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Evidence for a clumpy, rotating gas disk in a submillimeter galaxy at
z=4: We present Karl G. Jansky Very Large Array (VLA) observations of the CO(2-1)
emission in the z=4.05 submillimeter galaxy (SMG) GN20. These high-resolution
data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr
after the Big Bang. The data reveal a clumpy, extended gas reservoir, 14 +/- 4
kpc in diameter, in unprecedented detail. A dynamical analysis shows that the
data are consistent with a rotating disk of total dynamical mass 5.4 +/- 2.4 X
10^11 M_sun. We use this dynamical mass estimate to constrain the CO-to-H_2
mass conversion factor (alpha_CO), finding alpha_CO=1.1 +/- 0.6 M_sun (K km
s^-1 pc^2)^-1. We identify five distinct molecular gas clumps in the disk of
GN20 with masses a few percent of the total gas mass, brightness temperatures
of 16-31K, and surface densities of >3,200-4,500 X (alpha_CO/0.8) M_sun pc^-2.
Virial mass estimates indicate they could be self-gravitating, and we constrain
their CO-to-H_2 mass conversion factor to be <0.2-0.7 M_sun (K km s^-1
pc^2)^-1. A multiwavelength comparison demonstrates that the molecular gas is
concentrated in a region of the galaxy that is heavily obscured in the
rest-frame UV/optical. We investigate the spatially-resolved gas excitation and
find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with
star formation occuring over a large portion of the disk. We discuss the
implications of our results in the context of different fueling scenarios for
SMGs. | The role of environment in the morphological transformation of galaxies
in 9 intermediate redshift clusters: [abridged] We analyze a sample of 9 massive clusters at 0.4<z<0.6 observed
with MegaCam in 4 photometric bands (g,r,i,z) from the core to a radius of 5
Mpc (~4000 galaxies). Galaxy cluster candidates are selected using photometric
redshifts computed with HyperZ. Morphologies are estimated with galSVM in two
broad morphological types (early-type and late-type). We examine the
morphological composition of the red-sequence and the blue-cloud and study the
relations between galaxies and their environment through the morphology-density
relations (T-Sigma) and the morphology-radius relation (T-R) in a mass limited
sample (log(M/Msol)>9.5). We find that the red sequence is already in place at
z~0.5 and it is mainly composed of very massive (log(M/Msol)>11.3) early-type
galaxies. These massive galaxies seem to be already formed when they enter the
cluster, probably in infalling groups, since the fraction remains constant with
the cluster radius. Their presence in the cluster center could be explained by
a segregation effect reflecting an early assembly history. Any evolution that
takes place in the galaxy cluster population occurs therefore at lower masses
(10.3<log(M/Msol)<11.3). For these galaxies, the evolution, is mainly driven by
galaxy-galaxy interactions in the outskirts as revealed by the T-Sigma
relation. Finally, the majority of less massive galaxies (9.5<log(M/Msol)<10.3)
are late-type galaxies at all locations, suggesting that they have not started
the morphological transformation yet even if this low mass bin might be
affected by incompleteness. |
Pulsar timing array observations as possible hints for nonsingular
cosmology: Recent pulsar timing array (PTA) experiments have reported strong evidence of
the stochastic gravitational wave background (SGWB). If interpreted as
primordial gravitational waves (GWs), the signal favors a strongly blue-tilted
spectrum. Consequently, the nonsingular cosmology, which is able to predict a
strongly blue-tilted GW spectrum with $n_T \simeq 2$ on certain scales, offers
a potential explanation for the observed SGWB signal. In this paper, we present
a Genesis-inflation model capable of explaining the SGWB signal observed by the
PTA collaborations while also overcoming the initial singularity problem
associated with the inflationary cosmology. Furthermore, our model predicts
distinctive features in the SGWB spectrum, which might be examined by
forthcoming space-based gravitational wave experiments. | An Exploration of Heterogeneity in Supernova Type Ia Samples: We examine three SNe Type Ia datasets: Union2.1, JLA and Panstarrs to check
their consistency using cosmology blind statistical analyses as well as
cosmological parameter fitting. We find that Panstarrs dataset is the most
stable of the three to changes, although it does not, at the moment, go to high
enough redshifts to tightly constrain the dark energy equation of state, $w$.
Union2.1, drawn from many different sources, appears somewhat susceptible to
changes within the dataset. JLA reconstructs well for a smaller number of
cosmological parameters. At higher degrees of freedom, the dependence of its
errors on redshift can lead to varying results between subsets. Panstarrs is
inconsistent with the other two at about $2\sigma$, and JLA and Union2.1 are
about $1\sigma$ away from each other. For the $\Omega_{0m}-w$ cosmological
reconstruction, the $1\sigma$ range of values in $w$ for selected subsets of
each dataset is two times larger for JLA and Union2.1 as compared to Panstarrs.
The range in $\Omega_{0m}$ for the same subsets remains approximately similar
for all three datasets. Although there are differences in the fitting and
correction techniques used in the different samples, the most important
criterion is SNe selection, a slightly different SNe selection can lead to
noticeably different results both in the purely statistical analysis and
cosmological reconstruction. We note that a single, high quality low redshift
sample could help decrease the uncertainties in the result. We also note that
lack of homogeneity in the magnitude errors may bias the results and should
either be modeled, or its effect neutralized by using other, complementary
datasets. A supernova sample with high quality data at both high and low
redshifts, constructed from a few surveys to avoid heterogeneity in the sample,
and with homogeneous errors, would result in a more robust cosmological
reconstruction. |
Detecting relic gravitational waves in the CMB: Optimal parameters and
their constraints: The prospect of detecting relic gravitational waves (RGWs), through their
imprint in the cosmic microwave background radiation, provides an excellent
opportunity to study the very early Universe. In simplest viable theoretical
models the RGW background is characterized by two parameters, the
tensor-to-scalar ratio $r$ and the tensor spectral index $n_t$. In this paper,
we analyze the potential joint constraints on these two parameters, $r$ and
$n_t$, using the data from the upcoming cosmic microwave background radiation
experiments. Introducing the notion of the best pivot multipole $\ell_t^*$, we
find that at this pivot multipole the parameters $r$ and $n_t$ are
uncorrelated, and have the smallest variances. We derive the analytical
formulae for the best pivot multipole number $\ell_t^*$, and the variances of
the parameters $r$ and $n_t$. We verify these analytical calculations using
numerical simulation methods, and find agreement to within 20%. The analytical
results provides a simple way to estimate the detection ability for the relic
gravitational waves by the future observations of the cosmic microwave
background radiation. | Merger Response of Halo Anisotropy Properties: Anisotropy properties -- halo spin, shape, position offset, velocity offset,
and orientation -- are an important family of dark matter halo properties that
indicate the level of directional variation of the internal structures of
haloes. These properties reflect the dynamical state of haloes, which in turn
depends on the mass assembly history. In this work, we study the evolution of
anisotropy properties in response to merger activity using the IllustrisTNG
simulations. We find that the response trajectories of the anisotropy
properties significantly deviate from secular evolution. These trajectories
have the same qualitative features and timescales across a wide range of merger
and host properties. We propose explanations for the behaviour of these
properties and connect their evolution to the relevant stages of merger
dynamics. We measure the relevant dynamical timescales. We also explore the
dependence of the strength of the response on time of merger, merger ratio, and
mass of the main halo. These results provide insight into the physics of halo
mergers and their effects on the statistical behaviour of halo properties. This
study paves the way towards a physical understanding of scaling relations,
particularly to how systematics in their scatter are connected to the mass
assembly histories of haloes. |
Can varying the gravitational constant alleviate the tensions ?: Constraints on the cosmological concordance model parameters from observables
at different redshifts are usually obtained using the locally measured value of
the gravitational constant $G_N$. Here we relax this assumption, by considering
$G$ as a free parameter, either constant over the redshift range or dynamical
but limited to differ from fiducial value only above a certain redshift. Using
CMB data and distance measurements from galaxy clustering BAO feature, we
constrain the cosmological parameters, along with $G$, through a MCMC bayesian
inference method. Furthermore, we investigate whether the tensions on the
matter fluctuation $\sigma_8$ and Hubble $H_0$ parameter could be alleviated by
this new variable. We used different parameterisations spanning from a constant
$G$ to a dynamical $G$. In all the cases investigated in this work we found no
mechanism that alleviates the tensions when both CMB and BAO data are used with
$\xi_{\mathrm{g}} = G / G_N$ constrained to 1.0$\pm0.04$ (resp. $\pm0.01$) in
the constant (resp. dynamical) case. Finally, we studied the cosmological
consequences of allowing a running of the spectral index, since the later is
sensitive to a change in $G$. For the two parameterisations adopted, we found
no significant changes to the previous conclusions. | An Extended Zel'dovich Model for the Halo Mass Function: A new way to construct a fitting formula for the halo mass function is
presented. Our formula is expressed as a solution to the modified Jedamzik
matrix equation that automatically satisfies the normalization constraint. The
