recent star formation in outer disks is strongly correlated with the global
atomic gas fraction of the galaxy, but not its global molecular gas fraction.
We suggest that outer episodic star formation is triggered by gas accretion
events. | The Growth of the Stellar Seeds of Supermassive Black Holes: One of the most promising explanations for the origin of the billion solar
mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that
supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form
the seed BHs from which they grow. Here we review recent theoretical advances
which provide support for this scenario. Firstly, given sufficiently high
accretion rates of gas into the cores of primordial protogalaxies, it appears
that neither the high energy radiation emitted from the stellar surface nor the
limited lifetime of SMSs can prevent their growth to masses of up to > 100,000
solar masses. Secondly, recent cosmological simulations suggest that the high
fluxes of molecule-dissociating radiation which may be required in order to
achieve such high accretion rates may be more common in the early universe than
previously thought. We conclude that the majority of supermassive BHs may
originate from SMSs at high redshifts. |
Chain Early Dark Energy: Solving the Hubble Tension and Explaining
Today's Dark Energy: We propose a new model of Early Dark Energy (EDE) as a solution to the Hubble
tension in cosmology, the apparent discrepancy between local measurements of
the Hubble constant $H_0\simeq 74$ km s$^{-1}$ Mpc$^{-1}$ and $H_0\simeq 67$ km
s$^{-1}$ Mpc$^{-1}$ inferred from the Cosmic Microwave Background (CMB). In
Chain EDE, the Universe undergoes a series of first order phase transitions,
starting at a high energy vacuum in a potential, and tunneling down through a
chain of every lower energy metastable minima. As in all EDE models, the
contribution of the vacuum energy to the total energy density of the universe
is initially negligible, but reaches $\sim 10\%$ around matter-radiation
equality, before cosmological data require it to redshift away quickly -- at
least as fast as radiation. We indeed obtain this required behavior with a
series of $N$ tunneling events, and show that for $N>600$ the phase transitions
are rapid enough to allow fast percolation and thereby avoid large scale
anisotropies in the CMB. We construct a specific example of Chain EDE featuring
a scalar field in a quasiperiodic potential (a tilted cosine), which is
ubiquitous in axion physics and, therefore, carries strong theoretical
motivation. Interestingly, the energy difference between vacua can be roughly
the size of today's Dark Energy (meV scale). Therefore, the end result of Chain
EDE could provide a natural explanation of Dark Energy, if the tunneling
becomes extremely slow in the final step before the field reaches zero (or
negative) energy. We discuss a simple mechanism which can stop the scalar field
in the desired minimum. Thus Chain EDE offers the exciting prospect to explain
EDE and Dark Energy by the same scalar field. | Mass Calibration of Galaxy Clusters at Redshift 0.1-1.0 using Weak
Lensing in the Sloan Digital Sky Survey Stripe 82 Co-add: We present galaxy cluster mass-richness relations found in the Sloan Digital
Sky Survey Stripe 82 co-add using clusters found using a Voronoi tessellation
cluster finder. These relations were found using stacked weak lensing shear
observed in a large sample of galaxy clusters. These mass-richness relations
are presented for four redshift bins, $0.1 < z \leq 0.4$, $0.4 < z \leq 0.7$,
$0.7 < z \leq 1.0$ and $0.1 < z \leq 1.0$. We describe the sample of galaxy
clusters and explain how these clusters were found using a Voronoi tessellation
cluster finder. We fit an NFW profile to the stacked weak lensing shear signal
in redshift and richness bins in order to measure virial mass $(M_{200})$. We
describe several effects that can bias weak lensing measurements, including
photometric redshift bias, the effect of the central BCG, halo miscentering,
photometric redshift uncertainty and foreground galaxy contamination. We
present mass-richness relations using richness measure $N_{VT}$ with each of
these effects considered separately as well as considered altogether. We also
examine redshift evolution of the mass-richness relation. As a result we
present measurements of the mass coefficient ($M_{200|20}$) and the power law
slope ($\alpha$) for power law fits to the mass and richness values in each of
the redshift bins. We find values of the mass coefficient of $8.49 \pm 0.526$,
$14.1 \pm 1.78$, $30.2 \pm 8.74$ and $9.23 \pm 0.525 \times 10^{13}$ $h^{-1}$
$M_{sun}$ for each of the four redshift bins respectively. We find values of
the power law slope of $0.905 \pm 0.0585$, $0.948 \pm 0.100$, $1.33 \pm 0.260$
and $0.883 \pm 0.0500$ respectively. |
Optical Depth of the Cosmic Microwave Background due to Scattering and
Absorption: It is shown that, in addition to the Thomson scattering, the absorption due
to the electron-electron, electron-ion and the electron -atom collisions in a
partially ionized cosmic plasma would also contribute to the optical depth of
the cosmic microwave background (CMB). The absorption depth depends on the
plasma temperature and frequency of the CMB radiation. The absorption effects
are prominent at the low frequency part of the CMB spectrum. These effects when
included in the interpretation of the CMB spectrum may necessitate a revised
view of the ioniziation of the universe. | Testing cosmic isotropy with galaxies position angles distribution: We analyse the distribution of position angles of 1 million galaxies from the
Hyperleda catalogue, a sample that presents the galaxies coordinates in the
celestial sphere, information that allows us to look for a possible privileged
direction. Our analysis involves different tests and statistical methods, from
which it is possible to infer with high probability ($p$-value extremely low)
that the galactic planes are not randomly oriented in the sky. Whether this is
an evidence of a cosmological anisotropy or an observational bias due to local
effects is something deserving further studies. |
A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a
Dormant Black Hole: Supermassive black holes (SMBHs; $M\gtrsim10^5\msun$) are known to exist at
the centre of most galaxies with sufficient stellar mass. In the local
Universe, it is possible to infer their properties from the surrounding stars
or gas. However, at high redshifts we require active, continuous accretion to
infer the presence of the SMBHs, often coming in the form of long-term
accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt
stars orbiting nearby, resulting in bright flares from otherwise quiescent
black holes. Here, we report on a $\sim200$-s X-ray quasi-periodicity around a
previously dormant SMBH located in the centre of a galaxy at redshift
$z=0.3534$. This result may open the possibility of probing general relativity
beyond our local Universe. | The Concentration Dependence of the Galaxy-Halo Connection: Modeling
Assembly Bias with Abundance Matching: Empirical methods for connecting galaxies to their dark matter halos have
become essential for interpreting measurements of the spatial statistics of
galaxies. In this work, we present a novel approach for parameterizing the
degree of concentration dependence in the abundance matching method. This new
parameterization provides a smooth interpolation between two commonly used
matching proxies: the peak halo mass and the peak halo maximal circular
velocity. This parameterization controls the amount of dependence of galaxy
luminosity on halo concentration at a fixed halo mass. Effectively this
interpolation scheme enables abundance matching models to have adjustable
assembly bias in the resulting galaxy catalogs. With the new 400 Mpc/h DarkSky
Simulation, whose larger volume provides lower sample variance, we further show
that low-redshift two-point clustering and satellite fraction measurements from
SDSS can already provide a joint constraint on this concentration dependence
and the scatter within the abundance matching framework. |
Systematic differences in simple stellar population model results:
Application to the M31 globular-like cluster system: Simple stellar population (SSP) synthesis models are useful tools for
studying the nature of unresolved star clusters in external galaxies. However,
the plethora of currently available SSP models gives rise to significant and
poorly documented systematic differences. Here we consider the outputs of the
commonly used Bruzual & Charlot and GALEV models, as well as a recently updated
SSP model suite which attempts to include the contributions of binary merger
products in the form of blue straggler stars (BS-SSP). We rederive the ages,
metallicities, extinction values and masses of 445 previously observed
globular-like clusters in M31 based on chi-square minimisation of their
spectral energy distributions with respect to these three different SSP models
and adopting a Chabrier-like stellar initial mass function. A comparison
between our new results and previous estimates of the same parameters shows
that the Bruzual & Charlot models yield the youngest ages and lowest masses,
while adoption of the BS-SSP models results in the oldest ages and highest mass
estimates. Similarly, the GALEV SSP models produce the lowest metallicities,
with the highest values resulting from the BS-SSP model suite. These trends are
caused by intrinsic differences associated with the models, and are not
significantly affected by the well-known age-metallicity degeneracy. Finally,
we note that the mass function of the massive M31 star clusters is similar to
that of the Milky Way's globular clusters, which implies that the two star
cluster systems likely formed under similar environmental conditions. | Minkowski Functionals in Joint Galaxy Clustering & Weak Lensing Analyses: We investigate the inclusion of clustering maps in a weak lensing Minkowski
functional (MF) analysis of DES-like and LSST-like simulations to constrain
cosmological parameters. The standard 3x2pt approach to lensing and clustering
data uses two-point correlations as its primary statistic; MFs, morphological
statistics describing the shape of matter fields, provide additional
information for non-Gaussian fields. Previous analyses have studied MFs of
lensing convergence maps; in this project we explore their simultaneous
application to clustering maps. We employ a simplified linear galaxy bias
model, and using a lognormal curved sky measurement and Monte Carlo Markov
Chain (MCMC) sampling process for parameter inference, we find that MFs do not
yield any information in the $\Omega_{\rm m}$ -- $\sigma_8$ plane not already
generated by a 3x2pt analysis. However, we expect that MFs should improve
constraining power when nonlinear baryonic and other small-scale effects are
taken into account. As with a 3x2pt analysis, we find a significant improvement
to constraints when adding clustering data to MF-only and MF$+C_\ell$ shear
measurements, and strongly recommend future higher order statistics be measured
from both convergence and clustering maps. |
A close look at the Centaurus A group of galaxies III. Recent star
formation histories of late-type dwarfs around M83: We study the resolved stellar populations of dwarf galaxies in the nearby
Centaurus A/M83 group of galaxies. Our goal is to characterize their
evolutionary history and to investigate eventual similarities or differences
with the dwarf population in other group environments. This work presents the
analysis of five late-type (irregular) dwarfs found in the vicinity of the
giant spiral M83. Using archival HST/ACS data, we perform synthetic
color-magnitude diagram modeling to derive the star formation histories of
these late-type dwarfs. The target objects show heterogeneous star formation
histories, with average star formation rates of 0.08 to 0.70x10^{-2} M_odot/yr.
Some of them present prolonged, global bursts of star formation (~300-500 Myr).
The studied galaxies are all metal-poor ([Fe/H] ~-1.4). We further investigate
the spatial extent of different stellar populations, finding that the young
stars show a clumpy distribution, as opposed to the smooth, broad extent of the
old ones. The actively star forming regions have sizes of ~100 pc and lifetimes
of >~100 Myr, thus suggesting a stochastic star formation mode for the target
dwarf irregular galaxies. The galaxies formed ~20% to 70% of their stars more
than ~7 Gyr ago. The studied dwarfs have average star formation rates slightly
higher than their analogues in the Local Group, but comparable to those in the
M81 group. Our preliminary sample indicates that the neutral gas content of the
target dwarfs does seem to be affected by the group environment: galaxies
within a denser region have a much lower M_HI/<SFR> than the isolated ones,
meaning that they will exhaust their gas reservoir more quickly. | Stellar Masses of Lyman Break Galaxies, Lyman Alpha Emitters and Radio
Galaxies in Overdense Regions at z=4-6: We present new information on galaxies in the vicinity of luminous radio
galaxies and quasars at z=4,5,6. These fields were previously found to contain
overdensities of Lyman Break Galaxies (LBGs) or spectroscopic Lyman alpha
emitters. We use HST and Spitzer data to infer stellar masses, and contrast our
results with large samples of LBGs in more average environments as probed by
the Great Observatories Origins Deep Survey (GOODS). The following results were
obtained. First, LBGs in both overdense regions and in the field at z=4-5 lie
on a very similar sequence in a z'-[3.6] versus [3.6] color-magnitude diagram.
