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Cosmology inference at the field level from biased tracers in
redshift-space: Cosmology inference of galaxy clustering at the field level with the EFT
likelihood in principle allows for extracting all non-Gaussian information from
quasi-linear scales, while robustly marginalizing over any astrophysical
uncertainties. A pipeline in this spirit is implemented in the
\texttt{LEFTfield} code, which we extend in this work to describe the
clustering of galaxies in redshift space. Our main additions are: the
computation of the velocity field in the LPT gravity model, the fully nonlinear
displacement of the evolved, biased density field to redshift space, and a
systematic expansion of velocity bias. We test the resulting analysis pipeline
by applying it to synthetic data sets with a known ground truth at increasing
complexity: mock data generated from the perturbative forward model itself,
sub-sampled matter particles, and dark matter halos in N-body simulations. By
fixing the initial-time density contrast to the ground truth, while varying the
growth rate $f$, bias coefficients and noise amplitudes, we perform a stringent
set of checks. These show that indeed a systematic higher-order expansion of
the velocity bias is required to infer a growth rate consistent with the ground
truth within errors. Applied to dark matter halos, our analysis yields unbiased
constraints on $f$ at the level of a few percent for a variety of halo masses
at redshifts $z=0,\,0.5,\,1$ and for a broad range of cutoff scales
$0.08\,h/\mathrm{Mpc} \leq \Lambda \leq 0.20\,h/\mathrm{Mpc}$. Importantly,
deviations between true and inferred growth rate exhibit the scaling with halo
mass, redshift and cutoff that one expects based on the EFT of Large Scale
Structure. Further, we obtain a robust detection of velocity bias through its
effect on the redshift-space density field and are able to disentangle it from
higher-derivative bias contributions. | Magnetogenesis Experiments Using a Modified Chaplygin Gas EoS: We examine magnetogenesis in a multi-fluid environment. We find that the
various composition of a modified Chaplygin Gas (MCG) and Plasma Fluid (PF)
yield magnetic fields of non-negligible strengths. These fields are produced by
the battery effect and interactions between the two fluids may explain the
amplification observed in the simulation. Our simulations show that the
strongest fields are generated in a mixture with 50% MCG and 50% PF. |
Kinematic Signatures of Bulges Correlate with Bulge Morphologies and
Sérsic Index: We use the Marcario Low Resolution Spectrograph (LRS) at the
Hobby-Eberly-Telescope (HET) to study the kinematics of pseudobulges and
classical bulges in the nearby universe. We present major-axis rotational
velocities, velocity dispersions, and h3 and h4 moments derived from
high-resolution (sigma ~ 39 km/s) spectra for 45 S0 to Sc galaxies; for 27 of
the galaxies we also present minor axis data. We combine our kinematics with
bulge-to-disk decompositions. We demonstrate for the first time that purely
kinematic diagnostics of the bulge dichotomy agree systematically with those
based on S\'ersic index. Low S\'ersic index bulges have both increased
rotational support (higher v/sigma values) and on average lower central
velocity dispersions. Furthermore, we confirm that the same correlation also
holds when visual morphologies are used to diagnose bulge type. The previously
noted trend of photometrically flattened bulges to have shallower velocity
dispersion profiles turns to be significant and systematic if the S\'ersic
index is used to distinguish between pseudobulges and classical bulges. The
correlation between h3 and v/sigma observed in elliptical galaxies is also
observed in intermediate type galaxies, irrespective of bulge type. Finally, we
present evidence for formerly undetected counter rotation in the two systems
NGC 3945 and NGC 4736.
Based on observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania State
University, Stanford University, Ludwig-Maximilians-Universit\"at M\"unchen,
and Georg-August-Universit\"at G\"ottingen. | High-redshift Mini-haloes from Modulated Preheating: Intermittent type of primordial non-Gaussian fluctuations from modulated
preheating can produce an overabundance of $\sim 10^8M_\odot$ mini-haloes at
high redshift $z\gtrsim 20$. This may have a significant impact on the
formation of high-redshift supermassive black holes. |
Full-sky Gravitational Lensing Simulation for Large-area Galaxy Surveys
and Cosmic Microwave Background Experiments: We present 108 full-sky gravitational lensing simulation data sets generated
by performing multiple-lens plane ray-tracing through high-resolution
cosmological $N$-body simulations. The data sets include full-sky convergence
and shear maps from redshifts $z=0.05$ to $5.3$ at intervals of $150 \,
h^{-1}{\rm Mpc}$ comoving radial distance (corresponding to a redshift interval
of $\Delta z \simeq 0.05$ at the nearby universe), enabling the construction of
a mock shear catalog for an arbitrary source distribution up to $z=5.3$. The
dark matter halos are identified from the same $N$-body simulations with enough
mass resolution to resolve the host halos of the Sloan Digital Sky Survey
(SDSS) CMASS and Luminous Red Galaxies (LRGs). Angular positions and redshifts
of the halos are provided by a ray-tracing calculation, enabling the creation
of a mock halo catalog to be used for galaxy-galaxy and cluster-galaxy lensing.
The simulation also yields maps of gravitational lensing deflections for a
source redshift at the last scattering surface, and we provide 108 realizations
of lensed cosmic microwave background (CMB) maps in which the post-Born
corrections caused by multiple light scattering are included. We present basic
statistics of the simulation data, including the angular power spectra of
cosmic shear, CMB temperature and polarization anisotropies, galaxy-galaxy
lensing signals for halos, and their covariances. The angular power spectra of
the cosmic shear and CMB anisotropies agree with theoretical predictions within
$5\%$ up to $\ell = 3000$ (or at an angular scale $\theta > 0.5$ arcsin). The
simulation data sets are generated primarily for the ongoing Subaru Hyper
Suprime-Cam survey but are freely available for download at
http://cosmo.phys.hirosaki-u.ac.jp/takahasi/allsky_raytracing. | Solving small-scale clustering problems in approximate lightcone mocks: Realistic lightcone mocks are important in the clustering analyses of large
galaxy surveys. For simulations where only the snapshots are available, it is
common to create approximate lightcones by joining together the snapshots in
spherical shells. We assess the two-point clustering measurements of central
galaxies in approximate lightcones built from the Millennium-XXL simulation,
which are constructed using different numbers of snapshots. The monopole and
quadrupole of the real-space correlation function is strongly boosted on small
scales below 1 Mpc/h, due to some galaxies being duplicated at the boundaries
between snapshots in the lightcone. When more snapshots are used, the total
number of duplicated galaxies is approximately constant, but they are pushed to
smaller separations. The effect of this in redshift space is small, as long as
the snapshots are cut into shells in real space. Randomly removing duplicated
galaxies is able to reduce the excess clustering signal. Including satellite
galaxies will reduce the impact of the duplicates, since many small-scale pairs
come from satellites in the same halo. Galaxies that are missing from the
lightcone at the boundaries can be added to the lightcone by having a small
overlap between each shell. This effect will impact analyses that use very
small-scale clustering measurements, and when using mocks to test the impact of
fibre collisions. |
The Missing Baryon Problem via Cosmological Zoom-in Simulations: This thesis explores the missing baryon problem in a computational context.
An overview of the problem is given, along with a discussion regarding the
relevance of the Circumgalactic Medium (CMG) and cosmological Zoom-in
simulations. The mechanisms underlying the N-body code ChaNGa (H. Menon, et
al., Computational Astrophysics and Cosmology 2, 1 (2015), arXiv:1409.1929), as
well as the data visualization and analysis tools yt (M. J. Turk, et al., 192,
9 (2011), arXiv:1011.3514) and trident (Hummels, et al., 847, 59 (2017),
arXiv:1612.03935) are presented at a conceptual level. Finally, a series of
synthetic quasar absorption spectra produced by using trident on a ChaNGa
dataset from (S. Roca-Fabrega, et al., 917, 64 (2021), arXiv:2106.09738) at
redshift of $z\sim4$ are shown. The low relative flux exhibited by these
spectra render absorption features indistinguishable from background noise, and
possible explanations for this phenomena such as high redshift are discussed.
Though the resulting spectra exhibit serious obstacles for both qualitative and
quantitative interpretation, they provide a "proof-of-concept" for future work,
demonstrating trident's compatibility with ChaNGa's data format. Future
prospects for using trident to analyze the CGM as simulated by ChaNGa are
discussed, as well as possible extensions of this project. | What do we really know about Dark Energy?: In this paper I discuss what we truly know about dark energy. I shall argue
that up to date our single indication for the existence of dark energy comes
from distance measurements and their relation to redshift. Supernovae, CMB
anisotropies and observations of baryon acoustic oscillations, they all simply
tell us that the observed distance to a given redshift is larger than the one
expected from a Friedmann Lemaitre universe with matter only and the locally
measured Hubble parameter. |
On the evolution of environmental and mass properties of strong lens
galaxies in COSMOS: Among the 100 strong lens candidates found in the COSMOS field, 20 with
redshifts in the range [0.34,1.13], feature multiple images of background
sources. Using the multi-wavelength coverage of the field and its spectroscopic
follow-up, we characterize the evolution with redshift of the environment and
of the dark-matter (DM) fraction of the lens galaxies. We present new redshift
of the strong lens candidates. The lens environment is characterized by the
projected 10 closest galaxies around each lens and by the number of galaxies
with a projected distance less than 1Mpc at the lens galaxy redshift. In both
cases, we perform similar measurements on a control sample of twin non-lens
early type galaxies (ETGs). In addition, we identify group members and field
galaxies in the X-ray and optical catalogs of galaxy groups. From those
catalogs, we measure the external shear contribution at the lens galaxy
positions. The systems are then modeled using a SIE plus the external shear due
to the groups. We observe that the average stellar mass of lens galaxies
increases with z and that the environment of lens galaxies is compatible with
that of the twins. During the lens modeling, we notice that, when let free, the
external shear points in a direction which is the mean direction of the
external shear due to groups and of the closest galaxy to the lens. We notice
that the DM fraction of the lens galaxies within the Einstein radius decreases
as the redshift increases. Given these, we conclude that, while the environment
of lens galaxies is compatible with that of non-lens ETGS, their mass
properties evolves significantly with redshift: it is still not clear whether
this advocates in favor of a stronger lensing bias toward massive objects at
high redshift or is simply representative of the high proportion of massive and
high stellar density galaxies at high redshift. | Spherical and non-spherical bubbles in cosmological phase transitions: The cosmological remnants of a first-order phase transition generally depend
on the perturbations that the walls of expanding bubbles originate in the
plasma. Several of the formation mechanisms occur when bubbles collide and lose
their spherical symmetry. However, spherical bubbles are often considered in
the literature, in particular for the calculation of gravitational waves. We
study the steady state motion of bubble walls for different bubble symmetries.
Using the bag equation of state, we discuss the propagation of phase transition
fronts as detonations and subsonic or supersonic deflagrations. We consider the
cases of spherical, cylindrical and planar walls, and compare the energy
transferred to bulk motions of the relativistic fluid. We find that the
different wall geometries give similar perturbations of the plasma. For the
case of planar walls, we obtain analytical expressions for the kinetic energy
in the bulk motions. As an application, we discuss the generation of
gravitational waves. |
The Splashback Feature around DES Galaxy Clusters: Galaxy Density and
Weak Lensing Profiles: Splashback refers to the process of matter that is accreting onto a dark
matter halo reaching its first orbital apocenter and turning around in its
orbit. The cluster-centric radius at which this process occurs, r_sp, defines a
halo boundary that is connected to the dynamics of the cluster. A rapid decline
in the halo profile is expected near r_sp. We measure the galaxy number density
and weak lensing mass profiles around redMaPPer galaxy clusters in the first
year Dark Energy Survey (DES) data. For a cluster sample with mean M_200m mass
~2.5 x 10^14 M_sun, we find strong evidence of a splashback-like steepening of
the galaxy density profile and measure r_sp=1.13 +/- 0.07 Mpc/h, consistent
with earlier SDSS measurements of More et al. (2016) and Baxter et al. (2017).
Moreover, our weak lensing measurement demonstrates for the first time the
existence of a splashback-like steepening of the matter profile of galaxy
clusters. We measure r_sp=1.34 +/- 0.21 Mpc/h from the weak lensing data, in
good agreement with our galaxy density measurements. For different cluster and
galaxy samples, we find that consistent with LCDM simulations, r_sp scales with
R_200m and does not evolve with redshift over the redshift range of 0.3--0.6.
We also find that potential systematic effects associated with the redMaPPer
algorithm may impact the location of r_sp. We discuss progress needed to
understand the systematic uncertainties and fully exploit forthcoming data from
DES and future surveys, emphasizing the importance of more realistic mock
catalogs and independent cluster samples. | Spectral Energy Distributions of a set of HII regions in M33 (HerM33es): Within the framework of the HerM33es Key Project for Herschel and in
combination with multi-wavelength data, we study the Spectral Energy
Distribution (SED) of a set of HII regions in the Local Group Galaxy M33. Using
the Halpha emission, we perform a classification of a selected HII region
sample in terms of morphology, separating the objects in filled, mixed, shell
and clear shell objects. We obtain the SED for each HII region as well as a
representative SED for each class of objects. We also study the emission
distribution of each band within the regions. We find different trends in the
SEDs for each morphological type that are related to properties of the dust and
their associated stellar cluster. The emission distribution of each band within
the region is different for each morphological type of object. |
VIPERS: An Unprecedented View of Galaxies and Large-Scale Structure
Halfway Back in the Life of the Universe: The VIMOS Public Extragalactic Redshift Survey (VIPERS) is an ongoing ESO
Large Programme to map in detail the large-scale distribution of galaxies at
0.5 < z <1.2. With a combination of volume and sampling density that is unique
for these redshifts, it focuses on measuring galaxy clustering and related
cosmological quantities as part of the grand challenge of understanding the
origin of cosmic acceleration. VIPERS has also been designed to guarantee a
broader legacy, allowing detailed investigations of the properties and
evolutionary trends of z~1 galaxies. The survey strategy exploits the specific
advantages of the VIMOS spectrograph at the VLT, aiming at a final sample of
nearly 100,000 galaxy redshifts to iAB = 22.5 mag, which represents the largest
redshift survey ever performed with ESO telescopes. In this introductory
article we describe the survey construction, together with early results based
on a first sample of ~55,000 galaxies. | Macroscopic Dark Matter Constraints from Bolide Camera Networks: Macroscopic dark matter (macros) are a broad class of alternative candidates
to particle dark matter. These candidates would transfer energy primarily
through elastic scattering, and this linear energy deposition would produce
observable signals if a macro were to pass through the atmosphere. We produce
constraints for low mass macros from the null observation of bolides formed by
a passing macro, across two extensive networks of cameras built originally to
observe meteorites. The parameter space that could be probed with planned
upgrades to the existing array of cameras in one of these networks still
currently in use, the Desert Fireball Network in Australia, is estimated. |
The size--density relation of extragalactic HII regions: We investigate the size--density relation in extragalactic HII regions, with
the aim of understanding the role of dust and different physical conditions in
the ionized medium. First, we compiled several observational data sets for
Galactic and extragalactic HII regions and confirm that extragalactic HII
regions follow the same size (D)--density (n) relation as Galactic ones.
Motivated by the inability of static models to explain this, we then modelled
the evolution of the size--density relation of HII regions by considering their
star formation history, the effects of dust, and pressure-driven expansion. The
results are compared with our sample data whose size and density span roughly
six orders of magnitude. We find that the extragalactic size--density relation
does not result from an evolutionary sequence of HII regions but rather
reflects a sequence with different initial gas densities (``density
hierarchy''). Moreover, the size of many HII regions is limited by dust
absorption of ionizing photons, rather than consumption by ionizing neutral
hydrogen. Dust extinction of ionizing photons is particularly severe over the
entire lifetime of compact HII regions with typical gas densities of greater
than 10^3 cm^{-3}. Hence, as long as the number of ionizing photons is used to
trace massive star formation, much star-formation activity could be missed.
Such compact dense environments, the ones most profoundly obscured by dust,
have properties similar to ``maximum--intensity starbursts''. This implies that
submillimeter and infrared wavelengths may be necessary to accurately assess
star formation in these extreme conditions both locally and at high redshift. | Tachyonic Preheating in Plateau Inflation: Plateau inflation is an experimentally consistent framework in which the
scale of inflation can be kept relatively low. Close to the edge of the
plateau, scalar perturbations are subject to a strong tachyonic instability.
Tachyonic preheating is realized when, after inflation, the oscillating
inflaton repeatedly re-enters the plateau. We develop the analytic theory of
this process and expand the linear approach by including backreaction between
the coherent background and growing perturbations. For a family of plateau
models, the analytic predictions are confronted with numerical estimates. Our
analysis shows that the inflaton fragments in a fraction of an $e$-fold in all
examples supporting tachyonic preheating, generalizing the results of previous
similar studies. In these scenarios, the scalar-to-tensor ratio is tiny,
$r<10^{-7}$. |
Cosmology with Equivalence Principle Breaking in the Dark Sector: A long-range force acting only between nonbaryonic particles would be
associated with a large violation of the weak equivalence principle. We explore
cosmological consequences of this idea, which we label ReBEL (daRk Breaking
Equivalence principLe). A high resolution hydrodynamical simulation of the
distributions of baryons and dark matter confirms our previous findings that a
ReBEL force of comparable strength to gravity on comoving scales of about 1
Mpc/h causes voids between the concentrations of large galaxies to be more
nearly empty, suppresses accretion of intergalactic matter onto galaxies at low
redshift, and produces an early generation of dense dark matter halos. A
preliminary analysis indicates the ReBEL scenario is consistent with the
one-dimensional power spectrum of the Lyman-Alpha forest and the
three-dimensional galaxy auto-correlation function. Segregation of baryons and
DM in galaxies and systems of galaxies is a strong prediction of ReBEL. ReBEL
naturally correlates the baryon mass fraction in groups and clusters of
galaxies with the system mass, in agreement with recent measurements. | On the Heating Efficiency Derived from Observations of Young Super Star
Clusters in M82: Here we discuss the mechanical feedback that massive stellar clusters provide
to the interstellar medium of their host galaxy. We apply an analytic theory
developed in a previous study for M82-A1 to a sample of 10 clusters located in
the central zone of the starburst galaxy M82, all surrounded by compact and
dense HII regions. We claim that the only way that such HII regions can survive
around the selected clusters, is if they are embedded into a high pressure ISM
and if the majority of their mechanical energy is lost within the star cluster
volume via strong radiative cooling. The latter implies that these clusters
have a low heating efficiency, $\eta$, and evolve in the bimodal hydrodynamic
regime. In this regime the shock-heated plasma in the central zones of a
cluster becomes thermally unstable, loses its pressure and is accumulated
there, whereas the matter injected by supernovae and stellar winds outside of
this volume forms a high velocity outflow - the star cluster wind. We
calculated the heating efficiency for each of the selected clusters and found
that in all cases it does not exceed 10% . Such low heating efficiency values
imply a low mechanical energy output and the impact that the selected clusters
provide to the ISM of M82 is thus much smaller than what one would expect using
stellar cluster synthetic models. |
Contributions to the nonlinear integrated Sachs-Wolfe effect:
Birkinshaw-Gull effect and gravitational self-energy density: In this paper, we recompute contributions to the spectrum of the nonlinear
integrated Sachs-Wolfe (iSW)/Rees-Sciama effect in a dark energy cosmology.
Focusing on the moderate nonlinear regime, all dynamical fields involved are
derived from the density contrast in Eulerian perturbation theory. Shape and
amplitude of the resulting angular power spectrum are similar to that derived
in previous work. With our purely analytical approach we identify two distinct
contributions to the signal of the nonlinear iSW-effect: the change of the
gravitational self-energy density of the large scale structure with (conformal)
time and gravitational lenses moving with the large scale matter stream. In the
latter we recover the Birkinshaw-Gull effect. As the nonlinear iSW-effect
itself is inherently hard to detect, observational discrimination between its
individual contributions is almost excluded. Our analysis, however, yields
valuable insights into the theory of the nonlinear iSW-effect as a
post-Newtonian relativistic effect on propagating photons. | The Spitzer High Redshift Radio Galaxy Survey: We present results from a comprehensive imaging survey of 70 radio galaxies
at redshifts 1<z<5.2 using all three cameras onboard the Spitzer Space
Telescope. The resulting spectral energy distributions unambiguously show a
stellar population in 46 sources and hot dust emission associated with the
active nucleus in 59. Using a new restframe S_3um/S_1.6um versus S_um/S_3um
criterion, we identify 42 sources where the restframe 1.6um emission from the
stellar population can be measured. For these radio galaxies, the median
stellar mass is high, 2x10^11 M_sun, and remarkably constant within the range
1<z<3. At z>3, there is tentative evidence for a factor of two decrease in
stellar mass. This suggests that radio galaxies have assembled the bulk of
their stellar mass by z~3, but confirmation by more detailed decomposition of
stellar and AGN emission is needed.
The restframe 500 MHz radio luminosities are only marginally correlated with
stellar mass but are strongly correlated with the restframe 5um hot dust
luminosity. This suggests that the radio galaxies have a large range of
Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz
imaging of 14 radio galaxies and find that radio core dominance --- an
indicator of jet orientation --- is strongly correlated with hot dust
luminosity. While all of our targets were selected as narrow-lined, type 2
AGNs, this result can be understood in the context of orientation-dependent
models if there is a continuous distribution of orientations from obscured type
2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio
galaxies have nearby (<6") companions whose mid-IR colors are suggestive of
their being AGNs. This may indicate an association between radio galaxy
activity and major mergers. |
A Spectroscopic Search for Optical Emission Lines from Dark Matter Decay: We search for narrow-line optical emission from dark matter decay by stacking
dark-sky spectra from the Dark Energy Spectroscopic Instrument (DESI) at the
redshift of nearby galaxies from DESI's Bright Galaxy and Luminous Red Galaxy
samples. Our search uses regions separated by 5 to 20 arcsecond from the
centers of the galaxies, corresponding to an impact parameter of approximately
$50\,\rm kpc$. No unidentified spectral line shows up in the search, and we
place a line flux limit of
$10^{-19}\,\rm{ergs}/\rm{s}/\rm{cm}^{2}/\rm{arcsec}^{2}$ on emissions in the
optical band ($3000\lesssim\lambda\lesssim9000 \,\mathring{\rm A}$), which
corresponds to $34$ in AB magnitude in a normal broadband detection. This
detection limit suggests that the line surface brightness contributed from all
dark matter along the line of sight is two orders of magnitude lower than the
measured extragalactic background light (EBL), which rules out the possibility
that narrow optical-line emission from dark matter decay is a major source of
the EBL. | The Hunt for Primordial Interactions in the Large Scale Structures of
the Universe: The understanding of the primordial mechanism that seeded the cosmic
structures we observe today in the sky is one of the major goals in cosmology.
The leading paradigm for such a mechanism is provided by the inflationary
scenario, a period of violent accelerated expansion in the very early stages of
evolution of the Universe. While our current knowledge of the physics of
inflation is limited to phenomenological models which fit observations, an
exquisite understanding of the particle content and interactions taking place
during inflation would provide breakthroughs in our understanding of
fundamental physics at high energies. In this review, we summarize recent
theoretical progress in the modelling of the imprint of primordial interactions
in the large scale structures of the Universe. We focus specifically on the
effects of such interactions on the statistical distribution of dark matter
halos, providing a consistent treatment of the steps required to connect the
correlations generated among fields during inflation all the way to the
late-time correlations of halos. |
The Sloan Digital Sky Survey Peculiar Velocity Catalogue: We present a new catalogue of distances and peculiar velocities (PVs) of
$34,059$ early-type galaxies derived from Fundamental Plane (FP) measurements
using data from the Sloan Digital Sky Survey (SDSS). This
$7016\,\mathrm{deg}^{2}$ homogeneous sample comprises the largest set of
peculiar velocities produced to date and extends the reach of PV surveys up to
a redshift limit of $z=0.1$. Our SDSS-based FP distance measurements have a
mean uncertainty of 23%. Alongside the data, we produce an ensemble of 2,048
mock galaxy catalogues that reproduce the data selection function, and are used
to validate our fitting pipelines and check for systematic errors. We uncover a
significant trend between group richness and mean surface brightness within the
sample, which may hint at an environmental dependence within the FP or the
presence of unresolved systematics, and can result in biased peculiar
velocities. This is removed using multiple FP fits as function of group
richness, a procedure made tractable through a new analytic derivation for the
integral of a 3D Gaussian over non-trivial limits. Our catalogue is calibrated
to the zero-point of the CosmicFlows-III sample with an uncertainty of $0.004$
dex (not including cosmic variance or the error within CosmicFlows-III itself),
which is validated using independent cross-checks with the predicted zero-point
from the 2M++ reconstruction of our local velocity field. Finally, as an
example of what is possible with our new catalogue, we obtain preliminary bulk
flow measurements up to a depth of $135\,h^{-1}\mathrm{Mpc}$. We find a
slightly larger-than-expected bulk flow at high redshift, although this could
be caused by the presence of the Shapley supercluster which lies outside the
SDSS PV footprint. | Toy Models for Galaxy Formation versus Simulations: We describe simple useful toy models for key processes of galaxy formation in
its most active phase, at z > 1, and test the approximate expressions against
the typical behaviour in a suite of high-resolution hydro-cosmological
simulations of massive galaxies at z = 4-1. We address in particular the
evolution of (a) the total mass inflow rate from the cosmic web into galactic
haloes based on the EPS approximation, (b) the penetration of baryonic streams
into the inner galaxy, (c) the disc size, (d) the implied steady-state gas
content and star-formation rate (SFR) in the galaxy subject to mass
conservation and a universal star-formation law, (e) the inflow rate within the
disc to a central bulge and black hole as derived using energy conservation and
self-regulated Q ~ 1 violent disc instability (VDI), and (f) the implied steady
state in the disc and bulge. The toy models provide useful approximations for
the behaviour of the simulated galaxies. We find that (a) the inflow rate is
proportional to mass and to (1+z)^5/2, (b) the penetration to the inner halo is
~50% at z = 4-2, (c) the disc radius is ~5% of the virial radius, (d) the
galaxies reach a steady state with the SFR following the accretion rate into
the galaxy, (e) there is an intense gas inflow through the disc, comparable to
the SFR, following the predictions of VDI, and (f) the galaxies approach a
steady state with the bulge mass comparable to the disc mass, where the
draining of gas by SFR, outflows and disc inflows is replenished by fresh
accretion. Given the agreement with simulations, these toy models are useful
for understanding the complex phenomena in simple terms and for
back-of-the-envelope predictions. |
Reconstructing homospectral inflationary potentials: Purely geometrical arguments show that there exist classes of homospectral
inflationary cosmologies, i.e. different expansion histories producing the same
spectrum of comoving curvature perturbations. We develop a general algorithm to
reconstruct the potential of minimally-coupled single scalar fields from an
arbitrary expansion history. We apply it to homospectral expansion histories to
obtain the corresponding potentials, providing numerical and analytical
examples. The infinite class of homospectral potentials depends on two free
parameters, the initial energy scale and the initial value of the field,
showing that in general it is impossible to reconstruct a unique potential from
the curvature spectrum unless the initial energy scale and the field value are
fixed, for instance through observation of primordial gravitational waves. | Emission Corrections for Hydrogen Features of the Graves et. al 2007
Sloan Digital Sky Survey Averages of Early Type, Non-liner Galaxies: For purposes of stellar population analysis, emission corrections for Balmer
series indices on the Lick index system in Sloan Digital Sky Survey (SDSS)
stacked quiescent galaxy spectra are derived, along with corrections for
continuum shape and gross stellar content, as a function of the Mg $b$ Lick
index strength. These corrections are obtained by comparing the observed Lick
index measurements of the SDSS with new observed measurements of 13 Virgo
Cluster galaxies, and checked with model grids. From the H$\alpha$ Mg $b$
diagram a linear correction for the observed measurement is constructed using
best fit trend lines. Corrections for H$\beta$, H$\gamma$ and H$\delta$ are
constructed using stellar population models to predict continuum shape changes
as a function of Mg $b$ and Balmer series emission intensities typical of H{\sc
II} regions. The corrections themselves are fairly secure, but the
interpretation for H$\delta$ and H$\gamma$ indices is complicated by the fact
that the H$\delta$ and H$\gamma$ indices are sensitive to elemental abundances
other than hydrogen. |
Peaks and primordial black holes: the effect of non-Gaussianity: In light of recent developments in the field, we re-evaluate the effect of
local-type non-Gaussianity on the primordial black hole (PBH) abundance (and
consequently, upon constraints on the primordial power spectrum arising from
PBHs). We apply peaks theory to the full, non-linear compaction, finding that,
whilst the effect of non-Gaussianity is qualitatively similar to previous
findings, the effect is much less significant. It is found the non-Gaussianity
parameters $f_\mathrm{NL}^\mathrm{local}$ and $g_\mathrm{NL}^\mathrm{local}$
typically need to be approximately 1 or 2 orders of magntiude larger
respectively to have a similar to that previously found. The effect will be to
weaken the dependance of PBH constraints on the primordial power spectrum on
the non-Gaussianity parameters, as well as to dramatically weaken constraints
on the non-Gaussianity parameters (and/or PBH abundance) arising from the
non-observation of dark matter isocurvature modes. We also consider the
correlation between the curvature perturbation $\zeta$ and the compaction $C$,
finding that, whilst PBHs may form at rare peaks in $C$ these do not
necessarily correspond to rare peaks in $\zeta$ - casting some doubt on many of
the existing calculations of the PBH abundance. | Getting more out of V/Vm than just the mean: Banhatti (2009) set down the procedure to derive cosmological number density
n(z) from the differential distribution p(x) of the fractional luminosity
volume relative to the maximum volume, x \equiv V/Vm (0 \leq x \leq 1), using a
small sample of 76 quasars for illustrative purposes. This procedure is here
applied to a bigger sample of 286 quasars selected from Parkes half-Jansky
flat-spectrum survey at 2.7 GHz (Drinkwater et al 1997). The values of n(z) are
obtained for 8 values of redshift z from 0 to 3.5. The function n(z) can be
interpreted in terms of redshift distribution obtained by integrating the radio
luminosity function {\rho}(P, z) over luminosities P for the survey limiting
flux density S0 = 0.5 Jy. Keywords. V/Vm - luminosity-volume - cosmological
number density - redshift distribution - luminosity function - quasars [Note:
This somewhat modified version was submitted to MNRaS on 14 July 2016. It was
(almost) rejected, except if thoroughly revised.] |
Tidal Stirring of Disky Dwarfs with Shallow Dark Matter Density
Profiles: Enhanced Transformation into Dwarf Spheroidals: (Abridged) The origin of dSphs in the Local Group (LG) remains an enigma. The
tidal stirring model posits that late-type, rotationally-supported dwarfs
resembling present-day dwarf irregular (dIrr) galaxies can transform into dSphs
via interactions with Milky Way-sized hosts. Using collisionless N-body
simulations, we investigate for the first time how tidal stirring depends on
the dark matter (DM) density distribution in the central stellar region of the
progenitor disky dwarf. Specifically, we explore various asymptotic inner
slopes gamma of the dwarf DM density profiles (rho \propto r^{-gamma} as r ->
0). For a given orbit inside the primary, rotationally-supported dwarfs
embedded in DM halos with core-like density distributions (gamma = 0.2) and
mild density cusps (gamma = 0.6) demonstrate a substantially enhanced
likelihood and efficiency of transformation into dSphs compared to their
counterparts with steeper DM density profiles (gamma = 1). Such shallow DM
distributions are akin to those of observed dIrrs, highlighting tidal stirring
as a plausible model for the LG morphology-density relation. When gamma <1, a
single pericentric passage can induce dSph formation and disky dwarfs on
low-eccentricity or large-pericenter orbits are able to transform into dSphs;
these new results allow the tidal stirring model to explain the existence of
virtually all known dSphs across a wide range of distances from their hosts. A
subset of rotationally-supported dwarfs with gamma <1 are eventually disrupted
by the primary; those that survive as dSphs are generally on orbits that are
biased towards lower eccentricities and/or larger pericenters relative to those
of typical CDM satellites. The latter could explain the rather peculiar orbits
of several classic LG dSphs such as Fornax, Leo I, Tucana, and Cetus. | Prospects of High-Resolution X-ray Spectroscopy for AGN Feedback in
Galaxy Clusters: One of the legacies of the {\rm Chandra} era is the discovery of AGN-inflated
X-ray cavities in virtually all cool-core clusters, with mechanical
luminosities comparable to or larger than the cluster cooling rate, suggesting
that AGN might be responsible for heating clusters. This discovery poses a new
set of questions that cannot be addressed by X-ray imaging or modeling alone:
Are AGN actually responsible for halting cooling flows? How is the AGN energy
transferred to heat? How tight is the observed balance between heating and
cooling? Using numerical simulations and a new virtual X-ray observatory tool,
we demonstrate that high-resolution, high-throughput X-ray spectroscopy can
address these questions and that the International X-ray Observatory \ixo will
have the necessary capabilities to deliver these measurements. |
Local alignments of parsec-scale AGN radiojets: Context.Coherence in the characteristics of neighboring sources in 2D and 3D
space may suggest the existence of large-scale cosmic structures, which are
useful for cosmological studies. Numerous works have been conducted to detect
such features in global scalesas well as in confined areas of the sky. However,
results are often contradictory and their interpretation remains controversial.
