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A Measurement of the Cosmic Microwave Background Damping Tail from the
2500-square-degree SPT-SZ survey: We present a measurement of the cosmic microwave background (CMB) temperature
power spectrum using data from the recently completed South Pole Telescope
Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations
of 2540 deg$^2$ of sky with arcminute resolution at $150\,$GHz, and improves
upon previous measurements using the SPT by tripling the sky area. We report
CMB temperature anisotropy power over the multipole range $650<\ell<3000$. We
fit the SPT bandpowers, combined with the seven-year Wilkinson Microwave
Anisotropy Probe (WMAP7) data, with a six-parameter LCDM cosmological model and
find that the two datasets are consistent and well fit by the model. Adding SPT
measurements significantly improves LCDM parameter constraints; in particular,
the constraint on $\theta_s$ tightens by a factor of 2.7. The impact of
gravitational lensing is detected at $8.1\, \sigma$, the most significant
detection to date. This sensitivity of the SPT+WMAP7 data to lensing by
large-scale structure at low redshifts allows us to constrain the mean
curvature of the observable universe with CMB data alone to be
$\Omega_k=-0.003^{+0.014}_{-0.018}$. Using the SPT+WMAP7 data, we measure the
spectral index of scalar fluctuations to be $n_s=0.9623 \pm 0.0097$ in the LCDM
model, a $3.9\,\sigma$ preference for a scale-dependent spectrum with $n_s<1$.
The SPT measurement of the CMB damping tail helps break the degeneracy that
exists between the tensor-to-scalar ratio $r$ and $n_s$ in large-scale CMB
measurements, leading to an upper limit of $r<0.18$ (95%,C.L.) in the LCDM+$r$
model. Adding low-redshift measurements of the Hubble constant ($H_0$) and the
baryon acoustic oscillation (BAO) feature to the SPT+WMAP7 data leads to
further improvements. The combination of SPT+WMAP7+$H_0$+BAO constrains
$n_s=0.9538 \pm 0.0081$ in the LCDM model, a $5.7\,\sigma$ detection of $n_s <
1$, ... [abridged] | Epoch of reionization parameter estimation with the 21-cm bispectrum: We present the first application of the isosceles bispectrum to MCMC
parameter inference from the cosmic 21-cm signal. We extend the MCMC sampler
21cmMC to use the fast bispectrum code, BiFFT, when computing the likelihood.
We create mock 1000h observations with SKA1-low, using PyObs21 to account for
uv-sampling and thermal noise. Assuming the spin temperature is much higher
than that of the CMB, we consider two different reionization histories for our
mock observations: fiducial and late-reionization. For both models we find that
bias on the inferred parameter means and 1-$\sigma$ credible intervals can be
substantially reduced by using the isosceles bispectrum (calculated for a wide
range of scales and triangle shapes) together with the power spectrum (as
opposed to just using one of the statistics). We find that making the
simplifying assumption of a Gaussian likelihood with a diagonal covariance
matrix does not notably bias parameter constraints for the three-parameter
reionization model and basic instrumental effects considered here. This is true
even if we use extreme (unlikely) initial conditions which would be expected to
amplify biases. We also find that using the cosmic variance error calculated
with Monte-Carlo simulations using the fiducial model parameters whilst
assuming the late-reionization model for the simulated data also does not
strongly bias the inference. This implies we may be able to sparsely sample and
interpolate the cosmic variance error over the parameter space, substantially
reducing computational costs. All codes used in this work are
publicly-available. |
The Spitzer/IRAC view of black hole - bulge scaling relations: We present a mid-IR investigation of the scaling relations between
supermassive black hole masses (MBH) and the structural parameters of the host
spheroids in local galaxies. The work is based on two-dimensional bulge-disk
decompositions of Spitzer/IRAC 3.6 um images of 57 galaxies with MBH estimates.
Our estimates of effective radii (Re) and surface brightnesses, combined with
velocity dispersions (sigma) from the literature, define a FP relation
consistent with previous determinations but doubling the observed range in Re.
None of our galaxies is an outlier of the FP, demonstrating the accuracy of our
bulge-disk decomposition which also allows us to independently identify
pseudobulges in our sample. We calibrate M/L at 3.6 um by using the tight
Mdyn-Lbul relation (~0.1 dex of rms) and find that no color corrections are
required to estimate the stellar mass. The 3.6 um luminosity is thus the best
tracer of Mstar yet studied. We then explore the connection between MBH and
bulge structural parameters (luminosity, mass, effective radius). We find tight
correlations of MBH with both 3.6 um bulge luminosity and dynamical mass
(MBH/Mdyn~1/1000), with rms of ~0.35 dex, similar to the MBH-sigma relation.
Our results are consistent with previous determinations at shorter wavelengths.
By using our calibrated M/L, we rescale MBH-Lbul to obtain the MBH-Mstar
relation, which can be used as the local reference for high-z studies which
probe the cosmic evolution of MBH-galaxy relations and where the stellar mass
is inferred directly from luminosity measurements. The analysis of pseudobulges
shows that 4 out of 9 lie on the scaling relations within the observed scatter,
while those with small MBH are significantly displaced. We explore the
different origins for such behavior, while considering the possibility of
nuclear morphological components not reproduced by our two-dimensional
decomposition. | Reheating in 3-form inflation: We consider the 3-form field, which has been considered as a candidate for
realizing inflation, coupled to a scalar field which models the relativistic
matter particles produced during the reheating epoch. We have investigated the
stability conditions for this theory and found that introducing such a coupling
does not lead to any ghosts or Laplacian instabilities. We have also
investigated the reheating temperature and the production of particles due to
parametric resonances. We have found that this process is more efficient in
this theory compared to the result of the standard-scalar-field inflationary
scenario. |
Interplay of CMB Temperature, Space Curvature, and Expansion Rate
Parameters: The cosmic microwave background (CMB) temperature, $T$, surely the most
precisely measured cosmological parameter, has been inferred from {\it local}
measurements of the blackbody spectrum to an exquisite precision of 1 part in
$\sim 4700$. On the other hand, current precision allows inference of other
basic cosmological parameters at the $\sim 1\%$ level from CMB power spectra,
galaxy correlation and lensing, luminosity distance measurements of supernovae,
as well as other cosmological probes. A basic consistency check of the standard
cosmological model is an independent inference of $T$ at recombination. In this
work we first use the recent Planck data, supplemented by either the first year
data release of the dark energy survey (DES), baryon acoustic oscillations
(BAO) data, and the Pantheon SNIa catalog, to extract $T$ at the $\sim 1\%$
precision level. We then explore correlations between $T$, the Hubble
parameter, $H_{0}$, and the global spatial curvature parameter, $\Omega_{k}$.
Our parameter estimation indicates that imposing the local constraint from the
SH0ES experiment on $H_{0}$ results in significant statistical preference for
departure at recombination from the locally inferred $T$. However, only
moderate evidence is found in this analysis for tension between local and
cosmological estimates of $T$, if the local constraint on $H_{0}$ is relaxed.
All other dataset combinations that include the CMB with either BAO, SNIa, or
both, disfavor the addition of a new free temperature parameter even in the
presence of the local constraint on $H_{0}$. Analysis limited to the Planck
dataset suggests the temperature at recombination was higher than expected at
recombination at the $\gtrsim 95\%$ confidence level if space is globally flat. | Combining cluster number counts and galaxy clustering: The abundance of clusters and the clustering of galaxies are two of the
important cosmological probes for current and future large scale surveys of
galaxies, such as the Dark Energy Survey. In order to combine them one has to
account for the fact that they are not independent quantities, since they probe
the same density field. It is important to develop a good understanding of
their correlation in order to extract parameter constraints. We present a
detailed modelling of the joint covariance matrix between cluster number counts
and the galaxy angular power spectrum. We employ the framework of the halo
model complemented by a Halo Occupation Distribution model (HOD). We
demonstrate the importance of accounting for non-Gaussianity to produce
accurate covariance predictions. Indeed, we show that the non-Gaussian
covariance becomes dominant at small scales, low redshifts or high cluster
masses. We discuss in particular the case of the super-sample covariance (SSC),
including the effects of galaxy shot-noise, halo second order bias and
non-local bias. We demonstrate that the SSC obeys mathematical inequalities and
positivity. Using the joint covariance matrix and a Fisher matrix methodology,
we examine the prospects of combining these two probes to constrain
cosmological and HOD parameters. We find that the combination indeed results in
noticeably better constraints, with improvements of order 20\% on cosmological
parameters compared to the best single probe, and even greater improvement on
HOD parameters, with reduction of error bars by a factor 1.4-4.8. This happens
in particular because the cross-covariance introduces a synergy between the
probes on small scales. We conclude that accounting for non-Gaussian effects is
required for the joint analysis of these observables in galaxy surveys. |
Backreaction in late-time cosmology: We review the effect of the formation of nonlinear structures on the
expansion rate, spatial curvature and light propagation in the universe,
focusing on the possibility that it could explain cosmological observations
without the introduction of dark energy or modified gravity. We concentrate on
explaining the relevant physics and highlighting open questions. | Mass bias and cosmological constraints from Planck cluster clustering: We analysed the 3D clustering of the Planck sample of Sunyaev-Zeldovich (SZ)
selected galaxy clusters, focusing on the redshift-space two-point correlation
function (2PCF). We compared our measurements to theoretical predictions of the
standard $\Lambda$ cold dark matter ($\Lambda$CDM) cosmological model, deriving
an estimate of the Planck mass bias, $b_{\mathrm SZ}$, and cosmological
parameters. We measured the 2PCF of the sample in the cluster-centric radial
range $r\in[10,150]$ $h^{-1}$Mpc, considering 920 galaxy clusters with redshift
$z\leq0.8$. A Markov chain Monte Carlo analysis has been performed to constrain
$b_{\mathrm SZ}$, assuming priors on cosmological parameters from Planck Cosmic
Microwave Background (CMB) results. We also adopted priors on $b_{\mathrm SZ}$
from external data sets to constrain the cosmological parameters
$\Omega_{\mathrm m}$ and $\sigma_8$. We obtained $(1-b_{\mathrm
SZ})=0.62^{+0.14}_{-0.11}$, which is in agreement with the value required to
reconcile primary CMB and cluster count observations. By adopting priors on
$(1-b_{\mathrm SZ})$ from external data sets, we derived results on
$\Omega_{\mathrm m}$ that are fully in agreement and competitive, in terms of
uncertainties, with those derived from cluster counts. This confirms the
importance of including clustering in cosmological studies, in order to fully
exploit the information from galaxy cluster statistics. On the other hand, we
found that $\sigma_8$ is not constrained. |
RAY-RAMSES: a code for ray tracing on the fly in N-body simulations: We present a ray tracing code to compute integrated cosmological observables
on the fly in AMR N-body simulations. Unlike conventional ray tracing
techniques, our code takes full advantage of the time and spatial resolution
attained by the N-body simulation by computing the integrals along the line of
sight on a cell-by-cell basis through the AMR simulation grid. Moroever, since
it runs on the fly in the N-body run, our code can produce maps of the desired
observables without storing large (or any) amounts of data for post-processing.
We implemented our routines in the RAMSES N-body code and tested the
implementation using an example of weak lensing simulation. We analyse basic
statistics of lensing convergence maps and find good agreement with
semi-analytical methods. The ray tracing methodology presented here can be used
in several cosmological analysis such as Sunyaev-Zel'dovich and integrated
Sachs-Wolfe effect studies as well as modified gravity. Our code can also be
used in cross-checks of the more conventional methods, which can be important
in tests of theory systematics in preparation for upcoming large scale
structure surveys. | Accurate calculations of the WIMP halo around the Sun and prospects for
gamma ray detection: Weakly interacting massive particles (WIMPs) can be captured by heavenly
objects, like the Sun. Under the process of being captured by the Sun, they
will build up a population of WIMPs around it, that will eventually sink to the
core of the Sun. It has been argued with simpler estimates before that this
halo of WIMPs around the Sun could be a strong enough gamma ray source to be a
detectable signature for WIMP dark matter. We here revisit the problem using
detailed Monte Carlo simulations and detailed composition and structure
information about the Sun to estimate the size of the gamma ray flux. Compared
to earlier estimates, we find that the gamma ray flux from WIMP annihilations
in the Sun halo would be negligible and no current or planned detectors would
even be able to detect this flux. |
Updating the MACHO fraction of the Milky Way dark halo with improved
mass models: Recent interest in primordial black holes as a possible dark matter candidate
has motivated the reanalysis of previous methods for constraining massive
astrophysical compact objects in the Milky Way halo and beyond. In order to
derive these constraints, a model for the dark matter distribution around the
Milky Way must be used. Previous microlensing searches have assumed a
semi-isothermal density sphere for this task. We show this model is no longer
consistent with data from the Milky Way rotation curve, and test two
replacement models, namely NFW and power-law. The power-law model is the most
flexible as it can break spherical symmetry, and best fits the data. Thus, we
recommend the power-law model as a replacement, although it still lacks the
flexibility to fully encapsulate all possible shapes of the Milky Way halo. We
then use the power-law model to rederive some previous microlensing constraints
in the literature, while propagating the primary halo-shape uncertainties
through to our final constraints. Our analysis reveals that the microlensing
constraints towards the Large Magellanic Cloud weaken somewhat for MACHO masses
around $10\, M_\odot$ when this uncertainty is taken into account, but the
constraints tighten at lower masses. Exploring some of the simplifying
assumptions of previous constraints we also study the effect of wide mass
distributions of compact halo objects, as well as the effect of spatial
clustering on microlensing constraints. We find that both effects induce a
shift in the constraints towards smaller masses, and can effectively remove the
microlensing constraints from $M \sim 1-10 M_\odot$ for certain MACHO
populations. | Testing DARKexp against energy and density distributions of
Millennium-II halos: We test the DARKexp model for relaxed, self-gravitating, collisionless
systems against equilibrium dark matter halos from the Millennium-II
simulation. While limited tests of DARKexp against simulations and observations
have been carried out elsewhere, this is the first time the testing is done
with a large sample of simulated halos spanning a factor of ~ 50 in mass, and
using independent fits to density and energy distributions. We show that
DARKexp, a one shape parameter family, provides very good fits to the shapes of
density profiles, \rho(r), and differential energy distributions, N(E), of
individual simulated halos. The best fit shape parameter $\phi_{0}$ obtained
from the two types of fits are correlated, though with scatter. Our most
important conclusions come from \rho(r) and N(E) that have been averaged over
many halos. These show that the bulk of the deviations between DARKexp and
individual Millennium-II halos come from halo-to-halo fluctuations, likely
driven by substructure, and other density perturbations. The average \rho(r)
and N(E) are quite smooth and follow DARKexp very closely. The only deviation
that remains after averaging is small, and located at most bound energies for
N(E) and smallest radii for \rho(r). Since the deviation is confined to 3-4
smoothing lengths, and is larger for low mass halos, it is likely due to
numerical resolution effects. |
Optical Ring Cavity Search for Axion Dark Matter: We propose a novel experiment to search for axion dark matter which
differentiates the phase velocities of the left and right-handed polarized
photons. Our optical cavity measures the difference of the resonant frequencies
between two circular-polarizations of the laser beam. The design of our cavity
adopts double-pass configuration to realize a null experiment and give a high
common mode rejection of environmental disturbances. We estimate the potential
sensitivity to the axion-photon coupling constant $g_{a\gamma}$ for the axion
mass $m \lesssim 10^{-10}$ eV. In a low mass range $m \lesssim 10^{-15}$ eV, we
can achieve $g_{a\gamma} \lesssim 3\times 10^{-16} ~\text{GeV}^{-1}$ which is
beyond the current bound by several orders of magnitude. | Transients from initial conditions based on Lagrangian perturbation
theory in $N$-body simulations II: the effect of the transverse mode: We study the initial conditions for cosmological $N$-body simulations for
precision cosmology. In general, Zel'dovich approximation has been applied for
the initial conditions of $N$-body simulations for a long time. These initial
conditions provide incorrect higher-order growth. These error caused by setting
up the initial conditions by perturbation theory is called transients. We
investigated the impact of transient on non-Gaussianity of density field by
performing cosmological $N$-body simulations with initial conditions based on
first-, second-, and third-order Lagrangian perturbation theory in previous
paper. In this paper, we evaluates the effect of the transverse mode in the
third-order Lagrangian perturbation theory for several statistical quantities
such as power spectrum, non-Gaussianty, and multifractal dimensions. Then we
clarified that the effect of the transverse mode in the third-order Lagrangian
perturbation theory is quite small. |
Cosmic Recombination in the Presence of Primordial Magnetic Fields: Primordial magnetic fields (PMFs) may explain observations of magnetic fields
on extragalactic scales. They are most cleanly constrained by observations of
details of the cosmic microwave background radiation (CMB) Their effects on
cosmic recombination may even be at the heart of the resolution of the Hubble
tension. We present an in-detail analysis of the effects of PMFs on cosmic
recombination taking into account of all so far known relevant physical
processes. To this end we extend the public magneto-hydrodynamic code ENZO with
a new cosmic recombination routine, Monte-Carlo simulations of Lyman-$\alpha$
photon transport, and a Compton drag term in the baryon momentum equation. The
resulting code allows us to predict the impact of PMFs on the cosmic ionization
history and the clumping of baryons during cosmic recombination. We study the
specific case of non-helical PMFs with a Batchelor spectrum. Our results
identify the importance of mixing of Lyman-$\alpha$ photons between overdense-
and underdense- regions for small PMF strength. This mixing shows an attractor
to the fully mixed case and speeds up recombination beyond the speed-up due to
clumping. It leads to enhanced Silk damping which is strongly constrained by
CMB observations. We also show that the increase in the ionization fraction at
low redshift by hydrodynamic baryon heating due to PMF dissipation is
completely compensated by the faster recombination from baryon clumping. We
describe and explain the significant differences of these 3D simulations over
earlier three-zone models. | Parity-odd correlators of diffuse gamma rays and intergalactic magnetic
fields: We develop the connection between intergalactic helical magnetic fields and
parity odd signatures in the diffuse gamma ray sky. We find that the location
and the amplitude of a peak in a parity odd correlator, $Q(R)$, can be used to
infer the normal and helical power spectra of the intergalactic magnetic field.
When applied to Fermi-LAT data, the amplitude of the observed peak in $Q(R)$
gives $\sim 10^{-14}~{\rm G}$ intergalactic magnetic field strength, which is
consistent with an earlier independent estimate that only used the peak
location (Tashiro et al. 2014). We discuss features in the observed $Q(R)$ that
further support the intergalactic magnetic field hypothesis and make
predictions for future tests. |
What X-ray source counts can tell about large-scale matter distribution: Sources generating most of the X-ray background (XRB) are dispersed over a
wide range of redshifts. Thus, statistical characteristics of the source
distribution carry information on matter distribution on very large scales. We
test the possibility of detecting the variation in the X-ray source number
counts over the celestial sphere. A large number of Chandra pointings spread
over both galactic hemispheres are investigated. We searched for all the
point-like sources in the soft band of 0.5 - 2 keV and statistically assessed
the population of sources below the detection threshold. A homogeneous sample
of the number counts at fluxes above ~10^{-15} erg s^{-1} cm^{-2} was
constructed for more than 300 ACIS fields. The sources were counted within a
circular area of 15 arcmin diameter. The count correlations between overlapping
fields were used to assess the accuracy of the computational methods used in
the analysis. The average number of sources in the investigated sample amounts
to 46 per field. It is shown that the source number counts vary between fields
at a level exceeding the fluctuation amplitude expected for the random
(Poissonian) distribution. The excess fluctuations are attributed to the cosmic
variance generated by the large-scale structures. The rms variations of the
source counts due to the cosmic variance within the 15$ arcmin circle reach 8%
of the average number counts. An amplitude of the potential correlations of the
source counts on angular scales larger than the size of a single pointing
remains below the noise level. | Radio galaxy feedback in X-ray selected groups from COSMOS: the effect
on the ICM: We quantify the importance of the mechanical energy released by
radio-galaxies inside galaxy groups. We use scaling relations to estimate the
mechanical energy released by 16 radio-AGN located inside X-ray detected galaxy
groups in the COSMOS field. By comparing this energy output to the host groups'
gravitational binding energy, we find that radio galaxies produce sufficient
energy to unbind a significant fraction of the intra-group medium. This
unbinding effect is negligible in massive galaxy clusters with deeper potential
wells. Our results correctly reproduce the breaking of self-similarity observed
in the scaling relation between entropy and temperature for galaxy groups. |
Radio and X-ray properties of submillimeter galaxies in the A2125 field: We present the radio and X-ray properties of 1.2 mm MAMBO source candidates
in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at
z=0.247. The brightest, non-synchrotron mm source candidate in the field has a
photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks
Chandra X-ray exposure. These findings are consistent with this object being an
extremely dusty and luminous starburst galaxy at high-redshift, possibly the
most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA
imaging identifies counterparts for 83% of the 29 mm source candidates
identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority
of these objects are likely to lie at z <~ 3.5. The median mm-to-radio
wavelength photometric redshift of this radio-detected sample is z~2.2 (first
and third quartiles of 1.7 and 3.0), consistent with the median redshift
derived from optical spectroscopic surveys of the radio-detected subsample of
bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are
confirmed to be X-ray luminous in the high resolution Chandra imaging, while
another mm source candidate with potential multiple radio counterparts is also
detected in the X-ray regime. Both of these radio counterparts are positionally
consistent with the mm source candidate. One counterpart is associated with an
elliptical galaxy at z = 0.2425, but we believe that a second counterpart
associated with a fainter optical source likely gives rise to the mm emission
at z~1. | A Standard Ruler at Cosmic Dawn: The matter in our Universe comes in two flavors: dark and baryonic. Of these,
only the latter couples to photons, giving rise to the well-known baryon
acoustic oscillations and, in the process, generating supersonic relative
velocities between dark matter and baryons. These velocities---imprinted with
the acoustic scale in their genesis---impede the formation of the first stars
during cosmic dawn ($z\sim 20$), modulating the expected 21-cm signal from this
era. In a companion paper we showed, combining numerical simulations and
analytic models, that this modulation takes the form of robust velocity-induced
acoustic oscillations (VAOs), with a well-understood shape that is frozen at
recombination, and unaffected by the unknown astrophysics of star formation.
Here we propose using these VAOs as a standard ruler at cosmic dawn. We find
that three years of 21-cm power-spectrum data from the upcoming HERA
interferometer should be able to measure the Hubble expansion rate $H(z)$ at
$z=15-20$ to percent-level precision, ranging from $0.3\%$ to $11\%$ depending
on the strength of astrophysical feedback processes and foregrounds. This would
provide a new handle on the expansion rate of our Universe during an otherwise
unprobed epoch, opening a window to the mysterious cosmic-dawn era. |
The Emission Line Properties of Gravitationally-lensed 1.5 < z < 5
Galaxies: We present and analyse near-infrared spectroscopy for a sample of 28
gravitationally- lensed star-forming galaxies in the redshift range 1.5 < z <
5, observed mostly with the Keck II telescope. With typical magnifications of
~1.5-4 magnitudes, our survey provides a valuable census of star formation
rates, gas-phase metallicities and dynamical masses for a representative sample
of low luminosity galaxies seen at a formative period in cosmic history. We
find less evolution in the mass-metallicity relation compared to earlier work
that focused on more luminous systems with z - 2-3, especially in the low mass
(- 10^9 Msol) where our sample is - 0.25 dex more metal-rich. We interpret this
offset as a result of the lower star formation rates (typically a factor of -10
lower) for a given stellar mass in our sub-luminous systems. Taking this effect
into account, we conclude our objects are consistent with a fundamental
metallicity relation recently proposed from unlensed observations. | A black box for dark sector physics: Predicting dark matter annihilation
feedback with conditional GANs: Traditionally, incorporating additional physics into existing cosmological
simulations requires re-running the cosmological simulation code, which can be
computationally expensive. We show that conditional Generative Adversarial
Networks (cGANs) can be harnessed to predict how changing the underlying
physics alters the simulation results. To illustrate this, we train a cGAN to
learn the impact of dark matter annihilation feedback (DMAF) on the gas density
distribution. The predicted gas density slices are visually difficult to
distinguish from their real brethren and the peak counts differ by less than 10
per cent for all test samples (the average deviation is < 3 per cent). Finally,
we invert the problem and show that cGANs are capable of endowing smooth
density distributions with realistic substructure. The cGAN does however have
difficulty generating new knots as well as creating/eliminating bubble-like
structures. We conclude that trained cGANs can be an effective approach to
provide mock samples of cosmological simulations incorporating DMAF physics
from existing samples of standard cosmological simulations of the evolution of
cosmic structure. |
A Detailed Study of the Lobes of Eleven Powerful Radio Galaxies: Radio lobes of a sample of eleven very powerful classical double radio
galaxies were studied. Each source was rotated so that the symmetry axis of the
source was horizontal, and vertical cross-sectional cuts were taken across the
source at intervals of one beam size. These were used to study the
cross-sectional surface brightness profiles, the width of each slice, radio
emissivity as a function of position across each slice, the first and second
moments, and the average surface brightness, minimum energy magnetic field
strength, and pressure of each slice. A Gaussian provides a good description of
the surface brightness profile of cross-sectional slices. The Gaussian FWHM as
a function of distance from the hot spot first increases and then decreases
with distance from the hot spot. The width as a function of distance from the
hot spot is highly symmetric on each side of the source. The radio emissivity
is often close to flat across a slice, indicating a roughly constant emissivity
and pressure for that slice. Some slices show variations in radio emissivity
that indicate an ``edge-peaked'' pressure profile for that slice; these often
occur in slices near the local maxima of the bridge width. The emissivity does
not exhibit any signature of emission from a jet. The first moment is generally
quite close to zero indicating only small excursions of the ridge line from the
symmetry axis of the source. The second moment indicates the same source shape
as is found using the Gaussian FWHM. The average magnetic field strength and
pressure decrease with increasing distance from the hot spot, reaching a
roughly constant value at a location that is typically just before the location
of a local maximum of the bridge width. These results are interpreted in terms
of a heuristic model for the radio lobes. | Energetic constraints to chemo-photometric evolution of spiral galaxies: The problem of chemo-photometric evolution of late-type galaxies is dealt
with relying on prime physical arguments of energetic self-consistency between
chemical enhancement of galaxy mass, through nuclear processing inside stars,
and luminosity evolution of the system. Chemical enhancement is assessed in
terms of the so-called "yield metallicity", that is the metal abundance of
processed mass inside stars, as constrained by the galaxy photometric history. |
Artificial Neural Network Spectral Light Curve Template for Type Ia
Supernovae and its Cosmological Constraints: The spectral energy distribution (SED) sequence for type Ia supernovae (SN
Ia) is modeled by an artificial neural network. The SN Ia luminosity is
characterized as a function of phase, wavelength, a color parameter and a
decline rate parameter. After training and testing the neural network, the SED
sequence could give both the spectrum with wavelength range from 3000\AA~to
8000\AA~ and the light curve with phase from 20 days before to 50 days after
the maximum luminosity for the supernovae with different colors and decline
rates. Therefore, we call this the Artificial Neural Network Spectral Light
Curve Template (ANNSLCT) model. We retrain the Joint Light-curve Analysis (JLA)
supernova sample by using the ANNSLCT model and obtain the parameters for each
supernova to make a constraint on the cosmological $\Lambda$CDM model. We find
that the best fitting values of these parameters are almost the same as those
from the JLA sample trained with the Spectral Adaptive Lightcurve Template 2
(SALT2) model. So we believe that the ANNSLCT model could be used to analyze a
large number of SN Ia multi-color light curves measured in the current and
future observational projects. | Long Term Monitoring of the Dynamics and Particle Acceleration of Knots
in the Jet of Centaurus A: We present new and archival multi-frequency radio and X-ray data for
Centaurus A obtained over almost 20 years at the VLA and with Chandra, with
which we measure the X-ray and radio spectral indices of jet knots, flux
density variations in the jet knots, polarization variations, and proper
motions. We compare the observed properties with current knot formation models
and particle acceleration mechanisms. We rule out impulsive particle
acceleration as a formation mechanism for all of the knots as we detect the
same population of knots in all of the observations and we find no evidence of
extreme variability in the X-ray knots. We find the most likely mechanism for
all the stationary knots is a collision resulting in a local shock followed by
a steady state of prolonged, stable particle acceleration and X-ray synchrotron
emission. In this scenario, the X-ray-only knots have radio counterparts that
are too faint to be detected, while the radio-only knots are due to weak shocks
where no particles are accelerated to X-ray emitting energies. Although the
base knots are prime candidates for reconfinement shocks, the presence of a
moving knot in this vicinity and the fact that there are two base knots are
hard to explain in this model. We detect apparent motion in three knots;
however, their velocities and locations provide no conclusive evidence for or
against a faster moving `spine' within the jet. The radio-only knots, both
stationary and moving, may be due to compression of the fluid. |
Instabilities in neutrino systems induced by interactions with scalars: If there are scalar particles of small or moderate mass coupled very weakly
to Dirac neutrinos, in a minimal way, then neutrino-anti-neutrino clouds of
sufficient number density can experience an instability in which helicities are
suddenly reversed. The predicted collective evolution is many orders of
magnitude faster than given by cross-section calculations. The instabilities
are the analogue of the ``flavor-angle" instabilities (enabled by the Z
exchange force) that may drive very rapid flavor exchange among the neutrinos
that emerge from a supernova. These exchanges do require a tiny seed in
addition to the scalar couplings, but the transition time is proportional to
the negative of the logarithm of the seed strength, so that the size of this
parameter is comparatively unimportant. For our actual estimates we use a tiny
non-conservation of leptons; an alternative would be a neutrino magnetic moment
in a small magnetic field. The possibility of a quantum fluctuation as a seed
is also discussed. Operating in the mode of putting limits on the coupling
constant of the scalar field, for the most minimal coupling scheme, with
independent couplings to all three $\nu$, we find a rough limit on the
dimensionless coupling constant for a neutrino-flavor independent coupling of
$G<10^{-10}$, to avoid the effective number of light neutrinos in the early
universe being essentially six. If, on the other hand, we wish to fine-tune the
model to give a more modest excess (over three) in the effective neutrino
number, as may be needed according to recent WMAP analyses, it is easy to do
so.