characteristic parameters expressed in terms of the linear shear eigenvalues
are empirically determined by fitting the analytic formula to the numerical
results from the high-resolution N-body simulation and found to be independent
of scale, redshift and background cosmology. Our fitting formula with the
best-fit parameters is shown to work excellently in the wide mass-range at
various redshifts: The ratio of the analytic formula to the N-body results
departs from unity by up to 10% and 5% over 10^{11}<= M/(M_sun/h)<= 5x10^{15}
at z=0,\ 0.5 and 1 for the FoF-halo and SO-halo cases, respectively. |
The Cosmic Large-Scale Structure in X-rays (CLASSIX) Cluster Survey I:
Probing galaxy cluster magnetic fields with line of sight rotation measures: To search for a signature of an intracluster magnetic field, we compare
measurements of Faraday rotation of polarised extragalactic radio sources in
the line of sight of galaxy clusters with those outside. We correlated a
catalogue of 1383 rotation measures (RM) of extragalactic polarised radio
sources with X-ray luminous galaxy clusters from the CLASSIX survey (combining
REFLEX II and NORAS II). We compared the RM in the line of sight of clusters
within their projected radii of r_500 with those outside and found a
significant excess of the dispersion of the RM in the cluster regions. Since
the observed RM is the result of Faraday rotation in several presumably
uncorrelated magnetised cells of the intracluster medium, the observations
correspond to quantities averaged over several magnetic field directions and
strengths. Therefore the interesting quantity is the standard deviation of the
RM for an ensemble of clusters. We found a standard deviation of the RM inside
r_500 of about 120 +- 21 rad m^-2. This compares to about 56 +- 8 rad m^-2
outside. We show that the most X-ray luminous and thus most massive clusters
contribute most to the observed excess RM. Modelling the electron density
distribution in the intracluster medium with a self-similar model, we found
that the dispersion of the RM increases with the column density, and we deduce
a magnetic field value of about 2 - 6 (l/10kpc)^-1/2 microG assuming a constant
magnetic field strength, where l is the size of the coherently magnetised
intracluster medium cells. This magnetic field energy density amounts to a few
percent of the average thermal energy density in clusters. When we assumed the
magnetic energy density to be a constant fraction of the thermal energy
density, we deduced a slightly lower value for this fraction of 3 - 10
(l/10kpc)^-1/2 per mille. | Free-floating "planets'' in the macrolensed quasar Q2237+0305: It has been claimed that the variability of field quasars resembles
gravitational lensing by a large cosmological population of free-floating
planets with mass of about 10 Earths. But Galactic photometric monitoring
experiments, on the other hand, exclude a large population of such
planetary-mass gravitational lenses. These apparently contradictory pieces of
evidence can be reconciled if the objects under consideration have a mean
column-density that lies between the critical column-densities for
gravitational lensing in these two contexts. Dark matter in that form is known
to be weakly collisional, so that a core develops in galaxy halo density
profiles, and a preferred model has already been established. Here we consider
what such a model implies for Q2237+0305, which is the best-studied example of
a quasar that is strongly lensed by an intervening galaxy. We construct
microlensing magnification maps appropriate to the four macro-images of the
quasar -- all of which are seen through the bulge of the galaxy. Each of these
maps exhibits a caustic network arising from the stars, plus many small,
isolated caustics arising from the free-floating "planets" in the lens galaxy.
The "planets" have little influence on the magnification histograms but a large
effect on the statistics of the magnification gradients. We compare our
predictions to the published OGLE photometry of Q2237+0305 and find that these
data are consistent with the presence of the hypothetical "planets". However,
the evidence is relatively weak because the OGLE dataset is not well suited to
testing our predictions and requires low-pass filtering for this application.
New data from a large, space-based telescope are desirable to address this
issue. |
Statistical Analysis of an AGN sample with Simultaneous UV and X-ray
Observations with Swift: I report on the statistical analysis of a sample of about 100 AGN with
simultaneous UV and X-ray observations with Swift. I found clear correlations
between the X-ray spectral slope alpha-X, the UV slope alpha-UV, and the
optical-to-x-ray spectral slope alpha-ox with the Eddington ratio L/Ledd. I
also report on the bolometric corrections for L(0.2-2.0 keV) and L(5100A). A
major aspect of the statistical analysis is multi-variate analysis statistical
tools such as the Principal Component Analysis (PCA) and cluster analysis. This
analysis shows that the main driver of the AGN properties in this sample is the
Eddington ratio L/Ledd. Although separating Seyfert 1s into NLS1s and BLS1s is
a good classification, with the 2000 km/s cutoff line it is still arbitrary. A
better classification scheme may be to separate AGN into low and highL/Ledd AGN
as suggested from the cluster analysis. | Halos and galaxies in the standard cosmological model: results from the
Bolshoi simulation: We present the first results from the new Bolshoi N-body cosmological LCDM
simulation that uses cosmological parameters favored by current observations.
The Bolshoi simulation was done in a volume 250Mpc on a side using 8billion
particles with mass and force resolution adequate to follow subhalos down to a
completeness limit of Vcirc=50km/ s circular velocity. Using excellent
statistics of halos and subhalos (10M at every moment and 50M over the whole
history) we present accurate approximations for statistics such as the halo
mass function, the concentrations for distinct halos and subhalos, abundance of
halos as function of their circular velocity, the abundance and the spatial
distribution of subhalos. We find that at high redshifts the concentration
falls to a minimum of about 3.8 and then rises slightly for higher values of
halo mass. We find that while the Sheth-Tormen approximation for the mass
function of halos found by spherical overdensity is accurate at low redshifts,
it over-predicts the abundance of halos by nearly an order of magnitude by
z=10. We find that the number of subhalos scales with the circular velocity of
the host halo as Vhost**0.5, and that subhalos have nearly the same radial
distribution as dark matter particles at radii 0.3-2 times the host halo virial
radius. The subhalo velocity function n(>V) behaves as V**(-3). We give
normalization of this relation for different masses and redshifts. Finally, we
use an abundance-matching procedure to assign r-band luminosities to dark
matter halos as a function of halo Vcirc, and find that the luminosity-velocity
relation is in remarkably good agreement with the observed Tully-Fisher
relation for galaxies in the range 50-200km/s. |
Natural Braneworld Inflation in Light of Recent Results from Planck and
BICEP2: In this paper we report on a major theoretical observation in cosmology. We
present a concrete cosmological model for which inflation has natural beginning
and natural ending. Inflation is driven by a cosine-form potential, $V(\phi)=
\Lambda^4 (1-\cos(\phi/f))$, which begins at $\phi \lesssim \pi f$ and ends at
$\phi =\phi_{\text{end}} \lesssim 5 f/3$. The distance traversed by the
inflaton field $\phi$ is sub-Planckian. The Gauss-Bonnet term ${\cal R}^2$
arising as leading curvature corrections in the action $S = \int d^5{x}
\sqrt{-g_{5}} M^3 (- 6\lambda M^2 + R + \alpha M^{-2} {\cal R}^2)+ \int d^{4}x
\sqrt{-g_{4}} (\dot{\phi}^2/2 - V(\phi)- \sigma +{\cal L}_{\text{matter}})$
(where $\alpha$ and $\lambda$ are constants and $M$ is the five-dimensional
Planck mass) plays a key role to terminate inflation. The model generates
appropriate tensor-to-scalar ratio $r$ and inflationary perturbations that are
consistent with results from Planck and BICEP2. For example, for $N_*= 50-60$
and $n_s\sim 0.960\pm 0.005$, the model predicts that $M\sim 5.64\times
10^{16}\,{\text{GeV}}$ and $r\sim (0.14-0.21)$ [$N_*$ is the number of {\it
e}--folds of inflation and $n_s$ ($n_{t}$) is the scalar (tensor) spectrum
spectral index]. The ratio $-n_t/r$ is (13% -- 24%) less than its value in 4D
Einstein gravity, $-n_t/r=1/8$. The upper bound on the energy scale of
inflation $V^{1/4}=2.37\times 10^{16}\,{\text{GeV}}$ ($r<0.27$) implies that
$(-\lambda \alpha) \gtrsim 75 \times 10^{-5}$ and $\Lambda<2.17\times
10^{16}\,{\text{GeV}}$, which thereby rule out the case $\alpha=0$
(Randall-Sundrum model). The true nature of gravity is holographic as implied
by braneworld realization of string and M theory. The model correctly predicts
a late epoch cosmic acceleration with the dark energy equation of state ${\text
w}_{\text{DE}}\approx -1$. | New composition dependent cooling and heating curves for galaxy
evolution simulations: In this paper, we present a new calculation of composition-dependent
radiative cooling and heating curves of low-density gas, intended primarily for
use in numerical simulations of galaxy formation and evolution. These curves
depend on only five parameters: temperature, density, redshift, [Fe/H], and
[Mg/Fe]. They are easily tabulated and can be efficiently interpolated during a
simulation.
The ionization equilibrium of 14 key elements is determined for temperatures
between 10K and 10^9K and densities up to 100 amu/cm^3 taking into account
collisional and radiative ionization, by the cosmic UV background and an
interstellar radiation field, and by charge-transfer reactions. These elements,
ranging from H to Ni, are the ones most abundantly produced and/or released by
SNIa, SNII, and intermediate-mass stars. Self-shielding of the gas at high
densities by neutral Hydrogen is taken into account in an approximate way by
exponentially suppressing the H-ionizing part of the cosmic UV background for
HI densities above a threshold density of n_HI,crit=0.007 cm^-3. We discuss how
the ionization equilibrium, and the cooling and heating curves depend on the
physical properties of the gas.
