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The clustering of galaxies in the completed SDSS-III Baryon Oscillation
Spectroscopic Survey: theoretical systematics and Baryon Acoustic
Oscillations in the galaxy correlation function: We investigate the potential sources of theoretical systematics in the
anisotropic Baryon Acoustic Oscillation (BAO) distance scale measurements from
the clustering of galaxies in configuration space using the final Data Release
(DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS). We perform a
detailed study of the impact on BAO measurements from choices in the
methodology such as fiducial cosmology, clustering estimators, random
catalogues, fitting templates, and covariance matrices.
The theoretical systematic uncertainties in BAO parameters are found to be
0.002 in the isotropic dilation $\alpha$ and 0.003 in the quadrupolar dilation
$\epsilon$. The leading source of systematic uncertainty is related to the
reconstruction techniques. Theoretical uncertainties are sub-dominant compared
with the statistical uncertainties for BOSS survey, accounting
$0.2\sigma_{stat}$ for $\alpha$ and $0.25\sigma_{stat}$ for $\epsilon$
($\sigma_{\alpha,stat} \sim$0.010 and $\sigma_{\epsilon,stat}\sim$ 0.012
respectively). We also present BAO-only distance scale constraints from the
anisotropic analysis of the correlation function. Our constraints on the
angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$, including
both statistical and theoretical systematic uncertainties, are 1.5\% and 2.8\%
at $z_{\rm eff}=0.38$, 1.4\% and 2.4\% at $z_{\rm eff}=0.51$, and 1.7\% and
2.6\% at $z_{\rm eff}=0.61$. This paper is part of a set that analyzes the
final galaxy clustering dataset from BOSS. The measurements and likelihoods
presented here are cross-checked with other BAO analysis in \citet{Acacia16}.
The systematic error budget concerning the methodology on post-reconstruction
BAO analysis presented here is used in \citet{Acacia16} to produce the final
cosmological constraints from BOSS. | Forklens: Accurate weak lensing shear measurement on extremely noisy
images with deep learning: Weak gravitational lensing is one of the most important probes of the nature
of dark matter and dark energy. In order to extract cosmological information
from next-generation weak lensing surveys (e.g., Euclid, Roman, LSST, and CSST)
as much as possible, accurate measurements of weak lensing shear are required.
In this work, we present a fully deep-learning-based approach to measuring weak
lensing shear accurately. Our approach comprises two modules. The first one
contains a CNN with two branches for taking galaxy images and PSF
simultaneously, and the output of this module includes the galaxy's magnitude,
size, and shape. The second module includes a multiple-layer Neural Network to
calibrate weak lensing shear measurements. We name the program Forklens and
make it publicly available online. Applying Forklens to CSST-like mock images,
we achieve consistent accuracy with traditional approaches (such as
moment-based measurement and forward model fitting) on the sources with high
signal-to-noise ratios (S/N). For the sources with meagre S/N, Forklens
exhibits powerful latent denoising ability and offers accurate predictions on
galaxy shapes. The final shear measurements with Forklens deliver a
multiplicative bias $m=-0.4\pm3.0\times10^{-3}$ and an additive bias
$c=-0.5\pm1.9\times10^{-4}$. Our tests with CSST-like simulation show that
Forklens is competitive with other shear measurement algorithms such as
Metacalibration, while Forklens can potentially lower the S/N limit. Moreover,
the whole procedure of Forklens is automated and costs about 0.6 milliseconds
per galaxy, which is appropriate to adequately take advantage of the sky
coverage and depth of the upcoming weak lensing surveys. |
Axion Dark Matter eXperiment: Run 1B Analysis Details: Searching for axion dark matter, the ADMX collaboration acquired data from
January to October 2018, over the mass range 2.81--3.31 $\mu$eV, corresponding
to the frequency range 680--790 MHz. Using an axion haloscope consisting of a
microwave cavity in a strong magnetic field, the ADMX experiment excluded
Dine-Fischler-Srednicki-Zhitnisky (DFSZ) axions at 100% dark matter density
over this entire frequency range, except for a few gaps due to mode crossings.
This paper explains the full ADMX analysis for Run 1B, motivating analysis
choices informed by details specific to this run. | Evidence for cosmic acceleration with next-generation surveys: A
model-independent approach: We quantify the evidence for cosmic acceleration using simulations of $H(z)$
measurements from SKA- and Euclid-like surveys. We perform a non-parametric
reconstruction of the Hubble parameters and its derivative to obtain the
deceleration parameter $q(z)$ using the Gaussian Processes method. This is a
completely model-independent approach, so we can determine whether the Universe
is undergoing accelerated expansion {\it regardless} of any assumption of a
dark energy model. We find that Euclid-like and SKA-like band 1 surveys can
probe cosmic acceleration at over $3$ and $5\sigma$ confidence level,
respectively. By combining them with a SKA-like band 2 survey, which reaches
lower redshift ranges, the evidence for a current accelerated phase increases
to over $7\sigma$. This is a significant improvement from current $H(z)$
measurements from cosmic chronometers and galaxy redshift surveys, showing that
these surveys can underpin cosmic acceleration in a model-independent way. |
Reverberation Mapping Results for Five Seyfert 1 Galaxies: We present the results from a detailed analysis of photometric and
spectrophotometric data on five Seyfert 1 galaxies observed as a part of a
recent reverberation mapping program. The data were collected at several
observatories over a 140-day span beginning in 2010 August and ending in 2011
January. We obtained high sampling-rate light curves for Mrk 335, Mrk 1501,
3C120, Mrk 6, and PG2130+099, from which we have measured the time lag between
variations in the 5100 Angstrom continuum and the H-beta broad emission line.
We then used these measurements to calculate the mass of the supermassive black
hole at the center of each of these galaxies. Our new measurements
substantially improve previous measurements of MBH and the size of the broad
line-emitting region for four sources and add a measurement for one new object.
Our new measurements are consistent with photoionization physics regulating the
location of the broad line region in active galactic nuclei. | A comparison of structure formation in minimally and non-minimally
coupled quintessence models: We study structure formation in non-minimally coupled dark energy models,
where there is a coupling in the Lagrangian between a quintessence scalar field
and gravity via the Ricci scalar. We consider models with a range of different
non-minimal coupling strengths and compare these to minimally coupled
quintessence models with time-dependent dark energy densities. The equations of
state of the latter are tuned to either reproduce the equation of state of the
non-minimally coupled models or their background history. Thereby they provide
a reference to study the unique imprints of coupling on structure formation. We
show that the coupling between gravity and the scalar field, which effectively
results in a time-varying gravitational constant G, is not negligible and its
effect can be distinguished from a minimally coupled model. We extend previous
work on this subject by showing that major differences appear in the
determination of the mass function at high masses, where we observe differences
of the order of 40% at z=0. Our new results concern effects on the non-linear
matter power spectrum and on the lensing signal (differences of ~10% for both
quantities), where we find that non-minimally coupled models could be
distinguished from minimally coupled ones. |
Testing Secondary Models for the Origin of Radio Mini-Halos in Galaxy
Clusters: We present an MHD simulation of the emergence of a radio minihalo in a galaxy
cluster core in a "secondary" model, where the source of the
synchrotron-emitting electrons is hadronic interactions between cosmic-ray
protons with the thermal intracluster gas, an alternative to the
"reacceleration model" where the cosmic ray electrons are reaccelerated by
turbulence induced by core sloshing, which we discussed in an earlier work. We
follow the evolution of cosmic-ray electron spectra and their radio emission
using passive tracer particles, taking into account the time-dependent
injection of electrons from hadronic interactions and their energy losses. We
find that secondary electrons in a sloshing cluster core can generate diffuse
synchrotron emission with luminosity and extent similar to observed radio
minihalos. However, we also find important differences with our previous work.
We find that the drop in radio emission at cold fronts is less prominent than
that in our reacceleration-based simulations, indicating that in this flavor of
the secondary model the emission is more spatially extended than in some
observed minihalos. We also explore the effect of rapid changes in the magnetic
field on the radio spectrum. While the resulting spectra in some regions are
steeper than expected from stationary conditions, the change is marginal, with
differences in the synchrotron spectral index of $\Delta\alpha$ < 0.15-0.25,
depending on the frequency band. This is a much narrower range than claimed in
the best-observed minihalos and produced in the reacceleration model. Our
results provide important suggestions to constrain these models with future
observations. | A Multi-Parameter Investigation of Gravitational Slip: A detailed analysis of gravitational slip, a new post-general relativity
cosmological parameter characterizing the degree of departure of the laws of
gravitation from general relativity on cosmological scales, is presented. This
phenomenological approach assumes that cosmic acceleration is due to new
gravitational effects; the amount of spacetime curvature produced per unit mass
is changed in such a way that a universe containing only matter and radiation
begins to accelerate as if under the influence of a cosmological constant.
Changes in the law of gravitation are further manifest in the behavior of the
inhomogeneous gravitational field, as reflected in the cosmic microwave
background, weak lensing, and evolution of large-scale structure. The new
parameter, $\varpi_0$, is naively expected to be of order unity. However, a
multiparameter analysis, allowing for variation of all the standard
cosmological parameters, finds that $\varpi_0 = 0.09^{+0.74}_{-0.59} (2\sigma)$
where $\varpi_0=0$ corresponds to a $\Lambda$CDM universe under general
relativity. Future probes of the cosmic microwave background (Planck) and
large-scale structure (Euclid) may improve the limits by a factor of four. |
Primordial fluctuations from deformed quantum algebras: We study the implications of deformed quantum algebras for the generation of
primordial perturbations from slow-roll inflation. Specifically, we assume that
the quantum commutator of the inflaton's amplitude and momentum in Fourier
space gets modified at energies above some threshold $M_{\star}$. We show that
when the commutator is modified to be a function of the momentum only, the
problem of solving for the post-inflationary spectrum of fluctuations is
formally equivalent to solving a one-dimensional Schr\"odinger equation with a
time dependent potential. Depending on the class of modification, we find
results either close to or significantly different from nearly scale invariant
spectra. For the former case, the power spectrum is characterized by step-like
behaviour at some pivot scale, where the magnitude of the jump is
$\mathcal{O}(H^{2}/M_{\star}^{2})$. ($H$ is the inflationary Hubble parameter.)
We use our calculated power spectra to generate predictions for the cosmic
microwave background and baryon acoustic oscillations, hence demonstrating that
certain types of deformations are incompatible with current observations. | No Shock Across Part of a Radio Relic in the Merging Galaxy Cluster ZwCl
2341.1+0000?: The galaxy cluster ZwCl 2341.1+0000 is a merging system at z=0.27, which
hosts two radio relics and a central, faint, filamentary radio structure. The
two radio relics have unusually flat integrated spectral indices of -0.49 +/-
0.18 and -0.76 +/- 0.17, values that cannot be easily reconciled with the
theory of standard diffusive shock acceleration of thermal particles at weak
merger shocks. We present imaging results from XMM-Newton and Chandra
observations of the cluster, aimed to detect and characterise density
discontinuities in the ICM. As expected, we detect a density discontinuity near
each of the radio relics. However, if these discontinuities are the shock
fronts that fuelled the radio emission, then their Mach numbers are
surprisingly low, both <=2. We studied the aperture of the density
discontinuities, and found that while the NW discontinuity spans the whole
length of the NW radio relic, the arc spanned by the SE discontinuity is
shorter than the arc spanned by the SE relic. This startling result is in
apparent contradiction with our current understanding of the origin of radio
relics. Deeper X-ray data are required to confirm our results and to determine
the nature of the density discontinuities. |
Extreme-Value Distributions and Primordial Black-Hole Formation: We argue that primordial black-hole formation must be described by means of
extreme-value theory. This is a consequence of the large values of the energy
density required to initiate the collapse of black holes in the early Universe
and the finite duration of their collapse. Compared to the Gaussian description
of the most extreme primordial density fluctuations, the holes' mass function
is narrower and peaks towards larger masses. Secondly, thanks to the shallower
fall-off of extreme-value distributions, the predicted abundance of primordial
black holes is boosted by $10^{7}$ orders of magnitude when extrapolating the
observed nearly scale-free power spectrum of the cosmic large-scale structure
to primordial black-hole mass scales. | Dynamics of the Tidal Fields and Formation of Star Clusters in Galaxy
Mergers: In interacting galaxies, strong tidal forces disturb the global morphology of
the progenitors and give birth to the long stellar, gaseous and dusty tails
often observed. In addition to this destructive effect, tidal forces can morph
into a transient, protective setting called compressive mode. Such modes then
shelter the matter in their midst by increasing its gravitational binding
energy. This thesis focuses on the study of this poorly known regime by
quantifying its properties thanks to numerical and analytical tools applied to
a spectacular merging system of two galaxies, commonly known as the Antennae
galaxies. N-body simulations of this pair yield compressive modes in the
regions where observations reveal a burst of star formation. Furthermore,
characteristic time- and energy scales of these modes match well those of
self-gravitating substructures such as star clusters and tidal dwarf galaxies.
These results suggest that the compressive modes of tidal fields plays an
important role in the formation and evolution of young clusters, at least in a
statistical sense, over a lapse of ~10 million years. Preliminary results from
simulations of stellar associations highlight the importance of embedding the
clusters in the evolving background galaxies to account precisely for their
morphology and internal evolution. |
Simulating the galaxy cluster "El Gordo" and identifying the merger
configuration: The observational features of the massive galaxy cluster "El Gordo" (ACT-CL
J0102-4915), such as the X-ray emission, the Sunyaev-Zel'dovich (SZ) effect,
and the surface mass density distribution, indicate that they are caused by an
exceptional ongoing high-speed collision of two galaxy clusters, similar to the
well-known Bullet Cluster. We perform a series of hydrodynamical simulations to
investigate the merging scenario and identify the initial conditions for the
collision in ACT-CL J0102-4915. By surveying the parameter space of the various
physical quantities that describe the two colliding clusters, including their
total mass (M), mass ratio (\xi), gas fractions (f_b), initial relative
velocity (V), and impact parameter (P), we find out an off-axis merger with
P~800h_{70}^{-1}kpc, V~2500km/s, M~3x10^{15}Msun, and \xi=3.6 that can lead to
most of the main observational features of ACT-CL J0102-4915. Those features
include the morphology of the X-ray emission with a remarkable wake-like
substructure trailing after the secondary cluster, the X-ray luminosity and the
temperature distributions, and also the SZ temperature decrement. The initial
relative velocity required for the merger is extremely high and rare compared
to that inferred from currently available Lambda cold dark matter (LCDM)
cosmological simulations, which raises a potential challenge to the LCDM model,
in addition to the case of the Bullet Cluster. | Internal Cluster Structure: The core structure of galaxy clusters is fundamentally important. Even though
self-gravitating systems have no stable equilibrium state due to their negative
heat capacity, numerical simulations find density profiles which are universal
in the sense that they are fairly flat within a scale radius and gradually
steepen farther outward, asymptotically approaching a logarithmic slope of
$\approx-3$ near the virial radius. We argue that the reason for the formation
of this profile is not satisfactorily understood. The ratio between the virial
radius and the scale radius, the so-called concentration, is found in
simulations to be closely related to the mass and the redshift and low for
cluster-sized haloes, but observed to be substantially higher at least in a
subset of observed clusters. Haloes formed from cold dark matter should
furthermore be richly substructured. We review theoretical and observational
aspects of cluster cores here, discuss modifications by baryonic physics and
observables that can provide better insight into the internal structure of
clusters. |
RXJ 0921+4529: a binary quasar or gravitational lens?: We report the new spectroscopic observations of the gravitational lens RXJ
021+4529 with the multi-mode focal reducer SCORPIO of the SAO RAS 6-m
telescope. The new spectral observations were compared with the previously
observed spectra of components A and B of RXJ 0921+4529, i.e. the same
components observed in different epochs. We found a significant difference in
the spectrum between the components that cannot be explained with microlensing
and/or spectral variation. We conclude that RXJ 0921+4529 is a binary quasar
system, where redshifts of quasars A and B are 1.6535 +/- 0.0005 and 1.6625 +/-
0.0015, respectively. | The intriguing HI gas in NGC 5253: an infall of a diffuse,
low-metallicity HI cloud?: (Abridged) We present new, deep HI line and 20-cm radio continuum data of the
very puzzling blue compact dwarf galaxy NGC 5253, obtained with the ATCA as
part of the `Local Volume HI Survey' (LVHIS). Our low-resolution HI maps show
the disturbed HI morphology that NGC 5253 possesses, including tails, plumes
and detached HI clouds. The high-resolution map reveals an HI plume at the SE
and an HI structure at the NW that surrounds an Ha shell. We confirm that the
kinematics of the neutral gas are highly perturbed and do not follow a rotation
pattern. We discuss the outflow and infall scenarios to explain such disturbed
kinematics, analyze the environment in which it resides, and compare it
properties with those observed in similar star-forming dwarf galaxies. The
radio-continuum emission of NGC 5253 is resolved and associated with the
intense star-forming region at the center of the galaxy. We complete the
analysis using multiwavelength data extracted from the literature. We estimate
the SFR using this multiwavelength approach. NGC 5253 does not satisfy the
Schmidt-Kennicutt law of star-formation, has a very low HI mass-to-light ratio
when comparing with its stellar mass, and seems to be slightly metal-deficient
in comparison with starbursts of similar baryonic mass. Taking into account all
available multiwavelength data, we conclude that NGC 5253 is probably
experiencing the infall of a diffuse, low-metallicity HI cloud along the minor
axis of the galaxy, which is comprising the ISM and triggering the powerful
starburst. The tidally disturbed material observed at the east and north of the
galaxy is a consequence of this interaction, which probably started more than
100 Myr ago. The origin of this HI cloud may be related with a strong
interaction between NGC 5253 and the late-type spiral galaxy M 83 in the past. |
Spectropolarimetric evidence for a kicked supermassive black hole in the
Quasar E1821+643: We report spectropolarimetric observations of the quasar E1821+643 (z=0.297),
which suggest that it may be an example of gravitational recoil due to
anisotropic emission of gravitational waves following the merger of a
supermassive black hole (SMBH) binary. In total flux, the broad Balmer lines
are redshifted by ~1000 km/s relative to the narrow lines and have highly red
asymmetric profiles, whereas in polarized flux the broad H_alpha line exhibits
a blueshift of similar magnitude and a strong blue asymmetry. We show that
these observations are consistent with a scattering model in which the
broad-line region has two components, moving with different bulk velocities
away from the observer and towards a scattering region at rest in the host
galaxy. If the high velocity system is identified as gas bound to the SMBH,
this implies that the SMBH is itself moving with a velocity ~2100 km/s relative
to the host galaxy. We discuss some implications of the recoil hypothesis and
also briefly consider whether our observations can be explained in terms of
scattering of broad-line emission originating from the active component of an
SMBH binary, or from an outflowing wind. | Galaxy cluster SZ detection with unbiased noise estimation: an iterative
approach: Multi-frequency matched filters (MMFs) are routinely used to detect galaxy
clusters from CMB data through the thermal Sunyaev-Zeldovich (tSZ) effect,
leading to cluster catalogues that can be used for cosmological inference. In
order to be applied, MMFs require knowledge of the cross-frequency power
spectra of the noise in the maps. This is typically estimated from the data and
taken to be equal to the power spectra of the data, assuming the contribution
from the tSZ signal of the detections to be negligible. Using both analytical
arguments and \textit{Planck}-like mock observations, we show that doing so
causes the MMF noise to be overestimated, inducing a loss of signal-to-noise.
Furthermore, the MMF cluster observable (the amplitude $\hat{y}_0$ or the
signal-to-noise $q$) does not behave as expected, which can potentially bias
cosmological inference. In particular, the observable becomes biased with
respect to its theoretical prediction and displays a variance that also differs
from its predicted value. We propose an iterative MMF (iMMF) approach designed
to mitigate these effects. In this approach, after a first standard MMF step,
the noise power spectra are reestimated by masking the detections from the
data, delivering an updated iterative cluster catalogue. Applying our iMMF to
our \textit{Planck}-like mock observations, we find that the aforementioned
effects are completely suppressed. This leads to a signal-to-noise gain
relative to the standard MMF, with more significant detections and a higher
number of them, and to a cluster observable with the expected theoretical
properties, thus eliminating any potential biases in the cosmological
constraints. |
Cosmic shear with small scales: DES-Y3, KiDS-1000 and HSC-DR1: We present a cosmological analysis of the combination of the DES-Y3,
KiDS-1000 and HSC-DR1 weak lensing samples under a joint harmonic-space
pipeline making use of angular scales down to $\ell_{\rm max}=4500$,
corresponding to significantly smaller scales ($\delta\theta\sim2.4'$) than
those commonly used in cosmological weak lensing studies. We are able to do so
by accurately modelling non-linearities and the impact of baryonic effects
using Baccoemu. We find $S_8\equiv\sigma_8\sqrt{\Omega_{\rm
m}/0.3}=0.795^{+0.015}_{-0.017}$, in relatively good agreement with CMB
constraints from Planck (less than $\sim1.8\sigma$ tension), although we obtain
a low value of $\Omega_{\rm m}=0.212^{+0.017}_{-0.032}$, in tension with Planck
at the $\sim3\sigma$ level. We show that this can be recast as an $H_0$ tension
if one parametrises the amplitude of fluctuations and matter abundance in terms
of variables without hidden dependence on $H_0$. Furthermore, we find that this
tension reduces significantly after including a prior on the distance-redshift
relationship from BAO data, without worsening the fit. In terms of baryonic
effects, we show that failing to model and marginalise over them on scales
$\ell\lesssim2000$ does not significantly affect the posterior constraints for
DES-Y3 and KiDS-1000, but has a mild effect on deeper samples, such as HSC-DR1.
This is in agreement with our ability to only mildly constrain the parameters
of the Baryon Correction Model with these data | Power-law solutions and accelerated expansion in scalar-tensor theories: We find exact power-law solutions for scalar-tensor theories and clarify the
conditions under which they can account for an accelerated expansion of the
Universe. These solutions have the property that the signs of both the Hubble
rate and the deceleration parameter in the Jordan frame may be different from
the signs of their Einstein-frame counterparts. For special parameter
combinations we identify these solutions with asymptotic attractors that have
been obtained in the literature through dynamical-system analysis. We establish
an effective general-relativistic description for which the geometrical
equivalent of dark energy is associated with a time dependent equation of
state. The present value of the latter is consistent with the observed
cosmological ``constant". We demonstrate that this type of power-law solutions
for accelerated expansion cannot be realized in f(R) theories. |
Measuring ultra-large scale effects in the presence of 21cm intensity
mapping foregrounds: \textsc{Hi} intensity mapping will provide maps of the large-scale
distribution of neutral hydrogen (\textsc{Hi}) in the universe. These are prime
candidates to be used to constrain primordial non-Gaussianity using the Large
Scale Structure of the Universe as well as to provide further tests of
Einstein's theory of Gravity (GR). But \textsc{Hi} maps are contaminated by
foregrounds, which can be several orders of magnitude above the cosmological
signal. Here we quantify how degenerated are the large-scale effects ($f_{\rm
NL}$ and GR effects) with the residual foregrounds. We conclude that a joint
analysis does not provide a catastrophic degradation of constraints and
provides a framework to determine the marginal errors of large scale-effects in
the presence of foregrounds. Similarly, we conclude that the macroscopical
properties of the foregrounds can be measured with high precision.
Notwithstanding, such results are highly dependent on accurate forward
modelling of the foregrounds, which incorrectly done catastrophically bias the
best fit values of cosmological parameters, foreground parameterisations, and
large-scale effects. | A window for cosmic strings: Particle emission, in addition to gravitational radiation from cosmic string
loops, affects the resulting loop distribution and hence the corresponding
observational consequences of cosmic strings. Here we focus on two models in
which loops of length $\ell$ are produced from the infinite string network with
a given power-law. For both models we find that, due to particle production,
the Stochastic Gravitational Wave Background (SGWB) is cut off outside the
region of parameter space probed by any current or planned GW experiment.
Therefore the present constraints from the LIGO-Virgo-Kagra (LVK) collaboration
still hold. However for one of these models, if a fraction $\gtrsim O(10^{-3})$
of these particles cascades into $\gamma$-rays, and if the gravitational
backreaction scale follows the Polchinski-Rocha model, then the string tension
is tightly constrained from below by measurements of the Diffuse $\gamma$-Ray
Background, and from above by the SGWB. With reasonable assumptions, the joint
constraint on the string tension set by these two possible observables reduces
the available parameter space of this cosmic string model to a narrow band.
Future upgrades to LVK will either rule out this model or detect strings. |
Weighing the Giants V: Galaxy Cluster Scaling Relations: We present constraints on the scaling relations of galaxy cluster X-ray
luminosity, temperature and gas mass (and derived quantities) with mass and
redshift, employing masses from robust weak gravitational lensing measurements.
These are the first such results obtained from an analysis that simultaneously
accounts for selection effects and the underlying mass function, and directly
incorporates lensing data to constrain total masses. Our constraints on the
scaling relations and their intrinsic scatters are in good agreement with
previous studies, and reinforce a picture in which departures from self-similar
scaling laws are primarily limited to cluster cores. However, the data are
beginning to reveal new features that have implications for cluster
astrophysics and provide new tests for hydrodynamical simulations. We find a
positive correlation in the intrinsic scatters of luminosity and temperature at
fixed mass, which is related to the dynamical state of the clusters. While the
evolution of the nominal scaling relations over the redshift range $0.0<z<0.5$
is consistent with self similarity, we find tentative evidence that the
luminosity and temperature scatters respectively decrease and increase with
redshift. Physically, this likely related to the development of cool cores and
the rate of major mergers. We also examine the scaling relations of redMaPPer
richness and Compton $Y$ from Planck. While the richness--mass relation is in
excellent agreement with recent work, the measured $Y$--mass relation departs
strongly from that assumed in the Planck cluster cosmology analysis. The latter
result is consistent with earlier comparisons of lensing and Planck
scaling-relation-derived masses. | A 10 deg$^2$ Lyman-$α$ survey at z=8.8 with spectroscopic
follow-up: strong constraints on the LF and implications for other surveys: Candidate galaxies at redshifts of $z \sim 10$ are now being found in
extremely deep surveys, probing very small areas. As a consequence, candidates
are very faint, making spectroscopic confirmation practically impossible. In
order to overcome such limitations, we have undertaken the CF-HiZELS survey,
which is a large area, medium depth near infrared narrow-band survey targeted
at $z=8.8$ Lyman-$\alpha$ (Ly$\alpha$) emitters (LAEs) and covering 10 deg$^2$
in part of the SSA22 field with the Canada-France-Hawaii Telescope. We surveyed
a comoving volume of $4.7\times 10^6$ Mpc$^3$ to a Ly$\alpha$ luminosity limit
of $6.3\times10^{43}$ erg s$^{-1}$. We look for Ly$\alpha$ candidates by
applying the following criteria: i) clear emission line source, ii) no optical
detections ($ugriz$ from CFHTLS), iii) no visible detection in the optical
stack ($ugriz > 27$), iv) visually checked reliable NB$_J$ and $J$ detections
and v) $J-K \leq 0$. We compute photometric redshifts and remove a significant
amount of dusty lower redshift line-emitters at $z \sim 1.4 $ or $2.2$. A total
of 13 Ly$\alpha$ candidates were found, of which two are marked as strong
candidates, but the majority have very weak constraints on their SEDs. Using
follow-up observations with SINFONI/VLT we are able to exclude the most robust
candidates as Ly$\alpha$ emitters. We put a strong constraint on the Ly$\alpha$
luminosity function at $z \sim 9$ and make realistic predictions for ongoing
and future surveys. Our results show that surveys for the highest redshift LAEs
are susceptible of multiple contaminations and that spectroscopic follow-up is
absolutely necessary. |
Cosmological Parameter Uncertainties from SALT-II Type Ia Supernova
Light Curve Models: We use simulated SN Ia samples, including both photometry and spectra, to
perform the first direct validation of cosmology analysis using the SALT-II
light curve model. This validation includes residuals from the light curve
training process, systematic biases in SN Ia distance measurements, and the
bias on the dark energy equation of state parameter w. Using the SN-analysis
package SNANA, we simulate and analyze realistic samples corresponding to the
data samples used in the SNLS3 analysis: 120 low-redshift (z < 0.1) SNe Ia, 255
SDSS SNe Ia (z < 0.4), and 290 SNLS SNe Ia (z <= 1). To probe systematic
uncertainties in detail, we vary the input spectral model, the model of
intrinsic scatter, and the smoothing (i.e., regularization) parameters used
during the SALT-II model training. Using realistic intrinsic scatter models
results in a slight bias in the ultraviolet portion of the trained SALT-II
model, and w biases (winput - wrecovered) ranging from -0.005 +/- 0.012 to
-0.024 +/- 0.010. These biases are indistinguishable from each other within
uncertainty; the average bias on w is -0.014 +/- 0.007. | Coleman-Weinberg linear inflation: metric vs. Palatini formulation: It has been previously shown that the linear inflation appears naturally as a
solution of Coleman-Weinberg inflation, provided that the inflaton has a
non-minimal coupling to gravity and the Planck scale is dynamically generated.