\pacs{13.15.+g} | SDSS J094604.90+183541.8: A Gravitationally Lensed Quasar at z=4.8: We report the discovery of a gravitationally lensed quasar identified
serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS
J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red
galaxy, but the SDSS spectrum has the features of both a z=0.388 galaxy and a
z=4.8 quasar. We have obtained additional imaging that resolves the system into
two quasar images separated by 3.06 arcsec and a bright galaxy that is strongly
blended with one of the quasar images. We confirm spectroscopically that the
two quasar images represent a single lensed source at z=4.8 with a total
magnification of 3.2, and we derive a model for the lensing galaxy. This is the
highest redshift lensed quasar currently known. We examine the issues
surrounding the selection of such an unusual object from existing data and
briefly discuss implications for lensed quasar surveys. |
Dependences of Type Ia Supernovae Lightcurve Parameters on the Host
Galaxy Star Formation Rate and Metallicity: We present the dependences of the properties of type Ia Supernovae (SNe Ia)
on their host galaxies by analyzing the multi-band lightcurves of 118
spectroscopically confirmed SNe Ia observed by the Sloan Digital Sky Survey
(SDSS) Supernova Survey and the spectra of their host galaxies. We derive the
equivalent width of the \rm{H}$\alpha$ emission line, star formation rate, and
gas-phase metallicity from the spectra and compare these with the lightcurve
widths and colors of SNe Ia. In addition, we compare host properties with the
deviation of the observed distance modulus corrected for lightcurve parameters
from the distance modulus determined by the best fit cosmological parameters.
This allows us to investigate uncorrected systematic effects in the magnitude
standardization. We find that SNe Ia in host galaxies with a higher star
formation rate have synthesized on average a larger $^{56}$Ni mass and show
wider lightcurves. The $^{56}$Ni mass dependence on metallicity is consistent
with a prediction of Timmes et al. 2003 based on nucleosynthesis. SNe Ia in
metal-rich galaxies ({$\log_{10}(O/H)+12>8.9$) have become 0.13 $\pm$ 0.06
magnitude brighter after corrections for their lightcurve widths and colors,
which corresponds to up to 6% uncertainty in the luminosity distance. We
investigate whether parameters for standardizing SN Ia maximum magnitude differ
among samples with different host characteristics. The coefficient of the color
term is larger by 0.67 $\pm$ 0.19 for SNe Ia in metal-poor hosts than those in
metal-rich hosts when no color cuts are imposed. | The Carnegie Hubble Program: The Infrared Leavitt Law in IC 1613: We have observed the dwarf galaxy IC 1613, at multiple epochs in the
mid--infrared using Spitzer and contemporaneously in the near--infrared using
the new FourStar near-IR camera on Magellan. We have constructed Cepheid
period--luminosity relations in the J, H, K_s, [3.6] and [4.5] bands and have
used the run of their apparent distance moduli as a function of wavelength to
derive the line--of--sight reddening and distance to IC1613. Using a nine--band
fit, we find E(B-V) = 0.05 +- 0.01 mag and an extinction--corrected distance
modulus of mu_{0} = 24.29 +- 0.03_{statistical} +- 0.03_{systematic} mag. By
comparing our multi--band and [3.6] distance moduli to results from the tip of
the red giant branch and red clump distance indicators, we find that
metallicity has no measurable effect on Cepheid distances at 3.6 microns in the
metallicity range -1.0 < [Fe/H] < 0.2, hence derivations of the Hubble constant
at this wavelength require no correction for metallicity. |
Is a symmetric matter-antimatter universe excluded?: We consider a non-standard cosmological model in which the universe contains
as much matter as antimatter on large scales and presents a local baryon
asymmetry. A key ingredient in our approach is that the baryon density
distribution follows Gaussian fluctuations around a null value $\eta = 0$.
Spatial domains featuring a positive (resp. negative) baryonic density value
constitute regions dominated by matter (resp. antimatter). At the domains'
annihilation interface, the typical density is going smoothly to zero, rather
than following an abrupt step as assumed in previous symetric matter-antimatter
models. As a consequence, the Cosmic Diffuse Gamma Background produced by
annihilation is drastically reduced, allowing to easily pass COMPTEL's
measurements limits. Similarly the Compton $y$ distorsion and CMB 'ribbons' are
lowered by an appreciable factor. Therefore this model essentially escape
previous constrainst on symetric matter-antimatter models. However, we produce
an estimation of the CMB temperature fluctuations that would result from this
model and confront it to data acquired from the Planck satellite. We construct
a angular power spectrum in $\delta T / T_{CMB}$ assuming is can be
approximated as an average of $C_\ell$ over a Gaussian distribution of
$\Omega_B$ using Lewis & Challinor's CAMB software. The resulting $C_\ell$ are
qualitatively satisfying. We quantify the goodness of fit using a simple
$\chi^2$ test. We consider two distinct scenarios in which the fluctuations on
$\Omega_B$ are compensated by fluctuations on $\Omega_{CDM}$ to assure a
spatially flat $\Omega_\kappa = 0$ universe or not. In both cases, out best fit
have $\Delta \chi^2 \gtrsim 2400$ (with respect to a fiducial $\Lambda$CDM
model), empirically excluding our model by several tens of standard deviations. | Cosmological structure formation in complex scalar field dark matter
versus real ultralight axions: a comparative study using CLASS: (abridged) We continue the study of $\Lambda$SFDM cosmologies, which differ
from $\Lambda$CDM in that CDM is replaced by scalar field dark matter (SFDM) by
calculating the evolution of the background Universe, as well as linear
perturbations, focusing on scalar modes. We consider models with complex scalar
field with a repulsive, quartic self-interaction (SI), and models without SI,
referred to as fuzzy dark matter (FDM). To this end, we modify the Boltzmann
code CLASS, to incorporate the physics of complex SFDM which has as one of its
characteristics that its equation of state is maximally stiff in the very early
Universe, dominating then over all the other cosmic components, even over
radiation. We calculate CMB and matter power spectra as well as unconditional
Press-Schechter halo mass functions for various models, expanding previous
literature that were limited either to the background, or to a semi-analytical
approach to SFDM density perturbations neglecting the early stiff phase.
Comparing our results of each, SFDM and FDM, with real-field ultralight axion
models (ULAs) without SI, we characterize the differences between the
respective background evolution and linear structure growth. Our calculations
confirm previous results of recent literature, implying that SFDM models with
$\gtrsim$ kpc-size halo cores are disfavored, questioning their ability to
explain the small-scale problems on dwarf-galactic scales. Also we find that
the kinetic energy due to the phase of the complex field leads to marked
differences between SFDM/FDM versus ULAs. The mild falloff in the SFDM power
spectrum toward high k is similar to that of CDM but based on different
effects, namely the rapidly shrinking Jeans mass for SFDM as opposed to the
Meszaros effect for CDM. In addition, we find that the sharp cutoff in the ULA
power spectrum is also followed by a mild falloff, albeit at very small power. |
Minor merger-induced cold fronts in Abell 2142 and RXJ1720.1+2638: We present evidence for the existence of substructure in the "relaxed
appearing" cold front clusters Abell 2142 and RXJ1720.1+2638. The detection of
these substructures was made possible by comprehensive multi-object optical
spectroscopy obtained with the Hectospec and DEep Imaging Multi-Object
Spectrograph instruments on the 6.5m MMT and 10m Keck II telescope,
respectively. These observations produced 956 and 400 spectroscopically
confirmed cluster members within a projected radius of 3Mpc from the centers of
Abell 2142 and RXJ1720.1+2638, respectively. The substructure manifests itself
as local peaks in the spatial distribution of member galaxies and also as
regions of localized velocity substructure. For both Abell 2142 and
RXJ1720.1+2638, we identify group-scale substructures which, when considering
the morphology of the cold fronts and the time since pericentric passage of a
perturber estimated from the cold front radii, could plausibly have perturbed
the cluster cores and generated the cold fronts observed in Chandra images. The
results presented here are consistent with cold fronts being the result of
merger activity and with cold fronts in relaxed appearing clusters being due to
minor merger activity. | Can primordial parity violation explain the observed cosmic
birefringence?: Recently, the cross-correlation between $E$- and $B$-mode polarization of the
cosmic microwave background (CMB), which is well explained by cosmic
birefringence with rotation angle $\beta\approx 0.3$ deg, has been found in CMB
polarization data. We carefully investigate the possibility of explaining the
observed $EB$ correlation by the primordial chiral gravitational waves (CGWs),
which can be generated in the parity-violating theories in the primordial
Universe. We found that the CGWs scenario does not work due to the
overproduction of the $BB$ auto-correlation which far exceeds the observed one
by SPTPol and POLARBEAR. |
Consistency Relation and Non-Gaussianity in a Galileon Inflation: We study a particular Galileon inflation in the light of Planck2015
observational data in order to constraint the model parameter space. We study
the spectrum of the primordial modes of the density perturbations by expanding
the action up to the second order in perturbations. Then we pursue by expanding
the action up to the third order and find the three point correlation functions
to find the amplitude of the non-Gaussianity of the primordial perturbations in
this setup. We study the amplitude of the non-Gaussianity both in equilateral
and orthogonal configurations and test the model with recent observational
data. Our analysis shows that for some ranges of the non-minimal coupling
parameter, the model is consistent with observation and it is also possible to
have large non-Gaussianity which would be observable by future improvements in
experiments. Moreover, we obtain the tilt of the tensor power spectrum and test
the standard inflationary consistency relation ($r=-8n_T$) against the latest
bounds from the Planck2015 dataset. We find a slight deviation from the
standard consistency relation in this setup. Nevertheless, such a deviation
seems not to be sufficiently remarkable to be detected confidently. | Effect of Population III Multiplicity on Dark Star Formation: We numerically study the mutual interaction between dark matter (DM) and
Population III (Pop III) stellar systems in order to explore the possibility of
Pop III dark stars within this physical scenario. We perform a cosmological
simulation, initialized at z ~ 100, which follows the evolution of gas and DM.
We analyze the formation of the first minihalo at z ~ 20 and the subsequent
collapse of the gas to densities of 10^12 cm^-3. We then use this simulation to
initialize a set of smaller-scale `cut-out' simulations in which we further
refine the DM to have spatial resolution similar to that of the gas. We test
multiple DM density profiles, and we employ the sink particle method to
represent the accreting star-forming region. We find that, for a range of DM
configurations, the motion of the Pop III star-disk system serves to separate
the positions of the protostars with respect to the DM density peak, such that
there is insufficient DM to influence the formation and evolution of the
protostars for more than ~ 5000 years. In addition, the star-disk system causes
gravitational scattering of the central DM to lower densities, further
decreasing the influence of DM over time. Any DM-powered phase of Pop III stars
will thus be very short-lived for the typical multiple system, and DM will not
serve to significantly prolong the life of Pop III stars. |
The Chemical Evolution of Narrow Emission Line Galaxies: the Key to
their Formation Processes: Using the largest sample of narrow emission line galaxies available so far,
we show that their spectral characteristics are correlated with different
physical parameters, like the chemical abundances, the morphologies, the masses
of the bulge and the mean stellar age of the stellar populations of the host
galaxies. It suggests that the spectral variations observed in standard
spectroscopic diagnostic diagrams are not due solely to variations of
ionization parameters or structures but reflect also the chemical evolution of
the galaxies, which in turn can be explained by different galaxy formation
processes. | Scalar instabilities in bimetric gravity: The Vainshtein mechanism and
structure formation: We investigate the observational consequences of scalar instabilities in
bimetric theory, under the assumption that the Vainshtein mechanism restores
general relativity within a certain distance from gravitational sources. We
argue that early time instabilities have a negligible impact on observed
structures. Assuming that the instabilities affect sub-horizon density
fluctuations, we constrain the redshift, z_i, below which instabilities are
ruled out. For the "minimal" beta_1-model, observational constraints are close
to the theoretical expectations of z_i = 0.5, potentially allowing the model to
be ruled in or out with a more detailed study, possibly including secondary
cosmic microwave background constraints. |
A new way to test the Cosmological Principle: measuring our peculiar
velocity and the large scale anisotropy independently: We present a novel approach to disentangle two key contributions to the
largest-scale anisotropy of the galaxy distribution: (i) the intrinsic dipole
due to clustering and anisotropic geometry, and (ii) the kinematic dipole due
to our peculiar velocity. Including the redshift and angular size of galaxies,
in addition to their fluxes and positions allows us to measure both the
direction and amplitude of our velocity independently of the intrinsic dipole
of the source distribution. We find that this new approach applied to future
galaxy surveys (LSST and Euclid) and a SKA radio continuum survey will allow to
measure our velocity ($\beta = v/c$) with a relative error in the amplitude
$\sigma(\beta)/\beta \sim (1.3 - 4.5)\%$ and in direction, $\theta_{\beta} \sim
0.9^\circ - 3.9^\circ$, well beyond what can be achieved when analysing only
the number count dipole. We also find that galaxy surveys are able to measure
the intrinsic large-scale anisotropy with a relative uncertainty of $\lesssim
5\%$ (measurement error, not including cosmic variance). Our method enables two
simultaneous tests of the Cosmological Principle: comparing the observations of
our peculiar velocity with the CMB dipole, and testing for a significant
intrinsic anisotropy on large scales which would indicate effects beyond the
standard cosmological model. | Cosmological simulations of the same spiral galaxy: connecting the dark
matter distribution of the host halo with the subgrid baryonic physics: The role of baryonic physics, star formation, and stellar feedback, in
shaping the galaxies and their host halos is an evolving topic. The dark matter
aspects are illustrated in this work by showing distribution features in a
Milky-Way-sized halo. We focus on the halo morphology, geometry, and profile as
well as the phase space distribution using one dark matter only and five
hydrodynamical cosmological high-resolution simulations of the same halo with
different subgrid prescriptions for the baryonic physics (Kennicut versus
multi-freefall star formation and delayed cooling versus mechanical supernovae
feedback). If some general properties like the relative halo-galaxy orientation
are similar, the modifications of the gravitational potential due to the
presence of baryons are found to induce different dark matter distributions
(rounder and more concentrated halo). The mass density profile as well as the
velocity distribution are modified distinctively according to the specific
resulting baryonic distribution highlighting the variability of those
properties (e.g inner power index from 1.3 to 1.8, broader speed distribution).
The uncertainties on those features are of paramount importance for dark matter
phenomenology, particularly when dealing with dark matter dynamics or direct
and indirect detection searches. As a consequence, dark matter properties and
prospects using cosmological simulations require improvement on baryonic
physics description. Modeling such processes is a key issue not only for galaxy
formation but also for dark matter investigations. |
Baryon Acoustic Oscillations reconstruction with pixels: Gravitational non-linear evolution induces a shift in the position of the
baryon acoustic oscillations (BAO) peak together with a damping and broadening
of its shape that bias and degrades the accuracy with which the position of the
peak can be determined. BAO reconstruction is a technique developed to undo
part of the effect of non-linearities. We present and analyse a reconstruction
method that consists of displacing pixels instead of galaxies and whose
implementation is easier than the standard reconstruction method. We show that
this method is equivalent to the standard reconstruction technique in the limit
where the number of pixels becomes very large. This method is particularly
useful in surveys where individual galaxies are not resolved, as in 21cm
intensity mapping observations. We validate this method by reconstructing mock
pixelated maps, that we build from the distribution of matter and halos in
real- and redshift-space, from a large set of numerical simulations. We find
that this method is able to decrease the uncertainty in the BAO peak position
by 30-50% over the typical angular resolution scales of 21 cm intensity mapping
experiments. | The possible resolution of Boltzmann brains problem in phantom cosmology: We consider the well-known Boltzmann brains problem in frames of simple
phantom energy models with little rip and big rip singularity. It is showed
that these models (i) satisfy to observational data and (ii) may be free from
Boltzmann brains problem. The human observers in phantom models can exist only
in during for a certain period $t<t_{f}$ ($t_{f}$ is lifetime of universe) via
Bekenstein bound. If fraction of unordered observers in this part of universe
history is negligible in comparison with ordered observers than Boltzmann
brains problem doesn't appear. The bounds on model parameters derived from such
requirement don't contradict to allowable range from observational data. |
Combining Full-Shape and BAO Analyses of Galaxy Power Spectra: A 1.6%
CMB-independent constraint on H0: We present cosmological constraints from a joint analysis of the pre- and
post-reconstruction galaxy power spectrum multipoles from the final data
release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric
constraints are obtained from the positions of BAO peaks in reconstructed
spectra, analyzed in combination with the unreconstructed spectra in a
full-shape (FS) likelihood using a joint covariance matrix, giving stronger
parameter constraints than FS-only or BAO-only analyses. We introduce a new
method for obtaining constraints from reconstructed spectra based on a
correlated theoretical error, which is shown to be simple, robust, and
applicable to any flavor of density-field reconstruction. Assuming $\Lambda$CDM
with massive neutrinos, we analyze data from two redshift bins
$z_\mathrm{eff}=0.38,0.61$ and obtain $1.6\%$ constraints on the Hubble
constant $H_0$, using only a single prior on the current baryon density
$\omega_b$ from Big Bang Nucleosynthesis (BBN) and no knowledge of the power
spectrum slope $n_s$. This gives $H_0 =
68.6\pm1.1\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$, with the inclusion of BAO
data sharpening the measurement by $40\%$, representing one of the strongest
current constraints on $H_0$ independent of cosmic microwave background data.
Restricting to the best-fit slope $n_s$ from Planck (but without additional
priors on the spectral shape), we obtain a $1\%$ $H_0$ measurement of $67.8\pm
0.7\,\mathrm{km\,s}^{-1}\mathrm{Mpc}^{-1}$. We find strong constraints on the
cosmological parameters from a joint analysis of the FS, BAO, and Planck data.
This sets new bounds on the sum of neutrino masses $\sum m_\nu <
0.14\,\mathrm{eV}$ (at $95\%$ confidence) and the effective number of
relativistic degrees of freedom $N_\mathrm{eff} = 2.90^{+0.15}_{-0.16}$, though
contours are not appreciably narrowed by the inclusion of BAO data. | Cosmological evolution of Witten superconducting string networks: We consider the evolution of current-carrying cosmic string networks
described by the charge-velocity-dependent one scale (CVOS) model beyond the
linear equation of state regime, specifically focusing on the Witten
superconducting model. We find that, generically, for almost chiral currents,
the network evolution reduces dynamically to that of the linear case, which has
been discussed in our previous work. However, the Witten model introduces a
maximum critical current which constrains the network scaling behaviour during
the radiation era when currents can grow and approach this limit. Unlike the
linear model, only if the energy density in the critical current is comparable
to the bare string tension will there be substantial backreaction on the
network evolution, thus changing the observational predictions of
superconducting strings from those expected from a Nambu-Goto network. During
the matter era, if there are no external sources, then dynamical effects dilute
these network currents and they disappear at late times. |
Molecular Gas Evolution across a Spiral Arm in M 51: We present sensitive and high angular resolution CO(1-0) data obtained by the
Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations
toward the nearby grand-design spiral galaxy M 51. The angular resolution of
0.7" corresponds to 30 pc, which is similar to the typical size of Giant
Molecular Clouds (GMCs), and the sensitivity is also high enough to detect
typical GMCs. Within the 1' field of view centered on a spiral arm, a number of
GMC-scale structures are detected as clumps. However, only a few clumps are
found to be associated with each Giant Molecular Association (GMA), and more
than 90% of the total flux is resolved out in our data. Considering the high
sensitivity and resolution of our data, these results indicate that GMAs are
not mere confusion of GMCs but plausibly smooth structures. In addition, we
have found that the most massive clumps are located downstream of the spiral
arm, which suggests that they are at a later stage of molecular cloud evolution
across the arm and plausibly are cores of GMAs. By comparing with H-alpha and
Pa-alpha images, most of these cores are found to have nearby star forming
regions. We thus propose an evolutionary scenario for the interstellar medium,
in which smaller molecular clouds collide to form smooth GMAs at spiral arm
regions and then star formation is triggered in the GMA cores. Our new CO data
have revealed the internal structure of GMAs at GMC scales, finding the most
massive substructures on the downstream side of the arm in close association
with the brightest H II regions. | GW190425, GW190521 and GW190814: Three candidate mergers of primordial
black holes from the QCD epoch: The two recent gravitational-wave events GW190425 and GW190814 from the third
observing run of LIGO/Virgo have both a companion which is unexpected if
originated from a neutron star or a stellar black hole, with masses
$[1.6-2.5]~M_\odot$ and $[2.5-2.7]~M_\odot$ and merging rates $
460^{+1050}_{-360} $ and $ 7^{+16}_{-6}$ events/yr/Gpc$^3$ respectively, at
90\% c.l.. Moreover, the recent event GW190521 has black hole components with
masses 67 and $91~M_\odot$, and therefore lies in the so-called
pair-instability mass gap, where there should not be direct formation of
stellar black holes. The possibility that all of these compact objects are
Primordial Black Holes (PBHs) is investigated. The known thermal history of the
Universe predicts that PBH formation is boosted at the time of the QCD
transition, inducing a peak in their distribution at this particular mass
scale, and a bump around $30-50~M_\odot$. We find that the merging rates
inferred from GW190425, GW190521 and GW190814 are consistent with PBH binaries
formed by capture in dense halos in the matter era or in the early universe. At
the same time, the rate of black hole mergers around $30~M_\odot$ and of
sub-solar PBH mergers do not exceed the LIGO/Virgo limits. Such PBHs could
explain a significant fraction, or even the totality of the Dark Matter, but
they must be sufficiently strongly clustered in order to be consistent with
current astrophysical limits. |
Stellar population and kinematics of NGC404: NGC404 is a nearly face-on nearby low-luminosity lenticular galaxy. Probing
its characteristics provides a wealth of information on the details of possible
evolution processes of dS0 galaxies which may not be possible in other, more
distant objects. In order to study its kinematics and star formation history,
we obtained long slit spectroscopy at the OHP 1m93 telescope along the major
and minor axes of NGC404. The spectra have a resolution R = 3600 covering a
wavelength range from 4600 to 5500 A. The data are fitted against the Pegase.HR
stellar population models to derive simultaneously the internal stellar
kinematics, ages and metallicities. Firstly, the global properties of the
galaxy are analyzed by fitting a single model and to the data and looking at
the kinematic variations and SSP equivalent age and metallicities as a function
of radius. Afterwards, the stellar populations are decomposed into 4 components
that are individually analyzed. NGC404 clearly shows two radial velocity
inversions along its major axis. The kinematically decoupled core rotates in
the same direction as the neutral hydrogen shell that surrounds the galaxy. We
resolved the star formation history in the core of the galaxy ino 4 events: A
very young (< 150 Myr, and [Fe/H] = 0.4) component with constant on-going star
formation, a second young (430 Myr) component with [Fe/H] = 0.1, an
intermediate population (1.7 Gyr) which has [Fe/H] = -0.05 and, finally, an old
(12 Gyr) component with [Fe/H] = -1.26. The two young components fade very
quickly with radius, leaving only the intermediate and old population at a
radius of 25" (370 pc) from the centre. We conclude that NGC404 had a spiral
morphology about 1 Gyr ago and that one or many merger events has triggered a
morphological transition. | New constraints on the distance duality relation from the local data: The cosmic distance duality relation (DDR), which connects the angular
diameter distance and luminosity distance through a simple formula
$D_A(z)(1+z)^2/D_L(z)\equiv1$, is an important relation in cosmology.
Therefore, testing the validity of DDR is of great importance. In this paper,
we test the possible violation of DDR using the available local data including
type Ia supernovae (SNe Ia), galaxy clusters and baryon acoustic oscillations
(BAO). We write the modified DDR as $D_A(z)(1+z)^2/D_L(z)=\eta(z)$, and
consider two different parameterizations of $\eta(z)$, namely
$\eta_1(z)=1+\eta_0 z$ and $\eta_2(z)=1+\eta_0 z/(1+z)$. The luminosity
distance from SNe Ia are compared with the angular diameter distance from
galaxy clusters and BAO at the same redshift. Two different cluster data are
used here, i.e. elliptical clusters and spherical clusters. The parameter
$\eta_0$ is obtained using the Markov chain Monte Carlo methods. It is found
that $\eta_0$ can be strictly constrained by the elliptical clusters + BAO
data, with the best-fitting values $\eta_0=-0.04\pm 0.12$ and $\eta_0=-0.05\pm
0.22$ for the first and second parametrizations, respectively. However, the
spherical clusters + BAO data couldn't strictly constrain $\eta_0$ due to the
large intrinsic scatter. In any case studied here, no evidence for the
violation of DDR is found. |
3D-structure of the Canes Venatici I Cloud: We present the improved distance moduli of 30 galaxies in the Canes Venatici
I Cloud using advanced Tip of Red Giant Branch (TRGB) method (Makarov et.al.
2006). The method was determined for accurate estimation of the distances even
if TRGB situated near photometric limit. The data were taken from the Archive
of the Hubble Space Telescope (HST). Based on ACS and WFPC2 images of the HST
we construct the color-magnitude diagrams of the resolved stellar population of
the galaxies using Dolphot and HSTPhot packages.