The main advantage of the work presented here is that, within the confines of
a well-defined chemical evolution model and adopting the ionization equilibrium
approximation, it provides accurate cooling and heating curves for a wide range
of physical and chemical gas properties, including the effects of
self-shielding. The latter is key to resolving the formation of cold, neutral,
high-density clouds suitable for star formation in galaxy simulations. |
Evidence of a double-double morphology in B0818+214: The so-called double-double structure in radio sources is the most
conspicuous signature of their restarted activity. Observations indicate that
in the majority of double-double radio sources (DDRS), the span of the radio
lobes is larger than 0.7 Mpc. This lower limit is also suggested by theory.
However, it seemed likely that the apparent core of B0818+214, a radio galaxy
with an overall linear size of its radio structure below that limit, could
harbour a compact double well aligned with the outer lobes so that the whole
object would fulfil the criteria of a DDRS. Here, we present evidence that the
central component of B0818+214, when magnified through the EVN+MERLIN 18-cm
observations, shows two FR II-like lobes. As the separation of the inner lobes
is not greater than 5.7 kpc, they are immersed in the ISM of the host galaxy.
This circumstance is the likely reason why the inner double has become visible,
despite the predictions of the theory according to which B0818+214 as a whole
is too small for a new double to develop inside the cocoon inflated during the
previous active phase. Moreover, we speculate that its host galaxy is not
active at the moment and so the inner double may be in the coasting phase often
observed in other medium-sized symmetric objects with intermittent activity. It
could be, therefore, that two different mechanisms of accretion disk
instabilities, ionisation and radiation-pressure driven, may be independently
responsible for triggering active phases, manifesting as the outer and the
inner doubles, respectively. | Measurement of the cosmogenic activation of germanium detectors in
EDELWEISS-III: We present a measurement of the cosmogenic activation in the germanium
cryogenic detectors of the EDELWEISS III direct dark matter search experiment.
The decay rates measured in detectors with different exposures to cosmic rays
above ground are converted into production rates of different isotopes. The
measured production rates in units of nuclei/kg/day are 82 $\pm$ 21 for $^3$H,
2.8 $\pm$ 0.6 for $^{49}$V, 4.6 $\pm$ 0.7 for $^{55}$Fe, and 106 $\pm$ 13 for
$^{65}$Zn. These results are the most accurate for these isotopes. A lower
limit on the production rate of $^{68}$Ge of 74 nuclei/kg/day is also
presented. They are compared to model predictions present in literature and to
estimates calculated with the ACTIVIA code. |
Nonlinear structure formation in Nonlocal Gravity: We study the nonlinear growth of structure in nonlocal gravity models with
the aid of N-body simulation and the spherical collapse and halo models. We
focus on a model in which the inverse-squared of the d'Alembertian operator
acts on the Ricci scalar in the action. For fixed cosmological parameters, this
model differs from $\Lambda{\rm CDM}$ by having a lower late-time expansion
rate and an enhanced and time-dependent gravitational strength ($\sim 6\%$
larger today). Compared to $\Lambda{\rm CDM}$ today, in the nonlocal model,
massive haloes are slightly more abundant (by $\sim 10\%$ at $M \sim 10^{14}
M_{\odot}/h$) and concentrated ($\approx 8\%$ enhancement over a range of mass
scales), but their linear bias remains almost unchanged. We find that the
Sheth-Tormen formalism describes the mass function and halo bias very well,
with little need for recalibration of free parameters. The fitting of the halo
concentrations is however essential to ensure the good performance of the halo
model on small scales. For $k \gtrsim 1 h/{\rm Mpc}$, the amplitude of the
nonlinear matter and velocity divergence power spectra exhibits a modest
enhancement of $\sim 12\%$ to $15\%$, compared to $\Lambda{\rm CDM}$ today.
This suggests that this model might only be distinguishable from $\Lambda{\rm
CDM}$ by future observational missions. We point out that the absence of a
screening mechanism may lead to tensions with Solar System tests due to local
time variations of the gravitational strength, although this is subject to
assumptions about the local time evolution of background averaged quantities. | Parametrizing growth in dark energy and modified gravity models: It is well-known that an extremely accurate parametrization of the growth
function of matter density perturbations in $\Lambda$CDM cosmology, with errors
below $0.25 \%$, is given by $f(a)=\Omega_{m}^{\gamma} \,(a)$ with $\gamma
\simeq 0.55$. In this work, we show that a simple modification of this
expression also provides a good description of growth in modified gravity
theories. We consider the model-independent approach to modified gravity in
terms of an effective Newton constant written as $\mu(a,k)=G_{eff}/G$ and show
that $f(a)=\beta(a)\Omega_{m}^{\gamma} \,(a)$ provides fits to the numerical
solutions with similar accuracy to that of $\Lambda$CDM. In the
time-independent case with $\mu=\mu(k)$, simple analytic expressions for
$\beta(\mu)$ and $\gamma(\mu)$ are presented. In the time-dependent (but
scale-independent) case $\mu=\mu(a)$, we show that $\beta(a)$ has the same time
dependence as $\mu(a)$. As an example, explicit formalae are provided in the
DGP model. In the general case, for theories with $\mu(a,k)$, we obtain a
perturbative expansion for $\beta(\mu)$ around the General Relativity case
$\mu=1$ which, for $f(R)$ theories, reaches an accuracy below $1 \%$. Finally,
as an example we apply the obtained fitting functions in order to forecast the
precision with which future galaxy surveys will be able to measure the $\mu$
parameter. |
Constraints on non-flat cosmologies with massive neutrinos after Planck
2015: We investigate two dark energy cosmological models (i.e., the $\Lambda$CDM
and $\phi$CDM models) with massive neutrinos assuming two different neutrino
mass hierarchies in both the spatially flat and non-flat scenarios, where in
the $\phi$CDM model the scalar field possesses an inverse power-law potential,
$V(\phi)\propto {\phi}^{-\alpha}$ ($\alpha>0$). Cosmic microwave background
data from Planck 2015, baryon acoustic oscillations data from 6dFGS, SDSS-MGS,
BOSS-LOWZ and BOSS CMASS-DR11, the JLA compilation of Type Ia supernova
apparent magnitude observations, and the Hubble Space Telescope $H_0$ prior,
are jointly employed to constrain the model parameters. We first determine
constraints assuming three species of degenerate massive neutrinos. In the
spatially flat (non-flat) $\Lambda$CDM model, the sum of neutrino masses is
bounded as $\Sigma m_{\nu} < 0.165 (0.299)$ eV at 95% confidence level (CL).
Correspondingly, in the flat (non-flat) $\phi$CDM model, we find $\Sigma
m_{\nu} < 0.164 (0.301)$ eV at 95% CL. The inclusion of spatial curvature as a
free parameter results in a significant broadening of confidence regions for
$\Sigma m_{\nu}$ and other parameters. In the scenario where the total neutrino
mass is dominated by the heaviest neutrino mass eigenstate, we can obtain the
similar conclusions as those obtained in the degenerate neutrino mass scenario.
In addition, the results show that the bounds on $\Sigma m_{\nu}$ based on two
different neutrino mass hierarchies have insignificant differences in the
spatially flat case for both the $\Lambda$CDM and $\phi$CDM models, however,
the corresponding differences are larger in the non-flat case. | Kinematics of the parsec-scale radio jet in 3C48: We present results on the compact steep-spectrum quasar 3C 48 from
observations with the VLBA, MERLIN and EVN at multiple radio frequencies. In
the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright
knots. The active nucleus is embedded in the southernmost VLBI component A,
which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz.
A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly
polarized VLBI components are located at component C $\sim$0.25 arcsec north of
the core. The polarization angles at C show gradual changes across the jet
width at all observed frequencies, indicative of a gradient in the
emission-weighted intrinsic polarization angle across the jet and possibly a
systematic gradient in the rotation measure; moreover, the percentage of
polarization increases near the curvature at C, likely consistent with the
presence of a local jet-ISM interaction and/or changing magnetic-field
directions. The hot spot B shows a higher rotation measure, and has no detected
proper motion. These facts provide some evidence for a stationary shock in the
vicinity of B. Comparison of the present VLBI observations with those made 8.43
years ago suggests a proper motion of $\beta_{app}=3.7\pm0.4 c$ for A2 to the
north. The apparent superluminal motion suggests that the relativistic jet
plasma moves at a velocity of $\gtrsim0.96 c$ if the jet is viewed at an
inclination angle less than $20\degr$. A simple precessing jet model and a
hydrodynamical isothermal jet model with helical-mode Kelvin-Helmholtz
instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined
by the bright knots. |
Constraints on $f(R)$ and nDGP Modified Gravity Model Parameters with
Cluster Abundances and Galaxy Clustering: We present forecasted cosmological constraints from combined measurements of
galaxy cluster abundances from the Simons Observatory and galaxy clustering
from a DESI-like experiment on two well-studied modified gravity models, the
chameleon-screened $f(R)$ Hu-Sawicki model and the nDGP braneworld Vainshtein
model.
