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Full-sky map of the ISW and Rees-Sciama effect from Gpc simulations: We present a new method for constructing maps of the secondary temperature
fluctuations imprinted on the cosmic microwave background (CMB) radiation by
photons propagating through the evolving cosmic gravitational potential. Large
cosmological N-body simulations are used to calculate the complete non-linear
evolution of the peculiar gravitational potential. Tracing light rays back
through the past lightcone of a chosen observer accurately captures the
temperature perturbations generated by linear (the integrated Sachs-Wolfe or
ISW effect) and non-linear (the Rees-Sciama or RS effect) evolution. These
effects give rise to three kinds of non-linear features in the temperature
maps. (a) In overdense regions, converging flows of matter induce cold spots of
order 100 Mpc in extent which can dominate over the ISW effect at high
redshift, and are surrounded by hot rings. (b) In underdense regions, the RS
effect enhances ISW cold spots which can be surrounded by weak hot rings. (c)
Transverse motions of large lumps of matter produce characteristic dipole
features, consisting of adjacent hot and cold spots separated by a few tens of
Megaparsecs. These non-linear features are not easily detectable; they modulate
the ISW sky maps at about the 10 percent level. The RS effect causes the
angular power spectrum to deviate from linear theory at l~50 and generates
non-Gaussianity, skewing the one-point distribution function to negative
values. Cold spots of similar angular size, but much smaller amplitude than the
CMB cold spot reported by Cruz et al. are produced. Joint analysis of our maps
and the corresponding galaxy distribution may enable techniques to be developed
to detect these non-linear, non-Gaussian features. Our maps are available at
http://astro.dur.ac.uk/~cai/ISW | Cosmic Microwave Background anisotropies generated by cosmic strings
with small-scale structure: We study the impact of kinks on the cosmic microwave background (CMB)
anisotropies generated by cosmic string networks. To do so, we extend the
Unconnected Segment Model to describe the stress-energy tensor of a network of
cosmic strings with kinks and implement this extension in CMBACT to compute the
CMB anisotropies generated by these wiggly string networks. Our results show
that the inclusion of kinks leads, in general, to an enhancement of the
temperature and polarization angular power spectra, when compared to those
generated by cosmic string networks without small-scale structure with the same
energy density, on scales corresponding to the distance between kinks. This
enhancement, that is more prominent in the case of the temperature
anisotropies, is essentially caused by a significant increase of the
vector-mode anisotropies, since kinks, due to their shape, generate vortical
motions of matter -- a phenomenon that is not taken into account when resorting
to an effective description of wiggly cosmic strings. |
Fluid phonons, protoinflationary dynamics and large-scale gravitational
fluctuations: We explore what can be said on the effective temperature and sound speed of a
statistical ensemble of fluid phonons present at the onset of a conventional
inflationary phase. The phonons are the actual normal modes of the gravitating
and irrotational fluid that dominates the protoinflationary dynamics. The
bounds on the tensor to scalar ratio result in a class of novel constraints
involving the slow roll parameter, the sound speed of the phonons and the
temperature of the plasma prior to the onset of inflation. If the current size
of the Hubble radius coincides with the inflationary event horizon redshifted
down to the present epoch, the sound speed of the phonons can be assessed from
independent measurements of the tensor to scalar ratio and of the tensor
spectral index. | A core-halo pattern of entropy creation in gravitational collapse: This paper presents a kinetic theory model of gravitational collapse due to a
small perturbation. Solving the relevant equations yields a pattern of entropy
destruction in a spherical core around the perturbation, and entropy creation
in a surrounding halo. This indicates collisional "de-relaxation" in the core,
and collisional relaxation in the halo. Core-halo patterns are ubiquitous in
the astrophysics of gravitational collapse, and are found here without any of
the prior assumptions of such a pattern usually made in analytical models.
Motivated by this analysis, the paper outlines a possible scheme for
identifying structure formation in a set of observations or a simulation. This
scheme involves a choice of coarse-graining scale appropriate to the structure
under consideration, and might aid exploration of hierarchical structure
formation, supplementing the usual density-based methods for highlighting
astrophysical and cosmological structure at various scales. |
Local Gravity versus Local Velocity: Solutions for $β$ and nonlinear
bias: (abridged) We perform a reconstruction of the cosmological large scale flows
in the nearby Universe using two complementary observational sets. The first,
the SFI++ sample of Tully-Fisher (TF) measurements of galaxies, provides a
direct probe of the flows. The second, the whole sky distribution of galaxies
in the 2MASS redshift survey (2MRS), yields a prediction of the flows given the
cosmological density parameter, $\Omega$, and a biasing relation between mass
and galaxies. We aim at an unbiased comparison between the peculiar velocity
fields extracted from the two data sets and its implication on the cosmological
parameters and the biasing relation. We expand the fields in a set of
orthonormal basis functions, each representing a plausible realization of a
cosmological velocity field. Our analysis completely avoids the strong error
covariance in the smoothed TF velocities by the use of orthonormal basis
functions and employs elaborate realistic mock data sets to extensively
calibrate the errors in 2MRS predicted velocities. We relate the 2MRS galaxy
distribution to the mass density field by a linear bias factor, $b$, and
include a luminosity dependent, $\propto L^\alpha$, galaxy weighting. We assess
the agreement between the fields as a function of $\alpha$ and
$\beta=f(\Omega)/b$, where $f$ is the growth factor of linear perturbations.
The agreement is excellent with a reasonable $\chi^2$ per degree of freedom.
For $\alpha=0$, we derive $0.28<\beta<0.37$ and $0.24<\beta<0.43$,
respectively, at the 68.3% and 95.4% confidence levels (CLs). For $\beta=0.33$,
we get $\alpha<0.25$ and $\alpha<0.5$, respectively, at the 68.3% and 95.4%
CLs. We set a constraint on the fluctuation normalization, finding $\sigma_8 =
0.73 \pm 0.1$, in very good agreement with the latest WMAP results. | The highest-frequency detection of a radio relic: 16-GHz AMI
observations of the `Sausage' cluster: We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin
Imager at $16$ GHz and present the first high radio-frequency detection of
diffuse, non-thermal cluster emission. This cluster hosts a variety of bright,
extended, steep-spectrum synchrotron-emitting radio sources, associated with
the intra-cluster medium, called radio relics. Most notably, the northern,
Mpc-wide, narrow relic provides strong evidence for diffusive shock
acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse
extension of the southern relic, which is not visible in the lower
radio-frequency maps. The northern radio relic is unequivocally detected and
measures an integrated flux of $1.2\pm0.3$ mJy. While the low-frequency ($<2$
GHz) spectrum of the northern relic is well represented by a power-law, it
clearly steepens towards $16$ GHz. This result is inconsistent with diffusive
shock acceleration predictions of ageing plasma behind a uniform shock front.
The steepening could be caused by an inhomogeneous medium with
temperature/density gradients or by lower acceleration efficiencies of high
energy electrons. Further modelling is necessary to explain the observed
spectrum. |
The case for a directional dark matter detector and the status of
current experimental efforts: We present the case for a dark matter detector with directional sensitivity.
This document was developed at the 2009 CYGNUS workshop on directional dark
matter detection, and contains contributions from theorists and experimental
groups in the field. We describe the need for a dark matter detector with
directional sensitivity; each directional dark matter experiment presents their
project's status; and we close with a feasibility study for scaling up to a one
ton directional detector, which would cost around $150M. | Radio properties of H2O maser host galaxies: The 6 cm and 20 cm radio continuum properties of all 85 galaxies with
reported 22 GHz H2O maser emission and luminosity distance D > 0.5 Mpc are
studied. For the total of 55 targets for which both 6 cm and 20 cm measurements
exist and for the subsample of 42 sources with masers related to active
galactic nuclei (AGN), a spectral index could be determined from an assumed
power-law dependence. The mean value of the resulting spectral index is in both
cases 0.66+-0.07. Comparing radio properties of the maser galaxies with a
sample of Seyferts without detected H2O maser, we find that (1) the spectral
indices agree within the error limits, and (2) maser host galaxies have higher
nuclear radio continuum luminosities, exceeding those of the comparison sample
by factors of order 5. Only considering the subsample of galaxies with masers
associated with AGN, there seems to be a trend toward rising maser luminosity
with nuclear radio luminosity (both at 6 cm and 20 cm). However, when
accounting for the Malmquist effect, the correlation weakens to a level, which
is barely significant. Overall, the study indicates that nuclear radio
luminosity is a suitable indicator to guide future AGN maser searches and to
enhance detection rates, which are otherwise quite low (<10%). |
Calibration of GRB Luminosity Relations with Cosmography: For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a
cosmology-independent way, a new method has been proposed to obtain luminosity
distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia,
and then calibrating GRB relations at high redshift. In this paper, following
the basic assumption in the interpolation method that objects at the same
redshift should have the same luminosity distance, we propose another approach
to calibrate GRB luminosity relations with cosmographic fitting directly from
SN Ia data. In cosmography, there is a well-known fitting formula which can
reflect the Hubble relation between luminosity distance and redshift with
cosmographic parameters which can be fitted from observation data. Using the
Cosmographic fitting results from the Union set of SNe Ia, we calibrate five
GRB relations using GRB sample at $z\leq1.4$ and deduce distance moduli of GRBs
at $1.4< z \leq 6.6$ by generalizing above calibrated relations at high
redshift. Finally, we constrain the dark energy parameterization models of the
Chevallier-Polarski-Linder (CPL) model, the Jassal-Bagla-Padmanabhan (JBP)
model and the Alam model with GRB data at high redshift, as well as with the
Cosmic Microwave Background radiation (CMB) and the baryonic acoustic
oscillation (BAO) observations, and we find the $\Lambda$CDM model is
consistent with the current data in 1-$\sigma$ confidence region. | Core or cusps: The central dark matter profile of a redshift one strong
lensing cluster with a bright central image: We report on SPT-CLJ2011-5228, a giant system of arcs created by a cluster at
$z=1.06$. The arc system is notable for the presence of a bright central image.
The source is a Lyman Break galaxy at $z_s=2.39$ and the mass enclosed within
the 14 arc second radius Einstein ring is $10^{14.2}$ solar masses. We perform
a full light profile reconstruction of the lensed images to precisely infer the
parameters of the mass distribution. The brightness of the central image
demands that the central total density profile of the lens be shallow. By
fitting the dark matter as a generalized Navarro-Frenk-White profile---with a
free parameter for the inner density slope---we find that the break radius is
$270^{+48}_{-76}$ kpc, and that the inner density falls with radius to the
power $-0.38\pm0.04$ at 68 percent confidence. Such a shallow profile is in
strong tension with our understanding of relaxed cold dark matter halos; dark
matter only simulations predict the inner density should fall as $r^{-1}$. The
tension can be alleviated if this cluster is in fact a merger; a two halo model
can also reconstruct the data, with both clumps (density going as $r^{-0.8}$
and $r^{-1.0}$) much more consistent with predictions from dark matter only
simulations. At the resolution of our Dark Energy Survey imaging, we are unable
to choose between these two models, but we make predictions for forthcoming
Hubble Space Telescope imaging that will decisively distinguish between them. |
The Abundance Gradient in the Extremely Faint Outer Disk of NGC 300: In earlier work, we showed for the first time that the resolved stellar disk
of NGC 300 is very extended with no evidence for truncation, a phenomenon that
has since been observed in other disk galaxies. We revisit the outer disk of
NGC 300 in order to determine the metallicity of the faint stellar population.
With the GMOS camera at Gemini South, we reach 50% completeness at (g',
i')=(26.8-27.4,26.1-27.0) in photometric conditions and 0.7" seeing. At these
faint depths, careful consideration must be given to the background galaxy
population. The mean colors of the outer disk stars fall within the spread of
colors for the background galaxies, but the stellar density dominates the
background galaxies by ~2:1. The predominantly old stellar population in the
outer disk exhibits a negative abundance gradient - as expected from models of
galaxy evolution - out to about 10 kpc where the abundance trend changes sign.
We present two scenarios to explain the flattening, or upturn, in the
metallicity gradient of NGC 300 and discuss the implication this has for the
broader picture of galaxy formation. | Constraining broad-line regions from time lags of broad emission lines
relative to radio emission: In this paper, a new method is proposed to estimate the broad-line region
sizes of UV lines $R^{\rm{uv}}_{\rm{BLR}}$. It is applied to 3C 273. First, we
derive the time lags of radio emission relative to broad emission lines
Ly$\alpha$ and C IV by the ZDCF method. The broad lines lag the 5, 8, 15, 22
and 37 GHz emission. The measured lags $\tau^{\rm{uv}}_{\rm{ob}}$ are of the
order of years. For a given line, $\tau^{\rm{uv}}_{\rm{ob}}$ decreases as the
radio frequency increases. This trend results from the radiative cooling of
relativistic electrons. Both UV lines have a lag of
$\tau^{\rm{uv}}_{\rm{ob}}=-2.74^{+0.06}_{-0.25}$ yr relative to the 37 GHz
emission. These results are consistent with those derived from the Balmer lines
in Paper I. Second, we derive the time lags of the lines Ly$\alpha$, CIV,
H$\gamma$, H$\beta$ and H$\alpha$ relative to the 37 GHz emission by the FR/RSS
Monte Carlo method. The measured lags are
$\tau_{\rm{ob}}=-3.40^{+0.31}_{-0.05}$, $-3.40^{+0.41}_{-0.14}$,
$-2.06^{+0.36}_{-0.92}$, $-3.40^{+1.15}_{-0.20}$ and $-3.56^{+0.35}_{-0.18}$ yr
for the lines Ly$\alpha$, CIV, H$\gamma$, H$\beta$ and H$\alpha$, respectively.
These estimated lags are consistent with those derived by the ZDCF method
within the uncertainties. Based on the new method, we derive
$R^{\rm{uv}}_{\rm{BLR}}=2.54^{+0.71}_{-0.35}$--$4.01^{+0.90}_{-1.16}$ and
$2.54^{+0.80}_{-0.43}$--$4.01^{+0.98}_{-1.24}$ light-years for the Ly$\alpha$
and CIV lines, respectively. Considering the uncertainties, these estimated
sizes are consistent with those obtained in the classical reverberation mapping
for the UV lines and the Balmer lines. This indicates that their emitting
regions are not separated so large as in the classical mapping of the UV and
optical lines. These results seem to depart from the stratified ionization
structures obtained in the classical mapping. |
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). II. Constraints on
star formation in ram-pressure stripped gas: Context: Several galaxies in the Virgo cluster are known to have large HI gas
tails related to a recent ram-pressure stripping event. The Virgo cluster has
been extensively observed at 1539 A in the far-ultraviolet for the GALEX
Ultraviolet Virgo Cluster Survey (GUViCS), and in the optical for the Next
Generation Virgo Survey (NGVS), allowing a study of the stellar emission
potentially associated with the gas tails of 8 cluster members. On the
theoretical side, models of ram-pressure stripping events have started to
include the physics of star formation. Aim: We aim to provide quantitative
constraints on the amount of star formation taking place in the ram-pressure
stripped gas, mainly on the basis of the far-UV emission found in the GUViCS
images in relation with the gas content of the tails. Methods: We have
performed three comparisons of the young stars emission with the gas column
density: visual, pixel-by-pixel and global. We have compared our results to
other observational and theoretical studies. Results: We find that the level of
star formation taking place in the gas stripped from galaxies by ram-pressure
is low with respect to the available amount of gas. Star formation is lower by
at least a factor 10 compared to the predictions of the Schmidt Law as
determined in regular spiral galaxy disks. It is also lower than measured in
dwarfs galaxies and the outer regions of spirals, and than predicted by some
numerical simulations. We provide constraints on the star formation efficiency
in the ram-pressure stripped gas tails, and compare these with current models. | A gravitational-wave standard siren measurement of the Hubble constant: The detection of GW170817 in both gravitational waves and electromagnetic
waves heralds the age of gravitational-wave multi-messenger astronomy. On 17
August 2017 the Advanced LIGO and Virgo detectors observed GW170817, a strong
signal from the merger of a binary neutron-star system. Less than 2 seconds
after the merger, a gamma-ray burst (GRB 170817A) was detected within a region
of the sky consistent with the LIGO-Virgo-derived location of the
gravitational-wave source. This sky region was subsequently observed by optical
astronomy facilities, resulting in the identification of an optical transient
signal within $\sim 10$ arcsec of the galaxy NGC 4993. These multi-messenger
observations allow us to use GW170817 as a standard siren, the
gravitational-wave analog of an astronomical standard candle, to measure the
Hubble constant. This quantity, which represents the local expansion rate of
the Universe, sets the overall scale of the Universe and is of fundamental
importance to cosmology. Our measurement combines the distance to the source
inferred purely from the gravitational-wave signal with the recession velocity
inferred from measurements of the redshift using electromagnetic data. This
approach does not require any form of cosmic "distance ladder;" the
gravitational wave analysis can be used to estimate the luminosity distance out
to cosmological scales directly, without the use of intermediate astronomical
distance measurements. We determine the Hubble constant to be
$70.0^{+12.0}_{-8.0} \, \mathrm{km} \, \mathrm{s}^{-1} \, \mathrm{Mpc}^{-1}$
(maximum a posteriori and 68% credible interval). This is consistent with
existing measurements, while being completely independent of them. Additional
standard-siren measurements from future gravitational-wave sources will provide
precision constraints of this important cosmological parameter. |
Mitigating Complex Dust Foregrounds in Future CMB Polarization
Experiments: Polarized Galactic foregrounds are one of the primary sources of systematic
error in measurements of the B-mode polarization of the Cosmic Microwave
Background (CMB). Experiments are becoming increasingly sensitive to
complexities in the foreground frequency spectra that are not captured by
standard parametric models, potentially affecting our ability to efficiently
separate out these components. Employing a suite of dust models encompassing a
variety of physical effects, we simulate observations of a future seven-band
CMB experiment to assess the impact of these complexities on parametric
component separation. We identify configurations of frequency bands that
minimize the `model errors' caused by fitting simple parametric models to more
complex `true' foreground spectra, which bias the inferred CMB signal. We find
that: (a) fits employing a simple two parameter modified blackbody (MBB) dust
model tend to produce significant bias in the recovered polarized CMB signal in
the presence of physically realistic dust foregrounds; (b) generalized MBB
models with three additional parameters reduce this bias in most cases, but
non-negligible biases can remain, and can be hard to detect; and (c) line of
sight effects, which give rise to frequency decorrelation, and the presence of
iron grains are the most problematic complexities in the dust emission for
recovering the true CMB signal. More sophisticated simulations will be needed
to demonstrate that future CMB experiments can successfully mitigate these more
physically realistic dust foregrounds. | On the nature of disks at high redshift seen by JWST/CEERS with
contrastive learning and cosmological simulations: Visual inspections of the first optical rest-frame images from JWST have
indicated a surprisingly high fraction of disk galaxies at high redshifts.
Here, we alternatively apply self-supervised machine learning to explore the
morphological diversity at $z \geq 3$. Our proposed data-driven representation
scheme of galaxy morphologies, calibrated on mock images from the TNG50
simulation, is shown to be robust to noise and to correlate well with the
physical properties of the simulated galaxies, including their 3D structure. We
apply the method simultaneously to F200W and F356W galaxy images of a
mass-complete sample ($M_*/M_\odot>10^9$) at $ 3 \leq z \leq 6$ from the first
JWST/NIRCam CEERS data release. We find that the simulated and observed
galaxies do not exactly populate the same manifold in the representation space
from contrastive learning. We also find that half the galaxies classified as
disks -- either CNN-based or visually -- populate a similar region of the
representation space as TNG50 galaxies with low stellar specific angular
momentum and non-oblate structure. Although our data-driven study does not
allow us to firmly conclude on the true nature of these galaxies, it suggests
that the disk fraction at $z \geq 3$ remains uncertain and possibly
overestimated by traditional supervised classifications. Deeper imaging and
spectroscopic follow-ups as well as comparisons with other simulations will
help to unambiguously determine the true nature of these galaxies, and
establish more robust constraints on the emergence of disks at very high
redshift. |
Halo/Galaxy Bispectrum with Equilateral-type Primordial Trispectrum: We investigate the effect of equilateral-type primordial trispectrum on the
halo/galaxy bispectrum. We consider three types of equilateral primordial
trispectra which are generated by quartic operators naturally appeared in the
effective field theory of inflation and can be characterized by three
non-linearity parameters, $g_{\rm NL} ^{\dot{\sigma}^4}$, $g_{\rm NL}
^{\dot{\sigma}^2 (\partial \sigma)^2}$, and $g_{\rm NL} ^{(\partial
\sigma)^4}$. Recently, constraints on these parameters have been investigated
from CMB observations by using WMAP9 data. In order to consider the halo/galaxy
bispectrum with the equilateral-type primordial trispectra, we adopt the
integrated Perturbation Theory (iPT) in which the effects of primordial
non-Gaussianity are wholly encapsulated in the linear primordial polyspectrum
for the evaluation of the biased polyspectrum. We show the shapes of the
halo/galaxy bispectrum with the equilateral-type primordial trispectra, and
find that the primordial trispectrum characterized by $g_{\rm NL}
^{\dot{\sigma}^4}$ provides the same scale-dependence as the gravity-induced
halo/galaxy bispectrum. Hence, it would be difficult to obtain the constraint
on $g_{\rm NL} ^{\dot{\sigma}^4}$ from the observations of the halo/galaxy
bispectrum. On the other hand, the primordial trispectra characterized by
$g_{\rm NL} ^{\dot{\sigma}^2 (\partial \sigma)^2}$ and $g_{\rm NL} ^{(\partial
\sigma)^4}$ provide the common scale-dependence which is different from that of
the gravity-induced halo/galaxy bispectrum on large scales. Hence future
observations of halo/galaxy bispectrum would give constraints on the
non-linearity parameters, $g_{\rm NL} ^{\dot{\sigma}^2 (\partial \sigma)^2}$
and $g_{\rm NL} ^{(\partial \sigma)^4}$ independently from CMB observations and
it is expected that these constraints can be comparable to ones obtained by
CMB. | Response approach to the squeezed-limit bispectrum: application to the
correlation of quasar and Lyman-$α$ forest power spectrum: The squeezed-limit bispectrum, which is generated by nonlinear gravitational
evolution as well as inflationary physics, measures the correlation of three
wavenumbers, in the configuration where one wavenumber is much smaller than the
other two. Since the squeezed-limit bispectrum encodes the impact of a
large-scale fluctuation on the small-scale power spectrum, it can be understood
as how the small-scale power spectrum "responds" to the large-scale
fluctuation. Viewed in this way, the squeezed-limit bispectrum can be
calculated using the response approach even in the cases which do not submit to
perturbative treatment. To illustrate this point, we apply this approach to the
cross-correlation between the large-scale quasar density field and small-scale
Lyman-$\alpha$ forest flux power spectrum. In particular, using separate
universe simulations which implement changes in the large-scale density,
velocity gradient, and primordial power spectrum amplitude, we measure how the
Lyman-$\alpha$ forest flux power spectrum responds to the local,
long-wavelength quasar overdensity, and equivalently their squeezed-limit
bispectrum. We perform a Fisher forecast for the ability of future experiments
to constrain local non-Gaussianity using the bispectrum of quasars and the
Lyman-$\alpha$ forest. Combining with quasar and Lyman-$\alpha$ forest power
spectra to constrain the biases, we find that for DESI the expected $1-\sigma$
constraint is ${\rm err}[f_{\rm NL}]\sim60$. Ability for DESI to measure
$f_{\rm NL}$ through this channel is limited primarily by the aliasing and
instrumental noise of the Lyman-$\alpha$ forest flux power spectrum. The
combination of response approach and separate universe simulations provides a
novel technique to explore the constraints from the squeezed-limit bispectrum
between different observables. |
The detailed nature of active central cluster galaxies: We present detailed integral field unit (IFU) observations of the central few
kiloparsecs of the ionised nebulae surrounding four active central cluster
galaxies (CCGs) in cooling flow clusters (Abell 0496, 0780, 1644 and 2052). Our
sample consists of CCGs with H{\alpha} filaments, and have existing data from
the X-ray regime available. Here, we present the detailed optical emission-line
(and simultaneous absorption line) data over a broad wavelength range to probe
the dominant ionisation processes, excitation sources, morphology and
kinematics of the hot gas (as well as the morphology and kinematics of the
stars). This, combined with the other multiwavelength data, will form a
complete view of the different phases (hot and cold gas and stars) and how they
interact in the processes of star formation and feedback detected in central
galaxies in cooling flow clusters, as well as the influence of the host
cluster. We derive the optical dust extinction maps of the four nebulae. We
also derive a range of different kinematic properties, given the small sample
size. For Abell 0496 and 0780, we find that the stars and gas are kinematically
decoupled, and in the case of Abell 1644 we find that these components are
aligned. For Abell 2052, we find that the gaseous components show rotation even
though no rotation is apparent in the stellar components. To the degree that
our spatial resolution reveals, it appears that all the optical forbidden and
hydrogen recombination lines originate in the same gas for all the galaxies.
Based on optical diagnostic ratios ([OIII]{\lambda}5007/H{\beta} against
[NII]{\lambda}6584/H{\alpha}, [SII]{\lambda}{\lambda}6717,6731/H{\alpha}, and
[OI]{\lambda}6300/H{\alpha}), all galaxies show extended LINER emission, but
that at least one has significant Seyfert emission areas, and at least one
other has significant HII like emission line ratios for many pixels. ABRIDGED. | Imprints of Reionization in Galaxy Clustering: Reionization, the only phase transition in the Universe since recombination,
is a key event in the cosmic history of baryonic matter. We derive, in the
context of the large-scale bias expansion, the imprints of the epoch of
reionization in the large-scale distribution of galaxies, and identify two
contributions of particular importance. First, the Compton scattering of CMB
photons off the free electrons lead to a drag force on the baryon fluid. This
drag induces a relative velocity between baryons and CDM which is of the same
order of magnitude as the primordially-induced relative velocity, and enters in
the evolution of the relative velocity as calculated by Boltzmann codes. This
leads to a unique contribution to galaxy bias involving the matter velocity
squared. The second important effect is a modulation of the galaxy density by
the ionizing radiation field through radiative-transfer effects, which is
captured in the bias expansion by so-called higher-derivative terms. We
constrain both of these imprints using the power spectrum of the BOSS DR12
galaxy sample. While they do not lead to a shift in the baryon acoustic
oscillation scale, including these terms is important for unbiased cosmology
constraints from the shape of the galaxy power spectrum. |
New tools for probing the phase space structure of dark matter halos: We summarize recent developments in the use of spectral methods for analyzing
large numbers of orbits in N-body simulations to obtain insights into the
global phase space structure of dark matter halos. The fundamental frequencies
of oscillation of orbits can be used to understand the physical mechanism by
which the shapes of dark matter halos evolve in response to the growth of
central baryonic components. Halos change shape primarily because individual
orbits change their shapes adiabatically in response to the growth of a
baryonic component, with those at small radii become preferentially rounder.
Chaotic scattering of orbits occurs only when the central point mass is very
compact and is equally effective for centrophobic long-axis tube orbits as it
is for centrophilic box orbits. | The relationship between star formation rates, local density and stellar
mass up to z ~ 3 in the GOODS NICMOS Survey: We investigate the relation between star formation rates and local galaxy
environment for a stellar mass selected galaxy sample in the redshift range 1.5
< z < 3. We use near-infra-red imaging from an extremely deep Hubble Space
Telescope survey, the GOODS-NICMOS Survey (GNS) to measure local galaxy
densities based on the nearest neighbour approach, while star-formation rates
are estimated from rest-frame UV-fluxes. Due to our imaging depth we can
examine galaxies down to a colour-independent stellar mass completeness limit
of log M\ast = 9.5 M\odot at z ~ 3. We find a strong dependence of star
formation activity on galaxy stellar mass over the whole redshift range, which
does not depend on local environment. The average star formation rates are
largely independent of local environment apart from in the highest relative
over-densities. Galaxies in over-densities of a factor of > 5 have on average
lower star formation rates by a factor of 2 - 3, but only up to redshifts of z
~ 2. We do not see any evidence for AGN activity influencing these relations.
We also investigate the influence of the very local environment on
star-formation activity by counting neighbours within 30 kpc radius. This shows
that galaxies with two or more close neighbours have on average significantly
lower star formation rates as well as lower specific star formation rates up to
z ~ 2.5. We suggest that this might be due to star formation quenching induced
by galaxy merging processes. |
Growth of perturbations in an expanding universe with Bose-Einstein
condensate dark matter: We study the growth of perturbations in an expanding Newtonian universe with
Bose-Einstein condensate dark matter. We first ignore special relativistic
effects and derive a differential equation governing the evolution of the
density contrast in the linear regime taking into account quantum pressure and
self-interaction. This equation can be solved analytically in several cases. We
argue that an attractive self-interaction can enhance the Jeans instability and
fasten the formation of structures. Then, we take into account pressure effects
(coming from special relativity) in the evolution of the cosmic fluid and add
the contribution of radiation, baryons and dark energy (cosmological constant).
For a BEC dark matter with repulsive self-interaction (positive pressure) the
scale factor increases more rapidly than in the standard \Lambda CDM model
where dark matter is pressureless while for a BEC dark matter with attractive
self-interaction (negative pressure) it increases less rapidly. We study the
linear development of the perturbations in these two cases and show that the
perturbations grow faster in a BEC dark matter than in a pressureless dark
matter. This confirms a recent result of Harko (2011). Finally, we consider a
"dark fluid" with a generalized equation of state p=(\alpha \rho + k \rho
^2)c^2 having a component p=k \rho ^2 c^2 similar to a BEC dark matter and a
component p=\alpha \rho c^2 mimicking the effect of the cosmological constant
(dark energy). We find optimal parameters that give a good agreement with the
standard \Lambda CDM model assuming a finite cosmological constant. | The Evolution of Early-type Galaxies Selected by Their Spatial
Clustering: Aims: We present a new method that uses luminosity or stellar mass functions
combined with clustering measurements to select samples of galaxies at
different redshifts likely to follow a progenitor-to-descendant relationship.