This is interpreted as a sequence in stellar mass (log[M*/Msun] = 9-11) in
which galaxies become increasingly red due to dust and age as their star
formation rate (SFR) increases. Second, the two radio galaxies are among the
most massive objects (log[M*/Msun]~11) known to exist at z~4-5, and are
extremely rare based on the low number density of such objects as estimated
from the ~25x larger area GOODS survey. We suggest that the presence of these
massive galaxies and supermassive black holes has been boosted through rapid
accretion of gas or merging inside overdense regions. Third, the total stellar
mass found in the z=4 ``proto-cluster'' TN1338 accounts for <30% of the stellar
mass on the cluster red sequence expected to have formed at z>4, based on a
comparison with the massive X-ray cluster Cl1252 at z=1.2. Although future
near-infrared observations should determine whether any massive galaxies are
currently being missed, one possible explanation for this mass difference is
that TN1338 evolves into a smaller cluster than Cl1252. This raises the
interesting question of whether the most massive protocluster regions at z>4
remain yet to be discovered. |
The Cosmogrid Simulation: Statistical Properties of Small Dark Matter
Halos: We present the results of the "Cosmogrid" cosmological N-body simulation
suites based on the concordance LCDM model. The Cosmogrid simulation was
performed in a 30Mpc box with 2048^3 particles. The mass of each particle is
1.28x10^5 Msun, which is sufficient to resolve ultra-faint dwarfs. We found
that the halo mass function shows good agreement with the Sheth & Tormen
fitting function down to ~10^7 Msun. We have analyzed the spherically averaged
density profiles of the three most massive halos which are of galaxy group size
and contain at least 170 million particles. The slopes of these density
profiles become shallower than -1 at the inner most radius. We also find a
clear correlation of halo concentration with mass. The mass dependence of the
concentration parameter cannot be expressed by a single power law, however a
simple model based on the Press-Schechter theory proposed by Navarro et al.
gives reasonable agreement with this dependence. The spin parameter does not
show a correlation with the halo mass. The probability distribution functions
for both concentration and spin are well fitted by the log-normal distribution
for halos with the masses larger than ~10^8 Msun. The subhalo abundance depends
on the halo mass. Galaxy-sized halos have 50% more subhalos than ~10^{11} Msun
halos have. | Optimal constraint on g_NL from CMB: An optimal method to constrain the non-linearity parameter g_NL of the
local-type non-Gaussianity from CMB data is proposed. Our optimal estimator for
g_NL is separable and can be efficiently computed in real space. Combining the
exact filtering of CMB maps with the full covariance matrix, our method allows
us to extract cosmological information from observed data as much as possible
and obtain a tighter constraint on g_NL than previous studies. Applying our
method to the WMAP 9-year data, we obtain the constraint g_NL = (-3.3 +- 2.2)
10^5, which is a few times tighter than previous ones. We also make a forecast
for PLANCK data by using the Fisher matrix analysis. |
BLR Physical Conditions in Extreme Population A Quasars: a Method to
Estimate Central Black Hole Mass at High Redshift: We describe a method for determination of physical conditions in the broad
line regions of a significant subsample of Seyfert-1 nuclei and quasars.
Several diagnostic ratios based on intermediate (AlIII 1860, SiIII 1892) and
high (CIV 1549, SiIV 1397) ionization lines in the UV spectra of quasars are
used to constrain density, ionization and metallicity of the emitting gas. We
apply the method to two extreme Population A quasars - the prototypical NLSy1 I
Zw 1 and a high-z\ NLSy1-like object, SDSS J120144.36+011611.6. We find
well-defined physical conditions: low ionization (ionization parameter $<
10^{-2}$), high density (10$^{12} - 10^{13}$ cm^{-3}) and significant metal
enrichment. Ionization parameter and density can be derived independently for
each source with an uncertainty that is always less than $\pm 0.3$ in
logarithm. We use the product density times ionization parameter to estimate
the broad line region radius and the virial black hole mass. Estimates of black
hole masses based on the "photoionization" analysis described in this paper are
probably more accurate than those derived from the radius - luminosity
correlation. | Directional detection as a strategy to discover Galactic Dark Matter: Directional detection of Galactic Dark Matter is a promising search strategy
for discriminating genuine WIMP events from background ones. Technical progress
on gaseous detectors and read-outs has permitted the design and construction of
competitive experiments. However, to take full advantage of this powerful
detection method, one need to be able to extract information from an observed
recoil map to identify a WIMP signal. We present a comprehensive formalism,
using a map-based likelihood method allowing to recover the main incoming
direction of the signal and its significance, thus proving its galactic origin.
This is a blind analysis intended to be used on any directional data.
Constraints are deduced in the ($\sigma_n, m_\chi$) plane and systematic
studies are presented in order to show that, using this analysis tool,
unambiguous dark matter detection can be achieved on a large range of exposures
and background levels. |
Flexion measurement in simulations of Hubble Space Telescope data: We present a simulation analysis of weak gravitational lensing flexion and
shear measurement using shapelet decomposition, and identify differences
between flexion and shear measurement noise in deep survey data. Taking models
of galaxies from the Hubble Space Telescope Ultra Deep Field (HUDF) and
applying a correction for the HUDF point spread function we generate lensed
simulations of deep, optical imaging data from Hubble's Advanced Camera for
Surveys (ACS), with realistic galaxy morphologies. We find that flexion and
shear estimates differ in our measurement pipeline: whereas intrinsic galaxy
shape is typically the dominant contribution to noise in shear estimates, pixel
noise due to finite photon counts and detector read noise is a major
contributor to uncertainty in flexion estimates, across a broad range of galaxy
signal-to-noise. This pixel noise also increases more rapidly as galaxy
signal-to-noise decreases than is found for shear estimates. We provide simple
power law fitting functions for this behaviour, for both flexion and shear,
allowing the effect to be properly accounted for in future forecasts for
flexion measurement. Using the simulations we also quantify the systematic
biases of our shapelet flexion and shear measurement pipeline for deep Hubble
data sets such as Galaxy Evolution from Morphology and SEDs, Space Telescope
A901/902 Galaxy Evolution Survey or the Cosmic Evolution Survey. Flexion
measurement biases are found to be significant but consistent with previous
studies. | Circular polarization of the cosmic microwave background from vector and
tensor perturbations: Circular polarization of the cosmic microwave background (CMB) can be induced
by Faraday conversion of the primordial linearly polarized radiation as it
propagates through a birefringent medium. Recent work has shown that the
dominant source of birefringence from primordial density perturbations is the
anisotropic background CMB. Here we extend prior work to allow for the
additional birefringence that may arise from primordial vector and tensor
perturbations. We derive the formulas for the power spectrum of the induced
circular polarization and apply those to the standard cosmology. We find the
root-variance of the induced circular polarization to be $\sqrt{<V^2>}\sim
3\times 10^{-14}$ for scalar perturbations and $\sqrt{<V^2>}\sim 7\times
10^{-18} (r/0.06)$ for tensor perturbations with a tensor-to-scalar ratio $r$. |
Forecast analysis and focal plane optimization for a multi-frequency CMB
B-modes polarization experiment: the case of LSPE: We present an optimization scheme for the focal plane of a multi-frequency
CMB B-modes experiment with a fixed number of detectors and apply it to the
specific case of LSPE experiment. Optimal focal planes are identified on the
ground of different figures of merit defined in terms of the forecasted
uncertainty $\sigma_r$ on the tensor--to-scalar ratio $r$ and the expected map
variance from foreground and instrumental noise residuals. We then perform a
forecast analysis in order to assess the precision achievable in B-modes
measurements. | Dark Energy Survey Year 1 Results: The Impact of Galaxy Neighbours on
Weak Lensing Cosmology with im3shape: We use a suite of simulated images based on Year 1 of the Dark Energy Survey
to explore the impact of galaxy neighbours on shape measurement and shear
cosmology. The hoopoe image simulations include realistic blending, galaxy
positions, and spatial variations in depth and PSF properties. Using the
im3shape maximum-likelihood shape measurement code, we identify four mechanisms
by which neighbours can have a non-negligible influence on shear estimation.
These effects, if ignored, would contribute a net multiplicative bias of $m
\sim 0.03 - 0.09$ in the DES Y1 im3shape catalogue, though the precise impact
will be dependent on both the measurement code and the selection cuts applied.
This can be reduced to percentage level or less by removing objects with close
neighbours, at a cost to the effective number density of galaxies
$n_\mathrm{eff}$ of 30%. We use the cosmological inference pipeline of DES Y1
to explore the cosmological implications of neighbour bias and show that
omitting blending from the calibration simulation for DES Y1 would bias the
inferred clustering amplitude $S_8\equiv \sigma_8 (\Omega _\mathrm{m}
/0.3)^{0.5}$ by $2 \sigma$ towards low values. Finally, we use the hoopoe
simulations to test the effect of neighbour-induced spatial correlations in the
multiplicative bias. We find the impact on the recovered $S_8$ of ignoring such
correlations to be subdominant to statistical error at the current level of
precision. |
AMiBA: scaling relations between the integrated Compton-y and X-ray
derived temperature, mass, and luminosity: We investigate the scaling relations between the X-ray and the thermal
Sunyaev-Zel'dovich Effect (SZE) properties of clusters of galaxies, using data
taken during 2007 by the Y.T. Lee Array for Microwave Background Anisotropy
(AMiBA) at 94 GHz for the six clusters A1689, A1995, A2142, A2163, A2261, and
A2390. The scaling relations relate the integrated Compton-y parameter Y_{2500}
to the X-ray derived gas temperature T_{e}, total mass M_{2500}, and bolometric
luminosity L_X within r_{2500}. Our results for the power-law index and
normalization are both consistent with the self-similar model and other studies
in the literature except for the Y_{2500}-L_X relation, for which a physical
explanation is given though further investigation may be still needed. Our
results not only provide confidence for the AMiBA project but also support our
understanding of galaxy clusters. | Revealing the Structure of the Inflationary Landscape through Primordial
non-Gaussianity: In this thesis, we show how the structure of the landscape potential of the
primordial Universe may be probed through the primordial density perturbations
responsible for the origin of the cosmic microwave background anisotropies and
the large-scale structure of our Universe. Isocurvature fields may have
fluctuated across the barriers separating local minima of the landscape
potential during inflation. We analyze how this process could have impacted the
evolution of the primordial curvature perturbations. If the typical distance
separating consecutive minima of the landscape potential and the height of the
potential barriers are smaller than the Hubble expansion rate parametrizing
inflation, the probability distribution function of isocurvature fields becomes
non-Gaussian due to the appearance of bumps and dips associated with the
structure of the potential. We show that this non-Gaussianity can be
transferred to the statistics of primordial curvature perturbations. The type
of non-Gaussian structure that emerges in the distribution of curvature
perturbations cannot be fully probed with the standard methods of polyspectra;
instead, the probability distribution function is needed.
To substantiate our claims, we offer a concrete model consisting of an
isocurvature perturbation with a sinusoidal potential and a linear derivative
coupling between the isocurvature and curvature field. This result is
generalized to arbitrary potentials and briefly studied beyond first-order
perturbation theory. Finally, we undertake a study of primordial
non-Gaussianity of the local type, where we use our results to reconstruct and
constrain the shape of the landscape potential with the help of Cosmic
Microwave Background observations by the Planck telescope and explore prospects
for observable quantities in the Large-Scale Structure of our universe towards
constraining its primordial statistics. |
Dissociation of dark matter and gas in cosmic large-scale structure: The partial spatial separation of cold dark matter (DM) and gas is a
ubiquitous feature in the formation of cosmic large-scale structure. This
separation, termed dissociation, is prominent in galaxy clusters that formed
through collisions of massive progenitors, such as the famous `Bullet' cluster.
A direct comparison of the incidence of such dissociated structures with
theoretical predictions is challenged by the rarity of strongly dissociated
systems and the difficulty to quantify dissociation. This paper introduces a
well-defined dimensionless dissociation index $S\in[-1,1]$ that encodes the
quadrupole difference between DM and gas in a custom region. Using a simulation
of cosmic large-scale structure with cold DM and ideal non-radiating gas, in
$\Lambda$CDM cosmology, we find that 90 per cent of the haloes are positively
dissociated ($S>0$), meaning their DM is more elongated than their gas. The
spatial density of highly dissociated massive structures appears consistent
with observations. Through idealised $N$-body+SPH simulations of colliding
gaseous DM haloes, we further explore the details of how ram-pressure causes
dissociation in binary collisions. A suite of 300 such simulations reveals a
scale-free relation between the orbital parameters of binary collisions and the
resulting dissociation. Building on this relation, we conclude that the
frequency of dissociated structures in non-radiative cosmological simulations
is nearly fully accounted for by the major (mass ratio $>1:10$) binary
collisions predicted by such simulations. In principle, our results allow us to
constrain the orbital parameters that produced specific observed dissociated
clusters. | Super-sample covariance of the thermal Sunyaev-Zel'dovich effect: The thermal Sunyaev-Zel'dovich (tSZ) effect is a powerful probe of cosmology.
