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Relativistic Astrophysics with Resonant Multiple Inspirals: We show that a massive black hole binary might resonantly trap a small third
body (e.g. a neutron star) down to a stage when the binary becomes relativistic
due to its orbital decay by gravitational radiation. The final fate of the
third body would be quite interesting for relativistic astrophysics. For
example, the parent binary could expel the third body with a velocity more than
10% of the speed of light. We also discuss the implications of this three-body
system for direct gravitational wave observation. | Identification of galaxy cluster substructures with the Caustic method: We investigate the power of the caustic technique for identifying
substructures of galaxy clusters from optical redshift data alone. The caustic
technique is designed to estimate the mass profile of galaxy clusters to radii
well beyond the virial radius, where dynamical equilibrium does not hold. Two
by-products of this technique are the identification of the cluster members and
the identification of the cluster substructures. We test the caustic technique
as a substructure detector on two samples of 150 mock redshift surveys of
clusters; the clusters are extracted from a large cosmological $N$-body
simulation of a $\Lambda$CDM model and have masses of $M_{200} \sim 10^{14}
h^{-1} M_{\odot}$ and $M_{200} \sim 10^{15} h^{-1} M_{\odot}$ in the two
samples. We limit our analysis to substructures identified in the simulation
with masses larger than $10^{13} h^{-1} M_{\odot}$. With mock redshift surveys
with 200 galaxies within $3R_{200}$, (1) the caustic technique recovers $\sim
30-50$\% of the real substructures, and (2) $\sim 15-20$\% of the substructures
identified by the caustic technique correspond to real substructures of the
central cluster, the remaining fraction being low-mass substructures, groups or
substructures of clusters in the surrounding region, or chance alignments of
unrelated galaxies. These encouraging results show that the caustic technique
is a promising approach for investigating the complex dynamics of galaxy
clusters. |
The Parameterized Post-Friedmann Framework for Theories of Modified
Gravity: Concepts, Formalism and Examples: A unified framework for theories of modified gravity will be an essential
tool for interpreting the forthcoming deluge of cosmological data. We present
such a formalism, the Parameterized Post-Friedmann framework (PPF), which
parameterizes the cosmological perturbation theory of a wide variety of
modified gravity models. PPF is able to handle spin-0 degrees of freedom from
new scalar, vector and tensor fields, meaning that it is not restricted to
simple models based solely on cosmological scalar fields. A direct
correspondence is maintained between the parameterization and the underlying
space of theories, which allows us to build up a `dictionary' of modified
gravity theories and their PPF correspondences. In this paper we describe the
construction of the parameterization and demonstrate its use through a number
of worked examples relevant to the current literature. We indicate how the
formalism will be implemented numerically, so that the dictionary of modified
gravity can be pitted against forthcoming observations. | Cosmological perturbations in extended electromagnetism. General gauge
invariant approach: A certain vector-tensor (VT) theory is revisited. It was proposed and
analyzed as a theory of electromagnetism without the standard gauge invariance.
Our attention is first focused on a detailed variational formulation of the
theory, which leads to both a modified Lorentz force and the true energy
momentum tensor of the vector field. The theory is then applied to cosmology. A
complete gauge invariant treatment of the scalar perturbations is presented.
For appropriate gauge invariant variables describing the scalar modes of the
vector field (A-modes), it is proved that the evolution equations of these
modes do not involve the scalar modes appearing in General Relativity
(GR-modes), which are associated to the metric and the energy momentum tensor
of the cosmological fluids. However, the A-modes modify the standard gauge
invariant equations describing the GR-modes. By using the new formalism, the
evolution equations of the A-perturbations are derived and separately solved
and, then, the correction terms --due to the A-perturbations-- appearing in the
evolution equations of the GR-modes are estimated. The evolution of these
correction terms is studied for an appropriate scale. The relevance of these
terms depends on both the spectra and the values of the normalization constants
involved in extended electromagnetism. Further applications of the new
formalism will be presented elsewhere. |
Evolution of Cluster Red-Sequence Galaxies from redshift 0.8 to 0.4:
ages, metallicities and morphologies: We present a comprehensive analysis of the stellar population properties
(age, metallicity and the alpha-element enhancement [E/Fe]) and morphologies of
red-sequence galaxies in 24 clusters and groups from z~0.75 to z~0.45. The
dataset, consisting of 215 spectra drawn from the ESO Distant Cluster Survey,
constitutes the largest spectroscopic sample at these redshifts for which such
an analysis has been conducted. Analysis reveals that the evolution of the
stellar population properties of red-sequence galaxies depend on their mass:
while the properties of most massive are well described by passive evolution
and high-redshift formation, the less massive galaxies require a more extended
star formation history. We show that these scenarios reproduce the index-sigma
relations as well as the galaxy colours. The two main results of this work are
(1) the evolution of the line-strength indices for the red-sequence galaxies
can be reproduced if 40% of the galaxies with sigma < 175 km/s entered the
red-sequence between z=0.75 to z=0.45, in agreement with the fraction derived
in studies of the luminosity functions, and (2) the percentage the red-sequence
galaxies exhibiting early-type morphologies (E and S0) decreases by 20% from
z=0.75 to z=0.45. This can be understood if the red-sequence gets populated at
later times with disc galaxies whose star formation has been quenched. We
conclude that the processes quenching star formation do not necessarily produce
a simultaneous morphological transformation of the galaxies entering the
red-sequence. | How Common are the Magellanic Clouds?: We introduce a probabilistic approach to the problem of counting dwarf
satellites around host galaxies in databases with limited redshift information.
This technique is used to investigate the occurrence of satellites with
luminosities similar to the Magellanic Clouds around hosts with properties
similar to the Milky Way in the object catalog of the Sloan Digital Sky Survey.
Our analysis uses data from SDSS Data Release 7, selecting candidate
Milky-Way-like hosts from the spectroscopic catalog and candidate analogs of
the Magellanic Clouds from the photometric catalog. Our principal result is the
probability for a Milky-Way-like galaxy to host N_{sat} close satellites with
luminosities similar to the Magellanic Clouds. We find that 81 percent of
galaxies like the Milky Way are have no such satellites within a radius of 150
kpc, 11 percent have one, and only 3.5 percent of hosts have two. The
probabilities are robust to changes in host and satellite selection criteria,
background-estimation technique, and survey depth. These results demonstrate
that the Milky Way has significantly more satellites than a typical galaxy of
its luminosity; this fact is useful for understanding the larger cosmological
context of our home galaxy. |
Anomalies in the CMB from a cosmic bounce: We explore a model of the early universe in which the inflationary epoch is
preceded by a cosmic bounce, and argue that this scenario provides a common
origin to several of the anomalous features that have been observed at large
angular scales in the cosmic microwave background (CMB). More concretely, we
show that a power suppression, a dipolar asymmetry, and a preference for
odd-parity correlations, with amplitude and scale dependence in consonance with
observations, are expected from this scenario. The model also alleviates the
tension in the lensing amplitude. These signals originate from the indirect
effect that non-Gaussian correlations between CMB modes and super-horizon
wavelengths induce in the power spectrum. We do not restrict to any specific
theory, but rather derive features common to a family bouncing models. | Implications of Planck results for models with local type
non-Gaussianity: We discuss implications of Planck results for models with local type
non-Gaussianity. In light of the recent results of the Planck satellite, we
constrain model parameters of several representative models and give the
prediction of trispectrum, in particular, gNL. We also consider interesting
possibilities that trispectrum appears as the first signature of the
non-Gaussianities of the curvature perturbations, that is, fNL is small while
gNL can be significantly large. |
Statistical anisotropy in CMB spectral distortions: Measurements of the cosmic microwave background (CMB) spectral $y$-distortion
anisotropy offer a test for the statistical isotropy of the primordial density
perturbations on $0.01\lesssim k{\rm Mpc}\lesssim 1$. We compute the 1-point
ensemble averages of the $y$-distortion anisotropies which vanish for the
statistically isotropic perturbations. For the quadrupole statistical
anisotropy, we find $4\pi\langle y_{2m}\rangle=-6.8A_2\times
10^{-9}Y_{2m}(\mathbf d )$ with the quadruple Legendre coefficient of the
anisotropic powerspectrum $A_2$ and the $\ell=2$ spherical harmonics
$Y_{2m}(\mathbf d )$ for the preferred direction $\mathbf d $. Also, we discuss
the cosmic variance of the $y$-distortion anisotropy in the statistically
anisotropic Universe. | A reliable cluster detection technique using photometric redshifts:
introducing the 2TecX algorithm: We present a new cluster detection algorithm designed for finding
high-redshift clusters using optical/infrared imaging data. The algorithm has
two main characteristics. First, it utilises each galaxy's full redshift
probability function, instead of an estimate of the photometric redshift based
on the peak of the probability function and an associated Gaussian error.
Second, it identifies cluster candidates through cross-checking the results of
two substantially different selection techniques (the name 2TecX representing
the cross-check of the two techniques). These are adaptations of the Voronoi
Tesselations and Friends-Of-Friends methods. Monte-Carlo simulations of mock
catalogues show that cross-checking the cluster candidates found by the two
techniques significantly reduces the detection of spurious sources.
Furthermore, we examine the selection effects and relative strengths and
weaknesses of either method. The simulations also allow us to fine-tune the
algorithm's parameters, and define completeness and mass limit as a function of
redshift. We demonstrate that the algorithm isolates high-redshift clusters at
a high level of efficiency and low contamination. |
The THESAN project: properties of the intergalactic medium and its
connection to Reionization-era galaxies: The high-redshift intergalactic medium (IGM) and the primeval galaxy
population are rapidly becoming the new frontier of extra-galactic astronomy.
We investigate the IGM properties and their connection to galaxies at
$z\geq5.5$ under different assumptions for the ionizing photon escape and the
nature of dark matter, employing our novel THESAN radiation-hydrodynamical
simulation suite, designed to provide a comprehensive picture of the emergence
of galaxies in a full reionization context. Our simulations have realistic
`late' reionization histories, match available constraints on global IGM
properties and reproduce the recently-observed rapid evolution of the mean free
path of ionizing photons. We additionally examine high-z Lyman-$\alpha$
transmission. The optical depth evolution is consistent with data, and its
distribution suggests an even-later reionization than simulated, although with
a strong sensitivity to the source model. We show that the effects of these two
unknowns can be disentangled by characterising the spectral shape and
separation of Lyman-$\alpha$ transmission regions, opening up the possibility
to observationally constrain both. For the first time in simulations, THESAN
reproduces the modulation of the Lyman-$\alpha$ flux as a function of galaxy
distance, demonstrating the power of coupling a realistic galaxy formation
model with proper radiation-hydrodynamics. We find this feature to be extremely
sensitive on the timing of reionization, while being relatively insensitive to
the source model. Overall, THESAN produces a realistic IGM and galaxy
population, providing a robust framework for future analysis of the high-z
Universe. | Constraints on primordial curvature spectrum from primordial black holes
and scalar-induced gravitational waves: The observational data of primordial black holes and scalar-induced
gravitational waves can constrain the primordial curvature perturbation at
small scales. We parameterize the primordial curvature perturbation by a broken
power law form and find that it is consistent with many inflation models that
can produce primordial black holes, such as nonminimal derivative coupling
inflation, scalar-tensor inflation, Gauss-Bonnet inflation, and K/G inflation.
The constraints from primordial black holes on the primordial curvature power
spectrum with the broken power law form are obtained, where the fraction of
primordial black holes in dark matter is calculated by the peak theory. Both
the real-space top-hat and the Gauss window functions are considered. The
constraints on the amplitude of primordial curvature perturbation with Gauss
window function are around three times larger than those with real-space
top-hat window function. The constraints on the primordial curvature
perturbation from the NANOGrav 12.5yrs data sets are displayed, where the
NANOGrav signals are assumed as the scalar-induced gravitational waves, and
only the first five frequency bins are used. |
Emulating cosmological multifields with generative adversarial networks: We explore the possibility of using deep learning to generate multifield
images from state-of-the-art hydrodynamic simulations of the CAMELS project. We
use a generative adversarial network to generate images with three different
channels that represent gas density (Mgas), neutral hydrogen density (HI), and
magnetic field amplitudes (B). The quality of each map in each example
generated by the model looks very promising. The GAN considered in this study
is able to generate maps whose mean and standard deviation of the probability
density distribution of the pixels are consistent with those of the maps from
the training data. The mean and standard deviation of the auto power spectra of
the generated maps of each field agree well with those computed from the maps
of IllustrisTNG. Moreover, the cross-correlations between fields in all
instances produced by the emulator are in good agreement with those of the
dataset. This implies that all three maps in each output of the generator
encode the same underlying cosmology and astrophysics. | X-ray luminosity functions of different morphological and X-ray type AGN
populations: Luminosity functions are one of the most important observational clues when
studying galaxy evolution over cosmic time. In this paper we present the X-ray
luminosity functions of X-ray detected AGN in the SXDS and GWS fields. The
limiting fluxes of our samples are 9.0x10^(-15) and 4.8x10^(-16)
erg/cm^2/sec^(-1) in the 0.5 - 7.0 keV band in the two fields, respectively. We
carried out analysis in three X-ray bands and in two redshift intervals up to z
< 1.4. Moreover, we derive the luminosity functions for different optical
morphologies and X-ray types. We confirm strong luminosity evolution in all
three bands, finding the most luminous objects at higher redshift. However, no
signs of density evolution are found in any tested X-ray band. We obtain
similar results for compact and early-type objects. Finally, we observe the
`Steffen effect', where X-ray type-1 sources are more numerous at higher
luminosities in comparison with type-2 sources. |
Quantified HI Morphology IV: The Merger Fraction and Rate in WHISP: The morphology of the atomic hydrogen (HI) disk of a spiral galaxy is the
first component to be disturbed by a gravitational interaction such as a merger
between two galaxies. We use a simple parametrisation of the morphology of HI
column density maps of Westerbork HI Spiral Project (WHISP) to select those
galaxies that are likely undergoing a significant interaction. Merging galaxies
occupy a particular part of parameter space defined by Asymmetry (A), the
relative contribution of the 20% brightest pixels to the second order moment of
the column density map (M20) and the distribution of the second order moment
over all the pixels (GM). Based on their HI morphology, we find that 13% of the
WHISP galaxies are in an interaction (Concentration-M20) and only 7% based on
close companions in the data-cube. This apparent discrepancy can be attributed
to the difference in visibility time scales: mergers are identifiable as close
pairs for 0.5 Gyr but ~1 Gyr by their disturbed HI morphology. Expressed as
volume merger rates, the two estimates agree very well: 7 and 6.8 x 10^-3
mergers Gyr^-1 Mpc^-3 for paired and morphologically disturbed HI disks
respectively. The consistency of our merger fractions to those published for
bigger surveys such as the Sloan Digital Sky Survey, shows that HI morphology
can be a very viable way to identify mergers in a large HI survey. The
relatively high value for the volume merger rate may be a bias in the selection
or WHISP volume. The expected boon in high-resolution HI data by the planned
MeerKAT, ASKAP and WSRT/APERTIF radio observatories will reveal the importance
of mergers in the local Universe and, with the advent of SKA, over cosmic
times. | Gravitational Lensing Corrections in Flat LambdaCDM Cosmology: We compute the deflection angle to order (m/r_0)^2 and m/r_0*Lambda r_0^2 for
a light ray traveling in a flat LambdaCDM cosmology which encounters a
completely condensed mass region. We use a Swiss cheese model for the
inhomogeneities and find that the most significant correction to the Einstein
angle occurs not because of the non-linear terms but instead occurs because the
condensed mass is embedded in a background cosmology.The Swiss cheese model
predicts a decrease in the deflection angle of ~2% for weakly lensed galaxies
behind the rich cluster A1689, and that the reduction can be as large as ~5%
for similar rich clusters at z\approx 1. Weak lensing deflection angles caused
by galaxies can likewise be reduced by as much as ~4%. We show that the lowest
order correction in which Lambda appears is proportional to m/r_0*\sqrt{Lambda
r_0^2} and could cause as much as a ~0.02% increase in the deflection angle for
light that passes through a rich cluster. The lowest order non-linear
correction in the mass is proportional to m/r_0*\sqrt{m/r_0} and can increase
the deflection angle by ~0.005% for weak lensing by galaxies. |
Gauging Fine-Tuning: We introduce a mathematical framework for quantifying fine-tuning in general
physical settings. In particular, we identify two distinct perspectives on
fine-tuning, namely, a local and a global perspective --- and develop
corresponding measures. These measures apply broadly to settings characterized
by an arbitrary number of observables whose values are dependent on an
arbitrary number of parameters. We illustrate our formalism by quantifying
fine-tuning as it arises in two pertinent astrophysical settings: (i) in models
where a significant fraction of the dark matter in the universe is in the form
of primordial black holes, and (ii) in scenarios that derive the fraction of
protons in habitable dark-matter halos from underlying models of cosmic
inflation. | Implications on the blazar sequence and inverse Compton models from
Fermi bright blazars: In this paper, we use the quasi-simultaneous spectra of Fermi bright blazars
and Fermi detected narrow line Seyfert 1 (NLS1) to study the blazar sequence
and inverse Compton (IC) models. I. The synchrotron peak luminosities (L_{s})
significantly inverse correlate with the synchrotron peak frequencies
(\nu_{s}), L_{s}\propto\nu_{s}^{-0.44}, which is consistent with the blazar
sequence. In addition to the correlation, there are some blazars showing low
\nu_{s} and low L_{s}. To study the relation between these low \nu_{s} low
L_{s} blazars and the blazar sequence, we present correlations of the parameter
L_{s}\nu_{s}^{1/4} with the ratio of Compton to synchrotron peak frequencies
(r_{Cs}\equiv\nu_{C}/\nu_{s}) and with the ratio of Compton to synchrotron
luminosities (CD\equiv L_{C}/L_{s}). The results indicate that both
correlations are significant with a Pearson's probability for null correlation
of p=0.0218 and p=0.0286 respectively. This does not support the idea that the
low \nu_{s} low L_{s} blazars are sources with less beaming. Another
possibility, as suggested by Ghisellini & Tavecchio, is that these blazars have
relative lower black hole masses. To test this, we collect the black hole
masses of 30 blazars from archives, and find that the hole mass correlates with
the parameter L_{s}\nu_{s}^{0.44} (p=0.0344). Therefore, the black hole masses
of low \nu_{s} low L_{s} blazars are statistically small. The NLS1s are thought
to have lower black hole masses. We find that the four NLS1s detected by Fermi
have low \nu_{s} and low L_{s}. This supports the above result. II. The ratio
r_{Cs} correlates with CD significantly (p=0.00375). The external Compton (EC)
model can naturally explain this correlation, while synchrotron self Compton
(SSC) model can not. This agrees with the findings of many authors that the EC
process dominates the gamma-ray emission of Flat Spectrum Radio Quasars. |
Shear and rotation in Chaplygin cosmology: We study the effect of shear and rotation on results previously obtained
dealing with the application of the spherical collapse model (SCM) to
generalized Chaplygin gas (gCg) dominated universes. The system is composed of
baryons and gCg and the collapse is studied for different values of the
parameter $\alpha$ of the gCg. We show that the joint effect of shear and
rotation is that of slowing down the collapse with respect to the simple SCM.
This result is of utmost importance for the so-called unified dark matter
models, since the described slow down in the growth of density perturbation can
solve one of the main problems of the quoted models, namely the instability
described in previous papers [e.g., H. B. Sandvik {\it et al.}, Phys. Rev. D
{\bf 69}, 123524 (2004)] at the linear perturbation level. | A decrease of the gas exchanges between galaxies and the IGM, from 12 to
6 billion years ago: Using a representative sample of 65 intermediate mass galaxies at z \sim 0.6,
we have inves- tigated the interplay between the main ingredients of chemical
evolution: metal abundance, gas mass, stellar mass and SFR. All quantities have
been estimated using deep spectroscopy and photometry from UV to IR and
assuming an inversion of the Schmitt-Kennicutt law for the gas fraction. Six
billion years ago, galaxies had a mean gas fraction of 32% \pm 3, i.e. twice
that of their local counterparts. Using higher redshift samples from the
literature, we explore the gas-phases and estimate the evolution of the mean
gas fraction of distant galaxies over the last 11 Gy. The gas fraction
increases linearly at the rate of 4% per Gyr from z \sim 0 to z \sim 2.2. We
also demonstrate for a statistically representative sample that < 4% of the z
\sim 0.6 galaxies are undergoing outflow events, in sharp contrast with z \sim
2.2 galaxies. The observed co-evolution of metals and gas over the past 6 Gyr
favours a scenario in which the population of intermediate mass galaxies
evolved as closed-systems, converting their own gas reservoirs into stars. |
The dust morphology of the elliptical Galaxy M86 with SPIRE: We present Herschel-SPIRE observations at 250-500um of the giant elliptical
galaxy M86 and examine the distribution of the resolved cold dust emission and
its relation with other galactic tracers. The SPIRE images reveal three dust
components: emission from the central region; a dust lane extending
north-south; and a bright emission feature 10kpc to the south-east. We estimate
that approximately 10^6 solar masses of dust is spatially coincident with
atomic and ionized hydrogen, originating from stripped material from the nearby
spiral NGC4438 due to recent tidal interactions with M86. The gas-to-dust ratio
of the cold gas component ranges from ~20-80. We discuss the different heating
mechanisms for the dust features. | Probing cosmology with weak lensing selected clusters I: Halo approach
and all-sky simulations: We explore a variety of statistics of clusters selected with cosmic shear
measurement by utilizing both analytic models and large numerical simulations.
We first develop a halo model to predict the abundance and the clustering of
weak lensing selected clusters. Observational effects such as galaxy shape
noise are included in our model. We then generate realistic mock weak lensing
catalogs to test the accuracy of our analytic model. To this end, we perform
full-sky ray-tracing simulations that allow us to have multiple realizations of
a large continuous area. We model the masked regions on the sky using the
actual positions of bright stars, and generate 200 mock weak lensing catalogs
with sky coverage of ~1000 squared degrees. We show that our theoretical model
agrees well with the ensemble average of statistics and their covariances
calculated directly from the mock catalogues. With a typical selection
threshold, ignoring shape noise correction causes overestimation of the
clustering of weak lensing selected clusters with a level of about 10%, and
shape noise correction boosts the cluster abundance by a factor of a few. We
calculate the cross-covariances using the halo model with accounting for the
effective reduction of the survey area due to masks. The covariance of the
cosmic shear auto power spectrum is affected by the mode-coupling effect that
originates from sky masking. Our model and the results can be readily used for
cosmological analysis with ongoing and future weak lensing surveys. |
Contribution of the first galaxies to the cosmic
far-infrared/sub-millimeter background - I. Mean background level: We study the contribution of the first galaxies to the
far-infrared/sub-millimeter (FIR/sub-mm) extragalactic background light (EBL)
by implementing an analytical model for dust emission. We explore different
dust models, assuming different grain size distributions and chemical
compositions. According to our findings, observed re-radiated emission from
dust in dwarf-size galaxies at $z \sim 10$ would peak at a wavelength of $\sim
500 \mu {\rm m}$ with observed fluxes of $\sim 10^{-3} - 10^{-2}$ nJy, which is
below the capabilities of current observatories. In order to be detectable,
model sources at these high redshifts should exhibit luminosities of $\gtrsim
10^{12} L_{\odot}$, comparable to that of local ultra-luminous systems. The
FIR/sub-mm EBL generated by primeval galaxies peaks at $\sim 500 \mu {\rm m}$,
with an intensity ranging from $\sim 10^{-4}$ to $10^{-3} {\rm nW \ m^{-2} \
sr^{-1}}$, depending on dust properties. These values are $\sim 3 - 4$ orders
of magnitude below the absolute measured cosmic background level, suggesting
that the first galaxies would not contribute significantly to the observed
FIR/sub-mm EBL. Our model EBL exhibits a strong correlation with the
dust-to-metal ratio, where we assume a fiducial value of $D = 0.005$,
increasing almost proportionally to it. Thus, measurements of the FIR/sub-mm
EBL could provide constraints on the amount of dust in the early Universe. Even
if the absolute signal from primeval dust emission may be undetectable, it
might still be possible to obtain information about it by exploring angular
fluctuations at $\sim 500 \mu {\rm m}$, close to the peak of dust emission from
the first galaxies. | Comments on arXiv:1006.0972 "XENON10/100 dark matter constraints in
comparison with CoGeNT and DAMA: examining the Leff dependence": Savage et al. have recently put forward the claim that results from the
XENON10 experiment are incompatible with the totality of both DAMA/LIBRA and
CoGeNT experimental regions. In this brief note the source of this erroneous
conclusion is identified in a misinterpretation of the XENON10 efficiency in
the detection of S1 light from low-energy nuclear recoils. |
The Relation Between Compact, Quiescent High Redshift Galaxies and
Massive Nearby Elliptical Galaxies: Evidence for Hierarchical, Inside-Out
Growth: Recent studies have shown that massive quiescent galaxies at high redshift
are much more compact than present-day galaxies of the same mass. Here we
compare the radial stellar density profiles and the number density of a sample
of massive galaxies at z ~ 2.3 to nearby massive elliptical galaxies. We
confirm that the average stellar densities of the z ~ 2.3 galaxies within the
effective radius, rho(<r_e), are two orders of magnitude higher than those of
local elliptical galaxies of the same stellar mass. However, we also find that
the densities measured within a constant physical radius of 1 kpc, rho(<1 kpc),
are higher by a factor of 2-3 only. This suggests that inside-out growth
scenarios are plausible, in which the compact high redshift galaxies make up
the centers of normal nearby ellipticals. The compact galaxies are common at
high redshift, which enables us to further constrain their evolution by
requiring that the number density of their descendants does not exceed
constraints imposed by the z=0 galaxy mass function. We infer that size growth
must be efficient, with (r_{1+2}/r_1) ~ (M_{1+2}/M_1)^2. A simple model where
compact galaxies with masses ~ 10^11 Msun primarily grow through minor mergers
produces descendants with the approximate sizes, stellar densities, and number
density of elliptical galaxies with masses 2-3 x10^11 Msun in the local
Universe. We note that this model also predicts evolution in the M_BH - sigma
relation, such that the progenitors of elliptical galaxies have lower black
hole masses at fixed velocity dispersion. The main observational uncertainty is
the conversion from light to mass; measurements of kinematics are needed to
calibrate the masses and stellar densities of the high redshift galaxies. | Secondary graviton spectra and waterfall-like fields: The secondary spectra of the gravitons induced by a waterfall-like field are
computed and the general bounds on the spectral energy density of the tensor
modes of the geometry are translated into explicit constraints on the amplitude
and slope of the waterfall spectrum. The obtained results are compared with the
primary gravitational wave spectra of the concordance model and of its
neighboring extensions as well as with the direct Ligo/Virgo bounds on
stochastic backgrounds of relic gravitons. Space-borne interferometers (such as
Lisa, Bbo, Decigo) seem to be less relevant but their potential implications
are briefly outlined. |
PSZ2G091:A massive double cluster at z=0.822 observed by the NIKA2
camera: PSZ2 G091.83+26.11 is a massive galaxy cluster with M500 = 7.43 x 10^14 Msun
at z = 0.822. This object exhibits a complex morphology with a clear bimodality
observed in X-rays. However, it was detected and analysed in the Planck sample
as a single, spherical cluster following a universal profile [1]. This model
can lead to miscalculations of thermodynamical quantities, like the pressure
profile. As future multiwavelength cluster experiments will detect more and
more objects at higher redshifts (where we expect the fraction of merging
objects to be higher), it is crucial to quantify this systematic effect. In
this work, we use high-resolution observations of PSZ2 G091.83+26.11 by the
NIKA2 camera to integrate the morphological characteristics of the cluster in
our modelling. This is achieved by fitting a two-halo model to the SZ image and
then by reconstruction of the resulting projected pressure profile. We then
compare these results with the spherical assumption. | Cosmological studies from tomographic weak lensing peak abundances and
impacts of photo-z errors: Weak lensing peak abundance analyses have been applied in different surveys
and demonstrated to be a powerful statistics in extracting cosmological
information complementary to cosmic shear two-point correlation studies. Future
large surveys with high number densities of galaxies enable tomographic peak
analyses. Focusing on high peaks, we investigate quantitatively how the
tomographic redshift binning can enhance the cosmological gains. We also
perform detailed studies about the degradation of cosmological information due
to photometric redshift (photo-z) errors. We show that for surveys with the
number density of galaxies $\sim40\,{\rm arcmin^{-2}}$, the median redshift
$\sim1$, and the survey area of $\sim15000\,{\rm deg^{2}}$, the 4-bin
tomographic peak analyses can reduce the error contours of $(\Omega_{{\rm
m}},\sigma_{8})$ by a factor of $5$ comparing to 2-D peak analyses in the ideal
case of photo-z error being absent. More redshift bins can hardly lead to
significantly better constraints. The photo-z error model here is parametrized
by $z_{{\rm bias}}$ and $\sigma_{{\rm ph}}$ and the fiducial values of $z_{{\rm
bias}}=0.003$ and $\sigma_{{\rm ph}}=0.02$ is taken. We find that using
tomographic peak analyses can constrain the photo-z errors simultaneously with
cosmological parameters. For 4-bin analyses, we can obtain $\sigma(z_{{\rm
bias}})/z_{{\rm bias}}\sim10\%$ and $\sigma(\sigma_{{\rm ph}})/\sigma_{{\rm
ph}}\sim5\%$ without assuming priors on them. Accordingly, the cosmological
constraints on $\Omega_{{\rm m}}$ and $\sigma_{8}$ degrade by a factor of
$\sim2.2$ and $\sim1.8$, respectively, with respect to zero uncertainties on
photo-z parameters. We find that the uncertainty of $z_{{\rm bias}}$ plays more
significant roles in degrading the cosmological constraints than that of
$\sigma_{{\rm ph}}$. |
Primordial Power Spectrum Reconstruction From CMB Weak Lensing Power
Spectrum: We use the modified Richardson-Lucy deconvolution algorithm to reconstruct
the Primordial Power Spectrum from the Weak Lensing Power spectrum
reconstructed from the CMB anisotropies. This provides an independent window to
observe and constrain the PPS $P_R(k)$ along different $k$ scales as compared
to CMB Temperature Power Spectrum. The Weak Lensing Power spectrum does not
contain secondary variations in power and hence is cleaner, unlike the
Temperature Power spectrum which suffers from lensing which is visible in its
PPS reconstructions. We demonstrate that the physical behaviour of the weak
lensing kernel is different from the temperature kernel and reconstructs broad
features over $k$. We provide an in-depth analysis of the error propagation
using simulated data and Monte-Carlo sampling, based on Planck best-fit
cosmological parameters to simulate the data and cosmic variance limited error
bars. The error and initial condition analysis provides a clear picture of the
optimal reconstruction region for the estimator and we provide and algorithm
for $P_R(k)$ sampling to be used based on the given data, errors and its
binning properties. Eventually we plan to use this method on actual mission
data and provide a cross reference to PPS reconstructed from other sectors and
any possible features in them. | Observations of flat-spectrum radio sources at 850 microns from the
James Clerk Maxwell Telescope II. April 2000 to June 2005: Calibrated data for 143 flat-spectrum extragalactic radio sources are
presented at a wavelength of 850 microns covering a five-year period from April
2000. The data, obtained at the James Clerk Maxwell Telescope using the SCUBA
camera in pointing mode, were analysed using an automated pipeline process
based on the Observatory Reduction and Acquisition Control - Data Reduction
(ORAC-DR) system. This paper describes the techniques used to analyse and
calibrate the data, and presents the database of results along with a
representative sample of the better-sampled lightcurves. A re-analysis of
previously published data from 1997 to 2000 is also presented. The combined
catalogue, comprising 10493 flux density measurements, provides a unique and
valuable resource for studies of extragalactic radio sources. |
The Large Scale Structure Bootstrap: perturbation theory and bias
expansion from symmetries: We investigate the role played by symmetries in the perturbative expansion of
the large-scale structure. In particular, we establish which of the
coefficients of the perturbation theory kernels are dictated by symmetries and
which not. Up to third order in perturbations, for the dark matter density
contrast (and for the dark matter velocity) only three coefficients are not
fixed by symmetries and depend on the particular cosmology. For generic biased
tracers, where number/mass and momentum conservation cannot be imposed in
general, this number rises to seven in agreement with other bias expansions
discussed in the literature. A crucial role in our analysis is provided by
extended Galilean invariance, which follows from diffeomorphism invariance in
the non-relativistic limit. We identify a full hierarchy of extended Galilean
invariance constraints, which fix the analytic structure of the perturbation
theory kernels as the sums of an increasing number of external momenta vanish.