As the method uses clustering information, we refer to galaxy samples selected
this way as clustering-selected samples. We apply this method to infer the
number of mergers during the evolution of MUSYC early-type galaxies (ETGs) from
z~1 to the present-day. Methods: The method consists in using clustering
information to infer the typical dark-matter halo mass of the hosts of the
selected progenitor galaxies. Using LambdaCDM predictions, it is then possible
to follow these haloes to a later time where the sample of descendants will be
that with the clustering of these descendant haloes. Results: This technique
shows that ETGs at a given redshift evolve into brighter galaxies at lower
redshifts (considering rest-frame, passively evolved optical luminosities).
This indicates that the stellar mass of these galaxies increases with time and
that, in principle, a stellar mass selection at different redshifts does not
provide samples of galaxies in a progenitor-descendant relationship.
Conclusions: The comparison between high redshift ETGs and their likely
descendants at z=0 points to a higher number density for the progenitors by a
factor 5.5+-4.0, implying the need for mergers to decrease their number density
by today. Because the luminosity densities of progenitors and descendants are
consistent, our results show no need for significant star-formation in ETGs
since z=1, which indicates that the needed mergers are dry, i.e. gas free. |
Solitons in the dark: non-linear structure formation with fuzzy dark
matter: We present the results of a full cosmological simulation with the new code
SCALAR, where dark matter is in form of fuzzy dark matter, described by a light
scalar field with a mass of $m_{\rm B} = 2.5 \times 10^{-22}$ eV and evolving
according to the Schr\"{o}dinger-Poisson system of equations. In comoving
units, the simulation volume is $2.5 ~ h^{-1} {\rm Mpc}$ on a side, with a
resolution of $20~h^{-1}{\rm pc}$ at the finest refinement level. We analyse
the formation and the evolution of central solitonic cores, which are found to
leave their imprints on dark matter density profiles, resulting in shallower
central densities, and on rotation curves, producing an additional circular
velocity peak at small radii from the center. We find that the suppression of
structures due to the quantum nature of the scalar field results in an
shallower halo mass function in the low-mass end compared to the case of a
$\Lambda$CDM simulation, in which dark matter is expected to cluster at all
mass scales even if evolved with the same initial conditions used for fuzzy
dark matter. Furthermore, we verify the scaling relations characterising the
solution to the Schr\"{o}dinger-Poisson system, for both isolated and merging
halos, and we find that they are preserved by merging processes. We
characterise each fuzzy dark matter halo in terms of the dimensionless quantity
$\Xi \propto \left | E_{\rm halo} \right |/M_{\rm halo}^3$ and we show that the
core mass is tightly linked to the halo mass by the core-halo mass relation
$M_{\rm core}/M_{\rm halo} \propto \Xi^{1/3}$. We also show that the core
surface density of the simulated fuzzy dark matter halos does not follow the
scaling with the core radius as observed for dwarf galaxies, representing a big
challenge for the fuzzy dark matter model as the sole explanation of core
formation. | Degenerate Fermi gas perturbations at standard background cosmology: The hypothesis of a tiny fraction of the cosmic inventory evolving
cosmologically as a degenerate Fermi gas test fluid at some dominant
cosmological background is investigated. Our analytical results allow for
performing preliminary computations to the evolution of perturbations for
relativistic and non-relativistic test fluids. The density fluctuation,
$\delta$, the fluid velocity divergence, $\theta$, and an explicit expression
for the dynamics of the shear stress, $\sigma$, are obtained for a degenerate
Fermi gas in the background regime of radiation. Extensions to the dominance of
matter and to the $\Lambda$CDM cosmological background are also investigated
and lessons concerning the formation of large structures of degenerate Fermi
gas are depicted. |
Reconstructing the massive black hole cosmic history through
gravitational waves: The massive black holes we observe in galaxies today are the natural
end-product of a complex evolutionary path, in which black holes seeded in
proto-galaxies at high redshift grow through cosmic history via a sequence of
mergers and accretion episodes. Electromagnetic observations probe a small
subset of the population of massive black holes (namely, those that are active
or those that are very close to us), but planned space-based gravitational-wave
observatories such as the Laser Interferometer Space Antenna (LISA) can measure
the parameters of ``electromagnetically invisible'' massive black holes out to
high redshift. In this paper we introduce a Bayesian framework to analyze the
information that can be gathered from a set of such measurements. Our goal is
to connect a set of massive black hole binary merger observations to the
underlying model of massive black hole formation. In other words, given a set
of observed massive black hole coalescences, we assess what information can be
extracted about the underlying massive black hole population model. For
concreteness we consider ten specific models of massive black hole formation,
chosen to probe four important (and largely unconstrained) aspects of the input
physics used in structure formation simulations: seed formation, metallicity
``feedback'', accretion efficiency and accretion geometry. For the first time
we allow for the possibility of ``model mixing'', by drawing the observed
population from some combination of the ``pure'' models that have been
simulated. A Bayesian analysis allows us to recover a posterior probability
distribution for the ``mixing parameters'' that characterize the fractions of
each model represented in the observed distribution. Our work shows that LISA
has enormous potential to probe the underlying physics of structure formation. | GOODS-Herschel: Ultra-deep XMM-Newton observations reveal
AGN/star-formation connection: Models of galaxy evolution assume some connection between the AGN and star
formation activity in galaxies. We use the multi-wavelength information of the
CDFS to assess this issue. We select the AGNs from the 3Ms XMM-Newton survey
and measure the star-formation rates of their hosts using data that probe
rest-frame wavelengths longward of 20 um. Star-formation rates are obtained
from spectral energy distribution fits, identifying and subtracting an AGN
component. We divide the star-formation rates by the stellar masses of the
hosts to derive specific star-formation rates (sSFR) and find evidence for a
positive correlation between the AGN activity (proxied by the X-ray luminosity)
and the sSFR for the most active systems with X-ray luminosities exceeding
Lx=10^43 erg/s and redshifts z~1. We do not find evidence for such a
correlation for lower luminosity systems or those at lower redshifts. We do not
find any correlation between the SFR (or the sSFR) and the X-ray absorption
derived from high-quality XMM-Newton spectra either, showing that the
absorption is likely to be linked to the nuclear region rather than the host,
while the star-formation is not nuclear. Comparing the sSFR of the hosts to the
characteristic sSFR of star-forming galaxies at the same redshift we find that
the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN
- sSFR connection. Limiting our analysis to the highest X-ray luminosity AGNs
(X-ray QSOs with Lx>10^44 erg/s), we find that the highest-redshift QSOs (with
z>2) reside predominantly in starburst hosts, with an average sSFR more than
double that of the "main sequence", and we find a few cases of QSOs at z~1.5
with specific star-formation rates compatible with the main-sequence, or even
in the "quiescent" region. (abridged) |
How to add massive neutrinos to your $Λ$CDM simulation --
extending cosmology rescaling algorithms: Providing accurate predictions for the spatial distribution of matter and
luminous tracers in the presence of massive neutrinos is an important task,
given the imminent arrival of highly accurate large-scale structure
observations. In this work, we address this challenge by extending
cosmology-rescaling algorithms to massive neutrino cosmologies. In this way, a
$\Lambda$CDM simulation can be modified to provide nonlinear structure
formation predictions in the presence a hot component of arbitrary mass, and,
if desired, to include non-gravitational modifications to the clustering of
matter on large scales. We test the accuracy of the method by comparing its
predictions to a suite of simulations carried out explicitly including a
neutrino component in its evolution equations. We find that, for neutrino
masses in the range $M_\nu \in [0.06, 0.3] ~ \mathrm{eV}$ the matter power
spectrum is recovered to better than $1\%$ on all scales
$k<2~h~\mathrm{Mpc}^{-1}$. Similarly, the halo mass function is predicted at a
few percent level over the range $M_{\rm halo} \in [10^{12}, 10^{15}] ~ h^{-1}
~ \mathrm{M}_{\odot}$, and so do also the multipoles of the galaxy 2-point
correlation function in redshift space over $r \in [0.1, 200] ~ h^{-1} ~
\mathrm{Mpc}$. We provide parametric forms for the necessary transformations,
as a function of $\Omega_{\rm m}$ and $\Omega_{\nu}$ for various target
redshifts. | Extensions to $Λ$CDM at Intermediate Redshifts to Solve the
Tensions ?: Models of dark energy or modified gravity that tries to alleviate the
tensions on the Hubble constant ($H_0$) and the matter fluctuation parameter
($\sigma_8$) are usually parameterized as function of either late or early time
cosmic evolution. In this work we rather focus on one that could privilege
extensions to $\Lambda$CDM on intermediate redshifts by mean of a Gaussian-like
window function with a free moving centre $a_{Gwin}$ combined with a modified
gravity parameter $\mu_{Gwin}$ and an extension of the equation of state
parameter $\omega_{Gwin}$. Using different combinations of the latest available
current datasets subject of the discrepancies, such as the cosmic microwave
(CMB) background power spectrum, the baryonic acoustic scale (BAO) in galaxy
distribution, Weak lensing (WL) shear and galaxy clustering cross correlations
and local hubble constant measurements, we investigate whether such model could
alleviate each or both $H_0$ and $\sigma_8$ tensions. We found when combining
all probes that the $\sigma_8$ tension is alleviated while the $H_0$ is reduced
with a small preference for a positive $\omega_{Gwin}$ without a particular
preference for a redshift or a $\mu_{Gwin}$ different from its equivalent
$\Lambda$CDM value. However, if we follow another approach and compare the two
sets of the probes subject of discrepancy i.e. CMB+BAO vs WL+local $H_0$, we
found that the model is able of solving the $\sigma_8$ discrepancy at the
expense of a enlargement of the constraints, while the Hubble constant
discrepancy is not that affected due to the fact that the two likelihood
contours are stretched in parallel directions. We conclude that modifying
$\Lambda$CDM cosmology at intermediate redshifts within our model, and the
constraints from the datasets used in this study, are not likely a viable
solution to solve both tensions. |
Probing topological relation between high density and low density region
of 2MASS with hexagon cells: We introduce a new 2-D hexagon technique to probe the topological structure
of the universe, in which we map regions of the sky with high and low galaxy
densities onto a 2-D lattice of hexagon unit cells, We define filled cells as
corresponding to high density regions and empty cells as corresponding to low
density region. The number of filled cells and empty cells are kept same by
controlling the size of the cells. By analyzing the six neighbors of each
hexagon we can get and compare statistical topological properties of the high
density and low density regions in the universe, in order to have a better
understanding of the evolution of the universe. We apply this hexagon method on
2MASS data and discover significant topological differences between the high
density and low density regions. Both regions have significant (>5 Sigma)
topological shifts from the binomial distribution or the random distribution. | Measuring the speed of light with Baryon Acoustic Oscillations: In this letter we describe a new method to use Baryon Acoustic Oscillations
(BAO) to derive a constraint on the possible variation of the speed of light.
The method relies on the fact that there is a simple relation between the
angular diameter distance $(D_{A})$ maximum and the Hubble function $(H)$
evaluated at the same maximum-condition redshift, which includes speed of light
$c$. We note the close analogy of the BAO probe with a laboratory experiment:
here we have $D_{A}$ which plays the role of a standard (cosmological) ruler,
and $H^{-1}$, with the dimension of time, as a (cosmological) clock. We
evaluate if current or future missions such as Euclid can be sensitive enough
to detect any variation of $c$. |
Multi-Transition Study of M51's Molecular Gas Spiral Arms: Two selected regions in the molecular gas spiral arms in M51 were mapped with
the Owens Valley Radio Observatory (OVRO) mm-interferometer in the 12CO(2-1),
13CO(1-0), C18O(1-0), HCN(1-0) and HCO+(1-0) emission lines. The CO data have
been combined with the 12CO(1-0) data from Aalto et al. (1999) covering the
central 3.5kpc to study the physical properties of the molecular gas. All CO
data cubes were short spacing corrected using IRAM 30m (12CO(1-0): NRO 45m)
single dish data. A large velocity gradient (LVG) analysis finds that the giant
molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180pc
(120pc) resolution with an average kinetic temperature of T_kin = 20(16)K and
H_2 density of n(H_2) = 120(240)cm^(-3) when assuming virialized clouds (a
constant velocity gradient dv/dr. The associated conversion factor between H_2
mass and CO luminosity is close to the Galactic value for most regions
analyzed. Our findings suggest that the GMC population in the spiral arms of
M51 is similar to those of the Milky Way and therefore the strong star
formation occurring in the spiral arms has no strong impact on the molecular
gas in the spiral arms. Extinction inferred from the derived H_2 column density
is very high (A_V about 15 - 30 mag), about a factor of 5-10 higher than the
average value derived toward HII regions. Thus a significant fraction of the
ongoing star formation could be hidden inside the dust lanes of the spiral
arms. A comparison of MIPS 24um and H_alpha data, however, suggests that this
is not the case and most of the GMCs studied here are not (yet) forming stars.
We also present low (4.5") resolution OVRO maps of the HCN(1-0) and HCO+(1-0)
emission at the location of the brightest 12CO(1-0) peak. | Constraining Light Gravitino Mass from Cosmic Microwave Background: We investigate the possibilities of constraining the light gravitino mass
m_{3/2} from future cosmic microwave background (CMB) surveys. A model with
light gravitino with the mass m_{3/2}<O(10) eV is of great interest since it is
free from the cosmological gravitino problem and, in addition, can be
compatible with many baryogenesis/leptogenesis scenarios such as the thermal
leptogenesis. We show that the lensing of CMB anisotropies can be a good probe
for m_{3/2} and obtain an expected constraint on m_{3/2} from precise
measurements of lensing potential in the future CMB surveys, such as the
PolarBeaR and CMBpol experiments. If the gravitino mass is m_{3/2}=1 eV, we
will obtain the constraint for the gravitino mass as m_{3/2} < 3.2 eV (95%
C.L.) for the case with Planck+PolarBeaR combined and
m_{3/2}=1.04^{+0.22}_{-0.26} eV (68% C.L.) for CMBpol. The issue of Bayesian
model selection is also discussed. |
The primordial non-Gaussianity of local type (f_NL) in the WMAP 5-year
data: the length distribution of CMB skeleton: We present skeleton studies of non-Gaussianity in the CMB temperature
anisotropy observed in the WMAP5 data. The local skeleton is traced on the 2D
sphere by cubic spline interpolation which leads to more accurate estimation of
the intersection positions between the skeleton and the secondary pixels than
conventional linear interpolation. We demonstrate that the skeleton-based
estimator of non-Gaussianity of the local type (f_NL) - the departure of the
length distribution from the corresponding Gaussian expectation - yields an
unbiased and sufficiently converged f_NL-likelihood.
We analyse the skeleton statistics in the WMAP5 combined V- and W-band data
outside the Galactic base-mask determined from the KQ75 sky-coverage. The
results are consistent with Gaussian simulations of the the best-fitting
cosmological model, but deviate from the previous results determined using the
WMAP1 data. We show that it is unlikely that the improved skeleton tracing
method, the omission of Q-band data, the modification of the
foreground-template fitting method or the absence of 6 extended regions in the
new mask contribute to such a deviation. However, the application of the Kp0
base-mask in data processing does improve the consistency with the WMAP1
results.
The f_NL-likelihoods of the data are estimated at 9 different smoothing
levels. It is unexpected that the best-fit values show positive correlation
with the smoothing scales. Further investigation argues against a point-source
or goodness-of-fit explanation but finds that about 30% of either Gaussian or
f_NL samples having better goodness-of-fit than the WMAP5 show a similar
correlation. We present the estimate f_NL=47.3+/-34.9 (1sigma error) determined
from the first four smoothing angles and f_NL=76.8+/-43.1 for the combination
of all nine. The former result may be overestimated at the 0.21sigma-level
because of point sources. | Hubble Space Telescope Studies of Nearby Type Ia Supernovae: The Mean
Maximum Light Ultraviolet Spectrum and its Dispersion: We present the first results of an ongoing campaign using the STIS
spectrograph on-board the Hubble Space Telescope (HST) whose primary goal is
the study of near ultraviolet (UV) spectra of local Type Ia supernovae (SNe
Ia). Using events identified by the Palomar Transient Factory and subsequently
verified by ground-based spectroscopy, we demonstrate the ability to locate and
classify SNe Ia as early as 16 days prior to maximum light. This enables us to
trigger HST in a non-disruptive mode to obtain near UV spectra within a few
days of maximum light for comparison with earlier equivalent ground-based
spectroscopic campaigns conducted at intermediate redshifts, z ~ 0.5. We
analyze the spectra of 12 Type Ia supernovae located in the Hubble flow with
0.01 < z < 0.08. Although a fraction of our eventual sample, these data,
together with archival data, already provide a substantial advance over that
previously available. Restricting samples to those of similar phase and
stretch, the mean UV spectrum agrees reasonably closely with that at
intermediate redshift, although some differences are found in the metallic
absorption features. A larger sample will determine whether these differences
reflect possible sample biases or are a genuine evolutionary effect.
Significantly, the wavelength-dependent dispersion, which is larger in the UV,
follows similar trends to that observed at intermediate redshift and is driven,
in part, by differences in the various metallic features. While the origin of
the UV dispersion remains uncertain, our comparison suggests that it may
reflect compositional variations amongst our sample rather than being
predominantly an evolutionary effect. |
Zero average values of cosmological perturbations as an indispensable
condition for the theory and simulations: We point out a weak side of the commonly used determination of scalar
cosmological perturbations lying in the fact that their average values can be
nonzero for some matter distributions. It is shown that introduction of the
finite-range gravitational potential instead of the infinite-range one resolves
this problem. The concrete illustrative density profile is investigated in
detail in this connection. | Predicting Galaxy Star Formation Rates via the Co-evolution of Galaxies
and Halos: In this paper, we test the age matching hypothesis that the star formation
rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter
halo formation history, and as such, that more quiescent galaxies reside in
older halos. This simple model has been remarkably successful at predicting
color-based galaxy statistics at low redshift as measured in the Sloan Digital
Sky Survey (SDSS). To further test this method with observations, we present
new SDSS measurements of the galaxy two-point correlation function and
galaxy-galaxy lensing as a function of stellar mass and SFR, separated into
quenched and star-forming galaxy samples. We find that our age matching model
is in excellent agreement with these new measurements. We also employ a galaxy
group finder and show that our model is able to predict: (1) the relative SFRs
of central and satellite galaxies, (2) the SFR-dependence of the radial
distribution of satellite galaxy populations within galaxy groups, rich groups,
and clusters and their surrounding larger scale environments, and (3) the
interesting feature that the satellite quenched fraction as a function of
projected radial distance from the central galaxy exhibits an ~ r^-.15 slope,
independent of environment. The accurate prediction for the spatial
distribution of satellites is intriguing given the fact that we do not
explicitly model satellite-specific processes after infall, and that in our
model the virial radius does not mark a special transition region in the
evolution of a satellite, contrary to most galaxy evolution models. The success
of the model suggests that present-day galaxy SFR is strongly correlated with
halo mass assembly history. |
Cosmic neutrinos: dispersive and non-linear: We present a description of cosmic neutrinos as a dispersive fluid. In this
approach, the neutrino phase space is reduced to density and velocity fields
alongside a scale-dependent sound speed. This sound speed depends on redshift,
the initial neutrino phase space density and the cold dark matter gravitational
potential. The latter is a new coupling between neutrinos and large scale
structure not described by previous fluid approaches. We compute the sound
speed in linear theory and find that it asymptotes to constants at small and
large scales regardless of the gravitational potential. By comparing with
neutrino N-body simulations, we measure the small scale sound speed and find it
to be lower than linear theory predictions. This allows for an explanation of
the discrepency between N-body and linear response predictions for the neutrino
power spectrum: neutrinos are still driven predominantly by the cold dark
matter, but the sound speed on small scales is not stable to perturbations and
decreases. Finally, we present a calibrated model for the neutrino power
spectrum that requires no additional integrations outside of standard Boltzmann
codes. | Probing cosmology and gastrophysics with fast radio bursts:
Cross-correlations of dark matter haloes and cosmic dispersion measures: For future surveys of fast radio bursts (FRBs), we clarify information
available from cosmic dispersion measures (DMs) through cross-correlation
analyses of foreground dark matter haloes (hosting galaxies and galaxy
clusters) with their known redshifts. With a halo-model approach, we predict
that the cross-correlation with cluster-sized haloes is less affected by the
details of gastrophysics, providing robust cosmological information. For less
massive haloes, the cross-correlation at angular scales of $<10\,
\mathrm{arcmin}$ is sensitive to gas expelled from the halo centre due to
galactic feedback. Assuming $20000$ FRBs over $20000 \, {\rm deg}^2$ with a
localisation error being 3 arcmin, we expect that the cross-correlation signal
at halo masses of $10^{12}-10^{14}\, M_\odot$ can be measured with a level of
$\sim 1\%$ precision in a redshift range of $0<z<1$. Such precise measurements
enable one to put a 1.5\% level constraint on $\sigma_8\,
(\Omega_\mathrm{M}/0.3)^{0.5}$ and a 3\% level constraint on
$(\Omega_\mathrm{b}/0.049)(h/0.67)(f_\mathrm{e}/0.95)$ ($\sigma_8$,
$\Omega_\mathrm{M}$, $\Omega_\mathrm{b}$, $h$ and $f_\mathrm{e}$ are the linear
mass variance smoothed at $8\, h^{-1}\mathrm{Mpc}$, mean mass density, mean
baryon density, the present-day Hubble parameter and fraction of free electrons
in cosmic baryons today), whereas the gas-to-halo mass relation in galaxies and
clusters can be constrained with a level of $10\%-20\%$. Furthermore the
cross-correlation analyses can break the degeneracy among $\Omega_\mathrm{b}$,
$h$ and $f_\mathrm{e}$, inherent in the DM-redshift relation. Our proposal
opens new possibilities for FRB cosmology, while it requires extensive galaxy
redshift catalogues and further improvement of the halo model. |
The small scale dynamo and the amplification of magnetic fields in
massive primordial haloes: While present standard model of cosmology yields no clear prediction for the
initial magnetic field strength, efficient dynamo action may compensate for
initially weak seed fields via rapid amplification. In particular, the
small-scale dynamo is expected to exponentially amplify any weak magnetic field
in the presence of turbulence. We explore whether this scenario is viable using
cosmological magneto-hydrodynamics simulations modeling the formation of the
first galaxies, which are expected to form in so-called atomic cooling halos
with virial temperatures $\rm T_{vir} \geq 10^{4}$ K. As previous calculations
have shown that a high Jeans resolution is needed to resolve turbulent
structures and dynamo effects, our calculations employ resolutions of up to 128
cells per Jeans length. The presence of the dynamo can be clearly confirmed for
resolutions of at least 64 cells per Jeans length, while saturation occurs at
approximate equipartition with turbulent energy. As a result of the large
Reynolds numbers in primordial galaxies, we expect saturation to occur at early
stages, implying magnetic field strengths of \sim0.1 $\mu$G at densities of
10^4 cm^{-3}. | Gravitational waves from type II axion-like curvaton model and its
implication for NANOGrav result: The recent report of NANOGrav is gathering attention since its signal can be
explained by the stochastic gravitational waves (GWs) with $\Omega_{\rm GW}\sim
10^{-9}$ at $f\sim 10^{-8}$Hz. The PBH formation scenario is one of the
candidates for the NANOGrav signal, which can simultaneously explain the
observed $30 M_\odot$ black holes in the binary merger events in LIGO-Virgo
collaboration. We focus on the type II axion-like curvaton model of the PBH
formation. In type II model the complex field whose phase part is the axion
rolls down from the origin of the potential. It is found that type II model
achieves the broad power spectrum of the density perturbations and can
simultaneously explain the LIGO-Virgo events and the NANOGrav signal. We also
improve the treatment of the non-Gaussianity of perturbations in our model to
accurately estimate the amplitude of the induced GWs. |
Synergies between Vera C. Rubin Observatory, Nancy Grace Roman Space
Telescope, and Euclid Mission: Constraining Dark Energy with Type Ia
Supernovae: We review the needs of the supernova community for improvements in survey
coordination and data sharing that would significantly boost the constraints on
dark energy using samples of Type Ia supernovae from the Vera C. Rubin
Observatories, the \textit{Nancy Grace Roman Space Telescope}, and the
\textit{Euclid} Mission. We discuss improvements to both statistical and
systematic precision that the combination of observations from these
experiments will enable. For example, coordination will result in improved
photometric calibration, redshift measurements, as well as supernova distances.
We also discuss what teams and plans should be put in place now to start
preparing for these combined data sets. Specifically, we request coordinated
efforts in field selection and survey operations, photometric calibration,
spectroscopic follow-up, pixel-level processing, and computing. These efforts
will benefit not only experiments with Type Ia supernovae, but all time-domain
studies, and cosmology with multi-messenger astrophysics. | Isotropic AGN Heating with Small Radio Quiet Bubbles in the NGC 5044
Group: (abridged) A Chandra observation of the X-ray bright group NGC 5044 shows
that the X-ray emitting gas has been strongly perturbed by recent outbursts
from the central AGN and also by motion of the central dominant galaxy relative
to the group gas. The NGC 5044 group hosts many small radio quiet cavities with
a nearly isotropic distribution, cool filaments, a semi-circular cold front and
a two-armed spiral shaped feature of cool gas. A GMRT observation of NGC 5044
at 610 MHz shows the presence of extended radio emission with a "torus-shaped"
morphology. The largest X-ray filament appears to thread the radio torus,
suggesting that the lower entropy gas within the filament is material being
uplifted from the center of the group. The radio emission at 235 MHz is much
more extended than the emission at 610 MHz, with little overlap between the two
frequencies. One component of the 235 MHz emission passes through the largest
X-ray cavity and is then deflected just behind the cold front. A second
detached radio lobe is also detected at 235 MHz beyond the cold front. All of
the smaller X-ray cavities in the center of NGC 5044 are undetected in the GMRT
observations. Since the smaller bubbles are probably no longer momentum driven
by the central AGN, their motion will be affected by the group "weather" as
they buoyantly rise outward. Hence, most of the enthalpy within the smaller
bubbles will likely be deposited near the group center and isotropized by the
group weather. The total mechanical power of the smaller radio quiet cavities
is $P_c = 9.2 \times 10^{41}$erg s$^{-1}$ which is sufficient to suppress about
one-half of the total radiative cooling within the central 10 kpc. This is
consistent with the presence of H$\alpha$ emission within this region which
shows that at least some of the gas is able to cool. |
Primordial magnetic non-Gaussianity with generic vacua and detection
prospects in CMB spectral distortions: Assuming a slow-roll inflationary model where conformal invariance of the
Maxwell action is broken via a non-minimal kinetic coupling term, we
investigate the non-Gaussian three-point cross-correlation function between the
primordial curvature perturbation and the primordial magnetic field, under a
fairly general choice of initial vacua for both the scalar and the gauge field
sectors. Among the possible triangular configurations of the resulting
cross-bispectrum, we find that the squeezed limit leads to local-type
non-Gaussianity allowing a product form decomposition in terms of the scalar
and magnetic power spectra, which is a generic result independent of any
specific choice of the initial states. We subsequently explore its detection
prospects in the CMB via correlations between pre-recombination $\mu$-type
spectral distortions and temperature anisotropies, sourced by such a primordial
cross-correlation. Our analysis with several proposed next-generation CMB
missions forecasts a low value of the signal-to-noise ratio (SNR) for the $\mu
T$ spectrum if both the vacua are assumed to be pure Bunch-Davies. On the
contrary, the SNR may be enhanced significantly for non-Bunch-Davies initial
states for the magnetic sector within allowed bounds from current CMB data. | MAGIC observations of the giant radio galaxy M87 in a low emission state
between 2005 and 2007: We present the results of a long M87 monitoring campaign in very high energy
$\gamma$-rays with the MAGIC-I Cherenkov telescope. A total of 150 hours of
data was gathered between 2005 and 2007. No flaring activity was found during
that time. Nevertheless, we have found an apparently steady and weak signal at
the level of $7\sigma$. We present the spectrum between 100 GeV and 2 TeV,
which is consistent with a simple power law with a spectral index
$-2.21\pm0.21$ and a flux normalization (at 300 GeV) of $5.4\pm1.1 \times
10^{-8} \frac{1}{\mathrm{TeV s m}^{2}}$. It complements well with the
previously published Fermi spectrum, covering an energy range of four orders of
magnitude without apparent change in the spectral index. |
New constraints on primordial non-Gaussianity from missing two-loop
contributions of scalar induced gravitational waves: We analyze the energy density spectrum of \acp{SIGW} using the NANOGrav
15-year data set, thereby constraining the primordial non-Gaussian parameter
$f_{\mathrm{NL}}$. For the first time, we calculate the seventeen missing
two-loop diagrams proportional to $f_{\mathrm{NL}}A_{\zeta}^3$ that correspond
to the two-point correlation function $\langle h^{\lambda,(3)}_{\mathbf{k}}
h^{\lambda',(2)}_{\mathbf{k}'} \rangle$ for local-type primordial
non-Gaussianity. The total energy density spectrum of \acp{SIGW} can be
significantly suppressed by these two-loop diagrams. If \acp{SIGW} dominate the
\acp{SGWB} observed in \ac{PTA} experiments, the parameter interval
$f_{\mathrm{NL}}\in [-5,-1]$ is notably excluded based on NANOGrav 15-year data
set. After taking into account abundance of \acp{PBH} and the convergence of
the cosmological perturbation expansion, we find that the only possible
parameter range for $f_{\mathrm{NL}}$ might be $-1\le f_{\mathrm{NL}}< 0$. | Generalized local ansatz for scale-dependent primordial
non-Gaussianities and future galaxy surveys: We revisit a possible scale-dependence of local-type primordial
non-Gaussianities induced by super-horizon evolution of scalar field
perturbations. We develop the formulation based on $\delta N$ formalism and
derive the generalized form of the local-type bispectrum and also trispectrum
which allows us to implement the scale-dependence and suitably compare model
prediction with observational data. We propose simple but phenomenologically
meaningful expressions, which encompass the information of a wide range of
physically motivated models. We also formulate large-scale power spectrum and
bispectrum of biased objects in the presence of the scale-dependent primordial
non-Gaussianities. We perform the Fisher analysis for future galaxy surveys and
give the projected constraints on the parameters of the generalized local-form
of primordial non-Gaussianities. |
The scalar bi-spectrum during preheating in single field inflationary
models: In single field inflationary models, preheating refers to the phase that
immediately follows inflation, but precedes the epoch of reheating. During this
phase, the inflaton typically oscillates at the bottom of its potential and
gradually transfers its energy to radiation. At the same time, the amplitude of
the fields coupled to the inflaton may undergo parametric resonance and, as a
consequence, explosive particle production can take place. A priori, these
phenomena could lead to an amplification of the super-Hubble scale curvature
perturbations which, in turn, would modify the standard inflationary
predictions. However, remarkably, it has been shown that, although the
Mukhanov-Sasaki variable does undergo narrow parametric instability during
preheating, the amplitude of the corresponding super-Hubble curvature
perturbations remain constant. Therefore, in single field models, metric
preheating does not affect the power spectrum of the large scale perturbations.