A Fisher analysis is conducted using $\sigma_8$ constraints derived from
thermal Sunyaev-Zel'dovich (tSZ) selected galaxy clusters, as well as linear
and mildly non-linear redshift-space 2-point galaxy correlation functions. We
find that the cluster abundances drive the constraints on the nDGP model while
$f(R)$ constraints are led by galaxy clustering. The two tracers of the
cosmological gravitational field are found to be complementary, and their
combination significantly improves constraints on the $f(R)$ in particular in
comparison to each individual tracer alone.
For a fiducial model of $f(R)$ with $\text{log}_{10}(f_{R0})=-6$ and $n=1$ we
find combined constraints of $\sigma(\text{log}_{10}(f_{R0}))=0.48$ and
$\sigma(n)=2.3$, while for the nDGP model with $n_{\text{nDGP}}=1$ we find
$\sigma(n_{\text{nDGP}})=0.087$. Around a fiducial General Relativity (GR)
model, we find a $95\%$ confidence upper limit on $f(R)$ of
$f_{R0}\leq5.68\times 10^{-7}$. Our results present the exciting potential to
utilize upcoming galaxy and CMB survey data available in the near future to
discern and/or constrain cosmic deviations from GR. | Deep LBT/LUCI Spectroscopy of a Lyman-alpha Emitter Candidate at z ~ 7.7: We present deep spectroscopic observations of a Lyman-alpha emitter (LAE)
candidate at z ~ 7.7 using the infrared spectrograph LUCI on the 2 x 8.4m Large
Binocular Telescope (LBT). The candidate is the brightest among the four z ~
7.7 LAE candidates found in a narrow-band imaging survey by Krug et al. 2012.
Our spectroscopic data include a total of 7.5 hours of integration with
LBT/LUCI and are deep enough to significantly (3.2-4.9 sigma) detect the
Lyman-alpha emission line of this candidate, based on its Lyman-alpha flux 1.2
x 10^{-17} erg s^{-1} cm^{-2} estimated from the narrow-band photometry.
However, we do not find any convincing signal at the expected position of its
Lyman-alpha emission line, suggesting that this source is not an LAE at z ~
7.7. The non-detection in this work, together with the previous studies of z ~
7.7 LAEs, puts a strong constraint on the bright-end Lyman-alpha luminosity
function (LF) at z ~ 7.7. We find a rapid evolution of the Lyman-alpha LF from
z ~ 6.5 to 7.7: the upper limit of the z ~ 7.7 LF is more than 5 times lower
than the z ~ 6.5 LF at the bright end (f > 1.0 x 10^{-17} erg s^{-1} cm^{-2},
or L > 6.9 x 10^{42} erg s^{-1}). This is likely caused by an increasing
neutral fraction in the IGM that substantially attenuates Lyman-alpha emission
at z ~ 7.7. |
Multi-field dark energy: cosmic acceleration on a steep potential: We argue that dark energy with multiple fields is theoretically
well-motivated and predicts distinct observational signatures, in particular
when cosmic acceleration takes place along a trajectory that is highly
non-geodesic in field space. Such models provide novel physics compared to
$\Lambda$CDM and quintessence by allowing cosmic acceleration on steep
potentials. From the theoretical point of view, these theories can easily
satisfy the conjectured swampland constraints and may in certain cases be
technically natural, potential problems which are endemic to standard
single-field dark energy. Observationally, we argue that while such multi-field
models are likely to be largely indistinguishable from the concordance
cosmology at the background level, dark energy perturbations can cluster,
leading to an enhanced growth of large-scale structure that may be testable as
early as the next generation of cosmological surveys. | Renyi entropy as a measure of cosmic homogeneity: We propose a method for testing homogeneity in three dimensional spatial
distributions using Renyi entropy. We apply the proposed method to data from
cosmological N-body simulations and Monte Carlo simulations of homogeneous
Poisson point process. We show that the method can effectively characterize the
inhomogeneities and identify any transition scale to homogeneity, if present in
such distributions. The proposed method can be used to study the cosmic
homogeneity in present and future generation galaxy redshift surveys. |
Lyman-alpha Emitters in Ionized Bubbles: Constraining the Environment
and Ionized Fraction: Lyman-alpha emitters (LAEs) are excellent probes of the reionization process,
as they must be surrounded by large ionized bubbles in order to be visible
during the reionization era. Large ionized regions are thought to correspond to
over-dense regions and may be protoclusters, making them interesting test-beds
for early massive structures. Close associations containing several LAEs are
often assumed to mark over-dense, ionized bubbles. Here, we develop the first
framework to quantify the ionization and density fields of high-z galaxy
associations. We explore the interplay between (i) the large-scale density of a
survey field, (ii) Poisson noise due to the small number density of bright
sources at high redshifts (z~7), and (iii) the effects of the ionized fraction
on the observation of LAEs. We use Bayesian statistics, a simple model of
reionization, and a Monte-Carlo simulation to construct a more comprehensive
method for calculating the large-scale density of LAE regions than previous
works. We find that Poisson noise has a strong effect on the inferred density
of a region and show how the ionized fraction can be inferred. We then apply
our framework to the strongest association yet identified: Hu et al. (2021)
found 14 LAEs in a volume of ~50,000 cMpc^3 inside the COSMOS field at z~7. We
show that this is most likely a 2.5-sigma over-density inside of an ionized or
nearly ionized bubble. We also show that this LAE association implies that the
global ionized fraction is Q = 0.60 (+0.08,-0.09), within the context of a
simple reionization model. | Formation of galactic nuclei with multiple supermassive black holes at
high redshifts: We examine the formation of groups of multiple supermassive black holes
(SMBHs) in gas-poor galactic nuclei due to the high merger rate of galaxies at
high redshifts. We calculate the relative likelihood of binary, triple, and
quadruple SMBH systems, by considering the timescales for relevant processes
and combining merger trees with N-body simulations for the dynamics of stars
and SMBHs in galactic nuclei. Typical haloes today with mass $M_0\approx
10^{14}$ M$_\odot$ have an average mass $M_{z=6}=5\times 10^{11}$ M$_\odot$ at
$z\sim 6$, while rare haloes with current mass $M_0\gtrsim 10^{15}$ M$_\odot$
have an average mass $M_{z=6}=5\times 10^{12}$ M$_\odot$ at that redshift.
These cluster-size haloes are expected to host single galaxies at $z\sim 6$. We
expect about 30% galaxies within haloes with present-day mass $M_0\approx
10^{14}$ M$_\odot$ to contain more than two SMBHs at redshifts $2\lesssim
z\lesssim 6$. For larger present-day haloes, with $M_0\gtrsim 10^{15}$
M$_\odot$, this fraction is almost 60%. The existence of multiple SMBHs at high
redshifts can potentially explain the mass deficiencies observed in the cores
of massive elliptical galaxies, which are up to 5 times the mass of their
central BHs. Multiple SMBHs would also lead to an enhanced rate of tidal
disruption of stars, modified gravitational wave signals compared to isolated
BH binaries, and slingshot ejection of SMBHs from galaxies at high speeds in
excess of 2000 km s$^{-1}$. |
Effect of intermediate Minkowskian evolution on CMB bispectrum: We consider a non-inflationary early Universe scenario in which relevant
scalar perturbations get frozen out at some point, but then are defrosted and
follow a long nearly Minkowskian evolution before the hot era. This
intermediate stage leaves specific imprint on the CMB 3-point function, largely
independent of details of microscopic physics. In particular, the CMB
bispectrum undergoes oscillations in the multipole l space with roughly
constant amplitude. The latter is in contrast to the oscillatory bispectrum
enhanced in the flattened triangle limit, as predicted by inflation with
non-Bunch--Davies vacuum. Given this and other peculiar features of the
bispectrum, stringent constraints imposed by the Planck data may not apply. The
CMB 3-point function is suppressed by the inverse duration squared of the
Minkowskian evolution, but can be of observable size for relatively short
intermediate Minkowskian stage. | The Gravitational Wave Background and Higgs False Vacuum Inflation: For a narrow band of values of the top quark and Higgs boson masses, the
Standard Model Higgs potential develops a shallow local minimum at energies of
about $10^{16}$ GeV, where primordial inflation could have started in a cold
metastable state. For each point of that band, the highness of the Higgs
potential at the false minimum is calculable, and there is an associated
prediction for the inflationary gravitational wave background, namely for the
tensor to scalar ratio $r$. We show that the recent measurement of $r$ by the
BICEP2 collaboration, $r=0.16 _{-0.05}^{+0.06}$ at $1\sigma$, combined with the
most up-to-date measurements of the top quark and Higgs boson masses, reveals
that the hypothesis that a Standard Model shallow false minimum was the source
of inflation in the early Universe is viable. |
Low-Ionization Outflows in High Eddington Ratio Quasars: The broad MgII doublet has been much studied in connection with its
potentially important role as a virial estimator of black hole mass in high
redshift quasars. An important task is therefore identification of any line
components likely related to broadening by non-virial motions. High s/n median
composite spectra (binned in the "4D eigenvector 1" context of Sulentic et al.
2007) were constructed for the brightest 680 SDSS DR7 quasars in the 0.4 < z <
0.75 range where both MgII 2800 and Hbeta are recorded in the same spectra.
