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Mixture Models for Photometric Redshifts: Determining photometric redshifts to high accuracy is paramount to measure
distances in wide-field cosmological experiments. With only photometric
information at hand, photo-zs are prone to systematic uncertainties in the
intervening extinction and the unknown underlying spectral-energy distribution
of different astrophysical sources. Here, we aim to resolve these model
degeneracies and obtain a clear separation between intrinsic physical
properties of astrophysical sources and extrinsic systematics. We aim at
estimates of the full photo-z probability distributions, and their
uncertainties. We perform a probabilistic photo-z determination using Mixture
Density Networks (MDN). The training data-set is composed of optical ($griz$)
point-spread-function and model magnitudes and extinction measurements from the
SDSS-DR15, and WISE midinfrared ($3.4 \mu$m and $4.6 \mu$m) model magnitudes.
We use Infinite Gaussian Mixture models to classify the objects in our data-set
as stars, galaxies or quasars, and to determine the number of MDN components to
achieve optimal performance. The fraction of objects that are correctly split
into the main classes is 94%. Our method improves the bias of photometric
redshift estimation (i.e. the mean $\Delta z$ = (zp - zs)/(1 + zs)) by one
order of magnitude compared to the SDSS photo-z, and decreases the fraction of
$3 \sigma$ outliers (i.e. 3rms$(\Delta z) < \Delta z$). The relative,
root-mean-square systematic uncertainty in our resulting photo-zs is down to
1.7% for low-redshift galaxies (zs $<$ 0.5). We have demonstrated the
feasibility of machine-learning based methods that produce full probability
distributions for photo-z estimates with a performance that is competitive with
state-of-the art techniques. Our method can be applied to wide-field surveys
where extinction can vary significantly across the sky and with sparse
spectroscopic calibration samples. | Quasars as a tracer of large-scale structures in the distant universe: We study the dependence of the number density and properties of quasars on
the background galaxy density using the currently largest spectroscopic
datasets of quasars and galaxies. We construct a galaxy number density field
smoothed over the variable smoothing scale of between approximately 10 and
$20\,h^{-1}$Mpc over the redshift range of $0.46<z<0.59$ using the Sloan
Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS (CMASS)
galaxies. The quasar sample is prepared from the SDSS I/II DR7. We examine the
correlation of incidence of quasars with the large-scale background density and
dependence of quasar properties such as bolometric luminosity, black hole mass,
and Eddington ratio on the large-scale density. We find a monotonic correlation
between the quasar number density and large-scale galaxy number density, which
is fitted well with a power law relation, $n_Q\propto\rho_G^{0.618}$. We detect
weak dependences of quasar properties on the large-scale density such as a
positive correlation between black hole mass and density, and a negative
correlation between luminosity and density. We discuss the possibility of using
quasars as a tracer of large-scale structures at high redshifts, which may be
useful for studies of growth of structures in the high redshift universe. |
Superfluid Dark Matter around Black Holes: Superfluid dark matter, consisting of self-interacting light particles that
thermalize and condense to form a superfluid in galaxies, provides a novel
theory that matches the success of the standard $\Lambda$CDM model on
cosmological scales while simultaneously offering a rich phenomenology on
galactic scales. Within galaxies, the dark matter density profile consists of a
nearly homogeneous superfluid core surrounded by an isothermal envelope. In
this work we compute the density profile of superfluid dark matter around
supermassive black holes at the center of galaxies. We show that, depending on
the fluid equation of state, the dark matter profile presents distinct
power-law behaviors, which can be used to distinguish it from the standard
results for collisionless dark matter. | Ruling out the Modified Chaplygin Gas Cosmologies: The Modified Chaplygin Gas (MCG) model belongs to the class of a unified
models of dark energy (DE) and dark matter (DM). It is characterized by an
equation of state (EoS) $p_c = B\rho - A/\rho^{\alpha}$, where the case $B=0$
corresponds to the Generalized Chaplygin Gas (GCG) model. Using a perturbative
analysis and power spectrum observational data we show that the MCG model is
not a sucessful candidate for the cosmic medium unless $B=0$. In this case, it
reduces to the usual GCG model. |
Cosmology from Clustering, Cosmic Shear, CMB Lensing, and Cross
Correlations: Combining Rubin Observatory and Simons Observatory: In the near future, the overlap of the Rubin Observatory Legacy Survey of
Space and Time (LSST) and the Simons Observatory (SO) will present an ideal
opportunity for joint cosmological dataset analyses. In this paper we simulate
the joint likelihood analysis of these two experiments using six two-point
functions derived from galaxy position, galaxy shear, and CMB lensing
convergence fields. Our analysis focuses on realistic noise and systematics
models and we find that the dark energy Figure-of-Merit (FoM) increases by 53%
(92%) from LSST-only to LSST+SO in Year 1 (Year 6). We also investigate the
benefits of using the same galaxy sample for both clustering and lensing
analyses, and find the choice improves the overall signal-to-noise by ~30-40%,
which significantly improves the photo-z calibration and mildly improves the
cosmological constraints. Finally, we explore the effects of catastrophic
photo-z outliers finding that they cause significant parameter biases when
ignored. We develop a new mitigation approach termed "island model", which
corrects a large fraction of the biases with only a few parameters while
preserving the constraining power. | The Inhomogeneous Reionization Times of Present-day Galaxies: Today's galaxies experienced cosmic reionization at different times in
different locations. For the first time, reionization ($50\%$ ionized)
redshifts, $z_R$, at the location of their progenitors are derived from new,
fully-coupled radiation-hydrodynamics simulation of galaxy formation and
reionization at $z > 6$, matched to N-body simulation to z = 0. Constrained
initial conditions were chosen to form the well-known structures of the local
universe, including the Local Group and Virgo, in a (91 Mpc)$^3$ volume large
enough to model both global and local reionization. Reionization simulation
CoDa I-AMR, by CPU-GPU code EMMA, used (2048)$^3$ particles and (2048)$^3$
initial cells, adaptively-refined, while N-body simulation CoDa I-DM2048, by
Gadget2, used (2048)$^3$ particles, to find reionization times for all galaxies
at z = 0 with masses $M(z=0)\ge 10^8 M_\odot$. Galaxies with $M(z=0) \gtrsim
10^{11} M_\odot$ reionized earlier than the universe as a whole, by up to
$\sim$ 500 Myrs, with significant scatter. For Milky-Way-like galaxies, $z_R$
ranged from 8 to 15. Galaxies with $M(z=0) \lesssim 10^{11} M_\odot$ typically
reionized as late or later than globally-averaged $50\%$ reionization at
$\langle z_R\rangle =7.8$, in neighborhoods where reionization was completed by
external radiation. The spread of reionization times within galaxies was
sometimes as large as the galaxy-to-galaxy scatter. The Milky Way and M31
reionized earlier than global reionization but later than typical for their
mass, neither dominated by external radiation. Their most massive progenitors
at $z>6$ had $z_R$ = 9.8 (MW) and 11 (M31), while their total masses had $z_R$
= 8.2 (both). |
Photo-$z$ with CuBAN$z$: An improved photometric redshift estimator
using Clustering aided Back Propagation Neural network: We present an improved photometric redshift estimator code, CuBAN$z$, that is
publicly available at https://goo.gl/fpk90V}{https://goo.gl/fpk90V. It uses the
back propagation neural network along with clustering of the training set,
which makes it more efficient than existing neural network codes. In CuBAN$z$,
the training set is divided into several self learning clusters with galaxies
having similar photometric properties and spectroscopic redshifts within a
given span. The clustering algorithm uses the color information (i.e. $u-g$,
$g-r$ etc.) rather than the apparent magnitudes at various photometric bands as
the photometric redshift is more sensitive to the flux differences between
different bands rather than the actual values. Separate neural networks are
trained for each cluster using all possible colors, magnitudes and
uncertainties in the measurements. For a galaxy with unknown redshift, we
identify the closest possible clusters having similar photometric properties
and use those clusters to get the photometric redshifts using the particular
networks that were trained using those cluster members. For galaxies that do
not match with any training cluster, the photometric redshifts are obtained
from a separate network that uses entire training set. This clustering method
enables us to determine the redshifts more accurately. SDSS Stripe 82 catalog
has been used here for the demonstration of the code. For the clustered sources
with redshift range $z_{\rm spec}<0.7$, the residual error ($\langle (z_{{\rm
spec}}-z_{{\rm phot}})^2\rangle^{1/2} $) in the training/testing phase is as
low as 0.03 compared to the existing ANNz code that provides residual error on
the same test data set of 0.05. Further, we provide a much better estimate of
the uncertainty of the derived photometric redshift. | Updated Mass Scaling Relations for Nuclear Star Clusters and a
Comparison to Supermassive Black Holes: We investigate whether nuclear star clusters and supermassive black holes
follow a common set of mass scaling relations with their host galaxy's
properties, and hence can be considered to form a single class of central
massive object. We have compiled a large sample of galaxies with measured
nuclear star cluster masses and host galaxy properties from the literature and
fit log-linear scaling relations. We find that nuclear star cluster mass,
M_{NC}, correlates most tightly with the host galaxy's velocity dispersion: log
M_{NC} = (2.11 \pm 0.31) log (\sigma/54) + (6.63 \pm 0.09), but has a slope
dramatically shallower than the relation defined by supermassive black holes.
We find that the nuclear star cluster mass relations involving host galaxy (and
spheroid) luminosity and stellar and dynamical mass, intercept with but are in
general shallower than the corresponding black hole scaling relations. In
particular M_{NC} \propto {M}_{Gal,dyn}^{0.55 \pm 0.15}; the nuclear cluster
mass is not a constant fraction of its host galaxy or spheroid mass. We
conclude that nuclear stellar clusters and supermassive black holes do not form
a single family of central massive objects. |
Analysis of carbon monoxied absorption at z=2.5 to constrain variation
of the proton-to-electron mass ratio: Absorption by carbon monoxide in the spectrum of quasar SDSS
J000015.16+004833.2 is investigated in order to derive a constraint on the
temporal variation of the proton-to-electron mass ratio, mu. The spectrum was
recorded using VLT/UVES, and it was partially corrected for long-range
wavelength scale distortions using the supercalibration technique. Eight
vibrational CO singlet-singlet bands belonging to the A-X electronic absorption
system, and the perturbing d3-X(5, 0) singlet-triplet band are detected in the
damped Lyman-alpha system at z =2.52. The spectra are modelled using a
comprehensive fitting technique, resulting in a final value of Dmu/mu=(1.8 +/-
2.2 +/- 0.4)x10e(-5), which is consistent with no variation over a look-back
time of 11.2 Gyrs. | Angular bispectrum and trispectrum of scalar-induced
gravitational-waves: all contributions from primordial non-Gaussianity $\fnl$
and $\gnl$: Studying the primordial non-Gaussianity of inflationary perturbations is
crucial for testing the inflation paradigm of the early universe. In this work,
we conduct a comprehensive analysis of the angular bispectrum and trispectrum
of scalar-induced gravitational waves (SIGWs) in the presence of local-type
primordial non-Gaussianity parameterized by $\fnl$ and $\gnl$, deriving their
semi-analytical formulae for the first time. Our findings indicate that it is
the presence of primordial non-Gaussianity that leads to a non-Gaussian SIGW
background, suggesting that the angular bispectrum and trispectrum of SIGWs
could serve as probes of the primordial non-Gaussianity. Our numerical results
further illustrate that $\fnl$ and $\gnl$ exert significant impacts on the
spectral amplitudes, potentially reaching up to $10^{-5}$ for the former and
$10^{-8}$ for the latter. In particular, we demonstrate that the angular
bispectrum and trispectrum exhibit characteristic dependence on the angular
multipoles and frequency bands. They hold potentials to be measured by
gravitational-wave detectors that may advance our understanding of the origin
of the universe. |
Oscillating Bispectra and Galaxy Clustering: A Novel Probe of
Inflationary Physics with Large-Scale Structure: Many models of inflation predict oscillatory features in the bispectrum of
primordial fluctuations. Since it has been shown that primordial
non-Gaussianity can lead to a scale-dependent halo bias, we investigate the
effect of oscillations in the three-point function on the clustering of
dark-matter halos. Interestingly, we find that features in the inflaton
potential such as oscillations or sharp steps get imprinted in the mass
dependence of the non-Gaussian halo bias. In this paper, we focus on models
displaying a sharp feature in the inflaton potential as well as Resonant
non-Gaussianity. In both cases, we find a strong scale dependence for the
non-Gaussian halo bias with a slope similar to that of the local model. In the
resonant case, we find that the non-Gaussian bias oscillates with halo mass, a
novel feature that is unique to this type of models. In the case of a sharp
feature in the inflaton potential, we find that the clustering of halos is
enhanced at the mass scale corresponding to the Fourier mode that exited the
horizon when the inflaton was crossing the feature in the potential. Both of
these are new effects that open the possibility of characterizing the
inflationary potential with large-scale-structure surveys. We briefly discuss
the prospects for detecting these non-Gaussian effects. | Constraints on Non-Gaussian primordial curvature perturbation from the
LIGO-Virgo-KAGRA third observing run: The scalar-induced gravitational waves (SIGW), arising from large amplitude
primordial density fluctuations, provide a unique observational test for
directly probing the epoch of inflation. In this work, we provide constraints
on the SIGW background by taking into account the non-Gaussianity in the
primordial density fluctuations, using the third observing run (O3) data of the
LIGO-Virgo-KAGRA collaboration. We find that the non-Gaussianity gives a
non-negligible effect on the GW energy density spectrum and starts to affect
the analysis of the O3 data when the non-Gaussianity parameter is $F_{\rm NL} >
3.55$. Furthermore, the constraints exhibit asymptotic behavior given by
$F_{\rm NL} A_g = \rm{const.}$ at large $F_{\rm NL}$ limit, where $A_g$ denotes
the amplitude of the curvature perturbations. In the limit of large $F_{\rm
NL}$, we placed a 95% confidence level upper limit $F_{\rm NL} A_g \leq 0.13,
0.09, 0.10$ at fixed scales of $10^{16}, 10^{16.5}, 10^{17}~{\rm Mpc}^{-1}$,
respectively. |
A multi-wavelength study of Supernova Remnants in six nearby galaxies.
II. New optically selected Supernova Remnants: We present results from a study of optically emitting Supernova Remnants
(SNRs) in six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4395, NGC 4449
and NGC 5204) based on deep narrow band H{\alpha} and [SII] images as well as
spectroscopic observations. The SNR classification was based on the detected
sources that fulfill the well-established emission line flux criterion of
[SII]/H{\alpha} > 0.4. This study revealed ~400 photometric SNRs down to a
limiting H{\alpha} flux of 10^(-15) erg sec^(-1) cm^(-2). Spectroscopic
observations confirmed the shock-excited nature of 56 out of the 96 sources
with ([SII]/H{\alpha})$_{phot}$> 0.3 (our limit for an SNR classification) for
which we obtained spectra. 11 more sources were spectroscopically identified as
SNRs although their photometric [SII]/H{\alpha} ratio was below 0.3. We discuss
the properties of the optically-detected SNRs in our sample for different types
of galaxies and hence different environments, in order to address their
connection with the surrounding interstellar medium. We find that there is a
difference in [NII]/H{\alpha} line ratios of the SNR populations between
different types of galaxies which indicates that this happens due to
metallicity. We cross-correlate parameters of the optically detected SNRs
([SII]/H{\alpha} ratio, luminosity) with parameters of coincident X- ray
emitting SNRs, resulted from our previous studies in the same sample of
galaxies, in order to understand their evolution and investigate possible
selection effects. We do not find a correlation between their H{\alpha} and
X-ray luminosities, which we attribute to the presence of material in a wide
range of temperatures. We also find evidence for a linear relation between the
number of luminous optical SNRs (10^(37) erg sec^(-1)) and SFR in our sample of
galaxies. | Subaru Telescope limits on cosmological variations in the fine-structure
constant: Previous, large samples of quasar absorption spectra have indicated some
evidence for relative variations in the fine-structure constant
($\Delta\alpha/\alpha$) across the sky. However, they were likely affected by
long-range distortions of the wavelength calibration, so it is important to
establish a statistical sample of more reliable results, from multiple
telescopes. Here we triple the sample of $\Delta\alpha/\alpha$ measurements
from the Subaru Telescope which have been `supercalibrated' to correct for
long-range distortions. A blinded analysis of the metallic ions in 6
intervening absorption systems in two Subaru quasar spectra provides no
evidence for $\alpha$ variation, with a weighted mean of
$\Delta\alpha/\alpha=3.0\pm2.8_{\rm stat}\pm2.0_{\rm sys}$ parts per million
(1$\sigma$ statistical and systematic uncertainties). The main remaining
systematic effects are uncertainties in the long-range distortion corrections,
absorption profile models, and errors from redispersing multiple quasar
exposures onto a common wavelength grid. The results also assume that
terrestrial isotopic abundances prevail in the absorbers; assuming only the
dominant terrestrial isotope is present significantly lowers
$\Delta\alpha/\alpha$, though it is still consistent with zero. Given the
location of the two quasars on the sky, our results do not support the evidence
for spatial $\alpha$ variation, especially when combined with the 21 other
recent measurements which were corrected for, or resistant to, long-range
distortions. Our spectra and absorption profile fits are publicly available. |
Tapering the sky response for angular power spectrum estimation from
low-frequency radio-interferometric data: It is important to correctly subtract point sources from
radio-interferometric data in order to measure the power spectrum of diffuse
radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm
signal. It is computationally very expensive and challenging to image a very
large area and accurately subtract all the point sources from the image. The
problem is particularly severe at the sidelobes and the outer parts of the main
lobe where the antenna response is highly frequency dependent and the
calibration also differs from that of the phase center. Here we show that it is
possible to overcome this problem by tapering the sky response. Using simulated
150 MHz observations, we demonstrate that it is possible to suppress the
contribution due to point sources from the outer parts by using the Tapered
Gridded Estimator to measure the angular power spectrum C_l of the sky signal.
We also show from the simulation that this method can self-consistently compute
the noise bias and accurately subtract it to provide an unbiased estimation of
C_l. | The Metron Project -- I. The Metron Project Science Program: In this paper, the first in a series of four articles, the scientific goals
of the Metron project are highlighted, and the characteristics of the cosmic
objects available for study within its framework are provided. The Metron
interferometer radio telescope should include arrays of meter-range dipole
antennas placed on Earth, in outer space or on the far side of the Moon (or a
combination of these options). Working in the meter range will enable the study
of the so-called cosmological epoch of ``Dark Ages'', which is challenging to
observe but highly interesting for understanding the origin of the first stars,
galaxies, and black holes, as well as for the search for new cosmological
objects and processes. One possibility is to search for absorption in the 21 cm
line within extended halos around early protogalaxies and supermassive
primordial black holes, whose existence is predicted in a number of models.
Another goal of Metron may be to clarify the anomalous absorption in the 21 cm
line previously detected by the EDGES telescopes and to observe radio emissions
from stars' and exoplanets' magnetospheres. The Metron project aims to achieve
unprecedented resolution for the meter range, which is expected to yield new
world-class scientific results. Meter-range antennas and receivers are
relatively simple and inexpensive, and the construction of interferometric
arrays from them can be accomplished in a relatively short period of time. |
Faint-end Quasar Luminosity Functions from Cosmological Hydrodynamic
Simulations: We investigate the predictions for the faint-end quasar luminosity function
(QLF) and its evolution using fully cosmological hydrodynamic simulations which
self-consistently follow star formation, black hole growth and associated
feedback processes. We find remarkably good agreement between predicted and
observed faint end of the optical and X-ray QLFs (the bright end is not
accessible in our simulated volumes) at z < 2. At higher redshifts our
simulations tend to overestimate the QLF at the faintest luminosities. We show
that although the low (high) luminosity ranges of the faint-end QLF are
dominated by low (high) mass black holes, a wide range of black hole masses
still contributes to any given luminosity range. This is consistent with the
complex lightcurves of black holes resulting from the detailed hydrodynamics
followed in the simulations. Consistent with the results on the QLFs, we find
good agreement for the evolution of the comoving number density (in optical,
soft and hard X-ray bands) of AGN for luminosities above 10^43 erg/s. However,
the luminosity density evolution from the simulation appears to imply a peak at
higher redshift than constrained from hard X-ray data (but not in optical). Our
predicted excess at the faintest fluxes at z >= 2 does not lead to an
overestimate to the total X-ray background and its contribution is at most a
factor of two larger than the unresolved fraction of the 2-8 keV background.
Even though this could be explained by some yet undetected, perhaps heavily
obscured faint quasar population, we show that our predictions for the faint
sources at high redshifts (which are dominated by the low mass black holes) in
the simulations are likely affected by resolution effects. | Testing the MOND Paradigm of Modified Dynamics with Galaxy-Galaxy
Gravitational Lensing: MOND predicts that the asymptotic gravitational potential of an isolated,
bounded (baryonic) mass, M, is phi(r)=(MGa0)^{1/2}ln(r); a0 is the MOND
constant. Relativistic MOND theories predict that the lensing effects of M are
dictated by phi(r) as general-relativity lensing is dictated by the Newtonian
potential. Thus, MOND predicts that the asymptotic Newtonian potential deduced
from galaxy-galaxy gravitational lensing will have: (1) a logarithmic r
dependence, and (2) a normalization (parametrized standardly as 2s^2) that
depends only on M: s=(MGa0/4)^{1/4}. I compare these predictions with recent
results of galaxy-galaxy lensing, and find agreement on all counts. For the
"blue"-lenses subsample ("spiral" galaxies) MOND reproduces the observations
well with an r'-band M/L of 1-3 solar units, and for "red" lenses ("elliptical"
galaxies) with M/L of 3-6 solar units, both consistent with baryons only. In
contradistinction, Newtonian analysis requires, typically, M/L values of about
130 solar units, bespeaking a mass discrepancy of a factor of about 40.
Compared with the staple, rotation-curve tests, MOND is here tested in a wider
population of galaxies, through a different phenomenon, using relativistic test
objects, and is probed to several-times-lower accelerations--as low as a few
percent of a0. |
Observable tests of self-interacting dark matter in galaxy clusters:
cosmological simulations with SIDM and baryons: We present BAHAMAS-SIDM, the first large-volume, (400/h Mpc)^3, cosmological
simulations including both self-interacting dark matter (SIDM) and baryonic
physics. These simulations are important for two primary reasons: 1) they
include the effects of baryons on the dark matter distribution 2) the baryon
particles can be used to make mock observables that can be compared directly
with observations. As is well known, SIDM haloes are systematically less dense
in their centres, and rounder, than CDM haloes. Here we find that that these
changes are not reflected in the distribution of gas or stars within galaxy
clusters, or in their X-ray luminosities. However, gravitational lensing
observables can discriminate between DM models, and we present a menu of tests
that future surveys could use to measure the SIDM interaction strength. We
ray-trace our simulated galaxy clusters to produce strong lensing maps.
Including baryons boosts the lensing strength of clusters that produce no
critical curves in SIDM-only simulations. Comparing the Einstein radii of our
simulated clusters with those observed in the CLASH survey, we find that at
velocities around 1000 km/s an SIDM cross-section of sigma/m > 1 cm^2/g is
likely incompatible with observed cluster lensing. | Peanuts at an Angle: Detecting and Measuring the Three-Dimensional
Structure of Bars in Moderately Inclined Galaxies: We show that direct detection and measurement of the vertically thickened
parts of bars (so-called "boxy" or "peanut-shaped" bulges) is possible not only
for edge-on galaxies but also for galaxies with moderate inclinations (i < 70
deg), and that examples are relatively common in the nearby universe.
Analysis of a sample of 78 nearby, moderately inclined (i < 65 deg)
early-type (S0--Sb) barred galaxies shows that the isophotal signature of the
box/peanut can usually be detected for inclinations as low as i ~ 40 deg -- and
in exceptional cases down to i ~ 30 deg. In agreement with the predictions from
N-body simulations, the signature is most easily detectable when the bar's
position angle is within ~ 50 deg of the galaxy major axis; in particular,
galaxies where the bar lies very close to the minor axis do not show the
signature clearly or at all. For galaxies with i = 40--65 deg and relative
angles < 45 deg, we find evidence for the signature ~ 2/3 of the time; the true
frequency of box/peanut structures in bars may be higher.
Comparison with N-body models also allows us to link observed photometric
morphology with 3D physical structures, and thus estimate the relative sizes of
box/peanut structures and bars. For our local sample, we find that box/peanut
structures range in radial size (measured along the bar major axis) from
0.4--3.8 kpc (mean = 1.5 +/- 0.9 kpc) and span 0.26--0.58 of the bar length
(mean of 0.38 +/- 0.08). This is a clear observational confirmation that when
bars thicken, it is not the entire bar which does so, but only the inner part.
This technique can also be used to identify galaxies with bars which have not
vertically thickened. We suggest that NGC 3049 and IC 676 may be particularly
good examples, and that the fraction of S0--Sb bars which lack box/peanut
structures is at least ~ 13%. |
A Spectroscopically Confirmed Double Source Plane Lens System in the
Hyper Suprime-Cam Subaru Strategic Program: We report the serendipitous discovery of HSC J142449-005322, a double source
plane lens system in the Hyper Suprime-Cam Subaru Strategic Program. We dub the
system Eye of Horus. The lens galaxy is a very massive early-type galaxy with
stellar mass of ~7x10^11 Msun located at z_L=0.795. The system exhibits two
arcs/rings with clearly different colors, including several knots. We have
performed spectroscopic follow-up observations of the system with FIRE on
Magellan. The outer ring is confirmed at z_S2=1.988 with multiple emission
lines, while the inner arc and counterimage is confirmed at z_S1=1.302. This
makes it the first double source plane system with spectroscopic redshifts of
both sources. Interestingly, redshifts of two of the knots embedded in the
outer ring are found to be offset by delta_z=0.002 from the other knots,
suggesting that the outer ring consists of at least two distinct components in
the source plane. We perform lens modeling with two independent codes and
successfully reproduce the main features of the system. However, two of the
lensed sources separated by ~0.7 arcsec cannot be reproduced by a smooth
potential, and the addition of substructure to the lens potential is required
to reproduce them. Higher-resolution imaging of the system will help decipher
the origin of this lensing feature and potentially detect the substructure. | The Bosma effect revisited - I. HI and stellar disc scaling models: The observed proportionality between the centripetal contribution of the
dynamically insignificant HI gas in the discs of spiral galaxies and the
dominant contribution of DM - the "Bosma effect" - has been repeatedly
mentioned in the literature but largely ignored. We have re-examined the
evidence for the Bosma effect by fitting Bosma effect models for 17 galaxies in
the THINGS data set, either by scaling the contribution of the HI gas alone or
by using both the observed stellar disc and HI gas as proxies. The results are
compared with two models for exotic cold DM: internally consistent cosmological
NFW models with constrained compactness parameters, and URC models using fully
unconstrained Burkert density profiles. The Bosma models that use the stellar
discs as additional proxies are statistically nearly as good as the URC models
and clearly better than the NFW ones. We thus confirm the correlation between
the centripetal effects of DM and that of the interstellar medium of spiral
galaxies. The edificacy of "maximal disc" models is explained as the natural
consequence of "classic" Bosma models which include the stellar disc as a proxy
in regions of reduced atomic gas. The standard explanation - that the effect
reflects a statistical correlation between the visible and exotic DM - seems
highly unlikely, given that the geometric forms and hence centripetal
signatures of spherical halo and disc components are so different. A literal
interpretation of the Bosma effect as being due to the presence of significant
amounts of disc DM requires a median visible baryon to disc DM ratio of about
40%. |
Isocurvature modes: joint analysis of the CMB power spectrum and
bispectrum: We perform a joint analysis of the power spectrum and the bispectrum of the
CMB temperature and polarization anisotropies to improve the constraints on
isocurvature modes. We construct joint likelihoods, both for the existing
Planck data, and to make forecasts for the future LiteBIRD and CMB-S4
experiments. We assume a general two-field inflation model with five free
parameters, leading to one isocurvature mode (which can be CDM density,
neutrino density or neutrino velocity) arbitrarily correlated with the
adiabatic mode. We theoretically assess in which cases (of detecting and/or
fixing parameters) improvements can be expected, to guide our subsequent
numerical analyses. We find that for Planck, which detected neither
isocurvature modes nor primordial non-Gaussianity, the joint analysis does not
improve the constraints in the general case. However, if we fix additional
parameters in the model, the improvements can be highly significant depending
on the chosen parameter values. For LiteBIRD+CMB-S4 we study in which regions
of parameter space compatible with the Planck results the joint analysis will
improve the constraints or the significance of a detection. We find that, while
for CDM isocurvature this region is very small, for the neutrino isocurvature
modes it is much larger. In particular for neutrino velocity it can be about
half of the Planck-allowed region, where the joint analysis reduces the
isocurvature error bars by up to 70%. In addition the joint analysis can also
improve the error bars of some of the standard cosmological parameters, by up
to 30% for $\theta_{MC}$ for example, by breaking the degeneracies with the
correlation parameter between adiabatic and isocurvature modes. | Discovery of Very High Energy gamma-rays from the blazar S5 0716+714: The MAGIC collaboration reports the detection of the blazar S5 0716+714
z=0.31+-0.08 in very high energy gamma-rays. The observations were performed in
November 2007 and in April 2008, and were triggered by the KVA telescope due to
the high optical state of the object. An overall significance of the signal
accounts to S =5.8sigma for 13.1 hours of data. Most of the signal S = 6.9sigma
comes from the April 2008 data sample during a higher optical state of the
object suggesting a possible correlation between the VHE gamma-ray and optical
emissions. The differential energy spectrum of the 2008 data sample follows a
power law with a photon index of Gamma = 3.45+-0.54_(stat)+-0.2_(syst), and the
integral flux above 400GeV is at the level of
7.5+-2.2_(stat)+-2.3_(syst)*10^-12 cm^-2 s^-1 corresponding to a 9% Crab Nebula
flux. Modeling of the broad band spectral energy distribution indicates that a
structured jet model appears to be more promising in describing the available
data than a simple one zone synchrotron self-Compton model. |
On the Nonlinear Evolution of Cosmic Web: Lagrangian Dynamics Revisited: We investigate the nonlinear evolution of cosmic morphologies of the
large-scale structure by examining the Lagrangian dynamics of various tensors
of a cosmic fluid element, including the velocity gradient tensor, the Hessian
matrix of the gravitational potential as well as the deformation tensor.