The statistical errors in the tSZ power spectrum measurements are dominated by
the presence of massive clusters in a survey volume that are easy to identify
on individual cluster basis. First, we study the impact of super sample
covariance (SSC) on the tSZ power spectrum measurements, and find that the
sample variance is dominated by the connected non-Gaussian (cNG) covariance
arising mainly from Poisson number fluctuations of massive clusters in the
survey volume. Second, we find that removing such individually-detected,
massive clusters from the analysis significantly reduces the cNG contribution,
thereby leading the SSC to be a leading source of the sample variance. We then
show, based on Fisher analysis, that the power spectrum measured from the
remaining diffuse tSZ effects can be used to obtain tight constraints on
cosmological parameters as well as the hydrostatic mass bias parameter. Our
method offers complementary use of individual tSZ cluster counts and the power
spectrum measurements of diffuse tSZ signals for cosmology and intracluster gas
physics. |
Estimating small angular scale CMB anisotropy with high resolution
N-body simulations: weak lensing: We estimate the impact of weak lensing by strongly nonlinear cosmological
structures on the cosmic microwave background. Accurate calculation of large
$\ell$ multipoles requires N-body simulations and ray-tracing schemes with both
high spatial and temporal resolution. To this end we have developed a new code
that combines a gravitational Adaptive Particle-Particle, Particle-Mesh (AP3M)
solver with a weak lensing evaluation routine. The lensing deviations are
evaluated while structure evolves during the simulation so that all evolution
steps--rather than just a few outputs--are used in the lensing computations.
The new code also includes a ray-tracing procedure that avoids periodicity
effects in a universe that is modeled as a 3-D torus in the standard way.
Results from our new simulations are compared with previous ones based on
Particle-Mesh simulations. We also systematically investigate the impact of box
volume, resolution, and ray-tracing directions on the variance of the computed
power spectra. We find that a box size of $512 h^{-1}$ Mpc is sufficient to
provide a robust estimate of the weak lensing angular power spectrum in the
$\ell$-interval (2,000--7,000). For a reaslistic cosmological model the power
$[\ell(\ell+1)C_{\ell}/2\pi]^{1/2}$ takes on values of a few $\mu K$ in this
interval, which suggests that a future detection is feasible and may explain
the excess power at high $\ell$ in the BIMA and CBI observations. | What is the probability that direct detection experiments have observed
Dark Matter?: In Dark Matter direct detection we are facing the situation of some
experiments reporting positive signals which are in conflict with limits from
other experiments. Such conclusions are subject to large uncertainties
introduced by the poorly known local Dark Matter distribution. We present a
method to calculate an upper bound on the joint probability of obtaining the
outcome of two potentially conflicting experiments under the assumption that
the Dark Matter hypothesis is correct, but completely independent of
assumptions about the Dark Matter distribution. In this way we can quantify the
compatibility of two experiments in an astrophysics independent way. We
illustrate our method by testing the compatibility of the hints reported by
DAMA and CDMS-Si with the limits from the LUX and SuperCDMS experiments. The
method does not require Monte Carlo simulations but is mostly based on using
Poisson statistics. In order to deal with signals of few events we introduce
the so-called "signal length" to take into account energy information. The
signal length method provides a simple way to calculate the probability to
obtain a given experimental outcome under a specified Dark Matter and
background hypothesis. |
On the rise and fall of galactic ionizing output at the end of
reionization: Quasar absorption spectra measurements suggest that reionization proceeded
rapidly, ended late at $z \sim 5.5$, and was followed by a flat evolution of
the ionizing background. Simulations that can reproduce this behavior often
rely on a fine-tuned galaxy ionizing emissivity, which peaks at $z \sim 6 - 7$
and drops by a factor of $1.5-2.5$ by $z \sim 5$. This is puzzling since the
abundance of galaxies has been observed to grow monotonically during this
period. Explanations for this include effects such as dust obscuration of
ionizing photon escape and feedback due to photo-heating of the IGM. We explore
the possibility that this drop in emissivity is instead an artifact of one or
more modeling deficiencies in reionization simulations. These include possibly
incorrect assumptions about the ionizing spectrum and/or inaccurate modeling of
the clumpiness of the IGM. Our results suggest that the need for a drop could
be alleviated if simulations are underestimating the IGM opacity from massive,
star-forming halos. Other potential modeling issues either have a small effect
or require a steeper drop when remedied. We construct an illustrative model in
which the emissivity is nearly flat at the end of reionization, evolving only
$\sim 0.05$ dex at $5 < z < 7$. More realistic scenarios, however, require a
$\sim 0.1-0.3$ dex drop. We also study the evolution of the Ly$\alpha$
effective optical depth distribution in these scenarios and compare them to
recent measurements. We find models that feature a hard ionizing spectrum
and/or are driven by faint, low-bias sources can most easily reproduce the mean
transmission and optical depth distribution of the forest simultaneously.
Lastly, we show that the reduced speed of light approximation and low spatial
resolution in the forest can lead to erroneous conclusions about the end of
reionization. | A one-parameter formula for testing slow-roll dark energy: observational
prospects: Numerous upcoming observations, such as WFIRST, BOSS, BigBOSS, LSST, Euclid,
and Planck, will constrain dark energy (DE)'s equation of state with great
precision. They may well find the ratio of pressure to energy density, $w$, is
-1, meaning DE is equivalent to a cosmological constant. However, many
time-varying DE models have also been proposed. A single parametrization to
test a broad class of them and that is itself motivated by a physical picture
is therefore desirable. We suggest the simplest model of DE has the same
mechanism as inflation, likely a scalar field slowly rolling down its
potential. If this is so, DE will have a generic equation of state and the
Universe will have a generic dependence of the Hubble constant on redshift
independent of the potential's starting value and shape. This equation of state
and expression for the Hubble constant offer the desired model-independent but
physically motivated parametrization, because they will hold for most of the
standard scalar-field models of DE such as quintessence and phantom DE. Up
until now two-parameter descriptions of $w$ have been available, but this work
finds an additional approximation that leads to a single-parameter model. Using
it, we conduct a $\chi^2$ analysis and find that experiments in the next seven
years should be able to distinguish any of these time-varying DE models on the
one hand from a cosmological constant on the other to 73% confidence if $w$
today differs from -1 by 3.5%. In the limit of perfectly accurate measurements
of $\Omega_m$ and $H_0$, this confidence would rise to 96%. We also include
discussion of the current status of DE experiment, a table compiling the
techniques each will use, and tables of the precisions of the experiments for
which this information was available at the time of publication. |
The evolution of the rest-frame J- and H-band luminosity function of
galaxies to z=3.5: We present the rest-frame J- and H-band luminosity function (LF) of field
galaxies, based on a deep multi-wavelength composite sample from the MUSYC,
FIRES and FIREWORKS survey public catalogues, covering a total area of 450
arcmin^2. The availability of flux measurements in the Spitzer IRAC 3.6, 4.5,
5.8, and 8 um channels allows us to compute absolute magnitudes in the
rest-frame J and H bands up to z=3.5 minimizing the dependence on the stellar
evolution models. We compute the LF in the four redshift bins 1.5<z<2.0,
2.0<z<2.5, 2.5<z<3.0 and 3.0<z<3.5. Combining our results with those already
available at lower redshifts, we find that (1) the faint end slope is
consistent with being constant up to z=3.5, with alpha=-1.05+/-0.03 for the
rest-frame J band and alpha=-1.15+/-0.02 for the rest-frame H band; (2) the
normalization phi* decreases by a factor of 6 between z=0 and z~1.75 and by a
factor 3 between z~1.75 and z=3.25; (3) the characteristic magnitude M* shows a
brightening from z=0 to z~2 followed by a slow dimming to z=3.25. We finally
compute the luminosity density (LD) in both rest-frame J and H bands. The
analysis of our results together with those available in the literature shows
that the LD is approximately constant up to z~1, and it then decreases by a
factor of 6 up to z=3.5. | Imaging HII Regions from Galaxies and Quasars During Reionisation with
SKA: The ionisation structure of the Intergalactic Medium (IGM) during
reionisation is sensitive to the unknown galaxy formation physics that
prevailed at that time. This structure introduces non-Gaussian statistics into
the redshifted 21 cm fluctuation amplitudes that can only be studied through
tomographic imaging, which will clearly discriminate between different galaxy
formation scenarios. Imaging the ionisation structure and cosmological HII
regions during reionisation is therefore a key goal for the SKA. For example,
the SKA1-LOW baseline design with a 1 km diameter core will resolve HII regions
expected from galaxy formation models which include strong feedback on low-mass
galaxy formation. Imaging the smaller HII regions that result from galaxy
formation in the absence of SNe feedback will also be possible for SKA1-LOW in
the later stages of reionisation, but may require the greater sensitivity of
SKA early in the reionisation era. In addition to having baselines long enough
to resolve the HII regions, the field of view for SKA1-LOW reionisation
experiments should be at least several degrees in order to image the largest HI
structures towards the end of reionisation. The baseline design with 35 meter
diameter stations has a field of view within a single primary pointing which is
sufficient for this purpose. |
Tree-level unitarity in Higgs inflation in the metric and the Palatini
formulation: We calculate the tree-level amplitudes for electrically neutral $2\to2$
scattering for the Standard Model Higgs doublet non-minimally coupled to the
Ricci scalar. We consider both the metric and the Palatini formulation of
gravity. We find the partial wave unitarity limit for a general background
field value. Our results are in agreement with previous work. In the
electroweak vacuum, tree-level unitarity is violated at $\sim
M_\text{Planck}/\xi$ in the metric formulation, and at $\sim
M_\text{Planck}/\sqrt{\xi}$ in the Palatini formulation. In the inflationary
large field background, the unitarity limit is at $\sim
M_\text{Planck}/\sqrt{\xi}$ in both formulations. We compare the unitarity
violation energy to scales relevant during inflation. We also calculate a
direct collider limit on $\xi$ in the Palatini formulation,
$\xi<2.5\times10^{31}$. | The halo model with beyond-linear halo bias: unbiasing cosmological
constraints from galaxy-galaxy lensing and clustering: We determine the error introduced in a joint halo model analysis of
galaxy-galaxy lensing and galaxy clustering observables when adopting the
standard approximation of linear halo bias. Considering the Kilo-Degree Survey,
we forecast that ignoring the non-linear halo bias would result in up to
5$\sigma$ offsets in the recovered cosmological parameters describing structure
growth, $S_8$, and the matter density parameter, $\Omega_{\mathrm{m}}$. We
include the scales $10^{-1.3}<r_{\rm{p}} \ / h^{-1}\, \mathrm{Mpc}<10$ in the
data vector, and the direction of these offsets are shown to depend on the
freedom afforded to the halo model through other nuisance parameters. We
conclude that a beyond-linear halo bias correction must therefore be included
in future cosmological halo model analyses of large-scale structure observables
on non-linear scales. |
Deciphering baryonic feedback with galaxy clusters: Upcoming cosmic shear analyses will precisely measure the cosmic matter
distribution at low redshifts. At these redshifts, the matter distribution is
affected by galaxy formation physics, primarily baryonic feedback from star
formation and active galactic nuclei. Employing measurements from the
Magneticum and IllustrisTNG simulations and a dark matter + baryon (DMB) halo
model, this paper demonstrates that Sunyaev-Zel'dovich (SZ) effect observations
of galaxy clusters, whose masses have been calibrated using weak gravitational
lensing, can constrain the baryonic impact on cosmic shear with statistical and
systematic errors subdominant to the measurement errors of DES-Y3 and LSST-Y1.