Aims.We investigate the potential alignment of parsec-scale radio jets in
localized regions of the coordinates-redshift space. Methods.We use data from
the Astrogeo VLBI FITS image database to deduce jet directions of radio
sources. We perform the search for statistical alignments between nearby
sources and explore the impact of instrumental biases. Results.We unveil four
regions for which the alignment between jet directions deviates from randomness
at a significance level of more than 5 sigma and is unlikely due to
instrumental systematics. Intriguingly, their locations coincide with other
known large-scale cosmic structures and/or regions of alignments.
Conclusions.If the alignments found are the result of physical processes, the
discovered regions may designate some of the largest structures known to date. | Observational Constraints on the Cosmology with Holographic Dark Fluid: We consider the holographic Friedman-Robertson-Walker (hFRW) universe on the
4-dimensional membrane embedded in the 5-dimensional bulk spacetime and fit the
parameters with the observational data. In order to fully account for the
phenomenology of this scenario, we consider the models with the brane
cosmological constant and the negative bulk cosmological constant. The
contribution from the bulk is represented as the holographic dark fluid on the
membrane. We derive the universal modified Friedmann equation by including all
of these effects in both braneworld and holographic cutoff approaches. For
three specific models, namely, the pure hFRW model, the one with the brane
cosmological constant, and the one with the negative bulk cosmological
constant, we compare the model predictions with the observations. The
parameters in the considered hFRW models are constrained with observational
data. In particular, it is shown that the model with the brane cosmological
constant can fit data as well as the standard $\Lambda$CDM universe. We also
find that the $\sigma_8$ tension observed in different large-structure
experiments can be effectively relaxed in this holographic scenario. |
Large-scale Stability and Astronomical Constraints for Coupled
Dark-Energy Models: We study large-scale inhomogeneous perturbations and instabilities of
interacting dark energy (IDE) models. Past analysis of large-scale perturbative
instabilities, has shown that we can only test IDE models with observational
data when its parameter ranges are either $w_{x}\geq -1$ and $\xi \geq 0,$ or
$w_{x}\leq -1~$ and $~\xi \leq 0$, where $w_{x}$ is the dark energy equation of
state (EoS), and $\xi$ is a coupling parameter governing the strength and
direction of the energy transfer. We show that by adding a factor $(1+w_{x})$
to the background energy transfer, the whole parameter space can be tested
against all the data and thus, the instabilities in such interaction models can
be removed. We test three classes of interaction model using the latest
astronomical data from different sources. Precise constraints are found. Our
analysis shows that a very small but non-zero deviation from pure
$\Lambda$-cosmology is suggested by the observational data while the
no-interaction scenario can be recovered at the 68.3% confidence-level. In
particular, for three IDE models, identified as IDE 1, IDE 2, and IDE 3, the
68.3% CL constraints on the interaction coupling strengths are, $\xi=
0.0360_{-0.0360}^{+0.0091}$ (IDE 1), $\xi= 0.0433_{-0.0433}^{+0.0062}$ (IDE 2),
$\xi= 0.1064_{-0.1064}^{+0.0437}$ (IDE 3). In addition, we find that the dark
energy EoS tends towards the phantom region taking the 68.3% CL constraints,
$w_x= -1.0230_{-0.0257}^{+0.0329}$ (IDE 1), $w_x= -1.0247_{-0.0302}^{+0.0289}$
(IDE 2), and $w_x= -1.0275_{-0.0318}^{+0.0228}$ (IDE 3). However, the
possibility of $w_{x}>-1$ is also not rejected by the astronomical data used
here. Moreover, we find in all IDE models that, as the value of Hubble constant
decreases, the behavior of the dark energy EoS shifts from phantom to
quintessence type with its EoS very close to that a simple cosmological
constant at the present time. | Screened fifth forces lower the TRGB-calibrated Hubble constant too: The local distance ladder measurement of the Hubble constant requires a
connection between geometric distances at low redshift and Type Ia supernovae
in the Hubble flow, which may be achieved through either the Cepheid
period--luminosity relation or the luminosity of the Tip of the Red Giant
Branch (TRGB) feature of the Hertzsprung--Russell diagram. Any potential
solution to the Hubble tension that works by altering the distance ladder must
produce consistency of both the Cepheid and TRGB $H_0$ calibrations with the
CMB. In this paper we extend our models of screened fifth forces (Desmond et al
2019) to cover the TRGB framework. A fifth force lowers TRGB luminosity, so a
reduction in inferred $H_0$ requires that the stars that calibrate the
luminosity---currently in the LMC---are on average less screened than those
that calibrate the supernova magnitude. We show that even under pessimistic
assumptions for the extinction to the LMC, full consistency with Planck can be
achieved for a fifth force strength in unscreened RGB stars $\sim$0.2 that of
Newtonian gravity. This is allowed by the comparison of Cepheid and TRGB
distance measurements to nearby galaxies. Our results indicate that the
framework of Desmond et al (2019) is more versatile than initially
demonstrated, capable of ameliorating the Hubble tension on a second front. |
The Power Spectrum of Cosmological Number Densities: We study the cosmological power spectra (PS) of the differential and integral
galaxy volume number densities $\gamma_i$ and $\gamma_i^{*}$, constructed with
the cosmological distances $d_i$ $(i=A,G,L,Z)$, where $d_A$ is the angular
diameter distance, $d_G$ is the galaxy area distance, $d_L$ is the luminosity
distance and $d_z$ is the redshift distance. Theoretical and observational
quantities were obtained in the FLRW spacetime with a non-vanishing $\Lambda$.
The radial correlation $\Xi_i$, as defined in the context of these densities,
is discussed in the wave number domain. All observational quantities were
computed using luminosity function (LF) data obtained from the FORS Deep Field
galaxy survey. The theoretical and observational PS of $\gamma_i$,
$\gamma_i^{\ast}$, $\Xi_i$ and $\gamma_i / \gamma_i^\ast$ were calculated by
performing Fourier transforms on these densities previously derived by
Iribarrem et al. (2012) from the observed values $\gamma_{obs}$ and
${\gamma^\ast}_{obs}$ obtained using the galactic absolute magnitudes and
galaxy LF Schechter's parameters presented in Gabasch et al. (2004, 2006) in
the range $0.5 \le z \le5.0$. The results show similar behavior of the PS
obtained from $\gamma$ and $\gamma^{\ast}$ using $d_L$, $d_z$ and $d_G$ as
distance measures. The PS of the densities defined with $d_A$ have a different
and inconclusive behavior, as this cosmological distance reaches a maximum at
$z\approx 1.6$ in the adopted cosmology. For the other distances, our results
suggest that the PS of ${\gamma_i}_{obs}$, ${\gamma^\ast_i}_{obs}$ and
${\gamma_i / \gamma^{\ast}_i}_{obs}$ have a general behavior approximately
similar to the PS obtained with the galaxy two-point correlation function and,
by being sample size independent, they may be considered as alternative
analytical tools to study the galaxy distribution. | Testing Einstein Gravity with Cosmic Growth and Expansion: We test Einstein gravity using cosmological observations of both expansion
and structure growth, including the latest data from supernovae (Union2.1), CMB
(WMAP7), weak lensing (CFHTLS) and peculiar velocity of galaxies (WiggleZ). We
fit modified gravity parameters of the generalized Poisson equations
simultaneously with the effective equation of state for the background
evolution, exploring the covariances and model dependence. The results show
that general relativity is a good fit to the combined data. Using a Pad{\'e}
approximant form for the gravity deviations accurately captures the time and
scale dependence for theories like $f(R)$ and DGP gravity, and weights high and
low redshift probes fairly. For current observations, cosmic growth and
expansion can be fit simultaneously with little degradation in accuracy, while
removing the possibility of bias from holding one aspect fixed. |
Self-supervised component separation for the extragalactic submillimeter
sky: We use a new approach based on self-supervised deep learning networks
originally applied to transparency separation in order to simultaneously
extract the components of the extragalactic submillimeter sky, namely the
cosmic microwave background (CMB), the cosmic infrared background (CIB), and
the Sunyaev-Zel'dovich (SZ) effect. In this proof-of-concept paper, we test our
approach on the WebSky extragalactic simulation maps in a range of frequencies
from 93 to 545 GHz, and compare with one of the state-of-the-art traditional
methods, MILCA, for the case of SZ. We first visually compare the images, and
then statistically analyse the full-sky reconstructed high-resolution maps with
power spectra. We study the contamination from other components with cross
spectra, and particularly emphasise the correlation between the CIB and the SZ
effect and compute SZ fluxes around positions of galaxy clusters. The
independent networks learn how to reconstruct the different components with
less contamination than MILCA. Although this is tested here in an ideal case
(without noise, beams, or foregrounds), this method shows significant potential
for application in future experiments such as the Simons Observatory (SO) in
combination with the Planck satellite. | Revisiting the He II to H I ratio in the Intergalactic Medium: We estimate the He II to H I column density ratio, \eta = N(He II)/N(H I), in
the intergalactic medium towards the high redshift (z_{em} = 2.885) bright
quasar QSO HE 2347-4342 using Voigt-profile fitting of the H I transitions in
the Lyman series and the He II Lyman-$\alpha$ transition as observed by the
FUSE satellite. In agreement with previous studies, we find that $\eta > 50$ in
most of the Lyman-$\alpha$ forest except in four regions where it is much
smaller ($\eta \sim 10-20$) and therefore inconsistent with photo-ionization by
the UV background flux. We detect O VI and C IV absorption lines associated
with two of these regions ($z_{\rm abs}$ = 2.6346 and 2.6498). We show that if
we constrain the fit of the H I and/or He II absorption profiles with the
presence of metal components, we can accommodate $\eta$ values in the range
15-100 in these systems assuming broadening is intermediate between pure
thermal and pure turbulent. While simple photo-ionization models reproduce the
observed N(O VI)/N(C IV) ratio, they fail to produce low $\eta$ values contrary
to models with high temperature (i.e T $\ge 10^5$ K). The Doppler parameters
measured for different species suggest a multiphase nature of the absorbing
regions. Therefore, if low $\eta$ values were to be confirmed, we would favor a
multi-phase model in which most of the gas is at high temperature ($>$ 10$^5$
K) but the metals and in particular C IV are due to lower temperature ($\sim$
few $10^4$ K) photo-ionized gas. |
Topological acceleration in relativistic cosmology: Heuristic approaches in cosmology bypass more difficult calculations that
would more strictly agree with the standard Einstein equation. These give us
the well-known Friedmann-Lemaitre-Robertson-Walker (FLRW) models, and, more
recently, the feedback effect of the global topology of spatial sections on the
acceleration of test particles. Forcing the FLRW heuristic model on
observations leads to dark energy, which, pending fully relativistic
calculations, is best interpreted as an artefact. Could topological
acceleration also be an artefact of using a heuristic approach? A multiply
connected exact solution of the Einstein equation shows that topological
acceleration is present in at least one fully relativistic case---it is not an
artefact of Newtonian-like thinking. | Effects of time-varying $β$ in SNLS3 on constraining interacting
dark energy models: It has been found that, for the Supernova Legacy Survey three-year (SNLS3)
data, there is strong evidence for the redshift-evolution of color-luminosity
parameter $\beta$. In this paper, adopting the $w$-cold-dark-matter ($w$CDM)
model and considering its interacting extensions (with three kinds of
interaction between dark sectors), we explore the evolution of $\beta$ and its
effects on parameter estimation. In addition to the SNLS3 data, we also take
into account the Planck distance priors data of the cosmic microwave background
(CMB), the galaxy clustering (GC) data extracted from SDSS DR7 and BOSS, as
well as the direct measurement of Hubble constant from the Hubble Space
Telescope (HST) observation. We find that, for all the interacting dark energy
(IDE) models, adding a parameter of $\beta$ can reduce $\chi^2$ by $\sim$ 34,
indicating that $\beta_1 = 0$ is ruled out at 5.8$\sigma$ confidence level
(CL). Furthermore, it is found that varying $\beta$ can significantly change
the fitting results of various cosmological parameters: for all the dark energy
models considered in this paper, varying $\beta$ yields a larger $\Omega_{c0}$
and a larger $w$; on the other side, varying $\beta$ yields a smaller $h$ for
the $w$CDM model, but has no impact on $h$ for the three IDE models. This
implies that there is a degeneracy between $h$ and $\gamma$. Our work shows
that the evolution of $\beta$ is insensitive to the interaction between dark
sectors, and then highlights the importance of considering $\beta$'s evolution
in the cosmology fits. |
Paradigms and Scenarios for the Dark Matter Phenomenon: Well known scaling laws among the structural properties of the dark and the
luminous matter in disc systems are too complex to be arisen by two inert
components that just share the same gravitational field. This brings us to
critically focus on the 30-year-old paradigm, that, resting on a priori
knowledge of the nature of Dark Matter (DM), has led us to a restricted number
of scenarios, especially favouring the collisionless $\Lambda$ Cold Dark Matter
one. Motivated by such observational evidence, we propose to resolve the dark
matter mystery by following a new Paradigm: the nature of DM must be
guessed/derived by deeply analyzing the properties of the dark and luminous
mass distribution at galactic scales. The immediate application of this
paradigm leads us to propose the existence of a direct interaction between Dark
and Standard Model particles, which has finely shaped the inner regions of
galaxies. | Predicted Constraints on Cosmic String Tension from Planck and Future
CMB Polarization Measurements: We perform a Fisher matrix calculation of the predicted uncertainties on
estimates of the cosmic string tension Gmu from upcoming observational data
(namely, cosmic microwave background power spectra from the Planck satellite
and an idealized future polarization experiment). We employ simulations that
are more general than others commonly used in the literature, leaving the mean
velocity of strings, correlation length of the string network, and "wiggliness"
(which parametrizes smaller-scale structure along the strings) as free
parameters that can be observationally measured. In a new code, StringFast, we
implement a method for efficient computation of the C_l spectra induced by a
network of strings, which is fast enough to be used in Markov Chain Monte Carlo
analyses of future data. Performing a calculation with the string parameters
left free results in projected constraints on Gmu that are larger than those
obtained by fixing their values a priori, typically by a factor of ~2-7. We
also find that if Gmu is equal to the current observational maximum, Planck
will be able to make a confident detection of strings. However, if Gmu is two
orders of magnitude smaller, even a perfect, lensing-free measurement of
polarization power spectra will not be able to detect a nonzero string tension
at better than 2 sigma confidence. |
Accuracy requirements to test the applicability of the random cascade
model to supersonic turbulence: A model, which is widely used for inertial rang statistics of supersonic
turbulence in the context of molecular clouds and star formation, expresses
(measurable) relative scaling exponents Z_p of two-point velocity statistics as
a function of two parameters, beta and Delta. The model relates them to the
dimension D of the most dissipative structures, D=3-Delta/(1-beta). While this
description has proved most successful for incompressible turbulence
(beta=Delta=2/3, and D=1), its applicability in the highly compressible regime
remains debated. For this regime, theoretical arguments suggest D=2 and
Delta=2/3, or Delta=1. Best estimates based on 3D periodic box simulations of
supersonic isothermal turbulence yield Delta=0.71 and D=1.9, with uncertainty
ranges of Delta in [0.67, 0.78] and D in [2.04,1.60]. With these 5-10\%
uncertainty ranges just marginally including the theoretical values of
Delta=2/3 and D=2, doubts remain whether the model indeed applies and, if it
applies, for what values of beta and Delta. We use a Monte Carlo approach to
mimic actual simulation data and examine what factors are most relevant for the
fit quality. We estimate that 0.1% (0.05%) accurate Z_p, with p=1...5, should
allow for 2% (1%) accurate estimates of beta and Delta in the highly
compressible regime, but not in the mildly compressible regime. We argue that
simulation-based Z_p with such accuracy are within reach of today's computer
resources. If this kind of data does not allow for the expected high quality
fit of beta and Delta, then this may indicate the inapplicability of the model
for the simulation data. In fact, other models than the one we examine here
have been suggested. | Inflation with strongly non-geodesic motion: theoretical motivations and
observational imprints: A new class of inflationary attractors characterized by a strongly
non-geodesic motion has been discovered and explored in the past few years. I
describe how they naturally arise in negatively curved field space, allowing to
inflate on potentials that are steep in Planck units, albeit without
alleviating the ever-present naturalness issue of inflation. In these
scenarios, fluctuations often experience a transient tachyonic instability,
which can be described by a single-field effective field theory with an
imaginary speed of sound. Independently of the precise ultraviolet origin of
the latter, this leaves a peculiar imprint in the form of a high-level of
primordial non-Gaussianities of flattened type for all higher-order correlation
functions. On small scales, a transient phase of strongly non-geodesic motion
provides a mechanism to generate primordial black holes and can leave specific
signatures in the form of oscillations in the frequency profile of the
stochastic gravitational wave background. |
Visibility-based Power Spectrum Estimation for Low-Frequency Radio
Interferometric Observations: We present a visibility based estimator namely, the Tapered Gridded Estimator
(TGE) to estimate the power spectrum of the diffuse sky signal. The TGE has
three novel features. First, the estimator uses gridded visibilities to
estimate the power spectrum which is computationally much faster than
individually correlating the visibilities. Second, a positive noise bias is
removed by subtracting the auto-correlation of the visibilities which is
responsible for the noise bias. Third, the estimator allows us to taper the
field of view so as to suppress the contribution from the sources in the outer
regions and the sidelobes of the telescope's primary beam. We first consider
the two dimensional (2D) TGE to estimate the angular power spectrum $C_{\ell}$.
We have also extended the TGE to estimate the three dimensional (3D) power
spectrum $P({\bf k})$ of the cosmological 21-cm signal. Analytic formulas are
presented for predicting the variance of the binned power spectrum. Both the
estimators and their variance predictions are validated using simulations of
$150 \, {\rm MHz}$ GMRT observations. We have applied the 2D TGE to estimate
$C_{\ell}$ using visibility data for two of the fields observed by TIFR GMRT
Sky Survey (TGSS). We find that the sky signal, after subtracting the point
sources, is likely dominated by the diffuse Galactic synchrotron radiation
across the angular multipole range $240 \le \ell \lesssim 500$. | Lens models and magnification maps of the six Hubble Frontier Fields
clusters: We present strong-lensing models, as well as mass and magnification maps, for
the cores of the six HST Frontier Fields galaxy clusters. Our parametric lens
models are constrained by the locations and redshifts of multiple image systems
of lensed background galaxies. We use a combination of photometric redshifts
and spectroscopic redshifts of the lensed background sources obtained by us
(for Abell 2744 and Abell S1063), collected from the literature, or kindly
provided by the lensing community. Using our results, we (1) compare the
derived mass distribution of each cluster to its light distribution, (2)
quantify the cumulative magnification power of the HFF clusters, (3) describe
how our models can be used to estimate the magnification and image multiplicity
of lensed background sources at all redshifts and at any position within the
cluster cores, and (4) discuss systematic effects and caveats resulting from
our modeling methods. We specifically investigate the effect of the use of
spectroscopic and photometric redshift constraints on the uncertainties of the
resulting models. We find that the photometric redshift estimates of lensed
galaxies are generally in excellent agreement with spectroscopic redshifts,
where available. However, the flexibility associated with relaxed redshift
priors may cause the complexity of large-scale structure that is needed to
account for the lensing signal to be underestimated. Our findings thus
underline the importance of spectroscopic arc redshifts, or tight photometric
redshift constraints, for high precision lens models.
All products from our best-fit lens models (magnification, convergence,
shear, deflection field) and model simulations for estimating errors are made
available via the Mikulski Archive for Space Telescopes. |
A probabilistic framework for cosmological inference of peculiar
velocities: We present a Bayesian hierarchical framework for a principled data analysis
pipeline of peculiar velocity surveys, which makes explicit the inference
problem of constraining cosmological parameters from redshift-independent
distance indicators. We demonstrate our method for a Fundamental Plane-based
survey. The essence of our approach is to work closely with observables (e.g.
angular size, surface brightness, redshift, etc), through which we bypass the
use of summary statistics by working with the probability distributions. The
hierarchical approach improves upon the usual analysis in several ways. In
particular, it allows a consistent analysis without having to make prior
assumptions about cosmology during the calibration phase. Moreover, calibration
uncertainties are correctly accounted for in parameter estimation. Results are
presented for a new, fully analytic posterior marginalised over all latent
variables, which we expect to allow for more principled analyses in upcoming
surveys. A maximum a posteriori estimator is also given for peculiar velocities
derived from Fundamental Plane data. | New method to revisit the gravitational lensing analysis of the Bullet
Cluster using radio waves: Gravitational lensing studies of the Bullet Cluster suggested convincingly in
favor of the existence of dark matter. However, it was performed without the
knowledge of the original orientation of each galaxy before gravitational
lensing. A potential improvement to this issue lies in the measurement of the
original orientation from the polarization direction of radio waves emitted
from each galaxy. In this context, Francfort et al. derived a formula that can
utilize the information about the original orientation of each galaxy to obtain
what is called {\it shear}. However, we demonstrate that shear in their formula
should be replaced by {\it reduced shear} when the change in sizes of images of
galaxies is taken into account. As the previous gravitational lensing analysis
of the Bullet Cluster used reduced shear, we suggest applying our improved
formula directly for the reanalysis once we obtain the polarization direction
of radio waves. In particular, we show that our new formula can yield a more
accurate analysis than the previous one, if the polarization direction can be
measured more precisely than $10^\circ$. Moreover, the approach discussed in
this work is generically applicable to the gravitational lensing analysis of
clusters, not only limited to the Bullet Cluster. |
Signatures of First Stars in Galaxy Surveys: Multi-Tracer Analysis of
the Supersonic Relative Velocity Effect and the Constraints from the BOSS
Power Spectrum Measurements: We study the effect of the supersonic relative velocity between dark matter
and baryons on large-scale galaxy clustering and derive the constraint on the
relative velocity bias parameter from the Baryonic Oscillation Spectroscopic
Survey (BOSS) power spectrum measurements. Recent work has shown that the
relative velocity effect may have a dramatic impact on the star formation at
high redshifts, if first stars are formed in minihalos around z~20, or if the
effect propagates through secondary effects to stars formed at later redshifts.
