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Problems with the sources of the observed gravitational waves and their
resolution: Recent direct registration of gravitational waves by LIGO and astronomical
observations of the universe at redshifts 5-10 demonstrate that the standard
astrophysics and cosmology are in tension with the data. The origin of the
source of the GW150914 event, which presumably is a binary of coalescing black
holes with masses about 30 solar masses, each with zero spin, as well as the
densely populated universe at z= 5-10 by superheavy black holes, blight
galaxies, supernovae, and dust does not fit the standard astrophysical picture.
It is shown here that the model of primordial black hole (PBH) formation,
suggested in 1993, nicely explains all these and more puzzles, including those
in contemporary universe, such as MACHOs and the mass spectrum of the observed
solar mass black holes.. The mass spectrum and density of PBH is predicted. The
scenario may possibly lead to abundant antimatter in the universe and even in
the Galaxy. | Systematic errors in the measurement of neutrino masses due to baryonic
feedback processes: Prospects for stage IV lensing surveys: We examine the importance of baryonic feedback effects on the matter power
spectrum on small scales, and the implications for the precise measurement of
neutrino masses through gravitational weak lensing. Planned large galaxy
surveys such as the Large Synoptic Sky Telescope (LSST) and Euclid are expected
to measure the sum of neutrino masses to extremely high precision, sufficient
to detect non-zero neutrino masses even in the minimal mass normal hierarchy.
We show that weak lensing of galaxies while being a very good probe of neutrino
masses, is extremely sensitive to baryonic feedback processes. We use publicly
available results from the Overwhelmingly Large Simulations (OWLS) project to
investigate the effects of active galactic nuclei feedback, the nature of the
stellar initial mass function, and gas cooling rates, on the measured weak
lensing shear power spectrum. Using the Fisher matrix formalism and priors from
CMB+BAO data, we show that when one does not account for feedback, the measured
neutrino mass may be substantially larger or smaller than the true mass,
depending on the dominant feedback mechanism, with the mass error |\Delta m_nu|
often exceeding the mass m_nu itself. We also consider gravitational lensing of
the cosmic microwave background (CMB) and show that it is not sensitive to
baryonic feedback on scales l < 2000, although CMB experiments that aim for
sensitivities sigma(m_nu) < 0.02 eV will need to include baryonic effects in
modeling the CMB lensing potential. A combination of CMB lensing and galaxy
lensing can help break the degeneracy between neutrino masses and baryonic
feedback processes. We conclude that future large galaxy lensing surveys such
as LSST and Euclid can only measure neutrino masses accurately if the matter
power spectrum can be measured to similar accuracy. |
Two- and three-dimensional wide-field weak lensing mass maps from the
Hyper Suprime-Cam Subaru Strategic Program S16A data: We present wide-field (167 deg$^2$) weak lensing mass maps from the Hyper
Supreme-Cam Subaru Strategic Program (HSC-SSP). We compare these weak lensing
based dark matter maps with maps of the distribution of the stellar mass
associated with luminous red galaxies. We find a strong correlation between
these two maps with a correlation coefficient of $\rho=0.54\pm0.03$ (for a
smoothing size of $8'$). This correlation is detected even with a smaller
smoothing scale of $2'$ ($\rho=0.34\pm 0.01$). This detection is made uniquely
possible because of the high source density of the HSC-SSP weak lensing survey
($\bar{n}\sim 25$ arcmin$^{-2}$). We also present a variety of tests to
demonstrate that our maps are not significantly affected by systematic effects.
By using the photometric redshift information associated with source galaxies,
we reconstruct a three-dimensional mass map. This three-dimensional mass map is
also found to correlate with the three-dimensional galaxy mass map.
Cross-correlation tests presented in this paper demonstrate that the HSC-SSP
weak lensing mass maps are ready for further science analyses. | Photometric SN Ia Candidates from the Three-Year SDSS-II SN Survey Data: We analyze the three-year SDSS-II Superernova (SN) Survey data and identify a
sample of 1070 photometric SN Ia candidates based on their multi-band light
curve data. This sample consists of SN candidates with no spectroscopic
confirmation, with a subset of 210 candidates having spectroscopic redshifts of
their host galaxies measured, while the remaining 860 candidates are purely
photometric in their identification. We describe a method for estimating the
efficiency and purity of photometric SN Ia classification when spectroscopic
confirmation of only a limited sample is available, and demonstrate that SN Ia
candidates from SDSS-II can be identified photometrically with ~91% efficiency
and with a contamination of ~6%. Although this is the largest uniform sample of
SN candidates to date for studying photometric identification, we find that a
larger spectroscopic sample of contaminating sources is required to obtain a
better characterization of the background events. A Hubble diagram using SN
candidates with no spectroscopic confirmation, but with host galaxy
spectroscopic redshifts, yields a distance modulus dispersion that is only ~20
- 40% larger than that of the spectroscopically-confirmed SN Ia sample alone
with no significant bias. A Hubble diagram with purely photometric
classification and redshift-distance measurements, however, exhibit biases that
require further investigation for precision cosmology. |
Seeding supermassive black holes with a non-vortical dark-matter
subcomponent: A perfect irrotational fluid with the equation of state of dust, Irrotational
Dark Matter (IDM), is incapable of virializing and instead forms a
cosmoskeleton of filaments with supermassive black holes at the joints. This
stark difference from the standard cold dark matter (CDM) scenario arises
because IDM must exhibit potential flow at all times, preventing shell-crossing
from occurring. This scenario is applicable to general non-oscillating
scalar-field theories with a small sound speed. Our model of combined IDM and
CDM components thereby provides a solution to the problem of forming the
observed billion-solar-mass black holes at redshifts of six and higher. In
particular, as a result of the reduced vortical flow, the growth of the black
holes is expected to be more rapid at later times as compared to the standard
scenario. | MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA
Experiments. VIII. Faraday rotation in parsec-scale AGN jets: We report observations of Faraday rotation measures (RMs) for a sample of 191
extragalactic radio jets observed within the MOJAVE program. Multifrequency
VLBA observations were carried out over twelve epochs in 2006 at four
frequencies between 8 and 15 GHz. We detect parsec-scale Faraday RMs in 149
sources and find the quasars to have larger RMs on average than BL Lac objects.
The median core RMs are significantly higher than in the jet components. This
is especially true for quasars where we detect a significant negative
correlation between the magnitude of the RM and the de-projected distance from
the core. We perform detailed simulations of the observational errors of total
intensity, polarization and Faraday rotation, and concentrate on the errors of
transverse Faraday RM gradients in unresolved jets. Our simulations show that
the finite image restoring beam size has a significant effect on the observed
RM gradients, and spurious gradients can occur due to noise in the data if the
jet is less than two beams wide in polarization. We detect significant
transverse RM gradients in four sources (0923+392, 1226+023, 2230+114 and
2251+158). In 1226+023 the RM is for the first time seen to change sign from
positive to negative over the transverse cuts, which supports the presence of a
helical magnetic field in the jet. In this source we also detect variations in
the jet RM over a time scale of three months, which are difficult to explain
with external Faraday screens and suggest internal Faraday rotation. By
comparing fractional polarization changes in jet components between the four
frequency bands to depolarization models we find that an external purely random
Faraday screen viewed through only a few lines of sight can explain most of our
polarization observations but in some sources, such as 1226+023 and 2251+158,
internal Faraday rotation is needed. |
Comparison and Combination of CRF Catalogues: In 2007, a joint IERS/IVS Working Group has been established to consider
practical issues of creating the next ICRF generation, ICRF-2. The goal of the
WG is to seek after ways to improve the existing ICRF. In this study we
investigate a possibility of ICRF improvement by means of using combined ICRF
catalogue instead of a catalogue computed in a single analysis centre, even
though using most advanced models and software. In this work, we present a new
version of Pulkovo combined catalogue of radio source positions computed using
the method proposed in \cite{SokMal07}. Radio source catalogues that were
submitted in 2007 in the framework of the WG activity were used as input for
mutual comparison and combination. Four combined catalogues have been
calculated: Two first of them provide a stochastic improvement of the ICRF, and
last two of them allow us to account also for systematic errors in the current
ICRF version. | Using hybrid GPU/CPU kernel splitting to accelerate spherical
convolutions: We present a general method for accelerating by more than an order of
magnitude the convolution of pixelated functions on the sphere with a
radially-symmetric kernel. Our method splits the kernel into a compact
real-space component and a compact spherical harmonic space component. These
components can then be convolved in parallel using an inexpensive commodity GPU
and a CPU. We provide models for the computational cost of both real-space and
Fourier space convolutions and an estimate for the approximation error. Using
these models we can determine the optimum split that minimizes the wall clock
time for the convolution while satisfying the desired error bounds. We apply
this technique to the problem of simulating a cosmic microwave background (CMB)
anisotropy sky map at the resolution typical of the high resolution maps
produced by the Planck mission. For the main Planck CMB science channels we
achieve a speedup of over a factor of ten, assuming an acceptable fractional
rms error of order 1.e-5 in the power spectrum of the output map. |
Constraints on small-scale cosmological fluctuations from SNe lensing
dispersion: We provide predictions on small-scale cosmological density power spectrum
from supernova lensing dispersion. Parameterizing the primordial power spectrum
with running $\alpha$ and running of running $\beta$ of the spectral index, we
exclude large positive $\alpha$ and $\beta$ parameters which induce too large
lensing dispersions over current observational upper bound. We ran cosmological
N-body simulations of collisionless dark matter particles to investigate
non-linear evolution of the primordial power spectrum with positive running
parameters. The initial small-scale enhancement of the power spectrum is
largely erased when entering into the non-linear regime. For example, even if
the linear power spectrum at $k>10h {\rm Mpc}^{-1}$ is enhanced by $1-2$ orders
of magnitude, the enhancement much decreases to a factor of $2-3$ at late time
($z \leq 1.5$). Therefore, the lensing dispersion induced by the dark matter
fluctuations weakly constrains the running parameters. When including
baryon-cooling effects (which strongly enhance the small-scale clustering), the
constraint is comparable or tighter than the PLANCK constraint, depending on
the UV cut-off. Further investigations of the non-linear matter spectrum with
baryonic processes is needed to reach a firm constraint. | An empirical nonlinear power spectrum overdensity-response: Context. The overdensity inside a cosmological sub-volume and the tidal
fields from its surroundings affect the matter distribution of the region. The
resulting difference between the local and global power spectra is
characterized by the response function.
Aims. Our aim is to provide a new, simple, and accurate formula for the power
spectrum overdensity response at highly nonlinear scales based on the results
of cosmological simulations and paying special attention to the lognormal
nature of the density field.
Methods. We measured the dark matter power spectrum amplitude as a function
of the overdensity ($\delta_W$) in $N$-body simulation subsamples. We show that
the response follows a power-law form in terms of $(1+\delta_W)$, and we
provide a new fit in terms of the variance, $\sigma(L)$, of a sub-volume of
size $L$.
Results. Our fit has a similar accuracy and a comparable complexity to
second-order standard perturbation theory on large scales, but it is also valid
for nonlinear (smaller) scales, where perturbation theory needs higher-order
terms for a comparable precision. Furthermore, we show that the lognormal
nature of the overdensity distribution causes a previously unidentified bias:
the power spectrum amplitude for a subsample with an average density is
typically underestimated by about $-2\sigma^2$. Although this bias falls to the
sub-percent level above characteristic scales of $200Mpch^{-1}$, taking it into
account improves the accuracy of estimating power spectra from zoom-in
simulations and smaller high-resolution surveys embedded in larger
low-resolution volumes. |
Revealing the Local Cosmic Web from Galaxies by Deep Learning: The 80% of the matter in the Universe is in the form of dark matter that
comprises the skeleton of the large-scale structure called the Cosmic Web. As
the Cosmic Web dictates the motion of all matter in galaxies and inter-galactic
media through gravity, knowing the distribution of dark matter is essential for
studying the large-scale structure. However, the Cosmic Web's detailed
structure is unknown because it is dominated by dark matter and warm-hot
inter-galactic media, both of which are hard to trace. Here we show that we can
reconstruct the Cosmic Web from the galaxy distribution using the
convolutional-neural-network-based deep-learning algorithm. We find the mapping
between the position and velocity of galaxies and the Cosmic Web using the
results of the state-of-the-art cosmological galaxy simulations, Illustris-TNG.
We confirm the mapping by applying it to the EAGLE simulation. Finally, using
the local galaxy sample from Cosmicflows-3, we find the dark-matter map in the
local Universe. We anticipate that the local dark-matter map will illuminate
the studies of the nature of dark matter and the formation and evolution of the
Local Group. High-resolution simulations and precise distance measurements to
local galaxies will improve the accuracy of the dark-matter map. | New Multiply-Lensed Galaxies Identified in ACS/NIC3 Observations of
Cl0024+1654 Using an Improved Mass Model: We present an improved strong-lensing analysis of Cl0024+1654 ($z$=0.39)
using deep HST/ACS/NIC3 images, based on 33 multiply-lensed images of 11
background galaxies. These are found with a model that assumes mass
approximately traces light, with a low order expansion to allow for flexibility
on large scales. The model is constrained initially by the well known 5-image
system ($z$=1.675) and refined as new multiply-lensed systems are identified
using the model. Photometric redshifts of these new systems are then used to
constrain better the mass profile by adopting the standard cosmological
relation between redshift and lensing distance. Our model requires only 6 free
parameters to describe well all positional and redshift data. The resulting
inner mass profile has a slope of $d\log M/d\log r\simeq -0.55$, consistent
with new weak-lensing measurements where the data overlap, at $r\simeq200$
kpc/$h_{70}$. The combined profile is well fitted by a high concentration NFW
mass profile, $C_{\rm vir}\sim 8.6\pm1.6$, similar to other well studied
clusters, but larger than predicted with standard $\Lambda$CDM. A well defined
radial critical curve is generated by the model and is clearly observed at $r
\simeq 12\arcsec$, outlined by elongated images pointing towards the centre of
mass. The relative fluxes of the multiply-lensed images are found to agree well
with the modelled magnifications, providing an independent consistency check. |
Tree-less 3d Friends-of-Friends using Spatial Hashing: I describe a fast algorithm for the identification of connected sets of
points where the point-wise connections are determined by a fixed spatial
distance - a task commonly referred to in the cosmological simulation community
as Friends-of-Friends (FOF) group finding. This technique sorts particles into
fine cells sufficiently compact to guarantee their cohabitants are linked, and
uses locality sensitive hashing to search for neighbouring (blocks of) cells.
Tests on N-body simulations of up to a billion particles exhibit speed
increases of factors up to 20x compared with FOF via trees (a factor around 8
is typical), and is consistently complete in less than the time of a k-d tree
construction, giving it an intrinsic advantage over tree-based methods. The
code is open-source and available online at https://github.com/pec27/hfof . | The signature of the scattering between dark sectors in large scale
cosmic microwave background anisotropies: We study the interaction between dark sectors by considering the momentum
transfer caused by the dark matter scattering elastically within the dark
energy fluid. Describing the dark scattering analogy to the Thomson scattering
which couples baryons and photons, we examine the impact of the dark scattering
in CMB observations. Performing global fitting with the latest observational
data, we find that for a dark energy equation of state $w<-1$, the CMB gives
tight constraints on dark matter-dark energy elastic scattering. Assuming a
dark matter particle of proton mass, we derive an elastic scattering cross
section of $\sigma_D < 3.295 \times 10^{-10} \sigma_T$ where $\sigma_T$ is the
cross section of Thomson scattering. For $w>-1$, however, the constraints are
poor. For $w=-1$, $\sigma_D$ can formally take any value. |
The scaling relation between richness and mass of galaxy clusters: a
Bayesian approach: We use a sample of 53 galaxy clusters at 0.03 < z < 0.1 with available masses
derived from the caustic technique and with velocity dispersions computed using
208 galaxies on average per cluster, in order to investigate the scaling
between richness, mass and velocity dispersion. A tight scaling between
richness and mass is found, with an intrinsic scatter of only 0.19 dex in mass
and with a slope one, i.e. clusters which have twice as many galaxies are twice
as massive. When richness is measured without any knowledge of the cluster mass
or linked parameters (such as r200), it can predict mass with an uncertainty of
0.29+/-0.01 dex. As a mass proxy, richness competes favourably with both direct
measurements of mass given by the caustic method, which has typically 0.14 dex
errors (vs 0.29) and X-ray luminosity, which offers a similar 0.30 dex
uncertainty. The similar performances of X-ray luminosity and richness in
predicting cluster masses has been confirmed using cluster masses derived from
velocity dispersion fixed by numerical simulations. These results suggest that
cluster masses can be reliably estimated from simple galaxy counts, at least at
the redshift and masses explored in this work. This has important applications
in the estimation of cosmological parameters from optical cluster surveys,
because in current surveys clusters detected in the optical range outnumber, by
at least one order of magnitude, those detected in X-ray. Our analysis is
robust from astrophysical and statistical perspectives. The data and code used
for the stochastic computation is distributed with the paper. [Abridged] | Terrestrial WIMP/Axion astronomy: Predicting signals in direct dark matter (DM) detection experiments requires
an understanding of the astrophysical structure of the local halo. Any
uncertainty in this understanding will feed directly into all experimental
results. However our terrestrial experiments are in a position to study this
same astrophysical dependence, and in fact represent our only probe of the
local halo on sub-milliparsec scales. This is best achieved in the case of WIMP
dark matter if directionally sensitive experiments are feasible, but requires
novel parameterizations of the velocity distribution to make model independent
claims. For axions the prospects are much greater, haloscopes would be able to
make better measurements of the local DM distribution than astrometric probes. |
Diffuse neutrino supernova background as a cosmological test: The future detection and measurement of the diffuse neutrino supernova
background will shed light on the rate of supernovae events in the Universe,
the star formation rate and the neutrino spectrum from each supernova. Little
has been said about what those measurements will tell us about the expansion
history of the universe. The purpose of this article is to show that the
detection of the diffuse supernova neutrino background will be a complementary
tool for the study and possible discrimination of cosmological models. In
particular, we study three different cosmological models: the $\Lambda$ Cold
Dark Matter model, the Logotropic universe and a bulk viscous matter-dominated
universe. By fitting the free parameters of each model with the supernova Ia
probe, we found that the predicted number of events computed with the best fit
parameters for the $\Lambda$-Cold dark matter model and with the Logotropic
model are the same, while a bulk viscous matter-dominated cosmological model
predicts $\sim 3$ times more events. We show that the current limit set by
Super-Kamiokande on the diffuse supernova neutrino background flux gives
complementary constraints on the free parameters of a bulk viscous
matter-dominated universe. Furthermore, this limit implies, within a $\Lambda$
Cold Dark Matter model, that the universe should be expanding with $H_0 > 21.5
~\rm{Km/sec/Mpc}$ independently of the content of dark matter $\Omega_m$. | Single-object Imaging and Spectroscopy to Enhance Dark Energy Science
from LSST: Single-object imaging and spectroscopy on telescopes with apertures ranging
from ~4 m to 40 m have the potential to greatly enhance the cosmological
constraints that can be obtained from LSST. Two major cosmological probes will
benefit greatly from LSST follow-up: accurate spectrophotometry for nearby and
distant Type Ia supernovae will expand the cosmological distance lever arm by
unlocking the constraining power of high-z supernovae; and cosmology with time
delays of strongly-lensed supernovae and quasars will require additional
high-cadence imaging to supplement LSST, adaptive optics imaging or
spectroscopy for accurate lens and source positions, and IFU or slit
spectroscopy to measure detailed properties of lens systems. We highlight the
scientific impact of these two science drivers, and discuss how additional
resources will benefit them. For both science cases, LSST will deliver a large
sample of objects over both the wide and deep fields in the LSST survey, but
additional data to characterize both individual systems and overall systematics
will be key to ensuring robust cosmological inference to high redshifts.
Community access to large amounts of natural-seeing imaging on ~2-4 m
telescopes, adaptive optics imaging and spectroscopy on 8-40 m telescopes, and
high-throughput single-target spectroscopy on 4-40 m telescopes will be
necessary for LSST time domain cosmology to reach its full potential. In two
companion white papers we present the additional gains for LSST cosmology that
will come from deep and from wide-field multi-object spectroscopy. |
AGN and QSOs in the eROSITA All-Sky Survey -- Part II: The large-scale
structure: The four-year X-ray all-sky survey (eRASS) of the eROSITA telescope aboard
the Spektrum-Roentgen-Gamma satellite will detect ~3 million active galactic
nuclei (AGN) with a median redshift of z~1 and a typical luminosity of
L_(0.5-2.0 keV) ~ 10^(44) erg/s. We show that this unprecedented AGN sample,
complemented with redshift information, will supply us with outstanding
opportunities for large-scale structure research. For the first time, detailed
redshift- and luminosity-resolved studies of the bias factor for X-ray selected
AGN will become possible. The eRASS AGN sample will not only improve the
redshift- and luminosity-resolution of these studies, but will also expand
their luminosity range beyond L_(0.5-2.0 keV) ~ 10^(44) erg/s, thus enabling a
direct comparison of the clustering properties of luminous X-ray AGN and
optical quasars. These studies will dramatically improve our understanding of
the AGN environment, triggering mechanisms, the growth of supermassive black
holes and their co-evolution with dark matter halos.
The eRASS AGN sample will become a powerful cosmological probe. It will
enable detecting baryonic acoustic oscillations (BAOs) for the first time with
X-ray selected AGN. With the data from the entire extragalactic sky, BAO will
be detected at a >~10sigma confidence level in the full redshift range and with
~8sigma confidence in the 0.8 < z < 2.0 range, which is currently not covered
by any existing BAO surveys. To exploit the full potential of the eRASS AGN
sample, photometric and spectroscopic surveys of large areas and a sufficient
depth will be needed. | Full bispectra from primordial scalar and tensor perturbations in the
most general single-field inflation model: We compute the full bispectra, namely both auto- and cross- bispectra, of
primordial curvature and tensor perturbations in the most general single-field
inflation model whose scalar and gravitational equations of motion are of
second order. The formulae in the limits of k-inflation and potential-driven
inflation are also given. These expressions are useful for estimating the full
bispectra of temperature and polarization anisotropies of the cosmic microwave
background radiation. |
Narrow Band X-ray Photometry as a Tool for Studying Galaxy and Cluster
Mass Distributions: We explore the utility of narrow band X-ray surface photometry as a tool for
making fully Bayesian, hydrostatic mass measurements of clusters of galaxies,
groups and early-type galaxies. We demonstrate that it is sufficient to measure
the surface photometry with the Chandra X-ray observatory in only three (rest
frame) bands (0.5--0.9 keV, 0.9--2.0 keV and 2.0--7.0 keV) in order to
constrain the temperature, density and abundance of the hot interstellar medium
(ISM). Adopting parametrized models for the mass distribution and radial
entropy profile and assuming spherical symmetry, we show that the constraints
on the mass and thermodynamic properties of the ISM that are obtained by
fitting data from all three bands simultaneously are comparable to those
obtained by fitting similar models to the temperature and density profiles
derived from spatially resolved spectroscopy, as is typically done. We
demonstrate that the constraints can be significantly tightened when exploiting
a recently derived, empirical relationship between the gas fraction and the
entropy profile at large scales, eliminating arbitrary extrapolations at large
radii. This "Scaled Adiabatic Model" (ScAM) is well suited to modest
signal-to-noise data, and we show that accurate, precise measurements of the
global system properties are inferred when employing it to fit data from even
very shallow, snapshot X-ray observations. The well-defined asymptotic
behaviour of the model also makes it ideally suited for use in
Sunyaev-Zeldovich studies of galaxy clusters. | The Dark Ages of the Universe and Hydrogen Reionization: One of the milestones in the cosmic history is the formation of the first
luminous objects and Hydrogen reionization. The standard theory of cosmic
structure formation predicts that the first generation of stars were born about
a few hundred million years after the Big Bang. The dark Universe was then lit
up once again, and eventually filled with ultraviolet photons emitted from
stars, galaxies, and quasars. The exact epoch of the cosmic reionization and
the details of the process, even the dominant sources, are not known except the
fact that the universe was reionized early on. Signatures of reionization are
expected to be imprinted in the cosmic microwave background radiation,
especially in its large scale polarization. Future CMB experiments, together
with other probes such as 21 cm surveys, will provide rich information on the
process of reionization. We review recent studies on reionization. The
implications from available observations in a wide range of wavelengths are
discussed. Results from state-of-the-art computer simulations are presented.
Finally, we discuss prospects for exploring the first few hundred million years
of the cosmic history. |
Instabilities in the Ionization Zones Around the First Stars: We consider the evolution of the ionization zone around Population III stars
with $M_*\sim 25-200 M_\odot$ in protogalaxies with $M\sim 10^7 M_\odot$ at
redshifts $z = 12$, assuming that the dark matter profile is a modified
isothermal sphere. We study the conditions for the growth of instabilities in
the ionization zones. The Rayleigh-Taylor and thermal instabilities develop
efficiently in the ionization zones around 25-40 $M_\odot$ stars, while this
efficiency is lower for stars with $\sim 120 M_\odot$. For more massive stars
($\sim 200 M_\odot$), the flux of ionizing photons is strong enough to
considerably reduce the gas density in the ionization zone, and the typical
lifetimes of stars ($\sim 2$ Myr) are insufficient for the growth of
instabilities. The gas in a protogalaxy with $M\sim 10^7 M_\odot$ with a 200
$M_\odot$ central star is completely ionized by the end of the star's lifetime;
in the case of a 120 $M_\odot$ central star, only one-third of the total mass
of gas is ionized. Thus, ionizing photons from stars with $M_*\simlt 120
M_\odot$ cannot leave protogalaxies with $M\simgt 10^7 M_\odot$. If the masses
of the central stars are 25 and 40 $M_\odot$, the gas in protogalaxies of this
mass remains essentially neutral. We discuss the consequences of the evolution
of the ionization zones for the propagation of the envelope after the supernova
explosions of the stars and the efficiency of enrichment of the intergalactic
medium in heavy elements. | Probing the Universe's Tilt with the Cosmic Infrared Background Dipole: Conventional interpretation of the observed cosmic microwave background (CMB)
dipole is that all of it is produced by local peculiar motions. Alternative
explanations requiring part of the dipole to be primordial have received
support from measurements of large-scale bulk flows. A test of the two
hypothesis is whether other cosmic dipoles produced by collapsed structures
later than last scattering coincide with the CMB dipole. One background is the
cosmic infrared background (CIB) whose absolute spectrum was measured to ~30%
by the COBE satellite. Over the 100 to 500 {\mu}m wavelength range its spectral
energy distribution can provide a probe of its alignment with CMB. This is
tested with the COBE FIRAS dataset which is available for such a measurement
because of its low noise and frequency resolution important for Galaxy
subtraction. Although the FIRAS instrument noise is in principle low enough to
determine the CIB dipole, the Galactic foreground is sufficiently close
spectrally to keep the CIB dipole hidden. A similar analysis is performed with
DIRBE, which - because of the limited frequency coverage - provides a poorer a
dataset. We discuss strategies for measuring the CIB dipole with future
instruments to probe the tilt and apply it to the Planck, Herschel and the
proposed Pixie missions. We demonstrate that a future FIRAS-like instrument
with instrument noise a factor of ~10 lower than FIRAS would make a
statistically significant measurement of the CIB dipole. We find that the
Planck and Herschel data sets will not allow a robust CIB dipole measurement.
The Pixie instrument promises a determination of the CIB dipole and its
alignment with either the CMB dipole or the dipole galaxy acceleration vector. |
Revealing the Dark Matter Halo with Axion Direct Detection: The next generation of axion direct detection experiments may rule out or
confirm axions as the dominant source of dark matter. We develop a general
likelihood-based framework for studying the time-series data at such
experiments, with a focus on the role of dark-matter astrophysics, to search
for signatures of the QCD axion or axion like particles. We illustrate how in
the event of a detection the likelihood framework may be used to extract
measures of the local dark matter phase-space distribution, accounting for
effects such as annual modulation and gravitational focusing, which is the
perturbation to the dark matter phase-space distribution by the gravitational
field of the Sun. Moreover, we show how potential dark matter substructure,
such as cold dark matter streams or a thick dark disk, could impact the signal.