We revisit the previous study by improving the discussion of reheating and by
comparing the results of the metric and the Palatini formulations of
non-minimal gravity. We find that both formulations predict linear inflation
but a different number of $e$-folds. If the non-minimal coupling is larger than
one, future experimental sensitivity can discriminate between the two
realizations. |
Does environment affect the star formation histories of early-type
galaxies?: Differences in the stellar populations of galaxies can be used to quantify
the effect of environment on the star formation history. We target a sample of
early-type galaxies from the Sloan Digital Sky Survey in two different
environmental regimes: close pairs and a general sample where environment is
measured by the mass of their host dark matter halo. We apply a blind source
separation technique based on principal component analysis, from which we
define two parameters that correlate, respectively, with the average stellar
age (eta) and with the presence of recent star formation (zeta) from the
spectral energy distribution of the galaxy. We find that environment leaves a
second order imprint on the spectra, whereas local properties - such as
internal velocity dispersion - obey a much stronger correlation with the
stellar age distribution. | Systematic simulations of modified gravity: chameleon models: In this work we systematically study the linear and nonlinear structure
formation in chameleon theories of modified gravity, using a generic
parameterisation which describes a large class of models using only 4
parameters. For this we have modified the N-body simulation code ECOSMOG to
perform a total of 65 simulations for different models and parameter values,
including the default LCDM. These simulations enable us to explore a
significant portion of the parameter space. We have studied the effects of
modified gravity on the matter power spectrum and mass function, and found a
rich and interesting phenomenology where the difference with the LCDM paradigm
cannot be reproduced by a linear analysis even on scales as large as
k~0.05h/Mpc, since the latter incorrectly assumes that the modification of
gravity depends only on the background matter density. Our results show that
the chameleon screening mechanism is significantly more efficient than other
mechanisms such as the dilaton and symmetron, especially in high-density
regions and at early times, and can serve as a guidance to determine the parts
of the chameleon parameter space which are cosmologically interesting and thus
merit further studies in the future. |
A test for skewed distributions of dark matter and a possible detection
in galaxy cluster Abell 3827: Simulations of self-interacting dark matter (SIDM) predict that dark matter
should lag behind galaxies during a collision. If the interaction is mediated
by a high-mass force carrier, the distribution of dark matter can also develop
asymmetric dark matter tails. To search for this asymmetry, we compute the
gravitational lensing properties of a mass distribution with a free {\em
skewness} parameter. We apply this to the dark matter around the four central
galaxies in cluster Abell~3827. In the galaxy whose dark matter peak has
previously been found to be offset, we tentatively measure a skewness
$s=0.23^{+0.05}_{-0.22}$ in the same direction as the peak offset. Our method
may be useful in future gravitational lensing analyses of colliding galaxy
clusters and merging galaxies. | Herschel observations of a z~2 stellar mass selected galaxy sample drawn
from the GOODS NICMOS Survey: We present a study of the far-IR properties of a stellar mass selected sample
of 1.5 < z < 3 galaxies with log(M_*/M_sun) > 9.5 drawn from the GOODS NICMOS
Survey (GNS), the deepest H-band Hubble Space Telescope survey of its type
prior to the installation of WFC3. We use far-IR and sub-mm data from the PACS
and SPIRE instruments on-board Herschel, taken from the PACS Evolutionary Probe
(PEP) and Herschel Multi-Tiered Extragalactic Survey (HerMES) key projects
respectively. We find a total of 22 GNS galaxies, with median log(M_*/M_sun) =
10.8 and z = 2.0, associated with 250 um sources detected with SNR > 3. We
derive mean total IR luminosity log L_IR (L_sun) = 12.36 +/- 0.05 and
corresponding star formation rate SFR_(IR+UV) = (280 +/- 40) M_sun/yr for these
objects, and find them to have mean dust temperature T_dust ~ 35 K. We find
that the SFR derived from the far-IR photometry combined with UV-based
estimates of unobscured SFR for these galaxies is on average more than a factor
of 2 higher than the SFR derived from extinction corrected UV emission alone,
although we note that the IR-based estimate is subject to substantial Malmquist
bias. To mitigate the effect of this bias and extend our study to fainter
fluxes, we perform a stacking analysis to measure the mean SFR in bins of
stellar mass. We obtain detections at the 2-4 sigma level at SPIRE wavelengths
for samples with log(M_*/M_sun) > 10. In contrast to the Herschel detected GNS
galaxies, we find that estimates of SFR_(IR+UV) for the stacked samples are
comparable to those derived from extinction corrected UV emission, although the
uncertainties are large. We find evidence for an increasing fraction of dust
obscured star formation with stellar mass, finding SFR_IR/SFR_UV \propto
M_*^{0.7 +/- 0.2}, which is likely a consequence of the mass--metallicity
relation. |
Cosmic Web Reconstruction through Density Ridges: Catalogue: We construct a catalogue for filaments using a novel approach called SCMS
(subspace constrained mean shift; Ozertem & Erdogmus 2011; Chen et al. 2015).
SCMS is a gradient-based method that detects filaments through density ridges
(smooth curves tracing high-density regions). A great advantage of SCMS is its
uncertainty measure, which allows an evaluation of the errors for the detected
filaments. To detect filaments, we use data from the Sloan Digital Sky Survey,
which consist of three galaxy samples: the NYU main galaxy sample (MGS), the
LOWZ sample and the CMASS sample. Each of the three dataset covers different
redshift regions so that the combined sample allows detection of filaments up
to z = 0.7. Our filament catalogue consists of a sequence of two-dimensional
filament maps at different redshifts that provide several useful statistics on
the evolution cosmic web. To construct the maps, we select spectroscopically
confirmed galaxies within 0.050 < z < 0.700 and partition them into 130 bins.
For each bin, we ignore the redshift, treating the galaxy observations as a 2-D
data and detect filaments using SCMS. The filament catalogue consists of 130
individual 2-D filament maps, and each map comprises points on the detected
filaments that describe the filamentary structures at a particular redshift. We
also apply our filament catalogue to investigate galaxy luminosity and its
relation with distance to filament. Using a volume-limited sample, we find
strong evidence (6.1$\sigma$ - 12.3$\sigma$) that galaxies close to filaments
are generally brighter than those at significant distance from filaments. | Optical and Near-IR long-term monitoring of NGC3783 and MR2251-178:
evidence for variable near-IR emission from thin accretion discs: We present long term near-IR light curves for two nearby AGN: NGC3783 and
MR2251-178. The near-IR data are complemented with optical photometry obtained
over the same period of time. The light curves in all bands are highly variable
and good correlations can be seen between optical and NIR variations.
Cross-correlation analysis for NGC 3783 suggests that some disc near-IR
emission is present in the J-band flux, while the H and K-bands are dominated
by emission from a torus located at the dust sublimation radius. For MR2251-178
the cross-correlation analysis and the optical-near-IR flux-flux plots suggest
that the near-IR flux is dominated by disc emission. We model the optical to
near-IR Spectral Energy Distributions (SED) of both sources and find that disc
flaring might be a necessary modification to the geometry of a thin disc in
order to explain the observations. The SED of MR2251-178 gives some indications
for the presence of NIR emission from a torus. Finally, we consider the
implications of the standard alpha disc model to explain the different origin
of the variable NIR emission in these AGN. |
Could M31 come from a major merger and eject the LMC away?: We investigated a scenario in which M31 could be the remnant of a major
merger and at the origin of the LMC. Galaxy merger simulations were run in
order to reproduce some M31 properties. We succeeded in reproducing some of the
most important M31 large-scale features like the thick disk or the polar ring,
and gave a possible explanation for the formation of the Giant Stream. We also
found that the LMC could be expelled by this high energetic phenomenon. | Accounting for sample selection in Bayesian analyses: Astronomers are often confronted with funky populations and distributions of
objects: brighter objects are more likely to be detected; targets are selected
based on colour cuts; imperfect classification yields impure samples. Failing
to account for these effects leads to biased analyses. In this paper we present
a simple overview of a Bayesian consideration of sample selection, giving
solutions to both analytically tractable and intractable models. This is
accomplished via a combination of analytic approximations and Monte Carlo
integration, in which dataset simulation is efficiently used to correct for
issues in the observed dataset. This methodology is also applicable for data
truncation, such as requiring densities to be strictly positive. Toy models are
included for demonstration, along with discussions of numerical considerations
and how to optimise for implementation. We provide sample code to demonstrate
the techniques. The methods in this paper should be widely applicable in fields
beyond astronomy, wherever sample selection effects occur. |
Parsec structure and properties of the jet of 3C273. Results of Space
VLBI data processing: We present result of processing of data of ground-space VLBI experiment
titled W068. Particularly, one part of data of that observational session is
successfully processed. These data were obtained on 2000 March 17 between 9:00
UT and 10:30 UT. 10 antennas of American interferometer VLBA (Very Long
Baseline Array) and Japan satellite VSOP (VLBI Space Observatory Programme)
were involved into this experiment. Moreover, 27 antennae of VLA (Very Large
Array)} were used as an additional ground antenna. Data were transferred from
archive of the NRAO (National Radio Astronomy Observatory, USA)and processed
with the software titled 'Astro Space Locator' (ASL for Windows). The main
result of this processing is the image of the quasar titled 3C273 with high
resolution and high accuracy. Using this image, we make some conclusions about
the radio structure of jet of this object. Our result is not in conflict with
other results of processing of the Space VLBI data for 3C273 published earlier
with many authors. We could add some new aspects into that results. The
reconstructed images of 3C273 for 6 centimeter wavelength range and values of
some parameters of this source are presented. | Imprints of Axion Superradiance in the CMB: Light axions ($m_a \lesssim 10^{-10}$ eV) can form dense clouds around
rapidly rotating astrophysical black holes via a mechanism known as rotational
superradiance. The coupling between axions and photons induces a parametric
resonance, arising from the stimulated decay of the axion cloud, which can
rapidly convert regions of large axion number densities into an enormous flux
of low-energy photons. In this work we consider the phenomenological
implications of a superradiant axion cloud undergoing resonant decay. We show
that the low energy photons produced from such events will be absorbed over
cosmologically short distances, potentially inducing massive shockwaves that
heat and ionize the IGM over Mpc scales. These shockwaves may leave observable
imprints in the form of anisotropic spectral distortions or inhomogeneous
features in the optical depth. |
Star Formation in the First Galaxies - II: Clustered Star Formation and
the Influence of Metal Line Cooling: Population III stars are believed to have been more massive than typical
stars today and to have formed in relative isolation. The thermodynamic impact
of metals is expected to induce a transition leading to clustered, low-mass
Population II star formation. In this work, we present results from three
cosmological simulations, only differing in gas metallicity, that focus on the
impact of metal fine-structure line cooling on the formation of stellar
clusters in a high-redshift atomic cooling halo. Introduction of sink particles
allows us to follow the process of gas hydrodynamics and accretion onto cluster
stars for 4 Myr corresponding to multiple local free-fall times. At
metallicities at least $10^{-3}\, Z_{\odot}$, gas is able to reach the CMB
temperature floor and fragment pervasively resulting in a stellar cluster of
size $\sim1$ pc and total mass $\sim1000\, M_{\odot}$. The masses of individual
sink particles vary, but are typically $\sim100\, M_{\odot}$, consistent with
the Jeans mass when gas cools to the CMB temperature, though some solar mass
fragments are also produced. At the low metallicity of $10^{-4}\, Z_{\odot}$,
fragmentation is completely suppressed on scales greater than 0.01 pc and total
stellar mass is lower by a factor of 3 than in the higher metallicity
simulations. The sink particle accretion rates, and thus their masses, are
determined by the mass of the gravitationally unstable gas cloud and the
prolonged gas accretion over many Myr. The simulations thus exhibit features of
both monolithic collapse and competitive accretion. Even considering possible
dust induced fragmentation that would occur at higher densities, the formation
of a bona fide stellar cluster seems to require metal line cooling and
metallicities of at least $10^{-3}\, Z_{\odot}$. | Tidal shear and the consistency of microscopic Lagrangian halo
approaches: We delineate the conditions under which the consistency relation for the
non-Gaussian bias and the universality of the halo mass function hold in the
context of microscopic Lagrangian descriptions of halos. The former is valid
provided that the collapse barrier depends only on the physical fields (instead
of fields normalized by their variance for example) and explicitly includes the
effect of {\it all} physical fields such as the tidal shear. The latter holds
provided that the response of the halo number density to a long-wavelength
density fluctuation is equivalent to the response induced by shifting the
spherical collapse threshold. Our results apply to any Lagrangian halo bias
prescription. Effective "moving" barriers, which are ubiquitous in the
literature, do not generally satisfy the consistency relation. Microscopic
barriers including the tidal shear lead to two additional, second-order
Lagrangian bias parameters which ensure that the consistency relation is
satisfied. We provide analytic expressions for them. |
Cleaning foregrounds from single-dish 21cm intensity maps with Kernel
Principal Component Analysis: The high dynamic range between contaminating foreground emission and the
fluctuating 21cm brightness temperature field is one of the most problematic
characteristics of 21cm intensity mapping data. While these components would
ordinarily have distinctive frequency spectra, making it relatively easy to
separate them, instrumental effects and calibration errors further complicate
matters by modulating and mixing them together. A popular class of foreground
cleaning method are unsupervised techniques related to Principal Component
Analysis (PCA), which exploit the different shapes and amplitudes of each
component's contribution to the covariance of the data in order to segregate
the signals. These methods have been shown to be effective at removing
foregrounds, while also unavoidably filtering out some of the 21cm signal too.
In this paper we examine, for the first time in the context of 21cm intensity
mapping, a generalised method called Kernel PCA, which instead operates on the
covariance of non-linear transformations of the data. This allows more flexible
functional bases to be constructed, in principle allowing a cleaner separation
between foregrounds and the 21cm signal to be found. We show that Kernel PCA is
effective when applied to simulated single-dish (autocorrelation) 21cm data
under a variety of assumptions about foregrounds models, instrumental effects
etc. It presents a different set of behaviours to PCA, e.g. in terms of
sensitivity to the data resolution and smoothing scale, outperforming it on
intermediate to large scales in most scenarios. | Constrained simulations of the local universe: II. The nature of the
local Hubble flow: Using a suite of N-body simulations in different Cold Dark Matter (CDM)
scenarios, with cosmological constant (\LCDM) and without (OCDM, SCDM), we
study the Hubble flow (\sigh) in Local Volumes (LV) around Local Group (LG)
like objects found in these simulations, and compare the numerical results with
the most recent observations. We show that \LCDM and OCDM models exhibit the
same behavior of \sigh. Hence, we demonstrate that the observed coldness of the
Hubble flow is not likely to be a manifestation of the dark energy, contrary to
previous claims. The coldness does not constitute a problem by itself but it
poses a problem to the standard \LCDM model only if the mean density within the
Local Volume is greater than twice the mean matter cosmic density. The lack of
blueshifted galaxies in the LV, outside of the LG can be considered as another
manifestation of the coldness of the flow. Finally, we show that the main
dynamical parameter that affects the coldness of the flow is the relative
isolation of the LG, and the absence of nearby Milky Way like objects within a
distance of about $3\mpc$. |
Initial conditions for the scalaron dark matter: The scalaron of the metric $f(R)$ gravity can constitute dark matter if its
mass is in the range $4\,\text{meV} \lesssim m \lesssim 1\,\text{MeV}$. We give
an overview of such $f (R)$ gravity theory minimally coupled to the Standard
Model. Similarly to other dark-matter models based on scalar fields, this model
has the issue of initial conditions. Firstly, the initial conditions for the
scalaron are to be tuned in order to produce the observed amount of dark
matter. Secondly, the primordial spatial inhomogeneities in the field are to be
sufficiently small because they generate entropy (or isocurvature)
perturbations, which are constrained by observations. We consider these issues
in the present paper. The initial conditions for the scalaron presumably emerge
at the inflationary stage. We point out that the homogeneous part of the
scalaron initial value is largely unpredictable because of quantum diffusion
during inflation. Thus, to account for the observed amount of dark matter, one
has to resort to anthropic considerations. Observational constraints on the
primordial spatial inhomogeneity of the scalaron are translated into upper
bounds on the energy scale of inflation, which happen to be low but not too
restrictive. | Testing the Quasar Hubble Diagram with LISA Standard Sirens: Quasars have recently been used as an absolute distance indicator, extending
the Hubble diagram to high redshift to reveal a deviation from the expansion
history predicted for the standard, $\Lambda$CDM cosmology. Here we show that
the Laser Interferometer Space Antenna (LISA) will efficiently test this claim
with standard sirens at high redshift, defined by the coincident gravitational
wave (GW) and electromagnetic (EM) observations of the merger of massive black
hole binaries (MBHBs). Assuming a fiducial $\Lambda$CDM cosmology for
generating mock standard siren datasets, the evidence for the $\Lambda$CDM
model with respect to an alternative model inferred from quasar data is
investigated. By simulating many realizations of possible future LISA
observations, we find that for $50\%$ of these realizations (median result) 4
MBHB standard siren measurements will suffice to strongly differentiate between
the two models, while 14 standard sirens will yield a similar result in $95\%$
of the realizations. In addition, we investigate the measurement precision of
cosmological parameters as a function of the number of observed LISA MBHB
standard sirens, finding that 15 events will on average achieve a relative
precision of 5\% for $H_0$, reducing to 3\% and 2\% with 25 and 40 events,
respectively. Our investigation clearly highlights the potential of LISA as a
cosmological probe able to accurately map the expansion of the universe at
$z\gtrsim 2$, and as a tool to cross-check and cross-validate cosmological EM
measurements with complementary GW observations. |
Photometric Reverberation Mapping of the Broad Emission Line Region in
Quasars: A method is proposed for measuring the size of the broad emission line region
(BLR) in quasars using broadband photometric data. A feasibility study, based
on numerical simulations, points to the advantages and pitfalls associated with
this approach. The method is applied to a subset of the Palomar-Green quasar
sample for which independent BLR size measurements are available. An agreement
is found between the results of the photometric method and the spectroscopic
reverberation mapping technique. Implications for the measurement of BLR sizes
and black hole masses for numerous quasars in the era of large surveys are
discussed. | Tickling the CMB damping tail: scrutinizing the tension between the ACT
and SPT experiments: The Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) have
recently provided new, very precise measurements of the cosmic microwave
background (CMB) anisotropy damping tail. The values of the cosmological
parameters inferred from these measurements, while broadly consistent with the
expectations of the standard cosmological model, are providing interesting
possible indications for new physics that are definitely worth of
investigation. The ACT results, while compatible with the standard expectation
of three neutrino families, indicate a level of CMB lensing, parametrized by
the lensing amplitude parameter A_L, that is about 70% higher than expected. If
not a systematic, this anomalous lensing amplitude could be produced by
modifications of general relativity or coupled dark energy. Vice-versa, the SPT
experiment, while compatible with a standard level of CMB lensing, prefers an
excess of dark radiation, parametrized by the effective number of relativistic
degrees of freedom N_eff. Here we perform a new analysis of these experiments
allowing simultaneous variations in both these, non-standard, parameters. We
also combine these experiments, for the first time in the literature, with the
recent WMAP9 data, one at a time. Including the Hubble Space Telescope (HST)
prior on the Hubble constant and information from baryon acoustic oscillations
(BAO) surveys provides the following constraints from ACT: N_eff=3.23\pm0.47,
A_L=1.65\pm0.33 at 68% c.l., while for SPT we have N_eff=3.76\pm0.34,
A_L=0.81\pm0.12 at 68% c.l.. In particular, the A_L estimates from the two
experiments, even when a variation in N_eff is allowed, are in tension at more
than 95% c.l.. |
Gemini GMOS and WHT SAURON integral-field spectrograph observations of
the AGN driven outflow in NGC 1266: We use the SAURON and GMOS integral field spectrographs to observe the active
galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is
relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN
feedback in action. We present maps of the kinematics and line strengths of the
ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and
report on the detection of Sodium D absorption. We use these tracers to explore
the structure of the source, derive the ionised and atomic gas kinematics and
investigate the gas excitation and physical conditions. NGC 1266 contains two
ionised gas components along most lines of sight, tracing the ongoing outflow
and a component closer to the galaxy systemic, the origin of which is unclear.
This gas appears to be disturbed by a nascent AGN jet. We confirm that the
outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic,
molecular and ionised gas and X-ray emitting plasma. The outflow has velocities
up to \pm900 km/s away from the systemic velocity, and is very likely to be
removing significant amounts of cold gas from the galaxy. The LINER-like
line-emission in NGC 1266 is extended, and likely arises from fast shocks
caused by the interaction of the radio jet with the ISM. These shocks have
velocities of up to 800 km/s, which match well with the observed velocity of
the outflow. Sodium D equivalent width profiles are used to set constraints on
the size and orientation of the outflow. The ionised gas morphology correlates
with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission,
supporting the suggestion that an AGN jet is providing the energy required to
drive the outflow. | Lyman-alpha Heating of Inhomogeneous High-redshift Intergalactic Medium: The intergalactic medium (IGM) prior to the epoch of reionization consists
mostly of neutral hydrogen gas. Ly-alpha photons produced by early stars
resonantly scatter off hydrogen atoms, causing energy exchange between the
radiation field and the gas. This interaction results in moderate heating of
the gas due to the recoil of the atoms upon scattering, which is of great
interest for future studies of the pre-reionization IGM in the HI 21 cm line.
We investigate the effect of this Ly-alpha heating in the IGM with linear
density, temperature, and velocity perturbations. Perturbations smaller than
the diffusion length of photons could be damped due to heat conduction by
Ly-alpha photons. The scale at which damping occurs and the strength of this
effect depend on various properties of the gas, the flux of Ly-alpha photons
and the way in which photon frequencies are redistributed upon scattering. To
find the relevant length scale and the extent to which Ly-alpha heating affects
perturbations, we calculate the gas heating rates by numerically solving
linearized Boltzmann equations in which scattering is treated by the
Fokker-Planck approximation. We find that (1) perturbations add a small
correction to the gas heating rate, and (2) the damping of temperature
perturbations occurs at scales with comoving wavenumber k>10^4 Mpc^{-1}, which
are much smaller than the Jeans scale and thus unlikely to substantially affect
the observed 21 cm signal. |
Primordial Black Hole Merger Rate in Self-Interacting Dark Matter Halo
Models: We study the merger rate of primordial black holes (PBHs) in self-interacting
dark matter (SIDM) halo models. To explore a numerical description for the
density profile of SIDM halo models, we use the result of a previously
performed simulation for SIDM halo models with $\sigma/m=10~{\rm
cm^{2}g^{-1}}$. We also propose a concentration-mass-time relation that can
explain the evolution of the halo density profile related to SIDM models.
Furthermore, we investigate the encounter condition of PBHs that may have been
randomly distributed in the medium of dark matter halos. Under these
assumptions, we calculate the merger rate of PBHs within each halo considering
SIDM halo models and compare the results with that obtained for cold dark
matter (CDM) halo models. To do this, we employ the definition of the time
after halo virialization as a function of halo mass. We indicate that SIDM halo
models for $f_{\rm PBH}>0.32$ can generate sufficient PBH mergers in such a way
that those exceed the one resulted from CDM halo models. By considering the
spherical-collapse halo mass function, we obtain similar results for the
cumulative merger rate of PBHs. Moreover, we calculate the redshift evolution
of the PBH total merger rate. To determine a constraint on the PBH abundance,
we study the merger rate of PBHs in terms of their fraction and masses and
compare those with the black hole merger rate estimated by the Advanced LIGO
(aLIGO)-Advanced Virgo (aVirgo) detectors during the third observing run. The
results demonstrate that within the context of SIDM halo models, the merger
rate of $10~M_{\odot}-10~M_{\odot}$ events can potentially fall within the
aLIGO-aVirgo window. We also estimate a relation between the fraction of PBHs
and their masses, which is well consistent with our findings. | A 1.75 kpc/h Separation Dual AGN at z=0.36 in the COSMOS Field: We present strong evidence for dual active galactic nuclei (AGN) in the
z=0.36 galaxy COSMOS J100043.15+020637.2. COSMOS Hubble Space Telescope (HST)
imaging of the galaxy shows a tidal tail, indicating that the galaxy recently
underwent a merger, as well as two bright point sources near the galaxy's
center. Both the luminosities of these sources (derived from the HST image) and
their emission line flux ratios (derived from Keck/DEIMOS slit spectroscopy)
suggest that both are AGN and not star-forming regions or supernovae.
Observations from zCOSMOS, Sloan Digital Sky Survey, XMM-Newton, Very Large
Array, and Spitzer fortify the evidence for AGN activity. With HST imaging we
measure a projected spatial offset between the two AGN of 1.75 +- 0.03 kpc/h,
and with DEIMOS we measure a 150 +- 40 km/s line-of-sight velocity offset
between the two AGN. Combined, these observations provide substantial evidence
that COSMOS J100043.15+020637.2 is a dual AGN in a merger-remnant galaxy. |
The spectrum of gravitational waves in an f(R) model with a bounce: We present an inflationary model preceded by a bounce in a metric $f(R)$
theory. In this model, modified gravity affects only the early stages of the
universe. We analyse the predicted spectrum of the gravitational waves in this
scenario using the method of the Bogoliubov coefficients. We show that there
are distinctive (oscillatory) signals on the spectrum for very low frequencies;
i.e., corresponding to modes that are currently entering the horizon. | Constraining decaying dark matter with BOSS data and the effective field
theory of large-scale structures: We update cosmological constraints on two decaying dark matter models in
light of BOSS-DR12 data analyzed under the Effective Field Theory of
Large-Scale Structures (EFTofLSS) formalism, together with Planck, Pantheon and
other BOSS measurements of the baryonic acoustic oscillation (BAO). In the
first model, a fraction $f_{\rm dcdm}$ of cold dark matter (CDM) decays into
dark radiation (DR) with a lifetime $\tau$. In the second model (recently
suggested as a potential resolution to the $S_8$ tension), all the CDM decays
with a lifetime $\tau$ into DR and a massive warm dark matter (WDM) particle,
with a fraction $\varepsilon$ of the CDM rest mass energy transferred to the
DR. Using numerical codes from the recent literature, we perform the first
calculation of the mildly non-linear (matter and galaxy) power spectra with the
EFTofLSS for these two models. In the case of DR products, we obtain the
constraints $f_{\rm dcdm}\lesssim0.022$ (95\% C.L.) for lifetimes shorter than
the age of the universe, and $\tau/f_{\rm dcdm} \gtrsim 250$ Gyr in the
long-lived regime assuming $f_{\rm dcdm}\to1$. We show that Planck data
contributes the most to these constraints, with EFTofBOSS providing a marginal
improvement over conventional BAO and redshift space distortions ($f\sigma_8$)
data. In the case of DR and WDM decay products, we find that EFTofBOSS data
significantly improves the constraints at 68\% C.L. on the CDM lifetime with a
$S_8$ prior from KiDS-1000. We show that, in order to fit EFTofBOSS data while
lowering $S_8$ to match KiDS-1000, the best-fit model has a longer lifetime
$\tau = 120$ Gyr, with a larger kick velocity $v_{\rm kick}/c \simeq
\varepsilon \simeq 1.2\%$, than that without EFTofBOSS ($\tau = 43$ Gyr,
$\varepsilon =0.6\%$). We anticipate that future surveys will provide exquisite
constraints on such models. |
Locating Bound Structure in an Accelerating Universe: Given the overwhelming evidence that the universe is currently undergoing an
accelerated expansion, the question of what are the largest gravitationally
bound structures remains. A couple of groups, Busha et al. 2003 (B03) and
Dunner et al. 2006 (D06), have attempted to analytically define these limits,
arriving at substantially different estimates due to differences in their
assumptions about the velocities at the present epoch. In an effort to locate
the largest bound structures in the universe, we selected the Aquarius (ASC),
Microscopium (MSC), Corona Borealis (CBSC), and Shapley (SSC) superclusters for
study, due to their high number density of rich Abell clusters. Simple N-body
simulations, which assumed negligible intercluster mass, were used to assess
the likelihood of these structures being gravitationally bound, and the
predictions of the models of B03 and D06 were compared with those results. We
find that ASC, and MSC contain pairs of clusters which are gravitationally
bound, A2541/A2546 and A3695/A3696 respectively, with no other structures
having a significant chance of being bound. For SSC, we find a group of five
clusters, A3554, A3556, A3558, A3560, and A3562 that are bound, with an
additional pair, A1736/A3559, having a slight chance of being bound. We find
that CBSC has no extended bound structure, contrary to the findings of Small et
al. 1998, who claim that the entire supercluster is bound. In regards to the
analytical models, we find that B03 will identify structure that is definitely
bound, but tends to underestimate the true extent of the structure, while D06
will identify all structure that is bound while overestimating its extent.