Composite spectra representing 90% of the quasars confirm previous findings
that FWHM(MgII 2800) is about 20% narrower than FWHM(Hbeta). The situation is
clearly different for the most extreme (Population A) sources which are the
highest Eddington radiators in the sample. In the median spectra of these
sources FWHM MgII 2800 is equal to or greater than FWHM(Hbeta) and shows a
significant blueshift relative to Hbeta. We interpret the MgII 2800 blueshift
as the signature of a radiation-driven wind or outflow in the highest accreting
quasars. In this interpretation the MgII 2800 line width -- affected by
blueshifted emission -- is unsuitable for virial mass estimation in ~ 10% of
quasars. | Map-based cosmology inference with lognormal cosmic shear maps: Most cosmic shear analyses to date have relied on summary statistics (e.g.
$\xi_+$ and $\xi_-$). These types of analyses are necessarily sub-optimal, as
the use of summary statistics is lossy. In this paper, we forward-model the
convergence field of the Universe as a lognormal random field conditioned on
the observed shear data. This new map-based inference framework enables us to
recover the joint posterior of the cosmological parameters and the convergence
field of the Universe. Our analysis properly accounts for the covariance in the
mass maps across tomographic bins, which significantly improves the fidelity of
the maps relative to single-bin reconstructions. We verify that applying our
inference pipeline to Gaussian random fields recovers posteriors that are in
excellent agreement with their analytical counterparts. At the resolution of
our maps -- and to the extent that the convergence field can be described by
the lognormal model -- our map posteriors allow us to reconstruct \it all \rm
summary statistics (including non-Gaussian statistics). We forecast that a
map-based inference analysis of LSST-Y10 data can improve cosmological
constraints in the $\sigma_8$--$\Omega_{\rm m}$ plane by $\approx 30\%$
relative to the currently standard cosmic shear analysis. This improvement
happens almost entirely along the $S_8=\sigma_8\Omega_{\rm m}^{1/2}$
directions, meaning map-based inference fails to significantly improve
constraints on $S_8$. |
CMB anisotropies generated by a stochastic background of primordial
magnetic fields with non-zero helicity: We consider the impact of a stochastic background of primordial magnetic
fields with non-vanishing helicity on CMB anisotropies in temperature and
polarization. We compute the exact expressions for the scalar, vector and
tensor part of the energy-momentum tensor including the helical contribution,
by assuming a power-law dependence for the spectra and a comoving cutoff which
mimics the damping due to viscosity. We also compute the parity-odd correlator
between the helical and non-helical contribution which generate the TB and EB
cross-correlation in the CMB pattern. We finally show the impact of including
the helical term on the power spectra of CMB anisotropies up to multipoles with
ell ~ O(10^3)$. | HerMES: deep number counts at 250, 350, and 500 microns in the COSMOS
and GOODS-N fields and the build-up of the cosmic infrared background: ABRIGED Herschel/SPIRE has provided confusion limited maps of deep fields at
250, 350, and 500um, as part of the HerMES survey. Due to confusion, only a
small fraction of the Cosmic Infrared Background can be resolved into
individually-detected sources. Our goal is to produce deep galaxy number counts
and redshift distributions below the confusion limit, which we then use to
place strong constraints on the origins of the cosmic infrared background and
on models of galaxy evolution.
We individually extracted the bright SPIRE with a method using the positions,
the flux densities, and the redshifts of the 24um sources as a prior, and
derived the number counts and redshift distributions of the bright SPIRE
sources. For fainter SPIRE sources, we reconstructed the number counts and the
redshift distribution below the confusion limit using the deep 24um catalogs
associated with photometric redshift and information provided by the stacking
of these sources into the deep SPIRE maps. Finally, by integrating all these
counts, we studied the contribution of the galaxies to the CIB as a function of
their flux density and redshift.
Through stacking, we managed to reconstruct the source counts per redshift
slice down to ~2 mJy in the three SPIRE bands, which lies about a factor 10
below the 5sigma confusion limit. None of the pre-existing population models
are able to reproduce our results at better than 3sigma. Finally, we
extrapolate our counts to zero flux density in order to derive an estimate of
the total contribution of galaxies to the CIB, finding 10.1, 6.5, and 2.8
nW/m2/sr at 250, 350, and 500um, respectively. These values agree well with
FIRAS absolute measurements, suggesting our number counts and their
extrapolation are sufficient to explain the CIB. Finally, combining our results
with other works, we estimate the energy budget contained in the CIB between 8
and 1000um: 26 nW/m2/sr. |
Growth of non-linear structures and spherical collapse in the Galileon
Ghost Condensate model: We present a detailed study of the collapse of a spherical matter overdensity
and the non-linear growth of large scale structures in the Galileon ghost
condensate (GGC) model. This model is an extension of the cubic covariant
Galileon (G3) which includes a field derivative of type
$(\nabla_\mu\phi\nabla^\mu\phi)^2$ in the Lagrangian. We find that the cubic
term activates the modifications in the main physical quantities whose time
evolution is then strongly affected by the additional term. Indeed, the GGC
model shows largely mitigated effects in the linearised critical density
contrast, non-linear effective gravitational coupling and the virial
overdensity with respect to G3 but still preserves peculiar features with
respect to the standard $\Lambda$CDM cosmological model, e.g. both the linear
critical density contrast and the virial overdensity are larger than those in
$\Lambda$CDM. The results of the spherical collapse model are then used to
predict the evolution of the halo mass function, non-linear matter and lensing
power spectra. While at low masses the GGC model presents about 10% fewer
objects with respect to $\Lambda$CDM, at higher masses for $z>0$ it predicts
10% ($z=0.5$)-20% ($z=1$) more objects per comoving volume. Using a
phenomenological approach to include the screening effect in the matter power
spectrum, we show that the difference induced by the modifications of gravity
are strongly dependent on the screening scale and that differences can be up to
20% with respect to $\Lambda$CDM. These differences translate to the lensing
power spectrum where qualitatively the largest differences with respect to the
standard cosmological model are for $\ell<10^3$. Depending on the screening
scale, they can be up to 25% on larger angular scales and then decrease for
growing $\ell$. These results are obtained for the best fit parameters from
linear cosmological data for each model. | A demonstration of the effect of fringe-rate filtering in the Hydrogen
Epoch of Reionization Array delay power spectrum pipeline: Radio interferometers targeting the 21cm brightness temperature fluctuations
at high redshift are subject to systematic effects that operate over a range of
different timescales. These can be isolated by designing appropriate Fourier
filters that operate in fringe-rate (FR) space, the Fourier pair of local
sidereal time (LST). Applications of FR filtering include separating effects
that are correlated with the rotating sky vs. those relative to the ground,
down-weighting emission in the primary beam sidelobes, and suppressing noise.
FR filtering causes the noise contributions to the visibility data to become
correlated in time however, making interpretation of subsequent averaging and
error estimation steps more subtle. In this paper, we describe fringe rate
filters that are implemented using discrete prolate spheroidal sequences, and
designed for two different purposes -- beam sidelobe/horizon suppression (the
`mainlobe' filter), and ground-locked systematics removal (the `notch' filter).
We apply these to simulated data, and study how their properties affect
visibilities and power spectra generated from the simulations. Included is an
introduction to fringe-rate filtering and a demonstration of fringe-rate
filters applied to simple situations to aid understanding. |
The changing Lya optical depth in the range 6<z<9 from MOSFIRE
spectroscopy of Y-dropouts: We present MOSFIRE spectroscopy of 13 candidate z~8 galaxies selected as
Y-dropouts as part of the BoRG pure parallel survey. We detect no significant
lya emission (our median 1-sigma rest frame equivalent width sensitivity is in
the range 2-16 AA). Using the Bayesian framework derived in a previous paper,
we perform a rigorous analysis of a statistical subsample of non-detections for
ten Y-dropouts, including data from the literature, to study the cosmic
evolution of the lya emission of Lyman Break Galaxies. We find that lya
emission is suppressed at z~8 by at least a factor of three with respect to z~6
continuing the downward trend found by previous studies of z-dropouts at z~7.
