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Physical Structure and Nature of Supernova Remnants in M101: Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have been
previously identified from ground-based H-alpha and [SII] images. We have used
archival Hubble Space Telescope (HST) H-alpha and broad-band images as well as
stellar photometry of 55 SNR candidates to examine their physical structure,
interstellar environment, and underlying stellar population. We have also
obtained high-dispersion echelle spectra to search for shocked high-velocity
gas in 18 SNR candidates, and identified X-ray counterparts to SNR candidates
using data from archival observations made by the Chandra X-ray Observatory.
Twenty-one of these 55 SNR candidates studied have X-ray counterparts, although
one of them is a known ultra-luminous X-ray source. The multi-wavelength
information has been used to assess the nature of each SNR candidate. We find
that within this limited sample, ~16% are likely remnants of Type Ia SNe and
~45% are remnants of core-collapse SNe. In addition, about ~36% are large
candidates which we suggest are either superbubbles or OB/HII complexes.
Existing radio observations are not sensitive enough to detect the non-thermal
emission from these SNR candidates. Several radio sources are coincident with
X-ray sources, but they are associated with either giant HII regions in M101 or
background galaxies. The archival HST H-alpha images do not cover the entire
galaxy and thus prevents a complete study of M101. Furthermore, the lack of HST
[SII] images precludes searches for small SNR candidates which could not be
identified by ground-based observations. Such high-resolution images are needed
in order to obtain a complete census of SNRs in M101 for a comprehensive
investigation of the distribution, population, and rates of SNe in this galaxy. | Particle production during inflation: A Bayesian analysis with CMB data
from Planck 2018: A class of inflationary models that involve rapid bursts of particle
productions predict observational signatures, such as bump-like features in the
primordial scalar power spectrum. In this work, we analyze such models by
comparing their predictions with the latest CMB data from Planck 2018. We
consider two scenarios of particle production. The first one is a simple
scenario consisting of a single burst of particle production during observable
inflation. The second one consists of multiple bursts of particle production
that lead to a series of bump-like features in the primordial power spectrum.
We find that the second scenario of the multi-bump model gives better fit to
the CMB data compared to the concordance $\Lambda$CDM model. We carried out
model comparisons using Bayesian evidences. From the observational constraints
on the amplitude of primordial features of the multi-bump model, we find that
the coupling parameter $g$ responsible for particle production is bound to be
$g< 0.05$. |
A Full $w$CDM Analysis of KiDS-1000 Weak Lensing Maps using Deep
Learning: We present a full forward-modeled $w$CDM analysis of the KiDS-1000 weak
lensing maps using graph-convolutional neural networks (GCNN). Utilizing the
$\texttt{CosmoGrid}$, a novel massive simulation suite spanning six different
cosmological parameters, we generate almost one million tomographic mock
surveys on the sphere. Due to the large data set size and survey area, we
perform a spherical analysis while limiting our map resolution to
$\texttt{HEALPix}$ $n_\mathrm{side}=512$. We marginalize over systematics such
as photometric redshift errors, multiplicative calibration and additive shear
bias. Furthermore, we use a map-level implementation of the non-linear
intrinsic alignment model along with a novel treatment of baryonic feedback to
incorporate additional astrophysical nuisance parameters. We also perform a
spherical power spectrum analysis for comparison. The constraints of the
cosmological parameters are generated using a likelihood free inference method
called Gaussian Process Approximate Bayesian Computation (GPABC). Finally, we
check that our pipeline is robust against choices of the simulation parameters.
We find constraints on the degeneracy parameter of $S_8 \equiv
\sigma_8\sqrt{\Omega_M/0.3} = 0.78^{+0.06}_{-0.06}$ for our power spectrum
analysis and $S_8 = 0.79^{+0.05}_{-0.05}$ for our GCNN analysis, improving the
former by 16%. This is consistent with earlier analyses of the 2-point
function, albeit slightly higher. Baryonic corrections generally broaden the
constraints on the degeneracy parameter by about 10%. These results offer great
prospects for full machine learning based analyses of on-going and future weak
lensing surveys. | A User's Guide to Extracting Cosmological Information from
Line-Intensity Maps: Line-intensity mapping (LIM) provides a promising way to probe cosmology,
reionization and galaxy evolution. However, its sensitivity to cosmology and
astrophysics at the same time is also a nuisance. Here we develop a
comprehensive framework for modelling the LIM power spectrum, which includes
redshift space distortions and the Alcock-Paczynski effect. We then identify
and isolate degeneracies with astrophysics so that they can be marginalized
over. We study the gains of using the multipole expansion of the anisotropic
power spectrum, providing an accurate analytic expression for their covariance,
and find a 10%-60% increase in the precision of the baryon acoustic oscillation
scale measurements when including the hexadecapole in the analysis. We discuss
different observational strategies when targeting other cosmological
parameters, such as the sum of neutrino masses or primordial non-Gaussianity,
finding that fewer and wider bins are typically more optimal. Overall, our
formalism facilitates an optimal extraction of cosmological constraints robust
to astrophysics. |
The Sunyaev-Zel'dovich Effect and Large-Scale Structure: The thermal Sunyaev-Zel'dovich (tSZ) effect is the inverse-Compton scattering
of cosmic microwave background (CMB) photons off hot, ionized electrons,
primarily located in galaxy groups and clusters. Recent years have seen immense
improvement in our ability to probe cosmology and the astrophysics of the
intracluster medium using the tSZ signal. Here, I describe cross-correlations
of the tSZ effect measured in Planck data with gravitational lensing maps from
Planck and the Canada-France-Hawaii Telescope Lensing Survey, as well as
hydrodynamical simulations which show that such measurements do not probe
"missing baryons," but rather the pressure of ionized gas in groups and
clusters over a wide range of halo masses and redshifts. I also present recent
measurements of higher-order tSZ statistics using data from the Atacama
Cosmology Telescope, which yield strong constraints on the amplitude of density
fluctuations. I describe stacking analyses of tSZ data from Planck, focusing on
the behavior of the gas pressure in low-mass galaxy groups. I close with a
prediction for the tSZ monopole, including relativistic corrections, which is
the largest guaranteed spectral distortion signal for the proposed Primordial
Inflation Explorer mission. The tSZ monopole will yield a direct measurement of
the total thermal energy in ionized electrons in the observable universe. | Gravitational wave signal from primordial magnetic fields in the Pulsar
Timing Array frequency band: The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA)
Collaborations have reported evidence for a common-spectrum process that can
potentially correspond to a stochastic gravitational wave background (SGWB) in
the 1--100 nHz frequency range. We consider the scenario in which this signal
is produced by magnetohydrodynamic (MHD) turbulence in the early Universe,
induced by a nonhelical primordial magnetic field at the energy scale
corresponding to the quark confinement phase transition. We perform MHD
simulations to study the dynamical evolution of the magnetic field and compute
the resulting SGWB. We show that the SGWB output from the simulations can be
very well approximated by assuming that the magnetic anisotropic stress is
constant in time, over a time interval related to the eddy turnover time. The
analytical spectrum that we derive under this assumption features a change of
slope at a frequency corresponding to the GW source duration that we confirm
with the numerical simulations. We compare the SGWB signal with the PTA data to
constrain the temperature scale at which the SGWB is sourced, as well as the
amplitude and characteristic scale of the initial magnetic field. We find that
the generation temperature is constrained to be in the 1--200 MeV range, the
magnetic field amplitude must be $>1$\% of the radiation energy density at that
time, and the magnetic field characteristic scale is constrained to be $>10$\%
of the horizon scale. We show that the turbulent decay of this magnetic field
will lead to a field at recombination that can help to alleviate the Hubble
tension and can be tested by measurements in the voids of the Large Scale
Structure with gamma-ray telescopes like the Cherenkov Telescope Array. |
The kinematic signature of the inspiral phase of massive binary black
holes: Supermassive black holes are expected to pair as a result of galaxy mergers,
and form a bound binary at parsec or sub-parsec scales. These scales are
unresolved even in nearby galaxies, and thus detection of non-active black hole
binaries must rely on stellar dynamics. Here we show that these systems could
be indirectly detected through the trail that the black holes leave as they
spiral inwards. We analyze two numerical simulations of inspiralling black
holes (equal masses and 10:1 mass ratio) in the stellar environment of a
galactic centre. We studied the effect of the binary on the structure of the
stellar population, with particular emphasis on projected kinematics and
directly measurable moments of the velocity distribution. We present those
moments as high-resolution 2D maps. As shown in past scattering experiments, a
torus of stars counter-rotating with respect to the black holes exists in
scales ~ 5 to 10 times larger than the binary separation. While this is seen in
the average velocity map in the unequal mass case, it is obscured by a more
strongly co-rotating outer region in the equal mass case; however, the inner
counter-rotation could still be detected by studying the higher moments of the
velocity distribution. Additionally, the maps reveal a dip in velocity
dispersion in the inner region, as well as more pronounced signatures in the
higher distribution moments. These maps could serve as templates for integral
field spectroscopy observations of nearby galactic centres. The discovery of
such signatures may help census the population of supermassive black hole
binaries and refine signal rate predictions for future space-based low
frequency gravitational wave detectors. | Primordial black holes from D-parity breaking in SO(10) grand unified
theory: The growing evidence of gravitational waves from binary black hole mergers
has renewed the interest in study of primordial black holes (PBH). Here we
study a mechanism for the formation of PBH from collapse of pseudo-topological
domain walls which form out of equilibrium during inflation and then collapse
post inflation. We apply the study to domain wall formation due to $D$-parity
embedded in a supersymmetric grand unified theory (GUT) based on $SO(10)$ and
compare the abundance of resulting PBH with the existing constraints. Thus the
macroscopic relics can then be used to constrain or rule out a GUT, or demand a
refinement of the theory of PBH formation in this class of GUTs. |
Initial conditions of the universe: Decaying tensor modes: Many models of the early universe predict that there should be primordial
tensor perturbations. These leave an imprint into the temperature and
polarisation anisotropies of the cosmic microwave background (CMB). The
differential equation describing the primordial tensor perturbations is a
second order differential equation and thus has two solutions. Canonically, the
decaying solution of this equation in radiation domination is dropped as it
diverges at early times and on superhorizon scales while it is then suppressed
at late times. Furthermore, if there is an inflationary phase prior to the
radiation domination phase, the amplitude of the decaying mode will also be
highly suppressed as it enters the radiation phase, thus its effect will be
negligible. In this study we remain agnostic to the early universe models
describing pre-radiation domination physics and allow this mode to be present
and see what effect it has on the CMB anisotropies. We find that the decaying
mode, if normalised at the same time on subhorizon scales as the growing mode
leaves an imprint on the CMB anisotropies that is identical to the growing
mode. Contrary to expectation, on large scales both modes are poorly
constrained for a scale invariant spectrum, and the apparent divergence of the
decaying mode does not lead to a divergent physical observable. Quantitatively,
the decaying mode can be more constrained both from temperature and
polarisation anisotropies. We use a model independent, non-parametric, approach
to constrain both of these primordial tensor perturbations using the
temperature and polarisation anisotropies. We find that both modes are best
constrained at the reionisation and recombination bumps and crucially, at the
reionisation bump the decaying mode can be distinguished from the growing mode. | Origin of optically passive spiral galaxies with dusty star-forming
regions: Outside-in truncation of star formation?: Recent observations have revealed that red, optically--passive spiral
galaxies with little or no optical emission lines, harbour significant amounts
of dust-obscured star formation. We propose that these observational results
can be explained if the spatial distributions of the cold gas and star-forming
regions in these spiral galaxies are significantly more compact than those in
blue star-forming spirals. Our numerical simulations show that if the sizes of
star-forming regions in spiral galaxies with disk sizes of R_d are ~ 0.3R_d,
such galaxies appear to have lower star formation rates as well as higher
degrees of dust extinction. This is mainly because star formation in these
spirals occurs only in the inner regions where both the gas densities and
metallicities are higher, and hence the dust extinction is also significantly
higher. We discuss whether star formation occurring preferentially in the inner
regions of spirals is closely associated with the stripping of halo and disk
gas via some sort of environmental effect. We suggest that the "outside-in
truncation of star formation" is the key to a better understanding of
apparently optically--passive spirals with dusty star-forming regions. |
Galaxy Number Counts and Implications for Strong Lensing: We compare galaxy number counts in HST/ACS fields containing
moderate-redshift (0.2<z<1.0) strong gravitational lenses with those in two
control samples: (1) the first square degree of the COSMOS survey, comprising
259 ACS fields and (2) 20 "pure parallel" fields randomly located on the sky.
Through a Bayesian analysis we determine the expectation values (mu_0) and
confidence levels of the underlying number counts for a range of apertures and
magnitude bins. Our analysis has produced the following results: (i) We infer
that our control samples are not consistent, with the number counts in the
COSMOS sample being significantly higher than in the pure parallel sample for
21 <= F814W <= 23. This result matches those found in previous analyses of
COSMOS data using different techniques. (ii) We find that small-size apertures,
centered on strong lenses, are overdense compared with randomly placed
apertures in the control samples, even compared to the COSMOS sample.
Correcting for the local clustering of elliptical galaxies, based on the
average two-point correlation function reduces this overdensity to the 1-2
sigma level. Thus, the overdensity of galaxies seen along a typical line of
sight to a lens can be explained mostly by the natural clustering of galaxies,
rather than being due to lenses lying along otherwise biased lines of sight.
However, a larger sample of lenses is needed to see if the remaining bias
persists when the lens-field uncertainties are smaller. (iii) There is
considerable scatter in the lines of sight to _individual_ lens systems, but
quantities that are linearly dependent on the external convergence (e.g., H_0)
should become unbiased if the extra galaxies that cause the bias can be
accounted for in the lens models either through direct modeling or via an
informed prior on the external convergence. The number counts can used to set
such an informed prior. | Seyfert galaxies: Nuclear Radio Structure and Unification: A radio study of a carefully selected sample of 20 Seyfert galaxies that are
matched in orientation-independent parameters, which are measures of intrinsic
active galactic nuclei (AGN) power and host galaxy properties is presented to
test the predictions of the unified scheme hypothesis. Our sample sources have
core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the
feasibility requirements. These simultaneous pc-scale and kpc-scale radio
observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal
tendency to show compact radio structures on mas-scales, (ii) the distributions
of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and
Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert
galaxies, (iv) similar distributions of source spectral indices in spite of the
fact that Seyferts show nuclear radio flux density variations, and (v) the
distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are
not significantly different as would be expected in the unified scheme. The
latter could be mainly due to a relatively large spread in the intrinsic sizes.
We also find that a starburst alone cannot power these radio sources. Finally,
an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample
shows results consistent with the predictions of the unified scheme. |
Spiral arm structures revealed in the M31 galaxy: Striking regularities are found in the northwestern arm of the M31 galaxy.
Star complexes located in this arm are all spaced 1.2 kpc apart and have
similar sizes of about 0.6 kpc. Within the same arm region Beck et al. (1989)
detected a regular magnetic field, and we found that its wavelength is the
spacing between the complexes. In this arm, groups of HII regions lie inside
star complexes, which, in turn, are located inside the gas and dust lane. In
contrast, the southwestern arm of M31 splits into a gas and dust lane upstream
and a dense stellar arm downstream, with HII regions located mostly along the
boundary between these components of the arm. The stellar density in the
southwestern arm is much higher than in the northwestern arm, and the former is
not fragmented into star complexes. The age gradient across this arm have been
found in earlier observations. According the classical SDW theory, these
drastic differences may be due due to their different pitch angles: about 0
degree for northwestern part of the arm and about 30 degree for the
southwestern segment. Data on M31, M51, M74, and some other galaxies suggest
that star complexes are mostly located in the arm segments that are not
accompanied by a dust lane upstream, i.e. do not host spiral shock wave. The
regularities in the distribution of complexes along a density wave spiral arm
are most probably due to the development of the Parker-Jeans instability, which
builds up star complexes if the initial SFR in the arm is low and, as a
sequence, magnetic field is regular along the arm. | Cosmic Acceleration from Causal Backreaction in a Smoothly Inhomogeneous
Universe: A phenomenological formalism is presented in which the apparent acceleration
of the universe is generated by large-scale structure formation, thus
eliminating the coincidence and magnitude fine-tuning problems of the
Cosmological Constant in the Concordance Model, as well as potential
instability issues with dynamical Dark Energy. The observed acceleration
results from the combined effect of innumerable local perturbations, due to
individually virialized systems, overlapping together in a
smoothly-inhomogeneous adjustment of the FRW metric, in a process governed by
the causal flow of inhomogeneity information outward from each clumped system.
We discuss several arguments from the literature claiming to place sharp limits
upon the strength of backreaction-related effects, and show why such arguments
are not applicable in a physically realistic cosmological analysis. A selection
of simply-parameterized models are presented, including several which are
capable of fitting the luminosity distance data from Type Ia supernovae
essentially as well as the best-fit flat $\Lambda$CDM model, without resort to
Dark Energy, any modification to gravity, or a local void. Simultaneously,
these models can reproduce measured cosmological parameters such as the age of
the universe, the matter density required for spatial flatness, the present-day
deceleration parameter, and the angular scale of the Cosmic Microwave
Background to within a reasonable proximity of their Concordance values. We
conclude by considering potential observational signatures for distinguishing
this cosmological formalism from $\Lambda$CDM or Dark Energy, as well as the
possible long-term fate of such a universe with ever-spreading spheres of
influence for its increasingly superposed perturbations. |
Measuring the spectrum of primordial gravitational waves with CMB, PTA
and Laser Interferometers: We investigate the possibility of measuring the primordial gravitational wave
(GW) signal across 21 decades in frequencies, using the cosmic microwave
background (CMB), pulsar timing arrays (PTA), and laser and atomic
interferometers. For the CMB and PTA experiments we consider the LiteBIRD
mission and the Square Kilometer Array (SKA), respectively. For the
interferometers we consider space mission proposals including the Laser
Interferometer Space Antenna (LISA), the Big Bang Observer (BBO), the
Deci-hertz Interferometer Gravitational wave Observatory (DECIGO), the
$\mu$Ares experiment, the Decihertz Observatory (DO), and the Atomic Experiment
for Dark Matter and Gravity Exploration in Space (AEDGE), as well as the
ground-based Einstein Telescope (ET) proposal. We implement the mathematics
needed to compute sensitivities for both CMB and interferometers, and derive
the response functions for the latter from the first principles. We also
evaluate the effect of the astrophysical foreground contamination in each
experiment. We present binned sensitivity curves and error bars on the energy
density parameter, $\Omega_{GW}h^2$, as a function of frequency for two
representative classes of models for the stochastic background of primordial
GW: the quantum vacuum fluctuation in the metric from single-field slow-roll
inflation, and the source-induced tensor perturbation from the spectator
axion-SU(2) inflation models. We find excellent prospects for joint
measurements of the GW spectrum by CMB and space-borne interferometers mission
proposals. | Multitracer CMB delensing maps from Planck and WISE data: Delensing, the removal of the limiting lensing B-mode background, is crucial
for the success of future cosmic microwave background (CMB) surveys in
constraining inflationary gravitational waves (IGWs). In recent work, delensing
with large-scale structure tracers has emerged as a promising method both for
improving constraints on IGWs and for testing delensing methods for future use.
However, the delensing fractions (i.e., the fraction of the lensing-B mode
power removed) achieved by recent efforts have been only $20-30\%$. In this
work, we provide a detailed characterization of a full-sky, dust-cleaned cosmic
infrared background (CIB) map for delensing and construct a further-improved
delensing template by adding additional tracers to increase delensing
performance. In particular, we build a multitracer delensing template by
combining the dust-cleaned Planck CIB map with a reconstructed CMB lensing map
from Planck and a galaxy number density map from the Wide-field Infrared Survey
Explorer (WISE) satellite. For this combination, we calculate the relevant
weightings by fitting smooth templates to measurements of all the cross- and
auto-spectra of these maps. On a large fraction of the sky
($f_\mathrm{sky}=0.43$), we demonstrate that our maps are capable of providing
a delensing factor of $43 \pm 1\%$; using a more restrictive mask
($f_\mathrm{sky}=0.11$), the delensing factor reaches $48 \pm 1\%$. For
low-noise surveys, our delensing maps, which cover much of the sky, can thus
improve constraints on the tensor-to-scalar ratio ($r$) by nearly a factor of
2. The delensing tracer maps are made publicly available, and we encourage
their use in ongoing and upcoming B-mode surveys. |
Weak-lensing-inferred scaling relations of galaxy clusters in the RCS2:
mass-richness, mass-concentration, mass-bias, and more: We study a sample of ~10^4 galaxy clusters in the redshift range 0.2<z<0.8
with masses M_200 > 5x10^13 h_70^-1 M_sun, discovered in the second
Red-sequence Cluster Survey (RCS2). The depth and excellent image quality of
the RCS2 enable us to detect the cluster-mass cross-correlation up to z~0.7. To
obtain cluster masses, concentrations and halo biases, we fit a cluster halo
model simultaneously to the lensing signal and to the projected density profile
of red-sequence cluster members, as the latter provides tight constraints on
the cluster miscentring distribution. We parametrise the mass-richness relation
as M_200 = A x (N_200/20)^alpha, and find A = (15.0 +- 0.8) x 10^13 h_70^-1
M_sun and alpha = 0.73 +- 0.07 at low redshift (0.2<z<0.35). At intermediate
redshift (0.35<z<0.55), we find a higher normalisation, which points at a
fractional increase of the richness towards lower redshift caused by the
build-up of the red-sequence. The miscentring distribution is well constrained.
Only ~30% of our BCGs coincide with the peak of the dark matter distribution.
The distribution of the remaining BCGs are modelled with a 2D-Gaussian, whose
width increases from 0.2 to 0.4 h_70^-1 Mpc towards higher masses; the ratio of
width and r_200 is constant with mass and has an average value of 0.44 +- 0.01.
The mass-concentration and mass-bias relation agree fairly well with literature
results at low redshift, but have a higher normalisation at higher redshifts,
which may be due to selection and projection effects. The concentration of the
satellite distribution decreases with mass and is correlated with the
concentration of the halo. | Using the polarization properties of double radio relics to probe the
turbulent compression scenario: Radio relics are Mpc-size synchrotron sources located in the outskirts of
some merging galaxy clusters. Binary-merging systems with favorable orientation
may host two almost symmetric relics, named double radio relics. Double radio
relics are seen preferentially edge-on and, thus, constitute a privileged
sample for statistical studies. Their polarization and Faraday rotation
properties give direct access to the relics origin and magnetic fields. In this
paper, we present a polarization and Rotation Measure (RM) synthesis study of
four clusters hosting double radio relics, namely 8C 0212+703, Abell 3365, PLCK
G287.0+32.9, previously missing polarization studies, and ZwCl 2341+0000, for
which conflicting results have been reported. We used 1-2 GHz Karl G. Jansky
Very Large Array observations. We also provide an updated compilation of known
double radio relics with important observed quantities. We studied their
polarization and Faraday rotation properties at 1.4 GHz and we searched for
correlations between fractional polarization and physical resolution, distance
from the cluster center, and shock Mach number. The weak correlations found
between these quantities are well reproduced by state-of-the-art
magneto-hydrodynamical simulations of radio relics, confirming that merger
shock waves propagate in a turbulent medium with tangled magnetic fields. Both
external and internal Faraday depolarization should play a fundamental role in
determining the polarization properties of radio relics at 1.4 GHz. Although
the number of double radio relics with RM information is still low, their
Faraday rotation properties (i.e., rest-frame RM and RM dispersion below 40 rad
m$^{-2}$ and non-Gaussian RM distribution) can be explained in the scenario in
which shock waves with Mach numbers larger than 2.5 propagate along the plane
of the sky and compress the turbulent intra-cluster medium. |
The preferentially magnified active nucleus in IRAS F10214+4724 - III.
VLBI observations of the radio core: We report 1.7 GHz Very Long Baseline Interferometry (VLBI) observations of
IRAS F10214+4724, a lensed z=2.3 obscured quasar with prodigious star
formation. We detect what we argue to be the obscured active nucleus with an
effective angular resolution of < 50 pc at z = 2.3 . The S_{1.7} = 210 micro-Jy
(9-\sigma) detection of this unresolved source is located within the HST
rest-frame ultraviolet/optical arc, however, >~100 mas northward of the arc
centre of curvature. This leads to a source plane inversion that places the
European VLBI Network detection to within milli-arcseconds of the modelled cusp
caustic, resulting in a very large magnification (\mu ~70), over an order of
magnitude larger than the CO (1-0) derived magnification of a spatially
resolved JVLA map, using the same lens model. We estimate the quasar bolometric
luminosity from a number of independent techniques and with our X-ray modelling
find evidence that the AGN may be close to Compton-thick, with an intrinsic
bolometric luminosity log(L_{bol,QSO} / L_sun) = 11.34 +- 0.27 dex. We make the
first black hole mass estimate of IRAS F10214+4724 and find log(M_{BH}/M_sun) =
8.36 +- 0.56 which suggests a low black hole accretion rate (\lambda = \dot{M}
/ \dot{M}_{Edd} ~ 3\pm^7_2 percent). We find evidence for a M_{BH}/M_{spheroid}
ratio that is 1-2 orders of magnitude larger than that of submillimetre
galaxies (SMGs) at z~2. At face value, this suggests IRAS F10214+4724 has
undergone a different evolutionary path compared to SMGs at the same epoch. A
primary result of this work is the demonstration that emission regions of
differing size and position can undergo significantly different magnification
boosts (> 1 dex) and therefore distort our view of high-redshift,
gravitationally lensed galaxies. | Modified gravity, gravitational waves and the large-scale structure of
the Universe: A brief report: The goal of this short report is to summarise some key results based on our
previous works on model independent tests of gravity at large scales in the
Universe, their connection with the properties of gravitational waves, and the
implications of the recent measurement of the speed of tensors for the
phenomenology of general families of gravity models for dark energy. |
Can galactic outflows explain the properties of Ly-alpha emitters?: We study the properties of Ly-alpha emitters in a cosmological framework by
computing the escape of Ly-alpha photons through galactic outflows. We combine
the GALFORM semi-analytical model of galaxy formation with a Monte Carlo
Ly-alpha radiative transfer code. The properties of Ly-alpha emitters at 0<z<7
are predicted using two outflow geometries: a Shell of neutral gas and a Wind
ejecting material, both expanding at constant velocity. We characterise the
differences in the Ly-alpha line profiles predicted by the two outflow
geometries in terms of their width, asymmetry and shift from the line centre
for a set of outflows with different hydrogen column densities, expansion
velocities and metallicities. In general, the Ly-alpha line profile of the
Shell geometry is broader and more asymmetric, and the Ly-alpha escape fraction
is lower than with the Wind geometry for the same set of parameters. In order
to implement the outflow geometries in the semi-analytical model GALFORM, a
number of free parameters in the outflow model are set by matching the
luminosity function of Ly-alpha emitters over the whole observed redshift
range. The models are consistent with the observationally inferred Ly-alpha
escape fractions, equivalent width distributions and with the shape of the
Ly-alpha line from composite spectra. Interestingly, our predicted UV
luminosity function of Ly-alpha emitters and the fraction of Ly-alpha emitters
in Lyman-break galaxy samples at high redshift are in partial agreement with
observations. Attenuation of the Ly-alpha line by the presence of a neutral
intergalactic medium at high redshift could be responsible for this
disagreement. We predict that Ly-alpha emitters constitute a subset of the
galaxy population with lower metallicities, lower instantaneous star formation
rates and larger sizes than the overall population at the same UV luminosity. | Cosmological Non-Linearities as an Effective Fluid: The universe is smooth on large scales but very inhomogeneous on small
scales. Why is the spacetime on large scales modeled to a good approximation by
the Friedmann equations? Are we sure that small-scale non-linearities do not
induce a large backreaction? Related to this, what is the effective theory that
describes the universe on large scales? In this paper we make progress in
addressing these questions. We show that the effective theory for the
long-wavelength universe behaves as a viscous fluid coupled to gravity:
integrating out short-wavelength perturbations renormalizes the homogeneous
background and introduces dissipative dynamics into the evolution of
long-wavelength perturbations. The effective fluid has small perturbations and
is characterized by a few parameters like an equation of state, a sound speed
and a viscosity parameter. These parameters can be matched to numerical
simulations or fitted from observations. We find that the backreaction of
small-scale non-linearities is very small, being suppressed by the large
hierarchy between the scale of non-linearities and the horizon scale. The
effective pressure of the fluid is always positive and much too small to
significantly affect the background evolution. Moreover, we prove that
virialized scales decouple completely from the large-scale dynamics, at all
orders in the post-Newtonian expansion. We propose that our effective theory be
used to formulate a well-defined and controlled alternative to conventional
perturbation theory, and we discuss possible observational applications.