Combined, the two models can provide lower and upper limits to the extent of
bound structures so long as there are no other significant structures nearby or
no significant dark matter exterior to the clusters. | Can filamentary accretion explain the orbital poles of the Milky Way
satellites?: Several scenarios have been suggested to explain the phase-space distribution
of the Milky Way (MW) satellite galaxies in a disc of satellites (DoS). To
quantitatively compare these different possibilities, a new method analysing
angular momentum directions in modelled data is presented. It determines how
likely it is to find sets of angular momenta as concentrated and as close to a
polar orientation as is observed for the MW satellite orbital poles. The method
can be easily applied to orbital pole data from different models. The observed
distribution of satellite orbital poles is compared to published angular
momentum directions of subhalos derived from six cosmological state-of-the-art
simulations in the Aquarius project. This tests the possibility that
filamentary accretion might be able to naturally explain the satellite orbits
within the DoS. For the most likely alignment of main halo and MW disc spin,
the probability to reproduce the MW satellite orbital pole properties turns out
to be less than 0.5 per cent in Aquarius models. Even an isotropic distribution
of angular momenta has a higher likelihood to produce the observed
distribution. The two Via Lactea cosmological simulations give results similar
to the Aquarius simulations. Comparing instead with numerical models of
galaxy-interactions gives a probability of up to 90 per cent for some models to
draw the observed distribution of orbital poles from the angular momenta of
tidal debris. This indicates that the formation as tidal dwarf galaxies in a
single encounter is a viable, if not the only, process to explain the
phase-space distribution of the MW satellite galaxies. |
Status of the OTELO Project: The OTELO project is the extragalactic survey currently under way using the
tunable filters of the OSIRIS instrument at the GTC. OTELO is already providing
the deepest emission line object survey of the universe up to a redshift 7. In
this contribution, the status of the survey and the first results obtained are
presented. | The lenticular galaxy NGC3607: stellar population, metallicity and
ionised gas: In this work we derive clues to the formation scenario and ionisation source
of the lenticular galaxy NGC 3607 by means of metallicity gradients, stellar
population and emission lines properties. We work with long-slit spectroscopy
from which we (i) study the radial distribution of the equivalent widths of
conspicuous metallic absorption features, (ii) infer on the star-formation
history (with a stellar population synthesis algorithm), and (iii) investigate
the ionisation source responsible for a few strong emission lines. Negative
radial gradients are observed for most of the absorption features of NGC 3607.
Compared to the external parts, the central region has a deficiency of alpha
elements and higher metallicity, which implies different star-formation
histories in both regions. At least three star formation episodes are detected,
with ages within 1-13 Gyr. The dynamical mass and the $Mg_2$ gradient slope are
consistent with mergers being important contributors to the formation mechanism
of NGC 3607. Emission-line ratios indicate the presence of a LINER at the
centre of NGC 3607. Contribution of hot, old stars to the gas ionisation
outside the central region is detected. Evidence drawn from this work suggest
small mergers as important contributors to the formation of NGC 3607, a
scenario consistent with the star-formation episodes. |
The environmental dependence of the stellar mass function at z~1:
Comparing cluster and field between the GCLASS and UltraVISTA surveys: We present the stellar mass functions (SMFs) of star-forming and quiescent
galaxies from observations of 10 rich clusters in the Gemini Cluster
Astrophysics Spectroscopic Survey (GCLASS) in the redshift range 0.86<z<1.34.
We compare our results with field measurements at similar redshifts using data
from a Ks-band selected catalogue of the COSMOS/UltraVISTA field. We construct
a Ks-band selected multi-colour catalogue for the clusters in 11 photometric
bands covering u-8um, and estimate photometric redshifts and stellar masses
using SED fitting techniques. To correct for interlopers in our cluster sample,
we use the deep spectroscopic component of GCLASS, which contains spectra for
1282 identified cluster and field galaxies taken with Gemini/GMOS. Both the
photometric and spectroscopic samples are sufficiently deep that we can probe
the SMF down to masses of 10^10 Msun. We distinguish between star-forming and
quiescent galaxies using the rest-frame U-V versus V-J diagram, and find that
the best-fitting Schechter parameters alpha and M* are similar within the
uncertainties for these galaxy types within the different environments.
However, there is a significant difference in the shape and normalisation of
the total SMF between the clusters and the field sample. This difference in the
total SMF is primarily a reflection of the increased fraction of quiescent
galaxies in high-density environments. We apply a simple quenching model that
includes components of mass- and environment-driven quenching, and find that in
this picture 45% of the star-forming galaxies, which normally would be forming
stars in the field, are quenched by the cluster. If galaxies in clusters and
the field quench their star formation via different mechanisms, these processes
have to conspire in such a way that the shapes of the quiescent and
star-forming SMF remain similar in these different environments. | Aemulus $ν$: Precise Predictions for Matter and Biased Tracer Power
Spectra in the Presence of Neutrinos: We present the Aemulus $\nu$ simulations: a suite of 150 $(1.05 h^{-1}\rm
Gpc)^3$ $N$-body simulations with a mass resolution of $3.51\times 10^{10}
\frac{\Omega_{cb}}{0.3} ~ h^{-1} M_{\odot}$ in a $w\nu$CDM cosmological
parameter space. The simulations have been explicitly designed to span a broad
range in $\sigma_8$ to facilitate investigations of tension between large scale
structure and cosmic microwave background cosmological probes. Neutrinos are
treated as a second particle species to ensure accuracy to $0.5\, \rm eV$, the
maximum neutrino mass that we have simulated. By employing Zel'dovich control
variates, we increase the effective volume of our simulations by factors of
$10-10^5$ depending on the statistic in question. As a first application of
these simulations, we build new hybrid effective field theory and matter power
spectrum surrogate models, demonstrating that they achieve $\le 1\%$ accuracy
for $k\le 1\, h\,\rm Mpc^{-1}$ and $0\le z \le 3$, and $\le 2\%$ accuracy for
$k\le 4\, h\,\rm Mpc^{-1}$ for the matter power spectrum. We publicly release
the trained surrogate models, and estimates of the surrogate model errors in
the hope that they will be broadly applicable to a range of cosmological
analyses for many years to come. |
The Pantheon+ Analysis: Evaluating Peculiar Velocity Corrections in
Cosmological Analyses with Nearby Type Ia Supernovae: Separating the components of redshift due to expansion and peculiar motion in
the nearby universe ($z<0.1$) is critical for using Type Ia Supernovae (SNe Ia)
to measure the Hubble constant ($H_0$) and the equation-of-state parameter of
dark energy ($w$). Here, we study the two dominant 'motions' contributing to
nearby peculiar velocities: large-scale, coherent-flow (CF) motions and
small-scale motions due to gravitationally associated galaxies deemed to be in
a galaxy group. We use a set of 584 low-$z$ SNe from the Pantheon+ sample, and
evaluate the efficacy of corrections to these motions by measuring the
improvement of SN distance residuals. We study multiple methods for modeling
the large and small-scale motions and show that, while group assignments and CF
corrections individually contribute to small improvements in Hubble residual
scatter, the greatest improvement comes from the combination of the two
(relative standard deviation of the Hubble residuals, Rel. SD, improves from
0.167 to 0.157 mag). We find the optimal flow corrections derived from various
local density maps significantly reduce Hubble residuals while raising $H_0$ by
$\sim0.4$ km s$^{-1}$ Mpc$^{-1}$ as compared to using CMB redshifts,
disfavoring the hypothesis that unrecognized local structure could resolve the
Hubble tension. We estimate that the systematic uncertainties in cosmological
parameters after optimally correcting redshifts are 0.06-0.11 km s$^{-1}$
Mpc$^{-1}$ in $H_0$ and 0.02-0.03 in $w$ which are smaller than the statistical
uncertainties for these measurements: 1.5 km s$^{-1}$ Mpc$^{-1}$ for $H_0$ and
0.04 for $w$. | Structure and History of Dark Matter Halos Probed with Gravitational
Lensing: We test with gravitational lensing data the dark matter (DM) halos embedding
the luminous baryonic component of galaxy clusters; our benchmark is provided
by their two-stage cosmogonical development that we compute with its variance,
and by the related '\alpha-profiles' we derive. The latter solve the Jeans
equation for the self-gravitating, anisotropic DM equilibria, and yield the
radial runs of the density \rho(r) and the velocity dispersion \sigma_r^2(r) in
terms of the DM 'entropy' K = \sigma_r^2/\rho^(2/3) ~ r^(\alpha) highlighted by
recent N-body simulations; the former constrains the slope to the narrow range
\alpha ~ 1.25 - 1.3. These physically based \alpha-profiles meet the overall
requirements from gravitational lensing observations, being intrinsically
flatter at the center and steeper in the outskirts relative to the empirical
NFW formula. Specifically, we project them along the l.o.s. and compare with a
recent extensive dataset from strong and weak lensing observations in and
around the cluster A1689. We find an optimal fit at both small and large scales
in terms of a halo constituted by an early body with \alpha ~ 1.25 and by
recent extensive outskirts, that make up an overall mass 10^15 M_sun with a
concentration parameter c ~ 10 consistent with the variance we compute in the
\LambdaCDM cosmogony. The resulting structure corresponds to a potential well
shallow in the outskirts as that inferred from the X rays radiated from the hot
electrons and baryons constituting the intracluster plasma. |
Reconstructing Small Scale Lenses from the Cosmic Microwave Background
Temperature Fluctuations: Cosmic Microwave Background (CMB) lensing is a powerful probe of the matter
distribution in the Universe. The standard quadratic estimator, which is
typically used to measure the lensing signal, is known to be suboptimal for
low-noise polarization data from next-generation experiments. In this paper we
explain why the quadratic estimator will also be suboptimal for measuring
lensing on very small scales, even for measurements in temperature where this
estimator typically performs well. Though maximum likelihood methods could be
implemented to improve performance, we explore a much simpler solution,
revisiting a previously proposed method to measure lensing which involves a
direct inversion of the background gradient. An important application of this
simple formalism is the measurement of cluster masses with CMB lensing. We find
that directly applying a gradient inversion matched filter to simulated lensed
images of the CMB can tighten constraints on cluster masses compared to the
quadratic estimator. While the difference is not relevant for existing surveys,
for future surveys it can translate to significant improvements in mass
calibration for distant clusters, where galaxy lensing calibration is
ineffective due to the lack of enough resolved background galaxies.
Improvements can be as large as $\sim 50\%$ for a cluster at $z = 2$ and a
next-generation CMB experiment with 1$\mu$K-arcmin noise, and over an order of
magnitude for lower noise levels. For future surveys, this simple
matched-filter or gradient inversion method approaches the performance of
maximum likelihood methods, at a fraction of the computational cost. | Extreme-Value Statistics of the Spin of Primordial Black Holes: How rare are extreme-spin primordial black holes? We show how, from an
underlying distribution of PBH spin, extreme-value statistics can be used to
quantify the rarity of spinning PBHs with Kerr parameter close to 1. Using the
Peaks-Over-Threshold method, we show how the probability that a PBH forms with
spin exceeding a sufficiently high threshold can be calculated using the
Generalised Pareto Distribution. This allows us to estimate the average number
of PBHs amongst which we can find a single PBH which formed with spin exceeding
a high threshold. We found that the primordial spin distribution gives rise to
exceedingly rare near-extremal spin PBHs at formation time: for typical
parameter values, roughly up to one in a hundred million PBHs would be formed
with spin exceeding the Thorne limit. We discuss conditions under which even
more extreme-spin PBHs may be produced, including modifying the skewness and
kurtosis of the spin distribution via a smooth transformation. We deduce from
our calculations that, if indeed asteroid-mass PBHs above the current
observational limit on evaporating PBHs of mass ~10^{17} g contribute
significantly to the dark matter, it is likely that some of them could be
near-extremal PBHs. |
A High Space Density of Luminous Lyman Alpha Emitters at z~6.5: We present the results of a systematic search for Lyman-alpha emitters (LAEs)
at $6 \lesssim z \lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic
Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8
\times10^5$ Mpc$^3$, comparable to many of the narrowband surveys despite their
larger area coverage. We find two LAEs at $z=6.38$ and $6.44$ with line
luminosities of L$_{\mathrm{Ly}\alpha} \sim 4.7 \times 10^{43}$ erg s$^{-1}$,
putting them among the brightest LAEs discovered at these redshifts. Taking
advantage of the broad spectral coverage of WISP, we are able to rule out
almost all lower-redshift contaminants. The WISP LAEs have a high number
density of $7.7\times10^{-6}$ Mpc$^{-3}$. We argue that the LAEs reside in
Mpc-scale ionized bubbles that allow the Lyman-alpha photons to redshift out of
resonance before encountering the neutral IGM. We discuss possible ionizing
sources and conclude that the observed LAEs alone are not sufficient to ionize
the bubbles. | The effects of non-linearity on the growth rate constraint from velocity
correlation functions: The two-point statistics of the cosmic velocity field, measured from galaxy
peculiar velocity (PV) surveys, can be used as a dynamical probe to constrain
the growth rate of large-scale structures in the universe. Most works use the
statistics on scales down to a few tens of Megaparsecs, while using a
theoretical template based on the linear theory. In addition, while the cosmic
velocity is volume-weighted, the observable line-of-sight velocity two-point
correlation is density-weighted, as sampled by galaxies, and therefore the
density-velocity correlation term also contributes, which has often been
neglected. These effects are fourth order in powers of the linear density
fluctuation $\delta_{\rm L}^4$, compared to $\delta_{\rm L}^2$ of the linear
velocity correlation function, and have the opposite sign. We present these
terms up to $\delta_{\rm L}^4$ in real space based on the standard perturbation
theory, and investigate the effect of non-linearity and the density-velocity
contribution on the inferred growth rate $f\sigma_8$, using $N$-body
simulations. We find that for a next-generation PV survey of volume $\sim {\cal
O}(500 \, h^{-1} \, {\rm Mpc})^3$, these effects amount to a shift of
$f\sigma_8$ by $\sim 10$ per cent and is comparable to the forecasted
statistical error when the minimum scale used for parameter estimation is
$r_{\rm min} = 20 \, h^{-1} \, {\rm Mpc}$. |
Testing the Large-Scale Environments of Cool-core and Noncool-core
Clusters with Clustering Bias: There are well-observed differences between cool-core (CC) and non-cool-core
(NCC) clusters, but the origin of this distinction is still largely unknown.
Competing theories can be divided into internal (inside-out), in which internal
physical processes transform or maintain the NCC phase, and external
(outside-in), in which the cluster type is determined by its initial
conditions, which in turn lead to different formation histories (i.e., assembly
bias). We propose a new method that uses the relative assembly bias of CC to
NCC clusters, as determined via the two-point cluster-galaxy cross-correlation
function (CCF), to test whether formation history plays a role in determining
their nature. We apply our method to 48 ACCEPT clusters, which have well
resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ
galaxy catalog. We find that the relative bias of NCC over CC clusters is $b =
1.42 \pm 0.35$ ($1.6\sigma$ different from unity). Our measurement is limited
by the small number of clusters with core entropy information within the BOSS
footprint, 14 CC and 34 NCC. Future compilations of X-ray cluster samples,
combined with deep all-sky redshift surveys, will be able to better constrain
the relative assembly bias of CC and NCC clusters and determine the origin of
the bimodality. | The relativistic galaxy number counts in the weak field approximation: We present a novel approach to compute systematically the relativistic
projection effects at any order in perturbation theory within the weak field
approximation. In this derivation the galaxy number counts is written
completely in terms of the redshift perturbation. The relativistic effects
break the symmetry along the line-of-sight and they source, contrarily to the
standard perturbation theory, the odd multipoles of the matter power spectrum
or 2-point correlation function, providing a unique signature for their
detection in Large Scale Structure surveys. We show that our approach agrees
with previous derivations (up to third order) of relativistic effects and, for
the first time, we derive a model for the transverse Doppler effect. Moreover,
we show that in the Newtonian limit this approach is consistent with standard
perturbation theory at any order. |
Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in
the Local Group: Within the Local Universe galaxies can be studied in great detail star by
star, and here we review the results of quantitative studies in nearby dwarf
galaxies. The Color-Magnitude Diagram synthesis method is well established as
the most accurate way to determine star formation history of galaxies back to
the earliest times. This approach received a large boost from the exceptional
data sets that wide field CCD imagers on the ground and the Hubble Space
Telescope could provide. Spectroscopic studies using large ground based
telescopes such as VLT, Magellan, Keck and HET have allowed the determination
of abundances and kinematics for significant samples of stars in nearby dwarf
galaxies. These studies have shown how the properties of stellar populations
can vary spatially and temporally. This leads to important constraints to
theories of galaxy formation and evolution. The combination of spectroscopy and
imaging and what they have taught us about dwarf galaxy formation and evolution
is the aim of this review. | LBT and Spitzer Spectroscopy of Star-Forming Galaxies at 1 < z < 3:
Extinction and Star Formation Rate Indicators: We present spectroscopic observations in the rest-frame optical and near- to
mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous
star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the
Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample
was selected to represent pure, actively star-forming systems, absent of active
galactic nuclei. The large lensing magnifications result in high
signal-to-noise spectra that can probe faint IR recombination lines, including
Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three
lensed galaxies with similar suites of unpublished data and observations from
the literature, resulting in the final sample of seven galaxies. We use the IR
recombination lines in conjunction with H-alpha observations to probe the
extinction, Av, of these systems, as well as testing star formation rate (SFR)
indicators against the SFR measured by fitting spectral energy distributions to
far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger
than previously known for a similar range of IR luminosities at these
redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of
extinction in the most IR luminous galaxies. We also measure extinction by
comparing SFR estimates from optical emission lines with those from far-IR
measurements. The comparison of results from these two independent methods
indicates a large variety of dust distribution scenarios at 1 < z < 3. Without
correcting for dust extinction, the H-alpha SFR indicator underestimates the
SFR; the size of the necessary correction depends on the IR luminosity and dust
distribution scenario. Individual SFR estimates based on the 6.2 micron PAH
emission line luminosity do not show a systematic discrepancy with extinction,
although a considerable, ~0.2 dex scatter is observed. |
Bulk flow in the combined 2MTF and 6dFGSv surveys: We create a combined sample of 10,904 late and early-type galaxies from the
2MTF and 6dFGSv surveys in order to accurately measure bulk flow in the local
Universe. Galaxies and groups of galaxies common between the two surveys are
used to verify that the difference in zero-points is $<0.02$ dex. We introduce
a maximum likelihood estimator ($\eta$MLE) for bulk flow measurements which
allows for more accurate measurement in the presence non-Gaussian measurement
errors. To calibrate out residual biases due to the subtle interaction of
selection effects, Malmquist bias and anisotropic sky distribution, the
estimator is tested on mock catalogues generated from 16 independent
large-scale GiggleZ and SURFS simulations. The bulk flow of the local Universe
using the combined data set, corresponding to a scale size of 40 h$^{-1}$ Mpc,
is $288\pm24$ km s$^{-1}$ in the direction $(l,b)=(296\pm6^{\circ},
21\pm5^{\circ})$. This is the most accurate bulk flow measurement to date, and
the amplitude of the flow is consistent with the $\Lambda$CDM expectation for
similar size scales. | A characterization of the NGC 4051 soft X-ray spectrum as observed by
XMM-Newton: Soft X-rays high resolution spectroscopy of obscured AGNs shows the existence
of a complex soft $X$-ray spectrum dominated by emission lines of He and H-like
transitions of elements from Carbon to Neon, as well as L-shell transitions due
to iron ions. In this paper we characterize the XMM-Newton RGS spectrum of the
Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the
physical properties of the emitting and absorbing gas in the soft X-ray regime.
X-ray high-resolution spectroscopy offers a powerful diagnostic tool since the
observed spectral features strongly depend on the physical properties of matter
(ionization parameter U, electron density n_e, hydrogen column density N_H),
which in turn are tightly related to the location and size of the X-ray
emitting clouds. We carried out a phenomenological study to identify the atomic
transitions detected in the spectra. This study suggests that the spectrum is
dominated by emission from a photoionised plasma. Then, we used the
photoionization code Cloudy to produce synthetic models for the emission line
component and the warm absorber observed during phases of high intrinsic
luminosity. The low state spectrum cannot be described by a single
photoionization component. A multi-ionization phase gas with ionization
parameter in the range log U = 0.63-1.90 and column density log N_H =
22.10-22.72 cm^-2 is required, while the electron density n_e remains
unconstrained. A warm absorber medium is required by the fit with parameters
log U = 0.85, log N_H = 23.40 and log n_e \ut< 5. The model is consistent with
an X-ray emitting regions at a distance > 5 x 10^-2 pc from the central engine. |
Approximating Density Probability Distribution Functions Across
Cosmologies: Using a suite of self-similar cosmological simulations, we measure the
probability distribution functions (PDFs) of real-space density, redshift-space
density, and their geometric mean. We find that the real-space density PDF is
well-described by a function of two parameters: $n_s$, the spectral slope, and
$\sigma_L$, the linear rms density fluctuation. For redshift-space density and
the geometric mean of real- and redshift-space densities, we introduce a third
parameter, $s_L={\sqrt{\langle(dv^L_{\rm pec}/dr)^2\rangle}}/{H}$. We find that
density PDFs for the LCDM cosmology is also well-parameterized by these three
parameters. As a result, we are able to use a suite of self-similar
cosmological simulations to approximate density PDFs for a range of
cosmologies. We make the density PDFs publicly available and provide an
analytical fitting formula for them. | Observational constraints on Chaplygin cosmology in a braneworld
scenario with induced gravity and curvature effect: We study cosmological dynamics and late-time evolution of an extended induced
gravity braneworld scenario. In this scenario, curvature effects are taken into
account via the Gauss-Bonnet term in the bulk action and there is also a
Chaplygin gas component on the brane. We show that this model mimics an
effective phantom behavior in a relatively wider range of redshifts than
previously formulated models. It also provides a natural framework for smooth
crossing of the phantom-divide line due to presence of the Chaplygin gas
component on the brane. We confront the model with observational data from type
Ia Supernovae, Cosmic Microwave Background and Baryon Acoustic Oscillations to
constraint the model parameters space. |
Beyond the power spectrum: primordial and secondary non-Gaussianity in
the microwave background: Cosmic microwave background observations are most commonly analyzed by
estimating the power spectrum. In the limit where the CMB statistics are
perfectly Gaussian, this extracts all the information, but the CMB also
contains detectable non-Gaussian contributions from secondary, and possibly
primordial, sources. We review possible sources of CMB non-Gaussianity and
describe statistical techniques which are optimized for measuring them,
complementing the power spectrum analysis. The machinery of $N$-point
correlation functions provides a unifying framework for optimal estimation of
primordial non-Gaussian signals or gravitational lensing. We review recent
results from applying these estimators to data from the WMAP satellite mission. | Cross-correlating 21cm intensity maps with Lyman Break Galaxies in the
post-reionization era: We investigate the cross-correlation between the spatial distribution of
Lyman Break Galaxies (LBGs) and the 21cm intensity mapping signal at
$z\sim[3-5]$. At these redshifts, galactic feedback is supposed to only
marginally affect the matter power spectrum, and the neutral hydrogen
distribution is independently constrained by quasar spectra. Using a high
resolution N-body simulation, populated with neutral hydrogen a posteriori, we
forecast for the expected LBG-21cm cross-spectrum and its error for a 21cm
field observed by the Square Kilometre Array (SKA1-LOW and SKA1-MID), combined
with a spectroscopic LBG survey with the same volume. The cross power can be
detected with a signal-to-noise ratio (SNR) up to ~10 times higher (and down to
~4 times smaller scales) than the 21cm auto-spectrum for this set-up, with the
SNR depending only very weakly on redshift and the LBG population. We also show
that while both the 21cm auto- and LBG-21cm cross-spectra can be reliably
recovered after the cleaning of smooth-spectrum foreground contamination, only
the cross-power is robust to problematic non-smooth foregrounds like polarized
synchrotron emission. |
The Cosmic Web of Baryons: Only about 10% of the baryons in the universe lie in galaxies as stars or
cold gas, with the remainder predicted to exist as a dilute gaseous filamentary
network known as the Cosmic Web. Some of this gas is detected through UV
absorption line studies, but half of the gas remains undetected. Growth of
structure simulations suggest that these "missing" baryons were shock heated in
unvirialized cosmic filaments to temperatures of 10^5.5-10^7 K, and that the
gas is chemically enriched by galactic superwinds. Most of the gas in this
temperature regime can be detected only by X-ray observations through
absorption and emission from the He-like and H-line ions of C, N, and O. This
white paper shows that an X-ray telescope such as IXO can test the most central
predictions of the Cosmic Web: the distribution of gas mass with temperature;
the dynamics of the gas and its relationship to nearby galaxies; and the
topology of the Cosmic Web material. | On the fast computation of the observer motion effects induced on
monopole frequency spectra for tabulated functions: Methods are studied to compute the boosting effects produced by the observer
motion that modifies and transfers to higher l the isotropic monopole frequency
spectrum of the cosmic background. Explicit analytical solutions for spherical
harmonic coefficients are presented and applied to various background spectra,
alleviating computational effort. High l frequency spectra are led by higher
order derivatives of the spectrum. Tabulated frequency spectra are computed
with a relatively poor frequency resolution in comparison with the Doppler
shift, calling for interpolation. They are affected by uncertainties due to
intrinsic inaccuracies in modelling, observational data or limited computation
accuracy, propagate and increase with the derivative order, possibly preventing
a trustworthy computation to higher l and of the observed monopole. We filter
the original function and the multipole spectra to derive reliable predictions
of the harmonic coefficients. For spectra expressed in Taylor series, we derive
explicit solutions for the harmonic coefficients up to l=6 in terms of spectra
derivatives. We consider filters and study the quality of these methods on
suitable analytical approximations, polluted with simulated noise. We consider
the extragalactic sources microwave background from radio loud AGN and the 21cm
line superimposed to the CMB. Gaussian pre-filtering coupled to a real space
filtering of derivatives allows accurate predictions up to l=6, while log-log
polynomial representation gives accurate solutions at any l. Describing the 21
cm model variety is difficult, so it is relevant to relax assumptions.
Pre-filtering gives accurate predictions up to l=3-4, while further filtering
or boosting amplification/deamplification method improves the results allowing
reasonable estimations. The methods can extend the range of realistic
background models manageable with a fast computation. |
The large area KX quasar catalogue: I. Analysis of the photometric
redshift selection and the complete quasar catalogue: The results of a large area, ~600 deg^2, K-band flux-limited spectroscopic
survey for luminous quasars are presented. The survey utilises the UKIRT
Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) in regions of sky
within the Sloan Digital Sky Survey (SDSS) footprint. The K-band excess (KX) of
all quasars with respect to Galactic stars is exploited in combination with a
photometric redshift/classification scheme to identify quasar candidates for
spectroscopic follow-up observations. The data contained within this
investigation will be able to provide new constraints on the fraction of
luminous quasars reddened by dust with E(B-V)<=0.5 mag. The spectroscopic
sample is defined using the K-band, 14.0<=K<=16.6, and SDSS i-band limits of
i=19.5, 19.7 and 22.0 over sky areas of 287, 150 and 196 deg^2, respectively.