New refined method of the distance determination allows us to clarify the 3D
structure of the Canes Venatici I Cloud. It consists of the central group of
galaxies around M94 and the outskirt which is situated in gravitational field
of the "core". The mass and mass-to-light ratio of the CVn have been estimated. | Comment on cluster analysis of radio loops in CMB data: A recent article (Liu et al. 2014) looks for evidence in the WMAP internal
linear combination map (ILC) of unmodeled emission from the galactic radio loop
known as Loop I. The statistically strongest result comes from a cluster
analysis that tests whether the "hot spots" within a $20^\circ$ annulus at Loop
I are preferentially located near the center line of the annulus. From this
cluster analysis the authors report a $p$-value of 0.018% when considering the
four highest bins (75-87 $\mu$K). I show that the reported statistical
significance has been overestimated. First, the analysis does not correctly
select the hot spots in the simulated sky realizations; second, it is sensitive
to the map pixelization used, and in particular, pixel size used is similar to
the relevant clustering distance. I have run 10,000 simulated sky realizations
to reproduce the analysis in Liu et al. and to calculate the effects of
incorrect hot spot selection and of pixelization. Accounting for both of these
effects, I find a corrected $p$-value of $\sim1\%$, both in the highest-bin
test and in the four-bin test. Finally, I note that even under the assumption
that Loop I contributes significant power to the ILC map, the observed
clustering remains very unlikely. Therefore, a result inconsistent with
statistical isotropy is not automatically strong evidence for a detection of
Loop I. I suggest additional tests that could clarify the degree to which the
cluster analysis supports a detection of Loop I in the CMB map. |
The largest structure of the Universe, defined by Gamma-Ray Bursts: Research over the past three decades has revolutionized the field of
cosmology while supporting the standard cosmological model. However, the
cosmological principle of Universal homogeneity and isotropy has always been in
question, since structures as large as the survey size have always been found
as the survey size has increased. Until now, the largest known structure in our
Universe is the Sloan Great Wall (SGW), which is more than 400 Mpc long and
located approximately one billion light-years away. Here we report the
discovery of a structure at least six times larger than the Sloan Great Wall
that is suggested by the distribution of gamma-ray bursts (GRBs). Gamma-ray
bursts are the most energetic explosions in the Universe. They are associated
with the stellar endpoints of massive stars and are found in and near distant
galaxies. Therefore, they are very good indicators of the dense part of the
Universe containing normal matter. As of July 2012, 283 GRB redshifts have been
measured. If one subdivides this GRB sample into nine radial parts and compares
the sky distributions of these subsamples (each containing 31 GRBs), one can
observe that the fourth subsample (1.6 < z < 2.1) differs significantly from
the others in that many of the GRBs are concentrated in the same angular area
of the sky. Using the two-dimensional Kolmogorov-Smirnov test, the significance
of this observation is found to be less than 0.05 per cent. Fourteen out of the
31 Gamma-Ray Bursts in this redshift band are concentrated in approximately 1/8
of the sky. The binomial probability to find such a deviation is p=0.0000055.
This huge structure lies ten times farther away than the Sloan Great Wall, at a
distance of approximately ten billion light-years. The size of the structure
defined by these GRBs is about 2000-3000 Mpc, or more than six times the size
of the largest known object (SGW) in the Universe. | The dominant role of mergers in the size evolution of massive early-type
galaxies since z ~ 1: In this paper we measure the merger fraction and rate, both minor and major,
of massive early-type galaxies (M_star >= 10^11 M_Sun) in the COSMOS field, and
study their role in mass and size evolution. We use the 30-band photometric
catalogue in COSMOS, complemented with the spectroscopy of the zCOSMOS survey,
to define close pairs with a separation 10h^-1 kpc <= r_p <= 30h-1 kpc and a
relative velocity Delta v <= 500 km s^-1. We measure both major (stellar mass
ratio mu = M_star,2/M_star,1 >= 1/4) and minor (1/10 <= mu < 1/4) merger
fractions of massive galaxies, and study their dependence on redshift and on
morphology. The merger fraction and rate of massive galaxies evolves as a
power-law (1+z)^n, with major mergers increasing with redshift, n_MM = 1.4, and
minor mergers showing little evolution, n_mm ~ 0. When split by their
morphology, the minor merger fraction for early types is higher by a factor of
three than that for spirals, and both are nearly constant with redshift. Our
results show that massive early-type galaxies have undergone 0.89 mergers (0.43
major and 0.46 minor) since z ~ 1, leading to a mass growth of ~30%. We find
that mu >= 1/10 mergers can explain ~55% of the observed size evolution of
these galaxies since z ~ 1. Another ~20% is due to the progenitor bias (younger
galaxies are more extended) and we estimate that very minor mergers (mu < 1/10)
could contribute with an extra ~20%. The remaining ~5% should come from other
processes (e.g., adiabatic expansion or observational effects). This picture
also reproduces the mass growth and velocity dispersion evolution of these
galaxies. We conclude from these results that merging is the main contributor
to the size evolution of massive ETGs at z <= 1, accounting for ~50-75% of that
evolution in the last 8 Gyr. Nearly half of the evolution due to mergers is
related to minor (mu < 1/4) events. |
CMB Polarization Systematics, Cosmological Birefringence and the
Gravitational Waves Background: Cosmic Microwave Background experiments must achieve very accurate
calibration of their polarization reference frame to avoid biasing the
cosmological parameters. In particular, a wrong or inaccurate calibration might
mimic the presence of a gravitational wave background, or a signal from
cosmological birefringence, a phenomenon characteristic of several
non-standard, symmetry breaking theories of electrodynamics that allow for
\textit{in vacuo} rotation if the polarization direction of the photon.
Noteworthly, several authors have claimed that the BOOMERanG 2003 (B2K)
published polarized power spectra of the CMB may hint at cosmological
birefringence. Such analyses, however, do not take into account the reported
calibration uncertainties of the BOOMERanG focal plane. We develop a formalism
to include this effect and apply it to the BOOMERanG dataset, finding a
cosmological rotation angle $\alpha=-4.3^\circ\pm4.1^\circ$. We also
investigate the expected performances of future space borne experiment, finding
that an overall miscalibration larger then $1^\circ$ for Planck and $0.2\circ$
for EPIC, if not properly taken into account, will produce a bias on the
constraints on the cosmological parameters and could misleadingly suggest the
presence of a GW background. | Tests of Chameleon Gravity: Theories of modified gravity where light scalars with non-trivial
self-interactions and non-minimal couplings to matter-chameleon and symmetron
theories-dynamically suppress deviations from general relativity in the solar
system. On other scales, the environmental nature of the screening means that
such scalars may be relevant. The highly-nonlinear nature of screening
mechanisms means that they evade classical fifth-force searches, and there has
been an intense effort towards designing new and novel tests to probe them,
both in the laboratory and using astrophysical objects, and by reinterpreting
existing datasets. The results of these searches are often presented using
different parametrizations, which can make it difficult to compare constraints
coming from different probes. The purpose of this review is to summarize the
present state-of-the-art searches for screened scalars coupled to matter, and
to translate the current bounds into a single parametrization to survey the
state of the models. Presently, commonly studied chameleon models are
well-constrained but less commonly studied models have large regions of
parameter space that are still viable. Symmetron models are constrained well by
astrophysical and laboratory tests, but there is a desert separating the two
scales where the model is unconstrained. The coupling of chameleons to photons
is tightly constrained but the symmetron coupling has yet to be explored. We
also summarize the current bounds on $f(R)$ models that exhibit the chameleon
mechanism (Hu \& Sawicki models). The simplest of these are well constrained by
astrophysical probes, but there are currently few reported bounds for theories
with higher powers of $R$. The review ends by discussing the future prospects
for constraining screened modified gravity models further using upcoming and
planned experiments. |
The Djorgovski-Gurzadyan dark energy integral equation and the Hubble
diagram: We consider the observational aspects of the value of dark energy density
from quantum vacuum fluctuations based initially on the Gurzadyan-Xue model. We
reduce the Djorgovski-Gurzadyan integral equation to a differential equation
for the co-moving horizon and then, by means of the obtained explicit form for
the luminosity distance, we construct the Hubble diagram for two classes of
observational samples. For supernova and gamma-ray burst data we show that this
approach provides viable predictions for distances up to $z \simeq 9$,
quantitatively at least as good as those provided by the lambda cold dark
matter ($\Lambda$CDM) model. The Hubble parameter dependence $H(z)$ of the two
models also reveals mutual crossing at $z=0.4018$, the interpretation of which
is less evident. | The Aemulus Project I: Numerical Simulations for Precision Cosmology: The rapidly growing statistical precision of galaxy surveys has lead to a
need for ever-more precise predictions of the observables used to constrain
cosmological and galaxy formation models. The primary avenue through which such
predictions will be obtained is suites of numerical simulations. These
simulations must span the relevant model parameter spaces, be large enough to
obtain the precision demanded by upcoming data, and be thoroughly validated in
order to ensure accuracy. In this paper we present one such suite of
simulations, forming the basis for the AEMULUS Project, a collaboration devoted
to precision emulation of galaxy survey observables. We have run a set of 75
(1.05 h^-1 Gpc)^3 simulations with mass resolution and force softening of
3.51\times 10^10 (Omega_m / 0.3) ~ h^-1 M_sun and 20 ~ h^-1 kpc respectively in
47 different wCDM cosmologies spanning the range of parameter space allowed by
the combination of recent Cosmic Microwave Background, Baryon Acoustic
Oscillation and Type Ia Supernovae results. We present convergence tests of
several observables including spherical overdensity halo mass functions, galaxy
projected correlation functions, galaxy clustering in redshift space, and
matter and halo correlation functions and power spectra. We show that these
statistics are converged to 1% (2%) for halos with more than 500 (200)
particles respectively and scales of r>200 ~ h^-1 kpc in real space or k ~ 3 h
Mpc^-1 in harmonic space for z\le 1. We find that the dominant source of
uncertainty comes from varying the particle loading of the simulations. This
leads to large systematic errors for statistics using halos with fewer than 200
particles and scales smaller than k ~ 4 h^-1 Mpc. We provide the halo catalogs
and snapshots detailed in this work to the community at
https://AemulusProject.github.io. |
The impact and response of minihalos and the inter-halo medium on cosmic
reionization: An ionization front (I-front) that propagates through an inhomogeneous medium
is slowed down by self-shielding and recombinations. We perform cosmological
radiation hydrodynamics simulations of the I-front propagation during the epoch
of cosmic reionization. The simulations resolve gas in minihalos (halo mass
$10^4\lesssim M_h[{\rm M}_\odot]\lesssim 10^8)$ that could dominate
recombinations, in a computational volume that is large enough to sample the
abundance of such halos. The numerical resolution is sufficient (gas particle
mass $\sim 20{\rm M}_\odot$, spatial resolution $< 0.1\;{\rm ckpc}$) to allow
accurate modelling of the hydrodynamic response of gas to photo-heating. We
quantify the photo-evaporation time of minihalos as a function of $M_h$ and its
dependence on the photo-ionization rate, $\Gamma_{-12}$, and the redshift of
reionization, $z_i$. The recombination rate can be enhanced over that of a
uniform medium by a factor $\sim 10-20$ early on. The peak value increases with
$\Gamma_{-12}$ and decreases with $z_i$, due to the enhanced contribution from
minihalos. The clumping factor, $c_r$, decreases to a factor of a few at $\sim
100\;{\rm Myr}$ after the passage of the I-front when the minihalos have been
photo-evaporated; this asymptotic value depends only weakly on $\Gamma_{-12}$.
Recombinations increase the required number of photons per baryon to reionize
the Universe by 20-100 per cent, with the higher value occurring when
$\Gamma_{-12}$ is high and $z_i$ is low. We complement the numerical
simulations with simple analytical models for the evaporation rate and the
inverse Str\"omgren layer. The study also demonstrates the proficiency and
potential of SPHM1RT to address astrophysical problems in high-resolution
cosmological simulations. | Heating the IGM by X-rays from Population III Binaries in High Redshift
Galaxies: Due to their long mean free path, X-rays are expected to have an important
impact on cosmic reionization by heating and ionizing the IGM on large scales,
especially after simulations have suggested that Population III stars may form
in pairs at redshifts as high as 20 - 30. We use the Pop III distribution and
evolution from a self-consistent cosmological radiation hydrodynamics
simulation of the formation of the first galaxies and a simple Pop III X-ray
binaries model to estimate their X-ray output in a high density region larger
than 100 comoving (Mpc)$^3$. We then combine three different methods --- ray
tracing, a one-zone model, and X-ray background modeling --- to investigate the
X-ray propagation, intensity distribution, and long term effects on the IGM
thermal and ionization state. The efficiency and morphology of photo-heating
and photo-ionization are dependent on the photon energies. The sub-keV X-rays
only impact the IGM near the sources while the keV photons contribute
significantly to the X-ray background and heat and ionize the IGM smoothly. The
X-rays just below 1 keV are most efficient in heating and ionizing the IGM. We
find that the IGM might be heated to over 100 K by $z=10$ and the high density
source region might reach 10$^4$ K, limited by atomic hydrogen cooling. This
may be important for predicting the 21-cm neutral hydrogen signals. But, on the
other hand, the free electrons from X-ray ionizations are not enough to
contribute significantly to the optical depth of CMB to the Thomson scattering. |
A new recipe for $Λ$CDM: It is well known that a canonical scalar field is able to describe either
dark matter or dark energy but not both. We demonstrate that a non-canonical
scalar field can describe both dark matter and dark energy within a unified
setting. We consider the simplest extension of the canonical Lagrangian ${\cal
L} \propto X^\alpha - V(\phi)$ where $\alpha \geq 1$ and $V$ is a sufficiently
flat potential. In this case the kinetic term in the Lagrangian behaves just
like a perfect fluid, whereas the potential term mimicks the cosmological
constant. For very large values, $\alpha \gg 1$, the equation of state of the
kinetic term drops to zero and the expansion rate of the universe mimicks
$\Lambda$CDM. The velocity of sound in this model, and the associated
gravitational clustering, is sensitive to the value of $\alpha$. For very large
values of $\alpha$ the clustering properties of our model resemble those of
cold dark matter (CDM). But for smaller values of $\alpha$, gravitational
clustering on small scales is suppressed, and our model has properties
resembling those of warm dark matter (WDM). Therefore our non-canonical model
has an interesting new property: while the background universe expands like
$\Lambda$CDM, its clustering properties can resemble those of either cold or
warm dark matter. | Bayesian analysis for a class of $α$-attractor inflationary models: We perform a Bayesian study of a generalization of the basic
$\alpha$-attractor T model given by the potential
$V(\phi)=V_0\left[1-\text{sech}^{p}\left(\phi/\sqrt{6\alpha}M_{pl}\right)\right]$
where $\phi$ is the inflaton field and the parameter $\alpha$ corresponds to
the inverse curvature of the scalar manifold in the conformal or superconformal
realizations of the attractor models. Such generalization is characterized by
the power $p$ which includes the basic or base model for $p=2$. Once the priors
for the parameters of the $\alpha$-attractor potential are set by numerical
exploration, we perform the corresponding statistical analysis for the cases
$p=1\, , 2\, , 3\, ,4$, and derive posteriors. Considering the original
$\alpha$-attractor potential as the base model, we calculate the evidence for
our generalization, and conclude that the $p=4$ model is preferred by the CMB
data. We also present constraints for the parameter $\alpha$. Interestingly,
all the cases studied prefer a specific value for the tensor-to-scalar ratio
given by $r\simeq 0.0025$. |
Anisotropic dark energy and ellipsoidal universe: A cosmological model with anisotropic dark energy is analyzed. The amount of
deviation from isotropy of the equation of state of dark energy, the skewness
\delta, generates an anisotropization of the large-scale geometry of the
Universe, quantifiable by means of the actual shear \Sigma_0. Requiring that
the level of cosmic anisotropization at the time of decoupling is such to solve
the "quadrupole problem" of cosmic microwave background radiation, we find that
|\delta| \sim 10^{-4} and |\Sigma_0| \sim 10^{-5}, compatible with existing
limits derived from the magnitude-redshift data on type Ia supernovae. | Signs of Interacting Vacuum and Dark Matter in the Universe: We consider the impact of dynamical dark energy (DDE) in the possible
solution of the existing tensions in the $\Lambda$CDM. We test both interacting
and non-interacting DE models with dark matter (DM). Among the former, the
running vacuum model (RVM) interacting with DM appears as a favored option. The
non-interacting scalar field model based on the potential $V\sim
\phi^{-\alpha}$, and the generic XCDM parametrization, also provide consistent
signs of DDE. The important novelty of our analysis with respect to the
existing ones in the literature is that we use the matter bispectrum, together
with the power spectrum. Using a complete and updated set of cosmological
observations on $SNIa+BAO+H(z)+LSS+CMB$, we find that the crucial triad
$BAO+LSS+CMB$ (i.e. baryonic acoustic oscillations, large scale structure
formation data and the cosmic microwave background) provide the bulk of the
signal. The bispectrum data is instrumental to get hold of the DDE signal, as
our analysis shows. If the bispectrum is not included, the DDE signal could not
be currently perceived at a significant confidence level. |
Describing variations of the Fisher-matrix across parameter space: Forecasts in cosmology, both with Monte-Carlo Markov-chain methods and with
the Fisher matrix formalism, depend on the choice of the fiducial model because
both the signal strength of any observable as well as the model nonlinearities
linking observables to cosmological parameters vary in the general case. In
this paper we propose a method for extrapolating Fisher-forecasts across the
space of cosmological parameters by constructing a suitable ba- sis. We
demonstrate the validity of our method with constraints on a standard dark
energy model extrapolated from a {\Lambda}CDM-model, as can be expected from
2-bin weak lensing to- mography with a Euclid-like survey, in the parameter
pairs $(\Omega_\text{m},\sigma_8)$, $(\Omega_\text{m}, w_0)$ and $(w_0,
w_\text{a})$. Our numerical results include very accurate extrapolations across
a wide range of cosmo- logical parameters in terms of shape, size and
orientation of the parameter likelihood, and a decomposition of the change of
the likelihood contours into modes, which are straightforward to interpret in a
geometrical way. We find that in particular the variation of the dark energy
figure of merit is well captured by our formalism. | Lensing smoothing of BAO wiggles: We study non-perturbatively the effect of the deflection angle on the BAO
wiggles of the matter power spectrum in real space. We show that from redshift
z~2 this introduces a dispersion of roughly 1 Mpc at BAO scale, which
corresponds approximately to a 1% effect. The lensing effect induced by the
deflection angle, which is completely geometrical and survey independent,
smears out the BAO wiggles. The effect on the power spectrum amplitude at BAO
scale is about 0.1% for z~2 and 0.2% for z~4. We compare the smoothing effects
induced by the lensing potential and non-linear structure formation, showing
that the two effects become comparable at z~4, while the lensing effect
dominates for sources at higher redshifts. We note that this effect is not
accounted through BAO reconstruction techniques. |
First CMB Constraints on Direction-Dependent Cosmological Birefringence
from WMAP-7: A Chern-Simons coupling of a new scalar field to electromagnetism may give
rise to cosmological birefringence, a rotation of the linear polarization of
electromagnetic waves as they propagate over cosmological distances. Prior work
has sought this rotation, assuming the rotation angle to be uniform across the
sky, by looking for the parity-violating TB and EB correlations a uniform
rotation produces in the CMB temperature/polarization. However, if the scalar
field that gives rise to cosmological birefringence has spatial fluctuations,
then the rotation angle may vary across the sky. Here we search for
direction-dependent cosmological birefringence in the WMAP-7 data. We report
the first CMB constraint on the rotation-angle power spectrum for multipoles
between L = 0 and L = 512. We also obtain a 68% confidence-level upper limit of
1 degree on the square root of the quadrupole of a scale-invariant
rotation-angle power spectrum. | Constraints on neutrino mass from Cosmic Microwave Background and Large
Scale Structure: Our tightest upper limit on the sum of neutrino mass eigenvalues $M_\nu$
comes from cosmological observations that will improve substantially in the
near future, enabling a detection. The combination of the Baryon Acoustic
Oscillation feature measured from the Dark Energy Spectroscopic Instrument and
a Stage-IV Cosmic Microwave Background experiment has been forecasted to
achieve $\sigma(M_\nu) < 1/3$ of the lower limit on $M_\nu$ from atmospheric
and solar neutrino oscillations
\citep{2013arXiv1309.5383A,2012PhRvD..86a3012F}. Here we examine in detail the
physical effects of neutrino mass on cosmological observables that make these
constraints possible. We also consider how these constraints would be improved
to ensure at least a $5\sigma$ detection. |
Searching for dark matter annihilation from individual halos:
uncertainties, scatter and signal-to-noise ratios: Individual extragalactic dark matter halos, such as those associated with
nearby galaxies and galaxy clusters, are promising targets for searches for
gamma-rays from dark matter annihilation. We review the predictions for the
annihilation flux from individual halos, focusing on the effect of current
uncertainties in the concentration-mass relation and the contribution from halo
substructure, and also estimating the intrinsic halo-to-halo scatter expected.
After careful consideration of recent simulation results, we conclude that the
concentrations of the smallest halos, while well determined at high redshift,
are still uncertain by a factor of 4-6 when extrapolated to low redshift. This
in turn produces up to two orders of magnitude uncertainty in the predicted
annihilation flux for any halo mass above this scale. Substructure evolution,
the small-scale cutoff to the power spectrum, cosmology, and baryonic effects
all introduce smaller, though cumulative, uncertainties. We then consider
intrinsic variations from halo to halo. These arise from variations in
concentration and substructure, leading to a scatter of $\sim$ 2.5 in the
predicted annihilation luminosity. Finally, we consider the problem of
detecting gamma-rays from annihilation, given the expected contributions from
other sources. We estimate the signal-to-noise ratio for gamma-ray detection as
a function of halo mass, assuming that cosmic rays from star formation are the
main noise source in the detection. This calculation suggests that group-scale
halos, individually or in stacks, may be a particularly interesting target for
the next generation of annihilation searches. | Bispectrum Supersample Covariance: Modes with wavelengths larger than the survey window can have significant
impact on the covariance within the survey window. The supersample covariance
has been recognized as an important source of covariance for the power spectrum
on small scales, and it can potentially be important for the bispectrum
covariance as well. In this paper, using the response function formalism, we
model the supersample covariance contributions to the bispectrum covariance and
the cross covariance between the power spectrum and the bispectrum. The
supersample covariances due to the long wavelength density and tidal
perturbations are investigated, and the tidal contribution is a few orders of
magnitude smaller than the density one because in configuration space the
bispectrum estimator involves angular averaging and the tidal response function
is anisotropic. The impact of the super-survey modes is quantified using
numerical measurements with periodic box and subbox setups. For the matter
bispectrum, the ratio between the supersample covariance correction and the
small scale covariance, which can be computed using a periodic box, is roughly
an order of magnitude smaller than that for the matter power spectrum. This is
because for the bispectrum, the small scale non-Gaussian covariance is
significantly larger than that for the power spectrum. For the cross
covariance, the supersample covariance is as important as for the power
spectrum covariance. The supersample covariance prediction with the halo model
response function is in good agreement with numerical results. |
Mass Function Predictions Beyond LCDM: The mass distribution of halos, as specified by the halo mass function, is a
key input for several cosmological probes. The sizes of $N$-body simulations
are now such that, for the most part, results need no longer be
statistics-limited, but are still subject to various systematic uncertainties.
We investigate and discuss some of the reasons for these differences.
Quantifying error sources and compensating for them as appropriate, we carry
out a high-statistics study of dark matter halos from 67 $N$-body simulations
to investigate the mass function and its evolution for a reference $\Lambda$CDM
cosmology and for a set of $w$CDM cosmologies. For the reference $\Lambda$CDM
cosmology (close to WMAP5), we quantify the breaking of universality in the
form of the mass function as a function of redshift, finding an evolution of as
much as 10% away from the universal form between redshifts $z=0$ and $z=2$. For
cosmologies very close to this reference we provide a fitting formula to our
results for the (evolving) $\Lambda$CDM mass function over a mass range of
$6\cdot 10^{11}-3\cdot 10^{15}$ M$_{\odot}$ to an estimated accuracy of about
2%. The set of $w$CDM cosmologies is taken from the Coyote Universe simulation
suite. The mass functions from this suite (which includes a $\Lambda$CDM
cosmology and others with $w\simeq-1$) are described by the fitting formula for
the reference $\Lambda$CDM case at an accuracy level of 10%, but with clear
systematic deviations. We argue that, as a consequence, fitting formulae based
on a universal form for the mass function may have limited utility in high
precision cosmological applications. | Results from EDGES High-Band: III. New Constraints on Parameters of the
Early Universe: We present new constraints on parameters of cosmic dawn and the epoch of
reionization derived from the EDGES High-Band spectrum ($90-190$ MHz). The
parameters are probed by evaluating global $21$ cm signals generated with the
recently developed Global21cm tool. This tool uses neural networks trained and
tested on $\sim 30,000$ spectra produced with semi-numerical simulations that
assume the standard thermal evolution of the cosmic microwave background and
the intergalactic medium. From our analysis, we constrain at $68\%$ (1) the
minimum virial circular velocity of star-forming halos to $V_{\rm c}<19.3$ km
s$^{-1}$, (2) the X-ray heating efficiency of early sources to $f_{\rm
X}>0.0042$, and (3) the low-energy cutoff of the X-ray spectral energy
distribution to $\nu_{\rm min}<2.3$ keV. We also constrain the star-formation
efficiency ($f_*$), the electron scattering optical depth ($\tau_{\rm e}$), and
the mean-free path of ionizing photons ($R_{\rm mfp}$). We re-compute the
constraints after incorporating into the analysis four estimates for the
neutral hydrogen fraction from high-$z$ quasars and galaxies, and a prior on
$\tau_{\rm e}$ from Planck $2018$. The largest impact of the external
observations is on the parameters that most directly characterize reionization.
Specifically, we derive the combined $68\%$ constraints $\tau_{\rm e}<0.063$
and $R_{\rm mfp}>27.5$ Mpc. The external observations also have a significant
effect on $V_{\rm c}$ due to its degeneracy with $\tau_{\rm e}$, while the
constraints on $f_*$, $f_{\rm X}$, and $\nu_{\rm min}$, remain primarily
determined by EDGES. |
Lepton Flavour Asymmetries and the Mass Spectrum of Primordial Black
Holes: We study the influence of lepton flavour asymmetries on the formation and the
mass spectrum of primordial black holes. We estimate the detectability of their
mergers with LIGO/Virgo and show that the currently published gravitational
wave events may actually be described by a primordial black hole spectrum from
non-zero asymmetries. We suggest to use gravitational-wave astronomy as a novel
tool to probe how lepton flavour asymmetric the Universe has been before the
onset of neutrino oscillations. | Direct Detections of Young Stars in Nearby Elliptical Galaxies: Small amounts of star formation in elliptical galaxies are suggested by
several results: surprisingly young ages from optical line indices, cooling
X-ray gas, and mid-IR dust emission. Such star formation has previously been
difficult to directly detect, but using UV Hubble Space Telescope (HST) Wide
Field Camera 3 (WFC3) imaging, we have identified individual young stars and
star clusters in four nearby ellipticals. This technique is orders of magnitude
more sensitive than other methods, allowing detections of star formation to
10^(-5) Msun/yr. Ongoing star formation is detected in all galaxies, including
three ellipticals that have previously exhibited potential signposts of star
forming conditions (NGC 4636, NGC 4697, and NGC 4374), as well as the typical
"red and dead" NGC 3379. The current star formation in our closest targets,
where we are most complete, is between 1-8x10^(-5) Msun/yr. The star formation
history was roughly constant from 0.5-1.5 Gyr (at 3-5x10^(-4) Msun/yr), but
decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a
mass between 10^2 - 10^4 Msun. The specific star formation rates of ~10^(-16)
yr^(-1) (at the present day) or ~10^(-14) yr^(-1) (when averaging over the past
Gyr) imply that a fraction 10^(-8) of the stellar mass is younger than 100 Myr
and 10^(-5) is younger than 1 Gyr, quantifying the level of frosting of recent
star formation over the otherwise passive stellar population. There is no
obvious correlation between either the presence or spatial distribution of
postulated star formation indicators and the star formation we detect. |
IDCS J1426.5+3508: Sunyaev-Zel'dovich Measurement of a Massive
IR-selected Cluster at z=1.75: We report 31 GHz CARMA observations of IDCS J1426.5+3508, an
infrared-selected galaxy cluster at z = 1.75. A Sunyaev-Zel'dovich decrement is
detected towards this cluster, indicating a total mass of M200 = (4.3 +/- 1.1)
x 10^{14} Msun in agreement with the approximate X-ray mass of ~5 x 10^{14}
Msun. IDCS J1426.5+3508 is by far the most distant cluster yet detected via the
Sunyaev-Zel'dovich effect, and the most massive z >= 1.4 galaxy cluster found
to date. Despite the mere ~1% probability of finding it in the 8.82 deg^2 IRAC
Distant Cluster Survey, IDCS J1426.5+3508 is not completely unexpected in LCDM
once the area of large, existing surveys is considered. IDCS J1426.5+3508 is,
however, among the rarest, most extreme clusters ever discovered, and indeed is
an evolutionary precursor to the most massive known clusters at all redshifts.