Finally, our way of reformulating results in second-order perturbation theory
in terms of a long-wavelength effective fluid provides the opportunity to
understand non-linear effects in a simple and physically intuitive way. |
Probing Cosmology with Baryon Acoustic Oscillations using Gravitational
Waves: The third-generation (3G) gravitational wave (GW) detectors such as the
Einstein telescope (ET) or Cosmic Explorer (CE) are expected to play an
important role in cosmology. With the help of 3G detectors, we will be able to
probe large-scale structure (LSS) features such as baryon acoustic oscillations
(BAO), galaxy bias, etc. We explore the possibility to do precision cosmology,
with the 3G GW detectors by measuring the angular BAO scale using localization
volumes of compact binary merger events. Through simulations, we show that with
a 3G detector network, by probing the angular BAO scale using purely GW
observations, we can constrain the Hubble constant for the standard model of
cosmology ($\Lambda$CDM) with $90\%$ credible regions as $H_0 = 59.4^{+
33.9}_{-17.7} ~\mathrm{km}~\mathrm{s}^{-1}~\mathrm{Mpc}^{-1}$. When combined
with BAO measurements from galaxy surveys, we show that it can be used to
constrain various models of cosmology such as parametrized models for dark
energy equations of state. We also show how cosmological constraints using BAO
measurements from GW observations in the 3G era will complement the same from
spectroscopic surveys. | NIKA: a mm camera for Sunyaev-Zel'dovich science in clusters of galaxies: Clusters of galaxies, the largest bound objects in the Universe, constitute a
cosmological probe of choice, which is sensitive to both dark matter and dark
energy. Within this framework, the Sunyaev-Zel'dovich (SZ) effect has opened a
new window for the detection of clusters of galaxies and for the
characterization of their physical properties such as mass, pressure and
temperature. NIKA, a KID-based dual band camera installed at the IRAM 30-m
telescope, was particularly well adapted in terms of frequency, angular
resolution, field-of-view and sensitivity, for the mapping of the thermal and
kinetic SZ effect in high-redshift clusters. In this paper, we present the NIKA
cluster sample and a review of the main results obtained via the measurement of
the SZ effect on those clusters: reconstruction of the cluster radial pressure
profile, mass, temperature and velocity. |
Higgs-induced spectroscopic shifts near strong gravity sources: We explore the consequences of the mass generation due to the Higgs field in
strong gravity astrophysical environments. The vacuum expectation value of the
Higgs field is predicted to depend on the curvature of spacetime, potentially
giving rise to peculiar spectroscopic shifts, named hereafter "Higgs shifts."
Higgs shifts could be searched through dedicated multiwavelength and
multispecies surveys with high spatial and spectral resolution near strong
gravity sources such as Sagittarius A* or broad searches for signals due to
primordial black holes. The possible absence of Higgs shifts in these surveys
should provide limits to the coupling between the Higgs particle and the
curvature of spacetime, a topic of interest for a recently proposed
Higgs-driven inflationary model. We discuss some conceptual issues regarding
the coexistence between the Higgs mechanism and gravity, especially for their
different handling of fundamental and composite particles. | Contributions from primordial non-Gaussianity and General Relativity to
the galaxy power spectrum: We compute the real space galaxy power spectrum, including the leading order
effects of General Relativity and primordial non-Gaussianity from the
$f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ parameters. Such contributions come
from the one-loop matter power spectrum terms dominant at large scales, and
from the factors of the non-linear bias parameter $b_{\mathrm{NL}}$ (akin to
the Newtonian $b_{\phi}$). We assess the detectability of these contributions
in Stage-IV surveys. In particular, we note that specific values of the bias
parameter may erase the primordial and relativistic contributions to the
configuration space power spectrum. |
Channeling in solid Xe, Ar and Ne direct dark matter detectors: The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger
scintillation or ionization signal than otherwise expected. We give estimates
of the fraction of channeled recoiling ions in solid Xe, Ar and Ne crystals
using analytic models produced since the 1960's and 70's to describe channeling
and blocking effects. | Halo bias in Lagrangian Space: Estimators and theoretical predictions: We present several methods to accurately estimate Lagrangian bias parameters
and substantiate them using simulations. In particular, we focus on the
quadratic terms, both the local and the non local ones, and show the first
clear evidence for the latter in the simulations. Using Fourier space
correlations, we also show for the first time, the scale dependence of the
quadratic and non-local bias coefficients. For the linear bias, we fit for the
scale dependence and demonstrate the validity of a consistency relation between
linear bias parameters. Furthermore we employ real space estimators, using both
cross-correlations and the Peak-Background Split argument. This is the first
time the latter is used to measure anisotropic bias coefficients. We find good
agreement for all the parameters among these different methods, and also good
agreement for local bias with ESP$\tau$ theory predictions. We also try to
exploit possible relations among the different bias parameters. Finally, we
show how including higher order bias reduces the magnitude and scale dependence
of stochasticity of the halo field. |
High-z cosmography at a glance: Cosmography is the tool that makes possible to untie the interpretation of
cosmological observations from the definition of any dynamical prior. We review
the constraints on the cosmographic parameter obtained using the most thorough
data set ensemble available. We focus on some specific topics about the
statistically based selection of the most stringent fitting expansion. | Optical Performances of Slewing Mirror Telescope for UFFO-Pathfinder: The Ultra-Fast Flash Observatory-Pathfinder (UFFO-P) is to be launched
onboard Lomonosov spacecraft in November 2011. It is to measure early
UV/Optical photons from Gamma Ray Bursts (GRBs). Slewing Mirror Telescope (SMT)
is one of two instruments designed for detection of UV/Optical images of the
GRBs. SMT is a Ritchey-Chr\'etien telescope of 100 mm in diameter with a
motorized slewing mirror at the entrance providing 17\times17 arcmin2 in Field
of View (FOV) and 4 arcsec in pixel resolution. Its sky coverage can be further
expanded up to 35 degrees in FOV by tilting a motorized slewing mirror. All
mirrors were fabricated to about RMS 0.02 waves in wave front error (WFE) and
84.7% (in average reflectivity) over 200nm~650nm range. SMT was aligned to RMS
0.05 waves in WFE (test wavelength 632.8nm). From the static gravity test
result, SMT optics system is expected to survive during launch. The technical
details of SMT assembly and laboratory performance test results are reported. |
The butterfly effect in the extreme-mass ratio inspiral problem: Measurements of gravitational waves from the inspiral of a stellar-mass
compact object into a massive black hole are unique probes to test General
Relativity (GR) and MBH properties, as well as the stellar distribution about
these holes in galactic nuclei. Current data analysis techniques can provide us
with parameter estimation with very narrow errors. However, an EMRI is not a
two-body problem, since other stellar bodies orbiting nearby will influence the
capture orbit. Any deviation from the isolated inspiral will induce a small,
though observable deviation from the idealised waveform which could be
misinterpreted as a failure of GR. Based on conservative analysis of mass
segregation in a Milky Way like nucleus, we estimate that the possibility that
another star has a semi-major axis comparable to that of the EMRI is
non-negligible, although probably very small. This star introduces an
observable perturbation in the orbit in the case in which we consider only loss
of energy via gravitational radiation. When considering the two first-order
non-dissipative post-Newtonian contributions (the periapsis shift of the
orbit), the evolution of the orbital elements of the EMRI turns out to be
chaotic in nature. The implications of this study are twofold. From the one
side, the application to testing GR and measuring MBHs parameters with the
detection of EMRIs in galactic nuclei with a millihertz mission will be even
more challenging than believed. From the other side, this behaviour could in
principle be used as a signature of mass segregation in galactic nuclei. | Astrophysics and cosmology with galaxy clusters: the WFXT perspective: We discuss the central role played by the X-ray study of hot baryons within
galaxy clusters to reconstruct the assembly of cosmic structures and to trace
the past history of star formation and accretion onto supermassive Black Holes
(BHs). We shortly review the progress in this field contributed by the current
generation of X-ray telescopes. Then, we focus on the outstanding scientific
questions that have been opened by observations carried out in the last years
and that represent the legacy of Chandra and XMM: (a) When and how is entropy
injected into the inter-galactic medium (IGM)? (b) What is the history of metal
enrichment of the IGM? (c) What physical mechanisms determine the presence of
cool cores in galaxy clusters? (d) How is the appearance of proto-clusters at
z~2 related to the peak of star formation activity and BH accretion? (e) What
do galaxy clusters tell us about the nature of primordial density perturbations
and on the history of their growth? We show that the most efficient
observational strategy to address these questions is to carry out a large-area
X-ray survey, reaching a sensitivity comparable to that of deep Chandra and XMM
pointings, but extending over several thousands of square degrees. A similar
survey can only be carried out with a Wide-Field X-ray Telescope (WFXT), which
combines a high survey speed with a sharp PSF across the entire FoV. We
emphasize the important synergies that WFXT will have with a number of future
ground-based and space telescopes, covering from the radio to the X-ray bands.
Finally, we discuss the immense legacy value that such a mission will have for
extragalactic astronomy at large. |
Re-acceleration of Nonthermal Particles at Weak Cosmological Shock Waves: We examine diffusive shock acceleration (DSA) of the pre-exisiting as well as
freshly injected populations of nonthermal, cosmic-ray (CR) particles at weak
cosmological shocks. Assuming simple models for thermal leakage injection and
Alfv\'enic drift, we derive analytic, time-dependent solutions for the two
populations of CRs accelerated in the test-particle regime. We then compare
them with the results from kinetic DSA simulations for shock waves that are
expected to form in intracluster media and cluster outskirts in the course of
large-scale structure formation. We show that the test-particle solutions
provide a good approximation for the pressure and spectrum of CRs accelerated
at these weak shocks. Since the injection is extremely inefficient at weak
shocks, the pre-existing CR population dominates over the injected population.
If the pressure due to pre-existing CR protons is about 5 % of the gas thermal
pressure in the upstream flow, the downstream CR pressure can absorb typically
a few to 10 % of the shock ram pressure at shocks with the Mach number $M \la
3$. Yet, the re-acceleration of CR electrons can result in a substantial
synchrotron emission behind the shock. The enhancement in synchrotron radiation
across the shock is estimated to be about a few to several for $M \sim 1.5$ and
$10^2-10^3$ for $M \sim 3$, depending on the detail model parameters. The
implication of our findings for observed bright radio relics is discussed. | An Introductory Review on Cosmic Reionization: The universe goes through several phase transitions during its formative
stages. Cosmic reionization is the last of them, where ultraviolet and X-ray
radiation escape from the first generations of galaxies heating and ionizing
their surroundings and subsequently the entire intergalactic medium. There is
strong observational evidence that cosmic reionization ended approximately one
billion years after the Big Bang, but there are still uncertainties that will
be clarified with upcoming optical, infrared, and radio facilities in the next
decade. This article gives an introduction to the theoretical and observational
aspects of cosmic reionization and discusses their role in our understanding of
early galaxy formation and cosmology. |
Predicting the frequencies of young and of tiny galaxies: A simple, 1-equation, galaxy formation model is applied to both the halo
merger tree derived from a high-resolution dissipationless cosmological
simulation and to 1/4 million Monte-Carlo halo merger trees. The galaxy
formation model involves a sharp entropy barrier against the accretion of gas
onto low-mass halos, the shock heating of infalling gas far from the central
regions of massive halos, and supernova feedback that drives the gas out of
shallow halo potential wells. With the first approach, we show that the large
majority of galaxies within group- and cluster-mass halos, known to be mainly
dwarf ellipticals, have acquired the bulk of their stellar mass through gas
accretion and not via galaxy mergers. With the second approach, we
qualitatively reproduce the downsizing trend of greater ages at greater masses
in stars and predict an upsizing trend of greater ages as one proceeds to
masses lower than 10^10 M_Sun. We find that the fraction of galaxies with very
young stellar populations (more than half the stellar mass formed within the
last 1.5 Gyr) is a function of present-day stellar mass, which peaks at 0.5% at
m_crit=10^7.5-9.5 M_Sun, roughly corresponding to the masses of blue compact
dwarfs. We predict that the stellar mass function of galaxies should not show a
maximum at m_stars > 10^{5.5}, M_Sun, with a power-law stellar mass function
with slope approx -1.6 if the IGM temperature in the outskirts of halos before
reionization is set by H2 cooling. We speculate on the nature of the lowest
mass galaxies. | New limits on Early Dark Energy from the South Pole Telescope: We present new limits on early dark energy (EDE) from the cosmic microwave
background (CMB) using data from the WMAP satellite on large angular scales and
South Pole Telescope (SPT) on small angular scales. We find a strong upper
limit on the EDE density of Omega_e < 0.018 at 95% confidence, a factor of
three improvement over WMAP data alone. We show that adding lower-redshift
probes of the expansion rate to the CMB data improves constraints on the dark
energy equation of state, but not the EDE density. We also explain how the
small-scale CMB temperature anisotropy constrains EDE. |
Probing the Early Universe with Axion Physics and Gravitational Waves: We show results for the expected reach of the network of experiments that is
being set up globally with the aim of detecting the "invisible" axion, in light
of a non-standard thermal history of the universe. Assuming that the axion is
the dark matter, we discuss the reach of a successful detection by a given
experimental setup in a particular axion mass window for different
modifications of the cosmological background before primordial nucleosynthesis
occurred. Results are presented both in the case where the present energy
budget in cold axions is produced through the vacuum realignment mechanism
alone, or in the case in which axionic strings also provide with additional
contributions to the axion energy density. We also show that in some
cosmological models, the spectrum of gravitational waves from the axionic
string network would be within reach of the future network of detectors like
LISA and DECIGO-BBO. We conclude that some scenarios describing the early
universe can be probed jointly by the experimental efforts on axion detection
and by gravity wave multi-messenger astronomy. | Measuring the low mass end of the Mbh - sigma relation: We show that high quality laser guide star (LGS) adaptive optics (AO)
observations of nearby early-type galaxies are possible when the tip-tilt
correction is done by guiding on nuclei while the focus compensation due to the
changing distance to the sodium layer is made 'open loop'. We achieve
corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black
hole mass (Mbh) one needs integral field observations of both high spatial
resolution and large field of view. With these data it is possible to determine
the lower limit to Mbh even if the spatial resolution of the observations are
up to a few times larger than the sphere of influence of the black hole. |
CMB spectroscopy at third-order in cosmological perturbations: Early energy injection to the Cosmic Microwave Background (CMB) from
dissipation of acoustic waves generates deviations from the blackbody spectrum
not only at second-order but also at third-order in cosmological perturbations.
We compute this new spectral distortion $\mathcal \kappa$ based on third-order
cosmological perturbation theory and show that $\kappa$ arises as a result of
mode coupling between spectral distortions and temperature perturbations. The
ensemble average of $\kappa$ can be directly sourced by (integrated) primordial
non-Gaussianity. In particular, we roughly estimate the signal as
$\kappa=f^{\rm loc.}_{\rm NL}\times \mathcal O(10^{-18})$ for local type
scale-independent non-Gaussianity. The signal is incredibly tiny; however, we
argue that it carries a specific frequency dependence different from other
types of CMB spectral distortions. Also, it should be noticed that $\kappa$ is
sensitive to extremely squeezed shapes of primordial bispectra that cannot be
constrained by the CMB anisotropies. Finally, we comment on other possible
applications of our results. | Planck 2013 results. XXX. Cosmic infrared background measurements and
implications for star formation: We present new measurements of CIB anisotropies using Planck. Combining HFI
data with IRAS, the angular auto- and cross frequency power spectrum is
measured from 143 to 3000 GHz, and the auto-bispectrum from 217 to 545 GHz. The
total areas used to compute the CIB power spectrum and bispectrum are about
2240 and 4400 deg^2, respectively. After careful removal of the contaminants,
and a complete study of systematics, the CIB power spectrum and bispectrum are
measured with unprecedented signal to noise ratio from angular multipoles
ell~150 to 2500, and ell~130 to 1100, respectively. Two approaches are
developed for modelling CIB power spectrum anisotropies. The first approach
takes advantage of the unique measurements by Planck at large angular scales,
and models only the linear part of the power spectrum, with a mean bias of dark
matter halos hosting dusty galaxies at a given redshift weighted by their
contribution to the emissivities. The second approach is based on a model that
associates star-forming galaxies with dark matter halos and their subhalos,
using a parametrized relation between the dust-processed infrared luminosity
and (sub-)halo mass. The two approaches simultaneously fit all auto- and cross-
power spectra very well. We find that the star formation history is well
constrained up to z~2. However, at higher redshift, the accuracy of the star
formation history measurement is strongly degraded by the uncertainty in the
spectral energy distribution of CIB galaxies. We also find that CIB galaxies
have warmer temperatures as redshift increases. The CIB bispectrum is steeper
than that expected from the power spectrum, although well fitted by a power
law; this gives some information about the contribution of massive halos to the
CIB bispectrum. |
Blue-tilted inflationary tensor spectrum and reheating in the light of
NANOGrav results: We discuss the possibility of explaining the recent NANOGrav results by
inflationary gravitational waves (IGWs) with a blue-tilted primordial spectrum.
Although such IGWs can account for the NANOGrav signal without contradicting
the upper bound on the tensor-to-scalar ratio at the cosmic microwave
background scale, the predicted spectrum is in strong tension with the upper
bound on the amplitude of the stochastic gravitational wave background by
big-bang nucleosynthesis (BBN) and the second LIGO-Virgo observation run.
However, the thermal history of the Universe, such as reheating and late-time
entropy production, affects the spectral shape of IGWs at high frequencies and
permits evading the upper bounds. We show that, for the standard reheating
scenario, when the reheating temperature is relatively low, a blue tensor
spectrum can explain the recent NANOGrav signal without contradicting the BBN
and the LIGO-Virgo constraints. We further find that, when one considers a
late-time entropy production, the NANOGrav signal can be explained even for an
instant reheating scenario. | Serendipitous Discovery of an Overdensity of Lyman-Alpha Emitters at
z~4.8 in the Cl1604 Supercluster Field: We present results of a spectroscopic search for Lyman-alpha emitters (LAEs)
in the Cl1604 supercluster field using the extensive spectroscopic Keck/DEIMOS
database taken as part of the Observations of Redshift Evolution in Large Scale
Environments (ORELSE) survey. A total of 12 slitmasks were observed and
inspected in the Cl1604 field, spanning a survey volume of 1.365x10^4 co-moving
Mpc^3. We find a total of 17 high redshift (4.39 < z < 5.67) LAE candidates
down to a limiting flux of 1.9x10^(-18) ergs/s/cm (~0.1L* at z~5), 13 of which
we classify as high quality. The resulting LAE number density is nearly double
that of LAEs found in the Subaru deep field at z~4.9 and nearly an order of
magnitude higher than in other surveys of LAEs at similar redshifts, an excess
that is essentially independent of LAE luminosity. We also report on the
discovery of two possible LAE group structures at z~4.4 and z~4.8 and
investigate the effects of cosmic variance of LAEs on our results. Fitting a
simple truncated single Gaussian model to a composite spectrum of the 13 high
quality LAE candidates, we find a best-fit stellar velocity dispersion of 136
km/s. Additionally, we see modest evidence of a second peak in the composite
spectrum, possibly caused by galactic outflows, as well as evidence for a
non-trivial Lyman-alpha escape fraction. We find an average LAE star formation
rate density (SFRD) of ~5x10^(-3) M_solar/yr/Mpc^3 with moderate evidence for
negative evolution in the LAE SFRD from z~4.6 to z~5.7. We measure a best-fit
luminosity function generally consistent with measurements from other surveys
at similar epochs. Finally, we investigate any possible effects from weak or
strong gravitational lensing induced by the foreground supercluster, finding
that our LAE candidates are minimally affected by lensing processes. |
Constraining cosmology with weak lensing voids: Upcoming surveys such as \LSST{} and \Euclid{} will significantly improve the
power of weak lensing as a cosmological probe. To maximise the information that
can be extracted from these surveys, it is important to explore novel
statistics that complement standard weak lensing statistics such as the
shear-shear correlation function and peak counts. In this work, we use a
recently proposed weak lensing observable -- weak lensing voids -- to make
parameter constraint forecasts for an LSST-like survey. We use the
\cosmoslics{} $w$CDM simulation suite to measure void statistics as a function
of cosmological parameters. The simulation data is used to train a Gaussian
process regression emulator that we use to generate likelihood contours and
provide parameter constraints from mock observations. We find that the void
abundance is more constraining than the tangential shear profiles, though the
combination of the two gives additional constraining power. We forecast that
without tomographic decomposition, these void statistics can constrain the
matter fluctuation amplitude, $S_8$ within 0.3\% (68\% confidence interval),
while offering 1.5, 1.5 and 2.7\% precision on the matter density parameter,
$\Omega_{\rm m}$, the reduced Hubble constant, $h$, and the dark energy
equation of state parameter, $w_0$, respectively. These results are tighter
than the constraints from the shear-shear correlation function with the same
observational specifications for $\Omega_m$, $S_8$ and $w_0$. The constraints
from the WL voids also have complementary parameter degeneracy directions to
the shear 2PCF for all combinations of parameters that include $h$, making weak
lensing void statistics a promising cosmological probe. | First Season QUIET Observations: Measurements of CMB Polarization Power
Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475: The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and
95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to
measure the anisotropy in the polarization of the CMB. QUIET primarily targets
the B modes from primordial gravitational waves. The combination of these
frequencies gives sensitivity to foreground contributions from diffuse Galactic
synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of
data were collected, first with the 19-element 43GHz array (3458hours) and then
with the 90-element 95GHz array. Each array observes the same four fields,
selected for low foregrounds, together covering ~1000deg^2. This paper reports
initial results from the 43GHz receiver which has an array sensitivity to CMB
fluctuations of 69uK sqrt(s). The data were extensively studied with a large
suite of null tests before the power spectra, determined with two independent
pipelines, were examined. Analysis choices, including data selection, were
modified until the null tests passed. Cross correlating maps with different
telescope pointings is used to eliminate a bias. This paper reports the EE, BB
and EB power spectra in the multipole range ell=25-475. With the exception of
the lowest multipole bin for one of the fields, where a polarized foreground,
consistent with Galactic synchrotron radiation, is detected with 3sigma
significance, the E-mode spectrum is consistent with the LCDM model, confirming
the only previous detection of the first acoustic peak. The B-mode spectrum is
consistent with zero, leading to a measurement of the tensor-to-scalar ratio of
r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation
technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent
boresight rotation leads to the lowest level of systematic contamination in the
B-mode power so far reported, below the level of r=0.1 |
Hunting down systematics in baryon acoustic oscillations after cosmic
high noon: Future dark energy experiments will require better and more accurate
theoretical predictions for the baryonic acoustic oscillations (BAO) signature
in the spectrum of cosmological perturbations. Here, we use large N-body
simulations of the \LambdaCDM Planck cosmology to study any possible systematic
shifts and damping in BAO due to the impact of nonlinear gravitational growth
of structure, scale dependent and non-local bias, and redshift-space
distortions. The effect of cosmic variance is largely reduced by dividing the
tracer power spectrum by that from a BAO-free simulation starting with the same
phases. This permits us to study with unprecedented accuracy (better than 0.02%
for dark matter and 0.07% for low-bias halos) small shifts of the pristine BAO
wavenumbers towards larger k, and non-linear damping of BAO wiggles in the
power spectrum of dark matter and halo populations in the redshift range z=0-1.
For dark matter, we provide an accurate parametrization of the evolution of
\alpha as a function of the linear growth factor D(z). For halo samples, with
bias ranging from 1.2 to 2.8, we measure a typical BAO shift of ~0.25%,
observed in real-space, which does not show an appreciable evolution with
redshift within the uncertainties. Moreover, we report a constant shift as a
function of halo bias. We find a different evolution of the damping of the
acoustic feature in all halo samples as compared to dark matter with haloes
suffering less damping, and also find some weak dependence on bias. A larger
BAO shift and damping is measured in redshift-space which can be well explained
by linear theory due to redshift-space distortions. A clear modulation in phase
with the acoustic scale is observed in the scale-dependent halo bias due to the
presence of the baryonic acoustic oscillations. | Structure and dynamics in low density regions: galaxy-galaxy
correlations inside cosmic voids: We compute the galaxy-galaxy correlation function of low-luminosity SDSS-DR7
galaxies $(-20 < M_{\rm r} - 5\log_{10}(h) < -18)$ inside cosmic voids
identified in a volume limited sample of galaxies at $z=0.085$. To identify
voids, we use bright galaxies with $M_{\rm r} - 5\log_{10}(h) < -20.0$. We find
that structure in voids as traced by faint galaxies is mildly non-linear as
compared with the general population of galaxies with similar luminosities.
This implies a redshift-space correlation function with a similar shape than
the real-space correlation albeit a normalization factor. The redshift space
distortions of void galaxies allow to calculate pairwise velocity distributions
which are consistent with an exponential model with a pairwise velocity
dispersion of $w \sim 50-70$ km/s, significantly lower than the global value of
$w \sim 500$ km/s. We also find that the internal structure of voids as traced
by faint galaxies is independent of void environment, namely the correlation
functions of galaxies residing in void-in-void or void-in-shell regions are
identical within uncertainties. We have tested all our results with the
semi-analytic catalogue MDPL2-\textsc{Sag} finding a suitable agreement with
the observations in all topics studied. |
Evolution of Dark Matter Halos and their Radio Emissions: Radio synchrotron emission is expected as a natural by-product of the
self-annihilation of super-symmetric dark matter particles. In this work we
discuss the general properties of the radio emission expected in a wide range
of dark matter halos, from local dwarf spheroidal galaxies to large and distant
galaxy clusters with the aim to determine the neutralino dark matter detection
prospects of the Square Kilometre Array (SKA). The analysis of the SKA
detection of dark matter(DM)-induced radio emission is presented for structures
spanning a wide range of masses and redshifts, and we also analyze the limits
that the SKA can set on the thermally averaged neutralino annihilation
cross-section in the event of non-detection. To this aim, we construct a model
of the redshift evolution of the radio emissions of dark matter halos and apply
it to generate predicted fluxes from a range of neutralino masses and
annihilation channels for the dark matter halos surrounding dwarf galaxies,
galaxies and galaxy clusters. Using the available SKA performance predictions
and its ability to determine an independent measure of the magnetic field in
cosmic structures, we explore both the detailed detection prospects and the
upper-bounds that might be placed on the neutralino annihilation cross-section
in the event of non-detection. We find that the SKA can access a neutralino
parameter space far larger than that of any preceding indirect-detection
experiment, also improving on the realistic CTA detection prospects, with the
possibility of setting cross-section upper-bounds up to four orders of
magnitude below the thermal relic density bound. Additionally, we find that
neutralino radio emissions carry redshift-independent signatures of the
dominant annihilation channel and of neutralino mass, offering therefore a
means to identify such non-thermal emissions within the observing frequency
range of the SKA. | Relativistic wide-angle galaxy bispectrum on the light-cone: Given the important role that the galaxy bispectrum has recently acquired in
cosmology and the scale and precision of forthcoming galaxy clustering
observations, it is timely to derive the full expression of the large-scale
bispectrum going beyond approximated treatments which neglect integrated terms
or higher-order bias terms or use the Limber approximation. On cosmological
scales, relativistic effects that arise from observing on the past light-cone
alter the observed galaxy number counts, therefore leaving their imprints on
N-point correlators at all orders. In this paper we compute for the first time
the bispectrum including all general relativistic, local and integrated,
effects at second order, the tracers' bias at second order, geometric effects
as well as the primordial non-Gaussianity contribution. This is timely
considering that future surveys will probe scales comparable to the horizon
where approximations widely used currently may not hold; neglecting these
effects may introduce biases in estimation of cosmological parameters as well
as primordial non-Gaussianity. |
The Low-mass, Highly Accreting Black Hole Associated with the Active
Galactic Nucleus 2XMM J123103.2+110648: Optical spectra and images taken with the Baade 6.5 meter Magellan telescope
confirm that 2XMM J123103.2+110648, a highly variable X-ray source with an
unusually soft spectrum, is indeed associated with a type 2 (narrow-line)
active nucleus at a redshift of z = 0.11871. The absence of broad Halpha or
Hbeta emission in an otherwise X-ray unabsorbed source suggests that it
intrinsically lacks a broad-line region. If, as in other active galaxies, the
ionized gas and stars in J1231+1106 are in approximate virial equilibrium, and
the black hole mass versus stellar velocity dispersion relation holds, the
exceptionally small velocity dispersion of 33.5 km/s for [O III] 5007 implies
that the black hole mass is approximately 10^5 solar masses, among the lowest
ever detected. Such a low black hole mass is consistent with the general
characteristics of the host, a small, low-luminosity, low-mass disk galaxy. We
estimate the Eddington ratio of the black hole to be > 0.5, in good agreement
with expectations based on the X-ray properties of the source. | Old Dark Energy: Dark energy dynamics in the recent universe is influenced by its evolution
through the long, matter dominated expansion history. A particular dynamical
property, the flow variable, remains constant in several classes of scalar
field models as long as matter dominates; the dark energy is only free to
diverge in behavior at recent times. This gives natural initial conditions for
Monte Carlo studies of dark energy dynamics. We propose a parametrization for
the later evolution that covers a wide range of possible behaviors, is
tractable in making predictions, and can be constrained by observations. We
compare the approach to directly parametrizing the potential, which does not
take into account the maturity of the dark energy dynamics. |
The value of the fine structure constant over cosmological times: The optical spectra of objects classified as QSOs in the SDSS DR6 are
analyzed with the aim of determining the value of the fine structure constant
in the past and then check for possible changes in the constant over
cosmological timescales. The analysis is done by measuring the position of the
fine structure lines of the [OIII] doublet (4959 and 5008) in QSO nebular
emission. From the sample of QSOs at redshifts z < 0.8 a subsample was selected
on the basis of the amplitude and width of the [OIII] lines. Two different
method were used to determine the position of the lines of the [OIII] doublet,
both giving similar results. Using a clean sample containing 1568 of such
spectra, a value of Delta alpha /alpha=(+2.4 +-2.5) x 10^{-5} (in the range of
redshifts 0-0.8) was determined. The use of a larger number of spectra allows a
factor ~5 improvement on previous constraints based on the same method. On the
whole, we find no evidence of changes in alpha on such cosmological timescales.