In this article, we investigate the corresponding effect on the scalar
bi-spectrum. Using the Maldacena's formalism, we analytically show that, for
modes of cosmological interest, the contributions to the scalar bi-spectrum as
the curvature perturbations evolve on super-Hubble scales during preheating is
completely negligible. Specifically, we illustrate that, certain terms in the
third order action governing the curvature perturbations which may naively be
expected to contribute significantly are exactly canceled by other
contributions to the bi-spectrum. We corroborate selected analytical results by
numerical investigations. We conclude with a brief discussion of the results we
have obtained. | Towards solving model bias in cosmic shear forward modeling: As the volume and quality of modern galaxy surveys increase, so does the
difficulty of measuring the cosmological signal imprinted in galaxy shapes.
Weak gravitational lensing sourced by the most massive structures in the
Universe generates a slight shearing of galaxy morphologies called cosmic
shear, key probe for cosmological models. Modern techniques of shear estimation
based on statistics of ellipticity measurements suffer from the fact that the
ellipticity is not a well-defined quantity for arbitrary galaxy light profiles,
biasing the shear estimation. We show that a hybrid physical and deep learning
Hierarchical Bayesian Model, where a generative model captures the galaxy
morphology, enables us to recover an unbiased estimate of the shear on
realistic galaxies, thus solving the model bias. |
Isotropic Radio Background from Quark Nugget Dark Matter: Recent measurements by the ARCADE2 experiment unambiguously show an excess in
the isotropic radio background at frequencies below the GHz scale. We argue
that this excess may be a natural consequence of the interaction of visible and
dark matter in the early universe if the dark matter consists of heavy nuggets
of quark matter. Explanation of the observed radio band excess requires the
introduction of no new parameters, rather we exploit the same dark matter model
and identical normalization parameters to those previously used to explain
other excesses of diffuse emission from the centre of our galaxy. These
previously observed excesses include the WMAP Haze of GHz radiation, keV X -ray
emission and MeV gamma-ray radiation. | Characteristic Functions for Cosmological Cross-Correlations: We introduce a novel unbiased, cross-correlation estimator for the one-point
statistics of cosmological random fields. One-point statistics are a useful
tool for analysis of highly non-Gaussian density fields, while
cross-correlations provide a powerful method for combining information from
pairs of fields and separating them from noise and systematics. We derive a new
Deconvolved Distribution Estimator that combines the useful properties of these
two methods into one statistic. Using two example models of a toy Gaussian
random field and a line intensity mapping survey, we demonstrate these
properties quantitatively and show that the DDE can be used for inference. This
new estimator can be applied to any pair of overlapping, non-Gaussian
cosmological observations, including large-scale structure, the
Sunyaev-Zeldovich effect, weak lensing, and many others. |
The impact of realistic models of mass segregation on the event rate of
extreme-mass ratio inspirals and cusp re-growth: One of the most interesting sources of gravitational waves (GWs) for LISA is
the inspiral of compact objects on to a massive black hole (MBH), commonly
referred to as an "extreme-mass ratio inspiral" (EMRI). The small object,
typically a stellar black hole (bh), emits significant amounts of GW along each
orbit in the detector bandwidth. The slowly, adiabatic inspiral of these
sources will allow us to map space-time around MBHs in detail, as well as to
test our current conception of gravitation in the strong regime. The event rate
of this kind of source has been addressed many times in the literature and the
numbers reported fluctuate by orders of magnitude. On the other hand, recent
observations of the Galactic center revealed a dearth of giant stars inside the
inner parsec relative to the numbers theoretically expected for a fully relaxed
stellar cusp. The possibility of unrelaxed nuclei (or, equivalently, with no or
only a very shallow cusp) adds substantial uncertainty to the estimates. Having
this timely question in mind, we run a significant number of direct-summation
$N-$body simulations with up to half a million particles to calibrate a much
faster orbit-averaged Fokker-Planck code. We then investigate the regime of
strong mass segregation (SMS) for models with two different stellar mass
components. We show that, under quite generic initial conditions, the time
required for the growth of a relaxed, mass segregated stellar cusp is shorter
than a Hubble time for MBHs with $M_\bullet \lesssim 5 \times 10^6 M_\odot$
(i.e. nuclei in the range of LISA). SMS has a significant impact boosting the
EMRI rates by a factor of $\sim 10$ for our fiducial models of Milky Way type
galactic nuclei. | Beyond Fisher Forecasting for Cosmology: The planning and design of future experiments rely heavily on forecasting to
assess the potential scientific value provided by a hypothetical set of
measurements. The Fisher information matrix, due to its convenient properties
and low computational cost, provides an especially useful forecasting tool.
However, the Fisher matrix only provides a reasonable approximation to the true
likelihood when data are nearly Gaussian distributed and observables have
nearly linear dependence on the parameters of interest. Also, Fisher
forecasting techniques alone cannot be used to assess their own validity.
Thorough sampling of the exact or mock likelihood can definitively determine
whether a Fisher forecast is valid, though such sampling is often prohibitively
expensive. We propose a simple test, based on the Derivative Approximation for
LIkelihoods (DALI) technique, to determine whether the Fisher matrix provides a
good approximation to the exact likelihood. We show that the Fisher matrix
becomes a poor approximation to the true likelihood in regions where
two-dimensional slices of level surfaces of the DALI approximation to the
likelihood differ from two-dimensional slices of level surfaces of the Fisher
approximation to the likelihood. We demonstrate that our method accurately
predicts situations in which the Fisher approximation deviates from the true
likelihood for various cosmological models and several data combinations, with
only a modest increase in computational cost compared to standard Fisher
forecasts. |
BAO from angular clustering: optimization and mitigation of theoretical
systematics: We study the methodology and potential theoretical systematics of measuring
Baryon Acoustic Oscillations (BAO) using the angular correlation functions in
tomographic bins. We calibrate and optimize the pipeline for the Dark Energy
Survey Year 1 dataset using 1800 mocks. We compare the BAO fitting results
obtained with three estimators: the Maximum Likelihood Estimator (MLE), Profile
Likelihood, and Markov Chain Monte Carlo. The fit results from the MLE are the
least biased and their derived 1-$\sigma$ error bar are closest to the Gaussian
distribution value after removing the extreme mocks with non-detected BAO
signal. We show that incorrect assumptions in constructing the template, such
as mismatches from the cosmology of the mocks or the underlying photo-$z$
errors, can lead to BAO angular shifts. We find that MLE is the method that
best traces this systematic biases, allowing to recover the true angular
distance values. In a real survey analysis, it may happen that the final data
sample properties are slightly different from those of the mock catalog. We
show that the effect on the mock covariance due to the sample differences can
be corrected with the help of the Gaussian covariance matrix or more
effectively using the eigenmode expansion of the mock covariance. In the
eigenmode expansion, the eigenmodes are provided by some proxy covariance
matrix. The eigenmode expansion is significantly less susceptible to
statistical fluctuations relative to the direct measurements of the covariance
matrix because of the number of free parameters is substantially reduced | Near-infrared spectroscopy of extreme BAL QSOs from the QUBRICS bright
quasar survey: We report on the spectral confirmation of 18 QSO candidates from the "QUasars
as BRIght beacons for Cosmology in the Southern hemisphere'' survey (QUBRICS),
previously observed in the optical band, for which we acquired new
spectroscopic data in the near-infrared band with the Folded-port InfraRed
Echellette spectrograph (FIRE) at the Magellan Baade telescope. In most cases,
further observations were prompted by the peculiar nature of the targets, whose
optical spectra displayed unexpected absorption features. All candidates have
been confirmed as bona fide QSOs, with average emission redshift $z\simeq 2.1$.
The analysis of the emission and absorption features in the spectra, performed
with Astrocook and QSFit, reveals that the large majority of these objects are
broad-absorption line (BAL) QSOs, with almost half of them displaying strong Fe
II absorption (typical of the so-called FeLoBAL QSOs). The detection of such a
large fraction of rare objects (which are estimated to account for less than
one percent of the general QSO population) is interpreted as an unexpected (yet
favourable) consequence of the particular candidate selection procedure adopted
within the QUBRICS survey. The measured properties of FeLoBAL QSOs observed so
far provide no evidence that they are a manifestation of a particular stage in
AGN evolution. In this paper we present an explorative analysis of the
individual QSOs, to serve as a basis for a further, more detailed
investigation. |
Tight Constraints on the Excess Radio Background at $z = 9.1$ from LOFAR: The ARCADE2 and LWA1 experiments have claimed an excess over the Cosmic
Microwave Background (CMB) at low radio frequencies. If the cosmological
high-redshift contribution to this radio background is between 0.1% and 22% of
the CMB at 1.42 GHz, it could explain the tentative EDGES Low-Band detection of
the anomalously deep absorption in the 21-cm signal of neutral hydrogen. We use
the upper limit on the 21-cm signal from the Epoch of Reionization ($z=9.1$)
based on 141 hours of observations with LOFAR to evaluate the contribution of
the high redshift Universe to the detected radio background. Marginalizing over
astrophysical properties of star-forming halos, we find (at 95% C.L.) that the
cosmological radio background can be at most 9.6% of the CMB at 1.42 GHz. This
limit rules out strong contribution of the high-redshift Universe to the
ARCADE2 and LWA1 measurements. Even though LOFAR places limit on the extra
radio background, excess of $0.1-9.6$% over the CMB (at 1.42 GHz) is still
allowed and could explain the EDGES Low-Band detection. We also constrain the
thermal and ionization state of the gas at $z = 9.1$ and put limits on the
properties of the first star-forming objects. We find that, in agreement with
the limits from EDGES High-Band data, LOFAR data constrain scenarios with
inefficient X-ray sources and cases where the Universe was ionized by stars in
massive halos only. | Energy-momentum correlations for Abelian Higgs cosmic strings: We report on the energy-momentum correlators obtained with recent numerical
simulations of the Abelian Higgs model, essential for the computation of cosmic
microwave background and matter perturbations of cosmic strings. Due to
significant improvements both in raw computing power and in our parallel
simulation framework, the dynamical range of the simulations has increased
four-fold both in space and time, and for the first time we are able to
simulate strings with a constant physical width in both the radiation and
matter eras. The new simulations improve the accuracy of the measurements of
the correlation functions at the horizon scale and confirm the shape around the
peak. The normalization is slightly higher in the high wave-number tails, due
to a small increase in the string density. We study for the first time the
behaviour of the correlators across cosmological transitions, and discover that
the correlation functions evolve adiabatically, ie the network adapts quickly
to changes in the expansion rate. We propose a new method for constructing
source functions for Einstein-Boltzmann integrators, comparing it with two
other methods previously used. The new method is more consistent, easier to
implement, and significantly more accurate. |
The Carnegie Supernova Project: Intrinsic Colors of Type Ia Supernovae: We present an updated analysis of the intrinsic colors of SNe Ia using the
latest data release of the Carnegie Supernova Project. We introduce a new
light-curve parameter very similar to stretch that is better suited for
fast-declining events, and find that these peculiar types can be seen as
extensions to the population of "normal" SNe Ia. With a larger number of
objects, an updated fit to the Lira relation is presented along with evidence
for a dependence on the late-time slope of the B-V color-curves with stretch
and color. Using the full wavelength range from u to H band, we place
constraints on the reddening law for the sample as a whole and also for
individual events/hosts based solely on the observed colors. The photometric
data continue to favor low values of Rv, though with large variations from
event to event, indicating an intrinsic distribution. We confirm the findings
of other groups that there appears to be a correlation between the derived
reddening law, Rv, and the color excess, E(B-V), such that larger E(B-V) tends
to favor lower Rv. The intrinsic u-band colors show a relatively large scatter
that cannot be explained by variations in Rv or by the Goobar (2008) power-law
for circumstellar dust, but rather is correlated with spectroscopic features of
the supernova and is therefore likely due to metallicity effects. | Role of Future SNIa Data from LSST in Reinvestigating Cosmological
Models: We study how future Type-Ia supernovae (SNIa) standard candles detected by
the Vera C. Rubin Observatory (LSST) can constrain some cosmological models. We
use a realistic three-year SNIa simulated dataset generated by the LSST Dark
Energy Science Collaboration (DESC) Time Domain pipeline, which includes a mix
of spectroscopic and photometrically identified candidates. We combine this
data with Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation
(BAO) measurements to estimate the dark energy model parameters for two models
-- the baseline $\Lambda$CDM and Chevallier-Polarski-Linder (CPL) dark energy
parametrization. We compare them with the current constraints obtained from
joint analysis of the latest real data from the Pantheon SNIa compilation, CMB
from Planck 2018 and BAO. Our analysis finds tighter constraints on the model
parameters along with a significant reduction of correlation between $H_0$ and
$\sigma_8$. We find that LSST is expected to significantly improve upon the
existing SNIa data in the critical analysis of cosmological models. |
Constraints on Pre-inflation Fluctuations in a Nearly Flat Open
ΛCDM Cosmology: We analyze constraints on parameters characterizing the pre-inflating
universe in an open inflation model with a present slightly open $\Lambda$CDM
universe. We employ an analytic model to show that for a broad class of
inflation-generating effective potentials, the simple requirement that some
fraction of the observed dipole moment represents a pre-inflation isocurvature
fluctuation allows one to set upper and lower limits on the magnitude and
wavelength scale of pre-inflation fluctuations in the inflaton field, and the
curvature of the pre-inflation universe, as a function of the fraction of the
total initial energy density in the inflaton field as inflation begins. We
estimate that if the pre-inflation contribution to the current CMB dipole is
near the upper limit set by the {\it Planck} Collaboration then the current
constraints on $\Lambda$CDM cosmological parameters allow for the possibility
of a significantly open $\Omega_{i} \le 0.4$ pre-inflating universe for a broad
range of the fraction of the total energy in the inflaton field at the onset of
inflation. This limit to $\Omega_{i}$ is even smaller if a larger dark-flow
tilt is allowed. | Entropic cosmology in a dissipative universe: The bulk viscosity of cosmological fluid and the creation of cold dark matter
both result in the generation of irreversible entropy (related to dissipative
processes) in a homogeneous and isotropic universe. To consider such effects,
the general cosmological equations are reformulated, focusing on a spatially
flat matter-dominated universe. A phenomenological entropic-force model is
examined that includes constant terms as a function of the dissipation rate
ranging from $\tilde{\mu} =0$, corresponding to a nondissipative $\Lambda$CDM
(lambda cold dark matter) model, to $\tilde{\mu} =1$, corresponding to a
fully-dissipative CCDM (creation of cold dark matter) model. A time evolution
equation is derived for the matter density contrast, in order to characterize
density perturbations in the present entropic-force model. It is found that the
dissipation rate affects the density perturbations even if the background
evolution of the late universe is equivalent to that of a fine-tuned pure
$\Lambda$CDM model. With increasing dissipation rate $\tilde{\mu}$, the
calculated growth rate for the clustering gradually deviates from observations,
especially at low redshifts. However, the growth rate for low $\tilde{\mu}$
(less than 0.1) is found to agree well with measurements. A low-dissipation
model predicts a smaller growth rate than does the pure $\Lambda$CDM model (for
which $\tilde{\mu} =0$). More detailed data are needed to distinguish the
low-dissipation model from the pure $\Lambda$CDM one. |
Probing the nature of the massive black hole binary candidate SDSS
J1536+0441: We present an imaging study of the black hole binary candidate SDSS
J1536+0441 (z=0.3893), based on deep, high resolution VzK images collected at
the ESO/VLT. The images clearly show an asymmetric elongation, indicating the
presence of a companion source at ~1" (~5 kpc projected distance) East from the
quasar. The host galaxy of the quasar is marginally resolved. We find that the
companion source is a luminous galaxy, the light profile of which suggests the
presence of an unresolved, faint nucleus (either an obscured AGN or a compact
stellar bulge). The study of the environment around the quasar indicates the
occurrence of a significant over-density of galaxies with a redshift compatible
with z~0.4. This suggests that it resides in a moderately rich cluster of
galaxies. | CMB-Galaxy correlation in Unified Dark Matter Scalar Field Cosmologies: We present an analysis of the cross-correlation between the CMB and the
large-scale structure (LSS) of the Universe in Unified Dark Matter (UDM) scalar
field cosmologies. We work out the predicted cross-correlation function in UDM
models, which depends on the speed of sound of the unified component, and
compare it with observations from six galaxy catalogues (NVSS, HEAO, 2MASS, and
SDSS main galaxies, luminous red galaxies, and quasars). We sample the value of
the speed of sound and perform a likelihood analysis, finding that the UDM
model is as likely as the LambdaCDM, and is compatible with observations for a
range of values of c_\infinity (the value of the sound speed at late times) on
which structure formation depends. In particular, we obtain an upper bound of
c_\infinity^2 \leq 0.009 at 95% confidence level, meaning that the LambdaCDM
model, for which c_\infinity^2 = 0, is a good fit to the data, while the
posterior probability distribution peaks at the value c_\infinity^2=10^(-4) .
Finally, we study the time dependence of the deviation from LambdaCDM via a
tomographic analysis using a mock redshift distribution and we find that the
largest deviation is for low-redshift sources, suggesting that future low-z
surveys will be best suited to constrain UDM models. |
Overview on spectral line source finding and visualisation: Here I will outline successes and challenges for finding spectral line
sources in large data cubes that are dominated by noise. This is a 3D challenge
as the sources we wish to catalog are spread over several spatial pixels and
spectral channels. While 2D searches can be applied, e.g., channel by channel,
optimal searches take into account the 3-dimensional nature of the sources. In
this overview I will focus on HI 21-cm spectral line source detection in
extragalactic surveys, in particular HIPASS, the "HI Parkes All-Sky Survey" and
WALLABY, the "ASKAP HI All-Sky Survey". I use the original HIPASS data to
highlight the diversity of spectral signatures of galaxies and gaseous clouds,
both in emission and absorption. Among others, I report the discovery of a 680
km/s wide HI absorption trough in the megamaser galaxy NGC 5793. Issues such as
source confusion and baseline ripples, typically encountered in single-dish HI
surveys, are much reduced in interferometric HI surveys. Several large HI
emission and absorption surveys are planned for the Australian Square Kilometre
Array Pathfinder (ASKAP): here we focus on WALLABY, the 21-cm survey of the sky
(Dec < +30 degr; z < 0.26) which will take about one year of observing time
with ASKAP. Novel phased array feeds ("radio cameras") will provide 30 square
degrees instantaneous field-of-view. WALLABY is expected to detect more than
500 000 galaxies, unveil their large-scale structures and cosmological
parameters, detect their extended, low-surface brightness disks as well as gas
streams and filaments between galaxies. It is a precursor for future HI surveys
with SKA Phase I and II, exploring galaxy formation and evolution. The
compilation of highly reliable and complete source catalogs will require
sophisticated source-finding algorithms as well as accurate source
parametrisation. | Position-Dependent Correlation Function of Weak Lensing Convergence: We provide a systematic study of the position-dependent correlation function
in weak lensing convergence maps and its relation to the squeezed limit of the
three-point correlation function (3PCF) using state-of-the-art numerical
simulations. We relate the position-dependent correlation function to its
harmonic counterpart, i.e., the position-dependent power spectrum or
equivalently the integrated bispectrum. We use a recently proposed improved
fitting function, BiHalofit, for the bispectrum to compute the theoretical
predictions as a function of source redshifts. In addition to low redshift
results ($z_s=1.0-2.0$), we also provide results for maps inferred from lensing
of the cosmic microwave background, i.e., $z_s=1100$. We include a {\em
Euclid}-type realistic survey mask and noise. In agreement with the recent
studies on the position-dependent power spectrum, we find that the results from
simulations are consistent with the theoretical expectations when appropriate
corrections are included. Performing a rough estimate, we find that the (S/N)
for the detection of the position-dependent correlation function from {\em
Euclid}-type mask with $f_{sky}=0.35$, can range between $6-12$ depending on
the value of the intrinsic ellipticity distribution parameter
$\sigma_{\epsilon} = 0.3-1.0$. For reconstructed $\kappa$ maps using an ideal
CMB survey the (S/N) $\approx 1.8$. We also found that a $10\%$ deviation in
$\sigma_8$ can be detected using IB for the optimistic case of
$\sigma_\epsilon=0.3$ with a (S/N) $\approx 5$. The (S/N) for such detection in
case of $\Omega_M$ is lower. |
Characterising cosmic inhomogeneity with anomalous diffusion: Dark matter (DM) clustering at the present epoch is investigated from a
fractal viewpoint in order to determine the scale where the self-similar
scaling property of the DM halo distribution transits to homogeneity. Methods
based on well-established `counts-in-cells' as well as new methods based on
anomalous diffusion and random walks are investigated. Both are applied to DM
halos of the biggest N-Body simulation in the `Dark Sky Simulations' (DS)
catalogue and an equivalent randomly distributed catalogue. Results based on
the smaller `Millennium Run' (MR) simulation are revisited and improved. It is
found that the MR simulation volume is too small and prone to bias to reliably
identify the onset of homogeneity. Transition to homogeneity is defined when
the fractal dimension of the clustered and random distributions cannot be
distinguished within the associated uncertainties. The `counts-in-cells' method
applied to the DS simulation then yields a homogeneity scale roughly consistent
with previous work ($\sim 150$$h^{-1}$Mpc). The characteristic length-scale for
anomalous diffusion to behave homogeneously is found to be at about
250$h^{-1}$Mpc. The behaviour of the fractal dimensions for a halo catalogue
with the same two-point function as the original but with shuffled Fourier
phases is investigated. The methods based on anomalous diffusion are shown to
be sensitive to the phase information, whereas the `counts-in-cells' methods
are not. | Dark matter around primordial black hole at the radiation-dominated
stage: The accumulation of dark matter particles near the primordial black holes
starts at the radiation-dominated cosmological stage and produces the central
density spikes. The spikes can be the bright gamma-ray sources due to dark
matter annihilation. We present the self-consistent derivation of the equation
of motion of particle in the metrics of primordial black hole immersed into
cosmological background. By numerical solution of this equation we find the
central dark matter density profile. The density growth is suppressed in the
central part of the profile compared with previous calculations. |
Polycyclic aromatic hydrocarbons in spatially resolved extragalactic
star forming complexes: The abundance of polycyclic aromatic hydrocarbons (PAHs) in low- and
high-metallicity galaxies has been widely discussed since the time when
detailed infrared data for extragalactic objects were first obtained. On the
scales of entire galaxies, a smaller PAH abundance in lower-metallicity
galaxies is often observed. We study this relationship for star-forming regions
in nearby galaxies, for a sample containing more than 200 HII complexes, using
spatially-resolved observations from the Herschel Space Observatory and Spitzer
Space Telescope. We use a model for the dust emission to estimate the physical
parameters (PAH abundance, metallicity, ultraviolet radiation field, etc.) of
these complexes. The same correlation of PAH abundance with metallicity, as
seen for entire galaxies, is apparently preserved at smaller scales, at least
when the Kobulnicky & Kewley metallicity calibration is used. We discuss
possible reasons for this correlation, noting that traces of less-effective PAH
formation in low-metallicity AGB stars should be smeared out by radial mixing
in galactic disks. Effective destruction by the harder and more intensive
ultraviolet field in low-metallicity environments is qualitatively consistent
with our data, as the ultraviolet field intensity, derived from the infrared
photometry, is indeed smaller in HII complexes with lower metallicity. | Theory of Magnetic Seed-Field Theory of Magnetic Seed-Field Generation
during the Cosmological First-Order Electroweak Phase Transition: We present a theory of the generation of magnetic seed fields in bubble
collisions during a first-order electroweak phase transition (EWPT) possible
for some choices of parameters in the minimal supersymmetric Standard Model.
The theory extends earlier work and is formulated to assess the importance of
surface dynamics in such collisions. We are led to linearized equations of
motion with O(3) symmetry appropriate for examining collisions in which the
Higgs field is relatively unperturbed from its mean value in the collision
volume. Coherent evolution of the charged $W$ fields within the bubbles is the
main source of the electromagnetic current for generating the seed fields, with
fermions also contributing through the conductivity terms. We present numerical
simulations within this formulation to quantify the role of the surface of the
colliding bubbles, particularly the thickness of the surface, and to show how
conclusions drawn from earlier work are modified. The main sensitivity arises
such that the steeper the bubble surface the more enhanced the seed fields
become. Consequently, the magnetic seed fields may be several times larger and
smoother over the collision volume than found in earlier studies. Our work thus
provides additional support to the supposition that magnetic fields produced
during the EWPT in the early universe seed the galactic and extra-galactic
magnetic fields observed today. |
Field Theories and Fluids for an Interacting Dark Sector: We consider the relationship between fluid models of an interacting dark
sector, and the field theoretical models that underlie such descriptions. This
question is particularly important in light of suggestions that such
interactions may help alleviate a number of current tensions between different
cosmological datasets. We construct consistent field theory models for an
interacting dark sector that behave exactly like the coupled fluid ones, even
at the level of linear perturbations, and can be trusted deep in the nonlinear
regime. As a specific example, we focus on the case of a Dirac, Born-Infeld
(DBI) field conformally coupled to a quintessence field. We show that the fluid
linear regime breaks before the field gradients become large; this means that
the field theory is valid inside a large region of the fluid nonlinear regime. | Non-parametric method for measuring gas inhomogeneities from X-ray
observations of galaxy clusters: We present a non-parametric method to measure inhomogeneities in the
intracluster medium (ICM) from X-ray observations of galaxy clusters. Analysing
mock Chandra X-ray observations of simulated clusters, we show that our new
method enables the accurate recovery of the 3D gas density and gas clumping
factor profiles out to large radii of galaxy clusters. We then apply this
method to Chandra X-ray observations of Abell 1835 and present the first
determination of the gas clumping factor from the X-ray cluster data. We find
that the gas clumping factor in Abell 1835 increases with radius and reaches
~2-3 at r=R_{200}. This is in good agreement with the predictions of
hydrodynamical simulations, but it is significantly below the values inferred
from recent Suzaku observations. We further show that the radially increasing
gas clumping factor causes flattening of the derived entropy profile of the ICM
and affects physical interpretation of the cluster gas structure, especially at
the large cluster-centric radii. Our new technique should be useful for
improving our understanding of the cluster structure and to advance the use of
galaxy clusters as cosmological probes, by helping to exploit rich data sets
provided by Chandra and XMM-Newton X-ray space telescopes. |
Pairwise Velocities of Dark Matter Halos: a Test for the Lambda Cold
Dark Matter Model using the Bullet Cluster: The existence of 1E0657-56 poses a challenge to the concordance Lambda cold
dark matter model. Here we investigate the velocity distribution of dark matter
halo pairs in large N-body simulations with differing box sizes (250Mpc/h-2
Gpc/h) and resolutions. We examine statistics such as the halo masses, pairwise
halo velocities (v_{12}), and pair separation distances. We then compare our
results to the initial conditions (ICs) required to reproduce the observational
properties of 1E0657-56 in non-cosmological hydrodynamical simulations. We find
that the high velocity tail of the v_{12} distribution extends to greater
velocities as we increase the box size. We also find that the number of
high-v_{12} pairs increases as we increase the particle count and resolution
with a fixed box size, however, this increase is mostly due to lower mass halos
which do not match the observed masses of 1E0657-56. We find that the redshift
evolution is not very strong for the v_{12} distribution function between z=0.0
and z~0.5. We identify some pairs whose v_{12} resemble the required ICs,
however, even the best candidates have either wrong halo mass ratios, or too
large separations. Our simulations suggest that it is very difficult to produce
such ICs at z=0.0, 0.296,& 0.489 in comoving volumes as large as (2Gpc/h)^3.