We discuss how imminent, highly sensitive Sunyaev-Zel'dovich experiments will
complement infrared techniques for statistical studies of the formation of the
most massive galaxy clusters in the z > 1.5 Universe, including potential
precursors to IDCS J1426.5+3508. | Principal Components of CMB non-Gaussianity: The skew-spectrum statistic introduced by Munshi & Heavens (2010) has
recently been used in studies of non-Gaussianity from diverse cosmological data
sets including the detection of primary and secondary non-Gaussianity of Cosmic
Microwave Background (CMB) radiation. Extending previous work, focussed on
independent estimation, here we deal with the question of joint estimation of
multiple skew-spectra from the same or correlated data sets. We consider the
optimum skew-spectra for various models of primordial non-Gaussianity as well
as secondary bispectra that originate from the cross-correlation of secondaries
and lensing of CMB: coupling of lensing with the Integrated Sachs-Wolfe (ISW)
effect, coupling of lensing with thermal Sunyaev-Zeldovich (tSZ), as well as
from unresolved point-sources (PS). For joint estimation of various types of
non-Gaussianity, we use the PCA to construct the linear combinations of
amplitudes of various models of non-Gaussianity, e.g. $f^{\rm loc}_{\rm
NL},f^{\rm eq}_{\rm NL},f^{\rm ortho}_{\rm NL}$ that can be estimated from CMB
maps. Bias induced in the estimation of primordial non-Gaussianity due to
secondary non-Gaussianity is evaluated. The PCA approach allows one to infer
approximate (but generally accurate) constraints using CMB data sets on any
reasonably smooth model by use of a lookup table and performing a simple
computation. This principle is validated by computing constraints on the DBI
bispectrum using a PCA analysis of the standard templates. |
Future constraints on the gravitational slip with the mass profiles of
galaxy clusters: The gravitational slip parameter is an important discriminator between large
classes of gravity theories at cosmological and astrophysical scales. In this
work we use a combination of simulated information of galaxy cluster mass
profiles, inferred by Strong+Weak lensing analyses and by the study of the
dynamics of the cluster member galaxies, to reconstruct the gravitational slip
parameter $\eta$ and predict the accuracy with which it can be constrained with
current and future galaxy cluster surveys. Performing a full-likelihood
statistical analysis, we show that galaxy cluster observations can constrain
$\eta$ down to the percent level already with a few tens of clusters. We
discuss the significance of possible systematics, and show that the cluster
masses and numbers of galaxy members used to reconstruct the dynamics mass
profile have a mild effect on the predicted constraints. | Influence of the Environment on PAH Emission in Star-Forming Regions: We investigate the emission properties of polycyclic aromatic hydrocarbons
(PAHs) in various metallicity environments with the Infrared Spectrograph on
board Spitzer. Local giant HII regions are used as references as they enable
access to the distinct interstellar medium components that contribute to the
mid-infrared spectrum of star-forming galaxies: photodissociation regions
(PDRs), photoionized gas, stellar clusters, and embedded regions. Three objects
are considered, NGC3603 in the Milky Way, 30Doradus in the Large Magellanic
Cloud, and N66 in the Small Magellanic Cloud. From the variations of the
PAH/14um ratio, we find that PAHs are destroyed in the ionized gas for a
radiation field such that [NeIII]/[NeII]>3. From the variations of the
PAH/Hu-alpha ratio, we find that the PAH emission sources in the giant HII
regions follow the same photodestruction law regardless of metallicity. We then
compare these results with observations of starburst galaxies, HII galaxies,
and blue compact dwarf galaxies (BCDs). While the integrated mid-infrared
spectra of BCDs are reminiscent of a warm dusty ionized gas, we observe a
significant contribution to the PAH emission in starburst galaxies that is not
arising from PDRs. |
Neutral Hydrogen Tully Fisher Relation: The case for Newtonian Gravity: Intrinsic luminosities are related to rotation velocities of disk galaxies by
Tully Fisher (TF) relations. The Baryonic TF (BTF) relation has recently been
explained with Dark Matter and Newtonian Gravity as well as Modified Newtonian
Dynamics (MOND). However, recent work has pointed out that the currently used
BTF relation ignores the contribution from hot gas and oversimplifies complex
galaxy-scale physics. In this Letter, we advocate the use of the Neutral
Hydrogen TF (HITF) relationship, which is free from dust obscuration and
stellar evolution effects, as a clean probe of gravity and dynamics in the weak
field regime. We incorporate the physics of hot gas from supernova feedback
which drives the porosity of the Interstellar Medium (ISM). A simple model that
includes supernovae feedback, is generalized to include a parametrized
effective gravitational force law. We test our model against a catalogue of
galaxies, spanning the full range of disks from dwarf galaxies to giant
spirals, to demonstrate that a Kennicutt-Schmidt (KS) law for star formation
and simple Newtonian gravity is adequate for explaining the observed HI scaling
relations. The data rules out MOND-like theories, within the scope of this
model. | Implications of hydrodynamical simulations for the interpretation of
direct dark matter searches: In recent years, realistic hydrodynamical simulations of galaxies like the
Milky Way have become available, enabling a reliable estimate of the dark
matter density and velocity distribution in the Solar neighborhood. We review
here the status of hydrodynamical simulations and their implications for the
interpretation of direct dark matter searches. We focus in particular on: the
criteria to identify Milky Way-like galaxies; the impact of baryonic physics on
the dark matter velocity distribution; the possible presence of substructures
like clumps, streams, or dark disks; and on the implications for the direct
detection of dark matter with standard and non-standard interactions. |
Gravitational waves from cosmological phase transitions: I discuss the generation of a stochastic background of gravitational waves
during a first order phase transition. I present simple general arguments which
explain the main features of the gravitational wave spectrum like the $k^3$
power law growth on large scales and a estimate for the peak amplitude. In the
second part I concentrate on the electroweak phase transition and argue that
the nucleosynthesis bound on its gravitational wave background seriously limits
seed magnetic fields which may have been generated during this transition. | Planck Early Results XXVI: Detection with Planck and confirmation by
XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive
galaxy cluster at z~1: We present first results on PLCK G266.6-27.3, a galaxy cluster candidate
detected at a signal-to-noise ratio of 5 in the Planck All Sky survey. An
XMM-Newton validation observation has allowed us to confirm that the candidate
is a bona fide galaxy cluster. With these X-ray data we measure an accurate
redshift, z = 0.94 +/- 0.02, and estimate the cluster mass to be M_500 = (7.8
+/- 0.8)e+14 solar masses. PLCK G266.6-27.3 is an exceptional system: its
luminosity of L_X(0.5-2.0 keV)=(1.4 +/- 0.05)e+45 erg/s, equals that of the two
most luminous known clusters in the z > 0.5 universe, and it is one of the most
massive clusters at z~1. Moreover, unlike the majority of high-redshift
clusters, PLCK G266.6-27.3 appears to be highly relaxed. This observation
confirms Planck's capability of detecting high-redshift, high-mass clusters,
and opens the way to the systematic study of population evolution in the
exponential tail of the mass function. |
Cosmic Magnetic Fields: from Stars and Galaxies to the Primordial
Universe: Most of the baryonic matter in the Universe is permeated by magnetic fields
which affect many, if not most, of astrophysical phenomena both, in compact
sources and in diffuse gas. Recent years have been marked by a worldwide surge
of interest in the astrophysical magnetic fields, their origin, and their
influence on the formation and evolution of astrophysical objects (stars,
galaxies, cooling flows). This growing interest is in part due to the fact that
it has become possible to trace magnetic fields in molecular clouds, over vast
extensions of the Milky Way and to study extragalactic magnetic fields,
including fields in clusters of galaxies. With the combination of various
techniques, such as Zeeman and Faraday rotation measurements with synchrotron
and aligned grain polarimetry, it is now possible to undertake quantitative
observational studies of magnetic fields, the results of which can be compared
with high resolution dynamo and MHD turbulence simulations. This brings the
field to a new stage.
In this paper, I will briefly review the importance of the cosmic magnetic
fields both from a theoretical and from an observational perspective, focusing
on their role in stellar and compact objects, in the interstellar medium and
star formation regions, and in galaxies, clusters of galaxies, and the
primordial Universe. | Microwave and radio emission of dusty star-forming galaxies: Implication
for the cosmic radio background: We use the most up-to-date cosmological evolution models of star-forming (SF)
galaxies and radio sources to compute the extragalactic number counts and the
cosmic background from 408MHz to 12THz. The model of SF galaxies reproduces the
constraints obtained by Spitzer, Herschel, and ground-based submm/mm
experiments: number counts, redshift distribution of galaxies, cosmic
background intensity and anisotropies. The template SEDs of this model are
extrapolated to the radio adding synchrotron, free-free, and spinning dust
emissions. To fix the synchrotron intensity, we use the IR/radio flux ratio,
q70, and a spectral index beta=-3. For a constant q70, our model added to the
AGN contribution provides a good fit to the number counts from 12THz to 408MHz
and to the CIB. Spinning dust accounts for up to 20% of the cosmic microwave
background produced by SF galaxies, but for less than 10% of the total
background when AGN are included. The SF galaxies account for 77.5% of the
number counts at 1.4GHz for a flux of 1e-4Jy. However, the model does not
explain the CRB measured with the ARCADE2 experiment. Considering the case when
q70 decreases strongly with redshift, this still does not explain the ARCADE2
results. It also yields to an overestimate of the low-flux number counts in the
radio. Thus, we rule out a steep variation of q70 with redshift at least for
z<3.5. Adding a population of faint SF galaxies at high redshift (Lir<1e11Lsun
and 4<z<6), which would reproduce the ARCADE2 results, leads to predictions of
the CIB much higher than what is observed, ruling out this as the explanation
for the ARCADE2 results. Considering our findings and previous studies, we
conclude that if the radio emission measured by ARCADE2 is astrophysical in
origin, it has to originate in the Galaxy or in a new kind of radio sources
(with no mid- to far-IR counterparts) or emission mechanism still to be
discovered. |
The Influence of AGN Feedback on Galaxy Cluster Observables: Galaxy clusters are valuable cosmological probes. However, cluster mass
estimates rely on observable quantities that are affected by complicated
baryonic physics in the intracluster medium (ICM), including feedback from
active galactic nuclei (AGN). Cosmological simulations have started to include
AGN feedback using subgrid models. In order to make robust predictions, the
systematics of different implementations and parametrizations need to be
understood. We have developed an AGN subgrid model in FLASH that supports a few
different black hole accretion models and feedback models. We use this model to
study the effect of AGN on X-ray cluster observables and its dependence on
model variations. | Extracting key information from spectroscopic galaxy surveys: We develop a novel method to extract key cosmological information, which is
primarily carried by the baryon acoustic oscillations and redshift space
distortions, from spectroscopic galaxy surveys based on a joint principal
component analysis (PCA) and massive optimized parameter estimation and data
compression (MOPED) algorithm. We apply this method to galaxy samples from BOSS
DR12, and find that a PCA manipulation is effective at extracting the
informative modes in the 2D correlation function, giving a tighter constraint
on BAO and RSD parameters compared to that using the lowest three multipole
moments by the traditional method; i.e. the Figure of Merit of BAO and RSD
parameters is improved by $\sim20\%$. We then perform a compression of the
informative PC modes for BAO and RSD parameters using the MOPED scheme,
reducing the dimension of the data vector to the number of interesting
parameters, manifesting the joint PCA and MOPED as a powerful tool for
clustering analysis with almost no loss of constraining power. |
Metallicity effects in the spectral classification of O-type stars.
Theoretical consideration: Based on an exteded grid of NLTE, line blanketed model atmospheres with
stellar winds as calculated by means of FASTWIND, we have investigated the
change in the strengths of strategic Helium transitions in the optical as
caused by a 0.3 decrease in metallicity with respect to solar abundances. Our
calculations predict that only part of the observed increase in Teff, of O-type
dwarfs could be explained by metallicity effects on the spectral type
indicators, while the rest must be attributed to other reasons (e.g., different
stellar structures as a function of metallicity or differences between observed
and theoretical wind parameters etc.). In addition, we found that using the He
II 4686 line to classify stars in low metallicity environments (Z < 0.3 solar)
might artificially increase the number of low luminosity (dwarfs and giants)
O-stars, on the expense of the number of O-supergiants. | Prospects for Delensing the Cosmic Microwave Background for Studying
Inflation: A detection of excess cosmic microwave background (CMB) B-mode polarization
on large scales allows the possibility of measuring not only the amplitude of
these fluctuations but also their scale dependence, which can be parametrized
as the tensor tilt $n_T$. Measurements of this scale dependence will be
hindered by the secondary B-mode polarization anisotropy induced by
gravitational lensing. Fortunately, these contaminating B modes can be
estimated and removed with a sufficiently good estimate of the intervening
gravitational potential and a good map of CMB E-mode polarization. We present
forecasts for how well these gravitational lensing B modes can be removed,
assuming that the lensing potential can be estimated either internally from CMB
data or using maps of the cosmic infrared background (CIB) as a tracer. We find
that CIB maps are as effective as CMB maps for delensing at the noise levels of
the current generation of CMB experiments, while the CMB maps themselves will
ultimately be best for delensing at polarization noise below $\Delta_P$=1
$\mu$K-arcmin. At this sensitivity level, CMB delensing will be able to measure
$n_T$ to an accuracy of 0.02 or better, which corresponds to the tensor tilt
predicted by the consistency relation for single-field slow-roll models of
inflation with $r=0.2$. However, CIB-based delensing will not be sufficient for
constraining $n_T$ in simple inflationary models. |
Photometric Redshifts for Next-Generation Surveys: Photometric redshifts are essential in studies of both galaxy evolution and
cosmology, as they enable analyses of objects too numerous or faint for
spectroscopy. The Rubin Observatory, Euclid, and Roman Space Telescope will
soon provide a new generation of imaging surveys with unprecedented area
coverage, wavelength range, and depth. To take full advantage of these
datasets, further progress in photometric redshift methods is needed. In this
review, we focus on the greatest common challenges and prospects for
improvement in applications of photo-$z$'s to the next generation of surveys:
- Gains in $performance$ -- i.e., the precision of redshift estimates for
individual galaxies -- could greatly enhance studies of galaxy evolution and
some probes of cosmology.
- Improvements in $characterization$ -- i.e., the accurate recovery of
redshift $distributions$ of galaxies in the presence of uncertainty on
individual redshifts -- are urgently needed for cosmological measurements with
next-generation surveys.
- To achieve both of these goals, improvements in the scope and treatment of
the samples of spectroscopic redshifts which make high-fidelity photo-$z$'s
possible will also be needed.
For the full potential of the next generation of surveys to be reached, the
characterization of redshift distributions will need to improve by roughly an
order of magnitude compared to the current state of the art, requiring progress
on a wide variety of fronts. We conclude by presenting a speculative evaluation
of how photometric redshift methods and the collection of the necessary
spectroscopic samples may improve by the time near-future surveys are
completed. | SZ Scaling Relations of Galaxy Groups and Clusters Near the North
Ecliptic Pole: SZ scaling relations have been used to test the self-similar prediction for
massive galaxy clusters, but little attention has been given to individual
galaxy groups. We investigate the scaling relations of galaxy groups and
clusters near the North Ecliptic Pole using X-ray and SZ observations. This
region of the sky is where both the ROSAT and Planck satellites achieved their
deepest observations, permitting the investigation of lower mass systems. Our
sample consists of 62 X-ray detected groups and clusters, spanning a mass range
of $10^{13.4}M_{\odot}<~M_{500}<10^{15}M_{\odot}$ and redshifts of
$0.03\lesssim z \lesssim 0.82$. We extract the total SZ flux from unresolved
Planck data and estimate the fraction of the SZ flux within $R_{500}$ assuming
two different pressure profiles. The SZ scaling relations were derived using a
Bayesian technique that accounts for censored data. We find a power law slope
of $1.73^{+0.19}_{-0.18}$ for the $Y_{SZ}-M_{500}$ relation which is consistent
with the self-similar prediction of 5/3. The slope of $0.89^{+0.09}_{-0.08}$
for the $Y_{SZ}-L_{X,500}$ relation is in agreement with other observational
studies but not the self-similar prediction of 5/4, and the $Y_{SZ}-Y_{X}$
relation lies below the 1:1 relation when the slope is fixed to unity. The
determined scaling relations are dependent on the selected pressure profile, so
resolved data are needed to determine the effects of AGN feedback. In addition,
we find a number of potential cluster candidates in the Planck Compton maps
that were not identified in our X-ray sample. |
A Groundbased Imaging Study of Galaxies Causing DLA, subDLA, and LLS
Absorption in Quasar Spectra: We present results from a search for galaxies that give rise to damped Lyman
alpha (DLA), subDLA, and Lyman limit system (LLS) absorption at redshifts 0.1
~< z ~< 1 in the spectra of background quasars. The sample was formed from a
larger sample of strong MgII absorbers (W_0^(2796) >= 0.3 A) whose HI column
densities were determined by measuring the Ly-alpha line in HST UV spectra.
Photometric redshifts, galaxy colors, and proximity to the quasar sightline, in
decreasing order of importance, were used to identify galaxies responsible for
the absorption. Our sample includes 80 absorption systems for which the
absorbing galaxies have been identified, of which 54 are presented here for the
first time. The main results of this study are: (i) the surface density of
galaxies falls off exponentially with increasing impact parameter, b, from the
quasar sightline relative to a constant background of galaxies, with an
e-folding length of ~46 kpc. Galaxies with b >~ 100 kpc calculated at the
absorption redshift are statistically consistent with being unrelated to the
absorption system. (ii) log N(HI) is inversely correlated with b at the 3.0
sigma level of significance. DLA galaxies are found systematically closer to
the quasar sightline, by a factor of two, than are galaxies which give rise to
subDLAs or LLSs. The median impact parameter is 17.4 kpc for the DLA galaxy
sample, 33.3 kpc for the subDLA sample, and 36.4 kpc for the LLS sample. (iii)
Absorber galaxy luminosity relative to L*, L/L*, is not significantly
correlated with W_0^(2796), log N(HI), or b. (iv) DLA, subDLA, and LLS galaxies
comprise a mix of spectral types, but are inferred to be predominantly late
type galaxies based on their spectral energy distributions. The implications of
these results are discussed. (Abridged) | Testing the Cosmic Anisotropy with Supernovae Data: Hemisphere
Comparison and Dipole Fitting: The cosmological principle is one of the cornerstones in modern cosmology. It
assumes that the universe is homogeneous and isotropic on cosmic scales. Both
the homogeneity and the isotropy of the universe should be tested carefully. In
the present work, we are interested in probing the possible preferred direction
in the distribution of type Ia supernovae (SNIa). To our best knowledge, two
main methods have been used in almost all of the relevant works in the
literature, namely the hemisphere comparison (HC) method and the dipole fitting
(DF) method. However, the results from these two methods are not always
approximately coincident with each other. In this work, we test the cosmic
anisotropy by using these two methods with the Joint Light-Curve Analysis (JLA)
and simulated SNIa datasets. In many cases, both methods work well, and their
results are consistent with each other. However, in the cases with two (or even
more) preferred directions, the DF method fails while the HC method still works
well. This might shed new light on our understanding of these two methods. |
The invariant Twist of Magnetic Fields in the Relativistic Jets of
Active Galactic Nuclei: The origin of cosmic magnetic (B) fields remains an open question. It is
generally believed that very weak primordial B fields are amplified by dynamo
processes, but it appears unlikely that the amplification proceeds fast enough
to account for the fields presently observed in galaxies and galaxy clusters.
In an alternative scenario, cosmic B fields are generated near the inner edges
of accretion disks in Active Galactic Nuclei (AGNs) by azimuthal electric
currents due to the difference between the plasma electron and ion velocities
that arises when the electrons are retarded by interactions with photons. While
dynamo processes show no preference for the polarity of the (presumably random)
seed field that they amplify, this alternative mechanism uniquely relates the
polarity of the poloidal B field to the angular velocity of the accretion disk,
resulting in a unique direction for the toroidal B field induced by disk
rotation. Observations of the toroidal fields of 29 AGN jets revealed by
parsec-scale Faraday rotation measurements show a clear asymmetry that is
consistent with this model, with the probability that this asymmetry came about
by chance being less than 1%. This lends support to the hypothesis that the
Universe is seeded by B fields that are generated in AGN via this mechanism and
subsequently injected into intergalactic space by the jet outflows. | Mass and magnification maps for the Hubble Space Telescope Frontier
Fields clusters: implications for high redshift studies: Extending over three Hubble Space Telescope (HST) cycles, the Hubble Frontier
Fields (HFF) initiative constitutes the largest commitment ever of HST time to
the exploration of the distant Universe via gravitational lensing by massive
galaxy clusters. We here present models of the mass distribution in the six HFF
cluster lenses, derived from a joint strong- and weak-lensing analysis anchored
by a total of 88 multiple-image systems identified in existing HST data. The
resulting maps of the projected mass distribution and of the gravitational
magnification effectively calibrate the HFF clusters as gravitational
telescopes. Allowing the computation of search areas in the source plane, these
maps are provided to the community to facilitate the exploitation of
forthcoming HFF data for quantitative studies of the gravitationally lensed
population of background galaxies. Our models of the gravitational
magnification afforded by the HFF clusters allow us to quantify the
lensing-induced boost in sensitivity over blank-field observations and predict
that galaxies at $z>10$ and as faint as m(AB)=32 will be detectable, up to 2
magnitudes fainter than the limit of the Hubble Ultra Deep Field. |
Thermal Friction as a Solution to the Hubble and Large-Scale Structure
Tensions: Thermal friction offers a promising solution to the Hubble and the
large-scale structure (LSS) tensions. This additional friction acts on a scalar
field in the early universe and extracts its energy density into dark
radiation, the cumulative effect being similar to that of an early dark energy
(EDE) scenario. The dark radiation automatically redshifts at the minimal
necessary rate to improve the Hubble tension. On the other hand, the addition
of extra radiation to the Universe can improve the LSS tension. We explore this
model in light of cosmic microwave background (CMB), baryon acoustic
oscillation and supernova data, including the SH0ES $H_0$ measurement and the
Dark Energy Survey Y1 data release in our analysis. Our results indicate a
preference for the regime where the scalar field converts to dark radiation at
very high redshifts, asymptoting effectively to an extra self-interacting
radiation species rather than an EDE-like injection. In this limit, thermal
friction can ease both the Hubble and the LSS tensions, but not resolve them.
We find the source of this preference to be the incompatibility of the CMB data
with the linear density perturbations of the dark radiation when injected at
redshifts close to matter-radiation equality. | Rhapsody-G simulations I: the cool cores, hot gas and stellar content of
massive galaxy clusters: We present the Rhapsody-G suite of cosmological hydrodynamic AMR zoom
simulations of ten massive galaxy clusters at the $M_{\rm vir}\sim10^{15}\,{\rm
M}_\odot$ scale. These simulations include cooling and sub-resolution models
for star formation and stellar and supermassive black hole feedback. The sample
is selected to capture the whole gamut of assembly histories that produce
clusters of similar final mass. We present an overview of the successes and
shortcomings of such simulations in reproducing both the stellar properties of
galaxies as well as properties of the hot plasma in clusters. In our
simulations, a long-lived cool-core/non-cool core dichotomy arises naturally,
and the emergence of non-cool cores is related to low angular momentum major
mergers. Nevertheless, the cool-core clusters exhibit a low central entropy
compared to observations, which cannot be alleviated by thermal AGN feedback.
For cluster scaling relations we find that the simulations match well the
$M_{500}-Y_{500}$ scaling of Planck SZ clusters but deviate somewhat from the
observed X-ray luminosity and temperature scaling relations in the sense of
being slightly too bright and too cool at fixed mass, respectively. Stars are
produced at an efficiency consistent with abundance matching constraints and
central galaxies have star formation rates consistent with recent observations.
While our simulations thus match various key properties remarkably well, we
conclude that the shortcomings strongly suggest an important role for
non-thermal processes (through feedback or otherwise) or thermal conduction in
shaping the intra-cluster medium. |
TeV blazars and their distance: Recently, a new method to constrain the distance of blazars with unknown
redshift using combined observations in the GeV and TeV regimes has been
developed, with the underlying assumption that the Very High Energy (VHE)
spectrum corrected for the absorption of TeV photons by the Extragalactic
Background Light (EBL) via photon-photon interaction should still be softer
than the gamma-ray spectrum observed by Fermi/LAT. The constraints found are
related to the real redshifts by a simple linear relation, that has been used
to infer the unknown distance of blazars. The sample will be revised with the
up-to-date spectra in both TeV and GeV bands, the method tested with the more
recent EBL models and finally applied to the unknown distance blazars detected
at VHE. | Galaxy Alignments in Very X-ray Luminous Clusters at z>0.5: We present the results of a search for galaxy alignments in 12 galaxy
clusters at z>0.5, a statistically complete subset of the very X-ray luminous
clusters from the MAssive Cluster Survey (MACS). Using high-quality images
taken with the Hubble Space Telescope (HST) that render measurement errors
negligible, we find no radial galaxy alignments within 500 kpc of the cluster
centres for a sample of 545 spectroscopically confirmed cluster members. A
mild, but statistically insignificant trend favouring radial alignments is
observed within a radius of 200 kpc and traced to galaxies on the cluster red
sequence. Our results for massive clusters at z>0.5 are in stark contrast to
the findings of previous studies which find highly significant radial
alignments of galaxies in nearby clusters at z~0.1 out to at least half the
virial radius using imaging data from the SDSS. The discrepancy becomes even
more startling if radial alignment becomes more prevalent at decreasing
clustercentric distance, as suggested by both our and previous work. We
investigate and discuss potential causes for the disparity between our findings
based on HST images of clusters at z>0.5 and those obtained using groundbased
images of systems at z~0.1. We conclude that the most likely explanation is
either dramatic evolution with redshift (in the sense that radial alignments
are less pronounced in dynamically younger systems) or the presence of
systematic biases in the analysis of SDSS imaging data that cause at least
partly spurious alignment signals. |
Detection of a Companion Lens Galaxy using the Mid-infrared Flux Ratios
of the Gravitationally Lensed Quasar H1413+117: We present the first resolved mid-IR (11 micron) observations of the
four-image quasar lens H1413+117 using the Michelle camera on Gemini North. All
previous observations (optical, near-IR, and radio) of this lens show a "flux
anomaly," where the image flux ratios cannot be explained by a simple, central
lens galaxy. We attempt to reproduce the mid-IR flux ratios, which are
insensitive to extinction and microlensing, by modeling the main lens as a
singular isothermal ellipsoid. This model fails to reproduce the flux ratios.
However, we can explain the flux ratios simply by adding to the model a nearby
galaxy detected in the H-band by HST/NICMOS-NIC2. This perturbing galaxy lies
4.0" from the main lens and it has a critical radius of 0.63" +/- 0.02" which
is similar to that of the main lens, as expected from their similar H-band
fluxes. More remarkably, this galaxy is not required to obtain a good fit to
the system astrometry, so this represents the first clear detection of an
object through its effect on the image fluxes of a gravitational lens. This is
a parallel to the detections of visible satellites from astrometric anomalies,
and provides a proof of the concept of searching for substructure in galaxies
using anomalous flux ratios. | Assembly Bias & Redshift-Space Distortions: Impact on cluster dynamics
tests of general relativity: The redshift-space distortion (RSD) of galaxies surrounding massive clusters
is emerging as a promising testbed for theories of modified gravity.
Conventional applications of this method rely upon the assumption that the
velocity field in the cluster environment is uniquely determined by the cluster
mass profile. Yet, real dark matter halos in N-body simulations are known to
violate the assumption that virial mass determines the configuration space
distribution, an effect known as assembly bias. In this Letter, I show that
assembly bias in simulated dark matter halos also manifests in velocity space.