Instead of the eigenvalue representation, the first two tensors, which
associate with the "kinematic" and "dynamical" cosmic web classification
algorithm respectively, are studied in a more convenient parameter space. These
parameters are defined as the rotational invariant coefficients of the
characteristic equation of the tensor. In the nonlinear local model (NLM) where
the magnetic part of Weyl tensor vanishes, these invariants are fully capable
of characterizing the dynamics. Unlike the Zeldovich approximation (ZA), where
various morphologies do not change before approaching a one-dimensional
singularity, the sheets in NLM are unstable for both overdense and underdense
perturbations. While it has long been known that the coupling between tidal
tensor and velocity shear would cause a filamentary final configuration of a
collapsing region, we show that the underdense perturbation are more subtle, as
the balance between the shear rate (tidal force) and the divergence (density)
could lead to different morphologies. Interestingly, this instability also sets
the basis for understanding some distinctions of the cosmic web identified
dynamically and kinematically. We show that the sheets with negative density
perturbation in the potential based algorithm would turn to filaments faster
than in the kinematic method, which could explain the distorted dynamical
filamentary structure observed in the simulation. | Towards a fully consistent parameterization of modified gravity: There is a distinct possibility that current and future cosmological data can
be used to constrain Einstein's theory of gravity on the very largest scales.
To be able to do this in a model-independent way, it makes sense to work with a
general parameterization of modified gravity. Such an approach would be
analogous to the Parameterized Post-Newtonian (PPN) approach which is used on
the scale of the Solar System. A few such parameterizations have been proposed
and preliminary constraints have been obtained. We show that the majority of
such parameterizations are only exactly applicable in the quasistatic regime.
On larger scales they fail to encapsulate the full behaviour of typical models
currently under consideration. We suggest that it may be possible to capture
the additions to the `Parameterized Post-Friedmann' (PPF) formalism by treating
them akin to fluid perturbations. |
H-ATLAS/GAMA: Dusty early-type galaxies and passive spirals: We present the dust properties and star-formation histories of local
submillimetre-selected galaxies in Herschel-ATLAS, classified by optical
morphology. The early-type galaxies (ETGs) that are detected contain as much
dust as typical spirals, and form a unique sample that has been blindly
selected at submillimetre wavelengths.
Comparing H-ATLAS galaxies to a control sample of optically selected
galaxies, we find 5.5% of luminous ETGs are detected in H-ATLAS. The H-ATLAS
ETGs contain a significant mass of cold dust: the mean dust mass is 5.5x10^7
Msun, with individual galaxies ranging from 9x10^5-4x10^8 Msun. This is
comparable to that of spirals in our sample, and is an order of magnitude more
dust than that found for the control ETGs, which have a median dust mass
inferred from stacking of (0.8-4.0)x10^6 Msun. The ETGs detected in H-ATLAS
have bluer NUV-r colours, higher specific star-formation rates and younger
stellar populations than ETGs which are optically selected, and may be
transitioning from the blue cloud to the red sequence. We also find that
H-ATLAS and control ETGs inhabit similar low-density environments. We conclude
that the dust in H-ATLAS and control ETGs cannot be solely from stellar
sources, and a large contribution from dust formed in the ISM or external
sources is required. Alternatively, dust destruction may not be as efficient as
predicted.
We also explore the properties of the most passive spiral galaxies in our
sample with SSFR<10^-11/yr. We find these passive spirals have lower
dust-to-stellar mass ratios, higher stellar masses and older stellar population
ages than normal spirals. The passive spirals inhabit low density environments
similar to those of the normal spiral galaxies in our sample. This shows that
the processes which turn spirals passive do not occur solely in the
intermediate density environments of group and cluster outskirts. (Abridged) | Fast generation of weak lensing maps by the inverse-Gaussianization
method: To take full advantage of the unprecedented power of upcoming weak lensing
surveys, understanding the noise, such as cosmic variance and geometry/mask
effects, is as important as understanding the signal itself. Accurately
quantifying the noise requires a large number of statistically independent
mocks for a variety of cosmologies. This is impractical for weak lensing
simulations, which are costly for simultaneous requirements of large box size
(to cover a significant fraction of the past light cone) and high resolution
(to robustly probe the small scale where most lensing signal resides).
Therefore fast mock generation methods are desired and are under intensive
investigation. We propose a new fast weak lensing map generation method, named
the inverse-Gaussianization method, based on the finding that a lensing
convergence field can be Gaussianized to excellent accuracy by a local
transformation [Yu et al, Phys. Rev. D 84, 023523 (2011)]. Given a simulation,
it enables us to produce as many as infinite statistically independent lensing
maps as fast as producing the simulation initial conditions. The proposed
method is tested against simulations for each tomography bin centered at lens
redshift $z \sim 0.5$, 1, and 2, with various statistics. We find that the
lensing maps generated by our method have reasonably accurate power spectra,
bispectra, and power spectrum covariance matrix. Therefore, it will be useful
for weak lensing surveys to generate realistic mocks. As an example of
application, we measure the probability distribution function of the lensing
power spectrum, from 16384 lensing maps produced by the inverse-Gaussianization
method. |
Revised Big Bang Nucleosynthesis with long-lived negatively charged
massive particles: updated recombination rates, primordial 9Be
nucleosynthesis, and impact of new 6Li limits: We extensively reanalyze effects of a long-lived negatively charged massive
particle, X-, on big bang nucleosynthesis (BBN). The BBN model with an X-
particle was originally motivated by the discrepancy between 6,7Li abundances
predicted in standard BBN model and those inferred from observations of
metal-poor stars. In this model 7Be is destroyed via the recombination with an
X- particle followed by radiative proton capture. We calculate precise rates
for the radiative recombinations of 7Be, 7Li, 9Be, and 4He with X-. In
nonresonant rates we take into account respective partial waves of scattering
states and respective bound states. The finite sizes of nuclear charge
distributions cause deviations in wave functions from those of point-charge
nuclei. For a heavy X- mass, m_X \gtrsim 100 GeV, the d-wave --> 2P transition
is most important for 7Li and 7,9Be, unlike recombination with electrons. Our
new nonresonant rate of the 7Be recombination for m_X=1000 GeV is more than 6
times larger than the existing rate. Moreover, we suggest a new important
reaction for 9Be production: the recombination of 7Li and X- followed by
deuteron capture. We derive binding energies of X-nuclei along with reaction
rates and Q-values. We then calculate BBN and find that the amount of 7Be
destruction depends significantly on the charge distribution of 7Be. Finally,
updated constraints on the initial abundance and the lifetime of the X- are
derived in the context of revised upper limits to the primordial 6Li abundance.
Parameter regions for the solution to the 7Li problem are revised, and the
primordial 9Be abundances is revised. | Constraining Reionization with Lyman Alpha Emitting Galaxies: Neutral diffuse intergalactic gas that existed during the Epoch of
Reionization (EoR) suppresses Lyman Alpha (Lya) flux emitted by background
galaxies. In this chapter I summarise the increasing observational support for
the claim that Lya photons emitted by galaxies at z>6 are suppressed by
intervening HI gas. I describe key physical processes that affect Lya transfer
during the EoR. I argue that in spite of the uncertainties associated with this
complex multiscale problem, the data on Lya emitting galaxies at z=0-6 strongly
suggests that the observed reduction in Lya flux from galaxies at z>6 is due to
additional intervening HI gas. The main question is what fraction of this
additional HI gas is in the diffuse neutral IGM. I summarise how future surveys
on existing and upcoming instruments are expected to reduce existing
observational uncertainties enormously. With these improved data we will likely
be able to nail down reionization with Lya emitting galaxies. |
Lyman-alpha emitters gone missing: evidence for late reionization?: We combine high resolution hydrodynamical simulations with an intermediate
resolution, dark matter only simulation and an analytical model for the growth
of ionized regions to estimate the large scale distribution and redshift
evolution of the visibility of Lyman-alpha emission in 6<=z<=8 galaxies. The
inhomogeneous distribution of neutral hydrogen during the reionization process
results in significant fluctuations in the Lyman-alpha transmissivity on large
scales. The transmissivity depends not only on the ionized fraction of the
intergalactic medium by volume and the amplitude of the local ionizing
background, but is also rather sensitive to the evolution of the relative
velocity shift of the Lyman-alpha emission line due to resonant scattering. We
reproduce a decline in the space density of Lyman-alpha emitting galaxies as
rapid as observed with a rather rapidly evolving neutral fraction between
z=6-8, and a typical Lyman-alpha line velocity offset of 100 km/s redward of
systemic at z=6 which decreases toward higher redshift. The new (02/2015)
Planck results indicate such a recent end to reionization is no longer
disfavoured by constraints from the cosmic microwave background. | CMB distortion anisotropies due to the decay of primordial magnetic
fields: We investigate the power spectrum of the distortion of Cosmic Microwave
Background (CMB) due to the decay of the primordial magnetic fields. It is
known that there are two-types of the CMB distortions, so-called \mu- and
y-types and we find that the signal of the y-type distortion becomes larger
than that of the \mu-type one. We also discuss cross power spectra between the
CMB distortions and the CMB temperature anisotropy, which are naturally
generated due to the existence of the primordial magnetic fields. We find that
such cross power spectra have small amplitudes compared with the auto-power
spectra of the CMB distortions because of the Silk damping effect of the
temperature anisotropy. We also investigate the possibility of detecting such
signal in the future CMB experiments, including not only absolutely calibrated
experiments such as PIXIE but also relatively calibrated experiments such as
LiteBIRD and CMBpol. |
Cold Accretion Disks and Lineless Quasars: The optical-UV continuum of quasars is broadly consistent with the emission
from a geometrically thin optically thick accretion disk (AD). The AD produces
the ionizing continuum which powers the broad and narrow emission lines. The
maximum AD effective temperature is given by Teff=fmax(Mdot/M^2)^1/4, where M
is the black hole mass, Mdot the accretion rate, and fmax is set by the black
hole spin a_*. For a low enough value of Mdot/M^2 the AD may become too cold to
produce ionizing photons. Such an object will form a lineless quasar. This
occurs for a local blackbody (BB) AD with a luminosity Lopt=10^46 erg/s for
M>3.6E9 Msun, when a_*=0, and for M>1.4E10 Msun, when a_*=0.998. Using the AD
based Mdot, derived from M and Lopt, and the reverberation based M, derived
from Lopt and the Hbeta FWHM, v, gives Teff \propto Lopt^-0.13v^-1.45. Thus,
Teff is mostly set by v. Quasars with a local BB AD become lineless for v>
8,000 km/s, when a_*=0, and for v> 16,000 km/s, when a_*=0.998. Higher values
of v are required if the AD is hotter than a local BB. The AD becoming
non-ionizing may explain why line emitting quasars with v>10,000 km/s are rare.
Weak low ionization lines may still be present if the X-ray continuum is
luminous enough, and such objects may form a population of weak emission line
quasars (WLQ). If correct, such WLQ should show a steeply falling SED at
lambda<1000A. Such an SED was observed by Hryniewicz et al. in SDSS
J094533.99+100950.1, a WLQ observed down to 570A, which is well modeled by a
rather cold AD SED. UV spectroscopy of z~1-2 quasars is required to eliminate
potential intervening Lyman limit absorption by the intergalactic medium (IGM),
and to explore if the SEDs of lineless quasars and some additional WLQ are also
well fit by a cold AD SED. | Measuring the Universe with galaxy redshift surveys: Galaxy redshift surveys are one of the pillars of the current standard
cosmological model and remain a key tool in the experimental effort to
understand the origin of cosmic acceleration. To this end, the next generation
of surveys aim at achieving sub-percent precision in the measurement of the
equation of state of dark energy $w(z)$ and the growth rate of structure
$f(z)$. This however requires comparable control over systematic errors,
stressing the need for improved modelling methods. In this contribution we
review at the introductory level some highlights of the work done in this
direction by the {\it Darklight} project. Supported by an ERC Advanced Grant,
{\it Darklight} developed novel techniques for clustering analysis, which were
tested through numerical simulations before being finally applied to galaxy
data as in particular those of the recently completed VIPERS redshift survey.
We focus in particular on: (a) advances on estimating the growth rate of
structure from redshift-space distortions; (b) parameter estimation through
global Bayesian reconstruction of the density field from survey data; (c)
impact of massive neutrinos on large-scale structure measurements. Overall,
{\it Darklight} has contributed to paving the way for forthcoming
high-precision experiments, such as {\it Euclid}, the next ESA cosmological
mission. |
Evidence against a supervoid causing the CMB Cold Spot: We report the results of the 2dF-VST ATLAS Cold Spot galaxy redshift survey
(2CSz) based on imaging from VST ATLAS and spectroscopy from 2dF AAOmega over
the core of the CMB Cold Spot. We sparsely surveyed the inner 5$^{\circ}$
radius of the Cold Spot to a limit of $i_{AB} \le 19.2$, sampling $\sim7000$
galaxies at $z<0.4$. We have found voids at $z=$ 0.14, 0.26 and 0.30 but they
are interspersed with small over-densities and the scale of these voids is
insufficient to explain the Cold Spot through the $\Lambda$CDM ISW effect.
Combining with previous data out to $z\sim1$, we conclude that the CMB Cold
Spot could not have been imprinted by a void confined to the inner core of the
Cold Spot. Additionally we find that our 'control' field GAMA G23 shows a
similarity in its galaxy redshift distribution to the Cold Spot. Since the GAMA
G23 line-of-sight shows no evidence of a CMB temperature decrement we conclude
that the Cold Spot may have a primordial origin rather than being due to
line-of-sight effects. | On estimating the cosmic molecular gas density from CO Line Intensity
Mapping observations: The Millimeter-wave Intensity Mapping Experiment (mmIME) recently reported a
detection of excess spatial fluctuations at a wavelength of 3 mm, which can be
attributed to unresolved emission of several CO rotational transitions between
$z\sim1-5$. We study the implications of this data for the high-redshift
interstellar medium using a suite of state-of-the-art semianalytic simulations
which have successfully reproduced many other sub-millimeter line observations
across the relevant redshift range. We find that the semianalytic predictions
are mildly in tension with the mmIME result, with a predicted CO power
$\sim3.5\sigma$ below what was observed. We explore some simple modifications
to the models which could resolve this tension. Increasing the molecular gas
abundance at the relevant redshifts to $\sim10^8\ M_\odot\ \rm{Mpc}^{-3}$, a
value well above that obtained from directly imaged sources, would resolve the
discrepancy, as would assuming a CO-$H_2$ conversion factor $\alpha_{\rm{CO}}$
of $\sim1.5\ M_{\odot}$ K$^{-1}$ $(\rm{km}/\rm{s})^{-1}$ pc$^{2}$, a value
somewhat lower than is commonly assumed. We go on to demonstrate that these
conclusions are quite sensitive to the detailed assumptions of our simulations,
highlighting the need for more careful modeling efforts as more intensity
mapping data become available. |
Variable gravity Universe: For variable gravity models the strength of gravity, as measured by Newton's
``constant'' or the Planck mass, depends on the value of a scalar field, the
cosmon. We discuss two simple four-parameter models with a quadratic or
constant cosmon potential. They are compatible with all presently available
cosmological observations, including inflation. The inflaton and the scalar
field of quintessence are the same cosmon field. Dark Energy constitutes a
small, almost constant fraction of the energy density during the radiation and
matter dominated epochs (Early Dark Energy). In the present epoch we witness a
transition to a new Dark Energy dominated epoch. Our models are free of a big
bang singularity. The stability of solutions generates an arrow of time. Our
picture of the Universe is unusual, with a shrinking or static scale factor,
while the masses of particles increase and the size of atoms shrinks. The
evolution of the universe can be very slow for all cosmological epochs
including inflation, with typical time scale $10^{10}$ yr, and in sharp
contrast to the usual big bang picture. The map to the equivalent Einstein
frame with constant particle masses and expanding scale factor can be singular
at the big bang. | Evolution of star formation and gas: In these lectures I review observations of star-forming molecular clouds in
our Galaxy and nearby galaxies to develop a physical intuition for
understanding star formation in the local and high-redshift Universe. A lot of
this material is drawn from early work in the field since much of the work was
done two decades ago and this background is not generally available in the
present literature. I also attempt to synthesise our well-developed
understanding of star formation in low-redshift galaxies with constraints from
theory and observations at high redshift to develop an intuitive model for the
evolution of galaxy mass and luminosity functions in the early Universe.
The overall goal of this contribution is to provide students with background
helpful for analysis of far-infrared (FIR) observations from Herschel and
millimetre/submillimetre (mm/submm) imaging with ALMA (the Atacama Large
Millimetre/submillimetre Array). These two instruments will revolutionise our
understanding of the interstellar medium (ISM) and associated star formation
and galaxy evolution, both locally and in the distant Universe. To facilitate
interpreting the FIR spectra of Galactic star-forming regions and high-redshift
sources, I develop a model for the dust heating and radiative transfer in order
to elucidate the observed infrared (IR) emissions. I do this because I am not
aware of a similar coherent discussion in the literature. |
Inflation model constraints from data released in 2015: We provide the latest constraints on the power spectra of both scalar and
tensor perturbations from the CMB data (including \textit{Planck}~2015, BICEP2
\& \textit{Keck Array} experiments) and the new BAO scales from SDSS-III BOSS
observation. We find that the inflation model with a convex potential is not
favored and both the inflation model with a monomial potential and the natural
inflation model are marginally disfavored at around $95\%$ confidence level.
But both the Brane inflation model and the Starobinsky inflation model fit the
data quite well. | Cosmological forecasts for future galaxy surveys with the linear point
standard ruler: Toward consistent BAO analyses far from a fiducial cosmology: The linear point (LP) standard ruler was identified as the basis of a purely
geometric method for exploiting the Baryon Acoustic Oscillations (BAO). The LP
exploits the BAO feature imprinted in the galaxy two-point correlation function
to measure cosmological distances independent of any specific cosmological
model. We forecast the expected precision of future and ongoing spectroscopic
galaxy surveys to measure distances leveraging the linear point. We investigate
the cosmological implications of our forecasted results. We focus in particular
on a relevant working example: the detection of the late-time cosmic
acceleration independent of other cosmological probes. Our findings show that,
even within the LCDM standard cosmological paradigm, estimated distances need
to be reliable over a very wide parameter range in order to realize their
maximum utility. This is particularly relevant if we aim to properly
characterize cosmological tensions. The LP is a promising candidate approach to
achieve this reliability. In contrast, widely employed procedures in BAO
analysis estimate distances keeping fixed cosmological parameters to fiducial
values close to cosmic-microwave-background constraints in flat-LCDM. It is
unclear whether they are purely geometric methods. Moreover, they rely on
untested extrapolations to explore the parameter space away from those fiducial
flat-LCDM values. We recommend that all BAO methodologies be validated across
the full range of models and parameters over which their results are quoted,
first by means of linear predictions and then N-body simulations. |
ALMA CO and VLT/SINFONI H2 observations of the Antennae overlap region:
mass and energy dissipation: We present an analysis of super-giant molecular complexes (SGMCs) in the
overlap region of the Antennae galaxy merger, based on ALMA CO(3-2)
interferometry and VLT/SINFONI imaging spectroscopy of H2 1-0 S(1) at angular
resolutions of 0.9" and 0.7", respectively. All but one SGMC have multiple
velocity components offset from each other by up to 150 km/s. H2 line emission
is found in all SGMCs and the kinematics of H2 and CO are well matched. H2/CO
line ratios vary by up to a factor of 10 among SGMCs and different velocity
components of the same SGMCs. We also identify the CO counterpart of a bright,
compact source of near-IR H2 line emission, which shows no Brgamma, and was
first identified with SINFONI. This source has the highest H2/CO line ratio,
and coincides with the steepest CO velocity gradient of the entire overlap
region. With a size of 50 pc and a virial mass of a few 10^7 Msun it is perhaps
a pre-cluster cloud that has not yet formed significant numbers of massive
stars. We present observational evidence that the H2 emission is powered by
shocks, and demonstrate how the H2 1-0 S(1) and the CO(3-2) lines can be used
as tracers of energy dissipation and gas mass, respectively. The variations in
the H2/CO line ratio may indicate that the SGMCs are dissipating their
turbulent kinetic energy at different rates. The compact source could represent
a short (~ 1 Myr) evolutionary stage in the early formation of super-star
clusters. | Cosmological perturbations: non-cold relics without the Boltzmann
hierarchy: We present a formulation of cosmological perturbation theory where the
Boltzmann hierarchies that evolve the neutrino phase-space distributions are
replaced by integrals that can be evaluated easily with fast Fourier
transforms. The simultaneous evaluation of these integrals combined with the
differential equations for the rest of the system (dark matter, photons,
baryons) are then solved with an iterative scheme that converges quickly. The
formulation is particularly powerful for massive neutrinos, where the effective
phase space is three-dimensional rather than two-dimensional, and even moreso
for three different neutrino mass eigenstates. Therefore, it has the potential
to significantly speed up the computation times of cosmological-perturbation
calculations. This approach should also be applicable to models with other
non-cold collisionless relics. |
Propagating photo-$z$ uncertainties: a functional derivative approach: Photometric redshifts are a key ingredient in the analysis and interpretation
of large-scale structure (LSS) surveys. The accuracy and precision of these
redshift estimates are directly linked to the constraining power of photometric
surveys. It is hence necessary to define precision and accuracy requirements
for the redshift calibration \revision{to not} infer biased results in the
final analysis. For weak gravitational lensing of the LSS, the photometry
culminates in the estimation of the source redshift distribution (SRD) in each
of the tomographic bins used in the analysis. The focus has been on shifts of
the mean of the SRDs and how well the calibration must be able to recover
those. Since the estimated SRDs are usually given as a normalized histogram
with corresponding errors, it would be advantageous to propagate these
uncertainties accordingly to see whether the requirements of the given survey
are indeed fulfilled. Here we propose the use of functional derivatives to
calculate the sensitivity of the final observables, e.g. the lensing angular
power spectrum, with respect to the SRD at a specific redshift. This allows the
propagation of arbitrarily shaped small perturbations to the SRD, without
having to run the whole analysis pipeline for each realization again. We apply
our method to an EUCLID survey and demonstrate it with SRDs of the KV450 data
set, recovering previous results. Lastly, we note that the moments of the SRD
of order larger than two will probably not be relevant when propagating
redshift uncertainties in cosmic shear analysis. | GERLUMPH Data Release 1: High-resolution cosmological microlensing
magnification maps and eResearch tools: As synoptic all-sky surveys begin to discover new multiply lensed quasars,
the flow of data will enable statistical cosmological microlensing studies of
sufficient size to constrain quasar accretion disc and supermassive black hole
properties. In preparation for this new era, we are undertaking the
GPU-Enabled, High Resolution cosmological MicroLensing parameter survey
(GERLUMPH). We present here the GERLUMPH Data Release 1, which consists of
12342 high resolution cosmological microlensing magnification maps and provides
the first uniform coverage of the convergence, shear and smooth matter fraction
parameter space. We use these maps to perform a comprehensive numerical
investigation of the mass-sheet degeneracy, finding excellent agreement with
its predictions. We study the effect of smooth matter on microlensing induced
magnification fluctuations. In particular, in the minima and saddle-point
regions, fluctuations are enhanced only along the critical line, while in the
maxima region they are always enhanced for high smooth matter fractions (~0.9).
We describe our approach to data management, including the use of an SQL
database with a Web interface for data access and online analysis, obviating
the need for individuals to download large volumes of data. In combination with
existing observational databases and online applications, the GERLUMPH archive
represents a fundamental component of a new microlensing eResearch cloud. Our
maps and tools are publicly available at http://gerlumph.swin.edu.au/. |
Halo intrinsic alignment: dependence on mass, formation time and
environment: In this paper we use high-resolution cosmological simulations to study halo
intrinsic alignment and its dependence on mass, formation time and large-scale
environment. In agreement with previous studies using N-body simulations, it is
found that massive halos have stronger alignment. For given mass, older halos
have stronger alignment than younger ones. By identifying the cosmic
environment of halo using Hessian matrix, we find that for given mass, halos in
cluster regions also have stronger alignment than those in filament. The
existing theory has not addressed these dependencies explicitly. In this work
we extend the linear alignment model with inclusion of halo bias and find that
the halo alignment with its mass and formation time dependence can be explained
by halo bias. However, the model can not account for the environment
dependence, as it is found that halo bias is lower in cluster and higher in
filament. Our results suggest that halo bias and environment are independent
factors in determining halo alignment. We also study the halo alignment
correlation function and find that halos are strongly clustered along their
major axes and less clustered along the minor axes. The correlated halo
alignment can extend to scale as large as $100h^{-1}$Mpc where its feature is
mainly driven by the baryon acoustic oscillation effect. | Nuisance parameters for large galaxy surveys: These notes are based on a lecture given at the 2016 Euclid Summer School in
Narbonne. I will first give a quick overview of the concept of nuisance
parameters in the context of large galaxy surveys. The second part will examine
the case study of intrinsic alignments, a potential important contamination of
weak lensing observables. |
Consistent Modeling of Velocity Statistics and Redshift-Space
Distortions in One-Loop Perturbation Theory: The peculiar velocities of biased tracers of the cosmic density field contain
important information about the growth of large scale structure and generate
anisotropy in the observed clustering of galaxies. Using N-body data, we show
that velocity expansions for halo redshift-space power spectra are converged at
the percent-level at perturbative scales for most line-of-sight angles $\mu$
when the first three pairwise velocity moments are included, and that the third
moment is well-approximated by a counterterm-like contribution. We compute
these pairwise-velocity statistics in Fourier space using both Eulerian and
Lagrangian one-loop perturbation theory using a cubic bias scheme and a
complete set of counterterms and stochastic contributions. We compare the
models and show that our models fit both real-space velocity statistics and
redshift-space power spectra for both halos and a mock sample of galaxies at
sub-percent level on perturbative scales using consistent sets of parameters,
making them appealing choices for the upcoming era of spectroscopic,
peculiar-velocity and kSZ surveys. | Running vacuum against the $H_0$ and $σ_8$ tensions: The cosmological term, $\Lambda$, was introduced $104$ years ago by Einstein
in his gravitational field equations. Whether $\Lambda$ is a rigid quantity or
a dynamical variable in cosmology has been a matter of debate for many years,
especially after the introduction of the general notion of dark energy (DE).