The relative velocity effect has particularly strong signatures in the large
scale clustering of these sources, including the BAO position. Assuming that a
small fraction of stars in low-redshift massive galaxies retain the memory of
the primordial relative velocity effect, galaxy clustering measurements can be
used to constrain the signatures of the first stars. Luminous red galaxies
contain some of the oldest stars in the Universe and are ideally suited to
search for this effect. Using the BOSS power spectrum measurements from the
Sloan Data Release 9, in combination with Planck, we derive the upper limit on
the fraction of the stars sensitive to relative velocity effect f_star<3.3% at
the 95% confidence level in the CMASS galaxy sample. If additional galaxy
sample not sensitive to the effect is available in a given survey, a joint
multi-tracer analysis can be applied to construct a sample-variance cancelling
combination, providing a model-independent way to verify the presence of the
relative velocity effect in the galaxy power spectrum on large scales. Such a
multi-tracer analysis in future galaxy surveys can greatly improve the current
constraint, achieving a 0.1% level in f_star. | The copula of the cosmological matter density field is non-Gaussian: Non-Gaussianity of the cosmological matter density field can be largely
reduced by a local Gaussianization transformation (and its approximations such
as the logrithmic transformation). Such behavior can be recasted as the
Gaussian copula hypothesis, and has been verified to very high accuracy at
two-point level. On the other hand, statistically significant non-Gaussianities
in the Gaussianized field have been detected in simulations. We point out that,
this apparent inconsistency is caused by the very limited degrees of freedom in
the copula function, which make it misleading as a diagnosis of residual
non-Gaussianity in the Gaussianized field. Using the copula density, we
highlight the departure from Gaussianity. We further quantify its impact in the
predicted n-point correlation functions. We explore a remedy of the Gaussian
copula hypothesis, which alleviates but not completely solves the above
problems. |
Conserved cosmological perturbations in USR inflation and bouncing
scenarios: Inflationary and bouncing scenarios are two frameworks that provide the
mechanism to overcome the horizon problem as well as generate the primordial
perturbations. In this work, we investigate the conservation of perturbations
in single-field models of both inflationary and bouncing scenarios, where the
quantity, $z = a \, \rm d \phi/{\rm d}\log a$, with $a$ representing the scale
factor and $\phi$ denoting the scalar field, decreases with time. We observe
that this behaviour occurs during the ultra-slow-roll phase in the context of
inflation and the contracting phase in the context of bounce. We show that the
conjugate momentum associated with the comoving curvature perturbation during
both the ultra-slow-roll phase and the contracting phase of bouncing scenarios
is conserved in the super-Hubble limit. We illustrate that, within the
framework of inflation, this conservation of momentum allows for the evolution
of perturbations across the ultra-slow-roll phase, enabling the calculation of
the power spectrum for modes that exit the Hubble radius before the
ultra-slow-roll phase begins. Similarly, in the context of a bounce, we can
determine the power spectrum after the bounce using this method. We support our
approach with both numerical and analytical arguments. | Simulations on a Moving Mesh: The Clustered Formation of Population III
Protostars: The cosmic dark ages ended a few hundred million years after the Big Bang,
when the first stars began to fill the universe with new light. It has
generally been argued that these stars formed in isolation and were extremely
massive - perhaps 100 times as massive as the Sun. In a recent study, Clark and
collaborators showed that this picture requires revision. They demonstrated
that the accretion disks that build up around Population III stars are strongly
susceptible to fragmentation and that the first stars should therefore form in
clusters rather than in isolation. We here use a series of high-resolution
hydrodynamical simulations performed with the moving mesh code AREPO to follow
up on this proposal and to study the influence of environmental parameters on
the level of fragmentation. We model the collapse of five independent minihalos
from cosmological initial conditions, through the runaway condensation of their
central gas clouds, to the formation of the first protostar, and beyond for a
further 1000 years. During this latter accretion phase, we represent the
optically thick regions of protostars by sink particles. Gas accumulates
rapidly in the circumstellar disk around the first protostar, fragmenting
vigorously to produce a small group of protostars. After an initial burst,
gravitational instability recurs periodically, forming additional protostars
with masses ranging from ~ 0.1 to 10 M_sun. Although the shape, multiplicity,
and normalization of the protostellar mass function depend on the details of
the sink-particle algorithm, fragmentation into protostars with diverse masses
occurs in all cases, confirming earlier reports of Population III stars forming
in clusters. Depending on the efficiency of later accretion and merging,
Population III stars may enter the main sequence in clusters and with much more
diverse masses than are commonly assumed. |
A Foreground Model Independent Bayesian CMB Temperature and Polarization
Signal Reconstruction and Cosmological Parameter Estimation over Large
Angular Scales: Recent CMB observations have resulted in very precise observational data. A
robust and reliable CMB reconstruction technique can lead to efficient
estimation of the cosmological parameters. We demonstrate the performance of
our methodology using simulated temperature and polarization observations using
cosmic variance limited future generation PRISM satellite mission. We generate
samples from the joint distribution by implementing the CMB inverse covariance
weighted internal-linear-combination (ILC) with the Gibbs sampling technique.
We use the Python Sky Model (PySM), d4f1s1 to generate the realistic foreground
templates. The synchrotron emission is parametrized by a spatially varying
spectral index, whereas the thermal dust emission is described as a
two-component dust model. We estimate the marginalized densities of CMB signal
and theoretical angular power spectrum utilizing the samples from the entire
posterior distribution. The best-fit cleaned CMB map and the corresponding
angular power spectrum are consistent with the CMB realization and the sky
angular power spectrum, implying an efficient foreground minimized
reconstruction. The likelihood function estimated by making use of the
Blackwell-Rao estimator is used for the estimation of the cosmological
parameters. Our methodology can estimate the tensor to scalar ratio $r\ge
0.0075$ for the chosen foreground models and the instrumental noise levels. Our
current work demonstrates an analysis pipeline starting from the reliable
estimation of CMB signal and its angular power spectrum to the case of
cosmological parameter estimation using the foreground model independent
Gibbs-ILC method. | X-ray Binaries and Star Clusters in the Antennae: Optical Cluster
Counterparts: We compare the locations of 82 X-ray binaries (XRBs) detected in the merging
Antennae galaxies by Zezas et al., based on observations taken with the Chandra
X-Ray Observatory, with a catalog of optically selected star clusters presented
by Whitmore et al., based on observations taken with the Hubble Space
Telescope. Within the 2 sigma positional uncertainty of 0.58", we find 22 XRBs
are coincident with star clusters, where only 2-3 chance coincidences are
expected. The ages of the clusters were estimated by comparing their UBVI,
Halpha colors with predictions from stellar evolutionary models. We find that
14 of the 22 coincident XRBs (64%) are hosted by star clusters with ages of 6
Myr or less. Five of the XRBs are hosted by young clusters with ages 10-100
Myr, while three are hosted by intermediate age clusters with 100-300 Myr.
Based on the results from recent N-body simulations, which suggest that black
holes are far more likely to be retained within their parent clusters than
neutron stars, we suggest that our sample consists primarily of black hole
binaries with different ages. |
The Structure of the X-ray and Optical Emitting Regions of the Lensed
Quasar Q 2237+0305: We use gravitational microlensing to determine the size of the X-ray and
optical emission regions of the quadruple lens system Q 2237+0305. The optical
half-light radius, log(R_{1/2,V}/cm)=16.41\pm0.18 (at lambda_{rest}=2018 \AA),
is significantly larger than the observed soft,
log(R_{1/2,soft}/cm)=15.76^{+0.41}_{-0.34} (1.1-3.5 keV in the rest frame), and
hard, log(R_{1/2,hard}/cm)=15.46^{+0.34}_{-0.29} (3.5-21.5 keV in the rest
frame), band X-ray emission. There is a weak evidence that the hard component
is more compact than the soft, with log(R_{1/2,soft}/R_{1/2,hard}) \sim
0.30^{+0.53}_{-0.45}. This wavelength-dependent structure agrees with recent
results found in other lens systems using microlensing techniques, and favors
geometries in which the corona is concentrated near the inner edge of the
accretion disk. While the available measurements are limited, the size of the
X-ray emission region appears to be roughly proportional to the mass of the
central black hole. | Testing consistency of general relativity with kinematic and dynamical
probes: In this work, we test consistency relations between a kinematic probe, the
observational Hubble data, and a dynamical probe, the growth rates for cosmic
large scale structure, which should hold if general relativity is the correct
theory of gravity on cosmological scales. Moreover, we summarize the
development history of parametrization in testings and make an improvement of
it. Taking advantage of the Hubble parameter given from both parametric and
non-parametric methods, we propose three equations and test two of them
performed by means of two-dimensional parameterizations, including one using
trigonometric functions we propose. As a result, it is found that the
consistency relations satisfies well at $1\sigma$ CL and trigonometric
functions turn out to be efficient tools in parameterizations. Furthermore, in
order to confirm the validity of our test, we introduce a model of modified
gravity, DGP model and compare the testing results in the cases of
$\Lambda$CDM, "DGP in GR" and DGP model with mock data. It can be seen that it
is the establishing of consistency relations which dominates the results of the
testing. Overall, the present observational Hubble data and growth rate data
favor convincingly that the general relativity is the correct theory of gravity
on cosmological scales. |
Dual Supermassive Black Hole Candidates in the AGN and Galaxy Evolution
Survey: Dual supermassive black holes (SMBHs) with kiloparsec scale separations in
merger-remnant galaxies are informative tracers of galaxy evolution, but the
avenue for identifying them in large numbers for such studies is not yet clear.
One promising approach is to target spectroscopic signatures of systems where
both SMBHs are fueled as dual active galactic nuclei (AGNs), or where one SMBH
is fueled as an offset AGN. Dual AGNs may produce double-peaked narrow AGN
emission lines, while offset AGNs may produce single-peaked narrow AGN emission
lines with line-of-sight velocity offsets relative to the host galaxy. We
search for such dual and offset systems among 173 Type 2 AGNs at z<0.37 in the
AGN and Galaxy Evolution Survey (AGES), and we find two double-peaked AGNs and
five offset AGN candidates. When we compare these results to a similar search
of the DEEP2 Galaxy Redshift Survey and match the two samples in color,
absolute magnitude, and minimum velocity offset, we find that the fraction of
AGNs that are dual SMBH candidates increases from z=0.25 to z=0.7 by a factor
of ~6 (from 2/70 to 16/91, or 2.9% to 18%). This may be associated with the
rise in the galaxy merger fraction over the same cosmic time. As further
evidence for a link with galaxy mergers, the AGES offset and dual AGN
candidates are tentatively ~3 times more likely than the overall AGN population
to reside in a host galaxy that has a companion galaxy (from 16/173 to 2/7, or
9% to 29%). Follow-up observations of the seven offset and dual AGN candidates
in AGES will definitively distinguish velocity offsets produced by dual SMBHs
from those produced by narrow-line region kinematics, and will help sharpen our
observational approach to detecting dual SMBHs. | Copacabana: A Probabilistic Membership Assignment Method for Galaxy
Clusters: Cosmological analyses using galaxy clusters in optical/NIR photometric
surveys require robust characterization of their galaxy content. Precisely
determining which galaxies belong to a cluster is crucial. In this paper, we
present the COlor Probabilistic Assignment of Clusters And BAyesiaN Analysis
(Copacabana) algorithm. Copacabana computes membership probabilities for {\it
all} galaxies within an aperture centred on the cluster using photometric
redshifts, colours, and projected radial probability density functions.
We use simulations to validate Copacabana and we show that it achieves up to
89\% membership accuracy with a mild dependency on photometric redshift
uncertainties and choice of aperture size. We find that the precision of the
photometric redshifts has the largest impact on the determination of the
membership probabilities followed by the choice of the cluster aperture size.
We also quantify how much these uncertainties in the membership probabilities
affect the stellar mass--cluster mass scaling relation, a relation that
directly impacts cosmology. Using the sum of the stellar masses weighted by
membership probabilities ($\mu_{\star}$) as the observable, we find that
Copacabana can reach an accuracy of 0.06 dex in the measurement of the scaling
relation. These results indicate the potential of Copacabana and $\mu_{\star}$
to be used in cosmological analyses of optically selected clusters in the
future. |
A halo model for cosmological Lyman-limit systems: We present an analytical model for cosmological Lyman-limit systems (LLSs)
that successfully reproduces the observed evolution of the mean free path (L)
of ionizing photons. The evolution of the co-moving mean free path is
predominantly a consequence of the changing meta galactic photo-ionization rate
and the increase with cosmic time of the minimum mass below which halos lose
their gas due to photo-heating. In the model, Lyman-limit absorption is caused
by highly ionized gas in the outskirt of dark matter halos. We exploit the
association with halos to compute statistical properties of LLSs and of their
bias, b. The latter increases from 1.5 to 2.6 from redshifts 2 to 6. Combined
with the rapid increase with redshift of the bias of the halos that host a
quasar, the model predicts a rapid drop in the value of L when measured in
quasar spectra from z=5 to 6, whereas the actual value of L falls more
smoothly. We derive an expression for the effective optical depth due to Lyman
limit absorption as a function of wavelength and show that it depends
sensitively on the poorly constrained number density of LLSs as a function of
column density. The optical depth drops below unity for all wavelengths below a
redshift of 2.5, which is therefore the epoch when the Universe first became
transparent to ionizing photons. | Free scalar dark matter candidates in R^2-inflation: the light, the
heavy and the superheavy: Gravity takes care of both inflation and subsequent reheating in
Starobinsky's R^2-model. The latter is due to inflaton gravitation decays
dominated by scalar particle production. It is tempting to suggest that dark
matter particles are also produced in this process. Since free scalars being
too hot cannot serve as viable dark matter (Phys.Lett.B700:157-162,2011), we
further study the issue considering two options: scalars with non-minimal
coupling to gravity and superheavy scalars generated at inflationary stage. We
found that the first option allows for viable warm or cold dark matter if
scalar mass exceeds 0.8 MeV. The second option implies supercold dark matter
with particle mass 10^16 GeV, which production is saturated at the end of
inflation when inflaton-dependent scalar mass rapidly changes and violates
adiabaticity. Similar result holds for superheavy fermion dark matter. |
The Kinetic Sunyaev-Zel'dovich Effect from Reionization: Simulated Full
Sky Maps at Arcminute Resolution: The kinetic Sunyaev-Zel'dovich (kSZ) effect results from Thomson scattering
by coherent flows in the reionized intergalactic medium. We present new results
based on ray-tracing a 10 Gpc scale simulation at 2-3 Mpc scale resolution to
create a full sky kSZ map. The simulation includes, self-consistently, the
effects of reionization on scales corresponding to multipoles
$10\lesssim\ell\lesssim{5000}$. We separate the kSZ map into Doppler
($\mathbf{v}$), Ostriker-Vishniac ($\delta\mathbf{v}$), patchy ($x\mathbf{v}$),
and third-order ($x\delta\mathbf{v}$) components, and compute explicitly all
the auto and cross correlations (e.g., $\langle\mathbf{v}\mathbf{v}\rangle$,
$\langle\delta\mathbf{v}{x}\mathbf{v}\rangle$, etc.) that contribute to the
total power. We find a complex dependence on the duration of reionization at
$\ell\sim{300}$ and evidence for a non-negligible (10-30 per cent) contribution
from connected four point ionization-velocity correlations,
$\langle{x}\mathbf{v}x\mathbf{v}\rangle_c$, that are usually neglected in
analytical models. We also investigate the Doppler-large scale structure (LSS)
correlation, focusing on two different probes: (1) cross power spectra with
linearly biased tracers of LSS and (2) cold spots from infall onto large, rare
\ion{H}{2} regions centered on peaks in the matter distribution at redshifts
$z>10$. Finally, the reionization history can be reconstructed at 5-10$\sigma$
significance by correlating 21-cm maps with existing CMB temperature maps at
$\ell\!<\!500$ --sophisticated velocity reconstruction methods can probe the
distribution of electrons in the IGM by using combined CMB and LSS measurements
well into the epoch of reionization. The resulting kSZ maps have been made
publicly available at http://www.cita.utoronto.ca/~malvarez/research/ksz-data. | The Matter Bispectrum in N-body Simulations with non-Gaussian Initial
Conditions: We present measurements of the dark matter bispectrum in N-body simulations
with non-Gaussian initial conditions of the local kind for a large variety of
triangular configurations and compare them with predictions from Eulerian
Perturbation Theory up to one-loop corrections. We find that the effects of
primordial non-Gaussianity at large scales, when compared to Perturbation
Theory, are well described by the initial component of the matter bispectrum,
linearly extrapolated at the redshift of interest. In addition, we find that,
for f_NL=100, the nonlinear corrections due to non-Gaussian initial conditions
are of the order of ~3, 4% for generic triangles up to ~20% for squeezed
configurations, at any redshift. We show that the predictions of Perturbation
Theory at tree-level fail to describe the simulation results at redshift z=0
already at scales corresponding to k ~ 0.02 - 0.08 h/Mpc, depending on the
triangle, while one-loop corrections can significantly extend their validity to
smaller scales. At higher redshift, one-loop Perturbation Theory provides
indeed quite accurate predictions, particularly with respect to the relative
correction due to primordial non-Gaussianity. |
Measuring bulk motion of X-ray clusters via the kinematic
Sunyaev-Zeldovich effect: summarizing the "dark flow" evidence and its
implications: In this review we present a comprehensive discussion of peculiar velocity
field measured recently on very large scales with a novel method using X-ray
galaxy clusters as tracers. The measurement is based on the kinematic component
of the Sunyaev-Zeldovich (KSZ) effect produced by Compton scattering of cosmic
microwave background (CMB) photons off the hot intracluster gas, and uses a
large catalog of X-ray selected clusters and all-sky CMB maps obtained with the
WMAP satellite. The method probes the dipole of the CMB temperature field
evaluated at the cluster positions and within the apertures in which the CMB
monopole contribution vanishes, thereby isolating the signal remaining from the
KSZ effect produced by coherently moving clusters. The detection of a highly
significant dipole out to the depth of at least ~ 800 Mpc casts doubt on the
notion that gravitational instability from the observed mass distribution is
the sole -- or even dominant -- cause of the detected motions. Rather it
appears that the flow may extend across the entire observable Universe.
Possible implications include the possibility to constrain the primeval
preinflationary structure of space-time and its landscape, and/or the need for
modifications of presently known physics (e.g. arising from a
higher-dimensional structure of gravity). We review these possibilities in
light of the measurements described here and specifically discuss the prospects
of future measurements and the issues they should resolve. We address the
consistency of these large-scale velocity measurements with those obtained on
smaller scales by studies using galaxies as tracers, and resolve the
discrepancies with two recent claims based on modified CMB analysis schemes. | Dissecting the Strong-lensing Galaxy Cluster MS 0440.5+0204. I. The Mass
Density Profile: We present a parametric strong lensing modeling of the galaxy cluster
MS\,0440.5+0204 (located at $z$ = 0.19). We have performed a strong lensing
mass reconstruction of the cluster using three different models. The first
model uses the image positions of four multiple imaged systems (providing 26
constraints). The second one combines strong lensing constraints with dynamical
information (velocity dispersion) of the cluster. The third one uses the mass
calculated from weak lensing as an additional constraint. Our three models
reproduce equally well the image positions of the arcs, with a root-mean-square
image equal to $\approx$0.5$\arcsec$. However, in the third model, the
inclusion of the velocity dispersion and the weak-lensing mass allows us to
obtain better constraints in the scale radius and the line-of-sight velocity
dispersion of the mass profile. For this model, we obtain $r_s$ =
132$^{+30}_{-32}$ kpc, $\sigma_s$ = 1203$^{+46}_{-47}$ km s$^{-1}$, M$_{200}$ =
3.1$^{+0.6}_{-0.6}$ $\times10^{14}$\,M$_{\odot}$, and a high concentration,
$c_{200}$ = 9.9$^{+2.2}_{-1.4}$. Finally, we used our derived mass profile to
calculate the mass up to 1.5 Mpc. We compare it with X-ray estimates previously
reported, finding a good agreement. |
The optical spectrum of PKS 1222+216 and its black hole mass: We investigate the optical spectral properties of the blazar PKS 1222+216
during a period of 3 years. While the continuum is highly variable the broad
line emission is practically constant. This supports a scenario in which the
broad line region is not affected by jet continuum variations. We thus infer
the thermal component of the continuum from the line luminosity and we show
that it is comparable with the continuum level observed during the phases of
minimum optical activity. The mass of the black hole is estimated through the
virial method from the FWHM of MgII, Hbeta, and Halpha broad lines and from the
thermal continuum luminosity. This yields a consistent black hole mass value of
6x10^8 solar masses. | The 21-cm forest as a simultaneous probe of dark matter and cosmic
heating history: The absorption features in spectra of high-redshift background radio sources,
caused by hyperfine structure lines of hydrogen atoms in the intervening
structures, are known collectively as the 21-cm forest. They provide a unique
probe of small-scale structures during the epoch of reionization, and can be
used to constrain the properties of the dark matter (DM) thought to govern
small-scale structure formation. However, the signals are easily suppressed by
heating processes that are degenerate with a warm DM model. Here we propose a
probe of both the DM particle mass and the heating history of the Universe,
using the one-dimensional power spectrum of the 21-cm forest. The
one-dimensional power spectrum measurement not only breaks the DM model
degeneracy but also increases the sensitivity, making the probe actually
feasible. Making 21-cm forest observations with the upcoming Square Kilometre
Array has the potential to simultaneously determine both the DM particle mass
and the heating level in the early Universe, shedding light on the nature of DM
and the first galaxies. |
Late-time vacuum phase transitions: Connecting sub-eV scale physics with
cosmological structure formation: We show that a particular class of postrecombination phase transitions in the
vacuum can lead to localized overdense regions on relatively small scales,
roughly 10^6 to 10^10 M_sun, potentially interesting for the origin of large
black hole seeds and for dwarf galaxy evolution. Our study suggests that this
mechanism could operate over a range of conditions which are consistent with
current cosmological and laboratory bounds. One byproduct of phase transition
bubble-wall decay may be extra radiation energy density. This could provide an
avenue for constraint, but it could also help reconcile the discordant values
of the present Hubble parameter (H_0) and sigma_8 obtained by cosmic microwave
background (CMB) fits and direct observational estimates. We also suggest ways
in which future probes, including CMB considerations (e.g., early dark energy
limits), 21-cm observations, and gravitational radiation limits, could provide
more stringent constraints on this mechanism and the sub-eV scale
beyond-standard-model physics, perhaps in the neutrino sector, on which it
could be based. Late phase transitions associated with sterile neutrino mass
and mixing may provide a way to reconcile cosmological limits and laboratory
data, should a future disagreement arise. | Testing the distance duality relation using type Ia supernovae and
ultracompact radio sources: We test the possible deviation of the cosmic distance duality relation
$D_A(z)(1+z)^2/D_L(z)\equiv 1$ using the standard candles/rulers in a fully
model-independent manner. Type-Ia supernovae are used as the standard candles
to derive the luminosity distance $D_L(z)$, and ultra-compact radio sources are
used as the standard rulers to obtain the angular diameter distance $D_A(z)$.
We write the deviation of distance duality relation as
$D_A(z)(1+z)^2/D_L(z)=\eta(z)$. Specifically, we use two parameterizations of
$\eta(z)$, i.e. $\eta_1(z)=1+\eta_0 z$ and $\eta_2(z)=1+\eta_0 z/(1+z)$. The
parameter $\eta_0$ is obtained using the Markov chain Monte Carlo methods by
comparing $D_L(z)$ and $D_A(z)$ at the same redshift. The best-fitting results
are $\eta_0=-0.06\pm 0.05$ and $-0.18\pm 0.16$ for the first and second
parameterizations, respectively. Our results depend on neither the cosmological
models, nor the matter contents or the curvature of the universe. |
Cosmic microwave background spectral distortions from Rayleigh
scattering at second order: Cosmic microwave background (CMB) spectral distortion from Rayleigh
scattering is calculated for the first time in rigorous second-order
cosmological perturbation theory. The new spectral distortion is sensitive to
acoustic dissipation at $10^{-2}<k{\rm Mpc}/h<1$, which slightly extends the
scale constrained by the CMB anisotropies. The spectral shape is different from
either temperature perturbations or any other traditional spectral distortions
from Compton scattering, such as $y$ and $\mu$. The new spectral distortion is
not formed in the late Universe, unlike the thermal Sunyaev-Zel'dovich effect
degenerated with the primordial $y$ distortions since photons must be hot for
Rayleigh scattering. Therefore, ideal measurements can distinguish the signal
from the other effects and extract new information during recombination.
Assuming cosmological parameters consistent with the recent CMB anisotropy
measurements, we find the new spectral distortion is $6.5\times 10^{-3}$Jy/str,
which is one order of magnitude smaller than the currently proposed target
sensitivity range of voyage 2050. | Quenching of Star Formation in Molecular Outflow Host NGC 1266: We detail the rich molecular story of NGC 1266, its serendipitous discovery
within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an
AGN-driven molecular outflow, potentially quenching all of its star formation
(SF) within the next 100 Myr. While major mergers appear to play a role in
instigating outflows in other systems, deep imaging of NGC 1266 as well as
stellar kinematic observations from SAURON, have failed to provide evidence
that NGC 1266 has recently been involved in a major interaction. The molecular
gas and the instantaneous SF tracers indicate that the current sites of star
formation are located in a hypercompact disk within 200 pc of the nucleus (Fig.
1; SF rate ~ 2 Msuns/yr). On the other hand, tracers of recent star formation,
such as the H{\beta} absorption map from SAURON and stellar population analysis
show that the young stars are distributed throughout a larger area of the
galaxy than current star formation. As the AGN at the center of NGC 1266
continues to drive cold gas out of the galaxy, we expect star formation rates
to decline as the star formation is ultimately quenched. Thus, NGC 1266 is in
the midst of a key portion of its evolution and continued studies of this
unique galaxy may help improve our understanding of how galaxies transition
from the blue to the red sequence (Alatalo et al. 2011). |
A precise symbolic emulator of the linear matter power spectrum: Computing the matter power spectrum, $P(k)$, as a function of cosmological
parameters can be prohibitively slow in cosmological analyses, hence emulating
this calculation is desirable. Previous analytic approximations are
insufficiently accurate for modern applications, so black-box, uninterpretable
emulators are often used. We utilise an efficient genetic programming based
symbolic regression framework to explore the space of potential mathematical
expressions which can approximate the power spectrum and $\sigma_8$. We learn
the ratio between an existing low-accuracy fitting function for $P(k)$ and that
obtained by solving the Boltzmann equations and thus still incorporate the
physics which motivated this earlier approximation. We obtain an analytic
approximation to the linear power spectrum with a root mean squared fractional
error of 0.2% between $k = 9\times10^{-3} - 9 \, h{\rm \, Mpc^{-1}}$ and across
a wide range of cosmological parameters, and we provide physical
interpretations for various terms in the expression. We also provide a simple
analytic approximation for $\sigma_8$ with a similar accuracy, with a root mean
squared fractional error of just 0.4% when evaluated across the same range of
cosmologies. This function is easily invertible to obtain $A_{\rm s}$ as a
function of $\sigma_8$ and the other cosmological parameters, if preferred. It
is possible to obtain symbolic approximations to a seemingly complex function
at a precision required for current and future cosmological analyses without
resorting to deep-learning techniques, thus avoiding their black-box nature and
large number of parameters. Our emulator will be usable long after the codes on
which numerical approximations are built become outdated. | Dark energy: investigation and modeling: Constantly accumulating observational data continue to confirm that about 70%
of the energy density today consists of dark energy responsible for the
accelerated expansion of the Universe. We present recent observational bounds
on dark energy constrained by the type Ia supernovae, cosmic microwave
background, and baryon acoustic oscillations. We review a number of theoretical
approaches that have been adopted so far to explain the origin of dark energy.
This includes the cosmological constant, modified matter models (such as
quintessence, k-essence, coupled dark energy, unified models of dark energy and
dark matter), modified gravity models (such as f(R) gravity, scalar-tensor
theories, braneworlds), and inhomogeneous models. We also discuss observational
and experimental constraints on those models and clarify which models are
favored or ruled out in current observations. |
Jet-regulated cooling catastrophe: We present the first implementation of Active Galactic Nuclei (AGN) feedback
in the form of momentum driven jets in an Adaptive Mesh Refinement (AMR)
cosmological resimulation of a galaxy cluster. The jets are powered by gas
accretion onto Super Massive Black Holes (SMBHs) which also grow by mergers.