The mean variation compatible with our results is 1/ <t> Delta
alpha/alpha=(+0.7 +- 0.7) x 10^{-14} yr^{-1}. The analysis was extended to the
[NeIII] and [SII] doublets, although their usefulness is limited due to the
fact that all these doublets in QSOs tend to be fainter than [OIII], and that
some of them are affected by systematics. | CMB bispectrum constraints on DHOST inflation: We present the first direct constraints on a Degenerate Higher Order Scalar
Tensor (DHOST) inflation model using the Planck 2018 Cosmic Microwave
Background (CMB) results on non-Gaussianities. We identify that the bispectrum
consists of a fixed contribution following from the power spectrum and a linear
combination of terms depending on five free parameters defining the cubic
perturbations to the DHOST model. The former peaks in the squeezed limit, while
the latter is maximised in the equilateral limit. We directly confront the
model predictions to the CMB bispectrum statistics via the public code CMB-BEST
and marginalize over the free parameters. We explicitly show that there are
viable DHOST inflationary models satisfying both power spectrum and bispectrum
constraints from Planck. However, rather surprisingly, the constraints exclude
certain models at the $6\sigma$-level even though they pass the conventional
fudge factor tests. In this case and despite having a handful of free
parameters, the model's large squeezed bispectrum cannot be cancelled out
without introducing a large bispectrum in other limits which are strongly
constrained by Planck's non-detection of primordial non-Gaussianity. We
emphasize that first-order approximations such as fudge factors, albeit
commonly used in the literature, may be misleading and provide weaker
constraints. A proper analysis of the constraints from Planck requires a more
robust approach, such as the one provided by the CMB-BEST code. |
Generalized tracker quintessence models for dark energy: We study the dynamical properties of tracker quintessence models using a
general parametrization of their corresponding potentials, and show that there
is a general condition for the appearance of a tracker behavior at early times.
Likewise, we determine the conditions under which the quintessence tracker
models can also provide an accelerating expansion of the universe with an
equation of state closer to $-1$. Apart from the analysis of the background
dynamics, we also include linear density perturbations of the quintessence
field in a consistent manner and using the same parametrization of the
potential, with which we show the influence they have on some cosmological
observables. The generalized tracker models are compared to observations, and
we discuss their appropriateness to ameliorate the fine-tuning of initial
conditions and their consistency with the accelerated expansion of the Universe
at late times. | Halo Gas and Galaxy Disk Kinematics Derived from Observations and LCDM
Simulations of MgII Absorption Selected Galaxies at Intermediate Redshift: We obtained ESI/Keck rotation curves of 10 MgII absorption selected galaxies
(0.3 < z < 1.0) for which we have WFPC-2/HST images and high resolution
HIRES/Keck and UVES/VLT quasar spectra of the MgII absorption profiles. We
perform a kinematic comparison of these galaxies and their associated halo MgII
absorption. For all 10 galaxies, the majority of the absorption velocities lie
in the range of the observed galaxy rotation velocities. In 7/10 cases, the
absorption velocities reside fully to one side of the galaxy systemic velocity
and usually align with one arm of the rotation curve. In all cases, a constant
rotating thick-disk model poorly reproduces the full spread of observed MgII
absorption velocities when reasonably realistic parameters are employed. In
2/10 cases, the galaxy kinematics, star formation surface densities, and
absorption kinematics have a resemblance to those of high redshift galaxies
showing strong outflows. We find that MgII absorption velocity spread and
optical depth distribution may be dependent on galaxy inclination. To further
aid in the spatial-kinematic relationships of the data, we apply quasar
absorption line techniques to a galaxy (v_c=180 km/s) embedded in LCDM
simulations. In the simulations, MgII absorption selects metal enriched "halo"
gas out to roughly 100 kpc from the galaxy, tidal streams, filaments, and small
satellite galaxies. Within the limitations inherent in the simulations, the
majority of the simulated MgII absorption arises in the filaments and tidal
streams and is infalling towards the galaxy with velocities between -200 < v_r
< -180 km/s. The MgII absorption velocity offset distribution (relative to the
simulated galaxy) spans ~200 km/s with the lowest frequency of detecting MgII
at the galaxy systematic velocity. |
Properties of holographic dark energy at the Hubble length: We consider holographic cosmological models of dark energy in which the
infrared cutoff is set by the Hubble's radius. We show that any interacting
dark energy model, regardless of its detailed form, can be recast as a non
interacting model in which the holographic parameter $c^{2}$ evolves slowly
with time. Two specific cases are analyzed. We constrain the parameters of both
models with observational data, and show that they can be told apart at the
perturbative level. | Constraints on the cosmic distance duality relation with simulated data
of gravitational waves from the Einstein Telescope: The cosmic distance duality relation (CDDR) has been test through several
astronomical observations in the last years. This relation establishes a simple
equation relating the angular diameter ($D_A$) and luminosity ($D_L$) distances
at a redshift $z$, $D_LD_A^{-1}(1+z)^{-2}=\eta=1$. However, only very recently
this relation has been observationally tested at high redshifts ($z \approx
3.6$) by using luminosity distances from type Ia supernovae (SNe Ia) and gamma
ray bursts (GRBs) plus angular diameter distances from strong gravitational
lensing (SGL) observations. The results show that no significant deviation from
the CDDR validity has been verified. In this work, we test the potentialities
of future luminosity distances from gravitational waves (GWs) sources to impose
limit on possible departures of CDDR jointly with current SGL observations. The
basic advantage of $D_L$ from GWs is being insensitive to non-conservation of
the number of photons. By simulating 600, 900 and 1200 data of GWs using the
Einstein Telescope (ET) as reference, we derive limits on $\eta(z)$ function
and obtain that the results will be at least competitive with current limits
from the SNe Ia $+$ GRBs $+$ SGLs analyses. |
Geometry of Keplerian disk systems and bounds on masses of their
components: We investigate accreting disk systems with polytropic gas in Keplerian
motion. Numerical data and partial analytic results show that the
self-gravitation of the disk speeds up its rotation -- its rotational frequency
is larger than that given by the well known strictly Keplerian formula that
takes into account the central mass only. Thus determination of central mass in
systems with massive disks requires great care -- the strictly Keplerian
formula yields only an upper bound. The effect of self-gravity depends on
geometric aspects of disk configurations. Disk systems with a small (circa
$10^{-4}$) ratio of the innermost radius to the outermost disk radius have the
central mass close to the upper limit, but if this ratio is of the order of
unity then the central mass can be smaller by many orders of magnitude from
this bound. | The Evolution of K* and the Halo Occupation Distribution since z=1.5:
Observations vs. Simulations: We study the evolution of the K-band luminosity function (LF) and the Halo
Occupation Distribution (HOD) using Subaru observations of 15 X-ray clusters at
z=0.8-1.5 and compare the results with mock clusters (0<z<1.3) extracted from
the Millennium Simulation and populated with galaxies using the semi-analytic
model (SAM) of Bower et al., matched in mass to our observed sample. We find
that the characteristic luminosity K* defined by a Shechter LF is consistent
with SAM predictions, which mimic well the evolution of K* in z>1 rich
clusters. However, we cannot distinguish between this model and a simple
stellar population synthesis model invoking passive evolution with a formation
redshift z~5 - consistent with the presence of an old red galaxy population
ubiquitous in rich clusters at z=1.5. We also see a small difference (\Delta
K*~0.5) between our clusters and studies of the field population at similar
redshifts, suggesting only a weak dependence of the luminous (L>L*) part of the
LF on environment. Turning to our HOD study, we find that within R_{500},
high-z clusters tend to host smaller numbers of galaxies to a magnitude K*+2
compared to their low-z counterparts. This behavior is also seen in the mock
samples and is relatively insensitive to the average mass of the cluster
haloes. In particular, we find significant correlations of the observed number
of member cluster galaxies (N) with both z and cluster mass:
$N(M,z)=(53\pm1)(1+z)^{-0.61^{+0.18}_{-0.20}}(M/10^{14.3})^{0.86\pm0.05}$.
Finally, we examine the spatial distribution of galaxies and provide a new
estimate of the concentration parameter for clusters at high z
($c_{g}=2.8^{+1.0}_{-0.8}$). Our result is consistent with predictions from
both our SAM mock clusters and literature's predictions for dark matter haloes.
The mock sample predictions rise slowly with decreasing redshift reaching
$c_{g}=6.3^{+0.39}_{-0.36}$ at z=0. |
Probing cluster dynamics in RXCJ1504.1-0248 via radial and
two-dimensional gas and galaxy properties: We studied one of the most X-ray luminous cluster of galaxies in the REFLEX
survey, RXC J1504.1-0248 (hereafter R1504; z=0.2153), using XMM-Newton X-ray
imaging spectroscopy, VLT/VIMOS optical spectroscopy, and WFI optical imaging.
The mass distributions were determined using both the so-called hydrostatic
method with X-ray imaging spectroscopy and the dynamical method with optical
spectroscopy, respectively, which yield M^{H.E.}_{500}=(5.81+/-0.49)*1.e14Msun
and M^{caustic}_{500}=(4.17+/-0.42)*1e14Msun. According to recent calibrations,
the richness derived mass estimates closely agree with the hydrostatic and
dynamical mass estimates. The line-of-sight velocities of spectroscopic members
reveal a group of galaxies with high-velocities (>1000 km/s) at a projected
distance of about r^{H.E.}_{500}=(1.18+/-0.03) Mpc south-east of the cluster
centroid, which is also indicated in the X-ray two-dimensional (2-D)
temperature, density, entropy, and pressure maps. The dynamical mass estimate
is 80% of the hydrostatic mass estimate at r^{H.E.}_{500}. It can be partially
explained by the ~20% scatter in the 2-D pressure map that can be propagated
into the hydrostatic mass estimate. The uncertainty in the dynamical mass
estimate caused by the substructure of the high velocity group is ~14%. The
dynamical mass estimate using blue members is 1.23 times that using red
members. The global properties of R1504 obey the observed scaling relations of
nearby clusters, although its stellar-mass fraction is rather low. | The Chemical Imprint of Silicate Dust on the Most Metal-Poor Stars: We investigate the impact of dust-induced gas fragmentation on the formation
of the first low-mass, metal-poor stars (< 1Msun) in the early universe.
Previous work has shown the existence of a critical dust-to-gas ratio, below
which dust thermal cooling cannot cause gas fragmentation. Assuming the first
dust is silicon-based, we compute critical dust-to-gas ratios and associated
critical silicon abundances ([Si/H]crit). At the density and temperature
associated with protostellar disks, we find that a standard Milky Way grain
size distribution gives [Si/H]crit = -4.5 +/- 0.1, while smaller grain sizes
created in a supernova reverse shock give [Si/H]crit = -5.3 +/- 0.1. Other
environments are not dense enough to be influenced by dust cooling. We test the
silicate dust cooling theory by comparing to silicon abundances observed in the
most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low
enough to rule out dust-induced gas fragmentation with a standard grain size
distribution. Moreover, two of these stars have such low silicon abundances
that even dust with a shocked grain size distribution cannot explain their
formation. Adding small amounts of carbon dust does not significantly change
these conclusions. Additionally, we find that these stars exhibit either high
carbon with low silicon abundances or the reverse. A silicate dust scenario
thus suggests that the earliest low-mass star formation in the most metal-poor
regime may have proceeded through two distinct cooling pathways: fine structure
line cooling and dust cooling. This naturally explains both the carbon-rich and
carbon-normal stars at extremely low [Fe/H]. |
Lessons on early structure formation from a mature galaxy cluster
observed at cosmic noon: We demonstrate a new approach of indirectly constraining both early star and
structure formation via mature galaxy clusters at cosmic noon (z~2), using the
cluster XLSSC 122 as an example. With the standard Press Schechter formalism,
we infer a rapid evolution of the star formation efficiency (the ratio of
stellar to halo mass) from 10^-4 to 0.01 during z~20-13, based on the age
distribution of stars in post-starburst galaxies of XLSSC 122, measured by HST
photometry assuming no dust extinction. Here, we consider all low-mass haloes,
including minihaloes, that host the first stars and galaxies (5*10^5 Msun <
M_halo < 10^10 Msun). We also place new constraints on fuzzy dark matter models
of m_a < 5*10^-21 eV/c^2 for the ultra-light boson mass, from the abundance of
galaxies with star formation at z > 13 in XLSSC 122. Our exploratory results
are consistent with existing constraints. More comprehensive results will be
obtained if our approach is extended to a large sample of clusters or field
post-starburst galaxies at cosmic noon, with improved modelling of halo and
stellar populations. | Observational constraints to a unified cosmological model: We propose a phenomenological unified model for dark matter and dark energy
based on an equation of state parameter $w$ that scales with the $\arctan$ of
the redshift. The free parameters of the model are three constants:
$\Omega_{b0}$, $\alpha$ and $\beta$. Parameter $\alpha$ dictates the transition
rate between the matter dominated era and the accelerated expansion period. The
ratio $\beta / \alpha$ gives the redshift of the equivalence between both
regimes. Cosmological parameters are fixed by observational data from
Primordial Nucleosynthesis (PN), Supernovae of the type Ia (SNIa), Gamma-Ray
Bursts (GRB) and Baryon Acoustic Oscillations (BAO). The calibration of the 138
GRBs events is performed using the 580 SNIa of the Union2.1 data set and a new
set of 79 high-redshift GRBs is obtained. The various sets of data are used in
different combinations to constraint the parameters through statistical
analysis. The unified model is compared to the $\Lambda$CDM model and their
differences are emphasized. |
Searching for dark matter isocurvature initial conditions with N-body
Simulations: Small fraction of isocurvature perturbations may exist and correlate with
adiabatic perturbations in the primordial perturbations. Naively switching off
isocurvature perturbations may lead to biased results. We study the effect of
dark matter isocurvature on the structure formation through N-body simulations.
From the best fit values, we run four sets of simulation with different initial
conditions and different box sizes. We find that, if the fraction of dark
matter isocurvature is small, we can not detect its signal through matter power
spectrum and two point correlation function with large scale survey. However,
the halo mass function can give an obvious signal. Compared to 5% difference on
matter power spectrum, it can get 37% at $z = 3$ on halo mass function. This
indicates that future high precise cluster count experiment can give stringent
constraints on dark matter isocurvature perturbations. | Tomography of the Cosmic Dawn and Reionization Eras with Multiple
Tracers: The Cosmic Dawn and Reionization epochs remain a fundamental but challenging
frontier of astrophysics and cosmology. We advocate a large-scale, multi-tracer
approach to develop a comprehensive understanding of the physics that led to
the formation and evolution of the first stars and galaxies. We highlight the
line intensity mapping technique to trace the multi-phase reionization topology
on large scales, and measure reionization history in detail. Besides 21cm, we
advocate for Lya tomography mapping during the epoch of Wouthuysen-Field
coupling as an additional probe of the cosmic dawn era. |
A low Hubble Constant from galaxy distribution observations: An accurate determination of the Hubble constant remains a puzzle in
observational cosmology. The possibility of a new physics has emerged with a
significant tension between the current expansion rate of our Universe measured
from the cosmic microwave background by the Planck satellite and from local
methods. In this paper, new tight estimates on this parameter are obtained by
considering two data sets from galaxy distribution observations: galaxy cluster
gas mass fractions and baryon acoustic oscillation measurements. Priors from
the Big Bang nucleosynthesis (BBN) were also considered. By considering the
flat $\Lambda$CDM and XCDM models, and the non-flat $\Lambda$CDM model, our
main results are: $H_0=65.9^{+1.5}_{-1.5}$ km s$^{-1}$ Mpc$^{-1}$,
$H_0=65.9^{+4.4}_{-4.0}$ km s$^{-1}$ Mpc$^{-1}$ and $H_0=64.3^{+ 4.5}_{- 4.4}$
km s$^{-1}$ Mpc$^{-1}$ in $2\sigma$ c.l., respectively. These estimates are in
full agreement with the Planck satellite results. Our analyses in these
cosmological scenarios also support a negative value for the deceleration
parameter at least in 3$\sigma$ c.l.. | Cosmic density field reconstruction from Ly-alpha forest data: We present a novel, fast method to recover the density field through the
statistics of the transmitted flux in high redshift quasar absorption spectra.
The proposed technique requires the computation of the probability distribution
function of the transmitted flux (P_F) in the Ly-alpha forest region and, as a
sole assumption, the knowledge of the probability distribution function of the
matter density field (P_Delta). We show that the probability density
conservation of the flux and matter density unveils a flux-density (F-Delta)
relation which can be used to invert the Ly-alpha forest without any assumption
on the physical properties of the intergalactic medium. We test our inversion
method at z=3 through the following steps: [i] simulation of a sample of
synthetic spectra for which P_Delta is known; [ii] computation of P_F; [iii]
inversion of the Ly-alpha forest through the F-Delta relation. Our technique,
when applied to only 10 observed spectra characterized by a signal-to noise
ratio S/N >= 100 provides an exquisite (relative error epsilon_Delta <~ 12 % in
>~ 50 % of the pixels) reconstruction of the density field in >~ 90 % of the
line of sight. We finally discuss strengths and limitations of the method. |
The Santa Fe Light Cone Simulation Project: II. The Prospects for Direct
Detection of the WHIM with SZE Surveys: Detection of the Warm-Hot Intergalactic Medium (WHIM) using Sunyaev-Zeldovich
effect (SZE) surveys is an intriguing possibility, and one that may allow
observers to quantify the amount of "missing baryons" in the WHIM phase. We
estimate the necessary sensitivity for detecting low density WHIM gas with the
South Pole Telescope (SPT) and Planck Surveyor for a synthetic 100 square
degree sky survey. This survey is generated from a very large, high dynamic
range adaptive mesh refinement cosmological simulation performed with the Enzo
code. We find that for a modest increase in the SPT survey sensitivity (a
factor of 2-4), the WHIM gas makes a detectable contribution to the integrated
sky signal. For a Planck-like satellite, similar detections are possible with a
more significant increase in sensitivity (a factor of 8-10). We point out that
for the WHIM gas, the kinematic SZE signal can sometimes dominate the thermal
SZE where the thermal SZE decrement is maximal (150 GHz), and that using the
combination of the two increases the chance of WHIM detection using SZE
surveys. However, we find no evidence of unique features in the thermal SZE
angular power spectrum that may aid in its detection. Interestingly, there are
differences in the power spectrum of the kinematic SZE, which may not allow us
to detect the WHIM directly, but could be an important contaminant in
cosmological analyses of the kSZE-derived velocity field. Corrections derived
from numerical simulations may be necessary to account for this contamination. | Moving mesh cosmology: the hydrodynamics of galaxy formation: We present a detailed comparison between the well-known SPH code GADGET and
the new moving-mesh code AREPO on a number of hydrodynamical test problems.
Through a variety of numerical experiments we establish a clear link between
test problems and systematic numerical effects seen in cosmological simulations
of galaxy formation. Our tests demonstrate deficiencies of the SPH method in
several sectors. These accuracy problems not only manifest themselves in
idealized hydrodynamical tests, but also propagate to more realistic simulation
setups of galaxy formation, ultimately affecting gas properties in the full
cosmological framework, as highlighted in papers by Vogelsberger et al. (2011)
and Keres et al. (2011). We find that an inadequate treatment of fluid
instabilities in GADGET suppresses entropy generation by mixing, underestimates
vorticity generation in curved shocks and prevents efficient gas stripping from
infalling substructures. In idealized tests of inside-out disk formation, the
convergence rate of gas disk sizes is much slower in GADGET due to spurious
angular momentum transport. In simulations where we follow the interaction
between a forming central disk and orbiting substructures in a halo, the final
disk morphology is strikingly different. In AREPO, gas from infalling
substructures is readily depleted and incorporated into the host halo
atmosphere, facilitating the formation of an extended central disk. Conversely,
gaseous sub-clumps are more coherent in GADGET simulations, morphologically
transforming the disk as they impact it. The numerical artefacts of the SPH
solver are particularly severe for poorly resolved flows, and thus inevitably
affect cosmological simulations due to their hierarchical nature. Our numerical
experiments clearly demonstrate that AREPO delivers a physically more reliable
solution. |
RR Lyrae variables in the Small Magellanic Cloud - II. The extended
area: chemical and structural analysis: We have performed the Fourier decomposition analysis of 8- and 13-year V-band
light curves of a carefully selected sample of 454 fundamental-mode RR Lyrae
variables (RRab type), detected in a 14 square degree area of the Small
Magellanic Cloud (SMC) and listed in the Optical Gravitational Lensing
Experiment, phase III, Catalogue of Variable Stars. The Fourier decomposition
parameters were used to derive metal abundances and distance moduli, following
the methodology described by Kapakos, Hatzidimitriou & Soszy\'nski. The average
metal abundance of the RRab stars on the new scale of Carretta et al. was found
to be <[Fe/H]C09> = -1.69pm0.41 dex (std, with a standard error of 0.02 dex). A
tentative metallicity gradient of -0.013pm0.007 dex/kpc was detected, with
increasing metal abundance towards the dynamical center of the SMC, but
selection effects are also discussed. The distance modulus of the SMC was
re-estimated and was found to be <\mu> = 19.13pm0.19 (std) in a distance scale
where the distance modulus of the Large Magellanic Cloud (LMC) is \mu_LMC =
18.52pm0.06(std). The average 1-sigma line-of-sight depth was found to be
sigma_int = 5.3pm0.4 kpc (std), while spatial variations of the depth were
detected. The SMC was found to be deeper in the north-eastern region, while
metal richer and metal poorer objects in the sample seem to belong to different
dynamical structures. The former have smaller scale height and may constitute a
thick disk, its width being 10.40pm0.02 kpc, and a bulge whose size (radius) is
estimated to be 2.09pm0.81 kpc. The latter seem to belong to a halo structure
with a maximum depth along the line of sight extending over 16 kpc in the SMC
central region and falling to 12 kpc in the outer regions. | Over half of the far-infrared background light comes from galaxies at z
>= 1.2: Submillimetre surveys during the past decade have discovered a population of
luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z
<= 4, these massive submillimetre galaxies go through a phase characterized by
optically obscured star formation at rates several hundred times that in the
local Universe. Half of the starlight from this highly energetic process is
absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K
with spectral energy distributions peaking at 100 microns in the rest frame. At
1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns.
The cumulative effect of these galaxies is to yield extragalactic optical and
far-infrared backgrounds with approximately equal energy densities. Since the
initial detection of the far-infrared background (FIRB), higher-resolution
experiments have sought to decompose this integrated radiation into the
contributions from individual galaxies. Here we report the results of an
extragalactic survey at 250, 350 and 500 microns. Combining our results at 500
microns with those at 24 microns, we determine that all of the FIRB comes from
individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of
it. As expected, at the longest wavelengths the signal is dominated by
ultraluminous galaxies at z > 1. |
Real space estimator for the weak lensing convergence from the CMB: We propose an estimator defined in real space for the reconstruction of the
weak lensing potential due to the intervening large scale structure from high
resolution maps of the cosmic microwave background. This estimator was
motivated as an alternative to the quadratic estimator in harmonic space to
surpass the difficulties of the analysis of maps containing galactic cuts and
point source excisions. Using maps synthesised by pixel remapping, we implement
the estimator for two experiments, namely one in the absence and one in the
presence of detector noise, and compare the reconstruction of the convergence
field with that obtained with the quadratic estimator defined in harmonic
space. We find good agreement between the input and the reconstructed power
spectra using the proposed real space estimator. We discuss interesting
features of the real space estimator and future extensions of this work. | Retarded Green's Functions In Perturbed Spacetimes For Cosmology and
Gravitational Physics: Electromagnetic and gravitational radiation do not propagate solely on the
null cone in a generic curved spacetime. They develop "tails," traveling at all
speeds equal to and less than unity. If sizeable, this off-the-null-cone effect
could mean objects at cosmological distances, such as supernovae, appear dimmer
than they really are. Their light curves may be distorted relative to their
flat spacetime counterparts. These in turn could affect how we infer the
properties and evolution of the universe or the objects it contains. Within the
gravitational context, the tail effect induces a self-force that causes a
compact object orbiting a massive black hole to deviate from an otherwise
geodesic path. This needs to be taken into account when modeling the
gravitational waves expected from such sources. Motivated by these
considerations, we develop perturbation theory for solving the massless scalar,
photon and graviton retarded Green's functions in perturbed spacetimes,
assuming these Green's functions are known in the background spacetime. In
particular, we elaborate on the theory in perturbed Minkowski spacetime in
significant detail; and apply our techniques to compute the retarded Green's
functions in the weak field limit of the Kerr spacetime to first order in the
black hole's mass and angular momentum. Our methods build on and generalizes
work appearing in the literature on this topic to date, and lays the foundation
for a thorough, first principles based, investigation of how light propagates
over cosmological distances, within a spatially flat inhomogeneous
Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) universe. This perturbative
scheme applied to the graviton Green's function, when pushed to higher orders,
may provide approximate analytic (or semi-analytic) results for the self-force
problem in the weak field limits of the Schwarzschild and Kerr black hole
geometries. |
Matter Under Extreme Conditions: The Early Years: Extreme conditions in natural flows are examined, starting with a turbulent
big bang. A hydro-gravitational-dynamics cosmology model is adopted.
Planck-Kerr turbulence instability causes Planck-particle turbulent combustion.
Inertial-vortex forces induce a non-turbulent kinetic energy cascade to
Planck-Kolmogorov scales where vorticity is produced, overcoming 10^113 Pa
Planck-Fortov pressures. The spinning, expanding fireball has a slight deficit
of Planck antiparticles. Space and mass-energy powered by gluon viscous
stresses expand exponentially at speeds >10^25 c. Turbulent temperature and
spin fluctuations fossilize at scales larger than ct, where c is light speed
and t is time. Because "dark-energy" antigravity forces vanish when inflation
ceases, and because turbulence produces entropy, the universe is closed and
will collapse and rebound. Density and spin fossils of big bang turbulent
mixing trigger structure formation in the plasma epoch. Fragmenting
protosuperclustervoids and protoclustervoids produce weak turbulence until the
plasma-gas transition give chains of protogalaxies with the morphology of
turbulence. Chain galaxy clusters observed at large redshifts ~8.6 support this
interpretation. Protogalaxies fragment into clumps, each with a trillion
Earth-mass H-He gas planets. These make stars, supernovae, the first chemicals,
the first oceans and the first life soon after the cosmological event. | Breaking degeneracies in the first galaxies with clustering: The high-redshift galaxy UV luminosity function (UVLF) has become essential
for understanding the formation and evolution of the first galaxies. Yet, UVLFs
only measure galaxy abundances, giving rise to a degeneracy between the mean
galaxy luminosity and its stochasticity. Here, we show that upcoming clustering
measurements with the James Webb Space Telescope (JWST), as well as with Roman,
will be able to break this degeneracy, even at redshifts $z \gtrsim 10$. First,
we demonstrate that current Subaru Hyper Suprime-Cam (HSC) measurements of the
galaxy bias at $z\sim 4-6$ point to a relatively tight halo-galaxy connection,
with low stochasticity. Then, we show that the larger UVLFs observed by JWST at
$z\gtrsim 10$ can be explained with either a boosted average UV emission or an
enhanced stochasticity. These two models, however, predict different galaxy
biases, which are potentially distinguishable in JWST and Roman surveys.