For example, we find that when the bulk dark matter halo is detected at
5$\sigma$ global significance, the unique time-dependent features imprinted by
the dark matter component of the Sagittarius stream, even if only a few percent
of the local dark matter density, may be detectable at $\sim$2$\sigma$
significance. A co-rotating dark disk, with lag speed $\sim$50 km$/$s, that is
$\sim$20$\%$ of the local DM density could dominate the signal, while colder
but as-of-yet unknown substructure may be even more important. Our likelihood
formalism, and the results derived with it, are generally applicable to any
time-series based approach to axion direct detection. | New Colour-Mass to Light Relations: the role of the Asymptotic Giant
Branch phase and of interstellar dust: Colour-M/L (mass-to-light) relations are a popular recipe to derive stellar
mass in external galaxies. Stellar mass estimates often rely on near infrared
(NIR) photometry, considered an optimal tracer since it is little affected by
dust and by the "frosting" effect of recent star formation episodes. However,
recent literature has highlighted that theoretical estimates of the NIR M/L
ratio strongly depend on the modelling of the Asymptotic Giant Branch (AGB)
phase. We use the latest Padova isochrones, with detailed modelling of the
Thermally Pulsing AGB phase, to update theoretical colour-M/L relations in the
optical and NIR and discuss the consequences for the estimated stellar masses
in external galaxies. We also discuss the effect of attenuation by interstellar
dust on colour-M/L relations in the statistical case of large galaxy samples. |
Radio Jets and Galaxies as Cosmic String Probes: The lensing effect of a cosmic string is studied, and some new methods are
proposed to detect the cosmic string. The technique for using jets as extended
gravitational lensing probes was firstly explored by Kronberg. We use the
"alignment-breaking parameter" $ \eta_G $ as a sensitive indicator of
gravitational distortion by a wiggly cosmic string. Then, we applied the
non-constant deflection angle to jets, and $ \eta_G $ of a specific jet is just
related to the projected slope of the jet. At least three jets in the sample of
Square Kilometer Array (SKA) would have significant signals ($ \eta_G >10^\circ
$) if the wiggly infinite cosmic string existed. The distortion of elliptical
object is also studied and used to do a statistical research on directions of
axes and ellipticities of galaxies. In the direction of the string, we find
that galaxies appear to be more elliptical for an observer and the distribution
of apparent ellipticity changes correspondingly. Ellipticity distribution of
current SDSS spiral sample has the signal-to-noise ratio up to 8.48 which is
large enough for astronomical observations. The future survey, such as Large
Synoptic Survey Telescope (LSST) and Dark Energy Survey (DES), would weaken the
requirement of special geometry in the data processing. As a result, all kinds
of distributions, including ellipticity axis distribution, would serve as
probes to detect wiggly strings in the near future. In brief, if a wiggly
cosmic string existed, these signals would be convenient to be observed with
the future weak lensing survey or other surveys in deep space. If there was no
lensing signal in these distributions, it would give the upper limit of the
abundance of infinite strings. | The challenge of large and empty voids in the SDSS DR7 redshift survey: We present catalogues of voids for the SDSS DR7 redshift survey and for
Millennium I simulation mock data. We aim to compare the observations with
simulations based on a $\Lambda$CDM model and a semi-analytic galaxy formation
model. We use the void statistics as a test for these models. We assembled a
mock catalogue that closely resembles the SDSS DR7 catalogue and carried out a
parallel statistical analysis of the observed and simulated catalogue. We find
that in the observation and the simulation, voids tend to be equally spherical.
The total volume occupied by the voids and their total number are slightly
larger in the simulation than in the observation. We find that large voids are
less abundant in the simulation and the total luminosity of the galaxies
contained in a void with a given radius is higher on average than observed by
SDSS DR7 survey. We expect these discrepancies to be even more significant in
reality than found here since the present value of $\sigma_8$ given by WMAP7 is
lower than the value of 0.9 used in the Millennium I simulation. The reason why
the simulation fails to produce enough large and dark voids might be the
failure of certain semi-analytic galaxy formation models to reduce the
small-scale power of $\Lambda$CDM and to produce sufficient power on large
scales. |
Exploring the Hubble Tension and Spatial Curvature from the Ages of Old
Astrophysical Objects: We use the age measurements of 114 old astrophysical objects (OAO) in the
redshift range $0\lesssim z\lesssim 8$ to explore the Hubble tension. The age
of the Universe at any $z$ is inversely proportional to the Hubble constant,
$H_0$, so requiring the Universe to be older than the OAO it contains at any
$z$ will lead to an upper limit on $H_0$. Assuming flat $\Lambda$CDM and
setting a Gaussian prior on the matter density parameter $\Omega_{\rm
m}=0.315\pm0.007$ informed by {\it Planck}, we obtain a 95\% confidence-level
upper limit of $H_0<70.6 \rm{~km} \rm{~s}^{-1} \rm{~Mpc}^{-1}$, representing a
$2\sigma$ tension with the measurement using the local distance ladder. We
find, however, that the inferred upper limit on $H_{0}$ depends quite
sensitively on the prior for $\Omega_{\rm m}$, and the Hubble tension between
early-time and local measurements of $H_{0}$ may be due in part to the
inference of both $\Omega_{\rm m}$ and $H_0$ in {\it Planck}, while the local
measurement uses only $H_{0}$. The age-redshift data may also be used for
cosmological model comparisons. We find that the $R_{\rm h}=ct$ universe
accounts well for the data, with a reasonable upper limit on $H_{0}$, while
Einstein-de Sitter fails to pass the cosmic-age test. Finally, we present a
model-independent estimate of the spatial curvature using the ages of 61
galaxies and the luminosity distances of 1,048 Pantheon Type Ia supernovae.
This analysis suggests that the geometry of the Universe is marginally
consistent with spatial flatness at a confidence level of $1.6\sigma$,
characterized as $\Omega_{k}=0.43^{+0.27}_{-0.27}$. | Exploring redshift-space distortions in large-scale structure: We explore and compare different ways large-scale structure observables in
redshift-space and real space can be connected. These include direct
computation in Lagrangian space, moment expansions and two formulations of the
streaming model. We derive for the first time a Fourier space version of the
streaming model, which yields an algebraic relation between the real- and
redshift-space power spectra which can be compared to earlier, phenomenological
models. By considering the redshift-space 2-point function in both
configuration and Fourier space, we show how to generalize the Gaussian
streaming model to higher orders in a systematic and computationally tractable
way. We present a closed-form solution to the Zeldovich power spectrum in
redshift space and use this as a framework for exploring convergence properties
of different expansion approaches. While we use the Zeldovich approximation to
illustrate these results, much of the formalism and many of the relations we
derive hold beyond perturbation theory, and could be used with ingredients
measured from N-body simulations or in other areas requiring decomposition of
Cartesian tensors times plane waves. We finish with a discussion of the
redshift-space bispectrum, bias and stochasticity and terms in Lagrangian
perturbation theory up to 1-loop order. |
From matter to galaxies: General relativistic bias for the one-loop
bispectrum: We write down the Lagrangian bias expansion in general relativity up to 4th
order in terms of operators describing the curvature of an early-time
hypersurface for comoving observers. They can be easily expanded in synchronous
or comoving gauges. This is necessary for the computation of the one-loop halo
bispectrum, where relativistic effects can be degenerate with a primordial
non-Gaussian signal. Since the bispectrum couples scales, an accurate
prediction of the squeezed limit behavior needs to be both non-linear and
relativistic. We then evolve the Lagrangian bias operators in time in comoving
gauge, obtaining non-local operators analogous to what is known in the
Newtonian limit. Finally, we show how to renormalize the bias expansion at an
arbitrary time and find that this is crucial in order to cancel unphysical
$1/k^2$ divergences in the large-scale power spectrum and bispectrum that could
be mistaken for a contamination to the non-Gaussian signal. | Entropy production and curvature perturbation from dissipative curvatons: Considering the curvaton field that follows dissipative slow-roll equation,
we show that the field can lead to entropy production and generation of
curvature perturbation after reheating. Spectral index is calculated to
discriminate warm and thermal scenarios of dissipative curvatons from the
standard curvaton model. In contrast to the original curvaton model, quadratic
potential is not needed in the dissipative scenario, since the growth in the
oscillating period is not essential for the model. |
Current observations with a decaying cosmological constant allow for
chaotic cyclic cosmology: We use the phase plane analysis technique of Madsen and Ellis to consider a
universe with a true cosmological constant as well as a cosmological "constant"
that is decaying. Time symmetric dynamics for the inflationary era allows
eternally bouncing models to occur. Allowing for scalar field dynamic
evolution, we find that if dark energy decays in the future, chaotic cyclic
universes exist provided the spatial curvature is positive. This is
particularly interesting in light of current observations which do not yet rule
out either closed universes or possible evolution of the cosmological constant.
We present only a proof of principle, with no definite claim on the physical
mechanism required for the present dark energy to decay. | Effects and Detectability of Quasi-Single Field Inflation in the
Large-Scale Structure and Cosmic Microwave Background: Quasi-single field inflation predicts a peculiar momentum dependence in the
squeezed limit of the primordial bispectrum which smoothly interpolates between
the local and equilateral models. This dependence is directly related to the
mass of the isocurvatons in the theory which is determined by the
supersymmetry. Therefore, in the event of detection of a non-zero primordial
bispectrum, additional constraints on the parameter controlling the
momentum-dependence in the squeezed limit becomes an important question. We
explore the effects of these non-Gaussian initial conditions on large-scale
structure and the cosmic microwave background, with particular attention to the
galaxy power spectrum at large scales and scale-dependence corrections to
galaxy bias. We determine the simultaneous constraints on the two parameters
describing the QSF bispectrum that we can expect from upcoming large-scale
structure and cosmic microwave background observations. We find that for
relatively large values of the non-Gaussian amplitude parameters, but still
well within current uncertainties, galaxy power spectrum measurements will be
able to distinguish the QSF scenario from the predictions of the local model. A
CMB likelihood analysis, as well as Fisher matrix analysis, shows that there is
also a range of parameter values for which Planck data may be able distinguish
between QSF models and the related local and equilateral shapes. Given the
different observational weightings of the CMB and LSS results, degeneracies can
be significantly reduced in a joint analysis. |
Near-infrared Extragalactic Background Light Fluctuations on Nonlinear
Scales: Several fluctuation studies on the near-infrared extragalactic background
light (EBL) find an excess power at tens of arcminute scales ($\ell\sim10^3$).
Emission from the intra-halo light (IHL) has been proposed as a possible
explanation for the excess signal. In this work, we investigate the emission
from the integrated galaxy light (IGL) and IHL in the power spectrum of EBL
fluctuations using the simulated galaxy catalog MICECAT. We find that at
$\ell\sim10^3$, the one-halo clustering from satellite galaxies has comparable
power to the two-halo term in the IGL power spectrum. In some previous EBL
analyses, the IGL model assumed a small one-halo clustering signal, which may
result in overestimating the IHL contribution to the EBL. We also investigate
the dependence of the IGL$+$IHL power spectrum on the IHL distribution as a
function of redshift and halo mass, and the spatial profile within the halo.
Our forecast suggests that the upcoming SPHEREx deep field survey can
distinguish different IHL models considered in this work with high
significance. Finally, we quantify the bias in the power spectrum from the
correlation of the mask and the signal, which has not been accounted for in
previous analyses. | Galaxy clusters in simulations of the local Universe: a matter of
constraints: To study the full formation and evolution history of galaxy clusters and
their population, high resolution simulations of the latter are flourishing.
However comparing observed clusters to the simulated ones on a one-to-one basis
to refine the models and theories down to the details is non trivial. The large
variety of clusters limits the comparisons between observed and numerical
clusters. Simulations resembling the local Universe down to the cluster scales
permit pushing the limit. Simulated and observed clusters can be matched on a
one-to-one basis for direct comparisons provided that clusters are well
reproduced besides being in the proper large scale environment. Comparing
random and local-Universe like simulations obtained with differently grouped
observational catalogs of peculiar velocities, this paper shows that the
grouping scheme used to remove non-linear motions in the catalogs that
constrain the simulations affects the quality of the numerical clusters. With a
less aggressive grouping scheme - galaxies still falling onto clusters are
preserved - combined with a bias minimization scheme, the mass of the dark
matter halos, simulacra for 5 local clusters - Virgo, Centaurus, Coma, Hydra
and Perseus - is increased by 39% closing the gap with observational mass
estimates. Simulacra are found on average in 89% of the simulations, an
increase of 5% with respect to the previous grouping scheme. The only exception
is Perseus. Since the Perseus-Pisces region is not well covered by the used
peculiar velocity catalog, the latest release let us foresee a better
simulacrum for Perseus in a near future. |
Constraining Fundamental Physics with Future CMB Experiments: The Planck experiment will soon provide a very accurate measurement of Cosmic
Microwave Background anisotropies. This will let cosmologists determine most of
the cosmological parameters with unprecedented accuracy. Future experiments
will improve and complement the Planck data with better angular resolution and
better polarization sensitivity. This unexplored region of the CMB power
spectrum contains information on many parameters of interest, including
neutrino mass, the number of relativistic particles at recombination, the
primordial Helium abundance and the injection of additional ionizing photons by
dark matter self-annihilation. We review the imprint of each parameter on the
CMB and forecast the constraints achievable by future experiments by performing
a Monte Carlo analysis on synthetic realizations of simulated data. We find
that next generation satellite missions such as CMBPol could provide valuable
constraints with a precision close to that expected in current and near future
laboratory experiments. Finally, we discuss the implications of this
intersection between cosmology and fundamental physics. | Hubble Tension and Gravitational Self-Interaction: One of the most important problems vexing the $\Lambda$CDM cosmological model
is the Hubble tension. It arises from the fact that measurements of the present
value of the Hubble parameter performed with low-redshift quantities, e.g., the
Type IA supernova, tend to yield larger values than measurements from
quantities originating at high-redshift, e.g., fits of cosmic microwave
background radiation. It is becoming likely that the discrepancy, currently
standing at $5\sigma$, is not due to systematic errors in the measurements.
Here we explore whether the self-interaction of gravitational fields in General
Relativity, which are traditionally neglected when studying the evolution of
the universe, can explain the tension. We find that with field self-interaction
accounted for, both low- and high-redshift data are simultaneously well-fitted,
thereby showing that gravitational self-interaction could explain the Hubble
tension. Crucially, this is achieved without introducing additional parameters. |
The Merger Environment of the WAT Hosting Cluster Abell 562: We present a Chandra X-ray observation and VLA radio observations of the
nearby (z=0.11) galaxy cluster Abell 562 and the wide angle tail (WAT) radio
source 0647+693. The cluster displays signatures of an ongoing merger leading
to the bending of the WAT source including an elongation of the X-ray surface
brightness distribution along the line that bisects the WAT, an excess of
displaced gas found between the radio lobes, and anisotropies within the ICM
projected temperature and abundance distributions. The most likely geometry of
the ongoing interaction is a head-on merger occurring along the WAT bending
axis. By combining observable properties of A562 and 0647+693 with common
values for the conditions within merging clusters at the time of core crossing,
we constrain the internal density (rho[ j ] = 0.001 rho[ICM]) of the jets and
plasma flow velocity within the lobes (v = 0.02c - 0.03c) of the WAT source. | Secondary ionization and heating by fast electrons: We examine the fate of fast electrons (with energies E>10 eV) in a thermal
gas of primordial composition. To follow their interactions with the background
gas, we construct a Monte Carlo model that includes: (1) electron-electron
scattering (which transforms the electron kinetic energy into heat), (2)
collisional ionization of hydrogen and helium (which produces secondary
electrons that themselves scatter through the medium), and (3) collisional
excitation (which produces secondary photons, whose fates we also follow
approximately). For the last process, we explicitly include all transitions to
upper levels n<=4, together with a well-motivated extrapolation to higher
levels. In all cases, we use recent calculated cross-sections at E<1 keV and
the Bethe approximation to extrapolate to higher energies. We compute the
fractions of energy deposited as heat, ionization (tracking HI and the helium
species separately), and excitation (tracking HI Lyman-alpha separately) under
a broad range of conditions appropriate to the intergalactic medium. The energy
deposition fractions depend on both the background ionized fraction and the
electron energy but are nearly independent of the background density. We find
good agreement with some, but not all, previous calculations at high energies.
Electronic tables of our results are available on request. |
Structure Formation in Dark Matter Particle Production Cosmology: We investigate a cosmological scenario in which the dark matter particles can
be created during the evolution of the Universe. By regarding the Universe as
an open thermodynamic system and using non-equilibrium thermodynamics, we
examine the mechanism of gravitational particle production. In this setup, we
study the large-scale structure (LSS) formation of the Universe in the
Newtonian regime of perturbations and derive the equations governing the
evolution of the dark matter overdensities. Then, we implement the cosmological
data from Planck 2018 CMB measurements, SNe Ia and BAO observations, as well as
the Riess et al. (2019) local measurement for $H_0$ to provide some
cosmological constraints for the parameters of our model. We see that the best
case of our scenario ($\chi_{{\rm tot}}^{2}=3834.40$) fits the observational
data better than the baseline $\Lambda$CDM model ($\chi_{{\rm tot}}^{2} =
3838.00$) at the background level. We moreover estimate the growth factor of
linear perturbations and show that the best case of our model
($\chi_{f\sigma_{8}}^{2}=39.85$) fits the LSS data significantly better than
the $\Lambda$CDM model ($\chi_{f\sigma_{8}}^{2}=45.29$). Consequently, our
model also makes a better performance at the level of the linear perturbations
compared to the standard cosmological model. | The black hole - bulge mass relation of Active Galactic Nuclei in the
Extended Chandra Deep Field - South Survey: We present results from a study to determine whether relations, established
in the local Universe, between the mass of supermassive black holes (SMBHs) and
their host galaxies are in place at higher redshifts. We establish a
well-constructed sample of 18 X-ray-selected, broad-line Active Galactic Nuclei
(AGN) in the Extended Chandra Deep Field South - Survey with 0.5 < z < 1.2.
This redshift range is chosen to ensure that HST imaging is available with at
least two filters that bracket the 4000 Angstrom break thus providing reliable
stellar mass estimates of the host galaxy by accounting for both young and old
stellar populations. We compute single-epoch, virial black hole masses from
optical spectra using the broad MgII emission line. For essentially all
galaxies in our sample, their total stellar mass content agrees remarkably
well, given their BH masses, with local relations of inactive galaxies and
active SMBHs. We further decompose the total stellar mass into bulge and disk
components separately with full knowledge of the HST point-spread-function. We
find that ~80% of the sample is consistent with the local M_BH - M_Bulge
relation even with 72% of the host galaxies showing the presence of a disk. In
particular, bulge dominated hosts are more aligned with the local relation than
those with prominent disks. We further discuss the possible physical mechanisms
that are capable building up the stellar mass of the bulge from an extended
disk of stars over the subsequent eight Gyrs. |
A Description of Quasar Variability Measured Using Repeated SDSS and
POSS Imaging: We provide a quantitative description and statistical interpretation of the
optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS)
has obtained repeated imaging in five UV-to-IR photometric bands for 33,881
spectroscopically confirmed quasars. About 10,000 quasars have an average of 60
observations in each band obtained over a decade along Stripe 82 (S82), whereas
the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed
time lags span the range from a day to almost 10 years, and constrain quasar
variability at rest-frame time lags of up to 4 years, and at rest-frame
wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of
quasars from the SDSS Data Release 7 that have been observed at least twice in
SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it
to analyze the ensemble properties of quasar variability. Based on a damped
random walk (DRW) model defined by a characteristic time scale and an
asymptotic variability amplitude that scale with the luminosity, black hole
mass, and rest wavelength for individual quasars calibrated in S82, we can
fully explain the ensemble variability statistics of the non-S82 quasars such
as the exponential distribution of large magnitude changes. All available data
are consistent with the DRW model as a viable description of the optical
continuum variability of quasars on time scales of ~5-2000 days in the rest
frame. We use these models to predict the incidence of quasar contamination in
transient surveys such as those from PTF and LSST. | Cosmological constraints from the tomographic cross-correlation of DESI
Luminous Red Galaxies and Planck CMB lensing: We use luminous red galaxies selected from the imaging surveys that are being
used for targeting by the Dark Energy Spectroscopic Instrument (DESI) in
combination with CMB lensing maps from the Planck collaboration to probe the
amplitude of large-scale structure over $0.4\le z\le 1$. Our galaxy sample,
with an angular number density of approximately $500\,\mathrm{deg}^{-2}$ over
18,000 sq.deg., is divided into 4 tomographic bins by photometric redshift and
the redshift distributions are calibrated using spectroscopy from DESI. We fit
the galaxy autospectra and galaxy-convergence cross-spectra using models based
on cosmological perturbation theory, restricting to large scales that are
expected to be well described by such models. Within the context of
$\Lambda$CDM, combining all 4 samples and using priors on the background
cosmology from supernova and baryon acoustic oscillation measurements, we find
$S_8=\sigma_8(\Omega_m/0.3)^{0.5}=0.73\pm 0.03$. This result is lower than the
prediction of the $\Lambda$CDM model conditioned on the Planck data. Our data
prefer a slower growth of structure at low redshift than the model predictions,
though at only modest significance. |
Detection of intrinsic cluster alignments to 100 Mpc/h in the SDSS: We measure the large-scale intrinsic alignments of galaxy clusters in the
Sloan Digital Sky Survey (SDSS) using subsets of two cluster catalogues: 6625
clusters with 0.1<z<0.3 from the maxBCG cluster catalogue (Koester et al. 2007,
7500 sq. deg.), and 8081 clusters with 0.08<z<0.44 from the Adaptive Matched
Filter catalogue (Dong et al. 2008, 6500 sq. deg.). We search for two types of
cluster alignments using pairs of clusters: the alignment between the projected
major axes of the clusters (`correlation' alignment), and the alignment between
one cluster major axis and the line connecting it to the other cluster in the
pair (`pointing' alignment). In each case, we use the cluster member galaxy
distribution as a tracer of the cluster shape. All measurements are carried out
with each catalogue separately, to check for dependence on cluster selection
procedure. We find a strong detection of the pointing alignment on scales up to
100 Mpc/h, at the 6 or 10-sigma level depending on the cluster selection
algorithm used. The correlation alignment is only marginally detected up to ~20
Mpc/h, at the 2 or 2.5-sigma level. These results support our current
theoretical understanding of galaxy cluster intrinsic alignments in the LCDM
paradigm, although further work will be needed to understand the impact of
cluster selection effects and observational measurement errors on the amplitude
of the detection. | Towards a self-consistent analysis of the anisotropic galaxy two- and
three-point correlation functions on large scales: application to mock galaxy
catalogues: We establish a practical method for the joint analysis of anisotropic galaxy
two- and three-point correlation functions (2PCF and 3PCF) on the basis of the
decomposition formalism of the 3PCF using tri-polar spherical harmonics. We
perform such an analysis with MultiDark Patchy mock catalogues to demonstrate
and understand the benefit of the anisotropic 3PCF. We focus on scales above
$80 h^{-1}\,{\rm Mpc}$, and use information from the shape and the baryon
acoustic oscillation (BAO) signals of the 2PCF and 3PCF. We also apply density
field reconstruction to increase the signal-noise ratio of BAO in the 2PCF
measurement, but not in the 3PCF measurement. In particular, we study in detail
the constraints on the angular diameter distance and the Hubble parameter. We
build a model of the bispectrum or 3PCF that includes the nonlinear damping of
the BAO signal in redshift space. We carefully account for various
uncertainties in our analysis including theoretical models of the 3PCF, window
function corrections, biases in estimated parameters from the fiducial values,
the number of mock realizations to estimate the covariance matrix, and bin
size. The joint analysis of the 2PCF and 3PCF monopole and quadrupole
components shows a $30\%$ a nd $20\%$ improvement in Hubble parameter
constraints before and after reconstruction of the 2PCF measurements,
respectively, compared to the 2PCF analysis alone. This study clearly shows
that the anisotropic 3PCF increases cosmological information from galaxy
surveys and encourages further development of the modeling of the 3PCF on
smaller scales than we consider. |
CMB likelihood approximation for banded probability distributions: We investigate sets of random variables that can be arranged sequentially
such that a given variable only depends conditionally on its immediate
predecessor. For such sets, we show that the full joint probability
distribution may be expressed exclusively in terms of uni- and bivariate
marginals. Under the assumption that the CMB power spectrum likelihood only
exhibits correlations within a banded multipole range, \Delta l, we apply this
expression to two outstanding problems in CMB likelihood analysis. First, we
derive a statistically well-defined hybrid likelihood estimator, merging two
independent (e.g., low- and high-l) likelihoods into a single expression that
properly accounts for correlations between the two. Applying this expression to
the WMAP likelihood, we verify that the effect of correlations on cosmological
parameters in the transition region is negligible in terms of cosmological
parameters for WMAP; the largest relative shift seen for any parameter is
0.06\sigma. However, because this may not hold for other experimental setups
(e.g., for different instrumental noise properties or analysis masks), but must
rather be verified on a case-by-case basis, we recommend our new hybridization
scheme for future experiments for statistical self-consistency reasons. Second,
we use the same expression to improve the convergence rate of the Blackwell-Rao
likelihood estimator, reducing the required number of Monte Carlo samples by
several orders of magnitude, and thereby extend it to high-l applications. | What Sets Temperature Gradients in Galaxy Clusters? Implications for
non-thermal pressure support and mass-observable scaling relations: We present a spherically symmetric model for the origin and evolution of the
temperature profiles in the hot plasma filling galaxy groups and clusters. We
find that the gas in clusters is generically not isothermal, and that the
temperature declines with radius at large distances from the cluster center
(outside the core- and scale radii). This temperature profile is determined by
the accretion history of the halo, and is not quantitatively well-described by
a polytropic model. We explain quantitatively how the large-scale temperature
gradient persists in spite of thermal conduction and convection. These results
are a consequence of the cosmological assembly of clusters and cannot be
reproduced with non-cosmological simulations of isolated halos. We show that
the variation in halo assembly histories produces a ~10% scatter in temperature
at fixed mass. On top of this scatter, conduction decreases the temperature of
the gas near the scale radius in massive clusters, which may bias hydrostatic
mass estimates inferred from x-ray and SZ observations. As an example
application of our model profiles, we use mixing-length theory to estimate the
turbulent pressure support created by the magnetothermal instability (MTI): in
agreement with our earlier MHD simulations, we find that the convection
produced by the MTI can provide ~5% non-thermal pressure support near r_500.
The magnitude of this turbulent pressure support is likely to be non-monotonic
in halo mass, peaking in ~10^14.5 M_sun halos. |
Inflaton Fragmentation and Oscillon Formation in Three Dimensions: Analytical arguments suggest that a large class of scalar field potentials
permit the existence of oscillons -- pseudo-stable, non-topological solitons --
in three spatial dimensions. In this paper we numerically explore oscillon
solutions in three dimensions. We confirm the existence of these field
configurations as solutions to the Klein-Gorden equation in an expanding
background, and verify the predictions of Amin and Shirokoff for the
characteristics of individual oscillons for their model. Further, we
demonstrate that significant numbers of oscillons can be generated via
fragmentation of the inflaton condensate, consistent with the analysis of Amin.
These emergent oscillons can easily dominate the post-inflationary universe.
Finally, both analytic and numerical results suggest that oscillons are stable
on timescales longer than the post-inflationary Hubble time. Consequently, the
post-inflationary universe can contain an effective matter-dominated phase,
during which it is dominated by localized concentrations of scalar field
matter. | Cosmological perturbation theory in Generalized Einstein-Aether models: We investigate the evolution of cosmological perturbations in models of dark
energy described by a time-like unit normalized vector field specified by a
general function $\mathcal{F}(\mathcal{K})$, so-called Generalized
Einstein-Aether models. First we study the background dynamics of such models
via a designer approach in an attempt to model this theory as dark energy. We
find that only one specific form of this designer approach matches $\Lambda$CDM
at background order and we also obtain a differential equation which
$\mathcal{F}(\mathcal{K})$ must satisfy for general $w$CDM cosmologies. We also
present the equations of state for perturbations in Generalized Einstein-Aether
models, which completely parametrize these models at the level of linear
perturbations. A generic feature of modified gravity models is that they
introduce new degrees of freedom. By fully eliminating these we are able to
express the gauge invariant entropy perturbation and the scalar, vector, and
tensor anisotropic stresses in terms of the perturbed fluid variables and
metric perturbations only. These can then be used to study the evolution of
perturbations in the scalar, vector, and tensor sectors and we use these to
evolve the Newtonian gravitational potentials. |
The formation of a thick disk through the heating of a thin disk:
Agreement with orbital eccentricities of stars in the solar neighborhood: We study the distribution of orbital eccentricities of stars in thick disks
generated by the heating of a pre-existing thin stellar disk through a minor
merger (mass ratio 1:10), using N-body/SPH numerical simulations of
interactions that span a range of gas fractions in the primary disk and initial
orbital configurations. The resulting eccentricity distributions have an
approximately triangular shape, with a peak at 0.2-0.35, and a relatively
smooth decline towards higher values. Stars originally in the satellite galaxy
tend to have higher eccentricities (on average from e = 0.45 to e = 0.75),
which is in general agreement with the models of Sales and collaborators,
although in detail we find fewer stars with extreme values and no evidence of
their secondary peak around e = 0.8. The absence of this high-eccentricity
feature results in a distribution that qualitatively matches the observations.
Moreover, the increase in the orbital eccentricities of stars in the solar
neighborhood with vertical distance from the Galactic mid-plane recently found
by Diericxk and collaborators can be qualitatively reproduced by our models,
but only if the satellite is accreted onto a direct orbit. We thus speculate
that if minor mergers were the dominant means of formating the Milky Way thick
disk, the primary mechanism should be merging with satellite(s) on direct
orbits. | How covariant is the galaxy luminosity function?: We investigate the error properties of certain galaxy luminosity function
(GLF) estimators. Using a cluster expansion of the density field, we show how,
for both volume and flux limited samples, the GLF estimates are covariant. The
covariance matrix can be decomposed into three pieces: a diagonal term arising
from Poisson noise; a sample variance term arising from large-scale structure
in the survey volume; an occupancy covariance term arising due to galaxies of
different luminosities inhabiting the same cluster. To evaluate the theory one
needs: the mass function and bias of clusters, and the conditional luminosity
function (CLF). We use a semi-analytic model (SAM) galaxy catalogue from the
Millennium run N-body simulation and the CLF of Yang et al. (2003) to explore
these effects. The GLF estimates from the SAM and the CLF qualitatively
reproduce results from the 2dFGRS. We also measure the luminosity dependence of
clustering in the SAM and find reasonable agreement with 2dFGRS results for
bright galaxies. However, for fainter galaxies, L<L*, the SAM overpredicts the
relative bias by ~10-20%. We use the SAM data to estimate the errors in the GLF
estimates for a volume limited survey of volume V~0.13 [Gpc/h]^3. We find that
different luminosity bins are highly correlated: for L<L* the correlation
coefficient is r>0.5. Our theory is in good agreement with these measurements.