We further dissect the contributions from different scales and halos with
different masses to cosmic shear, highlighting the dominant role of SZ clusters
at scales critical for cosmic shear analyses. These findings suggest a
promising avenue for future joint analyses of Cosmic Microwave Background (CMB)
and lensing surveys. | A Comparison of Cosmological Parameters Determined from CMB Temperature
Power Spectra from the South Pole Telescope and the Planck Satellite: The Planck cosmic microwave background (CMB) temperature data are best fit
with a LCDM model that is in mild tension with constraints from other
cosmological probes. The South Pole Telescope (SPT) 2540 $\text{deg}^2$ SPT-SZ
survey offers measurements on sub-degree angular scales (multipoles $650 \leq
\ell \leq 2500$) with sufficient precision to use as an independent check of
the Planck data. Here we build on the recent joint analysis of the SPT-SZ and
Planck data in \citet{hou17} by comparing LCDM parameter estimates using the
temperature power spectrum from both data sets in the SPT-SZ survey region. We
also restrict the multipole range used in parameter fitting to focus on modes
measured well by both SPT and Planck, thereby greatly reducing sample variance
as a driver of parameter differences and creating a stringent test for
systematic errors. We find no evidence of systematic errors from such tests.
When we expand the maximum multipole of SPT data used, we see low-significance
shifts in the angular scale of the sound horizon and the physical baryon and
cold dark matter densities, with a resulting trend to higher Hubble constant.
When we compare SPT and Planck data on the SPT-SZ sky patch to Planck full-sky
data but keep the multipole range restricted, we find differences in the
parameters $n_s$ and $A_se^{-2\tau}$. We perform further checks, investigating
instrumental effects and modeling assumptions, and we find no evidence that the
effects investigated are responsible for any of the parameter shifts. Taken
together, these tests reveal no evidence for systematic errors in SPT or Planck
data in the overlapping sky coverage and multipole range and, at most, weak
evidence for a breakdown of LCDM or systematic errors influencing either the
Planck data outside the SPT-SZ survey area or the SPT data at $\ell >2000$. |
Concordance and Discordance in Cosmology: The success of present and future cosmological studies is tied to the ability
to detect discrepancies in complex data sets within the framework of a
cosmological model. Tensions caused by the presence of unknown systematic
effects need to be isolated and corrected to increase the overall accuracy of
parameter constraints, while discrepancies due to new physical phenomena need
to be promptly identified. We develop a full set of estimators of internal and
mutual agreement and disagreement, whose strengths complement each other. These
allow to take into account the effect of prior information and compute the
statistical significance of both tensions and confirmatory biases. We apply
them to a wide range of state of the art cosmological probes and show that
these estimators can be easily used, regardless of model and data complexity.
We derive a series of results that show that discrepancies indeed arise within
the standard LCDM model. Several of them exceed the probability threshold of
95% and deserve a dedicated effort to understand their origin. | On the alignment of haloes, filaments and magnetic fields in the
simulated cosmic web: The continuous flow of gas and dark matter across scales in the cosmic web
can generate correlated dynamical properties of haloes and filaments (and the
magnetic fields they contain). With this work, we study the halo spin
properties and orientation with respect to filaments, and the morphology of the
magnetic field around these objects, for haloes with masses in the range
1e8-1e14 Msun and filaments up to 8 Mpc long. Furthermore, we study how these
properties vary in presence, or lack thereof, of different (astro)physical
processes and with different magnetic initial conditions. We perform
cosmological magnetohydrodynamical simulations with the Eulerian code Enzo and
we develop a simple and robust algorithm to study the filamentary connectivity
of haloes in three dimensions. We investigate the morphological and magnetic
properties and focus on the alignment of the magnetic field along filaments:
our analysis suggests that the degree of this alignment is partially dependent
on the physical processes involved, as well as on magnetic initial conditions.
We discuss the contribution of this effect on a potential attempt to detect the
magnetic field surrounding these objects: we find that it introduces a bias in
the estimation of the magnetic field from Faraday rotation measure techniques.
Specifically, given the strong tendency we find for extragalactic magnetic
fields to align with the filaments axis, the value of the magnetic field can be
underestimated by a factor 3, because this effect contributes to making the
line-of-sight magnetic field (for filaments in the plane of the sky) much
smaller than the total one. |
Satellites in the Local Group and Other Nearby Groups: In recent years the census of known satellites in our own Local Group and in
nearby galaxy groups has increased substantially due to sensitive wide-area
surveys. In the Local Group these surveys have more than doubled its known
galaxy content and extended the galaxy luminosity function to very faint total
magnitudes. Deep ground-based imaging and spectroscopic observations as well as
high-resolution imaging with the Hubble Space Telescope have revolutionized our
understanding of the chemical evolution and star formation histories of the
satellites. We often find long-lasting star formation episodes with low star
formation efficiencies. There is evidence for localized, stochastic enrichment,
and recent searches are now beginning to uncover even extremely metal-deficient
stars. In many satellites evidence for two or more distinct stellar
subpopulations is found. Differing fractions of old populations have been
detected in all satellites studied in sufficient detail so far. Kinematic
measurements support a picture in which satellites are dark-matter dominated,
although recent results indicate that the proposed common mass scale for dwarf
spheroidal galaxies may not hold for very low-mass satellites. When considering
satellite ensembles, we find global morphology-distance and gas-content -
distance relations in all groups studied thus far, but individual star
formation histories also strongly depend on a given satellite's intrinsic
properties. | Star Cluster Complexes and the Host Galaxy in Three HII Galaxies: Mrk
36, UM 408, and UM 461: We present a stellar population study of three HII galaxies (Mrk 36, UM 408,
and UM 461) based on the analysis of new ground-based high resolution
near-infrared J, H and Kp broad-band and Br narrow-band images obtained with
Gemini/NIRI. We identify and determine relative ages and masses of the
elementary star clusters and/or star cluster complexes of the starburst regions
in each of these galaxies by comparing the colors with evolutionary synthesis
models that include the contribution of stellar continuum, nebular continuum
and emission lines. We found that the current star cluster formation efficiency
in our sample of low luminosity HII galaxies is ~10%. Therefore, most of the
recent star formation is not in massive clusters. Our findings seem to indicate
that the star formation mode in our sample of galaxies is clumpy, and that
these complexes are formed by a few massive star clusters with masses > 10^4
Mo. The age distribution of these star cluster complexes shows that the current
burst started recently and likely simultaneously over short time scales in
their host galaxies, triggered by some internal mechanism. Finally, the
fraction of the total cluster mass with respect to the low surface brightness
(or host galaxy) mass, considering our complete range in ages, is less than 1%. |
Cosmological inference from Bayesian forward modelling of deep galaxy
redshift surveys: We present a large-scale Bayesian inference framework to constrain
cosmological parameters using galaxy redshift surveys, via an application of
the Alcock-Paczy\'nski (AP) test. Our physical model of the non-linearly
evolved density field, as probed by galaxy surveys, employs Lagrangian
perturbation theory (LPT) to connect Gaussian initial conditions to the final
density field, followed by a coordinate transformation to obtain the redshift
space representation for comparison with data. We generate realizations of
primordial and present-day matter fluctuations given a set of observations.
This hierarchical approach encodes a novel AP test, extracting several orders
of magnitude more information from the cosmological expansion compared to
classical approaches, to infer cosmological parameters and jointly reconstruct
the underlying 3D dark matter density field. The novelty of this AP test lies
in constraining the comoving-redshift transformation to infer the appropriate
cosmology which yields isotropic correlations of the galaxy density field, with
the underlying assumption relying purely on the cosmological principle. Such an
AP test does not rely explicitly on modelling the full statistics of the field.
We verify in depth via simulations that this renders our test robust to model
misspecification. This leads to another crucial advantage, namely that the
cosmological parameters exhibit extremely weak dependence on the currently
unresolved phenomenon of galaxy bias, thereby circumventing a potentially key
limitation. This is consequently among the first methods to extract a large
fraction of information from statistics other than that of direct density
contrast correlations, without being sensitive to the amplitude of density
fluctuations. We perform several statistical efficiency and consistency tests
on a mock galaxy catalogue, using the SDSS-III survey as template. | The Effect of Interstellar Absorption on Measurements of the Baryon
Acoustic Peak in the Lyman-α Forest: In recent years, the autocorrelation of the hydrogen Lyman-{\alpha} forest
has been used to observe the baryon acoustic peak at redshift 2 < z < 3.5 using
tens of thousands of QSO spectra from the BOSS survey. However, the
interstellar medium of the Milky-Way introduces absorption lines into the
spectrum of any extragalactic source. These lines, while weak and undetectable
in a single BOSS spectrum, could potentially bias the cosmological signal. In
order to examine this, we generate absorption line maps by stacking over a
million spectra of galaxies and QSOs. We find that the systematics introduced
are too small to affect the current accuracy of the baryon acoustic peak, but
might be relevant to future surveys such as the Dark Energy Spectroscopic
Instrument (DESI). We outline a method to account for this with future
datasets. |
Fast Pixel Space Convolution for CMB Surveys with Asymmetric Beams and
Complex Scan Strategies: FEBeCoP: Precise measurement of the angular power spectrum of the Cosmic Microwave
Background (CMB) temperature and polarization anisotropy can tightly constrain
many cosmological models and parameters. However, accurate measurements can
only be realized in practice provided all major systematic effects have been
taken into account. Beam asymmetry, coupled with the scan strategy, is a major
source of systematic error in scanning CMB experiments such as Planck, the
focus of our current interest. We envision Monte Carlo methods to rigorously
study and account for the systematic effect of beams in CMB analysis. Toward
that goal, we have developed a fast pixel space convolution method that can
simulate sky maps observed by a scanning instrument, taking into account real
beam shapes and scan strategy. The essence is to pre-compute the "effective
beams" using a computer code, "Fast Effective Beam Convolution in Pixel space"
(FEBeCoP), that we have developed for the Planck mission. The code computes
effective beams given the focal plane beam characteristics of the Planck
instrument and the full history of actual satellite pointing, and performs very
fast convolution of sky signals using the effective beams. In this paper, we
describe the algorithm and the computational scheme that has been implemented.
We also outline a few applications of the effective beams in the precision
analysis of Planck data, for characterizing the CMB anisotropy and for
detecting and measuring properties of point sources. | Interpreting the Low Frequency Radio Spectra of Starburst Galaxies: A
Pudding of Strömgren Spheres: The low frequency radio emission of starburst galaxies is informative, but it
can be absorbed in several ways. Most importantly, starburst galaxies are home
to many H II regions, whose free-free absorption blocks low frequency radio
waves. These H II regions are discrete objects, but most multiwavelength models
of starbursts assume a uniform medium of ionized gas, if they include the
absorption at all. I calculate the effective absorption coefficient of H II
regions in starbursts, which is ultimately a cross section times the density of
H II regions. The cross sections are calculated by assuming that H II regions
are Str\"omgren spheres. The coefficient asymptotes to a constant value at low
frequencies, because H II regions partially cover the starburst, and are buried
part way into the starburst's synchrotron emitting material. Considering
Str\"omgren spheres around either OB stars or Super Star Clusters, I
demonstrate the method by fitting to the low frequency radio spectrum of M82. I
discuss implications of the results for synchrotron spectrum shape, H II region
pressure, and free-free emission as a star-formation rate indicator. However,
these results are preliminary, and could be affected by systematics. I argue
that there is no volume-filling warm ionized medium in starbursts, and that H
II regions may be the most important absorption process down to ~10 MHz. Future
data at low and high radio frequency will improve our knowledge of the ionized
gas. |
Hubble Space Telescope Pixel Analysis of the Interacting Face-on Spiral
Galaxy NGC 5194 (M51A): A pixel analysis is carried out on the interacting face-on spiral galaxy NGC
5194 (M51A), using the HST/ACS images in the F435W, F555W and F814W (BVI)
bands. After 4x4 binning of the HST/ACS images to secure a sufficient
signal-to-noise ratio for each pixel, we derive several quantities describing
the pixel color-magnitude diagram (pCMD) of NGC 5194: blue/red color cut, red
pixel sequence parameters, blue pixel sequence parameters and blue-to-red pixel
ratio. The red sequence pixels are mostly older than 1 Gyr, while the blue
sequence pixels are mostly younger than 1 Gyr, in their luminosity-weighted
mean stellar ages. The color variation in the red pixel sequence from V = 20
mag arcsec^(-2) to V = 17 mag arcsec^(-2) corresponds to a metallicity
variation of \Delta[Fe/H] ~ 2 or an optical depth variation of \Delta\tau_V ~ 4
by dust, but the actual sequence is thought to originate from the combination
of those two effects. At V < 20 mag arcsec^(-2), the color variation in the
blue pixel sequence corresponds to an age variation from 5 Myr to 300 Myr under
the assumption of solar metallicity and \tau_V = 1. To investigate the spatial
distributions of stellar populations, we divide pixel stellar populations using
the pixel color-color diagram and population synthesis models. As a result, we
find that the pixel population distributions across the spiral arms agree with
a compressing process by spiral density waves: dense dust \rightarrow
newly-formed stars. The tidal interaction between NGC 5194 and NGC 5195 appears
to enhance the star formation at the tidal bridge connecting the two galaxies.