Our approach is especially relevant for non-standard models that respect the
same symmetries as $\Lambda$CDM and where perturbation theory at higher orders
has not been exhaustively explored, such as dark energy and modified gravity
scenarios. In this context, our results can be used to systematically extend
the bias expansion to higher orders and set up model independent analyses. | Mass function of haloes: scale invariant models: Press-Schechter theory gives a simple, approximate functional form of the
mass function of dark matter haloes. Sheth and Tormen (ST) refined this mass
function to give an improved analytical fit to results of N-body simulations.
These forms of the halo mass function are universal (independent of cosmology
and power spectrum) when scaled in suitable variables. Using large suites of
LCDM N-body simulations, studies in the last few years have shown that this
universality is only approximate. We explore whether some of the deviations
from universality can be attributed to the power spectrum by computing the mass
function in N-body simulations of various scale-free models in an Einstein-de
Sitter cosmology. This choice of cosmology does not introduce any scale into
the problem. These models have the advantage of being self-similar, hence
stringent checks can be imposed while running these simulations. This set of
numerical experiments is designed to isolate any power spectrum dependent
departures from universality of mass functions. We show explicitly that the
best fit ST parameters have a clear dependence on power spectrum. Our results
also indicate that an improved analytical theory with more parameters is
required in order to provide better fits to the mass function. |
A convenient approach to characterizing model uncertainty with
application to early dark energy solutions of the Hubble tension: Despite increasingly precise observations and sophisticated theoretical
models, the discrepancy between measurements of H0 from the cosmic microwave
background or from Baryon Acoustic Oscillations combined with Big-Bang
Nucleosynthesis versus those from local distance ladder probes -- commonly
known as the $H_0$ tension -- continues to perplex the scientific community. To
address this tension, Early Dark Energy (EDE) models have been proposed as
alternatives to $\Lambda$CDM, as they can change the observed sound horizon and
the inferred Hubble constant from measurements based on this. In this paper, we
investigate the use of Bayesian Model Averaging (BMA) to evaluate EDE as a
solution to the H0 tension. BMA consists of assigning a prior to the model and
deriving a posterior as for any other unknown parameter in a Bayesian analysis.
BMA can be computationally challenging in that one must approximate the joint
posterior of both model and parameters. Here we present a computational
strategy for BMA that exploits existing MCMC software and combines
model-specific posteriors post-hoc. In application to a comprehensive analysis
of cosmological datasets, we quantify the impact of EDE on the H0 discrepancy.
We find an EDE model probability of $\sim$90% whenever we include the H0
measurement from Type Ia Supernovae in the analysis, whereas the other data
show a strong preference for the standard cosmological model. We finally
present constraints on common parameters marginalized over both cosmological
models. For reasonable priors on models with and without EDE, the H0 tension is
reduced by at least 20%. | Perspectives on fundamental cosmology from Low Earth Orbit and the Moon: The next generation of space-based experiments will go hunting for answers to
cosmology's key open questions which revolve around inflation, dark matter and
dark energy. Low earth orbit and lunar missions within the European Space
Agency's Human and Robotic Exploration programme can push our knowledge forward
in all of these three fields. A radio interferometer on the Moon, a cold atom
interferometer in low earth orbit and a gravitational wave interferometer on
the Moon are highlighted as the most fruitful missions to plan and execute in
the mid-term. |
Bias on Tensor-to-Scalar Ratio Inference With Estimated Covariance
Matrices: We investigate simulation-based bandpower covariance matrices commonly used
in cosmological parameter inferences such as the estimation of the
tensor-to-scalar ratio $r$. We find that upper limits on $r$ can be biased low
by tens of percent. The underestimation of the upper limit is most severe when
the number of simulation realizations is similar to the number of observables.
Convergence of the covariance-matrix estimation can require a number of
simulations an order of magnitude larger than the number of observables, which
could mean $\mathcal{O}(10\ 000)$ simulations. This is found to be caused by an
additional scatter in the posterior probability of $r$ due to Monte Carlo noise
in the estimated bandpower covariance matrix, in particular, by spurious
non-zero off-diagonal elements. We show that matrix conditioning can be a
viable mitigation strategy in the case that legitimate covariance assumptions
can be made. | Cosmic explosions, life in the Universe and the Cosmological Constant: Galactic Gamma-Ray Bursts (GRBs) are copious sources of gamma-rays that can
pose a threat to complex life. Using recent determinations of their rate and
the probability of GRBs causing massive extinction, we explore what type of
universes are most likely to harbour advanced forms of life. For this purpose
we use cosmological N-body simulations to determine at what time and for what
value of the cosmological constant ($\Lambda$) the chances of life being
unaffected by cosmic explosions are maximised. We find that $\Lambda-$dominated
universes favour the survival of life against GRBs. Within a $\Lambda$CDM
cosmology, the parameters that govern the likelihood of life survival to GRBs
are dictated by the value of $\Lambda$ and the age of the Universe. We find
that we seem to live in a favorable point in this parameter phase space which
minimises the exposure to cosmic explosions, yet maximises the number of main
sequence (hydrogen-burning) stars around which advanced life forms can exist. |
Delensing CMB Polarization with External Datasets: One of the primary scientific targets of current and future CMB polarization
experiments is the search for a stochastic background of gravity waves in the
early universe. As instrumental sensitivity improves, the limiting factor will
eventually be B-mode power generated by gravitational lensing, which can be
removed through use of so-called delensing algorithms. We forecast prospects
for delensing using lensing maps which are obtained externally to CMB
polarization: either from large-scale structure observations, or from
high-resolution maps of CMB temperature. We conclude that the forecasts in
either case are not encouraging, and that significantly delensing large-scale
CMB polarization requires high-resolution polarization maps with sufficient
sensitivity to measure the lensing B-mode. We also present a simple formalism
for including delensing in CMB forecasts which is computationally fast and
agrees well with Monte Carlos. | The Effects of Potential Shape on Inhomogeneous Inflation: We study the robustness of single-field inflation against inhomogeneities. We
derive a simple analytic criterion on the shape of the potential for successful
inflation in the presence of inhomogeneities, and demonstrate its validity
using full 3+1 dimensional numerical relativity simulations on several classes
of popular models of single-field inflation. We find that models with convex
potentials are more robust to inhomogeneities than those with concave
potentials, and that concave potentials that vary on super-Planckian scales are
significantly more robust than those that vary on sub-Planckian scales. |
The Sources of Extreme Ultraviolet and Soft X-ray Backgrounds: Radiation in the extreme ultraviolet (EUV) and soft X-ray holds clues to the
location of the missing baryons, the energetics in stellar feedback processes,
and the cosmic enrichment history. Additionally, EUV and soft X-ray photons
help determine the ionization state of most intergalactic and circumgalactic
metals, shaping the rate at which cosmic gas cools. Unfortunately, this band is
extremely difficult to probe observationally due to absorption from the Galaxy.
In this paper, we model the contributions of various sources to the cosmic EUV
and soft X-ray backgrounds. We bracket the contribution from (1) quasars, (2)
X-ray binaries, (3) hot interstellar gas, (4) circumgalactic gas, (5)
virialized gas, and (6) supersoft sources, developing models that extrapolate
into these bands using both empirical and theoretical inputs. While quasars are
traditionally assumed to dominate these backgrounds, we discuss the substantial
uncertainty in their contribution. Furthermore, we find that hot intrahalo
gases likely emit an O(1) fraction of this radiation at low redshifts, and that
interstellar and circumgalactic emission potentially contribute tens of percent
to these backgrounds at all redshifts. We estimate that uncertainties in the
angular-averaged background intensity impact the ionization corrections for
common circumgalactic and intergalactic metal absorption lines by ~0.3-1 dex,
and we show that local emissions are comparable to the cosmic background only
at r_prox = 10-100 kpc from Milky Way-like galaxies. | Nuclear star formation activity and black hole accretion in nearby
Seyfert galaxies: Recent theoretical and observational works indicate the presence of a
correlation between the star formation rate (SFR) and the active galactic
nuclei (AGN) luminosity (and, therefore, the black hole accretion rate) of
Seyfert galaxies. This suggests a physical connection between the gas forming
stars on kpc scales and the gas on sub-pc scales that is feeding the black
hole. We compiled the largest sample of Seyfert galaxies to date with high
angular resolution (0.4-0.8 arcsec) mid-infrared (8-13 micron) spectroscopy.
The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames
catalogue. At a median distance of 33 Mpc, our data allow us to probe nuclear
regions on scales of 65 pc (median value). We found no general evidence of
suppression of the 11.3 micron polycyclic aromatic hydrocarbon (PAH) emission
in the vicinity of these AGN, and used this feature as a proxy for the SFR. We
detected the 11.3 micron PAH feature in the nuclear spectra of 45% of our
sample. The derived nuclear SFRs are, on average, five times lower than those
measured in circumnuclear regions of 600 pc in size (median value). However,
the projected nuclear SFR densities are a factor of 20 higher than those
measured on circumnuclear scales. This indicates that the SF activity per unit
area in the central 65 pc of Seyfert galaxies is much higher than at larger
distances from their nuclei. We studied the connection between the nuclear SFR
and the black hole accretion rate and showed that numerical simulations
reproduce fairly well our observed relation. |
A bias using the ages of the oldest astrophysical objects to address the
Hubble tension: Recently different cosmological measurements have shown a tension in the
value of the Hubble constant, $H_0$. Assuming the $\Lambda$CDM model, the
Planck satellite mission has inferred the Hubble constant from the cosmic
microwave background (CMB) anisotropies to be $H_0 = 67.4 \pm 0.5 \, \rm{km \,
s^{-1} \, Mpc^{-1}}$. On the other hand, low redshift measurements such as
those using Cepheid variables and supernovae Type Ia (SNIa) have obtained a
significantly larger value. For instance, Riess et al. reported $H_0 = 73.04
\pm 1.04 \, \rm{km \, s^{-1} \, Mpc^{-1}}$, which is $5\sigma$ apart of the
prediction from Planck observations. This tension is a major problem in
cosmology nowadays, and it is not clear yet if it comes from systematic effects
or new physics. The use of new methods to infer the Hubble constant is
therefore essential to shed light on this matter. In this paper, we discuss
using the ages of the oldest astrophysical objects (OAO) to probe the Hubble
tension. We show that, although this data can provide additional information,
the method can also artificially introduce a tension. Reanalyzing the ages of
114 OAO, we obtain that the constraint in the Hubble constant goes from
slightly disfavoring local measurements to favoring them. | Molecular Gas in NUclei of GAlaxies (NUGA) XIV. The barred LINER/Seyfert
2 galaxy NGC 3627: We present CO(1-0) and CO(2-1) maps of the interacting barred LINER/Seyfert 2
galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1" x
1.3" and 0.9" x 0.6", respectively. The molecular gas emission shows a nuclear
peak, an elongated bar-like structure of ~18" (~900 pc) diameter in both CO
maps and, in CO(1-0), a two-arm spiral feature from r~9" (~450 pc) to r~16"
(~800 pc). The inner ~18" bar-like structure, with a north/south orientation
(PA = 14{\deg}), forms two peaks at the extremes of this elongated emission
region. The kinematics of the inner molecular gas shows signatures of
non-circular motions associated both with the 18" bar-like structure and the
spiral feature detected beyond it. The 1.6 micron H-band 2MASS image of NGC
3627 shows a stellar bar with a PA = -21{\deg}, different from the PA (=
14{\deg}) of the CO bar-like structure, indicating that the gas is leading the
stellar bar. The torques computed with the HST-NICMOS F160W image and our PdBI
maps are negative down to the resolution limit of our images, ~60 pc in
CO(2-1). If the bar ends at ~3 kpc, coincident with corotation (CR), the
torques are negative between the CR of the bar and the nucleus, down to the
resolution limit of our observations. This scenario is compatible with a
recently-formed rapidly rotating bar which has had insufficient time to slow
down because of secular evolution, and thus has not yet formed an inner
Lindblad resonance (ILR). The presence of molecular gas inside the CR of the
primary bar, where we expect that the ILR will form, makes NGC 3627 a potential
smoking gun of inner gas inflow. The gas is fueling the central region, and in
a second step could fuel directly the active nucleus. |
A Stochastic Theory of the Hierarchical Clustering I. Halo Mass Function: We present a new theory for the hierarchical clustering of dark matter (DM)
halos based on stochastic differential equations, that constitutes a change of
perspective with respect to existing frameworks (e.g., the excursion set
approach); this work is specifically focused on the halo mass function. First,
we present a stochastic differential equation that describes fluctuations in
the mass growth of DM halos, as driven by a multiplicative white (Gaussian)
noise dependent on the spherical collapse threshold and on the power spectrum
of DM perturbations. We demonstrate that such a noise yields an average drift
of the halo population toward larger masses, that quantitatively renders the
standard hierarchical clustering. Then, we solve the Fokker-Planck equation
associated to the stochastic dynamics, and obtain the Press & Schechter mass
function as a (stationary) solution. Moreover, generalizing our treatment to a
mass-dependent collapse threshold, we obtain an exact analytic solution capable
of fitting remarkably well the N-body mass function over a wide range in mass
and redshift. All in all, the new perspective offered by the theory presented
here can contribute to better understand the gravitational dynamics leading to
the formation, evolution and statistics of DM halos across cosmic times. | The Vela Cloud: A Giant HI Anomaly in the NGC 3256 Group: We present Australia Telescope Compact Array (ATCA) observations of a
galaxy-sized intergalactic HI cloud (the Vela Cloud) in the NGC 3256 galaxy
group. The group contains the prominent merging galaxy NGC 3256, which is
surrounded by a number of HI fragments, the tidally disturbed galaxy NGC 3263,
and several other peculiar galaxies. The Vela Cloud, with an HI mass of 3-5 *
10**9 solar masses, resides southeast of NGC 3256 and west of NGC 3263, within
an area of 9' x 16' (100 kpc x 175 kpc for an adopted distance of 38 Mpc). In
our ATCA data the Vela Cloud appears as 3 diffuse components and contains 4
density enhancements. The Vela Cloud's properties, together with its group
environment, suggest that it has a tidal origin. Each density enhancement
contains ~10**8 solar masses of HI gas which is sufficient material for the
formation of globular cluster progenitors. However, if we represent the
enhancements as Bonnor-Ebert spheres, then the pressure of the surrounding HI
would need to increase by at least a factor of 6 in order to cause the collapse
of an enhancement. Thus we do not expect them to form massive bound stellar
systems like super star clusters or tidal dwarf galaxies. Since the HI density
enhancements have some properties in common with High Velocity Clouds, we
explore whether they may evolve to be identified with these starless clouds
instead. |
Turnaround overdensity as a cosmological observable: the case for a
local measurement of $Λ$: We demonstrate that, in the context of the $\Lambda$CDM model, it is in
principle possible to measure the value of the cosmological constant by
tracing, across cosmic time, the evolution of the turnaround radius of cosmic
structures. The novelty of the presented method is that it is local, in the
sense that it uses the effect of the cosmological constant on the relatively
short scales of cosmic structures and not on the dynamics of the Universe at
its largest scales. In this way, it can provide an important consistency check
for the standard cosmological model and can give signs of new physics, beyond
$\Lambda$CDM. | Reddening and Distance of the Local Group Starburst Galaxy IC 10: We estimate the reddening and distance of the nearest starburst galaxy IC 10
using deep near infrared $JHK_{S}$ photometry obtained with the Multi-Object
InfraRed Camera and Spectrograph (MOIRCS) on the Subaru telescope. We estimate
the foreground reddening toward IC 10 using $UBV$ photometry of IC 10 from the
Local Group Survey, obtaining $E(B-V)=0.52\pm 0.04$ mag. We derive the total
reddening including the internal reddening, $E(B-V)=0.98\pm 0.06$ mag, using
$UBV$ photometry of early-type stars in IC 10 and comparing $JHK_{S}$
photometry of red giant branch stars in IC 10 and the SMC. Using the 2MASS
point source catalog of 20 Galactic globular clusters, we derive a relation
between the metallicity [Fe/H]$_{CG97}$ and the slope of the red giant branch
in the $K_{S}- (J-K_{S})$ color-magnitude diagram. The mean metallicity of the
red giant branch stars in IC 10 is estimated to be
[Fe/H]$_{CG97}=-1.08\pm0.28$. The magnitude of the tip of the red giant branch
(TRGB) of IC 10 in the $K_{S}$ band is measured to be
$K_{S,TRGB}=18.28\pm0.01$. Based on the TRGB method, we estimate the distance
modulus of IC 10 to be $(m-M)_{0}=24.27\pm0.03{\rm (random)}\pm0.18{\rm
(systematic)}$, corresponding to the distance of $d=715\pm10\pm60$ kpc. This
confirms that IC 10 is a member of the Local Group. |
Early Universe cosmology with mirror dark matter: Mirror matter is a stable self-collisional dark matter candidate. If exact
mirror parity is a conserved symmetry of nature, there could exist a parallel
hidden (mirror) sector of the Universe which has the same kind of particles and
the same physical laws of our (visible) sector. The two sectors interact each
other predominantly via gravity, therefore mirror matter is naturally "dark".
Here I briefly review the cosmological signatures of mirror dark matter, as Big
Bang nucleosynthesis, primordial structure formation and evolution, cosmic
microwave background and large scale structure power spectra, together with its
compatibility with the interpretation of the DAMA annual modulation signal in
terms of photon--mirror-photon kinetic mixing. Summarizing the present status
of research and comparing theoretical results with observations/experiments, it
emerges that mirror matter is not just a viable, but a promising dark matter
candidate. | Evaluating K bands for Nancy Grace Roman Space Telescope Rest-Frame NIR
SN Ia Distances: Recently, the Nancy Grace Roman Space Telescope (Roman) Project raised the
possibility of adding another filter to Roman. Based on the Filter Working
Group's recommendations, this filter may be a K-band filter, extending
significantly redder than the current-reddest F184. Among other scientific
possibilities, this K filter raises the possibility of measuring SNe Ia in the
rest-frame NIR out to higher redshifts than is possible with the current filter
complement. I perform a simple survey optimization for NIR SN Ia distances with
Roman, simultaneously optimizing both filter cutoffs and survey strategy. I
find that the roughly optimal K band extends from 19,000A--23,000A (giving
exposure times roughly half that of a 20,000A--23,000A Ks filter). Moving the K
much redder than this range dramatically increases the thermal background,
while moving the K band much bluer limits the redshift reach. Thus I find any
large modification reduces or eliminates the gain over the current F184. I
consider both rest-frame Y band and rest-frame J band surveys. Although the
proposed K band is too expensive for a large rest-frame Y band survey, it
increases the rest-frame J Figure of Merit by 59%. |
Solar system tests of f(R) gravity: In this paper, we revisit the solar system tests of f(R) gravity. When the
Sun sits in a vacuum, the field f' is light, which leads to a metric different
from the observations. We reobtain this result in a simpler way by directly
focusing on the equations of motion for f(R) gravity in the Jordan frame. The
discrepancy between the metric in the f(R) gravity and the observations can be
alleviated by the chameleon mechanism. The implications from the chameleon
mechanism on the functional form f(R) are discussed. Considering the analogy of
the solar system tests to the false vacuum decay problem, the effective
potentials in different cases are also explored. The combination of analytic
and numerical approaches enables us to ascertain whether an f(R) model can pass
the solar system tests or not. | Parameter Estimation from Improved Measurements of the CMB from QUaD: We evaluate the contribution of cosmic microwave background (CMB)
polarization spectra to cosmological parameter constraints. We produce
cosmological parameters using high-quality CMB polarization data from the
ground-based QUaD experiment and demonstrate for the majority of parameters
that there is significant improvement on the constraints obtained from
satellite CMB polarization data. We split a multi-experiment CMB dataset into
temperature and polarization subsets and show that the best-fit confidence
regions for the LCDM 6-parameter cosmological model are consistent with each
other, and that polarization data reduces the confidence regions on all
parameters. We provide the best limits on parameters from QUaD EE/BB
polarization data and we find best-fit parameters from the multi-experiment CMB
dataset using the optimal pivot scale of k_p=0.013 Mpc-1 to be {omch2, ombh2,
H_0, A_s, n_s, tau}= {0.113, 0.0224, 70.6, 2.29 times 10^-9, 0.960, 0.086}. |
Streaming velocities and the baryon-acoustic oscillation scale: At the epoch of decoupling, cosmic baryons had supersonic velocities relative
to the dark matter that were coherent on large scales. These velocities
subsequently slow the growth of small-scale structure and, via feedback
processes, can influence the formation of larger galaxies. We examine the
effect of streaming velocities on the galaxy correlation function, including
all leading-order contributions for the first time. We find that the impact on
the BAO peak is dramatically enhanced (by a factor of ~5) over the results of
previous investigations, with the primary new effect due to advection: if a
galaxy retains memory of the primordial streaming velocity, it does so at its
Lagrangian, rather than Eulerian, position. Since correlations in the streaming
velocity change rapidly at the BAO scale, this advection term can cause a
significant shift in the observed BAO position. If streaming velocities impact
tracer density at the 1% level, compared to the linear bias, the recovered BAO
scale is shifted by approximately 0.5%. This new effect, which is required to
preserve Galilean invariance, greatly increases the importance of including
streaming velocities in the analysis of upcoming BAO measurements and opens a
new window to the astrophysics of galaxy formation. | The Formation of Population III Binaries from Cosmological Initial
Conditions: Previous high resolution cosmological simulations predict the first stars to
appear in the early universe to be very massive and to form in isolation. Here
we discuss a cosmological simulation in which the central 50 solar mass clump
breaks up into two cores, having a mass ratio of two to one, with one fragment
collapsing to densities of 10^{-8} g/cc. The second fragment, at a distance of
800 astronomical units, is also optically thick to its own cooling radiation
from molecular hydrogen lines, but is still able to cool via collision-induced
emission. The two dense peaks will continue to accrete from the surrounding
cold gas reservoir over a period of 10^5 years and will likely form a binary
star system. |
Galaxy formation from dry and hydro simulations: The effects of dry and wet merging on the Scaling Laws (SLs) of elliptical
galaxies (Es) are discussed. It is found that the galaxy SLs, possibly
established at high redshift by the fast collapse of gas-rich and clumpy
stellar distributions in preexisting dark matter halos following the
cosmological SLs, are compatible with a (small) number of galaxy mergers at
lower redshift. | Non-equilibrium statistical field theory for classical particles: Linear
and mildly non-linear evolution of cosmological density power spectra: We use the non-equlibrium statistical field theory for classical particles,
recently developed by Mazenko and Das and Mazenko, together with the free
generating functional we have previously derived for point sets initially
correlated in phase space, to calculate the time evolution of power spectra in
the free theory, i.e. neglecting particle interactions. We provide expressions
taking linear and quadratic momentum correlations into account. Up to this
point, the expressions are general with respect to the free propagator of the
microscopic degrees of freedom.
We then specialise the propagator to that expected for particles in cosmology
treated within the Zel'dovich approximation and show that, to linear order in
the momentum correlations, the linear growth of the cosmological power spectrum
is reproduced. Quadratic momentum correlations return a first contribution to
the non-linear evolution of the power spectrum, for which we derive a simple
closed expression valid for arbitrary wave numbers. This expression is a
convolution of the initial density power spectrum with itself, multiplied by a
mode-coupling kernel. We also derive the bispectrum expected in this theory
within these approximations and show that its connected part reproduces almost,
but not quite, the bispectrum expected in Eulerian perturbation theory of the
density contrast. |
Bounds for the scale of inflation and the tensor-to-scalar ratio in
Hybrid Natural Inflation: Recently we have studied in great detail a model of Hybrid Natural Inflation
(HNI) by constructing two simple effective field theories. These two versions
of the model allow inflationary energy scales as small as the electroweak scale
in one of them or as large as the Grand Unification scale in the other
therefore covering the whole range of possible energy scales. The inflationary
sector of the model is of the form $V(\phi)=V_0 \left(1+a \cos(\phi/f)\right)$
where $0\leq a<1$ and the end of inflation is triggered by an independent
waterfall field. One interesting characteristic of this type of models is that
the tensor-to-scalar ratio $r$ is a non-monotonic function of $\phi$ presenting
a {\it maximum} close to the inflection point $\phi_I=\pi/2$ of the potential.