$\Lambda$ is associated to the vacuum energy density, $\rho_{\rm vac}$, and one
may expect that it evolves slowly with the cosmological expansion. Herein we
present a devoted study testing this possibility using the promising class of
running vacuum models (RVM's). We use a large string $SNIa+BAO+H(z)+LSS+CMB$ of
modern cosmological data, in which for the first time the CMB part involves the
full Planck 2018 likelihood for these models. We test the dependence of the
results on the threshold redshift $z_*$ at which the vacuum dynamics is
activated in the recent past and find positive signals up to $\sim4.0\sigma$
for $z_*\simeq 1$. The RVM's prove very competitive against the standard
$\Lambda$CDM model and give a handle for solving the $\sigma_8$ tension and
alleviating the $H_0$ one. |
Technical aspects in dark matter investigations: Some theoretical and experimental aspects regarding the direct dark matter
field are mentioned. In particular some arguments, which play a relevant role
in the evaluation of model dependent interpretations of experimental results
and in comparisons, are shortly addressed. | M - sigma relation between SMBHs and the velocity dispersion of globular
cluster systems: We find evidence that the mass MBH of central supermassive black holes
(SMBHs) correlates with the velocity dispersion sigma_GC of globular cluster
systems of their host galaxies. This extends the well-known MBH - sigma_sph
relation between black hole mass and velocity dispersion of the host spheroidal
component. We compile published measurements of both MBH and sigma_GC for a
sample of 13 systems and find the relation log(MBH) = alpha + beta
log(sigma_GC/200) with alpha = 8.63 \pm 0.09 and beta = 3.76 \pm 0.52. We also
consider blue (metal-poor) and red (metal-rich) globular clusters
sub-populations separately and obtain a surprisingly tight correlation using
only the velocity dispersion sigma_GC^red of the red clusters with alpha = 8.73
\pm 0.09 and beta = 3.84 \pm 0.52 and an intrinsic scatter eps_0 = 0.22 dex
compared to eps_0 = 0.27 dex for the MBH - sigma_sph of our sample. We use our
MBH - sigma_GC relation to estimate the central black hole mass in five
galaxies for which sigma_GC^red is measured. |
HOLISMOKES -- XII. Time-delay Measurements of Strongly Lensed Type Ia
Supernovae using a Long Short-Term Memory Network: Strongly lensed Type Ia supernovae (LSNe Ia) are a promising probe to measure
the Hubble constant ($H_0$) directly. To use LSNe Ia for cosmography, a
time-delay measurement between the multiple images, a lens-mass model, and a
mass reconstruction along the line of sight are required. In this work, we
present the machine learning network LSTM-FCNN which is a combination of a Long
Short-Term Memory Network (LSTM) and a fully-connected neural network (FCNN).
The LSTM-FCNN is designed to measure time delays on a sample of LSNe Ia
spanning a broad range of properties, which we expect to find with the upcoming
Rubin Observatory Legacy Survey of Space and Time (LSST) and for which
follow-up observations are planned. With follow-up observations in $i$ band
(cadence of one to three days with a single-epoch $5\sigma$ depth of 24.5 mag),
we reach a bias-free delay measurement with a precision around 0.7 days over a
large sample of LSNe Ia. The LSTM-FCNN is far more general than previous
machine learning approaches such as the Random Forest (RF), where a RF has to
be trained for each observational pattern separately, and yet the LSTM-FCNN
outperforms the RF by a factor of roughly three. Therefore, the LSTM-FCNN is a
very promising approach to achieve robust time delays in LSNe Ia, which is
important for a precise and accurate constraint on $H_0$ | Hubble Tension: The Evidence of New Physics: The $\Lambda$CDM model provides a good fit to most astronomical observations
but harbors large areas of phenomenology and ignorance. With the improvements
in the precision and number of observations, discrepancies between key
cosmological parameters of this model have emerged. Among them, the most
notable tension is the 4$\sigma$ to 6$\sigma$ deviation between the Hubble
constant ($H_{0}$) estimations measured by the local distance ladder and the
cosmic microwave background (CMB) measurement. In this review, we revisit the
$H_{0}$ tension based on the latest research and sort out evidence from
solutions to this tension that might imply new physics beyond the $\Lambda$CDM
model. The evidence leans more towards modifying the late-time universe. |
WIMP decay as a possible Warm Dark Matter model: The Weakly Interacting Massive Particles(WIMPs) have long been the favored
CDM candidate in the standard $\Lambda$CDM model. However, owing to great
improvement in the experimental sensitivity in the past decade, some parameter
space of the SUSY-based WIMP model is ruled out. In addition, WIMP as the CDM
particle is also at variance with other astrophysical observables at small
scales. We consider a model that addresses both these issues. In the model, the
WIMP decays into a massive particle and radiation. We study the background
evolution and the first order perturbation theory (coupled Einstein-Boltzmann
equations) for this model and show that the dynamics can be captured by a
single parameter $r=m_L/q$, which is the ratio of the lighter mass and the
comoving momentum of the decay particle. We incorporate the relevant equations
in the existing Boltzmann code CLASS to compute the matter power spectra and
CMB angular power spectra. The decaying WIMP model is akin to a non-thermal
Warm Dark Matter(WDM) model and suppresses matter power at small scales, which
could alleviate several issues that plague the CDM model. We compare the
predictions of the model with CMB, galaxy clustering, and high-z HI data. Both
these data sets yield $r\gtrsim 10^6$, which can be translated into the bounds
on other parameters. In particular, we obtain the following lower bounds on the
thermally-averaged self-annihilation cross-section of WIMPs $\langle \sigma v
\rangle$, and the lighter mass $m_L$: $\langle \sigma v \rangle \gtrsim
4.9\times 10^{-34} \, \rm cm^3 \, sec^{-1}$ and $m_L \gtrsim 2.4 \, \rm keV$.
The lower limit on $m_L$ is comparable to constraints on the mass of
thermally-produced WDM particle. The limit on the self-annihilation
cross-section greatly expands the available parameter space as compared to the
stable WIMP scenario. | Constraints on the exponential $f(R)$ model from latest Hubble parameter
measurements: We investigate the viable exponential $f(R)$ gravity in the metric formalism
with $f(R)=-\beta R_s (1-e^{-R/R_s})$. The latest sample of the Hubble
parameter measurements with 23 data points is used to place bounds on this
$f(R)$ model. A joint analysis is also performed with the luminosity distances
of Type Ia supernovae and baryon acoustic oscillations in the clustering of
galaxies, and the shift parameters from the cosmic microwave background
measurements, which leads to $0.240<\Omega_m^0<0.296$ and $\beta>1.47$ at
1$\sigma$ confidence level. The evolutions of the deceleration parameter $q(z)$
and the effective equations of state $\omega_{de}^{eff}(z)$ and
$\omega_{tot}^{eff}(z)$ are displayed. By taking the best-fit parameters as
prior values, we work out the transition redshift (deceleration/acceleration)
$z_T$ to be about 0.77. It turns out that the recent observations are still
unable to distinguish the background dynamics in the $\Lambda$CDM and
exponential $f(R)$ models. |
Potential of radio telescopes as high-frequency gravitational wave
detectors: In the presence of magnetic fields, gravitational waves are converted into
photons and vice versa. We demonstrate that this conversion leads to a
distortion of the cosmic microwave background (CMB), which can serve as a
detector for MHz to GHz gravitational wave sources active before reionization.
The measurements of the radio telescope EDGES can be cast as a bound on the
gravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the
strongest (weakest) cosmic magnetic fields allowed by current astrophysical and
cosmological constraints. Similarly, the results of ARCADE 2 imply $h_c <
10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these
constraints exceed current laboratory constraints by about seven orders of
magnitude. Future advances in 21cm astronomy may conceivably push these bounds
below the sensitivity of cosmological constraints on the total energy density
of gravitational waves. | No-Go Theorems for Generalized Chameleon Field Theories: The chameleon, or generalizations thereof, is a light scalar that couple to
matter with gravitational strength, but whose manifestation depends on the
ambient matter density. A key feature is that the screening mechanism
suppressing its effects in high-density environments is determined by the local
scalar field value. Under very general conditions, we prove two theorems
limiting its cosmological impact: i) the Compton wavelength of such a scalar
can be at most Mpc at present cosmic density, which restricts its impact to
non-linear scales; ii) the conformal factor relating Einstein- and Jordan-frame
scale factors is essentially constant over the last Hubble time, which
precludes the possibility of self-acceleration. These results imply that
chameleon-like scalar fields have a negligible effect on the linear-scale
growth history; theories that invoke a chameleon-like scalar to explain cosmic
acceleration rely on a form of dark energy rather than a genuine modified
gravity effect. Our analysis applies to a broad class of chameleon, symmetron
and dilaton theories. |
The dipole anisotropy of AllWISE galaxies: We determine the dipole in the WISE galaxy catalogue. After reducing star
contamination to <0.1% by rejecting sources with high apparent motion and those
close to the Galactic plane, we eliminate low redshift sources to suppress the
non-kinematic, clustering dipole. We remove sources within {\pm}5{\deg} of the
super-galactic plane, as well as those within 1'' of 2MRS sources at redshift z
< 0.03. We enforce cuts on the source angular extent to preferentially select
distant ones. As we progress along these steps, the dipole converges in
direction to within 5{\deg} of the CMB dipole and its magnitude also
progressively reduces but stabilises at {\sim}0.012, corresponding to a
velocity >1000 km/s if it is solely of kinematic origin. However, previous
studies have shown that only {\sim}70% of the velocity of the Local Group as
inferred from the CMB dipole is due to sources at z < 0.03. We examine the Dark
Sky simulations to quantify the prevalence of such environments and find that
<2.1% of Milky Way-like observers in a {\Lambda}CDM universe should observe the
bulk flow (> 240 km/s extending to z > 0.03) that we do. We construct mock
catalogues in the neighbourhood of such peculiar observers in order to mimic
our final galaxy selection and quantify the residual clustering dipole. After
subtracting this the remaining dipole is 0.0048 {\pm} 0.0022, corresponding to
a velocity of 420 {\pm} 213 km/s which is consistent with the CMB. However the
sources (at z > 0.03) of such a large clustering dipole remain to be
identified. | Massive Clumps in Local Galaxies: Comparisons with High-Redshift Clumps: Local UV-bright galaxies in the Kiso survey include clumpy systems with
kpc-size star complexes that resemble clumpy young galaxies in surveys at high
redshift. We compare clump masses and underlying disks in several dozen
galaxies from each of these surveys to the star complexes and disks of normal
spirals. Photometry and spectroscopy for the Kiso and spiral sample come from
the Sloan Digital Sky Survey. We find that the largest Kiso clumpy galaxies
resemble UDF clumpies in terms of the star formation rates, clump masses, and
clump surface densities. Clump masses and surface densities in normal spirals
are smaller. If the clump masses are proportional to the turbulent Jeans mass
in the interstellar medium, then for the most luminous galaxies in the sequence
of normal:Kiso:UDF, the turbulent speeds and surface densities increase in the
proportions 1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe
B-band absolute magnitude. For the least luminous galaxies in the overlapping
magnitude range, the turbulent speed and surface density trends are 1.0:2.7:7.4
and 1.0:1.4:3.0, respectively. We also find that while all three types have
radially decreasing disk intensities when measured with ellipse-fit azimuthal
averages, the average profiles are more irregular for UDF clumpies (which are
viewed in their restframe UV) than for Kiso galaxies (viewed at g-band), and
major axis intensity scans are even more irregular for the UDF than Kiso
galaxies. Local clumpy galaxies in the Kiso survey appear to be intermediate
between UDF clumpies and normal spirals. |
CMB Scale Dependent Non-Gaussianity from Massive Gravity during
Inflation: We consider a cosmological model in which the tensor mode becomes massive
during inflation, and study the Cosmic Microwave Background (CMB) temperature
and polarization bispectra arising from the mixing between the scalar mode and
the massive tensor mode during inflation. The model assumes the existence of a
preferred spatial frame during inflation. The local Lorentz invariance is
already broken in cosmology due to the existence of a preferred rest frame. The
existence of a preferred spatial frame further breaks the remaining local SO(3)
invariance and in particular gives rise to a mass in the tensor mode. At linear
perturbation level, we minimize our model so that the vector mode remains
non-dynamical, while the scalar mode is the same as the one in single-field
slow-roll inflation. At non-linear perturbation level, this inflationary
massive graviton phase leads to a sizeable scalar-scalar-tensor coupling, much
greater than the scalar-scalar-scalar one, as opposed to the conventional case.
This scalar-scalar-tensor interaction imprints a scale dependent feature in the
CMB temperature and polarization bispectra. Very intriguingly, we find a
surprizing similarity between the predicted scale dependence and the
scale-dependent non-Gaussianities at low multipoles hinted in the WMAP and
Planck results. | NIR/Optical Selected Local Mergers --- Spatial Density and sSFR
Enhancement: Mergers play important roles in triggering the most active objects in the
universe, including (U)LIRGs and QSOs. However, whether they are also important
for the total stellar mass build-up in galaxies in general is unclear and
controversial. The answer to that question depends on the merger rate and the
average strength of merger induced star formation. In this talk, I will review
studies on spatial density and sSFR enhancement of local mergers found in
NIR/optical selected pair samples. In line with the current literature on
galaxy formation/evolution, special attention will be paid to the dependence of
the local merger rate and of the sSFR enhancement on four fundamental
observables: (1) stellar mass, (2) mass ratio, (3) separation, and (4)
environment. |
Astrophysical black holes in screened modified gravity: Chameleon, environmentally dependent dilaton, and symmetron gravity are three
models of modified gravity in which the effects of the additional scalar degree
of freedom are screened in dense environments. They have been extensively
studied in laboratory, cosmological, and astrophysical contexts. In this paper,
we present a preliminary investigation into whether additional constraints can
be provided by studying these scalar fields around black holes. By looking at
the properties of a static, spherically symmetric black hole, we find that the
presence of a non-uniform matter distribution induces a non-constant scalar
profile in chameleon and dilaton, but not necessarily symmetron gravity. An
order of magnitude estimate shows that the effects of these profiles on
in-falling test particles will be sub-leading compared to gravitational waves
and hence observationally challenging to detect. | Integral constraints in spectroscopic surveys: Clustering analyses of spectroscopic surveys are based upon density
fluctuations, which are estimated by comparing the observed tracer density
field to a selection function accounting for the survey density and geometry.
However, this survey selection function is commonly partly inferred from the
observed data itself, leading to so-called integral constraints, for which we
propose a complete derivation. We discuss the normalisation of the introduced
window functions, the shot noise contribution to the integral constraint
corrections and wide-angle effects. Using this formalism, we review the
well-known global integral constraint, arising when the expected mean galaxy
density is taken to be the measured one. Another, stronger, constraint is
imposed when the radial selection function itself is estimated from the data
redshift distribution, as is often the case in the literature. We find that the
impact of such a radial integral constraint can be as significant as the window
function effect at large scales, depending on the survey geometry. Equations
for this radial integral constraint are derived within our general formalism.
We assess the validity of our approach by performing a Redshift Space
Distortions (RSD) analysis on mock catalogues and emphasise that our results
may be even more useful for analyses focusing on larger scales. Finally, as a
further application, we show that unknown angular systematics can be mitigated
by nulling the density fluctuations on a chosen angular scale. The induced loss
of clustering is modelled by an angular integral constraint which can be
combined with the radial one. |
Influence of sources with a spectral peak in the detection of Cosmic
Dawn and Epoch of Reionization: Foreground removal is one of the biggest challenges in the detection of the
Cosmic Dawn (CD) and Epoch of Reionization (EoR). Various foreground
subtraction techniques have been developed based on the spectral smoothness of
foregrounds. However, the sources with a spectral peak (SP) at Megahertz may
break down the spectral smoothness at low frequencies (< 1000 MHz). In this
paper, we cross-match the GaLactic and Extragalactic All-sky Murchison
Widefield Array (GLEAM) extragalactic source catalogue with three other radio
source catalogues, covering the frequency range from 72 MHz to 1.4 GHz, to
search for sources with spectral turnover. 4,423 sources from the GLEAM
catalogue are identified as SP sources, representing approximately 3.2 per cent
of the GLEAM radio source population. We utilize the properties of SP source
candidates obtained from real observations to establish simulations and test
the impact of SP sources on the extraction of CD/EoR signals. We statistically
compare the differences introduced by SP sources in the residuals after
removing the foregrounds with three methods, which are polynomial fitting,
Principal Component Analysis (PCA), and fast independent component analysis
(FastICA). Our results indicate that the presence of SP sources in the
foregrounds has a negligible influence on extracting the CD/EoR signal. After
foreground subtraction, the contribution from SP sources to the total power in
the two-dimensional (2D) power spectrum within the EoR window is approximately
3 to 4 orders of magnitude lower than the CD/EoR signal. | On the large-scale instability in interacting dark energy and dark
matter fluids: Recently, Valiviita et al. (2008) have reported a large-scale early-time
instability in coupled dark energy and dark matter models. We take the same
form of energy-momentum exchange and specialise to the case when the
interaction rate is proportional to Hubble's parameter and the dark energy
density only. Provided the coupling is made small enough for a given equation
of state parameter, we show that the instability can be avoided. Expressions
are derived for non-adiabatic modes on super-horizon scales in both the
radiation and matter dominated regimes. We also examine the growth of dark
matter perturbations in the sub-horizon limit. There we find that the coupling
has almost no effect upon the growth of structure before dark energy begins to
dominate. Once the universe begins to accelerate, the relative dark matter
density fluctuations not only cease to grow as in uncoupled models, but
actually decay as the universe continues to expand. |
CMB lensing in a modified $Λ$CDM model in light of the $H_0$
tension: The observed discrepancy of the Hubble parameter measurements in the local
universe with the cosmic microwave background (CMB) data may indicate a new
physics. It is vital to test the alternative models that reconcile the Hubble
tension with other cosmological observations in this direction. The CMB lensing
is a crucial observation that relates the early universe perturbations to the
matter's late-time distribution. In this work, we study the prediction of the
\"u$\Lambda$CDM as a solution for $H_0$ tension for CMB lensing and the low-
and high-$\ell$'s temperature (TT) power spectrum internal inconsistency. We
show that this model relaxes the low- and high-$\ell$'s TT mild inconsistency
and the CMB lensing tensions simultaneously. Accordingly, \"u$\Lambda$CDM
having the same number of free parameters as $\Lambda$CDM with lensing
amplitude $A_L$ added, has a better fit with $\Delta \chi^2=-3.3$. | The effect of primordial non-Gaussianity on the skeleton of cosmic shear
maps: (abridged) We explore the imprints of deviations from Gaussian primordial
density fluctuations on the skeleton of the large-scale matter distribution as
mapped through cosmological weak lensing. We computed the skeleton length of
simulated effective convergence maps covering $\sim 35$ sq. deg each, extracted
from a suite of cosmological $n-$body runs with different levels of local
primordial non-Gaussianity. The latter is expected to alter the structure
formation process with respect to the fiducial Gaussian scenario, and thus to
leave a signature on the cosmic web. We found that alterations of the initial
conditions consistently modify both the cumulative and the differential
skeleton length, although the effect is generically smaller than the cosmic
variance and depends on the smoothing of the map prior to the skeleton
computation. Nevertheless, the qualitative shape of these deviations is rather
similar to their primordial counterparts, implying that skeleton statistics
retain good memory of the initial conditions. We performed a statistical
analysis in order to find out at what Confidence Level primordial
non-Gaussianity could be constrained by the skeleton test on cosmic shear maps
of the size we adopted. At 68.3% Confidence Level we found an error on the
measured level of primordial non-Gaussianity of $\Delta f_\mathrm{NL}\sim 300$,
while at 90% Confidence Level it is of $\Delta f_\mathrm{NL}\sim 500$. While
these values by themselves are not competitive with the current constraints,
weak lensing maps larger than those used here would have a smaller
field-to-field variance, and thus would likely lead to tighter constraints. A
rough estimate indicates $\Delta f_\mathrm{NL} \sim$ a few tens at 68.3%
Confidence Level for an all-sky weak lensing survey. |
2021-$H_0$ Odyssey: Closed, Phantom and Interacting Dark Energy
Cosmologies: Up-to-date cosmological data analyses have shown that \textit{(a)} a closed
universe is preferred by the Planck data at more than $99\%$ CL, and
\textit{(b)} interacting scenarios offer a very compelling solution to the
Hubble constant tension. In light of these two recent appealing scenarios, we
consider here an interacting dark matter-dark energy model with a non-zero
spatial curvature component and a freely varying dark energy equation of state
in both the quintessential and phantom regimes. When considering Cosmic
Microwave Background data only, a phantom and closed universe can perfectly
alleviate the Hubble tension, without the necessity of a coupling among the
dark sectors. Accounting for other possible cosmological observations
compromises the viability of this very attractive scenario as a global solution
to current cosmological tensions, either by spoiling its effectiveness
concerning the $H_0$ problem, as in the case of Supernovae Ia data, or by
introducing a strong disagreement in the preferred value of the spatial
curvature, as in the case of Baryon Acoustic Oscillations. | The constraint ability of Hubble parameter by gravitational wave
standard sirens on cosmological parameters: In this paper, we present the application of a new method measuring Hubble
parameter $H(z)$ by using the anisotropy of luminosity distance($d_{L}$) of the
gravitational wave(GW) standard sirens of neutron star(NS) binary system. The
method has never been put into practice so far due to the lack of the ability
of detecting GW. However, LIGO's success in detecting GW of black hole(BH)
binary system merger announced the potential possibility of this new method. We
apply this method to several GW detecting projects, including Advanced
LIGO(aLIGO), Einstein Telescope(ET) and DECIGO, and evaluate its constraint
ability on cosmological parameters of $H(z)$. It turns out that the $H(z)$ by
aLIGO and ET is of bad accuracy, while the $H(z)$ by DECIGO shows a good one.
We simulate $H(z)$ data at every 0.1 redshift span using the error information
of $H(z)$ by DECIGO, and put the mock data into the forecasting of cosmological
parameters. Compared with the previous data and method, we get an obviously
tighter constraint on cosmological parameters by mock data, and a concomitantly
higher value of Figure of Merit(FoM, the reciprocal of the area enclosed by the
$2\sigma$ confidence region). For a 3-year-observation by standard sirens of
DECIGO, the FoM value is as high as 170.82. If a 10-year-observation is
launched, the FoM could reach 569.42. For comparison, the FoM of 38 actual
observed $H(z)$ data(OHD) is 9.3. We also investigate the undulant universe,
which shows a comparable improvement on the constraint of cosmological
parameters. These improvement indicates that the new method has great potential
in further cosmological constraints. |
Semi-analytical frameworks for subhalos from the smallest to the largest
scale: Substructures of dark matter halo, called subhalos, provide important clues
to understand the nature of dark matter. We construct a useful model to
describe the properties of subhalo mass functions based on the well-known
analytical prescriptions, the extended Press-Schechter theory. The unevolved
subhalo mass functions at arbitrary mass scales become describable without
introducing free parameters. The different host halo evolution histories are
directly recast to their subhalo mass functions. As applications, we quantify
the effects from (i) the Poisson fluctuation, (ii) the host mass scatter, and
the (iii) different tidal evolution models on observables in the current
Universe with this scheme. The Poisson fluctuation dominates in the number
count of the mass ratio to the host of $\sim {\cal O}(10^{-2})$, where the
intrinsic scatter is smaller by a factor of a few. The host-mass scatter around
its mean does not affect the subhalo mass function. Different models of the
tidal evolution predict a factor of $\sim2$ difference in numbers of subhalos
with $\lesssim {\cal O}(10^{-5})$, while the dependence of the Poisson
fluctuation on the tidal evolution models is subtle. The scheme provides a new
tool for investigating the smallest-scale structures of our Universe which are
to be observed in near future experiments. | Impact of Neutrino Properties and Dark Matter on the Primordial Lithium
Production: The light elements up to 7Li were produced by the Standard Big Bang
nucleosynthesis (SBBN) in the early universe assuming standard conditions. All
observed primordial abundances of these light elements match very well the
predicted ones by this SBBN except for 7Li which seems to be overproduced. It
is rather challenging to resolve this discrepancy owing to the diverse
possibilities affecting the abundance of lithium. In the present work we focus
on non-standard possible solutions such as variation of chemical potential and
the neutrino temperatures. In addition, the effect of dark matter is also
analysed. We find that including these non-standard assumptions helps to reduce
the abundance of lithium as predicted by SBBN. We suggest that this could be a
possible step toward resolving the lithium problem. |
Heating Cluster Gas: It is now generally agreed that some process prevents the diffuse gas in
galaxy clusters from cooling significantly, although there is less agreement
about the nature of this process. I suggest that cluster gas may be heated by a
natural extension of the mechanism establishing the $\mbh-\sigma$ and $\mbh -
M_{\rm bulge}$ relations in galaxies, namely outflows resulting from
super--Eddington accretion on to the galaxy's central black hole. The black
holes in cD galaxies are sporadically fed at unusually high Eddington ratios.
These are triggered as the cluster gas tries to cool, but rapidly quenched by
the resulting shock heating. This mechanism is close to the optimum efficiency
for using accretion energy to reheat cluster gas, and probably more effective
than `radio mode' heating by jets for example. The excess energy is radiated in
active phases of the cD galaxy nucleus, probably highly anisotropically. | Planck intermediate results. LIV. The Planck Multi-frequency Catalogue
of Non-thermal Sources: This paper presents the Planck Multi-frequency Catalogue of Non-thermal (i.e.
synchrotron-dominated) Sources (PCNT) observed between 30 and 857 GHz by the
ESA Planck mission. This catalogue was constructed by selecting objects
detected in the full mission all-sky temperature maps at 30 and 143 GHz, with a
signal-to-noise ratio (S/N)>3 in at least one of the two channels after
filtering with a particular Mexican hat wavelet. As a result, 29400 source
candidates were selected. Then, a multi-frequency analysis was performed using
the Matrix Filters methodology at the position of these objects, and flux
densities and errors were calculated for all of them in the nine Planck
channels. The present catalogue is the first unbiased, full-sky catalogue of
synchrotron-dominated sources published at millimetre and submillimetre
wavelengths and constitutes a powerful database for statistical studies of
non-thermal extragalactic sources, whose emission is dominated by the central
active galactic nucleus. Together with the full multi-frequency catalogue, we
also define the Bright Planck Multi-frequency Catalogue of Non-thermal Sources
PCNTb, where only those objects with a S/N>4 at both 30 and 143 GHz were
selected. In this catalogue 1146 compact sources are detected outside the
adopted Planck GAL070 mask; thus, these sources constitute a highly reliable
sample of extragalactic radio sources. We also flag the high-significance
subsample PCNThs, a subset of 151 sources that are detected with S/N>4 in all
nine Planck channels, 75 of which are found outside the Planck mask adopted
here. The remaining 76 sources inside the Galactic mask are very likely
Galactic objects. |
Large-scale non-Gaussian mass function and halo bias: tests on N-body
simulations: The description of the abundance and clustering of halos for non-Gaussian
initial conditions has recently received renewed interest, motivated by the
forthcoming large galaxy and cluster surveys, which can potentially yield
constraints of order unity on the non-Gaussianity parameter f_{NL}. We present
tests on N-body simulations of analytical formulae describing the halo
abundance and clustering for non-Gaussian initial conditions. We calibrate the
analytic non-Gaussian mass function of Matarrese et al.(2000) and LoVerde et
al.(2008) and the analytic description of clustering of halos for non-Gaussian
initial conditions on N-body simulations. We find excellent agreement between
the simulations and the analytic predictions if we make the corrections delta_c
--> delta_c X sqrt{q} and delta_c --> \delta_c X q where q ~ 0.75, in the
density threshold for gravitational collapse and in the non-Gaussian fractional
correction to the halo bias, respectively. We discuss the implications of this
correction on present and forecasted primordial non-Gaussianity constraints. We
confirm that the non-Gaussian halo bias offers a robust and highly competitive
test of primordial non-Gaussianity. | Quantifying the Colour-Dependent Stochasticity of Large-Scale Structure: We address the question of whether massive red and blue galaxies trace the
same large-scale structure at z~0.6 using the CMASS sample of galaxies from
Data Release 12 of the Sloan Digital Sky Survey III. After splitting the
catalog into subsamples of red and blue galaxies using a simple colour cut, we
measure the clustering of both subsamples and construct the correlation
coefficient, r, using two statistics. The correlation coefficient quantifies
the stochasticity between the two subsamples, which we examine over
intermediate scales (20 < R < 100 Mpc/h). We find that on these intermediate
scales, the correlation coefficient is consistent with 1; in particular, we
find r > 0.95 taking into account both statistics and r > 0.974 using the
favored statistic. |
On the Renormalization of the Effective Field Theory of Large Scale
Structures: Standard perturbation theory (SPT) for large-scale matter inhomogeneities is
unsatisfactory for at least three reasons: there is no clear expansion
parameter since the density contrast is not small on all scales; it does not
fully account for deviations at large scales from a perfect pressureless fluid
induced by short-scale non-linearities; for generic initial conditions, loop
corrections are UV-divergent, making predictions cutoff dependent and hence
unphysical. The Effective Field Theory of Large Scale Structures successfully
addresses all three issues. Here we focus on the third one and show explicitly
that the terms induced by integrating out short scales, neglected in SPT, have
exactly the right scale dependence to cancel all UV-divergences at one loop,
and this should hold at all loops. A particularly clear example is an Einstein
deSitter universe with no-scale initial conditions P_in=A k^n. After
renormalizing the theory, we use self-similarity to derive a very simple result
for the final power spectrum for any n, excluding two-loop corrections and
higher. We show how the relative importance of different corrections depend on
n. For n=-1.5, relevant for our universe, pressure and dissipative corrections
are more important than the two-loop corrections. | NuRIA: Numerical Relativity Injection Analysis of spinning binary black
hole signals in Advanced LIGO data: The advent of gravitational wave (GW) astronomy has provided us with
observations of black holes more massive than those known from X-ray astronomy.