Galaxy-clustering measurements, therefore, will provide crucial insights into
the connection between the first galaxies and their dark-matter halos, and
identify the root cause of the enhanced abundance of $z \gtrsim 10$ galaxies
revealed with JWST during its first year of operations. |
The galaxy formation origin of the lensing is low problem: Recent analyses show that $\Lambda$CDM-based models optimised to reproduce
the clustering of massive galaxies overestimate their gravitational lensing by
about 30\%, the so-called lensing is low problem. Using a state-of-the-art
hydrodynamical simulation, we show that this discrepancy reflects shortcomings
in standard galaxy-halo connection models rather than tensions within the
$\Lambda$CDM paradigm itself. Specifically, this problem results from ignoring
a variety of galaxy formation effects, including assembly bias, segregation of
satellite galaxies relative to dark matter, and baryonic effects on the matter
distribution. All these effects contribute towards overestimating gravitational
lensing and, when combined, explain the amplitude and scale dependence of the
lensing is low problem. We conclude that simplistic galaxy-halo connection
models are inadequate to interpret clustering and lensing simultaneously, and
that it is crucial to employ more sophisticated models for the upcoming
generation of large-scale surveys. | Frequency-Domain Distribution of Astrophysical Gravitational-Wave
Backgrounds: The superposition of many astrophysical gravitational waves (GW) signals
below typical detection thresholds baths detectors in a stochastic
gravitational wave background (SGWB). In this work we present a Fourier space
approach to compute the frequency-domain distribution of stochastic
gravitational wave backgrounds produced by discrete sources. The expressions
for the moment generating function and the distribution of observed (discrete)
Fourier modes are provided. The results are then applied to the SGWB
originating from the mergers of compact stellar remnants (black holes and
neutron stars) in the Universe, which are found to exhibit a $-4$ power-law
tail. This tail is verified in the signal-to-noise ratio distribution of GWTC
events. Furthermore, the extent to which the subtraction of bright (loud)
mergers gaussianizes the resulting confusion noise of unresolved sources is
illustrated. The power-law asymptotic tail for the SGWB, and an exponentially
decaying tail in the case of the confusion background, are also derived
analytically. Our results generalize to any background of gravitational waves
emanating from discrete sources. |
Constraining gravity at large scales with the 2MASS Photometric Redshift
catalogue and Planck lensing: We present a new measurement of structure growth at $z \simeq 0.08$ obtained
by correlating the cosmic microwave background (CMB) lensing potential map from
the \textit{Planck} satellite with the angular distribution of the 2MASS
Photometric Redshift galaxies. After testing for, and finding no evidence for
systematic effects, we calculate the angular auto- and cross-power spectra. We
combine these spectra to estimate the amplitude of structure growth using the
bias-independent $D_G$ estimator introduced by Giannantonio et al. 2016. We
find that the relative amplitude of $D_G$ with respect to the predictions based
on \textit{Planck} cosmology is $A_D(z=0.08) = 1.00 \pm 0.21$, fully consistent
with the expectations for the standard cosmological model. Considering
statistical errors only, we forecast that a joint analysis between an LSST-like
photometric galaxy sample and lensing maps from upcoming ground-based CMB
surveys like the Simons Observatory and CMB-S4 can yield sub-percent
constraints on the growth history and differentiate between different models of
cosmic acceleration. | Transverse motions in CSOs?: The measurement of proper motions in CSOs is a powerful tool to determine the
dynamical evolution of the newly born extragalactic radio sources. We observed
3 CSOs with the VLBA in 2004 and in 2006 to monitor changes in their structure
and measure the separation velocity of the hot spots. It is important to
increase the size of the samples of CSOs with measured expansion velocity to
test the existance of frustrated objects, and put stringent constraints on the
current models. We found for all the three objects observed a transverse motion
of the hotspots, and we suggest as the more likey explanation a precession in
the jet axis. This behaviour likely inhibits or at least slows down the radio
source growth because the head of the hotspot continuously hits new regions of
the ISM. Therefore these radio sources may represent an old population of
GPS/CSOs. |
Euclid: Fast two-point correlation function covariance through linear
construction: We present a method for fast evaluation of the covariance matrix for a
two-point galaxy correlation function (2PCF) measured with the Landy-Szalay
estimator. The standard way of evaluating the covariance matrix consists in
running the estimator on a large number of mock catalogs, and evaluating their
sample covariance. With large random catalog sizes (data-to-random objects
ratio M>>1) the computational cost of the standard method is dominated by that
of counting the data-random and random-random pairs, while the uncertainty of
the estimate is dominated by that of data-data pairs. We present a method
called Linear Construction (LC), where the covariance is estimated for small
random catalogs of size M = 1 and M = 2, and the covariance for arbitrary M is
constructed as a linear combination of these. We validate the method with
PINOCCHIO simulations in range r = 20-200 Mpc/h, and show that the covariance
estimate is unbiased. With M = 50 and with 2 Mpc/h bins, the theoretical
speed-up of the method is a factor of 14. We discuss the impact on the
precision matrix and parameter estimation, and derive a formula for the
covariance of covariance. | Constraining cosmic string parameters with curl mode of CMB lensing: We present constraints on a cosmic string network with a measurement of weak
gravitational lensing from CMB temperature map. The cosmic string network
between observer and last scattering surface of CMB photons generates vector
and/or tensor metric perturbations, and the deflection of CMB photons by these
gravitational fields has curl mode which is not produced by the scalar metric
perturbations. In this paper, we use the power spectrum of curl mode obtained
from Planck to constrain the string tension, G\mu, and the reconnection
probability, P. In demonstrating the parameter constraints with Planck curl
mode, we also measure the lensing power spectrum from the Atacama Cosmology
Telescope (ACT) 2008 season data, which have better angular resolution with
lower instrumental noise on a much smaller chunk of the sky. Assuming P=1, the
upper bound on tension is G\mu = 6.6\times 10^{-5} with 2\sigma (95% C.L.),
using curl mode from Planck, which is weaker than that from the small-scale
temperature power spectrum. For small values of P, however, the constraint from
curl mode becomes tighter compared to that from temperature power spectrum. For
P\lsim 10^{-2}, we obtain the constraint on the combination of the string
parameters as G\mu P^{-1}\leq 3.4\times 10^{-5} at more than 2\sigma (95%
C.L.). |
The gravitational-wave luminosity distance in modified gravity theories: In modified gravity the propagation of gravitational waves (GWs) is in
general different from that in general relativity. As a result, the luminosity
distance for GWs can differ from that for electromagnetic signals, and is
affected both by the dark energy equation of state $w_{\rm DE}(z)$ and by a
function $\delta(z)$ describing modified propagation. We show that the effect
of modified propagation in general dominates over the effect of the dark energy
equation of state, making it easier to distinguish a modified gravity model
from $\Lambda$CDM. We illustrate this using a nonlocal modification of gravity,
that has been shown to fit remarkably well CMB, SNe, BAO and structure
formation data, and we discuss the prospects for distinguishing nonlocal
gravity from $\Lambda$CDM with the Einstein Telescope. We find that, depending
on the exact sensitivity, a few tens of standard sirens with measured redshift
at $z\sim 0.4$, or a few hundreds at $1 < z < 2$, could suffice. | Type II Supernovae: Model Light Curves and Standard Candle Relationships: A survey of Type II supernovae explosion models has been carried out to
determine how their light curves and spectra vary with their mass, metallicity,
and explosion energy. The presupernova models are taken from a recent survey of
massive stellar evolution at solar metallicity supplemented by new calculations
at subsolar metallicity. Explosions are simulated by the motion of a piston
near the edge of the iron core and the resulting light curves and spectra are
calculated using full multi-wavelength radiation transport. Formulae are
developed that describe approximately how the model observables (light curve
luminosity and duration) scale with the progenitor mass, explosion energy, and
radioactive nucleosynthesis. Comparison with observational data shows that the
explosion energy of typical supernovae (as measured by kinetic energy at
infinity) varies by nearly an order of magnitude -- from 0.5 to 4.0 x 10^51
ergs, with a typical value of ~0.9 x 10^51 ergs. Despite the large variation,
the models exhibit a tight relationship between luminosity and expansion
velocity, similar to that previously employed empirically to make SNe IIP
standardized candles. This relation is explained by the simple behavior of
hydrogen recombination in the supernova envelope, but we find a sensitivity to
progenitor metallicity and mass that could lead to systematic errors.
Additional correlations between light curve luminosity, duration, and color
might enable the use of SNe IIP to obtain distances accurate to ~20% using only
photometric data. |
Reconstructing Patchy Reionization with Deep Learning: The precision anticipated from next-generation cosmic microwave background
(CMB) surveys will create opportunities for characteristically new insights
into cosmology. Secondary anisotropies of the CMB will have an increased
importance in forthcoming surveys, due both to the cosmological information
they encode and the role they play in obscuring our view of the primary
fluctuations. Quadratic estimators have become the standard tools for
reconstructing the fields that distort the primary CMB and produce secondary
anisotropies. While successful for lensing reconstruction with current data,
quadratic estimators will be sub-optimal for the reconstruction of lensing and
other effects at the expected sensitivity of the upcoming CMB surveys. In this
paper we describe a convolutional neural network, ResUNet-CMB, that is capable
of the simultaneous reconstruction of two sources of secondary CMB
anisotropies, gravitational lensing and patchy reionization. We show that the
ResUNet-CMB network significantly outperforms the quadratic estimator at low
noise levels and is not subject to the lensing-induced bias on the patchy
reionization reconstruction that would be present with a straightforward
application of the quadratic estimator. | Can a spectator scalar field enhance inflationary tensor mode?: We consider the possibility of enhancing the inflationary tensor mode by
introducing a spectator scalar field with a small sound speed which induces
gravitational waves as a second order effect. We analytically obtain the power
spectra of gravitational waves and curvature perturbation induced by the
spectator scalar field. We found that the small sound speed amplifies the
curvature perturbation much more than the tensor mode and the current
observational constraint forces the induced gravitational waves to be
negligible compared with those from the vacuum fluctuation during inflation. |
The quenching of star formation in accretion-driven clumpy turbulent
tori of active galactic nuclei: Galactic gas-gas collisions involving a turbulent multiphase ISM share common
ISM properties: dense extraplanar gas visible in CO, large linewidths (>= 50
km/s), strong mid-infrared H_2 line emission, low star formation activity, and
strong radio continuum emission. Gas-gas collisions can occur in the form of
ICM ram pressure stripping, galaxy head-on collisions, compression of the
intragroup gas and/or galaxy ISM by an intruder galaxy which flies through the
galaxy group at a high velocity, or external gas accretion on an existing gas
torus in a galactic center. We suggest that the common theme of all these
gas-gas interactions is adiabatic compression of the ISM leading to an increase
of the turbulent velocity dispersion of the gas. The turbulent gas clouds are
then overpressured and star formation is quenched. Within this scenario we
developed a model for turbulent clumpy gas disks where the energy to drive
turbulence is supplied by external infall or the gain of potential energy by
radial gas accretion within the disk. The cloud size is determined by the size
of a C-type shock propagating in dense molecular clouds with a low ionization
fraction at a given velocity dispersion. We give expressions for the expected
volume and area filling factors, mass, density, column density, and velocity
dispersion of the clouds. The latter is based on scaling relations of
intermittent turbulence whose open parameters are estimated for the CND in the
Galactic Center. The properties of the model gas clouds and the external mass
accretion rate necessary for the quenching of the star formation rate due to
adiabatic compression are consistent with those derived from high-resolution
H_2 line observations. Based on these findings, a scenario for the evolution of
gas tori in galactic centers is proposed and the implications for star
formation in the Galactic Center are discussed. | Using gaps in N-body tidal streams to probe missing satellites: We use N-body simulations to model the tidal disruption of a star cluster in
a Milky-Way-sized dark matter halo, which results in a narrow stream comparable
to (but slightly wider than) Pal-5 or GD-1. The mean Galactic dark matter halo
is modeled by a spherical Navarro-Frenk-White (NFW) potential with subhalos
predicted by the LCDM cosmological model. The distribution and mass function of
the subhalos follow the results from the Aquarius simulation. We use a matched
filter approach to look for "gaps" in tidal streams at 12 length scales from
0.1 kpc to 5 kpc, which appear as characteristic dips in the linear densities
along the streams. We find that, in addition to the subhalos' perturbations,
the epicyclic overdensities (EOs) due to the coherent epicyclic motions of
particles in a stream also produce gap-like signals near the progenitor. We
measure the gap spectra - the gap formation rates as functions of gap length -
due to both subhalo perturbations and EOs, which have not been accounted for
together by previous studies. Finally, we project the simulated streams onto
the sky to investigate issues when interpreting gap spectra in observations. In
particular, we find that gap spectra from low signal-to-noise observations can
be biased by the orbital phase of the stream. This indicates that the study of
stream gaps will benefit greatly from high-quality data from future missions. |
Faint dwarf galaxies in the Next Generation Virgo cluster Survey: The Next Generation Virgo Cluster Survey (NGVS) is a CFHT Large Program that
is using the wide field of view capabilities of the MegaCam camera to map the
entire Virgo Cluster from its core to virial radius. The observing strategy has
been optimized to detect very low surface brightness structures in the cluster,
including intracluster stellar streams and faint dwarf spheroidal galaxies. We
present here the current status of this ongoing survey, with an emphasis on the
detection and analysis of the very low-mass galaxies in the cluster that have
been revealed by the NGVS. | Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a
Forest Tomographic Mapping of the COSMOS Field: Using moderate-resolution optical spectra from 58 background Lyman-break
galaxies and quasars at $z\sim 2.3-3$ within a $11.5'\times13.5'$ area of the
COSMOS field ($\sim 1200\,\mathrm{deg}^2$ projected area density or $\sim
2.4\,h^{-1}\,\mathrm{Mpc}$ mean transverse separation), we reconstruct a 3D
tomographic map of the foreground Ly$\alpha$ forest absorption at $2.2<z<2.5$
with an effective smoothing scale of
$\sigma_{3d}\approx3.5\,h^{-1}\,\mathrm{Mpc}$ comoving. Comparing with 61
coeval galaxies with spectroscopic redshifts in the same volume, we find that
the galaxy positions are clearly biased towards regions with enhanced IGM
absorption in the tomographic map. We find an extended IGM overdensity with
deep absorption troughs at $z=2.45$ associated with a recently-discovered
galaxy protocluster at the same redshift. Based on simulations matched to our
data, we estimate the enclosed dark matter mass within this IGM overdensity to
be $M_{\rm dm} (z=2.45) = (9\pm4)\times 10^{13}\,h^{-1}\,\mathrm{M_\odot}$, and
argue based on this mass and absorption strength that it will form at least one
$z\sim0$ galaxy cluster with $M(z=0) = (3\pm 2) \times
10^{14}\,h^{-1}\mathrm{M_\odot}$, although its elongated nature suggests that
it will likely collapse into two separate clusters. We also point out a compact
overdensity of six MOSDEF galaxies at $z=2.30$ within a $r\sim
1\,h^{-1}\,\mathrm{Mpc}$ radius and $\Delta z\sim 0.006$, which does not appear
to have a large associated IGM overdensity. These results demonstrate the
potential of Ly$\alpha$ forest tomography on larger volumes to study galaxy
properties as a function of environment, as well as revealing the large-scale
IGM overdensities associated with protoclusters and other features of
large-scale structure. |
Foreground Predictions for the Cosmic Microwave Background Power
Spectrum from Measurements of Faint Inverted Radio Sources at 5 GHz: We present measurements of a population of matched radio sources at 1.4 and 5
GHz down to a flux limit of 1.5 mJy in 7 sq. degs. of the NOAO Deep Field
South. We find a significant fraction of sources with inverted spectral indices
that all have 1.4 GHz fluxes less than 10 mJy, and are therefore too faint to
have been detected and included in previous radio source count models that are
matched at multiple frequencies. Combined with the matched source population at
1.4 and 5 GHz in 1 sq. deg. in the ATESP survey, we update models for the 5 GHz
differential number counts and distributions of spectral indices in 5 GHz flux
bins that can be used to estimate the unresolved point source contribution to
the cosmic microwave background temperature anisotropies. We find a shallower
logarithmic slope in the 5 GHz differential counts than in previously published
models for fluxes < 100 mJy as well as larger fractions of inverted spectral
indices at these fluxes. Because the Planck flux limit for resolved sources is
larger than 100 mJy in all channels, our modified number counts yield at most a
10% change in the predicted Poisson contribution to the Planck temperature
power spectrum. For a flux cut of 5 mJy with the South Pole Telescope and a
flux cut of 20 mJy with the Atacama Cosmology Telescope we predict a ~30% and
~10% increase, respectively, in the radio source Poisson power in the lowest
frequency channels of each experiment relative to that predicted by previous
models. | Scalar induced gravitational waves in inflation with gravitationally
enhanced friction: We study the scalar induced gravitational wave (GW) background in inflation
with gravitationally enhanced friction (GEF). The GEF mechanism, which is
realized by assuming a nonminimal derivative coupling between the inflaton
field and gravity, is used to amplify the small-scale curvature perturbations
to generate a sizable amount of primordial black holes. We find that the GW
energy spectra can reach the detectable scopes of the future GW projects, and
the power spectrum of curvature perturbations has a power-law form in the
vicinity of the peak. The scaling of the GW spectrum in the ultraviolet regions
is two times that of the power spectrum slope, and has a lower bound. In the
infrared regions, the slope of the GW spectrum can be described roughly by a
log-dependent form. These features of the GW spectrum may be used to check the
GEF mechanism if the scalar induced GWs are detected in the future. |
One-point remapping of Lagrangian perturbation theory in the mildly
non-linear regime of cosmic structure formation: On the smallest scales, three-dimensional large-scale structure surveys
contain a wealth of cosmological information which cannot be trivially
extracted due to the non-linear dynamical evolution of the density field.
Lagrangian perturbation theory (LPT) is widely applied to the generation of
mock halo catalogs and data analysis. In this work, we compare topological
features of the cosmic web such as voids, sheets, filaments and clusters, in
the density fields predicted by LPT and full numerical simulation of
gravitational large-scale structure formation. We propose a method designed to
improve the correspondence between these density fields, in the mildly
non-linear regime. We develop a computationally fast and flexible tool for a
variety of cosmological applications. Our method is based on a remapping of the
approximately-evolved density field, using information extracted from N-body
simulations. The remapping procedure consists of replacing the one-point
distribution of the density contrast by one which better accounts for the full
gravitational dynamics. As a result, we obtain a physically more pertinent
density field on a point-by-point basis, while also improving higher-order
statistics predicted by LPT. We quantify the approximation error in the power
spectrum and in the bispectrum as a function of scale and redshift. Our
remapping procedure improves one-, two- and three-point statistics at scales
down to 8 Mpc/h. | Metal-free galaxy candidates discovered in CLASH: The first metals in the universe are expected to form in population III stars
- primordial stars consisting entirely of hydrogen and helium. However, these
stars have so far remained elusive. Simulations indicate that galaxies
consisting exclusively, or almost exclusively, of population III stars may form
at z>6, and such galaxies may provide one of the best probes of the properties
of the population III star formation mode. By fitting Yggdrasil model spectra
to multiband photometry data, we have identified four population III galaxy
candidates in the Cluster Lensing and Supernova survey with Hubble (CLASH). We
rule out alternative mundane galaxies and low redshift interlopers through
similar fits to catalogs of spectra from more mundane objects. If confirmed
through spectroscopy, this would constitute the first detection of the "missing
link" between the early pristine universe and the metal-enriched universe. |
The Weak Lensing Bispectrum Induced By Gravity: Recent studies have demonstrated that {\em secondary} non-Gaussianity induced
by gravity will be detected with a high signal-to-noise (S/N) by future and
even by on-going weak lensing surveys. One way to characterise such
non-Gaussianity is through the detection of a non-zero three-point correlation
function of the lensing convergence field, or of its harmonic transform, the
bispectrum. A recent study analysed the properties of the squeezed
configuration of the bispectrum, when two wavenumbers are much larger than the
third one. We extend this work by estimating the amplitude of the (reduced)
bispectrum in four generic configurations, i.e., {\em squeezed, equilateral,
isosceles} and {\em folded}, and for four different source redshifts
$z_s=0.5,1.0,1.5,2.0$, by using an ensemble of all-sky high-resolution
simulations. We compare these results against theoretical predictions. We find
that, while the theoretical expectations based on widely used fitting functions
can predict the general trends of the reduced bispectra, a more accurate
theoretical modelling will be required to analyse the next generation of
all-sky weak lensing surveys. The disagreement is particularly pronounced in
the squeezed limit. | Constraining the WDM Particle Mass with Milky Way Satellites: Well-motivated particle physics theories predict the existence of particles
(such as sterile neutrinos) which acquire non-negligible thermal velocities in
the early universe. These particles could behave as warm dark matter (WDM) and
generate a small-scale cutoff in the linear density power spectrum which scales
approximately inversely with the particle mass. If this mass is of order a keV,
the cutoff occurs on the scale of dwarf galaxies. Thus, in WDM models the
abundance of small galaxies, such as the satellites that orbit in the halo of
the Milky Way, depends on the mass of the warm particle. The abundance also
scales with the mass of the host galactic halo. We use the \galform
semi-analytic model of galaxy formation to calculate the properties of galaxies
in universes in which the dark matter is warm. Using this method, we can
compare the predicted satellite luminosity functions to the observed data for
the Milky Way dwarf spheroidals, and determine a lower bound on the thermally
produced WDM particle mass. This depends strongly on the value of the Milky Way
halo mass and, to some extent, on the baryonic physics assumed; we examine both
of these dependencies. For our fiducial model we find that for a particle mass
of 3.3 keV (the 2$\sigma$ lower limit found by Viel et al. from a recent
analysis of the Lyman-$\alpha$ forest) the Milky Way halo mass is required to
be $> 1.4 \times 10^{12}$ \msun. For this same fiducial model, we also find
that all WDM particle masses are ruled out (at 95% confidence) if the halo of
the Milky Way has a mass smaller than $1.1 \times 10^{12}$ \msun, while if the
mass of the Galactic halo is greater than 1.8 $\times 10^{12}$ \msun, only WDM
particle masses larger than 2 keV are allowed. |
Can anisotropy in the galaxy distribution tell the bias?: We use information entropy to analyze the anisotropy in the mock galaxy
catalogues from dark matter distribution and simulated biased galaxy
distributions from $\Lambda$CDM N-body simulation. We show that one can recover
the linear bias parameter of the simulated galaxy distributions by comparing
the radial, polar and azimuthal anisotropies in the simulated galaxy
distributions with that from the dark matter distribution. This method for
determination of the linear bias requires only $O(N)$ operations as compared to
$O(N^{2})$ or at least $O(N \log N)$ operations required for the methods based
on the two-point correlation function and the power spectrum. We apply this
method to determine the linear bias parameter for the galaxies in the 2MASS
Redshift Survey (2MRS) and find that the 2MRS galaxies in the $K_{s}$ band have
a linear bias of $\sim 1.3$. | Evidence for Cold Accretion: Primitive Gas Flowing onto a Galaxy at
z~0.274: We present UV and optical observations from the Cosmic Origins Spectrograph
on the Hubble Space Telescope and Keck of a z= 0.27395 Lyman limit system (LLS)
seen in absorption against the QSO PG1630+377. We detect H I absorption with
log N(HI)=17.06\pm0.05 as well as Mg II, C III, Si III, and O VI in this
system. The column densities are readily explained if this is a multi-phase
system, with the intermediate and low ions arising in a very low metallicity
([Mg/ H] =-1.71 \pm 0.06) photoionized gas. We identify via Keck spectroscopy
and Large Binocular Telescope imaging a 0.3 L_* star-forming galaxy projected
37 kpc from the QSO at nearly identical redshift (z=0.27406, \Delta v = -26
\kms) with near solar metallicity ([O/ H]=-0.20 \pm 0.15). The presence of very
low metallicity gas in the proximity of a near-solar metallicity, sub-L_*
galaxy strongly suggests that the LLS probes gas infalling onto the galaxy. A
search of the literature reveals that such low metallicity LLSs are not
uncommon. We found that 50% (4/8) of the well-studied z < 1 LLSs have
metallicities similar to the present system and show sub-L_* galaxies with rho
< 100 kpc in those fields where redshifts have been surveyed. We argue that the
properties of these primitive LLSs and their host galaxies are consistent with
those of cold mode accretion streams seen in galaxy simulations. |
GALLUMI: A Galaxy Luminosity Function Pipeline for Cosmology and
Astrophysics: Observations of high-redshift galaxies have provided us with a rich tool to
study the physics at play during the epoch of reionisation. The luminosity
function (LF) of these objects is an indirect tracer of the complex processes
that govern galaxy formation, including those of the first dark-matter
structures. In this work, we present an extensive analysis of the UV galaxy LF
at high redshifts to extract cosmological and astrophysical parameters. We
provide a number of phenomenological approaches in modelling the UV LF and take
into account various sources of uncertainties and systematics in our analysis,
including cosmic variance, dust extinction, scattering in the halo-galaxy
connection, and the Alcock-Paczy\'{n}ski effect. Using UV LF measurements from
the Hubble Space Telescope together with external data on the matter density,
we derive the large-scale matter clustering amplitude to be
$\sigma_8=0.76^{+0.12}_{-0.14}$, after marginalising over the unknown
astrophysical parameters. We find that with current data this result is only
weakly sensitive to our choice of astrophysical modelling, as well as the
calibration of the underlying halo mass function. As a cross check, we run our
analysis pipeline with mock data from the IllustrisTNG hydrodynamical
simulations and find consistent results with their input cosmology. In
addition, we perform a simple forecast for future space telescopes, where an
improvement of roughly 30% upon our current result is expected. Finally, we
obtain constraints on astrophysical parameters and the halo-galaxy connection
for the models considered here. All methods discussed in this work are
implemented in the form of a versatile likelihood code, GALLUMI, which we make
public. | Damped and sub-damped Lyman-? absorbers in z > 4 QSOs: We present the results of a survey for damped (DLA, log N(H I) > 20.3) and
sub-damped Lyman-? systems (19.5 < log N(H I) < 20.3) at z > 2.55 along the
lines-of-sight to 77 quasars with emission redshifts in the range 4 < zem <
6.3. Intermediate resolution (R ? 4300) spectra have been obtained with the
Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total
of 100 systems with log N(H I) > 19.5 are detected of which 40 systems are
damped Lyman-? systems for an absorption length of ?X = 378. About half of the
lines of sight of this homogeneous survey have never been investigated for
DLAs. We study the evolution with redshift of the cosmological density of the
neutral gas and find, consis- tently with previous studies at similar
resolution, that ?DLA,H I decreases at z > 3.5. The overall cosmological
evolution of ?HI shows a peak around this redshift. The H I column density
distribution for log N(H I) ? 20.3 is ?tted, consistently with previous
surveys, with a single power-law of index ? ? -1.8$\pm$0.25. This power-law
overpredicts data at the high-end and a second, much steeper, power-law (or a
gamma function) is needed. There is a flattening of the function at lower H I
column densities with an index of ? ? ?1.4 for the column density range log N(H
I) = 19.5?21. The fraction of H I mass in sub-DLAs is of the order of 30%. The
H column density distribution does not evolve strongly from z ? 2.5 to z ? 4.5. |
Lensing of Fast Radio Bursts by Binaries to Probe Compact Dark Matter: The possibility that a fraction of the dark matter is comprised of massive
compact halo objects (MACHOs) remains unclear, especially in the 20-100
$M_{\odot}$ window. MACHOs could make up binaries, whose mergers may be
detected by LIGO as gravitational wave events. On the other hand, the
cosmological origin of fast radio burst (FRBs) has been confirmed. We
investigate the possibility of detecting fast radio bursts (FRBs) gravitational
lensed by MACHO binaries to constrain their properties. Since lensing events
could generate more than one images, lensing by binaries could cause
multiple-peak FRBs. The angular separation between these images is roughly
$10^{-3}$ mas, which is too small to be resolved. The typical time interval
between different images is roughly 1 millisecond (ms). The flux ratio between
different images is roughly from 10 to $10^3$. With the expected detection rate
of $10^4$ FRBs per year by the upcoming experiments, we could expect five
multi-peak FRBs observed per year with time interval larger than 1 ms and flux
ratio less than $10^3$ if the fraction of dark matter in MACHOs is $f\sim0.01$.