This finding suggests a dramatic evolution in the conditions of the
intergalactic or circumgalactic media in just 300 Myrs, consistent with the
onset of reionization or changes in the physical conditions of the first
generations of starforming regions. | Dark Matter Isocurvature from Curvature: Isocurvature fluctuations, where the relative number density of particle
species spatially varies, can be generated from initially adiabatic, or
curvature, fluctuations if the various species fall out of or were never in
thermal equilibrium. The freezing of the thermal relic dark matter abundance is
one such case, but for modes that are still outside the horizon the amplitude
is highly suppressed and originates from the small change in the local
expansion rate due to the local space curvature produced by the curvature
fluctuation. We establish a simple separate-universe method for calculating
this generation that applies to both freeze-in and freeze-out models, identify
three critical epochs for this process, and give general scaling behaviors for
the amplitude in each case: the freezing epoch, the kinetic decoupling epoch
and matter-radiation equality. Freeze-out models are typically dominated by
spatially modulated annihilation from the latter epochs and can generate much
larger isocurvature fluctuations compared with typical freeze-in models, albeit
still very small and observationally allowed by cosmic microwave background
measurements. We illustrate these results with concrete models where the dark
matter interactions are vector or scalar mediated. |
Weak lensing signal in Unified Dark Matter models: Weak gravitational lensing is a powerful tool for studying both the geometry
and the dynamics of the Universe. Its power spectrum contains information on
the sources emitting photons and on the large--scale structures that these
hotons cross. We calculate the weak lensing cosmic convergence and shear power
spectra, in linear theory and Limber's approximation, for two different classes
of cosmological models: the standard \LambdaCDM and Unified Dark Matter (UDM)
models. The latter models attempt to solve the problems of the dark matter in
the dynamics of galaxies and galaxy clusters and of the late-time acceleration
of the Universe expansion by introducing a scalar field that mimics both dark
matter and dark energy. A crucial feature of the UDM models is the speed of
sound c_\infty, that is the value of the sound speed at late times, on which
structure formation depends. In this paper, we provide the predictions of the
UDM models for the weak lensing signal,with various values of c_\infty. We
consider both the Cosmic Microwave Background and background galaxies at
different redshifts as sources for the weak lensing power spectra. We find that
the power spectra in UDM models are more sensitive to the variations of
c_\infty for sources located at low redshifts. Moreover, we find that for
c_\infty>10^{-3} (in units of the speed of light), the UDM weak lensing
convergence power spectrum C^{\kappa\kappa}(l) for background galaxies is
strongly suppressed with respect to the \LambdaCDM spectrum, particularly at
small angular scales l\gtrsim100. | Momentum space sampling of neutrinos in $N$-body simulations: Including massive neutrinos in $N$-body simulations is a challenging task due
to the large thermal velocities of the neutrinos. In particle based codes this
leads to problems of shot-noise due to insufficient sampling of the neutrino
momentum distribution function. In this paper we investigate the benefits and
drawbacks of a scheme first suggested in a paper by Banerjee et al. in which
the initial neutrino distribution is symmetrised in momentum space. We confirm
that this method reduce shot-noise significantly, but we also find that it
generates some spurious power in the neutrino power spectrum at intermediate
and small scales. We speculate that this happens because many neutrinos in the
simulation sample the same underlying dark matter structures while moving
through the simulation. By carefully tuning the number of directions in
momentum space of the initial neutrino distribution we show that some
improvements can be made over the case where initial neutrino directions are
purely random. At redshifts $z\gtrsim 3$ the method works very well, but at
smaller redshifts significant improvements are not possible due to the spurious
power generation. |
Double-Peaked Narrow Emission Lines in AGN: The Role of Rotating Disks: AGN with double-peaked narrow lines (DPAGN) may be caused by kiloparsec scale
binary AGN, bipolar outflows, or rotating gaseous disks. We examine the class
of DPAGN in which the two narrow line components have closely similar intensity
as being especially likely to involve disks or jets. Two spectroscopic
indicators support this likelihood. For DPAGN from Smith et al. (2010), the
"equal-peaked" objects (EPAGN) have [Ne V]/[O III] ratios lower than for a
control sample of non-double peaked AGN. This is unexpected for a pair of
normal AGN in a galactic merger, but may be consistent with [O III] emission
from a rotating ring with relatively little gas at small radii. Also, [O
III]/H-beta ratios of the redshifted and blueshifted systems in the EPAGN are
more similar to each other than in a control sample, suggestive of a single
ionizing source and inconsistent with the binary interpretation. | Analysis of the Early-Time Optical Spectra of SN 2011fe in M101: The nearby Type Ia supernova SN 2011fe in M101 (cz=241 km s^-1) provides a
unique opportunity to study the early evolution of a "normal" Type Ia
supernova, its compositional structure, and its elusive progenitor system. We
present 18 high signal-to-noise spectra of SN 2011fe during its first month
beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This
gives a clear picture of how various line-forming species are distributed
within the outer layers of the ejecta, including that of unburned material
(C+O). We follow the evolution of C II absorption features until they diminish
near maximum light, showing overlapping regions of burned and unburned material
between ejection velocities of 10,000 and 16,000 km s^-1. This supports the
notion that incomplete burning, in addition to progenitor scenarios, is a
relevant source of spectroscopic diversity among SNe Ia. The observed evolution
of the highly Doppler-shifted O I 7774 absorption features detected within five
days post-explosion indicate the presence of O I with expansion velocities from
11,500 to 21,000 km s^-1. The fact that some O I is present above C II suggests
that SN 2011fe may have had an appreciable amount of unburned oxygen within the
outer layers of the ejecta. |
Simulations of the Microwave Sky: We create realistic, full-sky, half-arcminute resolution simulations of the
microwave sky matched to the most recent astrophysical observations. The
primary purpose of these simulations is to test the data reduction pipeline for
the Atacama Cosmology Telescope (ACT) experiment; however, we have widened the
frequency coverage beyond the ACT bands to make these simulations applicable to
other microwave background experiments. Some of the novel features of these
simulations are that the radio and infrared galaxy populations are correlated
with the galaxy cluster populations, the CMB is lensed by the dark matter
structure in the simulation via a ray-tracing code, the contribution to the
thermal and kinetic Sunyaev-Zel'dovich (SZ) signals from galaxy clusters,
groups, and the IGM has been included, and the gas prescription to model the SZ
signals matches the most recent X-ray observations. Regarding the contamination
of cluster SZ flux by radio galaxies, we find for 148 GHz (90 GHz) only 3% (4%)
of halos have their SZ decrements contaminated at a level of 20% or more. We
find the contamination levels higher for infrared galaxies. However, at 90 GHz,
less than 20% of clusters with M_{200} > 2.5 x 10^{14} Msun and z<1.2 have
their SZ decrements filled in at a level of 20% or more. At 148 GHz, less than
20% of clusters with M_{200} > 2.5 x 10^{14} Msun and z<0.8 have their SZ
decrements filled in at a level of 50% or larger. Our models also suggest that
a population of very high flux infrared galaxies, which are likely lensed
sources, contribute most to the SZ contamination of very massive clusters at 90
and 148 GHz. These simulations are publicly available and should serve as a
useful tool for microwave surveys to cross-check SZ cluster detection, power
spectrum, and cross-correlation analyses. | Bose-Einstein condensation of photons in the matter-dominated universe: In 1914, Planck introduced the concept of a white body. In nature, no true
white bodies are known. We assume that the universe after last-scattering is an
ideal white body that contains a tremendously large number of thermal photons
and is at an extremely high temperature. Bose-Einstein condensation of photons
in an ideal white body is investigated within the framework of quantum
statistical mechanism. The computation shows that the transition temperature
$T_c$ is a monotonically increasing function of the number density $n$ of
photons. At finite temperature, we find that the condensate fraction $N_0(T)/N$
decreases continuously from unity to zero as the temperature increases from
zero to the transition temperature $T_c$. Further, we study the radiation
properties of an ideal white body. It is found that in the condensation region
of $T<T_c$, the spectral intensity $I(\omega,T)$ of white body radiation is
identical with Planck's law for blackbody radiation. |
Neutrino masses and cosmological parameters from a Euclid-like survey:
Markov Chain Monte Carlo forecasts including theoretical errors: We present forecasts for the accuracy of determining the parameters of a
minimal cosmological model and the total neutrino mass based on combined mock
data for a future Euclid-like galaxy survey and Planck. We consider two
different galaxy surveys: a spectroscopic redshift survey and a cosmic shear
survey. We make use of the Monte Carlo Markov Chains (MCMC) technique and
assume two sets of theoretical errors. The first error is meant to account for
uncertainties in the modelling of the effect of neutrinos on the non-linear
galaxy power spectrum and we assume this error to be fully correlated in
Fourier space. The second error is meant to parametrize the overall residual
uncertainties in modelling the non-linear galaxy power spectrum at small
scales, and is conservatively assumed to be uncorrelated and to increase with
the ratio of a given scale to the scale of non-linearity. It hence increases
with wavenumber and decreases with redshift. With these two assumptions for the
errors and assuming further conservatively that the uncorrelated error rises
above 2% at k = 0.4 h/Mpc and z = 0.5, we find that a future Euclid-like cosmic
shear/galaxy survey achieves a 1-sigma error on Mnu close to 32 meV/25 meV,
sufficient for detecting the total neutrino mass with good significance. If the
residual uncorrelated errors indeed rises rapidly towards smaller scales in the
non-linear regime as we have assumed here then the data on non-linear scales
does not increase the sensitivity to the total neutrino mass. Assuming instead
a ten times smaller theoretical error with the same scale dependence, the error
on the total neutrino mass decreases moderately from sigma(Mnu) = 18 meV to 14
meV when mildly non-linear scales with 0.1 h/Mpc < k < 0.6 h/Mpc are included
in the analysis of the galaxy survey data. | Three-dimensional weak gravitational lensing of the 21-cm radiation
background: We study weak gravitational lensing by the cosmic large-scale structure of
the 21-cm radiation background in the 3d-weak lensing formalism. The interplay
between source distance measured at finite resolution, visibility and lensing
terms is analysed in detail and the resulting total covariance $C_{\ell}(k,k')$
is derived. The effect of lensing correlates different multipoles through
convolution, breaking the statistical homogeneity of the 21-cm radiation
background. This homogeneity breaking can be exploited to reconstruct the
lensing field $\hat{\phi}_{\ell m}(\kappa)$ and noise lensing reconstruction
$N_{\ell}^{\hat{\phi}}$ by means of quadratic estimators. The effects related
to the actual measurement process (redshift precision and visibility terms)
change drastically the values of the off-diagonal terms of the total covariance
$C_{\ell}(k,k')$. It is expected that the detection of lensing effects on a
21-cm radiation background will require sensitive studies and high-resolution
observations by future low-frequency radio arrays such as the SKA survey. |
Line Emission from Radiation-Pressurized HII Regions I: Internal
Structure and Line Ratios: The emission line ratios [OIII]5007/H-beta and [NII]6584/H-alpha have been
adopted as an empirical way to distinguish between the fundamentally different
mechanisms of ionization in emission-line galaxies. However, detailed
interpretation of these diagnostics requires calculations of the internal
structure of the emitting HII regions, and these calculations depend on the
assumptions one makes about the relative importance of radiation pressure and
stellar winds. In this paper we construct a grid of quasi-static HII region
models to explore how choices about these parameters alter HII regions'
emission line ratios. We find that, when radiation pressure is included in our
models, HII regions reach a saturation point beyond which further increases in
the luminosity of the driving stars does not produce any further increase in
effective ionization parameter, and thus does not yield any further alteration
in an HII region's line ratio. We also show that, if stellar winds are assumed
to be strong, the maximum possible ionization parameter is quite low. As a
result of this effect, it is inconsistent to simultaneously assume that HII
regions are wind-blown bubbles and that they have high ionization parameters;
some popular HII region models suffer from this inconsistency. Our work in this
paper provides a foundation for a companion paper in which we embed the model
grids we compute here within a population synthesis code that enables us to
compute the integrated line emission from galactic populations of HII regions. | Kinematic Morphology of Large-scale Structure: Evolution from Potential
to Rotational Flow: As an alternative way of describing the cosmological velocity field, we
discuss the evolution of rotational invariants constructed from the velocity
gradient tensor. Compared with the traditional divergence-vorticity
decomposition, these invariants, defined as coefficients of characteristic
equation of the velocity gradient tensor, enable a complete classification of
all possible flow patterns in the dark-matter comoving frame, including both
potential and vortical flows. We show that this tool, first introduced in
turbulence two decades ago, proves to be very useful in understanding the
evolution of the cosmic web structure, and in classifying its morphology.