In the 1-10 Mpc environment surrounding a cluster, high-concentration "tracer"
halos exhibit a 10-20% larger pairwise-velocity dispersion profile relative to
low-concentration tracer halos of the same mass. This difference is comparable
to the size of the RSD signal predicted by f(R) models designed to account for
the cosmic acceleration. I use the age matching technique to study how
color-selection effects may influence the cluster RSD signal, finding a ~10%
effect due to redder satellites preferentially occupying higher mass halos, and
a ~5% effect due to assembly-biased colors of centrals. In order to use cluster
RSD measurements to robustly constrain modified gravity, we likely will need to
develop empirical galaxy formation models more sophisticated than any in the
current literature. |
Imprints of decaying dark matter on cosmic voids: The Standard Cosmological Model assumes that more than 85\% of matter is in
the form of collisionless and pressureless dark matter. Unstable decaying dark
matter has been proposed in the literature as an extension to the standard cold
dark matter model. In this paper we investigate a scenario when dark matter
decays and the resultant particle moves with respect to the dark matter. A
covariant hydrodynamical model is developed in which the decay is modeled by
the transfer of energy-momentum between two dark dust fluid components. We
parameterise the model in terms of the decay rate $\Gamma$ and injection
velocity $v_i$ of the resultant dark matter particles. We apply the framework
to study the evolution of cosmic voids which are environments with low content
of baryonic matter. Thus, unlike baryon-rich environments, voids provide an
opportunity to measure dark matter signals that are less contaminated by
complex baryonic processes. We find that the growth of S-type voids is modified
by the dark matter decay, leading to imprints at the present day. This paper
serves as a proof-of-concept that cosmic voids can be used to study dark mater
physics. We argue that future cosmological observations of voids should focus
on signs of reported features to either confirm or rule out the decaying dark
matter scenario. Lack of presence of reported features could put constraints of
the decay of dark matter in terms of $\Gamma > H_0^{-1}$ and $v_i<10$ km/s. | The influence of mergers on the cluster temperature function and
cosmological parameters derived from it: We develop a parameter-free analytic model to include the effects of mergers
into the theoretical modelling of the X-ray temperature function of galaxy
clusters. We include this description into our model for the cluster population
based on fluctuations of the gravitational potential, which avoids any
reference to mass. Comparisons with a numerical simulation reveal that the
theoretical model is in good agreement with the simulation results. We show
that building the model on the dynamics of spherical rather than ellipsoidal
collapse yields better results if emission-weighted temperatures are used,
while ellipsoidal collapse yields good agreement between model and simulation
for mass-weighted temperatures. Analysing two different samples of X-ray
clusters, we quantify the influence of mergers and a conversion between
different temperature definitions on the joint determination of Omega_m0 and
sigma_8. If effects of mergers are included, temperature functions based on
cluster masses and on the gravitational potential built on spherical collapse
are in good agreement with other cosmological probes without any conversion of
temperatures. |
Gravothermal Catastrophe with a Cosmological Constant: We investigate the effect of a cosmological constant on the gravothermal
catastrophe in the Newtonian limit. A negative cosmological constant acts as a
thermodynamic `destabilizer'. The Antonov radius gets smaller and the
instability occurs, not only for negative but also for positive energy values.
A positive cosmological constant acts as a `stabilizer' of the system, which,
in this case, exhibits a novel `reentrant behaviour'. In addition to the
Antonov radius we find a second critical radius, where an `inverse Antonov
transition' occurs; a series of local entropy maxima is restored. | A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows: I suggest that the main process that amplifies magnetic fields in cooling
flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main
processes that are behind the JEDD is the turbulence that is formed by the many
vortices formed in the inflation processes of bubbles, and the large scale
shear formed by the propagating jet. It is sufficient that a strong turbulence
exits in the vicinity of the jets and bubbles, just where the shear is large.
The typical amplification time of magnetic fields by the JEDD near the jets and
bubbles is approximately hundred million years. The amplification time in the
entire cooling flow region is somewhat longer. The vortices that create the
turbulence are those that also transfer energy from the jets to the
intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium
gas, and by exciting sound waves. The JEDD model adds magnetic fields to the
cyclical behavior of energy and mass in the jet-feedback mechanism (JFM) in
cooling flows. |
The Cosmological Parameters (2019): This is a review article for The Review of Particle Physics 2020 (aka the
Particle Data Book). It forms a compact review of knowledge of the cosmological
parameters at the end of 2019. Topics included are Parametrizing the Universe;
Extensions to the standard model; Probes; Bringing observations together;
Outlook for the future. | Galaxy and Mass Assembly (GAMA): Colour and luminosity dependent
clustering from calibrated photometric redshifts: We measure the two-point angular correlation function of a sample of
4,289,223 galaxies with r < 19.4 mag from the Sloan Digital Sky Survey as a
function of photometric redshift, absolute magnitude and colour down to M_r -
5log h = -14 mag. Photometric redshifts are estimated from ugriz model
magnitudes and two Petrosian radii using the artificial neural network package
ANNz, taking advantage of the Galaxy and Mass Assembly (GAMA) spectroscopic
sample as our training set. The photometric redshifts are then used to
determine absolute magnitudes and colours. For all our samples, we estimate the
underlying redshift and absolute magnitude distributions using Monte-Carlo
resampling. These redshift distributions are used in Limber's equation to
obtain spatial correlation function parameters from power law fits to the
angular correlation function. We confirm an increase in clustering strength for
sub-L* red galaxies compared with ~L* red galaxies at small scales in all
redshift bins, whereas for the blue population the correlation length is almost
independent of luminosity for ~L* galaxies and fainter. A linear relation
between relative bias and log luminosity is found to hold down to luminosities
L~0.03L*. We find that the redshift dependence of the bias of the L* population
can be described by the passive evolution model of Tegmark & Peebles (1998). A
visual inspection of a random sample of our r < 19.4 sample of SDSS galaxies
reveals that about 10 per cent are spurious, with a higher contamination rate
towards very faint absolute magnitudes due to over-deblended nearby galaxies.
We correct for this contamination in our clustering analysis. |
The Problem of Inertia in Friedmann Universes: In this paper we study the origin of inertia in a curved spacetime,
particularly the spatially flat, open and closed Friedmann universes. This is
done using Sciama's law of inertial induction, which is based on Mach's
principle, and expresses the analogy between the retarded far fields of
electrodynamics and those of gravitation. After obtaining covariant expressions
for electromagnetic fields due to an accelerating point charge in Friedmann
models, we adopt Sciama's law to obtain the inertial force on an accelerating
mass $m$ by integrating over the contributions from all the matter in the
universe. The resulting inertial force has the form $F = -kma$, where $k < 1 $
depends on the choice of the cosmological parameters such as $\Omega_{M}$,
$\Omega_{\Lambda}$, and $\Omega_{R}$ and is also red-shift dependent. | Warm dark matter does not do better than cold dark matter in solving
small-scale inconsistencies: Over the last decade, warm dark matter (WDM) has been repeatedly proposed as
an alternative scenario to the standard cold dark matter (CDM) one, potentially
resolving several disagreements between the CDM model and observations on small
scales. Here, we reconsider the most important CDM small-scale discrepancies in
the light of recent observational constraints on WDM. As a result, we find that
a conventional thermal (or thermal-like) WDM cosmology with a particle mass in
agreement with Lyman-$\alpha$ is nearly indistinguishable from CDM on the
relevant scales and therefore fails to alleviate any of the small-scale
problems. The reason for this failure is that the power spectrum of
conventional WDM falls off too rapidly. To maintain WDM as a significantly
different alternative to CDM, more evolved production mechanisms leading to
multiple dark matter components or a gradually decreasing small-scale power
spectrum have to be considered. |
The Layzer-Irvine Equation for Scalar-Tensor Theories: A Test of
Modified Gravity N-body Simulations: The Layzer-Irvine equation describes energy conservation for a pressure less
fluid interacting though quasi-Newtonian gravity in an expanding Universe. We
here derive a Layzer-Irvine equation for scalar field theories where the scalar
field is coupled to the matter fields, and show applications of this equation
by applying it to N-body simulations of modified gravity theories. There it can
be used as both a dynamical test of the accuracy of the solution and the
numerical implementation when solving the equation of motion. We also present
an equation that can be used as a new static test for an arbitrary matter
distribution. This allows us to test the N- body scalar field solver using a
matter distribution which resembles what we actually encounter in numerical
simulations. | CMB EB and TB cross-spectrum estimation via pseudo-spectrum techniques: We discuss methods for estimating EB and TB spectra of the Cosmic Microwave
Background anisotropy maps covering limited sky area. Such odd-parity
correlations are expected to vanish whenever parity is not broken. As this is
indeed the case in the standard cosmologies, any evidence to the contrary would
have a profound impact on our theories of the early Universe. Such correlations
could also become a sensitive diagnostic of some particularly insidious
instrumental systematics. In this work we introduce three different unbiased
estimators based on the so-called standard and pure pseudo-spectrum techniques
and later assess their performance by means of extensive Monte Carlo
simulations performed for different experimental configurations. We find that a
hybrid approach combining a pure estimate of B-mode multipoles with a standard
one for E-mode (or T) multipoles, leads to the smallest error bars for both EB
(or TB respectively) spectra as well as for the three other
polarization-related angular power spectra i.e. EE, BB and TE$. However, if
both E and B multipoles are estimated using the pure technique the loss of
precision for the EB spectrum is not larger than ~30%. Moreover, for the
experimental configurations considered here, the statistical uncertainties --
due to sampling variance and instrumental noise -- of the pseudo-spectrum
estimates is at most a factor ~1.4 for TT, EE and TE spectra and a factor ~2
for BB, TB and EB spectra, higher than the most optimistic Fisher estimate of
the variance. |
Gravitational Heating Helps Make Massive Galaxies Red and Dead: We study the thermal formation history of four simulated galaxies that were
shown in Naab et al. (2007) to reproduce a number of observed properties of
elliptical galaxies. The temperature of the gas in the galaxies is steadily
increasing with decreasing redshift, although much of the gas has a cooling
time shorter than the Hubble time. The gas is being heated and kept hot by
gravitational heating processes through the release of potential energy from
infalling stellar clumps. The energy is dissipated in supersonic collisions of
infalling gas lumps with the ambient gas and through the dynamical capturing of
satellite systems causing gravitational wakes that transfer energy to the
surrounding gas. Furthermore dynamical friction from the infalling clumps
pushes out dark matter, lowering the central dark matter density by up to a
factor of two from z=3 to z=0. In galaxies in which the late formation history
(z<2) is dominated by minor merging and accretion the energy released
(E~5x10^{59} ergs) from gravitational feedback is sufficient to form red and
dead elliptical galaxies by z~1 even in the absence of supernova and AGN
feedback. | Lifting the Veil of Dust from NGC 0959: The Importance of a Pixel-Based
2D Extinction Correction: We present the results of a study of the late-type spiral galaxy NGC 0959,
before and after application of the pixel-based dust extinction correction
described in Tamura et al. 2009 (Paper I). Galaxy Evolution Explorer (GALEX)
far-UV (FUV) and near-UV (NUV), ground-based Vatican Advanced Technology
Telescope (VATT) UBVR, and Spitzer/Infrared Array Camera (IRAC) 3.6, 4.5, 5.8,
and 8.0 micron images are studied through pixel Color-Magnitude Diagrams
(pCMDs) and pixel Color-Color Diagrams (pCCDs). We define groups of pixels
based on their distribution in a pCCD of (B - 3.6 micron) versus (FUV - U)
colors after extinction correction. In the same pCCD, we trace their locations
before the extinction correction was applied. This shows that selecting pixel
groups is not meaningful when using colors uncorrected for dust. We also trace
the distribution of the pixel groups on a pixel coordinate map of the galaxy.
We find that the pixel-based (two-dimensional) extinction correction is crucial
to reveal the spatial variations in the dominant stellar population, averaged
over each resolution element. Different types and mixtures of stellar
populations, and galaxy structures such as a previously unrecognized bar,
become readily discernible in the extinction-corrected pCCD and as coherent
spatial structures in the pixel coordinate map. |
Parity in Planck full-mission CMB temperature maps: In the standard model of cosmology, Cosmic Microwave Background (CMB) sky is
expected to show no symmetry preferences. Following our previous studies, we
explore the presence of any particular parity preference in the latest
full-mission CMB temperature maps from ESA's Planck probe. Specifically, in
this work, we will probe (a)symmetry in power between even and odd multipoles
of CMB via it's angular power spectrum from Planck 2015 data. Further we also
assess any specific preference for mirror parity (a)symmetry, by analysing the
power contained in $l+m$=even or odd mode combinations. | Debiasing Standard Siren Inference of the Hubble Constant with Marginal
Neural Ratio Estimation: Gravitational wave (GW) standard sirens may resolve the Hubble tension,
provided that standard siren inference of $H_0$ is free from systematic biases.
However, standard sirens from binary neutron star (BNS) mergers suffer from two
sources of systematic bias, one arising from the anisotropy of GW emission, and
the other from the anisotropy of electromagnetic (EM) emission from the
kilonova. For an observed sample of BNS mergers, the traditional Bayesian
approach to debiasing involves the direct computation of the detection
likelihood. This is infeasible for large samples of detected BNS merger due to
the high dimensionality of the parameter space governing merger detection. In
this study, we bypass this computation by fitting the Hubble constant to
forward simulations of the observed GW and EM data under a simulation-based
inference (SBI) framework using marginal neural ratio estimation. A key
innovation of our method is the inclusion of BNS mergers which were only
detected in GW, which allows for estimation of the bias introduced by EM
anisotropy. Our method corrects for $\sim$90$\%$ of the bias in the inferred
value of $H_0$ when telescope follow-up observations of BNS mergers have
extensive tiling of the merger localization region, using known telescope
sensitivities and assuming a model of kilonova emission. Our SBI-based method
thus enables a debiased inference of the Hubble constant of BNS mergers,
including both mergers with detected EM counterparts and those without. |
The X-ray to optical-UV luminosity ratio of X-ray selected Type 1 AGN in
XMM-COSMOS: We present a study of the X-ray to optical properties of a sample of 545
X-ray selected Type 1 AGN, from the XMM-COSMOS survey, over a wide range of
redshifts ($0.04<\z<4.25$) and X-ray luminosities ($40.6 \leq \Log \Lhard \leq
45.3$). About 60% of them are spectroscopically identified Type 1 AGN, while
the others have a reliable photometric redshift and are classified as Type 1
AGN on the basis of their multi-band Spectral Energy Distributions. We discuss
the relationship between UV and X-ray luminosity, as parameterized by the
$\alphaox$ spectral slope, and its dependence on redshift and luminosity. We
compare our findings with previous investigations of optically selected
broad-line AGN (mostly from SDSS). A highly significant correlation between
$\alphaox$ and $\lo$ is found, in agreement with previous investigations of
optically selected samples. We calculate bolometric corrections, $\kbol$, for
the whole sample using hard X-ray luminosities ($\Lhard$), and the Eddington
ratios for a subsample of 150 objects for which black hole mass estimates are
available. We confirm the trend of increasing bolometric correction with
increasing Eddington ratio as proposed in previous works. A tight correlation
is found between $\alphaox$ and $\kbol$, which can be used to estimate accurate
bolometric corrections using only optical and X-ray data. We find a significant
correlation between $\alphaox$ and Eddington ratio, in which $\alphaox$
increases for increasing Eddington ratios. | Dry minor mergers and size evolution of high-z compact massive
early-type galaxies: Recent observations show evidence that high-z (z\sim 2 - 3) early-type
galaxies (ETGs) are more compact than those with comparable mass at z\sim 0.
Such a size evolution is most likely explained by the `Dry Merger Sceanario'.
However, previous studies based on this scenario are not able to consistantly
explain both the properties of the high-z compact massive ETGs and the local
ETGs. We investigate the effect of multiple sequential dry minor mergers on the
size evolution of the compact massive ETGs. From an analysis of the Millennium
Simulation Database, we show that such minor (stellar mass ratio $M_{2}/M_{1} <
1/4$) mergers are extremely common during hierarchical structure formation. We
perform N-body simulations of sequential minor mergers with parabolic and
head-on orbits, including a dark matter component and a stellar component.
Typical mass ratios of the minor mergers are $1/20 < M_{2}/M_{1} < 1/10$. We
show that sequential minor mergers of compact satellite galaxies are the most
efficient at promoting size growth and decreasing the velocity dispersion of
the compact massive ETGs in our simulations. The change of stellar size and
density of the merger remnants is consistent with recent observations.
Furthermore, we construct the merger histories of candidates for the high-z
compact massive ETGs using the Millennium Simulation Database, and estimate the
size growth of the galaxies by the dry minor merger scenario. We can reproduce
the mean size growth factor between $z=2$ and $z=0$, assuming the most
efficient size growth obtained during sequential minor mergers in our
simulations. However, we note that our numerical result is only valid for
merger histories with typical mass ratios between 1/20 and 1/10 with parabolic
and head-on orbits, and that our most efficient size growth efficiency is
likely to an upper limit. |
Scaling relations of the slightly self-interacting cold dark matter in
galaxies and clusters: Recent observations in galaxies and clusters indicate dark matter density
profiles exhibit core-like structures which contradict to the numerical
simulation results of collisionless cold dark matter. The idea of
self-interacting cold dark matter (SICDM) has been invoked to solve the
discrepancies between the observations and numerical simulations. In this
article, I derive some important scaling relations in galaxies and clusters by
using the long-range SICDM model. These scaling relations give good agreements
with the empirical fittings from observational data in galaxies and clusters if
the dark matter particles are only slightly self-interacting. Also, there may
exist a universal critical optical depth $\tau_c$ that characterizes the
core-like structures. These results generally support the idea of SICDM to
tackle the long-lasting dark matter problem. | Unfolding the matter distribution using 3-D weak gravitational lensing: Combining redshift and galaxy shape information offers new exciting ways of
exploiting the gravitational lensing effect for studying the large scales of
the cosmos. One application is the three-dimensional reconstruction of the
matter density distribution which is explored in this paper. We give a
generalisation of an already known minimum-variance estimator of the 3-D matter
density distribution that facilitates the combination of thin redshift slices
of sources with samples of broad redshift distributions for an optimal
reconstruction. We show how, in principle, intrinsic alignments of source
ellipticities or shear/intrinsic alignment correlations can be accommodated,
albeit these effects are not the focus of this paper. We describe an efficient
and fast way to implement the estimator on a contemporary desktop computer.
Analytic estimates for the noise and biases in the reconstruction are given.
The bias -- a spread and shift of structures in radial direction -- can be
expressed in terms of a radial PSF, comprising the limitations of the
reconstruction due to source shot-noise and the unavoidably broad lensing
kernel. We conclude that a 3-D mass-density reconstruction on galaxy cluster
scales is feasible but, for foreseeable surveys, a map with a S/N>~3 threshold
is limited to structures with M200>~10^14 Msol/h, or 7x10^14 Msol/h, at low to
moderate redshifts (z=0.1 or 0.6). However, we find that a heavily smoothed
full-sky map of the very large-scale density field may also be possible as the
S/N of reconstructed modes increases towards larger scales. Future improvements
of the method can be obtained by including higher-order lensing information
(flexion) which could also be implemented into our algorithm. [ABRIDGED] |
The Redshift and Mass Dependence on the Formation of The Hubble Sequence
at z>1 from CANDELS/UDS: In this paper we present a detailed study of the structures and morphologies
of a sample of 1188 massive galaxies with Mstar>10^10Msun between redshifts
z=1-3 within the Ultra Deep Survey (UDS) region of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this
sample we determine how galaxy structure and morphology evolve with time. We
visually classify our sample into disks, ellipticals and peculiar systems and
correct for redshift effects on our classifications through simulations. We
find evolution in the fractions of galaxies at a given visual classification as
a function of redshift. The peculiar population is dominant at z>2 with a
substantial spheroid population, and a negligible disk population. We compute
the transition redshift, ztrans, where the combined fraction of spheroids and
disks is equal to that of peculiar galaxies, as ztrans=1.86+/-0.62 for galaxies
in our stellar mass range. We find that this changes as a function of stellar
mass, with Hubble-type systems becoming dominant at higher redshifts for higher
mass galaxies (ztrans=2.22+/-0.82), than for the lower mass galaxies
(ztrans=1.73+/-0.57). Higher mass galaxies become morphologically settled
before their lower mass counterparts, a form of morphological downsizing. We
furthermore compare our visual classifications with Sersic index, the
concentration, asymmetry and clumpiness (CAS) parameters, star formation rate
and rest frame U-B colour. We find links between the colour of a galaxy, its
star formation rate and how extended or peculiar it appears. Finally, we
discuss the negligible z>2 disk fraction based on visual morphologies and
speculate that this is an effect of forming disks appearing peculiar through
processes such as violent disk instabilities or mergers. We conclude that to
properly define high redshift morphology a new and more exact classification
scheme is needed. | Non-Linearity-Free prediction of the growth-rate $fσ_8$ using
Convolutional Neural Networks: The growth-rate $f\sigma_8(z)$ of the large-scale structure of the Universe
is an important dynamic probe of gravity that can be used to test for
deviations from General Relativity. However, in order for galaxy surveys to
extract this key quantity from cosmological observations, two important
assumptions have to be made: i) a fiducial cosmological model, typically taken
to be the cosmological constant and cold dark matter ($\Lambda$CDM) model and
ii) the modeling of the observed power spectrum from H$\alpha$ emitters,
especially at non-linear scales, which is particularly dangerous as most models
used in the literature are phenomenological at best. In this work, we propose a
novel approach involving convolutional neural networks (CNNs), trained on the
Quijote N-body simulations, to predict $f\sigma_8(z)$ directly and without
assuming a model for the non-linear part of the power spectrum, thus avoiding
the second of the aforementioned assumptions. We find that the predictions for
the value of $f\sigma_8$ from the CNN are in excellent agreement with the
fiducial values, while the errors are within a factor of order unity from those
of the traditionally optimistic Fisher matrix approach, assuming an ideal
fiducial survey matching the specifications of the Quijote simulations. Thus,
we find the CNN reconstructions provide a viable alternative in order to avoid
the theoretical modeling of the non-linearities at small scales when extracting
the growth-rate. |
Breaking of self-averaging properties and selection effects in the
Luminous Red Galaxies sample: We study the statistical properties of the Luminous Red Galaxies sample from
the Sloan Digital Sky Survey. In particular we test, by determining the
probability density function (PDF) of galaxy (conditional) counts in spheres,
whether statistical properties are self-averaging within the sample. We find
that there are systematic differences in the shape of the PDF and in the
location of its peak, signaling that there are major systematic effects in the
data which make the estimation of volume average quantities unreliable within
this sample. We discuss that these systematic effects are related to the
fluctuating behavior of the redshift counts which can be originated by
intrinsic fluctuations in the galaxy density field or by observational
selection effects. The latter possibility implies that more than 20 % of the
galaxies have not been observed and that such a selection should not be a
smooth function of redshift. | Physical Properties, Star Formation, and Active Galactic Nucleus
Activity in Balmer Break Galaxies at 0 < z < 1: We present a spectroscopic study with the derivation of the physical
properties of 37 Balmer break galaxies, which have the necessary lines to
locate them in star-forming-AGN diagnostic diagrams. These galaxies span a
redshift range from 0.045 to 0.93 and are somewhat less massive than similar
samples of previous works. The studied sample has multiwavelength photometric
data coverage from the ultraviolet to MIR Spitzer bands. We investigate the
connection between star formation and AGN activity via optical, mass-excitation
(MEx) and MIR diagnostic diagrams. Through optical diagrams, 31 (84%)
star-forming galaxies, 2 (5%) composite galaxies and 3 (8%) AGNs were
classified, whereas from the MEx diagram only one galaxy was classified as AGN.
A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands.
Of these, 3 AGN candidates were not classified as AGN in the optical diagrams,
suggesting they are dusty/obscured AGNs, or that nuclear star formation has
diluted their contributions. Furthermore, the relationship between SFR surface
density (\Sigma_{SFR}) and stellar mass surface density per time unit
(\Sigma_{M_{\ast}/\tau}) as a function of redshift was investigated using the
[OII] \lambda3727, 3729, H\alpha \lambda6563 luminosities, which revealed that
both quantities are larger for higher redshift galaxies. We also studied the
SFR and SSFR versus stellar mass and color relations, with the more massive
galaxies having higher SFR values but lower SSFR values than less massive
galaxies. These results are consistent with previous ones showing that, at a
given mass, high-redshift galaxies have on average larger SFR and SSFR values
than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values
than redder galaxies and for a given color the SSFR is larger for higher
redshift galaxies. |
The abundance of Bullet-groups in LCDM: We estimate the expected distribution of displacements between the two
dominant dark matter (DM) peaks (DM-DM displacements) and between DM and
gaseous baryon peak (DM-gas displacements) in dark matter halos with masses
larger than $10^{13}$ Msun/h. We use as a benchmark the observation of SL2S
J08544-0121, which is the lowest mass system ($1.0\times 10^{14}$ Msun/h)
observed so far featuring a bi-modal dark matter distribution with a dislocated
gas component. We find that $(50 \pm 10)$% of the dark matter halos with
circular velocities in the range 300 km/s to 700 km/s (groups) show DM-DM
displacements equal or larger than $186 \pm 30$ kpc/h as observed in SL2S
J08544-0121. For dark matter halos with circular velocities larger than 700
km/s (clusters) this fraction rises to 70 $\pm$ 10%. Using the same simulation
we estimate the DM-gas displacements and find that 0.1 to 1.0% of the groups
should present separations equal or larger than $87\pm 14$kpc/h corresponding
to our observational benchmark; for clusters this fraction rises to (7 $\pm$
3)%, consistent with previous studies of dark matter to baryon separations.
Considering both constraints on the DM-DM and DM-gas displacements we find that
the number density of groups similar to SL2S J08544-0121 is $\sim 6.0\times
10^{-7}$ Mpc$^{-3}$, three times larger than the estimated value for clusters.
These results open up the possibility for a new statistical test of LCDM by
looking for DM-gas displacements in low mass clusters and groups. | Chemical Evolution of Dwarf Irregular and Blue Compact Galaxies: Dwarf irregular and blue compact galaxies are very interesting objects since
they are relatively simple and unevolved. We present new models for the
chemical evolution of these galaxies by assuming different regimes of star
formation (bursting and continuous) and different kinds of galactic winds
(normal and metal-enhanced). Our results show that in order to reproduce all
the properties of these galaxies, including the spread in the chemical
abundances, the star formation should have proceeded in bursts and the number
of bursts should be not larger than 10 in each galaxy, and that metal-enhanced
galactic winds are required. A metal-enhanced wind efficiency increasing with
galactic mass can by itself reproduce the observed mass-metallicity relation
although also an increasing efficiency of star formation and/or number and/or
duration of bursts can equally well reproduce such a relation. Metal enhanced
winds together with an increasing amount of star formation with galactic mass
are required to explain most of the properties of these galaxies. Normal
galactic winds, where all the gas is lost at the same rate, do not reproduce
the features of these galaxies. We suggest that these galaxies should have
suffered a different number of bursts varying from 2 to 10 and that the
efficiency of metal-enhanced winds should have been not too high
($\lambda_{mw}\sim1$). We predict for these galaxies present time Type Ia SN
rates from 0.00084 and 0.0023 per century. Finally, by comparing the abundance
patterns of Damped Lyman-$\alpha$ objects with our models we conclude that they
are very likely the progenitors of the present day dwarf irregulars. (abridged) |
Measuring the temperature and profiles of Lyman-$α$ absorbers: The distribution of the absorption line broadening observed in the Ly$\alpha$
forest carries information about the temperature and widths of the filaments in
the intergalactic medium (IGM). In this work, we present and test a new method
for inferring the temperature of the IGM, the size of the absorbing filaments
and the photo-ionization rate of hydrogen from the properties of absorption
line broadening in the Ly$\alpha$ forest. We apply our method to mock spectra
from the reference model of the EAGLE cosmological simulation, and we
demonstrate that we are able to reconstruct the IGM properties. Our method
explicitly takes into account the degeneracy between IGM temperature, the
photo-ionization rate of hydrogen and the widths of the intergalactic
filaments. | Do current cosmological observations rule out all Covariant Galileons?: We revisit the cosmology of Covariant Galileon gravity in view of the most
recent cosmological data sets, including weak lensing. As a higher derivative
theory, Covariant Galileon models do not have a $\Lambda$CDM limit and predict
a very different structure formation pattern compared with the standard
$\Lambda$CDM scenario. Previous cosmological analyses suggest that this model
is marginally disfavoured, yet can not be completely ruled out. In this work we
use a more recent and extended combination of data, and we allow for more
freedom in the cosmology, by including a massive neutrino sector with three
different mass hierarchies. We use the Planck measurements of Cosmic Microwave
Background temperature and polarization; Baryonic Acoustic Oscillations
measurements by BOSS DR12; local measurements of $H_0$; the joint light-curve
analysis supernovae sample; and, for the first time, weak gravitational lensing
from the KiDS collaboration. We find, that in order to provide a reasonable
fit, a non-zero neutrino mass is indeed necessary, but we do not report any
sizable difference among the three neutrino hierarchies. Finally, the
comparison of the Bayesian Evidence to the $\Lambda$CDM one shows that in all
the cases considered, Covariant Galileon models are statistically ruled out by
cosmological data. |
A dynamical mass estimator for high z galaxies based on
spectroastrometry: Galaxy dynamical masses are important physical quantities to constrain galaxy
evolutionary models, especially at high redshifts. However, at z~2 the limited
signal to noise ratio and spatial resolution of the data usually do not allow
spatially resolved kinematical modeling and very often only virial masses can
be estimated from line widths. But even such estimates require a good knowledge
of galaxy size, which may be smaller than the spatial resolution.