Throughout its formation, the cluster experiences different dynamical states:
both a morphologically perturbed epoch at early times and a relaxed state at
late times allowing us to study the different modes of BH growth and associated
AGN jet feedback. BHs accrete gas efficiently at high redshift (z>2),
significantly pre-heating proto-cluster halos. Gas-rich mergers at high
redshift also fuel strong, episodic jet activity, which transports gas from the
proto-cluster core to its outer regions. At later times, while the cluster
relaxes, the supply of cold gas onto the BHs is reduced leading to lower jet
activity. Although the cluster is still heated by this activity as sound waves
propagate from the core to the virial radius, the jets inefficiently
redistribute gas outwards and a small cooling flow develops, along with
low-pressure cavities similar to those detected in X-ray observations. Overall,
our jet implementation of AGN feedback quenches star formation quite
efficiently, reducing the stellar content of the central cluster galaxy by a
factor 3 compared to the no AGN case. It also dramatically alters the shape of
the gas density profile, bringing it in close agreement with the beta model
favoured by observations, producing quite an isothermal galaxy cluster for
gigayears in the process. However, it still falls short in matching the lower
than Universal baryon fractions which seem to be commonplace in observed galaxy
clusters. | Kinetic Sunyaev-Zeldovich effect in modified gravity: We investigate the impact of modified theories of gravity on the kinetic
Sunyaev-Zeldovich (kSZ) effect of the cosmic microwave background. We focus on
a specific class of $f(R)$ models of gravity and compare their predictions for
the kSZ power spectrum to that of the $\Lambda$CDM model. We use a publicly
available modified version of Halofit to properly include the nonlinear matter
power spectrum of $f(R)$ in the modeling of the kSZ signal. We find that the
well-known modifications of the growth rate of structure in $f(R)$ can indeed
induce sizable changes in the kSZ signal, which are more significant than the
changes induced by modifications of the expansion history. We discuss prospects
of using the kSZ signal as a complementary probe of modified gravity, giving an
overview of assumptions and possible caveats in the modeling. |
Fe K line complex in the nuclear region of NGC 253: A bright, nearby edge-on starburst galaxy NGC 253 was studied using the
Suzaku, XMM and Chandra X-ray observatories. We detected with Suzaku and XMM
complex line structure of Fe K, which is resolved into three lines (Fe I at 6.4
keV, Fe XXV at 6.7 keV and Fe XXVI at 7.0 keV) around the center of NGC 253.
Especially, the Fe I and Fe XXVI lines are the first clear detections, with a
significance of >99.99 % and 99.89 % estimated by a Monte Carlo procedure.
Imaging spectroscopy with Chandra revealed that the emission is distributed in
~60 arcsec^2 region around the nucleus, which suggests that the source is not
only the buried AGN. The flux of highly ionized Fe lines can be explained by
the accumulation of 10-1000 supernova remnants that are the result of high
starforming activity, while the Fe I line flux is consistent with the
fluorescent line emission expected with the molecular clouds in the region. | Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich
data for six galaxy clusters: We present an analysis of observations made with the Arcminute Microkelvin
Imager (AMI) and the Canada-France-Hawaii Telescope (CFHT) of six galaxy
clusters in a redshift range of 0.16--0.41. The cluster gas is modelled using
the Sunyaev--Zel'dovich (SZ) data provided by AMI, while the total mass is
modelled using the lensing data from the CFHT. In this paper, we: i) find very
good agreement between SZ measurements (assuming large-scale virialisation and
a gas-fraction prior) and lensing measurements of the total cluster masses out
to r_200; ii) perform the first multiple-component weak-lensing analysis of
A115; iii) confirm the unusual separation between the gas and mass components
in A1914; iv) jointly analyse the SZ and lensing data for the relaxed cluster
A611, confirming our use of a simulation-derived mass-temperature relation for
parameterizing measurements of the SZ effect. |
Comment on "Joint Anisotropy and Source Count Constraints on the
Contribution of Blazars to the Diffuse Gamma-Ray Background": We show the conclusions claimed in the manuscript arXiv:1202.5309v1 by Cuoco,
Komatsu and Siegal-Gaskins (CKS) are not generally valid. The results in CKS
are based on a number of simplifying assumptions regarding the source
population below the detection threshold and the threshold flux itself, and do
not apply to many physical models of the blazar population. Physical blazar
population models that match the measured source counts above the observational
threshold can account for 60% of the diffuse gamma-ray background intensity
between 1-10 GeV, while the assumptions in CKS limit the intensity to <30%. The
shortcomings of the model considered in CKS arise from an over-simplified
blazar source model. A number of the simplifying assumptions are unjustified,
including: first, the adoption of an assumed power-law source-count
distribution, dN/dS, to arbitrary low source fluxes, which is not exhibited in
physical models of the blazar population; and, second, the lack of blazar
spectral information in calculating the anisotropy of unresolved gamma-ray
blazar emission. We also show that the calculation of the unresolved blazars'
anisotropy is very sensitive to the spectral distribution of the unresolved
blazars through the adopted source resolution threshold value, and must be
taken into account in an accurate anisotropy calculation. | AutoEnRichness: A hybrid empirical and analytical approach for
estimating the richness of galaxy clusters: We introduce AutoEnRichness, a hybrid approach that combines empirical and
analytical strategies to determine the richness of galaxy clusters (in the
redshift range of $0.1 \leq z \leq 0.35$) using photometry data from the Sloan
Digital Sky Survey Data Release 16, where cluster richness can be used as a
proxy for cluster mass. In order to reliably estimate cluster richness, it is
vital that the background subtraction is as accurate as possible when
distinguishing cluster and field galaxies to mitigate severe contamination.
AutoEnRichness is comprised of a multi-stage machine learning algorithm that
performs background subtraction of interloping field galaxies along the cluster
line-of-sight and a conventional luminosity distribution fitting approach that
estimates cluster richness based only on the number of galaxies within a
magnitude range and search area. In this proof-of-concept study, we obtain a
balanced accuracy of $83.20$ per cent when distinguishing between cluster and
field galaxies as well as a median absolute percentage error of $33.50$ per
cent between our estimated cluster richnesses and known cluster richnesses
within $r_{200}$. In the future, we aim for AutoEnRichness to be applied on
upcoming large-scale optical surveys, such as the Legacy Survey of Space and
Time and $\textit{Euclid}$, to estimate the richness of a large sample of
galaxy groups and clusters from across the halo mass function. This would
advance our overall understanding of galaxy evolution within overdense
environments as well as enable cosmological parameters to be further
constrained. |
Galaxies in X-ray Groups I: Robust Membership Assignment and the Impact
of Group Environments on Quenching: Understanding the mechanisms that lead dense environments to host galaxies
with redder colors, more spheroidal morphologies, and lower star formation
rates than field populations remains an important problem. As most candidate
processes ultimately depend on host halo mass, accurate characterizations of
the local environment, ideally tied to halo mass estimates and spanning a range
in halo mass and redshift are needed. In this work, we present and test a
rigorous, probabalistic method for assigning galaxies to groups based on
precise photometric redshifts and X-ray selected groups drawn from the COSMOS
field. The groups have masses in the range 10^13 < M_200c/M_sun < 10^14 and
span redshifts 0<z<1. We characterize our selection algorithm via tests on
spectroscopic subsamples, including new data obtained at the VLT, and by
applying our method to detailed mock catalogs. We find that our group member
galaxy sample has a purity of 84% and completeness of 92% within 0.5 R200c. We
measure the impact of uncertainties in redshifts and group centering on the
quality of the member selection with simulations based on current data as well
as future imaging and spectroscopic surveys. As a first application of our new
group member catalog which will be made publicly available, we show that member
galaxies exhibit a higher quenched fraction compared to the field at fixed
stellar mass out to z~1, indicating a significant relationship between star
formation and environment at group scales. We also address the suggestion that
dusty star forming galaxies in such groups may impact the high-l power spectrum
of the cosmic microwave background and find that such a population cannot
explain the low power seen in recent SZ measurements. | The large-scale general-relativistic correction for Newtonian mocks: We clarify the subtle issue of finding the correct mapping of Newtonian
simulations to light-cone observables at very large distance scales. A faithful
general-relativistic interpretation specifies a gauge, i.e. a chart that
relates the simulation data to points of the space-time manifold. It has
already been pointed out that the implicit gauge choice of Newtonian
simulations is indeed different from the Poisson gauge that is commonly adopted
for relativistic calculations, the difference being most significant at large
scales. It is therefore inconsistent, for example, to predict weak-lensing
observables from simulations unless this gauge issue is properly accounted for.
Using perturbation theory as well as fully relativistic N-body simulations we
quantify the systematic error introduced this way, and we discuss several
solutions that would render the calculations relativistically self-consistent. |
Detecting 21 cm EoR Signal using Drift Scans: Correlation of
Time-ordered Visibilities: We present a formalism to extract the EoR HI power spectrum for drift scans
using radio interferometers. Our main aim is to determine the coherence time
scale of time-ordered visibilities. We compute the two-point correlation
function of the HI visibilities measured at different times to address this
question. We determine, for a given baseline, the decorrelation of the
amplitude and the phase of this complex function. Our analysis uses primary
beams of four ongoing and future interferometers---PAPER, MWA, HERA, and
SKA1-Low. We identify physical processes responsible for the decorrelation of
the HI signal and isolate their impact by making suitable analytic
approximations. The decorrelation time scale of the amplitude of the
correlation function lies in the range of 2--20~minutes for baselines of
interest for the extraction of the HI signal. The phase of the correlation
function can be made small after scaling out an appropriate term, which also
causes the coherence time scale of the phase to be longer than the amplitude of
the correlation function. We find that our results are insensitive to the input
HI power spectrum and therefore they are directly applicable to the analysis of
the drift scan data. We also apply our formalism to a set of point sources and
statistically homogeneous diffuse correlated foregrounds. We find that point
sources decorrelate on a time scale much shorter than the HI signal. This
provides a novel mechanism to partially mitigate the foregrounds in a drift
scan. | Dark Energy Survey Year 3 results: Galaxy-halo connection from
galaxy-galaxy lensing: Galaxy-galaxy lensing is a powerful probe of the connection between galaxies
and their host dark matter halos, which is important both for galaxy evolution
and cosmology. We extend the measurement and modeling of the galaxy-galaxy
lensing signal in the recent Dark Energy Survey Year 3 cosmology analysis to
the highly nonlinear scales ($\sim 100$ kpc). This extension enables us to
study the galaxy-halo connection via a Halo Occupation Distribution (HOD)
framework for the two lens samples used in the cosmology analysis: a luminous
red galaxy sample (redMaGiC) and a magnitude-limited galaxy sample (MagLim). We
find that redMaGiC (MagLim) galaxies typically live in dark matter halos of
mass $\log_{10}(M_{h}/M_{\odot}) \approx 13.7$ which is roughly constant over
redshift ($13.3-13.5$ depending on redshift). We constrain these masses to
$\sim 15\%$, approximately $1.5$ times improvement over previous work. We also
constrain the linear galaxy bias more than 5 times better than what is inferred
by the cosmological scales only. We find the satellite fraction for redMaGiC
(MagLim) to be $\sim 0.1-0.2$ ($0.1-0.3$) with no clear trend in redshift. Our
constraints on these halo properties are broadly consistent with other
available estimates from previous work, large-scale constraints and
simulations. The framework built in this paper will be used for future HOD
studies with other galaxy samples and extensions for cosmological analyses. |
The clustering of galaxies in the completed SDSS-III Baryon Oscillation
Spectroscopic Survey: Angular clustering tomography and its cosmological
implications: We investigate the cosmological implications of studying galaxy clustering
using a tomographic approach applied to the final BOSS DR12 galaxy sample,
including both auto- and cross-correlation functions between redshift shells.
We model the signal of the full shape of the angular correlation function,
$\omega(\theta)$, in redshift bins using state-of-the-art modelling of
non-linearities, bias and redshift-space distortions. We present results on the
redshift evolution of the linear bias of BOSS galaxies, which cannot be
obtained with traditional methods for galaxy-clustering analysis. We also
obtain constraints on cosmological parameters, combining this tomographic
analysis with measurements of the cosmic microwave background (CMB) and type Ia
supernova (SNIa). We explore a number of cosmological models, including the
standard $\Lambda$CDM model and its most interesting extensions, such as
deviations from $w_\rm{DE} = -1$, non-minimal neutrino masses, spatial
curvature and deviations from general relativity using the growth-index
$\gamma$ parametrisation. These results are, in general, comparable to the most
precise present-day constraints on cosmological parameters, and show very good
agreement with the standard model. In particular, combining CMB,
$\omega(\theta)$ and SNIa, we find a value of $w_\rm{DE}$ consistent with $-1$
to a precision better than 5\% when it is assumed to be constant in time, and
better than 6\% when we also allow for a spatially-curved Universe. | Gravitational wave production from the decay of the Standard Model Higgs
field after inflation: During or towards the end of inflation, the Standard Model (SM) Higgs forms a
condensate with a large amplitude. Following inflation, the condensate
oscillates, decaying non-perturbatively into the rest of the SM species. The
resulting out-of-equilibrium dynamics converts a fraction of the energy
available into gravitational waves (GW). We study this process using classical
lattice simulations in an expanding box, following the energetically dominant
electroweak gauge bosons $W^\pm$ and $Z$. We characterize the GW spectrum as a
function of the running couplings, Higgs initial amplitude, and
post-inflationary expansion rate. As long as the SM is decoupled from the
inflationary sector, the generation of this background is universally expected,
independently of the nature of inflation. Our study demonstrates the efficiency
of GW emission by gauge fields undergoing parametric resonance. The initial
energy of the Higgs condensate represents however, only a tiny fraction of the
inflationary energy. Consequently, the resulting background is very suppressed,
with an amplitude $h^2 \Omega_{\rm GW}^{(o)} \lesssim 10^{-29}$ today. The
amplitude can be boosted to $h^2 \Omega_{\rm GW}^{(o)} \lesssim 10^{-16}$, if
following inflation the universe undergoes a kination-domination stage; however
the background is shifted in this case to high frequencies $f_p \lesssim
10^{11} {\rm Hz}$. In all cases the signal is out of the range of current or
planned GW detectors. This background will therefore remain, most likely, as a
curiosity of the SM. |
Evidence of different star formation histories for high- and
low-luminosity radio galaxies: We present the results of our investigation into the stellar populations of
24 radio galaxies at z~0.5 drawn from four complete, low-frequency selected
radio surveys. We use the strength of the 4000A break as an indicator of recent
star formation, and compare this with radio luminosity, optical spectral
classification and morphological classification. We find evidence of different
star formation histories for high- and low-luminosity radio sources; our group
of low radio luminosity sources (typically FRI-type sources) has systematically
older stellar populations than the higher radio luminosity group. Our sample is
also fairly well divided by optical spectral classification. We find that
galaxies classified as having low excitation spectra (LEGs) possess older
stellar populations than high excitation line objects (HEGs), with the HEGs
showing evidence for recent star formation. We also investigate the link
between radio morphology, as used by Owen & Laing (1989), and the stellar
populations. We find that there is a preference for the "fat-double" sources to
have older stellar populations than the "classical double" sources, although
this is also linked to these sources lying predominantly in the LEG and HEG
categories respectively. These results are consistent with the hypothesis that
HEGs are powered by accretion of cold gas, which could be supplied, for
example, by recent mergers, secular instabilities, or filamentary cold flows.
These processes could also trigger star formation in the host galaxy. The host
galaxies of the LEGs do not show evidence for recent star formation and an
influx of cold gas, and are consistent with being powered by the accretion of
the hot phase of the inter-stellar medium. | Instrumental systematics biases in CMB lensing reconstruction: a
simulation-based assessment: Weak gravitational lensing of the cosmic microwave background (CMB) is an
important cosmological tool that allows us to learn about the structure,
composition and evolution of the Universe. Upcoming CMB experiments, such as
the Simons Observatory (SO), will provide high-resolution and low-noise CMB
measurements. We consider the impact of instrumental systematics on the
corresponding high-precision lensing reconstruction power spectrum
measurements. We simulate CMB temperature and polarization maps for an SO-like
instrument and potential scanning strategy, and explore systematics relating to
beam asymmetries and offsets, boresight pointing, polarization angle, gain
drifts, gain calibration and electric crosstalk. Our analysis shows that the
majority of the biases induced by the systematics we modeled are below a
detection level of $\sim 0.6\sigma$. We discuss potential mitigation techniques
to further reduce the impact of the more significant systematics, and pave the
way for future lensing-related systematics analyses. |
Variability of the Spectral Energy Distribution of the Blazar S5
0716+714: The emission from blazars is known to be variable at all wavelengths. The
flux variability is often accompanied by spectral changes. Spectral energy
distribution (SED) changes must be associated with changes in the spectra of
emitting electrons and/or the physical parameters of the jet. Meaningful
modeling of blazar broadband spectra is required to understand the extreme
conditions within the emission region. Not only is the broadband SED crucial,
but also information about its variability is needed to understand how the
highest states of emission occur and how they differ from the low states. This
may help in discriminating between models. Here we present the results of our
SED modeling of the blazar S5 0716+714 during various phases of its activity.
The SEDs are classified into different bins depending on the optical brightness
state of the source. | Ionized gas outflow in the isolated S0 galaxy NGC 4460: We use integral-field and long-slit spectroscopy to study the bright extended
nebulosity discovered in the isolated lenticular galaxy NGC 4460 during a
recent H-alpha survey of nearby galaxies. An analysis of archival SDSS, GALEX,
and HST images indicates that current star formation is entirely concentrated
in the central kiloparsec of the galaxy disc. The observed ionized gas
parameters (morphology, kinematics and ionization state) can be explained by a
gas outflow above the plane of the galaxy caused by a star formation in the
circumnuclear region. Galactic wind parameters in NGC 4460: outflow velocity,
total kinetic energy - are several times smaller comparing with the known
galactic wind in NGC 253, which is explained substantially lower total star
formation rate. We discuss the cause of the star formation processes in NGC
4460 and in two other known isolated S0 and E galaxies of the Local volume: NGC
404 and NGC 855. We provide evidence suggesting that feeding of isolated
galaxies by intergalactic gas on a cosmological time scale is a steady process
without significant variations. |
Some results on the radio-SZ correlation for galaxy cluster radio halos: We present correlation results for the radio halo power in galaxy clusters
with the integrated thermal Sunyaev-Zel'dovich (SZ) effect signal, including
new results obtained at sub-GHz frequencies. The radio data is compiled from
several published works, and the SZ measurements are taken from the Planck ESZ
cluster catalog. The tight correlation between the radio halo power and the SZ
effect demonstrates a clear correspondence between the thermal and non-thermal
electron populations in the intra-cluster medium, as already has been shown in
X-ray based studies. The radio power varies roughly as the square of the global
SZ signal, but when the SZ signal is scaled to within the radio halo radius the
correlation becomes approximately linear, with reduced intrinsic scatter. We do
not find any strong indication of a bi-modal division in the radio halo cluster
population, as has been reported in the literature, which suggests that such
duality could be an artifact of X-ray selection. We compare the SZ signal
dependence of radio halos with simplified predictions from theoretical models,
and discuss some implications and shortcomings of the present work. | A flat space-time model of the Universe: We propose a model of the Universe based on Minkowski flat space-time metric.
In this model the space-time does not evolve. Instead the matter evolves such
that all the mass parameters increase with time. We construct a model based on
unimodular gravity to show how this can be accomplished within the framework of
flat space-time. We show that the model predicts the Hubble law if the masses
increase with time. Furthermore we show that it fits the high z supernova data
in a manner almost identical to the standard Big Bang model. Furthermore we
show that at early times the Universe is dominated by radiative energy density.
The phenomenon of recombination also arises in our model and hence predicts the
existence of CMBR. However a major difference with the standard Big Bang is
that the radiative temperature and energy density does not evolve in our model.
Furthermore we argue that the basic motivation for inflation is absent in our
model. |
The tension on the cosmological parameters from different observational
data: Planck measurements of the cosmic microwave background power spectra find a
lower value of the Hubble constant $H_0$ and a higher value of the fractional
matter energy density $\Omega_{m0}$ for the concordance $\Lambda$CDM model, and
these results are in tension with other measurements. The {\em Planck} group
argued that the tension came either from some sources of unknown systematic
errors in some astrophysical measurements or the wrong $\Lambda$CDM model
applied in fitting the data. We studied the reason for the tension on $H_0$
from different measurements by considering two dynamical dark energy models. We
found that there is no tension between different data, the constraint on $H_0$
is almost unchanged for different dark energy models and the tension with the
local measurements remains when the error bar on $H_0$ is tightened to be
around 1. We argue that the tension on $H_0$ is not caused by the fitting
model. | Neutrino clustering around spherical dark matter halos: Cold dark matter halos form within a smoothly distributed background of relic
neutrinos -- at least some of which are massive and non-relativistic at late
times. We calculate the accumulation of massive neutrinos around spherically
collapsing cold dark matter halos in a cosmological background. We identify the
physical extent of the "neutrino halo" in the spherical collapse model, which
is large in comparison with the virial radius of the dark matter, and
conditions under which neutrinos reaching the cold dark matter halo will remain
bound to the halo at late times. We calculate the total neutrino mass and bound
neutrino mass associated with isolated spherical halos for several neutrino
mass hierarchies and provide fitting formulae for these quantities in terms of
the cold dark matter halo mass and the masses of the individual neutrino
species. |
Pearson's random walk in the space of the CMB phases: evidence for
parity asymmetry: The temperature fluctuations of the Cosmic Microwave Background (CMB) are
supposed to be distributed randomly in both magnitude and phase, following to
the simplest model of inflation. In this paper, we look at the odd and even
multipoles of the spherical harmonic decomposition of the CMB, and the
different characteristics of these, giving rise to a parity asymmetry. We
compare the even and odd multipoles in the CMB power spectrum, and also the
even and odd mean angles. We find for the multipoles of the power spectrum,
that there is power excess in odd multipoles, compared to even ones, meaning
that we have a parity asymmetry. Further, for the phases, we present a random
walk for the mean angles, and find a significant separation for even/odd mean
angles, especially so for galactic coordinates. This is further tested and
confirmed with a directional parity test, comparing the parity asymmetry in
galactic and ecliptic coordinates. | The Effect of Starburst Metallicity on Bright X-Ray Binary Formation
Pathways: We investigate the characteristics of young (< 20 Myr) and bright (Lx > 1e36
erg/s) High-Mass X-ray Binaries (HMXBs) and find the population to be strongly
metallicity-dependent. We separate the model populations among two distinct
formation pathways: (1) systems undergoing active Roche Lobe Overflow (RLO),
and (2) wind accretion systems with donors in the (super)giant (SG) stage,
which we find to dominate the HMXB population. We find metallicity to primarily
affect the number of systems which move through each formation pathway, rather
than the observable parameters of systems which move through each individual
pathway. We discuss the most important model parameters affecting the HMXB
population at both low and high metallicities. Using these results, we show
that (1) the population of ultra-luminous X-Ray sources can be consistently
described by very bright HMXBs which undergo stable Roche Lobe overflow with
mild super-Eddington accretion and (2) the HMXB population of the bright
starburst galaxy NGC~1569 is likely dominated by one extremely metal-poor
starburst cluster. |
Delayed Enrichment by Unseen Galaxies: Explaining the Rapid Rise in IGM
CIV Absorption from z = 6-5: In the near future, measurements of metal absorption features in the
intergalactic medium (IGM) will become an important constraint on models of the
formation and evolution of the earliest galaxies, the properties of the first
stars, and the reionization and enrichment of the IGM. The first measurement of
a metal abundance in the IGM at a redshift approaching the epoch of
reionization already offers intriguing hints. Between z=5.8 and 4.7 (a 0.3 Gyr
interval only 1 Gyr after the big bang), the measured density of CIV absorbers
in the IGM increased by a factor of ~ 3.5 (Ryan-Weber et al. 2009; Becker,
Rauch & Sargent 2009). If these values prove to be accurate, they pose two
puzzles: (1) The total amount of CIV at z=5.8 implies too little star formation
to reionize the IGM by z=6 or to match the WMAP electron scattering optical
depth (tau). (2) The rapid growth from z = 6-5 is faster than the buildup of
stellar mass or the increase in the star formation rate density over the same
interval. We show that a delay of ~ 0.4-0.7 Gyr between the instantaneous
production of ionizing photons and the later production of metal absorption
features (added to the delay due to stellar lifetimes) can provide the full
explanation for both puzzles. We calculate the delay in metal production due to
finite stellar lifetimes alone and find that it is too short to explain the
rapid CIV density increase. The additional delay could naturally be explained
as the result of ~ 200 km/s outflows carrying carbon to distances of ~ 100 kpc,
the typical distance between galaxies and CIV absorbers in enrichment
simulations, and the typical outflow or absorption region scale observed at z ~
2-3. | Gravitational lensing as a probe of cold dark matter subhalos: In the cold dark matter scenario, dark matter halos are assembled
hierarchically from smaller subunits. Some of these subunits are disrupted
during the merging process, whereas others survive temporarily in the form of
subhalos. A long-standing problem with this picture is that the number of
subhalos predicted by simulations exceeds the number of luminous dwarf galaxies
seen in the the vicinity of large galaxies like the Milky Way. Many of the
subhalos must therefore have remained dark or very faint. If cold dark matter
subhalos are as common as predicted, gravitational lensing may in principle
offer a promising route to detection. In this review, we describe the many ways
through which lensing by subhalos can manifest itself, and summarize the
results from current efforts to constrain the properties of cold dark matter
subhalos using such effects. |
Effects of simulated cosmological magnetic fields on the galaxy
population: We investigate the effects of varying the intensity of the primordial
magnetic seed field on the global properties of the galaxy population in ideal
magnetohydrodynamic cosmological simulations performed with the moving-mesh
code AREPO. We vary the seed field in our calculations in a range of values
still compatible with the current cosmological upper limits. We show that above
a critical intensity of $\simeq 10^{-9}\,{\rm G}$, the additional pressure
arising from the field strongly affects the evolution of gaseous structures,
leading to a suppression of the cosmic star formation history, \rev{which is
stronger for larger seed fields. This directly reflects into a lower total
galaxy count above a fixed stellar mass threshold at all redshifts, and} a
lower galaxy number density at fixed stellar mass and a less massive stellar
component at fixed virial mass at all mass scales. These signatures may be
used, in addition to the existing methods, to derive tighter constraints on
primordial magnetic seed field intensities. | Core-collapse, evaporation and tidal effects: the life story of a
self-interacting dark matter subhalo: Self-interacting dark matter (SIDM) cosmologies admit an enormous diversity
of dark matter (DM) halo density profiles, from low-density cores to
high-density core-collapsed cusps. The possibility of the growth of high
central density in low-mass halos, accelerated if halos are subhalos of larger
systems, has intriguing consequences for small-halo searches with substructure
lensing. However, following the evolution of $\lesssim 10^8 M_\odot$ subhalos
in lens-mass systems ($\sim 10^{13}M_\odot$) is computationally expensive with
traditional N-body simulations. In this work, we develop a new hybrid
semi-analytical + N-body method to study the evolution of SIDM subhalos with
high fidelity, from core formation to core-collapse, in staged simulations. Our
method works best for small subhalos ($\lesssim 1/1000$ host mass), for which
the error caused by dynamical friction is minimal. We are able to capture the
evaporation of subhalo particles by interactions with host halo particles, an
effect that has not yet been fully explored in the context of subhalo
core-collapse. We find three main processes drive subhalo evolution: subhalo
internal heat outflow, host-subhalo evaporation, and tidal effects. The subhalo
central density grows only when the heat outflow outweighs the energy gain from
evaporation and tidal heating. Thus, evaporation delays or even disrupts
subhalo core-collapse. We map out the parameter space for subhalos to
core-collapse, finding that it is nearly impossible to drive core-collapse in
subhalos in SIDM models with constant cross sections. Any discovery of
ultra-compact dark substructures with future substructure lensing observations
favors additional degrees of freedom, such as velocity-dependence, in the cross
section. |
Directional detection of Dark Matter: Directional detection is a promising Dark Matter search strategy. Taking
advantage on the rotation of the Solar system around the galactic center
through the Dark Matter halo, it allows to show a direction dependence of WIMP
events. It requires the simultaneous measurement of the energy and the 3D track
of low energy recoils, which is a common challenge for all current projects of
directional detectors. The third CYGNUS workshop on directional dark matter
detection has brought together the scientific community working on both
theoretical and experimental aspects of the subject. In this paper, we give an
introductory revue of directional detection of Dark Matter, focusing on the
main recent progresses. | The properties of the extended warm ionised gas around low-redshift QSOs
and the lack of extended high-velocity outflows: (Abridged) We present a detailed analysis of a large sample of 31
low-redshift, mostly radio-quiet type 1 QSOs observed with integral field
spectroscopy to study their extended emission-line regions (EELRs). We focus on
the ionisation state of the gas, size and luminosity of extended narrow line
regions (ENLRs), which corresponds to those parts of the EELR dominated by
ionisation from the QSO, as well as the kinematics of the ionised gas. We
detect EELRs around 19 of our 31 QSOs (61%) after deblending the unresolved QSO
emission and the extended host galaxy light in the integral field data. We
identify 13 EELRs to be entirely ionised by the QSO radiation, 3 EELRs are
composed of HII regions and 3 EELRs display signatures of both ionisation
mechanisms at different locations. The typical size of the ENLR is 10kpc at a
median nuclear [OIII] luminosity of log(L([OIII])/[erg/s])=42.7+-0.15. We show
that the ENLR sizes are least a factor of 2 larger than determined with HST,
but are consistent with those of recently reported type 2 QSOs at matching
[OIII] luminosities. The ENLR of type 1 and type 2 QSOs appear to follow the
same size-luminosity relation. Furthermore, we show for the first time that the
ENLR size is much better correlated with the QSO continuum luminosity than with
the total/nuclear [OIII] luminosity. We show that ENLR luminosity and radio
luminosity are correlated, and argue that radio jets even in radio-quiet QSOs
are important for shaping the properties of the ENLR. Strikingly, the
kinematics of the ionised gas is quiescent and likely gravitationally driven in
the majority of cases and we find only 3 objects with radial gas velocities
exceeding 400km/s in specific regions of the EELR that can be associate with
radio jets. In general, these are significantly lower outflow velocities and
detection rates compared to starburst galaxies or radio-loud QSOs. |
Cooling and Heating Functions of Photoionized Gas: Cooling and heating functions of cosmic gas are a crucial ingredient for any
study of gas dynamics and thermodynamics in the interstellar and intergalactic
medium. As such, they have been studied extensively in the past under the
assumption of collisional ionization equilibrium. However, for a wide range of
applications, the local radiation field introduces a non-negligible, often
dominant, modification to the cooling and heating functions. In the most
general case, these modifications cannot be described in simple terms, and
would require a detailed calculation with a large set of chemical species using
a radiative transfer code (the well-known code Cloudy, for example). We show,
however, that for a sufficiently general variation in the spectral shape and
intensity of the incident radiation field, the cooling and heating functions
can be approximated as depending only on several photoionization rates, which
can be thought of as representative samples of the overall radiation field.