Based on the extrapolation of our cumulative v_{12} function, we find that one
needs a simulation with a comoving box size of (4.48Gpc/h)^3 and 2240^3 DM
particles in order to produce at least one pair of halos that resembles the
required v_{12} and observed masses of 1E0657-56. We find that the probability
of finding a halo pair with v_{12}>=3000km/s and masses >=10^{14}Msun to be
2.76x10^{-8} at z=0.489. We conclude that either 1E0657-56 is incompatible with
the concordance LCDM universe, or the ICs suggested by the non-cosmological
simulations must be revised to give a lower value of v_{12}. | Future constraints on neutrino isocurvature perturbations in the
curvaton scenario: In the curvaton scenario, residual isocurvature perturbations can be
imprinted in the cosmic neutrino component after the decay of the curvaton
field, implying in turn a non-zero chemical potential in the neutrino
distribution. We study the constraints that future experiments like Planck,
SPIDER or CMBPol will be able to put on the amplitude of isocurvature
perturbations in the neutrino component. We express our results in terms of the
square root \gamma of the non-adiabaticity parameter \alpha and of the extra
relativistic degrees of freedom \Delta N_eff. Assuming a fiducial model with
purely adiabatic fluctuations, we find that Planck (SPIDER) will be able to put
the following upper limits at the 1sigma level: \gamma < 5.3x10^-3 (1.2x10^-2)
and \Delta N_eff < 0.16 (0.40) . CMBPol will further improve these constraints
to \gamma < 1.5x10^-3 and \Delta N_eff < 0.043. Finally, we recast these bounds
in terms of the background neutrino degeneracy parameter \xi\ and the
corresponding perturbation amplitude \sigma_\xi, and compare with the bounds on
\xi\ that can be derived from Big Bang Nucleosynthesis. |
$S_8$ Tension in the Context of Dark Matter-Baryon Scattering: We explore an interacting dark matter (IDM) model that allows for a fraction
of dark matter (DM) to undergo velocity-independent scattering with baryons. In
this scenario, structure on small scales is suppressed relative to the cold DM
scenario. Using the effective field theory of large-scale structure, we perform
the first systematic analysis of BOSS full-shape galaxy clustering data for the
IDM scenario, and we find that this model alleviates the $S_8$ tension between
large-scale structure and Planck data. Adding the $S_8$ prior from DES to our
analysis further leads to a mild $\sim3\sigma$ preference for a non-vanishing
DM-baryon scattering cross-section, assuming $\sim 10\%$ of DM is interacting
and has a particle mass of 1 MeV. This result produces a modest $\sim 20$%
suppression of the linear power at $k\lesssim 1~h$/Mpc, consistent with other
small-scale structure observations. Similar scale-dependent power suppression
was previously shown to have the potential to resolve $S_8$ tension between
cosmological data sets. The validity of the specific IDM model explored here
will be critically tested with upcoming galaxy surveys at the interaction level
needed to alleviate the $S_8$ tension. | Bouncing alternatives to inflation: Although the inflationary paradigm is the most widely accepted explanation
for the current cosmological observations, it does not necessarily correspond
to what actually happened in the early stages of our Universe. To decide on
this issue, two paths can be followed: first, all the possible predictions it
makes must be derived thoroughly and compared with available data, and second,
all imaginable alternatives must be ruled out. Leaving the first task to all
other contributors of this volume, we concentrate here on the second option,
focusing on the bouncing alternatives and their consequences. |
Non-parametric reconstruction of cosmological matter perturbations: Perturbative quantities, such as the growth rate ($f$) and index ($\gamma$),
are powerful tools to distinguish different dark energy models or modified
gravity theories even if they produce the same cosmic expansion history. In
this work, without any assumption about the dynamics of the Universe, we apply
a non-parametric method to current measurements of the expansion rate $H(z)$
from cosmic chronometers and high-$z$ quasar data and reconstruct the growth
factor and rate of linearised density perturbations in the non-relativistic
matter component. Assuming realistic values for the matter density parameter
$\Omega_{m0}$, as provided by current CMB experiments, we also reconstruct the
evolution of the growth index $\gamma$ with redshift. We show that the
reconstruction of current $H(z)$ data constrains the growth index to
$\gamma=0.56 \pm 0.12$ (2$\sigma$) at $z = 0.09$, which is in full agreement
with the prediction of the $\Lambda$CDM model and some of its extensions. | Exploring the effects of primordial non-Gaussianity at galactic scales: While large scale primordial non-Gaussianity is strongly constrained by
present-day data, there are no such constraints at Mpc scales. Here we
investigate the effect of significant small-scale primordial non-Gaussianity on
structure formation and the galaxy formation process with collisionless
simulations: specifically, we explore four different types of
non-Gaussianities. All of these prescriptions lead to a distinct and
potentially detectable feature in the matter power spectrum around the
non-linear scale. The feature might have interesting consequences for the $S_8$
tension. We then show in particular that a negatively-skewed distribution of
the potential random field, hence positively skewed in terms of overdensities,
with $f_{\rm NL}$ of the order of 1000 at these scales, implies that typical
galaxy-sized halos reach half of their present-day mass at an earlier stage and
have a quieter merging history at $z<3$ than in the Gaussian case. Their
environment between 0.5 and 4 virial radii at $z=0$ is less dense than in the
Gaussian case. This quieter history and less dense environment has potentially
interesting consequences in terms of the formation of bulges and bars.
Moreover, we show that the two most massive subhalos around their host tend to
display an interesting anti-correlation of velocities, indicative of kinematic
coherence. All these hints will need to be statistically confirmed in
larger-box simulations with scale-dependent non-Gaussian initial conditions,
followed by hydrodynamical zoom-in simulations to explore the detailed
consequences of small-scale non-Gaussianities on galaxy formation. |
Determining the Hubble Constant without the Sound Horizon: A $3.6\%$
Constraint on $H_0$ from Galaxy Surveys, CMB Lensing and Supernovae: Many theoretical resolutions to the so-called "Hubble tension" rely on
modifying the sound horizon at recombination, $r_s$, and thus the acoustic
scale used as a standard ruler in the cosmic microwave background (CMB) and
large scale structure (LSS) datasets. As shown in a number of recent works,
these observables can also be used to compute $r_s$-independent constraints on
$H_0$ by making use of the horizon scale at matter-radiation equality, $k_{\rm
eq}$, which has different sensitivity to high redshift physics than $r_s$. As
such, $r_s$- and $k_{\rm eq}$-based measurements of $H_0$ (within a
$\Lambda$CDM framework) may differ if there is new physics present
pre-recombination. In this work, we present the tightest constraints on the
latter from current data, finding $H_0=64.8^{+2.2}_{-2.5}$ at 68% CL (in
$\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$ units) from a combination of
BOSS galaxy power spectra, Planck CMB lensing, and the newly released Pantheon+
supernova constraints, as well as physical priors on the baryon density,
neutrino mass, and spectral index. The BOSS and Planck measurements have
different degeneracy directions, leading to the improved combined constraints,
with a bound of $H_0 = 67.1^{+2.5}_{-2.9}$ ($63.6^{+2.9}_{-3.6}$) from BOSS
(Planck) alone. The results show some dependence on the neutrino mass bounds,
with the constraint broadening to $H_0 = 68.0^{+2.9}_{-3.2}$ if we instead
impose a weak prior on $\sum m_\nu$ from terrestrial experiments, or shifting
to $H_0 = 64.6\pm2.4$ if the neutrino mass is fixed to its minimal value. Even
without dependence on the sound horizon, our results are in $\approx 3\sigma$
tension with those obtained from the Cepheid-calibrated distance ladder, which
begins to cause problems for new physics models that vary $H_0$ by changing
acoustic physics or the expansion history immediately prior to recombination. | Cosmology with Doppler Lensing: Doppler lensing is the apparent change in object size and magnitude due to
peculiar velocities. Objects falling into an overdensity appear larger on its
near side, and smaller on its far side, than typical objects at the same
redshifts. This effect dominates over the usual gravitational lensing
magnification at low redshift. Doppler lensing is a promising new probe of
cosmology, and we explore in detail how to utilize the effect with forthcoming
surveys. We present cosmological simulations of the Doppler and gravitational
lensing effects based on the Millennium simulation. We show that Doppler
lensing can be detected around stacked voids or unvirialised over-densities.
New power spectra and correlation functions are proposed which are designed to
be sensitive to Doppler lensing. We consider the impact of gravitational
lensing and intrinsic size correlations on these quantities. We compute the
correlation functions and forecast the errors for realistic forthcoming
surveys, providing predictions for constraints on cosmological parameters.
Finally, we demonstrate how we can make 3-D potential maps of large volumes of
the Universe using Doppler lensing. |
Snowmass2021 Cosmic Frontier White Paper: Cosmology and Fundamental
Physics from the three-dimensional Large Scale Structure: Advances in experimental techniques make it possible to map the high redshift
Universe in three dimensions at high fidelity in the near future. This will
increase the observed volume by many-fold, while providing unprecedented access
to very large scales, which hold key information about primordial physics.
Recently developed theoretical techniques, together with the smaller size of
non-linearities at high redshift, allow the reconstruction of an order of
magnitude more "primordial modes", and should improve our understanding of the
early Universe through measurements of primordial non-Gaussianity and features
in the primordial power spectrum. In addition to probing the first epoch of
accelerated expansion, such measurements can probe the Dark Energy density in
the dark matter domination era, tightly constraining broad classes of dynamical
Dark Energy models. The shape of the matter power spectrum itself has the
potential to detect sub-percent fractional amounts of Early Dark Energy to $z
\sim 10^5$, probing Dark Energy all the way to when the Universe was only a few
years old. The precision of these measurements, combined with CMB observations,
also has the promise of greatly improving our constraints on the effective
number of relativistic species, the masses of neutrinos, the amount of spatial
curvature and the gravitational slip. Studies of linear or quasi-linear
large-scale structure with redshift surveys and the CMB currently provide our
tightest constraints on cosmology and fundamental physics. Pushing the redshift
and volume frontier will provide guaranteed, significant improvements in the
state-of-the-art in a manner that is easy to forecast and optimize. | The low-redshift intergalactic medium as seen in archival legacy
Hubble/STIS and FUSE data: We present a comprehensive catalog of ultraviolet HST/STIS and FUSE absorbers
in the low-redshift IGM at z<0.4. The catalog draws from the extensive
literature on IGM absorption, and it reconciles discrepancies among previous
catalogs through a critical evaluation of all reported absorption features in
light of new HST/COS data. We report on 746 HI absorbers down to a rest-frame
equivalent width of 12 milliAngstroms over a maximum redshift path length
Deltaz=5.38. We also confirm 111 OVI absorbers, 29 CIV absorbers, and numerous
absorption features due to other metal ions. We characterize the distribution
of absorber line frequency as a function of column density as a power law,
dN/dz \propto N^{-beta}, where beta=2.08+-0.12 for OVI and beta=1.68+-0.03 for
HI. Utilizing a more sophisticated accounting technique than past work, the
catalog accounts for ~43% of the baryons: 24+-2% in the photoionized Ly-alpha
forest and 19+-2% in the WHIM as traced by OVI. We discuss the large systematic
effects of various assumed metallicities and ionization states on these
calculations, and we implement recent simulation results in our estimates. |
Extended lens reconstructions with Grale: exploiting time domain,
substructural and weak-lensing information: The information about the mass density of galaxy clusters provided by the
gravitational lens effect has inspired many inversion techniques. In this
article, updates to the previously introduced method in Grale are described,
and explored in a number of examples. The first looks into a different way of
incorporating time delay information, not requiring the unknown source
position. It is found that this avoids a possible bias that leads to
"over-focusing" the images, i.e. providing source position estimates that lie
in a considerably smaller region than the true positions. The second is
inspired by previous reconstructions of the cluster of galaxies MACS
J1149.6+2223, where a multiply-imaged background galaxy contained a supernova,
SN Refsdal, of which four additional images were produced by the presence of a
smaller cluster galaxy. The inversion for the cluster as a whole, was not able
to recover sufficient detail interior to this quad. We show how constraints on
such different scales, from the entire cluster to a single member galaxy, can
now be used, allowing such small scale substructures to be resolved. Finally,
the addition of weak lensing information to this method is investigated. While
this clearly helps recover the environment around the strong lensing region,
the mass sheet degeneracy may make a full strong and weak inversion difficult,
depending on the quality of the ellipticity information at hand. We encounter
ring-like structure at the boundary of the two regimes, argued to be the result
of combining strong and weak lensing constraints, possibly affected by
degeneracies. | Holographic Λ(t)CDM model in a non-flat universe: The holographic $\Lambda(t)$CDM model in a non-flat universe is studied in
this paper. In this model, to keep the form of the stress-energy of the vacuum
required by general covariance, the holographic vacuum is enforced to exchange
energy with dark matter. It is demonstrated that for the holographic model the
best choice for the IR cutoff of the effective quantum field theory is the
event horizon size of the universe. We derive the evolution equations of the
holographic $\Lambda(t)$CDM model in a non-flat universe. We constrain the
model by using the current observational data, including the 557 Union2 type Ia
supernovae data, the cosmic microwave background anisotropy data from the 7-yr
WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results
show that the holographic $\Lambda(t)$CDM model tends to favor a spatially
closed universe (the best-fit value of $\Omega_{k0}$ is -0.042), and the 95%
confidence level range for the spatial curvature is $-0.101<\Omega_{k0}<0.040$.
We show that the interaction between the holographic vacuum and dark matter
induces an energy flow of which the direction is first from vacuum to dark
matter and then from dark matter to vacuum. Thus, the holographic
$\Lambda(t)$CDM model is just a time-varying vacuum energy scenario in which
the interaction between vacuum and dark matter changes sign during the
expansion of the universe. |
The radio SZ effect as a probe of the cosmological radio background: If there is a substantial cosmological radio background, there should be a
radio Sunyaev-Zeldovich (SZ) effect that goes along with it. The radio
background Comptonization leads to a slight photon excess at all wavelengths,
while Comptonization of the CMB at low frequencies leads to a decrement. For
levels of the radio background consistent with observations, these effects
cancel each other around $\nu\simeq 735~$MHz, with an excess at lower
frequencies and a decrement at higher frequencies. Assuming a purely
cosmological origin of the observed ARCADE radio excess, at $\nu \lesssim
20\,{\rm GHz}$ the signal scales as $\Delta T / T_{\rm CMB}\simeq 2\,y\left[
(\nu/735\,{\rm MHz})^{-2.59}-1\right]$ with frequency and the Compton-$y$
parameter of the cluster. For a typical cluster, the total radio SZ signal is
at the level of $\Delta T\simeq 1\,{\rm mK}$ around the null, with a steep
scaling towards radio frequencies. This is above current raw sensitivity limits
for many radio facilities at these wavelengths, providing a unique way to
confirm the cosmological origin of the ARCADE excess and probe its properties
(e.g., redshift dependence and isotropy). We also give an expression to compute
the radio-analogue of the kinematic SZ effect, highlighting that this might
provide a new tool to probe large-scale velocity fields and the cosmic
evolution of the radio background. | Future Constraints on the Reionization History and the Ionizing Sources
from Gamma-ray Burst Afterglows: We forecast the reionization history constraints, inferred from Lyman-alpha
damping wing absorption features, for a future sample of $\sim 20$ $z \geq 6$
gamma-ray burst (GRB) afterglows. We describe each afterglow spectrum by a
three-parameter model. First, L characterizes the size of the ionized region
(the "bubble size") around a GRB host halo. Second, $\langle{x_{\rm
HI}\rangle}$ is the volume-averaged neutral fraction outside of the ionized
bubble around the GRB, which is approximated as spatially uniform. Finally,
$N_{\mathrm{HI}}$ denotes the column-density of a local damped Lyman-alpha
absorber (DLA) associated with the GRB host galaxy. The size distribution of
ionized regions is extracted from a numerical simulation of reionization, and
evolves strongly across the Epoch of Reionization (EoR). The model DLA column
densities follow the empirical distribution determined from current GRB
afterglow spectra. We use a Fisher matrix formalism to forecast the
$\langle{x_{\rm HI}(z)\rangle}$ constraints that can be obtained from follow-up
spectroscopy of afterglows with SNR = 20 per R=3,000 resolution element at the
continuum. We find that the neutral fraction may be determined to better than
10-15\% (1-$\sigma$) accuracy from this data across multiple independent
redshift bins at $z \sim 6-10$, spanning much of the EoR, although the
precision degrades somewhat near the end of reionization. A more futuristic
survey with $80$ GRB afterglows at $z \geq 6$ can improve the precision here by
a factor of $2$ and extend measurements out to $z \sim 14$. We further discuss
how these constraints may be combined with estimates of the escape fraction of
ionizing photons, derived from the DLA column density distribution towards GRBs
extracted at slightly lower redshift. This combination will help in testing
whether we have an accurate census of the sources that reionized the universe. |
Streams and caustics: the fine-grained structure of LCDM haloes: We present the first and so far the only simulations to follow the
fine-grained phase-space structure of galaxy haloes formed from generic LCDM
initial conditions. We integrate the geodesic deviation equation in tandem with
the N-body equations of motion, demonstrating that this can produce numerically
converged results for the properties of fine-grained phase-space streams and
their associated caustics, even in the inner regions of haloes. Our effective
resolution for such structures is many orders of magnitude better than achieved
by conventional techniques on even the largest simulations. We apply these
methods to the six Milky Way-mass haloes of the Aquarius Project. At 8 kpc from
halo centre a typical point intersects about 10^14 streams with a very broad
range of individual densities; the ~10^6 most massive streams contribute about
half of the local dark matter density. As a result, the velocity distribution
of dark matter particles should be very smooth with the most massive
fine-grained stream contributing about 0.1% of the total signal. Dark matter
particles at this radius have typically passed 200 caustics since the Big Bang.
The peak densities on present-day caustics in the inner halo almost all lie
well below the mean local dark matter density. As a result caustics provide a
negligible boost (<0.1%) to the predicted local dark matter annihilation rate.
The effective boost is larger in the outer halo but never exceeds about 10%.
Thus fine-grained streams and their associated caustics have no effect on the
detectability of dark matter, either directly in Earth-bound laboratories, or
indirectly through annihilation radiation, with the exception that resonant
cavity experiments searching for axions may see the most massive local
fine-grained streams because of their extreme localisation in energy/momentum
space. (abridged) | Dark-energy dependent test of general relativity at cosmological scales: The $\Lambda$CDM framework offers a remarkably good description of our
universe with a very small number of free parameters, which can be determined
with high accuracy from currently available data. However, this does not mean
that the associated physical quantities, such as the curvature of the universe,
have been directly measured. Similarly, general relativity is assumed, but not
tested. Testing the relevance of general relativity for cosmology at the
background level includes a verification of the relation between its energy
contents and the curvature of space. Using an extended Newtonian formulation,
we propose an approach where this relation can be tested. Using the recent
measurements on cosmic microwave background, baryonic acoustic oscillations and
the supernova Hubble diagram, we show that the prediction of general relativity
is well verified in the framework of standard $\Lambda$CDM assumptions, i.e. an
energy content only composed of matter and dark energy, in the form of a
cosmological constant or equivalently a vacuum contribution.
However, the actual equation of state of dark fluids cannot be directly
obtained from cosmological observations. We found that relaxing the equation of
state of dark energy opens a large region of possibilities, revealing a new
type of degeneracy between the curvature and the total energy content of the
universe. |
Cosmological Parallax--Distance Formula: The standard cosmological parallax--distance formula, as found in the
literature, including text-books and reference books on cosmology, requires a
correction. This correction stems from the fact that in the standard text-book
derivation it has been ignored that any chosen baseline in a gravitationally
bound system does not partake in the cosmological expansion. Though the
correction is available in the literature for some time, the text-books still
continue to use the older, incorrect formula, and its full implications are not
yet fully realized. Apart from providing an alternate correct, closed-form
expression that is more suitable and convenient for computations for certain
limiting cases of FRW ($\Lambda=0$) world models, we also demonstrate how one
can compute parallax distance for the currently favored flat-space
accelerating-universe ($\Lambda>0, k=0$) cosmologies. Further, we show that the
correction in parallax distance at large redshifts could amount to a factor of
three or even more. Moreover, even in an infinite universe the parallax
distance does not increase indefinitely with redshift and that even the
farthest possible observable point may have a finite parallax angle, a factor
that needs to be carefully taken into account when using distant objects as the
background field against which the parallax of a foreground object is to be
measured. Some other complications that could arise in parallax measurements of
a distant source, like that due to the deflection of incoming light by the
gravitation field of the Sun and other planetary bodies in the solar system,
are pointed out. | Extinction in Star-Forming Disk Galaxies from Inclination-Dependent
Composite Spectra: Extinction in galaxies affects their observed properties. In scenarios
describing the distribution of dust and stars in individual disk galaxies, the
amplitude of the extinction can be modulated by the inclination of the
galaxies. In this work we investigate the inclination dependency in composite
spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data
Release 5. In a volume-limited sample within a redshift range 0.065-0.075 and a
r-band Petrosian absolute magnitude range -19.5 to -22 which exhibits a flat
distribution of inclination, the inclined relative to face-on extinction in the
stellar continuum is found empirically to increase with inclination in the g,
r, and i bands. Within the central 0.5 intrinsic half-light radius of the
galaxies, the g-band relative extinction in the stellar continuum for the
highly-inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with
previous studies. The extinction curve of the disk galaxies is given in the
restframe wavelengths 3700-8000 angstrom, identified with major optical
emission and absorption lines in diagnostics. The Balmer decrement remains
constant with inclination, suggesting a different kind of dust configuration
and/or reddening mechanism in the HII region from that in the stellar
continuum. One factor is shown to be the presence of spatially non-uniform
interstellar extinction, presumably caused by clumped dust in the vicinity of
the HII region. |
The stellar mass function and star formation rate-stellar mass relation
of galaxies at z ~ 4 - 7: We investigate the evolution of the star formation rate-stellar mass relation
(SFR-M*) and Galaxy Stellar Mass Function (GSMF) of z ~ 4-7 galaxies, using
cosmological simulations run with the smoothed particle hydrodynamics code
P-GADGET3(XXL). We explore the effects of different feedback prescriptions
(supernova driven galactic winds and AGN feedback), initial stellar mass
functions and metal cooling. We show that our fiducial model, with strong
energy-driven winds and early AGN feedback, is able to reproduce the observed
stellar mass function obtained from Lyman-break selected samples of star
forming galaxies at redshift 6 < z < 7. At z ~ 4, observed estimates of the
GSMF vary according to how the sample was selected. Our simulations are more
consistent with recent results from K-selected samples, which provide a better
proxy of stellar masses and are more complete at the high mass end of the
distribution. We find that in some cases simulated and observed SFR-M*
relations are in tension, and this can lead to numerical predictions for the
GSMF in excess of the GSMF observed. By combining the simulated SFR(M*)
relationship with the observed star formation rate function at a given
redshift, we argue that this disagreement may be the result of the uncertainty
in the SFR-M* (Luv-M*) conversion. Our simulations predict a population of
faint galaxies not seen by current observations. | Probing CMB Secondary Anisotropies through Minkowski Functionals: Secondary contributions to the anisotropy of the Cosmic Microwave Background
(CMB), such as the integrated Sachs-Wolfe (ISW) effect, the thermal
Sunyaev-Zel'dovich effect (tSZ), and the effect of gravitational lensing, have
distinctive non-Gaussian signatures, and full descriptions therefore require
information beyond that contained in their power spectra. In this paper we use
the recently introduced skew-spectra associated with the Minkowski Functionals
(MF) to probe the topology of CMB maps to probe the secondary non-Gaussianity
as a function of beam-smoothing in order to separate various contributions. We
devise estimators for these spectra in the presence of a realistic
observational masks and present expressions for their covariance as a function
of instrumental noise. Specific results are derived for the mixed ISW-lensing
and tSZ-lensing bispectra as well as contamination due to point sources for
noise levels that correspond to the Planck (143 GHz channel) and EPIC (150 GHz
channel) experiments. The cumulative signal to noise ration $S/N$ for one-point
generalized skewness-parameters can reach an order of ${\cal O}(10)$ for Planck
and two orders of magnitude higher for EPIC, i.e. ${\cal O}(10^3)$. We also
find that these three spectra skew-spectra are correlated, having correlation
coefficients $r \sim 0.5-1.0$; higher $l$ modes are more strongly correlated.
Though the values of $S/N$ increase with decreasing noise, the triplets of
skew-spectra that determine the MFs bcome more correlated; the $S/N$ ratios of
lensing-induced skew-spectra are smaller compared to that of a
frequency-cleaned tSZ map. |
Solving linear equations with messenger-field and conjugate gradients
techniques - an application to CMB data analysis: We discuss linear system solvers invoking a messenger-field and compare them
with (preconditioned) conjugate gradients approaches. We show that the
messenger-field techniques correspond to fixed point iterations of an
appropriately preconditioned initial system of linear equations. We then argue
that a conjugate gradient solver applied to the same preconditioned system, or
equivalently a preconditioned conjugate gradient solver using the same
preconditioner and applied to the original system, will in general ensure at
least a comparable and typically better performance in terms of the number of
iterations to convergence and time-to-solution. We illustrate our conclusions
on two common examples drawn from the Cosmic Microwave Background data
analysis: Wiener filtering and map-making. In addition, and contrary to the
standard lore in the CMB field, we show that the performance of the
preconditioned conjugate gradient solver can depend importantly on the starting
vector. This observation seems of particular importance in the cases of
map-making of high signal-to-noise sky maps and therefore should be of
relevance for the next generation of CMB experiments. | The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: cosmological constraints from the full shape of the
clustering wedges: We explore the cosmological implications of the clustering wedges, xi_perp(s)
and xi_para(s), of the CMASS Data Release 9 (DR9) sample of the Baryon
Oscillation Spectroscopic Survey (BOSS). These clustering wedges are defined by
averaging the full two-dimensional correlation function, xi(mu,s), over the
ranges 0<mu<0.5 and 0.5<mu<1, respectively. These measurements allow us to
constrain the parameter combinations D_A(z)/r_s(z_d)=9.03 +- 0.21 and
cz/(r_s(z_d)H(z)) = 12.14 +- 0.43 at the mean redsfhit of the sample, z=0.57.
We combine the information from the clustering wedges with recent measurements
of CMB, BAO and type Ia supernovae to obtain constraints on the cosmological
parameters of the standard LCDM model and a number of potential extensions. The
information encoded in the clustering wedges is most useful when the dark
energy equation of state is allowed to deviate from its standard LCDM value.
