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Cosmic String constraints from WMAP and the South Pole Telescope: The predictions of the inflationary LCDM paradigm match today's
high-precision measurements of the cosmic microwave background anisotropy
extremely well. The same data put tight limits on other sources of anisotropy.
Cosmic strings are a particularly interesting alternate source to constrain.
Strings are topological defects, remnants of inflationary-era physics that
persist after the big bang. They are formed in a variety of models of
inflation, including string theory models such as brane inflation. We assume a
"Nambu-Goto" model for strings, approximated by a collection of unconnected
segments with zero width, and show that measurements of temperature anisotropy
by the South Pole Telescope break a parameter degeneracy in the WMAP data,
permitting us to place a strong upper limit on the possible string contribution
to the CMB anisotropy: the power sourced by zero-width strings must be <1.75%
(95% CL) of the total or the string tension Gmu <1.7x10^{-7}. These limits
imply that the best hope for detecting strings in the CMB will come from B-mode
polarization measurements at arcminute scales rather than the degree scale
measurements pursued for gravitational wave detection. | The H0 trouble: Confronting Non-thermal Dark Matter and Phantom
Cosmology with the CMB, BAO, and Type Ia Supernovae data: We have witnessed different values of the Hubble constant being found in the
literature in the past years. Albeit, early measurements often result in an
$H_0$ much smaller than those from late-time ones, producing a statistically
significant discrepancy, and giving rise to the so-called Hubble tension. The
trouble with the Hubble constant is often treated as a cosmological problem.
However, the Hubble constant can be a laboratory to probe cosmology and
particle physics models. In our work, we will investigate if the possibility of
explaining the $H_0$ trouble using non-thermal dark matter production aided by
phantom-like cosmology is consistent with the Cosmic Background Radiation (CMB)
and Baryon Acoustic Oscillation (BAO) data. We performed a full Monte Carlo
simulation using CMB and BAO datasets keeping the cosmological parameters
$\Omega_b h^2$, $\Omega_c h^2$, $100\theta$, $\tau_{opt}$, and $w$ as priors
and concluded that a non-thermal dark matter production aided by phantom-like
cosmology yields at most $H_0=70.5$ km s$^{-1}$Mpc$^{-1}$ which is consistent
with some late-time measurements. However, if $H_0> 72$ km s$^{-1}$ Mpc$^{-1}$
as many late-time observations indicate, an alternative solution to the Hubble
trouble is needed. Lastly, we limited the fraction of relativistic dark matter
at the matter-radiation equality to be at most 1\%. |
Comparison between hemisphere comparison method and dipole-fitting
method in tracing the anisotropic expansion of the Universe use the Union2
dataset: Type-Ia supernovae (SNe Ia) are often used as the standard candles to probe
the anisotropic expansion of the Universe. In this paper, we make a
comprehensive comparison between the hemisphere comparison (HC) method and
dipole-fitting (DF) method in searching for the cosmological preferred
direction using the Union2 dataset, a compilation of 557 well-calibrated SNe
Ia. We find that the directions of the faintest SNe Ia derived from these two
methods are approximately opposite. Monte Carlo simulations show that the
results of the HC method strongly depend on the distribution of the data points
in the sky. The coincidence that the HC method and DF method give two
completely opposite directions may be due to the extremely nonuniform
distribution of the Union2 dataset. | Gemini GMOS spectroscopy of HeII nebulae in M33: We have carried out a narrow-band survey of the Local Group galaxy, M33, in
the HeII4686 emission line, to identify HeII nebulae in this galaxy. With
spectroscopic follow-up observations, we confirm three of seven candidate
objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We
also obtain spectra of associated ionizing stars for all the HII regions,
identifying two new WN stars. We demonstrate that the ionizing source for the
known HeII nebula, MA 1, is consistent with being the early-type WN star MC8
(M33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and
MA1. We were unable to identify the helium ionizing sources for HBW 673 and
BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the
[OIII]5007/Hbeta vs [NII]6584/Halpha diagnostic diagram, excitation mechanisms
apart from hot stellar continuum are needed to account for the nebular emission
in HBW 673, which appears to have no stellar source at all. |
ShapeFit: extracting the power spectrum shape information in galaxy
surveys beyond BAO and RSD: In the standard (classic) approach, galaxy clustering measurements from
spectroscopic surveys are compressed into baryon acoustic oscillations and
redshift space distortions measurements, which in turn can be compared to
cosmological models. Recent works have shown that avoiding this intermediate
step and fitting directly the full power spectrum signal (full modelling) leads
to much tighter constraints on cosmological parameters. Here we show where this
extra information is coming from and extend the classic approach with one
additional effective parameter, such that it captures, effectively, the same
amount of information as the full modelling approach, but in a
model-independent way. We validate this new method (ShapeFit) on mock catalogs,
and compare its performance to the full modelling approach finding both to
deliver equivalent results. The ShapeFit extension of the classic approach
promotes the standard analyses at the level of full modelling ones in terms of
information content, with the advantages of i) being more model independent;
ii) offering an understanding of the origin of the extra cosmological
information; iii) allowing a robust control on the impact of observational
systematics. | A New Radio Loudness Diagnostic for Active Galaxies: a
Radio-To-Mid-Infrared Parameter: We have studied the relationship between the nuclear (high-resolution) radio
emission, at 8.4 GHz (3.6 cm) and 1.4 GHz (20 cm), the [O IV] 25.89um, [Ne III]
15.56um and [Ne II] 12.81um emission lines and the black hole mass accretion
rate for a sample of Seyfert galaxies. In order to characterize the radio
contribution for the Seyfert nuclei we used the 8.4GHz/[O IV] ratio, assuming
that [O IV] scales with the luminosity of the AGN. From this we find that
Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and Seyfert 2's (i.e.,
Seyfert 1.8's, 1.9's, and 2.0's) have similar radio contributions, relative to
the AGN. On the other hand, sources in which the [Ne II] emission is dominated
either by the AGN or star formation have statistically different radio
contributions, with star formation dominated sources more "radio loud", by a
factor of ~2.8 on average, than AGN dominated sources. We show that star
formation dominated sources with relatively larger radio contribution have
smaller mass accretion rates. Overall, we suggest that 8.4GHz/[O IV], or
alternatively, 1.4GHz/[O IV] ratios, can be used to characterize the radio
contribution, relative to the AGN, without the limitation of previous methods
that rely on optical observables. |
Exotic Image Formation in Strong Gravitational Lensing by Clusters of
Galaxies. I: Cross-Section: In a recent paper we have discussed the higher order singularities in
gravitational lensing. We have shown that a singularity map, comprising of
$A_3$-lines and unstable (point) singularities ($A_4$ and $D_4$), is a compact
representation of high magnification regions corresponding to a given lens
model for all possible source redshifts. It marks all the optimal locations for
deep surveys in the lens plane. Here we present singularity maps for ten
different cluster lenses selected from the \textit{Hubble Frontier fields}
(HFF) and the \textit{Reionization Lensing Cluster Survey} (RELICS) surveys. We
have identified regions in the lens plane with a high magnification for sources
up to redshift ten. To determine the dependence of unstable (point)
singularities on lens mass model reconstruction techniques, we compared
singularity maps corresponding to the different mass models (provided by
various groups in the HFF survey) for each cluster lens. We find that the
non-parametric (free-form) method of lens mass reconstruction yields the least
number of point singularities. In contrast, mass models reconstructed by
various groups using a parametric approach have a significantly larger number
of point singularities. We also estimate the number of galaxies lying near
these unstable (point) singularities, which can be observed with the
\textit{James Webb Space Telescope} (JWST). We find that we expect to get at
least one hyperbolic umbilic and one swallowtail image formation for a source
at $z > 1$ for every five clusters with JWST. These numbers are much higher
than earlier estimates. | Effects of Small-Scale Absorption Systems on Neutral Islands during the
Late Epoch of Reionization: The reionization process is expected to be prolonged by the small-scale
absorbers (SSAs) of ionizing photons, which have been seen as Lyman-limit
systems in quasar absorption line observations. We use a set of semi-numerical
simulations to investigate the effects of absorption systems on the
reionization process, especially their impacts on the neutral islands during
the late Epoch of Reionization (EoR). Three models are studied, i.e. the
extreme case of no-SSA model with a high level of ionizing background, the
moderate-SSA model with a relatively high level of ionizing background, and the
dense-SSA model with a low level of ionizing background. We find that while the
characteristic scale of neutral regions decreases during the early and middle
stages of reionization, it stays nearly unchanged at about 10 comoving Mpc
during the late stage for the no-SSA and moderate-SSA models. However, in the
case of weak ionizing background in the dense-SSA model, the characteristic
island scale shows obvious evolution, as large islands break into many small
ones that are slowly ionized. The evolutionary behavior of neutral islands
during the late EoR thus provides a novel way to constrain the abundance of
SSAs. We discuss the 21-cm observation with the upcoming Square Kilometre
Array. The different models can be distinguished by either the 21-cm imaging or
the 21-cm power spectrum measurements. |
The history of star formation from the cosmic infrared background
anisotropies: We present a linear clustering model of cosmic infrared background (CIB)
anisotropies at large scales that is used to measure the cosmic star formation
rate density up to redshift 6, the effective bias of the CIB and the mass of
dark-matter halos hosting dusty star-forming galaxies. This is achieved using
the Planck CIB auto- and cross-power spectra (between different frequencies)
and CIBxCMB lensing cross-spectra measurements, as well as external constraints
(e.g. on the CIB mean brightness). We recovered an obscured star formation
history which agrees well with the values derived from infrared deep surveys
and we confirm that the obscured star formation dominates the unobscured one up
to at least z=4. The obscured and unobscured star formation rate densities are
compatible at $1\sigma$ at z=5. We also determined the evolution of the
effective bias of the galaxies emitting the CIB and found a rapid increase from
$\sim$0.8 at z$=$0 to $\sim$8 at z$=$4. At 2$<$z$<$4, this effective bias is
similar to that of galaxies at the knee of the mass functions and submillimeter
galaxies. This effective bias is the weighted average of the true bias with the
corresponding emissivity of the galaxies. The halo mass corresponding to this
bias is thus not exactly the mass contributing the most to the star formation
density. Correcting for this, we obtained a value of
log(M$_h$/M$_{\odot}$)=12.77$_{-0.125}^{+0.128}$ for the mass of the typical
dark matter halo contributing to the CIB at z=2. Finally, we also computed
using a Fisher matrix analysis how the uncertainties on the cosmological
parameters affect the recovered CIB model parameters and find that the effect
is negligible. | Crossing Statistic: Bayesian interpretation, model selection and
resolving dark energy parametrization problem: By introducing Crossing functions and hyper-parameters I show that the
Bayesian interpretation of the Crossing Statistics [1] can be used trivially
for the purpose of model selection among cosmological models. In this approach
to falsify a cosmological model there is no need to compare it with other
models or assume any particular form of parametrization for the cosmological
quantities like luminosity distance, Hubble parameter or equation of state of
dark energy. Instead, hyper-parameters of Crossing functions perform as
discriminators between correct and wrong models. Using this approach one can
falsify any assumed cosmological model without putting priors on the underlying
actual model of the universe and its parameters, hence the issue of dark energy
parametrization is resolved. It will be also shown that the sensitivity of the
method to the intrinsic dispersion of the data is small that is another
important characteristic of the method in testing cosmological models dealing
with data with high uncertainties. |
Testing coupled dark energy models with their cosmological background
evolution: We consider a cosmology in which dark matter and a quintessence scalar field
responsible for the acceleration of the Universe are allowed to interact.
Allowing for both conformal and disformal couplings, we perform a global
analysis of the constraints on our model using Hubble parameter measurements,
baryon acoustic oscillation distance measurements, and a Supernovae Type Ia
data set. We find that the additional disformal coupling relaxes the conformal
coupling constraints. Moreover we show that, at the background level, a
disformal interaction within the dark sector is preferred to both $\Lambda$CDM
and uncoupled quintessence, hence favouring interacting dark energy. | The circum-galactic gas around cosmologically simulated disks: We analyze the physical properties and infall rates of the circum-galactic
gas around disks obtained in multi-resolved, cosmological, AMR simulations. At
intermediate and low redshifts, disks are embedded into an extended, hot,
tenuous corona that contributes largely in fueling the disk with non-enriched
gas whereas the accretion of enriched gas from tidal streams occurs throughout
episodic events. We derive an infall rate close to the disk of the same value
as the one of the star formation rate in the disk and its temporal evolution as
a function of galacto-centric radius nicely shows that the growth of galactic
disks proceeds according to an inside-out formation scenario. |
Gravitational Waves from the Non-Perturbative Decay of Condensates along
Supersymmetric Flat Directions: It has recently been shown that specific non-perturbative effects may lead to
an explosive decay of flat direction condensates in supersymmetric theories. We
confirm explicitly the efficiency of this process with lattice simulations:
after few rotations of the condensates in their complex plane, most of their
energy is quickly converted into inhomogeneous fluctuations. We then point out
that this generates a gravitational wave background which depends on the
inflaton sector and falls in the Hz-kHz frequency range today. We compute the
resulting spectrum and study how it depends on the parameters. We show that
these gravity waves can be observable by upcoming experiments like Advanced
LIGO and depend crucially on (i) the initial VEV of flat directions when they
start to oscillate, (ii) their soft SUSY-breaking mass and (iii) the reheat
temperature of the universe. This signal could open a new observational window
on inflation and low-energy supersymmetry. | A Very Deep Chandra Observation of Abell 2052: Bubbles, Shocks, and
Sloshing: We present first results from a very deep (~650 ksec) Chandra X-ray
observation of Abell 2052, as well as archival VLA radio observations. The data
reveal detailed structure in the inner parts of the cluster, including bubbles
evacuated by the AGN's radio lobes, compressed bubble rims, filaments, and
loops. Two concentric shocks are seen, and a temperature rise is measured for
the innermost one. On larger scales, we report the first detection of an excess
surface brightness spiral feature. The spiral has cooler temperatures, lower
entropies, and higher abundances than its surroundings, and is likely the
result of sloshing gas initiated by a previous cluster-cluster or sub-cluster
merger. Initial evidence for previously unseen bubbles at larger radii related
to earlier outbursts from the AGN is presented. |
Environmental Dependence of the Kennicutt-Schmidt Relation in Galaxies: We present a detailed description of a phenomenological H2 formation model
and local star formation prescription based on the density of molecular (rather
than total) gas. Such approach allows us to avoid the arbitrary density and
temperature thresholds typically used in star formation recipes. We present
results of the model based on realistic cosmological simulations of high-z
galaxy formation for a grid of numerical models with varied dust-to-gas ratios
and interstellar far UV (FUV) fluxes. Our results show that both the
atomic-to-molecular transition on small, ~10 pc scales and the
Kennicutt-Schmidt (KS) relation on ~kpc scales are sensititive to the
dust-to-gas ratio and the FUV flux. The atomic-to-molecular transition as a
function of gas density or column density has a large scatter but is rather
sharp and shifts to higher densities with decreasing dust-to-gas ratio and/or
increasing FUV flux. Consequently, star formation is concentrated to higher gas
surface density regions, resulting in steeper slope and lower amplitude of the
KS relation at a given gas surface density, in less dusty and/or higher FUV
flux environments. These trends should have a particularly strong effect on the
evolution of low-mass, low surface brightness galaxies which typically have low
dust content and anemic star formation, but are also likely to be important for
evolution of the Milky Way-sized systems. We parameterize the dependencies
observed in our simulations in convenient fitting formulae, which can be used
to model the dependence of the KS relation on the dust-to-gas ratio and FUV
flux in semi-analytic models and in cosmological simulations that do not
include radiative transfer and H2 formation. | Binned Hubble parameter measurements and the cosmological
deceleration-acceleration transition: Weighted mean and median statistics techniques are used to combine 23
independent lower redshift, $z<1.04$, Hubble parameter, $H(z)$, measurements
and determine binned forms of $H(z)$. When these are combined with 5 higher
redshift, $1.3\leqslant z \leqslant 2.3$, $H(z)$ measurements the resulting
constraints on cosmological parameters, of three cosmological models, that
follow from the weighted-mean binned data are almost identical to those derived
from analyses using the 28 independent $H(z)$ measurements. This is consistent
with what is expected if the lower redshift measurements errors are Gaussian.
Plots of the binned weighted-mean $H(z)/(1+z)$ versus $z$ data are consistent
with the presence of a cosmological deceleration-acceleration transition at
redshift $z_{\rm da}=0.74 \pm 0.05$ \citep{farooq3}, which is expected in
cosmological models with present-epoch energy budget dominated by dark energy
as in the standard spatially-flat $\Lambda$CDM cosmological model. |
Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit
Implications: We present proper motions for the Large & Small Magellanic Clouds (LMC & SMC)
based on three epochs of \textit{Hubble Space Telescope} data, spanning a $\sim
7$ yr baseline, and centered on fields with background QSOs. The first two
epochs, the subject of past analyses, were obtained with ACS/HRC, and have been
reanalyzed here. The new third epoch with WFC3/UVIS increases the time baseline
and provides better control of systematics. The three-epoch data yield proper
motion random errors of only 1-2% per field. For the LMC this is sufficient to
constrain the internal proper motion dynamics, as will be discussed in a
separate paper. Here we focus on the implied center-of-mass proper motions:
mu_W(LMC) = -1.910 +/- 0.020 mas/yr, mu_N(LMC) = 0.229 +/- 0.047 mas/yr, and
mu_W(SMC) = -0.772 +/- 0.063 mas/yr, mu_N(SMC) = -1.117 +/- 0.061 mas/yr. We
combine the results with a revised understanding of the solar motion in the
Milky Way to derive Galactocentric velocities: v_{tot,LMC} = 321 +/- 24 km/s
and v_{tot,SMC} = 217 +/- 26 km/s. Our proper motion uncertainties are now
dominated by limitations in our understanding of the internal kinematics and
geometry of the Clouds, and our velocity uncertainties are dominated by
distance errors. Orbit calculations for the Clouds around the Milky Way allow a
range of orbital periods, depending on the uncertain masses of the Milky Way
and LMC. Periods $\lesssim 4$ Gyr are ruled out, which poses a challenge for
traditional Magellanic Stream models. First-infall orbits are preferred (as
supported by other arguments as well) if one imposes the requirement that the
LMC and SMC must have been a bound pair for at least several Gyr. | General relativistic effects on non-linear power spectra: Non-linear nature of Einstein equation introduces genuine relativistic higher
order corrections to the usual Newtonian fluid equations describing the
evolution of cosmological perturbations. We study the effect of such novel
non-linearities on the next-to-leading order matter and velocity power spectra
for the case of pressureless, irrotational fluid in a flat Friedmann
background. We find that pure general relativistic corrections are negligibly
small over all scales. Our result guarantees that, in the current paradigm of
standard cosmology, one can safely use Newtonian cosmology even in non-linear
regimes. |
Reionization constraints using Principal Component Analysis: Using a semi-analytical model developed by Choudhury & Ferrara (2005) we
study the observational constraints on reionization via a principal component
analysis (PCA). Assuming that reionization at z>6 is primarily driven by
stellar sources, we decompose the unknown function N_{ion}(z), representing the
number of photons in the IGM per baryon in collapsed objects, into its
principal components and constrain the latter using the photoionization rate
obtained from Ly-alpha forest Gunn-Peterson optical depth, the WMAP7 electron
scattering optical depth and the redshift distribution of Lyman-limit systems
at z \sim 3.5. The main findings of our analysis are: (i) It is sufficient to
model N_{ion}(z) over the redshift range 2<z<14 using 5 parameters to extract
the maximum information contained within the data. (ii) All quantities related
to reionization can be severely constrained for z<6 because of a large number
of data points whereas constraints at z>6 are relatively loose. (iii) The weak
constraints on N_{ion}(z) at z>6 do not allow to disentangle different feedback
models with present data. There is a clear indication that N_{ion}(z) must
increase at z>6, thus ruling out reionization by a single stellar population
with non-evolving IMF, and/or star-forming efficiency, and/or photon escape
fraction. The data allows for non-monotonic N_{ion}(z) which may contain sharp
features around z \sim 7. (iv) The PCA implies that reionization must be 99%
completed between 5.8<z<10.3 (95% confidence level) and is expected to be 50%
complete at z \approx 9.5-12. With future data sets, like those obtained by
Planck, the z>6 constraints will be significantly improved. | Effect of Separate Initial Conditions on the Lyman-$α$ Forest in
Simulations: Using a set of high resolution simulations, we quantify the effect of species
specific initial transfer functions on probes of the IGM via the Lyman-$\alpha$
forest. We focus on redshifts $2-6$, after H~{\sc i} reionization. We explore
the effect of these initial conditions on measures of the thermal state of the
low density IGM: the curvature, Doppler width cutoff, and Doppler width
distribution. We also examine the matter and flux power spectrum, and potential
consequences for constraints on warm dark matter models. We find that the
curvature statistic is at most affected at the $\approx2\%$ level at $z=6$. The
Doppler width cutoff parameters are affected by $\approx5\%$ for the intercept,
and $\approx8\%$ for the fit slope, though this is subdominant to sample
variation. The Doppler width distribution shows a $\approx30\%$ effect at
$z=3$, however the distribution is not fully converged with simulation box size
and resolution. The flux power spectrum is at most affected by $\approx5\%$ at
high redshift and small scales. We discuss numerical convergence with
simulation parameters. |
Structures in the fundamental plane of early-type galaxies: The fundamental plane of early-type galaxies is a rather tight
three-parameter correlation discovered more than twenty years ago. It has
resisted a both global and precise physical interpretation despite a consequent
number of works, observational, theoretical or using numerical simulations. It
appears that its precise properties depend on the population of galaxies in
study. Instead of selecting a priori these populations, we propose to
objectively construct homologous populations from multivariate analyses. We
have undertaken multivariate cluster and cladistic analyses of a sample of 56
low-redshift galaxy clusters containing 699 early-type galaxies, using four
parameters: effective radius, velocity dispersion, surface brightness averaged
over effective radius, and Mg2 index. All our analyses are consistent with
seven groups that define separate regions on the global fundamental plane, not
across its thickness. In fact, each group shows its own fundamental plane,
which is more loosely defined for less diversified groups. We conclude that the
global fundamental plane is not a bent surface, but made of a collection of
several groups characterizing several fundamental planes with different
thicknesses and orientations in the parameter space. Our diversification
scenario probably indicates that the level of diversity is linked to the number
and the nature of transforming events and that the fundamental plane is the
result of several transforming events. We also show that our classification,
not the fundamental planes, is universal within our redshift range (0.007 -
0.053). We find that the three groups with the thinnest fundamental planes
presumably formed through dissipative (wet) mergers. In one of them, this(ese)
merger(s) must have been quite ancient because of the relatively low
metallicity of its galaxies, Two of these groups have subsequently undergone
dry mergers to increase their masses. In the k-space, the third one clearly
occupies the region where bulges (of lenticular or spiral galaxies) lie and
might also have formed through minor mergers and accretions. The two least
diversified groups probably did not form by major mergers and must have been
strongly affected by interactions, some of the gas in the objects of one of
these groups having possibly been swept out. The interpretation, based on
specific assembly histories of galaxies of our seven groups, shows that they
are truly homologous. They were obtained directly from several observables,
thus independently of any a priori classification. The diversification scenario
relating these groups does not depend on models or numerical simulations, but
is objectively provided by the cladistic analysis. Consequently, our
classification is more easily compared to models and numerical simulations, and
our work can be readily repeated with additional observables. | Cosmological data analysis of f(R) gravity models: A class of well-behaved modified gravity models with long enough matter
domination epoch and a late-time accelerated expansion is confronted with SNIa,
CMB, SDSS, BAO and H(z) galaxy ages data, as well as current measurements of
the linear growth of structure. We show that the combination of geometrical
probes and growth data exploited here allows to rule out f(R) gravity models,
in particular, the logarithmic of curvature model. We also apply solar system
tests to the models in agreement with the cosmological data. We find that the
exponential of the inverse of the curvature model satisfies all the
observational tests considered and we derive the allowed range of parameters.
Current data still allows for small deviations of Einstein gravity. Future,
high precision growth data, in combination with expansion history data, will be
able to distinguish tiny modifications of standard gravity from the LambdaCDM
model. |
Reducing the $H_{0}$ tension with generalized Proca theory: We investigate the cosmological viability of the generalized proca theory. We
first implement the background and linear perturbation equations of motion in
the Boltzmann code and then study the constraints on the parameters of the
generalized proca theory after running MCMC against the cosmological data set.
With Planck + HST data, we obtain the constraint
$h=0.7334_{-0.0269}^{+0.0246}$, which indicates that the tension between early
universe and late time universe within this theory is removed. By adding other
late-time data sets (BAO, RSD, etc.) we show that the tension is reduced, as
the 2$\sigma$ allowed region for $h$ in Proca, $h=0.7041_{-0.0087}^{+0.0094}$,
overlaps with the 2$\sigma$ region of the HST data. | A Quasar Catalog with Simultaneous UV, Optical and X-ray Observations by
Swift: We have compiled a catalog of optically-selected quasars with simultaneous
observations in UV/optical and X-ray bands by the Swift Gamma Ray Burst
Explorer. Objects in this catalog are identified by matching the Swift
pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The
final catalog contains 843 objects, among which 637 have both UVOT and XRT
observations and 354 of which are detected by both instruments. The overall
X-ray detection rate is ~60% which rises to ~85% among sources with at least 10
ks of XRT exposure time. We construct the time-averaged spectral energy
distribution for each of the 354 quasars using UVOT photometric measurements
and XRT spectra. From model fits to these SEDs, we find that the big blue bump
contributes about 0.3 dex to the quasar luminosity. We re-visit the
alpha_ox-L_uv relation by selecting a clean sample with only type 1 radio-quiet
quasars; the dispersion of this relation is reduced by at least 15% compared to
studies that use non-simultaneous UV/optical and X-ray data. We only found a
weak correlation between L/L_Edd and alpha_uv. We do not find significant
correlations between alpha_x and alpha_ox, alpha_ox and alpha_uv, and alpha_x
and Log L(0.3-10 keV). The correlations between alpha_uv and alpha_x, alpha_ox
and alpha_x, alpha_ox and alpha_uv, L/L_Edd and alpha_x, and L/L_Edd and
alpha_ox are stronger amongst low-redshift quasars, indicating that these
correlations are likely driven by the changes of SED shape with accretion
state. |
Galaxy Assembly Bias on the Red Sequence: Using samples drawn from the Sloan Digital Sky Survey, we study the
relationship between local galaxy density and the properties of galaxies on the
red sequence. After removing the mean dependence of average overdensity (or
"environment") on color and luminosity, we find that there remains a strong
residual trend between luminosity-weighted mean stellar age and environment,
such that galaxies with older stellar populations favor regions of higher
overdensity relative to galaxies of like color and luminosity (and hence of
like stellar mass). Even when excluding galaxies with recent star-formation
activity (i.e., younger mean stellar ages) from the sample, we still find a
highly significant correlation between stellar age and environment at fixed
stellar mass. This residual age-density relation provides direct evidence for
an assembly bias on the red sequence such that galaxies in higher-density
regions formed earlier than galaxies of similar mass in lower-density
environments. We discuss these results in the context of the age-metallicity
degeneracy and in comparison to previous studies at low and intermediate
redshift. Finally, we consider the potential role of assembly bias in
explaining recent results regarding the evolution of post-starburst (or
post-quenching) galaxies and the environmental dependence of the type Ia
supernova rate. | Study of baryon acoustic oscillations with SDSS DR12 data and
measurements of $Ω_k$ and $Ω_\textrm{DE}(a)$. Part II: We define Baryon Acoustic Oscillation (BAO) observables $\hat{d}_\alpha(z,
z_c)$, $\hat{d}_z(z, z_c)$, and $\hat{d}_/(z, z_c)$ that do not depend on any
cosmological parameter. From each of these observables we recover the BAO
correlation length $d_\textrm{BAO}$ with its respective dependence on
cosmological parameters. These BAO observables are measured as a function of
redshift $z$ with the Sloan Digital Sky Survey (SDSS) data release DR12. From
the BAO measurements alone, or together with the correlation angle
$\theta_\textrm{MC}$ of the Cosmic Microwave Background (CMB), we constrain the
curvature parameter $\Omega_k$ and the dark energy density
$\Omega_\textrm{DE}(a)$ as a function of the expansion parameter $a$ in several
scenarios. These observables are further constrained with external measurements
of $h$ and $\Omega_\textrm{b} h^2$. We find some tension between the data and a
cosmology with flat space and constant dark energy density
$\Omega_\textrm{DE}(a)$. |
The haloes of bright satellite galaxies in a warm dark matter universe: High resolution N-body simulations of galactic cold dark matter haloes
indicate that we should expect to find a few satellite galaxies around the
Milky Way whose haloes have a maximum circular velocity in excess of 40 kms.