Because the scalar spectrum $\mathcal{P}_s(k)$ of density fluctuations when
written in terms of the potential is inversely proportional to $r$ we find that
$\mathcal{P}_s(k)$ presents a {\it minimum} at $\phi_{min}$. We use this
property of HNI together with the observation that the spectrum is decreasing
during the first 8 e-folds of observable inflation to determine bounds for the
inflationary energy scale $\Delta$ and for the tensor-to-scalar ratio $r$. | Galactic outflows and the kinematics of damped Lyman alpha absorbers: The kinematics of damped Lyman alpha absorbers (DLAs) are difficult to
reproduce in hierarchical galaxy formation models, particularly the
preponderance of wide systems. We investigate DLA kinematics at z=3 using
high-resolution cosmological hydrodynamical simulations that include a
heuristic model for galactic outflows. Without outflows, our simulations fail
to yield enough wide DLAs, as in previous studies. With outflows, predicted DLA
kinematics are in much better agreement with observations. Comparing two
outflow models, we find that a model based on momentum-driven wind scalings
provides the best match to the observed DLA kinematic statistics of Prochaska &
Wolfe. In this model, DLAs typically arise a few kpc away from galaxies that
would be identified in emission. Narrow DLAs can arise from any halo and galaxy
mass, but wide ones only arise in halos with mass >10^11 Mo, from either large
central or small satellite galaxies. This implies that the success of this
outflow model originates from being most efficient at pushing gas out from
small satellite galaxies living in larger halos. This increases the
cross-section for large halos relative to smaller ones, thereby yielding wider
kinematics. Our simulations do not include radiative transfer effects or
detailed metal tracking, and outflows are modeled heuristically, but they
strongly suggest that galactic outflows are central to understanding DLA
kinematics. An interesting consequence is that DLA kinematics may place
constraints on the nature and efficiency of gas ejection from high-z galaxies. |
Phase transition during inflation and the gravitational wave signal at
pulsar timing arrays: Gravitational wave signal offers a promising window into the dynamics of the
early universe. The recent results from pulsar timing arrays (PTAs) could be
the first glimpse of such new physics. In particular, they could point to new
details during the inflation, which can not be probed by other means. We
explore the possibility that the new results could come from the secondary
gravitational wave sourced by curvature perturbations, generated by a
first-order phase transition during the inflation. Based on the results of a
field-theoretic lattice simulation of the phase transition process, we show
that the gravitational wave signal generated through this mechanism can account
for the new results from the PTAs. We analyze the spectral shape of the signal
in detail. Future observations can use such information to distinguish the
gravitational wave signal considered here from other possible sources. | Reconstructing the intergalactic UV background with QSO absorption lines: We present a new approach to constrain the spectral energy distribution of
the intergalactic UV background observationally by studying metal absorption
systems. We study single-component metal line systems exhibiting various
well-measured species. Among the observed transitions at least two ratios of
ionization stages from the same element are required, e.g. CIII/CIV and
SiIII/SiIV. For each system photoionization models are constructed varying the
spectrum of the ionizing radiation. The spectral energy distribution can then
be constrained by comparing the models with the observed column density ratios.
Extensive tests with artificial absorbers show that the spectrum of the
ionizing radiation cannot be reconstructed unambiguously, but it is possible to
constrain the main characteristics of the spectrum. Furthermore, the resulting
physical parameters of the absorber, such as ionization parameter, metallicity,
and relative abundances, may depend strongly on the adopted ionizing spectrum.
Even in case of well-fitting models the uncertainties can be as high as ~0.5
dex for the ionization parameter and up to ~1.5 dex for the metallicity.
Therefore, it is essential to know the hardness of the UV background when
estimating the metallicity of the intergalactic medium. Applying the procedure
to a small sample of 3 observed single-component metal line systems yields a
soft ionizing radiation at z > 2 and a slightly harder spectrum at z < 2. The
resulting energy distributions exhibit strong HeII Ly alpha re-emission
features suggesting that reprocessing by intergalactic HeII is important.
Comparing to UV background spectra from the literature indicates that the
recent model of Madau & Haardt (2009) including sawtooth modulation due to
reprocessing by intergalactic HeII with delayed helium reionization fits the
investigated systems very well. |
The diffuse soft excess emission in the Coma cluster from the ROSAT
All-Sky Survey: RASS data near the North Galactic Pole was analyzed in order to study the
large-scale distribution of soft X-ray emission from the Coma cluster. These
RASS data constitute the only available X-ray observations of Coma that feature
an in situ -- temporally and spatially contiguous -- background, with unlimited
and continuous radial coverage. These unique characteristics of the RASS data
are used to deliver a final assessment on whether the soft excess previously
detected in the Coma cluster is due to background subtraction errors, or not.
This paper confirms the presence of soft X-ray excess associated with Coma, and
reports the detection of 1/4 keV band excess out to 5 Mpc from the cluster
center, the largest soft excess halo discovered to date. We propose that the
emission is related to filaments that converge towards Coma, and generated
either by non-thermal radiation caused by accretion shocks, or by thermal
emission from the filaments themselves. | MOND virial theorem applied to a galaxy cluster: Large values for the mass-to-light ratio (") in self-gravitating systems is
one of the most important evidences of dark matter. We propose a expression for
the mass-to-light ratio in spherical systems using MOND. Results for the COMA
cluster reveal that a modification of the gravity, as proposed by MOND, can
reduce significantly this value. |
A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to
Damped Lyman-alpha Systems - II. Dynamical Properties of the Galaxies towards
Q0302-223 and Q1009-0026: Details of processes through which galaxies convert their gas into stars need
to be studied in order to obtain a complete picture of galaxy formation. One
way to tackle these phenomena is to relate the HI gas and the stars in
galaxies. Here, we present dynamical properties of Damped and sub-Damped
Lyman-alpha Systems identified in H-alpha emission with VLT/SINFONI at near
infra-red wavelengths. While the DLA towards Q0302-223 is found to be
dispersion-dominated, the sub-DLA towards Q1009-0026 shows clear signatures of
rotation. We use a proxy to circular velocity to estimate the mass of the halo
in which the sub-DLA resides and find M_halo=10^12.6 M_sun. We also derive
dynamical masses of these objects, and find M_dyn=10^10.3 M_sun and 10^10.9
M_sun. For one of the two systems (towards Q0302-223), we are able to derive a
stellar mass of M_*=10^9.5 M_sun from Spectral Energy Distribution fit. The gas
fraction in this object is 1/3rd, comparable to similar objects at these
redshifts. Our work illustrates that detailed studies of quasar absorbers can
offer entirely new insights into our knowledge of the interaction between stars
and the interstellar gas in galaxies. | Free-streaming and Coupled Dark Radiation Isocurvature Perturbations:
Constraints and Application to the Hubble Tension: Dark radiation (DR) appears as a new physics candidate in various scenarios
beyond the Standard Model. While it is often assumed that perturbations in DR
are adiabatic, they can easily have an isocurvature component if more than one
field was present during inflation, and whose decay products did not all
thermalize with each other. By implementing the appropriate isocurvature
initial conditions (IC), we derive the constraints on both uncorrelated and
correlated DR density isocurvature perturbations from the full Planck 2018 data
alone, and also in combination with other cosmological data sets. Our study on
free-streaming DR (FDR) updates and generalizes the existing bound on neutrino
density isocurvature perturbations by including a varying number of
relativistic degrees of freedom, and for coupled DR (CDR) isocurvature, we
derive the first bound. We also show that for CDR qualitatively new physical
effects arise compared to FDR. One such effect is that for isocurvature IC, FDR
gives rise to larger CMB anisotropies compared to CDR -- contrary to the
adiabatic case. More generally, we find that a blue-tilt of DR isocurvature
spectrum is preferred. This gives rise to a larger value of the Hubble constant
$H_0$ compared to the standard $\Lambda$CDM+$\Delta N_{\rm eff}$ cosmology with
adiabatic spectra and relaxes the $H_0$ tension. |
HIFLUGCS: X-ray luminosity -- dynamical mass relation and its
implications for mass calibrations with the SPIDERS and 4MOST surveys: We present the X-ray luminosity (L) versus dynamical mass (M) relation for 63
nearby clusters in the HIFLUGCS. The luminosity measurements are obtained based
on ~1.3 Ms of clean XMM data and ROSAT pointed observations. The masses are
estimated using optical spectroscopic redshifts of 13647 cluster galaxies in
total. Given sufficient numbers of member galaxies in computing the dynamical
masses, the L-M relations agree between the disturbed and undisturbed clusters.
The cool-core clusters still dominate the scatter in the L-M relation even when
a core corrected X-ray luminosity is used, which indicates that the scatter
mainly reflects the structure formation history of the clusters. As shown by
the clusters with a small number of redshifts, the dynamical masses can be
underestimated leading to a biased scaling relation. To investigate the
potential of spectroscopic surveys to follow up high-redshift galaxy
clusters/groups observed in X-ray surveys for the identifications and mass
calibrations, we carried out Monte-Carlo re-sampling of the cluster galaxy
redshifts and calibrated the uncertainties of the redshift and dynamical mass
estimates when only reduced numbers of galaxy redshifts per cluster are
available. The re-sampling considers the SPIDERS and 4MOST configurations,
designed for the follow-up of the eROSITA clusters, and was carried out for
each cluster at the actual cluster redshift as well as at z=0.2, 0.4, 0.6, and
0.8. For following up very distant cluster/groups, we carried out the mass
calibration based on the re-sampling with only 10zs/cluster, and redshift
calibration based on the re-sampling with only 5zs/cluster and 10zs/cluster,
respectively. Our results demonstrate the power of combining upcoming X-ray and
optical spectroscopic surveys for mass calibration. The scatter in the
dynamical mass estimates for the clusters with at least ten members is within
50%. | The Clustering Of Galaxies Around Radio-Loud AGNs: We examine the hypothesis that mergers and close encounters between galaxies
can fuel AGNs by increasing the rate at which gas accretes towards the central
black hole. We compare the clustering of galaxies around radio-loud AGNs with
the clustering around a population of radio-quiet galaxies with similar masses,
colors and luminosities. Our catalog contains 2178 elliptical radio galaxies
with flux densities greater than 2.8 mJy at 1.4 GHz from the 6dFGS survey. We
find that radio AGNs with more than 200 times the median radio power have, on
average, more close (r<160 kpc) companions than their radio-quiet counterparts,
suggestive that mergers play a role in forming the most powerful radio
galaxies. For ellipticals of fixed stellar mass, the radio power is not a
function of large-scale environment nor halo mass, consistent with the radio
powers of ellipticals varying by orders of magnitude over billions of years. |
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of
Early-type Galaxies: We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M$_\odot$ and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M$_\odot$, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5. | On the relative effect of nodes and filaments of the cosmic web on the
quenching of galaxies and the orientation of their spin: Filaments and clusters of the cosmic web have an impact on the properties of
galaxies, switching off their star-formation, contributing to the build-up of
their stellar mass, and influencing the acquisition of their angular momentum.
In this work we make use of the IllustrisTNG simulation, coupled with the
DisPerSE cosmic web extraction algorithm, to test which is the galaxy property
most affected by the cosmic web and, conversely, to assess the differential
impact of the various cosmic web features on a given galaxy property. Our aim
is to use this information to better understand galaxy evolution and to
identify on which galaxy property future efforts should focus to detect the
cosmic web from the galaxy distribution. We provide a comprehensive analysis of
the relation between galaxy properties and cosmic web features. We also perform
extensive tests in which we try to disentangle the effect of local
overdensities of galaxies on their properties from the effect of the large
scale structure environment. Our results show that star-formation is the
quantity that shows the strongest variation with the distances from the cosmic
web features, but it is also the one that shows the strongest relation to the
local environment of galaxies. On the other hand, the direction of the angular
momentum of galaxies is the property that shows the weakest trends with
distance from cosmic web features, while also being more independent from the
local environment of galaxies. We conclude that the direction of the angular
momentum of galaxies and its use to improve our detection of the cosmic web
features could be the focus of futures studies benefiting from larger
statistical samples. |
Gravitational interaction of antimatter: Until now, there is no experimental evidence on the gravitational behaviour
of antimatter. While we may be confident that antimatter attracts antimatter,
we do not know anything on the interaction between matter and antimatter. We
investigate this issue on theoretical grounds. Starting from the CPT invariance
of physical laws, we transform matter into antimatter in the equations of both
electrodynamics and gravitation. In the former case, the result is the
well-known change of sign of the electric charge. In the latter, we find that
the gravitational interaction between matter and antimatter is a mutual
repulsion. This result supports cosmological models attempting to explain the
Universe accelerated expansion in terms of a matter-antimatter symmetry. | Violation of the Rotational Invariance in the CMB Bispectrum: We investigate a statistical anisotropy on the Cosmic Microwave Background
(CMB) bispectrum, which can be generated from the primordial non-Gaussianity
induced by quantum fluctuations of a vector field. We find new configurations
in the multipole space of the CMB bispectrum given by $\ell_1 = \ell_2 + \ell_3
+ 2, |\ell_2 - \ell_3| - 2$ and their permutations, which violate the
rotational invariance, such as an off-diagonal configuration in the CMB power
spectrum. We also find that in a model presented by Yokoyama and Soda (2008),
the amplitude of the statistically anisotropic bispectrum in the above
configurations becomes as large as that in other configurations such as $\ell_1
= \ell_2 + \ell_3$. As a result, it might be possible to detect these
contributions in future experiments, which would give us novel information
about the physics of the early Universe. |
Gravitational waves from intermediate-mass black holes in young clusters: Massive young clusters (YCs) are expected to host intermediate-mass black
holes (IMBHs) born via runaway collapse. These IMBHs are likely in binaries and
can undergo mergers with other compact objects, such as stellar mass black
holes (BHs) and neutron stars (NSs). We derive the frequency of such mergers
starting from information available in the Local Universe. Mergers of IMBH-NS
and IMBH-BH binaries are sources of gravitational waves (GWs), which might
allow us to reveal the presence of IMBHs. We thus examine their detectability
by current and future GW observatories, both ground- and space-based. In
particular, as representative of different classes of instruments we consider
Initial and Advanced LIGO, the Einstein gravitational-wave Telescope (ET) and
the Laser Interferometer Space Antenna (LISA). We find that IMBH mergers are
unlikely to be detected with instruments operating at the current sensitivity
(Initial LIGO). LISA detections are disfavored by the mass range of IMBH-NS and
IMBH-BH binaries: less than one event per year is expected to be observed by
such instrument. Advanced LIGO is expected to observe a few merger events
involving IMBH binaries in a 1-year long observation. Advanced LIGO is
particularly suited for mergers of relatively light IMBHs (~100 Msun) with
stellar mass BHs. The number of mergers detectable with ET is much larger: tens
(hundreds) of IMBH-NS (IMBH-BH) mergers might be observed per year, according
to the runaway collapse scenario for the formation of IMBHs. We note that our
results are affected by large uncertainties, produced by poor observational
constraints on many of the physical processes involved in this study, such as
the evolution of the YC density with redshift.[abridged] | Ultraviolet to infrared emission of z>1 galaxies: Can we derive reliable
star formation rates and stellar masses?: We seek to derive star formation rates (SFR) and stellar masses (M_star) in
distant galaxies and to quantify the main uncertainties affecting their
measurement. We explore the impact of the assumptions made in their derivation
with standard calibrations or through a fitting process, as well as the impact
of the available data, focusing on the role of IR emission originating from
dust. We build a sample of galaxies with z>1, all observed from the UV to the
IR (rest frame). The data are fitted with the code CIGALE, which is also used
to build and analyse a catalogue of mock galaxies. Models with different SFHs
are introduced. We define different set of data, with or without a good
sampling of the UV range, NIR, and thermal IR data. The impact of these
different cases on the determination of M_star and SFR are analysed.
Exponentially decreasing models with a redshift formation of the stellar
population z ~8 cannot fit the data correctly. The other models fit the data
correctly at the price of unrealistically young ages when the age of the single
stellar population is taken to be a free parameter. The best fits are obtained
with two stellar populations. As long as one measurement of the dust emission
continuum is available, SFR are robustly estimated whatever the chosen model
is, including standard recipes. M_star measurement is more subject to
uncertainty, depending on the chosen model and the presence of NIR data, with
an impact on the SFR-M_star scatter plot. Conversely, when thermal IR data from
dust emission are missing, the uncertainty on SFR measurements largely exceeds
that of stellar mass. Among all physical properties investigated here, the
stellar ages are found to be the most difficult to constrain and this
uncertainty acts as a second parameter in SFR measurements and as the most
important parameter for M_star measurements. |
Cosmic reionization after Planck II: contribution from quasars: In the light of the recent Planck downward revision of the electron
scattering optical depth, and of the discovery of a faint AGN population at $z
> 4$, we reassess the actual contribution of quasars to cosmic reionization. To
this aim, we extend our previous MCMC-based data-constrained semi-analytic
reionization model and study the role of quasars on global reionization
history. We find that, the quasars can alone reionize the Universe only for
models with very high AGN emissivities at high redshift. These models are still
allowed by the recent CMB data and most of the observations related to HI
reionization. However, they predict an extended and early HeII reionization
ending at $z\gtrsim4$ and a much slower evolution in the mean HeII Ly-$\alpha$
forest opacity than what the actual observation suggests. Thus when we further
constrain our model against the HeII Ly-$\alpha$ forest data, this
AGN-dominated scenario is found to be clearly ruled out at 2-$\sigma$ limits.
The data seems to favour a standard two-component picture where quasar
contributions become negligible at $z\gtrsim6$ and a non-zero escape fraction
of $\sim10\%$ is needed from early-epoch galaxies. For such models, mean
neutral hydrogen fraction decreases to $\sim10^{-4}$ at $z=6.2$ from $\sim0.8$
at $z=10.0$ and helium becomes doubly ionized at much later time, $z\sim3$. We
find that, these models are as well in good agreement with the observed thermal
evolution of IGM as opposed to models with very high AGN emissivities. | Molecular hydrogen in the z = 2.66 damped Lyman-alpha absorber toward Q
J0643-5041: We use high signal-to-noise ratio, high-resolution VLT-UVES data of Q
J0643-5041 amounting to a total of more than 23 hours exposure time and fit the
neutral hydrogen, metals and H2 absorption features with multiple-component
Voigt profiles. We study the relative populations of H2 rotational levels and
the fine-structure excitation of neutral carbon to determine the physical
conditions in the H2-bearing cloud. We find some evidence for part of the
quasar broad line emission region not being fully covered by the H2-bearing
cloud. We measure a total neutral hydrogen column density of log N(H) = 21.03
+/- 0.08. Molecular hydrogen is detected in several rotational levels, possibly
up to J = 7, in a single component. The corresponding molecular fraction is log
f = -2.19+0.07-0.08, where f = 2N(H2)/(2N(H2)+N(H)). The H2 Doppler parameter
is of the order of 1.5 km/s for J = 0, 1 and 2 and larger for J>2. The
molecular component has a kinetic temperature of T = 80 K, which yields a mean
thermal velocity of about 1 km/s, consistent with the Doppler broadening of the
lines. The UV ambient flux is of the order of the mean ISM Galactic flux. We
discuss the possible detection of HD and derive an upper limit of log N(HD) <
13.65 +/- 0.07 leading to log HD/(2 H2) < -5.19 +/- 0.07 which is consistently
lower than the primordial D/H ratio. Metals span about 210 km/s with [Zn/H] =
-0.91 +/- 0.09 relative to solar, with iron depleted relative to zinc [Zn/Fe] =
0.45 +/- 0.06, and with the rare detection of copper. We follow the procedures
used in our previous works to derive a constraint on the cosmological variation
of the proton-to-electron mass ratio of (7.4 +/- 4.3 (stat) +/- 5.1 (syst))
ppm. |
X-ray absorption by Broad Line Region Clouds in Mrk 766: We present a new analysis of a 9-day long XMM-Newton monitoring of the Narrow
Line Seyfert 1 galaxy Mrk 766. We show that the strong changes in spectral
shape which occurred during this observation can be interpreted as due to Broad
Line Region clouds crossing the line of sight to the X-ray source. Within the
occultation scenario, the spectral and temporal analysis of the eclipses
provides precise estimates of the geometrical structure, location and physical
properties of the absorbing clouds. In particular, we show that these clouds
have cores with column densities of at least a few 10^23 cm^-2 and velocities
in the plane of the sky of the order of thousands km/s. The three different
eclipses monitored by XMM-Newton suggest a broad range in cloud velocities (by
a factor ~4-5). Moreover, two iron absorption lines clearly associated with
each eclipse suggest the presence of highly ionized gas around the obscuring
clouds, and an outflow component of the velocity spanning from 3,000 to 15,000
km/s | A double take on early and interacting dark energy from JWST: The very first light captured by the James Webb Space Telescope (JWST)
revealed a population of galaxies at very high redshifts more massive than
expected in the canonical $\Lambda$CDM model of structure formation. Barring,
among others, a systematic origin of the issue, in this paper, we test
alternative cosmological perturbation histories. We argue that models with a
larger matter component $\Omega_m$ and/or a larger scalar spectral index $n_s$
can substantially improve the fit to JWST measurements. In this regard,
phenomenological extensions related to the dark energy sector of the theory are
appealing alternatives, with Early Dark Energy emerging as an excellent
candidate to explain (at least in part) the unexpected JWST preference for
larger stellar mass densities. Conversely, Interacting Dark Energy models,
despite producing higher values of matter clustering parameters such as
$\sigma_8$, are generally disfavored by JWST measurements. This is due to the
energy-momentum flow from the dark matter to the dark energy sector, implying a
smaller matter energy density. Upcoming observations may either strengthen the
evidence or falsify some of these appealing phenomenological alternatives to
the simplest $\Lambda$CDM picture. |
The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: Baryon Acoustic Oscillations in the correlation
function of LOWZ and CMASS galaxies in Data Release 12: We present distance scale measurements from the baryon acoustic oscillation
signal in the CMASS and LOWZ samples from the Data Release 12 of the Baryon
Oscillation Spectroscopic Survey (BOSS). The total volume probed is 14.5
Gpc$^3$, a 10 per cent increment from Data Release 11. From an analysis of the
spherically averaged correlation function, we infer a distance to $z=0.57$ of
$D_V(z)r^{\rm fid}_{\rm d}/r_ {\rm d}=2028\pm21$ Mpc and a distance to $z=0.32$
of $D_V(z)r^{\rm fid}_{\rm d}/r_{\rm d}=1264\pm22$ Mpc assuming a cosmology in
which $r^{\rm fid}_{\rm d}=147.10$ Mpc. From the anisotropic analysis, we find
an angular diameter distance to $z=0.57$ of $D_{\rm A}(z)r^{\rm fid}_{\rm
d}/r_{\rm d}=1401\pm21$ Mpc and a distance to $z=0.32$ of $981\pm20$ Mpc, a 1.5
per cent and 2.0 per cent measurement respectively. The Hubble parameter at
$z=0.57$ is $H(z)r_{\rm d}/r^{\rm fid}_{\rm d}=100.3\pm3.7$ km s$^{-1}$
Mpc$^{-1}$ and its value at $z=0.32$ is $79.2\pm5.6$ km s$^{-1}$ Mpc$^{-1}$, a
3.7 per cent and 7.1 per cent measurement respectively. These cosmic distance
scale constraints are in excellent agreement with a $\Lambda$CDM model with
cosmological parameters released by the recent Planck 2015 results. | The Mass-Richness Relation of MaxBCG Clusters from Quasar Lensing
Magnification using Variability: Accurate measurement of galaxy cluster masses is an essential component not
only in studies of cluster physics, but also for probes of cosmology. However,
different mass measurement techniques frequently yield discrepant results. The
SDSS MaxBCG catalog's mass-richness relation has previously been constrained
using weak lensing shear, Sunyaev-Zeldovich (SZ), and X-ray measurements. The
mass normalization of the clusters as measured by weak lensing shear is >~25%
higher than that measured using SZ and X-ray methods, a difference much larger
than the stated measurement errors in the analyses. We constrain the
mass-richness relation of the MaxBCG galaxy cluster catalog by measuring the
gravitational lensing magnification of type I quasars in the background of the
clusters. The magnification is determined using the quasars' variability and
the correlation between quasars' variability amplitude and intrinsic
luminosity. The mass-richness relation determined through magnification is in
agreement with that measured using shear, confirming that the lensing strength
of the clusters implies a high mass normalization, and that the discrepancy
with other methods is not due to a shear-related systematic measurement error.
We study the dependence of the measured mass normalization on the cluster halo
orientation. As expected, line-of-sight clusters yield a higher normalization;
however, this minority of haloes does not significantly bias the average
mass-richness relation of the catalog. |
Particle dark matter searches in the anisotropic sky: Anisotropies in the electromagnetic emission produced by dark matter
annihilation or decay in the extragalactic sky are a recent tool in the quest
for a particle dark matter evidence. We review the formalism to compute the
two-point angular power spectrum in the halo-model approach and discuss the
features and the relative size of the various auto- and cross-correlation
signals that can be envisaged for anisotropy studies. From the side of particle
dark matter signals, we consider the full multi-wavelength spectrum, from the
radio emission to X-ray and gamma-ray productions. We discuss the angular power
spectra of the auto-correlation of each of these signals and of the
cross-correlation between any pair of them. We then extend the search to
comprise specific gravitational tracers of dark matter distribution in the
Universe: weak-lensing cosmic shear, large-scale-structure matter distribution
and CMB-lensing. We have shown that cross-correlating a multi-wavelength dark
matter signal (which is a direct manifestation of its particle physics nature)
with a gravitational tracer (which is a manifestation of the presence of large
amounts of unseen matter in the Universe) may offer a promising tool to
demonstrate that what we call dark matter is indeed formed by elementary
particles. | Determination of the Local Dark Matter Density in our Galaxy: The rotation curve, the total mass and the gravitational potential of the
Galaxy are sensitive measurements of the dark matter halo profile. In this
publication cuspy and cored DM halo profiles are analysed with respect to
recent astronomical constraints in order to constrain the shape of the Galactic
DM halo and the local DM density. All Galactic density components (luminous
matter and DM) are parametrized. Then the total density distribution is
constrained by astronomical observations: 1) the total mass of the Galaxy, 2)
the total matter density at the position of the Sun, 3) the surface density of
the visible matter, 4) the surface density of the total matter in the vicinity
of the Sun, 5) the rotation speed of the Sun and 6) the shape of the velocity
distribution within and above the Galactic disc. The mass model of the Galaxy
is mainly constrained by the local matter density (Oort limit), the rotation
speed of the Sun and the total mass of the Galaxy from tracer stars in the
halo. It is shown from a statistical chi^2 fit to all data that the local DM
density is strongly positively (negatively) correlated with the scale length of
the DM halo (baryonic disc). Since these scale lengths are poorly constrained
the local DM density can vary from 0.2 to 0.4 GeV/cm^3 (0.005 - 0.01
M_sun/pc^3) for a spherical DM halo profile and allowing total Galaxy masses up
to 2 * 10^12 M_sun. For oblate DM halos and dark matter discs, as predicted in
recent N-body simulations, the local DM density can be increased significantly. |
Moment expansion of polarized dust SED: a new path towards capturing the
CMB $B$-modes with $\textit{LiteBIRD}$: Characterizing the polarized dust emission from our Galaxy will be decisive
for the quest for the Cosmic Microwave Background (CMB) primordial $B$-modes.