The combination of all datasets shows no evidence of a deviation from a
constant dark energy equation of state, in which case we find w_DE = -1.013 +-
0.064, in complete agreement with a cosmological constant. We explore potential
deviations from general relativity by constraining the growth rate f(z)=d ln
D(a)/ d ln a, in which case the combination of the CMASS clustering wedges with
CMB data implies f(z=0.57)=0.719 +- 0.094, in accordance with the predictions
of GR. Our results clearly illustrate the additional constraining power of
anisotropic clustering measurements with respect to that of angle-averaged
quantities. |
The Jet-Driven Outflow in the Radio Galaxy SDSS J1517+3353: Implications
for Double-Peaked Narrow-Line AGN: We report on the study of an intriguing active galaxy that was selected as a
potential multiple supermassive black hole merger in the early-type host SDSS
J151709.20+335324.7 (z=0.135). Ground-based SDSS imaging reveals two blue
structures on either side of the photometric center of the host galaxy,
separated from each other by about 5.7 kpc. The analysis of spatially resolved
emission line profiles from a Keck/HIRES spectrum reveal three distinct
kinematic subcomponents, one at rest and the other two moving at -350 km/s and
500 km/s with respect to the systemic velocity of the host galaxy. A comparison
of imaging and spectral data confirm a strong association between the kinematic
components and the spatial knots, which implies a highly disturbed and complex
active region in this object. Subsequent VLA radio imaging reveals a clear jet
aligned with the emission line gas, confirming that a jet-gas interaction is
the best explanation for emission line region. We use the broadband radio
measurements to examine the impact of the jet on the ISM of the host galaxy,
and find that the energy in the radio lobes can heat a significant fraction of
the gas to the virial temperature. Finally, we discuss tests that may help
future surveys distinguish between jet-driven kinematics and true black-hole
binaries. SDSS J151709.20+335324.7 is a remarkable laboratory for AGN feedback
and warrants deeper follow-up study. In the Appendix, we present
high-resolution radio imaging of a second AGN with double-peaked [O III] lines,
SDSS J112939.78+605742.6, which shows a sub-arcsecond radio jet. If the
double-peaked nature of the narrow lines in radio-loud AGN are generally due to
radio jet interactions, we suggest that extended radio structure should be
expected in most of such systems. | Gravitational waves from gauge preheating: We study gravitational wave production during Abelian gauge-field preheating
following inflation. We consider both scalar and pseudoscalar inflaton models
coupled directly to Abelian gauge fields via either a dilatonic coupling to the
gauge-field kinetic term or an axial coupling to a Chern-Simons term. In both
cases gravitational waves are produced efficiently during the preheating phase,
with a signature louder than most cosmological signals. These gravitational
waves can contribute to the radiation energy budget of Universe at a level
which will be probed by upcoming cosmic microwave background experiments
through $N_{\rm eff}$. For axially coupled fields the resulting gravitational
wave spectrum is helically polarized---a unique feature that can be used to
differentiate it from other stochastic gravitational wave backgrounds. We
compute the gravitational topological charge and demonstrate that gauge
preheating following axion inflation may be responsible for the
matter-antimatter asymmetry of the Universe via gravitational leptogenesis. |
From dwarf spheroidals to cDs: Simulating the galaxy population in a
LCDM cosmology: We apply updated semi-analytic galaxy formation models simultaneously to the
stored halo/subhalo merger trees of the Millennium and Millennium-II
simulations. These differ by a factor of 125 in mass resolution, allowing
explicit testing of resolution effects on predicted galaxy properties. We have
revised the treatments of the transition between the rapid infall and cooling
flow regimes of gas accretion, of the sizes of bulges and of gaseous and
stellar disks, of supernova feedback, of the transition between central and
satellite status as galaxies fall into larger systems, and of gas and star
stripping once they become satellites. Plausible values of efficiency and
scaling parameters yield an excellent fit not only to the observed abundance of
low-redshift galaxies over 5 orders of magnitude in stellar mass and 9
magnitudes in luminosity, but also to the observed abundance of Milky Way
satellites. This suggests that reionisation effects may not be needed to solve
the "missing satellite" problem except, perhaps, for the faintest objects. The
same model matches the observed large-scale clustering of galaxies as a
function of stellar mass and colour. The fit remains excellent down to ~30kpc
for massive galaxies. For M* < 6 x 10^10Msun, however, the model overpredicts
clustering at scales below 1 Mpc, suggesting that the sigma_8 adopted in the
simulations (0.9) is too high. Galaxy distributions within rich clusters agree
between the simulations and match those observed, but only if galaxies without
dark matter subhalos (so-called orphans) are included. Our model predicts a
larger passive fraction among low-mass galaxies than is observed, as well as an
overabundance of ~10^10Msun galaxies beyond z~0.6, reflecting deficiencies in
the way star-formation rates are modelled. | 21 cm intensity mapping with the Five hundred metre Aperture Spherical
Telescope: This paper describes a programme to map large-scale cosmic structures on the
largest possible scales by using the Five hundred metre Aperture Spherical
Telescope (FAST) to make a 21 cm (red-shifted) intensity map of the sky for the
range $0.5 < z < 2.5$. The goal is to map to the angular and spectral
resolution of FAST a large swath of the sky by simple drift scans with a
transverse set of beams. This approach would be complementary to galaxy surveys
and could be completed before the Square Kilometre Array (SKA) could begin a
more detailed and precise effort. The science would be to measure the
large-scale structure on the size of the baryon acoustic oscillations and
larger scale, and the results would be complementary to its contemporary
observations and significant. The survey would be uniquely sensitive to the
potential very large-scale features from inflation at the Grand Unified Theory
(GUT) scale and complementary to observations of the cosmic microwave
background. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Hierarchical
scaling and biasing: We investigate the higher-order correlation properties of the VIMOS Public
Extragalactic Redshift Survey (VIPERS) to test the hierarchical scaling
hypothesis at z~1 and the dependence on galaxy luminosity, stellar mass, and
redshift. We also aim to assess deviations from the linearity of galaxy bias
independently from a previously performed analysis of our survey (Di Porto et
al. 2014). We have measured the count probability distribution function in
cells of radii 3 < R < 10 Mpc/h, deriving $\sigma_{8g}$, the volume-averaged
two-,three-,and four-point correlation functions and the normalized skewness
$S_{3g}$ and kurtosis $S_{4g}$ for volume-limited subsamples covering the
ranges $-19.5 \le M_B(z=1.1)-5log(h) \le -21.0$, $9.0 < log(M*/M_{\odot}
h^{-2}) \le 11.0$, $0.5 \le z < 1.1$. We have thus performed the first
measurement of high-order correlations at z~1 in a spectroscopic redshift
survey. Our main results are the following. 1) The hierarchical scaling holds
throughout the whole range of scale and z. 2) We do not find a significant
dependence of $S_{3g}$ on luminosity (below z=0.9 $S_{3g}$ decreases with
luminosity but only at 1{\sigma}-level). 3) We do not detect a significant
dependence of $S_{3g}$ and $S_{4g}$ on scale, except beyond z~0.9, where the
dependence can be explained as a consequence of sample variance. 4) We do not
detect an evolution of $S_{3g}$ and $S_{4g}$ with z. 5) The linear bias factor
$b=\sigma_{8g}/\sigma_{8m}$ increases with z, in agreement with previous
results. 6) We quantify deviations from the linear bias by means of the Taylor
expansion parameter $b_2$. Our results are compatible with a null non-linear
bias term, but taking into account other available data we argue that there is
evidence for a small non-linear bias term. | Massive star formation in galaxies with excess UV emission: From an analysis of almost 2000 GALEX images of galaxies with morphological
types ranging from E to Sab, we have found a significant subset (28%) that show
UV emission outside $R_{25}$. We have obtained H$\alpha$ imaging of ten such
galaxies, and find that their star formation rates are similar in the UV and in
H$\alpha$, with values ranging from a few tenths to a few $M_{\odot} $ yr$
^{-1} $. Probably because our sample selection is biased towards star-forming
galaxies, these rates are comparable to those found in disk galaxies, although
the star formation rates of the elliptical galaxies in our sample are well
below $1\,M_{\odot} $ yr$ ^{-1}$. We confirm that the extended UV emission in
our sample is caused by massive star formation in outer spiral arms and/or
outer (pseudo) rings, rather than by alternative mechanisms such as the UV
upturn. |
Learning how to surf: Reconstructing the propagation and origin of
gravitational waves with Gaussian Processes: Soon, the combination of electromagnetic and gravitational signals will open
the door to a new era of gravitational-wave (GW) cosmology. It will allow us to
test the propagation of tensor perturbations across cosmic time and study the
distribution of their sources over large scales. In this work, we show how
machine learning techniques can be used to reconstruct new physics by
leveraging the spatial correlation between GW mergers and galaxies. We explore
the possibility of jointly reconstructing the modified GW propagation law and
the linear bias of GW sources, as well as breaking the slight degeneracy
between them by combining multiple techniques. We show predictions roughly
based on a network of Einstein Telescopes combined with a high-redshift galaxy
survey ($z\lesssim3$). Moreover, we investigate how these results can be
re-scaled to other instrumental configurations. In the long run, we find that
obtaining accurate and precise luminosity distance measurements (extracted
directly from the individual GW signals) will be the most important factor to
consider when maximizing constraining power. | Signals from the Early Universe: Black Holes, Gravitational Waves and
Particle Physics: We dedicate this thesis to the study of signatures coming from the primordial
epochs of the universe. We will focus in particular on Primordial Black Holes
(PBHs), which may be formed from perturbations generated during inflation and
might comprise a fraction of the dark matter in the universe. In the first part
of the thesis, we will address the PBH properties at the time of formation,
that are their masses, spins and abundance, and investigate the generation of
Gravitational Wave (GW) signals during their production. In the second part, we
will describe the PBHs evolution across the cosmic history due to their
assemble in binaries, phases of baryonic mass accretion and clustering effects.
We will then discuss GW signatures coming from their coalescence, compare these
predictions with present GW data detected by the LIGO/Virgo Collaboration (LVC)
and assess the role of future GW experiments like 3G detectors and LISA in
discovering these objects. Finally, in the third part, we will investigate some
aspects of the interplay between black holes and fundamental physics in the
early universe, focusing on the role of GWs to shed light on their properties. |
Dark calling Dark: Interaction in the dark sector in presence of
neutrino properties after Planck CMB final release: We investigate a well known scenario of interaction in the dark sector where
the vacuum energy is interacting with cold dark matter throughout the cosmic
evolution in light of the cosmic microwave background (CMB) data from final
Planck 2018 release. In addition to this minimal scenario, we generalize the
model baseline by including the properties of neutrinos, such as the neutrino
mass scale ($M_{\nu}$) and the effective number of neutrino species ($N_{\rm
eff}$) as free parameters, in order to verify the possible effects that such
parameters might generate on the coupling parameter, and vice versa. As already
known, we again confirm that in light of the Planck 2018 data, such dark
coupling can successfully solve the $H_0$ tension (with and without the
presence of neutrinos). Concerning the properties of neutrinos, we find that
$M_{\nu}$ may be wider than expected within the $\Lambda$CDM model and $N_{\rm
eff}$ is fully compatible with three neutrino species (similar to $\Lambda$CDM
prevision). The parameters characterizing the properties of neutrinos do not
correlate with the coupling parameter of the interaction model. When
considering the joint analysis of CMB from Planck 2018 and an estimate of $H_0$
from Hubble Space Telescope 2019 data, {\it we find an evidence for a non-null
value of the coupling parameter at more than 3$\sigma$ confidence-level.} We
also discuss the possible effects on the interacting scenario due to the
inclusion of baryon acoustic oscillations data with Planck 2018. Our main
results updating the dark sectors' interaction and neutrino properties in the
model baseline, represent a new perspective in this direction. Clearly, a
possible new physics in light of some dark interaction between dark energy and
dark matter can serve as an alternative to $\Lambda$CDM scenario to explain the
observable Universe, mainly in light of the current tension on $H_0$. | Cl 1103.7-1245 at z=0.96: the highest redshift galaxy cluster in the
EDisCS survey: We present new spectroscopic observations in a field containing the highest
redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy
redshifts and determine the velocity dispersions of the galaxy structures
located in this field. Together with the main cluster Cl1103.7$-$1245
(z=0.9580; sigma_{clus} = 522 +/- 111 km/s) we find a secondary structure at
z=0.9830, Cl1103.7-1245c. We then characterize the galaxy properties in both
systems, and find that they contain very different galaxy populations. The
cluster Cl1103.7-1245 hosts a mixture of passive elliptical galaxies and
star-forming spirals and irregulars. In the secondary structure Cl1103.7-1245c
all galaxies are lower-mass star-forming irregulars and peculiars. In addition,
we compare the galaxy populations in the Cl1103.7-1245 z=0.9580 cluster with
those in lower redshift EDisCS clusters with similar velocity dispersions. We
find that the properties of the galaxies in Cl1103.7-1245 follow the
evolutionary trends found at lower redshifts: the number of cluster members
increases with time in line with the expected growth in cluster mass, and the
fraction of passive early-type galaxies increases with time while star-forming
late types become less dominant. Finally, we find that the mean stellar masses
are similar in all clusters, suggesting that massive cluster galaxies were
already present at z~1. |
Unveiling the Dynamics of the Universe: We explore the dynamics and evolution of the Universe at early and late
times, focusing on both dark energy and extended gravity models and their
astrophysical and cosmological consequences. Modified theories of gravity not
only provide an alternative explanation for the recent expansion history of the
universe, but they also offer a paradigm fundamentally distinct from the
simplest dark energy models of cosmic acceleration. In this review, we perform
a detailed theoretical and phenomenological analysis of different modified
gravity models and investigate their consistency. We also consider the
cosmological implications of well motivated physical models of the early
universe with a particular emphasis on inflation and topological defects.
Astrophysical and cosmological tests over a wide range of scales, from the
solar system to the observable horizon, severely restrict the allowed models of
the Universe. Here, we review several observational probes -- including
gravitational lensing, galaxy clusters, cosmic microwave background temperature
and polarization, supernova and baryon acoustic oscillations measurements --
and their relevance in constraining our cosmological description of the
Universe. | Three-form cosmology: Cosmology of self-interacting three-forms is investigated. The minimally
coupled canonical theory can naturally generate a variety of isotropic
background dynamics, including scaling, possibly transient acceleration and
phantom crossing. An intuitive picture of the cosmological dynamics is
presented employing an effective potential. Numerical solutions and analytical
approximations are provided for scenarios which are potentially important for
inflation or dark energy. |
Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband
Monitoring during Strong Gamma-ray Activity: We present results from monitoring the multi-waveband flux, linear
polarization, and parsec-scale structure of the quasar PKS 1510-089,
concentrating on eight major gamma-ray flares that occurred during the interval
2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at
optical wavelengths, although the flux ratio of the two wavebands varied by an
order of magnitude. The optical polarization vector rotated by 720 degrees
during a 5-day period encompassing six of these flares. This culminated in a
very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of
emission passed through the highest-intensity, stationary feature (the "core")
seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate
down the jet at an apparent speed of 22c and emit strongly at gamma-ray
energies as a months-long X-ray/radio outburst intensified. We interpret these
events as the result of the knot following a spiral path through a mainly
toroidal magnetic field pattern in the acceleration and collimation zone of the
jet, after which it passes through a standing shock in the 43 GHz core and then
continues downstream. In this picture, the rapid gamma-ray flares result from
scattering of infrared seed photons from a relatively slow sheath of the jet as
well as from optical synchrotron radiation in the faster spine. The 2006-2009.7
radio and X-ray flux variations are correlated at very high significance; we
conclude that the X-rays are mainly from inverse Compton scattering of infrared
seed photons by 20-40 MeV electrons. | Reconstructing the Thermal Sunyaev-Zel'dovich Effect in 3D: The thermal Sunyaev-Zel'dovich (tSZ) effect measures the line-of-sight
projection of the thermal pressure of free electrons and lacks any redshift
information. By cross correlating the tSZ effect with an external cosmological
tracer we can recover a good fraction of this lost information. Weak lensing
(WL) is thought to provide an unbiased probe of the dark Universe, with many WL
surveys having sky coverage that overlaps with tSZ surveys. Generalising the
tomographic approach, we advocate the use of the spherical Fourier-Bessel (sFB)
expansion to perform an analysis of the cross-correlation between the projected
(2D) tSZ Compton $y$-parameter maps and 3D weak lensing convergence maps. We
use redshift dependent linear biasing and the halo model as a tool to
investigate the tSZ-WL cross-correlations in 3D. We use the Press-Schechter
(PS) and the Sheth-Tormen (ST) mass-functions in our calculations, finding that
the results are quite sensitive to detailed modelling. We provide detailed
analysis of surveys with photometric and spectroscopic redshifts. The
signal-to-noise (S/N) of the cross-spectra $\mathcal{C}_{\ell} (k)$ for
individual 3D modes, defined by the radial and tangential wave numbers
$(k;\ell)$, remains comparable to, but below, unity though optimal binning is
expected to improve this. The results presented can be generalised to analyse
other CMB secondaries, such as the kinetic Sunyaev-Zel'dovich (kSZ) effect. |
Clustering Fossils from the Early Universe: Many inflationary theories introduce new scalar, vector, or tensor degrees of
freedom that may then affect the generation of primordial density
perturbations. Here we show how to search a galaxy (or 21-cm) survey for the
imprint of primordial scalar, vector, and tensor fields. These new fields
induce local departures to an otherwise statistically isotropic two-point
correlation function, or equivalently, nontrivial four-point correlation
functions (or trispectra, in Fourier space), that can be decomposed into
scalar, vector, and tensor components. We write down the optimal estimators for
these various components and show how the sensitivity to these modes depends on
the galaxy-survey parameters. New probes of parity-violating early-Universe
physics are also presented. | Matter power spectrum in f(R) gravity with massive neutrinos: The effect of massive neutrinos on matter power spectrum is discussed in the
context of $f(R)$ gravity. It is shown that the anomalous growth of density
fluctuations on small scales due to the scalaron force can be compensated by
free streaming of neutrinos. As a result, models which predict observable
deviation of the equation-of-state parameter $w_\DE$ from $w_\DE=-1$ can be
reconciled with observations of matter clustering if the total neutrino mass is
$O(0.5 \eV)$. |
Spectroscopic Signatures of the Tidal Disruption of Stars by Massive
Black Holes: During the tidal disruption of a star by a massive black hole (BH) of mass
MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the
Eddington rate. A fraction of this gas is subsequently blown away from the BH,
producing an optically bright flare of radiation. We predict the spectra and
spectral evolution of tidal disruption events, focusing on the photoionized gas
outside this outflow's photosphere. The spectrum will show absorption lines
that are strongly blueshifted relative to the host galaxy, very broad
(0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI),
lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei
are a significant source of confusion in optical surveys for tidal disruption
events: we estimate that nuclear Type Ia supernovae are two orders of magnitude
more common than tidal disruption events at z ~ 0.1 for ground-based surveys.
Nuclear Type II supernovae occur at a comparable rate but can be excluded by
pre-selecting red galaxies. Supernova contamination can be reduced to a
manageable level using high-resolution follow-up imaging with adaptive optics
or the Hubble Space Telescope. Our predictions should help optical transient
surveys capitalize on their potential for discovering tidal disruption events. | Submillimeter sources behind the massive lensing clusters A370 and A2390: We report 850 micron Submillimeter Array (SMA) observations of four
gravitationally lensed submillimeter galaxies (SMGs), A370-2, A2390-1, A2390-3
and A2390-4, which were originally discovered with the Submillimeter
Common-User Bolometer Array (SCUBA). Our SMA detection of A370-2 with a
submillimeter flux of 7.95 +/- 0.60 mJy unambiguously identifies the
counterparts to this source at optical and radio wavelengths. A2390-1 is an
ultraluminous infrared galaxies with a submillimeter flux of 5.55 +/- 0.92 mJy
and a redshift of 1.8 +/- 0.2 computed from submillimeter/radio flux ratio
analysis. We resolve A2390-3 into two components, A2390-3a and A2390-3b, with
fluxes of 3.15 +/- 0.63 mJy and 1.92 +/- 0.60 mJy, respectively. The structure
of the system could be consistent with morphological distortion by
gravitational lensing. The lack of counterparts in the optical and infrared
indicates a heavily dust-enshrouded nature, and a non-detection in the radio
implies that these two sources probably lie at z > 4.7, which would make them
among the most distant SMGs known to date. Our non-detection of A2390-4
suggests either that there are multiple fainter submillimeter sources within
the SCUBA beam or that the SCUBA detection may have been false. Our precise
positions allow us to determine accurate amplifications and fluxes for all our
detected sources. Our new results give a shallower power-law fit (-1.10) to the
faint-end 850 micron cumulative number counts than previous work. We emphasize
the need for high-resolution observations of single-dish detected SMGs in order
to measure accurately the faint end of the 850 micron counts. |
Tomographic Constraints on Gravity from Angular Redshift Fluctuations in
the Late Universe: Fluctuations in sky maps of the galaxy redshifts, dubbed as angular redshift
fluctuations (ARF), contain precise information about the growth rate of
structures and the nature of gravity in the Universe. Specifically, ARF
constrain the combination of cosmological parameters $H/H_0\,f\sigma_8(z)$,
while being an intrinsically tomographic probe and largely insensitive to many
observational systematic errors, all this without requiring the assumption of
any redshift-to-distance relation under a given fiducial cosmology. We present
the first cosmological constraints derived from ARF by using BOSS LOWZ+CMASS
DR12 galaxy samples, obtaining 7\%-accurate constraints on $H/H_0 f\sigma_8(z)$
at more than 20 redshifts over the range $z \in [0.26,0.72]$. Our best-fitting
value is $10\%$ larger, but compatible at the $1.4\sigma$ level, than the
$\Lambda$CDM expectation set by {\it Planck} observations of the Cosmic
Microwave Background (CMB) radiation. Our tomographic measurements, combined
with these CMB data, provides one of the strongest constraints on the gravity
index $\gamma$, $\gamma=0.44^{+0.09}_{-0.07}$, which lies within $2\sigma$ from
the prediction of General Relativity ($\gamma_{\rm GR}\simeq 0.55$). | Testing physical models for dipolar asymmetry with CMB polarization: The cosmic microwave background (CMB) temperature anisotropies exhibit a
large-scale dipolar power asymmetry. To determine whether this is due to a
real, physical modulation or is simply a large statistical fluctuation requires
the measurement of new modes. Here we forecast how well CMB polarization data
from \Planck\ and future experiments will be able to confirm or constrain
physical models for modulation. Fitting several such models to the \Planck\
temperature data allows us to provide predictions for polarization asymmetry.
While for some models and parameters \Planck\ polarization will decrease error
bars on the modulation amplitude by only a small percentage, we show,
importantly, that cosmic-variance-limited (and in some cases even \Planck)
polarization data can decrease the errors by considerably better than the
expectation of $\sqrt 2$ based on simple $\ell$-space arguments. We project
that if the primordial fluctuations are truly modulated (with parameters as
indicated by \Planck\ temperature data) then \Planck\ will be able to make a
2$\sigma$ detection of the modulation model with 20--75\% probability,
increasing to 45--99\% when cosmic-variance-limited polarization is considered.
We stress that these results are quite model dependent. Cosmic variance in
temperature is important: combining statistically isotropic polarization with
temperature data will spuriously increase the significance of the temperature
signal with 30\% probability for \Planck. |
New Limits on Coupled Dark Energy from Planck: Recently, the Planck collaboration has released the first cosmological papers
providing the high resolution, full sky, maps of the cosmic microwave
background (CMB) temperature anisotropies. It is crucial to understand that
whether the accelerating expansion of our universe at present is driven by an
unknown energy component (Dark Energy) or a modification to general relativity
(Modified Gravity). In this paper we study the coupled dark energy models, in
which the quintessence scalar field nontrivially couples to the cold dark
matter, with the strength parameter of interaction $beta$. Using the Planck
data alone, we obtain that the strength of interaction between dark sectors is
constrained as $beta < 0.102$ at $95%$ confidence level, which is tighter than
that from the WMAP9 data alone. Combining the Planck data with other probes,
like the Baryon Acoustic Oscillation (BAO), Type-Ia supernovae ``Union2.1
compilation'' and the CMB lensing data from Planck measurement, we find the
tight constraint on the strength of interaction $beta < 0.052$ ($95%$ C.L.).
Interestingly, we also find a non-zero coupling $beta = 0.078 pm 0.022$ ($68%$
C.L.) when we use the Planck, the ``SNLS'' supernovae samples, and the prior on
the Hubble constant from the Hubble Space Telescope (HST) together. This
evidence for the coupled dark energy models mainly comes from a tension between
constraints on the Hubble constant from the Planck measurement and the local
direct $H_0$ probes from HST. | The Herschel Virgo cluster survey: V. Star-forming dwarf galaxies - dust
in metal-poor environments: We present the dust properties of a small sample of Virgo cluster dwarf
galaxies drawn from the science demonstration phase data set of the Herschel
Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 +
log(O/H) < 8.3) and star-formation rates < 10^{-1} M_{sun}/yr. We measure the
spectral energy distribution (SED) from 100 to 500 um and derive dust
temperatures and dust masses. The SEDs are fitted by a cool component of
temperature T < 20 K, implying dust masses around 10^{5} M_{sun} and
dust-to-gas ratios D within the range 10^{-3}-10^{-2}. The completion of the
full survey will yield a larger set of galaxies, which will provide more
stringent constraints on the dust content of star-forming dwarf galaxies. |
Intrinsic alignments of galaxies in the Horizon-AGN cosmological
hydrodynamical simulation: The intrinsic alignments of galaxies are recognised as a contaminant to weak
gravitational lensing measurements. In this work, we study the alignment of
galaxy shapes and spins at low redshift ($z\sim 0.5$) in Horizon-AGN, an
adaptive-mesh-refinement hydrodynamical cosmological simulation box of 100
Mpc/h a side with AGN feedback implementation. We find that spheroidal galaxies
in the simulation show a tendency to be aligned radially towards over-densities
in the dark matter density field and other spheroidals. This trend is in
agreement with observations, but the amplitude of the signal depends strongly
on how shapes are measured and how galaxies are selected in the simulation.
Disc galaxies show a tendency to be oriented tangentially around spheroidals in
three-dimensions. While this signal seems suppressed in projection, this does
not guarantee that disc alignments can be safely ignored in future weak lensing
surveys. The shape alignments of luminous galaxies in Horizon-AGN are in
agreement with observations and other simulation works, but we find less
alignment for lower luminosity populations. We also characterize the
systematics of galaxy shapes in the simulation and show that they can be safely
neglected when measuring the correlation of the density field and galaxy
ellipticities. | Minimal theory of massive gravity and constraints on the graviton mass: The Minimal theory of Massive Gravity (MTMG) is endowed non-linearly with
only two tensor modes in the gravity sector which acquire a non-zero mass. On a
homogeneous and isotropic background the theory is known to possess two
branches: the self-accelerating branch with a phenomenology in cosmology which,
except for the mass of the tensor modes, exactly matches the one of
$\Lambda$CDM; and the normal branch which instead shows deviation from General
Relativity in terms of both background and linear perturbations dynamics. For
the latter branch we study using several early and late times data sets the
constraints on today's value of the graviton mass $\mu_{0}$, finding that
$(\mu_{0}/H_{0})^{2}=0.119_{-0.098}^{+0.12}$ at $68\%$ CL, which in turn gives
an upper bound at $95\%$ CL as $\mu_{0}<8.4\times10^{-34}$ eV. This corresponds
to the strongest bound on the mass of the graviton for the normal branch of
MTMG. |
Population III Hypernovae: Population III supernovae have been of growing interest of late for their
potential to directly probe the properties of the first stars, particularly the
most energetic events that are visible near the edge of the observable
universe. But until now, hypernovae, the unusually energetic Type Ib/c
supernovae that are sometimes associated with gamma-ray bursts, have been
overlooked as cosmic beacons at the highest redshifts. In this, the latest of a
series of studies on Population III supernovae, we present numerical
simulations of 25 - 50 M$_{\odot}$ hypernovae and their light curves done with
the Los Alamos RAGE and SPECTRUM codes. We find that they will be visible at z
= 10 - 15 to the James Webb Space Telescope (JWST) and z = 4 - 5 to the
Wide-Field Infrared Survey Telescope (WFIRST), tracing star formation rates in
the first galaxies and at the end of cosmological reionization. If, however,
the hypernova crashes into a dense shell ejected by its progenitor, it is
expected that a superluminous event will occur that may be seen at z ~ 20, in
the first generation of stars. | The Shapes of the HI Velocity Profiles of the THINGS Galaxies: We analyze the shapes of the HI velocity profiles of The HI Nearby Galaxy
Survey (THINGS) to study the phase structure of the neutral interstellar medium
(ISM) and its relation to global galaxy properties. We use a method analogous
to the stacking method sometimes used in high redshift HI observations to
construct high signal-to-noise (S/N) profiles. We call these high S/N profiles
super profiles. We analyze and discuss possible systematics that may change the
observed shapes of the super profiles. After quantifying these effects and
selecting a sub-sample of unaffected galaxies, we find that the super profiles
are best described by a narrow and a broad Gaussian component, which are
evidence of the presence of the Cold Neutral Medium (CNM) and the Warm Neutral
Medium (WNM). The velocity dispersion of the narrow component range from ~3.4
to ~8.6 km/s with an average of 6.5+/-1.5 km/s, whereas that of the broad
component range from ~10.1 to ~24.3 km/s with an average of 16.8+/-4.3 km/s. We
find that the super profile parameters correlate with star formation indicators
such as metallicity, FUV-NUV colors and H_alpha luminosities. The flux ratio
between the narrow and broad components tends to be highest for high
metallicity, high star formation rate (SFR) galaxies. We show that the narrow
component identified in the super profiles is associated with the presence of
star formation, and possibly with molecular hydrogen. |
MIPS 24 Micron Observations of the Hubble Deep Field South: Probing the
IR-Radio Correlation of Galaxies at z > 1: We present MIPS 24 micron observations of the Hubble Deep Field South taken
with the Spitzer Space Telescope. The resulting image is 254 arcmin^2 in size
and has a sensitivity ranging between ~12 to ~30 microJy rms, with a median
sensitivity of ~20 microJy rms. A total of 495 sources have been cataloged with
a signal-to-noise ratio greater than 5 sigma. The source catalog is presented
as well as source counts which have been corrected for completeness and flux
boosting. The IR sources are then combined with MUSYC optical/NIR and ATHDFS
radio observations to obtain redshifts and radio flux densities of the sample.
We use the IR/radio flux density ratio (q_24) to explore the IR-radio
correlation for this IR sample and find q_24 = 0.71 +- 0.31 for sources
detected in both IR and radio. The results are extended by stacking IR sources
not detected in the radio observations and we derive an average q_24 for
redshift bins between 0 < z < 2.5. We find the high redshift (z > 1) sources
have an average q_{24} ratio which is better fit by local LIRG SEDs rather than
local ULIRG SEDs, indicating that high redshift ULIRGs differ in their IR/radio
properties. So ULIRGs at high redshift have SEDs different from those found
locally. Infrared faint radio sources are examined, and while nine radio
sources do not have a MIPS detection and are therefore radio-loud AGN, only one
radio source has an extreme IRAC 3.6 micron to radio flux density ratio
indicating it is a radio-loud AGN at z > 1. | Cross-Correlation of Diffuse Synchrotron and Large-Scale Structures: We explore for the first time the method of cross-correlation of radio
synchrotron emission and tracers of large-scale structure in order to detect
the diffuse IGM/WHIM. We performed a cross-correlation of a 34 x 34 degree area
of 2MASS galaxies for two redshift slices (0.03 < z < 0.04 and 0.06 < z < 0.07)
with the corresponding region of the 1.4 GHz Bonn survey. For this analysis, we
assumed that the synchrotron surface brightness is linearly proportional to
surface density of galaxies. We also sampled the cross-correlation function
using 24 distant fields of the same size from the Bonn survey, to better assess
the noise properties. Though we obtained a null result, we found that by adding
a signal weighted by the 2MASS image with a filament (peak) surface brightness
of 1 (7) mK and 7 (49) mK would produce a 3 sigma positive correlation for the
0.03 < z < 0.04 and 0.06 < z < 0.07 redshift slices respectively. These
detection thresholds correspond to minimum energy magnetic fields as low as 0.2
microG, close to some theoretical expectations for filament field values. This
injected signal is also below the rms noise of the Bonn survey, and
demonstrates the power of this technique and its utility for upcoming sensitive
continuum surveys such as GALFACTS at Arecibo and those planned with the
Murchison Widefield Array (MWA). |
Radio emission at the centre of the galaxy cluster Abell 3560: evidence
for core sloshing?: Previous radio observations of the galaxy cluster A3560 in the Shapley
Concentration showed complex radio emission associated with the brightest
cluster member.To understand its origin we observed it with the GMRT, the VLA
and ATCA at 240 and 610 MHz, 1.28,1.4, 2.3,4.8 and 8.4 GHz, and performed a
detailed morphological and spectral study of the radio emission associated with
the BCG. We also observed the cluster with XMM-Newton and Chandra to derive the
properties of the ICM. The radio emission of the N-E nucleus of the dumb-bell
BCG shows an active radio galaxy, plus aged diffuse emission, which is not
refurbished at present. Our Chandra data show that the radio active nucleus of
the BCG has extended X-ray emission, which we classify as a low-luminosity
corona. A residual image of the XMM-Newton brightness shows the presence of a
spiral-like feature, which we interpret as the signature of gas sloshing. The
presence of a subgroup is clear in the surface brightness residual map, and in
the XMM-Newton temperature analysis. The optical 2D analysis shows substructure
in A3560. A galaxy clump was found at the location of the X-ray subgroup, and
another group is present south of the cluster core, close to the spiral-like
feature. The aged part of the radio emission closely follows the spiral pattern
of the X-ray residual brightness distribution, while the two active radio lobes
are bent in a completely different direction. We conclude that the complex
radio emission associated with the cluster BCG is the result of a minor merger
event in A3560. The aged diffuse emission is strongly affected by the sloshing
motion in the ICM. On the other hand, the bent jets and lobes of the current
radio AGN activity may reflect a complex gas velocity field in the innermost
cluster regions and/or sloshing-induced oscillations in the motion of the cD
galaxy. | Dark matter and generation of galactic magnetic fields: A new scenario for creation of galactic magnetic fields is proposed which is
operative at the cosmological epoch of the galaxy formation, and which relies
on unconventional properties of dark matter. Namely, it requires existence of
feeble but long range interaction between the dark matter particles and
electrons. In particular, millicharged dark matter particles or mirror
particles with the photon kinetic mixing to the usual photon can be considered.