Yet, with the exception of the Magellanic Clouds and the Sagittarius dwarf,
which likely reside in subhaloes with significantly larger velocities than
this, the bright satellites of the Milky Way all appear to reside in subhaloes
with maximum circular velocities below 40 kms. As recently highlighted by
Boylan-Kolchin et al., this discrepancy implies that the majority of the most
massive subhaloes within a cold dark matter galactic halo are much too
concentrated to be consistent with the kinematic data for the bright Milky Way
satellites. Here we show that no such discrepancy exists if haloes are made of
warm, rather than cold dark matter because these haloes are less concentrated
on account of their typically later formation epochs. Warm dark matter is one
of several possible explanations for the observed kinematics of the satellites. | Massive neutrino self-interactions and inflation: Certain inflationary models like Natural inflation (NI) and Coleman-Weinberg
inflation (CWI) are disfavoured by cosmological data in the standard
$\Lambda\textrm{CDM}+r$ model (where $r$ is the scalar-to-tensor ratio), as
these inflationary models predict the regions in the $n_s-r$ parameter space
that are excluded by the cosmological data at more than 2$\sigma$ (here $n_s$
is the scalar spectral index). The same is true for single field inflationary
models with an inflection point that can account for all or majority of dark
matter in the form of PBHs (primordial black holes). Cosmological models
incorporating strongly self-interacting neutrinos (with a heavy mediator) are,
however, known to prefer lower $n_s$ values compared to the $\Lambda\rm CDM$
model. Considering such neutrino self-interactions can, thus, open up the
parameter space to accommodate the above inflationary models. In this work, we
implement the massive neutrino self-interactions with a heavy mediator in two
different ways: flavour-universal (among all three neutrinos), and
flavour-specific (involving only one neutrino species). We implement the new
interaction in both scalar and tensor perturbation equations of neutrinos.
Interestingly, we find that the current cosmological data can support the
aforementioned inflationary models at 2$\sigma$ in the presence of such
neutrino self-interactions. |
Witnessing the active assembly phase of massive galaxies since z = 1: We present an analysis of ~60 000 massive (stellar mass M_star > 10^{11}
M_sun) galaxies out to z = 1 drawn from 55.2 deg2 of the United Kingdom
Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) and the Sloan
Digital Sky Survey (SDSS) II Supernova Survey. This is by far the largest
survey of massive galaxies with robust mass estimates, based on infrared
(K-band) photometry, reaching to the Universe at about half its present age. We
find that the most massive (M_star > 10^{11.5} M_sun) galaxies have experienced
rapid growth in number since z = 1, while the number densities of the less
massive systems show rather mild evolution. Such a hierarchical trend of
evolution is consistent with the predictions of the current semi-analytic
galaxy formation model based on Lambda CDM theory. While the majority of
massive galaxies are red-sequence populations, we find that a considerable
fraction of galaxies are blue star-forming galaxies. The blue fraction is
smaller in more massive systems and decreases toward the local Universe,
leaving the red, most massive galaxies at low redshifts, which would support
the idea of active 'bottom-up' formation of these populations during 0 < z < 1. | A deeper look into the structure of ΛCDM haloes: correlations
between halo parameters from Einasto fits: We used high resolution dark matter only cosmological simulations to
investigate the structural properties of Lambda Cold Dark Matter ($\Lambda$CDM)
haloes over cosmic time. The haloes in our study range in mass from $\sim
10^{10}$ to $\sim 10^{12} \mathrm{M}_\odot$, and are resolved with $10^5$ to
$10^7$ particles. We fit the spherically averaged density profiles of DM haloes
with the three parameter Einasto function. For our sample of haloes, the
Einasto shape parameter, $\alpha$, is uncorrelated with the concentration, $c$,
at fixed halo mass, and at all redshifts. Previous reports of an
anti-correlation are traced to fitting degeneracies, which our fits are less
sensitive to due to our higher spatial resolution. However, for individual
haloes the evolution in $\alpha$ and $c$ is anti-correlated: at redshift $z=7$,
$\alpha \simeq 0.4$ and decreases with time, while $c\simeq 3$ and increases
with time. The evolution in structure is primarily due to accretion of mass at
larger radii. We suggest that $\alpha$ traces the evolutionary state of the
halo, with dynamically young haloes having high $\alpha$ (closer to a top-hat:
$\alpha^{-1}=0$), and dynamically relaxed haloes having low $\alpha$ (closer to
isothermal: $\alpha=0$). Such an evolutionary dependence reconciles the
increase of $\alpha$ vs peak height, $\nu$, with the dependence on the slope of
the power spectrum of initial density fluctuations found by previous studies. |
On the accelerated expansion of the cosmos: We present a short (and necessarily incomplete) review of the evidence for
the accelerated expansion of the Universe. The most direct probe of
acceleration relies on the detailed study of supernovae (SN) of type Ia.
Assuming that these are standardizable candles and that they fairly sample a
homogeneous and isotropic Universe, the evidence for acceleration can be tested
in a model- and calibration-independent way. Various light-curve fitting
procedures have been proposed and tested. While several fitters give consistent
results for the so-called Constitution set, they lead to inconsistent results
for the recently released SDSS SN. Adopting the SALT fitter and relying on the
Union set, cosmic acceleration is detected by a purely kinematic test at 7
sigma when spatial flatness is assumed and at 4 sigma without assumption on the
spatial geometry. A weak point of the described method is the local set of SN
(at z < 0.2), as these SN are essential to anchor the Hubble diagram. These SN
are drawn from a volume much smaller than the Hubble volume and could be
affected by local structure. Without the assumption of homogeneity, there is no
evidence for acceleration, as the effects of acceleration are degenerate with
the effects of inhomogeneities. Unless we sit in the centre of the Universe,
such inhomogeneities can be constrained by SN observations by means of tests of
the isotropy of the Hubble flow. | Can Coupled Dark Energy Speed Up the Bullet Cluster?: It has been recently shown that the observed morphological properties of the
Bullet Cluster can be accurately reproduced in hydrodynamical simulations only
when the infall pairwise velocity V_{c} of the system exceeds 3000km/s (or at
least possibly 2500 km/s) at the pair separation of 2R_{vir}, where R_{vir} is
the virial radius of the main cluster, and that the probability of finding such
a bullet-like system is extremely low in the standard \Lambda CDM cosmology. We
suggest here the fifth-force mediated by a coupled Dark Energy (cDE) as a
possible velocity-enhancing mechanism and investigate its effect on the infall
velocities of the bullet-like systems from the CoDECS (COupled Dark Energy
Cosmological Simulations) public database. Five different cDE models are
considered: three with constant coupling and exponential potential, one with
exponential coupling and exponential potential, and one with constant coupling
and supergravity potential. For each model, after identifying the bullet-like
systems, we determine the probability density distribution of their infall
velocities at the pair separations of (2-3)R_{vir}. Approximating each
probability density distribution as a Gaussian, we calculate the cumulative
probability of finding a bullet-like system with V_{c}>=3000 km/s or
V_{c}>=2500 km/s. Our results show that in all of the five cDE models the
cumulative probabilities increase compared to the \Lambda CDM case and that in
the model with exponential coupling P(V_{c}>=2500 km/s) exceeds 10^{-4}. The
physical interpretations and cosmological implications of our results are
provided. |
Warm-hot baryons comprise 5-10 per cent of filaments in the cosmic web: Observations of the cosmic microwave background indicate that baryons account
for 5% of the Universe's total energy content. In the local Universe, the
census of all observed baryons falls short of this estimate by a factor of two.
Cosmological simulations indicate that the missing baryons might not have
condensed into virialized haloes, but reside throughout the filaments of the
cosmic web (where matter density is larger than average) as a low-density
plasma at temperatures of $10^5-10^7$ kelvin, known as the warm-hot
intergalactic medium. There have been previous claims of the detection of warm
baryons along the line of sight to distant blazars and of hot gas between
interacting clusters. These observations were, however, unable to trace the
large-scale filamentary structure, or to estimate the total amount of warm
baryons in a representative volume of the Universe. Here we report X-ray
observations of filamentary structures of gas at $10^7$ kelvin associated with
the galaxy cluster Abell 2744. Previous observations of this cluster were
unable to resolve and remove coincidental X-ray point sources. After
subtracting these, we reveal hot gas structures that are coherent over scales
of 8 mergaparsecs. The filaments coincide with over-densities of galaxies and
dark matter, with 5-10% of their mass in baryonic gas. This gas has been heated
up by the cluster's gravitational pull and is now feeding its core. Our
findings strengthen evidence for a picture of the Universe in which a large
fraction of the missing baryons reside in the filaments of the cosmic web. | Star Formation Rates in Resolved Galaxies: Calibrations with Near and
Far Infrared Data for NGC5055 and NGC6946: We use the near--infrared Br\gamma hydrogen recombination line as a reference
star formation rate (SFR) indicator to test the validity and establish the
calibration of the {\it Herschel} PACS 70 \mu m emission as a SFR tracer for
sub--galactic regions in external galaxies. Br\gamma offers the double
advantage of directly tracing ionizing photons and of being relatively
insensitive to the effects of dust attenuation. For our first experiment, we
use archival CFHT Br\gamma and Ks images of two nearby galaxies: NGC\,5055 and
NGC\,6946, which are also part of the {\it Herschel} program KINGFISH (Key
Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the
extinction corrected Br\gamma emission to derive the SFR(70) calibration for
H{\sc ii} regions in these two galaxies. A comparison of the SFR(70)
calibrations at different spatial scales, from 200 pc to the size of the whole
galaxy, reveals that about 50% of the total 70\mu m emission is due to dust
heated by stellar populations that are unrelated to the current star formation.
We use a simple model to qualitatively relate the increase of the SFR(70)
calibration coefficient with decreasing region size to the star formation
timescale. We provide a calibration for an unbiased SFR indicator that combines
the observed H\alpha with the 70 \mu m emission, also for use in H{\sc ii}
regions. We briefly analyze the PACS 100 and 160 \mu m maps and find that
longer wavelengths are not as good SFR indicators as 70\mu m, in agreement with
previous results. We find that the calibrations show about 50% difference
between the two galaxies, possibly due to effects of inclination. |
Active Galactic Nuclei in Groups and Clusters of Galaxies: Detection and
Host Morphology: The incidence and properties of Active Galactic Nuclei (AGN) in the field,
groups, and clusters can provide new information about how these objects are
triggered and fueled, similar to how these environments have been employed to
study galaxy evolution. We have obtained new XMM-Newton observations of seven
X-ray selected groups and poor clusters with 0.02 < z < 0.06 for comparison
with previous samples that mostly included rich clusters and optically-selected
groups. Our final sample has ten groups and six clusters in this low-redshift
range (split at a velocity dispersion of $\sigma = 500$ km/s). We find that the
X-ray selected AGN fraction increases from $f_A(L_X>10^{41}; M_R<M_R^*+1) =
0.047^{+0.023}_{-0.016}$ in clusters to $0.091^{+0.049}_{-0.034}$ for the
groups (85% significance), or a factor of two, for AGN above an 0.3-8keV X-ray
luminosity of $10^{41}$ erg/s hosted by galaxies more luminous than $M_R^*+1$.
The trend is similar, although less significant, for a lower-luminosity host
threshold of $M_R = -20$ mag. For many of the groups in the sample we have also
identified AGN via standard emission-line diagnostics and find that these AGN
are nearly disjoint from the X-ray selected AGN. Because there are substantial
differences in the morphological mix of galaxies between groups and clusters,
we have also measured the AGN fraction for early-type galaxies alone to
determine if the differences are directly due to environment, or indirectly due
to the change in the morphological mix. We find that the AGN fraction in
early-type galaxies is also lower in clusters $f_{A,n>2.5}(L_X>10^{41};
M_R<M_R^*+1) = 0.048^{+0.028}_{-0.019}$ compared to $0.119^{+0.064}_{-0.044}$
for the groups (92% significance), a result consistent with the hypothesis that
the change in AGN fraction is directly connected to environment. | Recalibration of Pagel's method for HII regions considering the thermal
structure, the ionization structure, and the depletion of O into dust grains: Using a sample of 28 HII regions from the literature with measured
temperature inhomogeneity parameter, t^2, we present a statistical correction
to the chemical abundances determined with the Te(4363/5007) method. We used
the t^2 values to correct the oxygen gaseous abundances and consider the oxygen
depletion into dust to calculate the total abundances for these objects. This
correction is used to obtain a new calibration of Pagel's strong-line method,
R_{23}, to determine oxygen abundances in HII regions. Our new calibration
simultaneously considers the temperature structure, the ionization structure,
and the fraction of oxygen depleted into dust grains. Previous calibrations in
the literature have included one or two of these factors; this is the first
time all three are taken into account. This recalibration conciliates the
systematic differences among the temperatures found from different methods. We
find that the total correction due to thermal inhomogeneities and dust
depletion amounts to an increase in the O/H ratio of HII regions by factors of
1.7 to 2.2 (or 0.22 to 0.35 dex). This result has important implications in
various areas of astrophysics such as the study of the higher end of the
initial mass function, the star formation rate, and the mass-metallicity
relation of galaxies, among others. |
Kinetic power of quasars and statistical excess of MOJAVE superluminal
motions: The MOJAVE survey contains 101 quasars with a total of 354 observed radio
components that are different from the radio cores, among which 95% move with
apparent projected superluminal velocities with respect to the core, and 45%
have projected velocities larger than 10c (with a maximum velocity 60c).
Doppler boosting effects are analyzed to determine the statistics of the
superluminal motions. We integrate over all possible values of the Lorentz
factor the values of the kinetic energy corresponding to each component. The
calculation of the mass in the ejection is carried out by assuming the minimum
energy state. This kinetic energy is multiplied by the frequency at which the
portions of the jet fluid identified as "blobs" are produced. Hence, we
estimate the average total power released by the quasars in the form of kinetic
energy in the long term on pc-scales.
RESULTS. A selection effect in which both the core and the blobs of the
quasar are affected by huge Doppler-boosting enhancement increases the
probability of finding a jet ejected within 10 degrees of the line of sight
>~40 times above what one would expect for a random distribution of ejection,
which explains the ratios of the very high projected velocities given above.
The average total kinetic power of each MOJAVE quasar should be very high to
obtain this distribution: ~7E47 erg/s. This amount is much higher than previous
estimates of kinetic power on kpc-scales based on the analysis of cavities in
X-ray gas or radio lobes in samples of objects of much lower radio luminosity
but similar black hole masses. The kinetic power is a significant portion of
the Eddington luminosity, on the order of the bolometric luminosity, and
proportional on average to square root of the radio luminosity, although this
correlation might be induced by Malmquist-like bias. | Estimating black hole masses of blazars: Estimating black hole masses of blazars is still a big challenge. Because of
the contamination of jets, using the previously suggested size -- continuum
luminosity relation can overestimate the broad line region (BLR) size and black
hole mass for radio-loud AGNs, including blazars. We propose a new relation
between the BLR size and $H_{\beta}$ emission line luminosity and present
evidences for using it to get more accurate black hole masses of radio-loud
AGNs. For extremely radio-loud AGNs such as blazars with weak/absent emission
lines, we suggest to use the fundamental plane relation of their elliptical
host galaxies to estimate the central velocity dispersions and black hole
masses, if their velocity dispersions are not known but the host galaxies can
be mapped. The black hole masses of some well-known blazars, such as OJ 287, AO
0235+164 and 3C 66B, are obtained using these two methods and the M - $\sigma$
relation. The implications of their black hole masses on other related studies
are also discussed. |
Cosmological perturbations from a Spectator field during inflation: In this paper we will discuss analytically the perturbations created from a
slowly rolling subdominant spectator field which decays much before the end of
inflation. The quantum fluctuations of such a spectator field can seed
perturbations on very large scales and explain the temperature anisotropy in
the cosmic microwave background radiation with moderate non-Gaussianity,
provided the relevant modes leave the Hubble patch while the spectator is
slowly rolling. Furthermore, the perturbations are purely {\it adiabatic} since
the inflaton decay dominates and creates all the Standard Model degrees of
freedom. We will provide two examples for the spectator field potential, one
with a step function profile, and the other with an inflection point. In both
the cases we will compute higher order curvature perturbations, i.e.\ local
bispectrum and trispectrum, which can be constrained by the forthcoming Planck
data. | Standard Siren Cosmology with Gravitational Waves from Binary Black Hole
Mergers in Active Galaxy Nuclei: The detection of gravitational waves (GW) with an electromagnetic counterpart
enabled the first Hubble Constant $H_0$ measurement through the standard siren
method. Current constraints suggest that $\sim 20-80\%$ of LIGO/Virgo/KAGRA
(LVK) Binary Black Hole (BBH) mergers occur in Active Galactic Nuclei (AGN)
disks. The claim for a possible association of several BBH mergers with flaring
AGNs suggests that cosmological analyses using BBH and AGNs might be promising.
We explore standard siren analyses through a method that takes into account the
presence of background flaring AGNs, without requiring a unique host galaxy
identification, and apply it to realistic GW simulations. Depending on the
fraction of LVK BBHs that induce flares, we expect to constrain $H_0$ at the
$\sim 3.5-7\%$ ($\sim 2.5-5\%$) precision with $\sim 2$ years or $\sim 160$
events ($\sim 1$ year or $500$ events) of LVK at design (A+) sensitivity,
assuming that systematic BBH follow-up searches are performed. Assuming a more
restrictive $\Omega_{\rm m}$ prior and that at least $20\%$ of BBHs produces
detectable flares, we may reach a $3\%$ ($2\%$) precision in $H_0$ after 2 (1)
year of LVK at design (A+) sensitivity. We also show that a $\sim 5-10\%$
precision is possible with complete AGN catalogs and 1 year of LVK run, without
the need of time-critical follow-up observations. |
The Morphologies of Massive Galaxies at 1<z<3 in the CANDELS-UDS Field:
Compact Bulges, and the Rise and Fall of Massive Disks: We have used deep, HST, near-IR imaging to study the morphological properties
of the most massive galaxies at high z, modelling the WFC3/IR H-band images of
the ~200 galaxies in the CANDELS-UDS field with 1 < z_phot < 3, and stellar
masses M_star > 10^11 M_sun. We have used both single-Sersic and bulge+disk
models, have investigated the errors/biases introduced by uncertainties in the
background and the PSF, and have obtained formally-acceptable model fits to
>90% of the galaxies. Our results indicate that these massive galaxies at 1 < z
< 3 lie both on and below the local size-mass relation, with a median R_e~2.6
kpc, a factor of ~2.3 smaller than comparably-massive local galaxies. Moreover,
we find that bulge-dominated objects in particular show evidence for a growing
bimodality in the size-mass relation with increasing z, and by z > 2 the
compact bulges display effective radii a factor ~4 smaller than local
ellipticals of comparable mass. These trends appear to extend to the bulge
components of disk-dominated galaxies, and vice versa. We also find that, while
such massive galaxies at low z are bulge-dominated, at 1 < z < 2 they are
predominantly mixed bulge+disk systems, and by z > 2 they are mostly
disk-dominated. The majority of the disk-dominated galaxies are actively
forming stars, but this is also true for many of the bulge-dominated systems.
Interestingly, however, while most of the quiescent galaxies are
bulge-dominated, we find that a significant fraction (25-40%) of the most
quiescent galaxies have disk-dominated morphologies. Thus, while our results
show that the massive galaxy population is undergoing dramatic changes at this
crucial epoch, they also suggest that the physical mechanisms which quench
star-formation activity are not simply connected to those responsible for the
morphological transformation of massive galaxies into present-day giant
ellipticals. | Origin of the 12um Emission Across Galaxy Populations from WISE and SDSS
Surveys: We cross-matched Wide-field Infrared Survey Explorer (WISE) sources brighter
than 1 mJy at 12um with the Sloan Digital Sky Survey (SDSS) galaxy
spectroscopic catalog to produce a sample of ~10^5 galaxies at <z>=0.08, the
largest of its kind. This sample is dominated (70%) by star-forming (SF)
galaxies from the blue sequence, with total IR luminosities in the range
~10^8-10^12 L_sun. We identify which stellar populations are responsible for
most of the 12um emission. We find that most (~80%) of the 12um emission in SF
galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast,
the 12um emission in weak AGN (L[OIII]<10^7 L_sun) is produced by older stars,
with ages of ~1-3 Gyr. We find that L_[12um] linearly correlates with stellar
mass for SF galaxies. At fixed 12um luminosity, weak AGN deviate toward higher
masses since they tend to be hosted by massive, early-type galaxies with older
stellar populations. Star-forming galaxies and weak AGN follow different
L_[12um]-SFR (star formation rate) relations, with weak AGN showing excess 12um
emission at low SFR (~0.02-1 M_sun/yr). This is likely due to dust grains
heated by older stars. While the specific star formation rate (SSFR) of SF
galaxies is nearly constant, the SSFR of weak AGN decreases by ~3 orders of
magnitude, reflecting the very different star formation efficiencies between SF
galaxies and massive, early-type galaxies. Stronger type II AGN in our sample
(L_[OIII]>10^7 L_sun), act as an extension of massive SF galaxies, connecting
the SF and weak AGN sequences. This suggests a picture where galaxies form
stars normally until an AGN (possibly after a starburst episode) starts to
gradually quench the SF activity. We also find that 4.6-12um color is a useful
first-order indicator of SF activity in a galaxy when no other data are
available. |
21-cm Fluctuations from Charged Dark Matter: The epoch of the formation of the first stars, known as the cosmic dawn, has
emerged as a new arena in the search for dark matter. In particular, the first
claimed 21-cm detection exhibits a deeper global absorption feature than
expected, which could be caused by a low baryonic temperature, and has been
interpreted as a sign for electromagnetic interactions between baryons and dark
matter. This hypothesis has a striking prediction: large temperature
anisotropies sourced by the velocity-dependent cooling of the baryons. However,
in order to remain consistent with the rest of cosmological observations, only
part of the dark matter is allowed to be charged, and thus interactive. Here we
compute, for the first time, the 21-cm fluctuations caused by a charged
subcomponent of the dark matter, including both the pre- and post-recombination
evolution of all fluids. We find that, for the same parameters that can explain
the anomalous 21-cm absorption signal, any percent-level fraction of charged
dark matter would source novel 21-cm fluctuations with a unique acoustic
spectrum, and with an amplitude above any other known effects. These
fluctuations are uncorrelated with the usual adiabatic anisotropies, and would
be observable at high significance with interferometers such as LOFAR and HERA,
thus providing a novel probe of dark matter at cosmic dawn. | The CMB angular power spectrum via component separation: a study on
Planck data: We investigate the extent to which foreground cleaned CMB maps can be used to
estimate the cosmological parameters at small scales. We use the SMICA method,
a blind separation technique which works directly at the spectral level. In
this work we focus on the small scales of the CMB angular power spectrum, which
are chiefly affected by noise and extragalactic foregrounds, such as point
sources. We adapt SMICA to use only cross-spectra between data maps, thus
avoiding the noise bias. In this study, performed both on simulations and on
Planck 2015 data, we fit for extragalactic point sources by modeling them as
shot noise of two independent populations. In simulations we correctly recover
the point source emission law, and obtain a CMB angular power spectrum that has
an average foreground residual of one fifth of the CMB power at $\ell \geq$
2200. On Planck data, the recovered point source emission law corresponds to
external estimates, with some offsets at the highest and lowest frequencies,
possibly due to frequency decoherence of point sources. The CMB angular power
spectrum residuals are consistent with what we find in simulations. The
cosmological parameters obtained from the simulations and the data show offsets
up to 1$\sigma$ on average from their expected values. Biases on cosmological
parameters in simulations represent the expected level of bias in Planck data.