We find that the pixels corresponding to the central active galactic nucleus
(AGN) area of NGC 5194 show a tight sequence at the bright-end of the pCMD,
which are in the region of R ~ 100 pc and may be a photometric indicator of AGN
properties. | Formation and Evolution of Early-Type Galaxies: Spectro-Photometry from
Cosmo-Chemo-Dynamical Simulations: One of the major challenges in modern astrophysics is to understand the
origin and the evolution of galaxies, the bright, massive early type galaxies
(ETGs) in particular. Therefore, these galaxies are likely to be good probes of
galaxy evolution, star formation and, metal enrichment in the early Universe.
In this context it is very important to set up a diagnostic tool able to
combine results from chemo-dynamical N-Body-TSPH (NB-TSPH) simulations of ETGs
with those of spectro-photometric population synthesis and evolution so that
all key properties of galaxies can be investigated. The main goal of this paper
is to provide a preliminary validation of the software package before applying
it to the analysis of observational data. The galaxy models in use where
calculated by the Padova group in two different cosmological scenarios: the
SCDM, and the Lambda CDM. For these models, we recover their
spectro-photometric evolution through the entire history of the Universe. We
computed magnitudes and colors and their evolution with the redshift along with
the evolutionary and cosmological corrections for the model galaxies at our
disposal, and compared them with data for ETGs taken from the COSMOS and the
GOODS databases. Starting from the dynamical simulations and photometric models
at our disposal, we created synthetic images from which we derived the
structural and morphological parameters. The theoretical results are compared
with observational data of ETGs selected form the SDSS database. The simulated
colors for the different cosmological scenarios follow the general trend shown
by galaxies of the COSMOS and GOODS. Within the redshift range considered, all
the simulated colors reproduce the observational data quite well. |
Early mass varying neutrino dark energy: Nugget formation and Hubble
anomaly: We present a novel scenario, in which light ($\sim$ few \rm{eV}) dark
fermions (sterile neutrinos) interact with a scalar field like in mass varying
neutrino dark energy theories. As the $\rm{eV}$ sterile states naturally become
non-relativistic before the Matter Radiation Equality (MRE), we show that the
neutrino-scalar fluid develops strong perturbative instability followed by the
formation of neutrino-nuggets and the early dark energy behaviour disappears
around MRE. The stability of the nugget is achieved when the Fermi pressure
balances the attractive scalar force and we numerically find the mass and
radius of heavy cold nuggets by solving for the static configuration for the
scalar field. We find that for the case when DM nugget density is sub-dominant
and most of the early DE energy goes into scalar field dynamics, it can in
principle relax the Hubble anomaly. Especially when a kinetic energy dominated
phase appears after the phase transition, the DE density dilutes faster than
radiation and satisfy the requirements for solving $H_0$ anomaly. In our
scenario, unlike in originally proposed early dark energy theory, the dark
energy density is controlled by ($\rm{eV}$) neutrino mass and it does not
require a fine tuned EDE scale. We perform a MCMC analysis and confront our
model with Planck + SHOES and BAO data and find an evidence for non-zero
neutrino-scalar EDE density during MRE. Our analysis shows that this model is
in agreement of nearly 1.3$\sigma$ with SHOES measurement which is $H_0 = 74.03
\pm 1.42$ km/s/Mpc. | On the Physics of Radio Halos in Galaxy Clusters: Scaling Relations and
Luminosity Functions: The underlying physics of giant radio halos and mini halos in galaxy clusters
is still an open question, which becomes more pressing with the growing number
of detections. In this paper, we explore the possibility that radio-emitting
electrons are generated in hadronic cosmic ray (CR) proton interactions with
ambient thermal protons of the intra-cluster medium. Our CR model derives from
cosmological hydrodynamical simulations of cluster formation and additionally
accounts for CR transport in the form of CR streaming and diffusion. This opens
the possibility of changing the radio halo luminosity by more than an order of
magnitude on a dynamical time scale. We build a mock galaxy cluster catalog
from the large MultiDark N-body LCDM simulation by adopting a phenomenological
gas density model for each cluster based on X-ray measurements that matches
Sunyaev-Zel'dovich (SZ) and X-ray scaling relations and luminosity function.
Using magnetic field strength estimates from Faraday rotation measure studies,
our model successfully reproduces the observed surface brightness profiles of
giant radio halos (Coma, A2163) as well as radio mini-halos (Perseus,
Ophiuchus), while obeying upper limits on the gamma-ray emission in these
clusters. Our model is also able to simultaneously reproduce the observed
bimodality of radio-loud and radio-quiet clusters at the same L_X as well as
the unimodal distribution of radio-halo luminosity versus the SZ flux Y;
thereby suggesting a physical solution to this apparent contradiction. For a
plausible fraction of 10% radio-loud clusters, our model matches the NVSS
radio-halo luminosity function. Constructing an analytical radio-halo
luminosity function, we demonstrate the unique prospects for low-frequency
radio surveys (such as the LOFAR Tier 1 survey) to detect ~3500 radio halos
back to redshift two and to probe the underlying physics of radio halos.
[abridged] |
The halo mass function in interacting Dark Energy models: We present a detailed investigation of the effects that a direct interaction
between Dark Energy (DE) and Cold Dark Matter (CDM) particles imprints on the
Halo Mass Function (HMF) of groups and clusters of galaxies. Making use of the
public halo catalogs of the {\small CoDECS} simulations, we derive the HMF for
several different types of coupled DE scenarios both based on the FoF algorithm
and on the SO halo identification for different values of the overdensity
threshold $\Delta_{c}$. We compare the computed HMFs for coupled DE cosmologies
with $\Lambda $CDM as well as with the predictions of the standard analytic
fitting functions. Our results show that the standard fitting functions still
reproduce reasonably well both the FoF and the SO HMFs of interacting DE
cosmologies at intermediate masses and at low redshifts, once rescaled to the
characteristic amplitude of linear density perturbations of each specific model
as given by $\sigma_{8}$. However, we also find that such apparent degeneracy
with $\sigma_{8}$ is broken both by the high-mass tail and by the redshift
evolution of our HMFs, with deviations beyond $\sim 10%$ for most of the models
under investigation. Furthermore, the discrepancy with respect to the
predictions of standard fitting functions rescaled with the characteristic
value of $\sigma_{8}$ shows -- for some models -- a strong dependence on the
spherical overdensity threshold $\Delta_{c}$ used for the halo identification.
We find that such effect is due to a significant increase of halo concentration
at low redshifts in these models, that is however absent in the majority of the
cosmological scenarios considered in this work. We can therefore conclude that
the universality of the HMF is violated by cosmological models that feature a
direct interaction between DE and CDM. | Force-feeding Black Holes: We propose that the growth of supermassive black holes is associated mainly
with brief episodes of highly super-Eddington infall of gas ("hyperaccretion").
This gas is not swallowed in real time, but forms an envelope of matter around
the black hole that can be swallowed gradually, over a much longer timescale.
However, only a small fraction of the black hole mass can be stored in the
envelope at any one time. We argue that any infalling matter above a few per
cent of the hole's mass is ejected as a result of the plunge in opacity at
temperatures below a few thousand degrees K, corresponding to the Hayashi
track. The speed of ejection of this matter, compared to the velocity
dispersion (sigma) of the host galaxy's core, determines whether the ejected
matter is lost forever or returns eventually to rejoin the envelope, from which
it can be ultimately accreted. The threshold between matter recycling and
permanent loss defines a relationship between the maximum black hole mass and
sigma that resembles the empirical M_BH-sigma relation. |
Far infrared constraints on the contamination by dust obscured galaxies
of high-z dropout searches: The spectral energy distributions (SED) of dusty galaxies at intermediate
redshift may look similar to very high redshift galaxies in the optical/near
infrared (NIR) domain. This can lead to the contamination of high redshift
galaxy searches based on broad band optical/NIR photometry by lower redshift
dusty galaxies as both kind of galaxies cannot be distinguished. The
contamination rate could be as high as 50%. {This work shows how the far
infrared (FIR) domain can help to recognize likely low-z interlopers in an
optical/NIR search for high-z galaxies.} We analyse the FIR SEDs of two
galaxies proposed as very high redshift ($z>7$) dropout candidates based on
deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at
100 and 160\,$\mu$m, with SPIRE/Herschel at 250, 350 and 500\,$\mu$m and with
LABOCA/APEX at 870\,$\mu$m. We find that redshifts $>7$ would imply extreme FIR
SEDs (with dust temperatures $>100$\,K and FIR luminosities
$>10^{13}$\,$L_{\odot}$). At z$\sim$2, instead, the SEDs of both sources would
be compatible with that of typical ULIRGs/SMGs. Considering all the data
available for these sources from visible to FIR we re-estimate the redshifts
and we find $z\sim$1.6--2.5. Due to the strong spectral breaks observed in
these galaxies, standard templates from the literature fail to reproduce the
visible-near IR part of the SEDs even when additional extinction is included.
These sources resemble strongly dust obscured galaxies selected in Spitzer
observations with extreme visible-to-FIR colors, and the galaxy GN10 at $z=4$.
Galaxies with similar SEDs could contaminate other high redshift surveys. | The ESO Distant Cluster Sample: galaxy evolution and environment out to
z=1: The ESO Distant Cluster Survey (EDisCS, P.I. Simon D.M. White, LP 166.A-0162)
is an ESO large programme aimed at studying clusters and cluster galaxies at
z=0.4-1. How different is the evolution of the star formation activity in
clusters, in groups and in the field? Does it depend on cluster mass and/or the
local galaxy density? How relevant are starburst and post-starburst galaxies in
the different environments? Is there an evolution in the galaxies' structures,
and if so, is this related to the changes in their star formation activity?
These are some of the main questions that have been investigated using the
EDisCS dataset. |
CMB bounds on dark matter annihilation: Nucleon energy-losses after
recombination: We consider the propagation and energy losses of protons and anti-protons
produced by dark matter annihilation at redshifts 100<z<~2000. In the case of
dark matter annihilations into quarks, gluons and weak gauge bosons, protons
and anti-protons carry about 20% of the energy injected into e^\pm and
\gamma's, but their interactions are normally neglected when deriving cosmic
microwave background bounds from altered recombination histories. Here, we
follow numerically the energy-loss history of typical protons/antiprotons in
the cosmological medium. We show that about half of their energy is channeled
into photons and e^\pm, and we present a simple prescription to estimate the
corresponding strengthening of the cosmic microwave background bounds on the
dark matter annihilation cross section. | Classifying the Large Scale Structure of the Universe with Deep Neural
Networks: We present the first application of deep neural networks to the semantic
segmentation of cosmological filaments and walls in the Large Scale Structure
of the Universe. Our results are based on a deep Convolutional Neural Network
(CNN) with a U-Net architecture trained using an existing state-of-the-art
manually-guided segmentation method. We successfully trained an tested an U-Net
with a Voronoi model and an N-body simulation. The predicted segmentation masks
from the Voronoi model have a Dice coefficient of 0.95 and 0.97 for filaments
and mask respectively. The predicted segmentation masks from the N-body
simulation have a Dice coefficient of 0.78 and 0.72 for walls and filaments
respectively. The relatively lower Dice coefficient in the filament mask is the
result of filaments that were predicted by the U-Net model but were not present
in the original segmentation mask.