Spectroastrometry is a technique which combines spatial and spectral resolution
to probe spatial scales significantly smaller than the spatial resolution of
the observations. Here we apply it to the case of high-z galaxies and present a
method based on spectroastrometry to estimate dynamical masses of high z
galaxies, which overcomes the problem of size determination with poor spatial
resolution. We construct and calibrate a "spectroastrometric" virial mass
estimator, modifying the "classical" virial mass formula. We apply our method
to the [O III] or H{\alpha} emission line detected in z~2-3 galaxies from
AMAZE, LSD and SINS samples and we compare the spectroastrometric estimator
with dynamical mass values resulting from full spatially resolved kinematical
modeling. The spectroastrometric estimator is found to be a good approximation
of dynamical masses, presenting a linear relation with a residual dispersion of
only 0.15 dex. This is a big improvement compared to the "classical" virial
mass estimator which has a non linear relation and much larger dispersion (0.47
dex) compared to dynamical masses. By applying our calibrated estimator to 16
galaxies from the AMAZE and LSD samples, we obtain masses in the ~10^7-10^10
M\odot range extending the mass range attainable with dynamical modeling. | The Hidden Mass and Large Spatial Extent of a Poststarburst Galaxy
Outflow: Outflowing winds of multiphase plasma have been proposed to regulate the
buildup of galaxies, but key aspects of these outflows have not been probed
with observations. Using ultraviolet absorption spectroscopy, we show that
"warm-hot" plasma at 10^{5.5} K contains 10-150 times more mass than the cold
gas in a poststarburst galaxy wind. This wind extends to distances >68
kiloparsecs, and at least some portion of it will escape. Moreover, the
kinematical correlation of the cold and warm-hot phases indicates that the
warm-hot plasma is related to the interaction of the cold matter with a hotter
(unseen) phase at >>10^{6} K. Such multiphase winds can remove substantial
masses and alter the evolution of poststarburst galaxies. |
Large-scale Motions in the Perseus Galaxy Cluster: By combining large-scale mosaics of ROSAT PSPC, XMM-Newton, and Suzaku X-ray
observations, we present evidence for large-scale motions in the intracluster
medium of the nearby, X-ray bright Perseus Cluster. These motions are suggested
by several alternating and interleaved X-ray bright, low-temperature,
low-entropy arcs located along the east-west axis, at radii ranging from ~10
kpc to over a Mpc. Thermodynamic features qualitatively similar to these have
previously been observed in the centers of cool core clusters, and were
successfully modeled as a consequence of the gas sloshing/swirling motions
induced by minor mergers. Our observations indicate that such sloshing/swirling
can extend out to larger radii than previously thought, on scales approaching
the virial radius. | The XXL Survey. XIII. Baryon content of the bright cluster sample: Traditionally, galaxy clusters have been expected to retain all the material
accreted since their formation epoch. For this reason, their matter content
should be representative of the Universe as a whole, and thus their baryon
fraction should be close to the Universal baryon fraction. We make use of the
sample of the 100 brightest galaxy clusters discovered in the XXL Survey to
investigate the fraction of baryons in the form of hot gas and stars in the
cluster population. We measure the gas masses of the detected halos and use a
mass--temperature relation directly calibrated using weak-lensing measurements
for a subset of XXL clusters to estimate the halo mass. We find that the
weak-lensing calibrated gas fraction of XXL-100-GC clusters is substantially
lower than was found in previous studies using hydrostatic masses. Our best-fit
relation between gas fraction and mass reads $f_{\rm
gas,500}=0.055_{-0.006}^{+0.007}\left(M_{\rm
500}/10^{14}M_\odot\right)^{0.21_{-0.10}^{+0.11}}$. The baryon budget of galaxy
clusters therefore falls short of the Universal baryon fraction by about a
factor of two at $r_{\rm 500}$. Our measurements require a hydrostatic bias
$1-b=M_X/M_{\rm WL}=0.72_{-0.07}^{+0.08}$ to match the gas fraction obtained
using lensing and hydrostatic equilibrium. Comparing our gas fraction
measurements with the expectations from numerical simulations, our results
favour an extreme feedback scheme in which a significant fraction of the
baryons are expelled from the cores of halos. This model is, however, in
contrast with the thermodynamical properties of observed halos, which might
suggest that weak-lensing masses are overestimated. We note that a mass bias
$1-b=0.58$ as required to reconcile Planck CMB and cluster counts should
translate into an even lower baryon fraction, which poses a major challenge to
our current understanding of galaxy clusters. [Abridged] |
Inflaton-driven early dark energy: By arranging the control parameters, we examine whether the mass varying
neutrino model PRD 103, 063540 (2021), enabling one to unify inflation with the
present dark energy, can be used for producing an early dark energy. The model
works in the following way. At early stages of the Big-Bang, the inflaton
trapped in the minimum at $\phi = 0$ gets uplifted due to interaction with
neutrinos and starts to roll down to one of the degenerate minima of the
effective potential and after a while gets anchored at this minimum, which in
turn evolves in time very slowly. Correspondingly, the early dark energy taking
place as a result of this dynamical symmetry breaking also varies in time very
slowly. Shortly before the recombination epoch, however, the symmetry is
restored and early dark energy disappears. A typical problem of the mass
varying neutrino models is that they can hardly provide the needed amount of
early dark energy at the tree-level because of smallness of neutrino masses.
Nevertheless, the quantum fluctuations of $\phi$ can do the job in providing
sufficient early dark energy under assumption that inflationary energy scale is
of the order of $1$\,TeV. Radiative as well as thermal corrections coming from
the neutrino sector do not affect the model significantly. As for the gravity
induced corrections to the effective potential - they can be safely ignored. | Daily modulation due to channeling in direct dark matter crystalline
detectors: The channeling of the ion recoiling after a collision with a WIMP in direct
dark matter crystalline detectors produces a larger scintillation or ionization
signal than otherwise expected. Channeling is a directional effect which
depends on the velocity distribution of WIMPs in the dark halo of our Galaxy
and could lead to a daily modulation of the signal. Here we compute upper
bounds to the expected amplitude of daily modulation due to channeling using
channeling fractions that we obtained with analytic models in prior work. After
developing the general formalism, we examine the possibility of finding a daily
modulation due to channeling in the data already collected by the DAMA/NaI and
DAMA/LIBRA experiments. We find that even the largest daily modulation
amplitudes (of the order of 10% in some instances) would not be observable for
WIMPs in the standard halo in the 13 years of data taken by the DAMA
collaboration. For these to be observable the DAMA total rate should be 1/40 of
what it is or the total DAMA exposure should be 40 times larger. The daily
modulation due to channeling will be difficult to measure in future
experiments. We find it could be observed for light WIMPs in solid Ne, assuming
no background. |
Reconstruction of cosmological matter perturbations in Modified Gravity: The analysis of perturbative quantities is a powerful tool to distinguish
between different Dark Energy models and gravity theories degenerated at the
background level. In this work, we generalise the integral solution of the
matter density contrast for General Relativity gravity to a wide class of
Modified Gravity (MG) theories. To calculate this solution is necessary prior
knowledge of the Hubble rate, the density parameter at the present epoch
($\Omega_{m0}$) and the functional form of the effective Newton's constant that
characterises the gravity theory. We estimate in a model-independent way the
Hubble expansion rate by applying a non-parametric reconstruction method to
model-independent cosmic chronometer data and high-$z$ quasar data. In order to
compare our generalised solution of the matter density contrast, using the
non-parametric reconstruction of $H(z)$ from observational data, with purely
theoretical one, we choose a parameterisation of the Screened MG and the
$\Omega_{m0}$ from WMAP-9 collaborations. Finally, we calculate the growth
index for the analysed cases, finding very good agreement between theoretical
values and the obtained ones using the approach presented in this work. | The Origins of AGN Obscuration: The 'Torus' as a Dynamical, Unstable
Driver of Accretion: Multi-scale simulations have made it possible to follow gas inflows onto
massive black holes (BHs) from galactic scales to the accretion disk. When
sufficient gas is driven towards the BH, gravitational instabilities
generically form lopsided, eccentric disks that propagate inwards. The lopsided
stellar disk exerts a strong torque on the gas disk, driving inflows that fuel
rapid BH growth. Here, we investigate whether the same gas disk is the 'torus'
invoked to explain obscured AGN. The disk is generically thick and has
characteristic ~1-10 pc sizes and masses resembling those required of the
torus. The scale heights and obscured fractions of the predicted torii are
substantial even in the absence of strong stellar feedback providing the
vertical support. Rather, they can be maintained by strong bending modes and
warps excited by the inflow-generating instabilities. Other properties commonly
attributed to feedback processes may be explained by dynamical effects:
misalignment between torus and host galaxy, correlations between local SFR and
turbulent gas velocities, and dependence of obscured fractions on AGN
luminosity or SFR. We compare the predicted torus properties with observations
of gas surface density profiles, kinematics, scale heights, and SFR densities
in AGN nuclei, and find that they are consistent. We argue that it is not
possible to reproduce these observations and the observed column density (N_H)
distribution without a clumpy gas distribution, but allowing for clumping on
small scales the predicted N_H distribution is in good agreement with
observations from 10^20-27 cm^-2. We examine how N_H scales with galaxy and AGN
properties, and find that AGN feedback may be necessary to explain some trends
with luminosity and/or redshift. The torus is not merely a bystander or passive
fuel source for accretion, but is itself the mechanism driving accretion. |
Small Field models with ACTPol and BICEP3 data -- Likelihood analysis: We perform a Bayesian analysis for small field models of inflation, using the
most recent datasets produced by Planck`18, ACTPol, and BICEP3. We employ
Artificial Neural Networks (ANN) to perform analyses with model coefficients,
instead of their proxy slow-roll parameters. The ANN connects the models with
their projected scalar index $n_s$ and index running $\alpha$, in lieu of the
less accurate Lyth-Riotto expressions. We recover the most likely coefficients
for a sixth degree polynomial inflationary potential, which yields a
tensor-to-scalar ratio $r\lesssim 0.03$. We do so for the case of joint Planck
and ACTPol datasets, and for each dataset alone. The BICEP3 data is included in
all three analyses. We show that these models are likely, with coefficients
that are tuned to about $\Delta\gtrsim 1/60$. Curiously, we also find a
significant tension between ACTPol and Planck datasets, which we try to account
for. | The impact of line-of-sight structures on measuring $H_0$ with strong
lensing time-delays: Measurements of The Hubble-Lemaitre constant from early- and local-universe
observations show a significant discrepancy. In an attempt to understand the
origin of this mismatch, independent techniques to measure H0 are required. One
such technique, strong lensing time delays, is set to become a leading
contender amongst the myriad methods due to forthcoming large strong lens
samples. It is therefore critical to understand the systematic effects inherent
in this method. In this paper, we quantify the influence of additional
structures along the line-of-sight by adopting realistic light cones derived
from the CosmoDC2 semi-analytical extra-galactic catalogue. Using multiple lens
plane ray-tracing to create a set of simulated strong lensing systems, we have
investigated the impact of line-of-sight structures on time-delay measurements
and in turn, on the inferred value of H0. We have also tested the reliability
of existing procedures for correcting for line-of-sight effects. We find that
if the integrated contribution of the line-of-sight structures is close to a
uniform mass sheet, the bias in H0 can be adequately corrected by including a
constant external convergence $\kappa_{ext}$ in the lens model. However, for
realistic line-of-sight structures comprising many galaxies at different
redshifts, this simple correction overestimates the bias by an amount that
depends linearly on the median external convergence. We, therefore, conclude
that lens modelling must incorporate multiple lens planes to account for
line-of-sight structures for accurate and precise inference of H0. |
Cosmology with kSZ: breaking the optical depth degeneracy with Fast
Radio Bursts: The small-scale cosmic microwave background (CMB) is dominated by
anisotropies from the kinematic Sunyaev-Zeldovich (kSZ) effect, and upcoming
experiments will measure it very precisely, but the optical depth degeneracy
limits the cosmological information that can be extracted. At the same time,
fast radio bursts (FRBs) are an exciting new frontier for astrophysics, but
their usefulness as cosmological probes is currently unclear. We show that FRBs
are uniquely suited for breaking the kSZ optical depth degeneracy. This opens
up new possibilities for constraining cosmology with the kSZ effect, and new
cosmological applications for FRBs. | Multi-frequency measurements of the NVSS foreground sources in the
Cosmic Background Imager fields. I. Data release: We present the results of the flux density measurements at 4.85 GHz and 10.45
GHz of a sample of 5998 NVSS radio sources with the Effelsberg 100 m telescope.
The initial motivation was the need to identify the NVSS radio sources that
could potentially contribute significant contaminating flux in the frequency
range at which the Cosmic Background Imager experiment operated. An efficient
way to achieve this challenging goal has been to compute the high frequency
flux density of those sources by extrapolating their radio spectrum. This is
determined by the three-point spectral index measured on the basis of the NVSS
entry at 1.4 GHz and the measurements at 4.85 GHz and 10.45 GHz carried out
with the 100 m Effelsberg telescope. These measurements are important since the
targeted sample probes the weak part of the flux density distribution, hence
the decision to make the data available. We present the table with flux density
measurements of 3434 sources that showed no confusion allowing reliable
measurements, their detection rates, their spectral index distribution and an
interpretation which explains satisfactorily the observed uncertainties. |
Exploring Inflationary Initial State With Large Scale Structure
Observations: We investigate for possible constraints on inflationary initial state from
Large Scale Structure (LSS) observations. Using a model-independent framework,
we build the template for the generic initial state and construct the matter
power spectrum through time evolution of the primordial power spectrum. We then
make use of the LSS data separately from the Sloan Digital Sky Survey - Data
Release 7 (SDSS-DR7) sample of Luminous Red Galaxies (LRG) and WiggleZ Dark
Energy Survey, and explore the plausible constraints on initial vacuum by
applying Bayesian parameter estimation method with Markov Chain Monte Carlo
(MCMC) simulation. Our analysis reveals that, along with the usual Bunch-Davies
vacuum, non-Bunch-Davies initial states are also fairly allowed so far as
present LSS data is concerned. | Weak lensing mass modeling bias and the impact of miscentring: Parametric modeling of galaxy cluster density profiles from weak lensing
observations leads to a mass bias, whose detailed understanding is critical in
deriving accurate mass-observable relations for constraining cosmological
models. Drawing from existing methods, we develop a robust framework for
calculating this mass bias in one-parameter fits to simulations of dark matter
halos. We show that our approach has the advantage of being independent of the
absolute noise level, so that only the number of halos in a given simulation
and the representativeness of the simulated halos for real clusters limit the
accuracy of the bias estimation. While we model the bias as a log-normal
distribution and the halos with a Navarro-Frenk-White profile, our method can
be generalized to any bias distribution and parametric model of the radial mass
distribution. We find that the log-normal assumption is not strictly valid in
the presence of miscentring of halos. We investigate the use of cluster centers
derived from weak lensing in the context of mass bias, and tentatively find
that such centroids can yield sensible mass estimates if the convergence peak
has a signal-to-noise ratio approximately greater than four. In this context we
also find that the standard approach to estimating the positional uncertainty
of weak lensing mass peaks using bootstrapping severely underestimates the true
positional uncertainty for peaks with low signal-to-noise ratios. Though we
determine the mass and redshift dependence of the bias distribution for a few
experimental setups, our focus remains providing a general approach to
computing such distributions. |
Pattern Speeds of Bars and Spiral Arms From H-alpha Velocity Fields: We have applied the Tremaine-Weinberg method to 10 late-type barred spiral
galaxies using data cubes, in H-alpha emission, from the GHAFAS and FANTOMM
Fabry-Perot spectrometers. We have combined the derived bar (and/or spiral)
pattern speeds with angular frequency plots to measure the corotation radii for
the bars in these galaxies. We base our results on a combination of this method
with a morphological analysis designed to estimate the corotation radius to
bar-length ratio using two independent techniques on archival near infrared
images, and although we are aware of the limitation of the application of the
Tremaine-Weinberg method using ionised gas observations, we find consistently
excellent agreement between bar and spiral arm parameters derived using
different methods. In general, the corotation radius, measured using the
Tremaine-Weinberg method, is closely related to the bar length, measured
independently from photometry and consistent with previous studies. Our
corotation/bar-length ratios and pattern speed values are in good agreement
with general results from numerical simulations of bars. In systems with
identified secondary bars, we measure higher H-alpha velocity dispersion in the
circumnuclear regions, whereas in all the other galaxies, we detect flat
velocity dispersion profiles. The excellent agreement between the
Tremaine-Weinberg method results and the morphological analysis and bar
parameters in numerical simulations, suggests that although the H-alpha
emitting gas does not obey the continuity equation, it can be used to derive
the bar pattern speed. | Cosmological Implications of the Tetron Model of Elementary Particles: Based on a possible solution to the tetron spin problem, a modification of
the standard Big Bang scenario is suggested, where the advent of a spacetime
manifold is connected to the appearance of tetronic bound states. The metric
tensor is constructed from tetron constituents and the reason for cosmic
inflation is elucidated. Furthermore, there are natural dark matter candidates
in the tetron model. The ratio of ordinary to dark matter in the universe is
calculated to be 1:5. |
Tailoring Strong Lensing Cosmographic Observations: Strong lensing time delay cosmography has excellent complementarity with
other dark energy probes, and will soon have abundant systems detected. We
investigate two issues in the imaging and spectroscopic followup required to
obtain the time delay distance. The first is optimization of spectroscopic
resources. We develop a code to optimize the cosmological leverage under the
constraint of constant spectroscopic time, and find that sculpting the lens
system redshift distribution can deliver a 40% improvement in dark energy
figure of merit. The second is the role of systematics, correlated between
different quantities of a given system or model errors common to all systems.
We show how the levels of different systematics affect the cosmological
parameter estimation, and derive guidance for the fraction of double image vs
quad image systems to follow as a function of differing systematics between
them. | Star formation and environment in clusters up to z~2.2: The dependence of galaxy star formation activity on environment - especially
in clusters - at high redshift is still poorly understood, as illustrated by
the still limited number of z>1.4 clusters on the one hand, and by the still
debated star formation-density relation at high redshift on the other hand. The
zphot~2.2 JKCS041 cluster allows to probe such environmental dependence of star
formation activity at an unprecedented combination of redshifts and
environments. Its study permits to enlarge the knowledge of high redshift
clusters and to put strong leverage on observational constraints for galaxy
evolution models. We analyze deep u\astg'r'i'z'JHKs images from the
CFHTLS/WIRDS surveys, which cover JKCS041 cluster field. We first estimate
photometric redshifts based on multi-wavelength photometry. We then lead a
careful analysis to test the presence of a Butcher-Oemler effect. We work on
galaxies within 2\timesr200 and with masses >1.34\times10^11 Msun, and use two
comparison clusters at z=0 and z=1 of similar mass. We estimate the radial
profiles of the fraction of blue galaxies, taking into account the star aging
with decreasing redshift. After confirming the high redshift nature of JKCS041,
we find no evidence for a Butcher-Oemler effect between z~2.2 and z~0 for
galaxies more massive than 1.34\times10^11 Msun. In the cluster center, a
change greater than \Deltafblue/\Deltaz=0.16 between z~0 and z~2.2 would be
easily detected. We also find that JKCS041 shows a consistent and systematic
increase of the fraction of star-forming galaxies with cluster-centric
distance, hence with decreasing density, for both a M>1.34\times10^11 Msun
selected sample and a lower mass sample. In particular, very few (less than
15%) star-forming galaxies are found within r200/2 among high mass
(M>1.34\times10^11 Msun) galaxies. Our results show that the present-day star
formation-density relation is already in place at z~2.2. |
Major Mergers Going Notts: Challenges for Modern Halo Finders: Merging haloes with similar masses (i.e., major mergers) pose significant
challenges for halo finders. We compare five halo finding algorithms' (AHF,
HBT, Rockstar, SubFind, and VELOCIraptor) recovery of halo properties for both
isolated and cosmological major mergers. We find that halo positions and
velocities are often robust, but mass biases exist for every technique. The
algorithms also show strong disagreement in the prevalence and duration of
major mergers, especially at high redshifts (z>1). This raises significant
uncertainties for theoretical models that require major mergers for, e.g.,
galaxy morphology changes, size changes, or black hole growth, as well as for
finding Bullet Cluster analogues. All finders not using temporal information
also show host halo and subhalo relationship swaps over successive timesteps,
requiring careful merger tree construction to avoid problematic mass accretion
histories. We suggest that future algorithms should combine phase-space and
temporal information to avoid the issues presented. | A Simple Analytic Treatment of Linear Growth of Structure with Baryon
Acoustic Oscillations: In linear perturbation theory, all information about the growth of structure
is contained in the Green's function, or equivalently, transfer function. These
functions are generally computed using numerical codes or by phenomenological
fitting formula anchored in accurate analytic results in the limits of large
and small scale. Here we present a framework for analytically solving all
scales, in particular the intermediate scales relevant for the baryon acoustic
oscillations (BAO). We solve for the Green's function and transfer function
using spherically-averaged overdensities and the approximation that the density
of the coupled baryon-photon fluid is constant interior to the sound horizon. |
Beyond the plane-parallel and Newtonian approach: Wide-angle redshift
distortions and convergence in general relativity: We extend previous analyses of wide-angle correlations in the galaxy power
spectrum in redshift space to include all general relativistic effects. These
general relativistic corrections to the standard approach become important on
large scales and at high redshifts, and they lead to new terms in the
wide-angle correlations. We show that in principle the new terms can produce
corrections of nearly 10 % on Gpc scales over the usual Newtonian
approximation. General relativistic corrections will be important for future
large-volume surveys such as SKA and Euclid, although the problem of cosmic
variance will present a challenge in observing this. | Kinematics of Arp 270: gas flows, nuclear activity and two regimes of
star formation: We have observed the Arp 270 system (NGC 3395 & NGC 3396) in H{\alpha}
emission using the GH{\alpha}FaS Fabry-Perot spectrometer on the 4.2m William
Herschel Telescope (La Palma). In NGC 3396, which is edge-on to us, we detect
gas inflow towards the centre, and also axially confined opposed outflows,
characteristic of galactic superwinds, and we go on to examine the possibility
that there is a shrouded AGN in the nucleus. The combination of surface
brightness, velocity and velocity dispersion information enabled us to measure
the radii, FWHM, and the masses of 108 HII regions in both galaxies. We find
two distinct modes of physical behaviour, for high and lower luminosity
regions. We note that the most luminous regions show especially high values for
their velocity dispersions and hypothesize that these occur because the higher
luminosity regions form from higher mass, gravitationally bound clouds while
those at lower luminosity HII regions form within molecular clouds of lower
mass, which are pressure confined. |
The 6dF Galaxy Survey: z \approx 0 measurement of the growth rate and
sigma_8: We present a detailed analysis of redshift-space distortions in the two-point
correlation function of the 6dF Galaxy Survey (6dFGS). The K-band selected
sub-sample which we employ in this study contains 81971 galaxies distributed
over 17000deg^2 with an effective redshift z = 0.067. By modelling the 2D
galaxy correlation function, xi(r_p,pi), we measure the parameter combination
f(z)sigma_8(z) = 0.423 +/- 0.055. Alternatively, by assuming standard gravity
we can break the degeneracy between sigma_8 and the galaxy bias parameter, b.
Combining our data with the Hubble constant prior from Riess et al (2011), we
measure sigma_8 = 0.76 +/- 0.11 and Omega_m = 0.250 +/- 0.022, consistent with
constraints from other galaxy surveys and the Cosmic Microwave Background data
from WMAP7. Combining our measurement of fsigma_8 with WMAP7 allows us to test
the relationship between matter and gravity on cosmic scales by constraining
the growth index of density fluctuations, gamma. Using only 6dFGS and WMAP7
data we find gamma = 0.547 +/- 0.088, consistent with the prediction of General
Relativity. We note that because of the low effective redshift of 6dFGS our
measurement of the growth rate is independent of the fiducial cosmological
model (Alcock-Paczynski effect). We also show that our conclusions are not
sensitive to the model adopted for non-linear redshift-space distortions. Using
a Fisher matrix analysis we report predictions for constraints on fsigma_8 for
the WALLABY survey and the proposed TAIPAN survey. The WALLABY survey will be
able to measure fsigma_8 with a precision of 4-10%, depending on the modelling
of non-linear structure formation. This is comparable to the predicted
precision for the best redshift bins of the Baryon Oscillation Spectroscopic
Survey (BOSS), demonstrating that low-redshift surveys have a significant role
to play in future tests of dark energy and modified gravity. | The Stellar Halos of Massive Elliptical Galaxies: We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald
Observatory 2.7m Harlan J. Smith Telescope to search for the chemical
signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is
an integral-field spectrograph with a uniquely wide field of view (107x107 sq
arcsec), allowing us to achieve remarkably high signal-to-noise ratios of
~20-70 per pixel in radial bins of 2-2.5 times the effective radii of the eight
galaxies in our sample. Focusing on a sample of massive elliptical galaxies
with stellar velocity dispersions sigma* > 150 km/s, we study the radial
dependence in the equivalent widths (EWs) of key metal absorption lines. By
twice the effective radius, the Mgb EWs have dropped by ~50%, and only a weak
correlation between sigma* and Mgb EW remains. The Mgb EWs at large radii are
comparable to those seen in the centers of elliptical galaxies that are
approximately an order of magnitude less massive. We find that the well-known
metallicity gradients often observed within an effective radius continue
smoothly to 2.5R_e, while the abundance ratio gradients remain flat. Much like
the halo of the Milky Way, the stellar halos of our galaxies have low
metallicities and high alpha-abundance ratios, as expected for very old stars
formed in small stellar systems. Our observations support a picture in which
the outer parts of massive elliptical galaxies are built by the accretion of
much smaller systems whose star formation history was truncated at early times. |
The NIKA2 Sunyaev-Zeldovich Large Program: The NIKA2 Guaranteed-Time SZ Large Program (LPSZ) is dedicated to the
high-angular resolution SZ mapping of a representative sample of 45 SZ-selected
galaxy clusters drawn from the catalogues of the Planck satellite, or of the
Atacama Cosmology Telescope. The LPSZ sample spans a mass range from $3$ to $11
\times 10^{14} M_{\odot}$ and a redshift range from $0.5$ to $0.9$, extending
to higher redshift and lower mass the previous samples dedicated to the cluster
mass calibration and universal properties estimation. The main goals of the
LPSZ are the measurement of the average radial profile of the ICM pressure up
to $R_{500}$ by combining NIKA2 with Planck or ACT data, and the estimation of
the scaling law between the SZ observable and the mass using NIKA2, XMM-Newton
and Planck/ACT data. Furthermore, combining LPSZ data with existing or
forthcoming public data in lensing, optical/NIR or radio domains, we will build
a consistent picture of the cluster physics and further gain knowledge on the
mass estimate as a function of the cluster morphology and dynamical state. | The GALEX Arecibo SDSS Survey. VI. Second Data Release and Updated Gas
Fraction Scaling Relations: We present the second data release from the GALEX Arecibo SDSS Survey (GASS),
an ongoing large Arecibo program to measure the HI properties for an unbiased
sample of ~1000 galaxies with stellar masses greater than 10^10 Msun and
redshifts 0.025<z<0.05. GASS targets are selected from the Sloan Digital Sky
Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging
surveys, and are observed until detected or until a gas mass fraction limit of
a few per cent is reached. This second data installment includes new Arecibo
observations of 240 galaxies, and marks the 50% of the complete survey. We
present catalogs of the HI, optical and ultraviolet parameters for these
galaxies, and their HI-line profiles. Having more than doubled the size of the
sample since the first data release, we also revisit the main scaling relations
of the HI mass fraction with galaxy stellar mass, stellar mass surface density,
concentration index, and NUV-r color, as well as the gas fraction plane
introduced in our earlier work. |
Evidence against Ryskin's model of cosmic acceleration: In this paper I examine how well Ryskin's model of emergent cosmic
acceleration fits several sets of cosmological observations. I find that while
Ryskin's model is somewhat compatible with the standard model of cosmological
acceleration ($\Lambda$CDM) for low redshift (z < 1) measurements, its
predictions diverge considerably from those of the standard model for
measurements made at high redshift (for which z > 1), and it is therefore not a
compelling substitute for the standard model. | Implicit Priors in Galaxy Cluster Mass and Scaling Relation
Determinations: Deriving the total masses of galaxy clusters from observations of the
intracluster medium (ICM) generally requires some prior information, in
addition to the assumptions of hydrostatic equilibrium and spherical symmetry.