This dependence is easy to tabulate and implement in cosmological or
galactic-scale simulations, thus economically accounting for an important but
rarely-included factor in the evolution of cosmic gas. We also show a few
examples where the radiation environment has a large effect, the most
spectacular of which is a quasar that suppresses gas cooling in its host halo
without any mechanical or non-radiative thermal feedback. | Lensing substructure quantification in RXJ1131-1231: A 2 keV lower bound
on dark matter thermal relic mass: We study the substructure content of the strong gravitational lens
RXJ1131-1231 through a forward modelling approach that relies on generating an
extensive suite of realistic simulations. We use a semi-analytic merger tree
prescription that allows us to stochastically generate substructure populations
whose properties depend on the dark matter particle mass. These synthetic halos
are then used as lenses to produce realistic mock images that have the same
features, e.g. luminous arcs, quasar positions, instrumental noise and PSF, as
the data. We then analyse the data and the simulations in the same way with
summary statistics that are sensitive to the signal being targeted and are able
to constrain models of dark matter statistically using Approximate Bayesian
Computing (ABC) techniques. In this work, we focus on the thermal relic mass
estimate and fix the semi-analytic descriptions of the substructure evolution
based on recent literature. We are able, based on the HST data for
RXJ1131-1231, to rule out a warm dark matter thermal relic mass below 2 keV at
the 2$\sigma$ confidence level. |
The AGN/starburst content in high redshift ULIRGs: We apply a simple model, tested on local ULIRGs, to disentangle the active
galactic nucleus (AGN) and starburst contributions in submillimiter and
24um-selected ULIRGs observed with the Spitzer-IRS spectrometer. We
quantitatively estimate the average AGN contribution to the stacked 6-8um
rest-frame spectra of these sources in different luminosity and redshift
ranges, and, under the assumption of similar infrared-to-bolometric ratios as
in local ULIRGs, the relative AGN/starburst contributions to the total infrared
luminosity. Though the starburst component is always dominant in
submillimeter-selected ULIRGs, we find a significant increase of the AGN
contribution at redshift z>2.3 with respect to lower z objects. Finally, we
quantitatively confirm that the mid-infrared emission of 24um-selected ULIRGs
is dominated by the AGN component, but the starburst component contributes
significantly to the bolometric luminosity. | Measuring the Hubble constant: Gravitational wave observations meet
galaxy clustering: We show how the distances to binary black holes measured in gravitational
wave observations with ground-based interferometers can be used to constrain
the redshift-distance relation and, thereby, measure the Hubble constant
($H_0$). Gravitational wave observations of stellar-mass binary black holes are
not expected to be accompanied by any electro-magnetic event that may help in
accessing their redshifts. We address this deficiency by using an optical
catalog to get the distribution of galaxies in redshift. Assuming that the
clustering of the binaries is correlated with that of the galaxies, we propose
using that correlation to measure $H_0$. We show that employing this method on
simulated data obtained for second-generation networks comprising at least
three detectors, e.g., advanced LIGO - advanced VIRGO network, one can measure
$H_0$ with an accuracy of $\sim$8% with detection of a reference population of
25 binaries, each with black holes of mass 10$M_\odot$. As expected, with
third-generation detectors like the Einstein telescope (ET), which will measure
distances much more accurately and to greater depths, one can obtain better
estimates for $H_0$. Specifically, we show that with 25 observations, ET can
constrain $H_0$ to an accuracy of $\sim$7%. This method can also be used to
estimate other cosmological parameters like the matter density $\Omega_m$ and
the dark energy equation of state. |
The GALEX Arecibo SDSS Survey. IV. Baryonic Mass-Velocity-Size Relations
of Massive Galaxies: We present dynamical scaling relations for a homogeneous and representative
sample of ~500 massive galaxies, selected only by stellar mass (>10^10 Msun)
and redshift (0.025<z<0.05) as part of the ongoing GALEX Arecibo SDSS Survey.
We compare baryonic Tully-Fisher (BTF) and Faber-Jackson (BFJ) relations for
this sample, and investigate how galaxies scatter around the best fits obtained
for pruned subsets of disk-dominated and bulge-dominated systems. The BFJ
relation is significantly less scattered than the BTF when the relations are
applied to their maximum samples, and is not affected by the inclination
problems that plague the BTF. Disk-dominated, gas-rich galaxies systematically
deviate from the BFJ relation defined by the spheroids. We demonstrate that by
applying a simple correction to the stellar velocity dispersions that depends
only on the concentration index of the galaxy, we are able to bring disks and
spheroids onto the same dynamical relation -- in other words, we obtain a
generalized BFJ relation that holds for all the galaxies in our sample,
regardless of morphology, inclination or gas content, and has a scatter smaller
than 0.1 dex. We find that disks and spheroids are offset in the stellar
dispersion-size relation, and that the offset is removed when corrected
dispersions are used instead. The generalized BFJ relation represents a
fundamental correlation between the global dark matter and baryonic content of
galaxies, which is obeyed by all (massive) systems regardless of morphology.
[abridged] | Cosmic Bulk Flow and the Local Motion from Cosmicflows-2: Full sky surveys of peculiar velocity are arguably the best way to map the
large scale structure out to distances of a few times 100 Mpc/h. Using the
largest and most accurate ever catalog of galaxy peculiar velocities
"Cosmicflows-2", the large scale structure has been reconstructed by means of
the Wiener filter and constrained realizations assuming as a Bayesian prior
model the LCDM model with the WMAP inferred cosmological parameters. The
present paper focuses on studying the bulk flow of the local flow field,
defined as the mean velocity of top-hat spheres with radii ranging out to R=500
Mpc/h. The estimated large scale structures, in general, and the bulk flow, in
particular, are determined by the tension between the observational data and
the assumed prior model. A prerequisite for such an analysis is the requirement
that the estimated bulk flow is consistent with the prior model. Such a
consistency is found here. At R=50(150) Mpc/h the estimated bulk velocity is
250+/-21 (239+/-38) km/s. The corresponding cosmic variance at these radii is
126(60)km/s, which implies that these estimated bulk flows are dominated by the
data and not by the assumed prior model. The estimated bulk velocity is
dominated by the data out to R~200 Mpc/h, where the cosmic variance on the
individual Supergalactic Cartesian components (of the r.m.s. values) exceeds
the variance of the Constrained Realizations by at least a factor of 2. The
supergalactic SGX and SGY components of the CMB dipole velocity are recovered
by the Wiener filter velocity field down to a very few km/s. The SGZ component
of the estimated velocity, the one that is most affected by the Zone of
Avoidance, is off by 126 km/s (an almost 2 sigma discrepancy). |
A deep search for molecular gas in two massive Lyman break galaxies at
z=3 and 4: vanishing CO-emission due to low metallicity?: We present deep IRAM Plateau de Bure Interferometer (PdBI) observations,
searching for CO-emission toward two massive, non-lensed Lyman break galaxies
(LBGs) at z=3.216 and 4.058. With one low significance CO detection (3.5 sigma)
and one sensitive upper limit, we find that the CO lines are >~ 3-4 times
weaker than expected based on the relation between IR and CO luminosities
followed by similarly, massive galaxies at z=0-2.5. This is consistent with a
scenario in which these galaxies have low metallicity, causing an increased
CO-to-H_2 conversion factor, i.e., weaker CO-emission for a given molecular
(H_2) mass. The required metallicities at z>3 are lower than predicted by the
fundamental metallicity relation (FMR) at these redshifts, consistent with
independent evidence. Unless our galaxies are atypical in this respect,
detecting molecular gas in normal galaxies at z>3 may thus remain challenging
even with ALMA. | Compact molecular disc and ionized gas outflows within 350 pc of the
active nucleus of Mrk 1066: We present stellar and gaseous kinematics of the inner 350 pc radius of the
Seyfert galaxy Mrk1066 derived from J and Kl bands data obtained with the
Gemini NIFS at a spatial resolution of 35 pc. The stellar velocity field is
dominated by rotation in the galaxy plane but shows an S-shape distortion along
the galaxy minor axis which seems to be due to an oval structure seen in an
optical continuum image. Along this oval, between 170 and 280 pc from the
nucleus we find a partial ring of low sigma (~50 km/s) attributed to an
intermediate age stellar population. Fro measurements of the emission-line
fluxes and profiles ([PII]1.19um, [FeII]1.26um, Pa-beta and H2 2.12um), we have
constructed maps for the gas centroid velocity, velocity dispersion, as well as
channel maps. The velocity fields for all emission lines are dominated by a
similar rotation pattern to that observed for the stars, but are distorted by
the presence of two structures: (i) a compact rotating disc with radius r~70
pc; (ii) outflows along the radio jet which is oriented approximately along the
galaxy major axis. The compact rotating disc is more conspicuous in the H2
emitting gas, which presents the smallest sigma values and most clear rotation
pattern, supporting a location in the galaxy plane. We estimate a gas mass for
the disc of ~10^7Msun. The H2 kinematics further suggests that the nuclear disc
is being fed by gas coming from the outer regions. The outflow is more
conspicuous in the [FeII] emitting gas, which presents the highest sigma values
(up to 150 km/s) and the highest blue and redshifts of up to 500 km/s, while
the highest stellar rotation velocity is only 130 km/s. We estimate a
mass-outflow rate in ionized gas of 0.06 Msun/yr. The derived kinematics for
the emitting gas is similar to that observed in previous studies supporting
that the H2 is a tracer of the AGN feeding and the [FeII] of its feedback. |
Globular cluster luminosity function as distance indicator: Globular clusters are among the first objects used to establish the distance
scale of the Universe. In the 1970-ies it has been recognized that the
differential magnitude distribution of old globular clusters is very similar in
different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the
so-called Globular Cluster Luminosity Function has been then established as a
secondary distance indicator. The intrinsic accuracy of the method has been
estimated to be of the order of ~0.2 mag, competitive with other distance
determination methods. Lately the study of the Globular Cluster Systems has
been used more as a tool for galaxy formation and evolution, and less so for
distance determinations. Nevertheless, the collection of homogeneous and large
datasets with the ACS on board HST presented new insights on the usefulness of
the Globular Cluster Luminosity Function as distance indicator. I discuss here
recent results based on observational and theoretical studies, which show that
this distance indicator depends on complex physics of the cluster formation and
dynamical evolution, and thus can have dependencies on Hubble type, environment
and dynamical history of the host galaxy. While the corrections are often
relatively small, they can amount to important systematic differences that make
the Globular Cluster Luminosity Function a less accurate distance indicator
with respect to some other standard candles. | Illuminating the dark universe with a very high density galaxy redshift
survey over a wide area: The nature of dark energy remains a profound mystery 20 years after the
discovery of cosmic acceleration. A very high number density galaxy redshift
survey over a wide area (HD GRS Wide) spanning the redshift range of 0.5<z<4
using the same tracer, carried out using massively parallel wide field
multi-object slit spectroscopy from space, will provide definitive dark energy
measurements with minimal observational systematics by design. The HD GRS Wide
will illuminate the nature of dark energy, and lead to revolutionary advances
in particle physics and cosmology. It will also trace the cosmic web of dark
matter and provide key insight into large-scale structure in the Universe. The
required observational facility can be established as part of the probe
portfolio by NASA within the next decade. |
Chaotic inflation in modified gravitational theories: We study chaotic inflation in the context of modified gravitational theories.
Our analysis covers models based on (i) a field coupling $\omega(\phi)$ with
the kinetic energy $X$ and a nonmimimal coupling $\zeta \phi^{2} R/2$ with a
Ricci scalar $R$, (ii) Brans-Dicke (BD) theories, (iii) Gauss-Bonnet (GB)
gravity, and (iv) gravity with a Galileon correction. Dilatonic coupling with
the kinetic energy and/or negative nonminimal coupling are shown to lead to
compatibility with observations of the Cosmic Microwave Background (CMB)
temperature anisotropies for the self-coupling inflaton potential
$V(\phi)=\lambda \phi^{4}/4$. BD theory with a quadratic inflaton potential,
which covers Starobinsky's $f(R)$ model $f(R)=R+R^{2}/(6M^{2})$ with the BD
parameter $\omega_{BD}=0$, gives rise to a smaller tensor-to-scalar ratio for
decreasing $\omega_{BD}$. In the presence of a GB term coupled to the field
$\phi$, we express the scalar/tensor spectral indices $n_{s}$ and $n_{t}$ as
well as the tensor-to-scalar ratio $r$ in terms of two slow-roll parameters and
place bounds on the strength of the GB coupling from the joint data analysis of
WMAP 7yr combined with other observations. We also study the Galileon-like
self-interaction $\Phi(\phi) X \square\phi$ with exponential coupling
$\Phi(\phi) \propto e^{\mu\phi}$. Using a CMB likelihood analysis we put bounds
on the strength of the Galileon coupling and show that the self coupling
potential can in fact be made compatible with observations in the presence of
the exponential coupling with $\mu>0$. | Constraining the Black Hole Mass Spectrum with Gravitational Wave
Observations I: The Error Kernel: Many scenarios have been proposed for the origin of the supermassive black
holes (SMBHs) that are found in the centres of most galaxies. Many of these
formation scenarios predict a high-redshift population of intermediate-mass
black holes (IMBHs), with masses in the range 100 to 100000 times that of the
Sun. A powerful way to observe these IMBHs is via gravitational waves the black
holes emit as they merge. The statistics of the observed black hole population
should, in principle, allow us to discriminate between competing astrophysical
scenarios for the origin and formation of SMBHs. However, gravitational wave
detectors such as LISA will not be able to detect all such mergers nor assign
precise black hole parameters to the merger, due to weak gravitational wave
signal strengths. In order to use LISA observations to infer the statistics of
the underlying population, these errors must be taken into account. We describe
here a method for folding the LISA gravitational wave parameter error estimates
into an `error kernel' designed for use at the population model level. The
effects of this error function are demonstrated by applying it to several
recent models of black hole mergers, and some tentative conclusions are made
about LISA's ability to test scenarios of the origin and formation of
supermassive black holes. |
Hidden in the background: a local approach to CMB anomalies: We investigate a framework aiming to provide a common origin for the
large-angle anomalies detected in the Cosmic Microwave Background (CMB), which
are hypothesized as the result of the statistical inhomogeneity developed by
different isocurvature fields of mass $m\sim H$ present during inflation. The
inhomogeneity arises as the combined effect of $(i)$ the initial conditions for
isocurvature fields (obtained after a fast-roll stage finishing many
$e$-foldings before cosmological scales exit the horizon), $(ii)$ their
inflationary fluctuations and $(iii)$ their coupling to other degrees of
freedom. Our case of interest is when these fields (interpreted as the
precursors of large-angle anomalies) leave an observable imprint only in
isolated patches of the Universe. When the latter intersect the last scattering
surface, such imprints arise in the CMB. Nevertheless, due to their
statistically inhomogeneous nature, these imprints are difficult to detect, for
they become hidden in the background similarly to the Cold Spot. We then
compute the probability that a single isocurvature field becomes inhomogeneous
at the end of inflation and find that, if the appropriate conditions are given
(which depend exclusively on the preexisting fast-roll stage), this probability
is at the percent level. Finally, we discuss several mechanisms (including the
curvaton and the inhomogeneous reheating) to investigate whether an initial
statistically inhomogeneous isocurvature field fluctuation might give rise to
some of the observed anomalies. In particular, we focus on the Cold Spot, the
power deficit at low multipoles and the breaking of statistical isotropy. | Internal Robustness: systematic search for systematic bias in SN Ia data: A great deal of effort is currently being devoted to understanding,
estimating and removing systematic errors in cosmological data. In the
particular case of type Ia supernovae, systematics are starting to dominate the
error budget. Here we propose a Bayesian tool for carrying out a systematic
search for systematic contamination. This serves as an extension to the
standard goodness-of-fit tests and allows not only to cross-check raw or
processed data for the presence of systematics but also to pin-point the data
that are most likely contaminated. We successfully test our tool with mock
catalogues and conclude that the Union2.1 data do not possess a significant
amount of systematics. Finally, we show that if one includes in Union2.1 the
supernovae that originally failed the quality cuts, our tool signals the
presence of systematics at over 3.8-sigma confidence level. |
Cosmological constraints on the Hu-Sawicki modified gravity scenario: In this paper we place new constraints on a f(R) modified gravity model
recently proposed by Hu and Sawicki. After checking that the Hu and Sawicki
model produces a viable cosmology, i.e. a matter dominated epoch followed by a
late-time acceleration, we constrain some of its parameters by using recent
observations from the UNION compilation of luminosity distances of Supernovae
type Ia, including complementary information from Baryonic Acoustic
Oscillations, Hubble expansion, and age data. We found that the data considered
is unable to place significant constraints on the model parameters and we
discuss the impact of a different assumption of the background model in cosmic
parameters inference. | Scaling laws for weakly interacting cosmic (super)string and p-brane
networks: In this paper we find new scaling laws for the evolution of $p$-brane
networks in $N+1$-dimensional Friedmann-Robertson-Walker universes in the
weakly-interacting limit, giving particular emphasis to the case of cosmic
superstrings ($p=1$) living in a universe with three spatial dimensions (N=3).
In particular, we show that, during the radiation era, the root-mean-square
velocity is ${\bar v} =1/{\sqrt 2}$ and the characteristic length of
non-interacting cosmic string networks scales as $L \propto a^{3/2}$ ($a$ is
the scale factor), thus leading to string domination even when gravitational
backreaction is taken into account. We demonstrate, however, that a small
non-vanishing constant loop chopping efficiency parameter $\tilde c$ leads to a
linear scaling solution with constant $L H \ll 1$ ($H$ is the Hubble parameter)
and ${\bar v} \sim 1/{\sqrt 2}$ in the radiation era, which may allow for a
cosmologically relevant cosmic string role even in the case of light strings.
We also determine the impact that the radiation-matter transition has on the
dynamics of weakly interacting cosmic superstring networks. |
Galaxy Clusters in the Context of Superfluid Dark Matter: It has recently been proposed, by assuming that dark matter is a superfluid,
that MOND-like effects can be achieved on small scales whilst preserving the
success of $\Lambda$CDM on large scales. Here we aim to provide the first set
of spherical models of galaxy clusters in the context of superfluid dark
matter. We first outline the theoretical structure of the superfluid core and
the surrounding "normal phase" dark halo of quasi-particles in thermal
equlibrium. The latter should encompass the largest part of galaxy clusters.
Here, we set the SfDM transition at the radius where the density and pressure
of the superfluid and normal phase coincides, neglecting the effect of phonons
in the suprefluid core. We then apply the theory to a sample of galaxy
clusters, and directly compare the SfDM predicted mass profiles to data. We
find that the superfluid formulation can reproduce the X-ray dynamical mass
profile of clusters. The SfDM fits however display slight under-predictions of
the gravity in the central regions which might be partly related to our
neglecting of the effect of phonons in these regions. We conclude that this
superfluid formulation is successful in describing galaxy clusters, but further
work will be needed to determine whether the parameter choice is consistent
with galaxies. Our model could be made more realistic by exploring
non-sphericity and the SfDM transition condition we impose. | Galilean-invariant scalar fields can strengthen gravitational lensing: The mystery of dark energy suggests that there is new gravitational physics
on long length scales. Yet light degrees of freedom in gravity are strictly
limited by Solar System observations. We can resolve this apparent
contradiction by adding a Galilean-invariant scalar field to gravity. Called
Galileons, these scalars have strong self-interactions near overdensities, like
the Solar System, that suppress their dynamical effect. These nonlinearities
are weak on cosmological scales, permitting new physics to operate. In this
Letter, we point out that a massive gravity inspired coupling of Galileons to
stress energy gravity can have a surprising consequence: enhanced gravitational
lensing. Because the enhancement appears at a fixed scaled location for a wide
range of dark matter halo masses, stacked cluster analysis of weak lensing data
should be able to detect or constrain this effect. |
Galactic and Circumgalactic OVI and its Impact on the Cosmological Metal
and Baryon Budgets at 2<z<3.5: We present the first results from our NASA Keck Observatory Database of
Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the
properties of the highly ionized gas of high redshift galaxies and their
circumgalactic medium (CGM) at 2<z<4. We select absorbers optically thick at
the Lyman limit ({\tau}LL > 1, log N(HI) > 17.3) as probes of these galaxies
and their CGM where both transitions of the O VI doublet have little
contamination from the Ly {\alpha}, {\beta} forests. We found 20 absorbers that
satisfy these rules: 7 Lyman limit systems (LLSs), 8 super-LLSs (SLLSs) and 5
damped Ly{\alpha} (DLAs). The O VI detection rate is 100% for the DLAs, 71% for
the LLSs, and 63% for the SLLSs. When O VI is detected, log N(OVI)=14.9+/-0.3,
an average O VI column density substantially larger and with a smaller
dispersion than found in blind O VI surveys at similar redshifts. Strong O VI
absorption is therefore nearly ubiquitous in the CGM of z~2-3 galaxies. The
total velocity widths of the O VI profiles are also large (200<Dv(OVI)<400
km/s). These properties are quite similar to those seen for O VI in low z
star-forming galaxies, and therefore we hypothesize that these strong CGM O VI
absorbers (with {\tau}LL > 1) at 2<z<3.5 also probe outflows of star-forming
galaxies. The LLSs and SLLSs with no O VI absorption have properties consistent
with those seen in cosmological simulations tracing cold streams feeding
galaxies. When the highly ionized (Si IV and O VI) gas is taken into account,
we determine that the {\tau}LL > 1 absorbers could contain as much as 3-14% of
the cosmic baryon budget at z~2-3, only second to the Ly{\alpha} forest. We
conservatively show that 5-20% of the metals ever produced at z~2-3 are in form
of highly ionized metals ejected in the CGM of galaxies. | Is there a black hole in NGC 4382?: We present HST STIS observations of the galaxy NGC 4382 (M85) and
axisymmetric models of the galaxy to determine mass-to-light ration (M/L,
V-band) and central black hole mass (M_BH). We find M/L = 3.74 +/- 0.1 (solar
units) and M_BH = 1.3 (+5.2, -1.2) \times 10^7 M_sun at an assumed distance of
17.9 Mpc, consistent with no black hole. The upper limit, M_BH < 9.6 \times
10^7 M_sun (2{\sigma}) or M_BH < 1.4 \times 10^8 M_sun (3{\sigma}) is
consistent with the current M-{\sigma} relation, which predicts M_BH = 8.8
\times 10^7 M_sun at {\sigma}_e = 182 km/s, but low for the current M-L
relation, which predicts M_BH = 7.8 \times 10^8 M_sun at L_V = 8.9 \times 10^10
L_sun,V. HST images show the nucleus to be double, suggesting the presence of a
nuclear eccentric stellar disk, in analogy to the Tremaine disk in M31. This
conclusion is supported by the HST velocity dispersion profile. Despite the
presence of this non-axisymmetric feature and evidence of a recent merger, we
conclude that the reliability of our black hole mass determination is not
hindered. The inferred low black hole mass may explain the lack of nuclear
activity. |
Disruption of Cosmic String Wakes by Gaussian Fluctuations: We study the stability of cosmic string wakes against the disruption by the
dominant Gaussian fluctuations which are present in cosmological models. We
find that for a string tension given by $G \mu = 10^{-7}$ wakes remain locally
stable until a redshift of $z = 6$, and for a value of $G \mu = 10^{-14}$ they
are stable beyond a redshift of $z = 20$. We study a global stability criterion
which shows that wakes created by strings at times after $t_{eq}$ are
identifiable up to the present time, independent of the value of $G \mu$.