The incomplete modelling of its potentially complex spectral properties could
lead to biases in the CMB polarization analyses and to a spurious detection of
the tensor-to-scalar ratio $r$. It is crucial for future surveys like the
$LiteBIRD$ satellite, which aims at constraining the primordial signal leftover
by Inflation with an accuracy on $r$ of the order 1e-3. Variations of the dust
properties along and between lines of sight lead to distortions of the spectral
energy distribution (SED) that can not be easily anticipated by standard
component separation methods. This issue can be tackled with a moment expansion
of the dust SED, an innovative parametrization method imposing minimal
assumptions on the sky complexity. In this paper, we apply this formalism to
the $B$-mode cross-angular power spectra computed from simulated $LiteBIRD$
polarization data at frequencies between 100 and 402 GHz, containing CMB, dust
and instrumental noise. The spatial variation of the dust spectral parameters
(spectral index $\beta$ and temperature $T$) in our simulations, lead to
significant biases on $r$ if not properly taken into account. Performing the
moment expansion in $\beta$, reduces the bias but do not lead to reliable
enough estimates of $r$. We introduce for the first time the expansion of the
cross-angular power spectra SED in $\beta$ and $T$, showing that, at the
$LiteBIRD$ sensitivity, it is required to take into account the SED complexity
due to temperature variations to prevent analysis biases on $r$. Thanks to this
expansion and despite the existing correlations between some of the dust
moments and the CMB signal, responsible for a rise of the error on $r$, we can
measure an unbiased value of $r$ with an uncertainty of $\sigma(r)$=8.8e-4. | Influence of Gamma-Ray Emission on the Isotopic Composition of Clouds in
the Interstellar Medium: We investigate one mechanism of the change in the isotopic composition of
cosmologically distant clouds of interstellar gas whose matter was subjected
only slightly to star formation processes. According to the standard
cosmological model, the isotopic composition of the gas in such clouds was
formed at the epoch of Big Bang nucleosynthesis and is determined only by the
baryon density in the Universe. The dispersion in the available cloud
composition observations exceeds the errors of individual measurements. This
may indicate that there are mechanisms of the change in the composition of
matter in the Universe after the completion of Big Bang nucleosynthesis. We
have calculated the destruction and production rates of light isotopes (D, 3He,
4He) under the influence of photonuclear reactions triggered by the gamma-ray
emission from active galactic nuclei (AGNs). We investigate the destruction and
production of light elements depending on the spectral characteristics of the
gamma-ray emission. We show that in comparison with previous works, taking into
account the influence of spectral hardness on the photonuclear reaction rates
can increase the characteristic radii of influence of the gamma-ray emission
from AGNs by a factor of 2-8. The high gamma-ray luminosities of AGNs observed
in recent years increase the previous estimates of the characteristic radii by
two orders of magnitude. This may suggest that the influence of the emission
from AGNs on the change in the composition of the medium in the immediate
neighborhood (the host galaxy) has been underestimated. |
Spectral synthesis including massive binaries: We have constructed a new code to produce synthetic spectra of stellar
populations that includes massive binaries. We have tested this code against
the broadband colours of unresolved young massive stellar clusters in nearby
galaxies, the equivalent widths of the Red and Blue Wolf-Rayet bumps in
star-forming SDSS galaxies and the UV and optical spectra of the star forming
regions Tol-A and B in NGC5398. In each case we find a good agreement between
our models and observations. We find that in general binary populations are
bluer and have fewer red supergiants, and thus significantly less flux in the
I-band and at longer wavelengths, than single star populations. Also we find
that Wolf-Rayet stars occur over a wider range of ages up to 10^7 years in a
stellar population including binaries, increasing the UV flux and Wolf-Rayet
spectral features at later times. In addition we find that nebula emission
contributes significantly to these observed properties and must be considered
when comparing stellar models with observations of unresolved stellar
populations. We conclude that incorporation of massive stellar binaries can
improve the agreement between observations and synthetic spectral synthesis
codes, particularly for systems with young stellar populations. | Comprehensive Constraints on Dark Radiation Injection After BBN: We derive constraints on the injection of free-streaming dark radiation after
big bang nucleosynthesis (BBN) by considering the decay of a massive hidden
sector particle into dark radiation. Such a scenario has the potential to
alleviate the Hubble tension by introducing a new energy component to the
evolution of the early universe. We employ observations of the cosmic microwave
background (CMB) from $\textit{Planck}$ 2018 and SPT-3G, measurements of the
primordial deuterium abundance, Pantheon+ Type Ia supernovae data, and baryon
acoustic oscillation (BAO) measurements from BOSS DR12 to constrain these decay
scenarios. Pre-recombination decays are primarily restricted by observations of
the CMB via their impact on the effective number of relativistic species. On
the other hand, long-lived decay scenarios in which the massive particle
lifetime extends past recombination tend to decrease the late-time matter
density inferred from the CMB and are thus subject to constraints from
Pantheon+ and BAO. We find that, when marginalizing over lifetimes of $\tau_Y =
[10^{-12.08}, 10^{-1.49}]$ Gyr, the decaying particle is limited at $2\sigma$
to only contribute a maximum of $3\%$ of the energy density of the universe.
With limits on these decays being so stringent, neither short-lived nor
long-lived scenarios are successful at substantially mitigating the Hubble
tension. |
Shocks, Seyferts and the SNR connection: a Chandra observation of the
Circinus galaxy: We analyse new Chandra observations of the nearest (D=4 Mpc) Seyfert 2 active
galaxy, Circinus, and match them to pre-existing radio, infrared and optical
data to study the kpc-scale emission. The proximity of Circinus allows us to
observe in striking detail the structure of the radio lobes, revealing for the
first time edge-brightened emission both in X-rays and radio. After considering
various other possible scenarios, we show that this extended emission in
Circinus is most likely caused by a jet-driven outflow, which is driving shells
of strongly shocked gas into the halo of the host galaxy. In this context, we
estimate Mach numbers M=2.7-3.6 and M=2.8-5.3 for the W and E shells
respectively. We derive temperatures of 0.74 (+0.06, -0.05) keV and 0.8-1.8 keV
for the W and E shells, and an expansion velocity of ~900-950 km/s. We estimate
that the total energy (thermal and kinetic) involved in creating both shells is
~2x10^55 erg, and their age is ~10^6 years. Comparing these results with those
we previously obtained for Centaurus A, NGC 3801 and Mrk 6, we show that these
parameters scale approximately with the radio power of the parent AGN. The
spatial coincidence between the X-ray and edge-brightened radio emission in
Circinus resembles the morphology of some SNR shocks. This parallel has been
expected for AGN, but has never been observed before. We investigate what
underlying mechanisms both types of systems may have in common, arguing that,
in Circinus, the edge-brightening in the shells may be accounted for by a B
field enhancement caused by shock compression, but do not preclude some local
particle acceleration. These results can be extrapolated to other low-power
systems, particularly those with late type hosts. | Keck Observations of the Young Metal-Poor Host Galaxy of the
Super-Chandrasekhar-Mass Type Ia Supernova SN 2007if: We present Keck LRIS spectroscopy and $g$-band photometry of the metal-poor,
low-luminosity host galaxy of the super-Chandrasekhar mass Type Ia supernova SN
2007if. Deep imaging of the host reveals its apparent magnitude to be
$m_g=23.15\pm0.06$, which at the spectroscopically-measured redshift of
$z_{helio}=0.07450\pm0.00015$ corresponds to an absolute magnitude of
$M_g=-14.45\pm0.06$. Galaxy $g-r$ color constrains the mass-to-light ratio,
giving a host stellar mass estimate of $\log(M_*/M_\odot)=7.32\pm0.17$. Balmer
absorption in the stellar continuum, along with the strength of the 4000\AA\
break, constrain the age of the dominant starburst in the galaxy to be
$t_\mathrm{burst}=123^{+165}_{-77}$ Myr, corresponding to a main-sequence
turn-off mass of $M/M_\odot=4.6^{+2.6}_{-1.4}$. Using the R$_{23}$ method of
calculating metallicity from the fluxes of strong emission lines, we determine
the host oxygen abundance to be $12+\log(O/H)_\mathrm{KK04}=8.01\pm0.09$,
significantly lower than any previously reported spectroscopically-measured
Type Ia supernova host galaxy metallicity. Our data show that SN 2007if is very
likely to have originated from a young, metal-poor progenitor. |
Cosmological constraints on the gas depletion factor in galaxy clusters: The evolution of the X-ray emitting gas mass fraction ($f_{gas}$) in massive
galaxy clusters can be used as an independent cosmological tool to probe the
expansion history of the Universe. Its use, however, depends upon a crucial
quantity, i.e., the depletion factor $\gamma$, which corresponds to the ratio
by which $f_{gas}$ is depleted with respect to the universal baryonic mean.
This quantity is not directly observed and hydrodynamical simulations performed
in a specific cosmological model (e.g., a flat $\Lambda$CDM cosmology) have
been used to calibrate it. In this work, we obtain for the first time
self-consistent observational constraints on the gas depletion factor combining
40 X-ray emitting gas mass fraction measurements and luminosity distance
measurements from type Ia supernovae. Using Gaussian Processes to reconstruct a
possible redshift evolution of $\gamma$, we find no evidence for such
evolution, which confirms the current results from hydrodynamical simulations.
Moreover, our constraints on $\gamma$ can be seen as a data prior for
cosmological analyses on different cosmological models. The current
measurements are systematic limited, so future improvements will depend heavily
on a better mass calibration of galaxy clusters and their measured density
profiles. | Evolution of the First Supernovae in Protogalaxies: Dynamics of Mixing
of Heavy Elements: The paper considers the evolution of the supernova envelopes produced by
Population III stars with masses of $M_*\sim 25-200 M_\odot$ located in
non-rotating protogalaxies with masses of $M\sim 10^7 M_\odot$ at redshifts
$z=12$, with dark-matter density profiles in the form of modified isothermal
spheres. The supernova explosion occurs in the ionization zone formed by a
single parent star. The properties of the distribution of heavy elements
(metals) produced by the parent star are investigated, as well as the
efficiency with which they are mixed with the primordial gas in the supernova
envelope. In supernovae with high energies ($E\simgt 5\times 10^{52}$ erg), an
appreciable fraction of the gas can be ejected from the protogalaxy, but nearly
all the heavy elements remain in the protogalaxy. In explosions with lower
energies ($E\simlt 3\times 10^{52}$ erg), essentially no gas and heavy elements
are lost from the protogalaxy: during the first one to threemillion years, the
gas and heavy elements are actively carried from the central region of the
protogalaxy ($r\sim 0.1 r_{vir}$, where $r_{vir}$ is the virial radius of the
protogalaxy), but an appreciable fraction of the mass of metals subsequently
returns when the hot cavity cools and the envelope collapses. Supernovae with
high energies ($E\simgt 5\times 10^{52}$ erg) are characterized by a very low
efficiency of mixing of metals; their heavy elements are located in the small
volume occupied by the disrupted envelope (in a volume comparable with that of
the entire envelope), with most of the metals remaining inside the hot,
rarified cavity of the envelope. (abridged) |
The Relation between Black Hole Mass and Host Spheroid Stellar Mass out
to z~2: We combine Hubble Space Telescope images from the Great Observatories Origins
Deep Survey with archival Very Large Telescope and Keck spectra of a sample of
11 X-ray selected broad-line active galactic nuclei in the redshift range 1<z<2
to study the black hole mass - stellar mass relation out to a lookback time of
10 Gyrs. Stellar masses of the spheroidal component are derived from
multi-filter surface photometry. Black hole masses are estimated from the width
of the broad MgII emission line and the 3000A nuclear luminosity. Comparing
with a uniformly measured local sample and taking into account selection
effects, we find evolution in the form M_BH/M_spheroid ~ (1+z)^(1.96+/-0.55),
in agreement with our earlier studies based on spheroid luminosity. However,
this result is more accurate because it does not require a correction for
luminosity evolution and therefore avoids the related and dominant systematic
uncertainty. We also measure total stellar masses. Combining our sample with
data from the literature, we find M_BH/M_host ~ (1+z)^(1.15+/-0.15), consistent
with the hypothesis that black holes (in the range M_BH ~ 10^8-9 M_sun) predate
the formation of their host galaxies. Roughly one third of our objects reside
in spiral galaxies; none of the host galaxies reveal signs of interaction or
major merger activity. Combined with the slower evolution in host stellar
masses compared to spheroid stellar masses, our results indicate that secular
evolution or minor mergers play a non-negligible role in growing both BHs and
spheroids. | Precision cosmology with voids in the final BOSS data: We report novel cosmological constraints obtained from cosmic voids in the
final BOSS DR12 dataset. They arise from the joint analysis of geometric and
dynamic distortions of average void shapes (i.e., the stacked void-galaxy
cross-correlation function) in redshift space. Our model uses tomographic
deprojection to infer real-space void profiles and self-consistently accounts
for the Alcock-Paczynski (AP) effect and redshift-space distortions (RSD)
without any prior assumptions on cosmology or structure formation. It is
derived from first physical principles and provides an extremely good
description of the data at linear perturbation order. We validate this model
with the help of mock catalogs and apply it to the final BOSS data to constrain
the RSD and AP parameters $f/b$ and $D_AH/c$, where $f$ is the linear growth
rate, $b$ the linear galaxy bias, $D_A$ the comoving angular diameter distance,
$H$ the Hubble rate, and $c$ the speed of light. In addition, we include two
nuisance parameters in our analysis to marginalize over potential systematics.
We obtain $f/b=0.540\pm0.091$ and $D_AH/c=0.588\pm0.004$ from the full void
sample at a mean redshift of $z=0.51$. In a flat $\Lambda$CDM cosmology, this
implies $\Omega_\mathrm{m}=0.312\pm0.020$ for the present-day matter density
parameter. When we use additional information from the survey mocks to
calibrate our model, these constraints improve to $f/b=0.347\pm0.023$,
$D_AH/c=0.588\pm0.003$, and $\Omega_\mathrm{m}=0.310\pm0.017$. However, we
emphasize that the calibration depends on the specific model of cosmology and
structure formation assumed in the mocks, so the calibrated results should be
considered less robust. Nevertheless, our calibration-independent constraints
are among the tightest of their kind to date, demonstrating the immense
potential of using cosmic voids for cosmology in current and future data. |
Data Compression and Covariance Matrix Inspection: Cosmic Shear: Covariance matrices are among the most difficult pieces of end-to-end
cosmological analyses. In principle, for two-point functions, each component
involves a four-point function, and the resulting covariance often has hundreds
of thousands of elements. We investigate various compression mechanisms capable
of vastly reducing the size of the covariance matrix in the context of cosmic
shear statistics. This helps identify which of its parts are most crucial to
parameter estimation. We start with simple compression methods, by isolating
and "removing" 200 modes associated with the lowest eigenvalues, then those
with the lowest signal-to-noise ratio, before moving on to more sophisticated
schemes like compression at the tomographic level and, finally, with the
Massively Optimized Parameter Estimation and Data compression (MOPED). We find
that, while most of these approaches prove useful for a few parameters of
interest, like $\Omega_m$, the simplest yield a loss of constraining power on
the intrinsic alignment (IA) parameters as well as $S_8$. For the case
considered -- cosmic shear from the first year of data from the Dark Energy
Survey -- only MOPED was able to replicate the original constraints in the
16-parameter space. Finally, we apply a tolerance test to the elements of the
compressed covariance matrix obtained with MOPED and confirm that the IA
parameter $A_{\mathrm{IA}}$ is the most susceptible to inaccuracies in the
covariance matrix. | Quantification of the multi-streaming effect in Redshift Space
Distortion: Both multi-streaming (random motion) and bulk motion cause the Finger-of-God
(FoG) effect in redshift space distortion (RSD). We apply a direct measurement
of the multi-streaming effect in RSD from simulations, proving that it induces
an additional, non-negligible FoG damping to the redshift space density power
spectrum. We show that, including the multi-streaming effect, the RSD modelling
is significantly improved. We also provide a theoretical explanation based on
halo model for the measured effect, including a fitting formula with one to two
free parameters. The improved understanding of FoG helps break the
$f\sigma_8-\sigma_v$ degeneracy in RSD cosmology, and has the potential of
significantly improving cosmological constraints. |
A new way to test the WIMP dark matter models: In this paper, we investigate the possibility of testing the weakly
interacting massive particle (WIMP) dark matter (DM) models by applying the
simplest phenomenological model which introduces an interaction term between
dark energy (DE) and WIMP DM, i.e., $Q = 3\gamma_{DM} H\rho_{DM}$. In general,
the coupling strength $\gamma_{DE}$ is close to $0$ as the interaction between
DE and WIMP DM is very weak, thus the effect of $\gamma_ {DE}$ on the evolution
of $Y$ associated with DM energy density can be safely neglected. Meanwhile,
our numerical calculation also indicates that $x_f\approx20$ is associated with
DM freeze-out temperature, which is the same as the vanishing interaction
scenario. As for DM relic density, it will be magnified by
$\frac{2-3\gamma_{DM}}{2}[{2\pi g_* m_{DM}^3}/{(45 s_0 x_f^3})]^{\gamma_{DM}}$
times, which provides a new way to test WIMP DM models. As an example, we
analyze the case in which WIMP DM is a scalar DM. (SGL+SNe+Hz) and
(CMB+BAO+SNe) cosmological observations will give
$\gamma_{DM}=0.134^{+0.17}_{-0.069}$ and $\gamma_{DM}=-0.0008\pm0.0016$,
respectively. After further considering the constraints from DM direct
detection experiment, DM indirect detection experiment, and DM relic density,
we find that the allowed parameter space of the scalar DM model will be
completely excluded for the former cosmological observations, while it will
increase for the latter ones. Those two cosmological observations lead to an
almost paradoxical conclusion. Therefore, one could expect more stringent
constraints on the WMIP DM models, with the accumulation of more accurate
cosmological observations in the near future. | Confronting brane inflation with Planck and pre-Planck data: In this paper, we compare brane inflation models with the Planck data and the
pre-Planck data (which combines WMAP, ACT, SPT, BAO and H0 data). The Planck
data prefer a spectral index less than unity at more than 5\sigma confidence
level, and a running of the spectral index at around 2\sigma confidence level.
We find that the KKLMMT model can survive at the level of 2\sigma only if the
parameter $\beta$ (the conformal coupling between the Hubble parameter and the
inflaton) is less than $\mathcal{O}(10^{-3})$, which indicates a certain level
of fine-tuning. The IR DBI model can provide a slightly larger negative running
of spectral index and red tilt, but in order to be consistent with the
non-Gaussianity constraints from Planck, its parameter also needs fine-tuning
at some level. |
The iron and oxygen content of LMC Classical Cepheids and its
implications for the Extragalactic Distance Scale and Hubble constant: Classical Cepheids are primary distance indicators and a crucial stepping
stone to determining the present-day Hubble constant Ho to the precision and
accuracy required to constrain apparent deviations from the LCDM Concordance
Cosmological Model. We have measured the iron and oxygen abundances of of 89
Cepheids in the LMC, one of the anchors of the local Distance Scale,
quadrupling the prior sample and including 68 of the 70 Cepheids used to
constrain Ho by the SH0ES program. The goal is to constrain the extent to which
the Cepheid luminosity is influenced by their chemical composition, an
important contributor to the uncertainty on the determination of the Ho itself
and a critical factor in the internal consistency of the distance ladder. We
have derived stellar parameters and abundances from a self-consistent
spectroscopic analysis based on Equivalent Width of absorption lines. The
[Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of
-0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex.
The latter is fully compatible with the measurement error and supports the low
dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The
uniformity of the abundance has the important consequence that the LMC Cepheids
alone cannot provide any meaningful constraint on the dependence of the Cepheid
Period-Luminosity relation on chemical composition at any wavelength. This
revises a prior claim based on a small sample of 22 LMC Cepheids that there was
little dependence (or uncertainty) between composition and NIR luminosity, a
conclusion which would produce a conflict between anchors of the distance
ladder with different mean abundance. The chemical homogeneity of the LMC
Cepheid population makes it an ideal environment to calibrate the metallicity
dependence between the more metal poor SMC and metal rich Milky Way and
NGC4258. | The structure of massive quiescent galaxies at z~3 in the CANDELS-COSMOS
field: In this letter, we use a two-color (J-L) vs. (V-J) selection criteria to
search massive, quiescent galaxy candidates at 2.5<z<4.0 in the CANDELS-COSMOS
field. We construct a H-selected catalogue and complement it with public
auxiliary data. We finally obtain 19 passive VJL-selected (hereafter pVJL)
galaxies as the possible massive quiescent galaxy candidates at z~3 by several
constrains. We find the sizes of our pVJL galaxies are on average 3-4 times
smaller than those of local ETGs with analogous stellar mass. The compact size
of these z~3 galaxies can be modelled by assuming their formation at z ~ 4-6
according to the dissipative collapse of baryons. Up to z<4, the
mass-normalized size evolution can be described by $r_e\propto (1+z)^{-1.0}$.
Low Sersic index and axis ratio, with median values n~1.5 and b/a~0.65
respectively, indicate most of pVJL galaxies are disk-dominated. Despite large
uncertainty, the inner region of the median mass profile of our pVJL galaxies
is similar to those of quiescent galaxies (QGs) at 0.5<z<2.5 and local
Early-type galaxies (ETGs). It indicates local massive ETGs have been formed
according to an inside-out scenario: the compact galaxies at high redshift make
up the cores of local massive ETGs and then build up the outskirts according to
dissipationless minor mergers. |
Particle number dependence in the non-linear evolution of N-body
self-gravitating systems: Simulations of purely self-gravitating N-body systems are often used in
astrophysics and cosmology to study the collisionless limit of such systems.
Their results for macroscopic quantities should then converge well for
sufficiently large N. Using a study of the evolution from a simple space of
spherical initial conditions - including a region characterised by so-called
"radial orbit instability" - we illustrate that the values of N at which such
convergence is obtained can vary enormously. In the family of initial
conditions we study, good convergence can be obtained up to a few dynamical
times with N $ \sim 10^3$ - just large enough to suppress two body relaxation -
for certain initial conditions, while in other cases such convergence is not
attained at this time even in our largest simulations with N $\sim 10^5$. The
qualitative difference is due to the stability properties of fluctuations
introduced by the N-body discretisation, of which the initial amplitude depends
on N. We discuss briefly why the crucial role which such fluctuations can
potentially play in the evolution of the N-body system could, in particular,
constitute a serious problem in cosmological simulations of dark matter. | Constraining low redshift [CII] Emission by Cross-Correlating FIRAS and
BOSS Data: We perform a tomographic cross-correlation analysis of archival FIRAS data
and the BOSS galaxy redshift survey to constrain the amplitude of [CII]
$^2P_{3/2}\rightarrow$ $^2P_{1/2}$ fine structure emission. Our analysis
employs spherical harmonic tomography (SHT), which is based on the angular
cross-power spectrum between FIRAS maps and BOSS galaxy over-densities at each
pair of redshift bins, over a redshift range of $0.24<z<0.69$. We develop the
SHT approach for intensity mapping, where it has several advantages over
existing power spectral estimators. Our analysis constrains the product of the
[CII] bias and [CII] specific intensity, $b_{[CII]}I_{[CII]i}$, to be $<0.31$
MJy/sr at $z {\approx} 0.35$ and $<0.28$ MJy/sr at $z {\approx} 0.57$ at $95\%$
confidence. These limits are consistent with most current models of the [CII]
signal, as well as with higher-redshift [CII] cross-power spectrum measurements
from the Planck satellite and BOSS quasars. We also show that our analysis, if
applied to data from a more sensitive instrument such as the proposed PIXIE
satellite, can detect pessimistic [CII] models at high significance. |
Supermassive Black Hole Formation by Direct Collapse: Keeping
Protogalactic Gas H_2--Free in Dark Matter Halos with Virial Temperatures
T_vir >~ 10^4 K: In the absence of H_2 molecules, the primordial gas in early dark matter
halos with virial temperatures just above T_vir >~ 10^4 K cools by collisional
excitation of atomic H. Although it cools efficiently, this gas remains
relatively hot, at a temperature near T ~ 8000 K, and consequently might be
able to avoid fragmentation and collapse directly into a supermassive black
hole (SMBH). In order for H_2--formation and cooling to be strongly suppressed,
the gas must be irradiated by a sufficiently intense ultraviolet (UV) flux. We
performed a suite of three--dimensional hydrodynamical adaptive mesh refinement
(AMR) simulations of gas collapse in three different protogalactic halos with
T_vir >~ 10^4 K, irradiated by a UV flux with various intensities and spectra.
We determined the critical specific intensity, Jcrit, required to suppress H_2
cooling in each of the three halos. For a hard spectrum representative of
metal--free stars, we find (in units of 10^{-21} erg s^{-1} Hz^{-1} sr^{-1}
cm^{-2}) 10^4<Jcrit<10^5, while for a softer spectrum, which is characteristic
of a normal stellar population, and for which H^{-} --dissociation is
important, we find 30<Jcrit<300. These values are a factor of 3--10 lower than
previous estimates. We attribute the difference to the higher, more accurate
H_2 collisional dissociation rate we adopted. The reduction in Jcrit
exponentially increases the number of rare halos exposed to super--critical
radiation. When H_2 cooling is suppressed, gas collapse starts with a delay,
but it ultimately proceeds more rapidly. The infall velocity is near the
increased sound speed, and an object as massive as M ~ 10^5 solar mass may form
at the center of these halos, compared to the M ~ 10^2 solar mass stars forming
when H_2--cooling is efficient. | The X-ray to [Ne V]3426 flux ratio: discovering heavily obscured AGN in
the distant Universe: We investigate the possibility of using the ratio between the 2-10 keV flux
and the [Ne V]3426 emission line flux (X/NeV) as a diagnostic diagram to
discover heavily obscured, possibly Compton-Thick Active Galactic Nuclei (AGN)
up to z~1.5. First, we calibrate a relation between X/NeV and the cold
absorbing column density N_H using a sample of 74 bright, nearby Seyferts with
both X-ray and [Ne V] data available in the literature. Similarly to what is
found for the X-ray to [O III]5007 flux ratio (X/OIII), we found that the X/NeV
ratio decreases towards large column densities. Essentially all local Seyferts
with X/NeV values below 15 are found to be Compton-Thick objects. Second, we
apply this diagnostic diagram to different samples of distant obscured and
unobscured QSOs in the SDSS: blue, unobscured, type-1 QSOs in the redshift
range z=[0.1-1.5] show X/NeV values typical of unobscured Seyfert 1s in the
local Universe. Conversely, SDSS type-2 QSOs at z~0.5 classified either as
Compton-Thick or Compton-Thin on the basis of their X/OIII ratio, would have
been mostly classified in the same way based on the X/NeV ratio. We apply the
X/NeV diagnostic diagram to 9 SDSS obscured QSOs in the redshift range
z=[0.85-1.31], selected by means of their prominent [Ne V]3426 line and
observed with Chandra ACIS-S for 10ks each. Based on the X/NeV ratio,
complemented by X-ray spectral analysis, 2 objects appear good Compton-Thick
QSO candidates, 4 objects appear as Compton-Thin QSOs, while 3 have an
ambiguous classification. When excluding from the sample broad lined QSOs with
a red continuum and thus considering only genuine narrow-line objects, the
efficiency in selecting Compton-Thick QSOs through the [Ne V] line is about 50%
(with large errors, though), more similar to what is achieved with [O III]
selection. [abridged] |
On the Formation of cD Galaxies and their Parent Clusters: In order to study the mechanism of formation of cD galaxies we search for
possible dependencies between the K-band luminosity of cDs and the parameters
of their host clusters which we select to have a dominant cD galaxy,
corresponding to a cluster morphology of Bautz-Morgan (BM) type I. As a
comparison sample we use cD galaxies in clusters where they are not dominant,
which we define here as non-BMI (NBMI) type clusters. We find that for 71 BMI
clusters the absolute K-band luminosity of cDs depends on the cluster richness,
but less strongly on the cluster velocity dispersion. Meanwhile, for 35 NBMI
clusters the correlation between cD luminosity and cluster richness is weaker,
and is absent between cD luminosity and velocity dispersion. In addition, we
find that the luminosity of the cD galaxy hosted in BMI clusters tends to
increase with the cD's peculiar velocity with respect to the cluster mean
velocity. In contrast, for NBMI clusters the cD luminosity decreases with
increasing peculiar velocity. Also, the X-ray luminosity of BMI clusters
depends on the cluster velocity dispersion, while in NBMI clusters such a
correlation is absent. These findings favour the cannibalism scenario for the
formation of cD galaxies. We suggest that cDs in clusters of BMI type were
formed and evolved preferentially in one and the same cluster. In contrast, cDs
in NBMI type clusters were either originally formed in clusters that later
merged with groups or clusters to form the current cluster, or are now in the
process of merging. | Suzaku and XMM-Newton Observations of the Fornax cluster: Temperature
and Metallicity Distribution: Suzaku observed a central region and five offset regions within 0.2 r180 in
the Fornax cluster, a nearby poor cluster, and XMM-Newton mapped the cluster
with 15 pointings out to 0.3 r180. The distributions of O, Mg, Si, S, and Fe in
the intracluster medium (ICM) were studied with Suzaku, and those of Fe and
temperature were studied with XMM. The temperature of the ICM gradually
decreases with radius from 1.3 keV at 0.04 r180 to 1 keV at 0.2-0.3 r180. If
the new solar abundances of Lodders et al. (2003) and a single-temperature
plasma model are adopted, O, Mg, Si, S, and Fe show similar abundances: 0.4-0.6
solar within 0.02-0.2 r180. This Fe abundance is similar to those at 0.1-0.2
r180 in rich clusters and other groups of galaxies. At 0.2-0.3 r180, the Fe
abundance becomes 0.2-0.3 solar. A two-temperature plasma model yields ICM
abundances that are higher by a factor of 1.2-1.5, but gives similar abundance
ratios among O, Mg, Si, S, and Fe. The northern region has a lower ICM
temperature and higher brightness and Fe abundance, whereas the southern region
has a higher ICM temperature and lower brightness and Fe abundance. These
results indicate that the cD galaxy may have traveled from the north because of
recent dynamical evolution. The cumulative oxygen- and iron-mass-to-light
ratios within 0.3 r180 are more than an order of magnitude lower than those of
rich clusters and some relaxed groups of galaxies. Past dynamical evolution
might have hindered the strong concentration of hot gas in the Fornax cluster's
central region. Scatter in the IMLR and similarity in the element abundances in
the ICM of groups and clusters of galaxies indicate early metal synthesis. |
Luminous X-ray AGN in Clusters of Galaxies: We present a study of X-ray AGN overdensities in 16 Abell clusters, within
the redshift range 0.073<z<0.279, in order to investigate the effect of the hot
inter-cluster environment on the triggering of the AGN phenomenon. The X-ray
AGN overdensities, with respect to the field expectations, were estimated for
sources with L_x>= 10^{42} erg s^{-1} (at the redshift of the clusters) and
within an area of 1 h^{-1}_{72} Mpc radius (excluding the core). To investigate
the presence or not of a true enhancement of luminous X-ray AGN in the cluster
area, we also derived the corresponding optical galaxy overdensities, using a
suitable range of $r$-band magnitudes. We always find the latter to be
significantly higher (and only in two cases roughly equal) with respect to the
corresponding X-ray overdensities. Over the whole cluster sample, the mean
X-ray point-source overdensity is a factor of ~4 less than that corresponding
to bright optical galaxies, a difference which is significant at a >0.995
level, as indicated by an appropriate t-student test. We conclude that the
triggering of luminous X-ray AGN in rich clusters is strongly suppressed.