A null search multiple-peak FRBs for time interval larger than 1 ms and flux
ratio less than $10^3$ with $10^4$ FRBs would constrain the fraction $f$ of
dark matter in MACHOs to $f<0.001$. | Galaxy Power Spectrum Multipoles Covariance in Perturbation Theory: We compute the covariance of the galaxy power spectrum multipoles in
perturbation theory, including the effects of nonlinear evolution, nonlinear
and nonlocal bias, radial redshift-space distortions, arbitrary survey window
and shot noise. We rewrite the power spectrum FKP estimator in terms of the
usual windowed galaxy fluctuations and the fluctuations in the number of
galaxies inside the survey volume. We show that this leads to a stronger
super-sample covariance than assumed in the literature and causes a substantial
leakage of Gaussian information. We decompose the covariance matrix into
several contributions that provide an insight into its behavior for different
biased tracers. We show that for realistic surveys, the covariance of power
spectrum multipoles is already dominated by shot noise and super survey mode
coupling in the weakly non-linear regime. Both these effects can be accurately
modeled analytically, making a perturbative treatment of the covariance very
compelling. Our method allows for the covariance to be varied as a function of
cosmology and bias parameters very efficiently, with survey geometry entering
as fixed kernels that can be computed separately using fast fourier transforms
(FFTs). We find excellent agreement between our analytic covariance and that
estimated from BOSS DR12 Patchy mock catalogs in the whole range we tested, up
to $k=0.6$ h/Mpc. This bodes well for application to future surveys such as
DESI and Euclid. The CovaPT code that accompanies this paper is available at
https://github.com/JayWadekar/CovaPT |
New physics in light of the $H_0$ tension: an alternative view: The strong discrepancy between local and inverse distance ladder estimates of
the Hubble constant $H_0$ could be pointing towards new physics beyond
$\Lambda$CDM. Several attempts to address this tension through new physics rely
on extended models, featuring extra free parameters beyond the 6 $\Lambda$CDM
parameters. However, marginalizing over extra parameters has the effect of
broadening the uncertainties on the inferred parameters, and it is often the
case that within these models the $H_0$ tension is addressed due to larger
uncertainties rather than a genuine shift in the central value of $H_0$. What
happens if a physical theory is able to fix the extra parameters to a specific
set of non-standard values? The degrees of freedom of the model are reduced
with respect to the standard case where the extra parameters are free to vary.
Focusing on the dark energy equation of state $w$ and the effective number of
relativistic species $N_{\rm eff}$, I find that physical theories able to fix
$w \approx -1.3$ or $N_{\rm eff} \approx 3.95$ would lead to an estimate of
$H_0$ from CMB, BAO, and SNeIa data in perfect agreement with the local
distance ladder estimate, without broadening its uncertainty. These two
non-standard models are, from a model-selection perspective, strongly
disfavoured with respect to $\Lambda$CDM. However, models that predict $N_{\rm
eff} \approx 3.45$ would be able to bring the tension down to $1.5\sigma$ while
only being weakly disfavored with respect to $\Lambda$CDM, whereas models that
predict $w \approx -1.1$ would be able to bring the tension down to $2\sigma$
(at the cost of the preference for $\Lambda$CDM being definite). Finally, I
estimate dimensionless multipliers relating variations in $H_0$ to variations
in $w$ and $N_{\rm eff}$, which can be used to repeat the analysis of this
paper in light of future more precise local distance ladder estimates of $H_0$. | An Ultra-Steep Spectrum Radio Relic in the Galaxy Cluster Abell 2443: We present newly discovered radio emission in the galaxy cluster Abell 2443
which is (1) diffuse, (2) extremely steep spectrum, (3) offset from the cluster
center, (4) of irregular morphology and (5) not clearly associated with any of
the galaxies within the cluster. The most likely explanation is that this
emission is a cluster radio relic, associated with a cluster merger. We present
deep observations of Abell 2443 at multiple low frequencies (1425, 325 and 74
MHz) which help characterize the spectrum and morphology of this relic. Based
on the curved spectral shape of the relic emission and the presence of small
scale structure, we suggest that this new source is likely a member of the
radio phoenix class of radio relics. |
Linear perturbations in spherically symmetric dust cosmologies including
a cosmological constant: We study the dynamical behaviour of gauge-invariant linear perturbations in
spherically symmetric dust cosmologies including a cosmological constant. In
contrast to spatially homogeneous FLRW models, the reduced degree of spatial
symmetry causes a non-trivial dynamical coupling of gauge-invariant quantities
already at first order perturbation theory and the strength and influence of
this coupling on the spacetime evolution is investigated here. We present
results on the underlying dynamical equations augmented by a cosmological
constant and integrate them numerically. We also present a method to derive
cosmologically relevant initial variables for this setup. Estimates of angular
power spectra for each metric variable are computed and evaluated on the
central observer's past null cone. By comparing the full evolution to the
freely evolved initial profiles, the coupling strength will be determined for a
best fit radially inhomogeneous patch obtained in previous works (see Redlich
et. al. (2014)). We find that coupling effects are not noticeable within the
cosmic variance limit and can therefore safely be neglected for a relevant
cosmological scenario. On the contrary, we find very strong coupling effects in
a best fit spherical void model matching the distance redshift relation of SNe
which is in accordance with previous findings using parametric void models. | Galaxy Bias and non-Linear Structure Formation in General Relativity: Length scales probed by large scale structure surveys are becoming closer to
the horizon scale. Further, it has been recently understood that
non-Gaussianity in the initial conditions could show up in a scale dependence
of the bias of galaxies at the largest distances. It is therefore important to
include General Relativistic effects. Here we provide a General Relativistic
generalization of the bias, valid both for Gaussian and non-Gaussian initial
conditions. The collapse of objects happens on very small scales, while
long-wavelength modes are always in the quasi linear regime. Around every
collapsing region, it is therefore possible to find a reference frame that is
valid for all times and where the space time is almost flat: the Fermi frame.
Here the Newtonian approximation is applicable and the equations of motion are
the ones of the N-body codes. The effects of long-wavelength modes are encoded
in the mapping from the cosmological frame to the local frame. For the linear
bias, the effect of the long-wavelength modes on the dynamics is encoded in the
local curvature of the Universe, which allows us to define a General
Relativistic generalization of the bias in the standard Newtonian setting. We
show that the bias due to this effect goes to zero as the squared ratio of the
physical wavenumber with the Hubble scale for modes longer than the horizon, as
modes longer than the horizon have no dynamical effects. However, the bias due
to non-Gaussianities does not need to vanish for modes longer than the Hubble
scale, and for non-Gaussianities of the local kind it goes to a constant. As a
further application, we show that it is not necessary to perform large N-body
simulations to extract information on long-wavelength modes: N-body simulations
can be done on small scales and long-wavelength modes are encoded simply by
adding curvature to the simulation and rescaling the coordinates. |
Cosmological constraints from Type I radio-loud quasars: We obtain a new sample of 1192 Type I quasars with the UV-optical, radio and
X-ray wavebands coverage by combining \citet{Huang2022} and other matching data
of SDSS-DR16 with FIRST, XMM-Newton, and Chandra Source Catalog, and a sample
of 407 flat-spectrum radio-loud quasars (FSRLQs) of blazars from the
Roma-BZCAT, which can be used to investigate their multi-band luminosity
correlations and measure the luminosity distances of these Type I radio-loud
quasars (RLQs) samples. We check the correlation between X-ray, UV-optical, and
radio luminosity for various groupings of radio-quiet quasars (RQQs) and RLQs
by parameterizing X-ray luminosity as a sole function of UV-optical or radio
luminosity and as a joint function of UV-optical radio luminosity, which also
can be employed to determine these cosmological distances. By Bayesian
information criterion (BIC), the data suggest that the X-ray luminosity of RQQs
is indirectly correlative with radio luminosity because of the connection
between UV-optical and radio luminosity. But for RLQs, the X-Ray luminosity is
directly related to radio luminosity, and the correlations between X-ray,
optical/UV, and radio luminosity increase with the ratio of monochromatic
luminosities logR. Meanwhile, we compare the results from RLQs with different
UV-optical power law index ${\Gamma _{UV}}$, the goodness of fit for RLQs with
${\Gamma _{UV}}\le 1.6$ seems to be better. Finally, we apply a combination of
Type I RLQs and SN Ia Pantheon to verify the nature of dark energy concerning
whether or not its density deviates from the constant, and give the statistical
results. | Annihilation vs. Decay: Constraining dark matter properties from a
gamma-ray detection: Most proposed dark matter candidates are stable and are produced thermally in
the early Universe. However, there is also the possibility of unstable (but
long-lived) dark matter, produced thermally or otherwise. We propose a strategy
to distinguish between dark matter annihilation and/or decay in the case that a
clear signal is detected in gamma-ray observations of Milky Way dwarf
spheroidal galaxies with gamma-ray experiments. The sole measurement of the
energy spectrum of an indirect signal would render the discrimination between
these cases impossible. We show that by examining the dependence of the
intensity and energy spectrum on the angular distribution of the emission, the
origin could be identified as decay, annihilation, or both. In addition, once
the type of signal is established, we show how these measurements could help to
extract information about the dark matter properties, including mass,
annihilation cross section, lifetime, dominant annihilation and decay channels,
and the presence of substructure. Although an application of the approach
presented here would likely be feasible with current experiments only for very
optimistic dark matter scenarios, the improved sensitivity of upcoming
experiments could enable this technique to be used to study a wider range of
dark matter models. |
General formula for the running of local fNL: We compute the scale dependence of fNL for models of multi-field inflation,
allowing for an arbitrary field space metric. We show that, in addition to
multi-field effects and self interactions, the curved field space metric
provides another source of scale dependence, which arises from the field-space
Riemann curvature tensor and its derivatives. The scale dependence may be
detectable within the near future if the amplitude of fNL is not too far from
the current observational bounds. | Extragalactic CO emission lines in the CMB experiments: a forgotten
signal and a foreground: High resolution cosmic microwave background (CMB) experiments have allowed us
to precisely measure the CMB temperature power spectrum down to very small
scales (multipole $\ell \sim 3000$). Such measurements at multiple frequencies
enable separating the primary CMB anisotropies with other signals like CMB
lensing, thermal and kinematic Sunyaev-Zel'dovich effects (tSZ and kSZ), and
cosmic infrared background (CIB). In this paper, we explore another signal of
interest at these frequencies that should be present in the CMB maps:
extragalactic CO molecular rotational line emissions, which are the most widely
used tracers of molecular gas in the line intensity mapping experiments. Using
the SIDES simulations adopted for top hat bandpasses at 150 and 220 GHz, we
show that the cross-correlation of the CIB with CO lines has a contribution
similar to the CIB-tSZ correlation and the kSZ power, thereby contributing a
non-negligible amount to the total power at these scales. This signal,
therefore, may significantly impact the recently reported $\geq 3\sigma$
detection of the kSZ power spectrum from the South Pole Telescope (SPT)
collaboration, as the contribution of the CO lines is not considered in such
analyses. Our results also provide a new way of measuring the CO power spectrum
in cross-correlation with the CIB. Finally, these results show that the CO
emissions present in the CMB maps will have to be accounted for in all the CMB
auto-power spectrum and cross-correlation studies involving a LSS tracer. |
The X-factor in Galaxies: II. The molecular hydrogen -- star formation
relation: There is ample observational evidence that the star formation rate (SFR)
surface density, Sigma_SFR, is closely correlated with the surface density of
molecular hydrogen, Sigma_H2. This empirical relation holds both for
galaxy-wide averages and for individual >=kpc sized patches of the interstellar
medium (ISM), but appears to degrade substantially at a sub-kpc scale.
Identifying the physical mechanisms that determine the scale-dependent
properties of the observed Sigma_H2-Sigma_SFR relation remains a challenge from
a theoretical perspective. To address this question, we analyze the slope and
scatter of the Sigma_H2-Sigma_SFR relation using a set of cosmological, galaxy
formation simulations with a peak resolution of ~100 pc. These simulations
include a chemical network for molecular hydrogen, a model for the CO emission,
and a simple, stochastic prescription for star formation that operates on ~100
pc scales. Specifically, star formation is modeled as a Poisson process in
which the average SFR is directly proportional to the present mass of H2. The
predictions of our numerical model are in good agreement with the observed
Kennicutt-Schmidt and Sigma_H2-Sigma_SFR relations. We show that observations
based on CO emission are ill suited to reliably measure the slope of the latter
relation at low (<20 M_sun pc^-2) H2 surface densities on sub-kpc scales. Our
models also predict that the inferred Sigma_H2-Sigma_SFR relation steepens at
high H2 surface densities as a result of the surface density dependence of the
CO/H2 conversion factor. Finally, we show that on sub-kpc scales most of the
scatter in the relation is a consequence of discreteness effects in the star
formation process. In contrast, variations of the CO/H2 conversion factor are
responsible for most of the scatter measured on super-kpc scales. | Extreme value statistics of weak lensing shear peak counts: The statistics of peaks in weak gravitational lensing maps is a promising
technique to constrain cosmological parameters in present and future surveys.
Here we investigate its power when using general extreme value statistics which
is very sensitive to the exponential tail of the halo mass function. To this
end, we use an analytic method to quantify the number of weak lensing peaks
caused by galaxy clusters, large-scale structures and observational noise.
Doing so, we further improve the method in the regime of high signal-to-noise
ratios dominated by non-linear structures by accounting for the embedding of
those counts into the surrounding shear caused by large scale structures. We
derive the extreme value and order statistics for both over-densities (positive
peaks) and under-densities (negative peaks) and provide an optimized criterion
to split a wide field survey into sub-fields in order to sample the
distribution of extreme values such that the expected objects causing the
largest signals are mostly due to galaxy clusters. We find good agreement of
our model predictions with a ray-tracing $N$-body simulation. For a Euclid-like
survey, we find tight constraints on $\sigma_8$ and $\Omega_\text{m}$ with
relative uncertainties of $\sim 10^{-3}$. In contrast, the equation of state
parameter $w_0$ can be constrained only with a $10\%$ level, and $w_\text{a}$
is out of reach even if we include redshift information. |
Reinventing the slide rule for redshifts: the case for logarithmic
wavelength shift: Redshift is not a shift, it is defined as a fractional change in wavelength.
Nevertheless, it is a fairly common misconception that Delta-z c represents a
velocity where Delta-z is the redshift separation between two galaxies. When
evaluating large changes in a quantity, it is often more useful to consider
logarithmic differences. Defining zeta = ln lambda_obs - ln lambda_em results
in a more accurate approximation for line-of-sight velocity and, more
importantly, this means that the cosmological and peculiar velocity terms
become additive: Delta-zeta c can represent a velocity at any cosmological
distance. Logarithmic shift zeta, or equivalently ln(1+z), should arguably be
used for photometric redshift evaluation. For a comparative non-accelerating
universe, used in cosmology, comoving distance is proportional to zeta. This
means that galaxy population distributions in zeta, rather than z, are close to
being evenly distributed in comoving distance, and they have a more aesthetic
spacing when considering galaxy evolution. Some pedagogic notes on these
quantities are presented. | The impact of Lyman-$α$ emission line heating and cooling on the
cosmic dawn 21-cm signal: Allowing for enhanced Ly$\alpha$ photon line emission from Population III
dominated stellar systems in the first forming galaxies, we show the 21-cm
cosmic dawn signal at $10<z<30$ may substantially differ from standard
scenarios. Energy transfer by Ly$\alpha$ photons emerging from galaxies may
heat intergalactic gas if HII regions within galaxies are recombination bound,
or cool the gas faster than by adiabatic expansion if reddened by winds
internal to the haloes. In some cases, differential 21-cm antenna temperatures
near $-500$ mK may be achieved at $15<z<25$, similar to the signature detected
by the EDGES 21-cm cosmic dawn experiment. |
Emergent Universe from A Composition of Matter, Exotic Matter and Dark
Energy: A specific class of flat Emergent Universe (EU) is considered and its
viability is tested in view of the recent observations. Model parameters are
constrained from Stern data for Hubble Parameter and Redshift ($H(z)$ vs. $z$)
and from a model independent measurement of BAO peak parameter. It is noted
that a composition of Exotic matter, dust and dark energy, capable of producing
an EU, can not be ruled out with present data. Evolution of other relevant
cosmological parameters, viz. density parameter ($\Omega$), effective equation
of state (EOS) parameter ($\omega_{eff}$) are also shown. | The three hundred project: thermodynamical properties, shocks and gas
dynamics in simulated galaxy cluster filaments and their surroundings: Using cosmological simulations of galaxy cluster regions from The Three
Hundred project we study the nature of gas in filaments feeding massive
clusters. By stacking the diffuse material of filaments throughout the cluster
sample, we measure average gas properties such as density, temperature,
pressure, entropy and Mach number and construct one-dimensional profiles for a
sample of larger, radially-oriented filaments to determine their characteristic
features as cosmological objects. Despite the similarity in velocity space
between the gas and dark matter accretion patterns onto filaments and their
central clusters, we confirm some differences, especially concerning the more
ordered radial velocity dispersion of dark matter around the cluster and the
larger accretion velocity of gas relative to dark matter in filaments. We also
study the distribution of shocked gas around filaments and galaxy clusters,
showing that the surrounding shocks allow an efficient internal transport of
material, suggesting a laminar infall. The stacked temperature profile of
filaments is typically colder towards the spine, in line with the cosmological
rarefaction of matter. Therefore, filaments are able to isolate their inner
regions, maintaining lower gas temperatures and entropy. Finally, we study the
evolution of the gas density-temperature phase diagram of our stacked filament,
showing that filamentary gas does not behave fully adiabatically through time
but it is subject to shocks during its evolution, establishing a characteristic
z = 0, entropy-enhanced distribution at intermediate distances from the spine
of about 1 - 2 $h^{-1}$ Mpc for a typical galaxy cluster in our sample. |
Dark energy model with very large-scale inhomogeneity: We consider a dynamical model for dark energy based on an ultralight mass
scalar field with very large-scale inhomogeneities. This model may cause
observable impacts on the anisotropic properties of the cosmic microwave
background (CMB) intensity and luminosity distance. We formulate the model as
the cosmological perturbations of the superhorizon scales, focusing on the
local region of our universe. Moreover, we investigated the characteristic
properties of the late-time evolution of inhomogeneous dark energy. Our
numerical solutions show that the model can mimic the standard $\Lambda$CDM
cosmology while including spatially dependent dark energy with flexible ranges
of the model parameters. We put a constraint on the amplitude of these
inhomogeneities of the dark energy on very large scales with the observations
of the CMB anisotropies. We also discuss their influence on the estimation of
the luminosity distance. | Revised SWIRE photometric redshifts: We have revised the SWIRE Photometric Redshift Catalogue to take account of
new optical photometry in several of the SWIRE areas, and incorporating 2MASS
and UKIDSS near infrared data. Aperture matching is an important issue for
combining near infrared and optical data, and we have explored a number of
methods of doing this. The increased number of photometric bands available for
the redshift solution results in improvements both in the rms error and,
especially, in the outlier rate.
We have also found that incorporating the dust torus emission into the QSO
templates improves the performance for QSO redshift estimation. Our revised
redshift catalogue contains over 1 million extragalactic objects, of which
26288 are QSOs. |
The UV background photoionization rate at 2.3 < z < 4.6 as measured from
the Sloan Digital Sky Survey: (Abridged) We present the results from the largest investigation to date of
the proximity effect in the HI Lyalpha forest, using the fifth SDSS data
release. The sample consists of 1733 QSOs at redshifts z>2.3 and S/N>10. We
adopted the flux statistic to infer the evolution of the HI effective optical
depth in the Lyalpha forest between 2<z<4.5, finding very good agreement with
results from high-resolution QSO samples. We compared the average opacity close
to the quasar emission with its expected behavior in the Lyalpha forest and
estimated the signature of the proximity effect towards individual objects at
high significance in about 98% of the QSOs. Dividing the whole sample of
objects in eight subsets according to their emission redshift, we inferred the
proximity effect strength distribution (PESD) on each of them finding in all
cases a prominent peak and an extending tail towards values associated to a
weak effect. We provide for the first time observational evidence for an
evolution in the asymmetry of the PESD with redshift. Adopting the modal values
of the PESDs as our best and unbiased estimates of the UV background
photoionization rate (Gamma_HI), we determine its evolution within the range
2.3<z<4.6. Our measurements do not show any significant decline towards high
redshift and are located at Log(Gamma_HI)=-11.78\pm0.07 in units of s^-1. We
decompose the observed photoionization rate into two major contributors: quasar
and star-forming galaxies. By modeling the quasar contribution with different
luminosity functions we estimated their contribution to Gamma_HI, thus putting
a constraint on the residuals. We conclude that independently of the assumed
luminosity function, stars are dominating the UVB at z>3. | Point Source Detection and False Discovery Rate Control on CMB Maps: We discuss a new procedure to search for point sources in Cosmic Microwave
background maps; in particular, we aim at controlling the so-called False
Discovery Rate, which is defined as the expected value of false discoveries
among pixels which are labelled as contaminated by point sources. We exploit a
procedure called STEM, which is based on the following four steps: 1) needlet
filtering of the observed CMB maps, to improve the signal to noise ratio; 2)
selection of candidate peaks, i.e., the local maxima of filtered maps; 3)
computation of \emph{p-}values for local maxima; 4) implementation of the
multiple testing procedure, by means of the so-called Benjamini-Hochberg
method. Our procedures are also implemented on the latest release of Planck CMB
maps. |
Detecting Relic Gravitational Waves by Pulsar Timing Arrays: Effects of
Cosmic Phase Transitions and Relativistic Free-Streaming Gases: Relic gravitational waves (RGWs) generated in the early Universe form a
stochastic GW background, which can be directly probed by measuring the timing
residuals of millisecond pulsars. In this paper, we investigate the constraints
on the RGWs and on the inflationary parameters by the observations of current
and potential future pulsar timing arrays. In particular, we focus on effects
of various cosmic phase transitions (e.g. $e^{+}e^{-}$ annihilation, QCD
transition and SUSY breaking) and relativistic free-streaming gases (neutrinos
and dark fluids) in the general scenario of the early Universe, which have been
neglected in the previous works. We find that the phase transitions can
significantly damp the RGWs in the sensitive frequency range of pulsar timing
arrays, and the upper limits of tensor-to-scalar ratio $r$ increase by a factor
$\sim 2$ for both current and future observations. However, the effects of
free-steaming neutrinos and dark fluids are all too small to be detected.
Meanwhile, we find that, if the effective equation of state $w$ in the early
Universe is larger than $1/3$, i.e. deviating from the standard hot big bang
scenario, the detection of RGWs by pulsar timing arrays becomes much more
promising. | The Impact of Metallicity on the Rate of Type Ia Supernovae: The metallicity of a star strongly affects both its evolution and the
properties of the stellar remnant that results from its demise. It is generally
accepted that stars with initial masses below ~8 M_sun leave behind white
dwarfs and that some sub-population of these lead to Type Ia supernovae.
However, it is often tacitly assumed that metallicity has no effect on the rate
of SNe Ia. We propose that a consequence of the effects of metallicity is to
significantly increase the SN Ia rate in lower-metallicity galaxies, in
contrast to previous expectations. This is because lower-metallicity stars
leave behind higher-mass white dwarfs, which should be easier to bring to
explosion. We first model SN Ia rates in relation to galaxy masses and ages
alone, finding that the elevation in the rate of SNe Ia in lower-mass galaxies
measured by LOSS is readily explained. However, we then see that models
incorporating this effect of metallicity agree just as well. Using the same
parameters to estimate the cosmic SN Ia rate, we again find good agreement with
data up to z~2. We suggest that this degeneracy warrants more detailed
examination of host galaxy metallicities. We discuss additional implications,
including for hosts of high-z SNe Ia, the SN Ia delay time distribution,
super-Chandrasekhar SNe, and cosmology. |
Sunyaev-Zel'dovich Signal from Quasar Hosts: Implications for Detection
of Quasar Feedback: Several analytic and numerical studies have indicated that the interstellar
medium of a quasar host galaxy heated by feedback can contribute to a
substantial secondary signal in the cosmic microwave background (CMB) through
the thermal Sunyaev-Zel'dovich (SZ) effect. Recently, many groups have tried to
detect this signal by cross-correlating CMB maps with quasar catalogs. Using a
self-similar model for the gas in the intra-cluster medium and a realistic halo
occupation distribution (HOD) prescription for quasars we estimate the level of
SZ signal from gravitational heating of quasar hosts. The bias in the host halo
signal estimation due to unconstrained high mass HOD tail and yet unknown
redshift dependence of the quasar HOD restricts us from drawing any robust
conclusions at low redshift (z<1.5) from our analysis. However, at higher
redshifts (z>2.5), we find an excess signal in recent observations than what is
predicted from our model. The excess signal could be potentially generated from
additional heating due to quasar feedback. | A Bayesian comparison between $Λ$CDM and phenomenologically
emergent dark energy models: In this work we examine the recently proposed phenomenological emergent dark
energy (PEDE) model by \cite{Li:2019yem}, using the latest observational data
in both expansion and perturbation levels. Applying the statistical Bayesian
evidence as well as the AIC and BIC information criteria, we compare the PEDE
model with the concordance $\Lambda$CDM model in both flat and non-flat
universes. We combine the observational datasets as (i) expansion data (except
CMB), (ii) expansion data (including CMB) and (iii) expansion data jointed to
the growth rate dataset. Our statistical results show that the flat-
$\Lambda$CDM model is still the best model. In the case of expansion data
(including CMB), we observe that the flat- PEDE model is well consistent with
observations as well as the concordance $\Lambda$CDM universe. While in the
cases of (i) and (iii), the PEDE models in both of the flat and non-flat
geometries are not favored. In particular, we see that in the perturbation
level the PEDE model can not fit the observations as equally as standard
$\Lambda$CDM cosmology. As the ability of the model, we show that the PEDE
models can alleviate the tension of Hubble constant value appearing between the
local observations and Planck inferred estimation in standard cosmology. |
Evolution of Bulk Scale Factor in Warped Space-time: In this work the role of extra dimensions in the accelerated universe through
the scenario of higher-dimensional Friedmann-Robertson-Walker (FRW) cosmology
has been studied. For this purpose, we first consider warped space-time in the
standard flat brane scenario as the modified form of Robertson-Walker (RW)
metric in five-dimension (5D) space-time and then the variation of the bulk
scale factor (warp factor), with respect to both space-like and time-like extra
dimensions is obtained. Finally, it is shown that both of two types of extra
dimensions are important in this scenario and also the bulk scale factor plays
two different roles. | Darth Fader: Using wavelets to obtain accurate redshifts of spectra at
very low signal-to-noise: We present the DARTH FADER algorithm, a new wavelet-based method for
estimating redshifts of galaxy spectra in spectral surveys that is particularly
adept in the very low SNR regime. We use a standard cross-correlation method to
estimate the redshifts of galaxies, using a template set built using a PCA
analysis on a set of simulated, noise-free spectra. Darth Fader employs wavelet
filtering to both estimate the continuum & to extract prominent line features
in each galaxy spectrum. A simple selection criterion based on the number of
features present in the spectrum is then used to clean the catalogue: galaxies
with fewer than six total features are removed as we are unlikely to obtain a
reliable redshift estimate. Applying our wavelet-based cleaning algorithm to a
simulated testing set, we successfully build a clean catalogue including
extremely low signal-to-noise data (SNR=2.0), for which we are able to obtain a
5.1% catastrophic failure rate in the redshift estimates (compared with 34.5%
prior to cleaning). We also show that for a catalogue with uniformly mixed SNRs
between 1.0 & 20.0, with realistic pixel-dependent noise, it is possible to
obtain redshifts with a catastrophic failure rate of 3.3% after cleaning (as
compared to 22.7% before cleaning). Whilst we do not test this algorithm
exhaustively on real data, we present a proof of concept of the applicability
of this method to real data, showing that the wavelet filtering techniques
perform well when applied to some typical spectra from the SDSS archive. The
Darth Fader algorithm provides a robust method for extracting spectral features
from very noisy spectra. The resulting clean catalogue gives an extremely low
rate of catastrophic failures, even when the spectra have a very low SNR. For
very large sky surveys, this technique may offer a significant boost in the
number of faint galaxies with accurately determined redshifts. |
Decomposition of Spectra from Redshift Distortion Maps: We develop an optimized technique to extract density--density and
velocity--velocity spectra out of observed spectra in redshift space. The
measured spectra of the distribution of halos from redshift distorted mock map
are binned into 2--dimensional coordinates in Fourier space so as to be
decomposed into both spectra using angular projection dependence. With the
threshold limit introduced to minimize nonlinear suppression, the decomposed
velocity--velocity spectra are reasonably well measured up to scale k=0.07
h/Mpc, and the measured variances using our method are consistent with errors
predicted from a Fisher matrix analysis. The detectability is extendable to
k\sim 0.1 h/Mpc with more conservative bounds at the cost of weakened
constraint. | Consistency Relations for Large Field Inflation: Non-minimal Coupling: We derive the consistency relations for a chaotic inflation model with a
non-minimal coupling to gravity. For a quadratic potential in the limit of a
small non-minimal coupling parameter $\xi$ and for a quartic potential without
assuming small $\xi$, we give the consistency relations among the spectral
index $n_s$, the tensor-to-scalar ratio $r$ and the running of the spectral
index $\alpha$. We find that unlike $r$, $\alpha$ is less sensitive to $\xi$.