Taking into account our criteria it is possible to develop strategies to search
for the distinctive position space signals in cosmological maps which are
induced by wakes. | Bayesian estimation of our local motion from the Planck-2018 CMB
temperature map: The largest fluctuation in the CMB sky is the CMB dipole, which is believed
to be caused by the motion of our observation frame with respect to the CMB
rest frame. This motion accounts for the known motion of the Solar System
barycentre with a best-fit amplitude of $369$ km/s, in the direction ($\ell=
264^\circ$, $b=48^\circ$) in galactic coordinates. Along with the CMB dipole
signal, this motion also causes an inevitable signature of statistical
anisotropy in the higher multipoles due to the modulation and aberration of the
CMB temperature and polarization fields. This leads to a correlation between
adjacent CMB multipoles causing a non-zero value of the off-diagonal terms in
the covariance matrix which can be captured in terms of the dipolar spectra of
the bipolar spherical harmonics (BipoSH). In our work, we jointly infer the CMB
power spectrum and the BipoSH spectrum in a Bayesian framework using the
$\textit{Planck}$-2018 $\texttt{SMICA}$ temperature map. We detect amplitude
and direction of the local motion consistent with the canonical value $v=369$
km/s inferred from CMB dipole with a statistical significance of $4.54\sigma$,
$4.97\sigma$ and $5.23\sigma$ respectively from the masked temperature map with
the available sky fraction $40.1\%$, $59.1\%$, and $72.2\%$, confirming the
common origin of both the signals. The Bayes factor in favor of the canonical
value is between $7$ to $8$ depending on the choice of mask. But it strongly
disagrees (by a value of the Bayes factor about $10^{-10}-10^{-11}$) with a
higher value of local motion which one can infer from the amplitude of the
dipole signal obtained from the CatWISE2020 quasar catalog using the WISE and
NEOWISE data set. |
Dark matter profiles of SPARC galaxies: a challenge to fuzzy dark matter: Stellar and gas kinematics of galaxies are a sensitive probe of the dark
matter distribution in the halo. The popular fuzzy dark matter models predict
the peculiar shape of density distribution in galaxies: specific dense core
with sharp transition to the halo. Moreover, fuzzy dark matter predicts scaling
relations between the dark matter particle mass and density parameters. In this
work, we use a Bayesian framework and several dark matter halo models to
analyse the stellar kinematics of galaxies using the Spitzer Photometry and
Accurate Rotation Curves database. We then employ a Bayesian model comparison
to select the best halo density model. We find that more than half of the
galaxies prefer the fuzzy dark model against standard dark matter profiles
(NFW, Burkert, and cored NFW). While this seems like a success for fuzzy dark
matter, we also find that there is no single value for the particle mass that
provides a good fit for all galaxies. | Warm inflation as a way out of the swampland: We discuss how dissipative effects and the presence of a thermal radiation
bath, which are inherent characteristics of the warm inflation dynamics, can
evade the recently proposed Swampland conjectures. Different forms of
dissipation terms, motivated by both microphysical quantum field theory and
phenomenological models, are discussed and their viability to overcome the
assumed Swampland constraints is analyzed. |
Likelihood-free Cosmological Constraints with Artificial Neural
Networks: An Application on Hubble Parameters and SNe Ia: The errors of cosmological data generated from complex processes, such as the
observational Hubble parameter data (OHD) and the Type Ia supernova (SN Ia)
data, cannot be accurately modeled by simple analytical probability
distributions, e.g. Gaussian distribution. To constrain cosmological parameters
from these data, likelihood-free inference is usually used to bypass the direct
calculation of the likelihood. In this paper, we propose a new procedure to
perform likelihood-free cosmological inference using two artificial neural
networks (ANN), the Masked Autoregressive Flow (MAF) and the denoising
autoencoder (DAE). Our procedure is the first to use DAE to extract features
from data, in order to simplify the structure of MAF needed to estimate the
posterior. Tested on simulated Hubble parameter data with a simple Gaussian
likelihood, the procedure shows the capability of extracting features from data
and estimating posterior distributions without the need of tractable
likelihood. We demonstrate that it can accurately approximate the real
posterior, achieve performance comparable to the traditional MCMC method, and
the MAF gets better training results for small number of simulation when the
DAE is added. We also discuss the application of the proposed procedure to OHD
and Pantheon SN Ia data, and use them to constrain cosmological parameters from
the non-flat $\Lambda$CDM model. For SNe Ia, we use fitted light curve
parameters to find constraints on $H_0,\Omega_m,\Omega_\Lambda$ similar to
relevant work, using less empirical distributions. In addition, this work is
also the first to use Gaussian process in the procedure of OHD simulation. | Testing dark energy after pre-recombination early dark energy: In the studies on pre-recombination early dark energy (EDE), the evolution of
Universe after recombination is usually regarded as ${\Lambda}CDM$-like, which
corresponds that the equation of state of dark energy responsible for current
accelerated expansion is $w=-1$. However, in realistic models, $w$ might be
evolving. We consider the parametrizations of $w$ with respect to the redshift
$z$ in Axion-like EDE and AdS-EDE models, respectively. We performed the Monte
Carlo Markov chain analysis with recent cosmological data, and found that the
bestfit $w(z)$ is compatible with $w_0=-1,w_a=0$ (the cosmological constant)
and the evolution of $w$ is only marginally favored, which so has little effect
on lifting the bestfit value of ${H_0}$. |
Models of Stephan's Quintet: Hydrodynamic Constraints on the Group's
Evolution: We present smoothed particle hydrodynamic models of the interactions in the
compact galaxy group, Stephan's Quintet. This work is extension of the earlier
collisionless N-body simulations of Renaud et al. in which the large-scale
stellar morphology of the group was modeled with a series of galaxy-galaxy
interactions in the simulations. Including thermohydrodynamic effects in this
work, we further investigate the dynamical interaction history and evolution of
the intergalactic gas of Stephan's Quintet. The major features of the group,
such as the extended tidal features and the group-wide shock, enabled us to
constrain the models reasonably well, while trying to reproduce multiple
features of the system. We found that reconstructing the two long tails
extending from NGC 7319 toward NGC 7320c one after the other in two separate
encounters is very difficult and unlikely, because the second encounter usually
destroys or distorts the already-generated tidal structure. Our models suggest
the two long tails may be formed simultaneously from a single encounter between
NGC 7319 and 7320c, resulting in a thinner and denser inner tail than the outer
one. The tails then also run parallel to each other as observed. The model
results support the ideas that the group-wide shock detected in
multi-wavelength observations between NGC 7319 and 7318b and the starburst
region north of NGC 7318b are triggered by the high-speed collision between NGC
7318b and the intergalactic gas. Our models show that a gas bridge is formed by
the high-speed collision and clouds in the bridge continue to interact for some
tens of millions of years after the impact. This produces many small shocks in
that region, resulting a much longer cooling time than that of a single impact
shock. | The effect of ISM turbulence on the gravitational instability of
galactic discs: We investigate the gravitational instability of galactic discs, treating
stars and cold interstellar gas as two distinct components, and taking into
account the phenomenology of turbulence in the interstellar medium (ISM), i.e.
the Larson-type scaling relations observed in the molecular and atomic gas.
Besides deriving general properties of such systems, we analyse a large sample
of galaxies from The HI Nearby Galaxy Survey (THINGS), and show in detail how
interstellar turbulence affects disc instability in star-forming spirals. We
find that turbulence has a significant effect on both the inner and the outer
regions of the disc. In particular, it drives the inner gas disc to a regime of
transition between two instability phases and makes the outer disc more prone
to star-dominated instabilities. |
Quest for truly isolated galaxies: I describe attempts to identify and understand the most isolated galaxies
starting from my 1983 Leiden PhD thesis, continuing through a string of
graduate theses on various aspects of this topic, and concluding with an
up-to-date account of the difficulty to find really isolated objects. The
implication of some of the findings revealed on the way and presented here is
that the nearby Universe may contain many small dark-matter haloes, and that
some such haloes may possibly be accreting intergalactic gas to form dwarf
galaxies. | XMM-Newton Detects a Hot Gaseous Halo in the Fastest Rotating Spiral
Galaxy UGC 12591: We present our XMM-Newton observation of the fastest rotating spiral galaxy
UGC 12591. We detect hot gas halo emission out to 110 kpc from the galaxy
center, and constrain the halo gas mass to be smaller than 3.5e11 solar masses.
We also measure the temperature of the hot gas as T=0.64\pm0.03 keV. Combining
our X-ray constraints and the near-infrared and radio measurements in the
literature, we find a baryon mass fraction of 0.03-0.04 in UGC 12591,
suggesting a missing baryon mass of 75% compared with the cosmological mean
value. Combined with another recent measurement in NGC 1961, the result
strongly argues that the majority of missing baryons in spiral galaxies does
not reside in their hot halos. We also find that UGC 12591 lies significantly
below the baryonic Tully-Fisher relationship. Finally, we find that the baryon
fractions of massive spiral galaxies are similar to those of galaxy groups with
similar masses, indicating that the baryon loss is ultimately controlled by the
gravitational potential well. The cooling radius of this gas halo is small,
similar to NGC 1961, which argues that the majority of stellar mass of this
galaxy is not assembled as a result of cooling of this gas halo. |
Massive Primordial Black Holes: A review of the astronomical data of several last years on an astonishingly
high amount of black holes in the contemporary and early ($z\sim 10$) universe
is presented. Also the data on the recently observed peculiar stars in the
Galaxy are discussed. It is argued that practically all black holes in the
universe are primordial (PBH) and suggested that an inverted picture of the
galaxy formation is realized: supermassive black holes were formed prior to
galaxy formation and subsequently seeded the latter. Possibilities of
cosmological dark matter consisting of primordial black holes and of abundant
cosmological antimatter are considered.
A mechanism of 1993 anticipating all these phenomena and predicting an
extended log-normal mass spectrum of PBH is described. | Line Profiles of Intermediate Redshift Type Ia Supernovae: We present the temporal evolution of line profiles ranging from near
ultraviolet to optical wavelengths by analyzing 59 Subaru telescope spectra of
normal Type Ia Supernovae (SNe Ia) in the intermediate redshift range (0.05 < z
< 0.4) discovered by the Sloan Digital Sky Survey-II (SDSS-II) Supernova
Survey. We derive line velocities, peak wavelengths and pseudo-equivalent
widths (pEWs) of these lines. Additionally, we compare the line profiles around
the date of maximum brightness with those from their nearby counterparts. We
find that line profiles represented by their velocities and pEWs for
intermediate redshift SNe Ia are consistent with their nearby counterparts
within 2 $\sigma$. These findings support the picture that SNe Ia are a
"standard" candle for the intermediate redshift range as has been shown between
SNe Ia at nearby and high redshifts. There is a hint that the "MgII \lambda
4300" pEW distribution for intermediate redshift SNe Ia is larger than for the
nearby sample, which could be interpreted as a difference in the progenitor
abundance. |
The ability of Lisa, Taiji, and their networks to detect the stochastic
gravitational wave background generated by Cosmic Strings: The cosmic string contributes to our understanding and revelation of the
fundamental structure and evolutionary patterns of the universe, unifying our
knowledge of the cosmos and unveiling new physical laws and phenomena.
Therefore, we anticipate the detection of Stochastic Gravitational Wave
Background (SGWB) signals generated by cosmic strings in space-based detectors.
We have analyzed the detection capabilities of individual space-based
detectors, Lisa and Taiji, as well as the joint space-based detector network,
Lisa-Taiji, for SGWB signals produced by cosmic strings, taking into account
other astronomical noise sources. The results indicate that the Lisa-Taiji
network exhibits superior capabilities in detecting SGWB signals generated by
cosmic strings and can provide strong evidence. The Lisa-Taiji network can
achieve an uncertainty estimation of $\Delta G\mu/G\mu<0.5$ for cosmic string
tension $G\mu\sim4\times10^{-17}$, and can provide evidence for the presence of
SGWB signals generated by cosmic strings at $G\mu\sim10^{-17}$, and strong
evidence at $G\mu\sim10^{-16}$. Even in the presence of only SGWB signals, it
can achieve a relative uncertainty of $\Delta G\mu/G\mu<0.5$ for cosmic string
tension $G\mu<10^{-18}$, and provide strong evidence at $G\mu\sim10^{-17}$. | Characterizing the contaminating distance distribution for Bayesian
supernova cosmology: Measurements of the equation of state of dark energy from surveys of
thousands of Type Ia Supernovae (SNe Ia) will be limited by spectroscopic
follow-up and must therefore rely on photometric identification, increasing the
chance that the sample is contaminated by Core Collapse Supernovae (CC SNe).
Bayesian methods for supernova cosmology can remove contamination bias while
maintaining high statistical precision but are sensitive to the choice of
parameterization of the contaminating distance distribution. We use simulations
to investigate the form of the contaminating distribution and its dependence on
the absolute magnitudes, light curve shapes, colors, extinction, and redshifts
of core collapse supernovae. We find that the CC luminosity function dominates
the distance distribution function, but its shape is increasingly distorted as
the redshift increases and more CC SNe fall below the survey magnitude limit.
The shapes and colors of the CC light curves generally shift the distance
distribution, and their effect on the CC distances is correlated. We compare
the simulated distances to the first year results of the SDSS-II SN survey and
find that the SDSS distance distributions can be reproduced with simulated CC
SNe that are ~1 mag fainter than the standard Richardson et al. (2002)
luminosity functions, which do not produce a good fit. To exploit the full
power of the Bayesian parameter estimation method, parameterization of the
contaminating distribution should be guided by the current knowledge of the CC
luminosity functions, coupled with the effects of the survey selection and
magnitude-limit, and allow for systematic shifts caused by the parameters of
the distance fit. |
Observing the dark sector: Despite the observational success of the standard model of cosmology,
present-day observations do not tightly constrain the nature of dark matter and
dark energy and modifications to the theory of general relativity. Here, we
will discuss some of the ongoing and upcoming surveys that will revolutionize
our understanding of the dark sector. | Probing Ultra-light Axion Dark Matter from 21cm Tomography using
Convolutional Neural Networks: We present forecasts on the detectability of Ultra-light axion-like particles
(ULAP) from future 21cm radio observations around the epoch of reionization
(EoR). We show that the axion as the dominant dark matter component has a
significant impact on the reionization history due to the suppression of small
scale density perturbations in the early universe. This behavior depends
strongly on the mass of the axion particle.
Using numerical simulations of the brightness temperature field of neutral
hydrogen over a large redshift range, we construct a suite of training data.
This data is used to train a convolutional neural network that can build a
connection between the spatial structures of the brightness temperature field
and the input axion mass directly. We construct mock observations of the future
Square Kilometer Array survey, SKA1-Low, and find that even in the presence of
realistic noise and resolution constraints, the network is still able to
predict the input axion mass. We find that the axion mass can be recovered over
a wide mass range with a precision of approximately 20\%, and as the whole DM
contribution, the axion can be detected using SKA1-Low at 68\% if the axion
mass is $M_X<1.86 \times10^{-20}$eV although this can decrease to $M_X<5.25
\times10^{-21}$eV if we relax our assumptions on the astrophysical modeling by
treating those astrophysical parameters as nuisance parameters. |
Gravitational Grating: In this work, we study the interaction of the electromagnetic wave (EW) from
a distant quasar with the gravitational wave (GW) sourced by the binary stars.
While in the regime of geometric optics, the light bending due to this
interaction is negligible, we show that the phase shifting on the wavefront of
an EW can produce the diffraction pattern on the observer plane. The
diffraction of the light (with the wavelength of $\lambda_e$) by the
gravitational wave playing the role of {\it gravitational grating} (with the
wavelength of $\lambda_g$) has the diffraction angle of $\Delta\beta \sim
\lambda_e/\lambda_g$. The relative motion of the observer, the source of
gravitational wave and the quasar results in a relative motion of the observer
through the interference pattern on the observer plane. The consequence of this
fringe crossing is the modulation in the light curve of a quasar with the
period of few hours in the microwave wavelength. The optical depth for the
observation of this phenomenon for a Quasar with the multiple images strongly
lensed by a galaxy where the light trajectory of some of the images crosses the
lensing galaxy is $\tau \simeq 0.2$. By shifting the time delay of the light
curves of the multiple images in a strong-lensed quasar and removing the
intrinsic variations of a quasar, our desired signals, as a new method for
detection of GWs, can be detected. | Inferring astrophysical parameters using the 2D cylindrical power
spectrum from reionisation: Enlightening our understanding of the first galaxies responsible for driving
reionisation requires detecting the 21-cm signal from neutral hydrogen.
Interpreting the wealth of information embedded in this signal requires
Bayesian inference. Parameter inference from the 21-cm signal is primarily
restricted to the spherically averaged power spectrum (1D PS) owing to its
relatively straightforward derivation of an analytic likelihood function
enabling traditional Monte-Carlo Markov-Chain (MCMC) approaches. However, in
recent years, simulation-based inference (SBI) has become feasible which
removes the necessity of having an analytic likelihood, enabling more complex
summary statistics of the 21-cm signal to be used for Bayesian inference. In
this work, we use SBI, specifically marginal neural ratio estimation to learn
the likelihood-to-evidence ratio with Swyft, to explore parameter inference
using the cylindrically averaged 2D PS. Since the 21-cm signal is anisotropic,
the 2D PS should yield more constraining information compared to the 1D PS
which isotropically averages the signal. For this, we consider a mock 1000 hr
observation of the 21-cm signal using the SKA and compare the performance of
the 2D PS relative to the 1D PS. Additionally, we explore two separate
foreground mitigation strategies, perfect foreground removal and wedge
avoidance. We find the 2D PS outperforms the 1D PS by improving the
marginalised uncertainties on individual astrophysical parameters by up to
$\sim30-40$ per cent irrespective of the foreground mitigation strategy.
Primarily, these improvements stem from how the 2D PS distinguishes between the
transverse, $k_{\perp}$, and redshift dependent, $k_{\parallel}$ information
which enables greater sensitivity to the complex reionisation morphology. |
The ACS Fornax Cluster Survey. X. Color Gradients of Globular Cluster
Systems in Early-Type Galaxies: We use the largest homogeneous sample of globular clusters (GCs), drawn from
the ACSVCS and ACSFCS, to investigate the color gradients of GC systems in 76
early-type galaxies. We find that most GC systems possess an obvious negative
gradient in g-z color (bluer outwards). For GC systems displaying color
bimodality, both metal-rich and metal-poor GC subpopulations present shallower
but significant color gradients on average, and the mean gradients of these two
subpopulations are of roughly equal strength. The FOV of ACS mainly restricts
us to measuring the inner gradients of GC systems. These gradients, however,
can introduce an aperture bias when measuring the mean colors of GC
subpopulations from relatively narrow central pointings. Inferred corrections
to previous work imply a reduced significance for the relation between the mean
color of metal-poor GCs and their host galaxy luminosity. The GC color
gradients also show a dependence with host galaxy mass where the gradiens are
weakest at the ends of the mass spectrum--in massive galaxies and dwarf
galaxies--and strongest in galaxies of intermediate mass, around a stellar mass
of M_stellar~10^10M_sun. We also measure color gradients for field stars in the
host galaxies. We find that GC color gradients are systematically steeper than
field star color gradients, but the shape of the gradient-mass relation is the
same for both. If gradients are caused by rapid dissipational collapse and
weakened by merging, these color gradients support a picture where the inner GC
systems of most intermediate-mass and massive galaxies formed early and rapidly
with the most massive galaxies having experienced greater merging. The lack of
strong gradients in the GC systems of dwarfs, which probably have not
experienced many recent major mergers, suggests that low mass halos were
inefficient at retaining and mixing metals during the epoch of GC formation. | Computing observables in curved multifield models of inflation - A guide
(with code) to the transport method: We describe how to apply the transport method to compute inflationary
observables in a broad range of multiple-field models. The method is efficient
and encompasses scenarios with curved field-space metrics, violations of
slow-roll conditions and turns of the trajectory in field space. It can be used
for an arbitrary mass spectrum, including massive modes and models with
quasi-single-field dynamics. In this note we focus on practical issues. It is
accompanied by a Mathematica code which can be used to explore suitable models,
or as a basis for further development. |
Optical Spectroscopy of Halpha Filaments in Cool Core Clusters:
Kinematics, Reddening, and Sources of Ionization: We have obtained deep, high spatial and spectral resolution, long-slit
spectra of the Halpha nebulae in the cool cores of 9 galaxy clusters. This
sample provides a wealth of information on the ionization state, kinematics,
and reddening of the warm gas in the cool cores of galaxy clusters. We find
evidence for only small amounts of reddening in the extended, line-emitting
filaments, with the majority of filaments having E(B-V) < 0.2. The combination
of [O III]/Hb, [N II]/Ha, [S II]/Ha, and [O I]/Ha allow us to rule out
collisional ionization by cosmic rays, thermal conduction, and photoionization
by ICM X-rays and AGN as strong contributors to the ionization of the warm gas
in both nuclei and filaments. The data are adequately described by a composite
model of slow shocks and star formation. This model is further supported by an
observed correlation between the linewidths and low ionization line ratios
which becomes stronger in systems with more modest star formation activity
based on far ultraviolet observations. We find that the more extended, narrow
filaments tend to have shallower velocity gradients and narrower linewidths
than the compact filamentary complexes. We confirm that the widths of the
emission lines decrease with radius, from FWHM \sim 600 km/s in the nuclei to
FWHM ~ 100 km/s in the most extended filaments. We suggest that this radial
dependence of the velocity width may in fact be linked to ICM turbulence and,
thus, may provide a glimpse into the amount of turbulence in cool cores. In the
central regions (r < 10 kpc) of several systems the warm gas shows kinematic
signatures consistent with rotation. We find that the kinematics of the most
extended filaments in this sample are broadly consistent with both infall and
outflow, and recommend further studies linking the warm gas kinematics to both
radio and X-ray maps in order to further understand the observed kinematics. | Inhomogeneous cosmology in an anisotropic Universe: With the era of precision cosmology upon us, and upcoming surveys expected to
further improve the precision of our observations below the percent level,
ensuring the accuracy of our theoretical cosmological model is of the utmost
importance. Current tensions between our observations and predictions from the
standard cosmological model have sparked curiosity in extending the model to
include new physics. Although, some suggestions include simply accounting for
aspects of our Universe that are ignored in the standard model. One example
acknowledges the fact that our Universe contains significant density contrasts
on small scales; in the form of galaxies, galaxy clusters, filaments, and
voids. This small-scale structure is smoothed out in the standard model, by
assuming large-scale homogeneity of the matter distribution, which could have a
measurable effect due to the nonlinearity of Einstein's equations. This
backreaction of small-scale structures on the large-scale dynamics has been
suggested to explain the measured accelerating expansion rate of the Universe.
Current standard cosmological simulations ignore the effects of General
Relativity by assuming purely Newtonian dynamics. In this thesis, we take the
first steps towards quantifying the backreaction of small-scale structures by
performing cosmological simulations that solve Einstein's equations directly.
Simulations like these will allow us to quantify potentially important effects
on our observations that could become measurable as the precision of these
observations increases into the future. |
Improving Constraints on Inflation with CMB Delensing: The delensing of cosmic microwave background (CMB) maps will be increasingly
valuable for extracting as much information as possible from future CMB
surveys. Delensing provides many general benefits, including sharpening of the
acoustic peaks, more accurate recovery of the damping tail, and reduction of
lensing-induced $B$-mode power. In this paper we present several applications
of delensing focused on testing theories of early-universe inflation with
observations of the CMB. We find that delensing the CMB results in improved
parameter constraints for reconstructing the spectrum of primordial curvature
fluctuations, probing oscillatory features in the primordial curvature
spectrum, measuring the spatial curvature of the universe, and constraining
several different models of isocurvature perturbations. In some cases we find
that delensing can recover almost all of the constraining power contained in
unlensed spectra, and it will be a particularly valuable analysis technique to
achieve further improvements in constraints for model parameters whose
measurements are not expected to improve significantly when utilizing only
lensed CMB maps from next-generation CMB surveys. We also quantify the
prospects of testing the single-field inflation tensor consistency condition
using delensed CMB data; we find it to be out of reach of current and proposed
experimental technology and advocate for alternative detection methods. | Central regions of LIRGs: rings, hidden starbursts, Supernovae and star
clusters: We study star formation (SF) in very active environments, in luminous IR
galaxies, which are often interacting. A variety of phenomena are detected,
such as central starbursts, circumnuclear SF, obscured SNe tracing the history
of recent SF, massive super star clusters, and sites of strong off-nuclear SF.
All of these can be ultimately used to define the sequence of triggering and
propagation of star-formation and interplay with nuclear activity in the lives
of gas rich galaxy interactions and mergers. In this paper we present analysis
of high-spatial resolution integral field spectroscopy of central regions of
two interacting LIRGs. We detect a nuclear 3.3 um PAH ring around the core of
NGC 1614 with thermal-IR IFU observations. The ring's characteristics and
relation to the strong star-forming ring detected in recombination lines are
presented, as well as a scenario of an outward expanding starburst likely
initiated with a (minor) companion detected within a tidal feature. We then
present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an
intriguing triple encounter. The third component is a minor one, but,
nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows
and outflows are detected at the locations of the nuclei. Finally, we briefly
report on our on-going NIR adaptive optics imaging survey of several dozen
LIRGs. We have detected highly obscured core-collapse SNe in the central kpc,
and discuss the statistics of "missing SNe" due to dust extinction. We are also
determining the characteristics of hundreds of super star clusters in and
around the core regions of LIRGs, as a function of host-galaxy properties. |
Primordial Non-Gaussianity and the NRAO VLA Sky Survey: The NRAO VLA Sky Survey (NVSS) is the only dataset that allows an accurate
determination of the auto-correlation function (ACF) on angular scales of
several degrees for Active Galactic Nuclei (AGNs) at typical redshifts $z
\simeq 1$. Surprisingly, the ACF is found to be positive on such large scales
while, in the framework of the standard hierarchical clustering scenario with
Gaussian primordial perturbations it should be negative for a
redshift-independent effective halo mass of order of that found for
optically-selected quasars. We show that a small primordial non-Gaussianity can
add sufficient power on very large scales to account for the observed NVSS ACF.
The best-fit value of the parameter $f_{\rm NL}$, quantifying the amplitude of
primordial non-Gaussianity of local type is $f_{\rm NL}=62 \pm 27$ ($1\,\sigma$
error bar) and $25<f_{\rm NL}<117$ ($2\,\sigma$ confidence level),
corresponding to a detection of non-Gaussianity significant at the $\sim
3\,\sigma$ confidence level. The minimal halo mass of NVSS sources is found to
be $M_{\rm min}=10^{12.47\pm0.26}h^{-1}M_{\odot}$ ($1\,\sigma$) strikingly
close to that found for optically selected quasars. We discuss caveats and
possible physical and systematic effects that can impact on the results. | The Tolman Surface Brightness Test for the Reality of the Expansion. V.