These strong correlations can be attributed to sample variance. For a
flux-limited survey of similar volume, the estimates are only slightly less
correlated. We explore the importance of these effects for GLF model parameter
estimation. We show that neglecting to take into account the bin-to-bin
covariances can lead to significant systematic errors in best-fit parameters. |
Probing the nature of dark matter particles with stellar streams: A key prediction of the standard cosmological model -- which relies on the
assumption that dark matter is cold, i.e. non-relativistic at the epoch of
structure formation -- is the existence of a large number of dark matter
substructures on sub-galactic scales. This assumption can be tested by studying
the perturbations induced by dark matter substructures on cold stellar streams.
Here, we study the prospects for discriminating cold from warm dark matter by
generating mock data for upcoming astronomical surveys such as the Large
Synoptic Survey Telescope (LSST), and reconstructing the properties of the dark
matter particle from the perturbations induced on the stellar density profile
of a stream. We discuss the statistical and systematic uncertainties, and show
that the method should allow to set stringent constraints on the mass of
thermal dark matter relics, and possibly to yield an actual measurement of the
dark matter particle mass if it is in the $\mathcal{O}(1)$ keV range. | The final verdict by XMM-Newton: the X-ray obscured Seyfert galaxy
NGC5506 has a broad Fe K-alpha line: We present the first unambiguous evidence of a broad (Gaussian width ~330 eV)
component of the iron K-alpha fluorescent emission line in the X-ray obscured
Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a
spectroscopic monitoring campaign on this source performed with the XMM-Newton
observatory between February 2001 and January 2009. The broad line lacks
extreme redwards skewness. If modelled with a relativistic component, the
profile of the line is consistent with a flat emissivity radial dependence
(alpha~1.9). The disk inclination (~40 degrees) is nominally larger then
typically observed in unobscured AGN, in agreement with most measurements of
broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us
to decompose the full iron emission line complex, and to study its long-term
(timescales of weeks to years) variability pattern. The intensity of the
neutral and narrow iron K-alpha core remains constant during the monitoring
campaign. This indicates that the optically thick gas responsible for the
non-relativistic reprocessing of the primary AGN continuum in NGC5506 is
probably located in the torus rather than in the optical Broad Line Region. |
Component Separation of a Isotropic Gravitational Wave Background: A Gravitational Wave Background (GWB) is expected in the universe from the
superposition of a large number of unresolved astrophysical sources and
phenomena in the early universe. Each component of the background (e.g., from
primordial metric perturbations, binary neutron stars, milli-second pulsars
etc.) has its own spectral shape. Many ongoing experiments aim to probe GWB at
a variety of frequency bands. In the last two decades, using data from
ground-based laser interferometric gravitational wave (GW) observatories, upper
limits on GWB were placed in the frequency range of ~50-1000 Hz, considering
one spectral shape at a time. However, one strong component can significantly
enhance the estimated strength of another component. Hence, estimation of the
amplitudes of the components with different spectral shapes should be done
jointly. Here we propose a method for "component separation" of a statistically
isotropic background, that can, for the first time, jointly estimate the
amplitudes of many components and place upper limits. The method is rather
straightforward and needs negligible amount of computation. It utilises the
linear relationship between the measurements and the amplitudes of the actual
components, alleviating the need for a sampling based method, e.g., Markov
Chain Monte Carlo (MCMC) or matched filtering, which are computationally
intensive and cumbersome in a multi-dimensional parameter space. Using this
formalism we could also study how many independent components can be separated
using a given dataset from a network of current and upcoming ground based
interferometric detectors. | Unabsorbed Seyfert 2 galaxies: the case of "naked" AGN: Hawkins (2004) reported on a class of "naked" AGN characterized by strong
amplitude optical brightness variability and the complete absence of broad
emission lines in the optical spectrum. The variability suggests that the
nucleus is seen directly, however the absence of broad lines contradicts the
simple formulation of Unified Models for AGN. We present the results of
quasi-simultaneous spectroscopic observations with XMM-Newton and NTT (La
Silla) of two "naked" AGN. We confirm the "naked" nature of Q2131-427 for which
no broad emission line components have been detected in the optical spectrum
and its X-ray spectrum shows no signs of intrinsic absorption. The optical and
X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas
ratio and a Compton Thick nature is ruled out on the basis of the high
F(X)/F([OIII]) ratio. The Broad Line Region (BLR) may be completely absent in
this source, possibly as a consequence of its low Eddington ratio. On the other
hand, the optical spectrum of Q2130-431 shows H(alpha) and H(beta) broad
emission line components, revealing the presence of a BLR. A mild X-ray
absorption is expected in intermediate type 1.8 Seyfert galaxies like
Q2130-431, however we put a very low upper limit on the column density (< 2 x
10^(20) cm^(-2)), also the low Balmer decrement suggests that the BLR itself
does not suffer from reddening. We propose that in this object the BLR is
intrinsically weak, making a case of "true" intermediate Seyfert galaxy. We
also report on the X-ray detection of the Abell 3783 galaxy cluster in the
XMM-Newton field-of-view of the Q2131-427 observation. |
Controlling intrinsic-shear alignment in three-point weak lensing
statistics: Three-point weak lensing statistics provide cosmic information complementary
to that of two-point statistics. However, both statistics suffer from
intrinsic-shear alignment, which is one of their limiting systematics. The
nulling technique is a model-independent method developed to eliminate
intrinsic-shear alignment at the two-point level. In this paper we demonstrate
that the nulling technique can also be naturally generalized to the three-point
level, controlling the corresponding GGI systematics. We show that under the
assumption of exact redshift information the intrinsic-shear alignment
contamination can be completely eliminated. To show how well the nulling
technique performs on data with limited redshift information, we apply the
nulling technique to three-point weak lensing statistics from a fictitious
survey analogous to a typical future deep imaging survey, in which the
three-point intrinsic-shear alignment systematics is generated from a power-law
toy model. Using 10 redshift bins, the nulling technique leads to a factor of
10 suppression of the GGI/GGG ratio, and reduces the bias on cosmological
parameters to less than the original statistical error. More detailed redshift
information allowing for finer redshift bins leads to better reduction of bias.
The information loss during the nulling procedure doubles the statistical error
on cosmological parameters. A comparison of the nulling technique with an
unconditioned compression of the data suggests that part of the information
loss can be retained by considering higher-order nulling weights during the
nulling procedure. A combined analysis of two- and three-point statistics
confirms that the information contained in them is of comparable size and is
complementary to each other, both before and after nulling. | The Distribution of AGN Covering Factors: We review our knowledge of the most basic properties of the AGN obscuring
region - its location, scale, symmetry, and mean covering factor - and discuss
new evidence on the distribution of covering factors in a sample of ~9000
quasars with WISE, UKIDSS, and SDSS photometry. The obscuring regions of AGN
may be in some ways more complex than we thought - multi-scale, not symmetric,
chaotic - and in some ways simpler - with no dependence on luminosity, and a
covering factor distribution that may be determined by the simplest of
considerations - e.g. random misalignments. |
Auto-consistent metallicity and star formation history of the nearest
blue compact dwarf galaxy NGC 6789: We present a detailed auto-consistent study of the nearest blue compact dwarf
galaxy NGC 6789 by means of optical and UV archive photometry data and optical
long-slit ISIS-WHT spectroscopy observations of the five brightest star-forming
knots. The analysis of the spectra in all knots allowed the derivation of ionic
chemical abundances of oxygen, nitrogen, sulphur, argon and neon using measures
of both the high- and low-excitation electron temperatures, leading to the
conclusion that NGC 6789 is chemically homogeneous with low values of the
abundance of oxygen in the range 12+log(O/H) = 7.80-7.93, but presenting at the
same time higher values of the nitrogen-to-oxygen ratio than expected for its
metal regime.
We used archival HST/WFPC2 F555W and F814W observations of NGC 6789 to
perform a photometric study of the colour-magnitude diagram (CMD) of the
resolved stellar populations and derive its star formation history (SFH), which
is compatible with the presence of different young and old stellar populations
whose metallicities do not necessarily increase with age. We fit the observed
optical spectrum in all the five knots using the STARLIGHT code and a
combination of single stellar populations following the SFH obtained from the
CMD. We compare the resulting stellar masses and the relative fractions of the
ionising populations with a non-constrained SFH case. The properties of the
younger populations were obtained using CLOUDY photoionisation models, giving
similar ages in all the knots in the range 3-6 Myr and the estimation of the
dust absorption factor, which correlates with the observed GALEX FUV-NUV colour
indices. The total photometric extinction and dust-absorption corrected
H\alpha\ fluxes were finally used to derive the star formation rates. | Intrinsic tension in the supernova sector of the local Hubble constant
measurement and its implications: We reanalyse observations of type Ia supernovae (SNe) and Cepheids used in
the local determination of the Hubble constant and find strong evidence that SN
standardisation in the calibration sample (galaxies with observed Cepheids)
require a steeper slope of the colour correction than in the cosmological
sample (galaxies in the Hubble flow). The colour correction in the calibration
sample is consistent with being entirely due to an extinction correction due to
dust with properties similar to that of the Milky Way (R_B~4.6+/-0.4) and there
is no evidence for intrinsic scatter in the SN peak magnitudes. An immediate
consequence of this finding is that the local measurement of the Hubble
constant becomes dependent on the choice of SN reference colour, i.e., the
colour of an unreddened SN. Specifically, the Hubble constant inferred from the
same observations decreases gradually with the reference colour assumed in the
SN standardisation. We recover the Hubble constant measured by SH0ES for the
standard choice of reference colour (SALT2 colour parameter c=0) while for a
reference colour which coincides with the blue end of the observed SN colour
distribution (c~-0.13), the Hubble constant from Planck observations of the CMB
(assuming a flat LCDM cosmological model) is recovered. These results are
intriguing in that they may provide an avenue for resolving the Hubble tension.
However, since there is no obvious physical basis for the differences in colour
corrections in the two SN samples, the origin of these require further
investigations. |
Abundance of peaks and dips in three-dimensional mass and halo density
fields: a test for cosmology: Using cosmological N-body simulations, we study the abundance of local maxima
(peaks) and minima (dips) identified in the smoothed distribution of halos and
dark matter (DM) on scales of $10-100$s Mpcs. The simulations include Gaussian
and local-type $f_{\rm NL}$ non-Gaussian initial conditions. The expression
derived in the literature for the abundance (irrespective of height) of peaks
for Gaussian fields is surprisingly accurate for the evolved halo and DM
density fields for all initial conditions considered. Furthermore, the height
distribution is very well fitted by a log-normal on quasi-linear scales. The
abundance as a function of scale depends on the cosmological parameters ($H_0$
and background matter densities) through the shape of the power spectrum, but
it is insensitive to the clustering amplitude. Further, the abundance in the
smoothed halo distribution is substantially different in the non-Gaussian from
the Gaussian simulations. The interpretation of this effect is straightforward
in terms of the scale dependence of halo bias in non-Gaussian models. The
abundance of extrema extracted from three-dimensional large galaxy redshift
surveys could be a competitive probe of the cosmological parameters and initial
non-Gaussianity. It breaks the degeneracy between $f_{\rm NL}$ and the
clustering amplitude, making it complementary to counts of galaxy clusters and
peaks in weak-lensing maps. | Non-Gaussianity as a signature of thermal initial condition of inflation: We study non-Gaussianities in the primordial perturbations in single field
inflation where there is radiation era prior to inflation. Inflation takes
place when the energy density of radiation drops below the value of the
potential of a coherent scalar field. We compute the thermal average of the
two, three and four point correlation functions of inflaton fluctuations. The
three point function is proportional to the slow roll parameters and there is
an amplification in $f_{NL}$ by a factor of 65 to 90 due to the contribution of
the thermal bath, and we conclude that the bispectrum is in the range of
detectability with the 21-cm anisotropy measurements. The four point function
on the other hand appears in this case due to the thermal averaging and the
fact that thermal averaging of four-point correlation is not the same as the
square of the thermal averaging of the two-point function. Due to this fact
$\tau_{NL}$ is not proportional to the slow-roll parameters and can be as large
as -42. The non-Gaussianities in the four point correlation of the order 10 can
also be detected by 21-cm background observations. We conclude that a signature
of thermal inflatons is a large trispectrum non-Gaussianity compared to the
bispectrum non-Gaussianity. |
The Herschel view of the environment of the radio galaxy 4C+41.17 at z =
3.8: We present Herschel observations at 70, 160, 250, 350 and 500 micron of the
environment of the radio galaxy 4C+41.17 at z = 3.792. About 65% of the
extracted sources are securely identified with mid-IR sources observed with the
Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 micron. We derive simple
photometric redshifts, also including existing 850 micron and 1200 micron data,
using templates of AGN, starburst-dominated systems and evolved stellar
populations. We find that most of the Herschel sources are foreground to the
radio galaxy and therefore do not belong to a structure associated with
4C+41.17. We do, however, find that the SED of the closest (~ 25" offset)
source to the radio galaxy is fully consistent with being at the same redshift
as 4C+41.17. We show that finding such a bright source that close to the radio
galaxy at the same redshift is a very unlikely event, making the environment of
4C+41.17 a special case. We demonstrate that multi-wavelength data, in
particular on the Rayleigh-Jeans side of the spectral energy distribution,
allow us to confirm or rule out the presence of protocluster candidates that
were previously selected by single wavelength data sets. | Linear scale bounds on dark matter--dark radiation interactions and
connection with the small scale crisis of cold dark matter: One of the open questions in modern cosmology is the small scale crisis of
the cold dark matter paradigm. Increasing attention has recently been devoted
to self-interacting dark matter models as a possible answer. However, solving
the so-called "missing satellites" problem requires in addition the presence of
an extra relativistic particle (dubbed dark radiation) scattering with dark
matter in the early universe. Here we investigate the impact of different
theoretical models devising dark matter dark radiation interactions on large
scale cosmological observables. We use cosmic microwave background data to put
constraints on the dark radiation component and its coupling to dark matter. We
find that the values of the coupling allowed by the data imply a cut-off scale
of the halo mass function consistent with the one required to match the
observations of satellites in the Milky Way. |
Ultra-Light Dark Matter: Ultra-light dark matter (ULDM) is a class of dark matter models (DM) where DM
is composed by bosons with masses ranging from $10^{-24}\, \mathrm{eV} < m <
\mathrm{eV}$. These models have been receiving a lot of attention in the past
few years given their interesting property of forming a Bose-Einstein
condensate (BEC) or a superfluid on galactic scales. BEC and superfluidity are
one of the most striking quantum mechanical phenomena manifest on macroscopic
scales, and upon condensation, the particles behave as a single coherent state,
described by the wavefunction of the condensate. The idea is that condensation
takes place inside galaxies while outside DM behaves like a normal cold
particle DM. This wave nature of DM on galactic scales that arise upon
condensation can address some of the curiosities of the behaviour of DM on
small scales while maintaining the successes of LCDM on large scales. There are
many models in the literature that describe a DM component that condenses in
galaxies. In this review, we are going to describe those models and classify
them according to the different ways they achieve condensation. For that, we
review the phenomena of BEC and superfluidity, and apply this knowledge to the
DM in order to explain their construction and phenomenology. We describe the
small scale challenges these models aim to solve and how ULDM alleviates them.
These models present a rich phenomenology that is manifest in different
astrophysical consequences. We review here the astrophysical and cosmological
tests used to constrain those models, together with new and future observations
that promise to test these models in different regimes. We finalize by showing
some predictions that are a consequence of the wave nature of this component,
like vortices and interference, that could represent a smoking gun in the
search of these rich and interesting alternative class of DM. (Abridged) | Faint Dwarfs in Nearby Groups: The number and distribution of dwarf satellite galaxies remain a critical
test of cold dark matter-dominated structure formation on small scales. Until
recently, observational information about galaxy formation on these scales has
been limited mainly to the Local Group. We have searched for faint analogues of
Local Group dwarfs around nearby bright galaxies, using a spatial clustering
analysis of the photometric catalog of the Sloan Digital Sky Survey (SDSS) Data
Release 8. Several other recent searches of SDSS have detected clustered
satellite populations down to $\Delta m_r \equiv ({m}_{r,\, {\rm sat}} -\,
{m}_{r,\, {\rm main}}) \sim 6$-$8$, using photometric redshifts to reduce
background contamination. SDSS photometric redshifts are relatively imprecise,
however, for faint and nearby galaxies. Instead we use angular size to select
potential nearby dwarfs, and consider only the nearest isolated bright galaxies
as primaries. As a result, we are able to detect an excess clustering signal
from companions down to $\Delta m_r = 12$, four magnitudes fainter than most
recent studies. We detect an over-density of objects at separations $< 400$
kpc, corresponding to about $4.6 \pm 0.5$ satellites per central galaxy,
consistent with the satellite abundance expected from the Local Group given our
selection function. Although the sample of satellites detected is incomplete by
construction, since it excludes the least and most compact dwarfs, this
detection provides a lower bound on the average satellite luminosity function,
down to luminosities corresponding to the faintest "classical" dwarfs of the
Local Group. |
Blowing cold flows away: the impact of early AGN activity on the
formation of a brightest cluster galaxy progenitor: Supermassive black holes (BH) are powerful sources of energy that are already
in place at very early epochs of the Universe (by z=6). Using hydrodynamical
simulations of the formation of a massive M_vir=5 10^11 M_sun halo by z=6 (the
most massive progenitor of a cluster of M_vir=2 10^15 M_sun at z=0), we
evaluate the impact of Active Galactic Nuclei (AGN) on galaxy mass content, BH
self-regulation, and gas distribution inside this massive halo. We find that SN
feedback has a marginal influence on the stellar structure, and no influence on
the mass distribution on large scales. In contrast, AGN feedback alone is able
to significantly alter the stellar-bulge mass content by quenching star
formation when the BH is self-regulating, and by depleting the cold gas
reservoir in the centre of the galaxy. The growth of the BH proceeds first by a
rapid Eddington-limited period fed by direct cold filamentary infall. When the
energy delivered by the AGN is sufficiently large to unbind the cold gas of the
bulge, the accretion of gas onto the BH is maintained both by smooth gas inflow
and clump migration through the galactic disc triggered by merger-induced
torques. The feedback from the AGN has also a severe consequence on the baryon
mass content within the halo, producing large-scale hot superwinds, able to
blow away some of the cold filamentary material from the centre and reduce the
baryon fraction by more than 30 per cent within the halo's virial radius. Thus
in the very young universe, AGN feedback is likely to be a key process, shaping
the properties of the most massive galaxies. | Post-inflationary Dark Matter production and Leptogenesis: Metric versus
Palatini formalism: We investigate production of non-thermal dark matter particle and heavy
sterile neutrino from inflaton during the reheating era which is preceded by a
slow-roll inflationary epoch with a quartic potential and non-minimal coupling
($\xi$) between the inflaton and the gravity. We compare our analysis between
metric and Palatini formalism. For the latter with $\xi=0.5$ and number of
$e$-folds $\sim 60$, $r$ can be as small as $\sim {\cal O}\left(10^{-3}\right)$
which may be validated at $1-\sigma$ CL of prospective future reaches of
upcoming CMB observation such as CMB-S4~etc. We identify that permissible range
of Yukawa coupling $y_\chi$ between inflaton and fermionic DM $\chi$, to be
${\cal O}\left(10^{-3.5}\right)\gtrsim y_\chi \gtrsim {\cal
O}\left(10^{-20}\right)$ for metric formalism and ${\cal
O}\left(10^{-4}\right)\gtrsim y_\chi \gtrsim {\cal O}\left(10^{-11}\right)$ for
Palatini formalism which is consistent with current PLANCK data and also be
within the reach of future CMB experiments. For the scenario of leptogenesis
via the decay of sterile neutrino produced from inflaton decay, we also
investigate the parameter space of heavy neutrino mass $m_{N_1}$ and Yukawa
coupling $y_{N_1}$ of sterile neutrino with inflaton, which are consistent with
current CMB data and successful generation of the observed baryon asymmetry of
the universe via leptogenesis. In contrast to metric formalism, in the case of
Palatini formalism for successful leptogenesis to occur we find that $y_{N_1}$
has a very narrow allowable range and is severely constrained from the
consistency with CMB predictions. |
High Jet Efficiency and Simulations of Black Hole Magnetospheres: This article reports on a growing body of observational evidence that many
powerful lobe dominated (FR II) radio sources likely have jets with high
efficiency. This study extends the maximum efficiency line (jet power $\approx$
25 times the thermal luminosity) defined in Fernandes et (2010) so as to span
four decades of jet power. The fact that this line extends over the full span
of FR II radio power is a strong indication that this is a fundamental property
of jet production that is independent of accretion power. This is a valuable
constraint for theorists. For example, the currently popular "no net flux"
numerical models of black hole accretion produce jets that are 2 to 3 orders of
magnitude too weak to be consistent with sources near maximum efficiency. | Constraints on halo formation from cross-correlations with correlated
variables: Cross-correlations between biased tracers and the dark matter field encode
information about the physical variables which characterize these tracers.
However, if the physical variables of interest are correlated with one another,
then extracting this information is not as straightforward as one might naively
have thought. We show how to exploit these correlations so as to estimate
scale-independent bias factors of all orders in a model-independent way. We
also show that failure to account for this will lead to incorrect conclusions
about which variables matter and which do not. Morever, accounting for this
allows one to use the scale dependence of bias to constrain the physics of halo
formation; to date the argument has been phrased the other way around. We
illustrate by showing that the scale dependence of linear and nonlinear bias,
measured on nonlinear scales, can be used to provide consistent estimates of
how the critical density for halo formation depends on halo mass. Our methods
work even when the bias is nonlocal and stochastic, such as when, in addition
to the spherically averaged density field and its derivatives, the quadrupolar
shear field also matters for halo formation. In such models, the nonlocal bias
factors are closely related to the more familiar local nonlinear bias factors,
which are much easier to measure. Our analysis emphasizes the fact that biased
tracers are biased because they do not sample fields (density, velocity, shear,
etc.) at all positions in space in the same way that the dark matter does. |
X-ray Selected BL Lacertae Objects: Catalogue and Statistical Properties: This talk focuses on the statistical properties of X-ray selected BL Lacertae
objects (XBLs) whose catalogue has been compiled. It consists of 312 sources
from different X-ray surveys, unambiguously identified to mid-2010. Results of
the statistical research of different observational quantities (redshift,
muliwavelength luminosities, host/nucleus absolute Magnitudes, central black
hole masses, synchrotron peak frequencies, broadband spectral indices) are also
provided and existence of the correlation between them is proved. Overall flux
variability shows an increasing trend towards greater frequencies. XBL are
found to be much less active in point of intra-night optical variability
compared to radio-selected BL Lacs (RBLs). A separate list of 106 XBL
candidates is also created including the same characteristics for each source
as in the case of XBL catalogue. | Geodesic Deviation Equation in Bianchi Cosmologies: We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE. |
Generalised velocity-dependent one-scale model for current-carrying
strings: We develop an analytic model to quantitatively describe the evolution of
superconducting cosmic string networks. Specifically, we extend the
velocity-dependent one-scale (VOS) model to incorporate arbitrary currents and
charges on cosmic string worldsheets under two main assumptions, the validity
of which we also discuss. We derive equations that describe the string network
evolution in terms of four macroscopic parameters: the mean string separation
(or alternatively the string correlation length) and the root mean square (RMS)
velocity which are the cornerstones of the VOS model, together with parameters
describing the averaged timelike and spacelike current contributions. We show
that our extended description reproduces the particular cases of wiggly and
chiral cosmic strings, previously studied in the literature. This VOS model
enables investigation of the evolution and possible observational signatures of
superconducting cosmic string networks for more general equations of state, and
these opportunities will be exploited in a companion paper. | X-ray properties of radio-selected star forming galaxies in the
Chandra-COSMOS survey: X-ray surveys contain sizable numbers of star forming galaxies, beyond the
AGN which usually make the majority of detections. Many methods to separate the
two populations are used in the literature, based on X-ray and multiwavelength
properties. We aim at a detailed test of the classification schemes and to
study the X-ray properties of the resulting samples. We build on a sample of
galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et
al. (2008) according to their optical colours and observed with Chandra. A
similarly selected control sample of AGN is also used for comparison. We review
some X-ray based classification criteria and check how they affect the sample
composition. The efficiency of the classification scheme devised by Smolcic et
al. (2008) is such that ~30% of composite/misclassified objects are expected
because of the higher X-ray brightness of AGN with respect to galaxies. The
latter fraction is actually 50% in the X-ray detected sources, while it is
expected to be much lower among X-ray undetected sources. Indeed, the analysis
of the stacked spectrum of undetected sources shows, consistently, strongly
different properties between the AGN and galaxy samples. X-ray based selection
criteria are then used to refine both samples. The radio/X-ray luminosity
correlation for star forming galaxies is found to hold with the same
X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be
possible for sources at high redshift or high luminosity, tough it is likely
explained by a bias arising from the radio selection. Finally, we discuss the
X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys
according to different selection criteria, and compare them to the similar
determination from the Chandra Deep Fields. The classification scheme proposed
here may find application in future works and surveys. |
Cosmology and the Hubble Constant: On the Megamaser Cosmology Project
(MCP): The Hubble constant Ho describes not only the expansion of local space at
redshift z ~ 0, but is also a fundamental parameter determining the evolution
of the universe. Recent measurements of Ho anchored on Cepheid observations
have reached a precision of several percent. However, this problem is so
important that confirmation from several methods is needed to better constrain
Ho and, with it, dark energy and the curvature of space. A particularly direct
method involves the determination of distances to local galaxies far enough to
be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear
supermassive black holes. The goal of this article is to describe the relevance
of Ho with respect to fundamental cosmological questions and to summarize
recent progress of the the `Megamaser Cosmology Project' (MCP) related to the
Hubble constant. | Clustering of dark matter in the cosmic web as a probe of massive
neutrinos: The large-scale structure of the universe is distributed in a cosmic web.