If $r<0.1$, then $\xi$ is constrained to $\xi<0$ and $\alpha$ is predicted to
be $\alpha\simeq -8\times 10^{-4}$ for a quartic potential. For a general
monomial potential, $\alpha$ is constrained in the range $-2.7\times
10^{-3}<\alpha< -6\times 10^{-4}$ as long as $|\xi|\leq 10^{-3}$ if $r<0.1$. |
Constraining dark energy cosmologies with spatial curvature using
Supernovae JWST forecasting: Recent cosmological tensions, in particular, to infer the local value of the
Hubble constant $H_0$, have developed new independent techniques to constrain
cosmological parameters in several cosmologies. Moreover, even when the
concordance Cosmological Constant Cold Dark Matter ($\Lambda$CDM) model has
been well constrained with local observables, its physics has shown deviations
from a flat background. Therefore, to explore a possible deviation from a flat
$\Lambda$CDM model that could explain the $H_0$ value in tension with other
techniques, in this paper we study new cosmological constraints in spatial
curvature dark energy models. Additionally, to standard current Supernovae Type
Ia (SNIa) catalogs, we extend the empirical distance ladder method through an
SNIa sample using the capabilities of the James Webb Space Telescope (JWST) to
forecast SNIa up to $z \sim 6$, with information on the star formation rates at
high redshift. Furthermore, we found that our constraints provide an
improvement in the statistics associated with $\Omega_{m}$ when combining SNIa
Pantheon and SNIa Pantheon+ catalogs with JW forecasting data. | Using angular two-point correlations to self-calibrate the photometric
redshift distributions of DECaLS DR9: Calibrating the redshift distributions of photometric galaxy samples is
essential in weak lensing studies. The self-calibration method combines angular
auto- and cross-correlations between galaxies in multiple photometric redshift
(photo-$z$) bins to reconstruct the scattering rates matrix between redshift
bins. In this paper, we test a recently proposed self-calibration algorithm
using the DECaLS Data Release 9 and investigate to what extent the scattering
rates are determined. We first mitigate the spurious angular correlations due
to imaging systematics by a machine learning based method. We then improve the
algorithm for $\chi^2$ minimization and error estimation. Finally, we solve for
the scattering matrices, carry out a series of consistency tests and find
reasonable agreements: (1) finer photo-$z$ bins return a high-resolution
scattering matrix, and it is broadly consistent with the low-resolution matrix
from wider bins; (2) the scattering matrix from the Northern Galactic Cap is
almost identical to that from Southern Galactic Cap; (3) the scattering
matrices are in reasonable agreement with those constructed from the power
spectrum and the weighted spectroscopic subsample. We also evaluate the impact
of cosmic magnification. Although it changes little the diagonal elements of
the scattering matrix, it affects the off-diagonals significantly. The
scattering matrix also shows some dependence on scale cut of input
correlations, which may be related to a known numerical degeneracy between
certain scattering pairs. This work demonstrates the feasibility of the
self-calibration method in real data and provides a practical alternative to
calibrate the redshift distributions of photometric samples. |
Impact of a Warm Dark Matter late-time velocity dispersion on
large-scale structures: We investigate whether the late-time (at $z\leq 100$) velocity dispersion
expected in Warm Dark Matter scenarios could have some effect on the cosmic web
(i.e., outside of virialized halos). We consider effective hydrodynamical
equations, with a pressurelike term that agrees at the linear level with the
analysis of the Vlasov equation. Then, using analytical methods, based on
perturbative expansions and the spherical dynamics, we investigate the impact
of this term for a 1 keV dark matter particle. We find that the late-time
velocity dispersion has a negligible effect on the power spectrum on
perturbative scales and on the halo mass function. However, it has a
significant impact on the probability distribution function of the density
contrast at $z \sim 3$ on scales smaller than $0.1 h^{-1}$Mpc, which correspond
to Lyman-$\alpha$ clouds. Finally, we note that numerical simulations should
start at $z_i\geq 100$ rather than $z_i \leq 50$ to avoid underestimating
gravitational clustering at low redshifts. | Rethinking CMB foregrounds: systematic extension of foreground
parameterizations: Future high-sensitivity measurements of the cosmic microwave background (CMB)
anisotropies and energy spectrum will be limited by our understanding and
modeling of foregrounds. Not only does more information need to be gathered and
combined, but also novel approaches for the modeling of foregrounds,
commensurate with the vast improvements in sensitivity, have to be explored.
Here, we study the inevitable effects of spatial averaging on the spectral
shapes of typical foreground components, introducing a moment approach, which
naturally extends the list of foreground parameters that have to be determined
through measurements or constrained by theoretical models. Foregrounds are
thought of as a superposition of individual emitting volume elements along the
line of sight and across the sky, which then are observed through an
instrumental beam. The beam and line of sight averages are inevitable. Instead
of assuming a specific model for the distributions of physical parameters, our
method identifies natural new spectral shapes for each foreground component
that can be used to extract parameter moments (e.g., mean, dispersion,
cross-terms, etc.). The method is illustrated for the superposition of
power-laws, free-free spectra, gray-body and modified blackbody spectra, but
can be applied to more complicated fundamental spectral energy distributions.
Here, we focus on intensity signals but the method can be extended to the case
of polarized emission. The averaging process automatically produces
scale-dependent spectral shapes and the moment method can be used to propagate
the required information across scales in power spectrum estimates. The
approach is not limited to applications to CMB foregrounds but could also be
useful for the modeling of X-ray emission in clusters of galaxies. |
Inferring the properties of the sources of reionization using the
morphological spectra of the ionized regions: High-redshift 21-cm observations will provide crucial insights into the
physical processes of the Epoch of Reionization. Next-generation
interferometers such as the Square Kilometer Array will have enough sensitivity
to directly image the 21-cm fluctuations and trace the evolution of the
ionizing fronts. In this work, we develop an inferential approach to recover
the sources and IGM properties of the process of reionization using the number
and, in particular, the morphological pattern spectra of the ionized regions
extracted from realistic mock observations. To do so, we extend the Markov
Chain Monte Carlo analysis tool 21CMMC by including these 21-cm tomographic
statistics and compare this method to only using the power spectrum. We
demonstrate that the evolution of the number-count and morphology of the
ionized regions as a function of redshift provides independent information to
disentangle multiple reionization scenarios because it probes the average
ionizing budget per baryon. Although less precise, we find that constraints
inferred using 21-cm tomographic statistics are more robust to the presence of
contaminants such as foreground residuals. This work highlights that combining
power spectrum and tomographic analyses more accurately recovers the
astrophysics of reionization. | Cosmological constraints from standardized non-CMB observations: The current expansion of the Universe has been observed to be accelerating,
and the widely accepted spatially-flat concordance model of general
relativistic cosmology attributes this phenomenon to a constant dark energy, a
cosmological constant, which is measured to comprise about 70% of the total
energy budget of the current Universe. However, observational discrepancies and
theoretical puzzles have raised questions about this model, suggesting that
alternative cosmological models with non-zero spatial curvature and/or dark
energy dynamics might provide better explanations.
To explore these possibilities, we have conducted a series of studies using
standardized, lower-redshift observations to constrain six different
cosmological models with varying degrees of flatness and dark energy dynamics.
Through comparing these observations with theoretical predictions, we aim to
deepen our understanding of the evolution of the Universe and shed new light on
its mysteries. Our data provide consistent cosmological constraints across all
six models, with some suggesting the possibility of mild dark energy dynamics
and slight spatial curvature. However, these joint constraints do not rule out
the possibility of dark energy being a cosmological constant and the spatial
hypersurfaces being flat. Overall, our findings contribute to the ongoing
efforts to refine our understanding of the Universe and its properties, and
suggest that multiple cosmological models remain viable. |
Steady state solution of warped accretion discs: We consider a thin accretion disc warped due to the Bardeen-Petterson effect,
presenting both analytical and numerical solutions for the situation that the
two viscosity coefficients vary with radius as power law, with the two power
law indices not necessarily equal. The analytical solutions are compared with
numerical ones, showing that our new analytical solution is more accurate than
previous one, which overestimates the inclination changing in the outer disc.
Our new analytical solution is appropriate for moderately warped discs, while
for extremely misaligned disc, only numerical solution is appropriate. | On the Dearth of Compact, Massive, Red Sequence Galaxies in the Local
Universe: Using data from the Sloan Digital Sky Survey (SDSS; data release 7), we have
conducted a search for local analogs to the extremely compact, massive,
quiescent galaxies that have been identified at z > 2. We show that
incompleteness is a concern for such compact galaxies, particularly for low
redshifts (z < ~0.05) as a result of the SDSS spectroscopic target selection
algorithm. We have identified 63 massive red sequence galaxies at 0.066 < z <
0.12 that are smaller than the median size-mass relation by a factor of 2 or
more. Consistent with expectations from the virial theorem, the median offset
from the mass-velocity dispersion relation for these galaxies is 0.12 dex. We
do not find any galaxies with sizes and masses comparable to those observed at
z ~ 2, implying a decrease in the comoving number density (at fixed size and
mass) by a factor of > 5000. This result cannot be explained by incompleteness:
at 0.066 < z <0.12, the SDSS spectroscopic sample should typically be ~75%
complete for galaxies with the sizes and masses seen at high redshift, although
for the very smallest galaxies it may be as low as ~20%. To confirm that the
absence of such compact massive galaxies in SDSS is not a spectroscopic
selection effect, we have also looked for such galaxies in the SDSS photometric
catalog, using photometric redshifts. While we do find signs of a bias against
massive, compact galaxies, this analysis suggests that the SDSS spectroscopic
sample is missing at most a few objects in the regime we consider. Accepting
the high redshift results, it is clear that massive galaxies must undergo
significant structural evolution over z<2 in order to match the population seen
in the local universe. Our results suggest that a highly stochastic mechanism
like major mergers cannot be the primary driver of this strong size evolution. |
Do Disk Galaxies with Abnormally Low Mass-to-Light Ratios Exist?: We performed the photometric B, V and R observations of nine disk galaxies
that were suspected in having abnormally low total mass-to-light (M/L) ratios
for their observed color indices. We use our surface photometry data to analyze
the possible reasons for the anomalous M/L. We infer that in most cases this is
a result of errors in photometry or rotational velocity, however for some
galaxies we cannot exclude the real peculiarities of the galactic stellar
population. The comparison of the photometric and dynamical mass estimates in
the disk shows that the low M/L values for a given color of disks are probably
real for a few our galaxies: NGC 4826 (Sab), NGC 5347 (Sab), and NGC 6814 (Sb).
The small number of such galaxies suggests that the stellar initial mass
function is indeed universal, and that only a small fraction of galaxies may
have a non-typical low-mass star depleted initial mass function. Such galaxies
require more careful studies for understanding their star formation history. | The stellar content of low redshift radio galaxies from near-infrared
spectroscopy: We present medium spectral resolution near-infrared (NIR) HK-band spectra for
8 low redshift (z<0.06) radio galaxies to study the NIR stellar properties of
their host galaxies. As a homogeneous comparison sample, we used 9 inactive
elliptical galaxies that were observed with similar resolution and wavelength
range. The aim of the study is to compare the NIR spectral properties of radio
galaxies to those of inactive early-type galaxies and, furthermore, produce the
first NIR HK-band spectra for low redshift radio galaxies. For both samples
spectral indices of several diagnostic absorption features, SiI(1.589microns),
CO(1.619microns), NaI(2.207microns), CaI(2.263microns), CO(>2.29microns), were
measured. To characterize the age of the populations, the measured EWs of the
absorption features were fitted with the corresponding theoretical evolutionary
curves of the EWs calculated by the stellar synthesis model. On average, EW(CO
2.29) of radio galaxies is somewhat greater than that of inactive ellipticals.
Most likely, EW(CO 2.29) is not significantly affected by dilution, and thus
indicating that elliptical galaxies containing AGN are in a different stage in
their evolution than inactive ellipticals. This is also supported by comparing
other NIR features, such as CaI and NaI, with each other. Absorption features
are consistent with the intermediate age stellar population, suggesting that
host galaxies contain both an old and intermediate age components. It is
consistent with previous optical spectroscopy studies which have shown evidence
on the intermediate age (~2 Gyr) stellar population of radio galaxies, and also
in some of the early-type galaxies. The existence of intermediate age
population is a link between the star formation episode, possibly induced by
interaction or merging event, and the triggering of the nuclear activity. |
The ACS Nearby Galaxy Survey Treasury XI. The Remarkably Undisturbed NGC
2403 Disk: We present detailed analysis of color-magnitude diagrams of NGC2403, obtained
from a deep (m<28) Hubble Space Telescope (HST) Wide Field Planetary Camera 2
observation of the outer disk of NGC2403, supplemented by several shallow
(m<26) HST Advanced Camera for Surveys fields. We derive the spatially resolved
star formation history of NGC2403 out to 11 disk scale lengths. In the inner
portions of the galaxy, we compare the recent star formation rates (SFRs) we
derive from the resolved stars with those measured using GALEX FUV + Spitzer
24-micron fluxes, finding excellent agreement between the methods. Our
measurements also show that the radial gradient in recent SFR mirror s the disk
exponential profile to 11 scale lengths with no break, extending to SFR
densities a factor of 100 lower than those that can be measured with GALEX and
Spitzer (2x10^{-6} M_{\sun} yr^{-1} kpc^{-2}). Furthermore, we find that the
cumulative stellar mass of the disk was formed at similar times at all radii.
We compare these characteristics of NGC2403 to those of its "morphological
twins," NGC300 and M33, showing that the structure and age distributions of the
NGC2403 disk are more similar to those of the relatively isolated system NGC300
than to those of the Local Group analog M33. We also discuss the environments
and HI morphologies of these three nearby galaxies, comparing them to
integrated light studies of larger samples of more distant galaxy disks. Taken
together, the physical properties and evolutionary history of NGC2403 suggest
that the galaxy has had no close encounters with other M81 group members and
may be falling into the group for the first time. | Will Kinematic Sunyaev-Zel'dovich Measurements Enhance the Science
Return from Galaxy Redshift Surveys?: Yes. Future CMB experiments such as Advanced ACTPol and CMB-S4 should achieve
measurements with S/N of $> 0.1$ for the typical galaxies in redshift surveys.
These measurements will provide complementary measurements of the growth rate
of large scale structure $f$ and the expansion rate of the Universe $H$ to
galaxy clustering measurements. This paper emphasizes that there is significant
information in the anisotropy of the relative pairwise kSZ measurements. We
expand the relative pairwise kSZ power spectrum in Legendre polynomials and
consider up to its octopole. Assuming that the noise in the filtered maps is
uncorrelated between the positions of galaxies in the survey, we derive a
simple analytic form for the power spectrum covariance of the relative pairwise
kSZ temperature in redshift space. While many previous studies have assumed
optimistically that the optical depth of the galaxies $\tau_{\rm T}$ in the
survey is known, we marginalize over $\tau_{\rm T}$, to compute constraints on
the growth rate $f$ and the expansion rate $H$. For realistic sure parameters,
we find that combining kSZ and galaxy redshift survey data reduces the
marginalized $1$-$\sigma$ errors on $H$ and $f$ by $\sim50$-$70\%$ compared to
the galaxy-only analysis. |
Spinning Guest Fields during Inflation: Leftover Signatures: We consider the possibility of extra spinning particles during inflation,
focussing on the spin-2 case. Our analysis relies on the well-known fully
non-linear formulation of interacting spin-2 theories. We explore the parameter
space of the corresponding inflationary Lagrangian and identify regions therein
exhibiting signatures within reach of upcoming CMB probes. We provide a
thorough study of the early and late-time dynamics ensuring that stability
conditions are met throughout the cosmic evolution. We characterise in
particular the gravitational wave spectrum and three-point function finding a
local-type non-Gaussianity whose amplitude may be within the sensitivity range
of both the LiteBIRD and CMB-S4 experiments. | Improved CMB anisotropy constraints on primordial magnetic fields from
the post-recombination ionization history: We investigate the impact of a stochastic background of Primordial Magnetic
Fields (PMF) generated before recombination on the ionization history of the
Universe and on the Cosmic Microwave Background radiation (CMB).
Pre-recombination PMFs are dissipated during recombination and reionization via
decaying MHD turbulence and ambipolar diffusion. This modifies the local matter
and electron temperatures and thus affects the ionization history and Thomson
visibility function. We use this effect to constrain PMFs described by a
spectrum of power-law type, extending our previous study (based on a
scale-invariant spectrum) to arbitrary spectral index. We derive upper bounds
on the integrated amplitude of PMFs due to the separate effect of ambipolar
diffusion and MHD decaying turbulence and their combination. We show that
ambipolar diffusion is relevant for $n_{\rm B}>0$ whereas for $n_{\rm B}<0$ MHD
turbulence is more important. The bound marginalized over the spectral index on
the integrated amplitude of PMFs with a sharp cut-off is $\sqrt{\langle B^2
\rangle}<0.83$ nG. We discuss the quantitative relevance of the assumptions on
the damping mechanism and the comparison with previous bounds. |
First measurement of the Weyl potential evolution from the Year 3 Dark
Energy Survey data: Localising the $σ_8$ tension: We present the first measurement of the Weyl potential at four redshifts bins
using data from the first three years of observations of the Dark Energy Survey
(DES). The Weyl potential, which is the sum of the spatial and temporal
distortions of the Universe's geometry, provides a direct way of testing the
theory of gravity and the validity of the $\Lambda$CDM model. We find that the
measured Weyl potential is 2.3$\sigma$, respectively 3.1$\sigma$, below the
$\Lambda$CDM predictions in the two lowest redshift bins. We show that these
low values of the Weyl potential are at the origin of the $\sigma_8$ tension
between Cosmic Microwave Background (CMB) measurements and weak lensing
measurements. Interestingly, we find that the tension remains if no information
from the CMB is used. DES data on their own prefer a high value of the
primordial fluctuations, followed by a slow evolution of the Weyl potential. A
remarkable feature of our method is that the measurements of the Weyl potential
are model-independent and can therefore be confronted with any theory of
gravity, allowing efficient tests of models beyond General Relativity. | The Anisotropic Two-Point Correlation Functions of the Nonlinear
Traceless Tidal Field in the Principal-Axis Frame: Galaxies on the largest scales of the Universe are observed to be embedded in
the filamentary cosmic web which is shaped by the nonlinear tidal field. As an
efficient tool to quantitatively describe the statistics of this cosmic web, we
present the anisotropic two-point correlation functions of the nonlinear
traceless tidal field in the principal-axis frame, which are measured using
numerical data from an N-body simulation. We show that both of the nonlinear
density and traceless tidal fields are more strongly correlated along the
directions perpendicular to the eigenvectors associated with the largest
eigenvalues of the local tidal field. The correlation length scale of the
traceless tidal field is found to be ~20 Mpc/h, which is much larger than that
of the density field ~5 Mpc/h. We also provide analytic fitting formulae for
the anisotropic correlation functions of the traceless tidal field, which turn
out to be in excellent agreement with the numerical results. We expect that our
numerical results and analytic formula are useful to disentangle cosmological
information from the filamentary network of the large-scale structures. |
The importance of galaxy interactions in triggering type II quasar
activity: We present deep Gemini GMOS-S optical broad-band images for a complete sample
of 20 SDSS selected type II quasars with redshifts 0.3 < z < 0.41 and [OIII]
emission line luminosities greater than 10^8.5 solar luminosities. We use these
images to determine the significance of galaxy interactions in triggering
nuclear activity, finding that 15 (75%) show evidence for interaction in the
form of tails, shells, double nuclei etc. The median surface brightness of the
features is 23.4 mag arcsec sq and the range is 20.9-24.7 mag arcsec sq.
We find a similar rate of interaction in the type II quasars as in a
comparison sample of quiescent early-type galaxies at similar redshift (67 +/-
14%). However the surface brightness of the detected features is up to 2
magnitudes brighter for the type II quasars than for the quiescent early-types,
which have surface brightnesses in the range 22.1-26.1 mag arcsec sq and a
median surface brightness 24.3 mag arcsec sq. This may indicate that the
mergers witnessed in the comparison sample galaxies could have different
progenitors, or we may be viewing the interactions at different stages. We also
compare our results with a sample of radio-loud AGN and find a higher rate of
interaction signatures (95 +/- 21%) than in the type II quasars, but a very
similar range of surface brightnesses for the morphological features (20.9-24.8
mag arcsec sq), possibly indicating a similarity in the types of triggering
interactions.
The range of features detected in the type II quasars suggests that AGN
activity can be triggered before, during or after the coalescence of the black
holes. Overall, our results are consistent with the idea that galaxy
interaction plays an important role in the triggering of quasar activity. | Suzaku Studies of Wide-Band Spectral Variability of the Bright Type I
Seyfert Galaxy Markarian 509: The Type I Seyfert galaxy Markarian 509 was observed with Suzaku in 2010
November, for a gross time span of 2.2 days. Timing and spectral properties of
the 0.5-45 keV X-rays, detected with the XIS and HXD, consistently revealed the
presence of a soft spectral component that remained constant while the total X-
ray intensity varied by \pm10%. This stable soft component, found in the
0.5-3.0 keV range, was interpreted as a result of thermal Comptonization in a
corona with a temperature of ~ 0.5 keV and an optical depth of ~ 18. The
time-avearged 0.5-45 keV Suzaku spectrum was reproduced successfully, as a
combination of this thermal Comptonization component, a harder power-law of
photon index ~ 1.8, moderate reflection, and an iron K-emission line. By
analyzing four archival Suzaku datasets of the same object obtained in 2006,
the thermal Comptonization component, which was stable during the 2.2 day
pointing in 2010, was found to vary on time scales of a few weeks,
independently of the power-law component. Implications of these results are
discussed in terms of the "multi-zone Comptonization" view, obtained with
Suzaku from the black hole binary Cygnus X-1. |
A perfect power-law spectrum even at highest frequencies: The Toothbrush
relic: Radio relics trace shock fronts generated in the intracluster medium (ICM)
during cluster mergers. The particle acceleration mechanism at the shock fronts
is not yet completely understood. We observed the Toothbrush relic with the
Effelsberg and Sardinia Radio Telescope at 14.25 GHz and 18.6 GHz,
respectively. Unlike previously claimed, the integrated spectrum of the relic
closely follows a power law over almost three orders of magnitude in frequency,
with a spectral index of $\alpha_{\rm 58\,MHz}^{\rm 18.6\,GHz}=-1.16\pm0.03$.
Our finding is consistent with a power-law injection spectrum, as predicted by
diffusive shock acceleration theory. The result suggests that there is only
little magnetic field strength evolution downstream to the shock. From the lack
of spectral steepening, we find that either the Sunyaev-Zeldovich decrement
produced by the pressure jump is less extended than $\sim$ 600\,kpc along the
line of sight or, conversely, that the relic is located far behind in the
cluster. For the first time, we detect linearly polarized emission from the
"brush" at 18.6 GHz. Compared to 8.3 GHz, the degree of polarization across the
brush increases at 18.6 GHz, suggesting a strong Faraday depolarization towards
lower frequencies. The observed depolarization is consistent with an
intervening magnetized screen that arise from the dense ICM containing
turbulent magnetic fields. The depolarization, corresponding to a standard
deviation of the Rotation Measures as high as $\sigma_{\rm RM}= 212\pm23\rm
\,rad\,m^{-2}$, suggests that the brush is located in or behind the ICM. Our
findings indicate that the Toothbrush can be consistently explained by the
standard scenario for relic formation | Why reducing the cosmic sound horizon alone can not fully resolve the
Hubble tension: The mismatch between the locally measured expansion rate of the universe and
the one inferred from the cosmic microwave background measurements by Planck in
the context of the standard $\Lambda$CDM, known as the Hubble tension, has
become one of the most pressing problems in cosmology. A large number of
amendments to the $\Lambda$CDM model have been proposed in order to solve this
tension. Many of them introduce new physics, such as early dark energy,
modifications of the standard model neutrino sector, extra radiation,
primordial magnetic fields or varying fundamental constants, with the aim of
reducing the sound horizon at recombination $r_{\star}$. We demonstrate here
that any model which only reduces $r_{\star}$ can never fully resolve the
Hubble tension while remaining consistent with other cosmological datasets. We
show explicitly that models which achieve a higher Hubble constant with lower
values of matter density $\Omega_m h^2$ run into tension with the observations
of baryon acoustic oscillations, while models with larger $\Omega_mh^2$ develop
tension with galaxy weak lensing data. |
Subaru weak-lensing study of A2163: bimodal mass structure: We present a weak-lensing analysis of the merging cluster A2163 using
Subaru/Suprime-Cam and CFHT/Mega-Cam data and discuss the dynamics of this
cluster merger, based on complementary weak-lensing, X-ray, and optical
spectroscopic datasets. From two dimensional multi-component weak-lensing
analysis, we reveal that the cluster mass distribution is well described by
three main components, including a two component main cluster A2163-A with mass
ratio 1:8, and its cluster satellite A2163-B. The bimodal mass distribution in
A2163-A is similar to the galaxy density distribution, but appears as spatially
segregated from the brightest X-ray emitting gas region. We discuss the
possible origins of this gas-dark matter offset and suggest the gas core of the
A2163-A subcluster has been stripped away by ram pressure from its dark matter
component. The survival of this gas core to the tidal forces exerted by the
main cluster let us infer a subcluster accretion with a non-zero impact
parameter. Dominated by the most massive component of A2163-A, the mass
distribution of A2163 is well described by a universal Navarro-Frenk-White
profile as shown by a one-dimensional tangential shear analysis, while the
singular-isothermal sphere profile is strongly ruled out. Comparing this
cluster mass profile with profiles derived assuming intracluster medium
hydrostatic equilibrium (H.E.) in two opposite regions of the cluster
atmosphere has allowed us to confirm the prediction of a departure from H.E. in
the eastern cluster side, presumably due to shock heating. Yielding a cluster
mass estimate of M_{500}=11.18_{-1.46}^{+1.64}\times10^{14}h^{-1}Msun, our mass
profile confirm the exceptionally high mass of A2163, consistent with previous
analyses relying on the cluster dynamical analysis and Yx mass proxy. | TeVeS/MOND is in harmony with gravitational redshifts in galaxy clusters: Wojtak, Hansen and Hjorth have recently claimed to confirm general relativity
and to rule out the tensor-vector-scalar (TeVeS) gravitational theory based on
an analysis of the gravitational redshifts of galaxies in 7800 clusters. But
their ubiquitous modeling of the sources of cluster gravitational fields with
Navarro-Frenk-White mass profiles is neither empirically justified out to the
necessary radii in clusters, nor germane in the case of TeVeS. Using MONDian
isothermal sphere models consistently constructed within MOND (equivalent to
TeVeS models), we can fit the determined redshifts no worse than does general
relativity with dark halos. Wojtak, Hansen and Hjorth's work is further marred
by confusion between the primitive mu-function of TeVeS and the MOND
interpolation function. |
Inconsistency of an inflationary sector coupled only to Einstein gravity: From a model-building perspective, the inflationary sector might very well
have no direct couplings to other species, apart from inevitable gravitational
interactions. Within the context of General Relativity, a thermal universe can
still emerge after inflation if: $i)$ some radiation sector is excited towards
the end of inflation, and $ii)$ the post-inflationary equation of state becomes
sufficiently stiff $w \geq w_{\rm RD}\gtrsim 0.57$, with $w_{\rm RD}$ a
threshold depending on the inflationary scale $H_*$ and the initial
radiation-to-inflaton energy ratio $\Delta_*$. Furthermore, a stiff period in
the expansion history enhances significantly the inflationary gravitational
wave (GW) background, making this signal (potentially) observable by aLIGO,
LISA and other experiments. The very same enhancement leads however to an
inconsistency of the scenario: the energy of the GWs becomes too large compared
to the rest of the radiation sector, violating standard BBN and CMB bounds on
GW backgrounds. Except for very special scenarios where the initial radiation
sector comprises hundreds of fields with couplings tuned to specific values,
our result applies independently of $w$, $H_*$ and $\Delta_*$. This suggests
that in order to reheat the universe, the inflationary sector should be coupled
directly to other particle species. Alternatively the inflationary sector could
be implemented in modified gravity theories. | Large-scale structures in the $Λ$CDM Universe: network analysis
and machine learning: We perform an analysis of the Cosmic Web as a complex network, which is built
on a $\Lambda$CDM cosmological simulation. For each of nodes, which are in this
case dark matter halos formed in the simulation, we compute 10 network metrics,
which characterize the role and position of a node in the network. The relation
of these metrics to topological affiliation of the halo, i.e. to the type of
large scale structure, which it belongs to, is then investigated. In
particular, the correlation coefficients between network metrics and topology
classes are computed. We have applied different machine learning methods to
test the predictive power of obtained network metrics and to check if one could
use network analysis as a tool for establishing topology of the large scale
structure of the Universe. Results of such predictions, combined in the
confusion matrix, show that it is not possible to give a good prediction of the
topology of Cosmic Web (score is $\approx$ 70 $\%$ in average) based only on
coordinates and velocities of nodes (halos), yet network metrics can give a
hint about the topological landscape of matter distribution. |
Cosmology with interaction in the dark sector: Unless some unknown symmetry in Nature prevents or suppresses a non-minimal
coupling in the dark sector, the dark energy field may interact with the
pressureless component of dark matter. In this paper, we investigate some
cosmological consequences of a general model of interacting dark matter-dark
energy characterized by a dimensionless parameter $\epsilon$. We derive a
coupled scalar field version for this general class of scenarios and carry out
a joint statistical analysis involving SNe Ia data ({Legacy} and {Constitution}
sets), measurements of baryon acoustic oscillation peak at $z = 0.20$ (2dFGRS)
and $z = 0.35$ (SDSS), and measurements of the Hubble evolution $H(z)$. For the
specific case of vacuum decay ($w = -1$), we find that, although physically
forbidden, a transfer of energy from dark matter to dark energy is favored by
the data. | Effect of asphericity in caustic mass estimates of galaxy clusters: The caustic technique for measuring mass profiles of galaxy clusters relies
on the assumption of spherical symmetry. When applied to aspherical galaxy
clusters, the method yields mass estimates affected by the cluster orientation.