The survey includes >3200 known quasars from the SDSS and more than 250
additional confirmed quasars from the KX-selection. A well-defined sub-sample
of quasars in the redshift interval 1.0<=z<=3.5 includes 1152 objects from the
SDSS and 172 additional KX-selected quasars. The quasar selection is >95 per
cent complete with respect to known SDSS quasars and >95 per cent efficient,
largely independent of redshift and i-band magnitude. The properties of the new
KX-selected quasars confirm the known redshift-dependent effectiveness of the
SDSS quasar selection and provide a sample of luminous quasars experiencing
intermediate levels of extinction by dust. The catalogue represents an
important step towards the assembly of a well-defined sample of luminous
quasars that may be used to investigate the properties of quasars experiencing
intermediate levels of dust extinction within their host galaxies or due
intervening absorption line systems. | A Spitzer Study of Pseudobulges in S0 Galaxies : Secular Evolution of
Disks: In this Letter, we present a systematic study of lenticular (S0) galaxies
based on mid-infrared imaging data on 185 objects taken using the Spitzer Infra
Red Array Camera. We identify the S0s hosting pseudobulges based on the
position of the bulge on the Kormendy diagram and the S\'{e}rsic index of the
bulge. We find that pseudobulges preferentially occur in the fainter luminosity
class (defined as having total K-band absolute magnitude M_K fainter than
-22.66 in the AB system). We present relations between bulge and disk
parameters obtained as a function of the bulge type. The disks in the
pseudobulge hosting galaxies are found to have distinct trends on the r_e-r_d
and \mu_d (0) - r_d correlations compared to those in galaxies with classical
bulges. We show that the disks of pseudobulge hosts possess on average a
smaller scale length and have a fainter central surface brightness than their
counterparts occurring in classical bulge hosting galaxies. The differences
found for discs in pseudobulge and classical bulge hosting galaxies may be a
consequence of the different processes creating the central mass
concentrations. |
Serendipitous discovery of a strong-lensed galaxy in integral field
spectroscopy from MUSE: 2MASX J04035024-0239275 is a bright red elliptical galaxy at redshift 0.0661
that presents two extended sources at 2\arcsec~to the north-east and
1\arcsec~to the south-west. The sizes and surface brightnesses of the two blue
sources are consistent with a gravitationally-lensed background galaxy. In this
paper we present MUSE observations of this galaxy from the All-weather MUse
Supernova Integral-field Nearby Galaxies (AMUSING) survey, and report the
discovery of a background lensed galaxy at redshift 0.1915, together with other
15 background galaxies at redshifts ranging from 0.09 to 0.9, that are not
multiply imaged. We have extracted aperture spectra of the lens and all the
sources and fit the stellar continuum with STARLIGHT to estimate their stellar
and emission line properties. A trace of past merger and active nucleus
activity is found in the lensing galaxy, while the background lensed galaxy is
found to be star-forming. Modeling the lensing potential with a singular
isothermal ellipsoid, we find an Einstein radius of 1\farcs45$\pm$0\farcs04,
which corresponds to 1.9 kpc at the redshift of the lens and it is much smaller
than its effective radius ($r_{\rm eff}\sim$ 9\arcsec). Comparing the Einstein
mass and the STARLIGHT stellar mass within the same aperture yields a dark
matter fraction of $18 \% \pm 8$ \% within the Einstein radius. The advent of
large surveys such as the Large Synoptic Survey Telescope (LSST) will discover
a number of strong-lensed systems, and here we demonstrate how wide-field
integral field spectroscopy offers an excellent approach to study them and to
precisely model lensing effects. | Connecting Faint End Slopes of the Lyman-$α$ emitter and
Lyman-break Galaxy Luminosity Functions: We predict Lyman-$\alpha$ (Ly$\alpha$) luminosity functions (LFs) of
Ly$\alpha$-selected galaxies (Ly$\alpha$ emitters, or LAEs) at $z=3-6$ using
the phenomenological model of Dijkstra & Wyithe (2012). This model combines
observed UV-LFs of Lyman-break galaxies (LBGs, or drop out galaxies), with
constraints on their distribution of Ly$\alpha$ line strengths as a function of
UV-luminosity and redshift. Our analysis shows that while Ly$\alpha$ LFs of
LAEs are generally not Schechter functions, these provide a good description
over the luminosity range of $\log_{10}( L_{\alpha}/{\rm erg}\,{\rm
s}^{-1})=41-44$. Motivated by this result, we predict Schechter function
parameters at $z=3-6$. Our analysis further shows that (i) the faint end slope
of the Ly$\alpha$ LF is steeper than that of the UV-LF of Lyman-break galaxies,
(with a median $\alpha_{Ly\alpha} < -2.0$ at $z\gtrsim 4$), and (ii) a
turn-over in the Ly$\alpha$ LF of LAEs at Ly$\alpha$ luminosities $10^{40}$ erg
s$^{-1}<L_{\alpha}\lesssim 10^{41}$ erg s$^{-1}$ may signal a flattening of
UV-LF of Lyman-break galaxies at $-12>M_{\rm UV}>-14$. We discuss the
implications of these results - which can be tested directly with upcoming
surveys - for the Epoch of Reionization. |
Swift UV/Optical Telescope Imaging of Star Forming Regions in M81 and
Holmberg IX: We present Swift UV/Optical Telescope (UVOT) imaging of the galaxies M81 and
Holmberg IX. We combine UVOT imaging in three near ultraviolet (NUV) filters
(uvw2: 1928 {\AA}, uvm2: 2246 {\AA}, and uvw1: 2600 {\AA}) with ground based
optical imaging from the Sloan Digital Sky Survey to constrain the stellar
populations of both galaxies. Our analysis consists of three different methods.
First we use the NUV imaging to identify UV star forming knots and then perform
SED modeling on the UV/optical photometry of these sources. Second, we measure
surface brightness profiles of the disk of M81 in the NUV and optical. Last we
use SED fitting of individual pixels to map the properties of the two galaxies.
In agreement with earlier studies we find evidence for a burst in star
formation in both galaxies starting ~200 Myr ago coincident with the suggested
time of an M81-M82 interaction. In line with theories of its origin as a tidal
dwarf we find that the luminosity weighted age of Holmberg IX is a few hundred
million years. Both galaxies are best fit by a Milky Way dust extinction law
with a prominent 2175 {\AA} bump. In addition, we describe a stacked median
filter technique for modeling the diffuse background light within a galaxy, and
a Markov chain method for cleaning segment maps generated by SExtractor. | Detection of cross-correlation between gravitational lensing and gamma
rays: In recent years, many gamma-ray sources have been identified, yet the
unresolved component hosts valuable information on the faintest emission. In
order to extract it, a cross-correlation with gravitational tracers of matter
in the Universe has been shown to be a promising tool. We report here the first
identification of a cross-correlation signal between gamma rays and the
distribution of mass in the Universe probed by weak gravitational lensing. We
use the Dark Energy Survey Y1 weak lensing catalogue and the Fermi Large Area
Telescope 9-year gamma-ray data, obtaining a signal-to-noise ratio of 5.3. The
signal is mostly localised at small angular scales and high gamma-ray energies,
with a hint of correlation at extended separation. Blazar emission is likely
the origin of the small-scale effect. We investigate implications of the
large-scale component in terms of astrophysical sources and particle dark
matter emission. |
Stellar archeology of the nearby LINER galaxies NGC 4579 and NGC 4736: Stellar archeology of nearby LINER galaxies may reveal if there is a stellar
young population that may be responsible for the LINER phenomenon. We show
results for the classical LINER galaxies NGC 4579 and NGC 4736 and find no
evidence of such populations. | Ubiquitous seeding of supermassive black holes by direct collapse: We study for the first time the environment of massive black hole (BH) seeds
(~10^4-5 Msun) formed via the direct collapse of pristine gas clouds in massive
haloes (>10^7 Msun) at z>6. Our model is based on the evolution of dark matter
haloes within a cosmological N-body simulation, combined with prescriptions for
the formation of BH along with both Pop III and Pop II stars. We calculate the
spatially-varying intensity of Lyman Werner (LW) radiation from stars and
identify the massive pristine haloes in which it is high enough to shut down
molecular hydrogen cooling. In contrast to previous BH seeding models with a
spatially constant LW background, we find that the intensity of LW radiation
due to local sources, J_local, can be up to 10^6 times the spatially averaged
background in the simulated volume and exceeds the critical value, J_crit, for
the complete suppression of molecular cooling, in some cases by 4 orders of
magnitude. Even after accounting for possible metal pollution in a halo from
previous episodes of star formation, we find a steady rise in the formation
rate of direct collapse (DC) BHs with decreasing redshift from 10^{-3}/Mpc^3/z
at z=12 to 10^{-2}/Mpc^3/z at z=6. The onset of Pop II star formation at z~16
simultaneously marks the onset of the epoch of DCBH formation, as the increased
level of LW radiation from Pop II stars is able to elevate the local levels of
the LW intensity to J_local > J_crit while Pop III stars fail to do so at any
time. The number density of DCBHs is sensitive to the number of LW photons and
can vary by an order of magnitude at z=6 after accounting for reionisation
feedback. Haloes hosting DCBHs are more clustered than similar massive
counterparts that do not host DCBHs, especially at redshifts z>10. We also show
that planned surveys with JWST should be able to detect the supermassive
stellar precursors of DCBHs. |
The Epoch of Disk Settling: z~1 to Now: We present evidence from a sample of 544 galaxies from the DEEP2 Survey for
evolution of the internal kinematics of blue galaxies with stellar masses
ranging 8.0 < log M* (M_Sun) < 10.7 over 0.2<z<1.2. DEEP2 provides galaxy
spectra and Hubble imaging from which we measure emission-line kinematics and
galaxy inclinations, respectively. Our large sample allows us to overcome
scatter intrinsic to galaxy properties in order to examine trends in
kinematics. We find that at a fixed stellar mass galaxies systematically
decrease in disordered motions and increase in rotation velocity and potential
well depth with time. Massive galaxies are the most well-ordered at all times
examined, with higher rotation velocities and less disordered motions than less
massive galaxies. We quantify disordered motions with an integrated gas
velocity dispersion corrected for beam smearing (sigma_g). It is unlike the
typical pressure-supported velocity dispersion measured for early type galaxies
and galaxy bulges. Because both seeing and the width of our spectral slits
comprise a significant fraction of the galaxy sizes, sigma_g integrates over
velocity gradients on large scales which can correspond to non-ordered gas
kinematics. We compile measurements of galaxy kinematics from the literature
over 1.2<z<3.8 and do not find any trends with redshift, likely for the most
part because these datasets are biased toward the most highly star-forming
systems. In summary, over the last ~8 billion years since z=1.2, blue galaxies
evolve from disordered to ordered systems as they settle to become the
rotation-dominated disk galaxies observed in the Universe today, with the most
massive galaxies being the most evolved at any time. | Modelling the shapes of the largest gravitationally bound objects: We combine the physics of the ellipsoidal collapse model with the excursion
set theory to study the shapes of dark matter halos. In particular, we develop
an analytic approximation to the nonlinear evolution that is more accurate than
the Zeldovich approximation; we introduce a planar representation of halo axis
ratios, which allows a concise and intuitive description of the dynamics of
collapsing regions and allows one to relate the final shape of a halo to its
initial shape; we provide simple physical explanations for some empirical
fitting formulae obtained from numerical studies. Comparison with simulations
is challenging, as there is no agreement about how to define a non-spherical
gravitationally bound object. Nevertheless, we find that our model matches the
conditional minor-to-intermediate axis ratio distribution rather well, although
it disagrees with the numerical results in reproducing the minor-to-major axis
ratio distribution. In particular, the mass dependence of the minor-to-major
axis distribution appears to be the opposite to what is found in many previous
numerical studies, where low-mass halos are preferentially more spherical than
high-mass halos. In our model, the high-mass halos are predicted to be more
spherical, consistent with results based on a more recent and elaborate halo
finding algorithm, and with observations of the mass dependence of the shapes
of early-type galaxies. We suggest that some of the disagreement with some
previous numerical studies may be alleviated if we consider only isolated
halos. |
Galaxy And Mass Assembly (GAMA): The galaxy stellar mass function at z <
0.06: We determine the low-redshift field galaxy stellar mass function (GSMF) using
an area of 143 deg^2 from the first three years of the Galaxy And Mass Assembly
(GAMA) survey. The magnitude limits of this redshift survey are r < 19.4 mag
over two thirds and 19.8 mag over one third of the area. The GSMF is determined
from a sample of 5210 galaxies using a density-corrected maximum volume method.
This efficiently overcomes the issue of fluctuations in the number density
versus redshift. With H_0 = 70, the GSMF is well described between 10^8 and
10^11.5 Msun using a double Schechter function with mass^* = 10^10.66 Msun,
phi_1^* = 3.96 x 10^-3 Mpc^-3, alpha_1 = -0.35, phi_2^* = 0.79 x 10^-3 Mpc^-3
and alpha_2 = -1.47. This result is more robust to uncertainties in the
flow-model corrected redshifts than from the shallower Sloan Digital Sky Survey
main sample (r < 17.8 mag). The upturn in the GSMF is also seen directly in the
i-band and K-band galaxy luminosity functions. Accurately measuring the GSMF
below 10^8 Msun is possible within the GAMA survey volume but as expected
requires deeper imaging data to address the contribution from low
surface-brightness galaxies. | The Impact of Theoretical Uncertainties in the Halo Mass Function and
Halo Bias on Precision Cosmology: We study the impact of theoretical uncertainty in the dark matter halo mass
function and halo bias on dark energy constraints from imminent galaxy cluster
surveys. We find that for an optical cluster survey like the Dark Energy
Survey, the accuracy required on the predicted halo mass function to make it an
insignificant source of error on dark energy parameters is ~ 1%. The analogous
requirement on the predicted halo bias is less stringent (~ 5%), particularly
if the observable-mass distribution can be well constrained by other means.
These requirements depend upon survey area but are relatively insensitive to
survey depth. The most stringent requirements are likely to come from a survey
over a significant fraction of the sky that aims to observe clusters down to
relatively low mass, Mth ~ 10^13.7 Msun/h; for such a survey, the mass function
and halo bias must be predicted to accuracies of ~ 0.5% and ~ 1%, respectively.
These accuracies represent a limit on the practical need to calibrate ever more
accurate halo mass and bias functions. We find that improving predictions for
the mass function in the low-redshift and low-mass regimes is the most
effective way to improve dark energy constraints. |
The Scavenger Hunt for Quasar Samples to Be Used as Cosmological Tools: Although the $\Lambda$ Cold Dark Matter model is the most accredited
cosmological model, information at high redshifts ($z$) between type Ia
supernovae ($z=2.26$) and the Cosmic Microwave Background ($z=1100$) is crucial
to validate this model further. To this end, we have discovered a sample of
1132 quasars up to $z=7.54$ exhibiting a reduced intrinsic dispersion of the
relation between ultraviolet and X-ray fluxes, $\delta_\mathrm{F}=0.22$ vs.
$\delta_\mathrm{F}=0.29$ ($24\%$ less), than the original sample. This gold
sample, once we correct the luminosities for selection biases and redshift
evolution, enables us to determine the matter density parameter $\Omega_M$ with
a precision of 0.09. Unprecedentedly, this quasar sample is the only one that,
as a standalone cosmological probe, yields such tight constraints on $\Omega_M$
while being drawn from the same parent population of the initial sample. | The HST/ACS Coma Cluster Survey III. Structural Parameters of Galaxies
using single-Sérsic Fits: We present a catalogue of structural parameters for 8814 galaxies in the 25
fields of the HST/ACS Coma Treasury Survey. Parameters from S\'ersic fits to
the two-dimensional surface brightness distributions are given for all galaxies
from our published Coma photometric catalogue with mean effective surface
brightness brighter than 26.0 mag/sq. arcsec and brighter than 24.5 mag
(equivalent to absolute magnitude - 10.5), as given by the fits, all in
F814W(AB).
The sample comprises a mixture of Coma members and background objects; 424
galaxies have redshifts and of these 163 are confirmed members. The fits were
carried out using both the Gim2D and Galfit codes. We provide the following
parameters: Galaxy ID, RA, DEC, the total corrected automatic magnitude from
the photometric catalogue, the total magnitude of the model (F814W_AB), the
geometric mean effective radius Re, the mean surface brightness within the
effective radius <{\mu}>_e, the S\'ersic index n, the ellipticity and the
source position angle. The selection limits of the catalogue and the errors
listed for the S\'ersic parameters come from extensive simulations of the
fitting process using synthetic galaxy models. The agreement between Gim2D and
Galfit parameters is sensitive to details of the fitting procedure; for the
settings employed here the agreement is excellent over the range of parameters
covered in the catalogue. We define and present two goodness-of-fit indices
which quantify the degree to which the image can be approximated by a S\'ersic
model with concentric, coaxial elliptical isophotes; such indices may be used
to objectively select galaxies with more complex structures such as bulge-disk,
bars or nuclear components.
We make the catalog available in electronic format at Astro-WISE and MAST. |
Stacking Star Clusters in M51: Searching for Faint X-Ray Binaries: The population of low-luminosity (< 10^35 erg/s) X-Ray Binaries (XRBs) has
been investigated in our Galaxy and M31 but not further. To address this
problem, we have used data from the Chandra X-Ray Observatory and the Hubble
Space Telescope to investigate the faint population of XRBs in the grand-design
spiral galaxy M51. A matching analysis found 25 star clusters coincident with
20 X-ray point sources within 1.5" (60 pc). From X-ray and optical color-color
plots we determine that this population is dominated by high-mass XRBs. A
stacking analysis of the X-ray data at the positions of optically-identified
star clusters was completed to probe low-luminosity X-ray sources. No cluster
type had a significant detection in any X-ray energy band. An average globular
cluster had the largest upper limit, 9.23 x 10^34 erg/s, in the full-band (0.3
- 8 keV) while on average the complete sample of clusters had the lowest upper
limit, 6.46 x 10^33 erg/s in the hard-band (2 - 8 keV). We determined average
luminosities of the young and old star cluster populations and compared the
results to those from the Milky Way. We conclude that deeper X-ray data is
required to identify faint sources with a stacking analysis. | The Impact of Quadratic Biases on Cosmic Shear: In this paper we revisit potential biases in cosmic shear power spectra
caused by bias terms that multiply up to quadratic powers of the shear.
Expanding the multiplicative bias field as a series of independent spin-$s$
fields we find terms $m_s$ that multiply integer and half-integer powers of the
shear. We propagate these biases into shape measurement statistics and the
cosmic shear power spectrum. We find that such biases can be measured by
performing regression on calibration data. We find that for integer powers of
shear the impact of quadratic order terms on the power spectrum is an
additional bispectrum dependency; ignoring quadratic terms can lead to biases
in cosmological parameters of up to $2(m_2+m_{-2}-m_6)0.4\sigma$ for Stage-IV
dark energy experiments, but that the susceptibility to them can be decreased
by using methods to remove small-scale sensitivity. We also find, for
half-integer powers of the shear that, for a Stage-IV experiment, biases are
required to be known to better than approximately
$\sigma[m_0+15(m_1+m_3)+0.1(m_{-1}+m_5)]\leq 0.01$. In future, Stage-IV dark
energy experiments should seek to measure and minimise such all such bias
terms. |
On dataset tensions and signatures of new cosmological physics: Can new cosmic physics be uncovered through tensions amongst datasets?
Tensions in parameter determinations amongst different types of cosmological
observation, especially the `Hubble tension' between probes of the expansion
rate, have been invoked as possible indicators of new physics, requiring
extension of the $\Lambda$CDM paradigm to resolve. Within a fully Bayesian
framework, we show that the standard tension metric gives only part of the
updating of model probabilities, supplying a data co-dependence term that must
be combined with the Bayes factors of individual datasets. This shows that, on
its own, a reduction of dataset tension under an extension to $\Lambda$CDM is
insufficient to demonstrate that the extended model is favoured. Any analysis
that claims evidence for new physics {\it solely} on the basis of alleviating
dataset tensions should be considered incomplete and suspect. We describe the
implications of our results for the interpretation of the Hubble tension. | Prospects for precision cosmology with the 21 cm signal from the dark
ages: The 21 cm signal from the dark ages provides a potential new probe of
fundamental cosmology. While exotic physics could be discovered, here we
quantify the expected benefits within the standard cosmology. A measurement of
the global (sky-averaged) 21 cm signal to the precision of thermal noise from a
1,000 h integration would yield a measurement within 10% of a combination of
cosmological parameters. A 10,000 h integration would improve this measurement
to 3.2% and constrain the cosmic helium fraction to 9.9%. Precision cosmology
with 21 cm fluctuations requires a collecting area of 10 km$^2$ (corresponding
to 400,000 stations), which, with a 1,000 h integration, would exceed the same
global case by a factor of $\sim2$. Enhancing the collecting area or
integration time by an order of magnitude would yield a 0.5% parameter
combination, a helium measurement five times better than Planck and a
constraint on the neutrino mass as good as Planck. Our analysis sets a baseline
for upcoming lunar and space-based dark-ages experiments. |
Ongoing Massive Star Formation in NGC 604: NGC 604 is the second most massive H II region in the Local Group, thus an
important laboratory for massive star formation. Using a combination of
observational and analytical tools that include Spitzer spectroscopy, Herschel
photometry, Chandra imaging, and Bayesian Spectral Energy Distribution fitting,
we investigate the physical conditions in NGC 604, and quantify the amount of
massive star formation currently taking place. We derive an average age of 4
+/- 1 Myr and a total stellar mass of 1.6 (+1.6)(-1.0) x 10^5 M_sun for the
entire region, in agreement with previous optical studies. Across the region we
find an effect of the X-ray field on both the abundance of aromatic molecules
and the [Si II] emission. Within NGC 604 we identify several individual bright
infrared sources with diameters of about 15 pc and luminosity weighted masses
between 10^3 M_sun and 10^4 M_sun. Their spectral properties indicate that some
of these sources are embedded clusters in process of formation, which together
account for ~8% of the total stellar mass in the NGC 604 system. The variations
of the radiation field strength across NGC 604 are consistent with a sequential
star formation scenario, with at least two bursts in the last few million
years. Our results indicate that massive star formation in NGC 604 is still
ongoing, likely triggered by the earlier bursts. | Model-Independent Dark Energy Equation of State from Unanchored Baryon
Acoustic Oscillations: Ratios of line of sight baryon acoustic oscillation (BAO) peaks at two
redshifts only depend upon the average dark energy equation of states between
those redshifts, as the dependence on anchors such as the BAO scale or the
Hubble constant is canceled in a ratio. As a result, BAO ratios provide a probe
of dark energy which is independent of both the cosmic distance ladder and the
early evolution of universe. In this note, we use ratios to demonstrate that
the known tension between the Lyman alpha forest BAO measurement and other
probes arises entirely from recent (0.57<z<2.34) cosmological expansion. Using
ratios of the line of sight Lyman alpha forest and BOSS CMASS BAO scales, we
show that there is already more than 3 sigma tension with the standard
LambdaCDM cosmological model which implies that either (i) The BOSS Lyman alpha
forest measurement of the Hubble parameter was too low as a result of a
statistical fluctuation or systematic error or else (ii) the dark energy
equation of state falls steeply at high redshift. |
Improved model of large-field inflation with primordial black hole
production in Starobinsky-like supergravity: A viable model of large-field (chaotic) inflation with efficient production
of primordial black holes is proposed in Starobinsky-like (modified)
supergravity leading to the "no-scale-type" K\"ahler potential and the
Wess-Zumino-type ("renormalizable") superpotential. The cosmological tilts are
in good (within $1\sigma$) agreement with Planck measurements of the cosmic
microwave background radiation. In addition, the power spectrum of scalar
perturbations has a large peak at smaller scales, which leads to a production
of primordial black holes from gravitational collapse of large perturbations
with the masses about $10^{17}$ g. The masses are beyond the Hawking (black
hole) evaporation limit of $10^{15}$ g, so that those primordial black holes
may be viewed as viable candidates for part or the whole of the current dark
matter. The parameters of the superpotential were fine-tuned for those
purposes, while the cubic term in the superpotential is essential whereas the
quadratic term should vanish. The vacuum after inflation (relevant to
reheating) is Minkowskian. The energy density fraction of the gravitational
waves induced by the production of primordial black holes and their frequency
were also calculated in the second order with respect to perturbations. | A Study of Gravitational Lens Chromaticity with the Hubble Space
Telescope: We report Hubble Space Telescope observations of 6 gravitational lenses with
the Advanced Camera for Surveys. We measured the flux ratios between the lensed
images in 6 filters from 8140\AA\ to 2200\AA. In 3 of the systems,
HE0512$-$3329, B1600+434, and H1413+117, we were able to construct UV
extinction curves partially overlapping the 2175\AA\ feature and characterize
the properties of the dust relative to the Galaxy and the Magellanic Clouds. In
HE1104$-$1804 we detect chromatic microlensing and use it to study the physical
properties of the quasar accretion disk. For a Gaussian model of the disk
$\exp(-r^2/2 r_s^2)$, scaling with wavelength as $r_s \propto \lambda^p$, we
estimate $r_s(\lambda3363)=4^{+4}_{-2}$ ($7\pm 4$) light-days and $p=1.1\pm
0.6$ ($1.0\pm 0.6$) for a logarithmic (linear) prior on $r_s$. The remaining
two systems, FBQ0951+2635 and SBS1520+530, yielded no useful estimates of
extinction or chromatic microlensing. |
Reionization and feedback in overdense regions at high redshift: Observations of galaxy luminosity function at high redshifts typically focus
on fields of view of limited sizes preferentially containing bright sources.
These regions possibly are overdense and hence biased with respect to the
globally averaged regions. Using a semi-analytic model based on Choudhury &
Ferrara (2006) which is calibrated to match a wide range of observations, we
study the reionization and thermal history of the universe in overdense
regions. The main results of our calculation are: (i) Reionization and thermal
histories in the biased regions are markedly different from the average ones
because of enhanced number of sources and higher radiative feedback. (ii) The
galaxy luminosity function for biased regions is markedly different from those
corresponding to average ones. In particular, the effect of radiative feedback
arising from cosmic reionization is visible at much brighter luminosities.
(iii) Because of the enhanced radiative feedback within overdense locations,
the luminosity function in such regions is more sensitive to reionization
history than in average regions. The effect of feedback is visible for absolute
AB magnitude $M_{AB} \gtrsim -17$ at $z=8$, almost within the reach of present
day observations and surely to be probed by JWST. This could possibly serve as
an additional probe of radiative feedback and hence reionization at high
redshifts. | A search for HI 21cm absorption in strong MgII absorbers in the redshift
desert: We report results from a deep search for redshifted HI 21cm absorption in 55
strong MgII$\lambda$2796 absorbers (having $W (MgII) > 0.5 \AA$) at
intermediate redshifts, $0.58 < z_{\rm abs} < 1.70$, with the Green Bank
Telescope (GBT) and the Giant Metrewave Radio Telescope (GMRT). Nine detections
of HI 21cm absorption were obtained, all at $1.17 < z_{\rm abs} < 1.68$,
including three systems reported earlier by Gupta et al. (2007). Absorption was
not detected at $> 3\sigma$ significance in 32 other MgII absorbers, with 26 of
these providing strong upper limits to the HI 21cm optical depth,
$\tau_{3\sigma} < 0.013$ per $\sim 10$ km/s. For the latter 26 systems, the
spin temperature $T_s$ of the absorber must be $> [800 \times f]$ K (where $f$
is the covering factor), if the HI column density is $\ge 2 \times 10^{20}$
cm$^{-2}$, i.e. if the absorber is a damped Lyman-$\alpha$ system (DLA). Data
on the remaining 13 systems of the sample were affected by radio frequency
interference and were hence not useful.
Excluding "associated" systems (within 3000 km/s of the quasar redshift), the
detection rate of HI 21cm absorption in strong MgII absorbers is $x_{\rm
21,MgII} ({\bar z} = 1.1) = 25^{+11}_{-8}$%, at a $3\sigma$ optical depth
sensitivity of $\sim 0.013$ per 10 km/s. Comparing the detection rates of HI
21cm and damped Lyman-$\alpha$ absorption in strong MgII absorber samples
yields a detection rate of HI 21cm absorption in DLAs of $x_{\rm 21,DLA} ({\bar
z} = 1.1) = (73 \pm 27)$%, consistent with the detection rate of HI 21cm
absorption in low-$z$ DLAs. Since HI 21cm absorption arises in cold neutral
gas, this indicates that most gas-rich galaxies contain significant fractions
of cold HI by $z \sim 1$. (abridged) |
Warm Dark Matter from Higher-Dimensional Gauge Theories: Warm dark matter particles with masses in the keV range have been linked with
the large group representations in gauge theories through a high number of
species at decoupling. In this paper, we address WDM fermionic degrees of
freedom from such representations. Bridging higher-dimensional particle physics
theories with cosmology studies and astrophysical observations, our approach is
two-folded, i.e., it includes realistic models from higher-dimensional
representations and constraints from simulations tested against observations.
Starting with superalgebras in exceptional periodicity theories, we discuss
several symmetry reductions and we consider several representations that
accommodate a high number of degrees of freedom. We isolate a model that
naturally accommodates both the standard model representation and the fermionic
dark matter in agreement with both large and small-scale constraints. This
model considers an intersection of branes in $D=27+3$ in a manner that provides
the degrees of freedom for the standard model on one hand and 2048 fermionic
degrees of freedom for dark matter, corresponding to a $\sim$2 keV particle
mass, on the other. In this context, we discuss the theoretical implications
and the observable predictions. | Can We Detect the Color-Density Relation with Photometric Redshifts?: A variety of methods have been proposed to define and to quantify galaxy
environments. While these techniques work well in general with spectroscopic
redshift samples, their application to photometric redshift surveys remains
uncertain. To investigate whether galaxy environments can be robustly measured
with photo-z samples, we quantify how the density measured with the nearest
neighbor approach is affected by photo-z uncertainties by using the Durham mock
galaxy catalogs in which the 3D real-space environments and the properties of
galaxies are exactly known. Furthermore, we present an optimization scheme in
the choice of parameters used in the 2D projected measurements which yield the
tightest correlation with respect to the 3D real-space environments. By
adopting the optimized parameters in the density measurements, we show that the
correlation between the 2D projected optimized density and real-space density
can still be revealed, and the color-density relation is also visible out to $z
\sim 0.8$ even for a photo-z uncertainty ($\sigma_{\Delta_{z}/(1+z)}$) up to
0.06. We find that at the redshift $0.3 < z < 0.5$ a deep ($i \sim 25$)
photometric redshift survey with $\sigma_{\Delta_{z}/(1+z)} = 0.02$ yields a
comparable performance of small-scale density measurement to a shallower $i
\sim$ 22.5 spectroscopic sample with $\sim$ 10% sampling rate. Finally, we
discuss the application of the local density measurements to the Pan-STARRS1
Medium Deep survey, one of the largest deep optical imaging surveys. Using data
from $\sim5$ square degrees of survey area, our results show that it is
possible to measure local density and to probe the color-density relation with
3$\sigma$ confidence level out to $z \sim 0.8$ in the PS-MDS. The color-density
relation, however, quickly degrades for data covering smaller areas. |
Enhanced Warm H2 Emission in the Compact Group Mid-Infrared "Green
Valley": We present results from a Spitzer, mid-infrared spectroscopy study of a
sample of 74 galaxies located in 23 Hickson Compact Groups, chosen to be at a
dynamically-active stage of HI depletion. We find evidence for enhanced warm H2
emission (i.e. above that associated with UV excitation in star-forming
regions) in 14 galaxies (~20%), with 8 galaxies having extreme values of L(H2
S(0)-S(3))/L(7.7micron PAH), in excess of 0.07. Such emission has been seen
previously in the compact group HCG 92 (Stephan's Quintet), and was shown to be
associated with the dissipation of mechanical energy associated with a
large-scale shock caused when one group member collided, at high velocity, with
tidal debris in the intragroup medium. Similarly, shock excitation or turbulent
heating is likely responsible for the enhanced H2 emission in the compact group
galaxies, since other sources of heating (UV or X-ray excitation from star
formation or AGN) are insufficient to account for the observed emission. The
group galaxies fall predominantly in a region of mid-infrared color-color space
identified by previous studies as being connected to rapid transformations in
HCG galaxy evolution. Furthermore, the majority of H2-enhanced galaxies lie in
the optical "green valley" between the blue cloud and red-sequence, and are
primarily early-type disk systems. We suggest that H2-enhanced systems may
represent a specific phase in the evolution of galaxies in dense environments
and provide new insight into mechanisms which transform galaxies onto the
optical red sequence. | Probing Pre-galactic Metal Enrichment with High-Redshift Gamma-Ray
Bursts: We explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe
pre-galactic metal enrichment. We utilize the bright afterglow of a Pop III GRB
exploding in a primordial dwarf galaxy as a luminous background source, and
calculate the strength of metal absorption lines that are imprinted by the
first heavy elements in the intergalactic medium (IGM). To derive the GRB
absorption line diagnostics, we use an existing highly-resolved simulation of
the formation of a first galaxy which is characterized by the onset of atomic
hydrogen cooling in a halo with virial temperature >10^4 K. We explore the
unusual circumburst environment inside the systems that hosted Pop III stars,
modeling the density evolution with the self-similar solution for a champagne
flow. For minihalos close to the cooling threshold, the circumburst density is
roughly proportional to (1+z) with values of about a few cm^{-3}. In more
massive halos, corresponding to the first galaxies, the density may be larger,
n>100 cm^{-3}. The resulting afterglow fluxes may be detectable with the JWST
and VLA in the near-IR and radio wavebands, respectively, out to redshift z>20.