Studying the distribution and clustering of dark matter particles and halos may
open up a new horizon for studying the physics of the dark universe. In this
work, we investigate the nearest neighbour statistics and spherical contact
function in cosmological models with massive neutrinos. For this task, we use
the relativistic N-body code, gevolution and study particle snapshots at three
different redshifts. In each snapshot, we find the halos and evaluate the
letter functions for them. We show that a generic behaviour can be found in the
nearest neighbour, $G(r)$, and spherical contact functions, $F(r)$, which makes
these statistics promising tools to constrain the total neutrino mass. |
Cosmological Constraints on the Global Star Formation Law of Galaxies:
Insights From Baryon Acoustic Oscillation Intensity Mapping: Originally proposed as a cosmological probe of the large-scale structure,
line intensity mapping (LIM) also offers a unique window into the astrophysics
of galaxy evolution. Adding to the astrophysical explorations of LIM technique
that have traditionally focused on small, non-linear scales, we present a novel
method to study the global star formation law using forthcoming data from
large-scale baryonic acoustic oscillation (BAO) intensity mapping. Using the
amplitude of the percent-level but scale-dependent bias induced by baryon
fraction fluctuations on BAO scales, we show that combining auto- and
cross-correlation power spectra of two (or more) LIM signals allows to probe
the star formation law power index $\mathcal{N}$. We examine the prospect for
mapping H$\alpha$ and [OIII] lines across all scales, especially where imprints
of the baryon fraction deviation exist, with space missions like SPHEREx. We
show that although SPHEREx may only marginally probe $\mathcal{N}$ by accessing
a modest number of large-scale modes in its 200 deg$^2$ deep survey, future
infrared all-sky surveys reaching a comparable depth with an improved spectral
resolution ($R \gtrsim 400$) are likely to constrain $\mathcal{N}$ to a
precision of 10$-$30%, sufficient for distinguishing models with varying
feedback assumptions, out to $z\sim4$ using BAO intensity mapping. Leveraging
this effect, large, cosmic-variance-limited LIM surveys in the far future can
scrutinize the physical connection between galaxy evolution and the large-scale
cosmological environment, while performing stringent tests of the standard
cosmological model. | Scalable hierarchical BayeSN inference: Investigating dependence of SN
Ia host galaxy dust properties on stellar mass and redshift: We apply the hierarchical probabilistic SED model BayeSN to analyse a sample
of 475 SNe Ia (0.015 < z < 0.4) from Foundation, DES3YR and PS1MD to
investigate the properties of dust in their host galaxies. We jointly infer the
dust law $R_V$ population distributions at the SED level in high- and low-mass
galaxies simultaneously with dust-independent, intrinsic differences. We find
an intrinsic mass step of $-0.049\pm0.016$ mag, at a significance of
3.1$\sigma$, when allowing for a constant intrinsic, achromatic magnitude
offset. We additionally apply a model allowing for time- and
wavelength-dependent intrinsic differences between SNe Ia in different mass
bins, finding $\sim$2$\sigma$ differences in magnitude and colour around peak
and 4.5$\sigma$ differences at later times. These intrinsic differences are
inferred simultaneously with a difference in population mean $R_V$ of
$\sim$2$\sigma$ significance, demonstrating that both intrinsic and extrinsic
differences may play a role in causing the host galaxy mass step. We also
consider a model which allows the mean of the $R_V$ distribution to linearly
evolve with redshift but find no evidence for any evolution - we infer the
gradient of this relation $\eta_R = -0.38\pm0.70$. In addition, we discuss in
brief a new, GPU-accelerated Python implementation of BayeSN suitable for
application to large surveys which is publicly available and can be used for
future cosmological analyses; this code can be found here:
https://github.com/bayesn/bayesn. |
Intranight polarization variability in radio-loud and radio-quiet AGN: (Abriged) Intranight polarization variability in AGN has not been studied
extensively so far. Studying the variability in polarization makes it possibly
to distinguish between different emission mechanisms. Thus it can help
answering the question if intranight variability in radio-loud and radio-quiet
AGN is of the same or of fundamentally different origin. In this paper we
investigate intranight polarization variability in AGN. Our sample consists of
28 AGN at low to moderate redshifts (0.048 < z < 1.036), 12 of which are
radio-quiet quasars (RQQs) and 16 are radio-loud blazars. The subsample of
blazars consists of eight flat-spectrum radio-quasars (FSRQs) and eight BL Lac
objects. We find clear differences between the two samples. A majority of the
radio-loud AGN show moderate to high degrees of polarization, more than half of
them also show variability in polarization. There seems to be a dividing line
for polarization intranight variability at P~5 per cent over which all objects
vary in polarization. Only two out of 12 radio-quiet quasars show polarized
emission, both at levels of P<1 per cent. The lack of polarization intranight
variability in radio-quiet AGN points towards accretion instabilities being the
cause for intranight flux variability whereas the high duty cycle of
polarization variability in radio-loud objects is more likely caused by
instabilities in the jet or changes of physical conditions in the jet plasma. | The Simultaneous Medicina-Planck Experiment (SiMPlE): data acquisition,
reduction and first results: The Simultaneous Medicina-{\it Planck} Experiment (SiMPlE) is aimed at
observing a selected sample of 263 extragalactic and Galactic sources with the
Medicina 32-m single dish radio telescope in the same epoch as the Planck
satellite observations. The data acquired with a frequency coverage down to 5
GHz, also combined with Planck at frequencies above 30 GHz, will constitute a
useful reference catalogue of bright sources over the whole Northern
hemisphere. Furthermore, source observations performed in different epochs and
comparison with other catalogues allow the investigation of source
variabilities on different timescales. In this work, we describe the sample
selection, the on-going data acquisition campaign, the data reduction
procedures, the developed tools, and the comparison with other data-sets. We
present the data at 5 and 8.3 GHz for the SiMPlE Northern Sample consisting of
79 sources with $\delta \geq 45^\circ$ selected in our catalogue and observed
during the first 6 months of the project. A first analysis of their spectral
behaviour and long-term variability is also presented. |
A semi-analytical approach to perturbations in mutated hilltop inflation: We study cosmological perturbations and observational aspects for mutated
hilltop model of inflation. Employing mostly analytical treatment, we evaluate
observable parameters during inflation as well as post-inflationary
perturbations. This further leads to exploring observational aspects related to
Cosmic Microwave Background (CMB) radiation. This semi-analytical treatment
reduces complications related to numerical computation to some extent for
studying the different phenomena related to CMB angular power spectrum for
mutated hilltop inflation. | Filamentary Infall of Cold Gas and Escape of Lyman Alpha and Hydrogen
Ionizing Radiation from an Interacting High-Redshift Galaxy: We present observations of a peculiar Lyman alpha-emitting galaxy at redshift
3.344, discovered in a deep, blind spectroscopic survey for faint Lyman alpha
emitters with the Magellan II telescope in the Hubble Ultra Deep Field (HUDF).
The galaxy exhibits complex Lyman alpha emission, including an extended,
asymmetric component that is partially suppressed by damped Lyman alpha
absorption, and two spatially elongated, narrow emission features. Archival HST
ACS imaging shows evidence for tidal disruption of the stellar component. This
V=27 galaxy appears to give us unprecedented insights into two fundamental
stages in the formation of structure at high redshift: the inflow of gas into
ordinary galaxies, and the escape of ionizing radiation into the intergalactic
medium. Neutral hydrogen, falling in partly in form of a narrow filament,
appears to emit fluorescent Lyman alpha photons induced by the stellar ionizing
flux escaping from the disturbed galaxy. The in-falling material may represent
primary cold accretion or an interaction-triggered inflow. The rate of ionizing
photons required by the observed Lyman alpha emission is consistent with the
rate of photons produced by the observed stellar population, with roughly 50
percent of ionizing photons escaping from the immediate galaxy and encountering
the in-falling gas. The observational properties of the galaxy lend support to
a picture where galaxy interactions facilitate the escape of both Lyman alpha
and ionizing radiation. We argue that galaxies like the present object may be
common at high redshift. This galaxy may therefore be a late example of an
interacting population of dwarf galaxies contributing significantly to the
reionization of the universe. |
On Mitigation of the Uncertainty in Nonlinear Matter Clustering for
Cosmic Shear Tomography: We present a new method that deals with the uncertainty in matter-clustering
in cosmic shear power spectrum analysis that arises mainly due to poorly
understood nonlinear baryonic processes on small-scales. We show that the
majority of information about dark energy physics contained in the shear power
comes from these small-scales; removing these nonlinear scales from a cosmic
shear analysis results in a 50% cut in the accuracy of measurements of dark
energy parameters, marginalizing over all other parameters. In this paper we
propose a method to recover the information on small-scales by allowing cosmic
shear surveys to measure the nonlinear matter power spectrum themselves and
marginalize over all possible power spectra using path integrals. Information
is still recoverable in these nonlinear regimes from the geometric part of weak
lensing. In this self-calibration regime we find we recover 90% of the
information on dark energy. Including an informative prior, we find the
nonlinear matter power spectrum needs to be accurately known to 1% down to k=50
h/Mpc to recover 99% of the dark energy information. This presents a
significant theoretical challenge to understand baryonic effects on the scale
of galaxy haloes. However self-calibration from weak lensing may also provide
observational input to help constrain baryon physics. | VIMOS Ultra-Deep Survey (VUDS): Witnessing the Assembly of a Massive
Cluster at z~3.3: Using new spectroscopic observations obtained as part of the VIMOS Ultra-Deep
Survey (VUDS), we perform a systematic search for overdense environments in the
early universe ($z>2$) and report here on the discovery of Cl J0227-0421, a
massive protocluster at $z=3.29$. This protocluster is characterized by both
the large overdensity of spectroscopically confirmed members,
$\delta_{gal}=10.5\pm2.8$, and a significant overdensity in photometric
redshift members. The halo mass of this protocluster is estimated, by a variety
of methods, to be roughly $3\times10^{14}$ $\mathcal{M}_{\odot}$ at $z\sim3.3$,
which, evolved to $z=0$ results in a halo mass rivaling or exceeding that of
the Coma cluster. The properties of 19 spectroscopically confirmed member
galaxies are compared with a large sample of VUDS/VVDS galaxies in lower
density field environments at similar redshifts. We find tentative evidence for
an excess of redder, brighter, and more massive galaxies within the confines of
the protocluster relative to the field population, which suggests that we may
be observing the beginning of environmentally-induced quenching. The properties
of these galaxies are investigated, including a discussion of the brightest
protocluster galaxy which appears to be undergoing vigorous coeval nuclear and
starburst activity. The remaining member galaxies appear to have
characteristics which are largely similar to the field population. Though we
find weaker evidence of the suppression of the median star formation rates
amongst and differences in stacked spectra of member galaxies with respect to
the field, we defer any conclusions of these trends to future work with the
ensemble of protostructures that are found in the full VUDS sample. |
Revised estimates of CMB $B$-mode polarization induced by patchy
reionization: The search for primordial gravitational waves through the $B$-mode
polarization pattern in the CMB is one of the major goals of current and future
CMB experiments. Besides foregrounds, a potential hurdle in this search is the
anisotropic secondary $B$-mode polarization generated by the scattering of CMB
photons off free electrons produced during patchy cosmological reionization.
Robust predictions of these secondary anisotropies are challenging because of
uncertainties in the reionization history. In this paper, we revise estimates
of the reionization-induced $B$-mode signal by incorporating recent advances in
the understanding of reionization through observations of the Lyman-$\alpha$
forest. To derive these $B$-mode estimates, we use high-dynamic-range radiative
transfer simulations of reionization that are calibrated to the Ly$\alpha$
data. These simulations are also consistent with a variety of other
high-redshift observations. We find that around multipoles $\ell\approx 100$,
reionization induces $B$-mode power with $\ell(\ell+1)C_\ell^{BB}/2\pi\approx
4\times 10^{-6}\,\mu$K$^2$. This secondary signal is thus at the level of the
primordial signal with the tensor-to-scalar ratio $r<10^{-4}$, and can increase
by a factor of $\sim 50$ if reionization is sourced by highly clustered sources
residing in haloes with mass of $\sim 10^{11}$ M$_\odot$. Our findings suggest
that the contribution of patchy reionization to the search for primordial
gravitational waves is unlikely to be a concern for currently planned CMB
experiments. | Weak lensing reconstructions in 2D & 3D: implications for cluster
studies: We compare the efficiency with which 2D and 3D weak lensing mass mapping
techniques are able to detect clusters of galaxies using two state-of-the-art
mass reconstruction techniques: MRLens in 2D and GLIMPSE in 3D. We simulate
otherwise-empty cluster fields for 96 different virial mass-redshift
combinations spanning the ranges $3\times10^{13}h^{-1}M_\odot \le M_{vir}\le
10^{15}h^{-1}M_\odot$ and $0.05 \le z_{\rm cl} \le 0.75$, and for each generate
1000 realisations of noisy shear data in 2D and 3D. For each field, we then
compute the cluster (false) detection rate as the mean number of cluster
(false) detections per reconstruction over the sample of 1000 reconstructions.
We show that both MRLens and GLIMPSE are effective tools for the detection of
clusters from weak lensing measurements, and provide comparable quality
reconstructions at low redshift. At high redshift, GLIMPSE reconstructions
offer increased sensitivity in the detection of clusters, yielding cluster
detection rates up to a factor of $\sim 10\times$ that seen in 2D
reconstructions using MRLens. We conclude that 3D mass mapping techniques are
more efficient for the detection of clusters of galaxies in weak lensing
surveys than 2D methods, particularly since 3D reconstructions yield unbiased
estimators of both the mass and redshift of the detected clusters directly. |
Star Formation in Two Luminous Spiral Galaxies: We have examined star formation in two very luminous (M_V=-22 to -23) Sc-type
spiral galaxies, NGC 801 and UGC 2885, using ultra-deep Halpha images. We
combine these with UBV and 2MASS JHK images and HI maps to explore the star
formation characteristics of disk galaxies at high luminosity. Halpha traces
star formation in these galaxies to 4-6 disk scale lengths, but the lack of
detection of Halpha further out is likely due to loss of Lyman continuum
photons. Considering gravitational instabilities alone, we find that the gas
and stars in the outer regions are marginally stable in an average sense, but
considering dissipative gas and radial and azimuthal forcing, the outer regions
are marginally unstable to form spiral arms. Star formation is taking place in
spiral arms, which are regions of locally higher gas densities. Furthermore, we
have traced smooth exponential stellar disks over 3-orders of magnitude and 4-6
disk scale lengths, in spite of a highly variable gravitational instability
parameter. Thus, gravitational instability thresholds do not seem relevant to
the stellar disk. One possibility for creating an exponential disk is that the
molecular cloud densities and star formation rates have exponential profiles
and this forces the stellar disk to build up such a profile. Another
possibility is that the stellar disk is continuously adjusted to an exponential
shape regardless of the star formation profile, for example through global
dynamical process that scatter stars. However, such scattering processes are
only known to operate in spiral systems, in which case they cannot explain the
same dilemma of smooth exponential disks observed in dwarf irregular galaxies. | Cosmological horizon entropy and generalised second law for flat
Friedmann Universe: We discuss the generalized second law (GSL) and the constraints imposed by it
for two types of Friedmann universes. The first one is the Friedmann universe
with radiation and a positive cosmological constant, and the second one
consists of non-relativistic matter and a positive cosmological constant. The
time evolution of the event horizon entropy and the entropy of the contents
within the horizon are analyses in an analytical way by obtaining the Hubble
parameter. It is shown that the GSL constraint the temperature of both the
radiation and matter of the Friedmann universe. It is also shown that, even
though the net entropy of the radiation (or matter) is decreasing at
sufficiently large times as the universe expand, it exhibit an increase during
the early times when universe is decelerating. That is the entropy of the
radiation within the comoving volume is decreasing only when the universe has
got an event horizon. |
Kinematically detected polar rings/disks in blue compact dwarf galaxies: Polar ring galaxies are systems with nearly orthogonally rotated components.
We have found the gas on polar (or strongly inclined) orbits in two BCD
galaxies using ionized gas velocity fields taken with a Fabry-Perot
interferometer of the SAO RAS 6-m telescope. Our analysis shows that all
ionized gas in Mrk 33 is concentrated in a compact disk (3 kpc in diameter)
which rotates in the polar plane relative to the main stellar body. The gaseous
disk in Mrk 370 has a more complex structure with a heavily warped innermost
part. The presence of polar gaseous structures supports an idea that current
the burst of star formation in these galaxies is due to the external gas
accretion or merging. A possible fraction of polar structures among BCD
galaxies seems to be very large (up to 10-15%) | Are Brightest Halo Galaxies Central Galaxies?: It is generally assumed that the central galaxy in a dark matter halo, that
is, the galaxy with the lowest specific potential energy, is also the brightest
halo galaxy (BHG), and that it resides at rest at the centre of the dark matter
potential well. This central galaxy paradigm (CGP) is an essential assumption
made in various fields of astronomical research. In this paper we test the
validity of the CGP using a large galaxy group catalogue constructed from the
Sloan Digital Sky Survey. For each group we compute two statistics, ${\cal R}$
and ${\cal S}$, which quantify the offsets of the line-of-sight velocities and
projected positions of brightest group galaxies relative to the other group
members. By comparing the cumulative distributions of $|{\cal R}|$ and $|{\cal
S}|$ to those obtained from detailed mock group catalogues, we rule out the
null-hypothesis that the CGP is correct. Rather, the data indicate that in a
non-zero fraction $f_{\rm BNC}(M)$ of all haloes of mass $M$ the BHG is not the
central galaxy, but instead, a satellite galaxy. In particular, we find that
$f_{\rm BNC}$ increases from $\sim 0.25$ in low mass haloes ($10^{12} h^{-1}
{\rm M_{\odot}} \leq M \lsim 2 \times 10^{13} h^{-1}{\rm M_{\odot}}$) to $\sim
0.4$ in massive haloes ($M \gsim 5 \times 10^{13} h^{-1} {\rm M_{\odot}}$). We
show that these values of $f_{\rm BNC}$ are uncomfortably high compared to
predictions from halo occupation statistics and from semi-analytical models of
galaxy formation. We end by discussing various implications of a non-zero
$f_{\rm BNC}(M)$, with an emphasis on the halo masses inferred from satellite
kinematics. |
Cosmological transition epoch from gamma-ray burst correlations: The redshift $z_t$ and the jerk parameter $j_t$ of the transition epoch are
constrained by using two model-independent approaches involving the direct
expansion of the Hubble rate and the expansion of the deceleration parameter
around $z=z_t$. To extend our analysis to high-redshifts, we employ the
\emph{Amati}, \emph{Combo}, \emph{Yonetoku} and \emph{Dainotti} gamma-ray burst
correlations. The \textit{circularity problem} is prevented by calibrating
these correlations through the B\'ezier interpolation of the updated
observational Hubble data. Each gamma-ray burst data set is jointly fit with
type Ia supernovae and baryonic acoustic oscillations through a Monte Carlo
analysis, based on the Metropolis-Hastings algorithm, to obtain $z_t$, $j_t$
and the correlation parameters. The overall results are compatible with the
concordance model with some exceptions. We also focus on the behaviors of the
dark energy, verifying its compatibility with a cosmological constant, and the
matter density $\Omega_m$ and compare them with the expectations of the
concordance paradigm. | Galaxy evolution from deep multi-wavelength Infrared surveys: a prelude
to Herschel: [abridged] At the end of the Spitzer cryogenic mission and the onset of the
Herschel era, we review our current knowledge on galaxy evolution at IR
wavelengths. We also develop new tools for the analysis of background
fluctuations to constrain source counts in regimes of high confusion. We
analyse a large variety of new data on galaxy evolution and high-z source
populations from Spitzer surveys, as well as complementary data from sub-mm
(BLAST) and millimetric ground-based observations. These data confirm earlier
indications about a very rapid increase of galaxy volume emissivity up to z~1.
This is the fastest evolution rate observed for galaxies at any wavelengths.
The observed Spitzer counts at 24 micron require a combination of fast
evolution for the dominant population and a bumpy spectrum with substantial PAH
emission at z~1 to 2. Confusion-limited number counts at longer wavelengths
confirm these results. All the present data require that the fast observed
evolution from z=0 to 1 flattens around redshift 1 and then keeps approximately
constant up to z~2.5 at least. The present-day IR data provide clear evidence
for the existence of a distinct population of very luminous galaxies becoming
dominant at z > 1. Their cosmological evolution, peaking around z~2, shows a
faster decay with cosmic time than lower luminosity systems, whose maximal
activity is set around z~1, then supporting an earlier phase of formation for
the most luminous and massive galaxies. From a comparison of our results on the
comoving IR emissivity with recent estimates of the redshift-dependent stellar
mass functions of galaxies, we infer that a large fraction (>=50%) of the IR
activity at z > 1 should be due to obscured AGN accretion and that concomitant
SF in high-z luminous sources should follow a top-heavy IMF. |
Cosmology beyond BAO from the 3D distribution of the Lyman-$α$
forest: We propose a new method for fitting the full-shape of the Lyman-$\alpha$
(Ly$\alpha$) forest three-dimensional (3D) correlation function in order to
measure the Alcock-Paczynski (AP) effect. Our method preserves the robustness
of baryon acoustic oscillations (BAO) analyses, while also providing extra
cosmological information from a broader range of scales. We compute idealized
forecasts for the Dark Energy Spectroscopic Instrument (DESI) using the
Ly$\alpha$ auto-correlation and its cross-correlation with quasars, and show
how this type of analysis improves cosmological constraints. The DESI
Ly$\alpha$ BAO analysis is expected to measure $H(z_\mathrm{eff})r_\mathrm{d}$
and $D_\mathrm{M}(z_\mathrm{eff})/r_\mathrm{d}$ with a precision of $\sim0.9\%$
each, where $H$ is the Hubble parameter, $r_\mathrm{d}$ is the comoving BAO
scale, $D_\mathrm{M}$ is the comoving angular diameter distance and the
effective redshift of the measurement is $z_\mathrm{eff}\simeq2.3$. By fitting
the AP parameter from the full shape of the two correlations, we show that we
can obtain a precision of $\sim0.5-0.6\%$ on each of
$H(z_\mathrm{eff})r_\mathrm{d}$ and
$D_\mathrm{M}(z_\mathrm{eff})/r_\mathrm{d}$. Furthermore, we show that a joint
full-shape analysis of the Ly$\alpha$ auto-correlation and its
cross-correlation with quasars can measure the linear growth rate times the
amplitude of matter fluctuations in spheres of $8\;h^{-1}$Mpc,
$f\sigma_8(z_\mathrm{eff})$. Such an analysis could provide the first ever
measurement of $f\sigma_8(z_\mathrm{eff})$ at redshift $z_\mathrm{eff}>2$. By
combining this with the quasar auto-correlation in a joint analysis of the
three high-redshift two-point correlation functions, we show that DESI could be
able to measure $f\sigma_8(z_\mathrm{eff}\simeq2.3)$ with a precision of
$5-12\%$, depending on the smallest scale fitted. | Cosmology Without Windows: Quadratic Estimators for the Galaxy Power
Spectrum: Conventional algorithms for galaxy power spectrum estimation measure the true
spectrum convolved with a survey window function, which, for parameter
inference, must be compared with a similarly convolved theory model. In this
work, we directly estimate the unwindowed power spectrum multipoles using
quadratic estimators akin to those introduced in the late 1990s. Under Gaussian
assumptions, these are optimal and free from the leading-order effects of
pixellization and non-Poissonian shot-noise. They may be straightforwardly
computed given the survey data-set and a suite of simulations of known
cosmology. We implement the pixel-based maximum-likelihood estimator and a
simplification based on the FKP weighting scheme, both of which can be computed
via FFTs and conjugate gradient descent methods. Furthermore, the estimators
allow direct computation of spectrum coefficients in an arbitrary linear
compression scheme, without needing to first bin the statistic. Applying the
technique to a subset of the BOSS DR12 galaxies, we find that the pixel-based
quadratic estimators give statistically consistent power spectra, compressed
coefficients, and cosmological parameters to those obtained with the usual
windowed approaches. Due to the sample's low number density and compact window
function, the optimal weighting scheme gives little improvement over the
simplified form; this may change for dense surveys or those focusing on
primordial non-Gaussianity. The technique is shown to be efficient and robust,
and shows significant potential for measuring the windowless power spectrum and
bispectrum in the presence of weak non-Gaussianity. |
Tidal disruption rate of stars by spinning supermassive black holes: A supermassive black hole can disrupt a star when its tidal field exceeds the
star's self-gravity, and can directly capture stars that cross its event
horizon. For black holes with mass M > 10^7 solar masses, tidal disruption of
main-sequence stars occurs close enough to the event horizon that a Newtonian
treatment of the tidal field is no longer valid. The fraction of stars that are
directly captured is also no longer negligible. We calculate generically
oriented stellar orbits in the Kerr metric, and evaluate the relativistic tidal
tensor at pericenter for those stars not directly captured by the black hole.
We combine this relativistic analysis with previous calculations of how these
orbits are populated to determine tidal-disruption rates for spinning black
holes. We find, consistent with previous results, that black-hole spin
increases the upper limit on the mass of a black hole capable of tidally
disrupting solar-like stars to ~7 x 10^8 solar masses. More quantitatively, we
find that direct stellar capture reduces tidal-disruption rates by a factor 2/3
(1/10) at M = 10^7 (10^8) solar masses. The strong dependence of
tidal-disruption rates on black-hole spin for M > 10^8 solar masses implies
that future surveys like LSST that discover thousands of tidal disruption
events can constrain supermassive black-hole spin demographics. | Manufacturing cosmic rays in the evolving dynamical states of galaxy
clusters: Galaxy clusters are known to be reservoirs of Cosmic Rays (CRs), as inferred
from theoretical calculations or detection of CR-derived observables. CR
acceleration in clusters is mostly attributed to the dynamical activity that
produces shocks. Shocks in clusters emerge out of merger or accretion, but
which one is more effective in producing CRs? at which dynamical phase? and
why? To this aim, we study the production or injection of CRs through shocks
and its evolution in the galaxy clusters using cosmological simulations with
the {\sc enzo} code. Particle acceleration model considered here is primarily
the Diffusive Shock Acceleration (DSA) of thermal particles, but we also report
a tentative study with pre-existing CRs. Defining appropriate dynamical states
using the concept of virialization, we studied a sample of merging and
non-merging clusters. We report that the merger shocks (with Mach number
$\mathcal{M}\sim2-5$) are the most effective CR producers, while high-Mach
peripheral shocks (i.e. $\mathcal{M}>5$) are mainly responsible for the
brightest phase of CR injection in clusters. Clusters once merged, permanently
deviate from CR and X-ray mass scaling of non-merging systems, enabling us to
use it as a tool to determine the state of merger. Through a temporal and
spatial evolution study, we found a strong correlation between cluster merger
dynamics and CR injection. We observed that the brightest phase of X-ray and CR
injection from clusters occur respectively at about 1.0 and 1.5 Gyr after every
mergers, and CR injection peaks near to the cluster virial radius (i.e
$r_{200}$). Delayed CR injection peaks found in this study deserve further
investigation for possible impact on the evolution of CR-derived observables
from galaxy clusters. |
Modeling the Alignment Profile of Satellite Galaxies in Clusters: Analyzing the halo and galaxy catalogs from the Millennium simulations at
redshifts $z=0,\ 0.5,\ 1$, we determine the alignment profiles of cluster
galaxies by measuring the average alignments between the major axes of the
pseudo inertia tensors from all satellites within cluster's virial radius and
from only those satellites within some smaller radius as a function of the
top-hat scale difference. The alignment profiles quantify how well the
satellite galaxies retain the memory of the external tidal fields after merging
into their host clusters and how fast they lose the initial alignment tendency
as the cluster's relaxation proceeds. It is found that the alignment profile
drops faster at higher redshifts and on smaller mass scales. This result is
consistent with the picture that the faster merging of the satellites and
earlier onset of the nonlinear effect inside clusters tend to break the
preferential alignments of the satellites with the external tidal fields.
Modeling the alignment profile of cluster galaxies as a power-law of the
density correlation coefficient that is independent of the power spectrum
normalization ($\sigma_{8}$) and demonstrating that the density correlation
coefficient varies sensitively with the density parameter ($\Omega_{m}$) and
neutrino mass fraction ($f_{\nu}$), we suggest that the alignment profile of
cluster galaxies might be useful for breaking the $\Omega_{m}$-$\sigma_{8}$ and
$f_{\nu}$-$\sigma_{8}$ degeneracies. | Mass of the universe in a black hole: If spacetime torsion couples to the intrinsic spin of matter according to the
Einstein-Cartan-Sciama-Kibble theory of gravity, then the resulting
gravitational repulsion at supranuclear densities prevents the formation of
singularities in black holes. Consequently, the interior of every black hole
becomes a new universe that expands from a nonsingular bounce. We consider
gravitational collapse of fermionic spin-fluid matter with the stiff equation
of state in a stellar black hole. Such a collapse increases the mass of the
matter, which occurs through the Parker-Zel'dovich-Starobinskii quantum
particle production in strong, anisotropic gravitational fields. The subsequent
pair annihilation changes the stiff matter into an ultrarelativistic fluid. We
show that the universe in a black hole of mass $M_\textrm{BH}$ at the bounce
has a mass $M_\textrm{b}\sim M^2_\textrm{BH}
m^{1/2}_\textrm{n}/m^{3/2}_\textrm{Pl}$, where $m_\textrm{n}$ is the mass of a
neutron and $m_\textrm{Pl}$ is the reduced Planck mass. For a typical stellar
black hole, $M_\textrm{b}$ is about $10^{32}$ solar masses, which is $10^6$
larger than the mass of our Universe. As the relativistic black-hole universe
expands, its mass decreases until the universe becomes dominated by
nonrelativistic heavy particles. |
The flat-sky approximation to galaxy number counts -- redshift space
correlation function: We study the flat-sky approximation for galaxy number counts including
relativistic effects, and assess its performance and accuracy with respect to
the full-sky result. We find an agreement of up to 5% for the local and lensing
contributions to the 2-point correlation function and its multipoles at $z >
0.5$, and up to 1% for the multipoles alone at $z > 1$ and separations
$\lesssim 250$ Mpc/$h$, with a speed-up of over a factor of 1000. Using a
semi-analytic method, which has been implemented in a new version of the code
COFFE, along with the Limber approximation for the integrated contributions, we
further increase the performance, allowing the computation of the flat-sky
multipoles to be done over 10000 times faster than in the full-sky calculation,
which could be used to greatly speed-up Markov chain Monte Carlo sampling for
cosmological parameter estimation. | The AGN fraction of submm-selected galaxies and contributions to the
submm/mm-wave extragalactic background light: We present a comparison of the SCUBA Half Degree Extragalactic Survey
(SHADES) at 450, 850 and 1100 microns with deep guaranteed time 15 microns
AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24 microns in
the Lockman Hole East. The AKARI data was analysed using bespoke software based
in part on the drizzling and minimum-variance matched filtering developed for
SHADES, and was cross calibrated against Infrared Space Observatory (ISO)
fluxes. Our stacking analyses find AKARI 15um galaxies with >~200 microJy
contribute >10% of the 450 micron background, but only <4% of the 1100 micron
background, suggesting that different populations contribute at mm-wavelengths.
We confirm our earlier result that the ultra-deep 450 micron SCUBA-2 Cosmology
Survey will be dominated by populations already detected by AKARI and Spitzer
mid-infrared surveys. The superb mid-infrared wavelength coverage afforded by
combining Spitzer and AKARI photometry is an excellent diagnostic of AGN
contributions, and we find that (23-52)% of submm-selected galaxies have AGN
bolometric fractions f_AGN>0.3. |
Ultra-deep Spitzer Mid-Infrared Spectroscopy of LIRGs and ULIRGs at z ~
1-2: We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the
GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer
Space Telescope. These galaxies are selected among faint infrared sources (0.14
- 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the
major contributors to the cosmic infrared background at the most active epochs.
We estimate redshifts for 92% of the sample using PAH and Si absorption
features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their
total infrared luminosity dominated by emission from AGN. The averaged mid-IR
spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged
spectrum of local starbursts and HII-like ULIRGs, respectively. We find that
6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11
L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um).
Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um)
relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN
contributions to their dust emission lower than those of local counterparts. A
quantitative analysis of their morphology shows that most of the luminous IR
galaxies have morphologies similar to those of IR-quiet galaxies at the same
redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of
them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a
given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong
7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of
the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra,
we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/-
0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et
al. (2007). | Dark Energy Survey Year 1 Results: Constraints on Extended Cosmological
Models from Galaxy Clustering and Weak Lensing: We present constraints on extensions of the minimal cosmological models
dominated by dark matter and dark energy, $\Lambda$CDM and $w$CDM, by using a
combined analysis of galaxy clustering and weak gravitational lensing from the
first-year data of the Dark Energy Survey (DES Y1) in combination with external
data. We consider four extensions of the minimal dark energy-dominated
scenarios: 1) nonzero curvature $\Omega_k$, 2) number of relativistic species
$N_{\rm eff}$ different from the standard value of 3.046, 3) time-varying
equation-of-state of dark energy described by the parameters $w_0$ and $w_a$
(alternatively quoted by the values at the pivot redshift, $w_p$, and $w_a$),
and 4) modified gravity described by the parameters $\mu_0$ and $\Sigma_0$ that
modify the metric potentials. We also consider external information from Planck
CMB measurements; BAO measurements from SDSS, 6dF, and BOSS; RSD measurements
from BOSS; and SNIa information from the Pantheon compilation. Constraints on
curvature and the number of relativistic species are dominated by the external
data; when these are combined with DES Y1, we find
$\Omega_k=0.0020^{+0.0037}_{-0.0032}$ at the 68% confidence level, and $N_{\rm
eff}<3.28\, (3.55)$ at 68% (95%) confidence. For the time-varying
equation-of-state, we find the pivot value $(w_p, w_a)=(-0.91^{+0.19}_{-0.23},
-0.57^{+0.93}_{-1.11})$ at pivot redshift $z_p=0.27$ from DES alone, and $(w_p,
w_a)=(-1.01^{+0.04}_{-0.04}, -0.28^{+0.37}_{-0.48})$ at $z_p=0.20$ from DES Y1
combined with external data; in either case we find no evidence for the
temporal variation of the equation of state. For modified gravity, we find the
present-day value of the relevant parameters to be $\Sigma_0=
0.43^{+0.28}_{-0.29}$ from DES Y1 alone, and $(\Sigma_0,
\mu_0)=(0.06^{+0.08}_{-0.07}, -0.11^{+0.42}_{-0.46})$ from DES Y1 combined with
external data, consistent with predictions from GR. |
FIR line emission from high redshift galaxies: By combining high resolution, radiative transfer cosmological simulations of
z~6 galaxies with a sub-grid multi-phase model of their interstellar medium we
derive the expected intensity of several far infrared (FIR) emission lines ([C
II] 158 micron, [O I] 63 micron, and [N II] 122 micron) for different values of
the gas metallicity, Z. For Z = Z_sun the [C II] spectrum is very complex due
to the presence of several emitting clumps of individual size < 3 kpc; the peak
is displaced from the galaxy center by ~100 km/s. While the [O I] spectrum is
also similarly displaced, the [N II] line comes predominantly from the central
ionized regions of the galaxy. When integrated over ~500 km/s, the [C II] line
flux is 185 mJy km/s; 95% of such flux originates from the cold (T~250 K) H I
phase, and only 5% from the warm (T~5000 K) neutral medium. The [O I] and [N
II] fluxes are ~6 and ~90 times lower than the [C II] one, respectively. By
comparing our results with observations of Himiko, the most extended and
luminous Lyman Alpha Emitter (LAE) at z = 6.6, we find that the gas metallicity
in this source must be sub-solar. We conclude that the [C II] line from z~6
galaxies is detectable by the ALMA full array in 1.9 < t_ON < 7.7 hr observing
time, depending on Z. | Gravitational redshift of galaxies in clusters as predicted by general
relativity: The theoretical framework of cosmology is mainly defined by gravity, of which
general relativity is the current model. Recent tests of general relativity
within the \Lambda Cold Dark Matter (CDM) model have found a concordance
between predictions and the observations of the growth rate and clustering of
the cosmic web. General relativity has not hitherto been tested on cosmological
scales independent of the assumptions of the \Lambda CDM model. Here we report
observation of the gravitational redshift of light coming from galaxies in
clusters at the 99 per cent confidence level, based upon archival data. The
measurement agrees with the predictions of general relativity and its
modification created to explain cosmic acceleration without the need for dark
energy (f(R) theory), but is inconsistent with alternative models designed to
avoid the presence of dark matter. |
On the possibility for constraining cosmic topology from the celestial
distribution of astronomical objects: We present a method to constrain cosmic topology from the distribution of
astronomical objects projected on the celestial sphere. This is an extension of
the 3D method introduced in Fujii & Yoshii (2011) that is to search for a pair
of pairs of observed objects (quadruplet) linked by a holonomy, i.e., the
method we present here is to search for a pair of celestial sphere $n$-tuplets
for $n \geq 3$. We find, however, that this method is impractical to apply in
realistic situations due to the small signal to noise ratio. We conclude
therefore that it is unrealistic to constrain the topology of the Universe from
the celestial distribution, and the 3D catalogs are necessary for the purpose. | Primordial black hole formation from cosmological fluctuations: Primordial black holes (PBHs) are those which may have formed in the early
Universe and affected the subsequent evolution of the Universe through their
Hawking radiation and gravitational field. To constrain the early Universe from
the observational constraint on the abundance of PBHs, it is essential to
determine the formation threshold for primordial cosmological fluctuations,
which are naturally described by cosmological long-wavelength solutions. I will
briefly review our recent analytical and numerical results on the PBH
formation. |
A Method to Extract the Angular Power Spectrum of the Epoch of
Reionization from Low-Frequency Radio Interferometers: The redshifted 21cm signal of neutral hydrogen from the epoch of reionization
(EoR) is extremely weak and its first detection is therefore expected to be
statistical with first-generation low-frequency radio interferometers. In this
letter we propose a method to extract the angular power spectrum of EoR from
the visibility correlation coefficients p_{ij}(u,v), instead of the
visibilities V_{ij}(u,v) measured directly by radio interferometers in
conventional algorithm. The visibility correlation coefficients are defined as
p_{ij}(u,v)=V_{ij}(u,v)/\sqrt{|V_{ii}||V_{jj}|} by introducing the
auto-correlation terms V_{ii} and V_{jj} such that the angular power spectrum
C_{\ell} can be obtained through C_{\ell}=4pi^2T_0^2<|p_{ij}(u,v)|^2>,
independently of the primary beams of antennas. This also removes partially the
influence of receiver gains in the measurement of C_{\ell} because the
amplitudes of the gains cancel each other out in the statistical average
operation of <|p_{ij}(u,v)|^2>.We use the average system temperature T_0 as a
calibrator of C_{\ell}, which is dominated by the Milky Way and extragalactic
sources in our interested frequency range below 200 MHz. Finally we demonstrate
the feasibility of the novel method using the simulated sky maps as targets and
the 21 CentiMeter Array (21CMA) as interferometer. | Lensing Reconstruction in Post-Born Cosmic Microwave Background Weak
Lensing: The study of the Cosmic Microwave Background (CMB) lensing potential has
established itself by now as a robust way of probing the physics of large-scale
structure growth. The most common estimators of the lensing potential are
derived under the assumption of Gaussianity of the matter distribution and in
the Born approximation of the photon diffusion. In this paper we study the
performance of quadratic estimators when applied to realistic sky maps
extracted from multiple-lens ray tracing techniques in cosmological $N$-body
simulations. These are expected to model accurately the effects due to the
non-Gaussianity of the matter distribution induced by its nonlinearity and the
deviation from the Born approximation. We show that both these effects on their
own lead to reconstruction biases, but these tend to partially cancel each
other when both these effects are considered together. We forecast the impact
of these biases on the estimation of cosmological parameters for future
high-sensitivity CMB experiments like CMB-S4. We find that the cold dark matter
density, $\Omega_\textrm{cdm}$, the optical depth to reionization $\tau$, the
amplitude of primordial inflationary perturbations, $A_s$ and the sum of
neutrino masses, $M_\nu$, could be biased at the 1-2$\sigma$ level, if no
external data set is used. We also observe a reduction of the bias if external
data like baryon acoustic oscillations (BAO) is included. |
Observational constraints in Delta Gravity: CMB and supernovas: Delta Gravity is a gravitational model based on an extension of General
Relativity given by a new symmetry called $\tilde{\delta}$. In this model, new
matter fields are added to the original matter fields, motivated by the
additional symmetry. We call them $\tilde{\delta}$ matter fields. This model
predicts an accelerating Universe without the need to introduce a cosmological
constant. In this work, we study the Delta Gravity prediction about the scalar
CMB TT power spectrum using an analytical hydrodynamical approach. To fit the
Planck satellite's data with the DG model, we used a Markov Chain Monte Carlo
analysis. We also include a study about the compatibility between SNe-Ia and
CMB observations in the Delta Gravity Context. Finally, we obtain the scalar
CMB TT power spectrum and the fitted parameters needed to explain both SNe-Ia
Data and CMB measurements. The results are in a reasonable agreement with both
observations considering the analytical approximation. We also discuss if the
Hubble Constant and the Accelerating Universe are in concordance with the
observational evidence in the Delta Gravity context. | Probing the origin of VHE emission from M 87 with MWL observations in
2010: The large majority of extragalactic very high energy (VHE; E>100 GeV) sources
belongs to the class of active galactic nuclei (AGN), in particular the BL Lac
sub-class. AGNs are characterized by an extremely bright and compact emission
region, powered by a super-massive black hole (SMBH) and an accretion disk, and
relativistic outflows (jets) detected all across the electro-magnetic spectrum.
In BL Lac sources the jet axis is oriented close to the line of sight, giving
rise to a relativistic boosting of the emission. In radio galaxies, on the
other hand, the jet makes a larger angle to the line of sight allowing to
resolve the central core and the jet in great details. The giant radio galaxy M
87 with its proximity (1 6Mpc) and its very massive black hole ((3-6) x 10^9
M_solar) provides a unique laboratory to investigate VHE emission in such
objects and thereby probe particle acceleration to relativistic energies near
SMBH and in jets. M 87 has been established as a VHE emitter since 2005. The
VHE emission displays strong variability on time-scales as short as a day. It
has been subject of a large joint VHE and multi-wavelength (MWL) monitoring
campaign in 2008, where a rise in the 43 GHz VLBA radio emission of the
innermost region (core) was found to coincide with a flaring activity at VHE.
This had been interpreted as a strong indication that the VHE emission is
produced in the direct vicinity of the SMBH black hole. In 2010 again a flare
at VHE was detected triggering further MWL observations with the VLBA, Chandra,
and other instruments. At the same time M 87 was also observed with the
Fermi-LAT telescope at GeV energies and the European VLBI Network (EVN). In
this contribution preliminary results from the campaign will be presented. |
Clear detection of dusty torus signatures in a Weak-Line Radio Galaxy:
the case of PKS 0043-42: We report the clearest detection to date of dusty torus signatures in a
Weak-Line Radio Galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS)
rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42 (z=0.116) shows
a clear spectral turnover at wavelengths longer than ~20 micron suggestive of
warm dust, as well as a 9.7 micron silicate absorption feature. In addition,
the hard X-ray results, based on Chandra data, strongly support a picture in
which PKS 0043-42 has a torus and accretion disc more typical of Strong-Line
Radio Galaxies (SLRGs). The MIR and X-ray spectra are markedly different from
those of other WLRGs at similar redshifts, and here we show that the former can
be successfully fitted with clumpy torus models with parameters characteristic
of Type-2 AGN tori: close to edge-on (i=74 deg) and relatively broad (torus
angular width=60 deg), with an outer radius of 2 pc, hydrogen column density
~1.6x10^(23) cm^(-2), and AGN bolometric luminosity ~1.6x10^(44) erg s^(-1).
The presence of a compact torus in PKS 0043-42 provides evidence that this WLRG
is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a
diverse population, and PKS 0043-42 may represent a type of radio galaxy in
which the AGN activity has been recently re-triggered as a consequence of
intermittent gas supply, or in which the covering factor of the Narrow-Line
Region (NLR) clouds is relatively low. | Cosmic voids as cosmological laboratories: Cosmic voids are promising cosmological laboratories for studying the dark
energy phenomenon and alternative gravity theories. They are receiving special
attention nowadays in view of the new generation of galaxy spectroscopic
surveys, which are covering an unprecedented volume and redshift range. There
are two primary statistics in void studies: (i) the void size function, which
characterises the abundance of voids, and (ii) the void-galaxy
cross-correlation function, which contains information about the density and
velocity fields in these regions. However, it is necessary a complete
description of the effects of geometrical (Alcock-Paczynski effect, AP) and
dynamical (Kaiser effect, RSD) distortions around voids in order to design
reliable cosmological tests based on these statistics. Observational
measurements show prominent anisotropic patterns that lead to biased
cosmological constraints if they are not properly modelled. This thesis
addresses this problematic by presenting a theoretical and statistical
framework based on dynamical and cosmological foundations capable of describing
all the underlying effects involved: the expansion effect (t-RSD), the
off-centring effect (v-RSD), the AP-volume effect and the ellipticity effect
(e-RSD). These effects can be understood by studying the mapping of voids
between real and redshift space. In this way, we lay the foundations for a
proper modelling of the aforementioned statistics. In addition, we present a
new cosmological test based on two perpendicular projections of the correlation
function. The method is fiducial-cosmology free, which allows us to effectively
break any possible degeneracy between the cosmological parameters involved.
Moreover, it allows us to significantly reduce the number of mock catalogues
needed to estimate covariances. |
Cosmological MHD Simulations of Galaxy Cluster Radio Relics: Insights
and Warnings for Observations: Non-thermal radio emission from cosmic ray electrons in the vicinity of
merging galaxy clusters is an important tracer of cluster merger activity, and
is the result of complex physical processes that involve magnetic fields,
particle acceleration, gas dynamics, and radiation. In particular, objects
known as radio relics are thought to be the result of shock-accelerated
electrons that, when embedded in a magnetic field, emit synchrotron radiation
in the radio wavelengths. In order to properly model this emission, we utilize
the adaptive mesh refinement simulation of the magnetohydrodynamic evolution of
a galaxy cluster from cosmological initial conditions. We locate shock fronts
and apply models of cosmic ray electron acceleration that are then input into
radio emission models. We have determined the thermodynamic properties of this
radio-emitting plasma and constructed synthetic radio observations to compare
to observed galaxy clusters. We find a significant dependence of the observed
morphology and radio relic properties on the viewing angle of the cluster,
raising concerns regarding the interpretation of observed radio features in
clusters. We also find that a given shock should not be characterized by a
single Mach number. We find that the bulk of the radio emission comes from gas
with T>5x10^7, \rho~10^(-28)-10^(-27) g/cm^3, with magnetic field strengths of
0.1-1.0 \mu G and shock Mach numbers of M~3-6. We present an analysis of the
radio spectral index which suggests that the spatial variation of the spectral
index can mimic synchrotron aging. Finally, we examine the polarization
fraction and position angle of the simulated radio features, and compare to
observations. | Gravitational waves from p-form inflation: Recently it was shown that an inflationary background can be realized by any
$p$-form field non-minimally coupled to gravity. In this paper, we study
gravitational waves generated during p-form inflation. Even though the
background evolution is identical to that in conventional scalar field
inflation, the behavior of gravitational waves is different in p-form
inflation. In particular, we find that the propagation speed of gravitational
waves differs from unity in 2- and 3-form inflationary models. We point out
that the squared speed becomes negative in the large field models. The small
field models are free from pathologies and the correction to the spectrum of
gravitational waves turns out to be very small. |
Meridional tilt of the stellar velocity ellipsoid during bar buckling
instability: The structure and evolution of the stellar velocity ellipsoid plays an
important role in shaping galaxies undergoing bar driven secular evolution and
the eventual formation of a boxy/peanut bulge such as present in the Milky Way.
Using collisionless N-body simulations, we show that during the formation of
such a boxy/peanut bulge, the meridional shear stress of stars, which can be
measured by the meridional tilt of the velocity ellipsoid, reaches a
characteristic peak in its time evolution. It is shown that the onset of a bar
buckling instability is closely connected to the maximum meridional tilt of the
stellar velocity ellipsoid. Our findings bring new insight to this complex
gravitational instability of the bar which complements the buckling instability
studies based on orbital models. We briefly discuss the observed diagnostics of
the stellar velocity ellipsoid during such a phenomenon. | Baryon Asymmetries in the Natural Inflation Model: A variation of Affleck-Dine mechanism was proposed to generate the observed
baryon asymmetry in [1], in which the inflaton was assumed to be a complex
scalar field with a weakly broken $U(1)$ symmetry, and the baryon asymmetry
generation was easily unified with the stage of inflation and reheating. We
adapt this mechanism to natural inflation scenarios and compare the results
with those in chaotic inflation models. We compute the net particle number
obtained at the end of inflation and transform it into net baryon number after
reheatings. We observed that in natural inflation models, the desired
baryon-to-photon ratio can be achieved equally well as in chaotic models. |
On the proper kinetic quadrupole CMB removal and the quadrupole
anomalies: It has been pointed out recently that the quadrupole-octopole alignment in
the CMB data is significantly affected by the so-called kinetic Doppler
quadrupole (DQ), which is the temperature quadrupole induced by our proper
motion. Assuming our velocity is the dominant contribution to the CMB dipole we
have v/c = beta = (1.231 +/- 0.003) * 10^{-3}, which leads to a non-negligible
DQ of order beta^2. Here we stress that one should properly take into account
that CMB data are usually not presented in true thermodynamic temperature,
which induces a frequency dependent boost correction. The DQ must therefore be
multiplied by a frequency-averaged factor, which we explicitly compute for
several CMB maps finding that it varies between 1.67 and 2.47. This is often
neglected in the literature and turns out to cause a small but non-negligible
difference in the significance levels of some quadrupole-related statistics.
For instance the alignment significance in the SMICA 2013 map goes from
2.3sigma to 3.3sigma, with the frequency dependent DQ, instead of 2.9sigma
ignoring the frequency dependence in the DQ. Moreover as a result of a proper
DQ removal, the agreement across different map-making techniques is improved. | Exploiting the Einstein Telescope to solve the Hubble tension: We probe four cosmological models which, potentially, can solve the Hubble
tension according to the dark energy equation of state. In this context, we
demonstrate that the Einstein Telescope is capable of achieving a relative
accuracy below $1\%$ on the Hubble constant independently of the specific dark
energy model. We firstly build mock catalogs containing gravitational wave
events for one, five and ten years of observations, and above Signal-to-Noise
Ratio equal to nine. From these catalogs, we extract the events which are most
likely associated with possible electromagnetic counterpart detected by
THESEUS. Finally, we select four dark energy models, namely a non-flat
$\omega$CDM, an interacting dark energy, an emergent dark energy, and a time
varying gravitational constant model, to forecast the precision down to which
the Einstein Telescope can bound the corresponding cosmological parameters. We
foresee that the Hubble constant is always constrained with less than $1\%$
uncertainty, thereby offering a potential solution to the Hubble tension. The
accuracy on the other cosmological parameters is at most comparable with the
one currently obtained using multiple probes, except for the emergent dark
energy model for which the Einstein Telescope alone will be able to improve the
current limits by more than one order of magnitude. |
Consistency tests of the stability of fundamental couplings and
unification scenarios: We test the consistency of several independent astrophysical measurements of
fundamental dimensionless constants. In particular, we compare direct
measurements of the fine-structure constant $\alpha$ and the proton-to-electron
mass ratio $\mu=m_p/m_e$ (mostly in the optical/ultraviolet) with combined
measurements of $\alpha$, $\mu$ and the proton gyromagnetic ratio $g_p$ (mostly
in the radio band). We point out some apparent inconsistencies, which suggest
that hidden systematics may be affecting some of the measurements. These
findings demonstrate the importance of future more precise measurements with
ALMA, ESPRESSO and ELT-HIRES. We also highlight some of the implications of the
currently available measurements for fundamental physics, specifically for
unification scenarios. | DarkHistory: A code package for calculating modified cosmic ionization
and thermal histories with dark matter and other exotic energy injections: We present a new public Python package, DarkHistory, for computing the
effects of dark matter annihilation and decay on the temperature and ionization
history of the early universe. DarkHistory simultaneously solves for the
evolution of the free electron fraction and gas temperature, and for the
cooling of annihilation/decay products and the secondary particles produced in
the process. Consequently, we can self-consistently include the effects of both
astrophysical and exotic sources of heating and ionization, and automatically
take into account backreaction, where modifications to the
ionization/temperature history in turn modify the energy-loss processes for
injected particles. We present a number of worked examples, demonstrating how
to use the code in a range of different configurations, in particular for
arbitrary dark matter masses and annihilation/decay final states. Possible
applications of DarkHistory include mapping out the effects of dark matter
annihilation/decay on the global 21cm signal and the epoch of reionization, as
well as the effects of exotic energy injections other than dark matter
annihilation/decay. The code is available at
https://github.com/hongwanliu/DarkHistory with documentation at
https://darkhistory.readthedocs.io . Data files required to run the code can be
downloaded at https://doi.org/10.7910/DVN/DUOUWA . |
An expanded merger-tree description of cluster evolution: We model the formation and evolution of galaxy clusters in the framework of
an extended dark matter halo merger-tree algorithm that includes baryons and
incorporates basic physical considerations. Our modified treatment is employed
to calculate the probability density functions of the halo concentration
parameter, intracluster gas temperature, and the integrated Comptonization
parameter for different cluster masses and observation redshifts. Scaling
relations between cluster mass and these observables are deduced that are
somewhat different than previous results. Modeling uncertainties in the
predicted probability density functions are estimated. Our treatment and the
insight gained from the results presented in this paper can simplify the
comparison of theoretical predictions with results from ongoing and future
cluster surveys. | HAWK-I infrared supernova search in starburst galaxies: The use of SN rates to probe explosion scenarios and to trace the cosmic star
formation history received a boost from a number of synoptic surveys. There has
been a recent claim of a mismatch by a factor of two between star formation and
core collapse SN rates, and different explanations have been proposed for this
discrepancy.} We attempted an independent test of the relation between star
formation and supernova rates in the extreme environment of starburst galaxies,
where both star formation and extinction are extremely high. To this aim we
conducted an infrared supernova search in a sample of local starburts galaxies.
The rational to search in the infrared is to reduce the bias due to extinction,
which is one of the putative reasons for the observed discrepancy between star
formation and supernova rates. To evaluate the outcome of the search we
developed a MonteCarlo simulation tool that is used to predict the number and
properties of the expected supernovae based on the search characteristics and
the current understanding of starburst galaxies and supernovae. During the
search we discovered 6 supernovae (4 with spectroscopic classification) which
is in excellent agreement with the prediction of the MonteCarlo simulation tool
that is, on average, $5.3\pm2.3$ events. The number of supernovae detected in
starburst galaxies is consistent with that predicted from their high star
formation rate when we recognize that a major fraction ($\sim 60%$) of the
events remains hidden in the unaccessible, high density nuclear regions because
of a combination of reduced search efficiency and high extinction. |
Observable predictions of generalised inflationary scenarios: Inflation is an early period of accelerated cosmic expansion, thought to be
sourced by high energy physics. A key task today is to use the influx of
increasingly precise observational data to constrain the plethora of
inflationary models suggested by fundamental theories of interactions. This
requires a robust theoretical framework for quantifying the predictions of such
models; helping to develop such a framework is the aim of this thesis. We
provide the first complete quantization of subhorizon perturbations for the
well-motivated class of multi-field inflationary models with a non-trivial
field metric, which we show may yield interesting signatures in the bispectrum
of the Cosmic Microwave Background (CMB). The subsequent evolution of
perturbations in the superhorizon epoch is then considered, via a covariant
extension of the transport formalism. To develop intuition about the
relationship between inflationary dynamics and the evolution of cosmic
observables, we investigate analytic approximations of superhorizon
perturbation evolution. The validity of these analytic results is contingent on
reaching a state of adiabaticity which we discuss and illustrate in depth. We
then apply our analytic methods to elucidate the types of inflationary dynamics
that lead to an enhanced CMB non-Gaussianity, both in its bispectrum and
trispectrum. In addition to deriving a number of new simple relations between
the non-Gaussianity parameters, we explain dynamically how and why different
shapes of inflationary potential lead to particular observational signatures.
Candidate theories of high energy physics such as low energy effective string
theory also motivate single-field modifications to the Einstein-Hilbert action.
We show how a range of such corrections allow for consistency of single-field
chaotic inflationary models that are otherwise in tension with observational
data. | Transformation from spirals into S0s with bulge growth in groups of
galaxies: Recent observations have revealed that the time evolution of the S0 number
fraction at intermediate and high redshifts (0.2<z<0.8) is more dramatic in
groups of galaxies than in clusters. In order to understand the origin of S0s
in groups, we investigate numerically the morphological transformation of
spirals into S0s through group-related physical processes. Our chemodynamical
simulations show that spirals in group environments can be strongly influenced
by repetitive slow encounters with group member galaxies so that those with
thin disks and prominent spiral arm structures can be transformed into S0s with
thick disks and without prominent spiral arm structure. Such tidal interactions
can also trigger repetitive starbursts within the bulges of spirals and
consequently increase significantly the masses of their bulges. Owing to rapid
consumption of gas initially in spirals during the bulge growth, the S0s can
become gas-poor. The S0s transformed from spirals in this way have young and
metal-rich stellar populations in the inner regions of their bulges. The
simulated S0s have lower maximum rotational velocities and flatter radial
line-of-sight velocity dispersion profiles in comparison to their progenitor
spirals. The formation processes of S0s due to tidal interactions depend not
only on the masses and orbits of the progenitor spirals, but also on group
mass. A significant fraction (10-30%) of stars and gas can be stripped during
this spiral to S0 morphological transformation so that intragroup stars and gas
can be formed. Based on these results, we discuss structures, kinematics,
chemical properties, and the Tully-Fisher relation of S0s in groups. |
Primordial dark matter halos from fifth forces: We argue that primordial dark matter halos could be generated during
radiation domination by long range attractive forces stronger than gravity. In
this paper we derive the conditions under which these structures could dominate
the dark matter content of the Universe while passing microlensing constraints
and cosmic microwave background energy injection bounds. The dark matter
particles would be clumped in objects in the solar mass range with typical
sizes of the order of the solar system. Consequences for direct dark matter
searches are important. | Testing Yukawa-like potentials from f(R)-gravity in elliptical galaxies: We present the first analysis of extended stellar kinematics of elliptical
galaxies where a Yukawa--like correction to the Newtonian gravitational
potential derived from f(R)-gravity is considered as an alternative to dark
matter. In this framework, we model long-slit data and planetary nebulae data
out to 7 Re of three galaxies with either decreasing or flat dispersion
profiles. We use the corrected Newtonian potential in a dispersion-kurtosis
Jeans analysis to account for the mass-anisotropy degeneracy. We find that
these modified potentials are able to fit nicely all three elliptical galaxies
and the anisotropy distribution is consistent with that estimated if a dark
halo is considered. The parameter which measures the "strength" of the
Yukawa-like correction is, on average, smaller than the one found previously in
spiral galaxies and correlates both with the scale length of the Yukawa-like
term and the orbital anisotropy. |
The First Billion Years project: dark matter haloes going from
contraction to expansion and back again: We study the effect of baryons on the inner dark matter profile of the first
galaxies using the First Billion Years simulation between z=16-6 before secular
evolution sets in. Using a large statistical sample from two simulations of the
same volume and cosmological initial conditions, one with and one without
baryons, we are able to directly compare haloes with their baryon-free
counterparts, allowing a detailed study of the modifications to the dark matter
density profile due to the presence of baryons during the first billion years
of galaxy formation. For each of the ~ 5000 haloes in our sample we quantify
the impact of the baryons using eta, defined as the ratio of dark matter mass
enclosed in 100 pc in the baryonic run to its counterpart without baryons.