The results on cosmological parameters depend on the detail of the foreground
residual contamination in the spectrum, and need a tailored modeling of the
likelihood foreground model. |
Gravitational waves from an early matter era: We investigate the generation of gravitational waves due to the gravitational
instability of primordial density perturbations in an early matter-dominated
era which could be detectable by experiments such as LIGO and LISA. We use
relativistic perturbation theory to give analytic estimates of the tensor
perturbations generated at second order by linear density perturbations. We
find that large enhancement factors with respect to the naive second-order
estimate are possible due to the growth of density perturbations on sub-Hubble
scales. However very large enhancement factors coincide with a breakdown of
linear theory for density perturbations on small scales. To produce a
primordial gravitational wave background that would be detectable with LIGO or
LISA from density perturbations in the linear regime requires primordial
comoving curvature perturbations on small scales of order 0.02 for Advanced
LIGO or 0.005 for LISA, otherwise numerical calculations of the non-linear
evolution on sub-Hubble scales are required. | Quasar broad absorption line variability measurements using
reconstructions of un-absorbed spectra: We present a two-epoch Sloan Digital Sky Survey and Gemini/GMOS+William
Herschel Telescope/ISIS variability study of 50 broad absorption line quasars
of redshift range 1.9 < z < 4.2, containing 38 Si IV and 59 C IV BALs and
spanning rest-frame time intervals of approximately 10 months to 3.7 years. We
find that 35/50 quasars exhibit one or more variable BALs, with 58% of Si IV
and 46% of C IV BALs showing variability across the entire sample. On average,
Si IV BALs show larger fractional change in BAL pseudo equivalent width than C
IV BALs, as referenced to an unabsorbed continuum+emission-line spectrum
constructed using non-negative matrix factorisation. No correlation is found
between BAL variability and quasar luminosity, suggesting that ionizing
continuum changes do not play a significant role in BAL variability (assuming
the gas is in photoionization equilibrium with the ionizing continuum). A
subset of 14 quasars have one variable BAL from each of Si IV and C IV with
significant overlap in velocity space and for which variations are in the same
sense (strengthening or weakening) and which appear to be correlated (98%
confidence). We find examples of both appearing and disappearing BALs in
weaker/shallower lines with disappearance rates of 2.3% for C IV and 5.3% for
Si IV, suggesting average lifetimes of 142 and 43 years respectively. We
identify 5 objects in which the BAL is coincident with the broad emission-line,
but appears to cover only the continuum source. Assuming a clumpy inhomogeneous
absorber model and a typical size for the continuum source, we infer a maximum
cloud radius of 10^13 to 10^14 cm, assuming Eddington limited accretion. |
Hydrostatic Gas Constraints on Supermassive Black Hole Masses:
Implications for Hydrostatic Equilibrium and Dynamical Modelling in a Sample
of Early-Type Galaxies: We present new mass measurements for the supermassive black holes (SMBHs) in
the centres of three early-type galaxies. The gas pressure in the surrounding,
hot interstellar medium (ISM) is measured through spatially resolved
spectroscopy with the Chandra X-ray observatory, allowing the SMBH mass (Mbh)
to be inferred directly under the hydrostatic approximation. This technique
does not require calibration against other SMBH measurement methods and its
accuracy depends only on the ISM being close to hydrostatic, which is supported
by the smooth X-ray isophotes of the galaxies. Combined with results from our
recent study of the elliptical galaxy NGC4649, this brings to four the number
of galaxies with SMBHs measured in this way. Of these, three already have mass
determinations from the kinematics of either the stars or a central gas disc,
and hence join only a handful of galaxies with Mbh measured by more than one
technique. We find good agreement between the different methods, providing
support for the assumptions implicit in both the hydrostatic and the dynamical
models. The stellar mass-to-light ratios for each galaxy inferred by our
technique are in agreement with the predictions of stellar population synthesis
models assuming a Kroupa initial mass function (IMF). This concurrence implies
that no more than ~10-20% of the ISM pressure is nonthermal, unless there is a
conspiracy between the shape of the IMF and nonthermal pressure. Finally, we
compute Bondi accretion rates, finding that the two galaxies with the highest
rates exhibit little evidence of X-ray cavities, suggesting that the
correlation with the AGN jet power takes time to be established. | Neutral hydrogen in the post-reionization universe: The evolution of neutral hydrogen (HI) across redshifts is a powerful probe
of cosmology, large scale structure in the universe and the intergalactic
medium. Using a data-driven halo model to describe the distribution of HI in
the post-reionization universe ($z \sim $ 5 to 0), we obtain the best-fitting
parameters from a rich sample of observational data: low redshift 21-cm
emission line studies, intermediate redshift intensity mapping experiments, and
higher redshift Damped Lyman Alpha (DLA) observations. Our model describes the
abundance and clustering of neutral hydrogen across redshifts 0 - 5, and is
useful for investigating different aspects of galaxy evolution and for
comparison with hydrodynamical simulations. The framework can be applied for
forecasting future observations with neutral hydrogen, and extended to the case
of intensity mapping with molecular and other line transitions at intermediate
redshifts. |
Quadratic Isocurvature Cross-Correlation, Ward Identity, and Dark Matter: Sources of isocurvature perturbations and large non-Gaussianities include
field degrees of freedom whose vacuum expectation values are smaller than the
expansion rate of inflation. The inhomogeneities in the energy density of such
fields are quadratic in the fields to leading order in the inhomogeneity
expansion. Although it is often assumed that such isocurvature perturbations
and inflaton-driven curvature perturbations are uncorre- lated, this is not
obvious from a direct computational point of view due to the form of the
minimal gravitational interactions. We thus compute the irreducible
gravitational contributions to the quadratic isocurvature-curvature
cross-correlation. We find a small but non-decaying cross-correlation, which in
principle serves as a consistency prediction of this large class of
isocurvature perturbations. We apply our cross-correlation result to two dark
matter isocurvature perturbation scenarios: QCD axions and WIMPZILLAs. On the
technical side, we utilize a gravita- tional Ward identity in a novel manner to
demonstrate the gauge invariance of the computation. Furthermore, the detailed
computation is interpreted in terms of a soft-{\zeta} theorem and a
gravitational Ward identity. Finally, we also identify explicitly all the
counterterms that are necessary for renormalizing the isocurvature perturbation
composite operator in inflationary cosmological backgrounds. | The Lack of Diffuse, Nonthermal Hard X-ray Emission in the Coma Cluster:
The Swift BAT's Eye View: The Coma cluster of galaxies hosts the brightest radio halo known and has
therefore been the target of numerous searches for associated inverse Compton
(IC) emission, particularly at hard X-ray energies where the IC signal must
eventually dominate over thermal emission. The most recent search with the
Suzaku Hard X-ray Detector (HXD) failed to confirm previous IC detections with
RXTE and BeppoSAX, instead setting an upper limit 2.5 times below their
nonthermal flux. However, this discrepancy can be resolved if the IC emission
is very extended, beyond the scale of the cluster radio halo. Using
reconstructed sky images from the 58-month Swift BAT all sky survey, the
feasibility of such a solution is investigated. Building on Renaud et al., we
test and implement a method for extracting the fluxes of extended sources,
assuming specified spatial distributions. BAT spectra are jointly fit with an
XMM-Newton EPIC-pn spectrum derived from mosaic observations. We find no
evidence for large-scale IC emission at the level expected from the previously
detected nonthermal fluxes. For all nonthermal spatial distributions
considered, which span the gamut of physically reasonable IC models, we
determine upper limits for which the largest (most conservative) limit is
<4.2x10^{-12} erg/s/cm^2 (20-80 keV), which corresponds to a lower limit on the
magnetic field B>0.2uG. A nominal flux upper limit of <2.7x10^{-12} erg/s/cm^2,
with corresponding B>0.25uG, is derived for the most probable IC distribution
given the size of the radio halo and likely magnetic field radial profile. |
The Supernova that Destroyed a Protogalaxy: Prompt Chemical Enrichment
and Supermassive Black Hole Growth: The first primitive galaxies formed from accretion and mergers by z ~ 15, and
were primarily responsible for cosmological reionization and the chemical
enrichment of the early cosmos. But a few of these galaxies may have formed in
the presence of strong Lyman-Werner UV fluxes that sterilized them of H_2,
preventing them from forming stars or expelling heavy elements into the IGM
prior to assembly. At masses of 10^8 Ms and virial temperatures of 10^4 K,
these halos began to rapidly cool by atomic lines, perhaps forming 10^4 - 10^6
Ms Pop III stars and, later, the seeds of supermassive black holes. We have
modeled the explosion of a supermassive Pop III star in the dense core of a
line-cooled protogalaxy with the ZEUS-MP code. We find that the supernova (SN)
expands to a radius of ~ 1 kpc, briefly engulfing the entire galaxy, but then
collapses back into the potential well of the dark matter. Fallback fully mixes
the interior of the protogalaxy with metals, igniting a violent starburst and
fueling the rapid growth of a massive black hole at its center. The starburst
would populate the protogalaxy with stars in greater numbers and at higher
metallicities than in more slowly-evolving, nearby halos. The SN remnant
becomes a strong synchrotron source that can be observed with eVLA and eMERLIN
and has a unique signature that easily distinguishes it from less energetic SN
remnants. Such explosions, and their attendant starbursts, may well have marked
the birthplaces of supermassive black holes on the sky. | Leverage on small-scale primordial non-Gaussianity through
cross-correlations between CMB $E$-mode and $μ$-distortion anisotropies: Multi-field inflation models and non-Bunch-Davies vacuum initial conditions
both predict sizeable non-Gaussian primordial perturbations and anisotropic
$\mu$-type spectral distortions of the cosmic microwave background (CMB)
blackbody. While CMB anisotropies allow us to probe non-Gaussianity at
wavenumbers $k\simeq 0.05\,{\rm Mpc^{-1}}$, $\mu$-distortion anisotropies are
related to non-Gaussianity of primordial perturbation modes with much larger
wavenumbers, $k\simeq 740\,{\rm Mpc^{-1}}$. Through cross-correlations between
CMB and $\mu$-distortion anisotropies, one can therefore shed light on the
aforementioned inflation models. We investigate the ability of a future CMB
satellite imager like LiteBIRD to measure $\mu T$ and $\mu E$ cross-power
spectra between anisotropic $\mu$-distortions and CMB temperature and $E$-mode
polarization anisotropies in the presence of foregrounds, and derive LiteBIRD
forecasts on ${f_{\rm NL}^\mu(k\simeq 740\,{\rm Mpc^{-1}})}$. We show that $\mu
E$ cross-correlations with CMB polarization provide more constraining power on
$f_{\rm NL}^\mu$ than $\mu T$ cross-correlations in the presence of
foregrounds, and the joint combination of $\mu T$ and $\mu E$ observables adds
further leverage to the detection of small-scale primordial non-Gaussianity. We
find that LiteBIRD would detect ${f_{\rm NL}^\mu}=4500$ at $5\sigma$
significance after foreground removal, and achieve a minimum error of
${\sigma(f_{\rm NL}^\mu=0) \simeq 800}$ at 68\% CL by combining CMB temperature
and polarization. Due to the huge dynamic range of wavenumbers between CMB and
$\mu$-distortion anisotropies, such large $f^\mu_{\rm NL}$ values would still
be consistent with current CMB constraints in the case of very mild
scale-dependence of primordial non-Gaussianity. Anisotropic spectral
distortions thus provide a new path, complementary to CMB $B$-modes, to probe
inflation with LiteBIRD. |
Introducing the Photometric Maximum Likelihood Method: Galaxy Luminosity
Functions at z<1.2 in MUSYC-ECDFS: We present a new maximum likelihood method for the calculation of galaxy
luminosity functions from multi-band photometric surveys without spectroscopic
data. The method evaluates the likelihood of a trial luminosity function by
directly comparing the predicted distribution of fluxes in a multi-dimensional
photometric space to the observations, and thus does not require the
intermediate step of calculating photometric redshifts. We apply this algorithm
to ~27,000 galaxies with m_R<=25 in the MUSYC-ECDFS field, with a focus on
recovering the luminosity function of field galaxies at z<1.2. Our deepest LFs
reach M_r=-14 and show that the field galaxy LF deviates from a Schechter
function, exhibiting a steep upturn at intermediate magnitudes that is due to
galaxies of late spectral types. | The Dark Matter Density Profile of the Fornax Dwarf: We construct axisymmetric Schwarzschild models to measure the mass profile of
the local group dwarf galaxy Fornax. These models require no assumptions to be
made about the orbital anisotropy of the stars, as is the case for commonly
used Jeans models. We test a variety of parameterizations of dark matter
density profiles and find cored models with uniform density rho_c = (1.6 +/-
0.1) x 10^-2 M_sun pc^-3 fit significantly better than the cuspy halos
predicted by cold dark matter simulations. We also construct models with an
intermediate-mass black hole, but are unable to make a detection. We place a
1-sigma upper limit on the mass of a potential intermediate-mass black hole at
M_BH < 3.2 x 10^4 M_sun. |
Particle Physics and Astrophysics -- A whitepaper in response to a call
to the Astronomy and Astrophysics Community from the Committee on Astro2010
for State of the Profession Position Papers: We discuss some of the key science questions that are bringing particle
physicists and astrophysicists together, and comment on some of the cultural
and funding issues that have arisen as these two communities become
increasingly intertwined. | Prompt cusps and the dark matter annihilation signal: As the first dark matter objects gravitationally condense, a density cusp
forms immediately at every initial density maximum. Numerical simulations and
theoretical arguments suggest that these prompt cusps can survive until the
present day. We show that if dark matter is a thermally produced weakly
interacting massive particle, many thousands of prompt cusps with individual
masses similar to that of the Earth may be present in every solar mass of dark
matter. This radically alters predictions for the amount and spatial
distribution of dark matter annihilation radiation. The annihilation rate is
boosted by at least an order of magnitude compared to previous predictions,
both in the cosmological average and within galaxy-scale halos. Moreover, the
signal is predominantly boosted outside of the centers of galactic halos, so
alternative targets become significantly more attractive for indirect-detection
searches. For example, prompt cusps present new opportunities to test the dark
matter interpretation of the Galactic Center gamma-ray excess by searching for
similar spectral signatures in the isotropic gamma-ray background and
large-scale cosmic structure. |
VLT Spectropolarimetry of Broad Absorption Line QSOs: We present spectropolarimetry of 19 confirmed and 4 possible bright, southern
broad absorption line (BAL) quasars from the European Southern Observatory
(ESO) Very Large Telescope (VLT). A wide range of redshifts is covered in the
sample (from 0.9 to 3.4), and both low- and hi-ionization quasars are
represented, as well as radio-loud and radio-quiet BALQSOs. We continue to
confirm previously established spectropolarimetric properties of BALQSOs,
including the generally rising continuum polarization with shorter wavelengths
and comparatively large fraction with high broad-band polarization (6 of 19
with polarizations >2%). Emission lines are polarized less than or similar to
the continuum, except in a few unusual cases, and absorption troughs tend to
have higher polarizations. A search for correlations between polarization
properties has been done, identifying 2 significant or marginally significant
correlations. These are an increase in continuum polarization with decreasing
optical luminosity (increasing absolute B magnitude) and decreasing \ion{C}{4}
emission-line polarization with increased continuum polarization. | The Fermi blazars' divide based on the diagnostic of the SEDs peak
frequencies: We have studied the quasi-simultaneous Spectral Energy Distributions (SED) of
48 LBAS blazars, detected within the three months of the LAT Bright AGN Sample
(LBAS) data taking period, combining Fermi and Swift data with radio
NIR-Optical and hard-X/gamma-ray data. Using these quasi-simultaneous SEDs,
sampling both the low and the high energy peak of the blazars broad band
emission, we were able to apply a diagnostic tool based on the estimate of the
peak frequencies of the synchrotron (S) and Inverse Compton (IC) components.
Our analysis shows a Fermi blazars' divide based on the peak frequencies of the
SED. The robust result is that the Synchrotron Self Compton (SSC) region
divides in two the plane were we plot the peak frequency of the synchrotron SED
vs the typical Lorentz factor of the electrons most contributing to the
synchrotron emission and to the inverse Compton process. Objects within or
below this region, radiating likely via the SSC process, are
high-frequency-peaked BL Lac object (HBL), or low/intermediate-frequency peaked
BL Lac object (LBL/IBL). All of the IBLs/LBLs within or below the SSC region
are not Compton dominated. The objects lying above the SSC region, radiating
likely via the External radiation Compton (ERC) process, are Flat Spectrum
Radio Quasars and IBLs/LBLs. All of the IBLs/LBLs in the ERC region show a
significant Compton dominance. |
Next Generation Strong Lensing Time Delay Estimation with Gaussian
Processes: Strong gravitational lensing forms multiple, time delayed images of
cosmological sources, with the "focal length" of the lens serving as a
cosmological distance probe. Robust estimation of the time delay distance can
tightly constrain the Hubble constant as well as the matter density and dark
energy. Current and next generation surveys will find hundreds to thousands of
lensed systems but accurate time delay estimation from noisy, gappy lightcurves
is potentially a limiting systematic. Using a large sample of blinded
lightcurves from the Strong Lens Time Delay Challenge we develop and
demonstrate a Gaussian Process crosscorrelation technique that delivers an
average bias within 0.1% depending on the sampling, necessary for subpercent
Hubble constant determination. The fits are accurate (80% of them within 1 day)
for delays from 5-100 days and robust against cadence variations shorter than 6
days. We study the effects of survey characteristics such as cadence, season,
and campaign length, and derive requirements for time delay cosmology: in order
not to bias the cosmology determination by $0.5\sigma$, the mean time delay fit
accuracy must be better than 0.2%. | Probing the time variation of fine structure constant using galaxy
clusters and quintessence model: We explore a possible time variation of the fine structure constant ($\alpha
\equiv e^2/\hbar c$) using the Sunyaev-Zel'dovich effect measurements of galaxy
clusters along with their X-ray observations. Specifically, the ratio of the
integrated Compto-ionization parameter $Y_{SZ}D_A^2$ and its X-ray counterpart
$Y_X$ is used as an observable to constrain the bounds on the variation of
$\alpha$. Considering the violation of cosmic distance duality relation, this
ratio depends on the fine structure constant as $\sim \alpha^3$. We use the
quintessence model to provide the origin of $\alpha$ time variation. In order
to give a robust test on $\alpha$ variation, two galaxy cluster samples, the 61
clusters provided by the Planck collaboration and the 58 clusters detected by
the South Pole Telescope, are collected for analysis. Their X-ray observations
are given by the XMM-Newton survey. Our results give
$\zeta=-0.203^{+0.101}_{-0.099}$ for the Planck sample and
$\zeta=-0.043^{+0.165}_{-0.148}$ for the SPT sample, indicating that $\alpha$
is constant with redshift within $3\sigma$ and $1\sigma$ for the two samples,
respectively. |
The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: RSD measurement from the power spectrum and bispectrum
of the DR12 BOSS galaxies: We measure and analyse the bispectrum of the final, Data Release 12, galaxy
sample provided by the Baryon Oscillation Spectroscopic Survey, splitting by
selection algorithm into LOWZ and CMASS galaxies. The LOWZ sample contains
361\,762 galaxies with an effective redshift of $z_{\rm LOWZ}=0.32$, and the
CMASS sample 777\,202 galaxies with an effective redshift of $z_{\rm
CMASS}=0.57$. Combining the power spectrum, measured relative to the
line-of-sight, with the spherically averaged bispectrum, we are able to
constrain the product of the growth of structure parameter, $f$, and the
amplitude of dark matter density fluctuations, $\sigma_8$, along with the
geometric Alcock-Paczynski parameters, the product of the Hubble constant and
the comoving sound horizon at the baryon drag epoch, $H(z)r_s(z_d)$, and the
angular distance parameter divided by the sound horizon, $D_A(z)/r_s(z_d)$.
After combining pre-reconstruction RSD analyses of the power spectrum monopole,
quadrupole and bispectrum monopole; with post-reconstruction analysis of the
BAO power spectrum monopole and quadrupole, we find $f(z_{\rm
LOWZ})\sigma_8(z_{\rm LOWZ})=0.427\pm 0.056$, $D_A(z_{\rm LOWZ})/r_s(z_d)=6.60
\pm 0.13$, $H(z_{\rm LOWZ})r_s(z_d)=(11.55\pm 0.38)10^3\,{\rm kms}^{-1}$ for
the LOWZ sample, and $f(z_{\rm CMASS})\sigma_8(z_{\rm CMASS})=0.426\pm 0.029$,
$D_A(z_{\rm CMASS})/r_s(z_d)=9.39 \pm 0.10$, $H(z_{\rm
CMASS})r_s(z_d)=(14.02\pm 0.22)10^3\,{\rm kms}^{-1}$ for the CMASS sample. We
find general agreement with previous BOSS DR11 and DR12 measurements. Combining
our dataset with {\it Planck15} we perform a null test of General Relativity
(GR) through the $\gamma$-parametrisation finding
$\gamma=0.733^{+0.068}_{-0.069}$, which is $\sim2.7\sigma$ away from the GR
predictions. | Photospheric Magnitude Diagrams for Type II Supernovae: A Promising Tool
to Compute Distances: We develop an empirical color-based standardization for Type II supernovae
(SNe II), equivalent to the classical surface brightness method given in
Wesselink (1969). We calibrate it with SNe II with host galaxy distance
measured with Cepheids, and well-constrained shock breakout epoch and
extinction due to the host galaxy. We estimate the reddening with an analysis
of the B-V versus V-I color-color curves, similar to that of Natali et al.
(1994). With four SNe II meeting the above requirements, we build a
photospheric magnitude versus color diagram (similar to an HR diagram) with a
dispersion of 0.29 mag. We also show that when using time since shock breakout
instead of color as independent variable, the same standardization gives a
dispersion of 0.09 mag. Moreover, we show that the above time-based
standardization corresponds to the generalization of the standardized candle
method of Hamuy & Pinto (2002) for various epochs throughout the photospheric
phase. To test the new tool, we construct Hubble diagrams to different
subsamples of 50 low-redshift (cz<10^4 km s^-1) SNe II. For 13 SNe within the
Hubble flow (cz_CMB>3000 km s^-1) and with well-constrained shock breakout
epoch we obtain values of 68-69 km s^-1 Mpc^-1 for the Hubble constant, and an
mean intrinsic scatter of 0.12 mag or 6% in relative distances. |
Origins of weak lensing systematics, and requirements on future
instrumentation (or knowledge of instrumentation): The first half of this paper explores the origin of systematic biases in the
measurement of weak gravitational lensing. Compared to previous work, we expand
the investigation of PSF instability and fold in for the first time the effects
of non-idealities in electronic imaging detectors and imperfect galaxy shape
measurement algorithms. Together, these now explain the additive A(l) and
multiplicative M(l) systematics typically reported in current lensing
measurements. We find that overall performance is driven by a product of a
telescope/camera's *absolute performance*, and our *knowledge about its
performance*.
The second half of this paper propagates any residual shear measurement
biases through to their effect on cosmological parameter constraints. Fully
exploiting the statistical power of Stage IV weak lensing surveys will require
additive biases A<1.8e-12 and multiplicative biases M<4.0e-3. These can be
allocated between individual budgets in hardware, calibration data and
software, using results from the first half of the paper.
If instrumentation is stable and well-calibrated, we find extant shear
measurement software from GREAT10 already meet requirements on galaxies
detected at S/N=40. Averaging over a population of galaxies with a realistic
distribution of sizes, it also meets requirements for a 2D cosmic shear
analysis from space. If used on fainter galaxies or for 3D cosmic shear
tomography, existing algorithms would need calibration on simulations to avoid
introducing bias at a level similar to the statistical error. Requirements on
hardware and calibration data are discussed in more detail in a companion
paper. Our analysis is intentionally general, but is specifically being used to
drive the hardware and ground segment performance budget for the design of the
European Space Agency's recently-selected Euclid mission. | Constraints on the Cosmological parameters by means of the clusters mass
function: We present constraints on the values of $\Omega_m$, $n$, $\sigma_8$, obtained
from measurements of the X-ray luminosity function of galaxy clusters as
compiled in EMSS, RDCS and BCS galaxy cluster samples. The values obtained
$\Omega_m=0.25^{+0.15}_{-0.05}$, $n=-1^{+0.05}_{-0.05}$, and
$\sigma_8=0.8^{+0.1}_{-0.1}$ are in agreement with WMAP data. We then put
constraints on the quoted parameters and the dark-energy equation-of-state
parameter, $w$, using Chandra observations of 37 clusters with $<z>$=0.55
derived from 400 deg$^2$ ROSAT serendipitous survey and 49 brightest $z \simeq
0.05$ clusters detected in the All-Sky Survey. In the case of $\Lambda$CDM
model, we get $\Omega_m=0.25^{+0.1}_{-0.08}$ and
$\sigma_8=0.75^{+0.08}_{-0.05}$, while in the case of the $w$CDM model, we get
$\Omega_m=0.28^{+0.10}_{-0.10}$, $w=-1.25^{+0.30}_{-0.35}$, and
$\sigma_8=0.8^{+0.09}_{-0.09}$. Our results are consistent with those from
recent analyses of type Ia supernovae, cosmic microwave background
anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon
acoustic oscillations and cosmic shear. The improvement in data quality from
EMSS, RDCS, and BCS to Chandra observations leads to an improvement in the
constraints even if not of the same entity of the improvement in data. |
Cosmic Reionization after Planck: Could Quasars Do It All?: We assess a model of late cosmic reionization in which the ionizing
background radiation arises entirely from high redshift quasars and other
active galactic nuclei (AGNs). The low optical depth to Thomson scattering
reported by the Planck Collaboration pushes the redshift of instantaneous
reionization down to z=8.8^{+1.7}_{-1.4} and greatly reduces the need for
significant Lyman-continuum emission at very early times. We show that, if
recent claims of a numerous population of faint AGNs at z=4-6 are upheld, and
the high inferred AGN comoving emissivity at these epochs persists to higher,
z~10, redshifts, then active galaxies may drive the reionization of hydrogen
and helium with little contribution from normal star-forming galaxies. We
discuss an AGN-dominated scenario that satisfies a number of observational
constraints: the HI photoionization rate is relatively flat over the range
2<z<5, hydrogen gets fully reionized by z=5.7, and the integrated Thomson
scattering optical depth is tau=0.056, in agreement with measurements based on
the Lya opacity of the intergalactic medium (IGM) and cosmic microwave
background (CMB) polarization. It is a prediction of the model that helium gets
doubly reionized before redshift 4, the heat input from helium reionization
dominates the thermal balance of the IGM after hydrogen reionization, and z>5
AGNs provide a significant fraction of the unresolved X-ray background at 2
keV. Singly- and doubly-ionized helium contribute about 13% to tau, and the
HeIII volume fraction is already 50% when hydrogen becomes fully reionized. | Stable Large-Scale Perturbations in Interacting Dark-Energy Model: It is found that the evolutions of density perturbations on the super-Hubble
scales are unstable in the model with dark-sector interaction $Q$ proportional
to the energy density of cold dark matter (CDM) $\rho_m$ and constant equation
of state parameter of dark energy $w_d$. In this paper, to avoid the
instabilities, we suggest a new covariant model for the energy-momentum
transfer between DE and CDM. Then we show that the the large-scale
instabilities of curvature perturbations can be avoided in our model in the
universe filled only by DE and CDM. Furthermore, by including the additional
components of radiation and baryons, we calculate the dominant non-adiabatic
modes in the radiation era and find that the modes grow in the power law with
exponent at the order of unit. |
Cosmic Microwave Background Anisotropy numerical solution (CMBAns) I: An
introduction to $C_l$ calculation: Cosmological Boltzmann codes are often used by researchers for calculating
the CMB angular power spectra from different theoretical models, for
cosmological parameter estimation, etc. Therefore, the accuracy of a Boltzmann
code is of utmost importance. Different Markov Chain Monte Carlo based
parameter estimation algorithms typically require 10^3 - 10^4 iterations of
Boltzmann code. This makes the time complexity of such codes another critical
factor. In the last two decades, several Boltzmann packages, such as CMBFAST,
CAMB, CMBEasy, CLASS etc., have been developed. In this paper, we present a new
cosmological Boltzmann code, CMBAns, that can be used for accurate calculation
of the CMB power spectrum. At present, CMBAns is developed for a flat
background matrix. It is mostly written in the C language. However, we borrowed
the concept of class from C++. This gives researchers the flexibility to
develop their own independent package based on CMBAns, without an in-depth
understanding of the source code. We also develop multiple stand-alone
facilities which can be directly compiled and run on a given parameter set. In
this paper, we discuss all the mathematical formulation, approximation schemes,
integration methods etc., that are used in CMBAns. The package will be made
available through github for public use in the near future. | Optimal non-linear transformations for large scale structure statistics: Recently, several studies proposed non-linear transformations, such as a
logarithmic or Gaussianization transformation, as efficient tools to recapture
information about the (Gaussian) initial conditions. During non-linear
evolution, part of the cosmologically relevant information leaks out from the
second moment of the distribution. This information is accessible only through
complex higher order moments or, in the worst case, becomes inaccessible to the
hierarchy. The focus of this work is to investigate these transformations in
the framework of Fisher information using cosmological perturbation theory of
the matter field with Gaussian initial conditions. We show that at each order
in perturbation theory, there is a polynomial of corresponding order exhausting
the information on a given parameter. This polynomial can be interpreted as the
Taylor expansion of the maximally efficient "sufficient" observable in the
non-linear regime. We determine explicitly this maximally efficient observable
for local transformations. Remarkably, this optimal transform is essentially
the simple power transform with an exponent related to the slope of the power
spectrum; when this is -1, it is indistinguishable from the logarithmic
transform. This transform Gaussianizes the distribution, and recovers the
linear density contrast. Thus a direct connection is revealed between undoing
of the non-linear dynamics and the efficient capture of Fisher information. Our
analytical results were compared with measurements from the Millennium
Simulation density field. We found that our transforms remain very close to
optimal even in the deeply non-linear regime with \sigma^2 \sim 10. |
CMB $μ$ distortion from primordial gravitational waves: We propose a new mechanism of generating the $\mu$ distortion in cosmic
microwave background (CMB) originated from primordial gravitational waves. Such
$\mu$ distortion is generated by the damping of the temperature anisotropies
through the Thomson scattering, even on scales larger than that of Silk
damping. This mechanism is in sharp contrast with that from the primordial
curvature (scalar) perturbations, in which the temperature anisotropies mainly
decay by Silk damping effects. We estimate the size of the $\mu$ distortion
from the new mechanism, which can be used to constrain the amplitude of
primordial gravitational waves on smaller scales independently from the CMB
anisotropies, giving more wide-range constraint on their spectral index by
combining the amplitude from the CMB anisotropies. | The effect of pressure gradients on luminosity distance - redshift
relations: Inhomogeneous cosmological models have had significant success in explaining
cosmological observations without the need for dark energy. Generally, these
models imply inhomogeneous matter distributions alter the observable relations
that are taken for granted when assuming the Universe evolves according to the
standard Friedmann equations. Moreover, it has recently been shown that both
inhomogeneous matter and pressure distributions are required in both early and
late stages of cosmological evolution. These associated pressure gradients are
required in the early Universe to sufficiently describe void formation, whilst
late-stage pressure gradients stop the appearance of anomalous singularities.
In this paper we investigate the effect of pressure gradients on cosmological
observations by deriving the luminosity distance - redshift relations in
spherically symmetric, inhomogeneous spacetimes endowed with a perfect fluid.
By applying this to a specific example for the energy density distribution and
using various equations of state, we are able to explicitly show that pressure
gradients may have a non-negligble effect on cosmological observations. In
particular, we show that a non-zero pressure gradient can imply significantly
different residual Hubble diagrams for $z\lesssim1$ compared to when the
pressure is ignored. This paper therefore highlights the need to properly
consider pressure gradients when interpreting cosmological observations. |
The GREAT3 Challenge: The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is an image
analysis competition that aims to test algorithms to measure weak gravitational
lensing from astronomical images. The challenge started in October 2013 and
ends 30 April 2014. The challenge focuses on testing the impact on weak lensing
measurements of realistically complex galaxy morphologies, realistic point
spread function, and combination of multiple different exposures. It includes
simulated ground- and space-based data. The details of the challenge are
described in [15], and the challenge website and its leader board can be found
at http://great3challenge.info and
http://great3.projects.phys.ucl.ac.uk/leaderboard/, respectively. | A newly discovered DLA and associated Ly-alpha emission in the spectra
of the gravitationally lensed quasar UM 673A,B: The sightline to the brighter member of the gravitationally lensed quasar
pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z = 1.62650
which, because of its low redshift, has not been recognised before. Our high
quality echelle spectra of the pair, obtained with HIRES on the Keck I
telescope, show a drop in neutral hydrogen column density N(H I) by a factor of
at least 400 between UM 673A and B, indicating that the DLA's extent in this
direction is much less than the 2.7 kpc separation between the two sightlines
at z = 1.62650. By reassessing this new case together with published data on
other quasar pairs, we conclude that the typical size (radius) of DLAs at these
redshifts is R ~ (5 +/- 3) kpc, smaller than previously realised. Highly
ionized gas associated with the DLA is more extended, as we find only small
differences in the C IV absorption profiles between the two sightlines.
Coincident with UM 673B, we detect a weak and narrow Ly-alpha emission line
which we attribute to star formation activity at a rate SFR >~ 0.2 M_solar/yr.
The DLA in UM 673A is metal-poor, with an overall metallicity Z_DLA ~ 1/30
Z_solar, and has a very low internal velocity dispersion. It exhibits some
apparent peculiarities in its detailed chemical composition, with the elements
Ti, Ni, and Zn being deficient relative to Fe by factors of 2-3. The [Zn/Fe]
ratio is lower than those measured in any other DLA or Galactic halo star,
presumably reflecting somewhat unusual previous enrichment by stellar
nucleosynthesis. We discuss the implications of these results for the nature of
the galaxy hosting the DLA. |
The Megaparsec-Scale X-ray Jet of the BL Lac Object OJ287: We present an X-ray image of the BL Lacertae object OJ287 revealing a long
jet, curved by 55 degrees and extending 20", or 90 kpc from the nucleus. This
de-projects to >1 Mpc based on the viewing angle on parsec scales. Radio
emission follows the general X-ray morphology but extends even farther from the
nucleus. The upper limit to the isotropic radio luminosity, ~2E24 W/Hz, places
the source in the Fanaroff-Riley 1 (FR 1) class, as expected for BL Lac
objects. The spectral energy distribution indicates that the extended X-ray
emission is from inverse Compton scattering of cosmic microwave background
photons. In this case, the derived magnetic field is B ~ 5 microGauss, the
minimum electron energy is 7-40 m_e c^2, and the Doppler factor is delta ~ 8 in
a knot 8" from the nucleus. The minimum total kinetic power of the jet is
1-2E45 erg/s. Upstream of the bend, the width of the X-ray emission in the jet
is about half the projected distance from the nucleus. This implies that the
highly relativistic bulk motion is not limited to an extremely thin spine, as
has been proposed previously for FR 1 sources. The bending of the jet, the
deceleration of the flow from parsec to kiloparsec scales, and the knotty
structure can all be caused by standing shocks inclined by ~7 degrees to the
jet axis. Moving shocks resulting from major changes in the flow properties can
also reproduce the knotty structure, but such a model does not explain as many
of the observational details. | Stellar Populations and the Star Formation Histories of LSB Galaxies: I.