However, the observation of an intermediate-mass black hole (IMBH) remains a
big challenge. After their second observing run, the LIGO \& Virgo Scientific
collaborations (LVC) placed upper limits on the coalescence rate density of
non-precessing IMBH binaries (IMBHBs). In this article, we explore the
sensitivity of two of the search pipelines used by the LVC to signals from 69
numerically simulated IMBHBs with generic spins, out of which 27 have a
precessing orbital plane. In particular, we compare the matched-filter search
PyCBC, and the coherent model-independent search technique cWB. We find that,
in general, cWB is more sensitive to IMBHBs than PyCBC, with their difference
depending on the masses and spins of the source. Consequently, we use cWB to
place the first upper limits on the merger rate of generically spinning IMBH
binaries using publicly available data from the first Advanced LIGO observing
run. |
S-Z power spectrum produced by primordial magnetic fields: Primordial magnetic fields generated in the very early universe are one of
the candidates for the origin of magnetic fields observed in galaxy clusters.
After recombination, the Lorentz force acts on the residual ions and electrons
to generate density fluctuations of baryons. Accordingly these fluctuations
induce the early formation of dark halos which cause the Sunyaev-Zel'dovich
(S-Z) effect in cosmic microwave background radiation. This additional S-Z
effect due to primordial magnetic fields amplifies the angular power spectrum
of cosmic microwave temperature anisotropies on small scales. This
amplification depends on the comoving amplitude and the power law index of the
primordial magnetic fields spectrum. Comparing with the small scale CMB
observations, we obtained the constraints on the primordial magnetic fields,
i.e., B < 2.0 nGauss for n=-2.9 or B < 1.0 nGauss for n=-2.6, where B is the
comoving amplitude of magnetic fields at h^-1 Mpc and n is the power law index.
Future S-Z measurements have the potential to give constraints tighter than
those from temperature anisotropies and polarization of cosmic microwave
background induced by the magnetic fields at the recombination epoch. | The Sloan Bright Arcs Survey : Discovery of Seven New Strongly Lensed
Galaxies from z=0.66-2.94: We report the discovery of seven new, very bright gravitational lens systems
from our ongoing gravitational lens search, the Sloan Bright Arcs Survey
(SBAS). Two of the systems are confirmed to have high source redshifts z=2.19
and z=2.94. Three other systems lie at intermediate redshift with
z=1.33,1.82,1.93 and two systems are at low redshift z=0.66,0.86. The lensed
source galaxies in all of these systems are bright, with i-band magnitudes
ranging from 19.73-22.06. We present the spectrum of each of the source
galaxies in these systems along with estimates of the Einstein radius for each
system. The foreground lens in most systems is identified by a red sequence
based cluster finder as a galaxy group; one system is identified as a
moderately rich cluster. In total the SBAS has now discovered 19 strong lens
systems in the SDSS imaging data, 8 of which are among the highest surface
brightness z\simeq2-3 galaxies known. |
Tying Dark Matter to Baryons with Self-interactions: Self-interacting dark matter (SIDM) models have been proposed to solve the
small-scale issues with the collisionless cold dark matter (CDM) paradigm. We
derive equilibrium solutions in these SIDM models for the dark matter halo
density profile including the gravitational potential of both baryons and dark
matter. Self-interactions drive dark matter to be isothermal and this ties the
core sizes and shapes of dark matter halos to the spatial distribution of the
stars, a radical departure from previous expectations and from CDM predictions.
Compared to predictions of SIDM-only simulations, the core sizes are smaller
and the core densities are higher, with the largest effects in baryon-dominated
galaxies. As an example, we find a core size around 0.5 kpc for dark matter in
the Milky Way, more than an order of magnitude smaller than the core size from
SIDM-only simulations, which has important implications for indirect searches
of SIDM candidates. | ISM enrichment and local pollution in dwarf galaxies: The fate of metals after they are released in starburst episodes is still
unclear. What phases of the interstellar medium are involved, in which
timescales? Evidence has grown over the past few years that the neutral phase
of blue compact dwarf (BCD) galaxies may be metal- deficient as compared to the
ionized gas of their HII regions. These results have strong implications for
our understanding of the chemical evolution of galaxies. We review here the
main results and the main caveats in the abundance determination from far-UV
absorption-lines. We also discuss possible scenarios concerning the journey of
metals into the interstellar medium, or even their ejection from the galaxy
into the intergalactic medium. |
SPMHD simulations of Structure Formation: The intracluster medium of galaxy clusters is permeated by {\mu}G magnetic
fields. Observations with current and future facilities have the potential to
illuminate the role of these magnetic fields play in the astrophysical
processes of galaxy clusters. To obtain a greater understanding of how the
initial seed fields evolve to the magnetic fields in the intracluster medium
requires magnetohydrodynamic simulations. We critically assess the current
Smoothed Particle Magneto-Hydrodynamics (SPMHD) schemes, especially
highlighting the impact of a hyperbolic divergence cleaning scheme and
artificial resistivity switch on the magnetic field evolution in cosmological
simulations of the formation of a galaxy cluster using the N-body/SPMHD code
gcmhd++. The impact and performance of the cleaning scheme and two different
schemes for the artificial resistivity switch is demonstrated via idealized
test cases and cosmological simulations. We demonstrate that the hyperbolic
divergence cleaning scheme is effective at suppressing the growth of the
numerical divergence error of the magnetic field and should be applied to any
SPMHD simulation. Although the artificial resistivity is important in the
strong field regime, it can suppress the growth of the magnetic field in the
weak field regime, such as galaxy clusters. With sufficient resolution,
simulations with divergence cleaning can reproduce observed magnetic fields. We
conclude that the cleaning scheme alone is sufficient for galaxy cluster
simulations, but our results indicate that the SPMHD scheme must be carefully
chosen depending on the regime of the magnetic field. | Higgs Dark Energy: We study the classical dynamics of a non-abelian Higgs theory coupled to
gravity in an isotropic and homogeneous Universe. For non-minimal coupling,
this theory leads to a model of cosmic inflation that is very attractive due to
its simplicity and consistency with the latest experimental data. We show that
this theory can also explain the current accelerated expansion of the Universe,
provided that all the gravitational and bosonic degrees of freedom, together
with their symmetries, are correctly taken in account. |
Gas Accretion in the M32 Nucleus: Past & Present: Using adaptive optics assisted Gemini/NIFS data, I study the present and past
gas accretion in the central 3" of the M32 nucleus. From changes in the
spectral slope and CO line depths near the center, I find evidence for
unresolved dust emission resulting from BH accretion. With a luminosity of
~2e38 erg/s, this dust emission appears to be the most luminous tracer of
current BH accretion, two orders of magnitude more luminous than previously
detected X-ray emission. These observations suggest that using high resolution
infrared data to search for dust emission may be an effective way to detect
other nearby, low luminosity BHs, such as those in globular clusters. I also
examine the fossil evidence of gas accretion contained in the kinematics of the
stars in the nucleus. The higher-order moments (h3 and h4) of the line-of-sight
velocity distribution show patterns that are remarkably similar to those seen
on larger scales in elliptical galaxies and in gas-rich merger simulations. The
kinematics suggests the presence of two components in the M32 nucleus, a
dominant disk overlying a pressure supported component. I discuss possible
formation scenarios for the M32 nucleus in the context of the kinematic data as
well as previous stellar population studies. The kinematic measurements
presented here are the highest quality available for the nucleus of M32, and
may be useful for any future dynamical models of this benchmark system. | The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a
shallow and wide submillimeter imaging survey with SPIRE: A large sub-mm survey with Herschel will enable many exciting science
opportunities, especially in an era of wide-field optical and radio surveys and
high resolution cosmic microwave background experiments. The Herschel-SPIRE
Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250,
350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3
million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion
noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere
(3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which
have extensive multi-wavelength coverage and are easily accessible from ALMA.
Two thirds of the of the sources are expected to be at z > 1, one third at z >
2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary
anisotropy studies with Planck and ground-based CMB data. (c) Find at least
1200 strongly lensed bright sub-mm sources leading to a 2% test of general
relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an
unbiased study of the environmental dependence of star formation. (e) Perform
an unbiased survey for star formation and dust at high Galactic latitude and
make a census of debris disks and dust around AGB stars and white dwarfs. |
Why are there strong radio AGNs in the center of "non-cool core"
clusters?: Radio AGN feedback in X-ray cool cores has been proposed as a crucial
ingredient in the evolution of baryonic structures. However, it has long been
known that strong radio AGNs also exist in "noncool core" clusters, which
brings up the question whether an X-ray cool core is always required for radio
feedback. We present a systematic analysis of 152 groups and clusters to show
that every BCG with a strong radio AGN has an X-ray cool core. Those strong
radio AGNs in the center of the "noncool core" systems identified before are in
fact associated with small X-ray cool cores with typical radii of < 5 kpc (we
call them coronae). Small coronae are most likely of ISM origin and they carry
enough fuel to power radio AGNs. Our results suggest that the traditional cool
core/noncool core dichotomy is too simple. A better alternative is the cool
core distribution function with the enclosed X-ray luminosity. Other
implications of our results are also discussed, including a warning on the
simple extrapolation of the density profile to derive Bondi accretion rate. | Fast Calculation of Nonlinear Redshift-space Galaxy Power Spectrum
Including Selection Bias: We present a fast implementation of the next-to-leading order (1-loop)
redshift-space galaxy power spectrum by using FFTlog-based methods. [V.
Desjacques, D. Jeong, and F. Schmidt, JCAP 1812 (12), 035] have shown that the
1-loop galaxy power spectrum in redshift space can be computed with 28
independent loop integrals with 22 bias parameters. Analytical calculation of
the angular part of the loop integrals leaves the radial part in the form of a
spherical Bessel transformation that is ready to be integrated numerically by
using the FFTLog transformation. We find that the original 28 loop integrals
can be solved with a total of 85 unique FFTLog transformations, yet leading to
a few orders of magnitude speed up over traditional multi-dimensional
integration. The code used in this work is publicly available at
https://github.com/JosephTomlinson/GeneralBiasPk |
MERGHERS Pilot: MeerKAT discovery of diffuse emission in nine massive
Sunyaev-Zel'dovich-selected galaxy clusters from ACT: The MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio
Sources (MERGHERS) survey is a planned project to study a large statistical
sample of galaxy clusters with the MeerKAT observatory. Here we present the
results of a 16--hour pilot project, observed in response to the 2019 MeerKAT
Shared Risk proposal call, to test the feasibility of using MeerKAT for a large
cluster study using short (0.2--2.1\,hour) integration times. The pilot focuses
on 1.28\,GHz observations of 13 massive, low-to-intermediate redshift ($0.22 <
z < 0.65$) clusters from the Sunyaev-Zel'dovich-selected Atacama Cosmology
Telescope (ACT) DR5 catalogue that show multiwavelength indications of
dynamical disturbance. With a 70 per cent detection rate (9/13 clusters), this
pilot study validates our proposed MERGHERS observing strategy and provides
twelve detections of diffuse emission, eleven of them new, indicating the
strength of MeerKAT for such types of studies. The detections (signal-to-noise
ratio $\gtrsim6$) are summarised as follows: two systems host both relic(s) and
a giant radio halo, five systems host radio halos, and two have candidate radio
halos. Power values, $k$-corrected to 1.4 GHz assuming a fiducial spectral
index of $\alpha = -1.3 \pm 0.4$, are consistent with known radio halo and
relic scaling relations. | Measuring the Mass Distribution in Galaxy Clusters: Cluster mass profiles are tests of models of structure formation. Only two
current observational methods of determining the mass profile, gravitational
lensing and the caustic technique, are independent of the assumption of
dynamical equilibrium. Both techniques enable determination of the extended
mass profile at radii beyond the virial radius. For 19 clusters, we compare the
mass profile based on the caustic technique with weak lensing measurements
taken from the literature. This comparison offers a test of systematic issues
in both techniques. Around the virial radius, the two methods of mass
estimation agree to within about 30%, consistent with the expected errors in
the individual techniques. At small radii, the caustic technique overestimates
the mass as expected from numerical simulations. The ratio between the lensing
profile and the caustic mass profile at these radii suggests that the weak
lensing profiles are a good representation of the true mass profile. At radii
larger than the virial radius, the lensing mass profile exceeds the caustic
mass profile possibly as a result of contamination of the lensing profile by
large-scale structures within the lensing kernel. We highlight the case of the
closely neighboring clusters MS0906+11 and A750 to illustrate the potential
seriousness of contamination of the the weak lensing signal by unrelated
structures. |
Structural Parameters of Galaxies in CANDELS: We present global structural parameter measurements of 109,533 unique,
H_F160W-selected objects from the CANDELS multi-cycle treasury program. Sersic
model fits for these objects are produced with GALFIT in all available
near-infrared filters (H_F160W, J_F125W and, for a subset, Y_F105W). The
parameters of the best-fitting Sersic models (total magnitude, half-light
radius, Sersic index, axis ratio, and position angle) are made public, along
with newly constructed point spread functions for each field and filter. Random
uncertainties in the measured parameters are estimated for each individual
object based on a comparison between multiple, independent measurements of the
same set of objects. To quantify systematic uncertainties we create a mosaic
with simulated galaxy images with a realistic distribution of input parameters
and then process and analyze the mosaic in an identical manner as the real
data. We find that accurate and precise measurements -- to 10% or better -- of
all structural parameters can typically be obtained for galaxies with H_F160W <
23, with comparable fidelity for basic size and shape measurements for galaxies
to H_F160W ~ 24.5. | Shape of Clusters as a Probe of Screening Mechanisms in Modified Gravity: Scalar fields are crucial components in high energy physics and extensions of
General Relativity. The fact they are not observed in the solar system may be
due to a mechanism which screens their presence in high dense regions. We show
how observations of the ellipticity of galaxy clusters can discriminate between
models with and without scalar fields and even between different screening
mechanisms. Using nowadays X-ray observations we put novel constraints on the
different models. |
Superhorizon perturbations: A possible explanation of the
Hubble--Lemaître Tension and the Large Scale Anisotropy of the Universe: Current cosmological observations point to a serious discrepancy between the
observed Hubble parameter obtained using direct and cosmic microwave background
radiation (CMBR) measurements. Besides this, the so called Hubble--Lema\^itre
tension, we also find considerable evidence in diverse cosmological observables
that indicate violation of the cosmological principle. In this paper, we
suggest that both these discrepancies are related and can be explained by
invoking superhorizon perturbations in the Universe. We implement this by
considering a single superhorizon mode and showing that it leads to both a
dipole in large scale structures and a shift in the Hubble--Lema\^itre
parameter. Furthermore, the shift is found to be independent of redshift up to
a certain distance. This is nicely consistent with the data. | Constraints on scalar and tensor perturbations in phenomenological and
two-field inflation models: Bayesian evidences for primordial isocurvature
and tensor modes: We constrain cosmological models where the primordial perturbations have both
an adiabatic and a (possibly correlated) cold dark matter (CDM) or baryon
isocurvature component. We use both a phenomenological approach, where the
primordial power spectra are parametrized with amplitudes and spectral indices,
and a slow-roll two-field inflation approach where slow-roll parameters are
used as primary parameters. In the phenomenological case, with CMB data, the
upper limit to the CDM isocurvature fraction is \alpha<6.4% at k=0.002Mpc^{-1}
and 15.4% at k=0.01Mpc^{-1}. The median 95% range for the non-adiabatic
contribution to the CMB temperature variance is -0.030<\alpha_T<0.049.
Including the supernova (or large-scale structure, LSS) data, these limits
become: \alpha<7.0%, 13.7%, and -0.048<\alpha_T< 0.042 (or \alpha<10.2%, 16.0%,
and -0.071<\alpha_T<0.024). The CMB constraint on the tensor-to-scalar ratio,
r<0.26 at k=0.01Mpc^{-1}, is not affected by the nonadiabatic modes. In the
slow-roll two-field inflation approach, the spectral indices are constrained
close to 1. This leads to tighter limits on the isocurvature fraction, with the
CMB data \alpha<2.6% at k=0.01Mpc^{-1}, but the constraint on \alpha_T is not
much affected, -0.058<\alpha_T<0.045. Including SN (or LSS) data, these limits
become: \alpha< 3.2% and -0.056<\alpha_T<0.030 (or \alpha<3.4% and
-0.063<\alpha_T<-0.008). When all spectral indices are close to each other the
isocurvature fraction is somewhat degenerate with the tensor-to-scalar ratio.
In addition to the generally correlated models, we study also special cases
where the perturbation modes are uncorrelated or fully (anti)correlated. We
calculate Bayesian evidences (model probabilities) in 21 different cases for
our nonadiabatic models and for the corresponding adiabatic models, and find
that in all cases the data support the pure adiabatic model. |
Degeneracy between nonadiabatic dark energy models and $Λ$CDM: ISW
effect and the cross correlation of CMB with galaxy clustering data: As recently pointed out in Ref. [Phys.\ Rev.\ D {\bf 96}, 8, 083502 (2017)]
the evolution of the linear matter perturbations in nonadiabatic dynamical dark
energy models is almost indistinguishable (quasi-degenerated) to the standard
$\Lambda$CDM scenario. In this work we extend this analysis to CMB observables
in particular the integrated Sachs-Wolfe effect and its cross-correlation with
large scale structure. We find that this feature persists for such CMB related
observable reinforcing that new probes and analysis are necessary to reveal the
nonadiabatic features in the dark energy sector. | A Magellan-IMACS-IFU Search for Dynamical Drivers of Nuclear Activity.
I. Reduction Pipeline and Galaxy Catalog: Using the Inamori Magellan Areal Camera and Spectrograph (IMACS)
integral-field unit (IFU) on the 6.5m Magellan telescope, we have designed the
first statistically significant investigation of the two-dimensional
distribution and kinematics of ionized gas and stars in the central kiloparsec
regions of a well-matched sample of Seyfert and inactive control galaxies
selected from the Sloan Digital Sky Survey. The goals of the project are to use
the fine spatial sampling (0.2 arcsec/pixel) and large wavelength coverage
(4000-7000A) of the IMACS-IFU to search for dynamical triggers of nuclear
activity in the central region where active galactic nucleus (AGN) activity and
dynamical timescales become comparable, to identify and assess the impact of
AGN-driven outflows on the host galaxy and to provide a definitive sample of
local galaxy kinematics for comparison with future three-dimensional kinematic
studies of high-redshift systems. In this paper, we provide the first detailed
description of the procedure to reduce and calibrate data from the IMACS-IFU in
`long mode' to obtain two-dimensional maps of the distribution and kinematics
of ionized gas and stars. The sample selection criteria are presented,
observing strategy described and resulting maps of the sample galaxies
presented along with a description of the observed properties of each galaxy
and the overall observed properties of the sample. |
The HI content of dark matter halos at $z\approx 0$ from ALFALFA: We combine information from the clustering of HI galaxies in the 100% data
release of the Arecibo Legacy Fast ALFA survey (ALFALFA), and from the HI
content of optically-selected galaxy groups found in the Sloan Digital Sky
Survey (SDSS) to constrain the relation between halo mass $M_h$ and its average
total HI mass content $M_{\rm HI}$. We model the abundance and clustering of
neutral hydrogen through a halo-model-based approach, parametrizing the $M_{\rm
HI}(M_h)$ relation as a power law with an exponential mass cutoff. To break the
degeneracy between the amplitude and low-mass cutoff of the $M_{\rm HI}(M_h)$
relation, we also include a recent measurement of the cosmic HI abundance from
the $\alpha$.100 sample. We find that all datasets are consistent with a
power-law index $\alpha=0.44\pm 0.08$ and a cutoff halo mass $\log_{10}M_{\rm
min}/(h^{-1}M_\odot)=11.27^{+0.24}_{-0.30}$. We compare these results with
predictions from state-of-the-art magneto-hydrodynamical simulations, and find
both to be in good qualitative agreement, although the data favours a
significantly larger cutoff mass that is consistent with the higher cosmic HI
abundance found in simulations. Both data and simulations seem to predict a
similar value for the HI bias ($b_{\rm HI}=0.875\pm0.022$) and shot-noise power
($P_{\rm SN}=92^{+20}_{-18}\,[h^{-1}{\rm Mpc}]^3$) at redshift $z=0$. | Gravity in the Era of Equality: Towards solutions to the Hubble problem
without fine-tuned initial conditions: Discrepant measurements of the Universe's expansion rate ($H_0$) may signal
physics beyond the standard cosmological model. Here I describe two early
modified gravity mechanisms that reconcile the value of $H_0$ by increasing the
expansion rate in the era of matter-radiation equality. These mechanisms, based
on viable Horndeski theories, require significantly less fine-tuned initial
conditions than early dark energy with oscillating scalar fields. In Imperfect
Dark Energy at Equality (IDEE), the initial energy density dilutes slower than
radiation but faster than matter, naturally peaking around the era of equality.
The minimal IDEE model, a cubic Galileon, is too constrained by the cosmic
microwave background (Planck) and baryon acoustic oscillations (BAO) to relieve
the $H_0$ tension. In Enhanced Early Gravity (EEG), the scalar field value
modulates the cosmological strength of gravity. The minimal EEG model, an
exponentially coupled cubic Galileon, gives a Planck+BAO value $H_0=68.7 \pm
1.5$ (68\% c.l.), reducing the tension with SH0ES from $4.4\sigma$ to
$2.6\sigma$. Additionally, Galileon contributions to cosmic acceleration may
reconcile $H_0$ via Late-Universe Phantom Expansion (LUPE). Combining LUPE, EEG
and $\Lambda$ reduces the tension between Planck, BAO and SH0ES to $2.5\sigma$.
I will also describe additional tests of coupled Galileons based on local
gravity tests, primordial element abundances and gravitational waves. While
further model building is required to fully resolve the $H_0$ problem and
satisfy all available observations, these examples show the wealth of
possibilities to solve cosmological tensions beyond Einstein's General
Relativity. |
The Calibration of Monochromatic Far-Infrared Star Formation Rate
Indicators: (Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha
images are analyzed for a sample of 189 nearby star-forming and starburst
galaxies to investigate whether reliable star formation rate (SFR) indicators
can be defined using the monochromatic infrared dust emission centered at 70
and 160 micron. We compare recently published recipes for SFR measures using
combinations of the 24 micron and observed H-alpha luminosities with those
using 24 micron luminosity alone. From these comparisons, we derive a reference
SFR indicator for use in our analysis. Linear correlations between SFR and the
70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and
L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those
two luminosity limits, the relation between SFR and 70 micron (160 micron)
luminosity is non-linear and SFR calibrations become problematic. The
dispersion of the data around the mean trend increases for increasing
wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24
micron. The increasing dispersion is likely an effect of the increasing
contribution to the infrared emission of dust heated by stellar populations not
associated with the current star formation. The non-linear relation between SFR
and the 70 and 160 micron emission at faint galaxy luminosities suggests that
the increasing transparency of the interstellar medium, decreasing effective
dust temperature, and decreasing filling factor of star forming regions across
the galaxy become important factors for decreasing luminosity. The SFR
calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1.
At lower metallicity the infrared luminosity no longer reliably traces the SFR
because galaxies are less dusty and more transparent. | Cosmic axion thermalization: Axions differ from the other cold dark matter candidates in that they form a
degenerate Bose gas. It is shown that their huge quantum degeneracy and large
correlation length cause cold dark matter axions to thermalize through
gravitational self-interactions when the photon temperature reaches
approximately 500 eV. When they thermalize, the axions form a Bose-Einstein
condensate. Their thermalization occurs in a regime, herein called the
`condensed regime', where the Boltzmann equation is not valid because the
energy dispersion of the particles is smaller than their interaction rate. We
derive analytical expressions for the thermalization rate of particles in the
condensed regime, and check the validity of these expressions by numerical
simulation of a toy model. We revisit axion cosmology in light of axion
Bose-Einstein condensation. It is shown that axions are indistinguishable from
ordinary cold dark matter on all scales of observational interest, except when
they thermalize or rethermalize. The rethermalization of axions that are about
to fall in a galactic potential well causes them to acquire net overall
rotation as they go to the lowest energy state consistent with the total
angular momentum they acquired by tidal torquing. This phenomenon explains the
occurrence of caustic rings of dark matter in galactic halos. We find that
photons may reach thermal contact with axions and investigate the implications
of this possibility for the measurements of cosmological parameters. |
The DiskMass Survey. VII. The distribution of luminous and dark matter
in spiral galaxies: We present dynamically-determined rotation-curve mass decompositions of 30
spiral galaxies, which were carried out to test the maximum-disk hypothesis and
to quantify properties of their dark-matter (DM) halos. We used measured
vertical velocity dispersions of the disk stars to calculate dynamical mass
surface densities. Together with our atomic and molecular gas mass surface
densities, we derived the stellar mass surface densities, and thus have
absolute measurements of all dominant baryonic components. Using K-band surface
brightness profiles, we calculated the K-band mass-to-light ratio of the
stellar disks (M/L). Our result is consistent with all galaxies in the sample
having equal M/L, with a sample average and scatter of <M/L>=0.31+/-0.07.
Rotation-curves of the baryonic components were calculated from their mass
surface densities, and used with circular-speed measurements to derive the
structural parameters of the DM halos, modeled as either a pseudo-isothermal
sphere (pISO) or an NFW halo. All galaxies in our sample are submaximal, such
that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total
rotation-curves (Fb^{2.2hR}) are less than 0.75. We find this ratio to be
nearly constant between 1-6 hR within individual galaxies. We find a sample
average and scatter of <Fb^{2.2hR}>=0.57+/-0.07, with trends of larger
Fb^{2.2hR} for more luminous and higher-surface-brightness galaxies. To enforce
these being maximal, we need to scale M/L by a factor 3.6 on average. The DM
rotation curves are marginally better fit by a pISO than by an NFW halo. For
the nominal-M/L (submaximal) case, the derived NFW-halo parameters have values
consistent with LCDM N-body simulations, suggesting that the baryonic matter
has only had a minor effect on the DM distribution. In contrast, maximum-M/L
decompositions yield halo concentrations that are too low compared to the LCDM
simulations. | Primordial Nucleosynthesis After WMAP: During its early evolution, the hot, dense Universe provided a laboratory for
probing fundamental physics at high energies. By studying the relics from those
early epochs, such as the light elements synthesized during primordial
nucleosynthesis when the Universe was only a few minutes old, and the relic,
cosmic microwave photons, last scattered when the protons, alphas, and
electrons (re)combined some 400 thousand years later, the evolution of the
Universe may be used to test the standard models of cosmology and particle
physics and to set constraints on proposals of physics beyond these standard
models. |
The VMC Survey - VI. Quasars behind the Magellanic system: The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for different types of studies. We have searched
for criteria to identify candidate QSOs using observations from the VISTA
survey of the Magellanic Clouds system (VMC) that provides photometry in the
YJKs bands and 12 epochs in the Ks band. The (Y-J) versus (J-Ks) diagram has
been used to distinguish QSO candidates from Milky Way stars and stars of the
Magellanic Clouds. Then, the slope of variation in the Ks band has been used to
identify a sample of high confidence candidates. These criteria were developed
based on the properties of 117 known QSOs presently observed by the VMC survey.
VMC YJKs magnitudes and Ks light-curves of known QSOs behind the Magellanic
system are presented. About 75% of them show a slope of variation in Ks>10^-4
mag/day and the shape of the light-curve is in general irregular and without
any clear periodicity. The number of QSO candidates found in tiles including
the South Ecliptic Pole and the 30 Doradus regions is 22 and 26, respectively,
with a ~20% contamination by young stellar objects, planetary nebulae, stars
and normal galaxies. By extrapolating the number of QSO candidates to the
entire VMC survey area we expect to find about 1200 QSOs behind the LMC, 400
behind the SMC, 200 behind the Bridge and 30 behind the Stream areas, but not
all will be suitable for astrometry. Further, the Ks band light-curves can help
support investigations of the mechanism responsible for the variations. | In-flight polarization angle calibration for LiteBIRD: blind challenge
and cosmological implications: We present a demonstration of the in-flight polarization angle calibration
for the JAXA/ISAS second strategic large class mission, LiteBIRD, and estimate
its impact on the measurement of the tensor-to-scalar ratio parameter, r, using
simulated data. We generate a set of simulated sky maps with CMB and polarized
foreground emission, and inject instrumental noise and polarization angle
offsets to the 22 (partially overlapping) LiteBIRD frequency channels. Our
in-flight angle calibration relies on nulling the EB cross correlation of the
polarized signal in each channel. This calibration step has been carried out by
two independent groups with a blind analysis, allowing an accuracy of the order
of a few arc-minutes to be reached on the estimate of the angle offsets. Both
the corrected and uncorrected multi-frequency maps are propagated through the
foreground cleaning step, with the goal of computing clean CMB maps. We employ
two component separation algorithms, the Bayesian-Separation of Components and
Residuals Estimate Tool (B-SeCRET), and the Needlet Internal Linear Combination
(NILC). We find that the recovered CMB maps obtained with algorithms that do
not make any assumptions about the foreground properties, such as NILC, are
only mildly affected by the angle miscalibration. However, polarization angle
offsets strongly bias results obtained with the parametric fitting method. Once
the miscalibration angles are corrected by EB nulling prior to the component
separation, both component separation algorithms result in an unbiased
estimation of the r parameter. While this work is motivated by the conceptual
design study for LiteBIRD, its framework can be broadly applied to any CMB
polarization experiment. In particular, the combination of simulation plus
blind analysis provides a robust forecast by taking into account not only
detector sensitivity but also systematic effects. |
The Araucaria Project. The distance to the Small Magellanic Cloud from
late-type eclipsing binaries: We present a distance determination to the Small Magellanic Cloud (SMC) based
on an analysis of four detached, long period, late type eclipsing binaries
discovered by the OGLE Survey. The components of the binaries show negligible
intrinsic variability. A consistent set of stellar parameters was derived with
low statistical and systematic uncertainty. The absolute dimensions of the
stars are calculated with a precision of better than 3%.