Our results show that for a well-defined dataset such as the Voronoi model
the U-Net has excellent performance. In the case of the N-body dataset the
U-Net produced a filament mask of higher quality than the segmentation mask
obtained from a state-of-the art method. The U-Net performs better than the
method used to train it, being able to find even the tenuous filaments that the
manually-guided segmentation failed to identify.
The U-Net presented here can process a $512^3$ volume in a few minutes and
without the need of complex pre-processing. Deep CNN have great potential as an
efficient and accurate analysis tool for the next generation large-volume
computer N-body simulations and galaxy surveys. |
Blocking low-eccentricity EMRIs: A statistical direct-summation N-body
study of the Schwarzschild barrier: The capture of a compact object in a galactic nucleus by a massive black hole
(MBH), an extreme-mass ratio inspiral (EMRI), is the best way to map space and
time around it. Recent work on stellar dynamics has demonstrated that there
seems to be a complot in phase space acting on low-eccentricity captures, since
their rates decrease significantly by the presence of a blockade in the rate at
which orbital angular momenta change takes place. This so-called "Schwarzschild
barrier" is a result of the impact of relativistic precession on to the stellar
potential torques, and thus it affects the enhancement on lower-eccentricity
EMRIs that one would expect from resonant relaxation. We confirm and quantify
the existence of this barrier using a statistical sample of 2,500
direct-summation N-body simulations using both a post-Newtonian and also for
the first time in a direct-summation code a geodesic approximation for the
relativistic orbits. The existence of the barrier prevents low-eccentricity
EMRIs from approaching the central MBH, but high-eccentricity EMRIs, which have
been wrongly classified as "direct plunges" until recently, ignore the presence
of the barrier, because they are driven by two-body relaxation. Hence, since
the rates are significantly affected in the case of low-eccentricity EMRIs, we
predict that a LISA-like observatory such as eLISA will predominantly detect
high-eccentricity EMRIs. | More on crinkles in the last scattering surface: Inhomogeneous recombination can give rise to perturbations in the electron
number density which can be a factor of five larger than the perturbations in
baryon density. We do a thorough analysis of the second order anisotropies
generated in the cosmic microwave background (CMB) due to perturbations in the
electron number density. We show that solving the second order Boltzmann
equation for photons is equivalent to solving the first + second order
Boltzmann equations and then taking the second order part of the solution. We
find the approximate solution to the photon Boltzmann hierarchy in l modes and
show that the contributions from inhomogeneous recombination to the second
order monopole, dipole and quadrupole are numerically small. We also point out
that perturbing the electron number density in the first order tight coupling
and damping solutions for the monopole, dipole and quadrupole is not equivalent
to solving the second order Boltzmann equations for inhomogeneous
recombination. Finally we confirm our result in a previous paper that
inhomogeneous recombination gives rise to a local type non-Gaussianity
parameter f_{NL}~ -1. The signal to noise for the detection of the temperature
bispectrum generated by inhomogeneous recombination is ~ 1 for an ideal full
sky experiment measuring modes up to l_{max}=2500. |
Covariances for cosmic shear and galaxy-galaxy lensing in the response
approach: In this study, we measure the response of matter and halo projected power
spectra $P^{\rm 2D}_{\rm XY}(k)$ (X, Y are matter and/or halos), to a
large-scale density contrast, $\delta_{\rm b}$, using separate universe
simulations. We show that the fractional response functions, i.e.,
$\mathrm{d}\ln P^{\rm 2D}_{\rm XY}(k)/\mathrm{d}\delta_{\rm b}$, are identical
to their respective three-dimensional power spectra within simulation
measurement errors. Then, using various $N$-body simulation combinations
(small-box simulations with periodic boundary conditions and sub-volumes of
large-box simulations) to construct {mock observations of projected fields}, we
study how super-survey modes, in both parallel and perpendicular directions to
the projection direction, affect the covariance matrix of $P^{\rm 2D}_{\rm
XY}(k)$, known as super-sample covariance (SSC). Our results indicate that the
SSC term provides dominant contributions to the covariances of matter-matter
and matter-halo spectra at small scales but does not provide significant
contributions in the halo-halo spectrum. We observe that the large-scale
density contrast in each redshift shell causes most of the SSC effect, and we
did not observe a SSC signature arising from large-scale tidal field within the
levels of measurement accuracy. We also develop a response approach to
calibrate the SSC term for cosmic shear correlation function and galaxy--galaxy
weak lensing, and validate the method by comparison with the light-cone
ray-tracing simulations. Our method provides a reasonably accurate, albeit
computationally inexpensive, way to calibrate the covariance matrix for
clustering observables available from wide-area galaxy surveys. | The large-scale monopole of the power spectrum in a Euclid-like survey:
wide-angle effects, lensing, and the `finger of the observer': Radial redshift-space distortions due to peculiar velocities and other
light-cone effects shape the maps we build of the Universe. We address the open
question of their impact onto the monopole moment of the galaxy power spectrum,
$P_0(k)$. Specifically, we use an upgraded numerical implementation of the
LIGER method to generate $140$ mock galaxy density fields for a full
Euclid-like survey and we measure $P_0(k)$ in each of them utilising a standard
estimator. We compare the spectra obtained by turning on and off different
effects. Our results show that wide-angle effects due to radial peculiar
velocities generate excess power above the level expected within the
plane-parallel approximation. They are detectable with a signal-to-noise ratio
of 2.7 for $k<0.02\,h$ Mpc$^{-1}$. Weak-lensing magnification also produces
additional power on large scales which, if the current favourite model for the
luminosity function of H$\alpha$ emitters turns out to be realistic, can only
be detected with a signal-to-noise ratio of 1.3 at best. Finally, we
demonstrate that measuring $P_0(k)$ in the standard of rest of the observer
generates an additive component reflecting the kinematic dipole overdensity
caused by the peculiar velocity. This component is characterised by a damped
oscillatory pattern on large scales. We show that this `finger of the observer'
effect is detectable in some redshift bins and suggest that its measurement
could possibly open new research directions in connection with the
determination of the cosmological parameters, the properties of the galaxy
population under study, and the dipole itself. |
A physical model for the 0 < z < 8 redshift evolution of the galaxy UV
luminosity and stellar mass functions: We present a model to understand the redshift evolution of the UV luminosity
and stellar mass functions of Lyman Break Galaxies. Our approach is based on
the assumption that the luminosity and stellar mass of a galaxy is related to
its dark matter halo assembly and gas infall rate. Specifically, galaxies
experience a burst of star formation at the halo assembly time, followed by a
constant star formation rate, representing a secular star formation activity
sustained by steady gas accretion. Star formation from steady gas accretion is
the dominant contribution to the galaxy UV luminosity at all redshifts. The
model is calibrated by constructing a galaxy luminosity versus halo mass
relation at $z=4$ via abundance matching. After this luminosity calibration,
the model naturally fits the $z=4$ stellar mass function, and correctly
predicts the evolution of both luminosity and stellar mass functions from $z=0$
to $z=8$. While the details of star formation efficiency and feedback are
hidden within our calibrated luminosity versus halo mass relation, our study
highlights that the primary driver of galaxy evolution across cosmic time is
the build-up of dark matter halos, without the need to invoke a redshift
dependent efficiency in converting gas into stars. | Disformal transformation of cosmological perturbations: We investigate the gauge-invariant cosmological perturbations in the gravity
and matter frames in the general scalar-tensor theory where two frames are
related by the disformal transformation. The gravity and matter frames are the
extensions of the Einstein and Jordan frames in the scalar-tensor theory where
two frames are related by the conformal transformation, respectively. First, it
is shown that the curvature perturbation in the comoving gauge to the scalar
field is disformally invariant as well as conformally invariant, which gives
the predictions from the cosmological model where the scalar field is
responsible both for inflation and cosmological perturbations. Second, in case
that the disformally coupled matter sector also contributes to curvature
perturbations, we derive the evolution equations of the curvature perturbation
in the uniform matter energy density gauge from the energy (non)conservation in
the matter sector, which are independent of the choice of the gravity sector.
While in the matter frame the curvature perturbation in the uniform matter
energy density gauge is conserved on superhorizon scales for the vanishing
nonadiabatic pressure, in the gravity frame it is not conserved even if the
nonadiabatic pressure vanishes. The formula relating two frames gives the
amplitude of the curvature perturbation in the matter frame, once it is
evaluated in the gravity frame. |
Future virialized structures: An analysis of superstructures in SDSS-DR7: We construct catalogues of present superstructures that, according to a LCDM
scenario, will evolve into isolated, virialized structures in the future. We
use a smoothed luminosity density map derived from galaxies in SDSS-DR7 data
and separate high luminosity density peaks. The luminosity density map is
obtained from a volume-limited sample of galaxies in the spectroscopic galaxy
catalogue, within the SDSS-DR7 footprint area and in the redshift range 0.04 <
z < 0.12. Other two samples are constructed for calibration and testing
purposes, up to z = 0.10 and z = 0.15. The luminosity of each galaxy is spread
using an Epanechnikov kernel of 8Mpc/h radius, and the map is constructed on a
1 Mpc/h cubic cells grid. Future virialized structures (FVS) are identified as
regions with overdensity above a given threshold, calibrated using a LCDM
numerical simulation, and the criteria presented by D\"unner et al. (2006). We
assume a constant mass-to-luminosity ratio and impose the further condition of
a minimum luminosity of 10^{12}Lsol. According to our calibrations with a
numerical simulation, these criteria lead to a negligible contamination by less
overdense (non FVS) superstructures.We present a catalogue of superstructures
in the SDSS-DR7 area within redshift 0.04 < z < 0.12 and test the reliability
of our method by studying different subsamples as well as a mock catalogue.We
compute the luminosity and volume distributions of the superstructures finding
that about 10% of the luminosity (mass) will end up in future virialized
structures. The fraction of groups and X-ray clusters in these superstructures
is higher for groups/clusters of higher mass, suggesting that future cluster
mergers will involve the most massive systems. We also analyse known structures
in the present Universe and compare with our catalogue of FVS. | Accurate Masses for Navarro-Frenk-White Dark Matter Haloes: We consider the problem of estimating the virial mass of a dark halo from the
positions and velocities of a tracer population. Although a number of general
tools are available, more progress can be made if we are able to specify the
functional form of the halo potential (although not its normalization). Here,
we consider the particular case of the cosmologically motivated
Navarro-Frenk-White (NFW) halo and develop two simple estimators. We
demonstrate their effectiveness against numerical simulations and use them to
provide new mass estimates of Carina, Fornax, Sculptor, and Sextans dSphs. |
Physical Benchmarking for AI-Generated Cosmic Web: The potential of deep learning based image-to-image translations has recently
drawn a lot of attention; one intriguing possibility is that of generating
cosmological predictions with a drastic reduction in computational cost. Such
an effort requires optimization of neural networks with loss functions beyond
low-order statistics like pixel-wise mean square error, and validation of
results beyond simple visual comparisons and summary statistics. In order to
study learning-based cosmological mappings, we choose a tractable analytical
prescription - the Zel'dovich approximation - modeled using U-Net, a
convolutional image translation framework. A comprehensive list of metrics is
proposed, including higher-order correlation functions, conservation laws,
topological indicators, dynamical robustness, and statistical independence of
density fields. We find that the U-Net approach does well with some metrics but
has difficulties with others. In addition to validating AI approaches using
rigorous physical benchmarks, this study motivates advancements in
domain-specific optimization schemes for scientific machine learning. | Dark Matter Subhalos, Strong Lensing and Machine Learning: We investigate the possibility of applying machine learning techniques to
images of strongly lensed galaxies to detect a low mass cut-off in the spectrum
of dark matter sub-halos within the lens system. We generate lensed images of
systems containing substructure in seven different categories corresponding to
lower mass cut-offs ranging from $10^9M_\odot$ down to $10^6M_\odot$. We use
convolutional neural networks to perform a multi-classification sorting of
these images and see that the algorithm is able to correctly identify the lower
mass cut-off within an order of magnitude to better than 93% accuracy. |
Computer Simulations of Cosmic Reionization: The cosmic reionization of hydrogen was the last major phase transition in
the evolution of the universe, which drastically changed the ionization and
thermal conditions in the cosmic gas. To the best of our knowledge today, this
process was driven by the ultra-violet radiation from young, star-forming
galaxies and from first quasars. We review the current observational
constraints on cosmic reionization, as well as the dominant physical effects
that control the ionization of intergalactic gas. We then focus on numerical
modeling of this process with computer simulations. Over the past decade,
significant progress has been made in solving the radiative transfer of
ionizing photons from many sources through the highly inhomogeneous
distribution of cosmic gas in the expanding universe. With modern simulations,
we have finally converged on a general picture for the reionization process,
but many unsolved problems still remain in this young and exciting field of
numerical cosmology. | The fully non-linear post-Friedmann frame-dragging vector potential:
Magnitude and time evolution from N-body simulations: Newtonian simulations are routinely used to examine the matter dynamics on
non-linear scales. However, even on these scales, Newtonian gravity is not a
complete description of gravitational effects. A post-Friedmann approach shows
that the leading order correction to Newtonian theory is a vector potential in