Furthermore, searching for optical SDSS counterparts of all the X-ray sources,
associated with our clusters, we found that about half appear to be background
QSOs, while others are background and foreground AGN or stars. The true
overdensity of X-ray point sources, associated to the clusters, is therefore
even smaller than what our statistical approach revealed. | The VIMOS Public Extragalactic Redshift Survey (VIPERS): On the correct
recovery of the count-in-cell probability distribution function: We compare three methods to measure the count-in-cell probability density
function of galaxies in a spectroscopic redshift survey. From this comparison
we found that when the sampling is low (the average number of object per cell
is around unity) it is necessary to use a parametric method to model the galaxy
distribution. We used a set of mock catalogues of VIPERS, in order to verify if
we were able to reconstruct the cell-count probability distribution once the
observational strategy is applied. We find that in the simulated catalogues,
the probability distribution of galaxies is better represented by a Gamma
expansion than a Skewed Log-Normal. Finally, we correct the cell-count
probability distribution function from the angular selection effect of the
VIMOS instrument and study the redshift and absolute magnitude dependency of
the underlying galaxy density function in VIPERS from redshift $0.5$ to $1.1$.
We found very weak evolution of the probability density distribution function
and that it is well approximated, independently from the chosen tracers, by a
Gamma distribution. |
Properties of clumps and filaments around galaxy clusters: We report on the possibility of studying the proprieties of cosmic diffuse
baryons by studying self-gravitating clumps and filaments connected to galaxy
clusters. While filaments are challenging to detect with X-ray observations,
the higher density of clumps makes them visible and a viable tracer to study
the thermodynamical proprieties of baryons undergoing accretion along cosmic
web filaments onto galaxy clusters. We developed new algorithms to identify
these structures and applied them to a set of non-radiative cosmological
simulations of galaxy clusters at high resolution. We find that in those
simulated clusters, the density and temperature of clumps are independent of
the mass of the cluster where they reside. We detected a positive correlation
between the filament temperature and the host cluster mass. The density and
temperature of clumps and filaments also tended to correlate. Both the
temperature and density decrease moving outward. We observed that clumps are
hotter, more massive, and more luminous if identified closer to the cluster
center. Especially in the outermost cluster regions (~3*R500,c or beyond),
X-ray observations might already have the potential to locate cosmic filaments
based on the distribution of clumps and to allow one to study the
thermodynamics of diffuse baryons before they are processed by the intracluster
medium. | An improved fitting formula for the dark matter bispectrum: In this paper we present an improved fitting formula for the dark matter
bispectrum motivated by the previous phenomenological approach of Scoccimarro &
Couchman (2001). We use a set of LCDM simulations to calibrate the fitting
parameters in the k-range of 0.03 h/Mpc<k<0.4 h/Mpc and in the redshift range
of 0<z<1.5. This new proposed fit describes well the BAO-features although it
was not designed to. The deviation between the simulations output and our
analytic prediction is typically less than 5% and in the worst case is never
above 10%. We envision that this new analytic fitting formula will be very
useful in providing reliable predictions for the non-linear dark matter
bispectrum for LCDM models. |
Extracting bias using the cross-bispectrum: An EoR and 21 cm-[CII]-[CII]
case study: The amplitude of redshifted 21 cm fluctuations during the Epoch of
Reionization (EoR) is expected to show a distinctive "rise and fall" behavior
with decreasing redshift as reionization proceeds. On large scales (k <~ 0.1
Mpc^{-1}) this can mostly be characterized by evolution in the product of the
mean 21 cm brightness temperature and a bias factor, b_21(z). This quantity
evolves in a distinctive way that can help in determining the average
ionization history of the intergalactic medium (IGM) from upcoming 21 cm
fluctuation data sets. Here we consider extracting <T_21> b_21(z) using a
combination of future redshifted 21 cm and [CII] line-intensity mapping data
sets. Our method exploits the dependence of the 21 cm-[CII]-[CII]
cross-bispectrum on the shape of triangle configurations in Fourier space. This
allows one to determine <T_21> b_21(z) yet, importantly, is less sensitive to
foreground contamination than the 21 cm auto-spectrum, and so can provide a
valuable cross-check. We compare the results of simulated bispectra with
second-order perturbation theory: on large scales the perturbative estimate of
<T_21> b_21(z) matches the true value to within 10% for <x_i> <~ 0.8. We
consider the 21 cm auto-bispectrum and show that this statistic may also be
used to extract the 21 cm bias factor. Finally, we discuss the survey
requirements for measuring the cross-bispectrum. Although we focus on the 21
cm-[CII]-[CII] bispectrum during reionization, our method may be of broader
interest and can be applied to any two fields throughout cosmic history. | Star Formation Indicators and Line Equivalent Width in Lyman Alpha
Galaxies: The equivalent width (EW) of the Lyman Alpha (Lya) line is directly related
to the ratio of star formation rates determined from Lya flux and UV flux
density [SFR(Lya)/SFR(UV)]. We use published data --in the literature EW and
SFR(Lya)/SFR(UV) are treated as independent quantities-- to show that the
predicted relation holds for the vast majority of observed Lya emitting
galaxies (LAEs). We show that the relation between EW and SFR(Lya)/SFR(UV)
applies irrespective of a galaxy's `true' underlying star formation rate, and
that its only source of scatter is the variation in the spectral slope of the
UV continuum between individual galaxies. The derived relation, when combined
with the observed EW distribution, implies that the ratio SFR(UV)/SFR(Lya) is
described well by a log-normal distribution with a standard deviation of
~0.3-0.35. This result is useful when modelling the statistical properties of
LAEs. We further discuss why the relation between EW and SFR(Lya)/SFR(UV) may
help identifying galaxies with unusual stellar populations. |
Galaxy pairs align with galactic filaments: Context. Gravitational collapse theory and numerical simulations suggest that
the velocity field within large-scale galaxy filaments is dominated by motions
along the filaments.
Aims. Our aim is to check whether observational data reveal any preferred
orientation of galaxy pairs with respect to the underlying filaments as a
result of the expectedly anisotropic velocity field.
Methods. We use galaxy pairs and galaxy filaments identified from the Sloan
Digital Sky Survey data. For filament extraction, we use the Bisous model that
is based the marked point process technique. During the filament detection, we
use the centre point of each pair instead of the positions of galaxies to avoid
a built-in influence of pair orientation on the filament construction. For
pairs lying within filaments (3012 cases), we calculate the angle between the
line connecting galaxies of each pair and their host filament. To avoid
redshift-space distortions, the angle is measured in the plain of the sky.
Results. The alignment analysis shows that the orientation of galaxy pairs
correlates strongly with their host filaments. The alignment signal is stronger
for loose pairs, with at least 25% excess of aligned pairs compared to a random
distribution. The alignment of galaxy pairs and filaments measured from the
observational data is in good concordance with the alignment in the Millennium
simulation and thus provides support to the {\Lambda}CDM formalism. | A new candidate for probing Population III nucleosynthesis with
carbon-enhanced damped Lyman-alpha systems: We report the identification of a very metal-poor damped Lyman-alpha system
(DLA) at z_abs = 3.067295 that is modestly carbon-enhanced, with an iron
abundance of ~1/700 solar ([Fe/H] = -2.84) and [C,O/Fe] ~ +0.6. Such an
abundance pattern is likely to be the result of nucleosynthesis by massive
stars. On the basis of 17 metal absorption lines, we derive a 2 sigma upper
limit on the DLA's kinetic temperature of T_DLA <= 4700 K, which is broadly
consistent with the range of spin temperature estimates for DLAs at this
redshift and metallicity. While the best-fitting abundance pattern shows the
expected hallmarks of Population III nucleosynthesis, models of high-mass
Population II stars can match the abundance pattern almost as well. We discuss
current limitations in distinguishing between these two scenarios and the
marked improvement in identifying the remnants of Population III stars expected
from the forthcoming generation of 30-metre class telescopes. |
The Vainshtein Mechanism in the Cosmic Web: We investigate the dependence of the Vainshtein screening mechanism on the
cosmic web morphology of both dark matter particles and halos as determined by
ORIGAMI. Unlike chameleon and symmetron screening, which come into effect in
regions of high density, Vainshtein screening instead depends on the
dimensionality of the system, and screened bodies can still feel external
fields. ORIGAMI is well-suited to this problem because it defines morphologies
according to the dimensionality of the collapsing structure and does not depend
on a smoothing scale or density threshold parameter. We find that halo
particles are screened while filament, wall, and void particles are unscreened,
and this is independent of the particle density. However, after separating
halos according to their large scale morphological environment, we find no
difference in the screening properties of halos in filaments versus halos in
clusters. We find that the fifth force enhancement of dark matter particles in
halos is greatest well outside the virial radius. We confirm the theoretical
expectation that even if the internal field is suppressed by the Vainshtein
mechanism, the object still feels the fifth force generated by the external
fields, by measuring peculiar velocities and velocity dispersions of halos.
Finally, we investigate the morphology and gravity model dependence of halo
spins, concentrations, and shapes. | Forming intracluster gas in a galaxy protocluster at a redshift of 2.16: Galaxy clusters are the most massive gravitationally bound structures in the
Universe, comprising thousands of galaxies and pervaded by a diffuse, hot
``intracluster medium'' (ICM) that dominates the baryonic content of these
systems. The formation and evolution of the ICM across cosmic time is thought
to be driven by the continuous accretion of matter from the large-scale
filamentary surroundings and dramatic merger events with other clusters or
groups. Until now, however, direct observations of the intracluster gas have
been limited only to mature clusters in the latter three-quarters of the
history of the Universe, and we have been lacking a direct view of the hot,
thermalized cluster atmosphere at the epoch when the first massive clusters
formed. Here we report the detection (about $6\sigma$) of the thermal
Sunyaev-Zeldovich (SZ) effect in the direction of a protocluster. In fact, the
SZ signal reveals the ICM thermal energy in a way that is insensitive to
cosmological dimming, making it ideal for tracing the thermal history of cosmic
structures. This result indicates the presence of a nascent ICM within the
Spiderweb protocluster at redshift $z=2.156$, around 10 billion years ago. The
amplitude and morphology of the detected signal show that the SZ effect from
the protocluster is lower than expected from dynamical considerations and
comparable with that of lower-redshift group-scale systems, consistent with
expectations for a dynamically active progenitor of a local galaxy cluster. |
Baryonic effects on weak-lensing two-point statistics and its
cosmological implications: We develop an extension of \textit{the Halo Model} that describes
analytically the corrections to the matter power spectrum due to the physics of
baryons. We extend these corrections to the weak-lensing shear angular power
spectrum. Within each halo, our baryonic model accounts for: 1) a central
galaxy, the major stellar component whose properties are derived from abundance
matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an
adiabatically-contracted dark matter component. This analytic approach allows
us to compare our model to the dark-matter-only case. Our basic assumptions are
tested against the hydrodynamical simulations of Martizzi et. al. (2014), with
which a remarkable agreement is found. Our baryonic model has only one free
parameter, $M_{\rm crit}$, the critical halo mass that marks the transition
between feedback-dominated halos, mostly devoid of gas, and gas rich halos, in
which AGN feedback effects become weaker. We explore the entire cosmological
parameter space, using the angular power spectrum in three redshift bins as the
observable, assuming a Euclid-like survey. We derive the corresponding
constraints on the cosmological parameters, as well as the possible bias
introduced by neglecting the effects of baryonic physics. We find that, up to
$\ell_{max}$=4000, baryonic physics plays very little role in the cosmological
parameters estimation. However, if one goes up to $\ell_{max}$=8000, the
marginalized errors on the cosmological parameters can be significantly
reduced, but neglecting baryonic physics can lead to bias in the recovered
cosmological parameters up to 10$\sigma$. These biases are removed if one takes
into account the main baryonic parameter, $M_{\rm crit}$, which can also be
determined up to 1-2\%, along with the other cosmological parameters. | A limit on Planck-scale froth with ESPRESSO: Some models of quantum gravity predict that the very structure of spacetime
is `frothy' due to quantum fluctuations. Although the effect is expected to be
tiny, if these spacetime fluctuations grow over a large distance, the initial
state of a photon, such as its energy, is gradually washed out as the photon
propagates. Thus, in these models, even the most monochromatic light source
would gradually disperse in energy due to spacetime fluctuations over large
distances. In this paper, we use science verification observations obtained
with ESPRESSO at the Very Large Telescope to place a novel bound on the growth
of spacetime fluctuations. To achieve this, we directly measure the width of a
narrow Fe II absorption line produced by a quiescent gas cloud at redshift
z=2.34, corresponding to a comoving distance of ~5.8 Gpc. Using a heuristic
model where the energy fluctuations grow as sigma_E / E = (E/E_P)^alpha, where
E_P = 1.22 x 10^28 eV is the Planck energy, we rule out models with alpha <
0.634, including models where the quantum fluctuations grow as a random walk
process (alpha = 0.5). Finally, we present a new formalism where the
uncertainty accrued at discrete spacetime steps is drawn from a continuous
distribution. We conclude, if photons take discrete steps through spacetime and
accumulate Planck-scale uncertainties at each step, then our ESPRESSO
observations require that the step size must be at least >10^13.2 L_P, where
L_P is the Planck length. |
Velocity-dependent annihilation radiation from dark matter subhalos in
cosmological simulations: We use the suite of Milky Way-like galaxies in the Auriga simulations to
determine the contribution to annihilation radiation from dark matter subhalos
in three velocity-dependent dark matter annihilation models: Sommerfeld,
p-wave, and d-wave models. We compare these to the corresponding distribution
in the velocity-independent s-wave annihilation model. For both the
hydrodynamical and dark-matter-only simulations, only in the case of the
Sommerfeld-enhanced annihilation does the total annihilation flux from subhalos
exceed the total annihilation flux from the smooth halo component within the
virial radius of the halo. Progressing from Sommerfeld to the s, p, and d-wave
models, the contribution from the smooth component of the halo becomes more
dominant, implying that for the p-wave and d-wave models the smooth component
is by far the dominant contribution to the radiation. Comparing to the Galactic
center excess observed by Fermi-LAT, for all simulated halos the emission is
dominated by the smooth halo contribution. However, it is possible that for
Sommerfeld models, extrapolation down to mass scales below the current
resolution limit of the simulation would imply a non-negligible contribution to
the gamma-ray emission from the Galactic Center region. | Model-independent constraints on dark energy and modified gravity with
the SKA: Employing a nonparametric approach of the principal component analysis (PCA),
we forecast the future constraint on the equation of state $w(z)$ of dark
energy, and on the effective Newton constant $\mu(k,z)$, which parameterise the
effect of modified gravity, using the planned SKA HI galaxy survey. Combining
with the simulated data of Planck and Dark Energy Survey (DES), we find that
SKA Phase 1 (SKA1) and SKA Phase 2 (SKA2) can well constrain $3$ and $5$
eigenmodes of $w(z)$ respectively. The errors of the best measured modes can be
reduced to 0.04 and 0.023 for SKA1 and SKA2 respectively, making it possible to
probe dark energy dynamics. On the other hand, SKA1 and SKA2 can constrain $7$
and $20$ eigenmodes of $\mu(k,z)$ respectively within 10\% sensitivity level.
Furthermore, 2 and 7 modes can be constrained within sub percent level using
SKA1 and SKA2 respectively. This is a significant improvement compared to the
combined datasets without SKA. |
Considerations of Cosmic Acceleration: I discuss a solution to the dark energy problem, which arises when the
visible universe is approximated by a black hole, in a quasi-static
asymptotically-flat approximation. Using data, provided by WMAP7, I calculate
the Schwarzschild radius $r_S$ and compare to the measured physical radius of
the visible universe, bounded by the surface of last scatter. The ratio,
$\epsilon(t_0) = r/r_S$ is found to be comparable to $\epsilon = 1$, as allowed
by the holographic principle. The measurement of a shift parameter, $\sigma$,
introduced by Bond, Efstathiou and Tegmark in 1997, plays an important role in
the accuracy of the calculation. The approximation leads to a surprisingly
small discrepancy, presumably explicable by the de Sitter, and expanding,
nature of the actual universe. | A cosmological exclusion plot: Towards model-independent constraints on
modified gravity from current and future growth rate data: Most cosmological constraints on modified gravity are obtained assuming that
the cosmic evolution was standard $\Lambda$CDM in the past and that the present
matter density and power spectrum normalization are the same as in a
$\Lambda$CDM model. Here we examine how the constraints change when these
assumptions are lifted. We focus in particular on the parameter $Y$ (also
called $G_{\mathrm{eff}}$) that quantifies the deviation from the Poisson
equation. This parameter can be estimated by comparing with the
model-independent growth rate quantity $f\sigma_{8}(z)$ obtained through
redshift distortions. We reduce the model dependency in evaluating $Y$ by
marginalizing over $\sigma_{8}$ and over the initial conditions, and by
absorbing the degenerate parameter $\Omega_{m,0}$ into $Y$. We use all
currently available values of $f\sigma_{8}(z)$. We find that the combination
$\hat{Y}=Y\Omega_{m,0}$, assumed constant in the observed redshift range, can
be constrained only very weakly by current data, $\hat{Y}=0.28_{-0.23}^{+0.35}$
at 68\% c.l. We also forecast the precision of a future estimation of $\hat{Y}$
in a Euclid-like redshift survey. We find that the future constraints will
reduce substantially the uncertainty, $\hat{Y}=0.30_{-0.09}^{+0.08}$ , at 68\%
c.l., but the relative error on $\hat{Y}$ around the fiducial remains quite
high, of the order of 30\%. The main reason for these weak constraints is that
$\hat{Y}$ is strongly degenerate with the initial conditions, so that large or
small values of $\hat{Y}$ are compensated by choosing non-standard initial
values of the derivative of the matter density contrast.
Finally, we produce a forecast of a cosmological exclusion plot on the Yukawa
strength and range parameters, which complements similar plots on laboratory
scales but explores scales and epochs reachable only with large-scale galaxy
surveys. (abridged) |
Exploring cosmic homogeneity with the BOSS DR12 galaxy sample: In this study, we probe the transition to cosmic homogeneity in the Large
Scale Structure (LSS) of the Universe using the CMASS galaxy sample of BOSS
spectroscopic survey which covers the largest effective volume to date, $3\
h^{-3}\ \mathrm{Gpc}^3$ at $0.43 \leq z \leq 0.7$. We study the scaled
counts-in-spheres, $\mathcal{N}(<r)$, and the fractal correlation dimension,
$\mathcal{D}_2(r)$, to assess the homogeneity scale of the universe using a
$Landy\ \&\ Szalay$ inspired estimator.
Defining the scale of transition to homogeneity as the scale at which
$\mathcal{D}_2(r)$ reaches 3 within $1\%$, i.e. $\mathcal{D}_2(r)>2.97$ for
$r>\mathcal{R}_H$, we find $\mathcal{R}_H = (63.3\pm0.7) \ h^{-1}\
\mathrm{Mpc}$, in agreement at the percentage level with the predictions of the
$\Lambda$CDM model $\mathcal{R}_H=62.0\ h^{-1}\ \mathrm{Mpc}$. Thanks to the
large cosmic depth of the survey, we investigate the redshift evolution of the
transition to homogeneity scale and find agreement with the $\Lambda$CDM
prediction. Finally, we find that $\mathcal{D}_2$ is compatible with $3$ at
scales larger than $300\ h^{-1}\ $Mpc in all redshift bins.
These results consolidate the Cosmological Principle and represent a precise
consistency test of the $\Lambda CDM$ model. | Unified framework for Early Dark Energy from $α$-attractors: One of the most appealing approaches to ease the Hubble tension is the
inclusion of an early dark energy (EDE) component that adds energy to the
Universe in a narrow redshift window around the time of recombination and
dilutes faster than radiation afterwards. In this paper, we analyze EDE in the
framework of $\alpha$-attractor models. As well known, the success in
alleviating the Hubble tension crucially depends on the shape of the energy
injection. We show how different types of energy injections can be easily
obtained, thanks to the freedom in choosing the functional form of the
potential inspired by $\alpha$-attractor models. To confirm our intuition we
perform an MCMC analysis for three representative cases and find indeed that
$H_0$ is significantly larger than in $\Lambda$CDM like in other EDE models.
Unlike axion-driven EDE models with super Planckian decay constant, the
curvature of EDE models required by the data is natural in the context of
recent theoretical developments in $\alpha$-attractors. |
Charge-velocity-dependent one-scale linear model: We apply a recently developed formalism to study the evolution of a
current-carrying string network under the simple but generic assumption of a
linear equation of state. We demonstrate that the existence of a scaling
solution with non-trivial current depends on the expansion rate of the
universe, the initial root mean square current on the string, and the available
energy loss mechanisms. We find that the fast expansion rate after
radiation-matter equality will tend to rapidly dilute any pre-existing current
and the network will evolve towards the standard Nambu-Goto scaling solution
(provided there are no external current-generating mechanisms). During the
radiation era, current growth is possible provided the initial conditions for
the network generate a relatively large current and/or there is significant
early string damping. The network can then achieve scaling with a stable
non-trivial current, assuming large currents will be regulated by some leakage
mechanism. The potential existence of current-carrying string networks in the
radiation era, unlike the standard Nambu-Goto networks expected in the matter
era, could have interesting phenomenological consequences. | The Shearing HI Spiral Pattern of NGC 1365: The Tremaine-Weinberg equations are solved for a pattern speed that is
allowed to vary with radius. The solution method transforms an integral
equation for the pattern speed to a least squares problem with well established
procedures for statistical analysis. The method applied to the HI spiral
pattern of the barred, grand-design galaxy NGC 1365 produced convincing
evidence for a radial dependence in the pattern speed. The pattern speed
behaves approximately as 1/r, and is very similar to the material speed. There
are no clear indications of corotation or Lindblad resonances. Tests show that
the results are not selection biased, and that the method is not measuring the
material speed. Other methods of solving the Tremaine-Weinberg equations for
shearing patterns were found to produce results in agreement with those
obtained using the current method. Previous estimates that relied on the
assumptions of the density-wave interpretation of spiral structure are
inconsistent with the results obtained using the current method. The results
are consistent with spiral structure theories that allow for shearing patterns,
and contradict fundamental assumptions in the density-wave interpretation that
are often used for finding spiral arm pattern speeds. The spiral pattern is
winding on a characteristic timescale of ~ 500 Myrs. |
On the dark contents of the Universe: A Euclid survey approach: In this work we study the consequences of allowing non pressureless dark
matter when determining dark energy constraints. We show that present-day dark
energy constraints from low-redshift probes are extremely degraded when
allowing this dark matter variation. However, adding the cosmic microwave
background (CMB) we can recover the $w_{DM} = 0$ case constraints. We also show
that with the future Euclid redshift survey we expect to largely improve these
constraints; but, without the complementary information of the CMB, there is
still a strong degeneracy between dark energy and dark matter equation of state
parameters. | Distinguishing between $Λ$CDM and modified gravity with future
observations of cosmic growth rate: A probability of distinguishing between $\Lambda$CDM model and modified
gravity is studied by using the future observations for the growth rate of
cosmic structure (Euclid redshift survey). Adopting extended DGP model, Kinetic
Gravity Braiding model, and Galileon model as modified gravity, we compare
predicted cosmic growth rate by models to the mock observational data. The
growth rate $f\sigma_8$ in the original DGP model is suppressed compared with
the $\Lambda$CDM case, for the same value of the current density parameter of
matter $\Omega_{m,0}$, because of the suppression of effective gravitational
constant. In case of the kinetic gravity braiding model and the Galileon model,
the growth rate $f\sigma_8$ is enhanced compared with the $\Lambda$CDM case,
for the same value of $\Omega_{m,0}$, because of the enhancement of effective
gravitational constant. For future observational data of the cosmic growth rate
(Euclid), compatible value of $\Omega_{m,0}$ are different by models,
furthermore $\Omega_{m,0}$ can be stringently constrained. Thus, we find the
$\Lambda$CDM model is distinguishable from modified gravity by combining the
growth rate data of the Euclid with other observations. |
Constraints on Exotic Matter for An Emergent Universe: We study a composition of normal and exotic matter which is required for a
flat Emergent Universe scenario permitted by the equation of state
(EOS)($p=A\rho-B\rho^{1/2}$) and predict the range of the permissible values
for the parameters $A$ and $B$ to explore a physically viable cosmological
model. The permitted values of the parameters are determined taking into
account the $H(z)-z$ data obtained from observations, a model independent BAO
peak parameter and CMB shift parameter (WMAP7 data). It is found that although
$A$ can be very close to zero, most of the observations favours a small and
negative $A$. As a consequence, the effective Equation of State parameter for
this class of Emergent Universe solutions remains negative always. We also
compared the magnitude ($\mu (z)$) vs. redshift($z$) curve obtained in the
model with that obtained from the union compilation data. According to our
analysis the class of Emergent Universe solutions considered here is not ruled
out by the observations. | A High-Fidelity Realization of the Euclid Code Comparison $N$-body
Simulation with Abacus: We present a high-fidelity realization of the cosmological $N$-body
simulation from the Schneider et al. (2016) code comparison project. The
simulation was performed with our Abacus $N$-body code, which offers high force
accuracy, high performance, and minimal particle integration errors. The
simulation consists of $2048^3$ particles in a $500\ h^{-1}\mathrm{Mpc}$ box,
for a particle mass of $1.2\times 10^9\ h^{-1}\mathrm{M}_\odot$ with $10\
h^{-1}\mathrm{kpc}$ spline softening. Abacus executed 1052 global time steps to
$z=0$ in 107 hours on one dual-Xeon, dual-GPU node, for a mean rate of 23
million particles per second per step. We find Abacus is in good agreement with
Ramses and Pkdgrav3 and less so with Gadget3. We validate our choice of time
step by halving the step size and find sub-percent differences in the power
spectrum and 2PCF at nearly all measured scales, with $<0.3\%$ errors at $k<10\
\mathrm{Mpc}^{-1}h$. On large scales, Abacus reproduces linear theory better
than $0.01\%$. Simulation snapshots are available at
http://nbody.rc.fas.harvard.edu/public/S2016 . |
Lepton asymmetry, neutrino spectral distortions, and big bang
nucleosynthesis: We calculate Boltzmann neutrino energy transport with self-consistently
coupled nuclear reactions through the weak-decoupling-nucleosynthesis epoch in
an early universe with significant lepton numbers. We find that the presence of
lepton asymmetry enhances processes which give rise to nonthermal neutrino
spectral distortions. Our results reveal how asymmetries in energy and entropy
density uniquely evolve for different transport processes and neutrino flavors.