Before shell-crossing, different categories of potential flow are highly
associated with cosmic web structure, because of the coherent evolution of
density and velocity. This correspondence is even preserved at some level when
vorticity is generated after shell-crossing. The evolution from the potential
to vortical flow can be traced continuously by these invariants. With the help
of this tool, we show that the vorticity is generated in a particular way that
is highly correlated with the large-scale structure. This includes a distinct
spatial distribution and different types of alignment between cosmic web and
vorticity direction for various vortical flows. Incorporating shell-crossing
into closed dynamical systems is highly non-trivial, but we propose a possible
statistical explanation for some of these phenomena relating to the internal
structure of the three-dimensional invariants space. |
The FLAMES Tarantula Survey: The Tarantula survey is an ESO Large Programme which has obtained
multi-epochs spectroscopy of over 800 massive stars in the 30 Dor region in the
Large Magelanic Cloud. Here we briefly describe the main drivers of the survey
and the observational material derived. | An Implementation of Bayesian Lensing Shear Measurement: The Bayesian gravitational shear estimation algorithm developed by Bernstein
and Armstrong (2014) can potentially be used to overcome multiplicative noise
bias and recover shear using very low signal-to-noise ratio (S/N) galaxy
images. In that work the authors confirmed the method is nearly unbiased in a
simplified demonstration, but no test was performed on images with realistic
pixel noise. Here I present a full implementation for fitting models to galaxy
images, including the effects of a point spread function (PSF) and
pixelization. I tested the implementation using simulated galaxy images modeled
as Sersic profiles with n=1 (exponential) and n=4 (De Vaucouleurs'), convolved
with a PSF and a flat pixel response function. I used a round Gaussian model
for the PSF to avoid potential PSF-fitting errors. I simulated galaxies with
mean observed, post-PSF full-width at half maximum equal to approximately 1.2
times that of the PSF, with log-normal scatter. I also drew fluxes from a
log-normal distribution. I produced independent simulations, each with pixel
noise tuned to produce different mean S/N ranging from 10-1000. I applied a
constant shear to all images. I fit the simulated images to a model with the
true Sersic index to avoid modeling biases. I recovered the input shear with
fractional error less than 2 x 10^{-3} in all cases. In these controlled
conditions, and in the absence of other multiplicative errors, this
implementation is sufficiently unbiased for current surveys and approaches the
requirements for planned surveys. |
Probing the physical properties of the intergalactic medium using
gamma-ray bursts: We use Gamma-ray burst (GRB) spectra total continuum absorption to estimate
the key intergalactic medium (IGM) properties of hydrogen column density
($\mathit{N}\textsc{hxigm}$), metallicity, temperature and ionisation parameter
over a redshift range of $1.6 \leq z \leq 6.3$, using photo-ionisation (PIE)
and collisional ionisation equilibrium (CIE) models for the ionised plasma. We
use more realistic host metallicity, dust corrected where available, in
generating the host absorption model, assuming that the host intrinsic hydrogen
column density is equal to the measured ionisation corrected intrinsic neutral
column from UV spectra ($\textit{N}\textsc{h}\/\ \textsc{i,ic}$). We find that
the IGM property results are similar, regardless of whether the model assumes
all PIE or CIE. The $\mathit{N}\textsc{hxigm}$ scales as $(1 + z)^{1.0\/\ -\/\
1.9}$, with equivalent hydrogen mean density at $z = 0$ of $n_0 =
1.8^{+1.5}_{-1.2} \times 10^{-7}$ cm$^{-3}$. The metallicity ranges from
$\sim0.1Z\sun$ at $z \sim 2$ to $\sim0.001Z\sun$ at redshift $z > 4$. The PIE
model implies a less rapid decline in average metallicity with redshift
compared to CIE. Under CIE, the temperature ranges between $5.0 <$
log$(T/$K$)<\/\ 7.1$. For PIE the ionisation parameter ranges between $0.1 <$
log$(\xi) < 2.9$. Using our model, we conclude that the IGM contributes
substantially to the total absorption seen in GRB spectra and that this
contribution rises with redshift, explaining why the hydrogen column density
inferred from X-rays is substantially in excess of the intrinsic host
contribution measured in UV. | Supersonic Gas Streams Enhance the Formation of Massive Black Holes in
the Early Universe: The origin of super-massive black holes in the early universe remains poorly
understood.Gravitational collapse of a massive primordial gas cloud is a
promising initial process,but theoretical studies have difficulty growing the
black hole fast enough.We report numerical simulations of early black hole
formation starting from realistic cosmological conditions.Supersonic gas
motions left over from the Big Bang prevent early gas cloud formation until
rapid gas condensation is triggered in a proto-galactic halo. A protostar is
formed in the dense, turbulent gas cloud, and it grows by sporadic mass
accretion until it acquires 34,000 solar masses.The massive star ends its life
with a catastrophic collapse to leave a black hole -- a promising seed for the
formation of a monstrous black hole. |
Bayesian model comparison for simulation-based inference: Comparison of appropriate models to describe observational data is a
fundamental task of science. The Bayesian model evidence, or marginal
likelihood, is a computationally challenging, yet crucial, quantity to estimate
to perform Bayesian model comparison. We introduce a methodology to compute the
Bayesian model evidence in simulation-based inference (SBI) scenarios (also
often called likelihood-free inference). In particular, we leverage the
recently proposed learnt harmonic mean estimator and exploit the fact that it
is decoupled from the method used to generate posterior samples, i.e. it
requires posterior samples only, which may be generated by any approach. This
flexibility, which is lacking in many alternative methods for computing the
model evidence, allows us to develop SBI model comparison techniques for the
three main neural density estimation approaches, including neural posterior
estimation (NPE), neural likelihood estimation (NLE), and neural ratio
estimation (NRE). We demonstrate and validate our SBI evidence calculation
techniques on a range of inference problems, including a gravitational wave
example. Moreover, we further validate the accuracy of the learnt harmonic mean
estimator, implemented in the HARMONIC software, in likelihood-based settings.