We predict that the maximum of the afterglow emission shifts from near-IR to
millimeter bands with peak fluxes from mJy to Jy at different observed times.
GRBs are ideal tools for probing the metal enrichment in the early IGM, due to
their high luminosities and featureless power-law spectra. The metals in the
first galaxies produced by the first supernova (SN) explosions are likely to
reside in low-ionization stages. We show that if the afterglow can be observed
sufficiently early, analysis of the metal lines can distinguish whether the
first heavy elements were produced in a PISN, or a core-collapse (Type II) SN,
thus constraining the initial mass function of the first stars. |
The inner structure and kinematics of the Sagittarius dwarf galaxy as a
product of tidal stirring: The tidal stirring model envisions the formation of dwarf spheroidal (dSph)
galaxies in the Local Group via the tidal interaction of disky dwarf systems
with a larger host galaxy like the Milky Way. These progenitor disks are
embedded in extended dark halos and during the evolution both components suffer
strong mass loss. In addition, the disks undergo the morphological
transformation into spheroids and the transition from ordered to random motion
of their stars. Using collisionless N-body simulations we construct a model for
the nearby and highly elongated Sagittarius (Sgr) dSph galaxy within the
framework of the tidal stirring scenario. Constrained by the present known
orbit of the dwarf, the model suggests that in order to produce the majority of
tidal debris observed as the Sgr stream, but not yet transform the core of the
dwarf into a spherical shape, Sgr must have just passed the second pericenter
of its current orbit around the Milky Way. In the model, the stellar component
of Sgr is still very elongated after the second pericenter and morphologically
intermediate between the strong bar formed at the first pericenter and the
almost spherical shape existing after the third pericenter. This is thus the
first model of the evolution of the Sgr dwarf that accounts for its observed
very elliptical shape. At the present time there is very little intrinsic
rotation left and the velocity gradient detected along the major axis is almost
entirely of tidal origin. We model the recently measured velocity dispersion
profile for Sgr assuming that mass traces light and estimate its current total
mass within 5 kpc to be 5.2 x 10^8 M_sun. To have this mass at present, the
model requires that the initial virial mass of Sgr must have been as high as
1.6 x 10^10 M_sun, comparable to that of the Large Magellanic Cloud, which may
serve as a suitable analog for the pre-interaction, Sgr progenitor. | A model independent comparison of supernova and strong lensing
cosmography: implications for the Hubble constant tension: We use supernovae measurements, calibrated by the local determination of the
Hubble constant $H_0$ by SH0ES, to interpolate the distance-redshift relation
using Gaussian process regression. We then predict, independent of the
cosmological model, the distances that are measured with strong lensing time
delays. We find excellent agreement between these predictions and the
measurements. The agreement holds when we consider only the redshift dependence
of the distance-redshift relation, independent of the value of $H_0$. Our
results disfavor the possibility that lens mass modeling contributes a 10\%
bias or uncertainty in the strong lensing analysis, as suggested recently in
the literature. In general our analysis strengthens the case that residual
systematic errors in both measurements are below the level of the current
discrepancy with the CMB determination of $H_0$, and supports the possibility
of new physical phenomena on cosmological scales. With additional data our
methodology can provide more stringent tests of unaccounted for systematics in
the determinations of the distance-redshift relation in the late universe. |
On the use of semi-numerical simulations in predicting the 21-cm signal
from the epoch of reionization: We present a detailed comparison of three different simulations of the epoch
of reionization (EoR). The radiative transfer simulation (${\rm C}^2$-RAY)
among them is our benchmark. Radiative transfer codes can produce realistic
results, but are computationally expensive. We compare it with two
semi-numerical techniques: one using the same halos as ${\rm C}^2$-RAY as its
sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS).
These are vastly more computationally efficient than ${\rm C}^2$-RAY, but use
more simplistic physical assumptions. We evaluate these simulations in terms of
their ability to reproduce the history and morphology of reionization. We find
that both Sem-Num and CPS+GS can produce an ionization history and morphology
that is very close to ${\rm C}^2$-RAY, with Sem-Num performing slightly better
compared to CPS+GS.
We also study different redshift space observables of the 21-cm signal from
EoR: the variance, power spectrum and its various angular multipole moments. We
find that both semi-numerical models perform reasonably well in predicting
these observables at length scales relevant for present and future experiments.
However, Sem-Num performs slightly better than CPS+GS in producing the
reionization history, which is necessary for interpreting the future
observations. | Indirect Dark Matter Signatures in the Cosmic Dark Ages II. Ionization,
Heating and Photon Production from Arbitrary Energy Injections: Any injection of electromagnetically interacting particles during the cosmic
dark ages will lead to increased ionization, heating, production of Lyman-alpha
photons and distortions to the energy spectrum of the cosmic microwave
background, with potentially observable consequences. In this note we describe
numerical results for the low-energy electrons and photons produced by the
cooling of particles injected at energies from keV to multi-TeV scales, at
arbitrary injection redshifts (but focusing on the post-recombination epoch).
We use these data, combined with existing calculations modeling the cooling of
these low-energy particles, to estimate the resulting contributions to
ionization, excitation and heating of the gas, and production of low-energy
photons below the threshold for excitation and ionization. We compute corrected
deposition-efficiency curves for annihilating dark matter, and demonstrate how
to compute equivalent curves for arbitrary energy-injection histories. These
calculations provide the necessary inputs for the limits on dark matter
annihilation presented in the accompanying Paper I, but also have potential
applications in the context of dark matter decay or de-excitation, decay of
other metastable species, or similar energy injections from new physics. We
make our full results publicly available at
http://nebel.rc.fas.harvard.edu/epsilon, to facilitate further independent
studies. In particular, we provide the full low-energy electron and photon
spectra, to allow matching onto more detailed codes that describe the cooling
of such particles at low energies. |
Do black hole masses scale with classical bulge luminosities only? The
case of the two composite pseudobulge galaxies NGC3368 and NGC3489: It is now well established that all galaxies with a massive bulge component
harbour a central supermassive black hole (SMBH). The mass of the SMBH
correlates with bulge properties such as the bulge mass and the velocity
dispersion, which implies that the bulge and the SMBH of a galaxy have grown
together during the formation process. The spiral galaxy NGC3368 and the S0
galaxy NGC3489 both host a pseudobulge and a much smaller classical bulge
component at the centre. We present high resolution, near-infrared IFU data of
these two galaxies, taken with SINFONI at the VLT, and use axisymmetric orbit
models to determine the masses of the SMBHs. The SMBH mass of NGC3368 is
M_BH=7.5x10^6 M_sun with an error of 1.5x10^6 M_sun, which mostly comes from
the non-axisymmetry in the data. For NGC3489, a solution without black hole
cannot be excluded when modelling the SINFONI data alone, but can be clearly
ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for
which we obtain M_BH=6.00^{+0.56}_{-0.54} (stat) +/- 0.64 (sys) x 10^6 M_sun.
Although both galaxies seem to be consistent with the M_BH-sigma relation, at
face value they do not agree with the relation between bulge magnitude and
black hole mass when the total bulge magnitude (i.e., including both classical
bulge and pseudobulge) is considered; the agreement is better when only the
small classical bulge components are considered. However, taking into account
the ageing of the stellar population could change this conclusion. | Insights on the astrophysics of supermassive black hole binaries from
pulsar timing observations: Pulsar timing arrays (PTAs) are designed to detect the predicted
gravitational wave (GW) background produced by a cosmological population of
supermassive black hole (SMBH) binaries. In this contribution I review the
physics of such GW background, highlighting its dependence on the overall
binary population, the relation between SMBHs and their hosts, and their
coupling with the stellar and gaseous environment. The latter is particularly
relevant when it drives the binaries to extreme eccentricities (e>0.9), which
might be the case for stellar-driven systems. This causes a substantial
suppression of the low frequency signal, potentially posing a serious threat to
the effectiveness of PTA observations. A future PTA detection will allow to
directly observe for the first time subparsec SMBH binaries on their way to the
GW driven coalescence, providing important answers of the outstanding questions
related to the physics underlying the formation and evolution of these
spectacular sources. |
CARMA Survey Toward Infrared-bright Nearby Galaxies (STING) II:
Molecular Gas Star Formation Law and Depletion Time Across the Blue Sequence: We present an analysis of the relationship between molecular gas and current
star formation rate surface density at sub-kpc and kpc scales in a sample of 14
nearby star-forming galaxies. Measuring the relationship in the bright, high
molecular gas surface density ($\Shtwo\gtrsim$20 \msunpc) regions of the disks
to minimize the contribution from diffuse extended emission, we find an
approximately linear relation between molecular gas and star formation rate
surface density, $\nmol\sim0.96\pm0.16$, with a molecular gas depletion time
$\tdep\sim2.30\pm1.32$ Gyr. We show that, in the molecular regions of our
galaxies there are no clear correlations between \tdep\ and the free-fall and
effective Jeans dynamical times throughout the sample. We do not find strong
trends in the power-law index of the spatially resolved molecular gas star
formation law or the molecular gas depletion time across the range of galactic
stellar masses sampled (\mstar $\sim$$10^{9.7}-10^{11.5}$ \msun). There is a
trend, however, in global measurements that is particularly marked for low mass
galaxies. We suggest this trend is probably due to the low surface brightness
CO, and it is likely associated with changes in CO-to-H2 conversion factor. | Strongly Coupled Dark Energy Cosmologies: preserving LCDM success and
easing low scale problems II - Cosmological simulations: In this second paper we present the first Nbody cosmological simulations of
strongly coupled Dark Energy models (SCDEW), a class of models that alleviates
theoretical issues related to the nature of dark energy. SCDEW models assume a
strong coupling between Dark Energy (DE) and an ancillary Cold Dark Matter
(CDM) component together with the presence of an uncoupled Warm Dark Matter
component. The strong coupling between CDM and DE allows us to preserve small
scale fluctuations even if the warm particle is quite light ($\approx 100$ eV).
Our large scale simulations show that, for $10^{11}<M/M_\odot<10^{14}$, SCDEW
haloes exhibit a number density and distribution similar to a standard Lambda
Cold Dark Matter (LCDM) model, even though they have lower concentration
parameters. High resolution simulation of a galactic halo ($M\sim 10^{12}
M_{\odot} $) shows $\sim 60\%$ less substructures than its LCDM counterpart,
but the same cuspy density profile. On the scale of galactic satellites ($M\sim
10^{9} M_{\odot}$) SCDEW haloes dramatically differ from LCDM. Due to the high
thermal velocities of the WDM component they are almost devoid of any
substructures and present strongly cored dark matter density profiles. These
density cores extend for several hundreds of parsecs, in very good agreement
with Milky Way satellites observations. Strongly coupled models, thanks to
their ability to match observations on both large and small scales might
represent a valid alternative to a simple LCDM model. |
The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
Pairwise-Inverse-Probability and Angular Correction for Fibre Collisions in
Clustering Measurements: The completed eBOSS catalogues contain redshifts of 344080 QSOs over
0.8<z<2.2 covering 4808 deg$^2$, 174816 LRGs over 0.6<z<1.0 covering 4242
deg$^2$ and 173736 ELGs over 0.6<z<1.1 covering 1170 deg$^2$ in order to
constrain the expansion history of the Universe and the growth rate of
structure through clustering measurements. Mechanical limitations of the
fibre-fed spectrograph on the Sloan telescope prevent two fibres being placed
closer than 62", the fibre-collision scale, in a single pass of the instrument
on the sky. These `fibre collisions' strongly correlate with the intrinsic
clustering of targets and can bias measurements of the two-point correlation
function resulting in a systematic error on the inferred values of the
cosmological parameters. We combine the new techniques of
pairwise-inverse-probability weighting and the angular up-weighting to correct
the clustering measurements for the effect of fibre collisions. Using mock
catalogues we show that our corrections provide unbiased measurements, within
data precision, of both the projected correlation function $w_p$ and the
multipoles $\xi^l$ of the redshift-space correlation functions down to
0.1Mpc/h, regardless of the tracer type. We apply the corrections to the eBOSS
DR16 catalogues. We find that, on scales greater than s~20Mpc/h for $\xi^l$, as
used to make BAO and large-scale RSD measurements, approximate methods such as
Nearest-Neighbour up-weighting are sufficiently accurate given the statistical
errors of the data. Using the PIP method, for the first time for a
spectroscopic program of the Sloan Digital Sky Survey we are able to
successfully access the 1-halo term in the 3D clustering measurements down to
~0.1Mpc/h scales. Our results will therefore allow studies that use the
small-scale clustering measurements to strengthen the constraints on both
cosmological parameters and the halo-occupation distribution models. | Pulsar timing arrays and the challenge of massive black hole binary
astrophysics: Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs)
at nHz frequencies. The expected dominant signal is given by the superposition
of all waves emitted by the cosmological population of supermassive black hole
(SMBH) binaries. Such superposition creates an incoherent stochastic
background, on top of which particularly bright or nearby sources might be
individually resolved. In this contribution I describe the properties of the
expected GW signal, highlighting its dependence on the overall binary
population, the relation between SMBHs and their hosts, and their coupling with
the stellar and gaseous environment. I describe the status of current PTA
efforts, and prospect of future detection and SMBH binary astrophysics. |
Correlations between multiple tracers of the cosmic web: The large-scale structure of the Universe is a cosmic web of interconnected
clusters, filaments, and sheets of matter. This PhD comprises two complementary
projects investigating the cosmic web using correlations between three
different tracers: the cosmic microwave background (CMB), supernovae (SNe), and
large quasar groups (LQGs). In the first project we re-analyse the apparent
correlation between CMB temperature and SNe redshift reported by Yershov, Orlov
and Raikov. They presented evidence that the WMAP/Planck CMB pixel-temperatures
at SNe locations tend to increase with increasing redshift. They suggest this
could be caused by the Integrated Sachs-Wolfe effect and/or by residual
foreground contamination. Our analysis supports the prima facie existence of
the correlation but attributes it instead to a composite selection bias caused
by the chance alignment of seven deep survey fields with CMB hotspots. These
seven fields contain just 9.2% of the SNe sample. We estimate the likelihood of
their falling on CMB hotspots by chance is approximately 1 in 11. In the second
project we investigate for the first time the apparent coherent alignment of
LQGs in the redshift range 1.0 <= z <= 1.8. We find that the position angles
(PAs) of LQGs are correlated, specifically aligned and orthogonal, with a
maximum significance of ~2.4 sigma at typical angular (comoving) separations of
~30 degrees (~1.6 Gpc). Spatial coincidence between our LQG sample and regions
of quasar polarization alignment first reported by Hutsemekers, and the
similarity between LQG PAs and radio polarization angles reported by Pelgrims
and Hutsemekers, suggest an interesting result. | Towards an improved model of self-interacting dark matter haloes: In this work, we discuss the relation between the strength of the
self-interaction of dark matter particles and the predicted properties of the
inner density distributions of dark matter haloes. We present the results of
$N$-body simulations for 28 haloes performed with the same initial conditions
for cold dark matter and for self-interacting dark matter, for a range of
cross-sections. We provide a simple phenomenological description of these
results and compare with the semi-analytical model typically used in the
literature. Using these results, we then predict how the inner dark matter
surface density and core radius should depend on the self-interaction
cross-section for observed haloes. |
Preinflationary dynamics of $α-$attractor in loop quantum cosmology: We systematically study the preinflationary dynamics of the spatially flat
Friedmann-Lemaitre-Robertson-Walker universe filled with a single scalar field
that has the generalized $\alpha-$attractor potentials, in the framework of
loop quantum cosmology, in which the big bang singularity is replaced
generically by a non-singular quantum bounce due to purely quantum geometric
effects. The evolution can be divided into two different classes, one is
dominated initially (at the quantum bounce) by the kinetic energy of the scalar
field, and one is not. In both cases, we identify numerically the physically
viable initial conditions that lead to not only a slow-roll inflationary phase,
but also enough $e$-folds to be consistent with observations, and find that the
output of such a viable slow-roll inflationary phase is generic. In addition,
we also show that in the case when the evolution of the universe is dominated
initially by the kinetic energy of the scalar field (except for a very small
set in the phase space), the evolution before reheating is aways divided into
three different phases: {\em bouncing, transition and slow-roll inflation}.
This universal feature does not depend on the initial conditions of the system
nor on the specific potentials of the scalar field, as long as it is dominated
initially by the kinetic energy of the scalar field at the bounce. Moreover, we
carry out phase space analyses for the models under consideration and compare
our results with the power-law and Starobinsky potentials. | The second-order luminosity-redshift relation in a generic inhomogeneous
cosmology: After recalling a general non-perturbative expression for the
luminosity-redshift relation holding in a recently proposed "geodesic
light-cone" gauge, we show how it can be transformed to phenomenologically more
convenient gauges in which cosmological perturbation theory is better
understood. We present, in particular, the complete result on the
luminosity-redshift relation in the Poisson gauge up to second order for a
fairly generic perturbed cosmology, assuming that appreciable vector and tensor
perturbations are only generated at second order. This relation provides a
basic ingredient for the computation of the effects of stochastic
inhomogeneities on precision dark-energy cosmology whose results we have
anticipated in a recent letter. More generally, it can be used in connection
with any physical information carried by light-like signals traveling along our
past light-cone. |
Scale-dependent gravitational waves from a rolling axion: We consider a model in which a pseudo-scalar field $\sigma$ rolls for some
e-folds during inflation, sourcing one helicity of a gauge field. These fields
are only gravitationally coupled to the inflaton, and therefore produce scalar
and tensor primordial perturbations only through gravitational interactions.
These sourced signals are localized on modes that exit the horizon while the
roll of $\sigma$ is significant. We focus our study on cases in which the model
can simultaneously produce (i) a large gravitational wave signal, resulting in
observable B-modes of the CMB polarizations, and (ii) sufficiently small scalar
perturbations, so to be in agreement with the current limits from temperature
anisotropies. Different choice of parameters can instead lead to a localized
and visible departure from gaussianity in the scalar sector, either at CMB or
LSS scales. | The Epoch of Reionization in the R_h=ct Universe: The measured properties of the epoch of reionization (EoR) show that
reionization probably began around z ~ 12-15 and ended by z=6. In addition, a
careful analysis of the fluctuations in the cosmic microwave background
indicate a scattering optical depth tau ~ 0.066+/-0.012 through the EoR. In the
context of LCDM, galaxies at intermediate redshifts and dwarf galaxies at
higher redshifts now appear to be the principal sources of UV ionizing
radiation, but only for an inferred (ionizing) escape fraction f_ion ~ 0.2,
which is in tension with other observations that suggest a value as small as ~
0.05. In this paper, we examine how reionization might have progressed in the
alternative Friedmann-Robertson Walker cosmology known as the R_h=ct Universe,
and determine the value of f_ion required with this different rate of
expansion. We find that R_h=ct accounts quite well for the currently known
properties of the EoR, as long as its fractional baryon density falls within
the reasonable range 0.026 < Omega_b < 0.037. This model can also fit the EoR
data with f_ion ~ 0.05, but only if the Lyman continuum photon production is
highly efficient and Omega_b ~ 0.037. These results are still preliminary,
however, given their reliance on a particular form of the star-formation rate
density, which is still uncertain at very high redshifts. It will also be
helpful to reconsider the EoR in R_h=ct when complete structure formation
models become available. |
Estimates of unresolved point sources contribution to WMAP 5: We present an alternative estimate of the unresolved point source
contribution to the WMAP temperature power spectrum based on current knowledge
of sources from radio surveys in the 1.4-90 GHz range. We implement a
stochastic extrapolation of radio point sources in the NRAO-VLA Sky Survey
(NVSS) catalog, from the original 1.4 GHz to the ~ 100 GHz frequency range
relevant for CMB experiments. With a bootstrap approach, we generate an
ensemble of realizations that provides the probability distribution for the
flux of each NVSS source at the final frequency. The predicted source counts
agree with WMAP results for S > 1 Jy and the corresponding sky maps correlate
with WMAP observed maps in Q-, V- and W- bands, for sources with flux S > 0.2
Jy. The low-frequency radio surveys found a steeper frequency dependence for
sources just below the WMAP nominal threshold than the one estimated by the
WMAP team. This feature is present in our simulations and translates into a
shift of 0.3-0.4 \sigma in the estimated value of the tilt of the power
spectrum of scalar perturbation, n_s, as well as \omega_c. This approach
demonstrates the use of external point sources datasets for CMB data analysis. | The star formation history and chemical evolution of star forming
galaxies in the nearby universe: We have determined the O/H and N/O of a sample of 122751 SFGs from the DR7 of
the SDSS. For all these galaxies we have also determined their morphology and
their SFH using the code STARLIGHT. The comparison of the chemical abundance
with the SFH allows us to describe the chemical evolution in the nearby
universe (z < 0.25) in a manner which is consistent with the formation of their
stellar populations and morphologies. A 45% of the SFGs in our sample show an
excess of abundance in nitrogen relative to their metallicity. We also find
this excess to be accompanied by a deficiency of oxygen, which suggests that
this could be the result of effective starburst winds. However, we find no
difference in the mode of star formation of the nitrogen rich and nitrogen poor
SFGs. Our analysis suggests they all form their stars through a succession of
bursts of star formation extended over a few Gyr period. What produces the
chemical differences between these galaxies seems therefore to be the intensity
of the bursts: the galaxies with an excess of nitrogen are those that are
presently experiencing more intense bursts, or have experienced more intense
bursts in their past. We also find evidence relating the chemical evolution
process to the formation of the galaxies: the galaxies with an excess of
nitrogen are more massive, have more massive bulges and earlier morphologies
than those showing no excess. As a possible explanation we propose that the
lost of metals consistent with starburst winds took place during the formation
of the galaxies, when their potential wells were still building up, and
consequently were weaker than today, making starburst winds more efficient and
independent of the final mass of the galaxies. In good agreement with this
interpretation, we also find evidence consistent with downsizing, according to
which the more massive SFGs formed before the less massive ones. |
Conformal gravity: light deflection revisited and the galactic rotation
curve failure: We show how Conformal Gravity (CG) has to satisfy a fine-tuning condition to
describe the rotation curves of disk galaxies without the aid of dark matter.
Interpreting CG as a gauge natural theory yields conservation laws and their
associated superpotentials without ambiguities. We consider the light
deflection of a point-like lens and impose that the two Schwarzschild-like
metrics with and without the lens are identical at infinite distances from the
lens. The energy conservation law implies that the parameter $\gamma$ in the
linear term of the metric has to vanish, otherwise the two metrics are
physically inaccessible from each other. This linear term is responsible to
mimic the role of dark matter in disk galaxies and gravitational lensing
systems. Our analysis shows that removing the need of dark matter with CG thus
relies on a fine-tuning condition on $\gamma$. We also illustrate why the
results of previous investigations of gravitational lensing in CG largely
disagree. These discrepancies derive from the erroneous use of the deflection
angle definition adopted in General Relativity, where the vacuum solution is
asymptotically flat, unlike CG. In addition, the lens mass is identified with
various combinations of the metric parameters. However, these identifications
are arbitrary, because the mass is not a conformally invariant quantity, unlike
the conserved charge associated to the energy conservation law. Based on this
conservation law and by removing the fine-tuning condition on $\gamma$, i.e. by
setting $\gamma=0$, the energy difference between the metric with the
point-like lens and the metric without it defines a conformally invariant
quantity that can in principle be used for (1) a proper derivation of light
deflection in CG, and (2) the identification of the lens mass with a function
of the parameters $\beta$ and $k$ of the Schwarzschild-like metric. | Star Formation Properties in Barred Galaxies(SFB). I.
Ultraviolet-to-Infrared Imaging and Spectroscopic Studies of NGC 7479: Large-scale bars and minor mergers are important drivers for the secular
evolution of galaxies. Based on ground-based optical images and spectra as well
as ultraviolet data from the Galaxy Evolution Explorer and infrared data from
the Spitzer Space Telescope, we present a multi-wavelength study of star
formation properties in the barred galaxy NGC 7479, which also has obvious
features of a minor merger. Using various tracers of star formation, we find
that under the effects of both a stellar bar and a minor merger, star formation
activity mainly takes place along the galactic bar and arms, while the star
formation rate changes from the bar to the disk. With the help of spectral
synthesis, we find that strong star formation took place in the bar region
about 100 Myr ago, and the stellar bar might have been $\sim$10 Gyr old. By
comparing our results with the secular evolutionary scenario from Jogee et al.,
we suggest that NGC 7479 is possibly in a transitional stage of secular
evolution at present, and it may eventually become an earlier type galaxy or a
luminous infrared galaxy. We also note that the probable minor merger event
happened recently in NGC 7479, and we find two candidates for minor merger
remnants. |
Fitting cosmological data to the function $q(z)$ from GR Theory:
Modified Chaplygin Gas: In the Friedmann cosmology the deceleration of the expansion $q$ plays a
fundamental role. We derive the deceleration as a function of redshift $q(z)$
in two scenarios: $\Lambda$CDM model and modified Chaplygin gas ($MCG$) model.
The function for the $MCG$ model is then fitted to the cosmological data in
order to obtain the cosmological parameters that minimize $\chi^2$. We use the
Fisher matrix to construct the covariance matrix of our parameters and
reconstruct the q(z) function. We use Supernovae Ia, WMAP5 and BAO measurements
to obtain the observational constraints. We determined the present acceleration
as $q_0=-0.60 \pm 0.12$ for the $MCG$ model using the Constitution dataset of
SNeIa and BAO, and $q_0=-0.63 \pm 0.17$ for the Union dataset and BAO. The
transition redshift from deceleration to acceleration was found to be around
$0.6$ for both datasets. We have also determined the dark energy parameter for
the $MCG$ model: $\Omega_{X0}=0.834 \pm 0.028$ for the Constitution dataset and
$\Omega_{X0}=0.854 \pm 0.036$ using the Union dataset. | On a new method to analyse QSO spectra: A new method of analysis of QSO spectra, usually referred to as the "Thong
method", has been recently presented and made use of in a number of
publications. Several of these have been withdrawn because the authors have
been convicted of plagiarism. However, there exists no publication showing that
the method itself, which is an original contribution of the authors, is wrong.
The purpose of the present note is to show that it is and that the results
obtained when using it, including limits on the time variation of the fine
structure constant many times smaller than published by other authors, must
therefore be ignored and discarded. |
$φ^4$ inflation is not excluded: We present counter examples to the claim that the $\lambda \phi^4$ inflaton
potential is excluded by recent cosmological data. Finding counter examples
requires that the actually observed primordial fluctuations are generated at
the onset of the slow-roll regime of inflation. This set up for the initial
conditions is therefore different from the usual scenario of chaotic inflation
where inflation starts long before the observed fluctuations are created. The
primordial power spectrum of "just enough" chaotic inflation violates
scale-invariance in a way consistent with observations. | The extent of dust in NGC 891 from Herschel/SPIRE images: We analyse Herschel/SPIRE images of the edge-on spiral galaxy NGC 891 at 250,
350 and 500 micron. Using a 3D radiative transfer model we confirm that the
dust has a radial fall-off similar to the stellar disk. The dust disk shows a
break at about 12 kpc from the center, where the profile becomes steeper.