We show that in rotating protogalaxies circular electric currents can be
generated by the interactions of free electrons with dark matter particles in
the halo, while the impact of such interactions on galactic protons is
considerably weaker. The induced currents may be strong enough to create the
observed magnetic fields on the galaxy scales with the help of moderate dynamo
amplification. In addition, the angular momentum transfer from the rotating gas
to dark matter component could change the dark matter profile and formation of
cusps at galactic centers would be inhibited. The global motion of the ionized
gas could produce sufficiently large magnetic fields also in filaments and
galaxy clusters. |
Comparing compact binary parameter distributions I: Methods: Being able to measure each merger's sky location, distance, component masses,
and conceivably spins, ground-based gravitational-wave detectors will provide a
extensive and detailed sample of coalescing compact binaries (CCBs) in the
local and, with third-generation detectors, distant universe. These
measurements will distinguish between competing progenitor formation models. In
this paper we develop practical tools to characterize the amount of
experimentally accessible information available, to distinguish between two a
priori progenitor models. Using a simple time-independent model, we demonstrate
the information content scales strongly with the number of observations. The
exact scaling depends on how significantly mass distributions change between
similar models. We develop phenomenological diagnostics to estimate how many
models can be distinguished, using first-generation and future instruments.
Finally, we emphasize that multi-observable distributions can be fully
exploited only with very precisely calibrated detectors, search pipelines,
parameter estimation, and Bayesian model inference. | Quasar Host Environments: The view from Planck: We measure the far-infrared emission of the general quasar (QSO) population
using Planck observations of the Baryon Oscillation Spectroscopic Survey QSO
sample. By applying multi-component matched multi-filters to the seven highest
Planck frequencies, we extract the amplitudes of dust, synchrotron and thermal
Sunyaev-Zeldovich (SZ) signals for nearly 300,000 QSOs over the redshift range
$0.1<z<5$. We bin these individually low signal-to-noise measurements to obtain
the mean emission properties of the QSO population as a function of redshift.
The emission is dominated by dust at all redshifts, with a peak at $z \sim 2$,
the same location as the peak in the general cosmic star formation rate.
Restricting analysis to radio-loud QSOs, we find synchrotron emission with a
monochromatic luminosity at $100\,\rm{GHz}$ (rest-frame) rising from
$\overline{L_{\rm synch}}=0$ to $0.2 \, {\rm L_\odot} {\rm Hz}^{-1}$ between
$z=0$ and 3. The radio-quiet subsample does not show any synchrotron emission,
but we detect thermal SZ between $z=2.5$ and 4; no significant SZ emission is
seen at lower redshifts. Depending on the supposed mass for the halos hosting
the QSOs, this may or may not leave room for heating of the halo gas by
feedback from the QSO. |
Testing and Emulating Modified Gravity on Cosmological Scales: This thesis introduces a set of methods for testing models of modified
gravity using galaxy clusters. In particular, a technique for constraining
models with a chameleon screening is introduced. In addition, the outlined
technique is expanded to test a wider class of models, such as the theory of
emergent gravity. Finally, the first part of the thesis is concluded by
adapting the mentioned tests for model independent constraints. The obtained
results indicate that galaxy clusters can be used to obtain some of the most
powerful constraints on cosmological scales.
The second part of the thesis is dedicated to the topic of cosmological
emulators. More specifically, a technique of emulating cosmological N-body
simulation output data based on machine learning is introduced. Generative
adversarial networks (GANs) are used to emulate dark matter-only as well as
hydrodynamical simulation data. In addition, N-body modified gravity
simulations are explored as well. The presented investigation of the GAN
algorithm shows that such emulators offer a powerful, fast and efficient way of
producing simulation output data with different cosmological parameters. The
power spectrum analysis indicates a 1-20% difference between the training and
the generated data depending on the dataset used and whether Gaussian smoothing
is applied or not. | A wavelet-Galerkin algorithm of the E/B decomposition of CMB
polarization maps: We develop an algorithm of separating the $E$ and $B$ modes of the CMB
polarization from the noisy and discretized maps of Stokes parameter $Q$ and
$U$ in a finite area. A key step of the algorithm is to take a wavelet-Galerkin
discretization of the differential relation between the $E$, $B$ and $Q$, $U$
fields. This discretization allows derivative operator to be represented by a
matrix, which is exactly diagonal in scale space, and narrowly banded in
spatial space. We show that the effect of boundary can be eliminated by
dropping a few DWT modes located on or nearby the boundary. This method reveals
that the derivative operators will cause large errors in the $E$ and $B$ power
spectra on small scales if the $Q$ and $U$ maps contain Gaussian noise. It also
reveals that if the $Q$ and $U$ maps are random, these fields lead to the
mixing of the $E$ and $B$ modes. Consequently, the $B$ mode will be
contaminated if the powers of $E$ modes are much larger than that of $B$ modes.
Nevertheless, numerical tests show that the power spectra of both $E$ and $B$
on scales larger than the finest scale by a factor of 4 and higher can
reasonably be recovered, even when the power ratio of $E$- to $B$-modes is as
large as about 10$^2$, and the signal-to-noise ratio is equal to 10 and higher.
This is because the Galerkin discretization is free of false correlations, and
keeps the contamination under control. As wavelet variables contain information
of both spatial and scale spaces, the developed method is also effective to
recover the spatial structures of the $E$ and $B$ mode fields. |
Goldstone Bosons as Fractional Cosmic Neutrinos: It is suggested that Goldstone bosons may be masquerading as fractional
cosmic neutrinos, contributing about 0.39 to what is reported as the effective
number of neutrino types in the era before recombination. The broken symmetry
associated with these Goldstone bosons is further speculated to be the
conservation of the particles of dark matter. | Large-scale structure in mimetic Horndeski gravity: In this paper, we propose to use the mimetic Horndeski model as a model for
the dark universe. Both cold dark matter (CDM) and dark energy (DE) phenomena
are described by a single component, the mimetic field. In linear theory, we
show that this component effectively behaves like a perfect fluid with zero
sound speed and clusters on all scales. For the simpler mimetic cubic Horndeski
model, if the background expansion history is chosen to be identical to a
perfect fluid DE (PFDE) then the mimetic model predicts the same power spectrum
of the Newtonian potential as the PFDE model with zero sound speed. In
particular, if the background is chosen to be the same as that of LCDM, then
also in this case the power spectrum of the Newtonian potential in the mimetic
model becomes indistinguishable from the power spectrum in LCDM on linear
scales. A different conclusion may be found in the case of non-adiabatic
perturbations. We also discuss the distinguishability, using power spectrum
measurements from LCDM N-body simulations as a proxy for future observations,
between these mimetic models and other popular models of DE. For instance, we
find that if the background has an equation of state equal to -0.95 then we
will be able to distinguish the mimetic model from the PFDE model with unity
sound speed. On the other hand, it will be hard to do this distinction with
respect to the LCDM model. |
Cross-correlation between $Planck$ CMB lensing potential and galaxy
catalogues from HELP: We present the study of cross-correlation between Cosmic Microwave Background
(CMB) gravitational lensing potential map released by the \textit{Planck}
collaboration and photometric redshift galaxy catalogues from the
\textit{Herschel} Extragalactic Legacy Project (HELP), divided into four sky
patches: NGP, \textit{Herschel} Stripe-82, and two halves of SGP field,
covering in total $\sim 660$ deg$^{2}$ of the sky. We estimate the galaxy
linear bias parameter, $b_{0}$, from joint analysis of cross-power spectrum and
galaxy auto-power spectrum using Maximum Likelihood Estimation technique to
obtain values ranging from $0.70 \pm 0.01$ for SGP Part-2 to $1.02 \pm 0.02$
for SGP Part-1 field. We also estimate the amplitude of cross-correlation and
find the values spanning from $0.67 \pm 0.18$ for SGP Part-2 to $0.80 \pm 0.23$
for SGP Part-1 field, respectively. For NGP and SGP Part-1 fields the amplitude
is consistent with the expected value for the standard cosmological model
within $\sim 1\,\sigma$, while for \textit{Herschel} Stripe-82 and SGP Part-2
we find the amplitude to be smaller than expected with $\sim 1.5\,\sigma$ and
$\sim 2\,\sigma$ deviation, respectively. We perform several tests on various
systematic errors to study the reason for the deviation, however, value of the
amplitude turns out to be robust with respect to these errors. The only
significant change in the amplitude is observed when we replace the
minimum-variance CMB lensing map, used in the baseline analysis, by the lensing
map derived from the CMB temperature map with deprojected thermal
Sunyaev-Zeldovich signal. | Exploring the spectral properties of radio relics I: Integrated spectral
index and Mach number: Radio relics are the manifestation of electrons presumably being shock
(re-)accelerated to high energies in the outskirts of galaxy clusters. However,
estimates of the shocks' strength yield different results when measured with
radio or X-ray observations. In general, Mach numbers obtained from radio
observations are larger than the corresponding X-ray measurements. In this
work, we investigate this Mach number discrepancy. For this purpose, we used
the cosmological code ENZO to simulate a sample of galaxy clusters that host
bright radio relics. For each relic, we computed the radio Mach number from the
integrated radio spectrum and the X-ray Mach number from the X-ray surface
brightness and temperature jumps. Our analysis suggests that the differences in
the Mach number estimates follow from the way in which different observables
are related to different parts of the underlying Mach number distribution:
radio observations are more sensistive to the high Mach numbers present only in
a small fraction of a shock's surface, while X-ray measurements reflect the
average of the Mach number distribution. Moreover, X-ray measurements are very
sensitive to the relic's orientation. If the same relic is observed from
different sides, the measured X-ray Mach number varies significantly. On the
other hand, the radio measurements are more robust, as they are unaffected by
the relic's orientation. |
Dark Radiation and interacting scenarios: An extra dark radiation component can be present in the universe in the form
of sterile neutrinos, axions or other very light degrees of freedom which may
interact with the dark matter sector. We derive here the cosmological
constraints on the dark radiation abundance, on its effective velocity and on
its viscosity parameter from current data in dark radiation-dark matter coupled
models. The cosmological bounds on the number of extra dark radiation species
do not change significantly when considering interacting schemes. We also find
that the constraints on the dark radiation effective velocity are degraded by
an order of magnitude while the errors on the viscosity parameter are a factor
of two larger when considering interacting scenarios. If future Cosmic
Microwave Background data are analysed assuming a non interacting model but the
dark radiation and the dark matter sectors interact in nature, the
reconstructed values for the effective velocity and for the viscosity parameter
will be shifted from their standard 1/3 expectation, namely ceff=0.34 (+0.006
-0.003) and cvis=0.29 (+0.002 -0.001) at 95% CL for the future COrE mission
data. | Feedback in Galaxy Formation: I review the outstanding problems in galaxy formation theory, and the role of
feedback in resolving them. I address the efficiency of star formation, the
galactic star formation rate, and the roles of supernovae and supermassive
black holes. |
On the Variations of Fundamental Constants and AGN feedback in the QSO
host galaxy RXJ0911.4+0551 at z=2.79: We report on sensitive observations of the CO(7-6) and CI(2-1) transitions in
the z=2.79 QSO host galaxy RXJ0911.4+0551 using the IRAM Plateau de Bure
interferometer (PdBI). Our extremely high signal to noise spectra combined with
the narrow CO line width of this source (FWHM = 120 km/s) allows us to estimate
sensitive limits on the space-time variations of the fundamental constants
using two emission lines. Our observations show that the CI and CO line shapes
are in good agreement with each other but that the CI line profile is of order
10% narrower, presumably due to the lower opacity in the latter line. Both
lines show faint wings with velocities up to +/-250 km/s, indicative of a
molecular outflow. As such the data provide direct evidence for negative
feedback in the molecular gas phase at high redshift. Our observations allow us
to determine the observed frequencies of both transitions with so far unmatched
accuracy at high redshift. The redshift difference between the CO and CI lines
is sensitive to variations of dF/F with F=alpha^2/mu where alpha is the fine
structure constant and mu the proton-to-electron mass ratio. We find dF/F=6.9
+/-3.7 x 10^-6 at a lookback time of 11.3 Gyr, which within the uncertainties,
is consistent with no variations of the fundamental constants. | Addressing $H_0$ tension by means of VCDM: In this letter we propose a reduction of the $H_0$ tension puzzle by means of
a theory of minimally modified gravity which is dubbed VCDM. After confronting
the theory with the experiments, we find that the data allow for a low-redshift
transition in the expansion history of the universe at either $z\simeq 0.3 $ or
$z \simeq 1.8\,$, corresponding to one of the two local minima of the total
$\chi^2$. From the bestfit values the total fitness parameter is improved by
$\Delta \chi^2 \simeq 12$, for the data set considered. We then infer the local
Hubble expansion rate today within this theory by means of low redshift
Pantheon data. The resulting local Hubble expansion rate today is
$H^{\rm{loc}}_0=73.6\pm1.4$. We find the tension is reduced within the VCDM
theory. |
The Hubble Space Telescope GOODS NICMOS Survey: Overview and the
Evolution of Massive Galaxies at 1.5 < z < 3: We present the details and early results from a deep near-infrared survey
utilising the NICMOS instrument on the Hubble Space Telescope centred around
massive M_* > 10^11 M_0 galaxies at 1.7 < z < 2.9 found within the Great
Observatories Origins Deep Survey (GOODS) fields. The GOODS NICMOS Survey (GNS)
was designed to obtain deep F160W (H-band) imaging of 80 of these massive
galaxies, as well as other colour selected objects such as Lyman-break
drop-outs, BzK objects, Distant Red Galaxies, EROs, Spitzer Selected EROs,
BX/BM galaxies, as well as sub-mm galaxies. We present in this paper details of
the observations, our sample selection, as well as a description of features of
the massive galaxies found within our survey fields. This includes: photometric
redshifts, rest-frame colours, and stellar masses. We furthermore provide an
analysis of the selection methods for finding massive galaxies at high
redshifts, including colour selection, and how galaxy populations selected
through different methods overlap. We find that a single colour selection
method cannot locate all of the massive galaxies, with no one method finding
more than 70 percent. We however find that the combination of these colour
methods finds nearly all the massive galaxies, as selected by photometric
redshifts with the exception of apparently rare blue massive galaxies. By
investigating the rest-frame (U-B) vs. M_B diagram for these galaxies we
furthermore show that there exists a bimodality in colour-magnitude space at z
< 2, driven by stellar mass, such that the most massive galaxies are
systematically red up to z~2.5, while lower mass galaxies tend to be blue. We
also discuss the number densities for galaxies with stellar masses M_* > 10^11
M_0, whereby we find an increase of a factor of eight between z = 3 and z =
1.5, demonstrating that this is an epoch when massive galaxies establish most
of their mass. | Dust in External Galaxies: Existing (Spitzer Space Telescope) and upcoming (Herschel Space Telescope)
facilities are deepening our understanding of the role of dust in tracing the
energy budget and chemical evolution of galaxies. The tools we are developing
while exploring the local Universe will in turn become pivotal in the
interpretation of the high redshift Universe when near--future facilities (the
Atacama Large Millimeter Array [ALMA], the Sub--Millimeter Array [SMA], the
Large Millimeter Telescope [LMT], the James Webb Space Telescope [JWST]), and,
possibly, farther--future ones, will begin operations. |
Constraints on the epoch of dark matter formation from Milky Way
satellites: A small fraction of thermalized dark radiation that transitions into cold
dark matter (CDM) between big bang nucleosynthesis and matter-radiation
equality can account for the entire dark matter relic density. Because of its
transition from dark radiation, "late-forming dark matter" (LFDM) suppresses
the growth of linear matter perturbations and imprints the oscillatory
signatures of dark radiation perturbations on small scales. The cutoff scale in
the linear matter power spectrum is set by the redshift $z_T$ of the phase
transition; tracers of small-scale structure can therefore be used to infer the
LFDM formation epoch. Here, we use a forward model of the Milky Way (MW)
satellite galaxy population to address the question: How late can dark matter
form? For dark radiation with strong self-interactions, which arises in
theories of neutrinolike LFDM, we report $z_{T}>5.5\times 10^6$ at $95\%$
confidence based on the abundance of known MW satellite galaxies. This limit
rigorously accounts for observational incompleteness corrections, marginalizes
over uncertainties in the connection between dwarf galaxies and dark matter
halos, and improves upon galaxy clustering and Lyman-$\alpha$ forest
constraints by nearly an order of magnitude. We show that this limit can also
be interpreted as a lower bound on $z_T$ for LFDM that free-streams prior to
its phase transition, although dedicated simulations will be needed to analyze
this case in detail. Thus, dark matter created by a transition from dark
radiation must form no later than one week after the big bang. | Weighing Galaxy Clusters with Gas. II. On the Origin of Hydrostatic Mass
Bias in LambdaCDM Galaxy Clusters: The use of galaxy clusters as cosmological probes hinges on our ability to
measure their masses accurately and with high precision. Hydrostatic mass is
one of the most common methods for estimating the masses of individual galaxy
clusters, which suffer from biases due to departures from hydrostatic
equilibrium. Using a large, mass-limited sample of massive galaxy clusters from
a high-resolution hydrodynamical cosmological simulation, in this work we show
that in addition to turbulent and bulk gas velocities, acceleration of gas
introduces biases in the hydrostatic mass estimate of galaxy clusters. In
unrelaxed clusters, the acceleration bias is comparable to the bias due to
non-thermal pressure associated with merger-induced turbulent and bulk gas
motions. In relaxed clusters, the mean mass bias due to acceleration is small
(<3%), but the scatter in the mass bias can be reduced by accounting for gas
acceleration. Additionally, this acceleration bias is greater in the outskirts
of higher redshift clusters where mergers are more frequent and clusters are
accreting more rapidly. Since gas acceleration cannot be observed directly, it
introduces an irreducible bias for hydrostatic mass estimates. This
acceleration bias places limits on how well we can recover cluster masses from
future X-ray and microwave observations. We discuss implications for cluster
mass estimates based on X-ray, Sunyaev-Zeldovich effect, and gravitational
lensing observations and their impact on cluster cosmology. |
The Low Mass End of the Fundamental Relation for Gravitationally Lensed
Star Forming Galaxies at 1<z<6: We present VLT/X-shooter spectra of 13 galaxies in the redshift range 1< z <
6, which are strongly lensed by massive galaxy clusters. Spectroscopic
redshifts are measured for nine galaxies, while three sources have redshifts
determined from continuum breaks in their spectra. The stellar masses of the
galaxies span four orders of magnitude between 10^7 and 10^11 M_sun and have
luminosities at 1500 A rest-frame between 0.004 and 9 L^* after correcting for
the magnification. This allows us to probe a variety of galaxy types from
young, low-mass starburst galaxies to massive evolved galaxies. The lensed
galaxies with stellar masses less than 10^10 M_sun have a large scatter
compared to the fundamental relation between stellar mass, star formation rates
and oxygen abundances. We provide a modified fit to the fundamental relation
for low-mass, low-metallicity galaxies with a weaker dependence of the
metallicity on either the star formation rate or stellar mass compared to
low-redshift, high-mass and high-metallicity SDSS galaxies. | AGN Activity and Black Hole Masses in Low Surface Brightness Galaxies: We present medium resolution optical spectroscopy of a sample of nine Low
Surface Brightness (LSB) galaxies. For those that show clear signatures of AGN
emission, we have disentangled the AGN component from stellar light and any Fe
I and Fe II contribution. We have decomposed the H_alpha line into narrow and
broad components and determined the velocities of the broad components; typical
values lie between 900--2500 km/s. Of the galaxies in our study, UGC 6614, UGC
1922, UGC 6968 and LSBC F568-6 (Malin~2) show clear signatures of AGN activity.
We have calculated the approximate black hole masses for these galaxies from
the H_alpha line emission using the virial approximation. The black hole masses
are ~3x10^{5} M_sun for three galaxies and lie in the intermediate mass black
holes domain rather than the supermassive range. UGC 6614 harbors a BH of mass
3.8x10^{6} M_sun; it also shows an interesting feature blueward of H_alpha and
H_beta implying outflow of gas or a one-sided jet streaming towards us. We have
also measured the bulge stellar velocity dispersions using the Ca II Triplet
lines and plotted these galaxies on the M-sigma plot. We find that all the
three galaxies UGC 6614, UGC 6968 and F568-6 lie below the M-sigma relation for
nearby galaxies. Thus we find that although the bulges of LSB galaxies may be
well evolved, their nuclear black hole masses are lower than those found in
bright galaxies and lie offset from the M-sigma correlation. |
Limits on statistical anisotropy from BOSS DR12 galaxies using bipolar
spherical harmonics: We measure statistically anisotropic signatures imprinted in
three-dimensional galaxy clustering using bipolar spherical harmonics (BipoSHs)
in both Fourier space and configuration space. We then constrain a well-known
quadrupolar anisotropy parameter $g_{2M}$ in the primordial power spectrum,
parametrized by $P(\vec{k}) = \bar{P}(k) [ 1 + \sum_{M} g_{2M} Y_{2M}(\hat{k})
]$, with $M$ determining the direction of the anisotropy. Such an anisotropic
signal is easily contaminated by artificial asymmetries due to specific survey
geometry. We precisely estimate the contaminated signal and finally subtract it
from the data. Using the galaxy samples obtained by the Baryon Oscillation
Spectroscopic Survey Data Release 12, we find no evidence for violation of
statistical isotropy, $g_{2M}$ for all $M$ to be of zero within the $2\sigma$
level. The $g_{2M}$-type anisotropy can originate from the primordial curvature
power spectrum involving a directional-dependent modulation $g_* (\hat{k} \cdot
\hat{p})^2$. The bound on $g_{2M}$ is translated into $g_*$ as $-0.09 < g_* <
0.08$ with a $95\%$ confidence level when $\hat{p}$ is marginalized over. | A new analysis of galaxy 2-point functions in the BOSS survey, including
full-shape information and post-reconstruction BAO: We present a new method for consistent, joint analysis of the pre- and
post-reconstruction two-point functions of the BOSS survey. The
post-reconstruction correlation function is used to accurately measure the
distance-redshift relation and expansion history, while the pre-reconstruction
power spectrum multipoles constrain the broad-band shape and the rate-of-growth
of large-scale structure. Our technique uses Lagrangian perturbation theory to
self-consistently work at the level of two-point functions, i.e.\ directly with
the measured data, without approximating the constraints with summary
statistics normalized by the drag scale. Combining galaxies across the full
redshift range and both hemispheres we constrain $\Omega_m=0.303 \pm 0.0082$,
$H_0=69.23 \pm 0.77$ and $\sigma_8=0.733 \pm 0.047$ within the context of
$\Lambda$CDM. These constraints are in good agreement both with the Planck
primary CMB anisotropy data and recent cosmic shear surveys. |
A blind method to recover the mask of a deep galaxy survey: We present a blind method to determine the properties of a foreground
contamination, given by a visibility mask, that affects a deep galaxy survey.
Angular cross correlations of density fields in different redshift bins are
expected to vanish (apart from a contribution due to lensing), but are
sensitive to the presence of a foreground that modulates the flux limit across
the sky. After formalizing the expected effect of a foreground mask on the
measured galaxy density, under a linear, luminosity-dependent bias model for
galaxies, we construct two estimators that single out the mask contribution if
a sufficient number of independent redshift bins is available. These estimators
are combined to give a reconstruction of the mask. We use Milky-Way reddening
as a prototype for the mask. Using a set of 20 large mock catalogs covering
$1/4$-th of the sky and number-matched to $H\alpha$ emitters to mimic an
Euclid-like sample, we demonstrate that our method can reconstruct the mask and
its angular clustering at scales $\ell<100$, beyond which the cosmological
signal becomes dominant. The uncertainty of this reconstruction is quantified
to be $1/3$-rd of the sample variance of the signal. Such a reconstruction
requires knowledge of the average and square average of the mask, but we show
that it is possible to recover this information either from external models or
internally from the data. It also relies on knowledge of how the impact of the
foreground changes with redshift (due to the extinction curve in our case), but
this can be tightly constrained by cross correlations of different redshift
bins. The strong points of this blind reconstruction technique lies in the
ability to find "unknown unknowns" that affect a survey, and in the facility to
quantify, using sets of mock catalogs, how its uncertainty propagates to
clustering measurements. [Abridged] | The bulge-halo conspiracy in massive elliptical galaxies: implications
for the stellar initial mass function and halo response to baryonic processes: Recent studies have shown that massive elliptical galaxies have total mass
density profiles within an effective radius that can be approximated as
\rho_{tot}\propto r^{-\gamma'}, with mean slope <\gamma'>=2.08 \pm 0.03 and
scatter \sigma_\gamma'=0.16 \pm 0.02. The small scatter of the slope (known as
the bulge-halo conspiracy) is not generic in LCDM based models and therefore
contains information about the galaxy formation process. We compute the
distribution of \gamma' for LCDM-based models that reproduce the observed
correlations between stellar mass, velocity dispersion, and effective radius of
early-type galaxies in the SDSS. The models have a range of stellar initial
mass functions (IMFs) and dark halo responses to galaxy formation. The observed
distribution of \gamma' is well reproduced by a model with cosmologically
motivated but uncontracted dark matter haloes, and a Salpeter-type IMF. Other
models are on average ruled out by the data, even though they may happen in
individual cases. Models with adiabatic halo contraction (and lighter IMFs)
predict too small values of \gamma'. Models with halo expansion, or
mass-follows-light predict too high values of \gamma'. Our study shows that the
non-homologous structure of massive early-type galaxies can be precisely
reproduced by LCDM models if the IMF is not universal and if mechanisms such as
feedback from active galactic nuclei, or dynamical friction, effectively on
average counterbalance the contraction of the halo expected as a result of
baryonic cooling. |
Primordial non-Gaussianity with $μ$-type and $y$-type spectral
distortions: exploiting Cosmic Microwave Background polarization and dealing
with secondary sources: Cross-correlations between Cosmic Microwave Background (CMB) temperature and
$y$-spectral distortions anisotropies have been previously proposed as a way to
measure the local bispectrum parameter $f_{\rm NL}^{\rm loc.}$ in a range of
scales inaccessible to either CMB ($T$, $E$) bispectra or $T$-$\mu$
correlations. This is useful e.g. to test scale dependence of primordial
non-Gaussianity. Unfortunately, the primordial $y$-T signal is strongly
contaminated by the late-time correlation between the Integrated Sachs Wolfe
and Sunyaev-Zel'dovich (SZ) effects. Moreover, SZ itself generates a large
noise contribution in the $y$-parameter map. We consider two original ways to
address these issues. In order to remove the bias due to the SZ-CMB temperature
coupling, while also adding new signal, we include in the analysis the
cross-correlation between $y$-distortions and CMB {\em polarization}. In order
to reduce the noise, we propose to clean the $y$-map by subtracting a SZ
template, reconstructed via cross-correlation with external tracers (CMB and
galaxy-lensing signals). We combine this SZ template subtraction with the
previously adopted solution of directly masking detected clusters. Our final
forecasts show that, using $y$-distortions, a PRISM-like survey can achieve
$1\sigma(f_{\rm NL}^\text{loc.}) = 300$, while an ideal experiment will achieve
$1\sigma(f_{\rm NL}^\text{loc.}) = 130$, with improvements of a factor $\sim 3$
from adding the $y$-$E$ signal, and a further $20-30 \%$ from template
cleaning. These forecasts are much worse than current $f_{\rm NL}^\text{loc.}$
boundaries from {\em Planck}, but we stress again that they refer to completely
different scales. | Eliminating the LIGO bounds on primordial black hole dark matter: Primordial black holes (PBHs) in the mass range $(30$--$100)~M_{\odot}$ are
interesting candidates for dark matter, as they sit in a narrow window between
microlensing and cosmic microwave background constraints. There are however
tight constraints from the binary merger rate observed by the LIGO and Virgo
experiments. In deriving these constraints, PBHs were treated as point
Schwarzschild masses, while the more careful analysis in an expanding universe
we present here, leads to a time-dependent mass. This implies a stricter set of
conditions for a black hole binary to form and means that black holes coalesce
much more quickly than was previously calculated, namely well before the
LIGO/Virgo's observed mergers. The observed binaries are those coalescing
within galactic halos, with a merger rate consistent with data. This reopens
the possibility for dark matter in the form of LIGO-mass PBHs. |
Deep near-infrared imaging of the HE0450-2958 system: The QSO HE0450-2958 and the companion galaxy with which it is interacting,
both ultra luminous in the infrared, have been the subject of much attention in
recent years, as the quasar host galaxy remained undetected. This led to
various interpretations on QSO and galaxy formation and co-evolution, such as
black hole ejection, jet induced star formation, dust obscured galaxy, or
normal host below the detection limit. We carried out deep observations in the
near-IR in order to solve the puzzle concerning the existence of any host. The
object was observed with the ESO VLT and HAWK-I in the near-IR J-band for 8
hours. The images have been processed with the MCS deconvolution method
(Magain, Courbin & Sohy, 1998), permitting accurate subtraction of the QSO
light from the observations. The compact emission region situated close to the
QSO, called the blob, which previously showed only gas emission lines in the
optical spectra, is now detected in our near-IR images. Its high brightness
implies that stars likely contribute to the near-IR emission. The blob might
thus be interpreted as an off-centre, bright and very compact host galaxy,
involved in a violent collision with its companion. | Reactor sterile neutrinos, dark energy and the age of the universe: There are indications that the neutrino oscillation data from reactor
experiments and the LSND and MiniBooNE experiments show a preference for two
sterile neutrino species, both with masses in the eV region. We show that this
result has a significant impact on some important cosmological parameters.
Specifically, we use a combination of CMB, LSS and SN1A data and show that the
existence of two light, sterile neutrinos would rule out the cosmological
constant as dark energy at 95% confidence level, and lower the expansion age of
the universe to 12.58 \pm 0.26 Gyr. |
MOND theory: A general account of MOND theory is given. I start with the basic tenets of
MOND, which posit departure from standard dynamics in the limit of low
acceleration -- below an acceleration constant a0 -- where dynamics become
scale invariant. I list some of the salient predictions of these tenets. The
special role of a0 and its significance are then discussed. In particular, I
stress its coincidence with cosmologically relevant accelerations. The
deep-MOND limit and the consequences of its scale invariance are considered in
some detail.