Optical and H-alpha Imaging: This paper presents optical and H-alpha imaging for a large sample of LSB
galaxies selected from the PSS-II catalogs (Schombert et. al 1992). As noted in
previous work, LSB galaxies span a range of luminosities (-10 > M_V > -20) and
sizes (0.3 kpc < R_V25 < 10 kpc), although they are consistent in their
irregular morphology. Their H-alpha luminosities (L(H-alpha) range from 10^36
to 10^41 ergs s^-1 (corresponding to a range in star formation, using canonical
prescriptions, from 10^-5 to 1 M_solar yr^-1). Although their optical colors
are at the extreme blue edge for galaxies, they are similar to the colors of
dwarf galaxies (van Zee 2001) and gas-rich irregulars (Hunter & Elmegreen
2006). However, their star formation rates per unit stellar mass are a factor
of ten less than other galaxies of the same baryonic mass, indicating that they
are not simply quiescent versions of more active star forming galaxies. This
paper presents the data, reduction techniques and new philosophy of data
storage and presentation. Later papers in this series will explore the stellar
population and star formation history of LSB galaxies using this dataset. |
Fitting functions on the cheap: the relative nonlinear matter power
spectrum: We propose an alternative approach to the construction of fitting functions
to the nonlinear matter power spectrum extracted from $N$-body simulations
based on the relative matter power spectrum $\delta(k,a)$, defined as the
fractional deviation in the absolute matter power spectrum produced by a target
cosmology away from a reference $\Lambda$CDM prediction. From the computational
perspective, $\delta(k,a)$ is fairly insensitive to the specifics of the
simulation settings, and numerical convergence at the 1%-level can be readily
achieved without the need for huge computing capacity. Furthermore,
$\delta(k,a)$ exhibits several interesting properties that enable a piece-wise
construction of the full fitting function, whereby component fitting functions
are sought for single-parameter variations and then multiplied together to form
the final product. Then, to obtain 1%-accurate absolute power spectrum
predictions for any target cosmology only requires that the community as a
whole invests in producing one single ultra-precise reference $\Lambda$CDM
absolute power spectrum, to be combined with the fitting function to produce
the desired result. To illustrate the power of this approach, we have
constructed the fitting function RelFit using only five relatively inexpensive
$w$CDM simulations (box length $L=256 h^{-1}$Mpc, $N=1024^3$ particles,
initialised at $z_i=49$). In a 6-parameter space spanning
$\{\omega_m,A_s,n_s,w,\omega_b,h\}$, the output relative power spectra of
RelFit are consistent with the predictions of the CosmicEmu emulator to 1% or
better for a wide range of cosmologies up to $k\simeq 10$/Mpc. Thus, our
approach could provide an inexpensive and democratically accessible route to
fulfilling the 1%-level accuracy demands of the upcoming generation of
large-scale structure probes, especially in the exploration of "non-standard"
or "exotic" cosmologies on nonlinear scales. | Disentangling dark energy and cosmic tests of gravity from weak lensing
systematics: We consider the impact of key astrophysical and measurement systematics on
constraints on dark energy and modifications to gravity on cosmic scales. We
focus on upcoming photometric "Stage III" and "Stage IV" large scale structure
surveys such as DES, SuMIRe, Euclid, LSST and WFIRST. We illustrate the
different redshift dependencies of gravity modifications compared to intrinsic
alignments, the main astrophysical systematic. The way in which systematic
uncertainties, such as galaxy bias and intrinsic alignments, are modelled can
change dark energy equation of state and modified gravity figures of merit by a
factor of four. The inclusion of cross-correlations of cosmic shear and galaxy
position measurements helps reduce the loss of constraining power from the
lensing shear surveys. When forecasts for Planck CMB and Stage IV surveys are
combined, constraints on the dark energy equation of state and modified gravity
model are recovered, relative to those from shear data with no systematic
uncertainties, if fewer than 36 free parameters in total are used to describe
the galaxy bias and intrinsic alignment models as a function of scale and
redshift. To facilitate future investigations, we also provide a fitting
function for the matter power spectrum arising from the phenomenological
modified gravity model we consider. |
Emission and Absorption Properties of Low-Mass Type 2 Active Galaxies
with XMM-Newton: We present XMM-Newton observations of four low-redshift Seyfert galaxies
selected to have low host luminosities (M_g>-20 mag) and small stellar velocity
dispersions (sigma_star<45 km/s), which are among the smallest stellar velocity
dispersions found in any active galaxies. These galaxies show weak or no broad
optical emission lines and have likely black hole masses <10^6 M_sun. Three out
of four objects were detected with >3sigma significance in ~25 ks exposures and
two observations had high enough signal-to-noise ratios for rudimentary
spectral analysis. We calculate hardness ratios (-0.43 to 0.01) for the three
detected objects and use them to estimate photon indices in the range of
Gamma=1.1-1.8. Relative to [OIII], the type 2 objects are X-ray faint in
comparison with Seyfert 1 galaxies, suggesting that the central engines are
obscured. We estimate the intrinsic absorption of each object under the
assumption that the [OIII] emission line luminosities are correlated with the
unabsorbed X-ray luminosity. The results are consistent with moderate
(N_H~10^22 cm^-2) absorption over the Galactic values in three of the four
objects, which might explain the non-detection of broad-line emission in
optical spectra. One object in our sample, SDSS J110912.40+612346.7, is a near
identical type 2 counterpart of the late-type Seyfert 1 galaxy NGC 4395. While
the two objects have very similar [OIII] luminosities, the type 2 object has an
X-ray/[OIII] flux ratio nearly an order of magnitude lower than NGC 4395. The
most plausible explanation for this difference is absorption of the primary
X-ray continuum of the type 2 object, providing an indication that
obscuration-based unified models of active galaxies can apply even at the
lowest luminosities seen among Seyfert nuclei, down to L_bol~10^40-10^41 erg/s. | Quenched Cold Accretion of a Large Scale Metal-Poor Filament due to
Virial Shocking in the Halo of a Massive z=0.7 Galaxy: Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a
remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI
absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile
components, and resides at an impact parameter of D=58 kpc from a bright, high
mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6
Gyr old, solar metallicity stellar population. Ionization models suggest the
majority of the structure is cold gas surrounding a shock heated cloud that is
kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV
and OVI absorption, suggestive of a conductive interface near the shock. The
deduced metallicities are consistent with the moderate in situ enrichment
relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the
HI complex as a metal-poor filamentary structure being shock heated as it
accretes into the halo of the galaxy. The data support the scenario of an early
formation period (z > 4) in which the galaxy was presumably fed by cold-mode
gas accretion that was later quenched via virial shocking by the hot halo such
that, by intermediate redshift, the cold filamentary accreting gas is
continuing to be disrupted by shock heating. Thus, continued filamentary
accretion is being mixed into the hot halo, indicating that the star formation
of the galaxy will likely remain quenched. To date, the galaxy and the HI
absorption complex provide some of the most compelling observational data
supporting the theoretical picture in which accretion is virial shocked in the
hot coronal halos of high mass galaxies. |
Searching for a preferred direction with Union2.1 data: A cosmological preferred direction was reported from the type Ia supernovae
(SNe Ia) data in recent years. We use the Union2.1 data to give a simple
classification of such studies for the first time. Because the maximum
anisotropic direction is independent of isotropic dark energy models, we adopt
two cosmological models ($\Lambda$CDM, $w$CDM) for the hemisphere comparison
analysis and $\Lambda$CDM model for dipole fit approach. In hemisphere
comparison method, the matter density and the equation of state of dark energy
are adopted as the diagnostic qualities in the $\Lambda$CDM model and $w$CDM
model, respectively. In dipole fit approach, we fit the fluctuation of distance
modulus. We find that there is a null signal for the hemisphere comparison
method, while a preferred direction ($b=-14.3^\circ \pm 10.1^\circ,
l=307.1^\circ \pm 16.2^\circ$) for the dipole fit method. This result indicates
that the dipole fit is more sensitive than the hemisphere comparison method. | The transient and the late time attractor tachyon dark energy: Can we
distinguish it from quintessence ?: The string inspired tachyon field can serve as a candidate of dark energy.
Its equation of state parameter $w$ varies from 0 to -1. In case of tachyon
field potential $V(\phi)\to 0$ slower(faster) than $1/\phi^2$ at infinity, dark
energy(dark matter) is a late time attractor. We investigate the tachyon dark
energy models under the assumption that $w$ is close to -1. We find that all
the models exhibit unique behavior around the present epoch which is exactly
same as that of the thawing quintessence. |
Testing Black Hole Jet Scaling Relations in Low Luminosity AGN: We present the results of the analysis of a sample of 17 low-luminosity (L_x
< 1e42 erg/s), radio loud AGNs in massive galaxies. The sample is extracted
from the SDSS database and it spans uniformly a wide range in optical [OIII]
emission line and radio luminosity, but within a narrow redshift range (0.05 <
z < 0.11) and a narrow super massive black hole mass range (~ 1e8 M_sun). For
these sources we measured core X-ray emission with the Chandra X-ray telescope
and radio emission with the VLA. Our main goal is to establish which emission
component, if any, can be regarded as the most reliable accretion/jet-power
estimator at these regimes. In order to do so, we studied the correlation
between emission line properties, radio luminosity, radio spectral slopes and
X-ray luminosity, as well as more complex multi-variate relations involving
black hole mass, such as the fundamental plane of black hole activity. We find
that 15 out of 17 sources of our sample can be classified as Low-Excitation
Galaxies (LEG) and their observed properties suggest X-ray and radio emission
to originate from the jet basis. We also find that X-ray emission does not
appear to be affected by nuclear obscuration and can be used as a reliable
jet-power estimator. More generally, X-ray, radio and optical emission appear
to be related, although no tight correlation is found. In accordance with a
number of recent studies of this class of objects these findings may be
explained by a lack of cold (molecular) gaseous structures in the innermost
region of these massive galaxies. | A New Catalog of HII Regions in M31: We present a new catalog of HII regions in M31. The full disk of the galaxy
is covered in a 2.2 deg^2 mosaic of 10 fields observed with the Mosaic Camera
as part of the Local Group Galaxies survey. We used HIIphot, a code for
automated photometry of HII regions, to identify the regions and measure their
fluxes and sizes. A 10 {\sigma} detection level was used to exclude diffuse gas
fluctuations and star residuals after continuum subtraction. That selection
limit may result in missing some faint HII regions, but our catalog of 3691 HII
regions is still complete to a luminosity of LH{\alpha} = 10^34 erg/s. This is
five times fainter than the only previous CCD-based study which contained 967
objects in the NE half of M31. We determined the H{\alpha} luminosity function
(LF) by fitting a power law to luminosities larger than LH{\alpha} = 10^36.7
and determined a slope of 2.52\pm0.07. The in-arm and inter-arm LFs peak at
different luminosities but they have similar bright-end slopes. The inter- arm
regions are less populated (40% of total detected regions) and constitute only
14% of the total luminosity of LH{\alpha} = 5.6 /times 10^40 erg/s (after
extinction correction and considering 65% contribution from diffused ionized
gas). A star formation rate of 0.44 M\odot/yr was estimated from the H{\alpha}
total luminosity; this value is consistent with the determination from the
Spitzer 8 {\mu}m image. We removed all known and potential planetary nebulae,
yet we found a double peaked luminosity function. The inter-arm older
population suggests a starburst between 15 and 20 million years ago. This
result is in agreement with UV studies of the star formation history in M31
which found a star formation rate decrease in the recent past. We found a fair
spatial correlation between the HII regions and stellar clusters in selected
star forming regions. Most of the matched regions lie within the arm regions. |
CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular
Gas Reservoirs: We report the detection of CO(1-0) emission in the strongly lensed
high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX
J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200),
using the Expanded Very Large Array and the Green Bank Telescope. We report
lensing-corrected CO(1-0) line luminosities of L'(CO) = 0.34-18.4 x 10^10 K
km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for
the sources in our sample. Based on CO line ratios relative to previously
reported observations in J>=3 rotational transitions and line excitation
modeling, we find that the CO(1-0) line strengths in our targets are consistent
with single, highly-excited gas components with constant brightness temperature
up to mid-J levels. We thus do not find any evidence for luminous extended, low
excitation, low surface brightness molecular gas components. These properties
are comparable to those found in z>4 quasars with existing CO(1-0)
observations. These findings stand in contrast to recent CO(1-0) observations
of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show
evidence for multiple excitation components, including some low-excitation gas.
These findings are consistent with the picture that gas-rich quasars and SMGs
represent different stages in the early evolution of massive galaxies. | A model independent constraint on the temporal evolution of the speed of
light: We present a new, model-independent method to reconstruct the temporal
evolution of the speed of light $c(z)$ using astronomical observations. After
validating our pipeline using mock datasets, we apply our method to the latest
BAO and supernovae observations, and reconstruct $c(z)$ in the redshift range
of $z\in[0,1.5]$. We find no evidence of a varying speed of light, although we
see some interesting features of $\Delta c(z)$, the fractional difference
between $c(z)$ and $c_0$ (the speed of light in SI), \eg, $\Delta c(z)<0$ and
$\Delta c(z)>0$ at $0.2\lesssim z\lesssim0.5$ and $0.8\lesssim z\lesssim1.3$,
respectively, although the significance of these features is currently far
below statistical importance. |
Revisiting a negative cosmological constant from low-redshift data: Persisting tensions between high-redshift and low-redshift cosmological
observations suggest the dark energy sector of the Universe might be more
complex than the positive cosmological constant of the $\Lambda$CDM model.
Motivated by string theory, wherein symmetry considerations make consistent AdS
backgrounds (\textit (i.e.) maximally symmetric spacetimes with a negative
cosmological constant) ubiquitous, we explore a scenario where the dark energy
sector consists of two components: a negative cosmological constant, with a
dark energy component with equation of state $w_{\phi}$ on top. We test the
consistency of the model against low-redshift Baryon Acoustic Oscillation and
Type Ia Supernovae distance measurements, assessing two alternative choices of
distance anchors: the sound horizon at baryon drag determined by the
\textit{Planck} collaboration, and the Hubble constant determined by the SH0ES
program. We find no evidence for a negative cosmological constant, and mild
indications for an effective phantom dark energy component on top. A model
comparison analysis reveals the $\Lambda$CDM model is favoured over our
negative cosmological constant model. While our results are inconclusive,
should low-redshift tensions persist with future data, it would be worth
reconsidering and further refining our toy negative cosmological constant model
by considering realistic string constructions. | UCDs as Probes of the Major and Minor Merger Histories of Galaxies: Two competing theories posit that Ultra Compact Dwarfs (UCDs) form either as
the stripped nuclei of dwarf galaxies or as giant globular clusters (GGCs)
associated with the largest globular cluster (GC) systems. By focussing on the
field and group environments where young UCDs may be most common, we have
discovered the first UCD that is clearly the result of recent (<4 Gyr ago)
stripping of a companion galaxy. However, we have also found a definitive case
of a multiple-UCD system created via GC formation processes, which are likely
associated with major galaxy mergers. We demonstrate that it is possible to
reliably distinguish the two types of UCD, thereby probing both the major and
minor merger histories of individual galaxies. |
The fate of high redshift massive compact galaxies in dense environments: Massive compact galaxies seem to be more common at high redshift than in the
local universe, especially in denser environments. To investigate the fate of
such massive galaxies identified at z~2 we analyse the evolution of their
properties in three cosmological hydrodynamical simulations that form
virialised galaxy groups of mass ~10^13 Msun hosting a central massive
elliptical/S0 galaxy by redshift zero. We find that at redshift ~2 the
population of galaxies with M_*> 2 10^10 Msun is diverse in terms of mass,
velocity dispersion, star formation and effective radius, containing both very
compact and relatively extended objects. In each simulation all the compact
satellite galaxies have merged into the central galaxy by redshift 0 (with the
exception of one simulation where one of such satellite galaxy survives).
Satellites of similar mass at z = 0 are all less compact than their high
redshift counterparts. They form later than the galaxies in the z = 2 sample
and enter the group potential at z < 1, when dynamical friction times are
longer than the Hubble time. Also, by z = 0 the central galaxies have increased
substantially their characteristic radius via a combination of in situ star
formation and mergers. Hence in a group environment descendants of compact
galaxies either evolve towards larger sizes or they disappear before the
present time as a result of the environment in which they evolve. Since the
group-sized halos that we consider are representative of dense environments in
the LambdaCDM cosmology, we conclude that the majority of high redshift compact
massive galaxies do not survive until today as a result of the environment. | Status of neutrino properties and future prospects - Cosmological and
astrophysical constraints: Cosmological observations are a powerful probe of neutrino properties, and in
particular of their mass. In this review, we first discuss the role of
neutrinos in shaping the cosmological evolution at both the background and
perturbation level, and describe their effects on cosmological observables such
as the cosmic microwave background and the distribution of matter at large
scale. We then present the state of the art concerning the constraints on
neutrino masses from those observables, and also review the prospects for
future experiments. We also briefly discuss the prospects for determining the
neutrino hierarchy from cosmology, the complementarity with laboratory
experiments, and the constraints on neutrino properties beyond their mass. |
Limits in late time conversion of cold dark matter into dark radiation: Structure formation creates high temperature and density regions in the
Universe that allow the conversion of matter into more stable states, with a
corresponding emission of relativistic matter and radiation. An example of such
a mechanism is the supernova event, that releases relativistic neutrinos
corresponding to 99% of the binding energy of remnant neutron star. We take
this phenomena as a starting point for an assumption that similar processes
could occur in the dark sector, where structure formation would generate a late
time conversion of cold dark matter into a relativistic form of dark matter. We
performed a phenomenological study about the limits of this conversion, where
we assumed a transition profile that is a generalized version of the neutrino
production in supernovae events. With this assumption, we obtained an
interesting modification for the constraint over the cold dark matter density.
We show that when comparing with the standard \Lambda CDM cosmology, there is
no preference for conversion, although the best fit is within 1\sigma\ from the
standard model best fit. The methodology and the results obtained qualify this
conversion hypothesis, from the large scale structure point of view, as a
viable and interesting model to be tested in the future with small scale data,
and mitigate discrepancies between observations at this scale and the pure cold
dark matter model. | Searching for Extremal Spots in Planck Lensing Maps: A great deal of attention has been given to the so-called Cold Spot in maps
of the cosmic microwave background (CMB) temperature. We present a similar
analysis, searching for extremal spots in the CMB lensing convergence and
lensing potential maps from the Planck 2018 data release. We perform a
multi-scale and multi-filter analysis using the first three members of the
Mexican-hat wavelet family to search for extremal features of different shapes
and sizes. Although an initial analysis appears to show the existence of some
extremal spots at scales below about 5 degree, we conclude, after marginalising
over all scales and filters, that no significant features are detected in the
lensing maps. We conclude that in terms of maxima and minima of various sizes,
the lensing data have similar statistical properties to Gaussian simulations. |
Preparing for low surface brightness science with the Vera C. Rubin
Observatory: A Comparison of Observable and Simulated Intracluster Light
Fractions: Intracluster Light (ICL) provides an important record of the interactions
galaxy clusters have undergone. However, we are limited in our understanding by
our measurement methods. To address this we measure the fraction of cluster
light that is held in the Brightest Cluster Galaxy and ICL (BCG+ICL fraction)
and the ICL alone (ICL fraction) using observational methods (Surface
Brightness Threshold-SB, Non-Parametric Measure-NP, Composite Models-CM,
Multi-Galaxy Fitting-MGF) and new approaches under development (Wavelet
Decomposition-WD) applied to mock images of 61 galaxy clusters (14<log10
M_200c/M_solar <14.5) from four cosmological hydrodynamical simulations. We
compare the BCG+ICL and ICL fractions from observational measures with those
using simulated measures (aperture and kinematic separations). The ICL
fractions measured by kinematic separation are significantly larger than
observed fractions. We find the measurements are related and provide equations
to estimate kinematic ICL fractions from observed fractions. The different
observational techniques give consistent BCG+ICL and ICL fractions but are
biased to underestimating the BCG+ICL and ICL fractions when compared with
aperture simulation measures. Comparing the different methods and algorithms we
find that the MGF algorithm is most consistent with the simulations, and CM and
SB methods show the smallest projection effects for the BCG+ICL and ICL
fractions respectively. The Ahad (CM), MGF and WD algorithms are best set up to
process larger samples, however, the WD algorithm in its current form is
susceptible to projection effects. We recommend that new algorithms using these
methods are explored to analyse the massive samples that Rubin Observatory's
Legacy Survey of Space and Time will provide. | Towards Precision Constraints on Gravity with the Effective Field Theory
of Large-Scale Structure: We compare analytical computations with numerical simulations for dark-matter
clustering, in general relativity and in the normal branch of DGP gravity
(nDGP). Our analytical frameword is the Effective Field Theory of Large-Scale
Structure (EFTofLSS), which we use to compute the one-loop dark-matter power
spectrum, including the resummation of infrared bulk displacement effects. We
compare this to a set of 20 COLA simulations at redshifts $z = 0$, $z=0.5$, and
$z =1$, and fit the free parameter of the EFTofLSS, called the speed of sound,
in both $\Lambda$CDM and nDGP at each redshift. At one-loop at $z = 0$, the
reach of the EFTofLSS is $k_{\rm reach}\approx 0.14 \, h { \rm Mpc^{-1}}$ for
both $\Lambda$CDM and nDGP. Along the way, we compare two different infrared
resummation schemes and two different treatments of the time dependence of the
perturbative expansion, concluding that they agree to approximately $1\%$ over
the scales of interest. Finally, we use the ratio of the COLA power spectra to
make a precision measurement of the difference between the speeds of sound in
$\Lambda$CDM and nDGP, and verify that this is proportional to the modification
of the linear coupling constant of the Poisson equation. |
Physical Properties of the Narrow-Line Region of Low-Mass Active
Galaxies: We present spectroscopic observations of 27 active galactic nuclei (AGN) with
some of the lowest black hole (BH) masses known. We use the high spectral
resolution and small aperture of our Keck data, taken with the Echellette
Spectrograph and Imager, to isolate the narrow-line regions (NLRs) of these
low-mass BHs. We investigate their emission-line properties and compare them
with those of AGN with higher-mass black holes. While we are unable to
determine absolute metallicities, some of our objects plausibly represent
examples of the low-metallicity AGN described by Groves et al. (2006), based on
their [N II]/H_alpha ratios and their consistency with the Kewley & Ellison
(2008) mass-metallicity relation. We find tentative evidence for steeper far-UV
spectral slopes in lower-mass systems. Overall, NLR emission lines in these
low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs,
such as increasing blueshifts and broadening with increasing ionization
potential. Additionally, we see evidence of an intermediate line region whose
intensity correlates with L/L_Edd, as seen in higher-mass AGN. We highlight the
interesting trend that, at least in these low-mass AGN, the [O III] equivalent
width (EW) is highest in symmetric NLR lines with no blue wing. This trend of
increasing [O III] EW with line symmetry could be explained by a high covering
factor of lower ionization gas in the NLR. In general, low-mass AGN preserve
many well-known trends in the structure of the NLR, while exhibiting steeper
ionizing continuum slopes and somewhat lower gas-phase metallicities. | Features of the inflaton potential and the power spectrum of
cosmological perturbations: We discuss features of the inflaton potential that can lead to a strong
enhancement of the power spectrum of curvature perturbations. We show that a
steep decrease of the potential induces an enhancement of the spectrum by
several orders of magnitude, which may lead to the production of primordial
black holes. The same feature can also create a distinctive oscillatory pattern
in the spectrum of gravitational waves generated through the scalar
perturbations at second order. We study the additive effect of several such
features. We analyse a simplified potential, but also discuss the possible
application to supergravity models. |
A tomographic test of cosmological principle using the JLA compilation
of type Ia supernovae: We test the cosmological principle by fitting a dipolar modulation of
distance modulus and searching for an evolution of this modulation with respect
to cosmological redshift. Based on a redshift tomographic method, we divide the
Joint Light-curve Analysis compilation of supernovae of type Ia into different
redshift bins, and employ a Markov-Chain Monte-Carlo method to infer the
anisotropic amplitude and direction in each redshift bin. However, we do not
find any significant deviations from the cosmological principle, and the
anisotropic amplitude is stringently constrained to be less than a few
thousandths at $95\%$ confidence level. | Constraints on changes in the proton-electron mass ratio using methanol
lines: We report Karl G. Jansky Very Large Array (VLA) absorption spectroscopy in
four methanol (CH$_3$OH) lines in the $z = 0.88582$ gravitational lens towards
PKS1830-211. Three of the four lines have very different sensitivity
coefficients $K_\mu$ to changes in the proton-electron mass ratio $\mu$; a
comparison between the line redshifts thus allows us to test for temporal
evolution in $\mu$. We obtain a stringent statistical constraint on changes in
$\mu$ by comparing the redshifted 12.179 GHz and 60.531 GHz lines, $[\Delta
mu/\mu] \leq 1.1 \times 10^{-7}$ ($2\sigma$) over $0 < z \leq 0.88582$, a
factor of $\approx 2.5$ more sensitive than the best earlier results. However,
the higher signal-to-noise ratio (by a factor of $\approx 2$) of the VLA
spectrum in the 12.179 GHz transition also indicates that this line has a
different shape from that of the other three CH$_3$OH lines (at $> 4\sigma$
significance). The sensitivity of the above result, and that of all earlier
CH$_3$OH studies, is thus likely to be limited by unknown systematic errors,
probably arising due to the frequency-dependent structure of PKS1830-211. A
robust result is obtained by combining the three lines at similar frequencies,
48.372, 48.377 and 60.531 GHz, whose line profiles are found to be in good
agreement. This yields the $2\sigma$ constraint $[\Delta \mu/\mu] \lesssim 4
\times 10^{-7}$, the most stringent current constraint on changes in $\mu$. We
thus find no evidence for changes in the proton-electron mass ratio over a
lookback time of $\approx 7.5$ Gyrs. |
Quasar Factor Analysis -- An Unsupervised and Probabilistic Quasar
Continuum Prediction Algorithm with Latent Factor Analysis: Since their first discovery, quasars have been essential probes of the
distant Universe. However, due to our limited knowledge of its nature,
predicting the intrinsic quasar continua has bottlenecked their usage. Existing
methods of quasar continuum recovery often rely on a limited number of
high-quality quasar spectra, which might not capture the full diversity of the
quasar population. In this study, we propose an unsupervised probabilistic
model, Quasar Factor Analysis (QFA), which combines factor analysis (FA) with
physical priors of the intergalactic medium (IGM) to overcome these
limitations. QFA captures the posterior distribution of quasar continua through
generatively modeling quasar spectra. We demonstrate that QFA can achieve the
state-of-the-art performance, $\sim 2\%$ relative error, for continuum
prediction in the Ly$\alpha$ forest region compared to previous methods. We
further fit 90,678 $2<\mathrm{z}<3.5$, SNR$>2$ quasar spectra from Sloan
Digital Sky Survey Data Release 16 and found that for $\sim 30\%$ quasar
spectra where the continua were ill-determined with previous methods, QFA
yields visually more plausible continua. QFA also attains $\lesssim 1\%$ error
in the 1D Ly$\alpha$ power spectrum measurements at $\mathrm{z}\sim 3$ and
$\sim 4\%$ in $\mathrm{z}\sim 2.4$. In addition, QFA determines latent factors
representing more physically motivated than PCA. We investigate the evolution
of the latent factors and report no significant redshift or luminosity
dependency except for the Baldwin effect. The generative nature of QFA also
enables outlier detection robustly; we showed that QFA is effective in
selecting outlying quasar spectra, including damped Ly$\alpha$ systems and
potential Type II quasar spectra. | Dipole leakage and low CMB multipoles: A number of studies of WMAP-7 have highlighted that the power at the low
multipoles in CMB power spectrum are lower than their theoretically predicted
values. Angular correlation between the orientations of these low multipoles
have also been discovered. While these observations may have cosmological
ramification, it is important to investigate possible observational artifacts
that can mimic them. The CMB dipole which is almost 550 times higher than the
quadrupole can get leaked to the higher multipoles due to the non-circular beam
of the CMB experiment. In this paper an analytical method has been developed
and simulations are carried out to study the effect of the non-circular beam on
power leakage from the dipole. It has been shown that the small, but
non-negligible power from the dipole can get transferred to the quadrupole and
the higher multipoles due to the non-circular beam. Simulations have also been
carried out for Planck scan strategy and comparative results between WMAP and
Planck have been presented in the paper. |
A scalar field dark matter model and its role in the large scale
structure formation in the Universe: In this work we present a model of dark matter based on scalar-tensor theory
of gravity. With this scalar field dark matter model we study the non-linear
evolution of the large scale structures in the universe. The equations that
govern the evolution of the scale factor of the universe are derived together
with the appropriate Newtonian equations to follow the non-linear evolution of
the structures. Results are given in terms of the power spectrum that gives
quantitative information on the large-scale structure formation. The initial
conditions we have used are consistent with the so called concordance
$\Lambda$CDM model. | Intensity mapping with SDSS/BOSS Lyman-alpha emission, quasars and their
Lyman-alpha forest: We investigate the large-scale structure of Lyman-alpha emission intensity in
the Universe at redshifts z=2-3.5 using cross-correlation techniques. Our Lya
emission samples are spectra of BOSS Luminous Red Galaxies from Data Release 12
with the best fit model galaxies subtracted. We cross-correlate the residual
flux in these spectra with BOSS quasars, and detect a positive signal on scales
1-15 Mpc/h. We identify and remove a source of contamination not previously
accounted for, due to the effects of quasar clustering on cross-fibre light.