The enhanced distortions in the neutrino spectra alter the expected big bang
nucleosynthesis light element abundance yields relative to those in the
standard Fermi-Dirac neutrino distribution cases. These yields, sensitive to
the shapes of the neutrino energy spectra, are also sensitive to the phasing of
the growth of distortions and entropy flow with time/scale factor. We analyze
these issues and speculate on new sensitivity limits of deuterium and helium to
lepton number. | Phase-space consistency of stellar dynamical models determined by
separable augmented densities: Assuming the separable augmented density, it is always possible to construct
a distribution function of a spherical population with any given density and
anisotropy. We consider under what conditions the distribution constructed as
such is in fact non-negative everywhere in the accessible phase-space. We first
generalize known necessary conditions on the augmented density using fractional
calculus. The condition on the radius part R(r^2) (whose logarithmic derivative
is the anisotropy parameter) is equivalent to the complete monotonicity of
R(1/w)/w. The condition on the potential part on the other hand is given by its
derivative up to any order not greater than (3/2-beta) being non-negative where
beta is the central anisotropy parameter. We also derive a specialized
inversion formula for the distribution from the separable augmented density,
which leads to sufficient conditions on separable augmented densities for the
non-negativity of the distribution. The last generalizes the similar condition
derived earlier for the generalized Cuddeford system to arbitrary separable
systems. |
On the linearity of tracer bias around voids: The large-scale structure of the universe can only be observed via luminous
tracers of the dark matter. However, the clustering statistics of tracers are
biased and depend on various properties, such as their host-halo mass and
assembly history. On very large scales this tracer bias results in a constant
offset in the clustering amplitude, known as linear bias. Towards smaller
nonlinear scales, this is no longer the case and tracer bias becomes a
complicated function of scale and time. We focus on tracer bias centred on
cosmic voids, depressions of the density field that spatially dominate the
universe. We consider three types of tracers: galaxies, galaxy clusters and
AGN, extracted from the hydrodynamical simulation Magneticum Pathfinder. In
contrast to common clustering statistics that focus on auto-correlations of
tracers, we find that void-tracer cross-correlations are successfully described
by a linear-bias relation. The tracer-density profile of voids can thus be
related to their matter-density profile by a single number. We show that it
coincides with the linear tracer bias extracted from the large-scale
auto-correlation function and expectations from theory, if sufficiently large
voids are considered. For smaller voids we observe a shift towards higher
values. This has important consequences on cosmological parameter inference, as
the problem of unknown tracer bias is alleviated up to a constant number. The
smallest scales in existing datasets become accessible to simpler models,
providing numerous modes of the density field that have been disregarded so
far, but may help to further reduce statistical errors in constraining
cosmology. | The Impact of the Uncertainty in Single-Epoch Virial Black Hole Mass
Estimates on the Observed Evolution of the Black Hole - Bulge Scaling
Relations: Recent observations of the black hole (BH) - bulge scaling relations usually
report positive redshift evolution, with higher redshift galaxies harboring
more massive BHs than expected from the local relations. All of these studies
focus on broad line quasars with BH mass estimated from virial estimators based
on single-epoch spectra. Since the sample selection is largely based on quasar
luminosity, the cosmic scatter in the BH-bulge relation introduces a
statistical bias leading to on average more massive BHs given galaxy properties
at high redshift (Lauer et al. 2007). We here emphasize a previously
under-appreciated statistical bias resulting from the uncertainty of
single-epoch virial BH mass estimators and the shape of the underlying (true)
BH mass function, which leads to on average overestimation of the true BH
masses at the high-mass end (Shen et al. 2008). We demonstrate that the latter
virial mass bias can contribute a substantial amount to the observed excess in
BH mass at fixed bulge properties, comparable to the Lauer et al. bias. The
virial mass bias is independent of the Lauer et al. bias, hence if both biases
are at work, they can largely (or even fully) account for the observed BH mass
excess at high redshift. |
An analytical approximation of the scalar spectrum in the
ultra-slow-roll inflationary models: The ultra-slow-roll (USR) inflationary models predict large-amplitude scalar
perturbations at small scales which can lead to the primordial black hole
production and scalar-induced gravitational waves. In general scalar
perturbations in the USR models can only be obtained using numerical method
because the usual slow-roll approximation breaks. In this work, we propose an
analytical approach to estimate the scalar spectrum which is consistent with
the numerical result. We find that the USR inflationary models predict a peak
with power-law slopes in the scalar spectrum and energy spectrum of
gravitational waves, and we derive the expression of the spectral indexes in
terms of the inflationary potential. In turn, the inflationary potential near
the USR regime can be reconstructed from the negative spectral index of the
gravitational wave energy spectrum. | Analytical Gaussian Process Cosmography: Unveiling Insights into
Matter-Energy Density Parameter at Present: In this study, we introduce a novel analytical Gaussian Process (GP)
cosmography methodology, leveraging the differentiable properties of GPs to
derive key cosmological quantities analytically. Our approach combines cosmic
chronometer (CC) Hubble parameter data with growth rate (f) observations to
constrain the $\Omega_{\rm m0}$ parameter, offering insights into the
underlying dynamics of the Universe. By formulating a consistency relation
independent of specific cosmological models, we analyze under a flat FLRW
metric and first-order Newtonian perturbation theory framework. Our analytical
approach simplifies the process of Gaussian Process regression (GPR), providing
a more efficient means of handling large datasets while offering deeper
interpretability of results. We demonstrate the effectiveness of our
methodology by deriving precise constraints on $\Omega_{\rm m0}h^2$, revealing
$\Omega_{\rm m0}h^2=0.139\pm0.017$. Moreover, leveraging $H_0$ observations, we
further constrain $\Omega_{\rm m0}$, uncovering an inverse correlation between
mean $H_0$ and $\Omega_{\rm m0}$. Our investigation offers a proof of concept
for analytical GP cosmography, highlighting the advantages of analytical
methods in cosmological parameter estimation. |
Non-adiabatic perturbations in Ricci dark energy model: We show that the non-adiabatic perturbations between Ricci dark energy and
matter can grow both on superhorizon and subhorizon scales, and these
non-adiabatic perturbations on subhorizon scales can lead to instability in
this dark energy model. The rapidly growing non-adiabatic modes on subhorizon
scales always occur when the equation of state parameter of dark energy starts
to drop towards -1 near the end of matter era, except that the parameter
\alpha\ of Ricci dark energy equals to 1/2. In the case where \alpha\ = 1/2,
the rapidly growing non-adiabatic modes disappear when the perturbations in
dark energy and matter are adiabatic initially. However, an adiabaticity
between dark energy and matter perturbations at early time implies a
non-adiabaticity between matter and radiation, this can influence the ordinary
Sachs-Wolfe (OSW) effect. Since the amount of Ricci dark energy is not small
during matter domination, the integrated Sachs-Wolfe (ISW) effect is greatly
modified by density perturbations of dark energy, leading to a wrong shape of
CMB power spectrum. The instability in Ricci dark energy is difficult to be
alleviated if the effects of coupling between baryon and photon on dark energy
perturbations are included. | Cosmological constraints on the Multi Scalar Field Dark Matter model: The main aim of this paper is to provide cosmological constraints on the
Multi Scalar Field Dark Matter model (MSFDM), in which we assume the dark
matter is made up of different ultra-light scalar fields. As a first
approximation, we consider they are real and do not interact with each other.
We study the equations for both the background and perturbations for $N$-fields
and present the evolution of the density parameters, the mass power spectrum
and the CMB spectrum. In particular, we focus on two scalar fields with several
combinations for the potentials $V(\phi) = 1/2 m_{\phi}^2 \phi^2$, $V(\phi) =
m_{\phi}^2f^2\left[1+\cos(\phi/f)\right]$ and $V(\phi) =
m_{\phi}^2f^2\left[\cosh(\phi/f)-1\right]$, however the work, along with the
code, could be easily extended to more fields. We use the data from BAO, Big
Bang Nucleosynthesis, Lyman-$\alpha$ forest and Supernovae to find constraints
on the sampling parameters for the cases of a single field and double field,
along with the Bayesian evidence. We found that some combinations of the
potentials get penalized through the evidence, however for others there is a
preference as good as for the cold dark matter. |
The globular cluster NGC 2419: a crucible for theories of gravity: We present the analysis of a kinematic data set of stars in the globular
cluster NGC 2419, taken with Keck/DEIMOS. Combined with a reanalysis of deep
HST and Subaru imaging data, which provide an accurate luminosity profile of
the cluster, we investigate the validity of a large set of dynamical models of
the system, which are checked for stability via N-body simulations. We find
that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND)
are ruled out with extremely high confidence. However, a simple Michie model in
Newtonian gravity with anisotropic velocity dispersion provides an excellent
representation of the luminosity profile and kinematics. In contrast, with MOND
we find that Michie models that reproduce the luminosity profile either
over-predict the velocity dispersion on the outskirts of the cluster if the
mass to light ratio is kept at astrophysically-motivated values, or else they
under-predict the central velocity dispersion if the mass to light ratio is
taken to be very small. We find that the best Michie model in MOND is a factor
of 10000 less likely than the Newtonian model that best fits the system. A
likelihood ratio of 350 is found when we investigate more general models by
solving the Jeans equation with a Markov-Chain Monte Carlo scheme. We verified
with N-body simulations that these results are not significantly different when
the MOND external field effect is accounted for. If the assumptions that the
cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and
possesses a single dynamical tracer population of constant M/L are correct, we
conclude that the present observations provide a very severe challenge for
MOND. [abridged] | Probing Dark Energy models with neutrons: There is a deep connection between cosmology -- the science of the infinitely
large --and particle physics -- the science of the infinitely small. This
connection is particularly manifest in neutron particle physics. Basic
properties of the neutron -- its Electric Dipole Moment and its lifetime -- are
intertwined with baryogenesis and nucleosynthesis in the early Universe. I will
cover this topic in the first part, that will also serve as an introduction (or
rather a quick recap) of neutron physics and Big Bang cosmology. Then, the rest
of the manuscript will be devoted to a new idea: using neutrons to probe models
of Dark Energy. In the second part, I will present the chameleon theory: a
light scalar field accounting for the late accelerated expansion of the
Universe, which interacts with matter in such a way that it does not mediate a
fifth force between macroscopic bodies. However, neutrons can alleviate the
chameleon mechanism and reveal the presence of the scalar field with properly
designed experiments. In the third part, I will describe a recent experiment
performed with a neutron interferometer at the Institut Laue Langevin that sets
already interesting constraints on the chameleon theory. Last, the chameleon
field can be probed by measuring the quantum states of neutrons bouncing over a
mirror. In the fourth part I will present the status and prospects of the
GRANIT experiment at the ILL. |
ISIS: a new N-body cosmological code with scalar fields based on RAMSES.
Code presentation and application to the shapes of clusters: Several extensions of the standard cosmological model include scalar fields
as new degrees of freedom in the underlying gravitational theory. A particular
class of these scalar field theories include screening mechanisms intended to
hide the scalar field below observational limits in the solar system, but not
on galactic scales, where data still gives freedom to find possible signatures
of their presence. In order to make predictions to compare with observations
coming from galactic and clusters scales (i.e. in the non-linear regime of
cosmological evolution), cosmological N-body simulations are needed, for which
codes that can solve for the scalar field must be developed. We present a new
implementation of scalar-tensor theories of gravity which include screening
mechanisms. The code is based in the already existing code RAMSES, to which we
have added a non-linear multigrid solver that can treat a large class of scalar
tensor theories of modified gravity. We present details of the implementation
and the tests that we made to it. As application of the new code, we have
studied the influence that two particular modified gravity theories, the
symmetron and $f(R)$ gravity, have on the shape of cluster sized dark matter
halos and found consistent results with previous estimations made with a static
analysis. | The Disk-Halo Connection and Where Has All The Gas Gone?: The wealth of data in the past decades, and especially in the past 15 years
has transformed our picture of the gas around the Milky Way and other spiral
galaxies. There is good evidence for extraplanar gas that is a few kpc in
height and is seen in all gaseous phases: neutral; warm atomic; and hot, X-ray
emitting gas. This medium is seen not only around the Milky Way, but other
spiral galaxies and it is related to the star formation rate, so it is likely
produced by the activity in the disk through a galactic fountain. More extended
examples of halo gas are seen, such as the HVC around the Milky Way and around
M31. This gas is typically 10-20 kpc from the galaxy and is not seen beyond 50
kpc. This gas is most likely being accreted. A hot dilute halo (1E6 K) is
present with a similar size, although its size is poorly determined. An ongoing
controversy surrounds the relative amounts of outflow from the disk and
accretion onto galaxies such as the Milky Way. There is good evidence for
accretion of cold material onto the Milky Way and other galaxies, but it is not
clear if there is enough to modify the gas content and star formation
properties in the disk. The reservoir of accretion material is as yet
unidentified. Some of these findings may be related to the issue that galaxies
are baryon-poor: their baryon to dark matter ratio is well below the
cosmological value. The absence of baryons may be due to extremely violent
outflow events in the early stages of galaxy formation. We may be able to
understand this stage of galaxy evolution by applying our deepening
understanding of our local disk-halo environment. |
The Star Formation History and Extended Structure of the Hercules Milky
Way Satellite: We present imaging of the recently discovered Hercules Milky Way satellite
and its surrounding regions to study its structure, star formation history and
to thoroughly search for signs of disruption. We robustly determine the
distance, luminosity, size and morphology of Hercules utilizing a bootstrap
approach to characterize our uncertainties. We derive a distance to Hercules of
$133 \pm 6$ kpc via a comparison to empirical and theoretical isochrones. As
previous studies have found, Hercules is very elongated, with
$\epsilon=0.67\pm0.03$ and a half light radius of $r_{h} \simeq 230$ pc. Using
the color magnitude fitting package StarFISH, we determine that Hercules is old
($>12$ Gyr) and metal poor ($[Fe/H]\sim-2.0$), with a spread in metallicity, in
agreement with previous spectroscopic work. We infer a total absolute magnitude
of $M_V=-5.3\pm0.4$. Our innovative search for external Hercules structure both
in the plane of the sky and along the line of sight yields some evidence that
Hercules is embedded in a larger stream of stars. A clear stellar extension is
seen to the Northwest with several additional candidate stellar overdensities
along the position angle of Hercules out to $\sim$35' ($\sim$1.3 kpc). While
the association of any of the individual stellar overdensities with Hercules is
difficult to determine, we do show that the summed color magnitude diagram of
all three is consistent with Hercules' stellar population. Finally, we estimate
that any change in the distance to Hercules across its face is at most $\sim$6
kpc; and the data are consistent with Hercules being at the same distance
throughout. | Incidence of MgII absorbers towards Blazars and the GRB/QSO puzzle: In order to investigate the origin of the excess of strong MgII systems
towards GRB afterglows as compared to QSO sightlines, we have measured the
incidence of MgII absorbers towards a third class of objects: the Blazars. This
class includes the BL Lac object population for which a tentative excess of
MgII systems had already been reported. We observed with FORS1 at the ESO-VLT
42 Blazars with an emission redshift 0.8<z_em<1.9, to which we added the three
high z northern objects belonging to the 1Jy BL Lac sample. We detect 32 MgII
absorbers in the redshift range 0.35-1.45, leading to an excess in the
incidence of MgII absorbers compared to that measured towards QSOs by a factor
~2, detected at 3 sigma. The amplitude of the effect is similar to that found
along GRB sightlines. Our analysis provides a new piece of evidence that the
observed incidence of MgII absorbers might depend on the type of background
source. In front of Blazars, the excess is apparent for both 'strong' (w_
r(2796) > 1.0 A) and weaker (0.3 < w_r(2796) < 1.0 A) MgII systems. The
dependence on velocity separation with respect to the background Blazars
indicates, at the ~1.5 sigma level, a potential excess for beta = v/c ~0.1. We
show that biases involving dust extinction or gravitational amplification are
not likely to notably affect the incidence of MgII systems towards Blazars.
Finally we discuss the physical conditions required for these absorbers to be
gas entrained by the powerful Blazar jets. More realistic numerical modelling
of jet-ambient gas interaction is required to reach any firm conclusions as
well as repeat observations at high spectral resolution of strong MgII
absorbers towards Blazars in both high and low states. |
A covariant treatment of cosmic parallax: The Gaia satellite will soon probe parallax on cosmological distances. Using
the covariant formalism and considering the angle between a pair of sources, we
find parallax for both spacelike and timelike separation between observation
points. Our analysis includes both intrinsic parallax and parallax due to
observer motion. We propose a consistency condition that tests the FRW metric
using the parallax distance and the angular diameter distance. This test is
purely kinematic and relies only on geometrical optics, it is independent of
matter content and its relation to the spacetime geometry. We study
perturbations around the FRW model, and find that they should be taken into
account when analysing observations to determine the parallax distance. | Exotic Smoothness and Astrophysics: The problem of possible astrophysical consequences of the existence of exotic
differential structures on manifolds is discussed. It is argued that
corrections to the curvature of the form of a source like terms should be
expected in the Einstein equations if they are written in the "wrong"
differential structure. Examples of topologically trivial spaces on which
exotic differential structures act as a source of gravitational force even in
the absence of matter are given. Propagation of light in the presence of such
phenomena is also discussed. A brief review of exotic smoothness is added for
completeness. |
Connecting Primordial Gravitational Waves and Dark Energy: Cosmic acceleration manifested in the early universe as inflation, generating
primordial gravitational waves detectable in the cosmic microwave background
(CMB) radiation. Cosmic acceleration is occurring again at present as dark
energy, detectable in cosmic distance and structure surveys. We explore the
intriguing idea of connecting the two occurrences through quintessential
inflation by an $\alpha$-attractor potential without a cosmological constant.
For this model we demonstrate robustness of the connection $1+w_0\approx
4/(3N^2r)$ between the present day dark energy equation of state parameter
$w_0$ and the primordial tensor to scalar ratio $r$ for a wide range of initial
conditions. Analytics and numerical solutions produce current thawing behavior,
resulting in a tight relation $w_a\approx-1.53(1+w_0)\approx -0.2\,(4\times
10^{-3}/r)$. Upcoming CMB and galaxy redshift surveys can test this consistency
condition. Within this model, lack of detection of a dark energy deviation from
$\Lambda$ predicts a higher $r$, and lack of detection of $r$ predicts greater
dark energy dynamics. | On the evolution of inhomogeneous perturbations in the $Λ$CDM
model and $f(R)$ modified gravity theories: We focus on weak inhomogeneous models of the Universe at low redshifts,
described by the Lema\^itre-Tolman-Bondi (LTB) metric. The principal aim of
this work is to compare the evolution of inhomogeneous perturbations in the
$\Lambda$CDM cosmological model and $f(R)$ modified gravity theories,
considering a flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) metric for the
background. More specifically, we adopt the equivalent scalar-tensor formalism
in the Jordan frame, in which the extra degree of freedom of the $f(R)$
function is converted into a non-minimally coupled scalar field. We investigate
the evolution of local inhomogeneities in time and space separately, following
a linear perturbation approach. Then, we obtain spherically symmetric solutions
in both cosmological models. Our results allow us to distinguish between the
presence of a cosmological constant and modified gravity scenarios, since a
peculiar Yukawa-like solution for radial perturbations occurs in the Jordan
frame. Furthermore, the radial profile of perturbations does not depend on a
particular choice of the $f(R)$ function, hence our results are valid for any
$f(R)$ model. |
Loop corrections in the separate universe picture: In inflationary models that produce a spike of power on short scales,
back-reaction of small-scale substructure onto large-scale modes is enhanced.
We argue that the separate universe framework provides a highly convenient tool
to compute loop corrections that quantify this back-reaction. Each loop of
interest is characterized by large hierarchies in wavenumber and horizon exit
time. The separate universe framework highlights important factorizations
involving these hierarchies. We interpret each loop correction in terms of a
simple, classical, back-reaction model, and clarify the meaning of the
different volume scalings that have been reported in the literature. We argue
that significant back-reaction requires both short-scale nonlinearities and
long-short couplings that modulate the short-scale power spectrum. In the
absence of long-short couplings, only incoherent shot noise-like effects are
present, which are volume-suppressed. Dropping the shot noise, back-reaction
from a particular scale is controlled by a product of $f_{NL}$-like parameters:
an equilateral configuration measuring the nonlinearity of the short-scale
modes, and a squeezed configuration measuring the long-short coupling. These
may carry important scale dependence controlling the behaviour of the loop in
the decoupling limit where the hierarchy of scales becomes large. In
single-field models the long-short coupling may be suppressed by this
hierarchy, in which case the net back-reaction would be safely suppressed. We
illustrate our framework using explicit computations in a 3-phase
ultra-slow-roll scenario. Finally, we discuss different choices for the
smoothing scale used in the separate universe framework and argue the effect
can be absorbed into a renormalization of local operators. | Dark matter and Modified Newtonian Dynamics in a sample of high-redshift
galaxy clusters observed with Chandra: We compare the measurement of the gravitational mass of 38 high-redshift
galaxy clusters observed by Chandra using Modified Newtonian Dynamics (MOND)
and standard Newtonian gravity. Our analysis confirms earlier findings that
MOND cannot explain the difference between the baryonic mass and the total mass
inferred from the assumption of hydrostatic equilibrium. We also find that the
baryon fraction at $r_{2500}$ using MOND is consistent with the Wilkinson
Microwave Anisotropy Probe (WMAP) value of $\Omega_{B}/\Omega_{M}$ |
Features in the primordial power spectrum? A frequentist analysis: Features in the primordial power spectrum have been suggested as an
explanation for glitches in the angular power spectrum of temperature
anisotropies measured by the WMAP satellite. However, these glitches might just
as well be artifacts of noise or cosmic variance. Using the effective Delta
chi^2 between the best-fit power-law spectrum and a deconvolved primordial
spectrum as a measure of "featureness" of the data, we perform a full
Monte-Carlo analysis to address the question of how significant the recovered
features are. We find that in 26% of the simulated data sets the reconstructed
spectrum yields a greater improvement in the likelihood than for the actually
observed data. While features cannot be categorically ruled out by this
analysis, and the possibility remains that simple theoretical models which
predict some of the observed features might stand up to rigorous statistical
testing, our results suggest that WMAP data are consistent with the assumption
of a featureless power-law primordial spectrum. | MHD Simulations of AGN Jets in a Dynamic Galaxy Cluster Medium: We present a pair of 3-d magnetohydrodynamical simulations of intermittent
jets from a central active galactic nucleus (AGN) in a galaxy cluster extracted
from a high resolution cosmological simulation. The selected cluster was chosen
as an apparently relatively relaxed system, not having undergone a major merger
in almost 7 Gyr. Despite this characterization and history, the intra-cluster
medium (ICM) contains quite active "weather". We explore the effects of this
ICM weather on the morphological evolution of the AGN jets and lobes. The
orientation of the jets is different in the two simulations so that they probe
different aspects of the ICM structure and dynamics. We find that even for this
cluster that can be characterized as relaxed by an observational standard, the
large-scale, bulk ICM motions can significantly distort the jets and lobes.
Synthetic X-ray observations of the simulations show that the jets produce
complex cavity systems, while synthetic radio observations reveal bending of
the jets and lobes similar to wide-angle tail (WAT) radio sources. The jets are
cycled on and off with a 26 Myr period using a 50% duty cycle. This leads to
morphological features similar to those in "double-double" radio galaxies.
While the jet and ICM magnetic fields are generally too weak in the simulations
to play a major role in the dynamics, Maxwell stresses can still become locally
significant. |
Distant foreground and the Hubble constant tension: It is possible to explain the discrepancy (tension) between the local
measurement of the cosmological parameter $H_0$ (the Hubble constant) and its
value derived from the Planck-mission measurements of the Cosmic Microwave
Background (CMB) by considering contamination of the CMB by emission from some
medium surrounding distant extragalactic sources (a distant foreground), such
as extremely cold coarse-grain (grey) dust. As any other foreground, it would
alter the CMB power spectrum and contribute to the dispersion of CMB
temperature fluctuations. By generating random samples of CMB with different
dispersions, we have checked that the increased dispersion leads to a smaller
estimated value of $H_0$, the rest of the cosmological model parameters
remaining fixed. This might explain the reduced value of the {\it
Planck}-derived parameter $H_0$ with respect to the local measurements. The
cold grey dust for some time has been suspected to populate intergalactic space
and it is known to be almost undetectable, except for the effect of dimming
remote extragalactic sources. | Influence of Planck foreground masks in the large angular scale quadrant
CMB asymmetry: The measured CMB angular distribution shows a great consistency with the LCDM
model. However, isotropy violations were reported in CMB temperature maps of
both WMAP and Planck data. We investigate the influence of different masks
employed in the analysis of CMB angular distribution, in particular in the
excess of power in the Southeastern quadrant (SEQ) and the lack of power in the
Northeastern quadrant (NEQ). We compare the two-point correlation function
(TPCF) computed for each quadrant of the CMB foreground-cleaned temperature
maps to 1000 simulations generated assuming the LCDM best-fit power spectrum
using four different masks. In addition to the quadrants, we computed the TPCF
for circular regions in the map where the excess and lack of power are present.
We also compare the effect of Galactic cuts in the TPCF calculations as
compared to the simulations. We found consistent results for three masks,
namely mask-rulerminimal, U73 and U66. The results indicate that the excess of
power in the SEQ tends to vanish as the portion of the sky covered by the mask
increases and the lack of power in the NEQ remains virtually unchanged. When
UT78 mask is applied, the NEQ becomes no longer anomalous and the excess of
power in the SEQ becomes the most significant one among the masks.
Nevertheless, the asymmetry between the SEQ and NEQ is independent of the mask
and it is in disagreement with the isotropic model with at least 95% C.L. We
find that UT78 is in disagreement with the other analysed masks, specially
considering the SEQ and the NEQ individual analysis. Most importantly, the use
of UT78 washes out the anomaly in the NEQ. Furthermore, we found excess of
kurtosis, compared with simulations, in the NEQ for the regions not masked by
UT78 but masked by the other masks, indicating that the previous result could
be due to non-removed residual foregrounds by UT78. |
Strong clustering of primordial black holes from Affleck-Dine mechanism: Primordial black hole (PBH) is a fascinating candidate for the origin of
binary merger events observed by LIGO-Virgo collaboration. The spatial
distribution of PBHs at formation is an important feature to estimate the
merger rate. We investigate the clustering of PBHs formed by Affleck-Dine (AD)
baryogenesis, where dense baryon bubbles collapse to form PBHs. We found that
formed PBHs show a strong clustering due to the stochastic dynamics of the AD
field. Including the clustering, we evaluate the merger rate and isocurvature
perturbations of PBHs, which show significant deviations from those without
clustering. | The Massive and Distant Clusters of WISE Survey: SZ effect Verification
with the Atacama Compact Array -- Localization and Cluster Analysis: The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides a catalog
of high-redshift ($0.7\lesssim z\lesssim 1.5$) infrared-selected galaxy
clusters. However, the verification of the ionized intracluster medium,
indicative of a collapsed and nearly virialized system, is made challenging by
the high redshifts of the sample members. The main goal of this work is to test
the capabilities of the Atacama Compact Array (ACA; also known as the Morita
Array) Band 3 observations, centered at about 97.5 GHz, to provide robust
validation of cluster detections via the thermal Sunyaev-Zeldovich (SZ) effect.
Using a pilot sample that comprises ten MaDCoWS galaxy clusters, accessible to
ACA and representative of the median sample richness, we infer the masses of
the selected galaxy clusters and respective detection significance by means of
a Bayesian analysis of the interferometric data. Our test of the "Verification
with the ACA - Localization and Cluster Analysis" (VACA LoCA) program
demonstrates that the ACA can robustly confirm the presence of the virialized
intracluster medium in galaxy clusters previously identified in full-sky
surveys. In particular, we obtain a significant detection of the SZ effect for
seven out of the ten VACA LoCA clusters. We note that this result is
independent of the assumed pressure profile. However, the limited angular
dynamic range of the ACA in Band 3 alone, short observational integration
times, and possible contamination from unresolved sources limit the detailed
characterization of the cluster properties and the inference of the cluster
masses within scales appropriate for the robust calibration of mass-richness
scaling relations. |
Comparison of Millimeter-wave and X-Ray Emission in Seyfert Galaxies: We compare the emission at multiple wavelengths of an extended Seyfert galaxy
sample, including both types of Seyfert nuclei. We use the Caltech
Submillimeter Observatory to observe the CO J = 2-1 transition line in a sample
of 45 Seyfert galaxies and detect 35 of them. The galaxies are selected by
their joint soft X-ray (0.1-2.4 keV) and far-infrared ({\lambda} = 60-100
{\mu}m) emission from the ROSAT/IRAS sample. Since the CO line widths (W CO)
reflect the orbital motion in the gravitational potential of the host galaxy,
we study how the kinematics are affected by the central massive black hole
(BH), using the X-ray luminosity. A significant correlation is found between
the CO line width and hard (0.3-8 keV from Chandra and XMM-Newton) X-ray
luminosity for both types of Seyfert nuclei. Assuming an Eddington accretion to
estimate the BH mass (M BH) from the X-ray luminosity, the W CO-L X relation
establishes a direct connection between the kinematics of the molecular gas of
the host galaxy and the nuclear activity, and corroborates the previous studies
that show that the CO is a good surrogate for the bulge mass. We also find a
tight correlation between the (soft and hard) X-ray and the CO luminosities for
both Seyfert types. These results indicate a direct relation between the
molecular gas (i.e., star formation activity) of the host galaxy and the
nuclear activity. To establish a clear causal connection between molecular gas
and the fueling of nuclear activity, high-resolution maps (<100 pc) of the CO
emission of our sample will be required and provided in a forthcoming Atacama
Large Millimeter Array observation. | Constraints on the annihilation cross section of dark matter particles
from anisotropies in the diffuse gamma-ray background measured with Fermi-LAT: Annihilation of dark matter particles in cosmological halos (including a halo
of the Milky Way) contributes to the diffuse gamma-ray background (DGRB). As
this contribution will appear anisotropic in the sky, one can use the angular
power spectrum of anisotropies in DGRB to constrain properties of dark matter
particles. By comparing the updated analytic model of the angular power
spectrum of DGRB from dark matter annihilation with the power spectrum recently
measured from the 22-month data of Fermi Large Area Telescope (LAT), we place
upper limits on the annihilation cross section of dark matter particles as a
function of dark matter masses. We find that the current data exclude <\sigma
v> >~ 10^{-25} cm^3 s^{-1} for annihilation into b\bar{b} at the dark matter
mass of 10 GeV, which is a factor of three times larger than the canonical
cross section. The limits are weaker for larger dark matter masses. The limits
can be improved further with more Fermi-LAT data as well as by using the power
spectrum at lower multipoles (l <~ 150), which are currently not used due to a
potential Galactic foreground contamination. |
High mass star formation in normal late-type galaxies: observational
constraints to the IMF: We use Halpha and FUV GALEX data for a large sample of nearby objects to
study the high mass star formation activity of normal late-type galaxies. The
data are corrected for dust attenuation using the most accurate techniques at
present available, namely the Balmer decrement and the total far-infrared to
FUV flux ratio. The sample shows a highly dispersed distribution in the Halpha
to FUV flux ratio indicating that two of the most commonly used star formation
tracers give star formation rates with uncertainties up to a factor of 2-3. The
high dispersion is due to the presence of AGN, where the UV and the Halpha
emission can be contaminated by nuclear activity, highly inclined galaxies, for
which the applied extinction corrections are probably inaccurate, or starburst
galaxies, where the stationarity in the star formation history required for
transforming Halpha and UV luminosities into star formation rates is not
satisfied. Excluding these objects we reach an uncertainty of ~50% on the SFR.