During this epoch of rapid growth of galaxies, we find that many haloes of
these first galaxies show an enhancement of dark matter in the halo centre
compared to the baryon-free simulation, while many others show a deficit. We
find that the mean value of eta is close to unity, but there is a large
dispersion, with a standard deviation of 0.677. The enhancement is cyclical in
time and tracks the star formation cycle of the galaxy; as gas falls to the
centre and forms stars, the dark matter moves in as well. Supernova feedback
then removes the gas, and the dark matter again responds to the changing
potential. We study three physical models relating the motion of baryons to
that of the dark matter: adiabatic contraction, dynamical friction, and rapid
outflows. Abridged, see text for full abstract | Advection-dominated accretion, jets and the spectral energy distribution
of LINERs: Low-luminosity active galactic nuclei (LLAGNs) represent the bulk of the AGN
population in the present-day universe and they trace low-level accreting
supermassive black holes. The observational properties of LLAGNs suggest that
their central engines are intrinsically different from those of more luminous
AGNs. It has been suggested that accretion in LLAGNs occurs via an
advection-dominated accretion flow (ADAF) associated with strong jets. In order
to probe the accretion physics in LLAGNs as a class, we model the
multiwavelength spectral energy distributions (SEDs) of 24 LINERs (taken from a
recent compilation by Eracleous et al.) with a coupled accretion-jet model. The
accretion flow is modeled as an inner ADAF outside of which there is a
truncated standard thin disk. These SEDs include radio, near-IR to near-UV HST
data, and Chandra X-ray data. We find that the radio emission is severely
underpredicted by ADAF models but can be explained by the relativistic jet. The
origin of the X-ray radiation in most sources can be explained by three
distinct scenarios: the X-rays can be dominated by emission from the ADAF, the
jet, or from both components contributing at similar levels. From the model
fits, we estimate important parameters of the central engine of LINERs, such as
the mass accretion rate -- relevant for studies of the feeding of AGNs -- and
the mass-loss rate in the jet and the jet power -- relevant for studies of the
kinetic feedback from jets. |
Capture and Annihilation of Dark Matter in Milky Way Globular Clusters: Paper has been withdrawn due to a critical error in the numerical evaluation
of the capture fraction. | Linear Perturbation constraints on Multi-coupled Dark Energy: The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a
specific example of a cosmological model characterized by a non-standard
physics of the dark sector of the universe that nevertheless gives an expansion
history which does not significantly differ from the one of the standard
$\Lambda $CDM model. In this work, we present the first constraints on the McDE
scenario obtained by comparing the predicted evolution of linear density
perturbations with a large compilation of recent data sets for the growth rate
$f\sigma_{8}$, including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming
qualitative expectations, growth rate data provide much tighter bounds on the
model parameters as compared to the extremely loose bounds that can be obtained
when only the background expansion history is considered. In particular, the
$95\%$ confidence level on the coupling strength $|\beta |$ is reduced from
$|\beta |\leq 83$ (background constraints only) to $|\beta |\leq 0.88$
(background and linear perturbation constraints). We also investigate how these
constraints further improve when using data from future wide-field surveys such
as supernova data from LSST and growth rate data from Euclid-type missions. In
this case the $95\%$ confidence level on the coupling further reduce to $|\beta
|\leq 0.85$. Such constraints are in any case still consistent with a scalar
fifth-force of gravitational strength, and we foresee that tighter bounds might
be possibly obtained from the investigation of nonlinear structure formation in
McDE cosmologies.[Abridged] |
Stochastic formalism for U(1) gauge fields in axion inflation: We develop the stochastic formalism for $\mathrm{U}(1)$ gauge fields that has
the Chern-Simons coupling to a rolling pseudo-scalar field during inflation.
The Langevin equations for the physical electromagnetic fields are derived and
the analytic solutions are studied. Using numerical simulation we demonstrate
that the electromagnetic fields averaged over the Hubble scale continuously
change their direction and their amplitudes fluctuate around the analytically
obtained expectation values. Though the isotropy is spontaneously broken by
picking up a particular local Hubble patch, each Hubble patch is understood
independent and the isotropy is conserved globally by averaging all the Hubble
patches. | The Growth in Size and Mass of Cluster Galaxies since z=2: We study the formation and evolution of Brightest Cluster Galaxies starting
from a $z=2$ population of quiescent ellipticals and following them to $z=0$.
To this end, we use a suite of nine high-resolution dark matter-only
simulations of galaxy clusters in a $\Lambda$CDM universe. We develop a scheme
in which simulation particles are weighted to generate realistic and
dynamically stable stellar density profiles at $z=2$. Our initial conditions
assign a stellar mass to every identified dark halo as expected from abundance
matching; assuming there exists a one-to-one relation between the visible
properties of galaxies and their host haloes. We set the sizes of the luminous
components according to the observed relations for $z\sim2$ massive quiescent
galaxies. We study the evolution of the mass-size relation, the fate of
satellite galaxies and the mass aggregation of the cluster central. From $z=2$,
these galaxies grow on average in size by a factor 5 to 10 of and in mass by 2
to 3. The stellar mass growth rate of the simulated BCGs in our sample is of
1.9 in the range $0.3<z<1.0$ consistent with observations, and of 1.5 in the
range $0.0<z<0.3$. Furthermore the satellite galaxies evolve to the present day
mass-size relation by $z=0$. Assuming passively evolving stellar populations,
we present surface brightness profiles for our cluster centrals which resemble
those observed for the cDs in similar mass clusters both at $z=0$ and at $z=1$.
This demonstrates that the $\Lambda$CDM cosmology does indeed predict minor and
major mergers to occur in galaxy clusters with the frequency and mass ratio
distribution required to explain the observed growth in size of passive
galaxies since $z=2$. Our experiment shows that Brightest Cluster Galaxies can
form through dissipationless mergers of quiescent massive $z=2$ galaxies,
without substantial additional star formation. |
Seeking Observable Imprints of Small-Scale Structure on the Properties
of Dark Matter Haloes: The characteristic prediction of the Cold Dark Matter (CDM) model of
cosmological structure formation is that the Universe should contain a wealth
of small-scale structure -- low-mass dark matter haloes and subhaloes. However,
galaxy formation is inefficient in their shallow potential wells and so we
expect these low-mass haloes and subhaloes to be dark. Can we tell the
difference between a Universe in which low-mass haloes are present but dark and
one in which they never formed, thereby providing a robust test of the CDM
model? We address this question using cosmological simulations to examine how
properties of low-mass haloes that are potentially accessible to observation,
such as their spatial clustering, rate of accretions and mergers onto massive
galaxies and the angular momentum content of massive galaxies, differ between a
LCDM model and dark matter models in which low-mass halo formation is
suppressed. Adopting an effective cut-off mass scale M_cut below which
small-scale power is suppressed in the initial conditions, we study dark matter
models in which M_cut varies between 5e9 Msol/h and 1e11 Msol/h, equivalent to
the host haloes of dwarf and low mass galaxies. Our results show that both the
clustering strength of low-mass haloes around galaxy-mass primaries and the
rate at which they merge with these primaries is sensitive to the assumed value
of M_cut; in contrast, suppressing low-mass halo formation has little influence
on the angular momentum content of galaxy-mass haloes -- it is the quiescence
or violence of a halo's assembly history that has a more marked effect.
However, we expect that measuring the effect on spatial clustering or the
merger rate is likely to be observationally difficult for realistic values of
M_cut, and so isolating the effect of this small-scale structure would appear
to be remarkably difficult to detect, at least in the present day Universe. | Non-Gaussianity beyond slow roll in multi-field inflation: We study the non-Gaussianity generated during multiple-field inflation. We
provide an exact expression for the bispectrum parameter f_NL which is valid
beyond the slow-roll regime, valid for certain classes of inflationary models.
We then study a new, exact multi-field inflationary model considering a case
where the bispectrum grows to observable values at the end of inflation. We
show that in this case the trispectrum is also large and may even provide the
dominant signal of non-Gaussianity. |
The Radio Relics and Halo of El Gordo, a Massive $z=0.870$ Cluster
Merger: We present 610 MHz and 2.1 GHz imaging of the massive SZE-selected z=0.870
cluster merger ACT-CL J0102-4915 (El Gordo), obtained with the GMRT and the
ATCA, respectively. We detect two complexes of radio relics separated by 3.4'
(1.6 Mpc) along the system's NW-to-SE collision axis that have high integrated
polarizations (33%) and steep spectral indices, consistent with creation via
Fermi acceleration by shocks in the ICM. From the spectral index of the relics,
we compute a Mach number of 2.5^{+0.7}_{-0.3} and shock speed of
2500^{+400}_{-300} km/s. With our ATCA data, we compute the Faraday depth
across the NW relic and find a mean value of 11 rad/m^2 and standard deviation
of 6 rad/m^2. With the integrated line-of-sight gas density derived from new
Chandra observations, our Faraday depth measurement implies B_parallel~0.01 \mu
G in the cluster outskirts. The extremely narrow shock widths in the relics
(<23 kpc) prevent us from placing a meaningful constraint on |B| using cooling
time arguments. In addition to the relics, we detect a large (1.1 Mpc radius),
powerful (log L_1.4[W/Hz]= 25.66+-0.12) radio halo with a Bullet-like
morphology. The spectral-index map of the halo shows the synchrotron spectrum
is flattest near the relics, along the collision axis, and in regions of high
T_gas, all locations associated with recent energy injection. The spatial and
spectral correlation between the halo emission and cluster X-ray properties
supports primary-electron processes like turbulent reacceleration as the halo
production mechanism. The halo's integrated 610 MHz to 2.1 GHz spectral index
is 1.2+-0.1, consistent with the cluster's high T_gas in view of previously
established global scaling relations. El Gordo is the highest-redshift cluster
known to host a radio halo and/or radio relics, and provides new constraints on
the non-thermal physics in clusters at z>0.6. [abridged] | Star formation, starbursts and quenching across the Coma supercluster: We analyse Spitzer MIPS 24micron observations, and SDSS (DR7) optical
broadband photometry and spectra, to investigate the star formation (SF)
properties of galaxies residing in the Coma supercluster region. We find that
SF in dwarf galaxies is quenched only in the high density environment at the
centre of clusters and groups, but passively-evolving massive galaxies are
found in all environments, indicating that massive galaxies can become passive
via internal processes. We find AGN activity is suppressed in the cluster
cores. We present evidence for a strong dependence of the mechanism(s)
responsible for quenching SF in dwarf galaxies on the cluster potential. We
find a significant increase in the mean EW of Halpha among star-forming dwarf
galaxies in the infall regions of the Coma cluster and the core of Abell 1367
with respect to the overall supercluster population, indicative of the
infalling dwarf galaxies undergoing a starburst phase. We identify these
starburst galaxies as the precursors of the post-starburst k+A galaxies. We
find that 11.4% of all dwarf (z mag > 15) galaxies in the Coma cluster and 4.8%
in the Abell 1367 have k+A like spectra, while this fraction is just 2.1% when
averaged over the entire supercluster region. We show that in the centre of the
Coma cluster, the (24-z) colour of galaxies is correlated with their optical
(g-r) colour and Halpha emission. By analysing the projected phase space
distribution of galaxies detected at 24micron in Coma, we find that the
(optically) red 24 micron detected galaxies follow the general distribution of
`all' the spectroscopic members, but their (optically) blue counterparts show
interesting features, indicative of recent infall. |
Spectroscopic identifications of Spitzer sources in the
SWIRE/XMM-NEWTON/ELAIS-S1 field: a large fraction of Active Galactic Nuclei
with high F(24micron)/F(R) ratio: We present a catalog of optical spectroscopic identifications of sources
detected by Spitzer at 3.6 or 24 micron down to 10 and 280 microJy,
respectively, in the SWIRE/XMM-Newton/ELAIS-S1 field and classified via line
width analysis and diagnostic diagrams. A total of 1376 sources down to R~24.2
mag have been identified (1362 detected at 3.6 micron, 419 at 24 micron, and
405 at both) by low-resolution optical spectroscopy carried out with FORS2,
VIMOS, and EFOSC2 at the Very Large Telescope and 3.6m ESO telescopes. The
spectroscopic campaigns have been carried out over the central 0.6 square
degrees area of ELAIS-S1 which, in particular, has also been observed by
XMM-Newton and Chandra. We find the first direct optical spectroscopic evidence
that the fraction of active galactic nuclei (AGN; mostly AGN2) increases with
increasing F(24 micron)/F(R) ratio, reaching values of 70(+/-20)% in the range
316<F(24 micron)F(R)<1000. We present an IRAC-MIPS color-color diagram able to
separate AGN1 from obscured AGN2 candidates. After having corrected for the
spectroscopic incompleteness of our sample, it results that the AGN fraction at
F(24 micron)=0.8 mJy is ~22(+/-7)% and decreases slowly to ~19(+/-5)% down to
F(24 micron)=0.3 mJy. | A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images: Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed
an exceptional number of strongly lensed multiply-imaged galaxies, including
high-redshift candidates. Previous studies have used this data to obtain the
most detailed dark matter reconstructions of any galaxy cluster to date,
resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter,
A1689) non-parametrically, combining strongly lensed images and weak
distortions from wider field Subaru imaging, and we incorporate member galaxies
to improve the lens solution. Strongly lensed galaxies are often locally
affected by member galaxies, however, these perturbations cannot be recovered
in grid based reconstructions because the lensing information is too sparse to
resolve member galaxies. By adding luminosity-scaled member galaxy deflections
to our smooth grid we can derive meaningful solutions with sufficient accuracy
to permit the identification of our own strongly lensed images, so our model
becomes self consistent. We identify 11 new multiply lensed system candidates
and clarify previously ambiguous cases, in the deepest optical and NIR data to
date from Hubble and Subaru. Our improved spatial resolution brings up new
features not seen when the weak and strong lensing effects are used separately,
including clumps and filamentary dark matter around the main halo. Our
treatment means we can obtain an objective mass ratio between the cluster and
galaxy components, for examining the extent of tidal stripping of the luminous
member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside
the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond
region. Our model independence means we can objectively evaluate the
competitiveness of stacking cluster lenses for defining the geometric
lensing-distance-redshift relation in a model independent way. |
Testing emergent gravity with mass densities of galaxy clusters: We use a sample of 23 galaxy clusters to test the predictions of emergent
gravity (EG) as alternative to dark matter. Our sample has both weak-lensing
inferred total mass profiles as well as x-ray inferred baryonic gas mass
profiles. Using nominal assumptions about the weak-lensing and x-ray mass
profiles, we find that the EG predictions (based on no dark matter) are
acceptable fits only near the virial radius. In the cores and in the outskirts,
the mass profile shape differences allow us to confirm previous results that
the EG model can be ruled out at $>5\sigma$. However, when we account for
systematic uncertainties in the observed weak-lensing and x-ray profiles, we
find good agreement for the EG predictions. For instance, if the weak-lensing
total mass profiles are shallow in the core and the x-ray gas density profiles
are steep in the outskirts, EG can predict the observed dark matter profile in
$0.3 \le r \le 1$R$_{200}$, where R$_{200}$ is the radius which encloses
200$\times$ the critical density of the Universe. The required x-ray and
lensing shapes are within the current observational systematics-limited errors
on cluster profiles. We also show that EG itself allows flexibility in its
predictions, which can allow for good agreement between the observations and
the predictions. We conclude that we cannot formally rule our EG as an
alternative to dark matter on the cluster scale and that we require better
constraints on the weak-lensing and gas mass profile shapes in the region $0.3
\le r \le 1$R$_{200}$. | Simulating intergalactic gas for DESI-like small scale Lymanα
forest observations: Measurements of the Ly$\alpha$ forest based on large numbers of quasar
spectra from sky surveys such as SDSS/eBOSS accurately probe the distribution
of matter on small scales and thus provide important constraints on several
ingredients of the cosmological model. A main summary statistic derived from
those measurements is the one-dimensional power spectrum, P1D, of the
Ly$\alpha$ absorption. However, model predictions for P1D rely on expensive
hydrodynamical simulations of the intergalactic medium, which was the limiting
factor in previous analyses. Datasets from upcoming surveys such as DESI will
push observational accuracy near the 1%-level and probe even smaller scales.
This observational push mandate seven more accurate simulations as well as more
careful exploration of parameter space. In this work we evaluate the robustness
and accuracy of simulations and the statistical framework used to constrain
cosmological parameters. We present a comparison between the grid-based
simulation code Nyx and SPH-based code Gadget in the context ofP1D. In
addition, we perform resolution and box-size convergence tests using Nyx code.
We use a Gaussian process emulation scheme to reduce the number of simulations
required for exploration of parameter space without sacrificing the model
accuracy. We demonstrate the ability to produce unbiased parameter constraints
in an end-to-end inference test using mock eBOSS- and DESI-like data, and we
advocate for the usage of adaptive sampling schemes as opposed to using a fixed
Latin hypercube design. |
The Column Density Distribution and Continuum Opacity of the
Intergalactic and Circumgalactic Medium at Redshift <z>=2.4: We present new high-precision measurements of the opacity of the
intergalactic and circumgalactic medium (IGM, CGM) at <z>=2.4. Using Voigt
profile fits to the full Lyman alpha and Lyman beta forests in 15
high-resolution high-S/N spectra of hyperluminous QSOs, we make the first
statistically robust measurement of the frequency of absorbers with HI column
densities 14 < log(NHI) < 17.2. We also present the first measurements of the
frequency distribution of HI absorbers in the volume surrounding high-z
galaxies (the CGM, 300 pkpc), finding that the incidence of absorbers in the
CGM is much higher than in the IGM. In agreement with Rudie et al. (2012), we
find that there are fractionally more high-NHI absorbers than low-NHI absorbers
in the CGM compared to the IGM, leading to a shallower power law fit to the CGM
frequency distribution. We use these new measurements to calculate the total
opacity of the IGM and CGM to hydrogen-ionizing photons, finding significantly
higher opacity than most previous studies, especially from absorbers with
log(NHI) < 17.2. Reproducing the opacity measured in our data as well as the
incidence of absorbers with log(NHI) > 17.2 requires a broken power law
parameterization of the frequency distribution with a break near log(NHI) ~ 15.
We compute new estimates of the mean free path (mfp) to hydrogen-ionizing
photons at z=2.4, finding mfp = 147 +- 15 Mpc when considering only IGM
opacity. If instead, we consider photons emanating from a high-z star-forming
galaxy and account for the local excess opacity due to the surrounding CGM of
the galaxy itself, the mean free path is reduced to mfp = 121 +- 15 Mpc. These
mfp measurements are smaller than recent estimates and should inform future
studies of the metagalactic UV background and of ionizing sources at z~2-3. | Fitting string inflation to real cosmological data: the Fibre Inflation
case: In this paper we show how the string landscape can be constrained using
observational data. We illustrate this idea by focusing on Fibre Inflation
which is a promising class of string inflationary models in type IIB flux
compactifications. We determine the values of the microscopic flux-dependent
parameters which yield the best fit to the most recent cosmological datasets. |
Infrared Emission from High-Redshift Galaxies in Cosmological SPH
Simulations: We compute the infrared (IR) emission from high-redshift galaxies in
cosmological smoothed particle hydrodynamics simulations by coupling the output
of the simulation with the population synthesis code `GRASIL' by Silva et al.
Based on the stellar mass, metallicity and formation time of each star
particle, we estimate the full spectral energy distribution of each star
particle from ultraviolet to IR, and compute the luminosity function of
simulated galaxies in the Spitzer broadband filters for direct comparison with
the available Spitzer observations. | The cool core state of Planck SZ-selected clusters versus X-ray selected
samples: evidence for cool core bias: We characterized the population of galaxy clusters detected with the SZ
effect with Planck, by measuring the cool core state of the objects in a
well-defined subsample of the Planck catalogue. We used as indicator the
concentration parameter Santos et al. (2008). The fraction of cool core
clusters is $29 \pm 4 \%$ and does not show significant indications of
evolution in the redshift range covered by our sample. We compare the
distribution of the concentration parameter in the Planck sample with the one
of the X-ray selected sample MACS (Mann & Ebeling, 2011): the distributions are
significantly different and the cool core fraction in MACS is much higher ($59
\pm 5 \%$). Since X-ray selected samples are known to be biased towards cool
cores due to the presence of their prominent surface brightness peak, we
simulated the impact of the "cool core bias" following Eckert et al. (2011). We
found that it plays a large role in the difference between the fractions of
cool cores in the two samples. We examined other selection effects that could
in principle bias SZ-surveys against cool cores but we found that their impact
is not sufficient to explain the difference between Planck and MACS. The
population of X-ray under-luminous objects, which are found in SZ-surveys but
missing in X-ray samples (Planck Collaboration 2016), could possibly contribute
to the difference, as we found most of them to be non cool cores, but this
hypothesis deserves further investigation. |
Black hole formation from a general quadratic action for inflationary
primordial fluctuations: The most up to date femto- and micro-lensing constraints indicate that
primordial black holes of $\sim 10^{-16} M_\odot$ and $\sim 10^{-12} M_\odot$,
respectively, may constitute a large fraction of the dark matter. We describe
analytically and numerically the dynamics by which inflationary fluctuations
featuring a time-varying propagation speed or an effective Planck mass can lead
to abundant primordial black hole production. As an example, we provide an ad
hoc DBI-like model. A very large primordial spectrum originating from a small
speed of sound typically leads to strong coupling within the vanilla effective
theory of inflationary perturbations. However, we point out that ghost
inflation may be able to circumvent this problem. We consider as well black
hole formation in solid inflation, for which, in addition to an analogous
difficulty, we stress the importance of the reheating process. In addition, we
review the basic formalism for the collapse of large radiation density
fluctuations, emphasizing the relevance of an adequate choice of gauge
invariant variables. | Breaking the sigma_8-Omega_m degeneracy using the clustering of high-z
X-ray AGN: The clustering of X-ray selected AGN appears to be a valuable tool for
extracting cosmological information. Using the recent high-precision angular
clustering results of ~30000 XMM-Newton soft (0.5-2 keV) X-ray sources (Ebrero
et al. 2009), which have a median redshift of $z\sim 1$, and assuming a flat
geometry, a constant in comoving coordinates AGN clustering evolution and the
AGN bias evolution model of Basilakos et al. (2008), we manage to break the
Omega_m-sigma_8 degeneracy. The resulting cosmological constraints are:
Omega_m=0.27 (+0.03 -0.05), w=-0.90 (+0.10 -0.16) and sigma_8=0.74 (+0.14
-0.12), while the dark matter host halo mass, in which the X-ray selected AGN
are presumed to reside, is M=2.50 (+0.50 -1.50) X 10^13 h^{-1} M(solar). For
the constant Lambda model (w=-1) we find Omega_m=0.24 (+- 0.06) and
sigma_8=0.83 (+0.11 -0.16), in good agreement with recent studies based on
cluster abundances, weak lensing and the CMB, but in disagreement with the
recent bulk flow analysis. |
Scaling of the 1-halo terms with bias: In the Halo Model, galaxies are hosted by dark matter halos, while the halos
themselves are biased tracers of the underlying matter distribution.
Measurements of galaxy correlation functions include contributions both from
galaxies in different halos, and from galaxies in the same halo (the so-called
1-halo terms). We show that, for highly biased tracers, the 1-halo term of the
power spectrum obeys a steep scaling relation in terms of bias. We also show
that the 1-halo term of the trispectrum has a steep scaling with bias. The
steepness of these scaling relations is such that the 1-halo terms can become
key contributions to the $n$-point correlation functions, even at large scales.
We interpret these results through analytical arguments and semi-analytical
calculations in terms of the statistical properties of halos. | Fast generation of mock galaxy catalogues in modified gravity models
with COLA: We investigate the viability of producing galaxy mock catalogues with
COmoving Lagrangian Acceleration (COLA) simulations in Modified Gravity (MG)
models employing the Halo Occupation Distribution (HOD) formalism. In this
work, we focus on two theories of MG: $f(R)$ gravity with the chameleon
mechanism, and a braneworld model (nDGP) that incorporates the Vainshtein
mechanism. We use a suite of full $N$-body simulations in MG as a benchmark to
test the accuracy of COLA simulations. At the level of Dark Matter (DM), we
show that COLA accurately reproduces the matter power spectrum up to $k \sim 1
h {\rm Mpc}^{-1}$, while it is less accurate in reproducing the velocity field.
To produce halo catalogues, we find that the ROCKSTAR halo-finder does not
perform well with COLA simulations. On the other hand, using a simple
Friends-of-Friends (FoF) finder and an empirical mass conversion from FoF to
spherical over-density masses, we are able to produce halo catalogues in COLA
that are in good agreement with those in $N$-body simulations. To consider the
effects of the MG fifth force on the halo profile, we derive simple fitting
formulae for the concentration-mass and the velocity dispersion-mass relations
that we calibrate using ROCKSTAR halo catalogues in $N$-body simulations. We
then use these results to extend the HOD formalism to modified gravity
simulations in COLA. We use an HOD model with five parameters that we tune to
obtain galaxy catalogues in redshift space. We find that despite the great
freedom of the HOD model, MG leaves characteristic imprints in the redshift
space power spectrum multipoles and these features are well captured by the
COLA galaxy catalogues. |
Constraining Dark Matter models with extremely distant galaxies: The investigation of distant galaxy formation and evolution is a powerful
tool to constrain dark matter scenarios, supporting and in some cases
surpassing other astrophysical and experimental probes. The recent completion
of the Hubble Frontier Fields (HFF) programme combining ultra-deep Hubble Space
Telescope observations and the magnification power of gravitational lensing
produced by foreground galaxy clusters has enabled the detection of the
faintest primordial galaxies ever studied. Here we show how the number density
of such primordial galaxies allows to constrain a variety of DM models
alternative to CDM. In particular, it provides stringent limits on the mass of
thermal WDM candidates, on the parameter space of sterile neutrino production
models, and on other DM scenarios featuring particles in the keV mass range
which is also supported by recent detections of a 3.5keV X-ray line. These
constraints are robust and independent of the baryonic physics modeling of
galaxy formation and evolution. Fuzzy DM (ultralight DM particles) results
strongly disfavored. | Imprints of quasar duty cycle on the 21cm signal from the Epoch of
Reionization: Quasars contribute to the 21-cm signal from the Epoch of Reionization (EoR)
primarily through their ionizing UV and X-ray emission. However, their radio
continuum and Lyman-band emission also regulates the 21-cm signal in their
direct environment, potentially leaving the imprint of their duty cycle.
We develop a model for the radio and UV luminosity functions of quasars from
the EoR, and constrain it using recent observations. Our model is consistent
with the z~7.5 quasar from Banados et al 2017, and also predicts only a few
quasars suitable for 21-cm forest observations (10mJy) in the sky. We exhibit a
new effect on the 21-cm signal observed against the CMB: a radio-loud quasar
can leave the imprint of its duty cycle on the 21-cm tomography. We apply this
effect in a cosmological simulation and conclude that the effect of typical
radio-loud quasars is most likely negligible in an SKA field of view. For a
1-10mJy quasar the effect is stronger though hardly observable at SKA
resolution. Then we study the contribution of the lyman band Ly-alpha to
Ly-beta) emission of quasars to the Wouthuisen-Field coupling. The collective
effect of quasars on the 21-cm power spectrum is larger than the thermal noise
at low k, though featureless. However, a distinctive pattern around the
brightest quasars in an SKA field of view may be observable in the tomography,
encoding the duration of their duty cycle. This pattern has a high
signal-to-noise ratio for the brightest quasar in a typical SKA shallow survey. |
Turbulent pressure support and hydrostatic mass-bias in the intracluster
medium: The degree of turbulent pressure support by residual gas motions in galaxy
clusters is not well known. Mass modelling of combined X-ray and Sunyaev
Zel'dovich observations provides an estimate of turbulent pressure support in
the outer regions of several galaxy clusters. Here, we test two different
filtering techniques to disentangle bulk from turbulent motions in
non-radiative high-resolution cosmological simulations of galaxy clusters using
the cosmological hydro code ENZO. We find that the radial behavior of the ratio
of non-thermal pressure to total gas pressure as a function of cluster-centric
distance can be described by a simple polynomial function. The typical
non-thermal pressure support in the centre of clusters is $\sim$5%, increasing
to $\sim$15% in the outskirts, in line with the pressure excess found in recent
X-ray observations. While the complex dynamics of the ICM makes it impossible
to reconstruct a simple correlation between turbulent motions and hydrostatic
bias, we find that a relation between them can be established using the median
properties of a sample of objects. Moreover, we estimate the contribution of
radial accelerations to the non-thermal pressure support and conclude that it
decreases moving outwards from 40% (in the core) to 15% (in the cluster's
outskirts). Adding this contribution to one provided by turbulence, we show
that it might account for the entire observed hydrostatic bias in the innermost
regions of the clusters, and for less than 80% of it at $r > 0.8 r_{200, m}$. | Spatially Extended 21 cm Signal from Strongly Clustered UV and X-Ray
Sources in the Early Universe: We present our prediction for the local 21 cm differential brightness
temperature ($\delta T_{b}$) from a set of strongly clustered sources of
Population III (Pop III) and II (Pop II) objects in the early Universe, by a
numerical simulation of their formation and radiative feedback. These objects
are located inside a highly biased environment, which is a rare, high-density
peak ("Rarepeak") extending to $\sim7$ comoving Mpc. We study the impact of
ultraviolet (UV) and X-ray photons on the intergalactic medium (IGM) and the
resulting $\delta T_{b}$, when Pop III stars are assumed to emit X-ray photons
by forming X-ray binaries very efficiently. We parameterize the rest-frame
spectral energy distribution (SED) of X-ray photons, which regulates X-ray
photon-trapping, IGM-heating, secondary Lyman-alpha pumping and the resulting
morphology of $\delta T_{b}$. A combination of emission ($\delta T_{b}>0$) and
absorption ($\delta T_{b}<0$) regions appears in varying amplitudes and angular
scales. The boost of the signal by the high-density environment
($\delta\sim0.64$) and on a relatively large scale combine to make Rarepeak a
discernible, spatially-extended ($\theta\sim10'$) object for 21 cm observation
at $13\lesssim z\lesssim17$, which is found to be detectable as a single object
by SKA with integration time of $\sim1000$ hours. Power spectrum analysis by
some of the SKA precursors (LOFAR, MWA, PAPER) of such rare peaks is found
difficult due to the rarity of these peaks, and the contribution only by these
rare peaks to the total power spectrum remains subdominant compared to that by
all astrophysical sources. |
Are Outflows Biasing Single-Epoch CIV Black Hole Mass Estimates?: We use a combination of reverberation mapping data and single-epoch spectra
of the CIV emission line in a sample of both low and high-redshift active
galactic nuclei (AGNs) to investigate sources of the discrepancies between CIV-
and Hbeta-based single-epoch black hole mass estimates. We find that for all
reverberation mapped sources, there is a component of the line profile that
does not reverberate, and the velocity characteristics of this component vary
from object-to-object. The differing strength and properties of this
non-variable component are responsible for much of the scatter in CIV-based
black hole masses compared to Hbeta masses. The CIV mass bias introduced by
this non-variable component is correlated with the shape of the CIV line,
allowing us to make an empirical correction to the black hole mass estimates.