General aspects of MOND theories are then described, after which I list
briefly presently known theories, both nonrelativistic and relativistic. Most
full-fledged theories modify the gravitational action, hinge on a0, introduce
an interpolating function between the low and high accelerations, and obey MOND
requirements in the opposite limits. These theories have much heuristic value
as proofs of various concepts (e.g., that covariant MOND theories can be
written with correct gravitational lensing). But, probably, they are, at best,
effective theories of limited applicability.
I then outline several other promising approaches to constructing MOND
theories that strive to obtain MOND as an effective theory from deeper
concepts, for example, by modifying inertia and/or gravity as a result of
interactions with some omnipresent agent.
Some theories do enjoy a natural appearance of a cosmological-constant-like
contribution that, furthermore, exhibits the observed connection with a0.
However, none were shown to address fully the mass discrepancies in cosmology
and structure formation that are otherwise explained by cosmological dark
matter.
We have no clues as to whether and how MOND aspects enter non-gravitational
phenomena, but I discuss briefly some possibilities. | Evidence For A Mild Steepening And Bottom-Heavy IMF In Massive Galaxies
From Sodium And Titanium-Oxide Indicators: We measure equivalent widths (EW) - focussing on two unique features (NaI and
TiO2) of low-mass stars (<0.3M\odot) - for luminous red galaxy spectra from the
the Sloan Digital Sky Survey (SDSS) and X-Shooter Lens Survey (XLENS) in order
to study the low-mass end of the initial mass function (IMF). We compare these
EWs to those derived from simple stellar population models computed with
different IMFs, ages, [{\alpha}/Fe], and elemental abundances. We find that
models are able to simultaneously reproduce the observed NaD {\lambda}5895 and
Na I {\lambda}8190 features for lower-mass (\sim {\sigma}\ast) early-type
galaxies (ETGs) but deviate increasingly for more massive ETGs, due do strongly
mismatching NaD EWs. The TiO2 {\lambda}6230 and the Na I {\lambda}8190 features
together appear to be a powerful IMF diagnostic, with age and metallicity
effects orthogonal to the effect of IMF. We find that both features correlate
strongly with galaxy velocity dispersion. The XLENS ETG (SDSSJ0912+0029) and an
SDSS ETG (SDSSJ0041-0914) appear to require both an extreme dwarf-rich IMF and
a high sodium enhancement ([Na/Fe] = +0.4). In addition, lensing constraints on
the total mass of the XLENS system within its Einstein radius limit a
bottom-heavy IMF with a power-law slope to x \leq 3.0 at the 90% C.L. We
conclude that NaI and TiO features, in comparison with state-of-the-art SSP
models, suggest a mildly steepening IMF from Salpeter (dn/dm \propto m-x with x
= 2.35) to x \approx 3.0 for ETGs in the range {\sigma} = 200 - 335 km s-1. |
Differential Morphology Between Rest-frame Optical and UV Emission from
1.5 < z < 3 Star-forming Galaxies: We present the results of a comparative study of the rest-frame optical and
rest-frame ultraviolet morphological properties of 117 star-forming galaxies
(SFGs), including BX, BzK, and Lyman break galaxies with B<24.5, and 15 passive
galaxies in the region covered by the Wide Field Camera 3 Early Release Science
program. Using the internal color dispersion (ICD) diagnostic, we find that the
morphological differences between the rest-frame optical and rest-frame UV
light distributions in 1.4<z<2.9 SFGs are typically small (ICD~0.02). However,
the majority are non-zero (56% at >3 sigma) and larger than we find in passive
galaxies at 1.4<z<2, for which the weighted mean ICD is 0.013. The lack of
morphological variation between individual rest-frame ultraviolet bandpasses in
z~3.2 galaxies argues against large ICDs being caused by non-uniform dust
distributions. Furthermore, the absence of a correlation between ICD and galaxy
UV-optical color suggests that the non-zero ICDs in SFGs are produced by
spatially distinct stellar populations with different ages. The SFGs with the
largest ICDs (>~0.05) generally have complex morphologies that are both
extended and asymmetric, suggesting that they are mergers-in-progress or very
large galaxies in the act of formation. We also find a correlation between
half-light radius and internal color dispersion, a fact that is not reflected
by the difference in half-light radii between bandpasses. In general, we find
that it is better to use diagnostics like the ICD to measure the morphological
properties of the difference image than it is to measure the difference in
morphological properties between bandpasses. | Looking for Axion Dark Matter in Dwarf Spheroidals: We study the extent to which the decay of cold dark matter axions can be
probed with forthcoming radio telescopes such as the Square Kilometer Array
(SKA). In particular we focus on signals arising from dwarf spheroidal
galaxies, where astrophysical uncertainties are reduced and the expected
magnetic field strengths are such that signals arising from axion decay may
dominate over axion-photon conversion in a magnetic field. We show that with
$\sim100$ hours of observing time, SKA could improve current sensitivity by a
factor of about five. |
New constraints on time-dependent variations of fundamental constants
using Planck data: Observations of the CMB today allow us to answer detailed questions about the
properties of our Universe, targeting both standard and non-standard physics.
In this paper, we study the effects of varying fundamental constants (i.e., the
fine-structure constant, $\alpha_{\rm EM}$, and electron rest mass, $m_{\rm
e}$) around last scattering using the recombination codes CosmoRec and
Recfast++. We approach the problem in a pedagogical manner, illustrating the
importance of various effects on the free electron fraction, Thomson visibility
function and CMB power spectra, highlighting various degeneracies. We
demonstrate that the simpler Recfast++ treatment (based on a three-level atom
approach) can be used to accurately represent the full computation of CosmoRec.
We also include explicit time-dependent variations using a phenomenological
power-law description. We reproduce previous Planck 2013 results in our
analysis. Assuming constant variations relative to the standard values, we find
the improved constraints $\alpha_{\rm EM}/\alpha_{\rm EM,0}=0.9993\pm 0.0025$
(CMB only) and $m_{\rm e}/m_{\rm e,0}= 1.0039 \pm 0.0074$ (including BAO) using
Planck 2015 data. For a redshift-dependent variation, $\alpha_{\rm
EM}(z)=\alpha_{\rm EM}(z_0)\,[(1+z)/1100]^p$ with $\alpha_{\rm
EM}(z_0)\equiv\alpha_{\rm EM,0}$ at $z_0=1100$, we obtain $p=0.0008\pm 0.0025$.
Allowing simultaneous variations of $\alpha_{\rm EM}(z_0)$ and $p$ yields
$\alpha_{\rm EM}(z_0)/\alpha_{\rm EM,0} = 0.9998\pm 0.0036$ and $p = 0.0006\pm
0.0036$. We also discuss combined limits on $\alpha_{\rm EM}$ and $m_{\rm e}$.
Our analysis shows that existing data is not only sensitive to the value of the
fundamental constants around recombination but also its first time derivative.
This suggests that a wider class of varying fundamental constant models can be
probed using the CMB. | The growth index of matter perturbations and modified gravity: We place tight constraints on the growth index $\gamma$ by using the recent
growth history results of 2dFGRS, SDSS-LRG, VIMOS-VLT deep Survey (VVDS) and
{\em WiggleZ} datasets. In particular, we investigate several parametrizations
of the growth index $\gamma(z)$, by comparing their cosmological evolution
using observational growth rate data at different redshifts. Utilizing a
standard likelihood analysis we find that the use of the combined growth data
provided by the 2dFGRS, SDSS-LRG, VVDS and {\em WiggleZ} galaxy surveys, puts
the most stringent constraints on the value of the growth index. As an example,
assuming a constant growth index we obtain that $\gamma=0.602\pm 0.055$ for the
concordance $\Lambda$CDM expansion model. Concerning the
Dvali-Gabadadze-Porrati gravity model, we find $\gamma=0.503\pm 0.06$ which is
lower, and almost $3\sigma$ away, from the theoretically predicted value of
$\gamma_{DGP}\simeq 11/16$. Finally, based on a time varying growth index we
also confirm that the combined growth data disfavor the DGP gravity. |
Primordial black holes from cusp collapse on cosmic strings: Primordial black holes (PBHs) are of fundamental interest in cosmology and
astrophysics, and have received much attention as a dark matter candidate and
as a potential source of gravitational waves. One possible PBH formation
mechanism is the gravitational collapse of cosmic strings. Thus far, the
entirety of the literature on PBH production from cosmic strings has focused on
the collapse of (quasi)circular cosmic string loops, which make up only a tiny
fraction of the cosmic loop population. We demonstrate here a novel PBH
formation mechanism: the collapse of a small segment of cosmic string in the
neighbourhood of a cusp. Using the hoop conjecture, we show that collapse is
inevitable whenever a cusp appears on a macroscopically-large loop, forming a
PBH whose rest mass is smaller than the mass of the loop by a factor of the
dimensionless string tension squared, $(G\mu)^2$. Since cusps are generic
features of cosmic string loops, and do not rely on finely-tuned loop
configurations like circular collapse, this implies that cosmic strings produce
PBHs in far greater numbers than has previously been recognised. The resulting
PBHs are highly spinning and boosted to ultrarelativistic velocities; they
populate a unique region of the BH mass-spin parameter space, and are therefore
a "smoking gun" observational signature of cosmic strings. We derive new
constraints on $G\mu$ from the evaporation of cusp-collapse PBHs, and update
existing constraints on $G\mu$ from gravitational-wave searches. | A Molecular Star Formation Law in the Atomic Gas Dominated Regime in
Nearby Galaxies: We use the IRAM HERACLES survey to study CO emission from 33 nearby spiral
galaxies down to very low intensities. Using atomic hydrogen (HI) data, mostly
from THINGS, we predict the local mean CO velocity from the mean HI velocity.
By renormalizing the CO velocity axis so that zero corresponds to the local
mean HI velocity we are able to stack spectra coherently over large regions as
function of radius. This enables us to measure CO intensities with high
significance as low as Ico = 0.3 K km/s (H2_SD = 1 Msun/pc2), an improvement of
about one order of magnitude over previous studies. We detect CO out to radii
Rgal = R25 and find the CO radial profile to follow a uniform exponential
decline with scale length of 0.2 R25. Comparing our sensitive CO profiles to
matched profiles of HI, Halpha, FUV, and IR emission at 24um and 70um, we
observe a tight, roughly linear relation between CO and IR intensity that does
not show any notable break between regions that are dominated by molecular (H2)
gas (H2_SD > HI_SD) and those dominated by atomic gas (H2_SD < HI_SD). We use
combinations of FUV+24um and Halpha+24um to estimate the recent star formation
rate (SFR) surface density, SFR_SD, and find approximately linear relations
between SFR_SD and H2_SD. We interpret this as evidence for stars forming in
molecular gas with little dependence on the local total gas surface density.
While galaxies display small internal variations in the SFR-to-H2 ratio, we do
observe systematic galaxy-to-galaxy variations. These galaxy-to-galaxy
variations dominate the scatter in relations between CO and SFR tracers
measured at large scales. The variations have the sense that less massive
galaxies exhibit larger ratios of SFR-to-CO than massive galaxies. Unlike the
SFR-to-CO ratio, the balance between HI and H2 depends strongly on the total
gas surface density and radius. It must also depend on additional parameters. |
Improved Galactic Foreground Removal for B-Modes Detection with
Clustering Methods: Characterizing the sub-mm Galactic emission has become increasingly critical
especially in identifying and removing its polarized contribution from the one
emitted by the Cosmic Microwave Background (CMB). In this work, we present a
parametric foreground removal performed onto sub-patches identified in the
celestial sphere by means of spectral clustering. Our approach takes into
account efficiently both the geometrical affinity and the similarity induced by
the measurements and the accompanying errors. The optimal partition is then
used to parametrically separate the Galactic emission encoding thermal dust and
synchrotron from the CMB one applied on two nominal observations of forthcoming
experiments from the ground and from the space. Performing the parametric fit
singularly on each of the clustering derived regions results in an overall
improvement: both controlling the bias and the uncertainties in the CMB
$B-$mode recovered maps. We finally apply this technique using the map of the
number of clouds along the line of sight, $\mathcal{N}_c$, as estimated from HI
emission data and perform parametric fitting onto patches derived by clustering
on this map. We show that adopting the $\mathcal{N}_c$ map as a tracer for the
patches related to the thermal dust emission, results in reducing the $B-$mode
residuals post-component separation. The code is made publicly available. | Polarized galactic synchrotron and dust emission and their correlation: We present an analysis of the level of polarized dust and synchrotron
emission using the WMAP9 and Planck data. The primary goal of this study is to
inform the assessment of foreground contamination in the cosmic microwave
background (CMB) measurements below $\ell\sim200$ from 23 to 353 GHz. We
compute angular power spectra as a function of sky cut based on the Planck 353
GHz polarization maps. Our primary findings are the following. (1) There is a
spatial correlation between the dust emission as measured by Planck at 353 GHz
and the synchrotron emission as measured by WMAP at 23 GHz with
$\rho\approx0.4$ or greater for $\ell<20$ and $f_{\mathrm{sky}}\geq0.5$,
dropping to $\rho\approx0.2$ for $30<\ell<200$. (2) A simple foreground model
with dust, synchrotron, and their correlation fits well to all possible cross
spectra formed with the WMAP and Planck 353 GHz data given the current
uncertainties. (3) In the 50$\%$ cleanest region of the polarized dust map, the
ratio of synchrotron to dust amplitudes at 90 GHz for 50 $\leq \ell \leq$110 is
$0.3_{-0.2}^{+0.3}$. Smaller regions of sky can be cleaner although the
uncertainties in our knowledge of synchrotron emission are larger. A
high-sensitivity measurement of synchrotron below 90 GHz will be important for
understanding all the components of foreground emission near 90 GHz. |
The Local Group as a test system for Modified Newtonian Dynamics: The Local Group (LG) is {an appropriate} test system for Modified Newtonian
Dynamics, since the acceleration of M31 galaxy is fully in the deep MOND regime
$a \ll a_0$. We model the LG as a two body problem of $M31$ and the Milky Way
(MW) galaxies. {Extending previous studies, we also include the Cosmological
Constant.} The assumption that in the big bang the galaxies emerged from the
same place and approach to the measured distance and velocity today (the Timing
Argument), predicts the total mass for the LG: $(0.447 \pm 0.005)\cdot 10^{12}
M_{\odot}$. The corresponding motion of the LG predicts a past encounter. The
ratio between the baryonic mass that MOND considers to the mass that Newtonian
case predicted, which includes dark matter is $10.74 \pm 0.82$. This ratio
agrees with the ratio between the dark matter and baryonic matter in other
galaxies. | Dense Star-forming Gas and Dust in the Magellanic Clouds: The early stages of star formation are closely related to the ambient
conditions in the interstellar medium. Important questions such as dust
abundance, size distribution, temperature distribution, fraction of molecular
gas, fraction of dense gas, gas surface density and total amount of gas and
dust require separation of metallicity and radiation effects. The Magellanic
Clouds provide an ideal laboratory to carry out such studies. They are
prominent targets for space observatories (Spitzer, Herschel), but an important
role remains for large groundbased facilities, such as a 25 m class
sub-millimeter telescope on Dome C. |
Compactness of Cold Gas in High-Redshift Galaxies: Galaxies in the early Universe were more compact and contained more molecular
gas than today. In this paper, we revisit the relation between these empirical
findings, and we quantitatively predict the cosmic evolution of the surface
densities of atomic (HI) and molecular (H2) hydrogen in regular galaxies. Our
method uses a pressure-based model for the H2/HI-ratio of the Interstellar
Medium, applied to ~3*10^7 virtual galaxies in the Millennium Simulation. We
predict that, on average, the HI-surface density of these galaxies saturates at
Sigma_HI<10 Msun/pc^2 at all redshifts (z), while H2-surface densities evolve
dramatically as Sigma_H2(1+z)^2.4. This scaling is dominated by a (1+z)^2
surface brightness scaling originating from the (1+z)^-1 size scaling of
galaxies at high z. Current measurements of Sigma_H2 at high z, derived from
CO-observations, tend to have even higher values, which can be quantitatively
explained by a selection bias towards merging systems. However, despite the
consistency between our high-z predictions and the sparse empirical data, we
emphasize that the empirical data potentially suffer from serious selection
biases and that the semi-analytic models remain in many regards uncertain. As a
case study, we investigate the cosmic evolution of simulated galaxies, which
resemble the Milky Way at z=0. We explicitly predict their HI- and
H2-distribution at z=1.5, corresponding to the CO-detected galaxy BzK-21000,
and at z=3, corresponding to the primary science goal of the Atacama Large
Millimeter/submillimeter Array (ALMA). | Does Bose-Einstein condensation of CMB photons cancel μ distortions
created by dissipation of sound waves in the early Universe?: The difference in the adiabatic indices of photons and non-relativistic
baryonic matter in the early Universe causes the electron temperature to be
slightly lower than the radiation temperature. Thermalization of photons with a
colder plasma results in the accumulation of photons in the Rayleigh-Jeans
tail, aided by stimulated recoil, while the higher frequency spectrum tries to
approach Planck spectrum at the electron temperature
$T_{\gamma}^{final}=\Te<T_{\gamma}^{initial}$; i.e., Bose-Einstein condensation
of photons occurs. We find new solutions of the Kompaneets equation describing
this effect. No actual condensate is, in reality, possible since the process is
very slow and photons drifting to low frequencies are efficiently absorbed by
bremsstrahlung and double Compton processes. The spectral distortions created
by Bose-Einstein condensation of photons are within an order of magnitude (for
the present range of allowed cosmological parameters), with exactly the same
spectrum but opposite in sign, of those created by diffusion damping of the
acoustic waves on small scales corresponding to comoving wavenumbers $45< k<
10^4\, Mpc^{-1}$. The initial perturbations on these scales are completely
unobservable today due to their being erased completely by Silk damping. There
is partial cancellation of these two distortions, leading to suppression of
$\mu$ distortions expected in the standard model of cosmology. The net
distortion depends on the scalar power index $n_S$ and its running $d n_S/d\ln
k$, and may vanish for special values of parameters, for example, for a running
spectrum with, $n_S=1,d n_S/d\ln k=-0.038$. We arrive at an intriguing
conclusion: even a null result, non-detection of $\mu$-type distortion at a
sensitivity of $10^{-9}$, gives a quantitative measure of the primordial
small-scale power spectrum. |
Star formation and dust obscuration at z~2: galaxies at the dawn of
downsizing: We present first results of a study aimed to constrain the star formation
rate and dust content of galaxies at z~2. We use a sample of BzK-selected
star-forming galaxies, drawn from the COSMOS survey, to perform a stacking
analysis of their 1.4 GHz radio continuum as a function of different stellar
population properties, after removing AGN contaminants from the sample. Dust
unbiased star formation rates are derived from radio fluxes assuming the local
radio-IR correlation. The main results of this work are: i) specific star
formation rates are constant over about 1 dex in stellar mass and up to the
highest stellar mass probed; ii) the dust attenuation is a strong function of
galaxy stellar mass with more massive galaxies being more obscured than lower
mass objects; iii) a single value of the UV extinction applied to all galaxies
would lead to grossly underestimate the SFR in massive galaxies; iv) correcting
the observed UV luminosities for dust attenuation based on the Calzetti recipe
provide results in very good agreement with the radio derived ones; v) the mean
specific star formation rate of our sample steadily decreases by a factor of ~4
with decreasing redshift from z=2.3 to 1.4 and a factor of ~40 down the local
Universe.
These empirical SFRs would cause galaxies to dramatically overgrow in mass if
maintained all the way to low redshifts, we suggest that this does not happen
because star formation is progressively quenched, likely starting from the most
massive galaxies. | Correcting cosmological parameter biases for all redshift surveys
induced by estimating and reweighting redshift distributions: Photometric redshift uncertainties are a major source of systematic error for
ongoing and future photometric surveys. We study different sources of redshift
error caused by choosing a suboptimal redshift histogram bin width and propose
methods to resolve them. The selection of a too large bin width is shown to
oversmooth small scale structure of the radial distribution of galaxies. This
systematic error can significantly shift cosmological parameter constraints by
up to $6 \, \sigma$ for the dark energy equation of state parameter $w$.
Careful selection of bin width can reduce this systematic by a factor of up to
6 as compared with commonly used current binning approaches. We further discuss
a generalised resampling method that can correct systematic and statistical
errors in cosmological parameter constraints caused by uncertainties in the
redshift distribution. This can be achieved without any prior assumptions about
the shape of the distribution or the form of the redshift error. Our
methodology allows photometric surveys to obtain unbiased cosmological
parameter constraints using a minimum number of spectroscopic calibration data.
For a DES-like galaxy clustering forecast we obtain unbiased results with
respect to errors caused by suboptimal histogram bin width selection, using
only 5k representative spectroscopic calibration objects per tomographic
redshift bin. |
The Role of Turbulence in AGN Self-Regulation in Galaxy Clusters: Cool cores of galaxy clusters are thought to be heated by low-power active
galactic nuclei (AGN), whose accretion is regulated by feedback. However, the
interaction between the hot gas ejected by the AGN and the ambient intracluster
medium is extremely difficult to simulate, as it involves a wide range of
spatial scales and gas that is Rayleigh-Taylor (RT) unstable. Here we use a
subgrid model for RT-driven turbulence to overcome these problems and present
the first observationally-consistent hydrodynamical simulations of AGN
self-regulation in galaxy clusters. For a wide range of parameter choices the
cluster in our three-dimensional simulations regulates itself for at least
several Gyrs years. Heating balances cooling through a string of outbreaks with
a typical recurrence time of approximately 80 Myrs, a timescale that depends
only on the global cluster properties. | Constraints on dark energy with the LOSS SN Ia sample: We present a cosmological analysis of the Lick Observatory Supernova Search
(LOSS) Type Ia supernova (SN Ia) photometry sample introduced by Ganeshalingam
et al. (2010). These SNe provide an effective anchor point to estimate
cosmological parameters when combined with datasets at higher redshift. The
data presented by Ganeshalingam et al. (2010) have been rereduced in the
natural system of the KAIT and Nickel telescopes to minimise systematic
uncertainties. We have run the light-curve-fitting software SALT2 on our
natural-system light curves to measure light-curve parameters for LOSS light
curves and available SN Ia datasets in the literature. We present a Hubble
diagram of 586 SNe in the redshift range z=0.01-1.4 with a residual scatter of
0.176 mag. Of the 226 low-z objects in our sample, 91 objects are from LOSS,
including 45 SNe without previously published distances. Assuming a flat
Universe, we find that the best fit for the dark energy equation-of-state
parameter w = -0.86^+0.13_-0.16 (stat) +- 0.11 (sys) from SNe alone, consistent
with a cosmological constant. Our data prefer a Universe with an accelerating
rate of expansion with 99.999% confidence. When looking at Hubble residuals as
a function of host-galaxy morphology, we do not see evidence for a significant
trend, although we find a somewhat reduced scatter in Hubble residuals from SNe
residing within a projected distance < 10 kpc of the host-galaxy nucleus
(\sigma = 0.156 mag). We find that Hubble residuals do not correlate with the
expansion velocity of Si II \lambda 6355 measured in optical spectra near
maximum light. Our data are consistent with no presence of a local "Hubble
bubble." Improvements in cosmological analyses within low-z samples can be
achieved by better constraining calibration uncertainties in the zero points of
photometric systems. |
The rapid assembly of an elliptical galaxy of 400 billion solar masses
at a redshift of 2.3: Stellar archeology shows that massive elliptical galaxies today formed
rapidly about ten billion years ago with star formation rates above several
hundreds solar masses per year (M_sun/yr). Their progenitors are likely the
sub-millimeter-bright galaxies (SMGs) at redshifts (z) greater than 2. While
SMGs' mean molecular gas mass of 5x10^10 M_sun can explain the formation of
typical elliptical galaxies, it is inadequate to form ellipticals that already
have stellar masses above 2x10^11 M_sun at z ~ 2. Here we report
multi-wavelength high-resolution observations of a rare merger of two massive
SMGs at z = 2.3. The system is currently forming stars at a tremendous rate of
2,000 M_sun/yr. With a star formation efficiency an order-of-magnitude greater
than that of normal galaxies, it will quench the star formation by exhausting
the gas reservoir in only ~200 million years. At a projected separation of 19
kiloparsecs, the two massive starbursts are about to merge and form a passive
elliptical galaxy with a stellar mass of ~4x10^11 M_sun. Our observations show
that gas-rich major galaxy mergers, concurrent with intense star formation, can
form the most massive elliptical galaxies by z ~ 1.5. | The distance modulus in dark energy and Cardassian cosmologies via the
hypergeometric function: The presence of the dark energy allows both the acceleration and the
expansion of the universe. In the case of a constant equation of state for dark
energy we derived an analytical solution for the Hubble radius in terms of the
hypergeometric function. An approximate Taylor expansion of order seven is
derived for both the constant and the variable equation of state for dark
energy. In the case of the Cardassian cosmology we also derived an analytical
solution for the Hubble radius in terms of the hypergeometric function. The
astronomical samples of the distance modulus for Supernova (SN) of type Ia
allows the derivation of the involved cosmological in the case of constant
equation of state, variable equation of state and Cardassian cosmology. |
The X-ray luminous galaxies optically classified as star forming are
mostly narrow line Seyfert 1s: We aim to characterize the nature of galaxies whose optical emission line
diagnostics are consistent with star formation, but whose X-ray properties
strongly point towards the presence of an AGN. Understanding these sources is
of particular importance in assessing the completeness of AGN samples derived
from large galaxy surveys, selected solely on the basis of their optical
spectral properties.We construct a large sample of 211 NELGs, which have FWHMs
Hb emission line <1200 km/s from the SDSS-DR7 galaxy spectroscopic catalogue,
for which we are able to construct a classical diagnostic diagram, [OIII]/Hb
versus [NII]/Ha (hence z<0.4), and that are also detected in the hard energy
band and present in the 2XMM catalogue. This sample offers a large database by
which to investigate potential mismatches between optical diagnostics and X-ray
emission. Among these 211 objects, which based on our selection criteria are
all at z<0.4, we find that 145 galaxies are diagnosed as AGNs, having 2-10 keV
X-ray luminosities that span a wide range, from 10^40 erg/s to above 10^44
erg/s. Out of the remaining 66 galaxies, which are instead diagnosed as SF, we
find a bimodal distribution in which 28 have X-ray luminosities in excess of
10^42 erg/s, large T (>1), and large X/O ratio (>0.1), while the rest are
consistent with being simply SF galaxies. Those 28 galaxies exhibit the
broadest Hb line FWHMs, from ~300 to 1200 km/s, and their X-ray spectrum is
steeper than average and often displays a soft excess. We therefore conclude
that the population of X-ray luminous NELGs with optical lines consistent with
those of a starforming galaxy (which represent 19% of our whole sample) is
largely dominated by NLS1s. The occurrence of such sources in the overall
optically selected sample is small (<2%), hence the contamination of optically
selected galaxies by NLS1s is very small. | A fundamental equation for Supermassive Black Holes: We developed a theoretical model able to give a common origin to the
correlations between the mass of supermassive black holes and the mass,
velocity dispersion, kinetic energy and momentum parameter of the corresponding
host galaxies. Our model is essentially based on the transformation of the
angular momentum of the interstellar material, which falls into the black hole,
into the angular momentum of the radiation emitted in this process. In this
framework, we predict the existence of a relation of the form $M_bh \propto R_e
\sigma^3$, which is confirmed by the experimental data and can be the starting
point to understand the other popular scaling laws too. |
BAO Extractor: bias and redshift space effects: We study a new procedure to measure the sound horizon scale via Baryonic
Acoustic Oscillations (BAO). Instead of fitting the measured power spectrum
(PS) to a theoretical model containing the cosmological informations and all
the nonlinear effects, we define a procedure to project out (or to "extract")
the oscillating component from a given nonlinear PS. We show that the BAO scale
extracted in this way is extremely robust and, moreover, can be reproduced by
simple theoretical models at any redshift. By using N-body simulations, we
discuss the effect of the nonlinear evolution of the matter field, of redshift
space distortions and of scale-dependent halo bias, showing that all these
effects can be reproduced with sub-percent accuracy. We give a one-parameter
theoretical model based on a simple (IR) modification of 1-loop perturbation
theory, which reproduces the BAO scale from measurements of halo clustering in
redshift space at better than $0.1\%$ level and does not need any external UV
input, such as coefficients measured from N-body simulations. | Inflation in Symmergent Metric-Palatini Gravity: In this paper, we study the cosmological inflation phenomenon in symmergent
gravity theory. Symmergent gravity is a novel framework which merges gravity
and the standard model (SM) so that the gravity emerges from the matter loops
and restores the broken gauge symmetries along the way. Symmergent gravity is
capable of inducing the gravitational constant $G$ and the quadratic curvature
coefficient $c_O$ from the loop corrections of the matter sector in a flat
space-time. In the event that all the matter fields, including the beyond the
standard model (BSM) sector, are mass degenerate, the vacuum energy can be
expressed in terms of $G$ and $c_O$. The parameter which measures the deviation
from the mass degeneracy is dubbed $\hat{\alpha}$. The parameters, $c_O$ and
$\hat{\alpha}$, of symmergent gravity convey the information about the fermion
and boson balance in the matter (SM+BSM) sector in number and in mass,
respectively. In our analysis, we have investigated the space of the symmergent
parameters $c_O$ and $\hat{\alpha}$ wherein they produce results that comply
with the inflationary observables $n_s$, $r$, and $\mathrm{d}n_s/\mathrm{d}\ln
k$.