the metric. This vector potential can be calculated from N-body simulations,
requiring a method for extracting the velocity field. Here, we present the full
details of our calculation of the post-Friedmann vector potential, using the
Delauney Tesselation Field Estimator (DTFE) code. We include a detailed
examination of the robustness of our numerical result, including the effects of
box size and mass resolution on the extracted fields. We present the power
spectrum of the vector potential and find that the power spectrum of the vector
potential is $\sim 10^5$ times smaller than the power spectrum of the fully
non-linear scalar gravitational potential at redshift zero. Comparing our
numerical results to perturbative estimates, we find that the fully non-linear
result can be more than an order of magnitude larger than the perturbative
estimate on small scales. We extend the analysis of the vector potential to
multiple redshifts, showing that this ratio persists over a range of scales and
redshifts. We also comment on the implications of our results for the validity
and interpretation of Newtonian simulations. |
Interacting parametrized post-Friedmann method: We apply the interacting parametrized post-Friedmann (IPPF) method to a
coupled dark energy model where the interaction is proportional to dark matter
density at background level. In doing so, we perform a Markov Chain Monte-Carlo
analysis which combines several cosmological probes including the cosmic
microwave background (WMAP9+Planck) data, baryon acoustic oscillation (BAO)
measurements, JLA sample of supernovae, Hubble constant (HST), and
redshift-space distortion (RSD) measurements through the ${\rm f}\sigma_{8}{\rm
(z)}$ data points. The joint observational analysis of ${\rm
Planck+WP+JLA+BAO+HST+RSD}$ data leads to a coupling parameter,
$\xi_{c}=0.00140_{-0.00080}^{+0.00079}$ at $1\sigma$ level for vanishing
momentum transfer potential; this value is reduced a when the momentum transfer
potential is switched on, giving $\xi_{c}=0.00136_{-0.00073}^{+0.00080}$ at
$1\sigma$ level. The CMB power spectrum shows up a correlation between the
coupling parameter $\xi_{c}$ and the position of acoustic peaks or their
amplitudes. The first peak's height increases when $\xi_{c}$ takes larger
values and its position is shifted. We also obtain the matter power spectrum
may be affected by the strength of interaction coupling over scales bigger that
$10^{-2} {\rm h~ Mpc^{-1}}$, reducing its amplitude in relation to the vanilla
model. | Direct detection of Black Holes via electromagnetic radiation: Many black hole (BH) candidates exist, ranging from supermassive
($\sim10^{6}$--$10^{10}$ M$_{\odot}$) to stellar masses ($\sim 1$--$100$
M$_{\odot}$), all of them identified by indirect processes. Although there are
no known candidate BHs with sub-stellar masses, these might have been produced
in the primordial Universe. BHs emit radiation composed of photons, gravitons
and, later in their lifes, massive particles. We explored the detection of such
BHs with present day masses from $10^{-22}$ M$_{\odot}$ to $10^{-11}$
M$_{\odot}$. We determined the maximum distances ($d$) at which the current
best detectors should be placed in order to identify such isolated BHs.
Broadly, we conclude that in the visible and ultraviolet BHs can be directly
detected at $d\lesssim 10^7$ m while in the X-ray band the distances might
reach $\sim10^8$ m (of the order of the Earth-Moon distance) and in the
$\gamma$-ray band BHs might even be detected from as far as $\sim 0.1$ pc.
Since these results give us realistic hopes of directly detecting BHs, we
suggest the scrutiny of current and future space mission data to reach this
goal. |
The central dark matter content of early-type galaxies: scaling
relations and connections with star formation histories: We examine correlations between the masses, sizes, and star formation
histories for a large sample of low-redshift early-type galaxies, using a
simple suite of dynamical and stellar populations models. We confirm an
anti-correlation between size and stellar age, and survey for trends with the
central content of dark matter (DM). An average relation between central DM
density and galaxy size of <rho_DM> ~ Reff^-2 provides the first clear
indication of cuspy DM haloes in these galaxies -- akin to standard LCDM haloes
that have undergone adiabatic contraction. The DM density scales with galaxy
mass as expected, deviating from suggestions of a universal halo profile for
dwarf and late-type galaxies. We introduce a new fundamental constraint on
galaxy formation by finding that the central DM fraction decreases with stellar
age. This result is only partially explained by the size-age dependencies, and
the residual trend is in the opposite direction to basic DM halo expectations.
Therefore we suggest that there may be a connection between age and halo
contraction, and that galaxies forming earlier had stronger baryonic feedback
which expanded their haloes, or else lumpier baryonic accretion that avoided
halo contraction. An alternative explanation is a lighter initial mass function
for older stellar populations. | 4D Gauss-Bonnet gravity: cosmological constraints, $H_0$ tension and
large scale structure: We perform correct and reasonable cosmological constraints on the newly
proposed 4D Gauss-Bonnet gravity. Using the joint constraint from cosmic
microwave background, baryon acoustic oscillations, Type Ia supernovae, cosmic
chronometers and redshift space distortions, we obtain, so far, the strongest
constraint $\tilde{\alpha}=(1.2\pm5.2)\times 10^{-17}$, namely
$\alpha=(2.69\pm11.67)\times10^{48}$ eV$^{-2}$, among various observational
limitations from different information channels, which is tighter than previous
bound from the speed of gravitational wave by at least one order of magnitude.
We find that our bound is well supported by the observations of temperature and
lensing potential power spectra of cosmic microwave background from the
Planck-2018 final release. Very interestingly, the large $H_0$ tension between
the local measurement from the Hubble Space Telescope and global derivation
from the Planck-2018 final data under the assumption of $\Lambda$CDM can be
greatly resolved from $4.4\sigma$ to $1.94\sigma$ level in the 4D Gauss-Bonnet
gravity. In theory, we find that this model can partly relieve the coincidence
problem and the rescaling Gauss-Bonnet term, which needs the help of the
cosmological constant to explain current cosmic acceleration, is unable to
serve as dark energy alone. |
Five Supernova Survey Galaxies in the Southern Hemisphere: Supernova Ia
Rates: Based on the database of 56 supernovae (SNe) events discovered in 3838
galaxies of the southern hemisphere, we compute the rate of SNe of different
types along the Hubble sequence normalized to the optical and near-infrared
(NIR) luminosities as well as to the stellar mass of the galaxies. We find that
the rates of Type Ia SNe show a dependence on both morphology and colors of the
galaxies, and therefore, on the star-formation activity. The rate of SNe Ia can
be explained by assuming that at least 15% of Ia events in spiral galaxies
originate in relatively young stellar populations. We also find that the rates
show no modulation with nuclear activity or environment. | Impact of our local environment on cosmological statistics: We conduct a thorough investigation into the possibility that residing in an
overdense region of the Universe may induce bias in measurements of the
large-scale structure. We compute the conditional correlation function and
angular power spectrum of density and lensing fluctuations while holding the
local spherically averaged density fixed and show that for Gaussian fields this
has no effect on the angular power at $l>0$. We identify a range of scales
where a perturbative approach allows analytic progress to be made, and we
compute leading-order conditional power spectra using an Edgeworth expansion
and second-order perturbation theory. We find no evidence for any significant
bias to cosmological power spectra from our local density contrast. We show
that when smoothed over a large region around the observer, conditioning on the
local density typically affects density power spectra by less than a percent at
cosmological distances, below cosmic variance. We find that while typical
corrections to the lensing angular power spectrum can be at the 10% level on
the largest angular scales and for source redshifts $z_s \lesssim 0.1$, for the
typical redshifts targeted by upcoming wide imaging surveys the corrections are
sub-percent and negligible, in contrast to previous claims in the literature.
Using an estimate of the local spherically averaged density from a composite
galaxy redshift catalogue we find that the corrections from conditioning on our
own local density are below cosmic variance and subdominant to other non-linear
effects. We discuss the potential implications of our results for cosmology and
point out that a measurement of the local density contrast may be used as a
consistency test of cosmological models. |
Modeling the Fe K Line Profiles in Type I AGN with a Compton-Thick Disk
Wind: We have modeled a small sample of Seyfert galaxies that were previously
identified as having simple X-ray spectra with little intrinsic absorption. The
sources in this sample all contain moderately broad components of Fe K-shell
emission and are ideal candidates for testing the applicability of a
Compton-thick accretion-disk wind model to AGN emission components. Viewing
angles through the wind allow the observer to see the absorption signature of
the gas, whereas face-on viewing angles allow the observer to see the scattered
light from the wind. We find that the Fe K emission line profiles are well
described with a model of a Compton-thick accretion-disk wind of solar
abundances, arising tens to hundred of gravitational radii from the central
black hole. Further, the fits require a neutral component of Fe K alpha
emission that is too narrow to arise from the inner part of the wind, and
likely comes from a more distant reprocessing region. Our study demonstrates
that a Compton-thick wind can have a profound effect on the observed X-ray
spectrum of an AGN, even when the system is not viewed through the flow. | Lightcone mock catalogues from semi-analytic models of galaxy formation
- I. Construction and application to the BzK colour selection: We introduce a method for constructing end-to-end mock galaxy catalogues
using a semi-analytical model of galaxy formation, applied to the halo merger
trees extracted from a cosmological N-body simulation. The mocks that we
construct are lightcone catalogues, in which a galaxy is placed according to
the epoch at which it first enters the past lightcone of the observer, and
incorporate the evolution of galaxy properties with cosmic time. We determine
the position between the snapshot outputs at which a galaxy enters the
observer's lightcone by interpolation. As an application, we consider the
effectiveness of the BzK colour selection technique, which was designed to
isolate galaxies in the redshift interval 1.4<z<2.5. The mock catalogue is in
reasonable agreement with the observed number counts of all BzK galaxies, as
well as with the observed counts of the subsample of BzKs that are star-forming
galaxies. We predict that over 75 per cent of the model galaxies with
K_{AB}<=23, and 1.4<z<2.5, are selected by the BzK technique. Interloper
galaxies, outside the intended redshift range, are predicted to dominate bright
samples of BzK galaxies (i.e. with K_{AB}<=21). Fainter K-band cuts are
necessary to reduce the predicted interloper fraction. We also show that
shallow B-band photometry can lead to confusion in classifying BzK galaxies as
being star-forming or passively evolving. Overall, we conclude that the BzK
colour selection technique is capable of providing a sample of galaxies that is
representative of the 1.4<z<2.5 galaxy population. |
Constraining f(T) teleparallel gravity by Big Bang Nucleosynthesis: We use BBN observational data on primordial abundance of ${}^4He$ to
constrain f(T) gravity. The three most studied viable $f(T)$ models, namely the
power law, the exponential and the square-root exponential are considered, and
the BBN bounds are adopted in order to extract constraints on their free
parameters. For the power-law model, we find that the constraints are in
agreement with those acquired using late-time cosmological data. For the
exponential and the square-root exponential models, we show that for realiable
regions of parameters space they always satisfy the BBN bounds. We conclude
that viable f(T) models can successfully satisfy the BBN constraints. | Very Long Baseline Array Imaging of Parsec-scale Jet Structures in
Radio-loud Narrow-line Seyfert 1 Galaxies: We conducted very long baseline interferometry (VLBI) observations of five
radio-loud narrow-line Seyfert 1 (NLS1) galaxies in milliarcsecond resolutions
at 1.7 GHz (18 cm) using the Very Long Baseline Array (VLBA). Significant
parsec-scale structures were revealed for three out of the five sources with
high brightness temperature by direct imaging; this is convincing evidence for
nonthermal jets. FBQS J1644+2619 with an inverted spectrum showed a prominent
one-sided linear structure, indicating Doppler beaming with an intrinsic jet
speed of >0.74c. FBQS J1629+4007, also with an inverted spectrum, showed rapid
flux variability, indicating Doppler beaming with an intrinsic jet speed of
>0.88c. Thus, we found convincing evidence that these two NLS1s can generate at
least mildly or highly relativistic jets, which may make them apparently radio
loud even if they are intrinsically radio quiet. On the other hand, the other
three NLS1s had steep spectra and two of them showed significantly diffuse
pc-scale structures, which were unlikely to be strongly beamed. Thus, some
NLS1s have the ability to generate jets strong enough to make them
intrinsically radio loud without Doppler beaming. NLS1s as a class show a
number of extreme properties and radio-loud ones are very rare. We build on
these radio results to understand that the central engines of radio-loud NLS1s
are essentially the same as that of other radio-loud AGNs in terms of the
formation of nonthermal jets. |
Mass Calibration of the CODEX Cluster Sample using SPIDERS Spectroscopy
-- II. The X-ray Luminosity-Mass Relation: We perform the calibration of the X-ray luminosity--mass scaling relation on
a sample of 344 CODEX clusters with $z<0.66$ using the dynamics of their member
galaxies. Spectroscopic follow-up measurements have been obtained from the
SPIDERS survey, leading to a sample of 6,658 red member galaxies. We use the
Jeans equation to calculate halo masses, assuming an NFW mass profile and
analyzing a broad range of anisotropy profiles. With a scaling relation of the
form $L_{\rm{X}} \propto \text{A}_{\rm{X}}M_{\text{200c}}^{\text{B}_{\rm{X}}}
E(z)^2 (1+z)^{\gamma_{\rm{X}}}$, we find best fit parameters $
\text{A}_{\rm{X}}=5.7^{+0.4}_{-0.5}
(\pm0.6)\times10^{43}\,\mathrm{erg\,s^{-1}}$,
$\text{B}_{\rm{X}}=2.5\pm0.2(\pm0.07)$,
$\gamma_{\rm{X}}=-2.6^{+1.1}_{-1.2}(\pm0.74)$, where we include systematic
uncertainties in parentheses and for a pivot mass and redshift of
$3\times10^{14}M_\odot$ and 0.16, respectively. We compare our constraints with
previous results, and we combine our sample with the SPT SZE--selected cluster
subsample observed with \XMM\, extending the validity of our results to a wider
range of redshifts and cluster masses. | Using the Bullet Cluster as a Gravitational Telescope to Study z~7 Lyman
Break Galaxies: We use imaging obtained with the Hubble Space Telescope Wide Field Camera 3
to search for z_850 dropouts at z~7 and J_110 dropouts at z~9 lensed by the
Bullet Cluster. In total we find 10 z_850 dropouts in our 8.27 arcmin^2 field.