Corrected, our quasar-Lya emission cross-correlation is 50 % lower than that
seen by Croft et al. for DR10, but still significant. Because only 3% of space
is within 15 Mpc/h of a quasar, the result does not fully explore the global
large-scale structure of Lya emission. To do this, we cross-correlate with the
Lya forest. We find no signal in this case. The 95% upper limit on the global
Lya mean surface brightness from Lya emission-Lya forest cross-correlation is
mu < 1.2x10^-22 erg/s/cm^2/A/arcsec^2 This null result rules out the scenario
where the observed quasar-Lya emission cross-correlation is primarily due to
the large scale structure of star forming galaxies, Taken in combination, our
results suggest that Lya emitting galaxies contribute, but quasars dominate
within 15 Mpc/h. A simple model for Lya emission from quasars based on
hydrodynamic simulations reproduces both the observed forest-Lya emission and
quasar-Lya emission signals. The latter is also consistent with extrapolation
of observations of fluorescent emission from smaller scales r < 1 Mpc. |
Baryon acoustic oscillations signature in the three-point angular
correlation function from the SDSS-DR12 quasar survey: The clustering properties of the Universe at large-scales are currently being
probed at various redshifts through several cosmological tracers and with
diverse statistical estimators. Here we use the three-point angular correlation
function (3PACF) to probe the baryon acoustic oscillation (BAO) features in the
quasars catalogue from the twelfth data release of the Sloan Digital Sky
Survey, with mean redshift z = 2.225, detecting the BAO imprint with a
statistical significance of 2.9{\sigma}, obtained using lognormal mocks.
Following a quasi model-independent approach for the 3PACF, we find the BAO
transversal signature for triangles with sides $\theta_1 = 1.0^\circ$ and
$\theta_2 = 1.5^\circ$ and the angle between them of $\alpha = 1.59 \pm 0.17$
rad, a value that corresponds to the angular BAO scale ${\theta}_{BAO} =
1.82^\circ \pm 0.21^\circ$ , in excellent agreement with the value found in a
recent work (${\theta}_{BAO} = 1.77^\circ \pm 0.31^\circ$ ) applying the 2PACF
to similar data. Moreover, we performed two type of tests: one to confirm the
robustness of the BAO signal in the 3PACF through random displacements in the
dataset, and the other to verify the suitability of our random samples, a null
test that in fact does not show any signature that could bias our results. | Precise Cosmological Constraints from BOSS Galaxy Clustering with a
Simulation-Based Emulator of the Wavelet Scattering Transform: We perform a reanalysis of the BOSS CMASS DR12 galaxy dataset using a
simulation-based emulator for the Wavelet Scattering Transform (WST)
coefficients. Moving beyond our previous works, which laid the foundation for
the first galaxy clustering application of this estimator, we construct a
neural net-based emulator for the cosmological dependence of the WST
coefficients and the 2-point correlation function multipoles, trained from the
state-of-the-art suite of \textsc{AbacusSummit} simulations combined with a
flexible Halo Occupation Distribution (HOD) galaxy model. In order to confirm
the accuracy of our pipeline, we subject it to a series of thorough internal
and external mock parameter recovery tests, before applying it to reanalyze the
CMASS observations in the redshift range $0.46<z<0.57$. We find that a joint
WST + 2-point correlation function likelihood analysis allows us to obtain
marginalized 1$\sigma$ errors on the $\Lambda$CDM parameters that are tighter
by a factor of $2.5-6$, compared to the 2-point correlation function, and by a
factor of $1.4-2.5$ compared to the WST-only results. This corresponds to a
competitive $0.9\%$, $2.3\%$ and $1\%$ level of determination for parameters
$\omega_c$, $\sigma_8$ $\&$ $n_s$, respectively, and also to a $0.7\%$ $\&$
$2.5 \%$ constraint on derived parameters h and $f(z)\sigma_8(z)$, in agreement
with the \textit{Planck} 2018 results. Our results reaffirm the constraining
power of the WST and highlight the exciting prospect of employing higher-order
statistics in order to fully exploit the power of upcoming Stage-IV
spectroscopic observations. |
Squeezed bispectrum and one-loop corrections in transient constant-roll
inflation: In canonical single-field inflation, the production of primordial black holes
(PBH) requires a transient violation of the slow-roll condition. The transient
ultra slow-roll inflation is an example of such scenarios, and more generally,
one can consider the transient constant-roll inflation. We investigate the
squeezed bispectrum in the transient constant-roll inflation and find that
Maldacena's consistency relation holds for a sufficiently long-wavelength mode,
whereas it is violated for modes around the peak scale for the non-attractor
case. We also demonstrate how the one-loop corrections are modified compared to
the case of the transient ultra slow-roll inflation, focusing on representative
one-loop terms originating from a time derivative of the second slow-roll
parameter in the cubic action. We find that the perturbativity requirement on
those terms does not rule out the production of PBH from the transient
constant-roll inflation. Therefore, it is a simple counterexample of the
recently claimed no-go theorem of PBH production from single-field inflation. | Cosmological implications and structure formation from a time varying
vacuum: We study the dynamics of the FLRW flat cosmological models in which the
vacuum energy varies with time, $\Lambda(t)$. In this model we find that the
main cosmological functions such as the scale factor of the universe and the
Hubble flow are defined in terms of exponential functions. Applying a joint
likelihood analysis of the recent supernovae type Ia data, the Cosmic Microwave
Background shift parameter and the Baryonic Acoustic Oscillations traced by the
Sloan Digital Sky Survey (SDSS) galaxies, we place tight constraints on the
main cosmological parameters of the $\Lambda(t)$ scenario. Also, we compare the
$\Lambda(t)$ model with the traditional $\Lambda$ cosmology and we find that
the former model provides a Hubble expansion which compares well with that of
the $\Lambda$ cosmology. However, the $\Lambda(t)$ scenario predicts stronger
small scale dynamics, which implies a faster growth rate of perturbations with
respect to the usual $\Lambda$-cosmology, despite the fact that they share the
same equation of state parameter. In this framework, we find that galaxy
clusters in the $\Lambda(t)$ model appear to form earlier than in the $\Lambda$
model. |
Planck early results XIV: ERCSC validation and extreme radio sources: Planck's all sky surveys at 30-857 GHz provide an unprecedented opportunity
to follow the radio spectra of a large sample of extragalactic sources to
frequencies 2-20 times higher than allowed by past, large area, ground-based
surveys. We combine the results of the Planck Early Release Compact Source
Catalog (ERCSC) with quasi-simultaneous ground-based observations, as well as
archival data, at frequencies below or overlapping Planck frequency bands, to
validate the astrometry and photometry of the ERCSC radio sources and study the
spectral features shown in this new frequency window opened by Planck. The
ERCSC source positions and flux density scales are found to be consistent with
the ground-based observations. We present and discuss the spectral energy
distributions (SEDs) of a sample of "extreme" radio sources to illustrate the
richness of the ERCSC for the study of extragalactic radio sources. Variability
is found to play a role in the unusual spectral features of some of these
sources. | New insight into EM radiation from spinning dust and its influence on
the Cosmic Microwave Background: Dust is ubiquitous in the Universe and its influence on the observed
Electromagnetic (EM) radiation needs to be correctly addressed. In recent years
it became clear that scattering of EM radiation from interstellar dust grains
could change the local properties of the observed Cosmic Microwave Background
(CMB) radiation. Here we consider the relevant processes of emission and
scattering of EM radiation from spinning dust particles, and discuss their
possible influence on the CMB. In particular, we show that scattered radiation
can establish a correlation between different spectral components of galactic
dipolar emission. This could explain the observed correlation between the CMB
and the 100-micron thermal emission form interstellar dust. Another important
property of CMB is related with its polarisation anisotropies, and the
observation of a cosmological B-mode. We show that scattering of CMB radiation
from dust grains in the presence of a static magnetic field could indeed create
a B-mode spectral component, which is very similar to that due to primordial
gravitational waves. This can be described by a kind of Cotton-Mutton effect on
the CMB radiation. |
More Evidence for an Oscillation Superimposed on the Hubble Flow: In a recent investigation evidence was presented for a low-level sinusoidal
oscillation superimposed on top of the Hubble flow. This oscillation was in
V$_{CMB}$, in a sample of type Ia Supernovae sources with accurate distances,
and it was found to have a wavelength close to 40 Mpc. It became easily visible
after the removal of several previously identified discrete velocity
components. Its amplitude like that of the Hubble velocity showed an increase
with distance, as would be expected for a constant-amplitude space oscillation.
Here we report that this oscillation is also present in distance clumping in
these sources, with the same wavelength, but in phase quadrature. The discrete
velocity components do not play a role in detecting the distance clumping
wavelength. Assuming that time proceeds from high cosmological redshift to low,
the blue-shifted velocity peaks, which represent the contraction stage of the
velocity oscillation, then lead the density peaks. With the discrete velocity
components removed we also find evidence for at least one other, weaker
velocity oscillation. It is found to have a wavelength similar to one reported
in density clumping by previous investigators. In those cases the source
samples were much larger. | Dissecting the size evolution of elliptical galaxies since z~1: puffing
up vs minor merging scenarios: We have explored the buildup of the local mass-size relation of elliptical
galaxies using two visually classified samples. At low redshift we compiled a
subsample of 2,656 elliptical galaxies from SDSS, whereas at higher redshift
(up to z~1) we extracted a sample of 228 object from the HST/ACS images of the
GOODS. All the galaxies in our study have spectroscopic data, allowing us to
determine the age and mass of the stellar component. Using the fossil record
information contained in the stellar populations of our local sample, we do not
find any evidence for an age segregation at a given stellar mass depending on
the size of the galaxies. At a fixed dynamical mass there is only a <9% size
difference in the two extreme age quartiles of our sample. Consequently, the
local evidence does not support a scenario whereby the present-day mass-size
relation has been progressively established via a bottom-up sequence, where
older galaxies occupy the lower part this relation, remaining in place since
their formation. We find a trend in size that is insensitive to the age of the
stellar populations, at least since z~1. This result supports the idea that the
stellar mass-size relation is formed at z~1, with all galaxies populating a
region which roughly corresponds to 1/2 of the present size distribution. The
fact that the evolution in size is independent of stellar age, together with
the absence of an increase in the scatter of the relationship with redshift
does not support the puffing up mechanism. The observational evidence, however,
can not reject at this stage the minor merging hypothesis. We have made an
estimation of the number of minor merger events necessary to bring the high-z
galaxies into the local relation compatible with the observed size evolution.
Since z=0.8, if the merger mass ratio is 1:3 we estimate ~3+-1 minor mergers
and if the ratio is 1:10 we obtain ~8+-2 events. |
The Observed Growth of Massive Galaxy Clusters III: Testing General
Relativity on Cosmological Scales: This is the third of a series of papers in which we derive simultaneous
constraints on cosmological parameters and X-ray scaling relations using
observations of the growth of massive, X-ray flux-selected galaxy clusters. Our
data set consists of 238 clusters drawn from the ROSAT All-Sky Survey, and
incorporates extensive follow-up observations using the Chandra X-ray
Observatory. Here we present improved constraints on departures from General
Relativity (GR) on cosmological scales, using the growth index, gamma, to
parameterize the linear growth rate of cosmic structure. Using the method of
Mantz et al. (2009a), we simultaneously and self-consistently model the growth
of X-ray luminous clusters and their observable-mass scaling relations,
accounting for survey biases, parameter degeneracies and systematic
uncertainties. We combine the cluster growth data with gas mass fraction, SNIa,
BAO and CMB data. This combination leads to a tight correlation between gamma
and sigma_8. Consistency with GR requires gamma~0.55. Under the assumption of
self-similar evolution and constant scatter in the scaling relations, and for a
flat LCDM model, we measure gamma(sigma_8/0.8)^6.8=0.55+0.13-0.10, with
0.79<sigma_8<0.89. Relaxing the assumptions on the scaling relations by
introducing two additional parameters to model possible evolution in the
normalization and scatter of the luminosity-mass relation, we obtain consistent
constraints on gamma that are only ~20% weaker than those above. Allowing the
dark energy equation of state, w, to take any constant value, we simultaneously
constrain the growth and expansion histories, and find no evidence for
departures from either GR or LCDM. Our results represent the most robust
consistency test of GR on cosmological scales to date. (Abridged) | Primordial gravitational waves for universality classes of pseudoscalar
inflation: Current bounds from the polarization of the CMB predict the scale-invariant
gravitational wave (GW) background of inflation to be out of reach for upcoming
GW interferometers. This prospect dramatically changes if the inflaton is a
pseudoscalar, in which case its generic coupling to any abelian gauge field
provides a new source of GWs, directly related to the dynamics of inflation.
This opens up new ways of probing the scalar potential responsible for cosmic
inflation. Dividing inflation models into universality classes, we analyze the
possible observational signatures. One of the most promising scenarios is
Starobinsky inflation, which may lead to observational signatures both in
direct GW detection as well as in upcoming CMB detectors. In this case, the
complementarity between the CMB and direct GW detection, as well as the
possibility of a multi-frequency analysis with upcoming ground and space based
GW interferometers, may provide a first clue to the microphysics of inflation. |
Model-independent determination of cosmic curvature based on Padé
approximation: Given observations of the standard candles and the cosmic chronometers, we
apply Pad\'{e} parameterization to the comoving distance and the Hubble
paramter to find how stringent the constraint is set to the curvature parameter
by the data. A weak informative prior is introduced in the modeling process to
keep the inference away from the singularities. Bayesian evidence for different
order of Pad\'{e} parameterizations is evaluated during the inference to select
the most suitable parameterization in light of the data. The data we used
prefer a parameterization form of comoving distance as $D_{01}(z)=\frac{a_0
z}{1+b_1 z}$ as well as a competitive form $D_{02}(z)=\frac{a_0 z}{1+b_1 z +
b_2 z^2}$. Similar constraints on the spatial curvature parameter are
established by those models and given the Hubble constant as a byproduct:
$\Omega_k = 0.25^{+0.14}_{-0.13}$ (68\% confidence level [C.L.]), $H_0 = 67.7
\pm 2.0$ km/s/Mpc (68\% C.L.) for $D_{01}$, and $\Omega_k = -0.01 \pm 0.13$
(68\% C.L.), $H_0 = 68.8 \pm 2.0$ km/s/Mpc (68\% C.L.) for $D_{02}$. The
evidence of different models demonstrates the qualitative analysis of the
Pad\'{e} parameterizations for the comoving distance. | Polarization of cluster radio halos with upcoming radio interferometers: Synchrotron radio halos at the center of merging galaxy clusters provide the
most spectacular and direct evidence of the presence of relativistic particles
and magnetic fields associated with the intracluster medium. The study of
polarized emission from radio halos has been shown to be extremely important to
constrain the properties of intracluster magnetic fields. However, detecting
this polarized signal is a very hard task with the current radio facilities.We
investigate whether future radio observatories, such as the Square Kilometer
Array (SKA) and its precursors and pathfinders, will be able to detect the
polarized emission of radio halos in galaxy clusters.On the basis of
cosmological magnetohydrodynamical simulations with initial magnetic fields
injected by active galactic nuclei, we predict the expected radio halo
polarized signal at 1.4 GHz. We compare these expectations with the limits of
current radio facilities and explore the potential of the forthcoming radio
interferometers to investigate intracluster magnetic fields through the
detection of polarized emission from radio halos.The resolution and sensitivity
values that are expected to be obtained in future sky surveys performed at 1.4
GHz using the SKA precursors and pathfinders (like APERTIF and ASKAP) are very
promising for the detection of the polarized emission of the most powerful
(L1.4GHz>10e25 Watt/Hz) radio halos. Furthermore, the JVLA have the potential
to already detect polarized emission from strong radio halos, at a relatively
low resolution.However, the possibility of detecting the polarized signal in
fainter radio halos (L1.4GHz~10e24 Watt/Hz) at high resolution requires a
sensitivity reachable only with SKA. |
I. Analysis of candidates for interacting galaxy clusters: Merging galaxy clusters allows to study the different mass components, dark
and baryonic, separately. Also their occurrence enables to test the
$\Lambda$CDM scenario and they could put constrains in the self interacting
cross section of the dark matter particle. It is necessary to perform an
homogeneous analysis of these systems. Hence, based in a recently presented
sample of candidates for interacting galaxy clusters, we present the analysis
of two of these cataloged systems. In this work, the first of a serie devoted
to characterize galaxy clusters in merger process, we perform a weak lensing
analysis of A1204 and A2029/2033 clusters to derive the total masses of each
identified interacting structures together with a dynamical study based on a
two-body model. We also describe the gas and the mass distributions in the
field through a lensing and an X-ray analysis. This is the first of a series of
works which will analyze these type of systems to characterize them. Both
merging clusters candidates do not show evidence of having had a recent merger
event. Nevertheless, there is dynamical evidence that these systems could be
interacting or could interact in the future. It is necessary to include more
constrains in order to improve the methodology to classify merging galaxy
clusters. Characterization of these clusters is important in order to
understand in deep the nature of these systems and their connection with
dynamical studies. | Primordial Perturbations from Multifield Inflation with Nonminimal
Couplings: Realistic models of particle physics include many scalar fields. These fields
generically have nonminimal couplings to the Ricci curvature scalar, either as
part of a generalized Einstein theory or as necessary counterterms for
renormalization in curved background spacetimes. We develop a gauge-invariant
formalism for calculating primordial perturbations in models with multiple
nonminimally coupled fields. We work in the Jordan frame (in which the
nonminimal couplings remain explicit) and identify two distinct sources of
entropy perturbations for such models. One set of entropy perturbations arises
from interactions among the multiple fields. The second set arises from the
presence of nonminimal couplings. Neither of these varieties of entropy
perturbations will necessarily be suppressed in the long-wavelength limit, and
hence they can amplify the curvature perturbation, $\zeta$, even for modes that
have crossed outside the Hubble radius. Models that overproduce long-wavelength
entropy perturbations endanger the close fit between predicted inflationary
spectra and empirical observations. |
Entropic cosmology: a unified model of inflation and late-time
acceleration: Holography is expected as one of the promising descriptions of quantum
general relativity. We present a model for a cosmological system involving two
holographic screens and find that their equilibrium exactly yields a standard
Friedmann-Robertson-Walker universe. We discuss its cosmological implications
by taking into account higher order quantum corrections and quantum nature of
horizon evaporation. We will show that this model could give rise to a
holographic inflation at high energy scales and realize a late-time
acceleration in a unified approach. We test our model from the SN Ia
observations and find it can give a nice fit to the data. | The lensing properties of subhaloes in massive elliptical galaxies in
sterile neutrino cosmologies: We use high-resolution hydrodynamical simulations run with the EAGLE model of
galaxy formation to study the differences between the properties of - and
subsequently the lensing signal from - subhaloes of massive elliptical galaxies
at redshift 0.2, in Cold and Sterile Neutrino (SN) Dark matter models. We focus
on the two 7 keV SN models that bracket the range of matter power spectra
compatible with resonantly-produced SN as the source of the observed 3.5 keV
line. We derive an accurate parametrisation for the subhalo mass function in
these two SN models relative to CDM, as well as the subhalo spatial
distribution, density profile, and projected number density and the dark matter
fraction in subhaloes. We create mock lensing maps from the simulated haloes to
study the differences in the lensing signal in the framework of subhalo
detection. We find that subhalo convergence is well described by a log-normal
distribution and that signal of subhaloes in the power spectrum is lower in SN
models with respect to CDM, at a level of 10 to 80 per cent, depending on the
scale. However, the scatter between different projections is large and might
make the use of power-spectrum studies on the typical scales of current lensing
images very difficult. Moreover, in the framework of individual detections
through gravitational imaging a sample of ~30 lenses with an average
sensitivity of M_sub=5x10^7M_sun would be required to discriminate between CDM
and the considered sterile neutrino models. |
Near-infrared observations of type Ia supernovae: The best known
standard candle for cosmology: We present an analysis of the Hubble diagram for 12 Type Ia supernovae (SNe
Ia) observed in the near-infrared J and H bands. We select SNe exclusively from
the redshift range 0.03 < z < 0.09 to reduce uncertainties coming from peculiar
velocities while remaining in a cosmologically well-understood region. All of
the SNe in our sample exhibit no spectral or B-band light-curve peculiarities
and lie in the B-band stretch range of 0.8-1.15. Our results suggest that SNe
Ia observed in the near-infrared (NIR) are the best known standard candles. We
fit previously determined NIR light-curve templates to new high-precision data
to derive peak magnitudes and to determine the scatter about the Hubble line.
Photometry of the 12 SNe is presented in the natural system. Using a standard
cosmology of (H_0, Omega_m, Lambda) = (70,0.27,0.73) we find a median J-band
absolute magnitude of M_J = -18.39 with a scatter of 0.116 and a median H-band
absolute magnitude of M_H = -18.36 with a scatter of 0.085. The scatter in the
H band is the smallest yet measured. We search for correlations between
residuals in the J- and H-band Hubble diagrams and SN properties, such as SN
colour, B-band stretch and the projected distance from host-galaxy centre. The
only significant correlation is between the J-band Hubble residual and the J-H
pseudo-colour. We also examine how the scatter changes when fewer points in the
near-infrared are used to constrain the light curve. With a single point in the
H band taken anywhere from 10 days before to 15 days after B-band maximum light
and a prior on the date of H-band maximum set from the date of B-band maximum,
we find that we can measure distances to an accuracy of 6%. The precision of
SNe Ia in the NIR provides new opportunities for precision measurements of both
the expansion history of the universe and peculiar velocities of nearby
galaxies. | Phenomenology of Large Scale Structure in scalar-tensor theories: joint
prior covariance of $w_{\textrm{DE}}$, $Σ$ and $μ$ in Horndeski: Ongoing and upcoming cosmological surveys will significantly improve our
ability to probe the equation of state of dark energy, $w_{\rm DE}$, and the
phenomenology of Large Scale Structure. They will allow us to constrain
deviations from the $\Lambda$CDM predictions for the relations between the
matter density contrast and the weak lensing and the Newtonian potential,
described by the functions $\Sigma$ and $\mu$, respectively. In this work, we
derive the theoretical prior for the joint covariance of $w_{\rm DE}$, $\Sigma$
and $\mu$, expected in general scalar-tensor theories with second order
equations of motion (Horndeski gravity), focusing on their time-dependence at
certain representative scales. We employ Monte-Carlo methods to generate large
ensembles of statistically independent Horndeski models, focusing on those that
are physically viable and in broad agreement with local tests of gravity, the
observed cosmic expansion history and the measurement of the speed of
gravitational waves from a binary neutron star merger. We identify several
interesting features and trends in the distribution functions of $w_{\rm DE}$,
$\Sigma$ and $\mu$, as well as in their covariances; we confirm the high degree
of correlation between $\Sigma$ and $\mu$ in scalar-tensor theories. The
derived prior covariance matrices will allow us to reconstruct jointly $w_{\rm
DE}$, $\Sigma$ and $\mu$ in a non-parametric way. |
On the source of Faraday rotation in the jet of the radio galaxy 3C120: The source of Faraday rotation in the jet of the radio galaxy 3C120 is
analyzed through Very Long Baseline Array observations carried out between 1999
and 2007 at 86, 43, 22, 15, 12, 8, 5, 2, and 1.7 GHz. Comparison of
observations from 1999 to 2001 reveals uncorrelated changes in the linear
polarization of the underlying jet emission and the Faraday rotation screen:
while the rotation measure (RM) remains constant between approximately 2 and 5
mas from the core, the RM-corrected electric vector position angles (EVPAs) of
two superluminal components are rotated by almost 90 degrees when compared to
other components moving through similar jet locations. On the other hand, the
innermost 2 mas experiences a significant change in RM -- including a sign
reversal -- but without variations in the RM-corrected EVPAs. Similarly,
observations in 2007 reveal a double sign reversal in RM along the jet, while
the RM-corrected EVPAs remain perpendicular to the jet axis. Although the
observed coherent structure and gradient of the RM along the jet supports the
idea that the Faraday rotation is produced by a sheath of thermal electrons
that surrounds the emitting jet, the uncorrelated changes in the RM and
RM-corrected EVPAs indicate that the emitting jet and the source of Faraday
rotation are not closely connected physically and have different configurations
for the magnetic field and/or kinematical properties. Furthermore, the
existence of a region of enhanced RM whose properties remain constant over
three years requires a localized source of Faraday rotation, favoring a model
in which a significant fraction of the RM originates in foreground clouds. | The evolution of Brightest Cluster Galaxies in a hierarchical universe: We investigate the evolution of Brightest Cluster Galaxies (BCGs) from
redshift z~1.6 to z~0. We use the semi-analytic model of Croton et al. (2006)
with a new spectro-photometric model based on the Maraston (2005) stellar
populations and a new recipe for the dust extinction. We compare the model
predictions of the K-band luminosity evolution and the J-K, V-I and I-K colour
evolution with a series of datasets, including Collins et al. (Nature, 2009)
who argued that semi-analytic models based on the Millennium simulation cannot
reproduce the red colours and high luminosity of BCGs at z>1. We show instead
that the model is well in range of the observed luminosity and correctly
reproduces the colour evolution of BCGs in the whole redshift range up to
z~1.6. We argue that the success of the semi-analytic model is in large part
due to the implementation of a more sophisticated spectro-photometric model. An
analysis of the model BCGs shows an increase in mass by a factor ~2 since z~1,
and star formation activity down to low redshifts. While the consensus
regarding BCGs is that they are passively evolving, we argue that this
conclusion is affected by the degeneracy between star formation history and
stellar population models used in SED-fitting, and by the inefficacy of
toy-models of passive evolution to capture the complexity of real galaxies,
expecially those with rich merger histories like BCGs. Following this argument,
we also show that in the semi-analytic model the BCGs show a realistic mix of
stellar populations, and that these stellar populations are mostly old. In
addition, the age-redshift relation of the model BCGs follows that of the
universe, meaning that given their merger history and star formation history,
the ageing of BCGs is always dominated by the ageing of their stellar
populations. In a LambdaCDM universe, we define such evolution as "passive in
the hierarchical sense". |
Is Cosmological Constant Needed in Higgs Inflation?: The detection of B-mode shows a very powerful constraint to theoretical
inflation models through the measurement of the tensor-to-scalar ratio $r$.
Higgs boson is the most likely candidate of the inflaton field. But usually,
Higgs inflation models predict a small value of $r$, which is not quite
consistent with the recent results from BICEP2. In this paper, we explored
whether a cosmological constant energy component is needed to improve the
situation. And we found the answer is yes. For the so-called Higgs chaotic
inflation model with a quadratic potential, it predicts $r\approx 0.2$,
$n_s\approx0.96$ with e-folds number $N\approx 56$, which is large enough to
overcome the problems such as the horizon problem in the Big Bang cosmology.