The surface brightness - infrared color relation was used to derive the
distance to each binary. The four systems clump around a distance modulus of (m
- M)=18.99 with a dispersion of only 0.05 mag. Combining these results with the
distance published by Graczyk et al. for the eclipsing binary OGLE SMC113.3
4007 we obtain a mean distance modulus to the SMC of 18.965 +/- 0.025 (stat.)
+/- 0.048 (syst.) mag. This corresponds to a distance of 62.1 +/- 1.9 kpc,
where the error includes both uncertainties. Taking into account other recent
published determinations of the SMC distance we calculated the distance modulus
difference between the SMC and the LMC equal to 0.458 +/- 0.068 mag. Finally we
advocate mu_{SMC}=18.95 +/- 0.07 as a new "canonical" value of the distance
modulus to this galaxy. | Non-Equilibrium Populations of Hydrogen in High-Redshift Galaxies: We investigate the possibility of maser amplification in hydrogen
recombination lines from the galaxies of first generation, at z<~30. Combining
analytical and computational approaches, we show that the transitions between
the hydrogen Rydberg energy levels induced by the radiation from the ionizing
star and by the (warmer than currently) Cosmic Microwave Background can produce
noticeable differences in the population distribution, as compared with
previous computations for the contemporary H+ regions, most of which ignored
the processes induced by the star radiation. In particular, the low (n<~30)
alpha-transitions show an increased tendency toward population inversion, when
ionization of the H+ region is caused by a very hot star at high redshift. The
resulting maser/laser amplification can increase the brightness of the emitted
lines and make them detectable. However, the limiting effects of maser
saturation will probably not allow maser gains to exceed one or two orders of
magnitude. |
Multicolour Photometric Study of M31 Globular Clusters: We present the photometry of 30 globular clusters (GCs) and GC candidates in
15 intermediate-band filters covering from ~3000 to ~10000 \AA using the
archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan -
Connecticut (BATC) Multicolour Sky Survey. We transform these intermediate-band
photometric data to the photometry in the standard UBVRI broad-bands. These M31
GC candidates are selected from the Revised Bologna Catalogue (RBC V.3.5), and
most of these candidates do not have any photometric data. Therefore the
present photometric data are supplement to RBC V.3.5. We find that 4 out of 61
GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at
their locations. By linear fit of the distribution in colour-magnitude diagram
of blue GCs and GC candidates using the data from RBC V.3.5, and in this study
we find the ``blue-tilt'' of blue M31 GCs with a high confidence at 99.95% or
3.47 sigma for the confirmed GCs, and >99.99% or 4.87 sigma for GCs and GC
candidates. | Determination of Dark Energy by the Einstein Telescope: Comparing with
CMB, BAO and SNIa Observations: A design study is currently in progress for a third generation
gravitational-wave (GW) detector called Einstein Telescope (ET). An important
kind of source for ET will be the inspiral and merger of binary neutron stars
(BNS) up to $z \sim 2$. If BNS mergers are the progenitors of short-hard
$\gamma$-ray bursts, then some fraction of them will be seen both
electromagnetically and through GW, so that the luminosity distance and the
redshift of the source can be determined separately. An important property of
these `standard sirens' is that they are \emph{self-calibrating}: the
luminosity distance can be inferred directly from the GW signal, with no need
for a cosmic distance ladder. Thus, standard sirens will provide a powerful
independent check of the $\Lambda$CDM model. In previous work, estimates were
made of how well ET would be able to measure a subset of the cosmological
parameters (such as the dark energy parameter $w_0$) it will have access to,
assuming that the others had been determined to great accuracy by alternative
means. Here we perform a more careful analysis by explicitly using the
potential Planck CMB data as prior information for these other parameters. We
find that ET will be able to constrain $w_0$ and $w_a$ with accuracies $\Delta
w_0 = 0.099$ and $\Delta w_a = 0.302$, respectively. These results are compared
with projected accuracies for the JDEM Baryon Acoustic Oscillations project and
the SNAP Type Ia supernovae observations. |
No evidence for modifications of gravity from galaxy motions on
cosmological scales: The recent discovery of gravitational waves marks the culmination of a
sequence of successful tests of the general theory of relativity (GR) since its
formulation in 1915. Yet these tests remain confined to the scale of stellar
systems or the strong gravity regime. A departure from GR on larger,
cosmological scales has been advocated by the proponents of modified gravity
theories as an alternative to the Cosmological Constant to account for the
observed cosmic expansion history. While indistinguishable in these terms by
construction, such models on the other hand yield distinct values for the
linear growth rate of density perturbations and, as a consequence, for the
associated galaxy peculiar velocity field. Measurements of the resulting
anisotropy of galaxy clustering, when spectroscopic redshifts are used to
derive distances, have thus been proposed as a powerful probe of the validity
of GR on cosmological scales. However, despite significant effort in modelling
such redshift space distortions, systematic errors remain comparable to current
statistical uncertainties. Here, we present the results of a different
forward-modelling approach, which fully exploits the sensitivity of the galaxy
velocity field to modifications of GR. We use state-of-the-art, high-resolution
N-body simulations of a standard GR and a compelling f(R) model, one of GR's
simplest variants, to build simulated catalogues of stellar-mass-selected
galaxies through a robust match to the Sloan Digital Sky Survey observations.
We find that, well within the uncertainty of this technique, f(R) fails to
reproduce the observed redshift-space clustering on scales 1-10 Mpc/h. Instead,
the standard LCDM GR model agrees impressively well with the data. This result
provides a strong confirmation, on cosmological scales, of the robustness of
Einstein's general theory of relativity. | Quest for potentials in the quintessence scenario: The time variation of the equation of state $w$ for quintessence scenario
with a scalar field as dark energy is studied up to the third derivative
($d^3w/da^3$) with respect to the scale factor $a$, in order to predict the
future observations and specify the scalar potential parameters with the
observables. The third derivative of $w$ for general potential $V$ is derived
and applied to several types of potentials. They are the inverse power-law
($V=M^{4+\alpha}/Q^{\alpha}$), the exponential ($V=M^4\exp{(\beta M/Q)}$), the
cosine ($V=M^4(\cos (Q/f)+1)$) and the Gaussian types
($V=M^4\exp(-Q^2/\sigma^2)$), which are prototypical potentials for the
freezing and thawing models.
If the parameter number for a potential form is $ n$, it is necessary to find
at least for $n+2$ independent observations to identify the potential form and
the evolution of the scalar field ($Q$ and $ \dot{Q} $).
Such observations would be the values of $ \Omega_Q, w, dw/da. \cdots $, and
$ dw^n/da^n$.
Since four of the above mentioned potentials have two parameters, it is
necessary to calculate the third derivative of $w$ for them to estimate the
predict values.
If they are tested observationally, it will be understood whether the dark
energy could be described by the scalar field with this potential.
Numerical analysis for $d^3w/da^3$ are made under some specified parameters
in the investigated potentials.
It becomes possible to distinguish the freezing and thawing modes by the
accurate observing $dw/da$ and $d^2w/da^2$ in some parameters. |
Constraining H0 from Lyman-alpha Forest and Baryon Acoustic Oscillations: A new method is proposed to measure the Hubble constant H0 through the mean
transmitted flux observed from high redshift quasars. A semi-analytical model
for the cosmological-independent volume density distribution function is
adopted which allows one to obtain constraints over the cosmological parameters
once a moderate knowlegde of the InterGalactic Medium (IGM) parameters is
assumed. By assuming a flat LCDM cosmology, we show that such method alone
cannot provide good constraints on the pair of free parameters (h, Omega_m).
However, it is possible possible to break the degeneracy on the mass density
parameter by applying a joint analysis involving the baryon acoustic
oscillations (BAOs). Our analysis based on two different samples of Lyman-alpha
forest restricts the parameters on the intervals 0.58 < h < 0.91 and 0.215 <
Omega_m < 0.245 (1 sigma). Although the constraints are weaker comparatively to
other estimates, we point out that with a bigger sample and a better knowledge
of the IGM this method may present competitive results to measure the Hubble
constant independently of the cosmic distance ladder. | The GRB luminosity function in the internal shock model confronted to
observations: We compute the expected luminosity function of GRBs in the context of the
internal shock model. We assume that GRB central engines generate relativistic
outflows characterized by the respective distributions of injected kinetic
power Edot and contrast in Lorentz factor Kappa = Gamma_max/Gamma_min. We find
that if the distribution of contrast extends down to values close to unity
(i.e. if both highly variable and smooth outflows can exist) the luminosity
function has two branches. At high luminosity it follows the distribution of
Edot while at low luminosity it is close to a power law of slope -0.5. We then
examine if existing data can constrain the luminosity function. Using the log N
- log P curve, the Ep distribution of bright BATSE bursts and the XRF/GRB ratio
obtained by HETE2 we show that single and broken power-laws can provide equally
good fits of these data. Present observations are therefore unable to favor one
form of the other. However when a broken power-law is adopted they clearly
indicate a low luminosity slope ~ -0.6 +- 0.2, compatible with the prediction
of the internal shock model. |
Constraints on cosmic strings from ultracompact minihalos: Cosmic strings are expected to form loops. These can act as seeds for
accretion of dark matter, leading to the formation of ultracompact minihalos
(UCMHs). We perform a detailed study of the accretion of dark matter onto
cosmic string loops and compute the resulting mass distribution of UCMHs. We
then apply observational limits on the present-day abundance of UCMHs to derive
corresponding limits on the cosmic string tension $G\mu$. The bounds are
strongly dependent upon the assumed distribution of loop velocities and their
impacts on UCMH formation. Under the assumption that a loop can move up to a
thousand times its own radius and still form a UCMH, we find a limit of
$G\mu\le 5\times10^{-8}$. We show, in opposition to previous results, that
strong limits on the cosmic string tension are not obtainable from UCMHs when
more stringent (and realistic) requirements are placed on loop velocities. | Non-gaussianity in axion Nflation models: We study perturbations in the multi-field axion Nflation model, taking
account of the full cosine potential. We find significant differences with
previous analyses which made a quadratic approximation to the potential. The
tensor-to-scalar ratio and the scalar spectral index move to lower values,
which nevertheless provide an acceptable fit to observation. Most
significantly, we find that the bispectrum non-gaussianity parameter f_NL may
be large, typically of order 10 for moderate values of the axion decay
constant, increasing to of order 100 for decay constants slightly smaller than
the Planck scale. Such a non-gaussian fraction is detectable. We argue that
this property is generic in multi-field models of hilltop inflation. |
LoCuSS: Calibrating Mass-Observable Scaling Relations for Cluster
Cosmology with Subaru Weak Lensing Observations: We present a joint weak-lensing/X-ray study of galaxy cluster mass-observable
scaling relations, motivated by the critical importance of accurate calibration
of mass proxies for future X-ray missions, including eROSITA. We use a sample
of 12 clusters at z\simeq0.2 that we have observed with Subaru and XMM-Newton
to construct relationships between the weak-lensing mass (M), and three X-ray
observables: gas temperature (T), gas mass (Mgas), and quasi-integrated gas
pressure (Yx) at overdensities of \Delta=2500, 1000, and 500 with respect to
the critical density. We find that Mgas at \Delta\le1000 appears to be the most
promising mass proxy of the three, because it has the lowest intrinsic scatter
in mass at fixed observable: \sigma_lnM\simeq0.1, independent of cluster
dynamical state. The scatter in mass at fixed T and Yx is a factor of \sim2-3
larger than at fixed Mgas, which are indicative of the structural segregation
that we find in the M-T and M-Yx relationships. Undisturbed clusters are found
to be \sim40% and \sim20% more massive than disturbed clusters at fixed T and
Yx respectively at \sim2\sigma significance. In particular, A1914 - a
well-known merging cluster - significantly increases the scatter and lowers the
the normalization of the relation for disturbed clusters. We also investigated
the covariance between intrinsic scatter in M-Mgas and M-T relations, finding
that they are positively correlated. This contradicts the adaptive mesh
refinement simulations that motivated the idea that Yx may be a low scatter
mass proxy, and agrees with more recent smoothed particle hydrodynamic
simulations based on the Millennium Simulation. We also propose a method to
identify a robust mass proxy based on principal component analysis. The
statistical precision of our results are limited by the small sample size and
the presence of the extreme merging cluster in our sample. | Determining $H_0$ with Bayesian hyper-parameters: We re-analyse recent Cepheid data to estimate the Hubble parameter $H_0$ by
using Bayesian hyper-parameters (HPs). We consider the two data sets from Riess
et al 2011 and 2016 (labelled R11 and R16, with R11 containing less than half
the data of R16) and include the available anchor distances (megamaser system
NGC4258, detached eclipsing binary distances to LMC and M31, and MW Cepheids
with parallaxes), use a weak metallicity prior and no period cut for Cepheids.
We find that part of the R11 data is down-weighted by the HPs but that R16 is
mostly consistent with expectations for a Gaussian distribution, meaning that
there is no need to down-weight the R16 data set. For R16, we find a value of
$H_0 = 73.75 \pm 2.11 \, \mathrm{km} \, \mathrm{s}^{-1} \, \mathrm{Mpc}^{-1}$
if we use HPs for all data points (including Cepheid stars, supernovae type Ia,
and the available anchor distances), which is about 2.6 $\sigma$ larger than
the Planck 2015 value of $H_0 = 67.81 \pm 0.92 \,\mathrm{km}\, \mathrm{s}^{-1}
\, \mathrm{Mpc}^{-1}$ and about 3.1 $\sigma$ larger than the updated Planck
2016 value $66.93 \pm 0.62 \,\mathrm{km}\, \mathrm{s}^{-1} \,
\mathrm{Mpc}^{-1}$. We test the effect of different assumptions, and find that
the choice of anchor distances affects the final value significantly. If we
exclude the Milky Way from the anchors, then the value of $H_0$ decreases. We
find however no evident reason to exclude the MW data. The HP method used here
avoids subjective rejection criteria for outliers and offers a way to test
datasets for unknown systematics. |
Astrometric Microlensing by Local Dark Matter Subhalos: High-resolution N-body simulations of dark matter halos indicate that the
Milky Way contains numerous subhalos. When a dark matter subhalo passes in
front of a star, the light from that star will be deflected by gravitational
lensing, leading to a small change in the star's apparent position. This
astrometric microlensing signal depends on the inner density profile of the
subhalo and can be greater than a few microarcseconds for an intermediate-mass
subhalo (Mvir > 10000 solar masses) passing within arcseconds of a star.
Current and near-future instruments could detect this signal, and we evaluate
SIM's, Gaia's, and ground-based telescopes' potential as subhalo detectors. We
develop a general formalism to calculate a subhalo's astrometric lensing cross
section over a wide range of masses and density profiles, and we calculate the
lensing event rate by extrapolating the subhalo mass function predicted by
simulations down to the subhalo masses potentially detectable with this
technique. We find that, although the detectable event rates are predicted to
be low on the basis of current simulations, lensing events may be observed if
the central regions of dark matter subhalos are more dense than current models
predict (>1 solar mass within 0.1 pc of the subhalo center). Furthermore,
targeted astrometric observations can be used to confirm the presence of a
nearby subhalo detected by gamma-ray emission. We show that, for sufficiently
steep density profiles, ground-based adaptive optics astrometric techniques
could be capable of detecting intermediate-mass subhalos at distances of
hundreds of parsecs, while SIM could detect smaller and more distant subhalos. | Effects of plasma on gravitational lensing: We study gravitational lensing when plasma surrounds the lens. An extra
deflection angle is induced by the plasma in addition to the deflection
generated by gravity. An inhomogeneous plasma distribution generates a greater
effect than a homogeneous one, and may cause significant effects to be detected
in low frequency radio observations (a few hundred MHz). In particular, the
lensed image positions will be different between optical and radio
observations. The change of position due to a plasma can reach a few tens of
milli-arcsec, which is readily detectable. One can use the position difference
in different frequencies to estimate the density of plasma in the lens. The
magnification ratios between multiple images are mainly determined by other
properties of the lens, and are only weakly affected by the plasma. More
importantly, we find that the strong lensing time delay will be affected by the
plasma. Estimation of the Hubble constant from the time delay in low radio
frequency observation may be slightly biased due to plasma in the lens.
Unfortunately, the ionosphere of the Earth strongly affects low frequency radio
observations. Thus our ability to detect the effect depends on how well we are
able to calibrate out the ionosphere. |
Progenitor mass constraints for core-collapse supernovae from
correlations with host galaxy star formation: Using H-alpha emission as a tracer of on-going (<16 Myr old) and near-UV
emission as a tracer of recent (16-100 Myr old) star formation (SF), we present
constraints on core-collapse (CC) supernova (SN) progenitors through their
association with SF regions. We present statistics of a large sample of SNe;
163.5 type II (58 IIP, 13 IIL, 13.5 IIb, 19 IIn and 12 'impostors') and 96.5
type Ib/c (39.5 Ib and 52 Ic). Using pixel statistics our main findings and
conclusions are: 1) An increasing progenitor mass sequence is observed, implied
from an increasing association of SNe to host galaxy H-alpha emission. This
commences with the type Ia (SNIa) showing the weakest association, followed by
the SNII, then the SNIb, with the SNIc showing the strongest correlation to SF
regions. Thus our progenitor mass sequence runs Ia-II-Ib-Ic. 2) Overall SNIbc
are found to occur nearer to bright HII regions than SNII. This implies that
the former have shorter stellar lifetimes thus arising from more massive
progenitor stars. 3) While SNIIP do not closely follow the on-going SF, they
accurately trace the recent formation. This implies that their progenitors
arise from stars at the low end of the CC SN mass sequence, consistent with
direct detections of progenitors in pre-explosion imaging. 4) Similarly SNIIn
trace recent but not the on-going SF. This implies that, contrary to the
general consensus, the majority of these SNe do not arise from the most massive
stars. Results and constraints are also presented for the less numerous SNIIL,
IIb, and 'impostors'. Finally we present analysis of possible biases in the
data, the results of which argue strongly against any selection effects that
could explain the relative excess of SNIbc within bright HII regions. Thus
intrinsic progenitor differences in the sense of the mass sequence we propose
remain the most plausible explanation of our findings. | Black Hole growth and AGN obscuration by instability-driven inflows in
high-redshift disk galaxies fed by cold streams: Disk galaxies at high redshift have been predicted to maintain high gas
surface densities due to continuous feeding by intense cold streams leading to
violent gravitational instability, transient features and giant clumps.
Gravitational torques between the perturbations drive angular momentum out and
mass in, and the inflow provides the energy for keeping strong turbulence. We
use analytic estimates of the inflow for a self-regulated unstable disk at a
Toomre stability parameter Q~1, and isolated galaxy simulations capable of
resolving the nuclear inflow down to the central parsec. We predict an average
inflow rate ~10 Msun/yr through the disk of a 10^11 Msun galaxy, with
conditions representative of z~2 stream-fed disks. The inflow rate scales with
disk mass and (1+z)^{3/2}. It includes clump migration and inflow of the
smoother component, valid even if clumps disrupt. This inflow grows the bulge,
while only a fraction ~ 10^-3 of it needs to accrete onto a central black hole
(BH), in order to obey the observed BH-bulge relation. A galaxy of 10^11 Msun
at z~2 is expected to host a BH of ~10^8 Msun, accreting on average with
moderate sub-Eddington luminosity L_X ~ 10^42-43 erg/s, accompanied by brighter
episodes when dense clumps coalesce. We note that in rare massive galaxies at
z~6, the same process may feed 10^9 Msun BH at the Eddington rate. High central
gas column densities can severely obscure AGN in high-redshift disks, possibly
hindering their detection in deep X-ray surveys. |
A Pilot Study for the SCUBA-2 'All-Sky' Survey: We have carried out a pilot study for the SCUBA-2 'All-Sky' Survey, SASSy, a
wide and shallow mapping project at 850 microns, designed to find rare objects,
both Galactic and extragalactic. Two distinct sets of exploratory observations
were undertaken, and used to test the SASSy approach and data reduction
pipeline. The first was a 0.5 by 0.5 degrees map around the nearby galaxy NGC
2559. The galaxy was easily detected at 156 mJy, but no other convincing
sources are present in the map. Comparison with other galaxies with similar
wavelength coverage indicates that NGC 2559 has relatively warm dust. The
second observations cover 1 square degree around the W5-E HII region. As well
as diffuse structure in the map, a filtering approach was able to extract 27
compact sources with signal-to-noise greater than 6. By matching with data at
other wavelengths we can see that the SCUBA-2 data can be used to discriminate
the colder cores. Together these observations show that the SASSy project will
be able to meet its original goals of detecting new bright sources which will
be ideal for follow-up observations with other facilities. | Search for cold gas in z>2 damped Lyman-alpha systems: 21-cm and H_2
absorption: (Abridged) We present the results of a systematic GBT and GMRT survey for
21-cm absorption in a sample of 10 DLAs at 2<z_abs<3.4. Analysis of L-band VLBA
images of the background QSOs are also presented. We detect 21-cm absorption in
only one DLA (at z_abs = 3.1745 towards J1337+3152). Combining our data with
the data from the literature (a sample of 28 DLAs) and assuming the measured
core fraction at milliarcsecond scale to represent the gas covering factor, we
find that the HI gas in DLAs at z> 2 is predominantly constituted by WNM. The
detection rate of 21-cm absorption seems to be higher for systems with higher
N(HI) or metallicity. However, no clear correlation is found between the
integrated 21-cm optical depth (or spin temperature) and either N(HI),
metallicity or velocity spread of the low ionization species. There are 13 DLAs
in our sample for which high resolution optical spectra covering the expected
wavelength range of H_2 absorption are available. We report the detection of
H_2 molecules in the z_abs = 3.3871 21-cm absorber towards J0203+1134 (PKS
0201+113). In 8 cases, neither H_2 nor 21-cm absorption are detected. The lack
of 21-cm and H_2 absorption in these systems can be explained if most of the HI
in these DLAs originate from low density high temperature gas. In one case we
have a DLA with 21-cm absorption not showing H_2 absorption. In two cases, both
species are detected but do not originate from the same velocity component. In
the remaining 2 cases 21-cm absorption is not detected despite the presence of
H_2 with evidence for the presence of cold gas. All this is consistent with the
idea that the H_2 components seen in DLAs are compact (with sizes of < 15 pc)
and contain only a small fraction (i.e typically <10%) of the total N(HI)
measured in the DLAs. |
Ray-tracing log-normal simulation for weak gravitational lensing:
application to the cross-correlation with galaxies: We present an algorithm to self-consistently generate mock weak gravitational
lensing convergence fields and galaxy distributions in redshift space. We
generate three-dimensional cosmic density fields that follow a log-normal
distribution, and ray-trace them to produce convergence maps. As we generate
the galaxy distribution from the same density fields in a manner consistent
with ray-tracing, the galaxy-convergence cross-power spectrum measured from the
mock agrees with the theoretical expectation with high precision. We use this
simulation to forecast the quality of galaxy-shear cross-correlation
measurements from the Subaru Hyper Suprime-Cam (HSC) and Prime Focus
Spectrograph (PFS) surveys. We find that the nominal HSC and PFS surveys would
detect the cross power spectra with signal-to-noise ratios of 20 and 5 at the
lowest ($z = 0.7$) and highest ($z = 2.2$) redshift bins, respectively. | A possible geometrical origin of the accelerated expansion of the
universe: The modified geodetic brane cosmology (MGBC) is tested with observational
data. The MGBC is derived from the geodetic brane gravity action corrected by
the extrinsic curvature of the braneworld. The density parameter coming from
this additional term produces an accelerated expansion of geometrical origin.
Subject to the Supernovae Ia, Observable Hubble parameter, Baryon Acoustic
Oscillations and Cosmic Microwave Background probes, the obtained fit provides
enough evidence in the sense that the extrinsic curvature effect is able to
reproduce the accelerated expansion of the universe without need of invoking
dark energy, exotic matter or cosmological constant. Moreover the MGBC is free
of the problems present in other braneworld models. |
The impact of dark energy on galaxy formation. What does the future of
our Universe hold?: We investigate the effect of the accelerated expansion of the Universe due to
a cosmological constant, $\Lambda$, on the cosmic star formation rate. We
utilise hydrodynamical simulations from the EAGLE suite, comparing a
$\Lambda$CDM Universe to an Einstein-de Sitter model with $\Lambda=0$. Despite
the differences in the rate of growth of structure, we find that dark energy,
at its observed value, has negligible impact on star formation in the Universe.
We study these effects beyond the present day by allowing the simulations to
run forward into the future ($t>13.8$ Gyr). We show that the impact of
$\Lambda$ becomes significant only when the Universe has already produced most
of its stellar mass, only decreasing the total co-moving density of stars ever
formed by ${\approx}15\%$. We develop a simple analytic model for the cosmic
star formation rate that captures the suppression due to a cosmological
constant. The main reason for the similarity between the models is that
feedback from accreting black holes dramatically reduces the cosmic star
formation at late times. Interestingly, simulations without feedback from
accreting black holes predict an upturn in the cosmic star formation rate for
$t>15$ Gyr due to the rejuvenation of massive ($ > 10^{11} \mathrm{M}_{\odot}$)
galaxies. We briefly discuss the implication of the weak dependence of the
cosmic star formation on $\Lambda$ in the context of the anthropic principle. | The Mid-Infrared and Near-Ultraviolet Excess Emissions of Quiescent
Galaxies on the Red Sequence: We study the mid-infrared (IR) and near-ultraviolet (UV) excess emissions of
spectroscopically selected quiescent galaxies on the optical red sequence. We
use the Wide-field Infrared Survey Explorer ({\it WISE}) mid-IR and Galaxy
Evolution Explorer ({\it GALEX}) near-UV data for a spectroscopic sample of
galaxies in the Sloan Digital Sky Survey Data Release 7 to study the possible
connection between quiescent red-sequence galaxies with and without
mid-IR/near-UV excess. Among 648 12 $\mu$m detected quiescent red-sequence
galaxies without H$\alpha$ emission, 26% and 55% show near-UV and mid-IR excess
emissions, respectively. When we consider only bright ($M_{r}$ $<$ $-$21.5)
galaxies with early-type morphology, the fraction of galaxies with recent star
formation is still 39%. The quiescent red-sequence galaxies with mid-IR and
near-UV excess emissions are optically fainter and have slightly smaller
$D_{n}$4000 than those without mid-IR and near-UV excess emissions. We also
find that mid-IR weighted mean stellar ages of quiescent red-sequence galaxies
with mid-IR excess are larger than those with near-UV excess, and smaller than
those without mid-IR and near-UV excess. The environmental dependence of the
fraction of quiescent red-sequence galaxies with mid-IR and near-UV excess
seems strong even though the trends of quiescent red-sequence galaxies with
near-UV excess differ from those with mid-IR excess. These results indicate
that the recent star formation traced by near-UV ($\lesssim 1$ Gyr) and mid-IR
($\lesssim 2$ Gyr) excess is not negligible among nearby, quiescent, red,
early-type galaxies. We suggest a possible evolutionary scenario of quiescent
red-sequence galaxies from quiescent red-sequence galaxies with near-UV excess
to those with mid-IR excess to those without near-UV and mid-IR excess. |
How to assess the primordial origin of single gravitational-wave events
with mass, spin, eccentricity, and deformability measurements: A population of primordial black holes formed in the early Universe could
contribute to at least a fraction of the black-hole merger events detectable by
current and future gravitational-wave interferometers. With the ever-increasing
number of detections, an important open problem is how to discriminate whether
a given event is of primordial or astrophysical origin. We systematically
present a comprehensive and interconnected list of discriminators that would
allow us to rule out, or potentially claim, the primordial origin of a binary
by measuring different parameters, including redshift, masses, spins,
eccentricity, and tidal deformability. We estimate how accurately future
detectors (such as the Einstein Telescope and LISA) could measure these
quantities, and we quantify the constraining power of each discriminator for
current interferometers. We apply this strategy to the GWTC-3 catalog of
compact binary mergers. We show that current measurement uncertainties do not
allow us to draw solid conclusions on the primordial origin of individual
events, but this may become possible with next-generation ground-based
detectors. | Evolution of Resonant Self-interacting Dark Matter Halos: Recent analysis on the stellar kinematics of ultra-faint dwarf (UFD) galaxies
has put a stringent upper limit on the self-scattering cross section of dark
matter, i.e., $\sigma/m<{\cal O}(0.1)\,{\rm cm^2/g}$ at the scattering velocity
of ${\cal O}(10)\,{\rm km/s}$. Resonant self-interacting dark matter (rSIDM) is
one possibility that can be consistent with the UFDs and explain the low
central densities of rotation-supported galaxies; the cross section is
resonantly enhanced to be $\sigma/m = {\cal O}(1)\,{\rm cm^2/g}$ around the
scattering velocity of ${\cal O}(100)\,{\rm km/s}$ while being suppressed at
lower velocities. To further assess this possibility, since the inferred dark
matter distribution of halos from astrophysical observations is usually
compared to that in constant-cross section SIDM (cSIDM), whether the structures
of rSIDM halos can be approximated by the cSIDM halo profiles needs to be
clarified. In this work, we employ the grovothermal fluid method to investigate
the structural evolution of rSIDM halos in a wide mass range. We find that
except for halos in a specific mass range, the present structures of rSIDM
halos are virtually indistinguishable from those of the cSIDM halos. For halos
in the specific mass range, the resonant self-scattering renders a break in
their density profile. We demonstrate how such a density-profile break appears
in astrophysical observations, e.g., rotation curves and line-of-sight velocity
dispersion profiles. We show that for halos above the specific mass range, the
density-profile break thermalizes to disappear before the present. We
demonstrate that such distinctive thermalization dynamics can leave imprints on
the orbital classes of stars with similar ages and metallicities. |
An infrared-radio simulation of the extragalactic sky: from the Square
Kilometer Array to Herschel: To exploit synergies between the Herschel Space Observatory and next
generation radio facilities, we have extended the semi-empirical extragalactic
radio continuum simulation of Wilman et al. (2008) to the mid- and
far-infrared. Here we describe the assignment of infrared spectral energy
distributions (SEDs) to the star-forming galaxies and active galactic nuclei,
using Spitzer 24, 70 and 160 micron and SCUBA 850 micron survey results as the
main constraints.