We have shown that the vacuum energy together with the quadratic curvature
term arising in the symmergent gravity prescription are capable of inflating
the universe provided that the quadratic curvature coefficient $c_O$ is
negative (which corresponds to fermion dominance in number in the matter
sector) and the deviation from the mass degeneracy in the matter sector is
minute for both boson mass dominance and fermion mass dominance cases. |
Topology and Sizes of HII Regions during Cosmic Reionization: We use the results of large-scale simulations of reionization to explore
methods for characterizing the topology and sizes of HII regions during
reionization. We use four independent methods for characterizing the sizes of
ionized regions. Three of them give us a full size distribution: the
friends-of-friends (FOF) method, the spherical average method (SPA) and the
power spectrum (PS) of the ionized fraction. These latter three methods are
complementary: While the FOF method captures the size distribution of the small
scale H II regions, which contribute only a small amount to the total
ionization fraction, the spherical average method provides a smoothed measure
for the average size of the H II regions constituting the main contribution to
the ionized fraction, and the power spectrum does the same while retaining more
details on the size distribution. Our fourth method for characterizing the
sizes of the H II regions is the average size which results if we divide the
total volume of the H II regions by their total surface area, (i.e. 3V/A),
computed in terms of the ratio of the corresponding Minkowski functionals of
the ionized fraction field. To characterize the topology of the ionized
regions, we calculate the evolution of the Euler Characteristic. We find that
the evolution of the topology during the first half of reionization is
consistent with inside-out reionization of a Gaussian density field. We use
these techniques to investigate the dependence of size and topology on some
basic source properties, such as the halo mass-to-light ratio, susceptibility
of haloes to negative feedback from reionization, and the minimum halo mass for
sources to form. We find that suppression of ionizing sources within ionized
regions slows the growth of H II regions, and also changes their size
distribution. Additionally, the topology of simulations including suppression
is more complex. (abridged) | A Big-Bang Nucleosynthesis Limit on the Neutral Fermion Decays into
Neutrinos: Using the primordial helium abundance, an upper limit to the magnetic moments
for Dirac neutrinos had been provided by imposing restrictions on the number of
the additional helicity states. Considering non-thermal photons produced in the
decay of the heavy sterile mass eigenstates due to the neutrino magnetic
moment, we explore the constraints imposed by the observed abundances of all
the light elements produced during the Big Bang nucleosynthesis. |
Fake plunges are very eccentric real EMRIs in disguise ... they dominate
the rates and are blissfully ignorant of angular momentum barriers: The capture of a compact object in a galactic nucleus by a massive black hole
(MBH) is the best way to map space and time around it. Compact objects such as
stellar black holes on a capture orbit with a very high eccentricity have been
wrongly assumed to be lost for the system after an intense burst of radiation,
which has been described as a "direct plunge". We prove that these very
eccentric capture orbits spend actually a similar number of cycles in a
LISA-like detector as those with lower eccentricities if the central MBH is
spinning. Although the rates are higher for high-eccentricity EMRIs, the spin
also enhances the rates of lower-eccentricity EMRIs. This last kind have
received more attention because of the fact that high-eccentricity EMRIs were
thought to be direct plunges and thus negligible. On the other hand, recent
work on stellar dynamics has demonstrated that there seems to be a complot in
phase space acting on these lower-eccentricity captures, since their rates
decrease significantly by the presence of a blockade in the rate at which
orbital angular momenta change takes place. This so-called "Schwarzschild
barrier" is a result of the impact of relativistic precession on to the stellar
potential torques, and thus it affects the enhancement on lower-eccentricity
EMRIs that one would expect from resonant relaxation. We confirm and quantify
the existence of this barrier using a statitical sample of 2,500
direct-summation N-body simulations using both a post-Newtonian but also, and
for the first time, a geodesic approximation for the relativistic orbits. The
existence of the barrier prevents "traditional EMRIs" from approaching the
central MBH, but if the central MBH is spinning the rate will be anyway
dominated by highly-eccentric extreme-mass ratio inspirals, which insolently
ignore the presence of the barrier, because they are driven by two-body
relaxation. | Observing the Multiverse with Cosmic Wakes: Current theories of the origin of the Universe, including string theory,
predict the existence of a multiverse containing many bubble universes. These
bubble universes will generically collide, and collisions with ours produce
cosmic wakes that enter our Hubble volume, appear as unusually symmetric disks
in the cosmic microwave background (CMB) and disturb large scale structure
(LSS). There is preliminary observational evidence consistent with one or more
of these disturbances on our sky. However, other sources can produce similar
features in the CMB temperature map and so additional signals are needed to
verify their extra-universal origin. Here we find, for the first time, the
detailed three-dimensional shape and CMB temperature and polarization signals
of the cosmic wake of a bubble collision in the early universe consistent with
current observations. The predicted polarization pattern has distinctive
features that when correlated with the corresponding temperature pattern are a
unique and striking signal of a bubble collision. These features represent the
first verifiable prediction of the multiverse paradigm and might be detected by
current experiments such as Planck and future CMB polarization missions. A
detection of a bubble collision would confirm the existence of the Multiverse,
provide compelling evidence for the string theory landscape, and sharpen our
picture of the Universe and its origins. |
Multiscale Flow for Robust and Optimal Cosmological Analysis: We propose Multiscale Flow, a generative Normalizing Flow that creates
samples and models the field-level likelihood of two-dimensional cosmological
data such as weak lensing. Multiscale Flow uses hierarchical decomposition of
cosmological fields via a wavelet basis, and then models different wavelet
components separately as Normalizing Flows. The log-likelihood of the original
cosmological field can be recovered by summing over the log-likelihood of each
wavelet term. This decomposition allows us to separate the information from
different scales and identify distribution shifts in the data such as unknown
scale-dependent systematics. The resulting likelihood analysis can not only
identify these types of systematics, but can also be made optimal, in the sense
that the Multiscale Flow can learn the full likelihood at the field without any
dimensionality reduction. We apply Multiscale Flow to weak lensing mock
datasets for cosmological inference, and show that it significantly outperforms
traditional summary statistics such as power spectrum and peak counts, as well
as novel Machine Learning based summary statistics such as scattering transform
and convolutional neural networks. We further show that Multiscale Flow is able
to identify distribution shifts not in the training data such as baryonic
effects. Finally, we demonstrate that Multiscale Flow can be used to generate
realistic samples of weak lensing data. | The spherical collapse model in time varying vacuum cosmologies: We investigate the virialization of cosmic structures in the framework of
flat FLRW cosmological models, in which the vacuum energy density evolves with
time. In particular, our analysis focuses on the study of spherical matter
perturbations, as they decouple from the background expansion, "turn around"
and finally collapse. We generalize the spherical collapse model in the case
when the vacuum energy is a running function of the Hubble rate,
$\Lambda=\Lambda(H)$. A particularly well motivated model of this type is the
so-called quantum field vacuum, in which $\Lambda(H)$ is a quadratic function,
$\Lambda(H)=n_0+n_2\,H^2$, with $n_0\neq 0$. This model was previously studied
by our team using the latest high quality cosmological data to constrain its
free parameters, as well as the predicted cluster formation rate. It turns out
that the corresponding Hubble expansion history resembles that of the
traditional $\Lambda$CDM cosmology. We use this $\Lambda(t)$CDM framework to
illustrate the fact that the properties of the spherical collapse model (virial
density, collapse factor, etc.) depend on the choice of the considered vacuum
energy (homogeneous or clustered). In particular, if the distribution of the
vacuum energy is clustered, then, under specific conditions, we can produce
more concentrated structures with respect to the homogeneous vacuum energy
case. |
Impact of $1/f$ noise on cosmological parameter constraints for SKA
intensity mapping: We investigate the impact of $1/f$ noise on cosmology for an intensity
mapping survey with SKA1-MID Band\,1 and Band\,2. We use a Fisher matrix
approach to forecast constraints on cosmological parameters under the influence
of $1/f$ noise, adopting a semi-empirical model from an earlier work, which
results from the residual $1/f$ noise spectrum after applying a component
separation algorithm to remove smooth spectral components. Without $1/f$ noise,
the projected constraints are $4\%$ on $w_0$, $1\%$ on $h$, $2\%$ on $b_{\rm
HI}$ using Band\,1+\emph{Planck}, and $3\%$ on $w_0$, $0.5\%$ on $h$, $2\%$ on
$b_{\rm HI}$ using Band\,2+\emph{Planck}. A representative baseline $1/f$ noise
degrades these constraints by a factor of $\sim1.5$ for Band\,1+\emph{Planck},
and $\sim1.2$ for Band\,2+\emph{Planck}. On the power spectrum measurement,
higher redshift and smaller scales are more affected by $1/f$ noise, with
minimal contamination comes from $z\lesssim1$ and $\ell\lesssim100$. Subject to
the specific scan strategy of the adopted $1/f$ noise model, one prefers a
correlated in frequency with minimised spectral slope, a low knee frequency,
and a large telescope slew speed in order to reduce its impact. | A merger mystery: no extended radio emission in the merging cluster
Abell 2146: We present a new 400ks Chandra X-ray observation and a GMRT radio observation
at 325MHz of the merging galaxy cluster Abell 2146. The Chandra observation
reveals detailed structure associated with the major merger event including the
Mach M=2.1+/-0.2 bow shock located ahead of the dense subcluster core and the
first known example of an upstream shock (M=1.6+/-0.1). Surprisingly, the deep
GMRT observation at 325MHz does not detect any extended radio emission
associated with either shock front. All other merging galaxy clusters with
X-ray detected shock fronts, including the Bullet cluster, Abell 520, Abell 754
and Abell 2744, and clusters with candidate shock fronts have detected radio
relics or radio halo edges coincident with the shocks. We consider several
possible factors which could affect the formation of radio relics, including
the shock strength and the presence of a pre-existing electron population, but
do not find a favourable explanation for this result. We calculate a 3sigma
upper limit of 13mJy on extended radio emission, which is significantly below
the radio power expected by the observed P_{radio}-L_{X} correlation for
merging systems. The lack of an extended radio halo in Abell 2146 maybe due to
the low cluster mass relative to the majority of merging galaxy clusters with
detected radio halos. |
Modeling iterative reconstruction and displacement field in the large
scale structure: The next generation of galaxy surveys like the Dark Energy Spectroscopic
Instrument (DESI) and Euclid will provide datasets orders of magnitude larger
than anything available to date. Our ability to model nonlinear effects in late
time matter perturbations will be a key to unlock the full potential of these
datasets, and the area of initial condition reconstruction is attracting
growing attention. Iterative reconstruction developed in Ref. [1] is a
technique designed to reconstruct the displacement field from the observed
galaxy distribution. The nonlinear displacement field and initial linear
density field are highly correlated. Therefore, reconstructing the nonlinear
displacement field enables us to extract the primordial cosmological
information better than from the late time density field at the level of the
two-point statistics. This paper will test to what extent the iterative
reconstruction can recover the true displacement field and construct a
perturbation theory model for the postreconstructed field. We model the
iterative reconstruction process with Lagrangian perturbation theory~(LPT) up
to third order for dark matter in real space and compare it with $N$-body
simulations. We find that the simulated iterative reconstruction does not
converge to the nonlinear displacement field, and the discrepancy mainly
appears in the shift term, i.e., the term correlated directly with the linear
density field. On the contrary, our 3LPT model predicts that the iterative
reconstruction should converge to the nonlinear displacement field. We discuss
the sources of discrepancy, including numerical noise/artifacts on small
scales, and present an ad hoc phenomenological model that improves the
agreement. | ZOMG-I. How the cosmic web inhibits halo growth and generates assembly
bias: The clustering of dark matter haloes with fixed mass depends on their
formation history, an effect known as assembly bias. We use zoom N -body
simulations to investigate the origin of this phenomenon. For each halo at
redshift z=0, we determine the time in which the physical volume containing its
final mass becomes stable. We consider five examples for which this happens at
z~1.5 and two that do not stabilize by z=0. The zoom simulations show that
early-collapsing haloes do not grow in mass at z=0 while late-forming ones show
a net inflow. The reason is that 'accreting' haloes are located at the nodes of
a network of thin filaments feeding them. Conversely, each 'stalled' halo lies
within a prominent filament that is thicker than the halo size. Infalling
material from the surroundings becomes part of the filament while matter within
it recedes from the halo. We conclude that assembly bias originates from
quenching halo growth due to tidal forces following the formation of non-linear
structures in the cosmic web, as previously conjectured in the literature. Also
the internal dynamics of the haloes change: the velocity anisotropy profile is
biased towards radial (tangential) orbits in accreting (stalled) haloes. Our
findings reveal the cause of the yet unexplained dependence of halo clustering
on the anisotropy. Finally, we extend the excursion-set theory to account for
these effects. A simple criterion based on the ellipticity of the linear tidal
field combined with the spherical collapse model provides excellent predictions
for both classes of haloes. |
Dark matter-radiation interactions: the structure of Milky Way satellite
galaxies: In the thermal dark matter (DM) paradigm, primordial interactions between DM
and Standard Model particles are responsible for the observed DM relic density.
In Boehm et al. (2014), we showed that weak-strength interactions between DM
and radiation (photons or neutrinos) can erase small-scale density
fluctuations, leading to a suppression of the matter power spectrum compared to
the collisionless cold DM (CDM) model. This results in fewer DM subhaloes
within Milky Way-like DM haloes, implying a reduction in the abundance of
satellite galaxies. Here we use very high resolution N-body simulations to
measure the dynamics of these subhaloes. We find that when interactions are
included, the largest subhaloes are less concentrated than their counterparts
in the collisionless CDM model and have rotation curves that match
observational data, providing a new solution to the "too big to fail" problem. | The SWELLS survey. II. Breaking the disk-halo degeneracy in the spiral
galaxy gravitational lens SDSS J2141-0001: The degeneracy among the disk, bulge and halo contributions to galaxy
rotation curves prevents an understanding of the distribution of baryons and
dark matter in disk galaxies. In an attempt to break this degeneracy, we
present an analysis of the spiral galaxy strong gravitational lens SDSS
J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space
Telescope multicolor imaging, gas and stellar kinematics data derived from
long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the
Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bulge,
disk and halo components and infer the contribution of each component, using
information from gravitational lensing and gas kinematics. This analysis yields
a best-fitting total (disk plus bulge) stellar mass of log_{10}(Mstar/Msun) =
10.99(+0.11,-0.25). The photometric data combined with stellar population
synthesis models yield log_{10}(Mstar/Msun) = 10.97\pm0.07, and 11.21\pm0.07
for the Chabrier and Salpeter IMFs, respectively. Accounting for the expected
gas fraction of \simeq 20% reduces the lensing plus kinematics stellar mass by
0.10\pm0.05 dex, resulting in a Bayes factor of 11.9 in favor of a Chabrier
IMF. The dark matter halo is roughly spherical, with minor to major axis ratio
q_{halo}=0.91(+0.15,-0.13). The dark matter halo has a maximum circular
velocity of V_{max}=276(+17,-18) km/s, and a central density parameter of
log_{10}\Delta_{V/2}=5.9(+0.9,-0.5). This is higher than predicted for
uncontracted dark matter haloes in LCDM cosmologies, log_{10}\Delta_{V/2}=5.2,
suggesting that either the halo has contracted in response to galaxy formation,
or that the halo has a higher than average concentration. At 2.2 disk scale
lengths the dark matter fraction is f_{DM}=0.55(+0.20,-0.15), suggesting that
SDSS J2141-0001 is sub-maximal. |
Relationship between the CMB, SZ Cluster Counts, and Local Hubble
Parameter Measurements in a Simple Void Model: The discrepancy between the amplitudes of matter fluctuations inferred from
Sunyaev-Zel'dovich (SZ) cluster number counts, the primary temperature, and the
polarization anisotropies of the cosmic microwave background (CMB) measured by
the Planck satellite can be reconciled if the local universe is embedded in an
under-dense region as shown by Lee, 2014. Here using a simple void model
assuming the open Friedmann-Robertson-Walker geometry and a Markov Chain Monte
Carlo technique, we investigate how deep the local under-dense region needs to
be to resolve this discrepancy. Such local void, if exists, predicts the local
Hubble parameter value that is different from the global Hubble constant. We
derive the posterior distribution of the local Hubble parameter from a joint
fitting of the Planck CMB data and SZ cluster number counts assuming the simple
void model. We show that the predicted local Hubble parameter value of $H_{\rm
loc}=70.1\pm0.34~{\rm km\,s^{-1}Mpc^{-1}}$ is in better agreement with direct
local Hubble parameter measurements, indicating that the local void model may
provide a consistent solution to the cluster number counts and Hubble parameter
discrepancies. | The beginning of nonlinear stage of evolution of protostars at $ z=20: The results of the EDGES (Experiment to Detect the Global EoR Signature)
experiment (Bowman et al., 2018) is interpreted as the beginning of compression
stage of primary density fluctuations in a mini halo. Estimates of the mass of
these objects are given. |
Spectral Energy Distributions of HII regions in M33 (HerM33es): Within the framework of the Herschel M 33 extended survey HerM33es we study
the Spectral Energy Distribution (SED) of a set of HII regions in M 33 as a
function of the morphology. We present a catalogue of 119 HII regions
morphologically classified: 9 filled, 47 mixed, 36 shell, and 27 clear shell
HII regions. For each object we extract the photometry at twelve available
wavelength bands (from FUV-1516A to IR-250mi) and obtain the SED. We also
obtain emission line profiles across the regions to study the location of the
stellar, ionised gas, and dust components. We find trends for the SEDs related
to the morphology, showing that the star and gas-dust configuration affects the
ratios of the emission in different bands. The mixed and filled regions show
higher emission at 24mi than the shells and clear shells, which could be due to
the proximity of the dust to the stellar clusters in the case of mixed and
filled regions. The FIR peak for shells and clear shells seems to be located
towards longer wavelengths, indicating that the dust is colder for this type of
objects.The logarithmic 100/70mi ratio for filled and mixed regions remains
constant over one order of magnitude in Halpha and FUV surface brightness,
while the shells and clear shells exhibit a wider range of values of almost two
orders of magnitude. We derive dust masses and temperatures fitting the
individual SEDs with dust models proposed in the literature. The derived dust
mass range is between 10^2-10^4 Msun and the cold dust temperature spans
T(cold)~12-27 K. The spherical geometrical model proposed for the Halpha clear
shells is confirmed by the emission profile obtained from the observations and
is used to infer the electron density within the envelope: the typical electron
density is 0.7+-0.3 cm^-3, while filled regions can reach values two to five
times higher. | Constraints on Disformal Couplings from the Properties of the Cosmic
Microwave Background Radiation: Certain modified gravity theories predict the existence of an additional,
non-conformally coupled scalar field. A disformal coupling of the field to the
Cosmic Microwave Background (CMB) is shown to affect the evolution of the
energy density in the radiation fluid and produces a modification of the
distribution function of the CMB, which vanishes if photons and baryons couple
in the same way to the scalar. We find the constraints on the couplings to
matter and photons coming from the measurement of the CMB temperature evolution
and from current upper limits on the $\mu$--distortion of the CMB spectrum. We
also point out that the measured equation of state of photons differs from
$w_\gamma = 1/3$ in the presence of disformal couplings. |
Isocurvature bounds on axion-like particle dark matter in the
post-inflationary scenario: We assume that dark matter is comprised of axion-like particles (ALPs)
generated by the realignment mechanism in the post-inflationary scenario. This
leads to isocurvature fluctuations with an amplitude of order one for scales
comparable to the horizon at the time when the ALP field starts oscillating.
The power spectrum of these fluctuations is flat for small wave numbers,
extending to scales relevant for cosmological observables. Denoting the
relative isocurvature amplitude at $k_*$ = 0.05 Mpc$^{-1}$ by $f_{\rm iso}$,
Planck observations of the cosmic microwave background (CMB) yield $f_{\rm
iso}$ < 0.31 at the 2$\sigma$-level. This excludes the hypothesis of
post-inflationary ALP dark matter with masses $m_{a}$ < 10$^{-20}-$10$^{-16}$
eV, where the range is due to details of the ALP mass-temperature dependence.
Future CMB stage IV and 21-cm intensity mapping experiments may improve these
limits by 1$-$2 orders of magnitude in $m_{a}$. | First detection of stacked X-ray emission from cosmic web filaments: We report the first statistical detection of X-ray emission from cosmic web
filaments in ROSAT data. We selected 15,165 filaments at 0.2<z<0.6 ranging from
30 Mpc to 100 Mpc in length, identified in the Sloan Digital Sky Survey (SDSS)
survey. We stacked the X-ray count-rate maps from ROSAT around the filaments,
excluding resolved galaxy groups and clusters above the mass of ~3 * 10^13 Msun
as well as the detected X-ray point sources from the ROSAT, Chandra, and
XMM-Newton observations. The stacked signal results in the detection of the
X-ray emission from the cosmic filaments at a significance of 4.2 sigma in the
energy band of 0.56-1.21 keV. The signal is interpreted, assuming the
Astrophysical Plasma Emission Code (APEC) model, as an emission from the hot
gas in the filament-core regions with an average gas temperature of
0.9(+1.0-0.6) keV and a gas overdensity of ~30 at the center of the filaments.
Furthermore, we show that stacking the SRG/eROSITA data for ~2,000 filaments
only would lead to a ~5 sigma detection of their X-ray signal, even with an
average gas temperature as low as ~0.3 keV. |
CMB and matter power spectra from cross correlations of primordial
curvature and magnetic fields: A complete numerical calculation of the temperature anisotropies and the
polarization of the cosmic microwave background (CMB) is presented for a non
zero cross correlation of a stochastic magnetic field with the primordial
curvature perturbation. Such a cross correlation results, for example, if the
magnetic field is generated during inflation by coupling electrodynamics to a
scalar field which is identified with the curvaton. For a nearly scale
invariant magnetic field of 1 nG it is found that at low multipoles the
contribution due to the cross correlation dominates over that of the pure
magnetic mode. A similar behaviour on large scales is found for the linear
matter power spectrum. | Exploring the Properties of the M31 Halo Globular Cluster System: Following on from our discovery of a significant population of M31 outer halo
globular clusters (GCs), and updates to the Revised Bologna Catalogue of M31
GCs, we investigate the GC system of M31 out to an unprecedented radius
(~120kpc). We derive various ensemble properties, including the magnitude,
colour and metallicity distributions, as well as the GC number density profile.
One of our most significant findings is evidence for a flattening in the radial
GC number density profile in the outer halo. Intriguingly, this occurs at a
galactocentric radius of ~2 degrees (~30 kpc) which is the radius at which the
underlying stellar halo surface density has also been shown to flatten. The GCs
which lie beyond this radius are remarkably uniform in terms of their blue
(V-I)o colours, consistent with them belonging to an ancient population with
little to no metallicity gradient. Structural parameters are also derived for a
sample of 13 newly-discovered extended clusters (ECs) and we find the lowest
luminosity ECs have magnitudes and sizes similar to Palomar-type GCs in the
Milky Way halo. We argue that our findings provide strong support for a
scenario in which a significant fraction of the outer halo GC population of M31
has been accreted. |
Sparsely Sampling the Sky: Regular vs Random Sampling: The next generation of galaxy surveys, aiming to observe millions of
galaxies, are expensive both in time and cost. This raises questions regarding
the optimal investment of this time and money for future surveys. In a previous
work, it was shown that a sparse sampling strategy could be a powerful
substitute for the contiguous observations. However, in this previous paper a
regular sparse sampling was investigated, where the sparse observed patches
were regularly distributed on the sky. The regularity of the mask introduces a
periodic pattern in the window function, which induces periodic correlations at
specific scales. In this paper, we use the Bayesian experimental design to
investigate a random sparse sampling, where the observed patches are randomly
distributed over the total sparsely sampled area. We find that, as there is no
preferred scale in the window function, the induced correlation is evenly
distributed amongst all scales. This could be desirable if we are interested in
specific scales in the galaxy power spectrum, such as the Baryonic Acoustic
Oscillation (BAO) scales. However, for constraining the overall galaxy power
spectrum and the cosmological parameters, there is no preference over regular
or random sampling. Hence any approach that is practically more suitable can be
chosen and we can relax the regular-grid condition for the distribution of the
observed patches. | Weak Lensing Analysis of CODEX Clusters using Dark Energy Camera Legacy
Survey : Mass-Richness Relation: We present the weak lensing analysis of 279 CODEX clusters using imaging data
from 4200 $\text{deg}^{2}$ of the DECam Legacy Survey (DECaLS) Data Release 3.
The cluster sample results from a joint selection in X-ray, optical richness in
the range $20 \leq \lambda < 110$, and redshift in the range $0.1 \leq z \leq
0.2$. We model the cluster mass ($M_{\rm 200c}$) and the richness relation with
the expression $\left\langle M_{\rm 200c} | \lambda \right\rangle \propto M_{0}
\, (\lambda / 40)^{F_{\lambda}}$. By measuring the CODEX cluster sample as an
individual cluster, we obtain the best-fit values, $M_{0} =
3.24^{+0.29}_{-0.27} \times 10^{14} \text{M}_{\odot}$, and $F_{\lambda} = 1.00
^{+0.22}_{-0.22}$ for the richness scaling index, consistent with a power law
relation. Moreover, we separate the cluster sample into three richness groups;
$\lambda = 20 - 30, 30 - 50$ and $50 - 110$, and measure the stacked excess
surface mass density profile in each group. The results show that both methods
are consistent. In addition, we find an excellent agreement between our weak
lensing based scaling relation and the relation obtained with dynamical masses
estimated from cluster member velocity dispersions measured by the
SDSS-IV/SPIDERS team. This suggests that the cluster dynamical equilibrium
assumption involved in the dynamical mass estimates is statistically robust for
a large sample of clusters. |
Tau neutrinos from ultracompact dark matter minihalos and constraints on
the primordial curvature perturbations: The observations and research on the neutrinos provide a kind of indirect way
of revealing the properties of dark matter particles. For the detection of muon
neutrinos, the main issue is the large atmospheric background, which is caused
by the interactions between the cosmic rays and atoms within the atmosphere.
Compared with muon neutrinos, tau neutrinos have a smaller atmospheric
background especially for the downward-going direction. Except for the
classical neutrino sources, dark matter particles can also annihilate into the
neutrinos and are the potential high energy astrophysical sources. The
annihilation rate of dark matter particles is proportional to the square of
number density; therefore, the annihilation rate is large near the center of
dark matter halos especially for the new kind of dark matter structures named
ultracompact dark matter minihalos (UCMHs). In previous works, we have
investigated the potential muon neutrino flux from UCMHs due to dark matter
annihilation. Moreover, since the formation of UCMHs is related to the
primordial density perturbations of small scales, we get the constraints on the
amplitude of the primordial curvature perturbations of small scales, $1
\lesssim k \lesssim 10^{7} ~\rm Mpc^{-1}$. In this work, we focus on the
downward-going tau neutrinos from UCMHs due to dark matter annihilation.
Compared with the background of tau neutrino flux we get the constraints on the
mass fraction of UCMHs. Then using the limits on the mass fraction of UCMHs we
got the constraints on the amplitude of the primordial curvature perturbations
which are extended to the scale $k \sim 10^{8} ~ \rm Mpc^{-1}$ compared with
previous results. | Star-forming fractions and galaxy evolution with redshift in rich
X-ray-selected galaxy clusters: We have compared stacked spectra of galaxies, grouped by environment and
stellar mass, among 58 members of the redshift z = 1.24 galaxy cluster RDCS
J1252.9-2927 (J1252.9) and 134 galaxies in the z = 0.84 cluster RX J0152.7-1357
(J0152.7). These two clusters are excellent laboratories to study how galaxies
evolve from star-forming to passive at z ~ 1. We measured spectral indices and
star-forming fractions for our density- and mass-based stacked spectra. The
star-forming fraction among low-mass galaxies (< 7 x 10^10 M_sun) is higher in
J1252.9 than in J0152.7, at about 4 sigma significance. Thus star formation is
being quenched between z = 1.24 and z = 0.84 for a substantial fraction of
low-mass galaxies. Star-forming fractions were also found to be higher in
J1252.9 in all environments, including the core. Passive galaxies in J1252.9
have systematically lower D_n4000 values than in J0152.7 in all density and
mass groups, consistent with passive evolution at modestly super-solar
metallicities. |
Spatially resolved stellar, dust and gas properties of the
post-interacting Whirlpool Galaxy system: Using infrared imaging from the Herschel Space Observatory, observed as part
of the VNGS, we investigate the spatially resolved dust properties of the
interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales
of 1 kpc. Spectral energy distribution modelling of the new infrared images in
combination with archival optical, near- through mid-infrared images confirms
that both galaxies underwent a burst of star formation ~370-480 Myr ago and
provides spatially resolved maps of the stellar and dust mass surface
densities. The resulting average dust-to-stellar mass ratios are comparable to
other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at
log M(dust)/M(star)= -2.5+/-0.2 and NGC 5195 at log M(dust)/M(star)=
-3.5+/-0.3. The dust-to-stellar mass ratio is constant across NGC 5194
suggesting the stellar and dust components are coupled. In contrast, the mass
ratio increases with radius in NGC 5195 with decreasing stellar mass density.
Archival mass surface density maps of the neutral and molecular hydrogen gas
are also folded into our analysis. The gas-to-dust mass ratio, 94+/-17, is
relatively constant across NGC 5194. Somewhat surprisingly, we find the dust in
NGC 5195 is heated by a strong interstellar radiation field, over 20 times that
of the ISRF in the Milky Way, resulting in relatively high characteristic dust
temperatures (~30 K). This post-starburst galaxy contains a substantial amount
of low-density molecular gas and displays a gas-to-dust ratio (73+/-35) similar
to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such
high temperatures as there is no star formation in the galaxy and its active
galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which
exhibits only a modest enhancement in the amplitude of its ISRF. | Survey of H-alpha emission from thirty nearby dwarf galaxies: Measurements of the H-alpha flux from 30 neighboring dwarf galaxies are
presented. After correction for absorption, these fluxes are used to estimate
the star formation rate (SFR). The SFR for 18 of the galaxies according to the
H-alpha emission are compared with estimates of the SFR from FUV magnitudes
obtained with the GALEX telescope. These are in good agreement over the range
log[SFR] = [-3,0]M sun/yr. |
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