The Halpha to FUV flux ratio increases with their total stellar mass. If
limited to normal star forming galaxies, however, this relationship reduces to
a weak trend that might be totally removed using different extinction
correction recipes. In these objects the Halpha to FUV flux ratio seems also
barely related with the FUV-H colour, the H band effective surface brightness,
the total star formation activity and the gas fraction. The data are consistent
with a Kroupa and Salpeter initial mass function in the high mass stellar range
and imply, for a Salpeter IMF, that the variations of the slope cannot exceed
0.25, from g=2.35 for massive galaxies to g=2.60 in low luminosity systems. We
show however that these observed trends, if real, can be due to the different
micro history of star formation in massive galaxies with respect to dwarf. | The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing
Power Spectrum and its Implications for Structure Growth: We present new measurements of cosmic microwave background (CMB) lensing over
$9400$ sq. deg. of the sky. These lensing measurements are derived from the
Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB dataset, which
consists of five seasons of ACT CMB temperature and polarization observations.
We determine the amplitude of the CMB lensing power spectrum at $2.3\%$
precision ($43\sigma$ significance) using a novel pipeline that minimizes
sensitivity to foregrounds and to noise properties. To ensure our results are
robust, we analyze an extensive set of null tests, consistency tests, and
systematic error estimates and employ a blinded analysis framework. The
baseline spectrum is well fit by a lensing amplitude of
$A_{\mathrm{lens}}=1.013\pm0.023$ relative to the Planck 2018 CMB power spectra
best-fit $\Lambda$CDM model and $A_{\mathrm{lens}}=1.005\pm0.023$ relative to
the $\text{ACT DR4} + \text{WMAP}$ best-fit model. From our lensing power
spectrum measurement, we derive constraints on the parameter combination
$S^{\mathrm{CMBL}}_8 \equiv \sigma_8 \left({\Omega_m}/{0.3}\right)^{0.25}$ of
$S^{\mathrm{CMBL}}_8= 0.818\pm0.022$ from ACT DR6 CMB lensing alone and
$S^{\mathrm{CMBL}}_8= 0.813\pm0.018$ when combining ACT DR6 and Planck NPIPE
CMB lensing power spectra. These results are in excellent agreement with
$\Lambda$CDM model constraints from Planck or $\text{ACT DR4} + \text{WMAP}$
CMB power spectrum measurements. Our lensing measurements from redshifts
$z\sim0.5$--$5$ are thus fully consistent with $\Lambda$CDM structure growth
predictions based on CMB anisotropies probing primarily $z\sim1100$. We find no
evidence for a suppression of the amplitude of cosmic structure at low
redshifts |
First star formation with dark matter annihilation: We include an energy term based on Dark Matter (DM) self-annihilation during
the cooling and subsequent collapse of the metal-free gas, in halos hosting the
formation of the first stars in the Universe. We have found that the feedback
induced on the chemistry of the cloud does modify the properties of the gas
throughout the collapse. However, the modifications are not dramatic, and the
typical Jeans mass within the halo is conserved throughout the collapse, for
all the DM parameters we have considered. This result implies that the presence
of Dark Matter annihilations does not substantially modify the Initial Mass
Function of the First Stars, with respect to the standard case in which such
additional energy term is not taken into account. We have also found that when
the rate of energy produced by the DM annihilations and absorbed by the gas
equals the chemical cooling (at densities yet far from the actual formation of
a proto-stellar core) the structure does not halt its collapse, although that
proceeds more slowly by a factor smaller than few per cent of the total
collapse time. | ALMA Observations of SPT-Discovered, Strongly Lensed, Dusty,
Star-Forming Galaxies: We present Atacama Large Millimeter/submillimeter Array (ALMA) 860 micrometer
imaging of four high-redshift (z=2.8-5.7) dusty sources that were detected
using the South Pole Telescope (SPT) at 1.4 mm and are not seen in existing
radio to far-infrared catalogs. At 1.5 arcsec resolution, the ALMA data reveal
multiple images of each submillimeter source, separated by 1-3 arcsec,
consistent with strong lensing by intervening galaxies visible in near-IR
imaging of these sources. We describe a gravitational lens modeling procedure
that operates on the measured visibilities and incorporates
self-calibration-like antenna phase corrections as part of the model
optimization, which we use to interpret the source structure. Lens models
indicate that SPT0346-52, located at z=5.7, is one of the most luminous and
intensely star-forming sources in the universe with a lensing corrected FIR
luminosity of 3.7 X 10^13 L_sun and star formation surface density of 4200
M_sun yr^-1 kpc^-2. We find magnification factors of 5 to 22, with lens
Einstein radii of 1.1-2.0 arcsec and Einstein enclosed masses of 1.6-7.2x10^11
M_sun. These observations confirm the lensing origin of these objects, allow us
to measure the their intrinsic sizes and luminosities, and demonstrate the
important role that ALMA will play in the interpretation of lensed
submillimeter sources. |
An XMM-Newton spatially-resolved study of metal abundance evolution in
distant galaxy clusters: We present an XMM-Newton analysis of the X-ray spectra of 39 clusters of
galaxies at 0.4<z<1.4, covering a temperature range of 1.5<=kT<=11 keV. We
performed a spatially resolved spectral analysis to study how the abundance
evolves with redshift not only through a single emission measure performed on
the whole cluster but also spatially resolving the cluster emission. We do not
observe a statistically significant (>2sigma) abundance evolution with
redshift. The most significant deviation from no evolution (90% c.l.) is
observed in the emission from the whole cluster (r<0.6r500), that could be
parametrized as Z=A*(1+z)^(-0.8+/-0.5). Dividing the emission in 3 radial bins,
no significant evidence of abundance evolution could be observed fitting the
data with a power-law. A substantial agreement with measures presented in
previous works is found. The error-weighted mean of the spatially resolved
abundances in 3 redshift bins is consistent to be constant with z. Although the
large error bars in the measure of the weighted-mean abundance prevent us from
claiming any significant spatially resolved evolution, the trend with z in the
0.15-0.4r500 radial bin complements nicely the measures of Maughan et al., and
broadly agrees with theoretical predictions. We also found that the data points
derived from the spatially resolved analysis are well fitted by the relation
Z(r,z)=Z0*(1+(r/0.15r500)^2)^(-a)*((1+z)/1.6)^(-gamma), showing a significant
negative trend of Z with the radius and no significant evolution with the
redshift. The present study is the first attempt made to spatially resolve the
evolution of abundance with redshift. However, the sample size and the low
statistics associated with most of the clusters in the sample prevents us to
draw any statistically significant conclusion on the different evolutionary
path that the different regions of the clusters may have traversed. | Herschel observations of the Centaurus cluster - the dynamics of cold
gas in a cool core: Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have
distinctly different properties from other low redshift massive ellipticals.
The majority of the BCGs in cool-core clusters show signs of active star
formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy
cluster, at far-infrared (FIR) wavelengths with the Herschel space telescope.
Using the PACS spectrometer, we detect the two strongest coolants of the
interstellar medium, CII at 157.74 micron and OI at 63.18 micron, and in
addition NII at 121.90 micron. The CII emission is extended over a region of 7
kpc with a similar spatial morphology and kinematics to the optical H-alpha
emission. This has the profound implication that the optical hydrogen
recombination line, H-alpha, the optical forbidden lines, NII 6583 Angstrom,
the soft X-ray filaments and the far-infrared CII line all have the same energy
source. We also detect dust emission using the PACS and SPIRE photometers at
all six wavebands. We perform a detailed spectral energy distribution fitting
using a two-component modified black-body function and find a cold 19 K dust
component with mass 1.6x10^6 solar mass and a warm 46 K dust component with
mass 4.0x10^3 solar mass. The total FIR luminosity between 8 micron and 1000
micron is 7.5x10^8 solar luminosity, which using Kennicutt relation yields a
low star formation rate of 0.13 solar mass per yr. This value is consistent
with values derived from other tracers, such as ultraviolet emission. Combining
the spectroscopic and photometric results together with optical H-alpha, we
model emitting clouds consisting of photodissociation regions (PDRs) adjacent
to ionized regions. We show that in addition to old and young stellar
populations, there is another source of energy, such as cosmic rays, shocks or
reconnection diffusion, required to excite the H-alpha and CII filaments. |
Screening Solutions in Modified Gravity Theories: In this work, we illustrate through a simple example the possibility of
testing the chameleon screening mechanism in the Solar System using the
forthcoming LISA Pathfinder mission around gravitational saddle points. We find
distinctive tidal stress signatures for such models and consider the potential
for constraints. | Energy distribution and equation of state of the early Universe:
matching the end of inflation and the onset of radiation domination: We study the energy distribution and equation of state of the universe
between the end of inflation and the onset of radiation domination (RD),
considering observationally consistent single-field inflationary scenarios,
with a potential 'flattening' at large field values, and a monomial shape
$V(\phi) \propto |\phi|^p$ around the origin. As a proxy for (p)reheating, we
include a quadratic interaction $g^2\phi^2X^2$ between the inflaton $\phi$ and
a light scalar 'daughter' field $X$, with $g^2>0$. We capture the
non-perturbative and non-linear nature of the system dynamics with lattice
simulations, obtaining that: $i)$ the final energy transferred to $X$ depends
only on $p$, not on $g^2$, ; $ii)$ the final transfer of energy is always
negligible for $2 \leq p < 4$, and of order $\sim 50\%$ for $p \geq 4$; $iii)$
the system goes at late times to matter-domination for $p = 2$, and always to
RD for $p > 2$. In the latter case we calculate the number of e-folds until RD,
significantly reducing the uncertainty in the inflationary observables $n_s$
and $r$. |
Merging and Clustering of the Swift BAT AGN Sample: We discuss the merger rate, close galaxy environment, and clustering on
scales up to a Mpc of the SWIFT BAT hard X-ray sample of nearby (z<0.05),
moderate-luminosity active galactic nuclei (AGN). We find a higher incidence of
galaxies with signs of disruption compared to a matched control sample (18%
versus 1%) and of close pairs within 30 kpc (24% versus 1%). We also find a
larger fraction with companions compared to normal galaxies and optical
emission line selected AGN at scales up to 250 kpc. We hypothesize that these
merging AGN may not be identified using optical emission line diagnostics
because of optical extinction and dilution by star formation. In support of
this hypothesis, in merging systems we find a higher hard X-ray to [OIII] flux
ratio, as well as emission line diagnostics characteristic of composite or
star-forming galaxies, and a larger IRAS 60 um to stellar mass ratio. | Spectro-spatial evolution of the CMB II: generalised Boltzmann hierarchy: In this paper, we formulate a generalised photon Boltzmann hierarchy that
allows us to model the evolution and creation of spectral distortion
anisotropies in the early Universe. We directly build on our first paper in
this series, extending the thermalisation Green's function treatment to the
anisotropic case. We show that the problem can be described with the common
Boltzmann hierarchy for the photon field extended by new spectral parameters --
a step that reduces the complexity of the calculation by at least two orders of
magnitude. Our formalism describes the effects of i) Doppler and potential
driving, ii) spectral evolution by Compton scattering, iii) perturbed
thermalisation and iv) anisotropic heating on the distortion anisotropies. We
highlight some of the main physical properties of the equations and also
outline the steps for computing CMB power spectra including distortion
anisotropies. Limitations and extensions of the formulation are also briefly
discussed. The novel Boltzmann hierarchy given here is the basis for a series
of companion papers studying how distortion anisotropies evolve in the
perturbed Universe and which physical processes could be constrained using
future CMB imaging techniques. |
The Contribution of Radio Galaxy Contamination to Measurements of the
Sunyaev-Zel'dovich Decrement in Massive Galaxy Clusters at 140 GHz with
Bolocam: We describe in detail our characterization of the compact radio source
population in 140 GHz Bolocam observations of a set of 45 massive galaxy
clusters. We use a combination of 1.4 and 30 GHz data to select a total of 28
probable cluster-member radio galaxies and also to predict their 140 GHz flux
densities. All of these galaxies are steep-spectrum radio sources and they are
found preferentially in the cool-core clusters within our sample. In
particular, 11 of the 12 brightest cluster member radio sources are associated
with cool-core systems. Although none of the individual galaxies are robustly
detected in the Bolocam data, the ensemble-average flux density at 140 GHz is
consistent with, but slightly lower than, the extrapolation from lower
frequencies assuming a constant spectral index. In addition, our data indicate
an intrinsic scatter of 30 percent around the power-law extrapolated flux
densities at 140 GHz, although our data do not tightly constrain this scatter.
For our cluster sample, which is composed of high-mass and moderate-redshift
systems, we find that the maximum fractional change in the Sunyaev-Zel'dovich
signal integrated over any single cluster due to the presence of these radio
sources is 20 percent, and only 1/4 of the clusters show a fractional change of
more than 1 percent. The amount of contamination is strongly dependent on
cluster morphology, and nearly all of the clusters with more than 1 percent
contamination are cool-core systems. This result indicates that radio
contamination is not significant compared to current noise levels in 140 GHz
images of massive clusters and is in good agreement with the level of radio
contamination found in previous results based on lower frequency data or
simulations. | Elliptical galaxies with rapidly decreasing velocity dispersion
profiles: NMAGIC models and dark halo parameter estimates for NGC 4494: NGC 4494 is one of several intermediate-luminosity elliptical galaxies
inferred to have an unusually diffuse dark matter halo. We use the
chi^2-made-to-measure particle code NMAGIC to construct axisymmetric models of
NGC 4494 from photometric and various kinematic data. The extended kinematics
include light spectra in multiple slitlets out to 3.5 R_e, and hundreds of
planetary nebulae velocities out to ~7 R_e, thus allowing us to probe the dark
matter content and orbital structure in the halo. We use Monte Carlo
simulations to estimate confidence boundaries for the halo parameters, given
our data and modelling set-up. We find that the true potential of the dark
matter halo is recovered within Delta G (merit function)<26 (Delta chi^2<59) at
70% confidence level (C.L.), and within Delta G<32 (Delta chi^2<70) at 90%
C.L.. These numbers are much larger than the usually assumed Delta chi^2=2.3
(4.6) for 70% (90%) C.L. for two free parameters, perhaps case-dependent, but
calling into question the general validity of the standard assumptions used for
halo and black hole mass determinations. The best-fitting models for NGC 4494
have a dark matter fraction of about 0.6\pm0.1 at 5R_e (70% C.L.), and are
embedded in a dark matter halo with circular velocity ~200 km/s. The total
circular velocity curve (CVC) is approximately flat at v_c=220 km/s outside
~0.5R_e. The orbital anisotropy of the stars is moderately radial. These
results are independent of the assumed inclination of the galaxy, and edge-on
models are preferred. Comparing with the halos of NGC 3379 and NGC 4697, whose
velocity dispersion profiles also decrease rapidly from the center outwards,
the outer CVCs and dark matter halos are quite similar. NGC 4494 shows a
particularly high dark matter fraction inside ~3R_e, and a strong concentration
of baryons in the center. |
Stability of multi-field cosmological solutions in the presence of a
fluid: We explore the stability properties of multi-field solutions in the presence
of a perfect fluid, as appropriate to assisted quintessence scenarios. We show
that the stability condition for multiple fields $\phi_i$ in identical
potentials $V_i$ is simply $d^2V_i/d \phi_i^2 > 0$, exactly as in the absence
of a fluid. A possible new instability associated with the fluid is shown not
to arise in situations of cosmological interest. | Pressure profiles of distant Galaxy clusters with Planck-SPT data: We present a full set of numerical tools to extract Galaxy Cluster pressure
profiles from the joint analysis of Planck and South Pole Telescope (SPT)
observations. Pressure profiles are powerful tracers of the thermodynamic
properties and the internal structure of the clusters. Tracing the pressure
over the cosmic times allows to constraints the evolution of the cluster
structure and the contribution of astrophysical phenomena. SPT and Planck are
complementary to constrain the cluster structure at various spatial scales. The
SPT cluster catalogue counts 677 cluster candidates up to redshift 1.7, it is a
nearly mass limited sample, an ideal benchmark to test cluster evolution. We
developed a pipeline to first separate the cluster signal from the background
and foreground components and then jointly fit a parametric profile model on a
combination of Planck and SPT data. We validate our algorithm on a sub-sample
of six clusters, common to the SPT and the CHEX-MATE catalogues, comparing the
results with the profiles obtained from X-ray observations with XMM-Newton. |
Extrasolar planets as a probe of modified gravity: We propose a new method to test modified gravity theories, taking advantage
of the available data on extrasolar planets. We computed the deviations from
the Kepler third law and use that to constrain gravity theories beyond General
Relativity. We investigate gravity models which incorporate three screening
mechanisms: the Chameleon, the Symmetron and the Vainshtein. We find that data
from exoplanets orbits are very sensitive to the screening mechanisms putting
strong constraints in the parameter space for the Chameleon models and the
Symmetron, complementary and competitive to other methods, like interferometers
and solar system. With the constraints on Vainshtein we are able to work beyond
the hypothesis that the crossover scale is of the same order of magnitude than
the Hubble radius $r_c \sim H_0^{-1}$, which makes the screening work
automatically, testing how strong this hypothesis is and the viability of other
scales. | The behaviour of shape and velocity anisotropy in dark matter haloes: Dark matter haloes from cosmological N-body simulations typically have
triaxial shapes and anisotropic velocity distributions. Recently it has been
shown that the velocity anisotropy, beta, of cosmological haloes and major
merger remnants depends on direction in such a way that beta is largest along
the major axis and smallest along the minor axis. In this work we use a wide
range of non-cosmological N-body simulations to examine halo shapes and
direction-dependence of velocity anisotropy profiles. For each of our simulated
haloes we define 48 cones pointing in different directions, and from the
particles inside each cone we compute velocity anisotropy profiles. We find
that elongated haloes can have very distinct velocity anisotropies. We group
the behaviour of haloes into three different categories, that range from
spherically symmetric profiles to a much more complex behaviour, where
significant differences are found for beta along the major and minor axes. We
encourage future studies of velocity anisotropies in haloes from cosmological
simulations to calculate beta-profiles in cones, since it reveals information,
which is hidden from a spherically averaged profile. Finally, we show that
spherically averaged profiles often obey a linear relation between beta and the
logarithmic density slope in the inner parts of haloes, but this relation is
not necessarily obeyed, when properties are calculated in cones. |
The Embedded Transparent Lens and Fermat's Least-Time Principle: We present a simplified version of the lowest-order embedded point mass
gravitational lens theory and then make the extension of this theory to any
embedded transparent lens. Embedding a lens effectively reduces the
gravitational potential's range, i.e., partially shields the lensing potential
because the lens mass is made a contributor to the mean mass density of the
universe and not simply superimposed upon it. We give the time-delay function
for the embedded point mass lens from which we can derive the simplified lens
equation by applying Fermat's least-time principle. Even though rigorous
derivations are only made for the point mass in a flat background, the
generalization of the lens equation to lowest-order for any distributed lens in
any homogeneous background is obvious. We find from this simplified theory that
embedding can introduce corrections above the few percent level in weak lensing
shears caused by large clusters but only at large impacts. The potential part
of the time delay is also affected in strong lensing at the few percent level.
Additionally we again confirm that the presence of a cosmological constant
alters the gravitational deflection of passing photons. | The build up of the correlation between halo spin and the large scale
structure: Both simulations and observations have confirmed that the spin of
haloes/galaxies is correlated with the large scale structure (LSS) with a mass
dependence such that the spin of low-mass haloes/galaxies tend to be parallel
with the LSS, while that of massive haloes/galaxies tend to be perpendicular
with the LSS. It is still unclear how this mass dependence is built up over
time. We use N-body simulations to trace the evolution of the halo spin-LSS
correlation and find that at early times the spin of all halo progenitors is
parallel with the LSS. As time goes on, mass collapsing around massive halo is
more isotropic, especially the recent mass accretion along the slowest
collapsing direction is significant and it brings the halo spin to be
perpendicular with the LSS. Adopting the $fractional$ $anisotropy$ (FA)
parameter to describe the degree of anisotropy of the large-scale environment,
we find that the spin-LSS correlation is a strong function of the environment
such that a higher FA (more anisotropic environment) leads to an aligned
signal, and a lower anisotropy leads to a misaligned signal. In general, our
results show that the spin-LSS correlation is a combined consequence of mass
flow and halo growth within the cosmic web. Our predicted environmental
dependence between spin and large-scale structure can be further tested using
galaxy surveys. |
Testing Radiation Pressure Corrections to Reverberation Mapping Masses: This paper has been withdrawn by the author. The velocity structure of the
broad-line region is reflective of the radiation pressure over much longer
timescales than are probed by year-to-year changes in reverberation mapping
results. Hence, the paper's test of the Marconi et al. model is not valid. | Time-integrated directional detection of dark matter: The analysis of signals in directional dark matter (DM) detectors typically
assumes that the directions of nuclear recoils can be measured in the Galactic
rest frame. However, this is not possible with all directional detection
technologies. In nuclear emulsions, for example, the recoil events must be
detected and measured after the exposure time of the experiment. Unless the
entire detector is mounted and rotated with the sidereal day, the recoils
cannot be reoriented in the Galactic rest frame. We examine the effect of this
`time integration' on the primary goals of directional detection, namely: (1)
confirming that the recoils are anisotropic; (2) measuring the median recoil
direction to confirm their Galactic origin; and (3) probing below the neutrino
floor. We show that after time integration the DM recoil distribution retains a
preferred direction and is distinct from that of Solar neutrino-induced
recoils. Many of the advantages of directional detection are therefore
preserved and it is not crucial to mount and rotate the detector. Rejecting
isotropic backgrounds requires a factor of 2 more signal events compared with
an experiment with event time information, whereas a factor of 1.5-3 more
events are needed to measure a median direction in agreement with the
expectation for DM. We also find that there is still effectively no neutrino
floor in a time-integrated directional experiment. However to reach a cross
section an order of magnitude below the floor, a factor of 8 larger exposure is
required than with a conventional directional experiment. We also examine how
the sensitivity is affected for detectors with only 2D recoil track readout,
and/or no head-tail measurement. As for non-time-integrated experiments, 2D
readout is not a major disadvantage, though a lack of head-tail sensitivity is. |
Preconditioner-free Wiener filtering with a dense noise matrix: This work extends the Elsner & Wandelt (2013) iterative method for efficient,
preconditioner-free Wiener filtering to cases in which the noise covariance
matrix is dense, but can be decomposed into a sum whose parts are sparse in
convenient bases. The new method, which uses multiple messenger fields,
reproduces Wiener filter solutions for test problems, and we apply it to a case
beyond the reach of the Elsner & Wandelt (2013) method. We compute the Wiener
filter solution for a simulated Cosmic Microwave Background map that contains
spatially-varying, uncorrelated noise, isotropic $1/f$ noise, and large-scale
horizontal stripes (like those caused by the atmospheric noise). We discuss
simple extensions that can filter contaminated modes or inverse-noise filter
the data. These techniques help to address complications in the noise
properties of maps from current and future generations of ground-based
Microwave Background experiments, like Advanced ACTPol, Simons Observatory, and
CMB-S4. | Fundamental Cosmology from Precision Spectroscopy: I. Varying Couplings: The observational evidence for the acceleration of the universe demonstrates
that canonical theories of cosmology and particle physics are incomplete, if
not incorrect, and that new physics is out there, waiting to be discovered.
Forthcoming high-resolution ultra-stable spectrographs will play a crucial role
in this quest for new physics, by enabling a new generation of precision
consistency tests. Here we focus on astrophysical tests of the stability of
nature's fundamental couplings, and by using Principal Component Analysis
techniques further calibrated by existing VLT data we discuss how the
improvements that can be expected with ESPRESSO and ELT-HIRES will impact on
fundamental cosmology. In particular we show that a 20 to 30 night program on
ELT-HIRES will allow it to play a leading role in fundamental cosmology. |
Herschel-ATLAS: The link between accretion luminosity and star formation
in quasar host galaxies: We use the science demonstration field data of the Herschel-ATLAS to study
how star formation, traced by the far-infrared Herschel data, is related to
both the accretion luminosity and redshift of quasars selected from the Sloan
Digital Sky Survey and the 2SLAQ survey. By developing a maximum likelihood
estimator to investigate the presence of correlations between the far-infrared
and optical luminosities we find evidence that the star-formation in quasar
hosts is correlated with both redshift and quasar accretion luminosity.