Star-forming galaxies dominate the source counts, and a model in which their
far-infrared-radio correlation and infrared SED assignment procedure are
invariant with redshift underpredicts the observed 24 and 70 micron source
counts. The 70 micron deficit can be eliminated if the star-forming galaxies
undergo stronger luminosity evolution than originally assumed for the radio
simulation, a requirement which may be partially ascribed to known
non-linearity in the far-infrared--radio correlation at low luminosity if it
evolves with redshift. At 24 micron, the shortfall is reduced if the
star-forming galaxies develop SEDs with cooler dust and correspondingly
stronger Polycyclic Aromatic Hydrocarbon (PAH) emission features with
increasing redshift at a given far-infrared luminosity, but this trend may
reverse at z>1 in order not to overproduce the sub-mm source counts. The
resulting model compares favourably with recent BLAST results and we have
extended the simulation database to aid the interpretation of Herschel surveys.
Such comparisons may also facilitate further model refinement and revised
predictions for the SKA and its precursors. | Searching for a possible dipole anisotropy on acceleration scale with
147 rotationally supported galaxies: We report a possible dipole anisotropy on acceleration scale $g_{\dag}$ with
147 rotationally supported galaxies in local Universe. It is found that a
monopole and dipole correction for the radial acceleration relation can better
describe the SPARC data set. The monopole term is negligible but the dipole
magnitude is significant. It is also found that the dipole correction is mostly
induced by the anisotropy on the acceleration scale. The magnitude of
$\hat{g}_{\dag}$-dipole reaches up to $0.25\pm0.04$, and its direction is
aligned to $(l,b) = (171.30^{\circ}\pm7.18^{\circ},
-15.41^{\circ}\pm4.87^{\circ})$, which is very close to the maximum anisotropy
direction from the hemisphere comparison method. Furthermore, robust check
shows that the dipole anisotropy couldn't be reproduced by isotropic mock data
set. However, it is still premature to claim that the Universe is anisotropic
due to the small data samples and uncertainty in the current observations. |
Galaxy clustering in the DESI Legacy Survey and its imprint on the CMB: We use data from the DESI Legacy Survey imaging to probe the galaxy density
field in tomographic slices covering the redshift range $0<z<0.8$. After
careful consideration of completeness corrections and galactic cuts, we obtain
a sample of $4.9\times 10^7$ galaxies covering 17 739 deg$^2$. We derive
photometric redshifts with precision $\sigma_z/(1+z)=0.012 - 0.015$, and
compare with alternative estimates. Cross-correlation of the tomographic galaxy
maps with Planck maps of CMB temperature and lensing convergence probe the
growth of structure since $z=0.8$. The signals are compared with a fiducial
Planck $\Lambda$CDM model, and require an overall scaling in amplitude of
$A_\kappa=0.901\pm 0.026$ for the lensing cross-correlation and $A_{\rm ISW} =
0.984 \pm 0.349$ for the temperature cross-correlation, interpreted as the
Integrated Sachs-Wolfe effect. The ISW amplitude is consistent with the
fiducial $\Lambda$CDM prediction, but lies significantly below the prediction
of the AvERA model of R\'acz et al. (2017), which has been proposed as an
alternative explanation for cosmic acceleration. Within $\Lambda$CDM, our low
amplitude for the lensing cross-correlation requires a reduction either in
fluctuation normalization or in matter density compared to the Planck results,
so that $\Omega_m^{0.78}\sigma_8=0.297\pm 0.009$. In combination with the total
amplitude of CMB lensing, this favours a shift mainly in density:
$\Omega_m=0.274\pm0.024$. We discuss the consistency of this figure with
alternative evidence. A conservative compromise between lensing and primary CMB
constraints would require $\Omega_m=0.296\pm0.006$, where the 95% confidence
regions of both probes overlap. | Generalized Slow Roll for Large Power Spectrum Features: We develop a variant of the generalized slow roll approach for calculating
the curvature power spectrum that is well-suited for order unity deviations in
power caused by sharp features in the inflaton potential. As an example, we
show that predictions for a step function potential, which has been proposed to
explain order unity glitches in the CMB temperature power spectrum at
multipoles l=20-40, are accurate at the percent level. Our analysis shows that
to good approximation there is a single source function that is responsible for
observable features and that this function is simply related to the local slope
and curvature of the inflaton potential. These properties should make the
generalized slow roll approximation useful for inflation-model independent
studies of features, both large and small, in the observable power spectra. |
A fully data-driven algorithm for accurate shear estimation: Weak lensing by large-scale structure is a powerful probe of cosmology if the
apparent alignments in the shapes of distant galaxies can be accurately
measured. We study the performance of a fully data-driven approach, based on
MetaDetection, focusing on the more realistic case of observations with an
anisotropic PSF. Under the assumption that PSF anisotropy is the only source of
additive shear bias, we show how unbiased shear estimates can be obtained from
the observed data alone. To do so, we exploit the finding that the
multiplicative shear bias obtained with MetaDetection is nearly insensitive to
the PSF ellipticity. In practice, this assumption can be validated by comparing
the empirical corrections obtained from observations to those from simulated
data. We show that our data-driven approach meets the stringent requirements
for upcoming space and ground-based surveys, although further optimisation is
possible. | Metal jumps across sloshing cold fronts: the case of A496: Cold-fronts in cool-core clusters are thought to be induced by minor mergers
and to develop through a sloshing mechanism. While temperature and
surface-brightness jumps have been detected and measured in many systems, a
detailed characterization of the metal abundance across the discontinuity is
only available for a handful of objects. Within the sloshing scenario, we
expect the central cool and metal rich gas to be displaced outwards into lower
abundance regions, thus generating a metal discontinuity across the front. We
analyzed a long (120 ksec) XMM-Newton observation of A496 to study the metal
distribution and its correlation with the cold-fronts. We find Fe
discontinuities across the two main cold-fronts located ~60 kpc NNW and ~160
kpc South of the peak and a metal excess in the South direction. |
Resonant Reconciliation of Convex Models and the Planck: We consider single field chaotic inflationary models plus a cosine modulation
term, as in axion monodromy models, and augment it by a light scalar field with
similar cosine coupling. We show the power spectrum of curvature perturbations
of this model is dominated by the one-loop contribution to inflaton two-point
function which is enhanced due to resonant interactions. This allows to
disentangle the scale of scalar and tensor perturbations and hence to suppress
the ratio of tensor-to-scalar power spectra and alters the expression of scalar
spectral tilt from the simple chaotic models, thus opening the way to reconcile
chaotic models with convex potential and the Planck data. As in monodromy
inflation models, we also have a cosine modulation in spectral tilt. We mention
that contribution of resonance effects on non-Gaussianty is small and it
remains within the current bounds. Resonant production of light particles
toward the end of inflation may set the stage for a successful reheating model. | Sensitivity of dark matter haloes to their accretion histories: We apply our recently proposed "quadratic genetic modification" approach to
generating and testing the effects of alternative mass accretion histories for
a single $\Lambda$CDM halo. The goal of the technique is to construct different
formation histories, varying the overall contribution of mergers to the fixed
final mass. This enables targeted studies of galaxy and dark matter halo
formation's sensitivity to the smoothness of mass accretion. Here, we focus on
two dark matter haloes, each with four different mass accretion histories. We
find that the concentration of both haloes systematically decreases as their
merger history becomes smoother. This causal trend tracks the known correlation
between formation time and concentration parameters in the overall halo
population. At fixed formation time, we further establish that halo
concentrations are sensitive to the order in which mergers happen. This ability
to study an individual halo's response to variations in its history is highly
complementary to traditional methods based on emergent correlations from an
extended halo population. |
Inflation from Multiple Pseudo-Scalar Fields: PBH Dark Matter and
Gravitational Waves: We study a model of inflation with multiple pseudo-scalar fields coupled to a
$U(1)$ gauge field through Chern-Simons interactions. Because of parity
violating interactions, one polarization of the gauge field is amplified
yielding to enhanced curvature perturbation power spectrum. Inflation proceeds
in multiple stages as each pseudo-scalar field rolls towards its minimum
yielding to distinct multiple peaks in the curvature perturbations power
spectrum at various scales during inflation. The localized peaks in power
spectrum generate Primordial Black Holes (PBHs) which can furnish a large
fraction of Dark Matter (DM) abundance. In addition, gravitational waves (GWs)
with non-trivial spectra are generated which are in sensitivity range of
various forthcoming GW observatories. | Searching for nuclear stellar discs in simulations of star cluster
mergers: The nuclei of galaxies often host small stellar discs with scale-lengths of a
few tens of parsecs and luminosities up to 10^7 Lsun. To investigate the
formation and properties of nuclear stellar discs (NSDs), we look for their
presence in a set of N-body simulations studying the dissipationless merging of
multiple star clusters in galactic nuclei. A few tens of star clusters with
sizes and masses comparable to those of globular clusters observed in the Milky
Way are accreted onto a pre-existing nuclear stellar component: either a
massive super star cluster or a rapidly rotating, compact disc with a
scale-length of a few parsecs, mimicing the variety of observed nuclear
structures. Images and kinematic maps of the simulation time-steps are then
built and analysed as if they were real and at the distance of the Virgo
cluster. We use the Scorza-Bender method to search for the presence of disc
structures via photometric decomposition. In one case the merger remnant has
all the observed photometric and kinematic properties of NSDs observed in real
galaxies. This shows that current observations are consistent with most of the
NSD mass being assembled from the migration and accretion of star clusters into
the galactic centre. In the other simulation instead, we detect an elongated
structure from the unsharp masked image, that does not develop the photometric
or kinematic signature of a NSD. Thus, in the context of searches for a disc
structure, the Scorza-Bender method is a robust and necessary tool. |
The 21 cm Signature of Shock Heated and Diffuse Cosmic String Wakes: The analysis of the 21 cm signature of cosmic string wakes is extended in
several ways. First we consider the constraints on $G\mu$ from the absorption
signal of shock heated wakes laid down much later than matter radiation
equality. Secondly we analyze the signal of diffuse wake, that is those wakes
in which there is a baryon overdensity but which have not shock heated. Finally
we compare the size of these signals compared to the expected thermal noise per
pixel which dominates over the background cosmic gas brightness temperature and
find that the cosmic string signal will exceed the thermal noise of an
individual pixel in the Square Kilometre Array for string tensions $G\mu > 2.5
\times 10^{-8}$. | The Atlas3D project - X. On the origin of the molecular and ionised gas
in early-type galaxies: We make use of interferometric CO and HI observations, and optical
integral-field spectroscopy to probe the origin of the molecular and ionised
interstellar medium (ISM) in local early-type galaxies (ETGs). We find that
36\pm5% of our sample of fast rotating ETGs have their ionised gas
kinematically misaligned with respect to the stars, setting a strong lower
limit on the importance of externally acquired gas (e.g. from mergers and cold
accretion). Slow rotators have a flat distribution of misalignments, indicating
that the dominant source of gas is external. The molecular, ionised and atomic
gas in all the detected galaxies are always kinematically aligned, even when
they are misaligned from the stars, suggesting that all these three phases of
the ISM share a common origin. In addition, we find that the origin of the cold
and warm gas in fast-rotating ETGs is strongly affected by environment, despite
the molecular gas detection rate and mass fractions being fairly independent of
group/cluster membership. Galaxies in dense groups and the Virgo cluster nearly
always have their molecular gas kinematically aligned with the stellar
kinematics, consistent with a purely internal origin. In the field, however,
kinematic misalignments between the stellar and gaseous components indicate
that >46% of local fast-rotating ETGs have their gas supplied from external
sources. We discuss several scenarios which could explain the environmental
dichotomy, but find it difficult to simultaneously explain the kinematic
misalignment difference and the constant detection rate. Furthermore, our
results suggest that galaxy mass may be an important independent factor
associated with the origin of the gas, with the most massive fast-rotating
galaxies in our sample (M_K<-24 mag; stellar mass of >8x10^10 Msun) always
having kinematically aligned gas. (abridged) |
Exploiting Cross Correlations and Joint Analyses: In this report, we present a wide variety of ways in which information from
multiple probes of dark energy may be combined to obtain additional information
not accessible when they are considered separately. Fundamentally, because all
major probes are affected by the underlying distribution of matter in the
regions studied, there exist covariances between them that can provide
information on cosmology. Combining multiple probes allows for more accurate
(less contaminated by systematics) and more precise (since there is
cosmological information encoded in cross-correlation statistics) measurements
of dark energy. The potential of cross-correlation methods is only beginning to
be realized. By bringing in information from other wavelengths, the
capabilities of the existing probes of dark energy can be enhanced and
systematic effects can be mitigated further. We present a mixture of work in
progress and suggestions for future scientific efforts. Given the scope of
future dark energy experiments, the greatest gains may only be realized with
more coordination and cooperation between multiple project teams; we recommend
that this interchange should begin sooner, rather than later, to maximize
scientific gains. | Strong Gravitational Lens Statistics using the Herschel-ATLAS: The identification of strong gravitational lenses in large surveys has
historically been a rather time consuming exercise. Early data from the
Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) demonstrate
that lenses can be identified efficiently at submillimetre wavelengths using a
simple flux criteria. Motivated by that development, this work considers the
statistical properties of strong gravitational lens systems which have been,
and will be, found by the Herschel-ATLAS. Analytical models of lens statistics
are tested with the current best estimates for the various model ingredients.
These include the cosmological parameters, the mass function and the lens
density profile, for which we consider the singular isothermal sphere (SIS) and
the Navarro, Frenk & White (NFW) approximations. The five lenses identified in
the Herschel-ATLAS Science Demonstration Phase suggest a SIS density profile is
preferred, but cannot yet constrain \Omega_\Lambda to an accuracy comparable
with other methods. The complete Herschel-ATLAS data set should be sufficient
to yield competitive constraints on \Omega_\Lambda. Whilst this huge number of
lenses has great potential for constraining cosmological parameters, they will
be most powerful in constraining uncertainty in astrophysical processes.
Further investigation is needed to fully exploit this unprecedented data set. |
Cosmic vector for dark energy: constraints from SN, CMB and BAO: It has been recently shown that the presence of a vector field over
cosmological scales could explain the observed accelerated expansion of the
universe without introducing neither new scales nor unnatural initial
conditions in the early universe, thus avoiding the coincidence problem. Here,
we present a detailed analysis of the constraints imposed by SNIa, CMB and BAO
data on the vector dark energy model with general spatial curvature. We find
that contrary to standard cosmology, CMB data excludes a flat universe for this
model and, in fact, predicts a closed geometry for the spatial sections. We see
that CMB and SNIa Gold data are perfectly compatible at the 1-sigma level,
however SNIa Union dataset exhibits a 3-sigma tension with CMB. The same level
of tension is also found between SNIa and BAO measurements. | Measuring cosmic distances with galaxy clusters: In addition to cosmological tests based on the mass function and clustering
of galaxy clusters, which probe the growth of cosmic structure, nature offers
two independent ways of using clusters to measure cosmic distances. The first
uses measurements of the X-ray emitting gas mass fraction, which is an
approximately standard quantity, independent of mass and redshift, for the most
massive clusters. The second uses combined millimeter (mm) and X-ray
measurements of cluster pressure profiles. We review these methods, their
current status and the prospects for improvements over the next decade. For the
first technique, which currently provides comparable dark energy constraints to
type Ia supernova studies, improvements of a factor of 6 or more should be
readily achievable, together with tight constraints on the mean matter density
that are largely independent of the cosmological model assumed. Realizing this
potential will require a coordinated, multiwavelength approach, utilizing new
cluster surveys, X-ray, optical and mm facilities, and a continued emphasis on
improved hydrodynamical simulations. |
Supernova cosmology: legacy and future: The discovery of dark energy by the first generation of high-redshift
supernova surveys has generated enormous interest beyond cosmology and has
dramatic implications for fundamental physics. Distance measurements using
supernova explosions are the most direct probes of the expansion history of the
Universe, making them extremely useful tools to study the cosmic fabric and the
properties of gravity at the largest scales. The past decade has seen the
confirmation of the original results. Type Ia supernovae are among the leading
techniques to obtain high-precision measurements of the dark energy equation of
state parameter, and in the near future, its time dependence. The success of
these efforts depends on our ability to understand a large number of effects,
mostly of astrophysical nature, influencing the observed flux at Earth. The
frontier now lies in understanding if the observed phenomenon is due to vacuum
energy, albeit its unnatural density, or some exotic new physics. Future
surveys will address the systematic effects with improved calibration
procedures and provide thousands of supernovae for detailed studies. | The limited role of mergers in the black hole to bulge mass relation: We examine the intrinsic scatter in the correlation between black hole masses
and their host bulge masses, and find that it cannot be accounted for by
mergers alone. A simple merger scenario of small galaxies leads to a
proportionality relation between the late-time black hole and bulge masses,
with intrinsic scatter (in linear scale) increasing along the ridge line of the
relation as the square root of the mass. By examining a sample of 86 galaxies
with well measured black hole masses, we find that the intrinsic scatter
increases with mass more rapidly than expected from the merger-only scenario.
We discuss the possibility that the feedback mechanism that operated during
galaxy formation involved the presence of a cooling flow. |
Dynamics of Starbursting Dwarf Galaxies: I Zw 18: I Zw 18 is a prototype Blue Compact Dwarf (BCD), characterized by a strong
starburst and extremely low metallicity (Z ~ 0.02 Zsun). It has long been
considered a candidate young galaxy in the Local Universe, but recent studies
indicate the presence of old stars. We analysed archival VLA observations of
the 21 cm line and found that the HI associated to the starburst region forms a
compact fast-rotating disk. The HI column densities are very high, up to
~50-100 Msun/pc^2 (~0.6-1.2 x 10^22 atoms/cm^2). The rotation curve is flat
with a steep rise in the inner parts, indicating the presence of a strong
central concentration of mass. Mass models with a dark matter halo show that
baryons may dominate the gravitational potential in the inner regions. A radial
inflow/outflow motion of ~15 km/s is also present. I Zw 18 appears structurally
different from typical dwarf irregulars in terms of gas distribution, stellar
distribution and dynamics. It may be considered as a "miniature"
high-surface-brightness disk galaxy. These dynamical properties must be tightly
related to the starburst. They also shed new light on the question of the
descendants of BCDs. There is also extended HI emission towards the outlying
stellar complex I Zw 18 C and a ~13.5 kpc HI tail. An interaction/merger
between gas-rich dwarfs is the most likely explanation for the starburst. | The Persistence of Cool Galactic Winds in High Stellar Mass Galaxies
Between z~1.4 and ~1: We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption
line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy
sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field,
has a range in stellar mass (M_*) comparable to that of the sample at z~1.4
analyzed in a similar manner by Weiner et al. (2009; W09), but extends to lower
redshifts and has specific star formation rates which are lower by ~0.6 dex. We
identify outflows of cool gas from the Doppler shift of the MgII absorption
lines and find that the equivalent width (EW) of absorption due to outflowing
gas increases on average with M_* and star formation rate (SFR). We attribute
the large EWs measured in spectra of the more massive, higher-SFR galaxies to
optically thick absorbing clouds having large velocity widths. The outflows
have hydrogen column densities N(H) > 10^19.3 cm^-2, and extend to velocities
of ~500 km/s. While galaxies with SFR > 10 Msun/yr host strong outflows in both
this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log
M_*/Msun < 10.5) galaxies at lower redshifts. Using a simple galaxy evolution
model which assumes exponentially declining SFRs, we infer that strong outflows
persist in galaxies with log M_*/Msun > 10.5 as they age between z=1.4 and z~1,
presumably because of their high absolute SFRs. Finally, using high resolution
HST/ACS imaging in tandem with our spectral analysis, we find evidence for a
weak trend (at 1 sigma significance) of increasing outflow absorption strength
with increasing galaxy SFR surface density. |
First Data Release of the COSMOS Lyman-Alpha Mapping And Tomography
Observations: 3D Lyman-$α$ Forest Tomography at 2.05 < z < 2.55: Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative
background sources to probe the Lyman-$\alpha$ forest in addition to quasars,
yielding high sightline densities that enable 3D tomographic reconstruction of
the foreground absorption field. Here, we present the first data release from
the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which
was conducted with the LRIS spectrograph on the Keck-I telescope. Over an
observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we
used 240 galaxies and quasars at $2.17<z<3.00$, with a mean comoving transverse
separation of $2.37\,h^{-1}\,\mathrm{Mpc^3}$, as background sources probing the
foreground Lyman-$\alpha$ forest absorption at $2.05<z<2.55$. The
Lyman-$\alpha$ forest data was then used to create a Wiener-filtered
tomographic reconstruction over a comoving volume of $3.15\,\times
10^5\,h^{-3}\,\mathrm{Mpc^3}$ with an effective smoothing scale of
$2.5\,h^{-1}\,\mathrm{Mpc}$. In addition to traditional figures, this map is
also presented as a virtual-reality YouTube360 video visualization and
manipulable interactive figure. We see large overdensities and underdensities
that visually agree with the distribution of coeval galaxies from spectroscopic
redshift surveys in the same field, including overdensities associated with
several recently-discovered galaxy protoclusters in the volume. This data
release includes the redshift catalog, reduced spectra, extracted
Lyman-$\alpha$ forest pixel data, and tomographic map of the absorption. | On the interpretation of dark matter self-interactions in Abell 3827: Self-interactions of dark matter particles can potentially lead to an
observable separation between the dark matter halo and the stars of a galaxy
moving through a region of large dark matter density. Such a separation has
recently been observed in a galaxy falling into the core of the galaxy cluster
Abell 3827. We estimated the DM self-interaction cross section needed to
reproduce the observed effects and find that the sensitivity of Abell 3827 has
been significantly overestimated in a previous study. Our corrected estimate is
$\tilde{\sigma}/m_\text{DM} \sim 3\:\text{cm}^2\:\text{g}^{-1}$ when
self-interactions result in an effective drag force and $\sigma/m_\text{DM}
\sim 1.5\:\text{cm}^2\:\text{g}^{-1}$ for the case of contact interactions, in
some tension with previous upper bounds. |
Stellar metallicity of star-forming galaxies at z ~ 3: The stellar metallicity is a direct measure of the amount of metals present
in a galaxy, as a large part of the metals lie in its stars. In this paper we
investigate new stellar metallicity indicators suitable for high-z galaxies
studying the stellar photospheric absorption lines in the rest frame
ultraviolet, hence sampling predominantly young hot stars. We defined these new
indicators based on the equivalent widths (EW) of selected features using
theoretical spectra created with the evolutionary population synthesis code
Starburts99. We used them to compute the stellar metallicity for a sample of
UV-selected galaxies at z > 3 from the AMAZE survey using very deep (37h per
object) VLT/FORS spectra. Moreover, we applied the new metallicity indicators
to eight additional high redshift galaxies found in literature. We then
compared stellar and gas-phase metallicities measured from the emission lines
for all these galaxies, finding that within the errors the two estimates are in
good agreement, with possible tendency to have stellar metallicities lower than
the gas phase ones. For the first time, we are able to study the stellar
mass-metallicity relation at z > 3. We find that the metallicity of young, hot
stars in galaxies at z \sim 3 have similar values of the aged stars in local
SDSS galaxies, contrary to what observed for the gas phase metallicity. | Black hole growth and starburst activity at z = 0.6-4 in the Chandra
Deep Field South. Host galaxies properties of obscured AGN: The co-evolution of host galaxies and the active black holes which reside in
their centre is one of the most important topics in modern observational
cosmology. Here we present a study of the properties of obscured Active
Galactic Nuclei (AGN) detected in the CDFS 1Ms observation and their host
galaxies. We limited the analysis to the MUSIC area, for which deep K-band
observations obtained with ISAAC@VLT are available, ensuring accurate
identifications of the counterparts of the X-ray sources as well as reliable
determination of photometric redshifts and galaxy parameters, such as stellar
masses and star formation rates. In particular, we: 1) refined the
X-ray/infrared/optical association of 179 sources in the MUSIC area detected in
the Chandra observation; 2) studied the host galaxies observed and rest frame
colors and properties. We found that X-ray selected (L_X>10^{42} erg s^{-1})
AGN show Spitzer colors consistent with both AGN and starburst dominated
infrared continuum; the latter would not have been selected as AGN from
infrared diagnostics. The host galaxies of X-ray selected obscured AGN are all
massive (M_*>10^{10} M_sun) and, in 50% of the cases, are also actively forming
stars (1/SSFR<t_{Hubble}) in dusty environments. The median L/LEdd value of the
active nucleus is between 2% and 10% depending on the assumed M_{BH}/M_{*}
ratio. Finally, we found that the X-ray selected AGN fraction increases with
the stellar mass up to a value of ~30% at z>1 and M_*>3x10^{11} M_sun, a
fraction significantly higher than in the local Universe for AGN of similar
luminosities. |
Detectability of the cross-correlation between CMB lensing and
stochastic GW background from compact object mergers: The anisotropies of the Stochastic Gravitational-Wave Background (SGWB)
produced by merging compact binaries constitute a possible new probe of the
Large-Scale Structure (LSS). However, the significant shot noise contribution
caused by the discreteness of the GW sources and the poor angular resolution of
the instruments hamper the detection of the intrinsic anisotropies induced by
the LSS. In this work, we investigate the potential of cross-correlating
forthcoming high precision measurements of the SGWB energy density and the
Cosmic Microwave Background (CMB) lensing convergence to mitigate the effect of
shot noise. Combining a detailed model of stellar and galactic astrophysics
with a novel framework to distribute the GW emitters in the sky, we compute the
auto- and cross-correlation power spectra for the two cosmic fields, evaluate
the shot noise contribution and predict the signal-to-noise ratio. The results
of our analysis show that the SGWB energy density correlates significantly with
the CMB lensing convergence and that the cross-correlation between these two
cosmic fields reduces the impact of instrumental and shot noise. Unfortunately,
the S/N is not high enough to detect the intrinsic SGWB anisotropies.