Beyond this break, emission can be traced up to 90% of the optical disk in the
NE side. On the SW, we confirm dust emission associated with the extended,
asymmetric HI disk, previously detected by the Infrared Space Observatory
(ISO). This emission is marginally consistent with the large diffuse dust disk
inferred from radiative transfer fits to optical images. No excess emission is
found above the plane beyond that of the thin, unresolved, disk. |
Coupling quintessence kinetics to electromagnetism: We propose a general model where quintessence couples to electromagnetism via
its kinetic term. This novelty generalizes the linear dependence of the gauge
kinetic function on $\phi$, commonly adopted in the literature. The interaction
naturally induces a time variation of the fine-structure constant that can be
formulated within a disformally coupled framework, akin to a Gordon metric.
Through a suitable parametrization of the scalar field and the coupling
function, we test the model against observations sensitive to the variation of
$\alpha$. We undertake a Bayesian analysis to infer the free parameters with
data from Earth based, astrophysical and early Universe experiments. We find
that the evolution of $\alpha$ is specific to each cosmological era and slows
down at late times when dark energy accelerates the Universe. While the most
stringent bound on the interaction is obtained from atomic clocks measurements,
the quasars provide a constraint consistent with weak equivalence principle
tests. This promising model is to be further tested with upcoming and more
precise astrophysical measurements, such as those of the ESPRESSO spectrograph. | Constraints on quintessence and new physics from fundamental constant: Changes in the values of the fundamental constants mu, the proton to electron
mass ratio, and alpha, the fine structure constant due to rolling scalar fields
have been discussed both in the context of cosmology and in new physics such as
Super Symmetry (SUSY) models. This article examines the changes in these
fundamental constants in a particular example of such fields, freezing and
thawing slow roll quintessence. Constraints are placed on the product of a
cosmological quantity, w, the equation of state parameter, and the square of
the coupling constants for mu and alpha with the field, zeta_x, x = mu,alpha,
using the existing observational limits on the values of Delta x/x. Various
examples of slow rolling quintessence models are used to further quantify the
constraints. Some of the examples appear to be rejected by the existing data
which strongly suggests that conformation to the values of the fundamental
constants in the early universe is a standard test that should be applied to
any cosmological model or suggested new physics. |
Towards accurate cosmological predictions for rapidly oscillating scalar
fields as dark matter: As we are entering the era of precision cosmology, it is necessary to count
on accurate cosmological predictions from any proposed model of dark matter. In
this paper we present a novel approach to the cosmological evolution of scalar
fields that eases their analytic and numerical analysis at the background and
at the linear order of perturbations. We apply the method to a scalar field
endowed with a quadratic potential and revisit its properties as dark matter.
Some of the results known in the literature are recovered, and a better
understanding of the physical properties of the model is provided. It is shown
that the Jeans wavenumber defined as $k_J = a \sqrt{mH}$ is directly related to
the suppression of linear perturbations at wavenumbers $k>k_J$. We also discuss
some semi-analytical results that are well satisfied by the full numerical
solutions obtained from an amended version of the CMB code CLASS. Finally we
draw some of the implications that this new treatment of the equations of
motion may have in the prediction for cosmological observables. | Non-linear coupling in the dark sector as a running vacuum model: In this work we study a phenomenological non-gravitational interaction
between dark matter and dark energy. The scenario studied in this work extends
the usual interaction model proportional to the derivative of the dark
component density adding to the coupling a non-linear term of the form $Q =
\rho'/3(\alpha + \beta \rho)$. This dark sector interaction model could be
interpreted as a particular case of a running vacuum model of the type
$\Lambda(H) = n_0 + n_1 H^2 + n_2 H^4$ in which the vacuum decays into dark
matter. For a flat FRW Universe filled with dark energy, dark matter and
decoupled baryonic matter and radiation we calculate the energy density
evolution equations of the dark sector and solve them. The different sign
combinations of the two parameters of the model show clear qualitative
different cosmological scenarios, from basic cosmological insights we discard
some of them. The linear scalar perturbation equations of the dark matter were
calculated. Using the CAMB code we calculate the CMB and matter power spectra
for some values of the parameters $\alpha$ and $\beta$ and compare it with
$\Lambda$CDM. The model modify mainly the lower multipoles of the CMB power
spectrum remaining almost the same the high ones. The matter power spectrum for
low wave numbers is not modified by the interaction but after the maximum it is
clearly different. Using observational data from Planck, and various galaxy
surveys we obtain the constraints of the parameters, the best fit values
obtained are the combinations $\alpha = (3.7 \pm 7 )\times 10^{-4} $,
$-(1.5\times10^{-5} {\rm eV}^{-1})^{4} \ll \beta < (0.07 {\rm eV}^{-1})^4$. |
Finding AGN with wide-field VLBI observations: VLBI observations are a reliable method to identify AGN, since they require
high brightness temperatures for a detection to be made. However, because of
the tiny fields of view it is unpractical to carry out VLBI observations of
many sources using conventional methods. We used an extension of the DiFX
software correlator to image with high sensitivity 96 sources in the Chandra
Deep Field South, using only 9h of observing time with the VLBA. We detected 20
sources, 8 of which had not been identified as AGN at any other wavelength,
despite the comprehensive coverage of this field. The lack of X-ray
counterparts to 1/3 of the VLBI-detected sources, despite the sensitivity of
co-located X-ray data, demonstrates that X-ray observations cannot be solely
relied upon when searching for AGN activity. Surprisingly, we find that sources
classified as type 1 QSOs using X-ray data are always detected, in contrast to
the 10% radio-loud objects which are found in optically-selected QSOs. We
present the continuation of this project with the goal to image 1450 sources in
the Lockman Hole/XMM region. | On the Coherence of WMAP and Planck Temperature Maps: The recent data release of ESA's Planck mission together with earlier WMAP
releases provide the first opportunity to compare high resolution full sky
Cosmic Microwave Background temperature anisotropy maps. To quantify the
coherence of these maps beyond the power spectrum we introduce Generalized
Phases, unit vectors in the (2l+1) dimensional representation spaces. For a
Gaussian distribution, Generalized Phases are random and if there is
non-Gaussianity, they represent most of the non-Gaussian information. The
alignment of these unit vectors from two maps can be characterized by their
angle, 0 deg expected for full coherence, and 90 deg for random vectors. We
analyze maps from both missions with the same mask and Nside=512 resolution,
and compare both power spectra and Generalized Phases. We find excellent
agreement of the Generalize Phases of Planck Smica map with that of the WMAP
Q,V,W maps, rejecting the null hypothesis of no correlations at 5 sigma for l's
l<700, l<900 and l<1100, respectively, except perhaps for l<10. Using
foreground reduced maps for WMAP increases the phase coherence. The observed
coherence angles can be explained with a simple assumption of Gaussianity and a
WMAP noise model neglecting Planck noise, except for low-intermediate l's there
is a slight, but significant off-set, depending on WMAP band. On the same
scales WMAP power spectrum is about 2.6% higher at a very high significance,
while at higher l's there appears to be no significant bias. Using our
theoretical tools, we predict the phase alignment of Planck with a hypothetical
perfect noiseless CMB experiment, finding decoherence at l > 2900; below this
value Planck can be used most efficiently to constrain non-Gaussianity. |
Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics: Within the framework of modified Newtonian dynamics (MOND) we investigate the
kinematics of two dwarf spiral galaxies belonging to very different
environments, namely KK 246 in the Local Void and Holmberg II in the M81 group.
A mass model of the rotation curve of KK 246 is presented for the first time,
and we show that its observed kinematics are consistent with MOND. We re-derive
the outer rotation curve of Holmberg II, by modelling its HI data cube, and
find that its inclination should be closer to face-on than previously derived.
This implies that Holmberg II has a higher rotation velocity in its outer
parts, which, although not very precisely constrained, is consistent with the
MOND prediction. | The Outer Disks of Dwarf Irregular Galaxies: To explore the properties of extreme outer stellar disks, we obtained
ultra-deep V and GALEX UV images of 4 dwarf irregular galaxies and one Blue
Compact Dwarf galaxy and ultra-deep B images of 3 of these. Our V-band surface
photometry extends to 29.5 magnitudes arcsec^-2. We convert the FUV and V-band
photometry, along with Halpha photometry, into radial star formation rate
profiles that are sensitive to timescales from 10 Myrs to the lifetime of the
galaxy. We also compare the stellar distributions, surface brightness profiles,
and star formation rate profiles to HI-line emission maps, gas surface density
profiles, and gas kinematics. Our data lead us to two general observations:
First, the exponential disks in these irregular galaxies are extraordinarily
regular. The stellar disks continue to decline exponentially as far as our
measurements extend. In spite of lumpiness in the distribution of young stars
and HI distributions and kinematics that have significant unordered motions,
sporadic processes that have built the disks-star formation, radial movement of
stars, and perhaps even perturbations from the outside-have, nevertheless,
conspired to produce standard disk profiles. Second, there is a remarkable
continuity of star formation throughout these disks over time. In four out of
five of our galaxies the star formation rate in the outer disk measured from
the FUV tracks that determined from the V-band, to within factors of 5,
requiring star formation at a fairly steady rate over the galaxy's lifetime.
Yet, the HI surface density profiles generally decline with radius more
shallowly than the stellar light, and the gas is marginally gravitationally
stable against collapse into clouds. Outer stellar disks are challenging our
concepts of star formation and disk growth and provide a critical environment
in which to understand processes that mold galaxy disks. |
Perturbation Theory Trispectrum in the Time Renormalisation Approach: An accurate theoretical description of structure formation at least in the
mildly non-linear regime is essential for comparison with data from next
generation galaxy surveys. In a recent approach one follows the time evolution
of correlators directly and finds a hierarchy of evolution equations with
increasing order (Pietroni 2008). So far, in this so called time
renormalisation group method the trispectrum was neglected in order to obtain a
closed set of equations. In this work we study the influence of the trispectrum
on the evolution of the power spectrum. In order to keep the numerical cost at
a manageable level we use the tree-level trispectrum from Eulerian perturbation
theory. In comparison to numerical simulations we find improvement in the
mildly non-linear regime up to k = 0.25 h/Mpc. Beyond k = 0.25 h/Mpc the
perturbative description of the trispectrum fails and the method performs worse
than without the trispectrum included. Our results reinforce the conceptual
advantage of the time renormalisation group method with respect to perturbation
theory. | A search for massive UCDs in the Centaurus Galaxy Cluster: We recently initiated a search for ultra-compact dwarf galaxies (UCDs) in the
Centaurus galaxy cluster (Mieske et al. 2007), resulting in the discovery of 27
compact objects with -12.2<M_V<-10.9 mag. Our overall survey completeness was
15-20% within 120 kpc projected clustercentric distance. In order to better
constrain the luminosity distribution of the brightest UCDs in Centaurus, we
continue our search by substantially improving our survey completeness
specifically in the regime M_V<-12 mag (V_0<21.3 mag). Using VIMOS at the VLT,
we obtain low-resolution spectra of 400 compact objects with 19.3<V_0<21.3 mag
(-14<M_V<-12 mag at the Centaurus distance) in the central 25' of the Centaurus
cluster, which corresponds to a projected radius of ~150 kpc. Our survey yields
complete area coverage within ~120 kpc. For 94% of the sources included in the
masks we successfully measure a redshift. Due to incompleteness in the slit
assignment, our final completeness in the area surveyed is 52%. Among our
targets we find three new UCDs in the magnitude range -12.2<M_V<-12 mag, hence
at the faint limit of our survey. One of them is covered by archival HST WFPC2
imaging, yielding a size estimate of r_h <= 8-9 pc. At 95% confidence we can
reject the hypothesis that in the area surveyed there are more than 2 massive
UCDs with M_V<-12.2 mag and r_eff <=70 pc. Our survey hence confirms the
extreme rareness of massive UCDs. We find that the radial distributions of
Centaurus and Fornax UCDs with respect to their host clusters' centers agree
within the 2 sigma level. |
Testing parity-violating physics from cosmic rotation power
reconstruction: We study the reconstruction of the cosmic rotation power spectrum produced by
parity-violating physics, with an eye to ongoing and near future cosmic
microwave background (CMB) experiments such as BICEP Array, CMBS4, LiteBIRD and
Simons Observatory. In addition to the inflationary gravitational waves and
gravitational lensing, measurements of other various effects on CMB
polarization open new window into the early Universe. One of these is
anisotropies of the cosmic polarization rotation which probes the Chern-Simons
term generally predicted by string theory. The anisotropies of the cosmic
rotation are also generated by the primordial magnetism and in the Standard
Model extention framework. The cosmic rotation anisotropies can be
reconstructed as quadratic in CMB anisotropies. However, the power of the
reconstructed cosmic rotation is a CMB four-point correlation and is not
directly related to the cosmic-rotation power spectrum. Understanding all
contributions in the four-point correlation is required to extract the cosmic
rotation signal. Assuming a scale-invariant rotation spectrum motivated by the
inflationary cosmic-rotation models, we employ simulation to quantify each
contribution to the four-point correlation and find that (1) a secondary
contraction of the trispectrum increases the total signal-to-noise, (2) a bias
from the lensing-induced trispectrum is significant compared to the statistical
errors in, e.g., LiteBIRD and CMBS4-like experiments, (3) the use of a
realization-dependent estimator decreases the statistical errors by 10%-20%,
depending on experimental specifications, and (4) other higher-order
contributions are negligible at least for near future experiments. | Cosmic Microwave Background Bispectrum from the Lensing--Rees-Sciama
Correlation Reexamined: Effects of Non-linear Matter Clustering: The bispectrum of the cosmic microwave background (CMB) generated by a
correlation between a time-dependent gravitational potential and the weak
gravitational lensing effect provides a direct measurement of the influence of
dark energy on CMB. This bispectrum is also known to yield the most important
contamination of the so-called "local-form" primordial bispectrum, which can be
used to rule out all single-field inflation models. In this paper, we reexamine
the effect of non-linear matter clustering on this bispectrum. We compare three
different approaches: the 3rd-order perturbation theory (3PT), and two
empirical fitting formulae available in the literature, finding that detailed
modeling of non-linearity appears to be not very important, as most of the
signal-to-noise comes from the squeezed triangle, for which the correlation in
the linear regime dominates. The expected signal-to-noise ratio for an
experiment dominated by the cosmic variance up to $l_{\rm max}=1500$ is about
5, which is much smaller than the previous estimates including non-linearity,
but agrees with the estimates based on the linear calculation. We find that the
difference between the linear and non-linear predictions is undetectable, and
does not alter the contamination of the local-form primordial non-Gaussianity. |
Baryon acoustic oscillations reconstruction using convolutional neural
networks: We propose a new scheme to reconstruct the baryon acoustic oscillations (BAO)
signal, which contains key cosmological information, based on deep
convolutional neural networks (CNN). Trained with almost no fine-tuning, the
network can recover large-scale modes accurately in the test set: the
correlation coefficient between the true and reconstructed initial conditions
reaches $90\%$ at $k\leq 0.2 h\mathrm{Mpc}^{-1}$, which can lead to significant
improvements of the BAO signal-to-noise ratio down to
$k\simeq0.4h\mathrm{Mpc}^{-1}$. Since this new scheme is based on the
configuration-space density field in sub-boxes, it is local and less affected
by survey boundaries than the standard reconstruction method, as our tests
confirm. We find that the network trained in one cosmology is able to
reconstruct BAO peaks in the others, i.e. recovering information lost to
non-linearity independent of cosmology. The accuracy of recovered BAO peak
positions is far less than that caused by the difference in the cosmology
models for training and testing, suggesting that different models can be
distinguished efficiently in our scheme. It is very promising that Our scheme
provides a different new way to extract the cosmological information from the
ongoing and future large galaxy surveys. | The Faint-End Slope of the Redshift 5.7 Lyman Alpha Luminosity Function: Using new Keck DEIMOS spectroscopy, we examine the origin of the steep number
counts of ultra-faint emission-line galaxies recently reported by Dressler et
al. (2011). We confirm six Lyman Alpha emitters (LAEs), three of which have
significant asymmetric line profiles with prominent wings extending 300-400
km/s redward of the peak emission. With these six LAEs, we revise our previous
estimate of the number of faint LAEs in the Dressler et al. survey. Combining
these data with the density of bright LAEs in the Cosmic Origins Survey and
Subaru Deep Field provides the best constraints to date on the redshift 5.7 LAE
luminosity function (LF). Schechter function parameters, phi^* = 4.5 x 10^{-4}
Mpc^{-3}, L^* = 9.1 x 10^{42} erg s^{-1}, and alpha= -1.70, are estimated using
a maximum likelihood technique with a model for slit losses. To place this
result in the context of the UV-selected galaxy population, we investigate how
various parameterizations of the Lyman Alpha equivalent width distribution,
along with the measured UV-continuum LF, affect shape and normalization of the
Lyman Alpha LF. The nominal model, which uses z~6 equivalent widths from the
literature, falls short of the observed space density of LAEs at the bright
end, possibly indicating a need for higher equivalent widths. This
parameterization of the equivalent width distribution implies that as many as
50% of our faintest LAEs should have M_{UV} > -18.0, rendering them
undetectable in even the deepest Hubble Space Telescope surveys at this
redshift. Hence, ultra-deep emission-line surveys find some of the faintest
galaxies ever observed at the end of the reionization epoch. Such faint
galaxies likely enrich the intergalactic medium with metals and maintain its
ionized state. Observations of these objects provide a glimpse of the building
blocks of present-day galaxies at an early time. |
HeII emission in Lyman-alpha nebulae: AGN or cooling radiation?: We present a study of an extended Lyman-alpha (Lya) nebula located in a known
overdensity at z~2.38. The data include multiwavelength photometry covering the
rest-frame spectral range from 0.1 to 250um, and deep optical spectra of the
sources associated with the extended emission. Two galaxies are associated with
the Lya nebula. One of them is a dust enshrouded AGN, while the other is a
powerful starburst, forming stars at >~600 Msol/yr. We detect the HeII emission
line at 1640A in the spectrum of the obscured AGN, but detect no emission from
other highly ionized metals (CIV or NV) as is expected from an AGN. One
scenario that simultaneously reproduces the width of the detected emission
lines, the lack of CIV emission, and the geometry of the emitting gas, is that
the HeII and the Lya emission are the result of cooling gas that is being
accreted on the dark matter halo of the two galaxies, Ly1 and Ly2. Given the
complexity of the environment associated with our Lya nebula it is possible
that various mechanisms of excitation are at work simultaneously. | HERA Phase I Limits on the Cosmic 21-cm Signal: Constraints on
Astrophysics and Cosmology During the Epoch of Reionization: Recently, the Hydrogen Epoch of Reionization Array (HERA) collaboration has
produced the experiment's first upper limits on the power spectrum of 21-cm
fluctuations at z~8 and 10. Here, we use several independent theoretical models
to infer constraints on the intergalactic medium (IGM) and galaxies during the
epoch of reionization (EoR) from these limits. We find that the IGM must have
been heated above the adiabatic cooling threshold by z~8, independent of
uncertainties about the IGM ionization state and the nature of the radio
background. Combining HERA limits with galaxy and EoR observations constrains
the spin temperature of the z~8 neutral IGM to 27 K < T_S < 630 K (2.3 K < T_S
< 640 K) at 68% (95%) confidence. They therefore also place a lower bound on
X-ray heating, a previously unconstrained aspects of early galaxies. For
example, if the CMB dominates the z~8 radio background, the new HERA limits
imply that the first galaxies produced X-rays more efficiently than local ones
(with soft band X-ray luminosities per star formation rate constrained to
L_X/SFR = { 10^40.2, 10^41.9 } erg/s/(M_sun/yr) at 68% confidence), consistent
with expectations of X-ray binaries in low-metallicity environments. The z~10
limits require even earlier heating if dark-matter interactions (e.g., through
millicharges) cool down the hydrogen gas. Using a model in which an extra radio
background is produced by galaxies, we rule out (at 95% confidence) the
combination of high radio and low X-ray luminosities of L_{r,\nu}/SFR > 3.9 x
10^24 W/Hz/(M_sun/yr) and L_X/SFR<10^40 erg/s/(M_sun/yr). The new HERA upper
limits neither support nor disfavor a cosmological interpretation of the recent
EDGES detection. The analysis framework described here provides a foundation
for the interpretation of future HERA results. |
Extension of local-type inequality for the higher order correlation
functions: For the local-type primordial perturbation, it is known that there is an
inequality between the bispectrum and the trispectrum. By using the
diagrammatic method, we develop a general formalism to systematically construct
the similar inequalities up to any order correlation function. As an
application, we explicitly derive all the inequalities up to six and
eight-point functions. | MUSCLE-UPS: Improved Approximations of the Matter Field with the
Extended Press-Schechter Formalism and Lagrangian Perturbation Theory: Lagrangian algorithms to simulate the evolution of cold dark matter (CDM) are
invaluable tools to generate large suites of mock halo catalogues. In this
paper, we first show that the main limitation of current semi-analytical
schemes to simulate the displacement of CDM is their inability to model the
evolution of overdensities in the initial density field, a limit that can be
circumvented by detecting halo particles in the initial conditions. We thus
propose `MUltiscale Spherical Collapse Lagrangian Evolution Using
Press-Schechter' (muscle-ups), a new scheme that reproduces the results from
Lagrangian perturbation theory on large scales, while improving the modelling
of overdensities on small scales. In muscle-ups, we adapt the extended Press
and Schechter (EPS) formalism to Lagrangian algorithms of the displacement
field. For regions exceeding a collapse threshold in the density smoothed at a
radius $R$, we consider all particles within a radius $R$ collapsed. Exploiting
a multi-scale smoothing of the initial density, we build a halo catalogue on
the fly by optimizing the selection of halo candidates. This allows us to
generate a density field with a halo mass function that matches one measured in
$N$-body simulations. We further explicitly gather particles in each halo
together in a profile, providing a numerical, Lagrangian-based implementation
of the halo model. Compared to previous semi-analytical Lagrangian methods, we
find that muscle-ups improves the recovery of the statistics of the density
field at the level of the probability density function (PDF), the power
spectrum, and the cross correlation with the $N$-body result. |
An optical/NIR survey of globular clusters in early-type galaxies. I.
Introduction and data reduction procedures: Context: The combination of optical and near-infrared (NIR) colours has the
potential to break the age/metallicity degeneracy and offers a better
metallicity sensitivity than optical colours alone. Previous studies of
extragalactic globular clusters (GCs) with this colour combination, however,
have suffered from small samples or have been restricted to a few galaxies.
Aims: We compile a homogeneous and representative sample of GC systems with
multi-band photometry to be used in subsequent papers where ages and
metallicity distributions will be studied. Methods: We acquired deep K-band
images of 14 bright nearby early-type galaxies. The images were obtained with
the LIRIS near-infrared spectrograph and imager at the William Herschel
Telescope (WHT) and combined with optical ACS g and z images from the Hubble
Space Telescope public archive. Results: For the first time GC photometry of 14
galaxies are observed and reduced homogeneously in this wavelength regime. We
achieved a limiting magnitude of K~20-21. For the majority of the galaxies we
detect about 70 GCs each. NGC4486 and NGC4649, the cluster-richest galaxies in
the sample contain 301 and 167 GCs, respectively. We present tables containing
coordinates, photometry and sizes of the GCs available. | Chemo-dynamical simulations of dwarf galaxy evolution: In this review I give a summary of the state-of-the-art for what concerns the
chemo-dynamical numerical modelling of galaxies in general and of dwarf
galaxies in particular. In particular, I focus my attention on (i) initial
conditions; (ii) the equations to solve; (iii) the star formation process in
galaxies; (iv) the initial mass function; (v) the chemical feedback; (vi) the
mechanical feedback; (vii) the environmental effects. Moreover, some key
results concerning the development of galactic winds in galaxies and the fate
of heavy elements, freshly synthesised after an episode of star formation, have
been reported. At the end of this review, I summarise the topics and physical
processes, relevant for the evolution of galaxies, that in my opinion are not
properly treated in modern computer simulations of galaxies and that deserve
more attention in the future. |
Predicting the Merger Fraction of Lyman alpha Emitters from Redshift z~3
to z~7: Rapid mass assembly, likely from mergers or smooth accretion, has been
predicted to play a vital role in star-formation in high-redshift Lyman-alpha
(Lya) emitters. Here we predict the major merger, minor merger, and smooth
accreting Lya emitter fraction from z~3 to z~7 using a large dark matter
simulation, and a simple physical model that is successful in reproducing many
observations over this large redshift range. The central tenet of this model,
different from many of the earlier models, is that the star-formation in Lya
emitters is proportional to the mass accretion rate rather than the total halo
mass. We find that at z~3, nearly 35% of the Lya emitters accrete their mass
through major (3:1) mergers, and this fraction increases to about 50% at z~7.
This imply that the star-formation in a large fraction of high-redshift Lya
emitters is driven by mergers. While there is discrepancy between the model
predictions and observed merger fractions, some of this difference (~15%) can
be attributed to the mass-ratio used to define a merger in the simulation. We
predict that future, deeper observations which use a 3:1 definition of major
mergers will find >30% major merger fraction of Lya emitters at redshifts >3. | Constraints on primordial black hole dark matter from Galactic center
X-ray observations: Surprisingly high masses of the black holes inferred from the LIGO & Virgo
gravitational wave measurements have lead to speculations that the observed
mergers might be due to ${\cal O}(10) M_\odot$ primordial black holes (PBHs).
Furthermore, it has been suggested that the whole amount of dark matter (DM)
might be in that exotic form. We investigate constraints on the PBH DM using
NuSTAR Galactic center (GC) X-ray data. We used a robust Monte Carlo approach
in conjunction with a radiatively inefficient PBH accretion model with commonly
accepted model parameters. Compared to previous studies we allowed for multiple
forms of DM density profiles. Most importantly, our study includes treatment of
the gas turbulence, which significantly modifies the relative velocity between
PBHs and gas. We show that inclusion of the effects of gas turbulence and the
uncertainties related to the DM density profile reduces significantly the gas
accretion onto PBHs compared to the claimed values in previous papers. It is
highly improbable to obtain accreting PBHs brighter than the NuSTAR point
source limit using observationally determined gas velocities. As such, one can
safely conclude that GC X-ray observations cannot rule out ${\cal O}(10)
M_\odot$ PBH DM. |
Primordial Circular Polarization in the Cosmic Microwave Background: Circular ("V-mode") polarization is expected to be vanishing in the CMB,
since it is not produced in Thomson scattering. However, considering that the
conventional CMB anisotropies are generated via an early universe mechanism
such as inflation or a bouncing scenario, it is possible that circular
polarization could be primordially produced and survive to the surface of last
scattering. We study this in detail, and find a large class of inflationary
models that produce a nearly scale invariant spectrum of scalar V-mode
anisotropies. We study the inflationary production and subsequent evolution via
the Boltzmann hierarchy, and show that V-mode polarization present in the CMB
is suppressed by a factor of at least $10^{10^{20}}$ relative to the primordial
$V$, consistent with expectation of negligible V-mode polarization from
inflation. We consider alternative possibilities for sourcing $V$ primordially,
such as the V-mode polarization induced by circularly polarized primordial
gravitational waves, or producing $V$ after inflation, via new interactions at
recombination. | The Herschel Virgo Cluster Survey - VIII. The Bright Galaxy Sample: We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data
that cover the complete survey area (four 4 x 4 deg2 regions). We use these
data to measure and compare the global far infrared properties of 78 optically
bright galaxies that are selected at 500 \mum and detected in all five
far-infrared bands. We show that our measurements and calibration are broadly
consistent with previous data obtained by IRAS, ISO, Spitzer and Planck. We use
SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 \mum
cluster luminosity distributions. These luminosity distributions are not power
laws, but peaked, with small numbers of both faint and bright galaxies. We
measure a cluster 100-500 micron far-infrared luminosity density of 1.6(7.0)
\pm 0.2 x 10^9 Lsun/Mpc3. This compares to a cluster 0.4-2.5 \mum optical
luminosity density of 5.0(20.0) x 10^9 Lsun/Mpc3, some 3.2(2.9) times larger
than the far-infrared. A typical photon originates from an optical depth of
0.4\pm0.1. Most of our sample galaxies are well fitted by a single modified
blackbody (beta=2), leading to a mean dust mass of log Mdust = 7.31 Msun and
temperature of 20.0 K. We also derive both stellar and atomic hydrogen masses
from which we calculate mean values for the stars:gas(atomic) and gas(atomic):
dust mass ratios of 15.1 and 58.2 respectively. Using our derived dust, atomic
gas and stellar masses we estimate cluster mass densities of 8.6(27.8) x 10^6,
4.6(13.9) x 10^8, 7.8(29.7) x 10^9 Msun/Mpc3, respectively for dust, atomic gas
and stars. These values are higher than those derived for field galaxies by
factors of 39(126), 6(18) and 34(129) respectively. In the above
luminosity/mass densities are given using the whole sample with values in
brackets using just those galaxies that lie between 17 and 23 Mpc. We provide a
data table of flux densities in all the Herschel bands for all 78 bright Virgo
cluster galaxies. |
Three-point phase correlations: A new measure of non-linear large-scale
structure: We derive an analytical expression for a novel large-scale structure
observable: the line correlation function. The line correlation function, which
is constructed from the three-point correlation function of the phase of the
density field, is a robust statistical measure allowing the extraction of
information in the non-linear and non-Gaussian regime. We show that, in
perturbation theory, the line correlation is sensitive to the coupling kernel
F_2, which governs the non-linear gravitational evolution of the density field.