The required energy scale of the cosmological constant is roughly $\Lambda \sim
(10^{14} \text{GeV})^2 $, which means a mechanism is still needed to solve the
fine-tuning problem in the later time evolution of the universe, e.g. by
introducing some dark energy component. | Primordial vorticity and gradient expansion: The evolution equations of the vorticities of the electrons, ions and photons
in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by
combining the general relativistic gradient expansion and the drift
approximation within the Adler-Misner-Deser decomposition. The vorticity
transfer between the different species is discussed in this novel framework and
a set of general conservation laws, connecting the vorticities of the
three-component plasma with the magnetic field intensity, is derived. After
demonstrating that a source of large-scale vorticity resides in the spatial
gradients of the geometry and of the electromagnetic sources, the total
vorticity is estimated to lowest order in the spatial gradients and by
enforcing the validity of the momentum constraint. By acknowledging the current
bounds on the tensor to scalar ratio in the (minimal) tensor extension of the
$\Lambda$CDM paradigm the maximal comoving magnetic field induced by the total
vorticity turns out to be, at most, of the order of $10^{-37}$ G over the
typical comoving scales ranging between 1 and 10 Mpc. While the obtained
results seem to be irrelevant for seeding a reasonable galactic dynamo action,
they demonstrate how the proposed fully inhomogeneous treatment can be used for
the systematic scrutiny of pre-decoupling plasmas beyond the conventional
perturbative expansions. |
Uncovering strong MgII absorbing galaxies: Imaging below the Lyman limit: The nature of the galaxies that give rise to absorption lines, such as damped
Lyman-alpha systems (DLAs) or strong MgII lines, in quasar spectra is difficult
to investigate in emission. Taking advantage of the total absorption of the QSO
light bluewards of the Lyman limit of two DLAs at z>3.4, we look for the
continuum emission from intervening galaxies at z~2 that are identified via
strong metal absorption lines. The MgII absorbers have equivalent width large
enough to be potential DLA systems. Deep images are obtained with the FOcal
Reducer and Spectrograph (FORS1) on the Very Large Telescope for the fields
towards SDSS J110855+120953 and SDSS J140850+020522. These quasars have MgII
absorption lines at z=1.87 (W_r(MgII)=2.46 A) and z=1.98 (W_r(MgII)=1.89 A),
respectively, and each QSO has two intervening higher redshift DLAs at z>3. The
U and R bands of FORS1 lie blue and redwards of the Lyman limit of the
background DLAs, allowing us to search for emission from the foreground
galaxies directly along the lines of sight to the QSOs. No galaxies are found
close to the sight line of the QSO to a point source limit of U_AB=28.0. In
both fields, the closest objects lie at an impact parameter of 5 arcsec
corresponding to 40 kpc in projection at z=2, and have typical colours of star
forming galaxies at that redshift. However, the currently available data do not
allow us to confirm if the galaxies lie at the same redshifts as the absorption
systems. A more extended structure is visible in the SDSS J14085+020522 field
at an impact parameter of 0.8 arcsec or 7 kpc. If these objects are at z~2
their luminosities are 0.03-0.04 L* in both fields. The star formation rates
estimated from the UV flux are 0.5-0.6 M_sun yr^-1. (Abbreviated). | Phase-space shapes of clusters and rich groups of galaxies: Clusters and groups of galaxies are highly aspherical, with shapes
approximated by nearly prolate ellipsoids of revolution. An equally fundamental
property is the shape of these objects in velocity space which is the
anisotropy of the global velocity dispersion tensor. Here we make use of
kinematical data comprising around 600 nearby clusters and rich groups of
galaxies from the SDSS to place constraints on the phase-space shapes of these
objects, i.e. their shapes in both position and velocity space. We show that
the line of sight velocity dispersion normalised by a mass dependent velocity
scale correlates with the apparent elongation, with circular (elongated)
clusters exhibiting an excessive (decremental) normalised velocity dispersion.
This correlation holds for dynamically young or old clusters and, therefore, it
originates from projecting their intrinsic phase-space shapes rather than from
dynamical evolution. It signifies that clusters are preferentially prolate not
only in position space, but also in velocity space. The distribution of the
axial ratios in position space is found to be well approximated by a Gaussian
with a mean 0.66+/-0.01 and a dispersion 0.07+/-0.008. The velocity ellipsoids
representing the shapes in velocity space are more spherical, with a mean axial
ratio of 0.78+/-0.03. This finding has important implications for mass
measurements based on the line of sight velocity dispersion profiles in
individual clusters. For typical axial ratios of the velocity ellipsoids in the
analysed cluster sample, systematic errors on the mass estimates inferred from
the line of sight velocity dispersions become comparable to statistical
uncertainties for galaxy clusters with as few as 40 spectroscopic redshifts. |
Model-independent test of the FLRW metric, the flatness of the Universe,
and non-local measurement of $H_0r_\mathrm{d}$: Using measurements of $H(z)$ and $d_\mathrm{A}(z)$ from the Baryon
Oscillation Spectroscopic Survey (BOSS) DR12 and luminosity distances from the
Joint Lightcurve Analysis (JLA) compilation of supernovae (SN), we measure $H_0
r_\mathrm{d}$ without any model assumption. Our measurement of $H_0
r_\mathrm{d} = $($10033.20^{+333.10}_{-371.81}$ (SN) $\pm$ 128.19 (BAO)) km
s$^{-1}$ is consistent with Planck constrains for the flat {\Lambda}CDM model.
We also report that higher expansion history rates $h(z)$ (among the
possibilities) as well as lower-bound values of $H_0 r\mathrm{d}$ result in
better internal consistency among the independent data (H(z)rd and
$d_\mathrm{A}(z)/r_\mathrm{d}$ from BAO at $z=0.32$ and z=0.57 and
$d_\mathrm{L}$ from JLA) we used in this work. This can be interpreted as an
interesting and independent support of Planck cosmology without using any
cosmic microwave background data. We then combine these observables to test the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) metric and the flatness of the
Universe in a model-independent way at two redshifts, namely 0.32 and 0.57, by
introducing a new diagnostic for flat-FLRW, $\Theta(z)$, which only depends on
observables of BAO and SN data. Our results are consistent with a flat-FLRW
Universe within $2{\sigma}$. | Laboratory atomic transition data for precise optical quasar absorption
spectroscopy: Quasar spectra reveal a rich array of important astrophysical information
about galaxies which intersect the quasar line of sight. They also enable tests
of the variability of fundamental constants over cosmological time and
distance-scales. Key to these endeavours are the laboratory frequencies,
isotopic and hyperfine structures of various metal-ion transitions. Here we
review and synthesize the existing information about these quantities for 43
transitions which are important for measuring possible changes in the
fine-structure constant, alpha, using optical quasar spectra, i.e. those of Na,
Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the information
currently missing that precludes more transitions being used. We present an
up-to-date set of coefficients, q, which define the sensitivity of these
transitions to variations in alpha. New calculations of isotopic structures and
q coefficients are performed for SiII and TiII, including SiII 1808 and TiII
1910.6/1910.9 for the first time. Finally, simulated absorption-line spectra
are used to illustrate the systematic errors expected if the isotopic/hyperfine
structures are omitted from profile fitting analyses.
To ensure transparency, repeatability and currency of the data and
calculations, we supply a comprehensive database as Supporting Information.
This will be updated as new measurements and calculations are performed. |
Lyman-alpha emission properties of simulated galaxies: interstellar
medium structure and inclination effects: [abridged] Aims. The aim of this paper is to assess the impact of the
interstellar medium (ISM) physics on Lyman-alpha (Lya) radiation transfer and
to quantify how galaxy orientation with respect to the line of sight alters
observational signatures. Methods. We compare the results of Lya radiation
transfer calculations through the ISM of a couple of idealized galaxy
simulations with different ISM models. Results. First, the small-scale
structuration of the ISM plays a determinant role in shaping a galaxys Lya
properties.The artificially warm, and hence smooth, ISM of G1 yields an escape
fraction of 50 percent at the Lya line center, and produces symmetrical
double-peak profiles. On the contrary, in G2, most young stars are embedded in
thick star-forming clouds, and the result is a 10 times lower escape fraction.
G2 also displays a stronger outflowing velocity field, which favors the escape
of red-shifted photons, resulting in an asymmetric Lya line. Second, the Lya
properties of G2 strongly depend on the inclination at which it is observed:
From edge-on to face-on, the line goes from a double-peak profile with an
equivalent width of -5 Angstrom to a 15 times more luminous red-shifted
asymmetric line with EW 90 Angstrom. Conclusions. Lya radiation transfer
calculations can only lead to realistic properties in simulations where
galaxies are resolved into giant molecular clouds, putting these calculations
out of reach of current large scale cosmological simulations. Finally, we find
inclination effects to be much stronger for Lya photons than for continuum
radiation. This could potentially introduce severe biases in the selection
function of narrow-band Lya emitter surveys, which could indeed miss a
significant fraction of the high-z galaxy population. | On accretion of dark energy onto black- and worm-holes: We review some of the possible models that are able to describe the current
Universe which point out the future singularities that could appear. We show
that the study of the dark energy accretion onto black- and worm-holes
phenomena in these models could lead to unexpected consequences, allowing even
the avoidance of the considered singularities. We also review the debate about
the approach used to study the accretion phenomenon which has appeared in
literature to demonstrate the advantages and drawbacks of the different points
of view. We finally suggest new lines of research to resolve the shortcomings
of the different accretion methods. We then discuss future directions for new
possible observations that could help choose the most accurate model. |
A Population of X-ray Weak Quasars: PHL 1811 Analogs at High Redshift: We report the results from Chandra and XMM-Newton observations of a sample of
10 type 1 quasars selected to have unusual UV emission-line properties (weak
and blueshifted high-ionization lines; strong UV Fe emission) similar to those
of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were
identified by the Sloan Digital Sky Survey at high redshift (z~2.2); eight are
radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811
analogs are notably X-ray weak by a mean factor of ~13. These sources lack
broad absorption lines and have blue UV/optical continua, suggesting they are
intrinsically X-ray weak. However, their average X-ray spectrum appears to be
harder than those of typical quasars, which may indicate the presence of heavy
intrinsic X-ray absorption. Our radio-quiet PHL 1811 analogs support a
connection between an X-ray weak spectral energy distribution and PHL 1811-like
UV emission lines; this connection provides an economical way to identify X-ray
weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the
radio-quiet quasar population is estimated to be < 1.2%. We have investigated
correlations between relative X-ray brightness and UV emission-line properties
for a sample combining radio-quiet PHL 1811 analogs, PHL 1811, and typical type
1 quasars. These correlation analyses suggest that PHL 1811 analogs may have
extreme wind-dominated broad emission-line regions. Observationally,
radio-quiet PHL 1811 analogs appear to be a subset (~30%) of radio-quiet
weak-line quasars. The existence of a subset of quasars in which
high-ionization "shielding gas" covers most of the BELR, but little more than
the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two
radio-intermediate PHL 1811 analogs are X-ray bright. One of them appears to
have jet-dominated X-ray emission, while the nature of the other remains
unclear. | The XMM-LSS catalogue: X-ray sources and associated multiwavelength
data. Version II: We present the final release of the multi-wavelength XMM-LSS data
set,covering the full survey area of 11.1 square degrees, with X-ray data
processed with the latest XMM-LSS pipeline version. The present publication
supersedes the Pierre et al.(2007) catalogue pertaining to the initial 5 square
degrees. We provide X-ray source lists in the customary energy bands (0.5-2 and
2-10 keV) for a total of 6721 objects in the deep full-exposure catalogue and
5572 in the 10ks-limited one, above a detection likelihood of 15 in at least
one band. We also provide a multiwavelength catalogue, cross-correlating our
list with IR, NIR, optical and UV catalogues. Customary data products (X-ray
FITS images, CFHTLS and SWIRE thumbnail images) are made available together
with our interactively queriable database in Milan, while a static snapshot of
the catalogues will be supplied to CDS, as soon as final acceptance is
completed. |
Full-Sky Lensing Reconstruction of 21 cm Intensity Maps: Weak gravitational lensing of the 21 cm radiation is expected to be an
important cosmological probe for post-reionization physics. We investigate the
reconstruction of the matter density perturbations using a quadratic minimum
variance estimator. The next generation of line intensity mapping (LIM) surveys
such as HIRAX and CHIME will cover a larger sky fraction, which requires one to
account for the curvature in the sky. Thus, we extend the plane-parallel
flat-sky formalism for lensing reconstruction to account for a full-sky survey
using the Spherical Fourier-Bessel (SFB) expansion. Using the HIRAX 21 cm
survey as a basis, we make predictions for lensing-reconstruction noise in our
formalism and compare our results with the predictions from the plane-parallel
formalism. We find agreement with the plane-parallel noise power spectrum at
small scales and a significant deviation at scales $L\lesssim \ell_{\rm
res}-k_{\rm eq}R$ where $R$ is the radius of the shell volume, $k_{\rm eq}$ is
the wavenumber for matter-radiation equality, and $\ell_{\rm res}$ is the
angular resolution scale. Furthermore, we derive the SFB flat-sky
reconstruction noise and compare it with the full-sky SFB case as well as the
plane-parallel case, finding minor deviations from the full-sky noise due to
sphericity. We also determine that, in the absence of non-Gaussian statistics
of the intensity field but accounting for foregrounds, the signal-to-noise
ratio (SNR) for $C_\ell^{\phi\phi}$ using our SFB estimator increases by 107%.
This shows that accounting for the curved sky in LIM weak lensing will be
crucial for large-scale cosmology. | The Empirical Case For 10 GeV Dark Matter: In this article, I summarize and discuss the body of evidence which has
accumulated in favor of dark matter in the form of approximately 10 GeV
particles. This evidence includes the spectrum and angular distribution of
gamma rays from the Galactic Center, the synchrotron emission from the Milky
Way's radio filaments, the diffuse synchrotron emission from the Inner Galaxy
(the "WMAP Haze") and low-energy signals from the direct detection experiments
DAMA/LIBRA, CoGeNT and CRESST-II. This collection of observations can be
explained by a relatively light dark matter particle with an annihilation cross
section consistent with that predicted for a simple thermal relic (sigma v ~
10^-26 cm^3/s) and with a distribution in the halo of the Milky Way consistent
with that predicted from simulations. Astrophysical explanations for the gamma
ray and synchrotron signals, in contrast, have not been successful in
accommodating these observations. Similarly, the phase of the annual modulation
observed by DAMA/LIBRA (and now supported by CoGeNT) is inconsistent with all
known or postulated modulating backgrounds, but are in good agreement with
expectations for dark matter scattering. This scenario is consistent with all
existing indirect and collider constraints, as well as the constraints placed
by CDMS. Consistency with xenon-based experiments can be achieved if the
response of liquid xenon to very low-energy nuclear recoils is somewhat
suppressed relative to previous evaluations, or if the dark matter possesses
different couplings to protons and neutrons. |
Testing Primordial Black Holes with multi-band observations of the
stochastic gravitational wave background: The mass distribution of Primordial Black Holes (PBHs) is affected by drops
in the pressure of the early Universe plasma. For example, events in the
standard model of particle physics, such as the $W^\pm/Z^0$ decoupling, the
quark-hadron transition, the muon and pion becoming non-relativistic, and the
annihilation of electrons and positrons, cause a suppression in the Equation of
State parameter and leave peaks in the PBH mass function around
$10^{-6},\,2,\,60$, and $10^6\, M_\odot$, respectively, in the case of a nearly
scale-invariant primordial power spectrum. The superposition of unresolved
mergers of such PBHs results in a stochastic gravitational-wave background
(SGWB) that covers a wide range of frequencies and can be tested with future
gravitational wave (GW) detectors. In this paper, we discuss how its spectral
shape can be used to infer properties about inflation, the thermal history of
the Universe, and the dynamics of binary formation in dense halos encoded in
their merger rate formula. Although many of these physical effects are
degenerate within the sensitivity of a single detector, they can be
disentangled by the simultaneous observation of the SGWB at different
frequencies, highlighting the importance of multi-frequency observations of GWs
to characterize the physics of PBHs from the early to the late time Universe. | The Promise of Future Searches for Cosmic Topology: The shortest distance around the Universe through us is unlikely to be much
larger than the horizon diameter if microwave background anomalies are due to
cosmic topology. We show that observational constraints from the lack of
matched temperature circles in the microwave background leave many
possibilities for such topologies. We evaluate the detectability of microwave
background multipole correlations for sample cases. Searches for topology
signatures in observational data over the large space of possible topologies
pose a formidable computational challenge. |
Linear perturbations in Galileon gravity models: We study the cosmology of Galileon modified gravity models in the linear
perturbation regime. We derive the fully covariant and gauge invariant
perturbed field equations using two different methods, which give consistent
results, and solve them using a modified version of the {\tt CAMB} code. We
find that, in addition to modifying the background expansion history and
therefore shifting the positions of the acoustic peaks in the cosmic microwave
background (CMB) power spectrum, the Galileon field can cluster strongly from
early times, and causes the Weyl gravitational potential to grow, rather than
decay, at late times. This leaves clear signatures in the low-$l$ CMB power
spectrum through the modified integrated Sachs-Wolfe effect, strongly enhances
the linear growth of matter density perturbations and makes distinctive
predictions for other cosmological signals such as weak lensing and the power
spectrum of density fluctuations. The quasi-static approximation is shown to
work quite well from small to the near-horizon scales. We demonstrate that
Galileon models display a rich phenomenology due to the large parameter space
and the sensitive dependence of the model predictions on the Galileon
parameters. Our results show that some Galileon models are already ruled out by
present data and that future higher significance galaxy clustering, ISW and
lensing measurements will place strong constraints on Galileon gravity. | Reviewing the observational evidence against long-lived spiral arms in
galaxies: We review Foyle et al. (2011) previous results, by applying a Fourier
intensity phases method to a nine object sample of galaxies. It was found that
two of the objects (NGC 628 and NGC 5194), with strong two-arm patterns,
present positive evidence for long-lived spirals. Only one of the objects (NGC
3627) shows the contrary evidence. As determined by an analysis of resolved
mass maps, the rest of the objects can not be included in the analysis because
they belong to flocculent and multi-arm type of spiral arms, which are not
described by density wave theory. |
Low-Metallicity Star Formation in High-Redshift Galaxies at z~8: Based on the recent very deep near-infrared imaging of the Hubble Ultra Deep
Field with WFC3 on the Hubble Space Telescope, five groups published most
probable samples of galaxies at z~8, selected by the so-called dropout method
or photometric redshift; e.g., Y_105-dropouts (Y_105-J_125 > 0.8). These
studies are highly useful for investigating both the early star formation
history of galaxies and the sources of cosmic re-ionization. In order to better
understand these issues, we carefully examine if there are low-$z$ interlopers
in the samples of z~8 galaxy candidates. We focus on the strong emission-line
galaxies at z~2 in this paper. Such galaxies may be selected as Y_105-dropouts
since the [OIII] lambda 5007 emission line is redshifted into the J_125-band.
We have found that the contamination from such low-$z$ interlopers is
negligibly small. Therefore, all objects found by the five groups are free from
this type of contamination. However, it remains difficult to extract real z~8
galaxies because all the sources are very faint and the different groups have
found different candidates. With this in mind, we construct a robust sample of
eight galaxies at z~8 from the objects found by the five groups: each of these
eight objects has been selected by at least two groups. Using this sample, we
discuss their UV continuum slope. We also discuss the escape fraction of
ionizing photons adopting various metallicities. Our analysis suggests that
massive stars forming in low-metallicity gas (Z~5 \times 10^-4 Z_sun) can be
responsible for the completion of cosmic re-ionization if the escape fraction
of ionizing continuum from galaxies is as large as 0.5, and this is consistent
with the observed blue UV continua. | Halo Contraction Effect in Hydrodynamic Simulations of Galaxy Formation: The condensation of gas and stars in the inner regions of dark matter halos
leads to a more concentrated dark matter distribution. While this effect is
based on simple gravitational physics, the question of its validity in
hierarchical galaxy formation has led to an active debate in the literature. We
use a collection of several state-of-the-art cosmological hydrodynamic
simulations to study the halo contraction effect in systems ranging from dwarf
galaxies to clusters of galaxies, at high and low redshift. The simulations are
run by different groups with different codes and include hierarchical merging,
gas cooling, star formation, and stellar feedback. We show that in all our
cases the inner dark matter density increases relative to the matching
simulation without baryon dissipation, at least by a factor of several. The
strength of the contraction effect varies from system to system and cannot be
reduced to a simple prescription. We present a revised analytical model that
describes the contracted mass profile to an rms accuracy of about 10%. The
model can be used to effectively bracket the response of the dark matter halo
to baryon dissipation. The halo contraction effect is real and must be included
in modeling of the mass distribution of galaxies and galaxy clusters. |
The Size of Local Bispectrum and Trispectrum in a Non-Minimal Inflation: Focusing on the local type primordial non-Gaussianities, we study the
bispectrum and trispectrum during a non-minimal slow-roll inflation. We use the
so-called $\delta N$ formalism to investigate the super-horizon evolution of
the primordial perturbations in this setup. Firstly we obtain the main
equations of the model and introduce the framework of the $\delta N$ formalism
for this case. Then we give analytical expressions for the nonlinear parameters
describing the non-Gaussianity in the slow-roll approximation. We analyze the
bispectrum by its non-linear parameter, $f_{NL}$. Furthermore, we calculate
$\tau_{NL}$ and $g_{NL}$ which are non-linear parameters characterizing the
amplitude of trispectrum. Finally, by adopting a quadratic form for both the
potential and non-minimal coupling (NMC) function, we test our setup in the
light of Planck2015 data and constrain the model parameters space. Although the
non-Gaussianity parameters are so small in this setup, this model is consistent
with recent observation. We extend our analysis to see the situation in the
Einstein frame and compare the results in these two frames. | New perspectives on the BOSS small-scale lensing discrepancy for the
Planck $Λ$CDM Cosmology: We investigate the abundance, small-scale clustering and galaxy-galaxy
lensing signal of galaxies in the Baryon Oscillation Spectroscopic Survey
(BOSS). To this end, we present new measurements of the redshift and stellar
mass dependence of the lensing properties of the galaxy sample. We analyse to
what extent models assuming the Planck18 cosmology fit to the number density
and clustering can accurately predict the small-scale lensing signal. In
qualitative agreement with previous BOSS studies at redshift $z \sim 0.5$ and
with results from the Sloan Digital Sky Survey, we find that the expected
signal at small scales ($0.1 < r_{\rm p} < 3 \, h^{-1} \mathrm{Mpc}$) is higher
by $\sim 25\%$ than what is measured. Here, we show that this result is
persistent over the redshift range $0.1 < z < 0.7$ and for galaxies of
different stellar masses. If interpreted as evidence for cosmological
parameters different from the Planck CMB findings, our results imply $S_8 =
\sigma_8 \sqrt{\Omega_{\rm m} / 0.3} = 0.744 \pm 0.015$, whereas $S_8 = 0.832
\pm 0.013$ for Planck18. However, in addition to being in tension with CMB
results, such a change in cosmology alone does not accurately predict the
lensing amplitude at larger scales. Instead, other often neglected systematics
like baryonic feedback or assembly bias are likely contributing to the
small-scale lensing discrepancy. We show that either effect alone, though, is
unlikely to completely resolve the tension. Ultimately, a combination of the
two effects in combination with a moderate change in cosmological parameters
might be needed. |
Spectral Synthesis of Star-forming Galaxies in the Near-Infrared: The near-infrared spectral region is becoming a very useful wavelength range
to detect and quantify the stellar population of galaxies. Models are
developing to predict the contribution of TP-AGB stars, that should dominate
the NIR spectra of populations 0.3 to 2 Gyr old. When present in a given
stellar population, these stars leave unique signatures that can be used to
detect them unambiguously. However, these models have to be tested in a
homogeneous database of star-forming galaxies, to check if the results are
consistent with what is found from different wavelength ranges. In this work we
performed stellar population synthesis on the nuclear and extended regions of
23 star-forming galaxies to understand how the star-formation tracers in the
near-infrared can be used in practice. The stellar population synthesis shows
that for the galaxies with strong emission in the NIR, there is an important
fraction of young/intermediate population contributing to the spectra, which is
probably the ionisation source in these galaxies. Galaxies that had no emission
lines measured in the NIR were found to have older average ages and less
contribution of young populations. Although the stellar population synthesis
method proved to be very effective to find the young ionising population in
these galaxies, no clear correlation between these results and the NIR spectral
indexes were found. Thus, we believe that, in practice, the use of these
indexes is still very limited due to observational limitations. | FIRST-2MASS Red Quasars: Transitional Objects Emerging from the Dust: We present a sample of 120 dust-reddened quasars identified by matching radio
sources detected at 1.4 GHz in the FIRST survey with the near-infrared 2MASS
catalog and color-selecting red sources. Optical and/or near-infrared
spectroscopy provide broad wavelength sampling of their spectral energy
distributions that we use to determine their reddening, characterized by
E(B-V). We demonstrate that the reddening in these quasars is best-described by
SMC-like dust. This sample spans a wide range in redshift and reddening (0.1 <
z < 3, 0.1 < E(B-V) < 1.5), which we use to investigate the possible
correlation of luminosity with reddening. At every redshift, dust-reddened
quasars are intrinsically the most luminous quasars. We interpret this result
in the context of merger-driven quasar/galaxy co-evolution where these reddened
quasars are revealing an emergent phase during which the heavily obscured
quasar is shedding its cocoon of dust prior to becoming a "normal" blue quasar.
When correcting for extinction, we find that, depending on how the parent
population is defined, these red quasars make up < 15-20% of the luminous
quasar population. We estimate, based on the fraction of objects in this phase,
that its duration is 15-20% as long as the unobscured, blue quasar phase. |
Feedback, scatter and structure in the core of the PKS 0745-191 galaxy
cluster: We present Chandra X-ray Observatory observations of the core of the galaxy
cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback
and cold fronts with an associated spiral structure. The cavity energetics
imply they are powerful enough to compensate for cooling. Despite the evidence
for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a
few hundred solar masses per year cooling out of the X-ray phase, sufficient to
power the emission line nebula. The coolest X-ray emitting gas and brightest
nebula emission is offset by around 5 kpc from the radio and X-ray nucleus.