Using magnification maps from a combined weak and strong lensing mass
reconstruction of the Bullet Cluster and correcting for estimated completeness
levels, we calculate the surface density and luminosity function of our z_850
dropouts as a function of intrinsic (accounting for magnification) magnitude.
We find results consistent with published blank field surveys, despite using
much shallower data, and demonstrate the effectiveness of cluster surveys in
the search for z~7 galaxies. |
Towards mapping turbulence in the intra-cluster medium -- I. Sample
variance in spatially-resolved X-ray line diagnostics: X-ray observations of galaxy clusters provide insights on the nature of
gaseous turbulent motions, their physical scales and on the fundamental
processes they are related to. Spatially-resolved, high-resolution spectral
measurements of X-ray emission lines provide diagnostics on the nature of
turbulent motions in emitting atmospheres. Since they are acting on scales
comparable to the size of the objects, the uncertainty on these physical
parameters is limited by the number of observational measurements, through
sample variance. We propose a different and complementary approach for the
computation of sample variance to repeating numerical simulations (i.e.
Monte-Carlo sampling) by introducing new analytical developments for lines
diagnosis. We consider the model of a "turbulent gas cloud", consisting in
isotropic and uniform turbulence described by a universal Kolmogorov
power-spectrum with random amplitudes and phases in an optically thin medium.
Following a simple prescription for the 4-term correlation of Fourier
coefficients, we derive generic expressions for the sample mean and variance of
line centroid shift, line broadening and projected velocity structure function.
We perform a numerical validation based on Monte-Carlo simulations for two
popular models of gas emissivity based on the beta-model. Generic expressions
for the sample variance of line centroid shifts and broadening in arbitrary
apertures are derived and match the simulations within their range of
applicability. Generic expressions for the mean and variance of the structure
function are provided and verified against simulations. An application to the
Athena/X-IFU and XRISM/Resolve instruments forecasts the potential of
sensitive, spatially-resolved spectroscopy to probe the inertial range of
turbulent velocity cascades in a Coma-like galaxy cluster. | On the nature of faint mid-infrared sources in M33: We investigate the nature of 24micron sources in M33 which have weak or no
associated Halpha emission. Both bright evolved stars and embedded star forming
regions are visible as compact infrared sources in the 8 and 24micron maps of
M33 and contribute to the more diffuse and faint emission in these bands. Can
we distinguish the two populations? We carry out deep CO J=2-1 and J=1-0 line
searches at the location of compact mid-IR sources to unveil an ongoing star
formation process. We use different assumptions to estimate cloud masses from
pointed observations and analyze if SED and mid-IR colours can be used to
discriminate between evolved stars and star forming regions. Molecular emission
has been detected at the location of several sources at the level of 0.3 K km/s
or higher in at least one of the CO rotational lines. Even though there are no
giant molecular clouds beyond 4kpc in M33, our deep observations have revealed
that clouds of smaller mass are very common. Sources which are known to be
evolved variable stars show weaker or undetectable CO lines. Evolved stars
occupy a well defined region of the IRAC color-color diagrams. Star forming
regions are scattered throughout a larger area even though the bulk of the
distribution has different IRAC colors than evolved variable stars. We estimate
that about half of the 24 micron sources without an Halpha counterpart are
genuine embedded star forming regions. Sources with faint but compact Halpha
emission have an incomplete Initial Mass Function (IMF) at the high-mass end
and are compatible with a population of young clusters with a stochastically
sampled, universal IMF. |
Distant clusters of galaxies in the 2XMM/SDSS footprint: follow-up
observations with the LBT: Context: Galaxy clusters at high redshift are important to test cosmological
models and models for the growth of structure. They are difficult to find in
wide-angle optical surveys, however, leaving dedicated follow-up of X-ray
selected candidates as one promising identification route. Aims: We aim to
increase the number of galaxy clusters beyond the SDSS-limit, z ~ 0.75.
Methods: We compiled a list of extended X-ray sources from the 2XMMp catalogue
within the footprint of the Sloan Digital Sky Survey. Fields without optical
counterpart were selected for further investigation. Deep optical imaging and
follow-up spectroscopy were obtained with the Large Binocular Telescope,
Arizona (LBT), of those candidates not known to the literature. Results: From
initially 19 candidates, selected by visually screening X-ray images of 478
XMM-Newton observations and the corresponding SDSS images, 6 clusters were
found in the literature. Imaging data through r,z filters were obtained for the
remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy.
Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux,
temperature, and luminosity) are presented for the clusters with spectroscopic
redshifts. The distant clusters studied here constitute one additional redshift
bin for studies of the L-T relation, which does not seem to evolve from high to
low redshifts. ... | Planting a Lyman alpha forest on AbacusSummit: The full-shape correlations of the Lyman alpha (Ly$\alpha$) forest contain a
wealth of cosmological information through the Alcock-Paczy\'{n}ski effect.
However, these measurements are challenging to model without robustly testing
and verifying the theoretical framework used for analyzing them. Here, we
leverage the accuracy and volume of the $N$-body simulation suite
\textsc{AbacusSummit} to generate high-resolution Ly$\alpha$ skewers and
quasi-stellar object (QSO) catalogs. One of the main goals of our mocks is to
aid in the full-shape Ly$\alpha$ analysis planned by the Dark Energy
Spectroscopic Instrument (DESI) team. We provide optical depth skewers for six
of the fiducial cosmology base-resolution simulations ($L_{\rm box} =
2\,h^{-1}{\rm Gpc}$, $N = 6912^3$) at $z = 2.5$. We adopt a simple recipe based
on the Fluctuating Gunn-Peterson Approximation (FGPA) for constructing these
skewers from the matter density in an $N$-body simulation and calibrate it
against the 1D and 3D Ly$\alpha$ power spectra extracted from the
hydrodynamical simulation IllustrisTNG (TNG; $L_{\rm box} = 205\,h^{-1}{\rm
Mpc}$, $N = 2500^3$). As an important application, we study the non-linear
broadening of the baryon acoustic oscillation (BAO) peak and show the
cross-correlation between DESI-like QSOs and our Ly$\alpha$ forest skewers. We
find differences on small scales between the Kaiser approximation prediction
and our mock measurements of the Ly$\alpha$$\times$QSO cross-correlation, which
would be important to account for in upcoming analyses. The
\textsc{AbacusSummit} Ly$\alpha$ forest mocks open up the possibility for
improved modelling of cross correlations between Ly$\alpha$ and cosmic
microwave background (CMB) lensing and Ly$\alpha$ and QSOs, and for forecasts
of the 3-point Ly$\alpha$ correlation function. Our catalogues and skewers are
publicly available on Globus. |
Cosmological parameter estimation from large-scale structure deep
learning: We propose a light-weight deep convolutional neural network (CNN) to estimate
the cosmological parameters from simulated 3-dimensional dark matter
distributions with high accuracy. The training set is based on 465 realizations
of a cubic box with a side length of $256\ h^{-1}\ \rm Mpc$, sampled with
$128^3$ particles interpolated over a cubic grid of $128^3$ voxels. These
volumes have cosmological parameters varying within the flat $\Lambda$CDM
parameter space of $0.16 \leq \Omega_m \leq 0.46$ and $2.0 \leq 10^9 A_s \leq
2.3$. The neural network takes as an input cubes with $32^3$ voxels and has
three convolution layers, three dense layers, together with some batch
normalization and pooling layers. In the final predictions from the network we
find a $2.5\%$ bias on the primordial amplitude $\sigma_8$ that can not easily
be resolved by continued training. We correct this bias to obtain unprecedented
accuracy in the cosmological parameter estimation with statistical
uncertainties of $\delta \Omega_m$=0.0015 and $\delta \sigma_8$=0.0029, which
are several times better than the results of previous CNN works. Compared with
a 2-point analysis method using clustering region of 0-130 and 10-130 $h^{-1}$
Mpc, the CNN constraints are several times and an order of magnitude more
precise, respectively. Finally, we conduct preliminary checks of the
error-tolerance abilities of the neural network, and find that it exhibits
robustness against smoothing, masking, random noise, global variation,
rotation, reflection, and simulation resolution. Those effects are well
understood in typical clustering analysis, but had not been tested before for
the CNN approach. Our work shows that CNN can be more promising than people
expected in deriving tight cosmological constraints from the cosmic large scale
structure. | Spectroscopic Tomography: A First Weak Lensing Detection Using
Spectroscopic Redshifts Only: We describe the first spectroscopic tomographic (spectrotomographic) weak
lensing measurement for a galaxy cluster based only on background galaxies with
spectroscopically determined redshifts. We use the massive cluster A2029 to
demonstrate the power of combining spectroscopy and lensing to obtain accurate
masses and to overcome biases from contamination and photometric redshift
errors. We detect the shear signal from the cluster at $>3.9 \sigma$. The shear
signal scales with source redshift in a way that is consistent with the angular
diameter distance ratio variation in a $\Lambda$CDM Universe. Furthermore, the
amplitude of the measured signal is consistent with the X-ray mass. Upcoming
spectroscopic instruments such as the Prime Focus Spectrograph on Subaru will
permit spectrotomographic weak lensing measurements with S/N comparable to
current photometric-redshift-based weak lensing measurements for hundreds of
galaxy clusters. Thus, spectrotomography may enable sensitive cosmological
constraints that complement and are independent of other measurement
techniques. |
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