We compare our analytical expression with results from numerical simulations
and find a 1-sigma agreement for separations r<30 Mpc/h. Fitting formulae for
the power spectrum and the non-linear coupling kernel at small scales allow us
to extend our prediction into the strongly non-linear regime where we find a
1-sigma agreement with the simulations for r<2 Mpc/h. We discuss the advantages
of the line correlation relative to standard statistical measures like the
bispectrum. Unlike the latter, the line correlation is independent of the bias,
in the regime where the bias is local and linear. Furthermore, the variance of
the line correlation is independent of the Gaussian variance on the modulus of
the density field. This suggests that the line correlation can probe more
precisely the non-linear regime of gravity, with less contamination from the
power spectrum variance. | Towards Optimal Foreground Mitigation Strategies for Interferometric HI
Intensity Mapping in the Low-Redshift Universe: We conduct the first case study towards developing optimal foreground
mitigation strategies for neutral hydrogen (HI) intensity mapping using radio
interferometers at low redshifts. A pipeline for simulation, foreground
mitigation and power spectrum estimation is built, which can be used for
ongoing and future surveys using MeerKAT and Square Kilometre Array Observatory
(SKAO). It simulates realistic sky signals to generate visibility data given
instrument and observation specifications, which is subsequently used to
perform foreground mitigation and power spectrum estimation. A quadratic
estimator formalism is developed to estimate the temperature power spectrum in
visibility space. Using MeerKAT telescope specifications for observations in
the redshift range z~0.25-0.30 corresponding to the MeerKAT International GHz
Tiered Extragalactic Exploration (MIGHTEE) survey, we present a case study
where we compare different approaches of foreground mitigation. We find that
component separation in visibility space provides a more accurate estimation of
HI clustering comparing to foreground avoidance, with the uncertainties being
30 per cent smaller. Power spectrum estimation from image is found to be less
robust with larger bias and more information loss when compared to estimation
in visibility. We conclude that for z~0.25-0.30, the MIGHTEE survey will be
capable of measuring the HI power spectrum from k~0.5 Mpc$^{-1}$ to k~10
Mpc$^{-1}$ with high accuracy. We are the first to show that, at low redshift,
component separation in visibility space suppresses foreground contamination at
large line-of-sight scales, allowing measurement of HI power spectrum closer to
the foreground wedge, crucial for data analysis towards future detections. |
Modelling the Galactic Foreground and Beam Chromaticity for Global 21-cm
Cosmology: In order to characterize and model the beam-weighted foreground for global
21-cm signal experiments, we present a methodology for generating basis
eigenvectors that combines analytical and observational models of both the
galactic spectral index and sky brightness temperature with simulations of
beams having various angular and spectral dependencies and pointings. Each
combination creates a unique beam-weighted foreground. By generating
eigenvectors to fit each foreground model using Singular Value Decomposition
(SVD), we examine the effects of varying the components of the beam-weighted
foreground. We find that the eigenvectors for modelling an achromatic,
isotropic beam -- the ideal case -- are nearly identical regardless of the
unweighted foreground model used, and are practicably indistinguishable from
polynomial-based models. When anisotropic, chromatic beams weight the
foreground, however, a coupling is introduced between the spatial and spectral
structure of the foreground which distorts the eigenvectors away from the
polynomial models and induces a dependence of the basis upon the exact features
of the beam (chromaticity, pattern, pointing) and foreground (spectral index,
sky brightness temperature map). We find that the beam has a greater impact
upon the eigenvectors than foreground models. Any model which does not account
for its distortion may produce RMS uncertainties on the order of $\sim 10$ -
$10^3$ Kelvin for six-parameter, single spectrum fits. If the beam is
incorporated directly using SVD and training sets, however, the resultant
eigenvectors yield milli-Kelvin level uncertainties. Given a sufficiently
detailed description of the sky, our methodology can be applied to any
particular experiment with a suitably characterized beam for the purpose of
generating accurate beam-weighted foreground models. | Finding Rare AGN: X-ray Number Counts of Chandra Sources in Stripe 82: We present the first results of a wide area X-ray survey within the Sloan
Digital Sky Survey (SDSS) Stripe 82, a 300 deg$^2$ region of the sky with a
substantial investment in multi-wavelength coverage. We analyzed archival {\it
Chandra} observations that cover 7.5 deg$^2$ within Stripe 82 ("Stripe 82
ACX"), reaching 4.5$\sigma$ flux limits of 7.9$\times10^{-16}$,
3.4$\times10^{-15}$ and 1.8$\times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the soft
(0.5-2 keV), hard (2-7 keV) and full (0.5-7 keV) bands, to find 774, 239 and
1118 X-ray sources, respectively. Three hundred twenty-one sources are detected
only in the full band and 9 sources are detected solely in the soft band.
Utilizing data products from the {\it Chandra} Source Catalog, we construct
independent Log$N$-Log$S$ relationships, detailing the number density of X-ray
sources as a function of flux, which show general agreement with previous {\it
Chandra} surveys. We compare the luminosity distribution of Stripe 82 ACX with
the smaller, deeper CDF-S + E-CDFS surveys and with {\it Chandra}-COSMOS,
illustrating the benefit of wide-area surveys in locating high luminosity AGN.
We also investigate the differences and similarities of X-ray and optical
selection to uncover obscured AGN in the local Universe. Finally, we estimate
the population of AGN we expect to find with increased coverage of 100 deg$^2$
or 300 deg$^2$, which will provide unprecedented insight into the high
redshift, high luminosity regime of black hole growth currently
under-represented in X-ray surveys. |
The Challenge of the Largest Structures in the Universe to Cosmology: Large galaxy redshift surveys have long been used to constrain cosmological
models and structure formation scenarios. In particular, the largest structures
discovered observationally are thought to carry critical information on the
amplitude of large-scale density fluctuations or homogeneity of the universe,
and have often challenged the standard cosmological framework. The Sloan Great
Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts
doubt on the concordance cosmological model with a cosmological constant (i.e.
the flat LCDM model). Here we show that the existence of the SGW is perfectly
consistent with the LCDM model, a result that only our very large cosmological
N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report
on the discovery of a void complex in the SDSS much larger than the SGW, and
show that such size of the largest void is also predicted in the LCDM paradigm.
Our results demonstrate that an initially homogeneous isotropic universe with
primordial Gaussian random phase density fluctuations growing in accordance
with the General Relativity, can explain the richness and size of the observed
large-scale structures in the SDSS. Using the HR2 simulation we predict that a
future galaxy redshift survey about four times deeper or with 3 magnitude
fainter limit than the SDSS should reveal a largest structure of bright
galaxies about twice as big as the SGW. | Constraints on Primordial Black Holes: the Importance of Accretion: We consider the constraints on the fraction of dark matter in the universe in
the form of primordial black holes taking into account the crucial role of
accretion which may change both their mass and mass function. We show that
accretion may drastically weaken the constraints at the present epoch for
primordial black holes with masses larger than a few solar masses. |
Black hole formation from axion stars: The classical equations of motion for an axion with potential
$V(\phi)=m_a^2f_a^2 [1-\cos (\phi/f_a)]$ possess quasi-stable, localized,
oscillating solutions, which we refer to as "axion stars". We study, for the
first time, collapse of axion stars numerically using the full non-linear
Einstein equations of general relativity and the full non-perturbative cosine
potential. We map regions on an "axion star stability diagram", parameterized
by the initial ADM mass, $M_{\rm ADM}$, and axion decay constant, $f_a$. We
identify three regions of the parameter space: i) long-lived oscillating axion
star solutions, with a base frequency, $m_a$, modulated by self-interactions,
ii) collapse to a BH and iii) complete dispersal due to gravitational cooling
and interactions. We locate the boundaries of these three regions and an
approximate "triple point" $(M_{\rm TP},f_{\rm TP})\sim (2.4 M_{pl}^2/m_a,0.3
M_{pl})$. For $f_a$ below the triple point BH formation proceeds during winding
(in the complex $U(1)$ picture) of the axion field near the dispersal phase.
This could prevent astrophysical BH formation from axion stars with $f_a\ll
M_{pl}$. For larger $f_a\gtrsim f_{\rm TP}$, BH formation occurs through the
stable branch and we estimate the mass ratio of the BH to the stable state at
the phase boundary to be $\mathcal{O}(1)$ within numerical uncertainty. We
discuss the observational relevance of our findings for axion stars as BH
seeds, which are supermassive in the case of ultralight axions. For the QCD
axion, the typical BH mass formed from axion star collapse is $M_{\rm BH}\sim
3.4 (f_a/0.6 M_{pl})^{1.2} M_\odot$. | Relaxion window: We investigate cosmological constraints on the original relaxion scenario
proposed by Graham, Kaplan and Rajendran. We first discuss the appropriate sign
choice of the terms in the scalar potential, when the QCD axion is the relaxion
with a relaxion-inflaton coupling proposed in the original paper. We next
derive the cosmologically consistent ranges of the mass and a coupling of the
relaxion for both the QCD relaxion and non-QCD relaxion. The mass range is
obtained by $10^{-5}$ eV $\ll m_{\phi} \lesssim 10^4$ eV. We also find that a
strong correlation between the Hubble parameter at the relaxion stabilization
and the scale $\Lambda$ of non-QCD strong dynamics, which generates the
non-perturbative relaxion cosine potential. For a higher relaxion mass, a large
scale $\Lambda$ becomes available. However, for its lower mass, $\Lambda$
should be small and constructing such a particle physics model is challenging. |
Exploring degeneracies in modified gravity with weak lensing: By considering linear-order departures from general relativity, we compute a
novel expression for the weak lensing convergence power spectrum under
alternative theories of gravity. This comprises an integral over a 'kernel' of
general relativistic quantities multiplied by a theory-dependent 'source' term.
The clear separation between theory-independent and -dependent terms allows for
an explicit understanding of each physical effect introduced by altering the
theory of gravity. We take advantage of this to explore the degeneracies
between gravitational parameters in weak lensing observations. | Magnification by Galaxy Group Dark Matter Halos: We report on the detection of gravitational lensing magnification by a
population of galaxy groups, at a significance level of 4.9 sigma. Using X-ray
selected groups in the COSMOS 1.64 deg^2 field, and high-redshift Lyman break
galaxies as sources, we measure a lensing-induced angular cross-correlation
between the samples. After satisfying consistency checks that demonstrate we
have indeed detected a magnification signal, and are not suffering from
contamination by physical overlap of samples, we proceed to implement an
optimally weighted cross-correlation function to further boost the signal to
noise of the measurement. Interpreting this optimally weighted measurement
allows us to study properties of the lensing groups. We model the full
distribution of group masses using a composite-halo approach, considering both
the singular isothermal sphere and Navarro-Frenk-White profiles, and find our
best fit values to be consistent with those recovered using the weak-lensing
shear technique. We argue that future weak-lensing studies will need to
incorporate magnification along with shear, both to reduce residual systematics
and to make full use of all available source information, in an effort to
maximize scientific yield of the observations. |
Galaxy groups and haloes in the SDSS-DR7: In this work we introduce a new method to perform the identification of
groups of galaxies and present results of the identification of galaxy groups
in the Seventh Data Release of the Sloan Digital Sky Survey (SDSS-DR7). Our
methodology follows an approach that resembles the standard friends-of-friends
(FoF) method. However, it uses assumptions on the mass of the dark matter halo
hosting a group of galaxies to link galaxies in the group using a local linking
length. Our method does not assumes any ad-hoc parameter for the identification
of groups, nor a linking length or a density threshold. This parameter-free
nature of the method, and the robustness of its results, are the most important
points of our work. We describe the data used for our study and give details of
the implementation of the method. We obtain galaxy groups and halo catalogs for
four volume limited samples whose properties are in good agreement with
previous works. They reproduces the expected stellar mass functions and follow
the expected stellar-halo mass relation. We found that most of the stellar
content in groups of galaxies comes from objects with $M_r$ absolute magnitudes
larger than -19, meaning that it is important to resolve the low luminosity
components of groups of galaxies to acquire detailed information about their
properties. | Simulations of BAO reconstruction with a quasar Lyman-alpha survey: The imprint of Baryonic Acoustic Oscillations (BAO) on the matter power
spectrum can be constrained using the neutral hydrogen density in the
intergalactic medium as a tracer of the matter density. One of the goals of the
Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey
(SDSS-III) is to derive the Hubble expansion rate and the angular scale from
the BAO signal in the IGM. To this aim, the Lyman-alpha forest of 10^5 quasars
will be observed in the redshift range 2.2<z<3.5 and over 10,000 deg^2. We
simulated the BOSS QSO survey to estimate the statistical accuracy on the BAO
scale determination provided by such a large scale survey. In particular, we
discuss the effect of the poorly constrained estimate of the unabsorbed
intrinsic quasar spectrum. The volume of current N-body simulations being too
small for such studies, we resorted to Gaussian random field (GRF) simulations.
We validated the use of GRFs by comparing the output of GRF simulations with
that of the Horizon N-body simulation with the same initial conditions.
Realistic mock samples of QSO Lyman-\alpha forest were generated; their power
spectrum was computed and fitted to obtain the BAO scale. The rms of the
results for 100 different simulations provides an estimate of the statistical
error expected from the BOSS survey. We confirm the results from Fisher matrix
estimate. In the absence of error on the unabsorbed quasar spectrum, the BOSS
quasar survey should measure the BAO scale with an error of the order of 2.3%,
or the transverse and radial BAO scales separately with errors of the order of
6.8% and 3.9%, respectively. The significance of the BAO detection is assessed
by an average \Delta\chi^2=17 but for individual realizations \Delta\chi^2
ranges from 2 t o 35. The error on the unabsorbed quasar spectrum increases the
error on the BAO scale by 10 to 20% and results in a sub percent bias. |
The Clustering of Extremely Red Objects: We measure the clustering of Extremely Red Objects (EROs) in ~8 deg^2 of the
NOAO Deep Wide Field Survey Bo\"otes field in order to establish robust links
between ERO z~1.2 and local galaxy z<0.1 populations. Three different color
selection criteria from the literature are analyzed to assess the consequences
of using different criteria for selecting EROs. Specifically, our samples are
(R-K_s)>5.0 (28,724 galaxies), (I-K_s)>4.0 (22,451 galaxies) and (I-[3.6])>5.0
(64,370 galaxies). Magnitude-limited samples show the correlation length (r_0)
to increase for more luminous EROs, implying a correlation with stellar mass.
We can separate star-forming and passive ERO populations using the (K_s-[24])
and ([3.6]-[24]) colors to K_s=18.4 and [3.6]=17.5, respectively. Star-forming
and passive EROs in magnitude limited samples have different clustering
properties and host dark halo masses, and cannot be simply understood as a
single population. Based on the clustering, we find that bright passive EROs
are the likely progenitors of >4L^* elliptical galaxies. Bright EROs with
ongoing star formation were found to occupy denser environments than
star-forming galaxies in the local Universe, making these the likely
progenitors of >L^* local ellipticals. This suggests that the progenitors of
massive >4L^* local ellipticals had stopped forming stars by z>1.2, but that
the progenitors of less massive ellipticals (down to L^*) can still show
significant star formation at this epoch. | ATLBS: the Australia Telescope Low-brightness Survey: We present a radio survey carried out with the Australia Telescope Compact
Array. A motivation for the survey was to make a complete inventory of the
diffuse emission components as a step towards a study of the cosmic evolution
in radio source structure and the contribution from radio-mode feedback on
galaxy evolution. The Australia Telescope low-brightness survey (ATLBS) at 1388
MHz covers 8.42 sq deg of the sky in an observing mode designed to yield images
with exceptional surface brightness sensitivity and low confusion. The ATLBS
radio images, made with 0.08 mJy/beam rms noise and 50" beam, detect a total of
1094 sources with peak flux exceeding 0.4 mJy/beam. The ATLBS source counts
were corrected for blending, noise bias, resolution, and primary beam
attenuation; the normalized differential source counts are consistent with no
upturn down to 0.6 mJy. The percentage integrated polarization Pi_0 was
computed after corrections for the polarization bias in integrated polarized
intensity; Pi_0 shows an increasing trend with decreasing flux density.
Simultaneous visibility measurements made with longer baselines yielded images,
with 5" beam, of compact components in sources detected in the survey. The
observations provide a measurement of the complexity and diffuse emission
associated with mJy and sub-mJy radio sources. 10% of the ATLBS sources have
more than half of their flux density in extended emission and the fractional
flux in diffuse components does not appear to vary with flux density, although
the percentage of sources that have complex structure increases with flux
density. The observations are consistent with a transition in the nature of
extended radio sources from FR-II radio source morphology, which dominates the
mJy population, to FR-I structure at sub-mJy flux density. (Abridged) |
Strongly star-forming rotating disks in a complex merging system at z =
4,7 as revealed by ALMA: We performed a kinematical analysis of the [CII] line emission of the BR
1202-0725 system at z~4,7 using ALMA observations. The most prominent sources
of this system are a quasar and a submillimeter galaxy, separated by a
projected distance of about 24 kpc and characterized by very high SFR, higher
than 1000 Msun/yr. However, the ALMA observations reveal that these galaxies
apparently have undisturbed rotating disks, which is at variance with the
commonly accepted scenario in which strong star formation activity is induced
by a major merger. We also detected faint components which, after spectral
deblending, were spatially resolved from the main QSO and SMG emissions. The
relative velocities and positions of these components are compatible with
orbital motions within the gravitational potentials generated by the QSO host
galaxy and the SMG, suggesting that they are smaller galaxies in interaction or
gas clouds in accretion flows of tidal streams. We did not find any clear
spectral evidence for outflows caused by AGN or stellar feedback. This suggests
that the high star formation rates might be induced by interactions or minor
mergers with these companions, which do not affect the large-scale kinematics
of the disks, however. Our kinematical analysis also indicates that the QSO and
the SMG have similar Mdyn, mostly in the form of molecular gas, and that the
QSO host galaxy and the SMG are seen close to face-on with slightly different
disk inclinations: the QSO host galaxy is seen almost face-on (i~15), while the
SMG is seen at higher inclinations (i~25). Finally, the ratio between the black
hole mass of the QSO, obtained from XShooter spectroscopy, and the Mdyn of the
host galaxy is similar to value found in very massive local galaxies,
suggesting that the evolution of black hole galaxy relations is probably better
studied with dynamical than with stellar host galaxy masses. | Cosmology with Ricci-type dark energy: We consider the dynamics of a cosmological substratum of pressureless matter
and holographic dark energy with a cutoff length proportional to the Ricci
scale. Stability requirements for the matter perturbations are shown to single
out a model with a fixed relation between the present matter fraction
$\Omega_{m0}$ and the present value $\omega_{0}$ of the equation-of-state
parameter of the dark energy. This model has the same number of free parameters
as the $\Lambda$CDM model but it has no $\Lambda$CDM limit. We discuss the
consistency between background observations and the mentioned
stability-guaranteeing parameter combination. |
Temperature and abundance profiles of hot gas in galaxy groups - II.
Implications for feedback and ICM enrichment: We investigate the history of galactic feedback and chemical enrichment
within a sample of 15 X-ray bright groups of galaxies, on the basis of the
inferred Fe and Si distributions in the hot gas and the associated metal masses
produced by core-collapse and type Ia supernovae (SN). Most of these cool-core
groups show a central Fe and Si excess, which can be explained by prolonged
enrichment by SN Ia and stellar winds in the central early-type galaxy alone,
but with tentative evidence for additional processes contributing to core
enrichment in hotter groups. Inferred metal mass-to-light ratios inside r_500
show a positive correlation with total group mass but are generally
significantly lower than in clusters, due to a combination of lower global ICM
abundances and gas-to-light ratios in groups. This metal deficiency is present
for products from both SN Ia and SN II, and suggests that metals were either
synthesized, released from galaxies, or retained within the ICM less
efficiently in lower-mass systems. We explore possible causes, including
variations in galaxy formation and metal release efficiency, cooling-out of
metals, and gas and metal loss via AGN- or starburst-driven galactic winds from
groups or their precursor filaments. Loss of enriched material from filaments
coupled with post-collapse AGN feedback emerge as viable explanations, but we
also find evidence for metals to have been released less efficiently from
galaxies in cooler groups and for the ICM in these to appear chemically less
evolved, possibly reflecting more extended star formation histories in less
massive systems. Some implications for the hierarchical growth of clusters from
groups are briefly discussed. | Spitzer Quasar and ULIRG Evolution Study (QUEST). IV. Comparison of 1-Jy
Ultraluminous Infrared Galaxies with Palomar-Green Quasars: We report the results from a comprehensive study of 74 ultraluminous infrared
galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ~ 0.3$ observed
with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear
activity to the bolometric luminosity in these systems is quantified using six
independent methods that span a range in wavelength and give consistent results
within ~ +/-10-15% on average. The average derived AGN contribution in ULIRGs
is ~35-40%, ranging from ~15-35% among "cool" (f_25/f_60 =< 0.2) optically
classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and
Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs. ULIRGs
fall in one of three distinct AGN classes: (1) objects with small extinctions
and large PAH equivalent widths are highly starburst-dominated; (2) systems
with large extinctions and modest PAH equivalent widths have larger AGN
contributions, but still tend to be starburst-dominated; and (3) ULIRGs with
both small extinctions and small PAH equivalent widths host AGN that are at
least as powerful as the starbursts. The AGN contributions in class 2 ULIRGs
are more uncertain than in the other objects, and we cannot formally rule out
the possibility that these objects represent a physically distinct type of
ULIRGs. A morphological trend is seen along the sequence (1)-(2)-(3), in
general agreement with the standard ULIRG - QSO evolution scenario and
suggestive of a broad peak in extinction during the intermediate stages of
merger evolution. However, the scatter in this sequence, implies that black
hole accretion, in addition to depending on the merger phase, also has a strong
chaotic/random component, as in local AGN. (abridged) |
Dark matter from primordial quantum information: We suggest a general relation between the position of the cosmic microwave
background temperature power spectrum peaks and the inflationary slow roll
parameter $\epsilon$. This relation is based on interpreting the variable
setting the position of the peaks as the quantum distance between the end of
inflation and recombination. This distance is determined by the primordial
cosmological Fisher information introduced in arXiv:2002.04294. The
observational constraints set by cosmic microwave background temperature data
lead to a very stringent prediction for the value of the tensor-to-scalar
ratio: $r=0.01 \pm 0.002$. Future polarization data of the cosmic microwave
background should be able to measure this signal and corroborate or discard our
model. | Cosmological constraints on sterile neutrino oscillations from Planck: Both particle physics experiments and cosmological surveys can constrain the
properties of sterile neutrinos, but do so with different parameterizations
that naturally use different prior information. We present joint constraints on
the 3$+$1 sterile neutrino model oscillation parameters, $\Delta m_{41}^2$ and
$\sin^22\theta$, with log priors on those parameters using mostly cosmological
data from the Planck satellite. Two cases are considered, one where the sterile
neutrino mixes with electron neutrinos solely, and another where the sterile
neutrino mixes exclusively with muon neutrinos, allowing us to constrain the
mixing angles $\sin^22\theta_{14}$ and $\sin^22\theta_{24}.$ We find that
cosmological data are inconsistent with strong hints of a sterile neutrino
coming from some oscillation channels of the LSND and MiniBooNE experiments,
under the assumption that the sterile neutrinos mix with a single neutrino
flavour. We also forecast the sensitivity with which future CMB experiments
should be able to probe $\Delta m_{41}^2$ and $\sin^22\theta$. |
More evidence for extinction of activity in galaxies: This Research Note amends an article in which we showed that radio-loud
quasars can become radio-quiet. Exploring the analogy between galactic nuclei
and X-ray binaries (XRB), we pointed out there that this transition in quasars
could be identified with a switch from low/hard to high/soft state in
microquasars. Here, we present the evidence that traces of past occurrences of
this kind of phenomena can be found in normal but once active galaxies. Based
on the properties of a few such "post-active" galaxies that are representative
for a much wider group, it has been argued that they have reached the
evolutionary stages when their nuclei, which were radio-loud in the past, now,
mimicking the behaviour of XRBs, remain in the intermediate state on their way
towards quiescence or even have already entered the quiescent state. It follows
that the full evolutionary track of XRBs can be mapped onto the evolution of
galaxies. The above findings are in line with those reported recently for IC
2497, a galaxy that 70,000 years ago or less hosted a quasar but now appears as
a normal one. This scenario stems from the presence of Hanny's Voorwerp, a
nebulous object in its vicinity excited by that QSO in the epoch when IC 2497
was active. The post-active galaxies we deal with here are accompanied by
extremely weak and diffuse relic radio lobes that were inflated during their
former active period. These relics can be regarded as radio analogues of
Hanny's Voorwerp. | Model-independent Estimations for the Cosmic Curvature from the Latest
Strong Gravitational Lensing Systems: Model-independent measurements for the cosmic spatial curvature, which is
related to the nature of cosmic space-time geometry, plays an important role in
cosmology. On the basis of the Distance Sum Rule in the
Friedmann-Lema{\^i}tre-Robertson-Walker metric, (distance ratio) measurements
of strong gravitational lensing (SGL) systems together with distances from type
Ia supernovae observations have been proposed to directly estimate the spatial
curvature without any assumptions for the theories of gravity and contents of
the universe. However, previous studies indicated that a spatially closed
universe was strongly preferred. In this paper, we re-estimate the cosmic
curvature with the latest SGL data which includes 163 well-measured systems. In
addition, possible factors, e.g. combination of SGL data from different surveys
and stellar mass of the lens galaxy, which might affect estimations for the
spatial curvature, are considered in our analysis. We find that, except the
case where only SGL systems from the Sloan Lens ACS Survey are considered, a
spatially flat universe is consistently favored at very high confidence level
by the latest observations. It is suggested that the increasing number of
well-measured strong lensing events might significantly reduce the bias of
estimation for the cosmic curvature. |
Cosmological Constraint and Analysis on Holographic Dark Energy Model
Characterized by the Conformal-age-like Length: We present a best-fit analysis on the single-parameter holographic dark
energy model characterized by the conformal-age-like length,
$L=\frac{1}{a^4(t)}\int_0^tdt' a^3(t') $. Based on the Union2 compilation of
557 supernova Ia data, the baryon acoustic oscillation results from the SDSS
DR7 and the cosmic microwave background radiation data from the WMAP7, we show
that the model gives the minimal $\chi^2_{min}=546.273$, which is comparable to
$\chi^2_{\Lambda{\rm CDM}}=544.616$ for the $\Lambda$CDM model. The single
parameter $d$ concerned in the model is found to be $d=0.232\pm 0.006\pm
0.009$. Since the fractional density of dark energy $\Omega_{de}\sim d^2a^2$ at
$a \ll 1$, the fraction of dark energy is naturally negligible in the early
universe, $\Omega_{de} \ll 1$ at $a \ll 1$. The resulting constraints on the
present fractional energy density of matter and the equation of state are
$\Omega_{m0}=0.286^{+0.019}_{-0.018}^{+0.032}_{-0.028}$ and
$w_{de0}=-1.240^{+0.027}_{-0.027}^{+0.045}_{-0.044}$ respectively. The model
leads to a slightly larger fraction of matter comparing to the $\Lambda$CDM
model. We also provide a systematic analysis on the cosmic evolutions of the
fractional energy density of dark energy, the equation of state of dark energy,
the deceleration parameter and the statefinder. It is noticed that the equation
of state crosses from $w_{de}>-1$ to $w_{de}<-1$, the universe transits from
decelerated expansion ($q>0$) to accelerated expansion ($q<0$) recently, and
the statefinder may serve as a sensitive diagnostic to distinguish the CHDE
model with the $\Lambda$CDM model. | Low-velocity cosmic strings in accelerating universe: The standard cosmological model supposes that the dominant matter component
changes in the course of the evolution of the universe. We study the
homogeneous and isotropic universe with non-zero cosmological constant in the
epoch when the dominant matter component has a form of a gas of low-velocity
cosmic strings. It is shown that after the scale transformation of the time
variable such a model and the standard model of a spatially flat universe
filled with pressure-free matter provide the equivalent descriptions of
cosmological parameters as functions of time at equal values of the
cosmological constant. The exception is the behavior of the deceleration
parameter in the early universe. Pressure-free matter can obtain the properties
of a gas of low-velocity cosmic strings in the epoch when the global geometry
and total amount of matter in the universe as a whole obey an additional
constraint. This constraint follows from the quantum geometrodynamical approach
in the semiclassical approximation. In terms of general relativity, its
effective contribution to the field equations can be linked to the evolution in
time of the equation of state of matter caused by the processes of
redistribution of energy between matter components. |
On the giant supercluster binary-like system formed by the Corona
Borealis and Abell 2142: The recent hypothesis of a giant supercluster binary-like structure formed by
the Corona Borealis and its close companion Abell 2142 (supercluster) belongs
to a little known area of investigation as the dynamics of gravitationally
interacting galaxy supercluster pairs. From the observational point of view
this structure approximates the configuration of a binary-like system in linear
orbit interconnected by a huge filamentary structure which, if confirmed, it
would be the first case to date observed at z > 0.07. Given the importance to
disentangle this issue, a follow-up analysis has been performed on the region
constrained by the common envelop of the two superclusters in order to search
for new hints to confirm their mutual gravitational interaction. Observational
signatures of that interaction have been found mapping the inner peculiar
motions where the observed negative peculiar velocities measured within the
A2142 (supercluster) region suggest a general matter flow toward the Corona
Borealis supercluster. Besides, analyzing the effects on both superclusters due
to the mutual impact of the external tidal forces, turns out that their inner
dynamics remain unperturbed up to the turnaround radii. Outside, where the
binding forces are overlapped by the tidal ones, the outskirts of both
superclusters should be unstable and subject to fragmentation. Such a scenario
indicates that both superclusters interact with comparable and reciprocal tidal
perturbations leaving the whole system in a substantial dynamical equilibrium.