Although the cluster has a regular appearance, its core shows density,
temperature and pressure deviations over the inner 100 kpc, likely associated
with the cold fronts. After correcting for ellipticity and projection effects,
we estimate density fluctuations of ~4 per cent, while temperature, pressure
and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ,
able to accurately obtain thermodynamical cluster profiles, under the
assumptions of hydrostatic equilibrium and spherical symmetry. The
forward-fitting code compares model to observed profiles using Markov Chain
Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In
PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius
from the core, indicating a lack of hydrostatic equilibrium, deviations from
spherical symmetry or non-thermal sources of pressure. | Spectroastrometry of rotating gas disks for the detection of
supermassive black holes in galactic nuclei. I. Method and simulations: This is the first in a series of papers in which we study the application of
spectroastrometry in the context of gas kinematical studies aimed at measuring
the mass of supermassive black holes. The spectroastrometrical method consists
in measuring the photocenter of light emission in different wavelength or
velocity channels. In particular we explore the potential of spectroastrometry
of gas emission lines in galaxy nuclei to constrain the kinematics of rotating
gas disks and to measure the mass of putative supermassive black holes. By
means of detailed simulations and test cases, we show that the fundamental
advantage of spectroastrometry is that it can provide information on the
gravitational potential of a galaxy on scales significantly smaller (~ 1/10)
than the limit imposed by the spatial resolution of the observations. We then
describe a simple method to infer detailed kinematical informations from
spectroastrometry in longslit spectra and to measure the mass of nuclear mass
concentrations. Such method can be applied straightforwardly to integral field
spectra, which do not have the complexities due to a partial spatial covering
of the source in the case of longslit spectra. |
Can the CIB constrain the dark energy?: Galaxies are often used as tracers of the large scale structure (LSS) to
measure the Integrated Sachs-Wolfe effect (ISW) by cross-correlating the galaxy
survey maps with the Cosmic Microwave Background (CMB) map. We use the Cosmic
Infrared Background (CIB) as a tracer of the LSS to perform a theoretical
CIB-CMB cross-correlation to measure the ISW for different Planck HFI
frequencies. We discuss the detectability of this ISW signal using a
Signal-to-noise ratio analysis and find that the ISW detected this way can
provide us with the highest SNR for a single tracer ranging from 5 to 6.7
(maximum being for 857 GHz) with the CIB and CMB maps extracted over the whole
sky. A Fisher matrix analysis showed that this measurement of the ISW can
improve the constraints on the cosmological parameters; especially the equation
of state of the dark energy $w$ by $\sim 47\%$. Performing a more realistic
analysis including the galactic dust residuals in the CIB maps over realistic
sky fractions shows that the dust power spectra dominate over the CIB power
spectra at $\ell < 100$ and ISW can't be detected with high SNR. We perform the
cross-correlation on the existing CIB-CMB maps over $\sim 11\%$ of the sky in
the southern hemisphere and find that the ISW is not detected with the existing
CIB maps over such small sky fractions. | Spatial kinematics of Brightest Cluster Galaxies and their close
companions from Integral Field Unit spectroscopy: We present Integral Field Unit (IFU) spectroscopy of four brightest cluster
galaxies (BCGs) at z~0.1. Three of the BCGs have close companions within a
projected radius of 20 kpc and one has no companion within that radius. We
calculate the dynamical masses of the BCGs and their companions to be
1.4x10^11<M_dyn (M_solar)<1.5x10^12. We estimate the probability that the
companions of the BCGs are bound using the observed masses and velocity
offsets. We show that the lowest mass companion (1:4) is not bound while the
two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with
their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs
continue to grow from major merging even at z~0. We analyse the stellar
kinematics of these systems using the \lambda_R parameter developed by the
SAURON team. This offers a new and unique means to measure the stellar angular
momentum of BCGs and make a direct comparison to other early-type galaxies. The
BCGs and their companions have similar ellipticities to those of other
early-type galaxies but are more massive. We find that not all these massive
galaxies have low \lambda_R_e as one might expect. One of the four BCGs and the
two massive companions are found to be fast-rotating galaxies with high angular
momentum, thereby providing a new test for models of galaxy evolution and the
formation of Intra-Cluster Light. |
Galaxy evolution from "dis"integrated light: Masking the horizontal branch and giant stars allows unambiguous measurements
of mean age and metallicity in simple old stellar populations from metal and
hydrogen line strengths. Billion year resolution is possible in the luminous
halos of early type galaxies, constraining formation models. Most of the
nuisance parameters in stellar evolution are avoided by isolating the main
sequence for analysis. The initial mass function and s-process element
diagnostics may also be accessible. Integral field spectrographs have an
significant advantage for this work, which is confusion limited by the presence
of bright stars in medium to high surface brightness applications. | 2D stellar population and gas kinematics of the inner 1.5 kpc of the
post-starburst quasar SDSS J0210-0903: Post-Starburst Quasars (PSQs) are hypothesized to represent a stage in the
evolution of massive galaxies in which the star formation has been recently
quenched due to the feedback of the nuclear activity. In this paper our goal is
to test this scenario with a resolved stellar population study of the PSQ
J0210-0903, as well as of its emitting gas kinematics and excitation. We have
used optical Integral Field Spectroscopy obtained with the Gemini GMOS
instrument at a velocity resolution of ~120 km/s and spatial resolution of ~0.5
kpc. We find that old stars dominate the luminosity (at 4700 \AA) in the inner
0.3 kpc (radius), while beyond this region (at ~0.8 kpc) the stellar population
is dominated by both intermediate age and young ionizing stars. The gas
emission-line ratios are typical of Seyfert nuclei in the inner 0.3 kpc, where
an outflow is observed. Beyond this region the line ratios are typical of
LINERs and may result from the combination of diluted radiation from the
nucleus and ionization from young stars. The gas kinematics show a combination
of rotation in the plane of the galaxy and outflows, observed with a maximum
blueshift of -670 km/s. We have estimated a mass outflow rate in ionized gas in
the range 0.3--1.1 M_sun/yr and a kinetic power for the outflow of dE/dt ~
1.4--5.0 x 10^40 erg/s ~0.03% - 0.1% x L_bol. This outflow rate is two orders
of magnitude higher than the nuclear accretion rate of ~8.7 x 10^-3 M_sun/yr,
thus being the result of mass loading of the nuclear outflow by circumnuclear
galactic gas. Our observations support an evolutionary scenario in which the
feeding of gas to the nuclear region has triggered a circumnuclear starburst
100's Myr ago, followed by the triggering of the nuclear activity, producing
the observed gas outflow which may have quenched further star formation in the
inner 0.3 kpc. |
Observational constraints on the free parameters of an interacting
Bose-Einstein gas as a dark-energy model: Dark energy is modelled by a Bose-Einstein gas of particles with an
attractive interaction. It is coupled to cold dark matter, within a flat
universe, for the late-expansion description, producing variations in
particle-number densities. The model's parameters, and physical association,
are: $\Omega_{G0}$, $\Omega_{m0}$, the dark-energy rest-mass energy density and
the dark-matter term scaling as a mass term, respectively; $\Omega_{i0}$, the
self-interaction intensity; $x$, the energy exchange rate. Energy conservation
relates such parameters. The Hubble equation omits $\Omega_{G0}$, but also
contains $h$, the present-day expansion rate of the flat
Friedman--Lem\^aitre--Robertson--Walker metric, and $\Omega_{b0}$, the baryon
energy density, used as a prior. This results in the four effective chosen
parameters $\Omega_{b0}$, $h$, $\Omega_{m0}$, $\Omega_{i0}$, fit with the
Hubble expansion rate $H(z)$, and data from its value today, near distance, and
supernovas. We derive wide $1\sigma$ and $2\sigma$ likelihood regions
compatible with definite positive total CDM and IBEG mass terms. Additionally,
the best-fit value of parameter $x$ relieves the coincidence problem, and a
second potential coincidence problem related to the choice of $\Omega_{G0}$. | Minimal lensing solutions in the singular perturbative approach: This paper analyse the properties of minimal solutions for the reconstruction
of the lens potential in the singular perturbative approach. These minimal
solutions corresponds to an expansion with a minimal degree in Fourier
expansion of the perturbative fields. Using these minimal solutions prevent
spurious physically meaningless terms in the reconstruction of the fields. In
effect a perturbative analysis indicates that a small change in the source
model will corresponds to the higher order terms in the expansion of the
fields. The results of the perturbative analysis are valid not only for
slightly non-circular sources but also for more distorted sources to order two.
It is thus of crucial importance to minimize the number of terms used in the
modelling of the lens. Another important asset of the minimal solutions is that
they offers a de-coupling between the source and lens model and thus help to
break the source lens degeneracy issue. The possible drawback of minimal
solutions is to under-estimate the higher order terms in the solution. However
this bias has its merit since the detection of higher order terms using this
method will ensure that these terms are real. This type of analysis using
minimal solutions will be of particular interest when considering the
statistical analysis of a large number of lenses, especially in light of the
incoming satellite surveys. |
LATIS: Constraints on the Galaxy-halo Connection at $z \sim 2.5$ from
Galaxy-galaxy and Galaxy-Ly$α$ Clustering: The connection between galaxies and dark matter halos is often quantified
using the stellar mass-halo mass (SMHM) relation. Optical and near-infrared
imaging surveys have led to a broadly consistent picture of the evolving SMHM
relation based on measurements of galaxy abundances and angular correlation
functions. Spectroscopic surveys at $z \gtrsim 2$ can also constrain the SMHM
relation via the galaxy autocorrelation function and through the
cross-correlation between galaxies and Ly$\alpha$ absorption measured in
transverse sightlines; however, such studies are very few and have produced
some unexpected or inconclusive results. We use $\sim$3000 spectra of
$z\sim2.5$ galaxies from the Lyman-alpha Tomography IMACS Survey (LATIS) to
measure the galaxy-galaxy and galaxy-Ly$\alpha$ correlation functions in four
bins of stellar mass spanning $10^{9.2} \lesssim M_* / M_{\odot} \lesssim
10^{10.5}$. Parallel analyses of the MultiDark N-body and ASTRID hydrodynamic
cosmological simulations allow us to model the correlation functions, estimate
covariance matrices, and infer halo masses. We find that results of the two
methods are mutually consistent and are broadly in accord with standard SMHM
relations. This consistency demonstrates that we are able to accurately measure
and model Ly$\alpha$ transmission fluctuations $\delta_F$ in LATIS. We also
show that the galaxy-Ly$\alpha$ cross-correlation, a free byproduct of optical
spectroscopic galaxy surveys at these redshifts, can constrain halo masses with
similar precision to galaxy-galaxy clustering. | The AGN properties of the starburst galaxy NGC 7582: NGC 7582 was identified as a Starburst galaxy in the optical \cite[(Veron et
al. 1981)]{Veron et al.(1981)} but its X-Ray emission is typical of a Seyfert 1
galaxy \cite[(Ward et al. 1978)]{Ward et al.(1978)}. We analyzed a datacube of
this object obtained with the GMOS-IFU on the Gemini-South telescope. After a
subtraction of the stellar component using the {\sc starlight} code \cite[(Cid
Fernandes et al. 2005)]{Cid Fernandes et al. (2005)}, we looked for optical
signatures of the AGN. We detected a broad $H\alpha$ component (figure
\ref{fig1}) in the source where \cite[Bianchi et al.(2007)]{Bianchi et
al.(2007)} identified the AGN in an HST optical image. We also found a broad
$H\beta$ feature (figure \ref{fig2}), but its emission reveals a extended
source. We suggest that it is the light of the AGN scattered in the ionization
cone. We propose that NGC 7582 is a Seyfert 1 galaxy. A number of other
"hot-spots" and Wolf-Rayet features were also identified. |
Impact of a global quadratic potential on galactic rotation curves: We have made a conformal gravity fit to an available sample of 110 spiral
galaxies, and report here on the 20 of those galaxies whose rotation curve data
points extend the furthest from galactic centers. We identify the impact on the
20 galaxy data set of a universal de Sitter-like potential term $V(r)=-\kappa
c^2r^2/2$ that is induced by inhomogeneities in the cosmic background. This
quadratic term accompanies a universal linear potential term
$V(r)=\gamma_0c^2r/2$ that is associated with the cosmic background itself. We
find that when these two potential terms are taken in conjunction with the
contribution generated by the local luminous matter within the galaxies, the
conformal theory is able to account for the rotation curve systematics that is
observed in the entire 110 galaxy sample, without the need for any dark matter
whatsoever. With the two universal coefficients being found to be of global
magnitude, viz. $\kappa =9.54\times 10^{-54} {\rm cm}^{-2}$ and
$\gamma_0=3.06\times 10^{-30}{\rm cm}^{-1}$, our study suggests that invoking
the presence of dark matter may be nothing more than an attempt to describe
global effects in purely local galactic terms. With the quadratic potential
term having negative sign, galaxies are only able to support bound orbits up to
distances of order $\gamma_0/\kappa = 3.21\times 10^{23} {\rm cm}$, with global
physics thus imposing a natural limit on the size of galaxies. | Cosmology in one dimension: Symmetry role in dynamics, mass oriented
approaches to fractal analysis: The distribution of visible matter in the universe, such as galaxies and
galaxy clusters, has its origin in the week fluctuations of density that
existed at the epoch of recombination. The hierarchical distribution of the
universe, with its galaxies, clusters and super-clusters of galaxies indicates
the absence of a natural length scale. In the Newtonian formulation, numerical
simulations of a one-dimensional system permit us to precisely follow the
evolution of an ensemble of particles starting with an initial perturbation in
the Hubble flow. The limitation of the investigation to one dimension removes
the necessity to make approximations in calculating the gravitational field
and, on the whole, the system dynamics. It is then possible to accurately
follow the trajectories of particles for a long time. The simulations show the
emergence of a self-similar hierarchical structure in both the phase space and
the configuration space and invites the implementation of a multifractal
analysis. Here, after showing that symmetry considerations leads to the
construction of a family of equations of motion of the one-dimensional
gravitational system, we apply four different methods for computing generalized
dimensions $D_q$ of the distribution of particles in configuration space. We
first employ the conventional box counting and correlation integral methods
based on partitions of equal size and then the less familiar nearest-neighbor
and k-neighbor methods based on partitions of equal mass. We show that the
latter are superior for computing generalized dimensions for indices $q<-1$
which characterize regions of low density. |
Machine Learning Applied to the Reionization History of the Universe in
the 21 cm Signal: The Epoch of Reionization (EoR) features a rich interplay between the first
luminous sources and the low-density gas of the intergalactic medium (IGM),
where photons from these sources ionize the IGM. There are currently few
observational constraints on key observables related to the EoR, such as the
midpoint and duration of reionization. Although upcoming observations of the 21
cm power spectrum with next-generation radio interferometers such as the
Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array
(SKA) are expected to provide information about the midpoint of reionization
readily, extracting the duration from the power spectrum alone is a more
difficult proposition. As an alternative method for extracting information
about reionization, we present an application of convolutional neural networks
(CNNs) to images of reionization. These images are two-dimensional in the plane
of the sky, and extracted at a series of redshift values to generate "image
cubes" that are qualitatively similar to those of the HERA and the SKA will
generate in the near future. Additionally, we include the impact that the
bright foreground signal from the the Milky Way imparts on such image cubes
from interferometers, but do not include the noise induced from observations.
We show that we are able to recover the duration of reionization $\Delta$z to
within 5% using CNNs, assuming that the midpoint of reionization is already
relatively well constrained. These results have exciting impacts for estimating
$\tau$, the optical depth to the cosmic microwave background, which can help
constrain other cosmological parameters. | Prospects for resolving the Hubble constant tension with standard sirens: The Hubble constant ($H_0$) estimated from the local Cepheid-supernova (SN)
distance ladder is in 3-$\sigma$ tension with the value extrapolated from
cosmic microwave background (CMB) data assuming the standard cosmological
model. Whether this tension represents new physics or systematic effects is the
subject of intense debate. Here, we investigate how new, independent $H_0$
estimates can arbitrate this tension, assessing whether the measurements are
consistent with being derived from the same model using the posterior
predictive distribution (PPD). We show that, with existing data, the inverse
distance ladder formed from BOSS baryon acoustic oscillation measurements and
the Pantheon SN sample yields an $H_0$ posterior near-identical to the Planck
CMB measurement. The observed local distance ladder value is a very unlikely
draw from the resulting PPD. Turning to the future, we find that a sample of
$\sim50$ binary neutron star "standard sirens" (detectable within the next
decade) will be able to adjudicate between the local and CMB estimates. |
Baryon Acoustic Oscillations in the projected cross-correlation function
between the eBOSS DR16 quasars and photometric galaxies from the DESI Legacy
Imaging Surveys: We search for the Baryon Acoustic Oscillations in the projected
cross-correlation function binned into transverse comoving radius between the
SDSS-IV DR16 eBOSS quasars and a dense photometric sample of galaxies selected
from the DESI Legacy Imaging Surveys. We estimate the density of the
photometric sample of galaxies in this redshift range to be about 2900
deg$^{-2}$, which is deeper than the official DESI ELG selection, and the
density of the spectroscopic sample is about 20 deg$^{-2}$. In order to
mitigate the systematics related to the use of different imaging surveys close
to the detection limit, we use a neural network approach that accounts for
complex dependencies between the imaging attributes and the observed galaxy
density. We find that we are limited by the depth of the imaging surveys which
affects the density and purity of the photometric sample and its overlap in
redshift with the quasar sample, which thus affects the performance of the
method. When cross-correlating the photometric galaxies with quasars in $0.6
\leq z \leq 1.2$, the cross-correlation function can provide better constraints
on the comoving angular distance, $D_{\rm M}$ (6\% precision) compared to the
constraint on the spherically-averaged distance $D_{\rm V}$ (9\% precision)
obtained from the auto-correlation. Although not yet competitive, this
technique will benefit from the arrival of deeper photometric data from
upcoming surveys which will enable it to go beyond the current limitations we
have identified in this work. | Euclid preparation: VII. Forecast validation for Euclid cosmological
probes: The Euclid space telescope will measure the shapes and redshifts of galaxies
to reconstruct the expansion history of the Universe and the growth of cosmic
structures. Estimation of the expected performance of the experiment, in terms
of predicted constraints on cosmological parameters, has so far relied on
different methodologies and numerical implementations, developed for different
observational probes and for their combination. In this paper we present
validated forecasts, that combine both theoretical and observational expertise
for different cosmological probes. This is presented to provide the community
with reliable numerical codes and methods for Euclid cosmological forecasts. We
describe in detail the methodology adopted for Fisher matrix forecasts, applied
to galaxy clustering, weak lensing and their combination. We estimate the
required accuracy for Euclid forecasts and outline a methodology for their
development. We then compare and improve different numerical implementations,
reaching uncertainties on the errors of cosmological parameters that are less
than the required precision in all cases. Furthermore, we provide details on
the validated implementations that can be used by the reader to validate their
own codes if required. We present new cosmological forecasts for Euclid. We
find that results depend on the specific cosmological model and remaining
freedom in each setup, i.e. flat or non-flat spatial cosmologies, or different
cuts at nonlinear scales. The validated numerical implementations can now be
reliably used for any setup. We present results for an optimistic and a
pessimistic choice of such settings. We demonstrate that the impact of
cross-correlations is particularly relevant for models beyond a cosmological
constant and may allow us to increase the dark energy Figure of Merit by at
least a factor of three. |
Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies: In a sample of elliptical galaxies that span a large range of mass, a
previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically
decrease with increasing elliptical galaxy mass. Metallicity mixtures, age
effects, stellar chromospheric emission effects, and low-mass initial mass
function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less
than 0.3 dex is sufficient to blanket all observations. Feature gradients
within galaxies imply a global Ca deficit rather than a radius-dependent
phenomenon. Some, but not all, Type II supernova nucleosynthetic yield
calculations indicate a decreasing Ca/Fe yield ratio in more massive
supernovae, lending possible support to the hypothesis that more massive
elliptical galaxies have an IMF that favors more massive stars. No Type II
supernova nucleosynthetic yield calculations show significant leverage in the
Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems
unlikely that the Ca behavior can be explained as a built-in metallicity
effect, and this argues against explanations that vary only the Type II to Type
Ia supernova enrichment ratio. | LensWatch: I. Resolved HST Observations and Constraints on the
Strongly-Lensed Type Ia Supernova 2022qmx ("SN Zwicky"): Supernovae (SNe) that have been multiply-imaged by gravitational lensing are
rare and powerful probes for cosmology. Each detection is an opportunity to
develop the critical tools and methodologies needed as the sample of lensed SNe
increases by orders of magnitude with the upcoming Vera C. Rubin Observatory
and Nancy Grace Roman Space Telescope. The latest such discovery is of the
quadruply-imaged Type Ia SN 2022qmx (aka, "SN Zwicky"; Goobar et al. 2022) at z
= 0.3544. SN Zwicky was discovered by the Zwicky Transient Facility (ZTF) in
spatially unresolved data. Here we present follow-up Hubble Space Telescope
observations of SN Zwicky, the first from the multi-cycle "LensWatch" program
(www.lenswatch.org). We measure photometry for each of the four images of SN
Zwicky, which are resolved in three WFC3/UVIS filters (F475W, F625W, F814W) but
unresolved with WFC3/IR F160W, and produce an analysis of the lensing system
using a variety of independent lens modeling methods. We find consistency
between time delays estimated with the single epoch of HST photometry and the
lens model predictions constrained through the multiple image positions, with
both inferring time delays of <1 day. Our lens models converge to an Einstein
radius of (0.168+0.009-0.005)", the smallest yet seen in a lensed SN. The
"standard candle" nature of SN Zwicky provides magnification estimates
independent of the lens modeling that are brighter by ~1.5 mag and ~0.8 mag for
two of the four images, suggesting significant microlensing and/or additional
substructure beyond the flexibility of our image-position mass models. |
Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs
with Fermi: Dwarf spheroidal galaxies are known to be excellent targets for the detection
of annihilating dark matter. We present new limits on the annihilation cross
section of Weakly Interacting Massive Particles (WIMPs) based on the joint
analysis of seven Milky Way dwarfs using a frequentist Neyman construction and
Pass 7 data from the Fermi Gamma-ray Space Telescope. We exclude generic WIMP
candidates annihilating into b-bbar with mass less than 40 GeV that reproduce
the observed relic abundance. To within 95% systematic errors on the dark
matter distribution within the dwarfs, the mass lower limit can be as low as 19
GeV or as high as 240 GeV. For annihilation into tau+tau- these limits become
19 GeV, 13 GeV, and 80 GeV respectively. | Testing the consistency between cosmological measurements of distance
and age: We present a model independent method to test the consistency between
cosmological measurements of distance and age, assuming the distance duality
relation. We use type Ia supernovae, baryon acoustic oscillations, and
observational Hubble data, to reconstruct the luminosity distance D_L(z), the
angle averaged distance D_V(z) and the Hubble rate H(z), using Gaussian
processes regression technique. We obtain estimate of the distance duality
relation in the redshift range 0.1<z<0.73 and we find no evidence for
inconsistency between the data sets used. |
Implications of the $S_8$ tension for decaying dark matter with warm
decay products: Recent weak lensing surveys have revealed that the direct measurement of the
parameter combination $S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$ -- where
$\sigma_8$ is a measure of the amplitude of matter fluctuations on 8
$h^{-1}$Mpc scales -- is $\sim3\sigma$ discrepant with the value reconstructed
from cosmic microwave background (CMB) data assuming the $\Lambda$CDM model. In
this article, we show that it is possible to resolve the tension if dark matter
(DM) decays with a lifetime of $\Gamma^{-1} \simeq 55 \ \text{Gyrs}$ into one
massless and one massive product, and transfers a fraction $\varepsilon\simeq
0.7 \ \%$ of its rest mass energy to the massless component. The velocity-kick
received by the massive daughter leads to a suppression of gravitational
clustering below its free-streaming length, thereby reducing the $\sigma_8$
value as compared to that inferred from the standard $\Lambda$CDM model, in a
similar fashion to massive neutrino and standard warm DM. Contrarily to the
latter scenarios, the time-dependence of the power suppression and the
free-streaming scale allows the 2-body decaying DM scenario to accommodate CMB,
baryon acoustic oscillation, growth factor and un-calibrated supernova Ia data.
We briefly discuss implications for DM model building, galactic small-scale
structure problems and the recent Xenon-1T excess. Future experiments measuring
the growth factor to high accuracy at $0\lesssim z\lesssim1$ can further test
this scenario. | Detection of a Hot Gaseous Halo Around the Giant Spiral Galaxy NGC 1961: Hot gaseous halos are predicted around all large galaxies and are critically
important for our understanding of galaxy formation, but they have never been
detected at distances beyond a few kpc around a spiral galaxy. We used the
Chandra ACIS-I instrument to search for diffuse X-ray emission around an ideal
candidate galaxy: the isolated giant spiral NGC 1961. We observed four
quadrants around the galaxy for 30 ks each, carefully subtracting background
and point source emission, and found diffuse emission that appears to extend to
40-50 kpc. We fit $\beta$-models to the emission, and estimate a hot halo mass
within 50 kpc of $5\times10^9 M_{\odot}$. When this profile is extrapolated to
500 kpc (the approximate virial radius), the implied hot halo mass is
$1-3\times10^{11} M_{\odot}$. These mass estimates assume a gas metallicity of
$Z = 0.5 Z_{\odot}$. This galaxy's hot halo is a large reservoir of gas, but
falls significantly below observational upper limits set by pervious searches,
and suggests that NGC 1961 is missing 75% of its baryons relative to the cosmic
mean, which would tentatively place it below an extrapolation of the baryon
Tully-Fisher relationship of less massive galaxies. The cooling rate of the gas
is no more than 0.4 $M_{\odot}$/year, more than an order of magnitude below the
gas consumption rate through star formation. We discuss the implications of
this halo for galaxy formation models. |
Improved Method for Detecting Local Discontinuities in CMB data by
Finite Differencing: An unexpected distribution of temperatures in the CMB could be a sign of new
physics. In particular, the existence of cosmic defects could be indicated by
temperature discontinuities via the Kaiser-Stebbins effect. In this paper, we
show how performing finite differences on a CMB map, with the noise regularized
in harmonic space, may expose such discontinuities, and we report the results
of this process on the 7-year Wilkinson Microwave Anisotropy Probe data. | Weak Lensing Analysis of SPT selected Galaxy Clusters using Dark Energy
Survey Science Verification Data: We present weak lensing (WL) mass constraints for a sample of massive galaxy
clusters detected by the South Pole Telescope (SPT) via the Sunyaev-Zeldovich
effect (SZE). We use $griz$ imaging data obtained from the Science Verification
(SV) phase of the Dark Energy Survey (DES) to fit the WL shear signal of 33
clusters in the redshift range $0.25 \le z \le 0.8$ with NFW profiles and to
constrain a four-parameter SPT mass-observable relation. To account for biases
in WL masses, we introduce a WL mass to true mass scaling relation described by
a mean bias and an intrinsic, log-normal scatter. We allow for correlated
scatter within the WL and SZE mass-observable relations and use simulations to
constrain priors on nuisance parameters related to bias and scatter from WL. We
constrain the normalization of the $\zeta-M_{500}$ relation,
$A_\mathrm{SZ}=12.0_{-6.7}^{+2.6}$ when using a prior on the mass slope
$B_\mathrm{SZ}$ from the latest SPT cluster cosmology analysis. Without this
prior, we recover $A_\mathrm{SZ}=10.8_{-5.2}^{+2.3}$ and
$B_\mathrm{SZ}=1.30_{-0.44}^{+0.22}$. Results in both cases imply lower cluster
masses than measured in previous work with and without WL, although the
uncertainties are large. The WL derived value of $B_\mathrm{SZ}$ is $\approx
20\%$ lower than the value preferred by the most recent SPT cluster cosmology
analysis. The method demonstrated in this work is designed to constrain cluster
masses and cosmological parameters simultaneously and will form the basis for
subsequent studies that employ the full SPT cluster sample together with the
DES data. |
Radio Constraints on Heavily-Obscured Star-Formation within Dark
Gamma-Ray Burst Host Galaxies: Highly dust-obscured starbursting galaxies (submillimeter galaxies and their
ilk) represent the most extreme sites of star-formation in the distant universe
and contribute significantly to overall cosmic star-formation beyond z>1.5.
Some stars formed in these environments may also explode as GRBs and contribute
to the population of "dark" bursts. Here we present VLA wideband
radio-continuum observations of 15 heavily dust-obscured Swift GRBs to search
for radio synchrotron emission associated with intense star-formation in their
host galaxies. Most of these targets (11) are not detected. Of the remaining
four objects, one detection is marginal and for two others we cannot yet rule
out the contribution of a long-lived radio afterglow. The final detection is
secure, but indicates a star-formation rate roughly consistent with the
UV-inferred value. Most galaxies hosting obscured GRBs are therefore not
forming stars at extreme rates, and the amount of optical extinction seen along
a GRB afterglow sightline does not clearly correlate with the likelihood that
the host has a sufficiently high star-formation rate to be radio-detectable.
While some submillimeter galaxies do readily produce GRBs, these GRBs are often
not heavily obscured - suggesting that the outer (modestly obscured) parts of
these galaxies overproduce GRBs and the inner (heavily obscured) parts
underproduce GRBs relative to their respective contributions to star-formation,
hinting at strong chemical or IMF gradients within these systems. | Constraints on $S_8$ from a full-scale and full-shape analysis of
redshift-space clustering and galaxy-galaxy lensing in BOSS: We present a novel simulation-based cosmological analysis of galaxy-galaxy
lensing and galaxy redshift-space clustering. Compared to analysis methods
based on perturbation theory, our simulation-based approach allows us to probe
a much wider range of scales, $0.4 \, h^{-1} \, \mathrm{Mpc}$ to $63 \, h^{-1}
\, \mathrm{Mpc}$, including highly non-linear scales, and marginalises over
astrophysical effects such as assembly bias. We apply this framework to data
from the Baryon Oscillation Spectroscopic Survey LOWZ sample cross-correlated
with state-of-the-art gravitational lensing catalogues from the Kilo Degree
Survey and the Dark Energy Survey. We show that gravitational lensing and
redshift-space clustering when analysed over a large range of scales place
tight constraints on the growth-of-structure parameter $S_8 = \sigma_8
\sqrt{\Omega_{\rm m} / 0.3}$. Overall, we infer $S_8 = 0.792 \pm 0.022$ when
analysing the combination of galaxy-galaxy lensing and projected galaxy
clustering and $S_8 = 0.771 \pm 0.027$ for galaxy redshift-space clustering.
These findings highlight the potential constraining power of full-scale studies
over studies analysing only large scales, and also showcase the benefits of
analysing multiple large-scale structure surveys jointly. Our inferred values
for $S_8$ fall below the value inferred from the CMB, $S_8 = 0.834 \pm 0.016$.
While this difference is not statistically significant by itself, our results
mirror other findings in the literature whereby low-redshift large scale
structure probes infer lower values for $S_8$ than the CMB, the so-called
$S_8$-tension. |
Triaxial Cosmological Haloes and the Disc of Satellites: We construct simple triaxial generalisations of Navarro-Frenk-White haloes.
The models have elementary gravitational potentials, together with a density
that is cusped like 1/r at small radii and falls off like 1/r^3 at large radii.