Provenance of the Test and a New Representation of the Data for Three Remote
HST Galaxy Clusters: A new reduction is made of the HST photometric data for E galaxies in three
remote clusters at redshifts near z=0.85 in search for the Tolman surface
brightness (SB) signal for the reality of the expansion. Because of the strong
variation of SB of such galaxies with intrinsic size, and because the Tolman
test is about surface brightness, we must account for the variation. In an
earlier version of the test, Lubin & Sandage calibrated the variation out. In
contrast, the test is made here using fixed radius bins for both the local and
remote samples. Homologous positions in the galaxy image at which to compare
the surface brightness values are defined by radii at five Petrosian eta values
ranging from 1.0 to 2.0. Sersic luminosity profiles are used to generate two
diagnostic diagrams that define the mean SB distribution across the galaxy
image. A Sersic exponent, defined by the r^n family of Sersic profiles, of
n=0.46 fits both the local and remote samples. Diagrams of the dimming of the
<SB> with redshift over the range of Petrosian eta radii shows a highly
significance Tolman signal but degraded by luminosity evolution in the
look-back time. The expansion is real and a luminosity evolution exists at the
mean redshift of the HST clusters of 0.8 mag in R_cape and 0.4 mag in the
I_cape photometric rest-frame bands, consistent with the evolution models of
Bruzual and Charlot. |
Squeezed bispectrum from multi-field inflation with curved field space
metric: We investigate influences of the curved field-space metric of multi-field
inflationary models on the squeezed bispectrum. The reduced bispectrum in
squeezed limit is computed using the {\delta}N formalism. The calculation is
performed under the slow-roll approximation and assumption that field
derivative of the field-space metric is sufficiently small such that the
contributions from Riemann tensor of the field-space can be approximately
ignored. Based on these approximations, We compute the analytic expressions for
the reduced bispectrum in squeezed limit, and find that, for such a nearly flat
field-space metric, the field dependence of the metric can significantly alter
both amplitude and shape of the reduced bispectrum. The reduced bispectrum from
this nearly flat field-space metric can lead to spectral index of the halo bias
which amplitude is 2 -- 4 times larger than that from the flat field-space
model. This modification of the spectral index of the halo bias due to the
curved field-space metric could leave observable imprints in future galaxy
surveys. | A low-mass cut-off near the hydrogen burning limit for Salpeter-like
initial mass functions in early-type galaxies: We conduct a detailed investigation of the properties of the stellar initial
mass function (IMF) in two massive early-type lens galaxies with velocity
dispersions of sigma ~245 km/s and sigma ~325 km/s, for which both HST imaging
and X-Shooter spectra are available. We compare the inferences obtained from
two fully independent methods: (i) a combined gravitational lensing and stellar
dynamics (L&D) analysis of the data sets employing self-consistent axisymmetric
models, and (ii) a spectroscopic simple stellar population (SSP) analysis of
optical line-strength indices, assuming single power-law IMFs. The results from
the two approaches are found to be in agreement within the 1-sigma
uncertainties. Both galaxies are consistent with having a Salpeter IMF
(power-law slope of x = 2.35), which is strongly favoured over a Chabrier IMF
(x = 1.8), with probabilities inferred from the joint analysis of 89% and 99%,
respectively. Bottom-heavy IMFs significantly steeper than Salpeter (x >= 3.0)
are ruled out with decisive evidence (Bayes factor B > 1000) for both galaxies,
as they exceed the total mass derived from the L&D constraints. Our analysis
allows, for the first time, the inference of the low-mass cut-off of the IMF
(M_low). Combining the joint L&D and SSP analyses of both galaxies, we infer an
IMF slope of x = 2.22 +/- 0.14, consistent with Salpeter IMF, and a low-mass
limit M_low = 0.13 +/- 0.03 M_sun, just above the hydrogen burning limit. |
On the Origin of the Supergiant HI Shell and Putative Companion in NGC
6822: We present new Hubble Space Telescope Advanced Camera for Surveys imaging of
six positions spanning 5.8 kpc of the HI major axis of the Local Group dIrr NGC
6822, including both the putative companion galaxy and the large HI hole. The
resulting deep color magnitude diagrams show that NGC 6822 has formed >50% of
its stars in the last ~5 Gyr. The star formation histories of all six positions
are similar over the most recent 500 Myr, including low-level star formation
throughout this interval and a weak increase in star formation rate during the
most recent 50 Myr. Stellar feedback can create the giant HI hole, assuming
that the lifetime of the structure is longer than 500 Myr; such long-lived
structures have now been observed in multiple systems and may be the norm in
galaxies with solid-body rotation. The old stellar populations (red giants and
red clump stars) of the putative companion are consistent with those of the
extended halo of NGC 6822; this argues against the interpretation of this
structure as a bona fide interacting companion galaxy and against its being
linked to the formation of the HI hole via an interaction. Since there is no
evidence in the stellar population of a companion galaxy, the most likely
explanation of the extended HI structure in NGC 6822 is a warped disk inclined
to the line of sight. | Galaxy Formation and Reionization: Key Unknowns and Expected
Breakthroughs by the James Webb Space Telescope: The scheduled launch of James Webb Space Telescope (JWST) in late 2021 marks
a new start for studies of galaxy formation at high redshift z>~6 during the
era of Cosmic Reionization. JWST can capture sensitive, high-resolution images
and multi-object spectroscopy in the infrared that will transform our view of
galaxy formation during the first billion years of cosmic history. This review
summarizes our current knowledge of the role of galaxies in reionizing
intergalactic hydrogen ahead of JWST, achieved through observations with Hubble
Space Telescope and ground-based facilities including Keck, the Very Large
Telescope, Subaru, and the Atacama Large Millimeter/Submillimeter Array. We
identify outstanding questions in the field that JWST can address during its
mission lifetime, including with the planned JWST Cycle 1 programs. (Abridged) |
Probing the Cosmological Constant and Phase Transitions with Dark Matter: The Standard Model and its extensions predict multiple phase transitions in
the early universe. In addition to the electroweak phase transition, one or
several of these could occur at energies close to the weak scale. Such phase
transitions can leave their imprint on the relic abundance of TeV-scale dark
matter. In this paper, we enumerate several physical features of a generic
phase transition and parameterize the effect of each on the relic abundance. In
particular, we include among these effects the presence of the scalar field
vacuum energy and the cosmological constant, which is sensitive to UV physics.
Within the context of the Standard Model Higgs sector, we find that the relic
abundance of generic TeV-scale dark matter is affected by the vacuum energy at
the order of a fraction of a percent. For scalar field sectors with strong
first order phase transitions, an order one percent apparent tuning of coupling
constants may allow corrections induced by the vacuum energy to be of order
unity. | Lepto-hadronic modelling of blazar emission: The characteristic double-bumped spectral energy distribution (SED) of
blazars is explained by either leptonic or hadronic models. In the former,
Inverse Compton emission dominates the emission of the high energy bump, while
proton synchrotron emission and proton-gamma interactions dominate it in the
latter. We present a new stationary lepto-hadronic code that evaluates both the
leptonic and the hadronic interactions. Apart from the modelling of the SED
produced in a leptonic or hadronic model, the code permits the study of
interesting mixed lepto-hadronic scenarios, where both processes contribute
significantly to the high energy bump. A first application to data from the
high frequency peaked BL Lac object PKS 2155-304 is discussed. |
A Bayesian Framework for Cosmic String Searches in CMB Maps: There exists various proposals to detect cosmic strings from Cosmic Microwave
Background (CMB) or 21 cm temperature maps. Current proposals do not aim to
find the location of strings on sky maps, all of these approaches can be
thought of as a statistic on a sky map. We propose a Bayesian interpretation of
cosmic string detection and within that framework, we derive a connection
between estimates of cosmic string locations and cosmic string tension $G\mu$.
We use this Bayesian framework to develop a machine learning framework for
detecting strings from sky maps and outline how to implement this framework
with neural networks. The neural network we trained was able to detect and
locate cosmic strings on noiseless CMB temperature map down to a string tension
of $G\mu=5 \times10^{-9}$ and when analyzing a CMB temperature map that does
not contain strings, the neural network gives a 0.95 probability that
$G\mu\leq2.3\times10^{-9}$. | Concerning the Classical Cepheid VIc Wesenheit Function's Strong
Metallicity Dependence: Evidence is presented which supports findings that the classical Cepheid VIc
period-Wesenheit function is relatively insensitive to metallicity. The
viability of a recently advocated strong metallicity dependence was evaluated
by applying the proposed correction (gamma=-0.8 mag/dex) to distances
established for the Magellanic Clouds via a Galactic VIc Wesenheit calibration,
which is anchored to ten nearby classical Cepheids with measured HST
parallaxes. The resulting gamma-corrected distances for the Magellanic Clouds
(e.g., SMC, mu(0,gamma)~18.3) are in significant disagreement with that
established from a mean of >300 published estimates (NED-D), and a universal
Wesenheit template featuring eleven delta Scuti, SX Phe, RR Lyrae, and Type II
Cepheid variables with HST/Hipparcos parallaxes. Conversely, adopting a null
correction (i.e., gamma=0 mag/dex) consolidates the estimates. In tandem with
existing evidence, the results imply that variations in chemical composition
among Cepheids are a comparatively negligible source of uncertainty for
W(VIc)-based extragalactic distances and determinations of H_0. A new approach
is described which aims to provide additional Galactic Cepheid calibrators to
facilitate subsequent assessments of the VIc Wesenheit function's relative
(in)sensitivity to abundance changes. VVV/UKIDSS/2MASS JHKs photometry for
clusters in spiral arms shall be employed to establish a precise galactic
longitude-distance relation, which can be applied in certain cases to determine
the absolute Wesenheit magnitudes for younger Cepheids. |
Redshift Space Distortion of 21cm line at 1<z<5 with Cosmological
Hydrodynamic Simulations: We measure the scale dependence and redshift dependence of 21 cm line emitted
from the neutral hydrogen gas at redshift 1<z<5 using full cosmological
hydrodynamic simulations by taking the ratios between the power spectra of
HI-dark matter cross correlation and dark matter auto-correlation. The neutral
hydrogen distribution is computed in full cosmological hydrodynamic simulations
including star formation and supernova feedback under a uniform ultra-violet
background radiation. We find a significant scale dependence of HI bias at z>3
on scales of k>1h/Mpc, but it is roughly constant at lower redshift z<3. The
redshift evolution of HI bias is relatively slow compared to that of QSOs at
similar redshift range. We also measure a redshift space distortion (RSD) of HI
gas to explore the properties of HI clustering. Fitting to a widely applied
theoretical prediction, we find that the constant bias is consistent with that
measured directly from the real-space power spectra, and the velocity
dispersion is marginally consistent with the linear perturbation prediction.
Finally we compare the results obtained from our simulation and the Illustris
simulation, and conclude that the detailed astrophysical effects do not affect
the scale dependence of HI bias very much, which implies that the cosmological
analysis using 21 cm line of HI will be robust against the uncertainties
arising from small-scale astrophysical processes such as star formation and
supernova feedback. | Further Definition of the Mass-Metallicity Relation in Globular Cluster
Systems Around Brightest Cluster Galaxies: We combine the globular cluster data for fifteen Brightest Cluster Galaxies
and use this material to trace the mass-metallicity relations (MMR) in their
globular cluster systems (GCSs). This work extends previous studies which
correlate the properties of the MMR with those of the host galaxy. Our combined
data sets show a mean trend for the metal-poor (MP) subpopulation which
corresponds to a scaling of heavy-element abundance with cluster mass Z ~
M^(0.30+/-0.05). No trend is seen for the metal-rich (MR) subpopulation which
has a scaling relation that is consistent with zero. We also find that the
scaling exponent is independent of the GCS specific frequency and host galaxy
luminosity, except perhaps for dwarf galaxies.
We present new photometry in (g',i') obtained with Gemini/GMOS for the
globular cluster populations around the southern giant ellipticals NGC 5193 and
IC 4329. Both galaxies have rich cluster populations which show up as normal,
bimodal sequences in the colour-magnitude diagram.
We test the observed MMRs and argue that they are statistically real, and not
an artifact caused by the method we used. We also argue against asymmetric
contamination causing the observed MMR as our mean results are no different
from other contamination-free studies. Finally, we compare our method to the
standard bimodal fitting method (KMM or RMIX) and find our results are
consistent.
Interpretation of these results is consistent with recent models for globular
cluster formation in which the MMR is determined by GC self-enrichment during
their brief formation period. |
A Brief History of Curvature: The trace of the stress-energy tensor of the cosmological fluid, proportional
to the Ricci scalar curvature in general relativity, is determined on cosmic
scales for times ranging from the inflationary epoch to the present day in the
expanding Universe. The post-inflationary epoch and the thermal history of the
relativistic fluid, in particular the QCD transition from asymptotic freedom to
confinement and the electroweak phase transition, leave significant imprints on
the scalar curvature. These imprints can be of either sign and are orders of
magnitude larger than the values that would be obtained by naively
extrapolating the pressureless matter of the present epoch back into the
radiation-dominated epoch. | Constraints on Multicomponent Dark Energy from Cosmological Observations: Dark energy (DE) plays an important role in the expansion history of our
universe. But we only got limited knowledge about its nature and properties
after decades of study.In most numerical researches, DE is usually considered
as a dynamical whole. Actually, multicomponent DE models can also explain the
accelerating expansion of our universe, which is accepted theoretically but
lack of numerical researches. We try to study the multicomponent DE models from
observation by constructing $w_n$CDM models. The total energy density of DE is
separated into $n$ ($n=2,3,5$) parts equally and every part has a constant EOS
$w_i$ ($i=1,2...n$). We modify the Friedmann equation and the parameterized
post-Friedmann description of DE, then put constraints on $w_i$s from Planck
2018 TT,TE,EE$+$lowE$+$lensing, BAO data and PANTHEON samples. The
multicomponent DE models are favoured if any $w_n$CDM model is preferred by
observational data and there is no overlap between the highest and lowest
values of $w_i$s. We find the data combination supports the $w_n$CDM model when
$n$ is small and the $w_2$CDM model is slightly preferred by $\Delta
\chi^2_{\text{min}} = \Delta \text{AIC} =\Delta \text{BIC} = -2.48$ over the
CPL model, but the largest value of $w_i$ overlaps the smallest one. With
larger $n$, the maximum and minimum of $w_i$s do not overlap with each other,
but $\chi^2_{\text{min}}$ and AIC also increase. In brief, we find no obvious
evidence that DE is composed of different components. |
A slitless spectroscopic survey for Halpha emission-line objects in SMC
clusters: This paper checks on the roles of metallicity and evolutionary age in the
appearance of the so-called Be phenomenon. Slitless CCD spectra were obtained
covering the bulk of the Small Magellanic Cloud. For Halpha line emission twice
as strong as the ambient continuum, the survey is complete to spectral type
B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for
emission lines in 84 open clusters. 370 emission-line stars were found, among
them at least 231 near the main sequence. For 176 of them, photometry could be
found in the OGLE database. For comparison with a higher-metallicity
environment, the Galactic sample of the photometric Halpha survey by McSwain &
Gies (2005) was used. Among early spectral sub-types, Be stars are more
frequent by a factor 3-5 in the SMC than in the Galaxy. The distribution with
spectral type is similar in both galaxies, i.e. not strongly dependent on
metallicity. The fraction of Be stars does not seem to vary with local star
density. The Be phenomenon mainly sets in towards the end of the main-sequence
evolution (this trend may be more pronounced in the SMC); but some Be stars
already form with Be-star characteristics. In all probability, the fractional
critical angular rotation rate, \omc, is one of the main parameters governing
the occurrence of the Be phenomenon. If the Be character is only acquired
during the course of evolution, the key circumstance is the evolution of \omc,
which not only is dependent on metallicity but differently so for different
mass ranges. | Metallicity Evolution of Damped Lyman-alpha Systems out to z~5: We present chemical abundance measurements for 47 damped Lyman-alpha systems
(DLAs), 30 at z>4, observed with the Echellette Spectrograph and Imager and the
High Resolution Echelle Spectrometer on the Keck telescopes. HI column
densities of the DLAs are measured with Voigt profile fits to the Lyman-alpha
profiles, and we find an increased number of false DLA identifications with
SDSS at z>4 due to the increased density of the Lyman-alpha forest. Ionic
column densities are determined using the apparent optical depth method, and we
combine our new metallicity measurements with 195 from previous surveys to
determine the evolution of the cosmic metallicity of neutral gas. We find the
metallicity of DLAs decreases with increasing redshift, improving the
significance of the trend and extending it to higher redshifts, with a linear
fit of -0.22+-0.03 dex per unit redshift from z=0.09-5.06. The metallicity
'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for
finding DLAs with much lower metallicities. However, this floor is not
statistically different from a steep tail to the distribution. We also find
that the intrinsic scatter of metallicity among DLAs of ~0.5 dex continues out
to z~5. In addition, the metallicity distribution and the alpha/Fe ratios of
z>2 DLAs are consistent with being drawn from the same parent population with
those of halo stars. It is therefore possible that the halo stars in the Milky
Way formed out of gas that commonly exhibits DLA absorption at z>2. |
Another look at redshift drift and the backreaction conjecture: Earlier studies have conjectured that redshift drift is described by
spatially averaged quantities and thus becomes positive if the average
expansion of the Universe accelerates. This conclusion is reevaluated here by
considering exact light propagation in a simple toy-model with average
accelerated expansion. The toy-model and light propagation setup is explicitly
designed for concordance between spatial averages and averages along light
rays. While it is verified that redshift-distance relations are well described
by average quantities in this setup, it is found that the redshift drift is
not. Specifically, the redshift drift is negative despite the on-average
late-time accelerated expansion of the model. This result implies that
measuring redshift drift signals at low redshifts gives the potential for
directly falsifying the backreaction conjecture. However, the results are based
on a toy-model so it is in principle possible that the result is an artifact
and that redshift drift is in reality well described by spatially averaged
quantities. The result therefore highlights the importance of developing
\emph{exact} solutions to the Einstein equations which exhibit average
accelerated expansion without local expansion so that the relation between
spatial averages and observations can be firmly established. | PHIBSS: molecular gas, extinction, star formation and kinematics in the
z=1.5 star forming galaxy EGS13011166: We report matched resolution, imaging spectroscopy of the CO J=3-2 line (with
the IRAM Plateau de Bure millimeter interferometer) and of the H-alpha line
(with LUCI at the Large Binocular Telescope)in the massive z=1.53 main-sequence
galaxy EGS 13011166, as part of the "Plateau de Bure high-z, blue sequence
survey (PHIBSS). We combine these data with HST V-J-J-H-band maps to derive
spatially resolved distributions of stellar surface density, star formation
rate, molecular gas surface density, optical extinction and gas kinematics. The
spatial distribution and kinematics of the ionized and molecular gas are
remarkably similar and are well modeled by a turbulent, globally Toomre
unstable rotating disk. The stellar surface density distribution is smoother
than the clumpy rest-frame UV/optical light distribution, and peaks in an
obscured, star forming massive bulge near the dynamical center. The molecular
gas surface density and the effective optical screen extinction track each
other and are well modeled by a 'mixed' extinction model. The inferred slope of
the spatially resolved molecular gas to star formation rate relation depends
strongly on the adopted extinction model and can vary from 0.8 to 1.7. For the
preferred mixed dust-gas model we find a near linear slope. |
Cosmological Birefringence: an Astrophysical test of Fundamental Physics: We review the methods used to test for the existence of cosmological
birefringence, i.e. a rotation of the plane of linear polarization for
electromagnetic radiation traveling over cosmological distances, which might
arise in a number of important contexts involving the violation of fundamental
physical principles. The main methods use: (1) the radio polarization of radio
galaxies and quasars, (2) the ultraviolet polarization of radio galaxies, and
(3) the cosmic microwave background polarization. We discuss the main results
obtained so far, the advantages and disadvantages of each method, and future
prospects. | High $H_0$ Values from CMB E-mode Data: A Clue for Resolving the Hubble
Tension?: The E-mode (EE) CMB power spectra measured by Planck, ACTPol, and SPTpol
constrain the Hubble constant to be $70.0\pm2.7$, $72.4^{+3.9}_{-4.8}$, and
$73.1^{+3.3}_{-3.9}$ km s$^{-1}$ Mpc$^{-1}$ within the standard $\Lambda$CDM
model (posterior mean and central 68% interval bounds). These values are higher
than the constraints from the Planck temperature (TT) power spectrum, and
consistent with the Cepheid-supernova distance ladder measurement
$H_0=73.2\pm1.3$ km s$^{-1}$ Mpc$^{-1}$. If this preference for a higher value
was strengthened in a joint analysis it could provide an intriguing hint at the
resolution of the Hubble disagreement. We show, however, that combining the
Planck, ACTPol, and SPTpol EE likelihoods yields $H_0=68.7\pm1.3$ km s$^{-1}$
Mpc$^{-1}$, $2.4\sigma$ lower than the distance ladder measurement. This is due
to different degeneracy directions across the full parameter space,
particularly involving the baryon density, $\Omega_bh^2$, and scalar tilt,
$n_s$, arising from sensitivity to different multipole ranges. We show that the
E-mode $\Lambda$CDM constraints are consistent across the different experiments
within $1.4\sigma$, and with the Planck TT results at $0.8\sigma$. Combining
the Planck, ACTPol, and SPTpol EE data constrains the phenomenological lensing
amplitude, $A_L=0.89\pm0.10$, consistent with the expected value of unity. |
A Chandra view of the clumpy reflector at the heart of the Circinus
galaxy: We present a spectral and imaging analysis of the X-ray reflecting structure
at the heart of the Circinus galaxy, investigating the innermost regions
surrounding the central black hole. By studying an archival 200 ks Chandra
ACIS-S observation, we are able to image the extended clumpy structure
responsible for both cold reflection of the primary radiation and neutral iron
Ka line emission. We measure an excess of the equivalent width of the iron Ka
line which follows an axisymmetric geometry around the nucleus on a hundred pc
scale. Spectra extracted from different regions confirm a scenario in which the
dominant mechanism is the reflection of the nuclear radiation from
Compton-thick gas. Significant differences in the equivalent width of the iron
Ka emission line (up to a factor of 2) are found. It is argued that these
differences are due to different scattering angles with respect to the line of
sight rather than to different iron abundances. | Quijote-PNG: Quasi-maximum likelihood estimation of Primordial
Non-Gaussianity in the non-linear halo density field: We study primordial non-Gaussian signatures in the redshift-space halo field
on non-linear scales, using a quasi-maximum likelihood estimator based on
optimally compressed power spectrum and modal bispectrum statistics. We train
and validate the estimator on a suite of halo catalogues constructed from the
Quijote-PNG N-body simulations, which we release to accompany this paper. We
verify its unbiasedness and near optimality, for the three main types of
primordial non-Gaussianity (PNG): local, equilateral, and orthogonal. We
compare the modal bispectrum expansion with a $k$-binning approach, showing
that the former allows for faster convergence of numerical derivatives in the
computation of the score-function, thus leading to better final constraints. We
find, in agreement with previous studies, that the local PNG signal in the
halo-field is dominated by the scale-dependent bias signature on large scales
and saturates at $k \sim 0.2~h\,\mathrm{Mpc}^{-1}$, whereas the small-scale
bispectrum is the main source of information for equilateral and orthogonal
PNG. Combining power spectrum and bispectrum on non-linear scales plays an
important role in breaking degeneracies between cosmological and PNG
parameters; such degeneracies remain however strong for equilateral PNG. We
forecast that PNG parameters can be constrained with $\Delta
f_\mathrm{NL}^\mathrm{local} = 45$, $\Delta f_\mathrm{NL}^\mathrm{equil} =
570$, $\Delta f_\mathrm{NL}^\mathrm{ortho} = 110$, on a cubic volume of $1
\left({ {\rm Gpc}/{ {\rm h}}} \right)^3$, at $z = 1$, considering scales up to
$k_\mathrm{max} = 0.5~h\,\mathrm{Mpc}^{-1}$. |
The Statefinder hierarchy: An extended null diagnostic for concordance
cosmology: We show how higher derivatives of the expansion factor can be developed into
a null diagnostic for concordance cosmology (LCDM). It is well known that the
Statefinder -- the third derivative of the expansion factor written in
dimensionless form, a^{(3)}/aH^3, equals unity for LCDM. We generalize this
result to higher derivatives of the expansion factor and demonstrate that the
hierarchy, a^{(n)}/aH^n, can be converted to a form that stays pegged at unity
in concordance cosmology. This remarkable property of the Statefinder hierarchy
enables it to be used as an extended null diagnostic for the cosmological
constant. The Statefinder hierarchy combined with the growth rate of matter
perturbations defines a composite null diagnostic which can distinguish
evolving dark energy from LCDM. | The Halo Occupation Distribution of Active Galactic Nuclei: Using a fully cosmological hydrodynamic simulation that self-consistently
incorporates the growth and feedback of supermassive black holes and the
physics of galaxy formation, we examine the effects of environmental factors
(e.g., local gas density, black hole feedback) on the halo occupation
distribution of low luminosity active galactic nuclei (AGN). We decompose the
mean occupation function into central and satellite contribution and compute
the conditional luminosity functions (CLF). The CLF of the central AGN follows
a log-normal distribution with the mean increasing and scatter decreasing with
increasing redshifts. We analyze the light curves of individual AGN and show
that the peak luminosity of the AGN has a tighter correlation with halo mass
compared to instantaneous luminosity. We also compute the CLF of satellite AGN
at a given central AGN luminosity. We do not see any significant correlation
between the number of satellites with the luminosity of the central AGN at a
fixed halo mass. We also show that for a sample of AGN with luminosity above
10^42 ergs/s the mean occupation function can be modeled as a softened step
function for central AGN and a power law for the satellite population. The
radial distribution of AGN inside halos follows a power law at all redshifts
with a mean index of -2.33 +/- 0.08. Incorporating the environmental dependence
of supermassive black hole accretion and feedback, our formalism provides a
theoretical tool for interpreting current and future measurements of AGN
clustering. |
A relation of the PAH 3.3 um feature with star-forming activity for
galaxies with a wide range of infrared luminosity: For star-forming galaxies, we investigate a global relation between
polycyclic aromatic hydrocarbon (PAH) emission luminosity at 3.3 um, L_PAH3.3,
and infrared (8-1000 um) luminosity, L_IR, to understand how the PAH 3.3 um
feature relates to the star formation activity. With AKARI, we performed
near-infrared (2.5-5 um) spectroscopy of 184 galaxies which have L_IR \sim 10^8
- 10^13 L_sun. We classify the samples into infrared galaxies (IRGs; L_IR <
10^11 L_sun), luminous infrared galaxies (LIRGs; L_IR \sim 10^11 -10^12 L_sun)
and ultra luminous infrared galaxies (ULIRGs; L_IR > 10^12 L_sun). We exclude
sources which are likely contaminated by AGN activity, based on the rest-frame
equivalent width of the PAH emission feature (< 40 nm) and the power-law index
representing the slope of continuum emission (Gamma > 1; F_nu \propto
lambda^Gamma). Of these samples, 13 IRGs, 67 LIRGs and 20 ULIRGs show PAH
emission feature at lambda_rest= 3.3 um in their spectra. We find that the
L_PAH3.3/L_IR ratio considerably decreases toward the luminous end. Utilizing
the mass and temperature of dust grains as well as the BrAlpha emission for the
galaxies, we discuss the cause of the relative decrease in the PAH emission
with L_IR. | The Topology and Size of the Universe from CMB Temperature and
Polarization Data: We analyze seven year and nine year WMAP temperature maps for signatures of
three finite flat topologies M_0=T^3, M_1=T^2 x R^1, and M_2=S^1 x R^2. We use
Monte-Carlo simulations with the Feldman-Cousins method to obtain confidence
intervals for the size of the topologies considered. We analyze the V, W, and Q
frequency bands along with the ILC map and find no significant difference in
the results. The 95.5% confidence level lower bound on the size of the topology
is 1.5L_0 for M_0, 1.4L_0 for M_1, and 1.1L_0 for M_2, where L_0 is the radius
of the last scattering surface. Our results agree very well with the recently
released results from the Planck temperature data. We show that the likelihood
function is not Gaussian in the size, and therefore simulations are important
for obtaining accurate bounds on the size. We then introduce the formalism for
including polarization data in the analysis. The improvement that we find from
WMAP polarization maps is small because of the high level of instrumental
noise, but our forecast for Planck maps shows a much better improvement on the
lower bound for L. For the M_0 topology we expect an improvement on the lower
bound of L from 1.7L_0 to 1.9L_0 at 95.5% confidence level. Using both
polarization and temperature data is important because it tests the hypothesis
that deviations in the TT spectrum at small l originate in the primordial
perturbation spectrum. |
Metallicity distributions in and around galaxies: Metals are found in all baryonic phases and environments, and our knowledge
of their distribution `in and around galaxies' has significantly improved over
the past few years. Theoretical work has shown that the fraction of metals in
different baryonic components can vary significantly when different feedback
schemes are adopted. Therefore, studies of element abundances provide important
information about all gas-dynamical processes which determine the cosmic
evolution of baryons. I give here a brief review of recent observational
progress, describe the implications of recent theoretical studies, and discuss
briefly future prospects. | SuperModel Analysis of Abell 1246 and J255: on the Evolution of Galaxy
Clusters from High to Low Entropy States: We present an analysis of high-quality X-ray data out to the virial radius
for the two galaxy clusters Abell 1246 and GMBCG J255.34805+64.23661 (J255) by
means of our entropy-based SuperModel. For Abell 1246 we find that the
spherically-averaged entropy profile of the intracluster medium (ICM)
progressively flattens outwards, and that a nonthermal pressure component
amounting to ~20% of the total is required to support hydrostatic equilibrium
in the outskirts; there we also estimate a modest value C~1.6 of the ICM
clumping factor. These findings agree with previous analyses on other
cool-core, relaxed clusters, and lend further support to the picture by Lapi et
al. (2010) that relates the entropy flattening, the development of nonthermal
pressure component, and the azimuthal variation of ICM properties to weakening
boundary shocks. In this scenario clusters are born in a high-entropy state
throughout, and are expected to develop on similar timescales a low entropy
state both at the center due to cooling, and in the outskirts due to weakening
shocks. However, the analysis of J255 testifies how such a typical evolutionary
course can be interrupted or even reversed by merging especially at
intermediate redshift, as predicted by Cavaliere et al. (2011b). In fact, a
merger has rejuvenated the ICM of this cluster at z~0.45 by reestablishing a
high entropy state in the outskirts, while leaving intact or erasing only
partially the low-entropy, cool core at the center. |
Bounds on Ultralight Dark Matter from NANOGrav: The detection of the stochastic gravitational wave background by NANOGrav
imposes constraints on the mass of compact cores of ultralight dark matter,
also known as "solitons", surrounding supermassive black holes found at the
centers of large galaxies. The strong dynamical friction between the rotating
black holes and the solitons competes with gravitational wave emission,
resulting in a suppression of the characteristic strain in the nHz frequency
range. Our findings rule out solitons arising from the condensation of
ultralight dark matter particles with masses ranging from $1.3\times 10^{-21}$
eV to $1.4\times 10^{-20}$ eV. | LiteBIRD Science Goals and Forecasts. A Case Study of the Origin of
Primordial Gravitational Waves using Large-Scale CMB Polarization: We study the possibility of using the $LiteBIRD$ satellite $B$-mode survey to
constrain models of inflation producing specific features in CMB angular power
spectra. We explore a particular model example, i.e. spectator axion-SU(2)
gauge field inflation. This model can source parity-violating gravitational
waves from the amplification of gauge field fluctuations driven by a
pseudoscalar "axionlike" field, rolling for a few e-folds during inflation. The
sourced gravitational waves can exceed the vacuum contribution at reionization
bump scales by about an order of magnitude and can be comparable to the vacuum
contribution at recombination bump scales. We argue that a satellite mission
with full sky coverage and access to the reionization bump scales is necessary
to understand the origin of the primordial gravitational wave signal and
distinguish among two production mechanisms: quantum vacuum fluctuations of
spacetime and matter sources during inflation. We present the expected
constraints on model parameters from $LiteBIRD$ satellite simulations, which
complement and expand previous studies in the literature. We find that
$LiteBIRD$ will be able to exclude with high significance standard single-field
slow-roll models, such as the Starobinsky model, if the true model is the
axion-SU(2) model with a feature at CMB scales. We further investigate the
possibility of using the parity-violating signature of the model, such as the
$TB$ and $EB$ angular power spectra, to disentangle it from the standard
single-field slow-roll scenario. We find that most of the discriminating power
of $LiteBIRD$ will reside in $BB$ angular power spectra rather than in $TB$ and
$EB$ correlations. |
Learning cosmology and clustering with cosmic graphs: We train deep learning models on thousands of galaxy catalogues from the
state-of-the-art hydrodynamic simulations of the CAMELS project to perform
regression and inference. We employ Graph Neural Networks (GNNs), architectures
designed to work with irregular and sparse data, like the distribution of
galaxies in the Universe. We first show that GNNs can learn to compute the
power spectrum of galaxy catalogues with a few percent accuracy. We then train
GNNs to perform likelihood-free inference at the galaxy-field level. Our models
are able to infer the value of $\Omega_{\rm m}$ with a $\sim12\%-13\%$ accuracy
just from the positions of $\sim1000$ galaxies in a volume of $(25~h^{-1}{\rm
Mpc})^3$ at $z=0$ while accounting for astrophysical uncertainties as modelled
in CAMELS. Incorporating information from galaxy properties, such as stellar
mass, stellar metallicity, and stellar radius, increases the accuracy to
$4\%-8\%$. Our models are built to be translational and rotational invariant,
and they can extract information from any scale larger than the minimum
distance between two galaxies. However, our models are not completely robust:
testing on simulations run with a different subgrid physics than the ones used
for training does not yield as accurate results. | Primordial Black Holes and Cosmological Problems: It is argued that the bulk of black holes (BH) in the universe are primordial
(PBH). This assertion is strongly supported by the recent astronomical
observations, which allow to conclude that supermassive BHs with $M= (10^6 -
10^9) M_\odot$ "work" as seeds for galaxy formation, intermediate mass BHs, $ M
= (10^3 - 10^4) M_\odot$, do the same job for globular clusters and dwarf
galaxies, while black holes of a few solar masses are the constituents of dark
matter of the universe. The mechanism of PBH formation, suggested in 1993,
which predicted such features of the universe, is described. The model leads to
the log-normal mass spectrum of PBHs, which is determined by three constant
parameters. With proper adjustment of these parameters the above mentioned
features are quantitatively explained. In particular, the calculated density of
numerous superheavy BHs in the young universe, $ z = 5 - 10$, nicely fits the
data. The puzzling properties of the sources of the LIGO-discovered
gravitational waves are also naturally explained assuming that these sources
are PBHs. |
Nonminimally Assisted Inflation: A General Analysis: The effects of a scalar field, known as the "assistant field," which
nonminimally couples to gravity, on single-field inflationary models are
studied. The analysis provides analytical expressions for inflationary
observables such as the spectral index ($n_s$), the tensor-to-scalar ratio
($r$), and the local-type nonlinearity parameter ($f_{\rm NL}^{(\rm local)}$).