Nevertheless, a network composed of both present and future generation GW
interferometers, operating for at least 10 yrs, should be able to measure the
shot noise contribution. | The 6dF Galaxy Velocity Survey: Cosmological constraints from the
velocity power spectrum: We present scale-dependent measurements of the normalised growth rate of
structure $f\sigma_{8}(k, z=0)$ using only the peculiar motions of galaxies. We
use data from the 6-degree Field Galaxy Survey velocity sample (6dFGSv)
together with a newly-compiled sample of low-redshift $(z < 0.07)$ type Ia
supernovae. We constrain the growth rate in a series of $\Delta k \sim 0.03
h{\rm Mpc^{-1}}$ bins to $\sim35\%$ precision, including a measurement on
scales $>300 h^{-1}{\rm Mpc}$, which represents one of the largest-scale growth
rate measurement to date. We find no evidence for a scale dependence in the
growth rate, or any statistically significant variation from the growth rate as
predicted by the {\it Planck} cosmology. Bringing all the scales together, we
determine the normalised growth rate at $z=0$ to $\sim15\%$ in a manner {\it
independent} of galaxy bias and in excellent agreement with the constraint from
the measurements of redshift-space distortions from 6dFGS. We pay particular
attention to systematic errors. We point out that the intrinsic scatter present
in Fundamental-Plane and Tully-Fisher relations is only Gaussian in logarithmic
distance units; wrongly assuming it is Gaussian in linear (velocity) units can
bias cosmological constraints. We also analytically marginalise over zero-point
errors in distance indicators, validate the accuracy of all our constraints
using numerical simulations, and demonstrate how to combine different
(correlated) velocity surveys using a matrix `hyper-parameter' analysis.
Current and forthcoming peculiar velocity surveys will allow us to understand
in detail the growth of structure in the low-redshift universe, providing
strong constraints on the nature of dark energy. |
Quasars as Standard Candles V. Evaluation of a $\leq$ 0.06 dex intrinsic
dispersion in the LX-LUV relation: A characteristic feature of quasars is the observed non-linear relationship
between their monochromatic luminosities at rest-frame 2500 {\AA} and 2 keV.
This relationship is evident across all redshifts and luminosities and, due to
its non-linearity, can be implemented to estimate quasar distances and
construct a Hubble Diagram for quasars. Historically, a significant challenge
in the cosmological application of this relation has been its high observed
dispersion. Recent studies have demonstrated that this dispersion can be
reduced by excluding biased objects from the sample. Nevertheless, the
dispersion remains considerable ($\delta \sim 0.20$ dex), especially when
compared to the Phillips relation for supernovae Ia. Given the absence of a
comprehensive physical model for the relation, it remains unclear how much of
the remaining dispersion is intrinsically tied to the relation itself and how
much can be attributed to observational factors not addressed by the sample
selection and by the choice of X-ray and UV indicators. Potential contributing
factors include (i) the scatter produced by using X-ray photometric results
instead of spectroscopic ones, (ii) the intrinsic variability of quasars, and
(iii) the inclination of the accretion disc relative to our line of sight. In
this study, we thoroughly examine these three factors and quantify their
individual contributions to the observed dispersion. Based on our findings, we
argue that the intrinsic dispersion of the X-ray/UV luminosity relation is
likely below 0.06 dex. We also discuss why high-redshift subsamples can show a
significantly lower dispersion than the average one. | Momentum-driven feedback and the Mass-sigma relation in non-isothermal
galaxies: We solve for the velocity fields of momentum-conserving supershells driven
from galaxy centres by steady winds from supermassive black holes or nuclear
star clusters (central massive objects: CMOs). We look for the critical CMO
mass that allows such a shell to escape from its host galaxy. In the case that
the host galaxy dark matter halo is a singular isothermal sphere, we find that
the critical CMO mass derived by King, which scales with the halo velocity
dispersion as M_crit \propto \sigma^4, is necessary, but not by itself
sufficient, to drive shells to large radii in the halo. Furthermore, a CMO mass
at least 3 times the King value is required to drive the shell to the escape
speed of the halo. In the case of CMOs embedded in protogalaxies with
non-isothermal dark matter haloes, which we treat here for the first time, we
find a critical CMO mass that \textit{is sufficient} to drive \textit{any}
shell (under a steady wind) to escape \textit{any} galaxy with a peaked
circular speed profile. In the limit of large halo mass, relevant to real
galaxies, this critical CMO mass depends only on the value of the peak circular
speed of the halo, scaling as M_crit \propto V_c,pk^4. Our results therefore
relate to observational scalings between black hole mass and asymptotic
circular speed in galaxy spheroids. They also suggest a natural way of
extending analyses of M-\sigma relations for black holes in massive bulges, to
include similar relations for nuclear clusters in lower-mass and disc galaxies. |
Optimally Mapping Large-Scale Structures with Luminous Sources: Intensity mapping has emerged as a promising tool to probe the
three-dimensional structure of the universe. The traditional approach of galaxy
redshift surveys is based on individual galaxy detection, typically performed
by thresholding and digitizing large-scale intensity maps. By contrast,
intensity mapping uses the integrated emission from all sources in a 3D pixel
(or voxel) as an analog tracer of large-scale structure. In this work, we
develop a formalism to quantify the performance of both approaches when
measuring large-scale structures. We compute the Fisher information of an
arbitrary observable, derive the optimal estimator, and study its performance
as a function of source luminosity function, survey resolution, instrument
sensitivity, and other survey parameters. We identify regimes where each
approach is advantageous and discuss optimal strategies for different
scenarios. To determine the best strategy for any given survey, we develop a
metric that is easy to compute from the source luminosity function and the
survey sensitivity, and we demonstrate the application with several planned
intensity mapping surveys. | The Halo Occupation Distribution of Black Holes: Dependence on Mass: We investigate the halo occupation distribution (HOD) of black holes within a
hydrodynamic cosmological simulation that directly follows black hole growth.
Similar to the HOD of galaxies/subhalos, we find that the black hole occupation
number can be described by the form N_BH proportional to 1+ (M_Host)^alpha
where alpha evolves mildly with redshift indicating that a given mass halo
(M_Host) at low redshift tends to host fewer BHs than at high redshift (as
expected as a result of galaxy and BH mergers). We further divide the
occupation number into contributions from black holes residing in central and
satellite galaxies within a halo. The distribution of M_BH within halos tends
to consist of a single massive BH (distributed about a peak mass strongly
correlated with M_Host), and a collection of relatively low-mass secondary BHs,
with weaker correlation with M_Host. We also examine the spatial distribution
of BHs within their host halos, and find they typically follow a power-law
radial distribution (i.e. much more centrally concentrated than the subhalo
distribution). Finally, we characterize the host mass for which BH growth is
feedback dominated (e.g. star formation quenched). We show that halos with
M_Host > 3 * 10^12 M_sun have primary BHs that are feedback dominated by z~3
with lower mass halos becoming increasingly more affected at lower redshift. |
The Cosmological Constant as a Function of Extrinsic Curvature and
Spatial Curvature: In this paper we suppose that the cosmological constant will change when the
universe expends. For a general consideration, the cosmological constant is
assumed to be a function of scale factor and Hubble constant. According to the
ADM formulation, to the FRW metric, the extrinsic curvature $I$ equals
$-6H^{2}$ and spatial curvature $R$ equals $6k/a^{2}$. Therefore we suppose
cosmological constant is a function of extrinsic curvature and spatial
curvature. We investigate the cosmological evolution of FRW universe in these
models. At last we investigate two particular models which could fit the
observation data about dark energy well. Actually a changeless cosmological
constant is not essential. If when the universe expands, the cosmological
constant changes slowly and gradually flows to a constant, the observation data
about dark energy could also be fitted well by this kind of theory. | Early Dark Energy beyond slow-roll: implications for cosmic tensions: In this work, we explore the possibility that Early Dark Energy (EDE) is
dynamical in nature and study its effect on cosmological observables. We
introduce a parameterization of the equation of state allowing for an equation
of state $w$ differing considerably from cosmological constant (cc, $w={-1}$)
and vary both the initial $w_i$ as well final $w_f$ equation of state of the
EDE fluid. This idea is motivated by the fact that in many models of EDE, the
scalar field may have some kinetic energy when it starts to behave like EDE
before the CMB decoupling. We find that the present data have a mild preference
for non-cc early dark energy $( w_i= -0.78)$ using Planck+BAO+Pantheon+S$H_0$ES
data sets, leading to $\Delta \chi^2_{\rm min}$ improvement of -2.5 at the
expense of one more parameter. However, $w_i$ is only weakly constrained, with
$w_i < -0.56$ at $1\sigma$. We argue that allowing for $w_i\neq -1$ can play a
role in decreasing the $\sigma_8$ parameter. Yet, in practice the decrease is
only $\sim0.4\sigma$ and $\sigma_8$ is still larger than weak lensing
measurements. We conclude that while promising, a dynamical EDE cannot resolve
both $H_0$ and $\sigma_8$ tensions simultaneously. |
Probing dark energy with future redshift surveys: A comparison of
emission line and broad band selection in the near infrared: Future galaxy surveys will map the galaxy distribution in the redshift
interval $0.5<z<2$ using near-infrared cameras and spectrographs. The primary
science goal of such surveys is to constrain the nature of the dark energy by
measuring the large-scale structure of the Universe. This requires a tracer of
the underlying dark matter which maximizes the useful volume of the survey. We
investigate two potential survey selection methods: an emission line sample
based on the \ha line and a sample selected in the H-band. We present
predictions for the abundance and clustering of such galaxies, using two
published versions of the \galform galaxy formation model. Our models predict
that \ha selected galaxies tend to avoid massive dark matter haloes and instead
trace the surrounding filamentary structure; H-band selected galaxies, on the
other hand, are found in the highest mass haloes. This has implications for the
measurement of the rate at which fluctuations grow due to gravitational
instability. We use mock catalogues to compare the effective volumes sampled by
a range of survey configurations. To give just two examples: a redshift survey
down to $H_{\rm AB}=22$ samples an effective volume that is $\sim 5-10$ times
larger than that probed by an \ha survey with $\logfha > -15.4$; a flux limit
of at least $\logfha = -16$ is required for an \ha sample to become competitive
in effective volume. | The first measurement of temperature standard deviation along the
line-of-sight in galaxy clusters: Clusters of galaxies are mainly formed by merging of smaller structures,
according to the standard cosmological scenario. If the mass of a substructure
is >10% of that of a galaxy cluster, the temperature distribution of the
intracluster medium (ICM) in a merging cluster becomes inhomogeneous. Various
methods have been used to derive the two-dimensional projected temperature
distribution of the ICM. However, methods for studying temperature distribution
along the line-of-sight through the cluster were absent. In this paper, we
present the first measurement of the temperature standard deviation along the
line-of-sight, using as a reference case the multifrequency SZ measurements of
the Bullet Cluster. We find that the value of the temperature standard
deviation is high and equals to (10.6+/-3.8) keV in the Bullet Cluster. This
result shows that the temperature distribution in the Bullet Cluster is
strongly inhomogeneous along the line-of-sight and provides a new method for
studying galaxy clusters in depth. |
An investigation of the luminosity-metallicity relation for a large
sample of low-metallicity emission-line galaxies: (abridged) We present 8.2m VLT spectroscopic observations of 28 HII regions
in 16 emission-line galaxies and 3.6m ESO telescope spectroscopic observations
of 38 HII regions in 28 emission-line galaxies. These emission-line galaxies
were selected mainly from the Data Release 6 (DR6) of the Sloan Digital Sky
Survey (SDSS) as metal-deficient galaxy candidates. We collect photometric and
high-quality spectroscopic data for a large uniform sample of star forming
galaxies including new observations. Our aim is to study the
luminosity-metallicity (L-Z) relation for nearby galaxies, especially at its
low-metallicity end and compare it with that for higher-redshift galaxies. From
our new observations we find that the oxygen abundance in 61 out of the 66 HII
regions of our sample ranges from 12+logO/H=7.05 to 8.22. Our sample includes
27 new galaxies with 12+logO/H<7.6 which qualify as extremely metal-poor
star-forming galaxies (XBCDs). Among them are 10 HII regions with
12+logO/H<7.3. The new sample is combined with a further 93 low-metallicity
galaxies with accurate oxygen abundance determinations from our previous
studies, yielding in total a high-quality spectroscopic data set of 154 HII
regions. 9000 more galaxies with oxygen abundances, based mainly on the
Te-method, are compiled from the SDSS. Our data set spans a range of 8 mag with
respect to its absolute magnitude in SDSS g (-12>Mg>-20) and nearly 2 dex in
its oxygen abundance (7.0<12+logO/H<8.8), allowing us to probe the L-Z relation
in the nearby universe down to the lowest currently studied metallicity level.
The L-Z relation established on the basis of the present sample is consistent
with previous ones obtained for emission-line galaxies. | Topological Defects in Gravitational Lensing Shear Fields: Shear fields due to weak gravitational lensing have characteristic coherent
patterns. We describe the topological defects in shear fields in terms of the
curvature of the surface described by the lensing potential. A simple
interpretation of the characteristic defects is given in terms of the the
umbilical points of the potential surface produced by ellipsoidal halos. We
show simulated lensing shear maps and point out the typical defect
configurations. Finally, we show how statistical properties such as the
abundance of defects can be expressed in terms of the correlation function of
the lensing potential. |
The offsets between galaxies and their dark matter in Lambda-CDM: We use the "Evolution and Assembly of GaLaxies and their Environments" (
EAGLE ) suite of hydrodynamical cosmological simulations to measure offsets
between the centres of stellar and dark matter components of galaxies. We find
that the vast majority (>95%) of the simulated galaxies display an offset
smaller than the gravitational softening length of the simulations
(Plummer-equivalent $\epsilon = 700$ pc), both for field galaxies and
satellites in clusters and groups. We also find no systematic trailing or
leading of the dark matter along a galaxy's direction of motion. The offsets
are consistent with being randomly drawn from a Maxwellian distribution with
$\sigma \leq 196$ pc. Since astrophysical effects produce no feasible analogues
for the $1.62^{+0.47}_{-0.49}$ kpc offset recently observed in Abell 3827, the
observational result is in tension with the collisionless cold dark matter
model assumed in our simulations. | The LABOCA survey of the Extended Chandra Deep Field South: A
photometric redshift survey of submillimetre galaxies: [abridged] We derive photometric redshifts from 17-band optical to mid-IR
photometry of 74 robust counterparts to 68 of the 126 submillimetre galaxies
(SMGs) selected at 870um by LABOCA observations in the ECDFS. The median
photometric redshift of identified SMGs is z=2.2\pm0.1, the interquartile range
is z=1.8-2.7 and we identify 10 (~15%) high-redshift (z>3) SMGs. We derive a
simple redshift estimator for SMGs based on the 3.6 and 8um fluxes, which is
accurate to Delta_z~0.4 for SMGs at z<4. A statistical analysis of sources
around unidentified SMGs identifies a population of likely counterparts with a
redshift distribution peaking at z=2.5\pm0.3, which likely comprises ~60% of
the unidentified SMGs. This confirms that the bulk of the undetected SMGs are
coeval with those detected in the radio/mid-IR. We conclude that ~15% of all
the SMGs are below the flux limits of our survey and lie at z>3 and hence ~30%
of all SMGs have z>3. We estimate that the full S_870um>4mJy SMG population has
a median redshift of 2.5\pm0.6. In contrast to previous suggestions we find no
significant correlation between S_870um and redshift. The median stellar mass
of the SMGs derived from SED fitting is (9.2\pm0.9)x10^10Msun and the
interquartile range is (4.7-14)x10^10Msun, although we caution that uncertainty
in the star-formation histories results in a factor of ~5 uncertainty in these
stellar masses. The median characteristic dust temperature of SMGs is
35.9\pm1.4K and the interquartile range is 28.5-43.3K. The infrared luminosity
function shows that SMGs at z=2-3 typically have higher far-IR luminosities and
luminosity density than those at z=1-2. This is mirrored in the evolution of
the star-formation rate density (SFRD) for SMGs which peaks at z~2. The maximum
contribution of bright SMGs to the global SFRD (~5% for SMGs with S_870um>4mJy;
~50% for SMGs with S_870um>1mJy) also occurs at z~2. |
Spectral analysis of magnetic fields in simulated galaxy clusters: We introduce a new sample of galaxy clusters obtained from a cosmological
simulation covering an unprecedented dynamical range. All the clusters in our
sample show a clear signature of small-scale dynamo amplification. We show that
it is possible to use dynamo theory for studying the magnetic spectrum in the
intracluster medium. We study if the intrinsic variations on the spectra depend
on the dynamical history of each cluster or on some host cluster properties. | Stochastic gravitational wave background from the collisions of dark
matter halos: We investigate the effect of the dark matter (DM) halos collisions, namely
collisions of galaxies and galaxy clusters, through gravitational
bremsstrahlung, on the stochastic gravitational wave background. We first
calculate the gravitational wave signal of a single collision event, assuming
point masses and linear perturbation theory. Then we proceed to the calculation
of the energy spectrum of the collective effect of all dark matter collisions
in the Universe. Concerning the DM halo collision rate, we show that it is
given by the product of the number density of DM halos, which is calculated by
the extended Press-Schechter (EPS) theory, with the collision rate of a single
DM halo, which is given by simulation results, with a function of the linear
growth rate of matter density through cosmological evolution. Hence,
integrating over all mass and distance ranges, we finally extract the spectrum
of the stochastic gravitational wave background created by DM halos collisions.
As we show, the resulting contribution to the stochastic gravitational wave
background is of the order of $h_{c} \approx 10^{-29}$ in the band of $f
\approx 10^{-15} Hz$. However, in very low frequency band, it is larger. With
current observational sensitivity it cannot be detected. |
Mass assembly of galaxies: Smooth accretion versus mergers: Galaxies accrete their mass by means of both smooth accretion from the cosmic
web, and the mergers of smaller entities. We wish to quantify the respective
role of these two modes of accretion, which could determine the morphological
types of galaxies observed today. Multi-zoom cosmological simulations are used
to estimate as a function of time the evolution of mass in bound systems, for
dark matter as well as baryons. The baryonic contents of dark matter haloes are
studied. Merger histories are followed as a function of external density, and
the different ways in which mass is assembled in galaxies and the stellar
component accumulated are quantified. We find that most galaxies assemble their
mass through smooth accretion, and only the most massive galaxies also grow
significantly through mergers. The mean fraction of mass assembled by accretion
is 77 %, and by mergers 23 %. We present typical accretion histories of
hundreds of galaxies: masses of the most massive galaxies increase
monotonically in time, mainly through accretion, many intermediate-mass objects
also experience mass-loss events such as tidal stripping and evaporation.
However, our simulations suffer from the overcooling of massive galaxies caused
by the neglect of active galaxy nuclei (AGN) feedback. The time by which half
of the galay mass has assembled, both in dark matter and baryons, is a
decreasing function of mass, which is compatible with the observations of a
so-called downsizing. At every epoch in the universe, there are low-mass
galaxies actively forming stars, while more massive galaxies form their stars
over a shorter period of time within half the age of the universe. | Precision cosmology with the 2MASS clustering dipole: Comparison of peculiar velocities of galaxies with their gravitational
accelerations (induced by the density field) is one of the methods to constrain
the redshift distortion parameter \beta=(\Omega_m^0.55)/b, where \Omega_m is
the non-relativistic matter density parameter and b is the linear bias. In
particular, one can use the motion of the Local Group (LG) for that purpose.
Its peculiar velocity is known from the dipole component of the cosmic
microwave background, whereas its acceleration can be estimated with the use of
an all-sky galaxy catalog, from the so-called clustering dipole. At the moment,
the biggest dataset of that kind is the Two Micron All Sky Survey Extended
Source Catalog (2MASS XSC) containing almost 1 million galaxies and complete up
to ~300 Mpc/h. We applied 2MASS data to measure LG acceleration and used two
methods to estimate the beta parameter. Both of them yield \beta~0.4 with an
error of several per cent, which is the most precise determination of this
parameter from the clustering dipole to date. |
Dark energy equation of state parameter and its variation at low
redshifts: In this paper, we constrain dark energy models using a compendium of
observations at low redshifts. We consider the dark energy as a barotropic
fluid, with the equation of state a constant as well the case where dark energy
equation of state is a function of time. The observations considered here are
Supernova Type Ia data, Baryonic Acoustic Oscillation data and Hubble parameter
measurements. We compare constraints obtained from these data and also do a
combined analysis. The combined observational constraints put strong limits on
variation of dark energy energy density with redshift. For varying dark energy
models, the range of parameters preferred by the supernova type Ia data is in
tension with the other low redshift distance measurements. | Joint analysis constraints on the physics of the first galaxies with low
frequency radio astronomy data: The first billion years of cosmic history remains largely unobserved. We
demonstrate, using a novel machine learning technique, how combining upper
limits on the spatial fluctuations in the 21-cm signal with observations of the
sky-averaged 21-cm signal from neutral hydrogen can improve our understanding
of this epoch. By jointly analysing data from SARAS3 (redshift $z\approx15-25$)
and limits from HERA ($z\approx8$ and $10$), we show that such a synergetic
analysis provides tighter constraints on the astrophysics of galaxies 200
million years after the Big Bang than can be achieved with the individual data
sets. Although our constraints are weak, this is the first time data from a
sky-averaged 21-cm experiment and power spectrum experiment have been analysed
together. In synergy, the two experiments leave only $64.9^{+0.3}_{-0.1}$% of
the explored broad theoretical parameter space to be consistent with the joint
data set, in comparison to $92.3^{+0.3}_{-0.1}$% for SARAS3 and
$79.0^{+0.5}_{-0.2}$% for HERA alone. We use the joint analysis to constrain
star formation efficiency, minimum halo mass for star formation, X-ray
luminosity of early emitters and the radio luminosity of early galaxies. The
joint analysis disfavours at 68% confidence a combination of galaxies with
X-ray emission that is $\lesssim 33$ and radio emission that is $\gtrsim 32$
times as efficient as present day galaxies. We disfavour at $95$% confidence
scenarios in which power spectra are $\geq126$ mK$^{2}$ at $z=25$ and the
sky-averaged signals are $\leq-277$ mK. |
A tale of seven narrow spikes and a long trough: constraining the timing
of the percolation of HII bubbles at the tail-end of reionization with ULAS
J1120+0641: High-signal to noise observations of the Ly$\alpha$ forest transmissivity in
the z = 7.085 QSO ULAS J1120+0641 show seven narrow transmission spikes
followed by a long 240 cMpc/h trough. Here we use radiative transfer
simulations of cosmic reionization previously calibrated to match a wider range
of Ly$\alpha$ forest data to show that the occurrence of seven transmission
spikes in the narrow redshift range z = 5.85 - 6.1 is very sensitive to the
exact timing of reionization. Occurrence of the spikes requires the most under
dense regions of the IGM to be already fully ionised. The rapid onset of a long
trough at z = 6.12 requires a strong decrease of the photo-ionisation rate at
z$\sim$6.1 in this line-of-sight, consistent with the end of percolation at
this redshift. The narrow range of reionisation histories that we previously
found to be consistent with a wider range of Ly$\alpha$ forest data have a
reasonable probability of showing seven spikes and the mock absorption spectra
provide an excellent match to the spikes and the trough in the observed
spectrum of ULAS J1120+0641. Despite the large overall opacity of Ly$\alpha$ at
z > 5.8, larger samples of high signal-to-noise observations of rare
transmission spikes should therefore provide important further insights into
the exact timing of the percolation of HII bubbles at the tail-end of
reionization | Tracing the Cosmic Web substructure with Lagrangian submanifold: A new computational paradigm for the analysis of substructure of the Cosmic
Web in cosmological cold dark matter simulations is proposed. We introduce a
new data-field --- the flip-flop field ---which carries wealth of information
about the history and dynamics of the structure formation in the universe. The
flip-flop field is an ordered data set in Lagrangian space representing the
number of turns inside out sign reversals of an elementary volume of each
collisionless fluid element represented by a computational particle in a N-body
simulation. This field is computed using the Lagrangian submanifold, i.e. the
three-dimensional dark matter sheet in the six-dimensional space formed by
three Lagrangian and three Eulerian coordinates of the simulation particles. It
is demonstrated that the very rich substructure of dark matter haloes and the
void regions can be reliably and unambiguously recovered from the flip-flop
field. |
Peculiar-velocity cosmology with Types Ia and II supernovae: We present the Democratic Samples of Supernovae (DSS), a compilation of 775
low-redshift Type Ia and II supernovae (SNe Ia & II), of which 137 SN Ia
distances are derived via the newly developed snapshot distance method. Using
the objects in the DSS as tracers of the peculiar-velocity field, we compare
against the corresponding reconstruction from the 2M++ galaxy redshift survey.
Our analysis -- which takes special care to properly weight each DSS
subcatalogue and cross-calibrate the relative distance scales between them --
results in a measurement of the cosmological parameter combination $f\sigma_8 =
0.390_{-0.022}^{+0.022}$ as well as an external bulk flow velocity of
$195_{-23}^{+22}$ km s$^{-1}$ in the direction $(\ell, b) = (292_{-7}^{+7},
-6_{-4}^{+5})$ deg, which originates from beyond the 2M++ reconstruction.
Similarly, we find a bulk flow of $245_{-31}^{+32}$ km s$^{-1}$ toward $(\ell,
b) = (294_{-7}^{+7}, 3_{-5}^{+6})$ deg on a scale of $\sim 30 h^{-1}$ Mpc if we
ignore the reconstructed peculiar-velocity field altogether. Our constraint on
$f\sigma_8$ -- the tightest derived from SNe to date (considering only
statistical error bars), and the only one to utilise SNe II -- is broadly
consistent with other results from the literature. We intend for our data
accumulation and treatment techniques to become the prototype for future
studies that will exploit the unprecedented data volume from upcoming
wide-field surveys. | The Microlensing Properties of a Sample of 87 Lensed Quasars: Gravitational microlensing is a powerful tool for probing the physical
properties of quasar accretion disks and properties of the lens galaxy such as
its dark matter fraction and mean stellar mass. Unfortunately the number of
lensed quasars ($\sim 90$) exceeds our monitoring capabilities. Thus,
estimating their microlensing properties is important for identifying good
microlensing candidates as well as for the expectations of future surveys. In
this work we estimate the microlensing properties of a sample of 87 lensed
quasars. While the median Einstein radius crossing time scale is 20.6 years,
the median source crossing time scale is 7.3 months. Broadly speaking, this
means that on $\sim 10$ year timescales roughly half the lenses will be
quiescent, with the source in a broad demagnified valley, and roughly half will
be active with the source lying in the caustic ridges. We also found that the
location of the lens system relative to the CMB dipole has a modest effect on
microlensing timescales, and in theory microlensing could be used to confirm
the kinematic origin of the dipole. As a corollary of our study we analyzed the
accretion rate parameters in a sub-sample of 32 lensed quasars. At fixed black
hole mass, it is possible to sample a broad range of luminosities (i.e.,
Eddington factors) if it becomes feasible to monitor fainter lenses. |
The FMOS-Cosmos Survey of Star-Forming Galaxies at z~1.6 II. The
Mass-Metallicity Relation and the Dependence on Star Formation Rate and Dust
Extinction: We investigate the relationships between stellar mass, gas-phase oxygen
abundance (metallicity), star formation rate, and dust content of star-forming
galaxies at z$\sim$1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The
mass-metallicity relation at $z\sim1.6$ is steeper than the relation observed
in the local Universe. The steeper MZ relation at $z\sim1.6$ is mainly due to
evolution in the stellar mass where the MZ relation begins to turnover and
flatten. This turnover mass is 1.2 dex larger at $z\sim1.6$. The most massive
galaxies at $z\sim1.6$ ($\sim 10^{11}M_\odot$) are enriched to the level
observed in massive galaxies in the local Universe. The mass-metallicity
relation we measure at $z\sim1.6$ supports the suggestion of an empirical upper
metallicity limit that does not significantly evolve with redshift. We find an
anti-correlation between metallicity and star formation rate for galaxies at a
fixed stellar mass at $z\sim1.6$ which is similar to trends observed in the
local Universe. We do not find a relation between stellar mass, metallicity and
star formation rate that is independent of redshift; our data suggest that
there is redshift evolution in this relation. We examine the relation between
stellar mass, metallicity and dust extinction. We find that at a fixed stellar
mass dustier galaxies tend to be more metal rich. From examination of the
stellar masses, metallicities, SFRs and dust extinctions we conclude that
stellar mass is most closely related to dust extinction. | Equilibrium Structure and Radial Oscillations of Dark Matter Admixed
Neutron Stars: In [Leung et al., Phys. Rev. D 84, 107301 (2011)], we presented our results
on using a general relativistic two-fluid formalism to study the hydrostatic
equilibrium configuration of an admixture of degenerate dark matter and normal
nuclear matter. In this work, we present more analysis to complement our
previous findings. We study the radial oscillation modes of these compact stars
in detail. We find that these stars in general have two classes of oscillation
modes. For a given total mass of the star, the first class of modes is
insensitive to the dark-matter particle mass. They also reduce properly to the
oscillation modes of the corresponding ordinary neutron star, with the same
total mass, when the mass fraction of dark matter tends to zero. On the other
hand, the second class of modes is due mainly to the dark-matter fluid. In the
small dark-matter mass fraction limit, these modes are characterized purely by
the oscillations of dark matter, while the normal matter is essentially at
rest. In the intermediate regime where the mass fractions of the two fluids are
comparable, the normal matter oscillates with the dark matter due to their
coupling through gravity. In contrast to the first class of modes, the
frequencies of these dark-matter dominated modes depend sensitively on the mass
of dark-matter particles. |
Foreground removal for Square Kilometre Array observations of the Epoch
of Reionization with the Correlated Component Analysis: We apply the Correlated Component Analysis (CCA) method on simulated data of
the Square Kilometre Array, with the aim of accurately cleaning the 21 cm
reionization signal from diffuse foreground contamination. The CCA has been
developed for the Cosmic Microwave Background, but the application of the
Fourier-domain implementation of this method to the reionization signal is
straightforward.