Assuming a relationship of the form L_IR \propto L_QSO^{\theta} (1 +
z)^{\zeta}, we find {\theta} = 0.22 +/- 0.08 and {\zeta} = 1.6 +/- 0.4,
although there is substantial additional uncertainty in {\zeta} of order +/- 1,
due to uncertainties in the host galaxy dust temperature. We find evidence for
a large intrinsic dispersion in the redshift dependence, but no evidence for
intrinsic dispersion in the correlation between L_QSO and L_IR, suggesting that
the latter may be due to a direct physical connection between star formation
and black hole accretion. This is consistent with the idea that both the quasar
activity and star formation are dependent on the same reservoir of cold gas, so
that they are both affected by the influx of cold gas during mergers or heating
of gas via feedback processes. | Flaring Patterns in Blazars: Blazars radiate from relativistic jets launched by a supermassive black hole
along our line of sight; the subclass of FSRQs exhibits broad emission lines, a
telltale sign of a gas-rich environment and high accretion rate, contrary to
the other subclass of the BL Lacertae objects. We show that this dichotomy of
the sources in physical properties is enhanced in their flaring activity. The
BL Lac flares yielded spectral evidence of being driven by further acceleration
of highly relativistic electrons in the jet. Here we discuss spectral fits of
multi-lambda data concerning strong flares of the two flat spectrum radio
quasars 3C 454.3 and 3C 279 recently detected in gamma rays by the AGILE and
Fermi satellites. We find that optimal spectral fits are provided by external
Compton radiation enhanced by increasing production of thermal seed photons by
growing accretion. We find such flares to trace patterns on the jet power -
electron energy plane that diverge from those followed by flaring BL Lacs, and
discuss why these occur. |
Star Formation History of a Young Super-Star Cluster in NGC 4038/39:
Direct Detection of Low Mass Pre-Main Sequence Stars: We present an analysis of the near-infrared spectrum of a young massive star
cluster in the overlap region of the interacting galaxies NGC 4038/39 using
population synthesis models. Our goal is to model the cluster population as
well as provide rough constraints on its initial mass function (IMF). The
cluster shows signs of youth such as thermal radio emission and strong hydrogen
emission lines in the near-infrared. Late-type absorption lines are also
present which are indicative of late-type stars in the cluster. The strength
and ratio of these absorption lines cannot be reproduced through either
late-type pre-main sequence (PMS) stars or red supergiants alone. Thus we
interpret the spectrum as a superposition of two star clusters of different
ages, which is feasible since the 1" spectrum encompasses a physical region of
~90 pc and radii of super-star clusters are generally measured to be a few
parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the
late-type absorption features, which are due to PMS stars in the cluster, and
the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and
is needed to reproduce the overall depth of the late-type absorption features
in the spectrum. Both are required to accurately reproduce the near-infrared
spectrum of the object. Thus we have directly detected PMS objects in an
unresolved super-star cluster for the first time using a combination of
population synthesis models and pre-main sequence tracks. This analysis serves
as a testbed of our technique to constrain the low-mass IMF in young super-star
clusters as well as an exploration of the star formation history of young UC
HII regions. | The Fisher gAlaxy suRvey cOde ($\texttt{FARO}$): The Fisher gAlaxy suRvey cOde ($\texttt{FARO}$) is a new public Python code
that computes the Fisher matrix for galaxy surveys observables. The observables
considered are the linear multitracer 3D galaxy power spectrum, the linear
convergence power spectrum for weak lensing, and the linear multitracer power
spectrum for the correlation between galaxy distribution and convergence. The
code allows for tomographic and model-independent analysis in which, for
scale-independent growth, the following functions of redshift $A_a (z) \equiv
\sigma_{8}(z) \, b_a (z)$, $R(z) \equiv \sigma_{8}(z) \, f(z)$, $L(z) \equiv
\Omega_{m} \, \sigma_{8}(z) \, \Sigma (z)$ and $E(z) \equiv H(z)/H_0$, together
with the function of scale $\hat{P}(k)$, are taken as free parameters in each
redshift and scale bins respectively. In addition, a module for change of
variables is provided to project the Fisher matrix on any particular set of
parameters required. The code is built to be as fast as possible and
user-friendly. As an application example, we forecast the sensitivity of future
galaxy surveys like DESI, Euclid, J-PAS and LSST and compare their performance
on different redshift and scale ranges. |
Long-term implications of observing an expanding cosmological
civilization: Suppose that advanced civilizations, separated by a cosmological distance and
time, wish to maximize their access to cosmic resources by rapidly expanding
into the universe. How does the presence of one limit the expansionistic
ambitions of another, and what sort of boundary forms between their expanding
domains? We describe a general scenario for any expansion speed, separation
distance, and time. We then specialize to a question of particular interest:
What are the future prospects for a young and ambitious civilization if they
can observe the presence of another at a cosmological distance? We treat cases
involving the observation of one or two expanding domains. In the
single-observation case, we find that almost any plausible detection will limit
one's future cosmic expansion to some extent. Also, practical technological
limits to expansion speed (well below the speed of light) play an interesting
role. If a domain is visible at the time one embarks on cosmic expansion,
higher practical limits to expansion speed are beneficial only up to a certain
point. Beyond this point, a higher speed limit means that gains in the ability
to expand are more than offset by the first-mover advantage of the observed
domain. In the case of two visible domains, it is possible to be "trapped" by
them if the practical speed limit is high enough and their angular separation
in the sky is large enough, i.e. one's expansion in any direction will
terminate at a boundary with the two visible civilizations. Detection at an
extreme cosmological distance has surprisingly little mitigating effect on our
conclusions. | The High-z Quasar Hubble Diagram: Two recent discoveries have made it possible for us to begin using high-z
quasars as standard candles to construct a Hubble Diagram (HD) at z > 6. These
are (1) the recognition from reverberation mapping that a relationship exists
between the optical/UV luminosity and the distance of line-emitting gas from
the central ionizing source. Thus, together with a measurement of the velocity
of the line-emitting gas, e.g., via the width of BLR lines, such as Mg II, a
single observation can therefore in principle provide a determination of the
black hole's mass; and (2) the identification of quasar ULAS J1120+0641 at z =
7.085, which has significantly extended the redshift range of these sources,
providing essential leverage when fitting theoretical luminosity distances to
the data. In this paper, we use the observed fluxes and Mg II line-widths of
these sources to show that one may reasonably test the predicted high-z
distance versus redshift relationship, and we assemble a sample of 20 currently
available high-z quasars for this exercise. We find a good match between theory
and observations, suggesting that a more complete, high-quality survey may
indeed eventually produce an HD to complement the highly-detailed study already
underway (e.g., with Type Ia SNe, GRBs, and cosmic chronometers) at lower
redshifts. With the modest sample we have here, we show that the R_h=ct
Universe and LCDM both fit the data quite well, though the smaller number of
free parameters in the former produces a more favorable outcome when we
calculate likelihoods using the Akaike, Kullback, and Bayes Information
Criteria. These three statistical tools result in similar probabilities,
indicating that the R_h=ct Universe is more likely than LCDM to be correct, by
a ratio of about 85% to 15%. |
Gödel-type universes in f(R) gravity: The $f(R)$ gravity theories provide an alternative way to explain the current
cosmic acceleration without a dark energy matter component. If gravity is
governed by a $f(R)$ theory a number of issues should be reexamined in this
framework, including the violation of causality problem on nonlocal scale. We
examine the question as to whether the $f(R)$ gravity theories permit
space-times in which the causality is violated. We show that the field
equations of these $f(R)$ gravity theories do not exclude solutions with
breakdown of causality for a physically well-motivated perfect-fluid matter
content. We demonstrate that every perfect-fluid G\"{o}del-type solution of a
generic $f(R)$ gravity satisfying the condition $df/dR > 0$ is necessarily
isometric to the G\"odel geometry, and therefore presents violation of
causality. This result extends a theorem on G\"{o}del-type models, which has
been established in the context of general relativity. We also derive an
expression for the critical radius $r_c$ (beyond which the causality is
violated) for an arbitrary $f(R)$ theory, making apparent that the violation of
causality depends on both the $f(R)$ gravity theory and the matter content. As
an illustration, we concretely take a recent $f(R)$ gravity theory that is free
from singularities of the Ricci scalar and is cosmologically viable, and show
that this theory accommodates noncausal as well as causal G\"odel-type
solutions. | Parametrizing the local dark matter speed distribution: a detailed
analysis: In a recent paper, a new parametrization for the dark matter (DM) speed
distribution f(v) was proposed for use in the analysis of data from direct
detection experiments. This parametrization involves expressing the logarithm
of the speed distribution as a polynomial in the speed v. We present here a
more detailed analysis of the properties of this parametrization. We show that
the method leads to statistically unbiased mass reconstructions and exact
coverage of credible intervals. The method performs well over a wide range of
DM masses, even when finite energy resolution and backgrounds are taken into
account. We also show how to select the appropriate number of basis functions
for the parametrization. Finally, we look at how the speed distribution itself
can be reconstructed, and how the method can be used to determine if the data
are consistent with some test distribution. In summary, we show that this
parametrization performs consistently well over a wide range of input
parameters and over large numbers of statistical ensembles and can therefore
reliably be used to reconstruct both the DM mass and speed distribution from
direct detection data. |
Polar bulges and polar nuclear discs: the case of NGC 4698: The early-type spiral NGC 4698 is known to host a nuclear disc of gas and
stars which is rotating perpendicularly with respect to the galaxy main disc.
In addition, the bulge and main disc are characterised by a remarkable
geometrical decoupling. Indeed they appear elongated orthogonally to each
other. In this work the complex structure of the galaxy is investigated by a
detailed photometric decomposition of optical and near-infrared images. The
intrinsic shape of the bulge was constrained from its apparent ellipticity, its
twist angle with respect to the major axis of the main disc, and the
inclination of the main disc. The bulge is actually elongated perpendicular to
the main disc and it is equally likely to be triaxial or axisymmetric. The
central surface brightness, scalelength, inclination, and position angle of the
nuclear disc were derived by assuming it is infinitesimally thin and
exponential. Its size, orientation, and location do not depend on the observed
passband. These findings support a scenario in which the nuclear disc is the
end result of the acquisition of external gas by the pre-existing triaxial
bulge on the principal plane perpendicular to its shortest axis and
perpendicular to the galaxy main disc. The subsequent star formation either
occurred homogeneously all over the extension of the nuclear disc or through an
inside-out process that ended more than 5 Gyr ago. | Combining ILC and moment expansion techniques for extracting average-sky
signals and CMB anisotropies: The method of weighted addition of multi-frequency maps, more commonly
referred to as {\it Internal Linear Combination} (ILC), has been extensively
employed in the measurement of cosmic microwave background (CMB) anisotropies
and its secondaries along with similar application in 21cm data analysis. Here
we argue and demonstrate that ILC methods can also be applied to data from
absolutely-calibrated CMB experiments to extract average-sky signals in
addition to the conventional CMB anisotropies. The performance of the simple
ILC method is, however, limited, but can be significantly improved by adding
constraints informed by physics and existing empirical information. In recent
work, a moment description has been introduced as a technique of carrying out
high precision modeling of foregrounds in the presence of inevitable averaging
effects. We combine these two approaches to construct a heavily constrained
form of the ILC, dubbed \milc, which can be used to recover tiny monopolar
spectral distortion signals in the presence of realistic foregrounds and
instrumental noise. This is a first demonstration for measurements of the
monopolar and anisotropic spectral distortion signals using ILC and extended
moment methods. We also show that CMB anisotropy measurements can be improved,
reducing foreground biases and signal uncertainties when using the \milc. While
here we focus on CMB spectral distortions, the scope extends to the 21cm
monopole signal and $B$-mode analysis. We briefly discuss augmentations that
need further study to reach the full potential of the method. |
The KBC void and Hubble tension contradict $Λ$CDM on a Gpc scale
$-$ Milgromian dynamics as a possible solution: The KBC void is a local underdensity with the observed relative density
contrast $\delta \equiv 1 - \rho/\rho_{0} = 0.46 \pm 0.06$ between 40 and 300
Mpc around the Local Group. If mass is conserved in the Universe, such a void
could explain the $5.3\sigma$ Hubble tension. However, the MXXL simulation
shows that the KBC void causes $6.04\sigma$ tension with standard cosmology
($\Lambda$CDM). Combined with the Hubble tension, $\Lambda$CDM is ruled out at
$7.09\sigma$ confidence. Consequently, the density and velocity distribution on
Gpc scales suggest a long-range modification to gravity. In this context, we
consider a cosmological MOND model supplemented with $11 \, \rm{eV}/c^{2}$
sterile neutrinos. We explain why this $\nu$HDM model has a nearly standard
expansion history, primordial abundances of light elements, and cosmic
microwave background (CMB) anisotropies. In MOND, structure growth is
self-regulated by external fields from surrounding structures. We constrain our
model parameters with the KBC void density profile, the local Hubble and
deceleration parameters derived jointly from supernovae at redshifts $0.023 -
0.15$, time delays in strong lensing systems, and the Local Group velocity
relative to the CMB. Our best-fitting model simultaneously explains these
observables at the $1.14\%$ confidence level (${2.53 \sigma}$ tension) if the
void is embedded in a time-independent external field of ${0.055 \, a_{_0}}$.
Thus, we show for the first time that the KBC void can naturally resolve the
Hubble tension in Milgromian dynamics. Given the many successful a priori MOND
predictions on galaxy scales that are difficult to reconcile with $\Lambda$CDM,
Milgromian dynamics supplemented by $11 \, \rm{eV}/c^{2}$ sterile neutrinos may
provide a more holistic explanation for astronomical observations across all
scales. | Directional detection of Dark Matter: Directional detection of galactic Dark Matter is a promising search strategy
for discriminating genuine WIMP events from background ones. However, to take
full advantage of this powerful detection method, one need to be able to
extract information from an observed recoil map to identify a WIMP signal. We
present a comprehensive formalism, using a map-based likelihood method allowing
to recover the main incoming direction of the signal, thus proving its galactic
origin, and the corresponding significance. Constraints are then deduced in the
(sigma_n, m_chi) plane. |
The Network Behind the Cosmic Web: The concept of the cosmic web, viewing the Universe as a set of discrete
galaxies held together by gravity, is deeply engrained in cosmology. Yet,
little is known about the most effective construction and the characteristics
of the underlying network. Here we explore seven network construction
algorithms that use various galaxy properties, from their location, to their
size and relative velocity, to assign a network to galaxy distributions
provided by both simulations and observations. We find that a model relying
only on spatial proximity offers the best correlations between the physical
characteristics of the connected galaxies. We show that the properties of the
networks generated from simulations and observations are identical, unveiling a
deep universality of the cosmic web. | Survey design for Spectral Energy Distribution fitting: a Fisher Matrix
approach: The spectral energy distribution (SED) of a galaxy contains information on
the galaxy's physical properties, and multi-wavelength observations are needed
in order to measure these properties via SED fitting. In planning these
surveys, optimization of the resources is essential. The Fisher Matrix
formalism can be used to quickly determine the best possible experimental setup
to achieve the desired constraints on the SED fitting parameters. However,
because it relies on the assumption of a Gaussian likelihood function, it is in
general less accurate than other slower techniques that reconstruct the
probability distribution function (PDF) from the direct comparison between
models and data. We compare the uncertainties on SED fitting parameters
predicted by the Fisher Matrix to the ones obtained using the more thorough PDF
fitting techniques. We use both simulated spectra and real data, and consider a
large variety of target galaxies differing in redshift, mass, age, star
formation history, dust content, and wavelength coverage. We find that the
uncertainties reported by the two methods agree within a factor of two in the
vast majority (~ 90%) of cases. If the age determination is uncertain, the
top-hat prior in age used in PDF fitting to prevent each galaxy from being
older than the Universe needs to be incorporated in the Fisher Matrix, at least
approximately, before the two methods can be properly compared. We conclude
that the Fisher Matrix is a useful tool for astronomical survey design. |
The distribution of faint satellites around central galaxies in the CFHT
Legacy Survey: We investigate the radial number density profile and the abundance
distribution of faint satellites around central galaxies in the low redshift
universe using the CFHT Legacy Survey. We consider three samples of central
galaxies with magnitudes of M_r=-21, -22, and -23 selected from the Sloan
Digital Sky Survey (SDSS) group catalog of Yang et al.. The satellite
distribution around these central galaxies is obtained by cross-correlating
these galaxies with the photometric catalogue of the CFHT Legacy Survey. The
projected radial number density of the satellites obeys a power law form with
the best-fit logarithmic slope of -1.05, independent of both the central galaxy
luminosity and the satellite luminosity. The projected cross correlation
function between central and satellite galaxies exhibits a non-monotonic trend
with satellite luminosity. It is most pronounced for central galaxies with
M_r=-21, where the decreasing trend of clustering amplitude with satellite
luminosity is reversed when satellites are fainter than central galaxies by
more than 2 magnitudes. A comparison with the satellite luminosity functions in
the Milky Way and M31 shows that the Milky Way/M31 system has about twice as
many satellites as around a typical central galaxy of similar luminosity. The
implications for theoretical models are briefly discussed. | The complexity that the first stars brought to the Universe: Fragility
of metal enriched gas in a radiation field: The initial mass function (IMF) of the first (Population III) stars and
Population II (Pop II) stars is poorly known due to a lack of observations of
the period between recombination and reionization. In simulations of the
formation of the first stars, it has been shown that, due to the limited
ability of metal-free primordial gas to cool, the IMF of the first stars is a
few orders of magnitude more massive than the current IMF. The transition from
a high-mass IMF of the first stars to a lower-mass current IMF is thus
important to understand. To study the underlying physics of this transition, we
performed several simulations using the cosmological hydrodynamic adaptive mesh
refinement code Enzo for metallicities of 10^{-4}, 10^{-3}, 10^{-2}, and
10^{-1} Z_{\odot}. In our simulations we include a star formation prescription
that is derived from a metallicity dependent multi-phase ISM structure, an
external UV radiation field, and a mechanical feedback algorithm. We also
implement cosmic ray heating, photoelectric heating and gas-dust
heating/cooling, and follow the metal enrichment of the ISM. It is found that
the interplay between metallicity and UV radiation leads to the co-existence of
Pop III and Pop II star formation in non-zero metallicity (Z/Z_{\odot}
\geq10^{-2}) gas. A cold (T<100 K) and dense (\rho>10^{-22} g cm^{-3}) gas
phase is fragile to ambient UV radiation. In a metal-poor (Z/Z_{\odot}
\leq10^{-3}) gas, the cold and dense gas phase does not form in the presence of
a radiation field of F_{0}\sim10^{-5}-10^{-4} erg cm^{-2} s^{-1}. Therefore,
metallicity by itself is not a good indicator of the Pop III-Pop II transition.
Metal-rich (Z/Z_{\odot}\geq10^{-2}) gas dynamically evolves two to three orders
of magnitude faster than metal poor gas (Z/Z_{\odot}\leq10^{-3}). The
simulations including SNe show that pre-enrichment of the halo does not affect
the mixing of metals. |
Non-linear hydrodynamics of axion dark matter: relative velocity effects
and "quantum forces": The non-linear hydrodynamic equations for axion/scalar field dark matter (DM)
in the non-relativistic Madelung-Shcr\"{o}dinger form are derived in a simple
manner, including the effects of universal expansion and Hubble drag. The
hydrodynamic equations are used to investigate the relative velocity between
axion DM and baryons, and the moving-background perturbation theory (MBPT)
derived. Axions massive enough to be all of the DM do not affect the coherence
length of the relative velocity, but the MBPT equations are modified by the
inclusion of the axion effective sound speed. These MBPT equations are
necessary for accurately modelling the effects of axion DM on the formation of
the first cosmic structures, and suggest that the 21cm power spectrum could
improve constraints on axion mass by up to four orders of magnitude with
respect to the current best constraints. A further application of these results
uses the "quantum force" analogy to model scalar field gradient energy in a
smoothed-particle hydrodynamics model of axion DM. Such a model can treat axion
DM in the non-linear regime and could be incorporated into existing N-body
codes. | Spectroscopic Needs for Imaging Dark Energy Experiments: Photometric
Redshift Training and Calibration: Large sets of objects with spectroscopic redshift measurements will be needed
for imaging dark energy experiments to achieve their full potential, serving
two goals:_training_, i.e., the use of objects with known redshift to develop
and optimize photometric redshift algorithms; and_calibration_, i.e., the
characterization of moments of redshift (or photo-z error) distributions.
Better training makes cosmological constraints from a given experiment
stronger, while highly-accurate calibration is needed for photo-z systematics
not to dominate errors. In this white paper, we investigate the required scope
of spectroscopic datasets which can serve both these purposes for ongoing and
next-generation dark energy experiments, as well as the time required to obtain
such data with instruments available in the next decade. Large time allocations
on kilo-object spectrographs will be necessary, ideally augmented by infrared
spectroscopy from space. Alternatively, precision calibrations could be
obtained by measuring cross-correlation statistics using samples of bright
objects from a large baryon acoustic oscillation experiment such as DESI. We
also summarize the additional work on photometric redshift methods needed to
prepare for ongoing and future dark energy experiments. |
Comparing holographic dark energy models with statefinder: We apply the statefinder diagnostic to the holographic dark energy models,
including the original holographic dark energy (HDE) model, the new holographic
dark energy model, the new agegraphic dark energy (NADE) model, and the Ricci
dark energy model. In the low-redshift region the holographic dark energy
models are degenerate with each other and with the $\Lambda$CDM model in the
$H(z)$ and $q(z)$ evolutions. In particular, the HDE model is highly degenerate
with the $\Lambda$CDM model, and in the HDE model the cases with different
parameter values are also in strong degeneracy. Since the observational data
are mainly within the low-redshift region, it is very important to break this
low-redshift degeneracy in the $H(z)$ and $q(z)$ diagnostics by using some
quantities with higher order derivatives of the scale factor. It is shown that
the statefinder diagnostic $r(z)$ is very useful in breaking the low-redshift
degeneracies. By employing the statefinder diagnostic the holographic dark
energy models can be differentiated efficiently in the low-redshift region. The
degeneracy between the holographic dark energy models and the $\Lambda$CDM
model can also be broken by this method. Especially for the HDE model, all the
previous strong degeneracies appearing in the $H(z)$ and $q(z)$ diagnostics are
broken effectively. But for the NADE model, the degeneracy between the cases
with different parameter values cannot be broken, even though the statefinder
diagnostic is used. A direct comparison of the holographic dark energy models
in the $r$--$s$ plane is also made, in which the separations between the models
(including the $\Lambda$CDM model) can be directly measured in the light of the
current values $\{r_0,s_0\}$ of the models. | The Supermassive Black Hole at the Heart of Centaurus A: Revealed by
Gas- and Stellar Kinematics: At less than 4 Mpc distance the radio galaxy NGC 5128 (Centaurus A) is the
prime example to study the supermassive black hole and its influence on the
environment in great detail. To model and understand the feeding and feedback
mechanisms one needs an accurate determination of the mass of the supermassive
black hole. The aim of this review is to give an overview of the recent studies
that have been dedicated to measure the black hole mass in Centaurus A from
both gas and stellar kinematics. It shows how the advancement in observing
techniques and instrumentation drive the field of black hole mass measurements
and concludes that adaptive optics assisted integral field spectroscopy is the
key to identify the effects of the AGN on the surrounding ionised gas. Using
data from SINFONI at the ESO Very Large Telescope, the best-fit black hole mass
is M_BH=4.5 +1.7/-1.0 x 10^7 Msolar (from H_2 kinematics) and M_BH= (5.5 +/-
3.0) x 10^7 Msolar (from stellar kinematics; both with 3 sigma errors). This is
one of the cleanest gas vs star comparison of a M_BH determination, and brings
Centaurus A into agreement with the M_BH-sigma relation. |
The rotation curves shapes of late-type dwarf galaxies: We present rotation curves derived for a sample of 62 late-type dwarf
galaxies that have been observed as part of the Westerbork HI Survey of Spiral
and Irregular Galaxies (WHISP) project. The rotation curves were derived by
interactively fitting model data cubes to the observed cubes, taking rotation
curve shape, HI distribution, inclination, and the size of the beam into
account. This makes it possible to correct for the effects of beam smearing.
The dwarf galaxies in our sample have rotation-curve shapes that are similar to
those of late-type spiral galaxies, in the sense that their rotation curves,
when expressed in units of disk scale lengths, rise as steeply in the inner
parts and start to flatten at two disk scale lengths. None of the galaxies in
our sample have solid-body rotation curves that extend beyond three scale
lengths. The logarithmic outer rotation curve slopes are similar between
late-type dwarf and spiral galaxies. Thus, whether the flat part of the
rotation curve is reached seems to depend more on the extent of the rotation
curve than on its amplitude. We also find that the outer rotation curve shape
does not strongly depend on luminosity, at least for galaxies fainter than
M_R~-19. We find that in spiral galaxies and in the central regions of
late-type dwarf galaxies, the shape of the central distribution of light and
the inner rise of the rotation curve are related. This implies that galaxies
with stronger central concentrations of light also have higher central mass
densities, and it suggests that the luminous mass dominates the gravitational
potential in the central regions, even in low surface brightness dwarf
galaxies. | The coordinated key role of wet, mixed, and dry major mergers in the
buildup of massive early-type galaxies at z<~1: Hierarchical models predict that massive early-type galaxies (mETGs) derive
from the most massive and violent merging sequences occurred in the Universe.
However, the role of wet, mixed, and dry major mergers in the assembly of mETGs
is questioned by some recent observations. We have developed a semi-analytical
model to test the feasibility of the major-merger origin hypothesis for mETGs,
just accounting for the effects on galaxy evolution of the major mergers
strictly reported by observations. The model proves that it is feasible to
reproduce the observed number density evolution of mETGs since z~1, just
accounting for the coordinated effects of wet/mixed/dry major mergers. It can
also reconcile the different assembly redshifts derived by hierarchical models
and by mass downsizing data for mETGs, just considering that a mETG observed at
a certain redshift is not necessarily in place since then. The model predicts
that wet major mergers have controlled the mETGs buildup since z~1, although
dry and mixed mergers have also played an essential role in it. The bulk of
this assembly took place at 0.7<z<1, being nearly frozen at z<~0.7 due to the
negligible number of major mergers occurred per existing mETG since then. The
model suggests that major mergers have been the main driver for the
observational migration of mass from the massive end of the blue galaxy cloud
to that of the red sequence in the last ~8 Gyr. |
Lyman Break Analogs: Constraints on the Formation of Extreme Starbursts
at Low and High Redshift: Lyman Break Analogs (LBAs), characterized by high far-UV luminosities and
surface brightnesses as detected by GALEX, are intensely star-forming galaxies
in the low-redshift universe ($z\sim 0.2$), with star formation rates reaching
up to 50 times that of the Milky Way. These objects present metallicities,
morphologies and other physical properties similar to higher redshift Lyman
Break Galaxies (LBGs), motivating the detailed study of LBAs as local
laboratories of this high-redshift galaxy population. We present results from
our recent integral-field spectroscopy survey of LBAs with Keck/OSIRIS, which
shows that these galaxies have the same nebular gas kinematic properties as
high-redshift LBGs. We argue that such kinematic studies alone are not an
appropriate diagnostic to rule out merger events as the trigger for the
observed starburst. Comparison between the kinematic analysis and morphological
indices from HST imaging illustrates the difficulties of properly identifying
(minor or major) merger events, with no clear correlation between the results
using either of the two methods. Artificial redshifting of our data indicates
that this problem becomes even worse at high redshift due to surface brightness
dimming and resolution loss. Whether mergers could generate the observed
kinematic properties is strongly dependent on gas fractions in these galaxies.
We present preliminary results of a CARMA survey for LBAs and discuss the
implications of the inferred molecular gas masses for formation models. | Uncertainties in Parameters Estimated with Neural Networks: Application
to Strong Gravitational Lensing: In Hezaveh et al. 2017 we showed that deep learning can be used for model
parameter estimation and trained convolutional neural networks to determine the
parameters of strong gravitational lensing systems. Here we demonstrate a
method for obtaining the uncertainties of these parameters. We review the
framework of variational inference to obtain approximate posteriors of Bayesian
neural networks and apply it to a network trained to estimate the parameters of
the Singular Isothermal Ellipsoid plus external shear and total flux
magnification. We show that the method can capture the uncertainties due to
different levels of noise in the input data, as well as training and
architecture-related errors made by the network. To evaluate the accuracy of
the resulting uncertainties, we calculate the coverage probabilities of
marginalized distributions for each lensing parameter. By tuning a single
hyperparameter, the dropout rate, we obtain coverage probabilities
approximately equal to the confidence levels for which they were calculated,
resulting in accurate and precise uncertainty estimates. Our results suggest
that neural networks can be a fast alternative to Monte Carlo Markov Chains for
parameter uncertainty estimation in many practical applications, allowing more
than seven orders of magnitude improvement in speed. |
e-VLBI observations of GHz-Peaked Spectrum (GPS) radio sources in nearby
galaxies from the AT20G survey: GHz-peaked spectrum (GPS) radio sources are thought to be young objects which
later evolve into FR-I and FR-II radio galaxies. We have used the Australia
Telescope 20GHz (AT20G) survey catalogue to select a uniform sample of GPS
sources with spectral peaks above 5GHz, which should represent the youngest
members of this class. In this paper, we present e-VLBI observations of ten
such objects which are associated with nearby (z<0.15) galaxies and so
represent a new population of local, low--power GPS sources. Our e-VLBI
observations were carried out at 4.8GHz with the Australia Telescope Long
Baseline Array (LBA) using a real--time software correlator. All ten sources
were detected, and were unresolved on scales of ~100mas, implying that they are
typically less than 100pc in linear size. | IRAS F13308+5946: A Possible Transition Phase From Type I ULIRG To
Optical Quasar: We present a stellar population synthesis study of a type I luminous infrared
galaxy (LIRG): IRAS F13308+5946. It is a quasar with absolute magnitude Mi =
-22.56 and has a spectral feature of a Seyfert 1.5 galaxy. Optical images show
characteristics of later stages of a merger. With the help of the stellar
synthesis code STARLIGHT (Cid Fernandes et al. 2005) and both Calzetti et al.
(2000) and Leitherer et al.'s (2002) extinction curves, we estimate the past
infrared (IR) luminosities of the host galaxy and find it may have experienced
an ultraluminous infrared galaxy (ULIRG) phase for nearly 300 Myr, so this
galaxy has probably experienced a type I ULIRG phase. Both nuclear starburst
and active galactic nuclei (AGN) contribute to the present IR luminosity
budget, and starburst contributes ~70%. The mass of supermassive black-hole
(SMBH) is M_BH = 1.8*10^8 M_sun and the Eddington ratio L_bol/L_Edd is 0.12,
which both approximate to typical values of PG QSOs. These results indicate
that IRAS F13308+5946 is probably at the transitional phase from a type I ULIRG
to a classical QSO. |
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