The presence of the assistant field leads to a lowering of $n_s$ and $r$ in
most of the parameter space, compared to the original predictions. In some
cases, $n_s$ may increase due to the assistant field. This revives
compatibility between ruled-out single-field models and the latest observations
by Planck-BICEP/Keck. The results are demonstrated using three example models:
loop inflation, power-law inflation, and hybrid inflation. | Full-sky lensing shear at second order: We compute the reduced cosmic shear up to second order in the gravitational
potential without relying on the small angle or thin-lens approximation. This
is obtained by solving the Sachs equation which describes the deformation of
the infinitesimal cross-section of light bundle in the optical limit, and maps
galaxy intrinsic shapes into their angular images. The calculation is done in
the Poisson gauge without a specific matter content, including vector and
tensor perturbations generated at second order and taking account of the
inhomogeneities of a fixed redshift source plane. Our final result is expressed
in terms of spin-2 operators on the sphere and is valid on the full sky. Beside
the well known lens-lens and Born corrections that dominate on small angular
scales, we find new non-linear couplings. These are a purely general
relativistic intrinsic contribution, a coupling between the gravitational
potential at the source with the lens, couplings between the time delay with
the lens, couplings between two photon deflections, as well as non-linear
couplings due to the second-order vector and tensor components. The
inhomogeneity in the redshift of the source induces a coupling between the
photon redshift with the lens. All these corrections become important on large
angular scales and should thus be included when computing higher-order
observables such as the bispectrum, in full or partially full-sky surveys. |
Photodissociation of H2 in Protogalaxies: Modeling Self-Shielding in 3D
Simulations: The ability of primordial gas to cool in proto-galactic haloes exposed to
Lyman-Werner (LW) radiation is critically dependent on the self-shielding of
H_2. We perform radiative transfer calculations of LW line photons,
post-processing outputs from three-dimensional adaptive mesh refinement (AMR)
simulations of haloes with T_vir > 10^4 K at redshifts around z=10. We
calculate the optically thick photodissociation rate numerically, including the
effects of density, temperature, and velocity gradients in the gas, as well as
line overlap and shielding of H_2 by HI, over a large number of sight-lines. In
low-density regions (n<10^4 cm^-3) the dissociation rates exceed those obtained
using most previous approximations by more than an order of magnitude; the
correction is smaller at higher densities. We trace the origin of the
deviations primarily to inaccuracies of (i) the most common fitting formula
(Draine & Bertoldi 1996) for the suppression of the dissociation rate and (ii)
estimates for the effective shielding column density from local properties of
the gas. The combined effects of gas temperature and velocity gradients are
comparatively less important, typically altering the spherically averaged rate
only by a factor of less than two. We present a simple modification to the DB96
fitting formula for the optically thick rate which improves agreement with our
numerical results to within approx. 15 per cent, and can be adopted in future
simulations. We find that estimates for the effective shielding column can be
improved by using the local Sobolev length. Our correction to the H_2
self-shielding reduces the critical LW flux to suppress H_2-cooling in
T_vir>10^4 K haloes by an order of magnitude; this increases the number of such
haloes in which supermassive (approx. M=10^5 M_sun) black holes may have
formed. | Probing isocurvature perturbations with 21-cm global signal in the light
of HERA result: We argue that the 21-cm global signal can be a powerful probe of isocurvature
perturbations, particularly for the ones with blue-tilted spectra. Although the
21-cm global signal is much affected by astrophysical processes, which give
some uncertainties when cosmological models are investigated, recent results
from HERA have constrained several astrophysical parameters, whose information
can reduce the ambiguities originating from astrophysics. We show that the size
and spectral tilt of isocurvature perturbations can be well inferred from the
21-cm global signal once the information on astrophysics from the HERA results
is taken into account. |
Determination of the Kinematic Parameters from SNe Ia and Cosmic
Chronometers: In this work, by assuming a spatially flat Universe, we have tested 8
kinematic parametrization models with $H(z)$ data from Cosmic Chronometers and
SNe Ia from Pantheon compilation. Our aim is obtain the current values for the
Hubble constant ($H_0$), deceleration parameter ($q_0$), jerk ($j_0$) and snap
($s_0$) parameters independently from a dynamical model. By using a Bayesian
model comparison, three models are favoured: a model with the deceleration
parameter ($q$) linearly dependent on the redshift, $q$ linearly dependent on
the scale factor and a model with a constant jerk. The model with constant jerk
is slightly favoured by this analysis, furnishing $H_0=68.8^{+3.7}_{-3.6}$
km/s/Mpc, $q_0=-0.58\pm0.13$, $j_0=1.15^{+0.56}_{-0.53}$ and
$s_0=-0.25^{+0.40}_{-0.30}$. The other models are compatible with the constant
jerk model, except for the snap parameter, where we have found
$s_0=4.0^{+3.4}_{-3.0}$ for the model with $q$ linearly dependent on the scale
factor. (All uncertainties in the Abstract correspond to 95\% c.l.). | Testing the Interaction between Dark Energy and Dark Matter with Planck
Data: Interacting Dark Energy and Dark Matter is used to go beyond the standard
cosmology. We base our arguments on Planck data and conclude that an
interaction is compatible with the observations and can provide a strong
argument towards consistency of different values of cosmological parameters. |
The galaxy-wide distributions of mean electron density in the HII
regions of M51 and NGC 4449: Using ACS-HST images to yield continuum subtracted photometric maps in
H\alpha of the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, we
produced extensive (over 2000 regions for M51, over 200 regions for NGC4449)
catalogues of parameters of their HII regions: their H\alpha luminosities,
equivalent radii and coordinates with respect to the galaxy centers. From these
data we derived, for each region, its mean luminosity weighted electron
density, <n_e>, determined from the H\alpha luminosity and the radius, R, of
the region. Plotting these densities against the radii of the regions we find
excellent fits for <n_e> varying as R^{-1/2}. This relatively simple relation
has not, as far as we know, been predicted from models of HII region structure,
and should be useful in constraining future models. Plotting the densities
against the galactocentric radii, r, of the regions we find good exponential
fits, with scale lengths of close to 10 kpc for both galaxies. These values are
comparable to the scale lengths of the HI column densities for both galaxies,
although their optical structures, related to their stellar components are very
different. This result indicates that to a first approximation the HII regions
can be considered in pressure equilibrium with their surroundings. We also plot
the electron density of the HII regions across the spiral arms of M51, showing
an envelope which peaks along the ridge lines of the arms. | Constraining the star formation and the assembly histories of normal and
compact early-type galaxies at 1<z<2: [Abridged]We present a study based on a sample of 62 early-type galaxies
(ETGs) at 0.9<z_spec<2 aimed at constraining their past star formation and mass
assembly histories. The sample is composed of normal ETGs having effective
radii comparable to the mean radius of local ones and of compact ETGs having
effective radii from two to six times smaller. We do not find evidence of a
dependence of the compactness of ETGs on their stellar mass. We find that the
stellar mass of normal ETGs formed at z_form<3 while the stellar content of
compact ETGs formed at 2<z_form<10 with a large fraction of them characterized
by z_form>5. Earlier stars formed at z_form>5 are assembled in compact and more
massive (M_*>10^11 M_sun) ETGs while stars later formed (z_form<3) or resulting
from subsequent episodes of star formation are assembled both in compact and
normal ETGs. Thus, the older the stellar population the higher the mass of the
hosting galaxy but not vice versa. This suggests that the epoch of formation
may play a role in the formation of massive ETGs rather than the mass itself.
The possible general scheme in which normal <z>~1.5 ETGs are descendants of
high-z compact spheroids enlarged through subsequent dry mergers is not
compatible with the current models which predict a number of dry mergers two
orders of magnitude lower than the one needed. Moreover, we do not find
evidence supporting a dependence of the compactness of galaxies on their
redshift of assembly. Finally, we propose a simple scheme of formation and
assembly of the stellar mass of ETGs based on dissipative gas-rich merger which
can qualitatively account for the co-existence of normal and compact ETGs
observed at <z>~1.5 in spite of the same stellar mass, the lack of normal ETGs
with high z_form and the absence of correlation between compactness, stellar
mass and formation redshift. |
Effects of primordial magnetic fields on CMB: The origin of large-scale magnetic fields is an unsolved problem in
cosmology. In order to overcome, a possible scenario comes from the idea that
these fields emerged from a small primordial magnetic field (PMF), produced in
the early universe. This field could lead to the observed large-scales magnetic
fields but also, would have left an imprint on the cosmic microwave background
(CMB). In this work we summarize some statistical properties of this PMFs on
the FLRW background. Then, we show the resulting PMF power spectrum using
cosmological perturbation theory and some effects of PMFs on the CMB
anisotropies. | Lyα emitters in a cosmological volume I: the impact of radiative
transfer: Lyman-{\alpha} emitters (LAEs) are a promising target to probe the large
scale structure of the Universe at high redshifts, $z\gtrsim 2$. However, their
detection is sensitive to radiative transfer effects that depend on local
astrophysical conditions. Thus, modeling the bulk properties of this galaxy
population remains challenging for theoretical models. Here we develop a
physically-motivated scheme to predict LAEs in cosmological simulations. The
escape of Ly{\alpha} photons is computed using a Monte Carlo radiative transfer
code which outputs a Ly{\alpha} escape fraction. To speed-up the process of
assigning escape fractions to individual galaxies, we employ fitting formulae
that approximate the full Monte Carlo results within an accuracy of 10% for a
broad range of column densities, gas metallicities and gas bulk velocities. We
apply our methodology to the semi-analytical model GALFORM on a large N-body
simulation. The Ly{\alpha} photons escape through an outflowing neutral gas
medium, implemented assuming different geometries. This results in different
predictions for the typical column density and outflow velocities of the LAE
population. To understand the impact of radiative transfer on our predictions,
we contrast our models against a simple abundance matching assignment. Our full
models populate LAEs in less massive haloes than what is obtained with
abundance matching. Overall, radiative transfer effects result in better
agreement when confronting the properties of LAEs against observational
measurements. This suggest that incorporating the effects of Ly{\alpha}
radiative transfer in the analysis of this galaxy population, including their
clustering, can be important for obtaining an unbiased interpretation of future
datasets. |
Assisted coupled quintessence: We study models of quintessence consisting of a number of scalar fields
coupled to several dark matter components. In the case of exponential
potentials the scaling solutions can be described in terms of a single field.
The corresponding effective logarithmic slope and effective coupling can be
written in a simple form in terms of the individual slopes and couplings of the
original fields. We also investigate solutions where the scalar potential is
negligible, in particular those leading to transient matter dominated
solutions. Finally, we compute the evolution equations for the linear
perturbations which will allow these models to be tested against current and
future observational data. | Cosmological consequences of a scalar field with oscillating equation of
state. III. Unifying inflation with dark energy and small tensor-to-scalar
ratio: We investigate the inflationary consequences of the oscillating dark energy
model proposed by Ti\'an
[\href{https://doi.org/10.1103/PhysRevD.101.063531}{Phys. Rev. D {\bf 101},
063531 (2020)}], which aims to solve the cosmological coincidence problem with
multi-accelerating Universe (MAU). We point out that the inflationary dynamics
belong to slow-roll inflation. The spectral index of scalar perturbations and
the tensor-to-scalar ratio $r$ are shown to be consistent with current
\textit{Planck} measurements. Especially, this model predicts $r\sim10^{-7}$,
which is far below the observation limits. This result motivates us to explore
the smallness of $r$ in the general MAU. We propose a quintessential
generalization of the original model and prove $r<0.01$ in general. The null
detection to date of primordial gravitational waves provides a circumstantial
evidence for the MAU. After the end of inflation, the scalar field rolls toward
infinity instead of a local minimum, and meanwhile its equation of state is
oscillating with an average value larger than $1/3$. In this framework, we show
that gravitational particle creation at the end of inflation is capable of
reheating the Universe. |
Is the baryon acoustic oscillation peak a cosmological standard ruler?: In the standard model of cosmology, the Universe is static in comoving
coordinates; expansion occurs homogeneously and is represented by a global
scale factor. The baryon acoustic oscillation (BAO) peak location is a
statistical tracer that represents, in the standard model, a fixed
comoving-length standard ruler. Recent gravitational collapse should modify the
metric, rendering the effective scale factor, and thus the BAO standard ruler,
spatially inhomogeneous. Using the Sloan Digital Sky Survey, we show to high
significance (P < 0.001) that the spatial compression of the BAO peak location
increases as the spatial paths' overlap with superclusters increases. Detailed
observational and theoretical calibration of this BAO peak location environment
dependence will be needed when interpreting the next decade's cosmological
surveys. | Varying fundamental constants meet Hubble: Fundamental physical constants need not be constant, neither spatially nor
temporally. -- This seeming simple statement has profound implications for a
wide range of physical processes and interactions, and can be probed through a
number of observations. In this chapter, we highlight how CMB measurements can
constrain variations of the fine-structure constant and the electron rest mass
during the cosmological recombination era. The sensitivity of the CMB
anisotropies to these constants arises because they directly affect the cosmic
ionization history and Thomson scattering rate, with a number of subtle atomic
physics effects coming together. Recent studies have revealed that variations
of the electron rest mass can indeed alleviate the Hubble tension, as we
explain here. Future opportunities through measurements of the cosmological
recombination radiation are briefly mentioned, highlighting how these could
provide an exciting avenue towards uncovering the physical origin of the Hubble
tension experimentally. |
Cosmology with a SKA HI intensity mapping survey: HI intensity mapping (IM) is a novel technique capable of mapping the
large-scale structure of the Universe in three dimensions and delivering
exquisite constraints on cosmology, by using HI as a biased tracer of the dark
matter density field. This is achieved by measuring the intensity of the
redshifted 21cm line over the sky in a range of redshifts without the
requirement to resolve individual galaxies. In this chapter, we investigate the
potential of SKA1 to deliver HI intensity maps over a broad range of
frequencies and a substantial fraction of the sky. By pinning down the baryon
acoustic oscillation and redshift space distortion features in the matter power
spectrum -- thus determining the expansion and growth history of the Universe
-- these surveys can provide powerful tests of dark energy models and
modifications to General Relativity. They can also be used to probe physics on
extremely large scales, where precise measurements of spatial curvature and
primordial non-Gaussianity can be used to test inflation; on small scales, by
measuring the sum of neutrino masses; and at high redshifts where non-standard
evolution models can be probed. We discuss the impact of foregrounds as well as
various instrumental and survey design parameters on the achievable
constraints. In particular we analyse the feasibility of using the SKA1
autocorrelations to probe the large-scale signal. | A Gravitational Ising Model for the Statistical Bias of Galaxies: Evaluation of gravitational theories by means of cosmological data suffers
from the fact that galaxies are biased tracers of dark matter. Current bias
models focus primarily on high-density regions, whereas low-density regions
carry significant amounts of information relevant to the constraint of dark
energy and alternative gravity theories. Thus, proper treatment of both high
and low densities is important for future surveys. Accordingly, we here present
an interactionless Ising model for this bias, and we demonstrate that it
exhibits a remarkably good fit to both Millennium Simulation and Sloan Digital
Sky Survey data, at both density extremes. The quality of the fit indicates
that galaxy formation is (to first order) an essentially local process
determined by initial conditions. |
A possible Chandra and Hubble Space Telescope detection of extragalactic
WHIM towards PG 1116+215: (Abridged) We have analyzed Chandra LETG and XMM-Newton RGS spectra towards
the z=0.177 quasar PG 1116+215, a sightline that is rendered particularly
interesting by the HST detection of several OVI and HI broad Lyman-alpha
absorption lines that may be associated with the warm-hot intergalactic medium.
We performed a search for resonance K-alpha absorption lines from OVII and
OVIII at the redshifts of the detected far-ultraviolet lines. We detected an
absorption line in the Chandra spectra at 5.2 sigma confidence level at
wavelengths corresponding to OVIII K-alpha at z=0.0911+-0.0004+-0.0005
(statistical followed by systematic error). This redshift is within 3 sigma of
that of a HI broad Lyman-alpha of b=130 km/s at z=0.09279+-0.00005. We have
also analyzed the available XMM-Newton RGS data towards PG 1116+215.
Unfortunately, the XMM-Newton data are not suitable to investigate this line
because of instrumental features at the wavelengths of interest. At the same
redshift, the Chandra and XMM-Newton spectra have OVII K-alpha absorption line
features of significance 1.5 sigma and 1.8 sigma, respectively. We also
analyzed the available SDSS spectroscopic galaxy survey data towards PG
1116+215 in the redshift range of interest. We found evidence for a galaxy
filament that intersects the PG 1116+215 sightline and additional galaxy
structures that may host WHIM. The combination of HST, Chandra, XMM-Newton and
SDSS data indicates that we have likely detected a multi-temperature WHIM at
z=0.091-0.093 towards PG 1116+215. | Probing the molecular interstellar medium of M82 with Herschel-SPIRE
spectroscopy: We present the observations of the starburst galaxy M82 taken with the
Herschel SPIRE Fourier Transform Spectrometer. The spectrum (194-671 {\mu}m)
shows a prominent CO rotational ladder from J = 4-3 to 13-12 emitted by the
central region of M82. The fundamental properties of the gas are well
constrained by the high J lines observed for the first time. Radiative transfer
modeling of these high-S/N 12CO and 13CO lines strongly indicates a very warm
molecular gas component at ~500 K and pressure of ~3x10^6 K cm^-3, in good
agreement with the H_2 rotational lines measurements from Spitzer and ISO. We
suggest that this warm gas is heated by dissipation of turbulence in the
interstellar medium (ISM) rather than X-rays or UV flux from the straburst.
This paper illustrates the promise of the SPIRE FTS for the study of the ISM of
nearby galaxies. |
Induced gravitational waves from the cosmic coincidence: The induced gravitational wave (GW) background from enhanced primordial
scalar perturbations is one of the most promising observational consequences of
primordial black hole (PBH) formation from inflation. We investigate the
induced GW spectrum $\Omega_{\textrm{IGW}}$ from single-field inflation in the
general ultra-slow-roll (USR) framework, restricting the peak frequency band to
be inside $10^{-3}$-$1$ Hz and saturating PBH abundance to comprise all dark
matter (DM) in the ultralight asteroid-mass window. By invoking successful
baryogenesis driven by USR inflation, we verify the viable parameter space for
the specific density ratio between baryons and PBH DM observed today, the
so-called "cosmic coincidence." We show that the cosmic coincidence requirement
bounds the spectral index $n_{\rm UV}$ in the high frequency limit,
$\Omega_{\textrm{IGW}}(f\gg 1)\propto f^{-2n_{\rm UV}}$, into $0 < n_{\rm UV} <
1$, which implies that baryogenesis triggered by USR inflation for PBHs in the
mass range of $10^{-16}$-$10^{-12} M_\odot$ can be tested by upcoming Advanced
LIGO and Virgo data and next generation experiments such as LISA, Einstein
Telescope, TianQin and DECIGO. | Further Evidence for the Accretion Disk Origination of the Double-Peaked
Broad H$α$ of 3C390.3: In the letter, under the widely accepted theoretical accretion disk model for
the double-peaked emitter 3C390.3, the extended disk-like BLR can be well split
into ten rings, and then the time lags between the lines from the rings and the
continuum emission are estimated, based on the observed spectra around 1995. We
can find one much strong correlation between the determined time lags (in unit
of light-day) and the flux weighted radii (in unit of ${\rm R_G}$) of the
rings, which is well consistent with the expected results through the
theoretical accretion disk model. Moreover, through the strong correlation, the
black hole masses of 3C390.3 are independently estimated as $\sim10^9{\rm
M_{\odot}}$, the same as the reported black hole masses in the literature. The
consistencies provide further evidence to strongly support the accretion disk
origination of the double-peaked broad balmer lines of 3C390.3. |
Shear-flexion cross-talk in weak-lensing measurements: Gravitational flexion, caused by derivatives of the gravitational tidal
field, is potentially important for the analysis of the dark-matter
distribution in gravitational lenses, such as galaxy clusters or the
dark-matter haloes of galaxies. Flexion estimates rely on measurements of
galaxy-shape distortions with spin-1 and spin-3 symmetry. We show in this paper
that and how such distortions are generally caused not only by the flexion
itself, but also by coupling terms of the form (shear $\times$ flexion), which
have hitherto been neglected. Similar coupling terms occur between intrinsic
galaxy ellipticities and the flexion. We show, by means of numerical tests,
that neglecting these terms can introduce biases of up to 85% on the $F$
flexion and 150% on the $G$ flexion for galaxies with an intrinsic ellipticity
dispersion of $\sigma_{\epsilon}=0.3$. In general, this bias depends on the
strength of the lensing fields, the ellipticity dispersion, and the
concentration of the lensed galaxies. We derive a new set of equations relating
the measured spin-1 and spin-3 distortions to the lensing fields up to first
order in the shear, the flexion, the product of shear and flexion, and the
morphological properties of the galaxy sample. We show that this new
description is accurate with a bias $\leq 7%$ (spin-1 distortion) and $\leq 3%$
(spin-3 distortion) even close to points where the flexion approach breaks down
due to merging of multiple images. We propose an explanation why a spin-3
signal could not be measured yet and comment on the difficulties in using a
model-fitting approach to measure the flexion signal. | Colour gradients within SDSS DR7 galaxies: hints of recent evolution: The evolutionary path followed by a galaxy shapes its internal structure,
and, in particular, its internal colour variation. We present a study of the
internal colour variation within galaxies from the Seventh Data Release of the
Sloan Digital Sky Survey (SDSS DR7). We statistically study the connection
between the internal colour variation and global galactic properties, looking
for hints of the recent galactic evolution. Considering only galaxies with good
photometry and spectral measurements, we define four luminosity-threshold
samples within the redshift range 0.01<z<0.17, each containing more than 48000
galaxies. Colour gradients are calculated for these galaxies from the surface
brightness measurements provided by the SDSS DR7. Possible systematic effects
in their determination have been analysed. We find that, on average, galaxies
have redder cores than their external parts. We also find that it is more
likely to find steep colour gradients among late-type galaxies. This result
holds for a range of classifications based on both morphological and spectral
characteristics. In fact, our results relate, on average, steep colour
gradients to a higher presence of young stars within a galaxy. Our results also
suggest that nuclear activity is a marginal driver for creating steep colour
gradients in massive galaxies. We have selected pairs of interacting galaxies,
with a separation of 5 arcsec, in projected radius, and a difference in
redshift of 100 km/s, finding that they present steeper gradients than the
average population, skewed towards bluer cores. Our analysis implies that
colour gradients can be useful for selecting galaxies that have suffered a
recent (minor) burst of star formation. |
Primordial black hole dark matter from inflation: the reverse
engineering approach: Constraining the inflationary epoch is one of the aims of modern cosmology.
In order to fully exploit current and future small-scale observations, it is
necessary to devise tools to directly relate them to the early universes
dynamics. We present here a novel reverse engineer approach able to connect
fundamental late-time observables to consistent inflationary dynamics and,
eventually, to the inflaton potential. Employing this procedure, we are able to
describe which conditions can give rise to a raised plateau in the power
spectrum of curvature perturbations at small scales, which are not constrained
by CMB observations. Within this new phenomenologically-driven approach, we
find that inflation can generate a raised plateau in the spectrum of curvature
perturbations that potentially connects three fundamental observables: a
dominant component of the dark matter in the form of asteroid-mass/atomic-size
primordial black holes; detectable signals in stochastic gravitational waves
and a subdominant fraction of stellar-mass primordial black holes mergers. | Clustering of HI galaxies in HIPASS and ALFALFA: We investigate the clustering of HI-selected galaxies in the ALFALFA survey
and compare results with those obtained for HIPASS. Measurements of the angular
correlation function and the inferred 3D-clustering are compared with results
from direct spatial-correlation measurements. We are able to measure clustering
on smaller angular scales and for galaxies with lower HI masses than was
previously possible. We calculate the expected clustering of dark matter using
the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA
sample is somewhat more anti-biased with respect to dark matter than the HIPASS
sample. |
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