Here we employ mock redshift catalogues generated from cosmological simulations
to study the effect of clusters intrinsic shape and surrounding filamentary
structures on the caustic mass estimates. To this end, we develop a new method
for removing perturbations from large-scale structures, modelled as the
two-halo term, in a caustic analysis of stacked cluster data.
We find that the cluster masses inferred from kinematical data of ~10^14 Msun
clusters observed along the major axis are larger than masses from those
observed along the minor axis by a factor of 1.7 within the virial radius,
increasing to 1.8 within three virial radii. This discrepancy increases by 20%
for the most massive clusters. In addition a smaller but still significant mass
discrepancy arises when filamentary structures are present near a galaxy
cluster.
We find that the mean cluster mass from random sightlines is unbiased at all
radii and their scatter ranges from 0.14 to 0.17 within one and three virial
radii, with a 40% increase for the most massive clusters. We provide tables
which estimate the caustic mass bias given observational constraints on the
cluster orientation. |
The Globular Cluster/Central Black Hole Connection in Galaxies: We explore the relation between the total globular cluster population in a
galaxy (N_GC) and the the mass of its central black hole (M_BH). Using a sample
of 33 galaxies, twice as large as the original sample discussed by Burkert &
Tremaine (2010), we find that N_GC for elliptical and spiral galaxies increases
in almost precisely direct proportion to M_BH. The S0-type galaxies by contrast
do not follow a clear trend, showing large scatter in M_BH at a given N_GC.
After accounting for observational measurement uncertainty, we find that the
mean relation defined by the E and S galaxies must also have an intrinsic or
"cosmic" scatter of +-0.2 in either logN_GC or logM_BH. The residuals from this
correlation show no trend with globular cluster specific frequency. We suggest
that these two types of galaxy subsystems (central black hole and globular
cluster system) may be closely correlated because they both originated at high
redshift during the main epoch of hierarchical merging, and both require
extremely high-density conditions for formation. Lastly, we note that roughly
10% of the galaxies in our sample (one E, one S, and two S0) deviate strongly
from the main trend, all in the sense that their M_BH is at least 10x smaller
than would be predicted by the mean relation. | Self-Interacting Dark Matter from Gravitational Scattering: I show that gravitational scattering of dark-matter objects of 10^4 solar
masses and speeds of 10 km/s, provides the cross-section per unit mass required
in self-interacting dark matter models that alleviate the small-scale structure
challenges to the collisionless cold dark matter model. For primordial objects
of mass 10^4*(M_4) solar masses, moving at the velocity dispersion
characteristic of dwarf galaxies, 10*(v_1) km/s, the cross-section per unit
mass for gravitational scattering is 10*[M_4/(v_1)^4] cm^2/g. The steep decline
in interaction with increasing velocity explains why self-interaction is not
evident in data on massive galaxies and clusters of galaxies. |
Brans-Dicke gravity with a cosmological constant smoothes out
$Λ$CDM tensions: We analyze Brans-Dicke gravity with a cosmological constant, $\Lambda$, and
cold dark matter (BD-$\Lambda$CDM for short) in the light of the latest
cosmological observations on distant supernovae, Hubble rate measurements at
different redshifts, baryonic acoustic oscillations, large scale structure
formation data, gravitational weak-lensing and the cosmic microwave background
under full Planck 2015 CMB likelihood. Our analysis includes both the
background and perturbations equations. We find that BD-$\Lambda$CDM is
observationally favored as compared to the concordance $\Lambda$CDM model,
which is traditionally defined within General Relativity (GR). In particular,
some well-known persisting tensions of the $\Lambda$CDM with the data, such as
the excess in the mass fluctuation amplitude $\sigma_8$ and specially the acute
$H_0$-tension with the local measurements, essentially disappear in this
context. Furthermore, viewed from the GR standpoint, BD-$\Lambda$CDM cosmology
mimics quintessence at $\gtrsim3\sigma$ c.l. near our time. | Analytic Photometric Redshift Estimator for Type Ia Supernovae From the
Large Synoptic Survey Telescope: Accurate and precise photometric redshifts (photo-z's) of Type Ia supernovae
(SNe Ia) can enable the use of SNe Ia, measured only with photometry, to probe
cosmology. This dramatically increases the science return of supernova surveys
planned for the Large Synoptic Survey Telescope (LSST). In this paper we
describe a significantly improved version of the simple analytic photo-z
estimator proposed by Wang (2007) and further developed by Wang, Narayan, and
Wood-Vasey (2007). We apply it to 55,422 simulated SNe Ia generated using the
SNANA package with the LSST filters. We find that the estimated errors on the
photo-z's, \sigma_{z_{phot}}/(1+z_{phot}), can be used as filters to produce a
set of photo-z's that have high precision, accuracy, and purity. Using SN Ia
colors as well as SN Ia peak magnitude in the i band, we obtain a set of
photo-z's with 2 percent accuracy (with \sigma(z_{phot}-z_{spec})/(1+z_{spec})
= 0.02), a bias in z_{phot} (the mean of z_{phot}-z_{spec}) of -9 X 10^{-5},
and an outlier fraction (with |(z_{phot}-z_{spec})/(1+z_{spec})|>0.1) of 0.23
percent, with the requirement that \sigma_{z_{phot}}/(1+z_{phot})<0.01. Using
the SN Ia colors only, we obtain a set of photo-z's with similar quality by
requiring that \sigma_{z_{phot}}/(1+z_{phot})<0.007; this leads to a set of
photo-z's with 2 percent accuracy, a bias in z_{phot} of 5.9 X 10^{-4}, and an
outlier fraction of 0.32 percent. |
Merger rates of dark matter haloes from merger trees in the extended
Press-Schechter theory: We construct merger trees based on the extended Press-Schechter theory (EPS)
in order to study the merger rates of dark matter haloes over a range of
present day mass ($10^{10}M_{\sun}\leq M_0 \leq10^{15}M_{\sun}$), progenitor
mass $(5\times10^{-3}\leq \xi \leq1$) and redshift ($0\leq z\leq 3$). We used
the first crossing distribution of a moving barrier of the form
$B(S,z)=p(z)+q(z)S^{\gamma}$, proposed by Sheth & Tormen, to take into account
the ellipsoidal nature of collapse. We find that the mean merger rate per halo
$B_m/n$ depends on the halo mass $M$ as $M^{0.2}$ and on the redshift as
$(\mathrm{d}\delta_c(z)/\mathrm{d}z)^{1.1}$. Our results are in agreement with
the predictions of N-body simulations and this shows the ability of
merger-trees based on EPS theory to follow with a satisfactory agreement the
results of N-body simulations and the evolution of structures in a hierarchical
Universe. | Decaying Vacuum Cosmology and its Scalar Field Description: We discuss the cosmological consequences of an interacting model in the dark
sector in which the $\Lambda$ component evolves as a truncated power series of
the Hubble parameter. In order to constrain the free parameters of the model we
carry out a joint statistical analysis involving observational data from
current type Ia supernovae, recent estimates of the cosmic microwave background
shift parameter and baryon acoustic oscillations measurements. Finally, we
adopt a theoretical method to derive the coupled scalar field version for this
non-equilibrium decaying vacuum accelerating cosmology. |
The Clustering of the SDSS DR7 Main Galaxy Sample I: A 4 per cent
Distance Measure at z=0.15: We create a sample of spectroscopically identified galaxies with $z < 0.2$
from the Sloan Digital Sky Survey (SDSS) Data Release 7, covering 6813 deg$^2$.
Galaxies are chosen to sample the highest mass haloes, with an effective bias
of 1.5, allowing us to construct 1000 mock galaxy catalogs (described in Paper
II), which we use to estimate statistical errors and test our methods. We use
an estimate of the gravitational potential to "reconstruct" the linear density
fluctuations, enhancing the Baryon Acoustic Oscillation (BAO) signal in the
measured correlation function and power spectrum. Fitting to these
measurements, we determine $D_{V}(z_{\rm eff}=0.15) = (664\pm25)(r_d/r_{d,{\rm
fid}})$ Mpc; this is a better than 4 per cent distance measurement. This "fills
the gap" in BAO distance ladder between previously measured local and higher
redshift measurements, and affords significant improvement in constraining the
properties of dark energy. Combining our measurement with other BAO
measurements from BOSS and 6dFGS galaxy samples provides a 15 per cent
improvement in the determination of the equation of state of dark energy and
the value of the Hubble parameter at $z=0$ ($H_0$). Our measurement is fully
consistent with the Planck results and the $\Lambda$CDM concordance cosmology,
but increases the tension between Planck$+$BAO $H_0$ determinations and direct
$H_0$ measurements. | Dark Energy Survey Year 3 Results: High-precision measurement and
modeling of galaxy-galaxy lensing: We present and characterize the galaxy-galaxy lensing signal measured using
the first three years of data from the Dark Energy Survey (DES Y3) covering
4132 deg$^2$. These galaxy-galaxy measurements are used in the DES Y3
3$\times$2pt cosmological analysis, which combines weak lensing and galaxy
clustering information. We use two lens samples: a magnitude-limited sample and
the redMaGic sample, which span the redshift range $\sim 0.2-1$ with 10.7 M and
2.6 M galaxies respectively. For the source catalog, we use the Metacalibration
shape sample, consisting of $\simeq$100 M galaxies separated into 4 tomographic
bins. Our galaxy-galaxy lensing estimator is the mean tangential shear, for
which we obtain a total S/N of $\sim$148 for MagLim ($\sim$120 for redMaGic),
and $\sim$67 ($\sim$55) after applying the scale cuts of 6 Mpc/$h$. Thus we
reach percent-level statistical precision, which requires that our modeling and
systematic-error control be of comparable accuracy. The tangential shear model
used in the 3$\times$2pt cosmological analysis includes lens magnification, a
five-parameter intrinsic alignment model (TATT), marginalization over a
point-mass to remove information from small scales and a linear galaxy bias
model validated with higher-order terms. We explore the impact of these choices
on the tangential shear observable and study the significance of effects not
included in our model, such as reduced shear, source magnification and source
clustering. We also test the robustness of our measurements to various
observational and systematics effects, such as the impact of observing
conditions, lens-source clustering, random-point subtraction, scale-dependent
Metacalibration responses, PSF residuals, and B-modes. |
Effect of Neutrinos on Angular Momentum of Dark Matter Halo: Massive neutrinos are expected to affect the large-scale structure formation,
including the major component of solid substances, dark matter halos. How halos
are influenced by neutrinos is vital and interesting, and angular momentum (AM)
as a significant feature provides a statistical perspective for this issue.
Exploring halos from TianNu N-body cosmological simulation with the co-evolving
neutrino particles, we obtain some concrete conclusions. First, by comparing
the same halos with and without neutrinos, in contrast to the neutrino-free
case, over 89.71\% of halos have smaller halo moduli, over 71.06\% have smaller
particle-mass-reduced (PMR) AM moduli, and over 95.44\% change their
orientations of less than $0.65^\circ$. Moreover, the relative variation of PMR
modulus is more visible for low-mass halos. Second, to explore the PMR moduli
of halos in dense or sparse areas, we divide the whole box into big cubes, and
search for halos within a small spherical cell in a single cube. From the
two-level divisions, we discover that in denser cubes, the variation of PMR
moduli with massive neutrinos decreases more significantly. This distinction
suggests that neutrinos exert heavier influence on halos' moduli in compact
regions. With massive neutrinos, most halos (86.60\%) have lower masses than
without neutrinos. | The Atacama Cosmology Telescope: Dynamical masses for 44 SZ-selected
galaxy clusters over 755 square degrees: We present galaxy velocity dispersions and dynamical mass estimates for 44
galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect by the Atacama
Cosmology Telescope. Dynamical masses for 18 clusters are reported here for the
first time. Using \Nbody\ simulations, we model the different observing
strategies used to measure the velocity dispersions and account for systematic
effects resulting from these strategies. We find that the galaxy velocity
distributions may be treated as isotropic, and that an aperture correction of
up to 7 per cent in the velocity dispersion is required if the spectroscopic
galaxy sample is sufficiently concentrated towards the cluster centre.
Accounting for the radial profile of the velocity dispersion in simulations
enables consistent dynamical mass estimates regardless of the observing
strategy. Cluster masses $M_{200}$ are in the range
$(1-15)\times10^{14}M_\odot$. Comparing with masses estimated from the SZ
distortion assuming a gas pressure profile derived from X-ray observations
gives a mean SZ-to-dynamical mass ratio of $1.10\pm0.13$, but there is an
additional 0.14 systematic uncertainty due to the unknown velocity bias; the
statistical uncertainty is dominated by the scatter in the mass-velocity
dispersion scaling relation. This ratio is consistent with previous
determinations at these mass scales. |
Properties of M31. II: A Cepheid disk sample derived from the first year
of PS1 PAndromeda data: We present a sample of Cepheid variable stars towards M31 based on the first
year of regular M31 observations of the PS1 survey in the r_P1 and i_P1
filters. We describe the selection procedure for Cepheid variable stars from
the overall variable source sample and develop an automatic classification
scheme using Fourier decomposition and the location of the instability strip.
We find 1440 fundamental mode (classical \delta) Cep stars, 126 Cepheids in the
first overtone mode, and 147 belonging to the Population II types. 296 Cepheids
could not be assigned to one of these classes and 354 Cepheids were found in
other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31
known so far and the full catalog is presented in this paper. We briefly
describe the properties of our sample in its spatial distribution throughout
the M31 galaxy, in its age properties, and we derive an apparent
period-luminosity relation (PLR) in our two bands. The Population I Cepheids
nicely follow the dust pattern of the M31 disk, whereas the 147 Type II
Cepheids are distributed throughout the halo of M31. We outline the time
evolution of the star formation in the major ring found previously and find an
age gradient. A comparison of our PLR to previous results indicates a curvature
term in the PLR. | The spectral variability of quasar SDSS J030639.57+000343.1: We compiled a sample of 60 quasars with spectroscopy on at least six epochs
from the Sloan Digital Sky Survey (SDSS) to study the variabilities of the
spectral shape, the continuum and the emission lines luminosity. In this paper,
we present the results of SDSS J030639.57+000343.1. We found a strong
anti-correlation between the continuum luminosity at $5100 \AA$ and the
spectral index, implying a bluer-when-brighter trend. The luminosity of the
broad $\rm H_\alpha$ line is proportion to the continuum luminosity at $5100
\AA$. Correspondingly, we did not find strong correlation between the
equivalent width of broad $\rm H\alpha$ and the continuum luminosity, i.e. no
baldwin effect of broad $\rm H\alpha$ in this source. |
Fitting Spectral Energy Distributions of AGN - A Markov Chain Monte
Carlo Approach: We present AGNfitter: a Markov Chain Monte Carlo algorithm developed to fit
the spectral energy distributions (SEDs) of active galactic nuclei (AGN) with
different physical models of AGN components. This code is well suited to
determine in a robust way multiple parameters and their uncertainties, which
quantify the physical processes responsible for the panchromatic nature of
active galaxies and quasars. We describe the technicalities of the code and
test its capabilities in the context of X-ray selected obscured AGN using
multiwavelength data from the XMM-COSMOS survey. | A detailed study of the bridge of excess X-ray emission between the
galaxy clusters Abell 2029 and Abell 2033: We examine Suzaku, XMM-Newton, and Chandra observations of the Abell
2029/2033 system to investigate the nature of a bridge of X-ray emission
joining the two galaxy clusters. By modelling the contributions from the
outskirts of the two clusters, and excluding the emission from the southern
infalling group and the background group LOS9, we find a significant excess of
X-ray emission between the two clusters at the level of 6.5-7.0$\sigma$,
depending on the choice of model, that cannot be explained by the overlap of
the clusters. This excess component to the surface brightness is consistent
with being emission from a filament with roughly 1.0 Mpc wide. The derived
emission measure for the gas associated with the filament yields an average gas
density of $3.7^{+1.0}_{-0.7} \times 10^{-5}$ cm$^{-3}$, corresponding roughly
to 160 times the mean baryon density of the Universe. The Suzaku X-ray spectrum
of the excess emission indicates that it is significantly colder
($1.4_{-0.5}^{+0.7}$ keV) than the cluster outskirts emission from the two
clusters ($\sim$ 5 keV), statistically consistent with the temperature expected
from the hottest and densest parts of the warm-hot intergalactic medium (WHIM).
The geometry, density, and temperature are similar to those found from X-ray
studies of the Abell 222/223 filament. |
On the Source of the Dust Extinction in Type Ia Supernovae and the
Discovery of Anomalously Strong Na I Absorption: High-dispersion observations of the Na I D 5890, 5896 and K I 7665, 7699
interstellar lines, and the diffuse interstellar band at 5780 Angstroms in the
spectra of 32 Type Ia supernovae are used as an independent means of probing
dust extinction. We show that the dust extinction of the objects where the
diffuse interstellar band at 5780 Angstroms is detected is consistent with the
visual extinction derived from the supernova colors. This strongly suggests
that the dust producing the extinction is predominantly located in the
interstellar medium of the host galaxies and not in circumstellar material
associated with the progenitor system. One quarter of the supernovae display
anomalously large Na I column densities in comparison to the amount of dust
extinction derived from their colors. Remarkably, all of the cases of unusually
strong Na I D absorption correspond to "Blueshifted" profiles in the
classification scheme of Sternberg et al. (2011). This coincidence suggests
that outflowing circumstellar gas is responsible for at least some of the cases
of anomalously large Na I column densities. Two supernovae with unusually
strong Na I D absorption showed essentially normal K I column densities for the
dust extinction implied by their colors, but this does not appear to be a
universal characteristic. Overall, we find the most accurate predictor of
individual supernova extinction to be the equivalent width of the diffuse
interstellar band at 5780 Angstroms, and provide an empirical relation for its
use. Finally, we identify ways of producing significant enhancements of the Na
abundance of circumstellar material in both the single-degenerate and
double-degenerate scenarios for the progenitor system. | Impact of cosmological signatures in two-point statistics beyond the
linear regime: Some beyond $\Lambda$CDM cosmological models have dark-sector energy
densities that suffer phase transitions. Fluctuations entering the horizon
during such a transition can receive enhancements that ultimately show up as a
distinctive bump in the power spectrum relative to a model with no phase
transition. In this work, we study the non-linear evolution of such signatures
in the matter power spectrum and correlation function using N-body simulations,
perturbation theory and HMcode - a halo-model based method. We focus on
modelling the response, computed as the ratio of statistics between a model
containing a bump and one without it, rather than in the statistics themselves.
Instead of working with a specific theoretical model, we inject a parametric
family of Gaussian bumps into otherwise standard $\Lambda$CDM spectra. We find
that even when the primordial bump is located at linear scales, non-linearities
tend to produce a second bump at smaller scales. This effect is understood
within the halo model due to a more efficient halo formation. In redshift space
these nonlinear signatures are partially erased because of the damping along
the line-of-sight direction produced by non-coherent motions of particles at
small scales. In configuration space, the bump modulates the correlation
function reflecting as oscillations in the response, as it is clear in linear
Eulerian theory; however, they become damped because large scale coherent flows
have some tendency to occupy regions more depleted of particles. This mechanism
is explained within Lagrangian Perturbation Theory and well captured by our
simulations. |
Small field models with gravitational wave signature supported by CMB
data: We study scale dependence of the cosmic microwave background (CMB) power
spectrum in a class of small, single-field models of inflation which lead to a
high value of the tensor to scalar ratio. The inflaton potentials that we
consider are degree 5 polynomials, for which we precisely calculate the power
spectrum, and extract the cosmological parameters: the scalar index $n_s$, the
running of the scalar index $n_{\mathrm{run}}$ and the tensor to scalar ratio
$r$. We find that for non-vanishing $n_{\mathrm{run}}$ and for $r$ as small as
$r=0.001$, the precisely calculated values of $n_s$ and $n_{\mathrm{run}}$
deviate significantly from what the standard analytic treatment predicts. We
study in detail, and discuss the probable reasons for such deviations. As such,
all previously considered models (of this kind) are based upon inaccurate
assumptions. We scan the possible values of potential parameters for which the
cosmological parameters are within the allowed range by observations. The 5
parameter class is able to reproduce all of the allowed values of $n_s$ and
$n_{\mathrm{run}}$ for values of $r$ that are as high as 0.001. Subsequently
this study at once refutes previous such models built using the analytical
Stewart-Lyth term, and revives the small field brand, by building models that
do yield an appreciable $r$ while conforming to known CMB observables. | On the prior dependence of constraints on the tensor-to-scalar ratio: We investigate the prior dependence of constraints on cosmic tensor
perturbations. Commonly imposed is the strong prior of the single-field
inflationary consistency equation, relating the tensor spectral index nT to the
tensor-to-scalar ratio r. Dropping it leads to significantly different
constraints on nT, with both positive and negative values allowed with
comparable likelihood, and substantially increases the upper limit on r on
scales k = 0.01 Mpc^-1 to 0.05 Mpc^-1, by a factor of ten or more. Even if the
consistency equation is adopted, a uniform prior on r on one scale does not
correspond to a uniform one on another; constraints therefore depend on the
pivot scale chosen. We assess the size of this effect and determine the optimal
scale for constraining the tensor amplitude, both with and without the
consistency relation. |
Angular dependence of primordial trispectra and CMB spectral distortions: Under the presence of anisotropic sources in the inflationary era, the
trispectrum of the primordial curvature perturbation has a very specific
angular dependence between each wavevector that is distinguishable from the one
encountered when only scalar fields are present, characterized by an angular
dependence described by Legendre polynomials. We examine the imprints left by
curvature trispectra on the $TT\mu$ bispectrum, generated by the correlation
between temperature anisotropies (T) and chemical potential spectral
distortions ($\mu$) of the Cosmic Microwave Background (CMB). Due to the
angular dependence of the primordial signal, the corresponding $TT\mu$
bispectrum strongly differs in shape from $TT\mu$ sourced by the usual $g_{\rm
NL}$ or $\tau_{\rm NL}$ local trispectra, enabling us to obtain an unbiased
estimation. From a Fisher matrix analysis, we find that, in a
cosmic-variance-limited (CVL) survey of $TT\mu$, a minimum detectable value of
the quadrupolar Legendre coefficient is $d_2 \sim 0.01$, which is 4 orders of
magnitude better than the best value attainable from the $TTTT$ CMB
trispectrum. In the case of an anisotropic inflationary model with a
$f(\phi)F^2$ interaction (coupling the inflaton field $\phi$ with a vector
kinetic term $F^2$), the size of the curvature trispectrum is related to that
of quadrupolar power spectrum asymmetry, $g_*$. In this case, a CVL measurement
of $TT\mu$ makes it possible to measure $g_*$ down to $10^{-3}$. | Black hole foraging: feedback drives feeding: We suggest a new picture of supermassive black hole (SMBH) growth in galaxy
centers. Momentum-driven feedback from an accreting hole gives significant
orbital energy but little angular momentum to the surrounding gas. Once central
accretion drops, the feedback weakens and swept-up gas falls back towards the
SMBH on near-parabolic orbits. These intersect near the black hole with
partially opposed specific angular momenta, causing further infall and
ultimately the formation of a small-scale accretion disk. The feeding rates
into the disk typically exceed Eddington by factors of a few, growing the hole
on the Salpeter timescale and stimulating further feedback. Natural
consequences of this picture include (i) the formation and maintenance of a
roughly toroidal distribution of obscuring matter near the hole; (ii) random
orientations of successive accretion disk episodes; (iii) the possibility of
rapid SMBH growth; (iv) tidal disruption of stars and close binaries formed
from infalling gas, resulting in visible flares and ejection of hypervelocity
stars; (v) super-solar abundances of the matter accreting on to the SMBH; and
(vi) a lower central dark-matter density, and hence annihilation signal, than
adiabatic SMBH growth implies. We also suggest a simple sub-grid recipe for
implementing this process in numerical simulations. |
Arbitrarily coupled $p-$forms in cosmological backgrounds: In this paper we consider a model based on interacting $p-$forms and explore
some cosmological applications. Restricting to gauge invariant actions, we
build a general Lagrangian allowing for arbitrary interactions between the
$p-$forms (including interactions with a $0-$form, scalar field) in a given
background in $D$ dimensions. For simplicity, we restrict the construction to
up to first order derivatives of the fields in the Lagrangian. We discuss with
detail the four dimensional case and devote some attention to the mechanism of
topological mass generation originated by couplings of the form $B\wedge F$
between a $p-$form and a $(3-p)-$form. As a result, we show the system of the
interacting $p-$forms $(p=1,2,3)$ is equivalent to a parity violating, massive,
Proca vector field model. Finally, we discuss some cosmological applications.
In a first case we study a very minimalistic system composed by a $3-$form
coupled to a $0-$form. The $3-$form induces an effective potential which acts
as a cosmological constant term suitable to drive the late time accelerated
expansion of the universe dominated by dark energy. We study the dynamics of
the system and determine its critical points and stability. Additionally, we
study a system composed by a scalar field and a $1$-form. This case is
interesting because the presence of a coupled $1-$form can generate non
vanishing anisotropic signatures during the late time accelerated expansion. We
discuss the evolution of cosmological parameters such as the equation of state
in this model. | Deep Chandra X-ray Imaging of a Nearby Radio Galaxy 4C+29.30:
X-ray/Radio Connection: We report results from our deep Chandra X-ray observations of a nearby radio
galaxy, 4C+29.30 (z=0.0647). The Chandra image resolves structures on
sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting
the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus
is absorbed (N(H)=3.95 (+0.27/-0.33)x10^23 atoms/cm^2) with an unabsorbed
luminosity of L(2-10 keV) ~ (5.08 +/-0.52) 10^43 erg/s characteristic of Type 2
AGN. Regions of soft (<2 keV) X-ray emission that trace the hot interstellar
medium (ISM) are correlated with radio structures along the main radio axis
indicating a strong relation between the two. The X-ray emission beyond the
radio source correlates with the morphology of optical line-emitting regions.
We measured the ISM temperature in several regions across the galaxy to be kT ~
0.5 with slightly higher temperatures (of a few keV) in the center and in the
vicinity of the radio hotspots. Assuming these regions were heated by weak
shocks driven by the expanding radio source, we estimated the corresponding
Mach number of 1.6 in the southern regions. The thermal pressure of the X-ray
emitting gas in the outermost regions suggest the hot ISM is slightly
under-pressured with respect to the cold optical-line emitting gas and
radio-emitting plasma, which both seem to be in a rough pressure equilibrium.