Often, this information takes the form of particular parametrized functions
used to describe the cluster gas density and temperature profiles. In this
paper, we investigate the implicit priors on hydrostatic masses that result
from this fully parametric approach, and the implications of such priors for
scaling relations formed from those masses. We show that the application of
such fully parametric models of the ICM naturally imposes a prior on the slopes
of the derived scaling relations, favoring the self-similar model, and argue
that this prior may be influential in practice. In contrast, this bias does not
exist for techniques which adopt an explicit prior on the form of the mass
profile but describe the ICM non-parametrically. Constraints on the slope of
the cluster mass--temperature relation in the literature show a separation
based the approach employed, with the results from fully parametric ICM
modeling clustering nearer the self-similar value. Given that a primary goal of
scaling relation analyses is to test the self-similar model, the application of
methods subject to strong, implicit priors should be avoided. Alternative
methods and best practices are discussed. |
Vector Galileon and inflationary magnetogenesis: Cosmological inflation provides the initial conditions for the structure
formation. However, the origin of large-scale magnetic fields cannot be
addressed in this framework. The key issue for this long-standing problem is
the conformal invariance of the electromagnetic (EM) field in 4-D. While many
approaches have been proposed in the literature for breaking conformal
invariance of the EM action, here, we provide a completely new way of looking
at the modifications to the EM action and generation of primordial magnetic
fields during inflation. We explicitly construct a higher derivative EM action
that breaks conformal invariance by demanding three conditions - theory be
described by vector potential $A_\mu$ and its derivatives, Gauge invariance be
satisfied, and equations of motion be linear in second derivatives of vector
potential. The unique feature of our model is that appreciable magnetic fields
are generated at small wavelengths while tiny magnetic fields are generated at
large wavelengths that are consistent with current observations. | Testing the lognormality of the galaxy and weak lensing convergence
distributions from Dark Energy Survey maps: It is well known that the probability distribution function (PDF) of galaxy
density contrast is approximately lognormal; whether the PDF of mass
fluctuations derived from weak lensing convergence (kappa_WL) is lognormal is
less well established. We derive PDFs of the galaxy and projected matter
density distributions via the Counts in Cells (CiC) method. We use maps of
galaxies and weak lensing convergence produced from the Dark Energy Survey
(DES) Science Verification data over 139 deg^2. We test whether the underlying
density contrast is well described by a lognormal distribution for the
galaxies, the convergence and their joint PDF. We confirm that the galaxy
density contrast distribution is well modeled by a lognormal PDF convolved with
Poisson noise at angular scales from 10-40 arcmin (corresponding to physical
scales of 3-10 Mpc). We note that as kappa_WL is a weighted sum of the mass
fluctuations along the line of sight, its PDF is expected to be only
approximately lognormal. We find that the kappa_WL distribution is well modeled
by a lognormal PDF convolved with Gaussian shape noise at scales between 10 and
20 arcmin, with a best-fit chi^2/DOF of 1.11 compared to 1.84 for a Gaussian
model, corresponding to p-values 0.35 and 0.07 respectively, at a scale of 10
arcmin. Above 20 arcmin a simple Gaussian model is sufficient. The joint PDF is
also reasonably fitted by a bivariate lognormal. As a consistency check we
compare the variances derived from the lognormal modelling with those directly
measured via CiC. Our methods are validated against maps from the MICE Grand
Challenge N-body simulation. |
Hyper Suprime-Cam Year 3 Results: Measurements of Clustering of
SDSS-BOSS Galaxies, Galaxy-Galaxy Lensing and Cosmic Shear: We use the Sloan Digital Sky Survey (SDSS) BOSS galaxies and their overlap
with approximately 416 sq. degree of deep $grizy$-band imaging from the Subaru
Hyper Suprime-Cam Survey (HSC). We measure three two-point correlations that
form the basis of the cosmological inference presented in our companion papers,
Miyatake et al. and Sugiyama et al. We use three approximately volume limited
subsamples of spectroscopic galaxies by their $i$-band magnitude from the
SDSS-BOSS: LOWZ (0.1<z<0.35), CMASS1 (0.43<z<0.55) and CMASS2 (0.55<z<0.7),
respectively. We present high signal-to-noise ratio measurements of the
projected correlation functions of these galaxies, which is expected to be
proportional to the matter correlation function times the bias of galaxies on
large scales. In order to break the degeneracy between the amplitude of the
matter correlation and the bias of these galaxies, we use the distortions of
the shapes of galaxies in HSC due to weak gravitational lensing, to measure the
galaxy-galaxy lensing signal, which probes the galaxy-matter cross-correlation
of the SDSS-BOSS galaxies. We also measure the cosmic shear correlation
functions from HSC galaxies which is related to the projected matter
correlation function. We demonstrate the robustness of our measurements with a
variety of systematic tests. Our use of a single sample of HSC source galaxies
is crucial to calibrate any residual systematic biases in the inferred
redshifts of our galaxies. We also describe the construction of a suite of
mocks: i) spectroscopic galaxy catalogs which obey the clustering and abundance
of each of the three SDSS-BOSS subsamples, and ii) galaxy shape catalogs which
obey the footprint of the HSC survey and have been appropriately sheared by the
large-scale structure expected in a $\Lambda$-CDM model. We use these mock
catalogs to compute the covariance of each of our observables. | Gravitational instabilities of isothermal spheres in the presence of a
cosmological constant: Gravitational instabilities of isothermal spheres are studied in the presence
of a positive or negative cosmological constant, in the Newtonian limit. In
gravity, the statistical ensembles are not equivalent. We perform the analysis
both in the microcanonical and the canonical ensembles, for which the
corresponding instabilities are known as `gravothermal catastrophe' and
`isothermal collapse', respectively. In the microcanonical ensemble, no
equilibria can be found for radii larger than a critical value, which is
increasing with increasing cosmological constant. In contrast, in the canonical
ensemble, no equilibria can be found for radii smaller than a critical value,
which is decreasing with increasing cosmological constant. For a positive
cosmological constant, characteristic reentrant behaviour is observed. |
Effects of discontinuities of the derivatives of the inflaton potential: We study the effects of a class of features of the inflaton potential,
corresponding to discontinuties in its derivatives. We perform fully numerical
calculations and derive analytical approximations for the curvature
pertubations spectrum and the bispectrum which are in good agreement with the
numerical results.
The spectrum of primordial perturbations has oscillations around the scale
$k_0$ which leaves the horizon at the time $\tau_0$ when the feature occurs,
with the amplitude and phase of the oscillations determined by the size and the
order of the discontinuity. The large scale bispectrum in the squeezed and
equilateral limits have a very similar form and are linearly suppressed. Both
in the squeezed and equilateral small scale limit the bispectrum has an
oscillatory behavior whose phase depends on the parameters determining the
discontinuity, and whose amplitude is inversely proportional to the scale.
Given the generality of this class of features they could be used to model or
classify phenomenologically different types of non Gaussian features
encountered in observational data such as the cosmic microwave background
radiation or large scale structure. | How to generate a significant effective temperature for cold dark
matter, from first principles: I show how to reintroduce velocity dispersion into perturbation theory (PT)
calculations of structure in the Universe, i.e., how to go beyond the
pressureless fluid approximation, starting from first principles. This
addresses a possible deficiency in uses of PT to compute clustering on the
weakly non-linear scales that will be critical for probing dark energy.
Specifically, I show how to derive a non-negligible value for the (initially
tiny) velocity dispersion of dark matter particles, <\delta v^2>, where \delta
v is the deviation of particle velocities from the local bulk flow. The
calculation is essentially a renormalization of the homogeneous (zero order)
dispersion by fluctuations 1st order in the initial power spectrum. For power
law power spectra with n>-3, the small-scale fluctuations diverge and
significant dispersion can be generated from an arbitrarily small starting
value -- the dispersion level is set by an equilibrium between fluctuations
generating more dispersion and dispersion suppressing fluctuations. For an
n=-1.4 power law normalized to match the present non-linear scale, the
dispersion would be ~100 km/s. This n corresponds roughly to the slope on the
non-linear scale in the real \LambdaCDM Universe, but \LambdaCDM contains much
less initial small-scale power -- not enough to bootstrap the small starting
dispersion up to a significant value within linear theory (viewed very broadly,
structure formation has actually taken place rather suddenly and recently, in
spite of the usual "hierarchical" description). The next order PT calculation,
which I carry out only at an order of magnitude level, should drive the
dispersion up into balance with the growing structure, accounting for small
dispersion effects seen recently in simulations. |
Ripped ΛCDM: an observational contender to the consensus
cosmological model: Current observations do not rule out the possibility that the Universe might
end up in an abrupt event. Different such scenarios may be explored through
suitable parameterizations of the dark energy and then confronted to
cosmological background data. Here we parameterize a pseudorip scenario using a
particular sigmoid function and carry an in-depth multifaceted examination of
its evolutionary features and statistical performance. This depiction of a non
violent final fate of our cosmos seems to be arguably statistically favoured
over the consensus {\Lambda}CDM model according to some Bayesian
discriminators. | The stellar mass - halo mass relation from galaxy clustering in VUDS: a
high star formation efficiency at z~3: The relation between the galaxy stellar mass M_star and the dark matter halo
mass M_h gives important information on the efficiency in forming stars and
assembling stellar mass in galaxies. We present the stellar mass to halo mass
ratio (SMHR) measurements at redshifts 2<z<5, obtained from the VIMOS Ultra
Deep Survey. We use halo occupation distribution (HOD) modelling of clustering
measurements on ~3000 galaxies with spectroscopic redshifts to derive the dark
matter halo mass M_h, and SED fitting over a large set of multi-wavelength data
to derive the stellar mass M_star and compute the SMHR=M_star/M_h. We find that
the SMHR ranges from 1% to 2.5% for galaxies with M_star=1.3x10^9 M_sun to
M_star=7.4x10^9 M_sun in DM halos with M_h=1.3x10^{11} M_sun} to M_h=3x10^{11}
M_sun. We derive the integrated star formation efficiency (ISFE) of these
galaxies and find that the star formation efficiency is a moderate 6-9% for
lower mass galaxies while it is relatively high at 16% for galaxies with the
median stellar mass of the sample ~7x10^9 M_sun. The lower ISFE at lower masses
may indicate that some efficient means of suppressing star formation is at work
(like SNe feedback), while the high ISFE for the average galaxy at z~3 is
indicating that these galaxies are efficiently building-up their stellar mass
at a key epoch in the mass assembly process. We further infer that the average
mass galaxy at z~3 will start experiencing star formation quenching within a
few hundred millions years. |
Search for Wormhole Candidates: Accreting Wormholes with Monopole
Magnetic Fields: The existence of even the simplest magnetized wormholes may lead to
observable consequences. In the case where both the wormhole and the magnetic
field around its mouths are static and spherically symmetric, and gas in the
region near the wormhole falls radially into it, the former's spectrum contains
bright cyclotron or synchrotron lines due to the interaction of charged plasma
particles with the magnetic field. At the same time, due to spherical symmetry,
the radiation is non-polarized. The emission of this just-described exotic type
(non-thermal, but non-polarized) may be a wormhole signature. Also, in this
scenario, the formation of an accretion disk is still quite possible at some
distance from the wormhole, but a monopole magnetic field could complicate this
process and lead to the emergence of asymmetrical and one-sided relativistic
jets. | Shedding Light on the Galaxy Luminosity Function: From as early as the 1930s, astronomers have tried to quantify the
statistical nature of the evolution and large-scale structure of galaxies by
studying their luminosity distribution as a function of redshift - known as the
galaxy luminosity function (LF). Accurately constructing the LF remains a
popular and yet tricky pursuit in modern observational cosmology where the
presence of observational selection effects due to e.g. detection thresholds in
apparent magnitude, colour, surface brightness or some combination thereof can
render any given galaxy survey incomplete and thus introduce bias into the LF.
Over the last seventy years there have been numerous sophisticated
statistical approaches devised to tackle these issues; all have advantages --
but not one is perfect. This review takes a broad historical look at the key
statistical tools that have been developed over this period, discussing their
relative merits and highlighting any significant extensions and modifications.
In addition, the more generalised methods that have emerged within the last few
years are examined. These methods propose a more rigorous statistical framework
within which to determine the LF compared to some of the more traditional
methods. I also look at how photometric redshift estimations are being
incorporated into the LF methodology as well as considering the construction of
bivariate LFs. Finally, I review the ongoing development of completeness
estimators which test some of the fundamental assumptions going into LF
estimators and can be powerful probes of any residual systematic effects
inherent magnitude-redshift data. |
Newtonian acceleration scales in spiral galaxies: We revisit the issue of the constancy of the dark matter (DM) and baryonic
Newtonian acceleration scales within the DM scale radius by considering a large
sample of late - type galaxies. We rely on a Markov Chain Monte Carlo (MCMC)
method to estimate the parameters of the halo model and the stellar mass - to -
light ratio and then propagate the uncertainties from the rotation curve data
to the estimate of the acceleration scales. This procedure allows us to compile
a catalog of 58 objects with estimated values of the $B$ band absolute
magnitude $M_B$, the virial mass $M_{vir}$, the DM and baryonic Newtonian
accelerations (denoted as $g_{DM}(r_0)$ and $g_{bar}(r_0)$, respectively)
within the scale radius $r_0$ which we use to investigate whether it is
possible to define a universal acceleration scale. We find a weak but
statistically meaningful correlation with $M_{vir}$ thus making us argue
against the universality of the acceleration scales. However, the results
somewhat depend on the sample adopted so that a careful analysis of selection
effects should be carried out before any definitive conclusion can be drawn. | Lensing reconstruction from a patchwork of polarization maps: The lensing signals involved in CMB polarization maps have already been
measured with ground-based experiments such as SPTpol and POLARBEAR, and would
become important as a probe of cosmological and astrophysical issues in the
near future. Sizes of polarization maps from ground-based experiments are,
however, limited by contamination of long wavelength modes of observational
noise. To further extract the lensing signals, we explore feasibility of
measuring lensing signals from a collection of small sky maps each of which is
observed separately by a ground-based large telescope, i.e., lensing
reconstruction from a patchwork map of large sky coverage organized from small
sky patches. We show that, although the B-mode power spectrum obtained from the
patchwork map is biased due to baseline uncertainty, bias on the lensing
potential would be negligible if the B-mode on scales larger than the blowup
scale of $1/f$ noise is removed in the lensing reconstruction. As examples of
cosmological applications, we also show 1) the cross-correlations between the
reconstructed lensing potential and full-sky temperature/polarization maps from
satellite missions such as PLANCK and LiteBIRD, and 2) the use of the
reconstructed potential for delensing B-mode polarization of LiteBIRD
observation. |
Constraining galactic structures of mirror dark matter: The simplest model of mirror sector dark matter maintains exact mirror
symmetry, but has a baryon abundance $\Omega_{b'} = \beta \Omega_b$ and a
suppressed temperature $T' = x T$ in the mirror sector; hence it depends only
on two parameters, $\beta,x$. For sufficiently small $x$, early cosmological
observables may not constrain mirror baryons from constituting all of the dark
matter despite their strong self-interactions, depending on the unknown details
of structure formation in the hidden sector. Here we close this loophole by
simulating mirror structure formation, mapping out the allowed regions of
parameter space using cosmological and astronomical data. We find that the
Milky Way disk surface density and bulge mass constrain $\Omega_{b'}\lesssim
0.3 \Omega_{b}$ at the highest $T'$ allowed by BBN and CMB ($T'=0.5 T$), or
$\Omega_{b'}\lesssim 0.8 \Omega_{b}$ at lower values of $T'$. We also briefly
discuss the realization of the necessary temperature asymmetry between the SM
and the mirror sector in our model with unbroken mirror symmetry. | Signatures of Primordial non-Gaussianities in the Matter Power-Spectrum
and Bispectrum: the Time-RG Approach: We apply the time-renormalization group approach to study the effect of
primordial non-Gaussianities in the non-linear evolution of cosmological dark
matter density perturbations. This method improves the standard perturbation
approach by solving renormalization group-like equations governing the dynamics
of gravitational instability. The primordial bispectra constructed from the
dark matter density contrast and the velocity fields represent initial
conditions for the renormalization group flow. We consider local, equilateral
and folded shapes for the initial non-Gaussianity and analyze as well the case
in which the non-linear parameter f_{NL} parametrizing the strength of the
non-Gaussianity depends on the momenta in Fourier space through a power-law
relation, the so-called running non-Gaussianity. For the local model of
non-Gaussianity we compare our findings for the power-spectrum with those of
recent N-body simulations and find that they accurately fit the N-body data up
to wave-numbers k \sim 0.25 h/Mpc at z=0. We also present predictions for the
(reduced) matter bispectra for the various shapes of non-Gaussianity. |
Evolution of the u-band luminosity function from redshift 1.2 to 0: We produce and analyse u-band luminosity functions for the red and blue
populations of galaxies using data from the Sloan Digital Sky Survey (SDSS)
u-band Galaxy Survey (uGS) and Deep Evolutionary Exploratory Probe 2 (DEEP2)
survey. From a spectroscopic sample of 41575 SDSS uGS galaxies and 24561 DEEP2
galaxies, we produce colour magnitude diagrams and make use of the colour
bimodality of galaxies to separate red and blue populations. Luminosity
functions for eight redshift slices in the range 0.01 < z < 1.2 are determined
using the 1/Vmax method and fitted with Schechter functions showing that there
is significant evolution in M-star, with a brightening of 1.4 mags for the
combined population. The integration of the Schechter functions yields the
evolution in the u-band luminosity density out to z ~ 1. By parametrizing the
evolution as density proportional to (1+z)^beta, we find that beta = 1.36 +-
0.2 for the combined populations and beta = 2.09 +- 0.2 for the blue
population. By removing the contribution of the old stellar population to the
u-band luminosity density and correcting for dust attenuation, we estimate the
evolution in the star formation rate of the Universe to be beta(SFR) = 2.5 +-
0.3. Discrepancies between our result and higher evolution rates measured using
the infrared and far-UV can be reconciled by considering possibilities such as
an underestimated dust correction at high redshifts or evolution in the stellar
initial mass function. | Colour Gradients and the Colour-Magnitude Relation: Different Properties
of Brightest Cluster Galaxies and E/S0 Galaxies in the Sloan Digital Sky
Survey: We examine the colour-magnitude relation of approximately 5000 Brightest
Cluster Galaxies (BCGs) in the Sloan Digital Sky Survey, and compare with
non-BCG E/S0 galaxies. The colour-magnitude and colour-sigma (velocity
dispersion) relations are flatter in slope (by a factor of about 2) for BCGs
than for non-BCG E/S0s, and the BCGs also tend to be redder by 0.01 magnitudes
in g-r. We investigate radial colour gradients in both samples, using the ratio
of the de Vaucouleurs radii in the g and r bands. We find BCGs have
significantly flatter (by 23%) mean colour gradients than other high luminosity
E/S0s. In early-type galaxies, the colour gradients are strongest at
intermediate luminosities of Mr=-22. Colour gradients in E/S0s increase with
radius (up to 10kpc) and are negatively correlated with 10sigma + Mr (velocity
dispersion relative to luminosity) and with mass density. The gradients also
tend to decrease with increasing stellar age. These trends are weak or not seen
in BCGs, in which the mean colour gradient is low whatever the other
properties. We discuss possible explanations, which involve a greater amount of
dry merging in the formation history of the BCGs. |
Galaxy Pairs in the Local Group: Current models of galaxy formation predict that galaxy pairs of comparable
magnitudes should become increasingly rare with decreasing luminosity. This
seems at odds with the relatively high frequency of pairings among dwarf
galaxies in the Local Group. We use literature data to show that ~30% of all
satellites of the Milky Way and Andromeda galaxies brighter than M_V=-8 are
found in likely physical pairs of comparable luminosity. Besides the previously
recognised pairings of the Magellanic Clouds and of NGC 147/NGC 185, other
candidate pairs include the Ursa Minor and Draco dwarf spheroidals, as well as
the And I/And III satellites of M31. These pairs are much closer than expected
by chance if the radial and angular distributions of satellites were
uncorrelated; in addition, they have very similar line-of-sight velocities and
luminosities that differ by less than three magnitudes. In contrast, the same
criteria pair fewer than 4% of satellites in N-body/semi-analytic models that
match the radial distribution and luminosity function of Local Group
satellites. If confirmed in studies of larger samples, the high frequency of
dwarf galaxy pairings may provide interesting clues to the formation of faint
galaxies in the current cosmological paradigm. | Discovery and Follow-up of a Nearby Galaxy from the Arecibo Zone of
Avoidance Survey: The Arecibo L-Band Feed Array Zone of Avoidance (ALFA ZOA) Survey has
discovered a nearby galaxy, ALFA ZOA J1952+1428, at a heliocentric velocity of
+279 km s-1. The galaxy was discovered at low Galactic latitude by 21-cm
emission from neutral hydrogen (Hi). We have obtained follow-up observations
with the EVLA and the 0.9-m SARA optical telescope. The Hi distribution
overlaps an uncataloged, potential optical counterpart. The Hi linear size is
1.4 kpc at our adopted distance of D = 7 Mpc, but the distance estimate is
uncertain as Hubble's law is unreliable at low recessional velocities. The
optical counterpart has mB = 16.9 mag and B - R = 0.1 mag. These
characteristics, including MHI = 107.0 M\odot and LB = 107.5 L\odot, if at 7
Mpc, indicate that this galaxy is a blue compact dwarf, but this remains
uncertain until further follow-up observations are complete. Optical follow-up
observations are ongoing and near infrared follow-up observations have been
scheduled. |
Primordial black hole formation by vacuum bubbles II: The discoveries of LIGO/Virgo black holes in recent years have revitalized
the study of primordial black holes. In this work, we investigate a mechanism
where primordial black holes are formed by vacuum bubbles that randomly
nucleate during inflation through quantum tunneling. After inflation, these
bubbles typically run into the ambient radiation fluid with a large Lorentz
factor. In our previous work, we assumed the bubble fields are strongly coupled
to the standard model particles so that the bubble wall is impermeable. Here we
complete this picture by considering bubbles interacting with the fluid only
through gravity. By studying the scenario in several limits, we found that
black holes could form in either subcritical or supercritical regime. Depending
on the model parameters, the resulting mass spectrum of the black holes could
be wide or narrow, and may develop two peaks separated by a large mass range.
With different spectra, these black holes may account for the LIGO/Virgo black
holes, supermassive black holes, and may play an important role in dark matter. | Lyman-Alpha Emitter Galaxies at z ~ 2.8 in the Extended Chandra Deep
Field-South: I. Tracing the Large-Scale Structure via Lyman-Alpha Imaging: We present a narrowband survey with three adjacent filters for z=2.8--2.9
Lyman Alpha Emitter (LAE) galaxies in the Extended Chandra Deep Field South
(ECDFS), along with spectroscopic followup. With a complete sample of 96 LAEs
in the narrowband NB466, we confirm a large-scale structure at z~ 2.8. Compared
to the blank field in NB470 and NB475, the LAE density excess in the NB466
field is ~6.0+/-0.8 times the standard deviation expected at z~2.8, assuming a
linear bias of 2. The overdense large scale structure in NB466 can be
decomposed into 4 protoclusters, whose overdensities are 4.6 - 6.6. These 4
protoclusters are expected to evolve into a Coma-like cluster at z~ 0. In the
meanwhile, we investigate the average star-formation rates derived from
Ly{\alpha}, rest-frame UV and X-ray, the Ly{\alpha} luminosity functions, the
Ly{\alpha} photon densities and their dependence on the environment. We find
that the Ly{\alpha} photon density in the overdense field (NB466) is ~50\%
higher than that in the blank field (NB470+NB475). The 3 brightest LAEs,
including a quasar at z=2.81, are all detected in X-ray and in NB466. These
three LAE-AGNs contribute an extra 20--30\% Ly{\alpha} photon density.
Furthermore, we find that LAEs in overdense regions are younger and less dusty.
We conclude that the structure we found is a significant and rare density peak,
and narrowband imaging is an efficient method to detect and study such
structures in the high-z universe. |
A direct measurement of the linear bias of mid-infrared-selected quasars
at z~1 using cosmic microwave background lensing: We measure the cross-power spectrum of the projected mass density as traced
by the convergence of the cosmic microwave background lensing field from the
South Pole Telescope (SPT) and a sample of Type 1 and 2 (unobscured and
obscured) quasars at z~1 selected with the Wide-field Infrared Survey Explorer,
over 2500 deg^2. The cross-power spectrum is detected at ~7-sigma, and we
measure a linear bias b=1.67+/-0.24, consistent with clustering analyses. Using
an independent lensing map, derived from Planck observations, to measure the
cross-spectrum, we find excellent agreement with the SPT analysis. The bias of
the combined sample of Type 1 and 2 quasars determined in this work is similar
to that previously determined for Type 1 quasars alone; we conclude that that
obscured and unobscured quasars must trace the matter field in a similar way.