The CCA is a parametric method to estimate the frequency behaviour of the
foregrounds from the data by using second-order statistics. We test its
performance on foreground simulations of increasing complexity, designed to
challenge the parametric models adopted. We also drop the assumption of
spectral smoothness that most of the methods rely upon. We are able to clean
effectively the simulated data across the explored frequency range (100-200
MHz) for all the foreground simulations. This shows that the CCA method is very
promising for EoR component separation. | Quantum corrections to gravity and their implications for cosmology and
astrophysics: The quantum contributions to the gravitational action are relatively easy to
calculate in the higher derivative sector of the theory. However, the
applications to the post-inflationary cosmology and astrophysics require the
corrections to the Einstein-Hilbert action and to the cosmological constant,
and those we can not derive yet in a consistent and safe way. At the same time,
if we assume that these quantum terms are covariant and that they have relevant
magnitude, their functional form can be defined up to a single free parameter,
which can be defined on the phenomenological basis. It turns out that the
quantum correction may lead, in principle, to surprisingly strong and
interesting effects in astrophysics and cosmology. |
A candidate redshift z ~ 10 galaxy and rapid changes in that population
at an age of 500 Myr: Searches for very-high-redshift galaxies over the past decade have yielded a
large sample of more than 6,000 galaxies existing just 900-2,000 million years
(Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep
Field (HUDF09) data have yielded the first reliable detections of z ~ 8
galaxies that, together with reports of a gamma-ray burst at z ~ 8.2 (refs 10,
11), constitute the earliest objects reliably reported to date. Observations of
z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use
the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10
galaxies in the heart of the reionization epoch, only 500 Myr after the Big
Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show
that, regardless of source detections, the star formation rate density is much
smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This
demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in
both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200
Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest
galaxies. | The dark matter of galaxy voids: How do observed voids relate to the underlying dark matter distribution? To
examine the spatial distribution of dark matter contained within voids
identified in galaxy surveys, we apply Halo Occupation Distribution models
representing sparsely and densely sampled galaxy surveys to a high-resolution
N-body simulation. We compare these galaxy voids to voids found in the halo
distribution, low-resolution dark matter, and high-resolution dark matter. We
find that voids at all scales in densely sampled surveys - and medium- to
large-scale voids in sparse surveys - trace the same underdensities as dark
matter, but they are larger in radius by ~20%, they have somewhat shallower
density profiles, and they have centers offset by ~0.4Rv rms. However, in
void-to-void comparison we find that shape estimators are less robust to
sampling, and the largest voids in sparsely sampled surveys suffer
fragmentation at their edges. We find that voids in galaxy surveys always
correspond to underdensities in the dark matter, though the centers may be
offset. When this offset is taken into account, we recover almost identical
radial density profiles between galaxies and dark matter. All mock catalogs
used in this work are available at http://www.cosmicvoids.net. |
Automated detection of filaments in the large scale structure of the
universe: We present a new method to identify large scale filaments and apply it to a
cosmological simulation. Using positions of haloes above a given mass as node
tracers, we look for filaments between them using the positions and masses of
all the remaining dark-matter haloes. In order to detect a filament, the first
step consists in the construction of a backbone linking two nodes, which is
given by a skeleton-like path connecting the highest local dark matter (DM)
density traced by non-node haloes. The filament quality is defined by a density
and gap parameters characterising its skeleton, and filament members are
selected by their binding energy in the plane perpendicular to the filament.
This membership condition is associated to characteristic orbital times;
however if one assumes a fixed orbital timescale for all the filaments, the
resulting filament properties show only marginal changes, indicating that the
use of dynamical information is not critical for the method. We test the method
in the simulation using massive haloes($M>10^{14}$h$^{-1}M_{\odot}$) as
filament nodes. The main properties of the resulting high-quality filaments
(which corresponds to $\simeq33%$ of the detected filaments) are, i) their
lengths cover a wide range of values of up to $150 $h$^{-1}$Mpc, but are mostly
concentrated below 50h$^{-1}$Mpc; ii) their distribution of thickness peaks at
$d=3.0$h$^{-1}$Mpc and increases slightly with the filament length; iii) their
nodes are connected on average to $1.87\pm0.18$ filaments for $\simeq
10^{14.1}M_{\odot}$ nodes; this number increases with the node mass to $\simeq
2.49\pm0.28$ filaments for $\simeq 10^{14.9}M_{\odot}$ nodes. | Comparing the relation between star formation and galaxy mass in
different environments: Analyzing 24 mu m MIPS/Spitzer data and the [O II]3727 line of a sample of
galaxies at 0.4 < z < 0.8 from the ESO Distant Cluster Survey (EDisCS), we
investigate the ongoing star formation rate (SFR) and the specific star
formation rate (SSFR) as a function of stellar mass in galaxy clusters and
groups, and compare with field studies. As for the field, we find a decline in
SFR with time, indicating that star formation (SF) was more active in the past,
and a decline in SSFR as galaxy stellar mass increases, showing that the
current SF contributes more to the fractional growth of low-mass galaxies than
high-mass galaxies. However, we find a lower median SFR (by a factor of ~1.5)
in cluster star-forming galaxies than in the field. The difference is highly
significant when all Spitzer and emission-line galaxies are considered,
regardless of color. It remains significant at z>0.6 after removing red
emission-line (REL) galaxies, to avoid possible AGN contamination. While there
is overlap between the cluster and field SFR-Mass relations, we find a
population of cluster galaxies (10-25%) with reduced SFR for their mass. These
are likely to be in transition from star-forming to passive. Comparing
separately clusters and groups at z>0.6, only cluster trends are significantly
different from the field, and the average cluster SFR at a given mass is ~2
times lower than the field. We conclude that the average SFR in star-forming
galaxies varies with galaxy environment at a fixed galaxy mass. |
Power spectrum nulls due to non-standard inflationary evolution: The simplest models of inflation based on slow roll produce nearly scale
invariant primordial power spectra (PPS). But there are also numerous models
that predict radically broken scale invariant PPS. In particular, markedly
cuspy dips in the PPS correspond to nulls where the perturbation amplitude,
hence PPS, goes through a zero at a specific wavenumber. Near this wavenumber,
the true quantum nature of the generation mechanism of the primordial
fluctuations may be revealed. Naively these features may appear to arise from
fine tuned initial conditions. However, we show that this behavior arises under
fairly generic set of conditions involving super-Hubble scale evolution of
perturbation modes during inflation. We illustrate this with the well-studied
examples of punctuated inflation and the Starobinsky-break model. | Deprojecting the quenching of star formation in and near clusters: Using H_delta and D_n4000 as tracers of recent or ongoing efficient star
formation, we analyze the fraction of SDSS galaxies with recent or ongoing
efficient star formation (GORES) in the vicinity of 268 clusters. We confirm
the well-known segregation of star formation, and using Abel deprojection, we
find that the fraction of GORES increases linearly with physical radius and
then saturates. Moreover, we find that the fraction of GORES is modulated by
the absolute line-of-sight velocity (ALOSV): at all projected radii, higher
fractions of GORES are found in higher ALOSV galaxies. We model this velocity
modulation of GORES fraction using the particles in a hydrodynamical
cosmological simulation, which we classify into virialized, infalling and
backsplash according to their position in radial phase space at z=0. Our
simplest model, where the GORES fraction is only a function of class does not
produce an adequate fit to our observed GORES fraction in projected phase
space. On the other hand, assuming that in each class the fraction of GORES
rises linearly and then saturates, we are able to find well-fitting 3D models
of the fractions of GORES. In our best-fitting models, in comparison with 18%
in the virial cone and 13% in the virial sphere, GORES respectively account for
34% and 19% of the infalling and backsplash galaxies, and as much as 11% of the
virialized galaxies, possibly as a result of tidally induced star formation
from galaxy-galaxy interactions. At the virial radius, the fraction of GORES of
the backsplash population is much closer to that of the virialized population
than to that of the infalling galaxies. This suggests that the quenching of
efficient star formation is nearly complete in a single passage through the
cluster. |
On the origin of the angular momentum properties of gas and dark matter
in galactic halos and its implications: We perform a set of non-radiative hydrodynamical simulations of merging
spherical halos in order to understand the angular momentum (AM) properties of
the galactic halos seen in cosmological simulations. The universal shape of AM
distributions seen in simulations is found to be generically produced as a
result of mergers. The universal shape is such that it has an excess of low AM
material and hence cannot explain the exponential structure of disk galaxies. A
resolution to this is suggested by the spatial distribution of low AM material
which is found to be in the centre and a conical region close to the axis of
rotation. A mechanism that preferentially discards the material in the centre
and prevents the material along the poles from falling onto the disc is
proposed as a solution. We implement a simple geometric criteria for selective
removal of low AM material and show that in order for 90% of halos to host
exponential discs one has to reject at least 40% of material. Next, we explore
the physical mechanisms responsible for distributing the AM within the halo
during a merger. For dark matter there is an inside-out transfer of AM, whereas
for gas there is an outside-in transfer, which is due to differences between
collisionless and gas dynamics. We also explain the apparent high spin of dark
matter halos undergoing mergers and show that a criteria stricter than what is
currently used, would be required to detect such unrelaxed halos. Finally, we
demonstrate that the misalignment of AM between gas and dark matter only occurs
when the intrinsic spins of the merging halos are not aligned with the orbital
AM of the system. The self-misalignment (orientation of AM when measured in
radial shells not being constant), which could be the cause of warps and
anomalous rotation in disks galaxies, also occurs under similar conditions. | Search for non-Gaussianities in the WMAP data with the Scaling Index
Method: In the recent years, non-Gaussianity and statistical isotropy of the Cosmic
Microwave Background (CMB) was investigated with various statistical measures,
first and foremost by means of the measurements of the WMAP satellite. In this
Review, we focus on the analyses that were accomplished with a measure of local
type, the so-called Scaling Index Method (SIM). The SIM is able to detect
structural characteristics of a given data set, and has proven to be highly
valuable in CMB analysis. It was used for comparing the data set with
simulations as well as surrogates, which are full sky maps generated by
randomisation of previously selected features of the original map. During these
investigations, strong evidence for non-Gaussianities as well as asymmetries
and local features could be detected. In combination with the surrogates
approach, the SIM detected the highest significances for non-Gaussianity to
date. |
Correlating features in the primordial spectra: Heavy fields coupled to the inflaton reduce the speed of sound in the
effective theory of the adiabatic mode each time the background inflationary
trajectory deviates from a geodesic. This can result in features in the
primordial spectra. We compute the corresponding bispectrum and show that if a
varying speed of sound induces features in the power spectrum, the change in
the bispectrum is given by a simple formula involving the change in the power
spectrum and its derivatives. In this manner, we provide a uniquely
discriminable signature of a varying sound speed for the adiabatic mode during
inflation that indicates the influence of heavy fields. We find that features
in the bispectrum peak in the equilateral limit and, in particular, in the
squeezed limit we find considerable enhancement entirely consistent with the
single field consistency relation. From the perspective of the underlying
effective theory, our results generalize to a wide variety of inflationary
models where features are sourced by the time variation of background
quantities. A positive detection of such correlated features would be
unambiguous proof of the inflaton's nature as a single light scalar degree of
freedom embedded in a theory that is UV completable. | A self-consistent 3D model of fluctuations in the helium-ionizing
background: Large variations in the effective optical depth of the He II Ly$\alpha$
forest have been observed at $z\gtrsim2.7$, but the physical nature of these
variations is uncertain: either the Universe is still undergoing the process of
He II reionization, or the Universe is highly ionized but the He II-ionizing
background fluctuates significantly on large scales. In an effort to build upon
our understanding of the latter scenario, we present a novel model for the
evolution of ionizing background fluctuations. Previous models have assumed the
mean free path of ionizing photons to be spatially uniform, ignoring the
dependence of that scale on the local ionization state of the intergalactic
medium (IGM). This assumption is reasonable when the mean free path is large
compared to the average distance between the primary sources of He II-ionizing
photons, $\gtrsim L_\star$ quasars. However, when this is no longer the case,
the background fluctuations become more severe, and an accurate description of
the average propagation of ionizing photons through the IGM requires
additionally accounting for the fluctuations in opacity. We demonstrate the
importance of this effect by constructing 3D semi-analytic models of the helium
ionizing background from $z=2.5$-$3.5$ that explicitly include a spatially
varying mean free path of ionizing photons. The resulting distribution of
effective optical depths at large scales in the He II Ly$\alpha$ forest is very
similar to the latest observations with HST/COS at $2.5 \lesssim z \lesssim
3.5$. |
A mid-IR survey of local AGN with GTC/CanariCam: We describe a mid-infrared (MIR) survey of local AGN to be conducted with the
CanariCam instrument on the Gran Telescopio Canarias (GTC). We will obtain MIR
imaging and spectroscopy of a sample of ~100 AGN covering six orders of
magnitude in AGN luminosity, and including different AGN classes (e.g., LINERs,
Seyfert 1s and 2s, QSO). The main goals are: (1) to test unification of Type 1
and Type 2 AGN, (2) to study the star formation activity around AGN, and (3) to
explore the role of the dusty torus in low-luminosity AGN. | Irreducible background of gravitational waves from a cosmic defect
network: update and comparison of numerical techniques: Cosmological phase transitions in the early Universe may produce relics in
the form of a network of cosmic defects. Independently of the order of a phase
transition, topology of the defects, and their global or gauge nature, the
defects are expected to emit gravitational waves (GWs) as the network
energy-momentum tensor adapts itself to maintaining {scaling}. We show that the
evolution of any defect network (and for that matter any scaling source) emits
a GW background with spectrum $\Omega_{\rm GW} \propto f^3$ for $f \ll f_0$,
$\Omega_{\rm GW} \propto 1/f^2$ for $f_0 \lesssim f \lesssim f_{\rm eq}$, and
$\Omega_{\rm GW} \propto~const$ (i.e.~exactly scale-invariant) for $f \gg
f_{\rm eq}$, where $f_0$ and $ f_{\rm eq}$ denote respectively the frequencies
corresponding to the present and matter-radiation equality horizons. This
background represents an irreducible emission of GWs from any scaling network
of cosmic defects, with its amplitude characterized only by the symmetry
breaking scale and the nature of the defects. Using classical lattice
simulations we calculate the GW signal emitted by defects created after the
breaking of a global symmetry $O(N) \rightarrow O(N-1)$. We obtain the GW
spectrum for $N$ between 2 and 20 with two different techniques: integrating
over unequal time correlators of the energy momentum tensor, updating our
previous work on smaller lattices, and for the first time, comparing the result
with the real time evolution of the tensor perturbations sourced by the same
defects. Our results validate the equivalence of the two techniques. Using CMB
upper bounds on the defects' energy scale, we discuss the difficulty of
detecting this GW background in the case of global defects. |
Current constraints on early and stressed dark energy models and future
21 cm perspectives: Despite the great progress of current cosmological measurements, the nature
of the dominant component of the universe, coined dark energy, is still an open
question. Early Dark Energy is a possible candidate which may also alleviate
some fine tuning issues of the standard paradigm. Using the latest available
cosmological data, we find that the 95% CL upper bound on the early dark energy
density parameter is $\Omega_{\textrm{eDE}}$. On the other hand, the dark
energy component may be a stressed and inhomogeneous fluid. If this is the
case, the effective sound speed and the viscosity parameters are unconstrained
by current data. Future omniscope-like $21$cm surveys, combined with present
CMB data, could be able to distinguish between standard quintessence scenarios
from other possible models with $2\sigma$ significance, assuming a
non-negligible early dark energy contribution. The precision achieved on the
$\Omega_{\textrm{eDE}}$ parameter from these $21$ cm probes could be below
$\mathcal{O} (10\%)$. | Wide-angle tail galaxies in ATLAS: We present radio images of a sample of six Wide-Angle Tail (WAT) radio
sources identified in the ATLAS 1.4 GHz radio survey, and new spectroscopic
redshifts for four of these sources. These WATs are in the redshift range of
0.1469 - 0.3762, and we find evidence of galaxy overdensities in the vicinity
of four of the WATs from either spectroscopic or photometric redshifts. We also
present follow-up spectroscopic observations of the area surrounding the
largest WAT, S1189, which is at a redshift of ~0.22. The spectroscopic
observations, taken using the AAOmega spectrograph on the AAT, show an
overdensity of galaxies at this redshift. The galaxies are spread over an
unusually large area of ~12 Mpc with a velocity spread of ~4500 km/s. This
large-scale structure includes a highly asymmetric FRI radio galaxy and also
appears to host a radio relic. It may represent an unrelaxed system with
different sub-structures interacting or merging with one another. We discuss
the implications of these observations for future large-scale radio surveys. |
The intrinsic bispectrum of the CMB from isocurvature initial conditions: Non-linear effects in the early Universe generate non-zero bispectra of the
cosmic microwave background (CMB) temperature and polarization, even in the
absence of primordial non-Gaussianity. In this paper, we compute the
contributions from isocurvature modes to the CMB bispectra using a modified
version of the second-order Boltzmann solver SONG. We investigate the ability
of current and future CMB experiments to constrain these modes with
observations of the bispectrum. Our results show that the enhancement due to
single isocurvature modes mixed with the adiabatic mode is negligible for the
parameter ranges currently allowed by the most recent Planck results. However,
we find that a large compensated isocurvature mode can produce a detectable
bispectrum when its correlation with the adiabatic mode is appreciable. The
non-observation of this contribution in searches for the lensing bispectrum
from Planck allows us to place a new constraint on the relative amplitude of
the correlated part of the compensated isocurvature mode of $f_{\rm
CIP}=1\pm100$. We compute forecasts for future observations by COrE, SO, CMB-S4
and an ideal experiment and conclude that a dedicated search for the bispectrum
from compensated modes could rule out a number of scenarios realised in the
curvaton model. In addition, the CMB-S4 experiment could detect the most
extreme of those scenarios ($f_{\rm CIP}=16.5$) at 2 to 3-$\sigma$
significance. | z~4 Halpha Emitters in GOODS : Tracing the Dominant Mode for Growth of
Galaxies: We present evidence for unusually strong Halpha emission in galaxies with
spectroscopic redshifts in the range of 3.8<z<5.0, over the Great Observatories
Origins Deep Survey (GOODS) fields. Among 74 galaxies detected in the Spitzer
IRAC 3.6 and 4.5um bands, more than 70% of the galaxies show clear excess at
3.6um compared to the expected flux density from stellar continuum only. We
provide evidence that this 3.6um excess is due to Halpha emission redshifted
into the 3.6um band, and classify these 3.6um excess galaxies to be Halpha
emitter (HAE) candidates. The selection of HAE candidates using an excess in
broad-band filters is sensitive to objects whose rest-frame H$\alpha$
equivalent width is larger than 350A, star formation rates of 20-500 Msun/yr.
The Halpha-to-UV luminosity ratio of HAEs is on average larger than that of
local starbursts. Possible reasons for such strong Halpha emission in these
galaxies include different dust extinction properties, young stellar population
age, continuous star formation history, low metallicity, and top-heavy stellar
initial mass function. Although the correlation between UV slope beta and
L(Ha)/L(UV) raises the possibility that HAEs prefer a dust extinction curve
which is steeper in the UV, the most dominant factor that results in strong
Halpha emission appears to be star formation history. The Halpha equivalent
widths of HAEs are large despite their relatively old stellar population ages
constrained by SED fitting, suggesting that at least 60% of HAEs produce stars
at a constant rate. Under the assumption that the cold gas supply is sustained,
HAEs are able to produce ~50% of the observed stellar mass density at z~3 that
is caught in massive (M*>10^11 Msun) galaxies. This 'strong Halpha phase' of
star formation plays a dominant role in early galaxy growth, being a feasible
progenitors of massive red galaxies at lower redshifts. |
Galaxy Clusters as a probe of early dark energy: We study a class of early dark energy (EDE) models, in which, unlike in
standard dark energy models, a substantial amount of dark energy exists in the
matter-dominated era. We self-consistently include dark energy perturbations,
and show that these models may be successfully constrained using future
observations of galaxy clusters, in particular the redshift abundance, and the
Sunyaev-Zel'dovich (SZ) power spectrum. We make predictions for EDE models, as
well as LCDM for incoming X-ray (eROSITA) and microwave (South Pole Telescope)
observations. We show that galaxy clusters' mass function and the SZ power
spectrum will put strong constraints both on the equation of state of \de today
and the redshift at which EDE transits to present-day LCDM like behavior for
these models, thus providing complementary information to the geometric probes
of dark energy. Not including perturbations in EDE models leads to those models
being practically indistinguishable from LCDM. An MCMC analysis of future
galaxy cluster surveys provides constraints for EDE parameters that are
competitive with and complementary to background expansion observations such as
supernovae. | An improved measurement of baryon acoustic oscillations from the
correlation function of galaxy clusters at $z \sim 0.3$: We detect the peak of baryon acoustic oscillations (BAO) in the two-point
correlation function of a spectroscopic sample of $25226$ clusters selected
from the Sloan Digital Sky Survey. Galaxy clusters, as tracers of massive dark
matter haloes, are highly biased structures. The linear bias $b$ of the sample
considered in this work, that we estimate from the projected correlation
function, is $b \sigma_8 = 1.72 \pm 0.03$. Thanks to the high signal in the
cluster correlation function and to the accurate spectroscopic redshift
measurements, we can clearly detect the BAO peak and determine its position,
$s_p$, with high accuracy, despite the relative paucity of the sample. Our
measurement, $s_p = 104 \pm 7 \, \mathrm{Mpc} \, h^{-1}$, is in good agreement
with previous estimates from large galaxy surveys, and has a similar
uncertainty. The BAO measurement presented in this work thus provides a new
strong confirmation of the concordance cosmological model and demonstrates the
power and promise of galaxy clusters as key probes for cosmological
applications based on large scale structures. |
Quasars as Standard Candles IV. Analysis of the X-ray and UV indicators
of the disc-corona relation: Context: A non-linear relation between quasar monochromatic luminosities at
2500A and 2 keV holds at all observed redshifts and luminosities, and it has
been used to derive quasar distances and to build a Hubble Diagram of quasars.
The choice of the X-ray and UV indicators has so far been somewhat arbitrary,
and has typically relied on photometric data. Aims: We want to determine the
X-ray and UV proxies that provide the smallest dispersion of the relation, in
order to obtain more precise distance estimates, and to confirm the reliability
of the X-ray to UV relation as a distance indicator. Methods: We performed a
complete UV spectroscopic analysis of a sample of $\sim$1800 quasars with SDSS
optical spectra and XMM- Newton X-ray serendipitous observations. In the
X-rays, we analysed the spectra of all the sample objects at redshift z $>$1.9,
while we relied on photometric measurements at lower redshifts. As done in
previous studies, we analysed the relation in small redshift bins, using fluxes
instead of luminosities. Results: We show that the monochromatic fluxes at 1
keV and 2500A are, respectively, the best X-ray and UV continuum indicators
among those that are typically available. We also find a tight relation between
soft X-ray and Mg ii2800A line fluxes, and a marginal dependence of the X-ray
to UV relation on the width of the Mg ii line. Conclusions: Our analysis
suggests that the physical quantities that are more tightly linked to one
another are the soft X-ray flux at $\sim$1 keV and the ionizing UV flux
blueward of the Lyman limit. However, the "usual" monochromatic fluxes at 2 keV
and 2500A estimated from photometric data provide an almost as-tight X-ray to
UV relation, and can be used to derive quasar distances. The Hubble diagram
obtained using spectroscopic indicators is fully consistent with the one
presented in previous papers, based on photometric data. | Disc scalelengths out to redshift 5.8: We compute the exponential disc scalelength for 686 disc galaxies with
spectroscopic redshifts out to redshift 5.8 based on Hubble Space Telescope
archival data. We compare the results with our previous measurements based on
30000 nearby galaxies from the Sloan Digital Sky Survey. Our results confirm
the presence of a dominating exponential component in galaxies out to this
redshift. At the highest redshifts, the disc scalelength for the brightest
galaxies with absolute magnitude between -24 and -22 is up to a factor 8
smaller compared to that in the local Universe. This observed scalelength
decrease is significantly greater than the value predicted by a cosmological
picture in which baryonic disc scalelength scales with the virial radius of the
dark matter halo. |
J-PAS: The Javalambre-Physics of the Accelerated Universe Astrophysical
Survey: The Javalambre-Physics of the Accelerated Universe Astrophysical Survey
(J-PAS) is a narrow band, very wide field Cosmological Survey to be carried out
from the Javalambre Observatory in Spain with a purpose-built, dedicated 2.5m
telescope and a 4.7 sq.deg. camera with 1.2Gpix. Starting in late 2015, J-PAS
will observe 8500sq.deg. of Northern Sky and measure $0.003(1+z)$ photo-z for
$9\times10^7$ LRG and ELG galaxies plus several million QSOs, sampling an
effective volume of $\sim 14$ Gpc$^3$ up to $z=1.3$ and becoming the first
radial BAO experiment to reach Stage IV. J-PAS will detect $7\times 10^5$
galaxy clusters and groups, setting constrains on Dark Energy which rival those
obtained from its BAO measurements. Thanks to the superb characteristics of the
site (seeing ~0.7 arcsec), J-PAS is expected to obtain a deep, sub-arcsec image
of the Northern sky, which combined with its unique photo-z precision will
produce one of the most powerful cosmological lensing surveys before the
arrival of Euclid. J-PAS unprecedented spectral time domain information will
enable a self-contained SN survey that, without the need for external
spectroscopic follow-up, will detect, classify and measure $\sigma_z\sim 0.5\%$
redshifts for $\sim 4000$ SNeIa and $\sim 900$ core-collapse SNe. The key to
the J-PAS potential is its innovative approach: a contiguous system of 54
filters with $145\AA$ width, placed $100\AA$ apart over a multi-degree FoV is a
powerful "redshift machine", with the survey speed of a 4000 multiplexing low
resolution spectrograph, but many times cheaper and much faster to build. The
J-PAS camera is equivalent to a 4.7 sq.deg. "IFU" and it will produce a
time-resolved, 3D image of the Northern Sky with a very wide range of
Astrophysical applications in Galaxy Evolution, the nearby Universe and the
study of resolved stellar populations. | The AGN content in luminous IR galaxies at z\sim2 from a global SED
analysis including Herschel data: We use Herschel-PACS far-infrared data, combined with previous multi-band
information and mid-IR spectra, to properly account for the presence of an
active nucleus and constrain its energetic contribution in luminous infrared
(IR) sources at z\sim2. The sample is composed of 24 sources in the GOODS-South
field, with typical IR luminosity of 10^{12} Lo. Data from the 4 Ms Chandra
X-ray imaging in this field are also used to identify and characterize AGN
emission. We reproduce the observed spectral energy distribution (SED),
decomposed into a host-galaxy and an AGN component. A smooth-torus model for
circum-nuclear dust is used to account for the direct and re-processed
contribution from the AGN. We confirm that galaxies with typical
L_{8-1000um}\sim10^{12}Lo at z\sim2 are powered predominantly by
star-formation. An AGN component is present in nine objects (\sim35% of the
sample) at the 3sigma confidence level, but its contribution to the 8-1000 um
emission accounts for only \sim5% of the energy budget. The AGN contribution
rises to \sim23% over the 5-30 um range (in agreement with Spitzer IRS results)
and to \sim60% over the narrow 2-6 um range. The presence of an AGN is
confirmed by X-ray data for 3 (out of nine) sources, with X-ray spectral
analysis indicating the presence of significant absorption, i.e.
NH\sim10^{23}-10^{24} cm^{-2}. An additional source shows indications of
obscured AGN emission from X-ray data. The comparison between the
mid-IR--derived X-ray luminosities and those obtained from X-ray data suggests
that obscuration is likely present also in the remaining six sources that
harbour an AGN according to the SED-fitting analysis. |
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