We conclude that 4C+29.30 displays a complex view of interactions between the
jet-driven radio outflow and host galaxy environment, signaling feedback
processes closely associated with the central active nucleus. |
Analytic expressions for the background evolution of massive neutrinos
and dark matter particles: We provide exact analytic expressions for the density, pressure, average
number density and pseudo-pressure for massive neutrinos and generic dark
matter particles, both fermions and bosons. We then focus on massive neutrinos
and we compare our analytic expressions with the numerical implementation in
the CLASS Boltzmann code. We find that our modifications including the exact
analytic expressions are in agreement to better than $10^{-4}\%$ with the
default CLASS implementation in the estimation of the CMB power spectrum; our
modifications do not have an impact on the performance of the code. We also
provide several specific limits of our expressions at the relativistic regime,
but also at late times for the neutrino equation of state. | Molecular gas in Tidal Dwarf Galaxies: Exploring the conditions for star
formation: Tidal Dwarf Galaxies (TDGs), produced from material expelled in galactic
interactions, are well--suited to test the laws of star formation (SF) due to
their simple structure, high metallicity -- making CO a reliable tracer of the
molecular gas content -- and recent SF. Here, we study the conditions for the
onset of SF and for the rate at which SF proceeds once above a threshold in a
small sample of TDGs. We use data for the gas (atomic and molecular) surface
density and SF rate per area to test the laws of SF found for spiral and dwarf
galaxies in this more extreme environment. We find in general a good agreement
with the Schmidt law found for the total gas and for the molecular gas but note
that higher resolution CO observations are necessary to clarify some possible
discrepancies. We find, down to a scale of $\sim$1 kpc, in general a good
agreement between the peaks of SF and of the molecular gas, but also find in
some objects surprisingly large quantities of molecular gas at places where no
SF is occuring. A high column density of molecular gas is therefore not a
sufficient condition for the onset of SF. We find that the kinematical
properties of the gas are also relevant: in two objects our observations showed
that SF only occured in regions with a narrow line width. |
Current constraints on deviations from General Relativity using binning
in redshift and scale: We constrain deviations from general relativity (GR) including both redshift
and scale dependencies in the modified gravity (MG) parameters. In particular,
we employ the under-used binning approach and compare the results to functional
forms. We use available datasets such as Cosmic Microwave Background (CMB) from
Planck 2018, Baryonic Acoustic Oscillations (BAO) and Redshift Space
Distortions (BAO/RSD) from the BOSS DR12, the 6DF Galaxy Survey, the SDSS DR7
Main Galaxy Sample, the correlation of Lyman-$\alpha$ forest absorption and
quasars from SDSS-DR14, Supernova Type Ia (SNe) from the Pantheon compilation,
and DES Y1 data. Moreover, in order to maximize the constraining power from
available datasets, we analyze MG models where we alternatively set some of the
MG parameters to their GR values and vary the others. Using functional forms,
we find an up to 3.5-$\sigma$ tension with GR in $\Sigma$ (while $\mu$ is
fixed) when using Planck+SNe+BAO+RSD; this goes away when lensing data is
included, i.e. CMB lensing and DES (CMBL+DES). Using different binning methods,
we find that a tension with GR above 2-$\sigma$ in the (high-z, high-k) bin is
persistent even when including CMBL+DES to Planck+SNe+BAO+RSD. Also, we find
another tension above 2-$\sigma$ in the (low-z, high-k) bin, but that can be
reduced with the addition of lensing data. Furthermore, we perform a model
comparison using the Deviance Information Criterion statistical tool and find
that the MG model ($\mu=1$, $\Sigma$) is weakly favored by the data compared to
$\Lambda$CDM, except when DES data is included. Another noteworthy result is
that we find that the binning methods do not agree with the widely-used
functional parameterization where the MG parameters are proportional to
$\Omega_{\text{DE}}(a)$, and this is clearly apparent in the high-z and high-k
regime where this parameterization underestimates the deviations from GR. | Gravitational wave signals and cosmological consequences of
gravitational reheating: Reheating after inflation can proceed even if the inflaton couples to
Standard Model (SM) particles only gravitationally. However, particle
production during the transition between de-Sitter expansion and a decelerating
Universe is rather inefficient and the necessity to recover the visible
Universe leads to a non-standard cosmological evolution initially dominated by
remnants of the inflaton field. We remain agnostic to the specific dynamics of
the inflaton field and discuss a generic scenario in which its remnants behave
as a perfect fluid with a general barotropic parameter $w$. Using CMB and BBN
constraints we derive the allowed range of inflationary scales. We also show
that this scenario results in a characteristic primordial Gravitational Wave
(GW) spectrum which gives hope for observation in upcoming runs of LIGO as well
as in other planned experiments. |
Early-type galaxies in the PEARS survey: Probing the stellar populations
at moderate redshift: Using HST/ACS slitless grism spectra from the PEARS program, we study the
stellar populations of morphologically selected early-type galaxies in the
GOODS North and South fields. The sample - extracted from a visual
classification of the (v2.0) HST/ACS images and restricted to redshifts z>0.4 -
comprises 228 galaxies (F775W<24 ABmag) out to z~1.3 over 320 arcmin2, with a
median redshift zM=0.75. This work significantly increases our previous sample
from the GRAPES survey in the HUDF (18 galaxies over ~11 arcmin2; Pasquali et
al. 2006b). The grism data allow us to separate the sample into `red' and
`blue' spectra, with the latter comprising 15% of the total. Three different
grids of models parameterising the star formation history are used to fit the
low-resolution spectra. Over the redshift range of the sample - corresponding
to a cosmic age between 5 and 10 Gyr - we find a strong correlation between
stellar mass and average age, whereas the **spread** of ages (defined by the
RMS of the distribution) is roughly ~1 Gyr and independent of stellar mass. The
best-fit parameters suggest it is formation epoch and not formation timescale,
that best correlates with mass in early-type galaxies. This result - along with
the recently observed lack of evolution of the number density of massive
galaxies - motivates the need for a channel of (massive) galaxy formation
bypassing any phase in the blue cloud, as suggested by the simulations of Dekel
et al. (2009). | Featuring the primordial power spectrum: new constraints on interrupted
slow-roll from CMB and LRG data: Using the most recent data from the WMAP, ACT and SPT experiments, we update
the constraints on models with oscillatory features in the primordial power
spectrum of scalar perturbations. This kind of features can appear in models of
inflation where slow-roll is interrupted, like multifield models. We also
derive constraints for the case in which, in addition to cosmic microwave
observations, we also consider the data on the spectrum of luminous red
galaxies from the 7th SDSS catalog, and the SNIa Union Compilation 2 data. We
have found that: (i) considering a model with features in the primordial power
spectrum increases the agreement with data with the respect of the featureless
"vanilla" LCDM model by Delta(chi^2) ~ 7; (ii) the uncertainty on the
determination of the standard parameters is not degraded when features are
included; (iii) the best fit for the features model locates the step in the
primordial spectrum at a scale k ~ 0.005 Mpc^-1, corresponding to the scale
where the outliers in the WMAP7 data at ell=22 and ell=40 are located.; (iv) a
distinct, albeit less statistically significant peak is present in the
likelihood at smaller scales, with a Delta(chi^2) ~ 3.5, whose presence might
be related to the WMAP7 preference for a negative value of the running of the
scalar spectral index parameter; (v) the inclusion of the LRG-7 data do not
change significantly the best fit model, but allows to better constrain the
amplitude of the oscillations. |
Decaying Holographic Dark Energy and Emergence of Friedmann Universe: A universe started in almost de Sitter phase with time varying holographic
dark energy corresponding to a time varying cosmological term is considered.
The time varying cosmological dark energy and the created matter are consistent
with the Einstein's equation. The general conservation law for decaying dark
energy and created matter is stated. By asuming that the initial matter were
crated in relativistic form, we have analysed the possibility of evolving the
universe from de Sitter phase to Friedmann universe. | Radio selection of the most distant galaxy clusters: We show that the most distant X-ray detected cluster known to date, ClJ1001
at z=2.506, hosts a strong overdensity of radio sources. Six of them are
individually detected (within 10") in deep 0.75" resolution VLA 3GHz imaging,
with S(3GHz)>8uJy. Of the six, AGN likely affects the radio emission in two
galaxies while star formation is the dominant source powering the remaining
four. We searched for cluster candidates over the full COSMOS 2-square degree
field using radio-detected 3GHz sources and looking for peaks in Sigma5 density
maps. ClJ1001 is the strongest overdensity by far with >10sigma, with a simple
z_phot>1.5 preselection. A cruder photometric rejection of z<1 radio
foregrounds leaves ClJ1001 as the second strongest overdensity, while even
using all radio sources ClJ1001 remains among the four strongest projected
overdensities. We conclude that there are great prospects for future, deep and
wide-area radio surveys to discover large samples of the first generation of
forming galaxy clusters. In these remarkable structures widespread star
formation and AGN activity of massive galaxy cluster members, residing within
the inner cluster core, will ultimately lead to radio continuum as one of the
most effective means for their identification, with detection rates expected in
the ballpark of 0.1-1 per square degree at z>2.5. Samples of hundreds such
high-redshift clusters could potentially constrain cosmological parameters and
test cluster and galaxy formation models. |
Accurate halo-model matter power spectra with dark energy, massive
neutrinos and modified gravitational forces: We present an accurate non-linear matter power spectrum prediction scheme for
a variety of extensions to the standard cosmological paradigm, which uses the
tuned halo model previously developed in Mead (2015b). We consider dark energy
models that are both minimally and non-minimally coupled, massive neutrinos and
modified gravitational forces with chameleon and Vainshtein screening
mechanisms. In all cases we compare halo-model power spectra to measurements
from high-resolution simulations. We show that the tuned halo model method can
predict the non-linear matter power spectrum measured from simulations of
parameterised $w(a)$ dark energy models at the few per cent level for
$k<10\,h\mathrm{Mpc}^{-1}$, and we present theoretically motivated extensions
to cover non-minimally coupled scalar fields, massive neutrinos and Vainshtein
screened modified gravity models that result in few per cent accurate power
spectra for $k<10\,h\mathrm{Mpc}^{-1}$. For chameleon screened models we
achieve only 10 per cent accuracy for the same range of scales. Finally, we use
our halo model to investigate degeneracies between different extensions to the
standard cosmological model, finding that the impact of baryonic feedback on
the non-linear matter power spectrum can be considered independently of
modified gravity or massive neutrino extensions. In contrast, considering the
impact of modified gravity and massive neutrinos independently results in
biased estimates of power at the level of 5 per cent at scales
$k>0.5\,h\mathrm{Mpc}^{-1}$. An updated version of our publicly available
HMcode can be found at https://github.com/alexander-mead/HMcode | The self similarity of weak lensing peaks: We study the statistics of weak lensing convergence peaks, such as their
abundance and two-point correlation function (2PCF), for a wide range of
cosmological parameters $\Omega_m$ and $\sigma_8$ within the standard
$\Lambda$CDM paradigm, focusing on intermediate-height peaks with
signal-to-noise ratio (SNR) of $1.5$ to $3.5$. We find that the cosmology
dependence of the peak abundance can be described by a one-parameter fitting
formula that is accurate to within $\sim3\%$. The peak 2PCFs are shown to
feature a self-similar behaviour: if the peak separation is rescaled by the
mean inter-peak distance, catalogues with different minimum peak SNR values
have identical clustering, which suggests that the peak abundance and
clustering are closely interconnected. A simple fitting model for the rescaled
2PCF is given, which together with the peak abundance model above can predict
peak 2PCFs with an accuracy better than $\sim5\%$. The abundance and 2PCFs for
intermediate peaks have very different dependencies on $\Omega_m$ and
$\sigma_8$, implying that their combination can be used to break the degeneracy
between these two parameters. |
ConKer: evaluating isotropic correlations of arbitrary order: High order correlations in the cosmic matter density have become increasingly
valuable in cosmological analyses. However, computing such correlation
functions is computationally expensive. We aim to circumvent these challenges
by designing a new method of estimating correlation functions. This is realized
in ConKer, an algorithm that performs FFT convolutions of matter distributions
with spherical kernels. ConKer is applied to the CMASS sample of the SDSS DR12
galaxy survey and used to compute the isotropic correlation up to correlation
order n = 5. We also compare the n = 2 and n = 3 cases to traditional
algorithms to verify the accuracy of the new method. We perform a timing study
of the algorithm and find that two of the three components of the algorithm are
independent of the catalog size, N, while one component is O(N), which starts
dominating for catalogs larger than 10M objects. For n < 5 the dominant
calculation is O(N^(4/3logN)), where N is the number of the grid cells. For
higher n, the execution time is expected to be dominated by a component with
time complexity O(N^((n+2)/3)). We find ConKer to be a fast and accurate method
of probing high order correlations in the cosmic matter density. | CMB Faraday rotation as seen through the Milky Way: Faraday Rotation (FR) of CMB polarization, as measured through mode-coupling
correlations of E and B modes, can be a promising probe of a stochastic
primordial magnetic field (PMF). While the existence of a PMF is still
hypothetical, there will certainly be a contribution to CMB FR from the
magnetic field of the Milky Way. We use existing estimates of the Milky Way
rotation measure (RM) to forecast its detectability with upcoming and future
CMB experiments. We find that the galactic RM will not be seen in polarization
measurements by Planck, but that it will need to be accounted for by CMB
experiments capable of detecting the weak lensing contribution to the B-mode.
We then discuss prospects for constraining the PMF in the presence of FR due to
the galaxy under various assumptions that include partial de-lensing and
partial subtraction of the galactic FR. We find that a realistic future
sub-orbital experiment, covering a patch of the sky near the galactic poles,
can detect a scale-invariant PMF of 0.1 nano-Gauss at better than 95%
confidence level, while a dedicated space-based experiment can detect even
smaller fields. |
Buzzard to Cardinal: Improved Mock Catalogs for Large Galaxy Surveys: We present the Cardinal mock galaxy catalogs, a new version of the Buzzard
simulation that has been updated to support ongoing and future cosmological
surveys, including DES, DESI, and LSST. These catalogs are based on a
one-quarter sky simulation populated with galaxies out to a redshift of
$z=2.35$ to a depth of $m_{\rm{r}}=27$. Compared to the Buzzard mocks, the
Cardinal mocks include an updated subhalo abundance matching (SHAM) model that
considers orphan galaxies and includes mass-dependent scatter between galaxy
luminosity and halo properties. This model can simultaneously fit galaxy
clustering and group--galaxy cross-correlations measured in three different
luminosity threshold samples. The Cardinal mocks also feature a new color
assignment model that can simultaneously fit color-dependent galaxy clustering
in three different luminosity bins. We have developed an algorithm that uses
photometric data to improve the color assignment model further and have also
developed a novel method to improve small-scale lensing below the ray-tracing
resolution. These improvements enable the Cardinal mocks to accurately
reproduce the abundance of galaxy clusters and the properties of lens galaxies
in the Dark Energy Survey data. As such, these simulations will be a valuable
tool for future cosmological analyses based on large sky surveys. The cardinal
mock will be released upon publication at https://chunhaoto.com/cardinalsim. | Optimal Time-Series Selection of Quasars: We present a novel method for the optimal selection of quasars using
time-series observations in a single photometric bandpass. Utilizing the damped
random walk model of Kelly et al. (2009), we parameterize the ensemble quasar
structure function in Sloan Stripe 82 as a function of observed brightness. The
ensemble model fit can then be evaluated rigorously for and calibrated with
individual light curves with no parameter fitting. This yields a classification
in two statistics --- one describing the fit confidence and one describing the
probability of a false alarm --- which can be tuned, a priori, to achieve high
quasar detection fractions (99% completeness with default cuts), given an
acceptable rate of false alarms. We establish the typical rate of false alarms
due to known variable stars as <3% (high purity). Applying the classification,
we increase the sample of potential quasars relative to those known in Stripe
82 by as much as 29%, and by nearly a factor of two in the redshift range
2.5<z<3, where selection by color is extremeley inefficient. This represents
1875 new quasars in a 290 deg^2 field. The observed rates of both quasars and
stars agree well with the model predictions, with >99% of quasars exhibiting
the expected variability profile. We discus the utility of the method at
high-redshift and in the regime of noisy and sparse data. Our time series
selection complements well independent selection based on quasar colors and has
strong potential for identifying high redshift quasars for BAO and other
cosmology studies in the LSST era. |
The Environments of Local Luminous Infrared Galaxies: Star Formation
Rates increase with Density: This work studies the environments and star formation relationships of local
luminous infrared galaxies (LIRG) in comparison to other types of local and
distant (z~1) galaxies. The infrared (IR) galaxies are drawn from the IRAS
sample. The density of the environment is quantified using 6dF and Point Source
Catalogue redshift survey (PSCz) galaxies in a cylinder of 2h^-1 Mpc radius and
10h^-1 Mpc length. Our most important result shows the existence of a dramatic
density difference between local LIRGs and local non-LIRG IR galaxies. LIRGs
live in denser environments than non-LIRG IR galaxies implying that L_IR=10^11
h^-2 L_sun marks an important transition point among IR-selected local
galaxies. We also find that there is a strong correlation between the densities
around LIRGs and their L_IR luminosity, while the IR-activity of non-LIRG IR
galaxies does not show any dependence on environment. This trend is independent
of mass-bin selection. The SF-density trend in local LIRGs is similar to that
found in some studies of blue cloud galaxies at z~1 which show a correlation
between star formation and local density (the reversal of the relation seen for
local galaxies). This, together with the rapid decline of the number count of
LIRGs since z~1, could mean that local LIRGs are survivors of whatever process
transformed blue cloud galaxies at z~1 to the present day or local LIRGs came
into existence by similar process than high redshift LIRGs but at later stage. | Hunting for Statistical Anisotropy in Tensor Modes with B-mode
Observations: We investigate a possibility of constraining statistical anisotropies of the
primordial tensor perturbations by using future observations for the Cosmic
Microwave Background (CMB) B-mode polarization. By parameterizing a
statistically-anisotropic tensor power spectrum as $P_h ({\boldsymbol{k}}) =
P_h (k) \sum_n g_n \cos^n \theta_{\boldsymbol{k}}$, where
$\theta_{\boldsymbol{k}}$ is an angle of the direction of
$\hat{k}={\boldsymbol{k}}/k$ from a preferred direction, we find that it would
be possible for future B-mode observations such as CMB-S4 to detect the tensor
statistical anisotropy at the level of $g_n \sim {\mathcal O} (0.1)$. |
Stellar structures in the outer regions of M33: We present Subaru/Suprime-Cam deep V and I imaging of seven fields in the
outer regions of M33. Our aim is to search for stellar structures corresponding
to extended HI clouds found in a recent 21-cm survey of the galaxy. Three
fields probe a large HI complex to the southeastern (SE) side of the galaxy. An
additional three fields cover the northwestern (NW) side of the galaxy along
the HI warp. A final target field was chosen further north, at a projected
distance of approximately 25 kpc, to study part of the large stellar plume
recently discovered around M33. We analyse the stellar population at R > 10 kpc
by means of V, I colour magnitude diagrams reaching the red clump. Evolved
stellar populations are found in all fields out to 120' (~ 30 kpc), while a
diffuse population of young stars (~ 200 Myr) is detected out to a
galactocentric radius of 15 kpc. The mean metallicity in the southern fields
remains approximately constant at [M/H] = -0.7 beyond the edge of the optical
disc, from 40' out to 80'. Along the northern fields probing the outer \hi
disc, we also find a metallicity of [M/H] = -0.7 between 35' and 70' from the
centre, which decreases to [M/H] = -1.0 at larger angular radii out to 120'. In
the northernmost field, outside the disc extent, the stellar population of the
large stellar feature possibly related to a M33-M31 interaction is on average
more metal-poor ([M/H] = -1.3) and older (> 6 Gyr). An exponential disc with a
large scale-length (~ 7 kpc) fits well the average distribution of stars
detected in both the SE and NW regions from a galactocentric distance of 11 kpc
out to 30 kpc. The stellar distribution at large radii is disturbed and,
although there is no clear correlation between the stellar substructures and
the location of the HI clouds, this gives evidence for tidal interaction or
accretion events. | A near-infrared morphological comparison of high-redshift submm and
radio galaxies: massive star-forming discs vs relaxed spheroids: We present deep, high-quality K-band images of complete subsamples of
powerful radio and sub-mm galaxies at z=2. The data were obtained in the best
available seeing at UKIRT and Gemini North, with integration times scaled to
ensure that comparable rest-frame surface brightness levels are reached for all
galaxies. We fit two-dimensional axi-symmetric galaxy models to determine
galaxy morphologies at rest-frame optical wavelengths > 4000A, varying
luminosity, axial ratio, half-light radius, and Sersic index. We find that,
while some images show evidence of galaxy interactions, >95% of the rest-frame
optical light in all galaxies is well-described by these simple models. We also
find a clear difference in morphology between these two classes of galaxy; fits
to the individual images and image stacks reveal that the radio galaxies are
moderately large (<r{1/2}>=8.4+-1.1kpc; median r{1/2}=7.8), de Vaucouleurs
spheroids (<n> = 4.07+-0.27; median n=3.87), while the sub-mm galaxies appear
to be moderately compact (<r{1/2}>=3.4+-0.3kpc; median r{1/2}=3.1kpc)
exponential discs (<n>=1.44+-0.16; median n=1.08). We show that the z=2 radio
galaxies display a well-defined Kormendy relation but that, while larger than
other recently-studied high-z massive galaxy populations, they are still ~1.5
times smaller than their local counterparts. The scalelengths of the starlight
in the sub-mm galaxies are comparable to those reported for the molecular gas.
Their sizes are also similar to those of comparably massive quiescent galaxies
at z>1.5. In terms of stellar mass surface density, the majority of the radio
galaxies lie within the locus defined by local ellipticals. In contrast, while
best modelled as discs, most of the sub-mm galaxies have higher stellar mass
densities than local galaxies, and appear destined to evolve into present-day
massive ellipticals. |
The First Massive Black Hole Seeds and Their Hosts: We investigate the formation of the first massive black holes in high
redshift galaxies, with the goal of providing insights to which galaxies do or
do not host massive black holes. We adopt a novel approach to forming seed
black holes in galaxy halos in cosmological SPH+N-body simulations. The
formation of massive black hole seeds is dictated directly by the local gas
density, temperature, and metallicity, and motivated by physical models of
massive black hole formation. We explore seed black hole populations as a
function of halo mass and redshift, and examine how varying the efficiency of
massive black hole seed formation affects the relationship between black holes
and their hosts. Seed black holes tend to form in halos with mass between 10^7
and 10^9 Msun, and the formation rate is suppressed around z = 5 due to the
diffusion of metals throughout the intergalactic medium. We find that the time
of massive black hole formation and the occupation fraction of black holes are
a function of the host halo mass. By z = 5, halos with mass M_halo > 3 x 10^9
Msun host massive black holes regardless of the efficiency of seed formation,
while the occupation fraction for smaller halos increases with black hole
formation efficiency. Our simulations explain why massive black holes are found
in some bulgeless and dwarf galaxies, but we also predict that their occurrence
becomes rarer and rarer in low-mass systems. | The environment-dependence of the growth of the most massive objects in
the Universe: This paper investigates the growth of the most massive cosmological objects.
We utilize the Simsilun simulation, which is based on the approximation of the
silent universe. In the limit of spatial homogeneity and isotropy the silent
universes reduce to the standard FLRW models. We show that within the
approximation of the silent universe the formation of the most massive
cosmological objects differs from the standard background-dependent approaches.
For objects with masses above $10^{15} M_\odot$ the effect of spatial curvature
(overdense regions are characterized by positive spatial curvature) leads to
measurable effects. The effect is analogous to the effect that the background
cosmological model has on the formation of these objects (i.e. the higher
matter density and spatial curvature the faster the growth of cosmic
structures). We measure this by the means of the mass function and show that
the mass function obtained from the Simsilun simulation has a higher amplitude
at the high-mass end compared to standard mass function such as the
Press-Schechter or the Tinker mass function. For comparison, we find that the
expected mass of most massive objects using the Tinker mass function is
$4.4^{+0.8}_{-0.6} \, \times 10^{15} M_\odot$, whereas for the Simsilun
simulation is $6.3^{+1.0}_{-0.8} \, \times 10^{15} M_\odot$. We conclude that
the nonlinear relativistic effects could affect the formation of the most
massive cosmological objects, leading to a relativistic environment-dependence
of the growth rate of the most massive clusters. |
Causality and Primordial Tensor Modes: We introduce the real space correlation function of $B$-mode polarization of
the cosmic microwave background (CMB) as a probe of superhorizon tensor
perturbations created by inflation. By causality, any non-inflationary
mechanism for gravitational wave production after reheating, like global phase
transitions or cosmic strings, must have vanishing correlations for angular
separations greater than the angle subtended by the particle horizon at
recombination, i.e. $\theta \gtrsim 2^\circ$. Since ordinary $B$-modes are
defined non-locally in terms of the Stokes parameters $Q$ and $U$ and therefore
don't have to respect causality, special care is taken to define `causal
$\tilde B$-modes' for the analysis. We compute the real space $\tilde B$-mode
correlation function for inflation and discuss its detectability on
superhorizon scales where it provides an unambiguous test of inflationary
gravitational waves. The correct identification of inflationary tensor modes is
crucial since it relates directly to the energy scale of inflation. Wrongly
associating tensor modes from causal seeds with inflation would imply an
incorrect inference of the energy scale of inflation. We find that the
superhorizon $\tilde B$-mode signal is above cosmic variance for the angular
range $2^\circ < \theta < 4^\circ$ and is therefore in principle detectable. In
practice, the signal will be challenging to measure since it requires
accurately resolving the recombination peak of the $B$-mode power spectrum.
However, a future CMB satellite (CMBPol), with noise level $\Delta_P \simeq
1\mu$K-arcmin and sufficient resolution to efficiently correct for
lensing-induced $B$-modes, should be able to detect the signal at more than
3$\sigma$ if the tensor-to-scalar ratio isn't smaller than $r \simeq 0.01$. | Comment on the article "Anisotropies in the astrophysical
gravitational-wave background: The impact of black hole distributions" by
A.C. Jenkins et al. [arXiv:1810.13435]: We investigate the discrepancy pointed out by Jenkins et al. in Ref. [1]
between the predictions of anisotropies of the astrophysical gravitational wave
(GW) background, derived using different methods in Cusin et al. [2] and in
Jenkins et al. [3]. We show that this discrepancy is not due to our treatment
of galaxy clustering, contrary to the claim made in Ref. [1] and we show that
our modeling of clustering gives results in very good agreement with
observations. Furthermore we show that the power law spectrum used in Refs. [1]
and [3] to describe galaxy clustering is incorrect on large scales and leads to
a different scaling of the multipoles $C_\ell$. Moreover, we also explain that
the analytic derivation of the gravitational wave background correlation
function in Refs. [1] and [3] is mathematically ill-defined and predicts an
amplitude of the angular power spectrum which depends on the (arbitrary) choice
of a non-physical cut-off. |
$f(R)$ gravity: scalar perturbations in the late Universe: In this paper we study scalar perturbations of the metric for nonlinear
$f(R)$ models. We consider the Universe at the late stage of its evolution and
deep inside the cell of uniformity. We investigate the astrophysical approach
in the case of Minkowski spacetime background and two cases in the cosmological
approach, the large scalaron mass approximation and the quasi-static
approximation, getting explicit expressions for scalar perturbations for both
these cases. In the most interesting quasi-static approximation, the scalar
perturbation functions depend on both the nonlinearity function $f(R)$ and the
scale factor $a$. Hence, we can study the dynamical behavior of the
inhomogeneities (e.g., galaxies and dwarf galaxies) including into
consideration their gravitational attraction and the cosmological expansion,
and also taking into account the effects of nonlinearity. Our investigation is
valid for functions $f(R)$ which have stable de Sitter points in future with
respect to the present time, that is typical for the most popular $f(R)$
models. | Observational constraints on interacting vacuum energy with linear
interactions: We explore the bounds that can be placed on interactions between cold dark
matter and vacuum energy, with equation of state $w=-1$, using state-of-the-art
cosmological observations. We consider linear perturbations about a simple
background model where the energy transfer per Hubble time, $Q/H$, is a general
linear function of the dark matter density, $\rho_c$, and vacuum energy, $V$.
We explain the parameter degeneracies found when fitting cosmic microwave
background (CMB) anisotropies alone, and show how these are broken by the
addition of supernovae data, baryon acoustic oscillations (BAO) and
redshift-space distortions (RSD). In particular, care must be taken when
relating redshift-space distortions to the growth of structure in the presence
of non-zero energy transfer. Interactions in the dark sector can alleviate the
tensions between low-redshift measurements of the Hubble parameter, $H_0$, or
weak-lensing, $S_8$, and the values inferred from CMB data. However these
tensions return when we include constraints from supernova and BAO-RSD
datasets. In the general linear interaction model we show that, while it is
possible to relax both the Hubble and weak-lensing tensions simultaneously, the
reduction in these tensions is modest (reduced to less slightly than $4\sigma$
and $2\sigma$ respectively). |
No-go for the formation of heavy mass Primordial Black Holes in Single
Field Inflation: We examine the possibility of Primordial Black Holes (PBHs) formation in
single-field models of inflation. Using the adiabatic or wave function
renormalization scheme in the short-range modes, we show that one-loop
correction to the power spectrum is free from quadratic UV divergence. We
consider a framework in which PBHs are produced during the transition from Slow
Roll (SR) to Ultra Slow Roll (USR) followed by the end of inflation. We
demonstrate that the renormalized power spectrum softens the contribution of
the logarithmic IR divergence and severely restricts the possible mass range of
produced PBHs in the said transition, namely, $M_{\rm PBH}\sim 10^{2}{\rm gm}$
ala a no-go theorem. In particular, we find that the produced PBHs are
short-lived ($t^{\rm evap}_{\rm PBH}\sim 10^{-20}{\rm sec}$) and the
corresponding number of e-folds in the USR region is restricted to $\Delta
N_{\rm USR}\approx 2$. | Non-Baryonic Dark Matter in Cosmology: This paper is a broad-band review of the current status of non-baryonic dark
matter research. I start with a historical overview of the evidences of dark
matter existence, then I discuss how dark matter is distributed from small
scale to large scale, and I then verge the attention to dark matter nature:
dark matter candidates and their detection. I finally discuss some of the
limits of the $\Lambda$CDM model, with particular emphasis on the small scale
problems of the paradigm. |
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