The ellipticity varies with radius in a manner that can be tailored to the
user's specification. The closed periodic orbits in the planes perpendicular to
the short and long axes of the model are well-described by epicyclic theory,
and can be used as building blocks for long-lived discs. As an application, we
carry out the simulations of thin discs of satellites in triaxial dark halo
potentials. This is motivated by the recent claims of an extended, thin disc of
satellites around the M31 galaxy with a vertical rms scatter of ~12 kpc and a
radial extent of ~ 300 kpc (Ibata et al. 2013). We show that a thin satellite
disc can persist over cosmological times if and only if it lies in the planes
perpendicular to the long or short axis of a triaxial halo, or in the
equatorial or polar planes of a spheroidal halo. In any other orientation, then
the disc thickness doubles on ~5 Gyr timescales and so must have been born with
an implausibly small vertical scaleheight. | A Triple Rollover: A third multiply-imaged source at z~6 behind the
Jackpot gravitational lens: UUsing a five-hour adaptive-optics-assisted observation with MUSE, we have
identified a doubly-imaged Ly alpha source at redshift 5.975 behind the z=0.222
lens galaxy J0946+1006 ('the Jackpot'). The source separation implies an
Einstein radius of ~2.5 arcsec. Combined with the two previously-known Einstein
rings in this lens (radii 1.4 arcsec at z = 0.609 and 2.1 arcsec at z ~ 2.4),
this system is now a unique galaxy-scale triple-source-plane lens. We show that
existing lensing models for J0946+1006 successfully map the two new observed
images to a common point on the z=5.975 source plane. The new source will
provide further constraints on the mass distribution in the lens and in the two
previously known sources. The third source also probes two new distance scaling
factors which are sensitive to the cosmological parameters of the Universe. We
show that detection of a new multiply imaged emission-line source is not
unexpected in observations of this depth; similar data for other known lenses
should reveal a larger sample of multiple-image-plane systems for cosmography
and other applications. |
Primordial non-Gaussianity in the large scale structure of the Universe: Primordial non-Gaussianity is a potentially powerful discriminant of the
physical mechanisms that generated the cosmological fluctuations observed
today. Any detection of significant non-Gaussianity would thus have profound
implications for our understanding of cosmic structure formation. The large
scale mass distribution in the Universe is a sensitive probe of the nature of
initial conditions. Recent theoretical progress together with rapid
developments in observational techniques will enable us to critically confront
predictions of inflationary scenarios and set constraints as competitive as
those from the Cosmic Microwave Background. In this paper, we review past and
current efforts in the search for primordial non-Gaussianity in the large scale
structure of the Universe. | The Local Dark Matter Density: We present the recent robust determination of the value of the Dark Matter
density at the Sun's location ($\rho_\odot$) with a technique that does not
rely on a global mass-modeling of the Galaxy. The method is based on the local
equation of centrifugal equilibrium and depends on local and quite well known
quantities such as the angular Sun's velocity, the disk to dark contribution to
the circular velocity at the Sun, and the thin stellar disk scale length. This
determination is independent of the shape of the dark matter density profile,
the knowledge of the rotation curve at any radius, and the very uncertain
bulge/disk/dark-halo mass decomposition. The result is: $\rho_\odot=0.43
(0.11)(0.10)\,$GeV/cm$^{3}$, where the quoted uncertainties are due to the
uncertainty a) in the slope of the circular-velocity at the Sun location and b)
in the ratio between this radius and the exponential length scale of the
stellar disk. The devised technique is also able to take into account any
future improvement in the data relevant for the estimate. |
Constraints on the Tensor-to-Scalar ratio for non-power-law models: Recent cosmological observations hint at a deviation from the simple
power-law form of the primordial spectrum of curvature perturbations. In this
paper we show that in the presence of a tensor component, a turn-over in the
initial spectrum is preferred by current observations, and hence non-power-law
models ought to be considered. For instance, for a power-law parameterisation
with both a tensor component and running parameter, current data show a
preference for a negative running at more than $2.5\sigma$ C.L. As a
consequence of this deviation from a power-law, constraints on the
tensor-to-scalar ratio $r$ are slightly broader. We also present constraints on
the inflationary parameters for a model-independent reconstruction and the
Lasenby & Doran (LD) model. In particular, the constraints on the
tensor-to-scalar ratio from the LD model are: $r_{\rm LD}=0.11\pm{0.024}$. In
addition to current data, we show expected constraints from Planck-like and
CMB-Pol sensitivity experiments by using Markov-Chain-Monte-Carlo sampling
chains. For all the models, we have included the Bayesian Evidence to perform a
model selection analysis. The Bayes factor, using current observations, shows a
strong preference for the LD model over the standard power-law
parameterisation, and provides an insight into the accuracy of differentiating
models through future surveys. | Nonflat time-variable dark energy cosmology: We generalize the time-variable dark energy scalar field $\Phi$ model
($\Phi$CDM) to nonflat space. We show that even in the
space-curvature-dominated epoch the scalar field solution is a time-dependent
fixed point or attractor, with scalar field energy density that grows relative
to the energy density in spatial curvature. This is the first example of a
physically consistent and complete model of dynamical dark energy in a nonflat
geometry. |
Probing the circumgalactic baryons through cross-correlations: We study the cross-correlation of distribution of galaxies, the
Sunyaev-Zel'dovich (SZ) and X-ray power spectra of galaxies from current and
upcoming surveys and show these to be excellent probes of the nature, i.e.
extent, evolution and energetics, of the circumgalactic medium (CGM). The
SZ-galaxy cross-power spectrum, especially at large multipoles, depends on the
steepness of the pressure profile of the CGM. This property of the SZ signal
can, thus, be used to constrain the pressure profile of the CGM. The X-ray
cross power spectrum also has a similar shape. However, it is much more
sensitive to the underlying density profile. We forecast the detectability of
the cross-correlated galaxy distribution, SZ and X-ray signals by combining
South Pole Telescope-Dark Energy Survey (SPT-DES) and eROSITA-DES/eROSITA-LSST
(extended ROentgen Survey with an Imaging Telescope Array-Large Synoptic Survey
Telescope) surveys, respectively. We find that, for the SPT-DES survey, the
signal-to-noise ratio (SNR) peaks at high mass and redshift with SNR $\sim 9$
around $M_h\sim 10^{13} h^{-1} M_{\odot}$ and $z\sim 1.5\hbox{--} 2$ for flat
density and temperature profiles. The SNR peaks at $\sim 6 (12 )$ for the
eROSITA-DES (eROSITA-LSST) surveys. We also perform a Fisher matrix analysis to
find the constraint on the gas fraction in the CGM in the presence or absence
of an unknown redshift evolution of the gas fraction. Finally, we demonstrate
that the cross-correlated SZ-galaxy and X-ray-galaxy power spectrum can be used
as powerful probes of the CGM energetics and potentially discriminate between
different feedback models recently proposed in the literature; for example, one
can distinguish a `no active galactic nuclei feedback' scenario from a CGM
energized by `fixed-velocity hot winds' at greater than $3\sigma$. | Rejuvenating the Matter Power Spectrum III: The Cosmology Sensitivity of
Gaussianized Power Spectra: It was recently shown that applying a Gaussianizing transform, such as a
logarithm, to the nonlinear matter density field extends the range of useful
applicability of the power spectrum by a factor of a few smaller. Such a
transform dramatically reduces nonlinearities in both the covariance and the
shape of the power spectrum. Here, analyzing Coyote Universe real-space dark
matter density fields, we investigate the consequences of these transforms for
cosmological parameter estimation. The power spectrum of the log-density
provides the tightest cosmological parameter error bars (marginalized or not),
giving a factor of 2-3 improvement over the conventional power spectrum in all
five parameters tested. For the tilt, n_s, the improvement reaches a factor of
5. Similar constraints are achieved if the log-density power spectrum and
conventional power spectrum are analyzed together. Rank-order Gaussianization
seems just as useful as a log transform to constrain n_s, but not other
parameters. Dividing the overdensity by its dispersion in few-Mpc cells, while
it diagonalizes the covariance matrix, does not seem to help with parameter
constraints. We also provide a code that emulates these power spectra over a
range of concordance cosmological models. |
Primordial non-Gaussianity as a saviour for PBH overproduction in SIGWs
generated by Pulsar Timing Arrays for Galileon inflation: We investigate the explicit role of negative local non-Gaussianity, $f_{\rm
NL}$, in suppressing the abundance of primordial black holes (PBHs) in the
single-field model of Galileon inflation. PBH formation requires significantly
enhancing the scalar power spectrum, which greatly affects their abundance. The
associated frequencies in the nHz regime are also sensitive to the generation
of scalar-induced gravitational waves (SIGWs) which may explain the current
data from the pulsar timing arrays (PTAs). Our analysis using the threshold
statistics on the compaction function demonstrates that Galileon theory not
only avoids PBH overproduction using the curvature perturbation enhancements
that give $f_{\rm NL} \sim {\cal O}(-6)$, but also generates SIGWs that conform
well with the PTA data. | Tracing the high energy theory of gravity: an introduction to Palatini
inflation: We present an introduction to cosmic inflation in the context of Palatini
gravity, which is an interesting alternative to the usual metric theory of
gravity. In the latter case only the metric $g_{\mu\nu}$ determines the
geometry of space-time, whereas in the former case both the metric and the
space-time connection $\Gamma^\lambda_{\mu\nu}$ are a priori independent
variables - a choice which can lead to a theory of gravity different from the
metric one. In scenarios where the field(s) responsible for cosmic inflation
are coupled non-minimally to gravity or the gravitational sector is otherwise
extended, assumptions of the underlying gravitational degrees of freedom can
have a big impact on the observational consequences of inflation. We
demonstrate this explicitly by reviewing several interesting and well-motivated
scenarios including Higgs inflation, $R^2$ inflation, and $\xi$-attractor
models. We also discuss some prospects for future research and argue why
$r=10^{-3}$ is a particularly important goal for future missions that search
for signatures of primordial gravitational waves. |
Effects of Cosmic String Velocities and the Origin of Globular Clusters: With the hypothesis that cosmic string loops act as seeds for globular
clusters in mind, we study the role that velocities of these strings will play
in determining the mass distribution of globular clusters. Loops with high
enough velocities will not form compact and roughly spherical objects and can
hence not be the seeds for globular clusters. We compute the expected number
density and mass function of globular clusters as a function of both the string
tension and the peak loop velocity, and compare the results with the
observational data on the mass distribution of globular clusters in our Milky
Way. We determine the critical peak string loop velocity above which the
agreement between the string loop model for the origin of globular clusters
(neglecting loop velocities) and observational data is lost. | MontePython 3: boosted MCMC sampler and other features: MontePython is a parameter inference package for cosmology. We present the
latest development of the code over the past couple of years. We explain, in
particular, two new ingredients both contributing to improve the performance of
Metropolis-Hastings sampling: an adaptation algorithm for the jumping factor,
and a calculation of the inverse Fisher matrix, which can be used as a proposal
density. We present several examples to show that these features speed up
convergence and can save many hundreds of CPU-hours in the case of difficult
runs, with a poor prior knowledge of the covariance matrix. We also summarise
all the functionalities of MontePython in the current release, including new
likelihoods and plotting options. |
A weak lensing analysis of the Abell 383 cluster: In this paper we use deep CFHT and SUBARU $uBVRIz$ archival images of the
Abell 383 cluster (z=0.187) to estimate its mass by weak lensing. To this end,
we first use simulated images to check the accuracy provided by our KSB
pipeline. Such simulations include both the STEP 1 and 2 simulations, and more
realistic simulations of the distortion of galaxy shapes by a cluster with a
Navarro-Frenk-White (NFW) profile. From such simulations we estimate the effect
of noise on shear measurement and derive the correction terms. The R-band image
is used to derive the mass by fitting the observed tangential shear profile
with a NFW mass profile. Photometric redshifts are computed from the uBVRIz
catalogs. Different methods for the foreground/background galaxy selection are
implemented, namely selection by magnitude, color and photometric redshifts,
and results are compared. In particular, we developed a semi-automatic
algorithm to select the foreground galaxies in the color-color diagram, based
on observed colors. Using color selection or photometric redshifts improves the
correction of dilution from foreground galaxies: this leads to higher signals
in the inner parts of the cluster. We obtain a cluster mass that is ~ 20%
higher than previous estimates, and is more consistent the mass expected from
X--ray data. The R-band luminosity function of the cluster is finally computed. | Cornering Extended Starobinsky Inflation with CMB and SKA: Starobinsky inflation is an attractive, fundamental model to explain the
Planck measurements, and its higher-order extension may allow us to probe
quantum gravity effects. We show that future CMB data combined with the 21cm
intensity map from SKA will meaningfully probe such an extended Starobinsky
model. A combined analysis will provide a precise measurement and intriguing
insight into inflationary dynamics, even accounting for correlations with
astrophysical parameters. |
Quasar lensing: I review the observations of gravitationally lensed quasars. These systems
are important because they allow us to probe the properties of the lensing
galaxies at various scales, and they also allow insights into the structures of
the quasars themselves. Samples of quasar lenses also have the potential to act
as cosmographic probes. These areas are described, together with observational
and scientific prospects for the future. | The Ellipsoidal Universe and the Hubble tension: The Hubble tension resides in a statistically significant discrepancy between
early time and late time determinations of the Hubble constant. We discuss the
Hubble tension within the Ellipsoidal Universe cosmological model. We suggest
that allowing small anisotropies in the large-scale spatial geometry could
alleviate the tension. We, also, show that the discrepancy in the measurements
of the Hubble constant is reduced to a statistically acceptable level if we
assume sizeable cosmological anisotropies during the Dark Age. In addition, we
argue that the Ellipsoidal Universe cosmological model should resolve the $S_8$
tension. |
Scale-free primordial cosmology: The large-scale structure of the universe suggests that the physics
underlying its early evolution is scale-free. This was the historic motivation
for the Harrison-Zel'dovich-Peebles spectrum and for inflation. Based on a
hydrodynamical approach, we identify scale-free forms for the background
equation-of-state for both inflationary and cyclic scenarios and use these
forms to derive predictions for the spectral tilt and tensor-to-scalar ratio of
primordial density perturbations. For the case of inflation, we find three
classes of scale-free models with distinct predictions. Including all classes,
we show that scale-free inflation predicts tensor-to-scalar ratio $r >
10^{-4}$. We show that the observationally favored class is theoretically
disfavored because it suffers from an initial conditions problem and the
hydrodynamical form of an unlikeliness problem similar to that identified
recently for certain inflaton potentials. We contrast these results with those
for scale-free cyclic models. | Planck confronts large scale structure: methods to quantify discordance: Discordance in the $\Lambda$CDM cosmological model can be seen by comparing
parameters constrained by CMB measurements to those inferred by probes of large
scale structure. Recent improvements in observations, including final data
releases from both Planck and SDSS-III BOSS, as well as improved astrophysical
uncertainty analysis of CFHTLenS, allows for an update in the quantification of
any tension between large and small scales. This paper is intended, primarily,
as a discussion on the quantifications of discordance when comparing the
parameter constraints of a model when given two different data sets. We
consider KL-divergence, comparison of Bayesian evidences and other statistics
which are sensitive to the mean, variance and shape of the distributions.
However, as a by-product, we present an update to the similar analysis in
(Battye, Charnock and Moss; 2015) where we find that, considering new data and
treatment of priors, the constraints from the CMB and from a combination of LSS
probes are in greater agreement and any tension only persists to a minor
degree. In particular, we find the parameter constraints from the combination
of LSS probes which are most discrepant with the Planck2015+Pol+BAO parameter
distributions can be quantified at a 2.55$\sigma$ tension using the method
introduced in (Battye, Charnock and Moss; 2015). If instead we use the
distributions constrained by the combination of LSS probes which are in
greatest agreement with those from Planck2015+Pol+BAO this tension is only
0.76$\sigma$. |
Ferromagnetic properties of charged vector boson condensate: Bose-Einstein condensation of W bosons in the early universe is studied. It
is shown that, in the broken phase of the standard electroweak theory,
condensed W bosons form a ferromagnetic state with aligned spins. In this case
the primeval plasma may be spontaneously magnetized inside macroscopically
large domains and form magnetic fields which may be seeds for the observed
today galactic and intergalactic fields. However, in a modified theory, e.g. in
a theory without quartic self interactions of gauge bosons or for a smaller
value of the weak mixing angle, antiferromagnetic condensation is possible. In
the latter case W bosons form scalar condensate with macroscopically large
electric charge density i.e. with a large average value of the bilinear product
of W-vector fields but with microscopically small average value of the field
itself. | Gravitational lensing of gravitational waves: wave nature and prospects
for detection: We discuss the gravitational lensing of gravitational wave signals from
coalescing binaries. We delineate the regime where wave effects are significant
from the regime where geometric limit can be used. Further, we focus on the
effect of micro-lensing and the combined effect of strong lensing and
micro-lensing. We find that micro-lensing combined with strong lensing can
introduce time varying phase shift in the signal and hence can lead to
detectable differences in the signal observed for different images produced by
strong lensing. This, coupled with the coarse localization of signal source in
the sky for gravitational wave detections, can make it difficult to identify
the common origin of signal corresponding to different images and use
observables like time delay. In case we can reliably identify corresponding
images, micro-lensing of individual images can be used as a tool to constrain
properties of micro-lenses. Sources of gravitational waves can undergo
microlensing due to lenses in the disk/halo of the Galaxy, or due to lenses in
an intervening galaxy even in absence of strong lensing. In general the
probability for this is small with one exception: Extragalactic sources of
gravitational waves that lie in the galactic plane are highly likely to be
micro-lensed. Wave effects are extremely important for such cases. In case of
detections of such sources with low SNR, the uncertainty of occurrence of
microlensing or otherwise introduces an additional uncertainty in the
parameters of the source. |
GRB afterglow plateaus and Gravitational Waves: multi-messenger
signature of a millisecond magnetar?: The existence of a shallow decay phase in the early X-ray afterglows of
gamma-ray bursts is a common feature. Here we investigate the possibility that
this is connected to the formation of a highly magnetized millisecond pulsar,
pumping energy into the fireball on timescales longer than the prompt emission.
In this scenario the nascent neutron star could undergo a secular bar-mode
instability, leading to gravitational wave losses which would affect the
neutron star spin-down. In this case, nearby gamma-ray bursts with isotropic
energies of the order of 1e50 ergs would produce a detectable gravitational
wave signal emitted in association with an observed X-ray light-curve plateau,
over relatively long timescales of minutes to about an hour. The peak amplitude
of the gravitational wave signal would be delayed with respect to the gamma-ray
burst trigger, offering gravitational wave interferometers such as the advanced
LIGO and Virgo the challenging possibility of catching its signature on the
fly. | The Spatial Clustering of ROSAT All-Sky Survey AGNs II. Halo Occupation
Distribution Modeling of the Cross Correlation Function: This is the second paper of a series that reports on our investigation of the
clustering properties of AGNs in the ROSAT All-Sky Survey (RASS) through
cross-correlation functions (CCFs) with Sloan Digital Sky Survey (SDSS)
galaxies. In this paper, we apply the Halo Occupation Distribution (HOD) model
to the CCFs between the RASS Broad-line AGNs with SDSS Luminous Red Galaxies
(LRGs) in the redshift range 0.16<z<0.36 that was calculated in paper I. In our
HOD modeling approach, we use the known HOD of LRGs and constrain the HOD of
the AGNs by a model fit to the CCF. For the first time, we are able to go
beyond quoting merely a `typical' AGN host halo mass, M_h, and model the full
distribution function of AGN host dark matter halos. In addition, we are able
to determine the large-scale bias and the mean M_h more accurately. We explore
the behavior of three simple HOD models. Our first model (Model A) is a
truncated power-law HOD model in which all AGNs are satellites. With this
model, we find an upper limit to the slope (\alpha) of the AGN HOD that is far
below unity. The other two models have a central component, which has a step
function form, where the HOD is constant above a minimum mass, without (Model
B) or with (Model C) an upper mass cutoff, in addition to the truncated
power-law satellite component, similar to the HOD that is found for galaxies.
In these two models we find the upper limits of \alpha < 0.95 and \alpha < 0.84
for Model B and C respectively. Our analysis suggests that the satellite AGN
occupation increases slower than, or may even decrease with, M_h, in contrast
to the satellite's HODs of luminosity-threshold samples of galaxies, which, in
contrast, grow approximately as \propto M_h^\alpha with \alpha\approx 1. These
results are consistent with observations that the AGN fraction in groups and
clusters decreases with richness. |
Mass-Temperature relation in $Λ$CDM and modified gravity: We derive the mass-temperature relation using an improved top-hat model and a
continuous formation model which takes into account the effects of the ordered
angular momentum acquired through tidal-torque interaction between clusters,
random angular momentum, dynamical friction, and modifications of the virial
theorem to include an external pressure term usually neglected. We show that
the mass-temperature relation differs from the classical self-similar behavior,
$M \propto T^{3/2}$, and shows a break at $3--4$ keV, and a steepening with a
decreasing cluster temperature. We then compare our mass-temperature relation
with those obtained in the literature with $N$-body simulations for $f(R)$ and
symmetron models. We find that the mass-temperature relation is not a good
probe to test gravity theories beyond Einstein's general relativity, because
the mass-temperature relation of the $\Lambda$CDM model is similar to that of
the modified gravity theories. | Breaking a dark degeneracy: The gamma-ray signature of early matter
domination: The Universe's early thermal history is poorly constrained, and it is
possible that it underwent a period of early matter domination driven by a
heavy particle or an oscillating scalar field that decayed into radiation
before the onset of Big Bang nucleosynthesis. The entropy sourced by this
particle's decay reduces the cross section required for thermal-relic dark
matter to achieve the observed abundance. This degeneracy between dark matter
properties and the thermal history vastly widens the field of viable dark
matter candidates, undermining efforts to constrain dark matter's identity.
Fortunately, an early matter-dominated era also amplifies density fluctuations
at small scales and leads to early microhalo formation, boosting the dark
matter annihilation rate and bringing smaller cross sections into the view of
existing indirect-detection probes. Employing several recently developed models
of microhalo formation and evolution, we develop a procedure to derive
indirect-detection constraints on dark matter annihilation in cosmologies with
early matter domination. This procedure properly accounts for the unique
morphology of microhalo-dominated signals. While constraints depend on dark
matter's free-streaming scale, the microhalos make it possible to obtain upper
bounds as small as $\langle\sigma v\rangle \lesssim 10^{-32}$ cm$^3$s$^{-1}$
using Fermi-LAT observations of the isotropic gamma-ray background and the
Draco dwarf galaxy. |
Binary Quasars at High Redshift II: Sub-Mpc Clustering at z ~ 3-4: We present measurements of the small-scale (0.1<~ r <~ 1 Mpc/h) quasar
two-point correlation function at z>2.9, for a flux-limited (i<21) sample of 15
binary quasars compiled by Hennawi et al. (2009). The amplitude of the
small-scale clustering increases from z ~ 3 to z ~ 4. The small-scale
clustering amplitude is comparable to or lower than power-law extrapolations
(with slope gamma=2) from the large-scale correlation function of the i<20.2
quasar sample from the Sloan Digital Sky Survey. Using simple prescriptions
relating quasars to dark matter halos, we model the observed small-scale
clustering with halo occupation models. Reproducing the large-scale clustering
amplitude requires that the active fraction of the black holes in the central
galaxies of halos is near unity, but the level of small-scale clustering favors
an active fraction of black holes in satellite galaxies 0.1 <~ f_s <~ 0.5 at z
>~ 3. | A Natural Inflation inspired model: We propose a modification of the Natural Inflation (NI) potential in such a
way that the spontaneous symmetry breaking scale $f$ can take values less than
one (in Planck units). The proposed potential seems simple enough, however, its
consequences are difficult to calculate analytically. Therefore, we illustrate
the feasibility of the model by considering some numerical examples that easily
satisfy the conditions imposed on the observables $n_s$ and $r$ by the most
recent observations, while at the same time maintaining the number of e-folds
during the inflationary epoch within the expected range. |
Kinks and small-scale structure on cosmic strings: We discuss some hitherto puzzling features of the small-scale structure of
cosmic strings. We argue that kinks play a key role, and that an important
quantity to study is their sharpness distribution. In particular we suggest
that for very small scales the two-point correlation function of the string
tangent vector varies linearly with the separation and not as a fractional
power, as proposed by Polchinski and Rocha [Phys. Rev. D 74, 083504 (2006)].
However, our results are consistent with theirs, because the range of scales to
which this linearity applies shrinks as evolution proceeds. | Lensing corrections on galaxy-lensing cross correlations and
galaxy-galaxy auto correlations: We study the impact of lensing corrections on modeling cross correlations
between CMB lensing and galaxies, cosmic shear and galaxies, and galaxies in
different redshift bins. Estimating the importance of these corrections becomes
necessary in the light of anticipated high-accuracy measurements of these
observables. While higher order lensing corrections (sometimes also referred to
as post Born corrections) have been shown to be negligibly small for lensing
auto correlations, they have not been studied for cross correlations. We
evaluate the contributing four-point functions without making use of the Limber
approximation and compute line-of-sight integrals with the numerically stable
and fast FFTlog formalism. We find that the relative size of lensing
corrections depends on the respective redshift distributions of the lensing
sources and galaxies, but that they are generally small for high
signal-to-noise correlations. We point out that a full assessment and judgement
of the importance of these corrections requires the inclusion of lensing
Jacobian terms on the galaxy side. We identify these additional correction
terms, but do not evaluate them due to their large number. We argue that they
could be potentially important and suggest that their size should be measured
in the future with ray-traced simulations. We make our code publicly available. |
Galaxy clusters enveloped by vast volumes of relativistic electrons: The central regions of galaxy clusters are permeated by magnetic fields and
filled with relativistic electrons. When clusters merge, the magnetic fields
are amplified and relativistic electrons are re-accelerated by turbulence in
the intra cluster medium. These electrons reach energies of 1 -- 10 GeV and, in
the presence of magnetic fields, produce diffuse radio halos that typically
cover an area of ~1 square Mpc. Here we report observations of four clusters
whose radio halos are embedded in much more extended, diffuse radio emission,
filling a volume 30 times larger than that of radio halos. The emissivity in
these larger features is about 20 times lower than the emissivity in radio
halos. We conclude that relativistic electrons and magnetic fields extend far
beyond radio halos, and that the physical conditions in the outer regions of
the clusters are quite different from those in the radio halos. | Putting the Precision in Precision Cosmology: How accurate should your
data covariance matrix be?: Cosmological parameter estimation requires that the likelihood function of
the data is accurately known. Assuming that cosmological large-scale structure
power spectra data are multivariate Gaussian-distributed, we show the accuracy
of parameter estimation is limited by the accuracy of the inverse data
covariance matrix - the precision matrix. If the data covariance and precision
matrices are estimated by sampling independent realisations of the data, their
statistical properties are described by the Wishart and Inverse-Wishart
distributions, respectively. Independent of any details of the survey, we show
that the fractional error on a parameter variance, or a Figure-of-Merit, is
equal to the fractional variance of the precision matrix. In addition, for the
only unbiased estimator of the precision matrix, we find that the fractional
accuracy of the parameter error depends only on the difference between the
number of independent realisations and the number of data points, and so can
easily diverge. For a 5% error on a parameter error and N_D << 100 data-points,
a minimum of 200 realisations of the survey are needed, with 10% accuracy for
the data covariance. If the number of data-points N_D >>100 we need N_S > N_D
realisations and a fractional accuracy of <sqrt[2/N_D] in the data covariance.
As the number of power spectra data points grows to N_D>10^4 -10^6 this
approach will be problematic. We discuss possible ways to relax these
conditions: improved theoretical modelling; shrinkage methods;
data-compression; simulation and data resampling methods. |
Cosmological constraints and phenomenology of a beyond-Horndeski model: We study observational constraints on a specific dark energy model in the
framework of Gleyzes-Langlois-Piazza-Vernizzi theories, which extends the
Galileon ghost condensate (GGC) to the domain of beyond Horndeski theories. In
this model, we show that the Planck cosmic microwave background (CMB) data,
combined with datasets of baryon acoustic oscillations, supernovae type Ia, and
redshift-space distortions, give the tight upper bound $|\alpha_{\rm H}^{(0)}|
\le {\cal O}(10^{-6})$ on today's beyond-Horndeski (BH) parameter $\alpha_{\rm
H}$. This is mostly attributed to the shift of CMB acoustic peaks induced by
the early-time changes of cosmological background and perturbations arising
from the dominance of $\alpha_{\rm H}$ in the dark energy density. In
comparison to the $\Lambda$-cold-dark-matter ($\Lambda$CDM) model, our BH model
suppresses the large-scale integrated-Sachs-Wolfe (ISW) tail of CMB temperature
anisotropies due to the existence of cubic Galileons, and it modifies the
small-scale CMB power spectrum because of the different background evolution.
We find that the BH model considered fits the data better than $\Lambda$CDM
according to the $\chi^2$ statistics, yet the deviance information criterion
(DIC) slightly favors the latter. Given the fact that our BH model with
$\alpha_{\rm H}=0$ (i.e., the GGC model) is favored over $\Lambda$CDM even by
the DIC, there are no particular signatures for the departure from Horndeski
theories in current observations. | On a possible cosmological evolution of galaxy cluster $Y_{\rm X}-Y_{\rm
SZE}$ scaling relation: An important result from self-similar models that describe the process of
galaxy cluster formation is the simple scaling relation $Y_{\rm SZE}D_{\rm
A}^{2}/C_{\rm XSZE}Y_{\rm X}= C$. In this ratio, $Y_{\rm SZE}$ is the
integrated Sunyaev-Zel'dovich effect flux of a cluster, its x-ray counterpart
is $Y_{\rm X}$, $C_{\rm XSZE}$ and $C$ are constants and $D_{\rm A}$ is the
angular diameter distance to the cluster. In this paper, we consider the cosmic
distance duality relation validity jointly with type Ia supernovae observations
plus $61$ $Y_{\rm SZE}D_{\rm A}^{2}/C_{\rm XSZE}Y_{\rm X}$ measurements as
reported by the Planck Collaboration to explore if this relation is constant in
the redshift range considered ($z<0.5$). No one specific cosmological model is
used. As basic result, although the data sets are compatible with no redshift
evolution within 2$\sigma$ c.l., a Bayesian analysis indicates that other
$C(z)$ functions analyzed in this work cannot be discarded. It is worth to
stress that the observational determination of an universal $C(z)$ function
turns the $Y_{\rm SZE}D_{\rm A}^{2}/C_{\rm XSZE}Y_{\rm X}$ ratio in an useful
cosmological tool to determine cosmological parameters. |
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