Using this correction and accounting for other sources of scatter such as poor
data quality and data inhomogeneity reduces the scatter between the CIV and
Hbeta masses in our sample by a factor of ~2, to only ~0.2 dex. We discuss the
possibility that this non-variable CIV component originates in an
orientation-dependent outflow from either the proposed broad line region (BLR)
disk-wind or the intermediate line region (ILR), a high-velocity inner
extension of the narrow line region (NLR). | Turning Back the Clock: Inferring the History of the Eight O'clock Arc: We present the results from an optical and near-infrared spectroscopic study
of the ultraviolet-luminous z = 2.73 galaxy, the 8 o'clock arc. Due to
gravitational lensing, this galaxy is magnified by a factor of > 10, allowing
in-depth measurements which are usually unfeasible at such redshifts. In the
optical spectra, we measured the systemic redshift of the galaxy, z = 2.7322
+/- 0.0012, using stellar photospheric lines. This differs from the redshift of
absorption lines in the interstellar medium, z = 2.7302 +/- 0.0006, implying
gas outflows on the order of 160 km/s. With H and K-band near-infrared spectra,
we have measured nebular emission lines of Halpha, Hbeta, Hgamma, [N II] and [O
III], which have a redshift z = 2.7333 +/- 0.0001, consistent with the derived
systemic redshift. From the Balmer decrement, we measured the dust extinction
to be A_5500 = 1.17 +/- 0.36 mag. Correcting Halpha for dust extinction and the
assumed lensing factor, we measure a star-formation rate of ~ 270 Msol/yr,
which is higher than ~ 85% of star-forming galaxies at z ~ 2-3. Using
combinations of all detected emission lines, we find that the 8 o'clock arc has
a gas-phase metallicity of ~ 0.8 Zsol, showing that enrichment at high-redshift
is not rare, even in blue, star-forming galaxies. Studying spectra from two of
the arc components separately, we find that one component dominates the dust
extinction and star-formation rate, although the metallicities between the two
components are similar. We derive the mass via stellar population modeling, and
find that the arc has a total stellar mass of ~ 4 x 10^11 Msol, which falls on
the mass-metallicity relation at z ~ 2. Finally, we estimate the total gas
mass, and find it to be only ~ 12% of the stellar mass, implying that the 8
o'clock arc is likely nearing the end of a starburst. |
Reconstruction of Missing Data using Iterative Harmonic Expansion: In the cosmic microwave background or galaxy density maps, missing
fluctuations in masked regions can be reconstructed from fluctuations in the
surrounding unmasked regions if the original fluctuations are sufficiently
smooth. One reconstruction method involves applying a harmonic expansion
iteratively to fluctuations in the unmasked region. In this paper, we discuss
how well this reconstruction method can recover the original fluctuations
depending on the prior of fluctuations and property of the masked region. The
reconstruction method is formulated with an asymptotic expansion in terms of
the size of mask for a fixed iteration number. The reconstruction accuracy
depends on the mask size, the spectrum of the underlying density fluctuations,
the scales of the fluctuations to be reconstructed and the number of
iterations. For Gaussian fluctuations with the Harrison--Zel'dovich spectrum,
the reconstruction method provides more accurate restoration than naive methods
based on brute--forth matrix inversion or the singular value decomposition. We
also demonstrate that an isotropic non-Gaussian prior does not change the
results but an anisotropic non-Gaussian prior can yield a higher reconstruction
accuracy compared to the Gaussian prior case. | Radiative cooling implementations in simulations of primordial star
formation: We study the thermal evolution of primordial star-forming gas clouds using
three-dimensional cosmological simulations. We critically examine how
assumptions and approximations made in calculating radiative cooling rates
affect the dynamics of the collapsing gas clouds. We consider two important
molecular hydrogen cooling processes that operate in a dense primordial gas;
H_2 line cooling and continuum cooling by H_2 collision-induced emission. To
calculate the optically thick cooling rates, we follow the Sobolev method for
the former, whereas we perform ray-tracing for the latter. We also run the same
set of simulations using simplified fitting functions for the net cooling
rates. We compare the simulation results in detail. We show that the time- and
direction-dependence of hydrodynamic quantities such as gas temperature and
local velocity gradients significantly affects the optically thick cooling
rates. Gravitational collapse of the cloud core is accelerated when the cooling
rates are calculated by using the fitting functions. The structure and
evolution of the central pre-stellar disk are also affected. We conclude that
physically motivated implementations of radiative transfer are necessary to
follow accurately the thermal and chemical evolution of a primordial gas to
high densities. |
Catastrophic photometric redshift errors: weak lensing survey
requirements: We study the sensitivity of weak lensing surveys to the effects of
catastrophic redshift errors - cases where the true redshift is misestimated by
a significant amount. To compute the biases in cosmological parameters, we
adopt an efficient linearized analysis where the redshift errors are directly
related to shifts in the weak lensing convergence power spectra. We estimate
the number Nspec of unbiased spectroscopic redshifts needed to determine the
catastrophic error rate well enough that biases in cosmological parameters are
below statistical errors of weak lensing tomography. While the straightforward
estimate of Nspec is ~10^6 we find that using only the photometric redshifts
with z<=2.5 leads to a drastic reduction in Nspec to ~30,000 while negligibly
increasing statistical errors in dark energy parameters. Therefore, the size of
spectroscopic survey needed to control catastrophic errors is similar to that
previously deemed necessary to constrain the core of the z_s-z_p distribution.
We also study the efficacy of the recent proposal to measure redshift errors by
cross-correlation between the photo-z and spectroscopic samples. We find that
this method requires ~10% a priori knowledge of the bias and stochasticity of
the outlier population, and is also easily confounded by lensing magnification
bias. The cross-correlation method is therefore unlikely to supplant the need
for a complete spectroscopic redshift survey of the source population. | Energy injection in pre-recombination era and EDGES detection: We study the possibility of explaining the recent EDGES detection by an
energy injection in the pre-recombination era. Our aim is to show that the
residue of this energy injection could give the resultant increase in the
energy density at frequencies $x_e \equiv h\nu/(kT) \simeq 10^{-3}$, which is
needed to explain the EDGES result. We consider two models of energy injection:
Gaussian profile with a fixed redshift of injection and radiative decay of a
non-relativistic particle. We show that the energy injection should occur in
the redshift range $z\lesssim 4 \times 10^3$ to prevent free-free processes
from thermalizing the injected energy. The injected energy should be nearly
200--1000 times the CMB intensity at $x_e \simeq 10^{-3}$ to obtain the
requisite residue. A large fraction of the injected energy gets thermalized and
therefore distorts the CMB spectrum. We compute CMB spectral distortion for
both the models and show that the fractional change in CMB energy density,
$\Delta \rho_{\rm \scriptscriptstyle CMB}/\rho_{\rm \scriptscriptstyle CMB}
\simeq 10^{-6}$, which might be detectable with the proposed experiment PIXIE.
We also outline the implication of our proposed scenario for CMB anisotropies. |
Early Dark Energy at High Redshifts: Status and Perspectives: Early dark energy models, for which the contribution to the dark energy
density at high redshifts is not negligible, influence the growth of cosmic
structures and could leave observable signatures that are different from the
standard cosmological constant cold dark matter ($\Lambda$CDM) model. In this
paper, we present updated constraints on early dark energy using geometrical
and dynamical probes. From WMAP five-year data, baryon acoustic oscillations
and type Ia supernovae luminosity distances, we obtain an upper limit of the
dark energy density at the last scattering surface (lss), $\Omega_{\rm
EDE}(z_{\rm lss})<2.3\times10^{-2}$ (95% C.L.). When we include higher redshift
observational probes, such as measurements of the linear growth factors,
Gamma-Ray Bursts (GRBs) and Lyman-$\alpha$ forest (\lya), this limit improves
significantly and becomes $\Omega_{\rm EDE}(z_{\rm lss})<1.4\times10^{-3}$ (95%
C.L.). Furthermore, we find that future measurements, based on the
Alcock-Paczy\'nski test using the 21cm neutral hydrogen line, on GRBs and on
the \lya forest, could constrain the behavior of the dark energy component and
distinguish at a high confidence level between early dark energy models and
pure $\Lambda$CDM. In this case, the constraints on the amount of early dark
energy at the last scattering surface improve by a factor ten, when compared to
present constraints. We also discuss the impact on the parameter $\gamma$, the
growth rate index, which describes the growth of structures in standard and in
modified gravity models. | CfA4: Light Curves for 94 Type Ia Supernovae: We present multi-band optical photometry of 94 spectroscopically-confirmed
Type Ia supernovae (SN Ia) in the redshift range 0.0055 to 0.073, obtained
between 2006 and 2011. There are a total of 5522 light curve points. We show
that our natural system SN photometry has a precision of roughly 0.03 mag or
better in BVr'i', 0.06 mag in u', and 0.07 mag in U for points brighter than
17.5 mag and estimate that it has a systematic uncertainty of 0.014, 0.010,
0.012, 0.014, 0.046, and 0.073 mag in BVr'i'u'U, respectively. Comparisons of
our standard system photometry with published SN Ia light curves and comparison
stars reveal mean agreement across samples in the range of ~0.00-0.03 mag. We
discuss the recent measurements of our telescope-plus-detector throughput by
direct monochromatic illumination by Cramer et al (in prep.). This technique
measures the whole optical path through the telescope, auxiliary optics,
filters, and detector under the same conditions used to make SN measurements.
Extremely well-characterized natural-system passbands (both in wavelength and
over time) are crucial for the next generation of SN Ia photometry to reach the
0.01 mag accuracy level. The current sample of low-z SN Ia is now sufficiently
large to remove most of the statistical sampling error from the dark energy
error budget. But pursuing the dark-energy systematic errors by determining
highly-accurate detector passbands, combining optical and near-infrared (NIR)
photometry and spectra, using the nearby sample to illuminate the population
properties of SN Ia, and measuring the local departures from the Hubble flow
will benefit from larger, carefully measured nearby samples. |
3-pt Statistics of Cosmological Stochastic Gravitational Waves: We consider the 3-pt function (i.e. the bispectrum or non-Gaussianity) for
stochastic backgrounds of gravitational waves. We estimate the amplitude of
this signal for the primordial inflationary background, gravitational waves
generated during preheating, and for gravitational waves produced by
self-ordering scalar fields following a global phase transition. To assess
detectability, we describe how to extract the 3-pt signal from an idealized
interferometric experiment and compute the signal to noise ratio as a function
of integration time. The 3-pt signal for the stochastic gravitational wave
background generated by inflation is unsurprisingly tiny. For gravitational
radiation generated by purely causal, classical mechanisms we find that, no
matter how non-linear the process is, the 3-pt correlations produced vanish in
direct detection experiments. On the other hand, we show that in scenarios
where the B-mode of the CMB is sourced by gravitational waves generated by a
global phase transition, a strong 3-pt signal among the polarization modes
could also be produced. This may provide another method of distinguishing
inflationary B-modes. To carry out this computation, we have developed a
diagrammatic approach to the calculation of stochastic gravitational waves
sourced by scalar fluids, which has applications beyond the present scenario. | Color Dispersion and Milky Way Reddening Among Type Ia Supernovae: Past analyses of Type Ia Supernovae (SNe Ia) have identified an irreducible
scatter of 5-10% in distance widely attributed to an intrinsic dispersion in
luminosity. Another, equally valid, source of this scatter is intrinsic
dispersion in color. Misidentification of the true source of this scatter can
bias both the retrieved color-luminosity relation and cosmological parameter
measurements. The size of this bias depends on the magnitude of the intrinsic
color dispersion relative to the distribution of colors that correlate with
distance. We produce a realistic simulation of a misattribution of intrinsic
scatter, and find a negative bias in the recovered color-luminosity relation,
beta, of dbeta -1.0 (~33%) and a positive bias in the equation of state
parameter, w, of dw +0.04 (~4%). We re-analyze current published data sets with
the assumptions that the distance scatter is predominantly the result of color.
Unlike previous analyses, we find that the data are consistent with a Milky Way
reddening law R_V=3.1, and that a Milky Way dust model better predicts the
asymmetric color-luminosity trends than the conventional luminosity scatter
hypothesis. We also determine that accounting for color variation reduces the
correlation between various Host galaxy properties and Hubble residuals by
~20%. |
Reducing the weak lensing noise for the gravitational wave Hubble
diagram using the non-Gaussianity of the magnification distribution: Gravitational wave sources are a promising cosmological standard candle
because their intrinsic luminosities are determined by fundamental physics (and
are insensitive to dust extinction). They are, however, affected by weak
lensing magnification due to the gravitational lensing from structures along
the line of sight. This lensing is a source of uncertainty in the distance
determination, even in the limit of perfect standard candle measurements. It is
commonly believed that the uncertainty in the distance to an ensemble of
gravitational wave sources is limited by the standard deviation of the lensing
magnification distribution divided by the square root of the number of sources.
Here we show that by exploiting the non-Gaussian nature of the lensing
magnification distribution, we can improve this distance determination,
typically by a factor of 2--3; we provide a fitting formula for the effective
distance accuracy as a function of redshift for sources where the lensing noise
dominates. | Progenitor Diagnostics for Stripped Core-Collapse Supernovae: Measured
Metallicities at Explosion Sites: Metallicity is expected to influence not only the lives of massive stars but
also the outcome of their deaths as supernovae (SNe) and as gamma-ray bursts
(GRBs). However, there are surprisingly few direct measurements of the local
metallicities of different flavors of core-collapse SNe. Here we present the
largest existing set of host-galaxy spectra with H II region emission lines at
the sites of 35 stripped-envelope core-collapse SNe. We derive local oxygen
abundances in a robust manner in order to constrain the SN Ib/c progenitor
population. We obtain spectra at the SN sites, include SNe from targeted and
untargeted surveys, and perform the abundance determinatinos using three
different oxygen-abundance calibrations. The sites of SNe Ic (the demise of the
most heavily stripped stars having lost both the H and He layers) are
systematically more metal rich than those of SNe Ib (arising from stars that
retained their He layer) in all calibrations. A Kolmogorov-Smirnov test yields
the very low probability of 1% that SN Ib and SN Ic environment abundances,
which are different on average by ~0.2 dex (in the Pettini & Pagel scale), are
drawn from the same parent population. Broad-lined SNe Ic (without GRBs) occur
at metallicities between those of SNe Ib and SNe Ic. Lastly, we find that the
host-galaxy central oxygen abundance is not a good indicator of the local SN
metallicity; hence, large-scale SN surveys need to obtain local abundance
measurements in order to quantify the impact of metallicity on stellar death. |
The Earth's velocity for direct detection experiments: The Earth's velocity relative to the Sun in galactic coordinates is required
in the rate calculation for direct detection experiments. We provide a rigorous
derivation of this quantity to first order in the eccentricity of the Earth's
orbit. We also discuss the effect of the precession of the equinoxes, which has
hitherto received little explicit discussion. Comparing with other expressions
in the literature, we confirm that the expression of Lee, Lisanti and Safdi is
correct, while the expression of Lewin and Smith, the de facto standard
expression, contains an error. For calculations of the absolute event rate, the
leading order expression is sufficient while for modulation searches, an
expression with the eccentricity is required for accurate predictions of the
modulation phase. | Neutrino mass constraint from an Implicit Likelihood Analysis of BOSS
voids: Cosmic voids identified in the spatial distribution of galaxies provide
complementary information to two-point statistics. In particular, constraints
on the neutrino mass sum, $\sum m_\nu$, promise to benefit from the inclusion
of void statistics. We perform inference on the CMASS NGC sample of
SDSS-III/BOSS with the aim of constraining $\sum m_\nu$. We utilize the void
size function, the void galaxy cross power spectrum, and the galaxy auto power
spectrum. To extract constraints from these summary statistics we use a
simulation-based approach, specifically implicit likelihood inference. We
populate approximate gravity-only, particle neutrino cosmological simulations
with an expressive halo occupation distribution model. With a conservative
scale cut of kmax=0.15 h/Mpc and a Planck-inspired LCDM prior, we find upper
bounds on $\sum m_\nu$ of 0.43 and 0.35 eV from the galaxy auto power spectrum
and the full data vector, respectively (95% credible interval). We observe
hints that the void statistics may be most effective at constraining $\sum
m_\nu$ from below. We also substantiate the usual assumption that the void size
function is Poisson distributed. |
The IA Guide: A Breakdown of Intrinsic Alignment Formalisms: We summarize common notations and concepts in the field of Intrinsic
Alignments (IA). IA refers to physical correlations involving galaxy shapes,
galaxy spins, and the underlying cosmic web. Its characterization is an
important aspect of modern cosmology, particularly in weak lensing analyses.
This resource is both a reference for those already familiar with IA and
designed to introduce someone to the field by drawing from various studies and
presenting a collection of IA formalisms, estimators, modeling approaches,
alternative notations, and useful references. | Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect: Measurements of secondary cosmic microwave background (CMB) anisotropies,
such as the Sunyaev-Zel'dovich (SZ) effect, will enable new tests of neutrino
and dark sector properties. The kinetic SZ (kSZ) effect is produced by
cosmological flows, probing structure growth. Ultra-light axions (ULAs) are a
well-motivated dark-matter candidate. Here the impact of ULA dark matter (with
mass $10^{-27}~{\rm eV}$ to $10^{-23}~{\rm eV}$) on kSZ observables is
determined, applying new analytic expressions for pairwise cluster velocities
and Ostriker-Vishniac signatures in structure-suppressing models. For the
future CMB-S4 and ongoing DESI galaxy surveys, the kSZ effect (along with
primary anisotropies) will probe ULA fractions $\eta_a =
\Omega_{\rm{axion}}/\Omega_{\rm DM}$ as low as $\sim 5\%$ if $m_{a}\simeq
10^{-27}~{\rm eV}$ (at 95\% C.L.), with sensitivity extending up to
$m_{a}\simeq 10^{-25}~{\rm eV}$. If reionization and the primary CMB can be
adequately modeled, Ostriker-Vishniac measurements could probe values
$\eta_{a}\simeq 10^{-3}$ if $10^{-27}~{\rm eV}\lesssim m_{a}\lesssim
10^{-24}~{\rm eV}$, or $\eta_{a}\simeq 1$ if $m_{a}\simeq 10^{-22}~{\rm eV}$,
within the fuzzy dark matter window. |
Empirical optical k-Corrections for redshifts <= 0.7: The Smithsonian Hectospec Lensing Survey (SHELS) is a magnitude limited
spectroscopically complete survey for R<=21.0 covering 4 square degrees. SHELS
provides a large sample (15,513) of flux calibrated spectra. The wavelength
range covered by the spectra allows empirical determination of k-corrections
for the g- and r-band from z=0 to ~0.68 and 0.33, respectively, based on large
samples of spectra. We approximate the k-corrections using only two parameters
in a standard way: Dn4000 and redshift. We use Dn4000 rather than the standard
observed galaxy color because Dn4000 is a redshift independent tracer of the
stellar population of the galaxy. Our approximations for the k-corrections
using Dn4000 are as good as (or better than) those based on observed galaxy
color (g-r) (sigma of the scatter is ~0.08 mag). The approximations for the
k-corrections are available in an on-line calculator. Our results agree with
previously determined analytical approximations from single stellar population
(SSP) models fitted to multi-band optical and near-infrared photometry for
galaxies with a known redshift. Galaxies with the smallest Dn4000-the galaxies
with the youngest stellar populations-are always attenuated and/or contain
contributions from older stellar populations. We use simple single SSP fits to
the SHELS spectra to study the influence of emission lines on the k-correction.
The effects of emission lines can be ignored for rest-frame equivalent widths
<~ 100 A depending on required photometric accuracy. We also provide analytic
approximations to the k-corrections determined from our model fits for z<=0.7
as a function of redshift and Dn4000 for ugriz and UBVRI (sigma of the scatter
is typically ~0.10 mag). Again, the approximations using Dn4000 are as good (or
better than) those based on a suitably chosen observed galaxy color. We provide
all analytical approximations in an on-line calculator. | Lensing Magnification: A novel method to weigh high-redshift clusters
and its application to SpARCS: We introduce a novel method to measure the masses of galaxy clusters at high
redshift selected from optical and IR Spitzer data via the red-sequence
technique. Lyman-break galaxies are used as a well understood, high-redshift
background sample allowing mass measurements of lenses at unprecedented high
redshifts using weak lensing magnification. By stacking a significant number of
clusters at different redshifts with average masses of ~1-3x10^14M_sun, as
estimated from their richness, we can calibrate the normalisation of the
mass-richness relation. With the current data set (area: 6 deg^2) we detect a
magnification signal at the >3-sigma level. There is good agreement between the
masses estimated from the richness of the clusters and the average masses
estimated from magnification, albeit with large uncertainties. We perform tests
that suggest the absence of strong systematic effects and support the
robustness of the measurement. This method - when applied to larger data sets
in the future - will yield an accurate calibration of the mass-observable
relations at z>~1 which will represent an invaluable input for cosmological
studies using the galaxy cluster mass function and astrophysical studies of
cluster formation. Furthermore this method will probably be the least expensive
way to measure masses of large numbers of z>1 clusters detected in future
IR-imaging surveys. |
The symmetries and scaling of tidal tails in galaxies: (Abriged) We present analytic models for the formation and evolution of tidal
tails and related structures following impulsive disturbances in galaxy
collisions. Since the epicyclic approximation is not valid for large radial
excursions, we use orbital equations of the form we call p-ellipses. These have
been shown to provide accurate representations of orbits in power-law halo
potentials. In the case of a purely tidal disturbance the resulting tidal tails
have simple structure. Scalings for their maximum lengths and other
characteristics as functions of the tidal amplitude and the exponent of the
power-law potentials are described. The analytic model shows that azimuthal
caustics (orbit crossing zones) are produced generically in these tails at a
fixed azimuth relative to the point of closest approach. Long tails, with high
order caustics at their base are also produced at larger amplitudes. The
analysis is extended to nonlinear disturbances and multiple encounters, which
break the symmetries of tidal perturbations. As the strength of the nonlinear
terms is varied the structure of the resulting forms varies from symmetric
tails to one-armed plumes. Cases with two or more impulse disturbances are also
considered as the simplest analytic models distinguishing between prograde and
retrograde encounters. A specific mechanism for the formation of tidal dwarf
galaxies at the end of tails is suggested as a consequence of resonance effects
in prolonged encounters. Qualitative comparisons to Arp Atlas systems suggest
that the limiting analytic cases are realized in real systems. We identify a
few Arp systems which may have swallowtail caustics, where dissipative gas
streams converge and trigger star formation. UV and optical images reveal
luminous knots of young stars at these 'hinge clump' locations. | A Joint Analysis of BICEP2/Keck Array and Planck Data: We report the results of a joint analysis of data from BICEP2/Keck Array and
Planck. BICEP2 and Keck Array have observed the same approximately 400 deg$^2$
patch of sky centered on RA 0h, Dec. $-57.5\deg$. The combined maps reach a
depth of 57 nK deg in Stokes $Q$ and $U$ in a band centered at 150 GHz. Planck
has observed the full sky in polarization at seven frequencies from 30 to 353
GHz, but much less deeply in any given region (1.2 $\mu$K deg in $Q$ and $U$ at
143 GHz). We detect 150$\times$353 cross-correlation in $B$-modes at high
significance. We fit the single- and cross-frequency power spectra at
frequencies $\geq 150$ GHz to a lensed-$\Lambda$CDM model that includes dust
and a possible contribution from inflationary gravitational waves (as
parameterized by the tensor-to-scalar ratio $r$), using a prior on the
frequency spectral behavior of polarized dust emission from previous \planck\
analysis of other regions of the sky. We find strong evidence for dust and no
statistically significant evidence for tensor modes. We probe various model
variations and extensions, including adding a synchrotron component in
combination with lower frequency data, and find that these make little
difference to the $r$ constraint. Finally we present an alternative analysis
which is similar to a map-based cleaning of the dust contribution, and show
that this gives similar constraints. The final result is expressed as a
likelihood curve for $r$, and yields an upper limit $r_{0.05}<0.12$ at 95%
confidence. Marginalizing over dust and $r$, lensing $B$-modes are detected at
$7.0\,\sigma$ significance. |
The GALEX Arecibo SDSS Survey. I. Gas Fraction Scaling Relations of
Massive Galaxies and First Data Release: We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large program
that is gathering high quality HI-line spectra using the Arecibo radio
telescope for an unbiased sample of ~1000 galaxies with stellar masses greater
than 10^10 Msun and redshifts 0.025<z<0.05, selected from the SDSS
spectroscopic and GALEX imaging surveys. The galaxies are observed until
detected or until a low gas mass fraction limit (1.5-5%) is reached. This paper
presents the first Data Release, consisting of ~20% of the final GASS sample.
We use this data set to explore the main scaling relations of HI gas fraction
with galaxy structure and NUV-r colour. A large fraction (~60%) of the galaxies
in our sample are detected in HI. We find that the atomic gas fraction
decreases strongly with stellar mass, stellar surface mass density and NUV-r
colour, but is only weakly correlated with galaxy bulge-to-disk ratio (as
measured by the concentration index of the r-band light). We also find that the
fraction of galaxies with significant (more than a few percent) HI decreases
sharply above a characteristic stellar surface mass density of 10^8.5 Msun
kpc^-2. The fraction of gas-rich galaxies decreases much more smoothly with
stellar mass. One of the key goals of GASS is to identify and quantify the
incidence of galaxies that are transitioning between the blue, star-forming
cloud and the red sequence of passively-evolving galaxies. Likely transition
candidates can be identified as outliers from the mean scaling relations
between gas fraction and other galaxy properties. [abridged] | The Demographics of Broad-Line Quasars in the Mass-Luminosity Plane. I.
Testing FWHM-Based Virial Black Hole Masses: We jointly constrain the luminosity function (LF) and black hole mass
function (BHMF) of broad-line quasars with forward Bayesian modeling in the
quasar mass-luminosity plane, based on a homogeneous sample of ~ 58,000 SDSS
DR7 quasars at z ~ 0.3-5. We take into account the selection effect of the
sample flux limit; more importantly, we deal with the statistical scatter
between true BH masses and FWHM-based single-epoch virial mass estimates, as
well as potential luminosity-dependent biases of these mass estimates. The LF
is tightly constrained in the regime sampled by SDSS, and makes reasonable
predictions when extrapolated to ~ 3 magnitudes fainter. Downsizing is seen in
the model LF. On the other hand, we find it difficult to constrain the BHMF to
within a factor of a few at z>~0.7 (with MgII and CIV-based virial BH masses).
This is mainly driven by the unknown luminosity-dependent bias of these mass
estimators and its degeneracy with other model parameters, and secondly driven
by the fact that SDSS quasars only sample the tip of the active BH population
at high redshift. Nevertheless, the most likely models favor a positive
luminosity-dependent bias for MgII and possibly for CIV, such that at fixed
true BH mass, objects with higher-than-average luminosities have over-estimated
FWHM-based virial masses. There is tentative evidence that downsizing also
manifests itself in the active BHMF, and the BH mass density in broad-line
quasars contributes an insignificant amount to the total BH mass density at all
times. Within our model uncertainties, we do not find a strong BH mass
dependence of the mean Eddington ratio; but there is evidence that the mean
Eddington ratio (at fixed BH mass) increases with redshift. |
The Starburst-Driven Molecular Wind in NGC 253 and the Suppression of
Star Formation: The under-abundance of very massive galaxies in the universe is frequently
attributed to the effect of galactic winds. Although ionized galactic winds are
readily observable most of the expelled mass is likely in cooler atomic and
molecular phases. Expanding molecular shells observed in starburst systems such
as NGC 253 and M 82 may facilitate the entrainment of molecular gas in the
wind. While shell properties are well constrained, determining the amount of
outflowing gas emerging from such shells and the connection between this gas
and the ionized wind requires spatial resolution <100 pc coupled with
sensitivity to a wide range of spatial scales, hitherto not available. Here we
report observations of NGC 253, a nearby starburst galaxy (D~3.4 Mpc) known to
possess a wind, which trace the cool molecular wind at 50 pc resolution. At
this resolution the extraplanar molecular gas closely tracks the H{\alpha}
filaments, and it appears connected to molecular expanding shells located in
the starburst region. These observations allow us to directly measure the
molecular outflow rate to be > 3 Msun/yr and likely ~9 Msun/yr. This implies a
ratio of mass-outflow rate to star formation rate of at least {\eta}~1-3,
establishing the importance of the starburst-driven wind in limiting the star
formation activity and the final stellar content. | A robust assessment of the local anisotropy of the Hubble constant: Magnitude predictions of $\Lambda$CDM, as parametrized by the Planck
collaboration, are not consistent with the supernova data of the whole
Pantheon+ sample even when, in order to take into account the uncertainty about
its value, the Hubble constant is adjusted. This is a likely consequence of the
increase of the number of low-redshift supernovae in the Pantheon+ sample, with
respect to previous such samples. Indeed, when supernovae at redshifts below
0.035 are ignored, with H0=73.4 km/s/Mpc, $\Lambda$CDM predictions become
consistent with Pantheon+ data. Interestingly, this is also the case when
subsets of low-redshift supernovae roughly centered on the direction of the CMB
dipole are considered, together with high-redshift ones, at least when CMB and
peculiar velocities corrections are taken into account for the redshifts. These
results seem robust, since they are also obtained with a simple,
single-parameter tired-light model. |
Extracting cosmological signals from foregrounds in deep mm maps of the
sky: The high Galactic latitude sky at millimeter and submm wavelengths contains
significant cosmological information about the early Universe (in terms of the
cosmic microwave background) but also the process of structure formation in the
Universe from the far infrared background produced by early galaxies and the
Sunyaev-Zeldovich effect in clusters of galaxies. As the Planck mission will
produce full sky maps in this frequency range, deeper maps of selected
low-foregrounds patches of the sky can produce complementary and important
information. Here we analyze the performance of a balloon-borne survey covering
a 10^\circ x 10^\circ patch of the sky with a few arcminute resolution and very
high pixel sensitivity. We simulate the different components of the mm/submm
sky (i.e., CMB anisotropies, SZ effect, radio and infrared sources, far
infrared background, and interstellar dust) using current knowledge about each
of them. We then combine them, adding detector noise, to produce detailed
simulated observations in four observational bands ranging from 130 to 500 GHz.