The origin of such a dynamical dichotomy would be explained either by a much
more massive Corona Borealis supercluster than that estimated in the present
work or by a selection effect biasing the small sample of peculiar velocities
due to the remoteness of the system worsened by the large uncertainty on their
measurements. | A tale of two (or more) $h$'s: We use the large-scale structure galaxy data (LSS) from the BOSS and eBOSS
surveys, in combination with abundances information from Big Bang
Nucleosynthesis (BBN) to measure two values of the Hubble expansion rate,
$H_0=100h\,[{\rm km}\, {\rm s}^{-1}\,{\rm Mpc}^{-1}]$, each of them based on
very different physical processes. One is a (traditional) late-time-background
measurement based on determining the BAO scale and using BBN abundances on
baryons for calibrating its absolute size (BAO+BBN). This method anchors $H_0$
to the (standard) physics of the sound horizon scale at pre-recombination
times. The other is a newer early-time based measurement associated with the
broadband shape of the power spectrum. This second method anchors $H_0$ to the
physics of the matter-radiation equality scale, which also needs BBN
information for determining the suppression of baryons in the power spectrum
shape (shape+BBN). Within the $\Lambda$CDM model, we find very good consistency
among these two $H_0$'s: BAO+BBN (+growth) delivers $H_0=67.42_{-0.94}^{+0.88}$
$(67.37_{-0.95}^{+0.86})$ km s$^{-1}$Mpc$^{-1}$ , whereas the shape+BBN
(+growth) delivers $H_0 = 70.1_{-2.1}^{+2.1}$ $(70.1_{-2.1}^{+1.9})$ km
s$^{-1}$ Mpc$^{-1}$, where "growth" stands for information from the
late-time-perturbations captured by the growth of structure parameter. These
are the tightest sound-horizon free $H_0$ constraints from LSS data to date. As
a consequence to be viable, any $\Lambda$CDM extension proposed to address the
so-called "Hubble tension" needs to modify consistently not only the sound
horizon scale physics, but also the matter-radiation equality scale, in such a
way that both late- and early-based $H_0$'s return results mutually consistent
and consistent with the high $H_0$ value recovered by the standard cosmic
distance ladder (distance-redshift relation) determinations. |
A dynamical dark energy solution to Hubble-Lemaître tension in the
light of the multimessenger era: We show that the gravitational waves measurements have raised the opportunity
to measure $H_0$ with dark sirens to within 2$\sigma$, the accuracy required to
resolve the \hubble tension. There are two principal reasons for our results:
(1) upgrades to GW LIGO-Virgo transient catalogues GWTC-1 and GWTC-2 enhance
their sensitive with only 10\% of contamination fraction, and (2) new dark
sirens should help to constrain our dynamical EoS. In conjunction, sensitivity
upgrades and a new dark energy model will facilitate an accurate inference of
the \hubble constant $H_0$ to better with an $\pm 0.077$ error in comparison to
the LIGO dark siren with $+14.0$/$-7.0$, which would further solidify the role
of dark sirens in late dark energy for precision cosmology in the future. | A simple prediction of the non-linear matter power spectrum in
Brans-Dicke gravity from linear theory: Brans-Dicke (BD) was one of the first proposed scalar-tensor theories of
gravity, and effectively turns the gravitational constant of General Relativity
(GR) time-dependent. Constraints on the BD parameter $\omega$ serve as a
benchmark for testing GR, which is recovered in the limit $\omega \rightarrow
\infty$. Current small-scale astrophysical constraints $\omega \gtrsim 10^5$
are much tighter than large-scale cosmological constraints $\omega \gtrsim
10^3$, but these decouple if the true theory of gravity features screening. On
the largest cosmological scales BD approximates the most general second order
scalar-tensor (Horndeski) theory, so constraints here have wider implications.
These will improve with upcoming large-scale structure and CMB surveys. To
constrain BD with weak gravitational lensing, one needs its non-linear matter
power spectrum $P_{\rm BD}$. By comparing the boost $B = P_{\rm BD}/P_{\rm GR}$
from linear theory and non-linear $N$-body simulations, we show that the
non-linear boost can simply be predicted from linear theory if the ${\rm BD}$
and ${\rm GR}$ universes are parametrized in a way that makes their early
cosmological evolution and quasi-linear power today similar. In particular,
they need the same $H_0 / \sqrt{\smash[b]{G_{\rm eff}(a=0)}}$ and $\sigma_8$,
where $G_{\rm eff}$ are their (effective) gravitational strengths. Our
prediction is $1\%$ accurate for $\omega \geq 100$, $z \leq 3$ and $k \leq
1\,h/\rm{Mpc}$, and $2\%$ further up to $k \leq 5\,h/\rm{Mpc}$. It also holds
for $G_{\rm BD}$ that do not match Newton's constant today, so one can study GR
with different gravitational constants $G_{\rm GR}$ by sending $\omega
\rightarrow \infty$. We provide a code that computes $B$ with the linear
Einstein-Boltzmann solver hi_class and multiplies it by the non-linear $P_{\rm
GR}$ from EuclidEmulator2 to predict $P_{\rm BD}$. |
Using member galaxy luminosities as halo mass proxies of galaxy groups: Reliable halo mass estimation for a given galaxy system plays an important
role both in cosmology and galaxy formation studies. Here we set out to find
the way that can improve the halo mass estimation for those galaxy systems with
limited brightest member galaxies been observed. Using four mock galaxy samples
constructed from semi-analytical formation models, the subhalo abundance
matching method and the conditional luminosity functions, respectively, we find
that the luminosity gap between the brightest and the subsequent brightest
member galaxies in a halo (group) can be used to significantly reduce the
scatter in the halo mass estimation based on the luminosity of the brightest
galaxy alone. Tests show that these corrections can significantly reduce the
scatter in the halo mass estimations by $\sim 50\%$ to $\sim 70\%$ in massive
halos depending on which member galaxies are considered. Comparing to the
traditional ranking method, we find that this method works better for groups
with less than five members, or in observations with very bright magnitude cut. | The faintest Seyfert radio cores revealed by VLBI: In this letter, we report on dual-frequency European VLBI Network (EVN)
observations of the faintest and least luminous radio cores in Seyfert nuclei,
going to sub-mJy flux densities and radio luminosities around 10^19 W/Hz. We
detect radio emission from the nuclear region of four galaxies (NGC 4051, NGC
4388, NGC 4501, and NGC 5033), while one (NGC 5273) is undetected at the level
of ~100 microJy. The detected compact nuclei have rather different radio
properties: spectral indices range from steep (alpha>0.7) to slightly inverted
(alpha=-0.1), brightness temperatures vary from T_B=10^5 K to larger than 10^7
K and cores are either extended or unresolved, in one case accompanied by
lobe-like features (NGC 4051). In this sense, diverse underlying physical
mechanisms can be at work in these objects: jet-base or outflow solutions are
the most natural explanations in several cases; in the case of the undetected
NGC 5273 nucleus, the presence of an advection-dominated accretion flow (ADAF)
is consistent with the radio luminosity upper limit. |
On the gravitational stability and mass estimation of stellar disks: We estimate the masses of disks of galaxies using the marginal gravitational
stability criterion and compare them with the photometrical disk mass
evaluations. The comparison reveals that the stellar disks of most of spiral
galaxies we considered cannot be substantially overheated (at least within
several radial scalelengths) and are therefore unlikely to have experienced a
significant merging event in their history. However, for substantial part of
S0- type galaxies a stellar velocity dispersion is well in excess of the
gravitational stability threshold suggesting a major merger event in the past.
For four low surface brightness galaxies we found that the disk masses
corresponding to the marginal stability condition are significantly higher than
it may be expected from their brightness. Either their disks are dynamically
overheated, or they contain a large amount of non-luminous matter. | The VIMOS Public Extragalactic Survey (VIPERS): First Release of spectra: We release the spectra for the more than 57000 objects presented in the First
VIPERS Data Release. For each object we distribute the observed, wavelength and
flux calibrated spectrum, as well as cleaned spectra, where artifacts due to
fringing are removed. We also provide the sky and noise spectrum and the 2D
spectrum. Data can be downloaded from http://vipers.inaf.it. |
The heating of dust by old stellar populations in the Bulge of M31: We use new Herschel multi-band imaging of the Andromeda galaxy to analyze how
dust heating occurs in the central regions of galaxy spheroids that are
essentially devoid of young stars. We construct a dust temperature map of M31
through fitting modified blackbody SEDs to the Herschel data, and find that the
temperature within 2 kpc rises strongly from the mean value in the disk of 17
pm 1K to \sim35K at the centre. UV to near-IR imaging of the central few kpc
shows directly the absence of young stellar populations, delineates the radial
profile of the stellar density, and demonstrates that even the near-UV dust
extinction is optically thin in M31's bulge. This allows the direct calculation
of the stellar radiation heating in the bulge, U\ast(r), as a function of
radius. The increasing temperature profile in the centre matches that expected
from the stellar heating, i.e. that the dust heating and cooling rates track
each other over nearly two orders of magnitude in U\ast. The modelled dust
heating is in excess of the observed dust temperatures, suggesting that it is
more than sufficient to explain the observed IR emission. Together with the
wavelength dependent absorption cross section of the dust, this demonstrates
directly that it is the optical, not UV, radiation that sets the heating rate.
This analysis shows that neither young stellar populations nor stellar near-UV
radiation are necessary to heat dust to warm temperatures in galaxy spheroids.
Rather, it is the high densities of Gyr-old stellar populations that provide a
sufficiently strong diffuse radiation field to heat the dust. To the extent
which these results pertain to the tenuous dust found in the centres of
early-type galaxies remains yet to be explored. | An observational detection of the bridge effect of void filaments: The bridge effect of void filaments is a phrase coined by Park & Lee (2009b)
to explain the correlations found in a numerical experiment between the
luminosity of the void galaxies and the degree of the straightness of their
host filaments. Their numerical finding implies that a straight void filament
provides a narrow channel for the efficient transportation of gas and matter
particles from the surroundings into the void galaxies. Analyzing the Sloan
void catalog constructed by Pan et al (2012), we identify the filamentary
structures in void regions and determine the specific size of each void
filament as a measure of its straightness. To avoid possible spurious signals
caused by the Malmquist bias, we consider only those void filaments whose
redshifts are in the range of 0=< z <= 0.02 and find a clear tendency that the
void galaxies located in the more straight filaments are on average more
luminous, which is in qualitative agreement with the numerical prediction. It
is also shown that the strength of correlation increases with the number of the
member galaxies of the void filaments, which can be physically understood on
the grounds that the more stretched filaments can connect the dense
surroundings even to the galaxies located deep in the central parts of the
voids. This observational evidence may provide a key clue to the puzzling issue
of why the void galaxies have higher specific star formation rates and bluer
colors than their wall counterparts. |
The Faint End of the Cluster Galaxy Luminosity Function at High Redshift: We measure the faint end slope of the galaxy luminosity function (LF) for
cluster galaxies at 1<z<1.5 using Spitzer IRAC data. We investigate whether
this slope, alpha, differs from that of the field LF at these redshifts, and
with the cluster LF at low redshifts. The latter is of particular interest as
low-luminosity galaxies are expected to undergo significant evolution. We use
seven high-redshift spectroscopically confirmed galaxy clusters drawn from the
IRAC Shallow Cluster Survey to measure the cluster galaxy LF down to depths of
M* + 3 (3.6 microns) and M* + 2.5 (4.5 microns). The summed LF at our median
cluster redshift (z=1.35) is well fit by a Schechter distribution with
alpha[3.6] = -0.97 +/- 0.14 and alpha[4.5] = -0.91 +/- 0.28, consistent with a
flat faint end slope and is in agreement with measurements of the field LF in
similar bands at these redshifts. A comparison to alpha in low-redshift
clusters finds no statistically significant evidence of evolution. Combined
with past studies which show that M* is passively evolving out to z~1.3, this
means that the shape of the cluster LF is largely in place by z~1.3. This
suggests that the processes that govern the build up of the mass of low-mass
cluster galaxies have no net effect on the faint end slope of the cluster LF at
z<1.3. | Optimized Clustering Estimators for BAO Measurements Accounting for
Significant Redshift Uncertainty: We determine an optimized clustering statistic to be used for galaxy samples
with significant redshift uncertainty, such as those that rely on photometric
redshifts. To do so, we study the baryon acoustic oscillation (BAO) information
content as a function of the orientation of galaxy clustering modes with
respect to their angle to the line-of-sight (LOS). The clustering along the
LOS, as observed in a redshift-space with significant redshift uncertainty, has
contributions from clustering modes with a range of orientations with respect
to the true LOS. For redshift uncertainty $\sigma_z \geq 0.02(1+z)$ we find
that while the BAO information is confined to transverse clustering modes in
the true space, it is spread nearly evenly in the observed space. Thus,
measuring clustering in terms of the projected separation (regardless of the
LOS) is an efficient and nearly lossless compression of the signal for
$\sigma_z \geq 0.02(1+z)$. For reduced redshift uncertainty, a more careful
consideration is required. We then use more than 1700 realizations (combining
two separate sets) of galaxy simulations mimicking the Dark Energy Survey Year
1 sample to validate our analytic results and optimized analysis procedure. We
find that using the correlation function binned in projected separation, we can
achieve uncertainties that are within 10 per cent of those predicted by Fisher
matrix forecasts. We predict that DES Y1 should achieve a 5 per cent distance
measurement using our optimized methods. We expect the results presented here
to be important for any future BAO measurements made using photometric redshift
data. |
A new method to measure evolution of the galaxy luminosity function: We present a new efficient technique for measuring evolution of the galaxy
luminosity function. The method reconstructs the evolution over the
luminosity-redshift plane using any combination of three input dataset types:
1) number counts, 2) galaxy redshifts, 3) integrated background flux
measurements. The evolution is reconstructed in adaptively sized regions of the
plane according to the input data as determined by a Bayesian formalism. We
demonstrate the performance of the method using a range of different synthetic
input datasets. We also make predictions of the accuracy with which forthcoming
surveys conducted with SCUBA2 and the Herschel Space Satellite will be able to
measure evolution of the sub-millimetre luminosity function using the method. | Probing inflation with large-scale structure data: the contribution of
information at small scales: Upcoming full-sky large-scale structure surveys such as Euclid can probe the
primordial Universe. Using the specifications for the Euclid survey, we
estimate the constraints on the inflation potential beyond slow-roll. We use
mock Euclid and Planck data from fiducial cosmological models using the Wiggly
Whipped Inflation (WWI) framework, which generates features in the primordial
power spectrum. We include Euclid cosmic shear and galaxy clustering, with two
setups (Conservative and Realistic) for the non-linear cut-off. We find that
the addition of Euclid data gives an improvement in constraints in the WWI
potential, with the Realistic setup providing marginal improvement over the
Conservative for most models. This shows that Euclid may allow us to identify
oscillations in the primordial spectrum present at intermediate to small
scales. |
Testing model independent modified gravity with future large scale
surveys: Model-independent parametrisations of modified gravity have attracted a lot
of attention over the past few years and numerous combinations of experiments
and observables have been suggested to constrain the parameters used in these
models. Galaxy clusters have been mentioned, but not looked at as extensively
in the literature as some other probes. Here we look at adding galaxy clusters
into the mix of observables and examine how they could improve the constraints
on the modified gravity parameters. In particular, we forecast the constraints
from combining Planck satellite Cosmic Microwave Background (CMB) measurements
and Sunyaev-Zeldovich (SZ) cluster catalogue with a DES-like weak lensing
survey. We find that cluster counts significantly improve the constraints over
those derived using CMB and WL. We then look at surveys further into the
future, to see how much better it may be feasible to make the constraints. | Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A
Measurement of Circular Polarization at 40 GHz: We report circular polarization measurements from the first two years of
observation with the 40 GHz polarimeter of the Cosmology Large Angular Scale
Surveyor (CLASS). CLASS is conducting a multi-frequency survey covering 75% of
the sky from the Atacama Desert designed to measure the cosmic microwave
background (CMB) linear E and B polarization on angular scales $1^\circ
\lesssim \theta \leq 90^\circ$, corresponding to a multipole range of $2 \leq
\ell \lesssim 200$. The modulation technology enabling measurements of linear
polarization at the largest angular scales from the ground, the Variable-delay
Polarization Modulator, is uniquely designed to provide explicit sensitivity to
circular polarization (Stokes $V$). We present a first detection of circularly
polarized atmospheric emission at 40 GHz that is well described by a dipole
with an amplitude of $124\pm4\,\mathrm{\mu K}$ when observed at an elevation of
$45^\circ$, and discuss its potential impact as a foreground to CMB
experiments. Filtering the atmospheric component, CLASS places a 95% C.L. upper
limit of $0.4\,\mathrm{\mu K}^2$ to $13.5\,\mathrm{\mu K}^2$ on
$\ell(\ell+1)C_\ell^{VV}/(2\pi)$ between $1 \leq \ell \leq 120$, representing a
two-orders-of-magnitude improvement over previous limits. |
z=1 Multifractality of Swift short GRBs?: Aims. We analyze and characterize the angular distribution of selected
samples of gamma ray bursts (GRBs) from Batse and Swift data to confirm that
the division in two classes of short- and long-duration GRBs correspond also to
the existence of two distinct spatial populations. Methods. The angular
distribution is analyzed by using multifractal analysis and characterized by a
multifractal spectrum of dimensions. Different spectra of dimensions indicate
different angular distributions. Results. The spectra of dimensions of short
and long bursts indicate that the two populations have two different angular
distributions. Both Swift and BATSE long bursts appear to be homo- geneously
distributed in the sky with a monofractal distribution. Short GRBs follow
instead a multifractal distribution for both the two samples. Even if BATSE
data may not give a secure in- terpretation of their angular distribution
because of the instrumental selection effects that mainly favor the detection
of near GRBs, the results from Swift short GRBs confirm this behavior, also
when are included GRBs corrected by the redshift factor. The distributions
traced by short GRBs, up to z = 1, depict a universe with a structure similar
to that of a disordered porous material with uniformly distributed
heterogeneous irregular structures, appearing more clustered than what
expected. | Biases in the estimation of velocity dispersions and dynamical masses
for galaxy clusters: Using a set of 73 numerically simulated galaxy clusters, we have
characterised the statistical and physical biases for three velocity dispersion
and mass estimators, namely biweight, gapper and standard deviation, in the
small number of galaxies regime ($N_{gal} \leq 75$), both for the determination
of the velocity dispersion and the dynamical mass of the clusters via the
$\sigma-M$ relation. These results are used to define a new set of unbiased
estimators, that are able to correct for those statistical biases. By applying
these new estimators to a subset of simulated observations, we show that they
can retrieve bias-corrected values for both the mean velocity dispersion and
the mean mass. |
Optimal machine-driven acquisition of future cosmological data: We present maps classifying regions of the sky according to their information
gain potential as quantified by the Fisher information. These maps can guide
the optimal retrieval of relevant physical information with targeted
cosmological searches. Specifically, we calculate the response of observed
cosmic structures to perturbative changes in the cosmological model and chart
their respective contributions to the Fisher information. Our physical forward
modeling machinery transcends the limitations of contemporary analyses based on
statistical summaries to yield detailed characterizations of individual 3D
structures. We demonstrate this using galaxy counts data and showcase the
potential of our approach by studying the information gain of the Coma cluster.
We find that regions in the vicinity of the filaments and cluster core, where
mass accretion ensues from gravitational infall, are the most informative about
our physical model of structure formation in the Universe. Hence, collecting
data in those regions would be most optimal for testing our model predictions.
The results presented in this work are the first of their kind and elucidate
the inhomogeneous distribution of cosmological information in the Universe.
This study paves a new way forward to perform efficient targeted searches for
the fundamental physics of the Universe, where search strategies are
progressively refined with new cosmological data sets within an active learning
framework. | A theory of the dark matter: In an earlier paper I proposed a highly symmetric semi-classical initial
condition to describe the universe in the period leading up to the electroweak
transition and completely determine all cosmology after that. Nothing beyond
the Standard Model is assumed. Inflation is not needed. The initial symmetry
allows no adjustable parameters. It is a complete theory of the Standard Model
cosmological epoch, predictive and falsifiable. Here, the time evolution of the
initial condition is calculated in the classical approximation. The fields with
nontrivial classical values are the SU(2)-weak gauge field (the cosmological
gauge field or CGF) and the Higgs field. The CGF produces the electroweak
transition then evolves as a non-relativistic perfect fluid
($w_{\mathrm{CGF}}\approx 0$). At the present time, i.e. when $H=H_{0}$, the
CGF energy density satisfies $\Omega_{\Lambda}+\Omega_{\mathrm{CGF}}=1$. The
CGF is the dark matter. The dark matter is a classical phenomenon of the
Standard Model. The classsical universe contains only the dark matter, no
ordinary matter. At next to leading order the fluctuations of the Standard
Model fields will provide a calculable, relatively small amount of ordinary
matter such that
$\Omega_{\Lambda}+\Omega_{\mathrm{CGF}}+\Omega_{\mathrm{ordinary}}=1$. |
Testing an Inflation Model with Nonminimal Derivative Coupling in the
Light of PLANCK 2015 Data: We study the dynamics of a generalized inflationary model in which both the
scalar field and its derivatives are coupled to the gravity. We consider a
general form of the nonminimal derivative coupling in order to have a complete
treatment of the model. By expanding the action up to the second order in
perturbation, we study the spectrum of the primordial modes of the
perturbations. Also, by expanding the action up to the third order and
considering the three point correlation functions, the amplitude of the
non-Gaussianity of the primordial perturbations is studied both in equilateral
and orthogonal configurations. Finally, by adopting some sort of potentials, we
compare the model at hand with the Planck 2015 released observational data and
obtain some constraints on the model's parameters space. As an important
result, we show that the nonminimal couplings help to make models of chaotic
inflation, that would otherwise be in tension with Planck data, in better
agreement with the data. This model is consistent with observation at weak
coupling limit. | The Exceptional Soft X-ray Halo of the Galaxy Merger NGC 6240: We report on a recent ~150-ks long Chandra observation of the ultraluminous
infrared galaxy merger NGC 6240, which allows a detailed investigation of the
diffuse galactic halo. Extended soft X-ray emission is detected at the 3-sigma
confidence level over a diamond-shaped region with projected physical size of
~110x80 kpc, and a single-component thermal model provides a reasonably good
fit to the observed X-ray spectrum. The hot gas has a temperature of ~7.5
million K, an estimated density of 2.5x10^{-3} cm^{-3}, and a total mass of
~10^10 M_sun, resulting in an intrinsic 0.4-2.5 keV luminosity of 4x10^41 erg
s^{-1}. The average temperature of 0.65 keV is quite high to be obviously
related to either the binding energy in the dark-matter gravitational potential
of the system or the energy dissipation and shocks following the galactic
collision, yet the spatially-resolved spectral analysis reveals limited
variations across the halo. The relative abundance of the main alpha-elements
with respect to iron is several times the solar value, and nearly constant as
well, implying a uniform enrichment by type II supernovae out to the largest
scales. Taken as a whole, the observational evidence is not compatible with a
superwind originated by a recent, nuclear starburst, but rather hints at
widespread, enhanced star formation proceeding at steady rate over the entire
dynamical timescale (~200 Myr). The preferred scenario is that of a
starburst-processed gas component gently expanding into, and mixing with, a
pre-existing halo medium of lower metallicity (Z ~ 0.1 solar) and temperature
(kT ~ 0.25 keV). This picture cannot be probed more extensively with the
present data, and the ultimate fate of the diffuse, hot gas remains uncertain.
Under some favorable conditions, at least a fraction of it might be retained
after the merger completion, and evolve into the hot halo of a young elliptical
galaxy. |
Gravitational wave production after inflation for a hybrid inflationary
model: We discuss a cosmological scenario with a stochastic background of
gravitational waves sourced by the tensor perturbation due to a hybrid
inflationary model with cubic potential. The tensor-to-scalar ratio for the
present hybrid inflationary model is obtained as $r \approx 0.0006$.
Gravitational wave spectrum of this stochastic background, for large-scale CMB
modes, $10^{-4}Mpc^{-1}$ to $1Mpc^{-1}$ is studied. The present-day energy
spectrum of gravitational waves $\Omega_0^{gw}(f)$ is sensitively related to
the tensor power spectrum and r which is, in turn, dependent on the unknown
physics of the early cosmos. This uncertainty is characterized by two
parameters: $\hat{n_t}(f)$ logarithmic average over the primordial tensor
spectral index and $\hat{w}(f)$ logarithmic average over the effective equation
of state parameter. Thus, exact constraints in the $\hat{w}(f)$, $\hat{n_t}(f)$
plane can be obtained by comparing theoretical constraints of our model on r
and $\Omega_0^{gw}(f)$. We obtain a limit on $\hat{w}(10^{-15}Hz)$<$0.33$
around the modes probed by CMB scales. | Blind Observers of the Sky: The concept of blind analysis, a key procedure to remove the human-based
systematic error called confirmation bias, has long been an integral part of
data analysis in many research areas. In cosmology, blind analysis is recently
making its entrance, as the field progresses into a fully fledged
high-precision science. The credibility, reliability and robustness of results
from future sky-surveys will dramatically increase if the effect of
confirmation bias is kept under control by using an appropriate blinding
procedure. Here, we present a catalog-level blinding scheme for galaxy
clustering data apt to be used in future spectroscopic galaxy surveys. We shift
the individual galaxy positions along the line of sight based on 1) a geometric
shift mimicking the Alcock-Paczynski effect and 2) a perturbative shift akin to
redshift-space distortions. This procedure has several advantages. After
combining the two steps above, it is almost impossible to accidentally unblind.
The procedure induces a shift in cosmological parameters without changing the
galaxies' angular positions, hence without interfering with the effects of
angular systematics. Since the method is applied at catalog level, there is no
need to adopt several blinding schemes tuned to different summary statistics,
likelihood choices or types of analyses. By testing the method on mock catalogs
and the BOSS DR12 catalog we demonstrate its performance in blinding galaxy
clustering data for relevant cosmological parameters sensitive to the
background expansion rate and the growth rate of structures. |
Properties of z~3-6 Lyman break galaxies. II. Testing star formation
histories and the SFR-mass relation with ALMA and near-IR spectroscopy: We examine the dependence of derived physical parameters of distant Lyman
break galaxies (LBGs) on the assumed star formation histories (SFHs), their
implications on the SFR-mass relation, and we propose observational tests to
better constrain these quantities. We use our SED-fitting tool including
nebular emission to analyze a large sample of LBGs, assuming five different
star formation histories, extending our first analysis of this sample (de
Barros et al. 2012, paper I). In addition we predict the IR luminosities
consistently with the SED fits.
Compared to "standard" SED fits assuming constant SFR and neglecting nebular
lines, assuming variable SFHs yield systematically lower stellar masses, higher
extinction, higher SFR, higher IR luminosities, and a wider range of equivalent
widths for optical emission lines. Exponentially declining and delayed SFHs
yield basically identical results and generally fit best. Exponentially rising
SFHs yield similar masses, but somewhat higher extinction.
We find significant deviations between the derived SFR and IR luminosity from
the commonly used SFR(IR) or SFR(IR+UV) calibration, due to differences in the
SFHs and ages. Models with variable SFHs, favored statistically, yield
generally a large scatter in the SFR-mass relation. We show that the true
scatter in the SFR-mass relation can be significantly larger than inferred
using SFR(UV) and/or SFR(IR).
Different SFHs, and hence differences in the derived SFR-mass relation and in
the specific star formation rates, can be tested/constrained observationally
with future IR observations with ALMA. Measurement of emission lines, such as
Halpha and [OII]3727, can also provide useful constraints on the SED models. We
conclude that our findings of a large scatter in SFR-mass at high-z and an
increase of the specific star formation rate above z>~3 (paper I) can be tested
observationally. (abriged) | Encoding large scale cosmological structure with Generative Adversarial
Networks: Recently a type of neural networks called Generative Adversarial Networks
(GANs) has been proposed as a solution for fast generation of simulation-like
datasets, in an attempt to bypass heavy computations and expensive cosmological
simulations to run in terms of time and computing power. In the present work,
we build and train a GAN to look further into the strengths and limitations of
such an approach. We then propose a novel method in which we make use of a
trained GAN to construct a simple autoencoder (AE) as a first step towards
building a predictive model. Both the GAN and AE are trained on images issued
from two types of N-body simulations, namely 2D and 3D simulations. We find
that the GAN successfully generates new images that are statistically
consistent with the images it was trained on. We then show that the AE manages
to efficiently extract information from simulation images, satisfyingly
inferring the latent encoding of the GAN to generate an image with similar
large scale structures. |
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