This result has implications for our understanding of quasar unification and
evolution schemes. | Measuring cosmic velocities with 21cm intensity mapping and galaxy
redshift survey cross-correlation dipoles: We investigate the feasibility of measuring the effects of peculiar
velocities in large-scale structure using the dipole of the redshift-space
cross-correlation function. We combine number counts of galaxies with
brightness-temperature fluctuations from 21cm intensity mapping, demonstrating
that the dipole may be measured at modest significance ($\lesssim 2\sigma$) by
combining the upcoming radio survey CHIME with the future redshift surveys of
DESI and Euclid. More significant measurements ($\lesssim~10\sigma$) will be
possible by combining intensity maps from the SKA with these of DESI or Euclid,
and an even higher significance measurement ($\lesssim 100\sigma$) may be made
by combining observables completely internally to the SKA. We account for
effects such as contamination by wide-angle terms, interferometer noise and
beams in the intensity maps, non-linear enhancements to the power spectrum,
stacking multiple populations, sensitivity to the magnification slope, and the
possibility that number counts and intensity maps probe the same tracers. We
also derive a new expression for the covariance matrix of multi-tracer
redshift-space correlation function estimators with arbitrary orientation
weights, which may be useful for upcoming surveys aiming at measuring
redshift-space clustering with multiple tracers. |
Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the
NeVIII Population: We present a blind search for doublet intergalactic metal absorption with a
method dubbed `agnostic stacking'. Using a forward-modelling framework we
combine this with direct detections in the literature to measure the overall
metal population. We apply this novel approach to the search for NeVIII
absorption in a set of 26 high-quality COS spectra. We probe to an
unprecedented low limit of log N$>$12.3 at 0.47$\leq z \leq$1.34 over a
pathlength $\Delta$z = 7.36. This method selects apparent absorption without
requiring knowledge of its source. Stacking this mixed population dilutes
doublet features in composite spectra in a deterministic manner, allowing us to
measure the proportion corresponding to NeVIII absorption. We stack potential
NeVIII absorption in two regimes: absorption too weak to be significant in
direct line studies (12.3 $<$ log N $<$ 13.7), and strong absorbers (log N $>$
13.7). We do not detect NeVIII absorption in either regime. Combining our
measurements with direct detections, we find that the NeVIII population is
reproduced with a power law column density distribution function with slope
$\beta = -1.86 \substack{+0.18 \\ -0.26}$ and normalisation log $f_{13.7} =
-13.99 \substack{+0.20 \\ -0.23}$, leading to an incidence rate of strong
NeVIII absorbers $dn/dz =1.38 \substack{+0.97 \\ -0.82}$. We infer a cosmic
mass density for NeVIII gas with 12.3 $<$ log N $<$ 15.0 of $\Omega _{NeVIII} =
2.2 \substack{+1.6 \\ _-1.2} \times 10^{-8}$, a value significantly lower that
than predicted by recent simulations. We translate this density into an
estimate of the baryon density $\Omega _{b} \approx 1.8 \times 10^{-3}$,
constituting 4\% of the total baryonic mass. | A coupled generalized three-form dark energy model: A coupled dark energy model is considered, in which dark energy is
represented by a generalized three-form field and dark matter by dust. By
assuming the functions $N$ and $I$ in the model's Lagrangian as two power-law
functions of the three-form field, we obtain two fixed points of the autonomous
system of evolution equations, consisting of a attractor and a tracking saddle
point which can be used to alleviate the coincidence problem. After
marginalizing the present three-form field $\kappa X_{0}$ which is unable to be
strictly restricted, we confront the model with the latest Type Ia Supernova
(SN \uppercase\expandafter{\romannumeral1}a), Baryon Acoustic Oscillations
(BAO) and Cosmic Microwave Backround (CMB) radiation observations with the
fitting results $\Omega_{m0}= 0.280_{-0.048}^{+0.048}$ and
$\lambda=0.011_{-0.032}^{+0.032}$ in the $2\sigma$ confidence level, we also
find that the best fitting effective dark energy equation of state (EOS)
crosses $ -1$ at redshift around 0.2. |
Implications of Planck2015 for inflationary, ekpyrotic and anamorphic
bouncing cosmologies: The results from Planck2015, when combined with earlier observations from
WMAP, ACT, SPT and other experiments, were the first observations to disfavor
the "classic" inflationary paradigm. To satisfy the observational constraints,
inflationary theorists have been forced to consider plateau-like inflaton
potentials that introduce more parameters and more fine-tuning, problematic
initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness
problem.' Some propose turning instead to a "postmodern" inflationary paradigm
in which the cosmological properties in our observable universe are only
locally valid and set randomly, with completely different properties (and
perhaps even different physical laws) existing in most regions outside our
horizon. By contrast, the new results are consistent with the simplest versions
of ekpyrotic cyclic models in which the universe is smoothed and flattened
during a period of slow contraction followed by a bounce, and another promising
bouncing theory, anamorphic cosmology, has been proposed that can produce
distinctive predictions. | Constraining the interaction between dark sectors with future HI
intensity mapping observations: We study a model of interacting dark matter and dark energy, in which the two
components are coupled. We calculate the predictions for the 21-cm intensity
mapping power spectra, and forecast the detectability with future single-dish
intensity mapping surveys (BINGO, FAST and SKA-I). Since dark energy is turned
on at $z\sim 1$, which falls into the sensitivity range of these radio surveys,
the HI intensity mapping technique is an efficient tool to constrain the
interaction. By comparing with current constraints on dark sector interactions,
we find that future radio surveys will produce tight and reliable constraints
on the coupling parameters. |
Detecting the non-Gaussianity of the 21-cm signal during reionisation
with the Wavelet Scattering Transform: Detecting the 21-cm hyperfine transition from neutral hydrogen in the
intergalactic medium is our best probe for understanding the astrophysical
processes driving the Epoch of Reionisation (EoR). The primary means for a
detection of this 21-cm signal is through a statistical measurement of the
spatial fluctuations using the 21-cm power spectrum (PS). However, the 21-cm
signal is non-Gaussian meaning the PS, which only measures the Gaussian
fluctuations, is sub-optimal for characterising all of the available
information. The upcoming Square Kilometre Array (SKA) will perform a deep,
1000 hr observation over 100 deg$.^{2}$ specifically designed to recover direct
images of the 21-cm signal. In this work, we use the Wavelet Scattering
Transform (WST) to extract the non-Gaussian information directly from these
two-dimensional images of the 21-cm signal. The key advantage of the WST is its
stability with respect to statistical noise for measuring non-Gaussian
information, unlike the bispectrum whose statistical noise diverges. We
introduce a novel method to isolate this non-Gaussian information from mock
21-cm images and demonstrate its detection at 150 (177)~MHz ($z\sim8.5$ and
$\sim7$) for a fiducial model with signal-to-noise of $\sim$5~(8) assuming
perfect foreground removal and $\sim2$~(3) assuming foreground wedge avoidance. | Obscuring and feeding supermassive black holes with evolving nuclear
star clusters: Recently, high resolution observations with the help of the near-infrared
adaptive optics integral field spectrograph SINFONI at the VLT proved the
existence of massive and young nuclear star clusters in the centres of a sample
of Seyfert galaxies. With the help of high resolution hydrodynamical
simulations with the PLUTO-code, we follow the evolution of such clusters,
especially focusing on mass and energy feedback from young stars. This leads to
a filamentary inflow of gas on large scales (tens of parsec), whereas a
turbulent and very dense disc builds up on the parsec scale. Here, we
concentrate on the long-term evolution of the nuclear disc in NGC 1068 with the
help of an effective viscous disc model, using the mass input from the large
scale simulations and accounting for star formation in the disc. This two-stage
modelling enables us to connect the tens of parsec scale region (observable
with SINFONI) with the parsec scale environment (MIDI observations). At the
current age of the nuclear star cluster, our simulations predict disc sizes of
the order of 0.8 to 0.9 pc, gas masses of 1.0e6 Msun and mass transfer rates
through the inner boundary of 0.025 Msun/yr in good agreement with values
derived from observations. |
A point cloud approach to generative modeling for galaxy surveys at the
field level: We introduce a diffusion-based generative model to describe the distribution
of galaxies in our Universe directly as a collection of points in 3-D space
(coordinates) optionally with associated attributes (e.g., velocities and
masses), without resorting to binning or voxelization. The custom diffusion
model can be used both for emulation, reproducing essential summary statistics
of the galaxy distribution, as well as inference, by computing the conditional
likelihood of a galaxy field. We demonstrate a first application to massive
dark matter haloes in the Quijote simulation suite. This approach can be
extended to enable a comprehensive analysis of cosmological data, circumventing
limitations inherent to summary statistic -- as well as neural simulation-based
inference methods. | Efficient Mass Estimate at the Core of Strong Lensing Galaxy Clusters
Using the Einstein Radius: In the era of large surveys, yielding thousands of galaxy clusters, efficient
mass proxies at all scales are necessary in order to fully utilize clusters as
cosmological probes. At the cores of strong lensing clusters, the Einstein
radius can be turned into a mass estimate. This efficient method has been
routinely used in literature, in lieu of detailed mass models; however, its
scatter, assumed to be $\sim30\%$, has not yet been quantified. Here, we assess
this method by testing it against ray-traced images of cluster-scale halos from
the Outer Rim N-body cosmological simulation. We measure a scatter of $13.9\%$
and a positive bias of $8.8\%$ in $M(<\theta_E)$, with no systematic
correlation with total cluster mass, concentration, or lens or source
redshifts. We find that increased deviation from spherical symmetry increases
the scatter; conversely, where the lens produces arcs that cover a large
fraction of its Einstein circle, both the scatter and the bias decrease. While
spectroscopic redshifts of the lensed sources are critical for accurate
magnifications and time delays, we show that for the purpose of estimating the
total enclosed mass, the scatter introduced by source redshift uncertainty is
negligible compared to other sources of error. Finally, we derive and apply an
empirical correction that eliminates the bias, and reduces the scatter to
$10.1\%$ without introducing new correlations with mass, redshifts, or
concentration. Our analysis provides the first quantitative assessment of the
uncertainties in $M(<\theta_E)$, and enables its effective use as a core mass
estimator of strong lensing galaxy clusters. |
Calibrating photometric redshift measurements with the Multi-channel
Imager (MCI) of the China Space Station Telescope (CSST): The China Space Station Telescope (CSST) photometric survey aims to perform a
high spatial resolution (~0.15'') photometric imaging for the targets that
cover a large sky area (~17,500 deg^2) and wide wavelength range (from NUV to
NIR). It expects to explore the properties of dark matter, dark energy, and
other important cosmological and astronomical areas. In this work, we evaluate
whether the filter design of the Multi-channel Imager (MCI), one of the five
instruments of the CSST, can provide accurate photometric redshift (photo-z)
measurements with its nine medium-band filters to meet the relevant scientific
objectives. We generate the mock data based on the COSMOS photometric redshift
catalog with astrophysical and instrumental effects. The application of upper
limit information of low signal-to-noise ratio (SNR) data is adopted in the
estimation of photo-z. We investigate the dependency of photo-z accuracy on the
filter parameters, such as band position and width. We find that the current
MCI filter design can achieve good photo-z measurements with accuracy
sigma_z~0.017 and outlier fraction f_c~2.2%. It can effectively improve the
photo-z measurements of the main CSST survey using the Survey Camera (SC) to an
accuracy sigma_z~0.015 and outlier fraction f_c~1.5%. It indicates that the
original MCI filters are proper for the photo-z calibration. | Preferred axis in cosmology: The foundation of modern cosmology relies on the so-called cosmological
principle which states an homogeneous and isotropic distribution of matter in
the universe on large scales. However, recent observations, such as the
temperature anisotropy of the cosmic microwave background (CMB) radiation, the
motion of galaxies in the universe, the polarization of quasars and the
acceleration of the cosmic expansion, indicate preferred directions in the sky.
If these directions have a cosmological origin, the cosmological principle
would be violated, and modern cosmology should be reconsidered. In this paper,
by considering the preferred axis in the CMB parity violation, we find that it
coincides with the preferred axes in CMB quadrupole and CMB octopole, and they
all align with the direction of the CMB kinematic dipole. In addition, the
preferred directions in the velocity flows, quasar alignment, anisotropy of the
cosmic acceleration, the handedness of spiral galaxies, and the angular
distribution of the fine-structure constant are also claimed to be aligned with
the CMB kinematic dipole. Since CMB dipole was confirmed to be caused by the
motion of our local group of galaxies relative to the reference frame of the
CMB, the coincidence of all these preferred directions hints that these
anomalies have a common origin, which is not cosmological or due to a
gravitational effect. The systematical or contaminative errors in observation
or in data analysis, which can be directly related to the motion of our local
group of galaxies, can play an important role in explaining the anomalies. |
On the accuracy and precision of correlation functions and field-level
inference in cosmology: We present a comparative study of the accuracy and precision of correlation
function methods and full-field inference in cosmological data analysis. To do
so, we examine a Bayesian hierarchical model that predicts log-normal fields
and their two-point correlation function. Although a simplified analytic model,
the log-normal model produces fields that share many of the essential
characteristics of the present-day non-Gaussian cosmological density fields. We
use three different statistical techniques: (i) a standard likelihood-based
analysis of the two-point correlation function; (ii) a likelihood-free
(simulation-based) analysis of the two-point correlation function; (iii) a
field-level analysis, made possible by the more sophisticated data assimilation
technique. We find that (a) standard assumptions made to write down a
likelihood for correlation functions can cause significant biases, a problem
that is alleviated with simulation-based inference; and (b) analysing the
entire field offers considerable advantages over correlation functions, through
higher accuracy, higher precision, or both. The gains depend on the degree of
non-Gaussianity, but in all cases, including for weak non-Gaussianity, the
advantage of analysing the full field is substantial. | Primordial perturbations from dilaton-induced gauge fields: We study the primordial scalar and tensor perturbations in inflation scenario
involving a spectator dilaton field. In our setup, the rolling spectator
dilaton causes a tachyonic instability of gauge fields, leading to a copious
production of gauge fields in the superhorizon regime, which generates
additional scalar and tensor perturbations through gravitational interactions.
Our prime concern is the possibility to enhance the tensor-to-scalar ratio $r$
relative to the standard result, while satisfying the observational
constraints. To this end, we allow the dilaton field to be stabilized before
the end of inflation, but after the CMB scales exit the horizon. We show that
for the inflaton slow roll parameter $\epsilon \gtrsim 10^{-3}$, the
tensor-to-scalar ratio in our setup can be enhanced only by a factor of ${\cal
O}(1)$ compared to the standard result. On the other hand, for smaller
$\epsilon$ corresponding to a lower inflation energy scale, a much bigger
enhancement can be achieved, so that our setup can give rise to an observably
large $r\gtrsim 10^{-2}$ even when $\epsilon\ll 10^{-3}$. The tensor
perturbation sourced by the spectator dilaton can have a strong scale
dependence, and is generically red-tilted. We also discuss a specific model to
realize our scenario, and identify the parameter region giving an observably
large $r$ for relatively low inflation energy scales. |
One line to run them all: SuperEasy massive neutrino linear response in
$N$-body simulations: We present in this work a novel and yet extremely simple method for
incorporating the effects of massive neutrinos in cosmological $N$-body
simulations. This so-called "SuperEasy linear response" approach is based upon
analytical solutions to the collisionless Boltzmann equation in the clustering
and free-streaming limits, which are then connected by a rational function
interpolation function with cosmology-dependent coefficients given by simple
algebraic expressions of the cosmological model parameters. The outcome is a
{\it one-line modification} to the gravitational potential that requires only
the cold matter density contrast as a real-time input, and that can be
incorporated into any $N$-body code with a Particle--Mesh component with no
additional implementation cost. To demonstrate its power, we implement the
SuperEasy method in the publicly available \gadgetcode{} code, and show that
for neutrino mass sums not exceeding $\sum m_\nu \simeq 1$ eV, the total matter
and cold matter power spectra are in sub-1\% and sub-0.1\% agreement with those
from state-of-the-art linear response simulations in literature. Aside from its
minimal implementation cost, compared with existing massive neutrino simulation
methods, the SuperEasy approach has better memory efficiency, incurs no runtime
overhead relative to a standard $\Lambda$CDM simulation, and requires no
post-processing. The minimal nature of the method allows limited computational
resources to be diverted to modelling other physical effects of interest, e.g.,
baryonic physics via hydrodynamics. | A dynamical model for the Taffy galaxies UGC 12914/5: The spectacular head-on collision of the two gas-rich galaxies of the Taffy
system, UGC 12914/15, gives us a unique opportunity to study the consequences
of a direct ISM-ISM collision. To interpret existing multi-wavelength
observations, we made dynamical simulations of the Taffy system including a
sticky particle component. To compare simulation snapshots to HI and CO
observations, we assume that the molecular fraction of the gas depends on the
square root of the gas volume density. For the comparison of our simulations
with observations of polarized radio continuum emission, we calculated the
evolution of the 3D large-scale magnetic field for our simulations. The
induction equations including the time-dependent gas-velocity fields from the
dynamical model were solved for this purpose. Our simulations reproduce the
stellar distribution of the primary galaxy, UGC 12914, the prominent HI and CO
gas bridge, the offset between the CO and HI emission in the bridge, the bridge
isovelocity vectors parallel to the bridge, the HI double-line profiles in the
bridge region, the large line-widths (~200 km/s) in the bridge region, the high
field strength of the bridge large-scale regular magnetic field, the projected
magnetic field vectors parallel to the bridge and the strong total power radio
continuum emission from the bridge. The stellar distribution of the secondary
model galaxy is more perturbed than observed. The observed distortion of the HI
envelope of the Taffy system is not reproduced by our simulations which use
initially symmetric gas disks. The model allows us to define the bridge region
in three dimensions. We estimate the total bridge gas mass (HI, warm and cold
H2) to be 5 to 6 10^9 M_sun, with a molecular fraction M_H2/M_HI of about unity
(abrigded). |
Modeling assembly bias with machine learning and symbolic regression: Upcoming 21cm surveys will map the spatial distribution of cosmic neutral
hydrogen (HI) over unprecedented volumes. Mock catalogues are needed to fully
exploit the potential of these surveys. Standard techniques employed to create
these mock catalogs, like Halo Occupation Distribution (HOD), rely on
assumptions such as the baryonic properties of dark matter halos only depend on
their masses. In this work, we use the state-of-the-art magneto-hydrodynamic
simulation IllustrisTNG to show that the HI content of halos exhibits a strong
dependence on their local environment. We then use machine learning techniques
to show that this effect can be 1) modeled by these algorithms and 2)
parametrized in the form of novel analytic equations. We provide physical
explanations for this environmental effect and show that ignoring it leads to
underprediction of the real-space 21-cm power spectrum at $k\gtrsim 0.05$ h/Mpc
by $\gtrsim$10\%, which is larger than the expected precision from upcoming
surveys on such large scales. Our methodology of combining numerical
simulations with machine learning techniques is general, and opens a new
direction at modeling and parametrizing the complex physics of assembly bias
needed to generate accurate mocks for galaxy and line intensity mapping
surveys. | Rhapsody-G simulations: galaxy clusters as baryonic closed boxes and the
covariance between hot gas and galaxies: Within a sufficiently large cosmic volume, conservation of baryons implies a
simple `closed box' view in which the sum of the baryonic components must equal
a constant fraction of the total enclosed mass. We present evidence from
Rhapsody-G hydrodynamic simulations of massive galaxy clusters that the
closed-box expectation may hold to a surprising degree within the interior,
non-linear regions of haloes. At a fixed halo mass, we find a significant
anti-correlation between hot gas mass fraction and galaxy mass fraction (cold
gas + stars), with a rank correlation coefficient of -0.69 within $R_{500c}$.
Because of this anti-correlation, the total baryon mass serves as a low-scatter
proxy for total cluster mass. The fractional scatter of total baryon fraction
scales approximately as $0.02 (\Delta_c/100)^{0.6}$, while the scatter of
either gas mass or stellar mass is larger in magnitude and declines more slowly
with increasing radius. We discuss potential observational tests using cluster
samples selected by optical and hot gas properties; the simulations suggest
that joint selection on stellar and hot gas has potential to achieve 5% scatter
in total halo mass. |
Cosmological parameter inference from galaxy clustering: The effect of
the posterior distribution of the power spectrum: We consider the shape of the posterior distribution to be used when fitting
cosmological models to power spectra measured from galaxy surveys. At very
large scales, Gaussian posterior distributions in the power do not approximate
the posterior distribution $\mathcal{P}_R$ we expect for a Gaussian density
field $\delta_k$, even if we vary the covariance matrix according to the model
to be tested. We compare alternative posterior distributions with
$\mathcal{P}_R$, both mode-by-mode and in terms of expected measurements of
primordial non-Gaussianity parameterised by $f_\mathrm{NL}$. Marginalising over
a Gaussian posterior distribution $\mathcal{P}_f$ with fixed covariance matrix
yields a posterior mean value of $f_\mathrm{NL}$ which, for a data set with the
characteristics of Euclid, will be underestimated by $\triangle
f_\mathrm{NL}=0.4$, while for the data release 9 (DR9) of the Sloan Digital Sky
Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) it will be
underestimated by $\triangle f_\mathrm{NL}=19.1$. Adopting a different form of
the posterior function means that we do not necessarily require a different
covariance matrix for each model to be tested: this dependence is absorbed into
the functional form of the posterior. Thus, the computational burden of
analysis is significantly reduced. | Evidence for a wide range of UV obscuration in z ~ 2 dusty galaxies from
the GOODS-Herschel survey: Dusty galaxies at z ~ 2 span a wide range of relative brightness between
rest-frame mid-infrared (8um) and ultraviolet wavelengths. We attempt to
determine the physical mechanism responsible for this diversity. Dust-obscured
galaxies (DOGs), which have rest-frame mid-IR to UV flux density ratios > 1000,
might be abnormally bright in the mid-IR, perhaps due to prominent AGN and/or
PAH emission, or abnormally faint in the UV. We use far-infrared data from the
GOODS-Herschel survey to show that most DOGs with 10^12 L_Sun < L_IR < 10^13
L_Sun are not abnormally bright in the mid-IR when compared to other dusty
galaxies with similar IR (8--1000um) luminosities. We observe a relation
between the median IR to UV luminosity ratios and the median UV continuum
power-law indices for these galaxies, and we find that only 24% have specific
star formation rates which indicate the dominance of compact star-forming
regions. This circumstantial evidence supports the idea that the UV- and
IR-emitting regions in these galaxies are spatially coincident, which implies a
connection between the abnormal UV faintness of DOGs and dust obscuration. We
conclude that the range in rest-frame mid-IR to UV flux density ratios spanned
by dusty galaxies at z ~ 2 is due to differing amounts of UV obscuration. Of
galaxies with these IR luminosities, DOGs are the most obscured. We attribute
differences in UV obscuration to either: 1) differences in the degree of
alignment between the spatial distributions of dust and massive stars, or 2)
differences in the total dust content. |
Cosmological parameter estimation via iterative emulation of likelihoods: The interpretation of cosmological observables requires the use of
increasingly sophisticated theoretical models. Since these models are becoming
computationally very expensive and display non-trivial uncertainties, the use
of standard Bayesian algorithms for cosmological inferences, such as MCMC,
might become inadequate. Here, we propose a new approach to parameter
estimation based on an iterative Gaussian emulation of the target likelihood
function. This requires a minimal number of likelihood evaluations and
naturally accommodates for stochasticity in theoretical models. We apply the
algorithm to estimate 9 parameters from the monopole and quadrupole of a mock
power spectrum in redshift space. We obtain accurate posterior distribution
functions with approximately 100 times fewer likelihood evaluations than an
affine invariant MCMC, roughly independently from the dimensionality of the
problem. We anticipate that our parameter estimation algorithm will accelerate
the adoption of more accurate theoretical models in data analysis, enabling
more comprehensive exploitation of cosmological observables. | Information theory for fields: A physical field has an infinite number of degrees of freedom since it has a
field value at each location of a continuous space. Therefore, it is impossible
to know a field from finite measurements alone and prior information on the
field is essential for field inference. An information theory for fields is
needed to join the measurement and prior information into probabilistic
statements on field configurations. Such an information field theory (IFT) is
built upon the language of mathematical physics, in particular on field theory
and statistical mechanics. IFT permits the mathematical derivation of optimal
imaging algorithms, data analysis methods, and even computer simulation
schemes. The application of IFT algorithms to astronomical datasets provides
high fidelity images of the Universe and facilitates the search for subtle
statistical signals from the Big Bang. The concepts of IFT might even pave the
road to novel computer simulations that are aware of their own uncertainties. |
Synchronize your \textit{chrono-brane}: Testing a variable brane tension
model with strong gravitational lensing: Brane world models have shown to be promising to understand the late cosmic
acceleration, in particular because such acceleration can be naturally derived,
mimicking the dark energy behaviour just with a five dimensional geometry. In
this paper we present a strong lensing joint analysis using a compilation of
early-type galaxies acting as a lenses, united with the power of the well
studied strong lensing galaxy cluster Abell\,1689. We use the strong lensing
constraints to investigate a brane model with variable brane tension as a
function of the redshift. In our joint analysis we found a value $n =
7.8^{+0.9}_{-0.5}$, for the exponent related to the brane tension, showing that
$n$ deviates from a Cosmological Constant (CC) scenario (n=6). We obtain a
value for the deceleration parameter, $q(z)$ today, $q(0)=-1.2^{+0.6}_{-0.8}$,
and a transition redshift, $z_t=0.60\pm0.06$ (when the Universe change from an
decelerated phase to an accelerated one). These results are in contrast with
previous work that favors CC scenario, nevertheless our lensing analysis is in
agreement with a formerly reported conclusion suggesting that the variable
brane tension model is able to source a late cosmic acceleration without an
extra fluid as in the standard one. | Impact of Polarized Galactic Foreground Emission on CMB Lensing
Reconstruction and Delensing of B-Modes: Next generation CMB experiments such as CMB-S4 aim at measuring the CMB
lensing potential at sub-percent precision where most of the constraining power
will come from CMB polarization. We investigate the prospects of achieving this
goal in the presence of large-scale, diffuse galactic foreground emission by
using non-Gaussian sky simulations and exploit multi-frequency information to
clean those. We show that, while prior to foreground cleaning, cosmological
parameter estimates from the contaminated lensing potential estimation can be
significantly biased, these can be successfully mitigated by applying a
parametric foreground cleaning approach. We further observe no significant
additional bias in the delensed B-mode power spectrum after applying foreground
cleaning and are therefore able to obtain an unbiased measurement of the
tensor-to-scalar ratio, $r$, after delensing. |
Ultra-compact radio sources and the isotropy and homogeneity of the
Universe: A 2.29 GHz VLBI all-sky survey of ultra-compact radio sources has formed the
basis of a number of cosmological investigations, which examine the
relationship between angular-size and redshift. Here I use a sample of 468 such
sources with 0.5<z<=3.787, to investigate the isotropy of the Universe. The
sample is divided into hemispherical sub-samples, over an all-sky 5 degree x 5
degree array, each of which is allowed to determine a value of Omega_m,
assuming that we are living in a spatially flat homogeneous isotropic LambdaCDM
model. If we regard the latter as a null hypothesis, then it fails the test --
the results show significant anisotropy, the smallest value of Omega_m being
towards (l,b)=(253.9,24.1) degrees, the largest in the opposite direction. This
is close to the CMB dipole axis, but in the obverse sense. This is interpreted
as meaning that the Universe is not spatially homogeneous on the largest
scales, and is better represented at late times by a spherically symmetric
model with a density enhancement at its centre. | Patchy Screening of the Cosmic Microwave Background by Inhomogeneous
Reionization: We derive a constraint on patchy screening of the cosmic microwave background
from inhomogeneous reionization, using off-diagonal TB and TT correlations in
WMAP-7 temperature/polarization data. We interpret this as a constraint on the
rms optical-depth fluctuation \Delta\tau\ as a function of a coherence
multipole Lc. We relate these parameters to a comoving coherence scale, of
bubble size Rc, in a phenomenological model where reionization is instantaneous
but occurs on a crinkly surface, and also to the bubble size in a model of
"Swiss cheese" reionization where bubbles of fixed size are spread over some
range of redshifts. The current WMAP data are still too weak, by several orders
of magnitude, to constrain reasonable models, but forthcoming Planck and future
EPIC data should begin to approach interesting regimes of parameter space. We
also present constraints on the parameter space imposed by the recent results
from the EDGES experiment. |
A template of atmospheric molecular oxygen circularly polarized emission
for CMB experiments: We compute the polarized signal from atmospheric molecular oxygen due to
Zeeman effect in the Earth magnetic field for various sites suitable for CMB
measurements such as South Pole, Dome C (Antarctica) and Atacama desert
(Chile). We present maps of this signal for those sites and show their typical
elevation and azimuth dependencies. We find a typical circularly polarized
signal (V Stokes parameter) level of 50 - 300 \mu K at 90 GHz when looking at
the zenith; Atacama site shows the lowest emission while Dome C site presents
the lowest gradient in polarized brightness temperature (0.3 \mu K/deg at 90
GHz). The accuracy and robustness of the template are tested with respect to
actual knowledge of the Earth magnetic field, its variability and atmospheric
parameters. | Bias, redshift space distortions and primordial nongaussianity of
nonlinear transformations: application to Lyman alpha forest: On large scales a nonlinear transformation of matter density field can be
viewed as a biased tracer of the density field itself. A nonlinear
transformation also modifies the redshift space distortions in the same limit,
giving rise to a velocity bias. In models with primordial nongaussianity a
nonlinear transformation generates a scale dependent bias on large scales. We
derive analytic expressions for these for a general nonlinear transformation.
These biases can be expressed entirely in terms of the one point distribution
function (PDF) of the final field and the parameters of the transformation. Our
analysis allows one to devise nonlinear transformations with nearly arbitrary
bias properties, which can be used to increase the signal in the large scale
clustering limit. We apply the results to the ionizing equilibrium model of
Lyman-alpha forest, in which Lyman-alpha flux F is related to the density
perturbation delta via a nonlinear transformation. Velocity bias can be
expressed as an average over the Lyman-alpha flux PDF. At z=2.4 we predict the
velocity bias of -0.1, compared to the observed value of -0.13 +/- 0.03. Bias
and primordial nongaussianity bias depend on the parameters of the
transformation. Measurements of bias can thus be used to constrain these
parameters, and for reasonable values of the ionizing background intensity we
can match the predictions to observations. Matching to the observed values we
predict the ratio of primordial nongaussianity bias to bias to have the
opposite sign and lower magnitude than the corresponding values for the highly
biased galaxies, but this depends on the model parameters and can also vanish
or change the sign. |
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