Finally, we analyze the simulated maps and estimate the performance of the
instrument in extracting the relevant information about each of the components.
We find that the CMB angular power spectrum is accurately recovered up to l ~
3000. Using the Sunyaev-Zel'dovich effect, most of the galaxy clusters present
in our input map are detected (60% efficiency overall). Our results also show
that much stronger constrains can be placed on far infrared background models. | Dark Radiation and Inflationary Freedom: We perform a cosmological analysis in which we allow the primordial power
spectrum of scalar perturbations to assume a shape that is different with
respect to the usual power-law, arising from the simplest models of
cosmological inflation. We parametrize the primordial power spectrum with a
piecewise monotone cubic Hermite function and we use it to investigate how the
constraints on the various cosmological parameters change: we find that the
obtained limits are relaxed with respect to the power-law case, if CMB
polarization data are not included. Moreover, the cosmological analyses provide
us some indications about the shape of the reconstructed primordial power
spectrum, where we notice possible features around
$k\simeq0.002\,\mathrm{Mpc}^{-1}$ and $k\simeq0.0035\,\mathrm{Mpc}^{-1}$. If
confirmed in future analyses involving enhanced experimental data, these
features suggests that the simplest cosmological inflation models may be
incomplete. |
Generalizing thawing dark energy models: the standard vis-à-vis model
independent diagnostics: We propose a two parameter generalization for the dark energy equation of
state (EOS) $w_X$ for thawing dark energy models which includes PNGB, CPL and
Algebraic thawing models as limiting cases and confront our model with the
latest observational data namely SNe Ia, OHD, CMB, BOSS data. Our analysis
reveals that the phantom type of thawing dark energy is favoured upto $2
\sigma$ confidence level. These results also show that thawing dark energy EOS
is not unique from observational point of view. Though different thawing dark
energy models are not distinguishable from each other from best-fit values
(upto $2\sigma$ C.L.s) of matter density parameter ($\Omega_m^0$) and hubble
parameter ($H_0$) at present epoch, best-fit plots of linear growth of matter
perturbation ($f$) and average deceleration parameter ($q_{\rm av}$); the
difference indeed reflects in best-fit variations of thawing dark energy EOS,
model-independent geometrical diagnostics like the statefinder pair $\{r,s\}$
and $Om3$ parameter. We are thus led to the conclusion that unlike the standard
observables ($\Omega_m^0$, $H_0$, $f$, $q_{\rm av}$), the model-independent
parameters ($r,s,Om3$) and the variations of EOS (in terms of $w_X-w_X'$ plots)
serve as model discriminators for thawing dark energy models. | Modelling realistic horizontal branch morphologies and their impact on
spectroscopic ages of unresolved stellar systems: The presence of an extended blue horizontal branch (HB) in a stellar
population is known to affect the age inferred from spectral fitting to stellar
population synthesis models. However, most population synthesis models still
rely on theoretical isochrones which do not include realistic modelling of
extended HBs. In this work, we create detailed models for a range of old simple
stellar populations (SSPs), to create a variety of realistic HB morphologies,
from extended red clumps, to extreme blue HBs. We achieve this by utilising
stellar tracks from the BaSTI database and implementing a different mass loss
prescription for each SSP created, resulting in different HB morphologies. We
find that, for each metallicity, there is some HB morphology which maximises
Hbeta, making an underlying 14Gyr population look ~5-6Gyr old for the low and
intermediate metallicity cases, and as young as 2Gyr for a solar metallicity
SSP. We explore whether there are any spectral indices capable of breaking the
degeneracy between an old SSP with extended blue HB and a truly young or
intermediate age SSP, and find that the CaII index of Rose(1984) and the
strength of the MgII doublet at 2800A are promising candidates, in combination
with Hbeta and other metallicity indicators such as Mgb and Fe5406. We also run
Monte Carlo simulations to investigate the level of statistical fluctuations in
the spectra of typical stellar clusters. We find that fluctuations in spectral
indices are significant even for average to large globular clusters, and that
various spectral indices are affected in different ways, which has implications
for full-spectrum fitting methods. Hence we urge caution if these types of
stellar clusters are to be used as empirical calibrating objects for various
aspects of SPS models. (Abridged) |
The Star Formation History of Isolated Dwarf UGC4879: Recent observations of UGC4879 with the Advanced Camera for Surveys on the
Hubble Space Telescope confirm that it is a nearby isolated dwarf irregular
galaxy. We measure a distance of 1.36+/-0.03 Mpc using the Tip of the Red Giant
Branch method. This distance puts UGC4879 beyond the radius of first turnaround
of the Local Group and ~700 kpc from its nearest neighbor Leo A. This isolation
makes this galaxy an ideal laboratory for studying pristine star formation
uncomplicated by interactions with other galaxies. We present the star
formation history of UGC4879 derived from simulated color-magnitude diagrams. | Quantum Cosmological Perturbations: Predictions and Observations: I consider the generic model independent predictions of the theory of quantum
cosmological perturbations. To describe the stage of cosmic inflation, where
these perturbations are amplified, the hydrodynamical approch is used. The
inflationary stage is completely characterized by the deviation of the equation
of state from cosmological constant which is a smooth function of the number of
e-folds until the end of inflation. It is shown that in this case the spectral
index should deviate from the flat one at least by 3 percent irrespective of
any particular scenario. Given the value of the spectral index the lower bound
on the amount of the gravitational waves produced is derived. Finally the
relation between effective hydrodynamical description of inflation and
inflationary scenarios is discussed. |
An Accurate Cluster Selection Function for the J-PAS Narrow-Band
wide-field survey: The impending Javalambre Physics of the accelerating universe Astrophysical
Survey (J-PAS) will be the first wide-field survey of $\gtrsim$ 8500 deg$^2$ to
reach the `stage IV' category. Because of the redshift resolution afforded by
54 narrow-band filters, J-PAS is particularly suitable for cluster detection in
the range z$<$1. The photometric redshift dispersion is estimated to be only
$\sim 0.003$ with few outliers $\lesssim$ 4\% for galaxies brighter than
$i\sim23$ AB, because of the sensitivity of narrow band imaging to absorption
and emission lines. Here we evaluate the cluster selection function for J-PAS
using N-body+semi-analytical realistic mock catalogues. We optimally detect
clusters from this simulation with the Bayesian Cluster Finder, and we assess
the completeness and purity of cluster detection against the mock data. The
minimum halo mass threshold we find for detections of galaxy clusters and
groups with both $>$80\% completeness and purity is $M_h \sim 5 \times
10^{13}M_{\odot}$ up to $z\sim 0.7$. We also model the optical observable,
$M^*_{\rm CL}$-halo mass relation, finding a non-evolution with redshift and
main scatter of $\sigma_{M^*_{\rm CL} | M_{\rm h}}\sim 0.14 \,dex$ down to a
factor two lower in mass than other planned broad-band stage IV surveys, at
least. For the $M_{\rm h} \sim 1 \times 10^{14}M_{\odot}$ Planck mass limit,
J-PAS will arrive up to $z\sim 0.85$ with a $\sigma_{M^*_{\rm CL} | M_{\rm
h}}\sim 0.12 \, dex$. Therefore J-PAS will provide the largest sample of
clusters and groups up to $z\sim 0.8$ with a mass calibration accuracy
comparable to X-ray data. | Radial Profile of the 3.55 keV line out to $R_{200}$ in the Perseus
Cluster: The recent discovery of the unidentified emission line at 3.55 keV in
galaxies and clusters has attracted great interest from the community. As the
origin of the line remains uncertain, we study the surface brightness
distribution of the line in the Perseus cluster since that information can be
used to identify its origin. We examine the flux distribution of the 3.55 keV
line in the deep Suzaku observations of the Perseus cluster in detail. The 3.55
keV line is observed in three concentric annuli in the central observations,
although the observations of the outskirts of the cluster did not reveal such a
signal. We establish that these detections and the upper limits from the
non-detections are consistent with a dark matter decay origin. However, absence
of positive detection in the outskirts is also consistent with some unknown
astrophysical origin of the line in the dense gas of the Perseus core, as well
as with a dark matter origin with a steeper dependence on mass than the dark
matter decay. We also comment on several recently published analyses of the
3.55 keV line. |
Stacking the Cosmic Web in Fluorescent Lyman alpha Emission with MUSE: Cosmological simulations suggest that most of the matter in the Universe is
distributed along filaments connecting galaxies. Illuminated by the cosmic UV
background (UVB), these structures are expected to glow in fluorescent Lyman
alpha emission with a Surface Brightness (SB) that is well below current
observational limits for individual detections. Here, we perform a stacking
analysis of the deepest MUSE/VLT data using three-dimensional regions
(subcubes) with orientations determined by the position of neighbouring Lyman
alpha galaxies (LAEs) at 3<z<4. Our method should increase the probability of
detecting filamentary Lyman alpha emission, provided that these structures are
Lyman Limit Systems (LLSs). By stacking 390 oriented subcubes we reach a 2
sigma sensitivity level of SB ~ 0.44e-20 erg/s/cm^2/arcsec^2 in an aperture of
1 arcsec^2 x 6.25 Angstrom, which is three times below the expected fluorescent
Lyman alpha signal from the Haardt-Madau 2012 (HM12) UVB at z~3.5. No
detectable emission is found on intergalactic scales, implying that at least
two thirds of our subcubes do not contain oriented LLSs for a HM12 UVB. On the
other hand, significant emission is detected in the circum-galactic medium
(CGM) of galaxies in the direction of the neighbours. The signal is stronger
for galaxies with a larger number of neighbours and appears to be independent
of any other galaxy properties such as luminosity, redshift and neighbour
distance. We estimate that preferentially oriented satellite galaxies cannot
contribute significantly to this signal, suggesting instead that gas densities
in the CGM are typically larger in the direction of neighbouring galaxies on
cosmological scales. | Radio/gamma-ray time delay in the parsec-scale cores of active galactic
nuclei: We report the detection of a non-zero time delay between radio emission
measured by the VLBA at 15.4 GHz and gamma-ray radiation (gamma-ray leads
radio) registered by the Large Area Telescope (LAT) on board the Fermi
Gamma-Ray Space Telescope for a sample of 183 radio and gamma-ray bright active
galactic nuclei (AGNs). For the correlation analysis we used 100 MeV - 100 GeV
gamma-ray photon fluxes, taken from monthly binned measurements from the first
Fermi LAT catalog, and 15.4 GHz radio flux densities from the MOJAVE VLBA
program. The correlation is most pronounced if the core flux density is used,
strongly indicating that the gamma-ray emission is generated within the compact
region of the 15 GHz VLBA core. Determining the Pearson's r and Kendall's tau
correlation coefficients for different time lags, we find that for the majority
of sources the radio/gamma-ray delay ranges from 1 to 8 months in the
observer's frame and peaks at about 1.2 months in the source's frame. We
interpret the primary source of the time delay to be synchrotron opacity in the
nuclear region. |
AION: An Atom Interferometer Observatory and Network: We outline the experimental concept and key scientific capabilities of AION
(Atom Interferometer Observatory and Network), a proposed UK-based experimental
programme using cold strontium atoms to search for ultra-light dark matter, to
explore gravitational waves in the mid-frequency range between the peak
sensitivities of the LISA and LIGO/Virgo/ KAGRA/INDIGO/Einstein
Telescope/Cosmic Explorer experiments, and to probe other frontiers in
fundamental physics. AION would complement other planned searches for dark
matter, as well as probe mergers involving intermediate mass black holes and
explore early universe cosmology. AION would share many technical features with
the MAGIS experimental programme in the US, and synergies would flow from
operating AION in a network with this experiment, as well as with other atom
interferometer experiments such as MIGA, ZAIGA and ELGAR. Operating AION in a
network with other gravitational wave detectors such as LIGO, Virgo and LISA
would also offer many synergies. | Toward an Understanding of Foreground Emission in the BICEP2 Region: BICEP2 has reported the detection of a degree-scale B-mode polarization
pattern in the Cosmic Microwave Background (CMB) and has interpreted the
measurement as evidence for primordial gravitational waves. Motivated by the
profound importance of the discovery of gravitational waves from the early
Universe, we examine to what extent a combination of Galactic foregrounds and
lensed E-modes could be responsible for the signal. We reanalyze the BICEP2
results and show that the 100x150 GHz and 150x150 GHz data are consistent with
a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology
with r=0 and a significant dust polarization signal. We give independent
estimates of the dust polarization signal in the BICEP2 region using four
different approaches. While these approaches are consistent with each other,
the expected amplitude of the dust polarization power spectrum remains
uncertain by about a factor of three. The lower end of the prediction leaves
room for a primordial contribution, but at the higher end the dust in
combination with the standard CMB lensing signal could account for the BICEP2
observations, without requiring the existence of primordial gravitational
waves. By measuring the cross-correlations between the pre-Planck templates
used in the BICEP2 analysis and between different versions of a data-based
template, we emphasize that cross-correlations between models are very
sensitive to noise in the polarization angles and that measured
cross-correlations are likely underestimates of the contribution of foregrounds
to the map. These results suggest that BICEP1 and BICEP2 data alone cannot
distinguish between foregrounds and a primordial gravitational wave signal, and
that future Keck Array observations at 100 GHz and Planck observations at
higher frequencies will be crucial to determine whether the signal is of
primordial origin. (abridged) |
Dark Energy Survey: A 2.1% measurement of the angular Baryonic Acoustic
Oscillation scale at redshift $z_{\rm eff}$=0.85 from the final dataset: We present the angular diameter distance measurement obtained with the
Baryonic Acoustic Oscillation feature from galaxy clustering in the completed
Dark Energy Survey, consisting of six years (Y6) of observations. We use the Y6
BAO galaxy sample, optimized for BAO science in the redshift range 0.6<$z$<1.2,
with an effective redshift at $z_{\rm eff}$=0.85 and split into six tomographic
bins. The sample has nearly 16 million galaxies over 4,273 square degrees. Our
consensus measurement constrains the ratio of the angular distance to sound
horizon scale to $D_M(z_{\rm eff})/r_d$ = 19.51$\pm$0.41 (at 68.3% confidence
interval), resulting from comparing the BAO position in our data to that
predicted by Planck $\Lambda$CDM via the BAO shift parameter
$\alpha=(D_M/r_d)/(D_M/r_d)_{\rm Planck}$. To achieve this, the BAO shift is
measured with three different methods, Angular Correlation Function (ACF),
Angular Power Spectrum (APS), and Projected Correlation Function (PCF)
obtaining $\alpha=$ 0.952$\pm$0.023, 0.962$\pm$0.022, and 0.955$\pm$0.020,
respectively, which we combine to $\alpha=$ 0.957$\pm$0.020, including
systematic errors. When compared with the $\Lambda$CDM model that best fits
Planck data, this measurement is found to be 4.3% and 2.1$\sigma$ below the
angular BAO scale predicted. To date, it represents the most precise angular
BAO measurement at $z$>0.75 from any survey and the most precise measurement at
any redshift from photometric surveys. The analysis was performed blinded to
the BAO position and it is shown to be robust against analysis choices, data
removal, redshift calibrations and observational systematics. | A correlation between central supermassive black holes and the globular
cluster systems of early-type galaxies: Elliptical, lenticular, and early-type spiral galaxies show a remarkably
tight power-law correlation between the mass M_BH of their central supermassive
black hole (SMBH) and the number N_GC of globular clusters:
M_BH=m*N_GC^(1.08+/-0.04) with m=1.7*10^5 solar masses. Thus, to a good
approximation the SMBH mass is the same as the total mass of the globular
clusters. Based on a limited sample of 13 galaxies, this relation appears to be
a better predictor of SMBH mass (rms scatter 0.2 dex) than the M_BH-sigma
relation between SMBH mass and velocity dispersion sigma. The small scatter
reflects the fact that galaxies with high globular cluster specific frequency
S_N tend to harbor SMBHs that are more massive than expected from the
M_BH-sigma relation. |
Mass function and assembly of dark halos: an approach to inventory
isolated overdense regions in random fields: In order to attain a statistical description of the evolution of cosmic
density fluctuations in agreement with results from the numerical simulations,
we introduce a probability conditional formalism (CF) based on an inventory of
isolated overdense regions in a density random field. This formalism is a
useful tool for describing at the same time the mass function (MF) of dark
haloes, their mass aggregation histories (MAHs) and merging rates (MRs). The CF
focuses on virialized regions in a self-consistent way rather than in mass
elements, and it offers an economical description for a variety of random
fields. Within the framework of the CF, we confirm that, for a Gaussian field,
it is not possible to reproduce at the same time the MF, MAH, and MR of haloes,
both for a constant and moving barrier. Then, we develop an inductive method
for constraining the cumulative conditional probability from a given halo MF
description, and thus, using the CF, we calculate the halo MAHs and MRs. By
applying this method to the MF measured in numerical simulations by Tinker et
al. 2008, we find that a reasonable solution, justified by a mass conservation
argument, is obtained if ones introduce a rescaling -increment by ~30% - of the
virial mass used in simulations and a (slight) deviation from Gaussianity.
Thus, both the MAH and MR obtained by a Monte Carlo merger tree agree now with
the predictions of numerical simulations. We discuss on the necessity of
rescaling the virial mass in simulations when comparing with analytical
approaches on the ground of the matter not accounted as part of the halos and
the halo mass limit due to numerical. Our analysis supports the presence of a
diffuse dark matter component that is not taken into account in the measured
halo MFs inasmuch as it is not part of the collapsed structures. | Probing massive neutrinos with the Minkowski functionals of the galaxy
distribution: The characteristic signatures of massive neutrinos on large-scale structure
(LSS), if fully captured, can be used to put a stringent constraint on their
mass sum, $M_{\nu}$. Previous work utilizing N-body simulations has shown the
Minkowski functionals (MFs) of LSS can reveal the imprints of massive neutrinos
on LSS, provide important complementary information to two-point statistics and
significantly improve constraints on $M_{\nu}$. In this work, we take a step
forward and apply the statistics to the biased tracers of LSS, i.e. the
galaxies, and in redshift space. We perform a Fisher matrix analysis and
quantify the constraining power of the MFs by using the Molino mock galaxy
catalogs, which are constructed based on the halo occupation distribution (HOD)
framework with parameters for the SDSS $M_r < -21.5$ and -22 galaxy samples. We
find the MFs give tighter constraints on all of the cosmological parameters
that we consider than the power spectrum. The constraints on
$\Omega_{\mathrm{m}}, \Omega_{\mathrm{b}}, h, n_s, \sigma_8$, and $M_\nu$ from
the MFs are better by a factor of 1.9, 2.9, 3.7, 4.2, 2.5, and 5.7,
respectively, after marginalizing over the HOD parameters. Specifically, for
$M_{\nu}$, we obtain a 1$\sigma$ constraint of 0.059 eV with the MFs alone for
a volume of only $\left(1 h^{-1} \mathrm{Gpc}\right)^3$. |
Cosmological parameter extraction and biases from type Ia supernova
magnitude evolution: We study different one-parametric models of type Ia Supernova magnitude
evolution on cosmic time scales. Constraints on cosmological and Supernova
evolution parameters are obtained by combined fits on the actual data coming
from Supernovae, the cosmic microwave background, and baryonic acoustic
oscillations. We find that data prefer a magnitude evolution such that
high-redshift Supernova are brighter than would be expected in a standard
cosmos with a dark energy component. Data however are consistent with
non-evolving magnitudes at the one-sigma level, except special cases.
We simulate a future data scenario where SN magnitude evolution is allowed
for, and neglect the possibility of such an evolution in the fit. We find the
fiducial models for which the wrong model assumption of non-evolving SN
magnitude is not detectable, and for which at the same time biases on the
fitted cosmological parameters are introduced. Of the cosmological parameters
the overall mass density has the strongest chances to be biased due to the
wrong model assumption. Whereas early-epoch models with a magnitude offset ~z^2
show up to be not too dangerous when neglected in the fitting procedure, late
epoch models with magnitude offset ~sqrt(z) have high chances to bias the fit
results. | Re-examining the case for neutral gas near the redshift 7 quasar ULAS
J1120+0641: Signs of damping wing absorption attenuating the Lyman-$\alpha$ emission line
of the first known $z \sim 7$ quasar, ULAS J1120+0641, recently provided
exciting evidence of a significantly neutral IGM. This long-awaited signature
of reionization was inferred, in part, from a deficit of flux in the quasar's
Lyman-$\alpha$ emission line based on predictions from a composite of
lower-redshift quasars. The composite sample was chosen based on its C IV
emission line properties; however, as the original study by Mortlock et al.
noted, the composite contained a slight velocity offset in C IV compared to
ULAS J1120+0641. Here we test whether this offset may be related to the
predicted strength of the Lyman-$\alpha$ emission line. We confirm the
significant ($\sim 10$ per cent at r.m.s.) scatter in Lyman-$\alpha$ flux for
quasars of a given C IV velocity and equivalent width found by Mortlock et al.
We further find that among lower-redshift objects chosen to more closely match
the C IV properties of ULAS J1120+0641, its Lyman-$\alpha$ emission falls
within the observed distribution of fluxes. Among lower-redshift quasars chosen
to more closely match in C IV velocity and equivalent width, we find that ULAS
J1120+0641 falls within the observed distribution of Lyman-$\alpha$ emission
line strengths. This suggests that damping wing absorption may not be present,
potentially weakening the case for neutral gas around this object. Larger
samples of z$>$7 quasars may therefore be needed to establish a clearer picture
of the IGM neutral fraction at these redshifts. |
21-cm fluctuations from primordial magnetic fields: The fluid forces associated with primordial magnetic fields (PMFs) generate
small-scale fluctuations in the primordial density field, which add to the
$\mathrm{\Lambda CDM}$ linear matter power spectrum on small scales. These
enhanced small-scale fluctuations lead to earlier formation of galactic halos
and stars and thus affect cosmic reionization. We study the consequences of
these effects on 21 cm observables using the semi-numerical code 21cmFAST
v3.1.3. We find the excess small-scale structure generates strong stellar
radiation backgrounds in the early Universe, resulting in altered 21 cm global
signals and power spectra commensurate with earlier reionization. We restrict
the allowed PMF models using the CMB optical depth to reionization. Lastly, we
probe parameter degeneracies and forecast experimental sensitivities with an
information matrix analysis subject to the CMB optical depth bound. Our
forecasts show that interferometers like HERA are sensitive to PMFs of order
$\sim \mathrm{pG}$, nearly an order of magnitude stronger than existing and
next-generation experiments. | Much ado about no offset -- Characterising the anomalous multiple-image
configuration and the model-driven displacement between light and mass in the
multi-plane strong lens Abell 3827: Abell 3827 is a unique galaxy cluster with a dry merger in its core causing a
highly-resolved multiple-image configuration of a blue spiral galaxy at
$z_\mathrm{s}=1.24$. The surface brightness profiles of four merging galaxies
around $z_\mathrm{d}=0.099$ complicate a clear identification of the number of
images and finding corresponding small-scale features across them. The entailed
controversies about offsets between luminous and dark matter have never been
settled and dark-matter characteristics in tension with bounds from
complementary probes and simulations seemed necessary to explain this
multiple-image configuration. We resolve these issues with a systematic study
of possible feature matchings across all images and their impact on the
reconstructed mass density distribution. From the local lens properties
directly constrained by these feature matchings without imposing any global
lens model, we conclude that none of them are consistent with expected local
characteristics from standard single-lens-plane lensing, nor can they be
motivated by the light distribution in the cluster. Inspecting complementary
spectroscopic data, we show that all these results originate from an
insufficient constraining power of the data and seem to hint at a thick lens
and not at exotic forms of dark matter or modified gravity. If the thick-lens
hypothesis can be corroborated with follow-up multi-plane lens modelling, A3827
suffers from a full three-dimensional degeneracy in the distribution of dark
matter because combinations of shearings and scalings in a single lens plane
can also be represented by an effective shearing and a rotation caused by
multiple lens planes. |
Modelling the WMAP large-angle anomalies as an effect of a local density
inhomogeneity: We investigate large-angle scale temperature anisotropy in the Cosmic
Microwave Background (CMB) with the Wilkinson Microwave Anisotropy Probe (WMAP)
data and model the large-angle anomalies as the effect of the CMB quadrupole
anisotropies caused by the local density inhomogeneities. The quadrupole caused
by the local density inhomogeneities is different from the special relativity
kinematic quadrupole. If the observer inhabits a strong inhomogeneous region,
the local quadrupole should not be neglected. We calculate such local
quadrupole under the assumption that there is a huge density fluctuation field
in direction $(284^{\circ},74^{\circ})$, where the density fluctuation is
$10^{-3}$, and its center is $\sim 112h^{-1} \rm {Mpc}$ away from us. After
removing such mock signals from WMAP data, the power in quadrupole, $C_2$,
increases from the range $(200\sim260\mu \rm{K^2})$ to $\sim1000\mu \rm{K^2}$.
The quantity S, which is used to estimate the alignment between the quadrupole
and the octopole, decreases from $(0.7\sim0.74)$ to $(0.31\sim0.37)$, while the
model predict that $C_2=1071.5\mu \rm{K^2}$, $S=0.412$. So our local density
inhomogeneity model can, in part, explain the WMAP low-$\ell$ anomalies. | BAO signatures in the 2-point angular correlations and the Hubble
tension: An observational tension on estimates of the Hubble parameter, $H_0$, using
early and late Universe information, is being of intense discussion in the
literature. Additionally, it is of great importance to measure $H_0$
independently of CMB data and local distance ladder method. In this sense, we
analyze 15 measurements of the transversal BAO scale, $\theta_{\rm BAO}$,
obtained in a weakly model-dependent approach, in combination with other data
sets obtained in a model-independent way, namely, Big Bang Nucleosynthesis
(BBN) information, 6 gravitationally lensed quasars with measured time delays
by the H0LiCOW team, and measures of cosmic chronometers (CC). We find $H_0 =
74.88_{-2.1}^{+1.9}$ km s${}^{-1}$ Mpc${}^{-1}$ and $H_0 = 72.06_{-1.3}^{+1.2}$
km s${}^{-1}$ Mpc${}^{-1}$ from $\theta_{BAO}$+BBN+H0LiCOW and
$\theta_{BAO}$+BBN+CC, respectively, in fully accordance with local
measurements. Moreover, we estimate the sound horizon at drag epoch, $r_{\rm
d}$, independent of CMB data, and find $r_{\rm d}=144.1_{-5.5}^{+5.3}$ Mpc
(from $\theta_{BAO}$+BBN+H0LiCOW) and $r_{\rm d} =150.4_{-3.3}^{+2.7}$ Mpc
(from $\theta_{BAO}$+BBN+CC). In a second round of analysis, we test how the
presence of a possible spatial curvature, $\Omega_k$, can influence the main
results. We compare our constraints on $H_0$ and $r_{\rm d}$ with other
reported values. Our results show that it is possible to use a robust
compilation of transversal BAO data, $\theta_{BAO}$, jointly with other
model-independent measurements, in such a way that the tension on the Hubble
parameter can be alleviated. |
Colour and stellar population gradients in galaxies: We discuss the colour, age and metallicity gradients in a wide sample of
local SDSS early- and late-type galaxies. From the fitting of stellar
population models we find that metallicity is the main driver of colour
gradients and the age in the central regions is a dominant parameter which
rules the scatter in both metallicity and age gradients. We find a consistency
with independent observations and a set of simulations. From the comparison
with simulations and theoretical considerations we are able to depict a general
picture of a formation scenario. | Luminosity distance and redshift in the Szekeres inhomogeneous
cosmological models: The Szekeres inhomogeneous models can be used to model the true lumpy
universe that we observe. This family of exact solutions to Einstein's
equations was originally derived with a general metric that has no symmetries.
In this work, we develop and use a framework to integrate the angular diameter
and luminosity distances in the general Szekeres models. We use the affine null
geodesic equations in order to derive a set of first-order ordinary
differential equations that can be integrated numerically to calculate the
partial derivatives of the null vector components. These equations allow the
integration in all generality of the distances in the Szekeres models and some
examples are given. The redshift is determined from simultaneous integration of
the null geodesic equations. This work does not assume spherical or axial
symmetry, and the results will be useful for comparisons of the general
Szekeres inhomogeneous models to current and future cosmological data. |
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