These results highlight the potential of HARMONIC as a sampler-agnostic method
to estimate the model evidence in both likelihood-based and simulation-based
scenarios. | Eddington accreting Black Holes in the Epoch of Reionization: The evolution of the luminosity function (LF) of Active Galactic Nuclei
(AGNs) at $z \gtrsim 5$ represents a key constraint to understand their
contribution to the ionizing photon budget necessary to trigger the last phase
transition in the Universe, i.e. the epoch of Reionization. Recent searches for
bright high-z AGNs suggest that the space densities of this population at $z>4$
has to be revised upwards, and sparks new questions about their evolutionary
paths. Gas accretion is the key physical mechanism to understand both the
distribution of luminous sources and the growth of central Super-Massive Black
Holes (SMBHs). In this work, we model the high-z AGN-LF assuming that high-z
luminous AGN shine at their Eddington limit: we derive the expected evolution
as a function of the ``duty-cycle'' ($f_{\rm dc}$), i.e. the fraction of
life-time that a given SMBH spends accreting at the Eddington rate. Our results
show that intermediate values ($f_{\rm dc} \simeq 0.1$) predict the best
agreement with the ionizing background and photoionization rate, but do not
provide enough ionizing photons to account for the observed evolution of the
hydrogen neutral fraction. Smaller values ($f_{\rm
dc} \lesssim 0.05$) are required for AGNs to be the dominant population
responsible for Hydrogen reionization in the Early Universe. We then show that
this low-$f_{\rm dc}$ evolution can be reconciled with the current constraints
on Helium reionization, although it implies a relatively large number of
inactive SMBHs at $z\gtrsim5$, in tension with SMBH growth models based on
heavy seeding. |
Redshift-drift as a test for discriminating between decelerating
inhomogeneous and accelerating universe models: Exact inhomogeneous solutions of Einstein's equations have been used in the
literature to build models reproducing the cosmological data without dark
energy. However, owing to the degrees of freedom pertaining to these models, it
is necessary to get rid of the degeneracy often exhibited by the problem of
distinguishing between them and accelerating universe models. We give an
overview of redshift drift in inhomogeneous cosmologies, and explain how it
serves to this purpose. One class of models which fits the data is the Szekeres
Swiss-cheese class where non-spherically symmetric voids exhibit a typical size
of about 400 Mpc. We present our calculation of the redshift drift in this
model, and compare it with the results obtained by other authors for alternate
scenarios. | Is the 2008 NASA/ESA double Einstein ring actually a ringhole signature?: It is argued that whereas the Shatskiy single rings produced by the
gravitational inner field of a spherically symmetric wormhole could not be used
to identify the presence of such tunnelings in the universe or the existence of
a parallel universe, the image which the inner gravitational field of a
ringhole with toroidal symmetry would allow us to detect from a single luminous
source is that of two concentric bright rings, and this is a signature that
cannot be attributed to any other single astronomical object in whichever
universe it may be placed. At the beginning of 2008 the NASA/ESA Hubble Space
Telescope revealed a never-before-seen phenomenon in space: a pair of glowing
rings, one nestled inside the other like a bull's-eye pattern. It is also
argued that such a discovery may well be attributed to the first astronomical
ringhole found in the universe. After all, a ringhole is a perfectly valid
solution to the Einstein equations and the stuff which makes it possible is
becoming more and more familiar in cosmology. |
Cosmological parameter estimation with Genetic Algorithms: Genetic algorithms are a powerful tool in optimization for single and
multi-modal functions. This paper provides an overview of their fundamentals
with some analytical examples. In addition, we explore how they can be used as
a parameter estimation tool in cosmological models to maximize the likelihood
function, complementing the analysis with the traditional Markov Chain Monte
Carlo methods. We analyze that genetic algorithms provide fast estimates by
focusing on maximizing the likelihood function, although they cannot provide
confidence regions with the same statistical meaning as Bayesian approaches.
Moreover, we show that implementing sharing and niching techniques ensures an
effective exploration of the parameter space, even in the presence of local
optima, always helping to find the global optima. This approach is invaluable
in the cosmological context, where exhaustive space exploration of parameters
is essential. We use dark energy models to exemplify the use of genetic
algorithms in cosmological parameter estimation, including a multimodal
problem, and we also show how to use the output of a genetic algorithm to
obtain derived cosmological functions. This paper concludes that genetic
algorithms are a handy tool within cosmological data analysis, without
replacing the traditional Bayesian methods but providing different advantages. | Measuring growth index in a universe with sterile neutrinos: Consistency tests for the general relativity (GR) can be performed by
constraining the growth index $\gamma$ using the measurements of redshift-space
distortions (RSD) in conjunction with other observations. In previous studies,
deviations from the GR expected value of $\gamma\approx 0.55$ at the
2--3$\sigma$ level were found. In this work, we reconsider the measurement of
$\gamma$ in a universe with sterile neutrinos. We constrain the sterile
neutrino cosmological model using the RSD measurements combined with the cosmic
microwave background data (Planck temperature data plus WMAP 9-yr polarization
data), the baryon acoustic oscillation data, the Hubble constant direct
measurement, the Planck Sunyaev-Zeldovich cluster counts data, and the galaxy
shear data. We obtain the constraint result of the growth index,
$\gamma=0.584^{+0.047}_{-0.048}$, well consistent with the GR expected value
(the consistency is at the 0.6$\sigma$ level). For the parameters of sterile
neutrino, we obtain $N_{\rm{eff}}=3.62^{+0.26}_{-0.42}$ and
$m_{\nu,{\rm{sterile}}}^{\rm{eff}}=0.48^{+0.11}_{-0.14}$ eV. We also consider
the BICEP2 data and perform an analysis on the model with tensor modes. Similar
fit results are obtained, showing that once light sterile neutrino is
considered in the universe, GR will become well consistent with the current
observations. |
Independent Measurements of the Dynamical Masses of Six Galaxy Clusters
in the Local Universe: We present independent measurements of the masses of the galaxy clusters in
the local universe by employing the Dynamical Mass Estimator (DME) originally
developed by Falco et al in 2014. In the catalog of the galaxy groups/clusters
constructed by Tempel et al. from the Sloan Digital Sky Survey Data Release 10,
we search for those as the targets around which the neighbor galaxies
constitute thin straight filamentary structures in the configuration space
spanned by the redshifts and the projected distances. Out of the $29$ Sloan
clusters that have $100$ or more member galaxies, a total of six targets are
found to have filamentary structures in their bound zones. For each of the six
targets, we construct the profile of the recession velocities of the filament
galaxies, which depends on the cluster mass and the angle of the filament
relative the line of the sight direction. Fitting the constructed profile to
the universal formula with constant amplitude and slope, we statistically
determine the dynamical mass of each cluster and compare it with the previous
estimates made by a conventional method. The weak and strong points of the DME
as well as its prospect for the measurements of the dynamical masses of the
high-$z$ clusters are discussed. | Radiation Pressure Supported Starburst Galaxies & The Fueling of Active
Galactic Nuclei: Radiation pressure from the absorption and scattering of starlight by dust
grains may be a crucial feedback mechanism in starburst galaxies and the
self-gravitating parsec-scale disks that accompany the fueling of active
galactic nuclei. I review the case for radiation pressure in both
optically-thin and highly optically-thick contexts. I describe the conditions
for which Eddington-limited star formation yields a characteristic flux of
~10^{13} L_sun/kpc^2, and I discuss the physical circumstances for which the
flux from radiation pressure supported disks is below or above this value. In
particular, I describe the young stellar disk on ~0.1 pc scales at the Galactic
Center. I argue that its bolometric flux at formation, ~10^{15} L_sun/kpc^2,
and the observed stellar mass and scale height imply that the disk may have
been radiation pressure supported during formation. |
Limits on Dark Matter Annihilation Signals from the Fermi LAT 4-year
Measurement of the Isotropic Gamma-Ray Background: We search for evidence of dark matter (DM) annihilation in the isotropic
gamma-ray background (IGRB) measured with 50 months of Fermi Large Area
Telescope (LAT) observations. An improved theoretical description of the
cosmological DM annihilation signal, based on two complementary techniques and
assuming generic weakly interacting massive particle (WIMP) properties, renders
more precise predictions compared to previous work. More specifically, we
estimate the cosmologically-induced gamma-ray intensity to have an uncertainty
of a factor ~20 in canonical setups. We consistently include both the Galactic
and extragalactic signals under the same theoretical framework, and study the
impact of the former on the IGRB spectrum derivation. We find no evidence for a
DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our
limits are competitive for DM particle masses up to tens of TeV and, indeed,
are the strongest limits derived from Fermi LAT data at TeV energies. This is
possible thanks to the new Fermi LAT IGRB measurement, which now extends up to
an energy of 820 GeV. We quantify uncertainties in detail and show the
potential this type of search offers for testing the WIMP paradigm with a
complementary and truly cosmological probe of DM particle signals. | Gamma-Ray Bursts, Quasars, Baryonic Acoustic Oscillations, and
Supernovae Ia: new statistical insights and cosmological constraints: The recent $\sim 4 \, \sigma$ Hubble constant, $H_{0}$, tension is observed
between the value of $H_{0}$ from the Cosmic Microwave Background (CMB) and
Type Ia Supernovae (SNe Ia). It is a decade since this tension is excruciating
the modern astrophysical community. To shed light on this problem is key to
consider probes at intermediate redshifts between SNe Ia and CMB and reduce the
uncertainty on $H_0$. Toward these goals, we fill the redshift gap by employing
Gamma-Ray Bursts (GRBs) and Quasars (QSOs), reaching $z=9.4$ and $z=7.6$,
respectively, combined with Baryonic Acoustic Oscillations (BAO) and SNe Ia. To
this end, we employ the ``Dainotti GRB 3D relation" among the rest-frame end
time of the X-ray plateau emission, its corresponding luminosity, and the peak
prompt luminosity, and the ``Risaliti-Lusso" QSO relation between ultraviolet
and X-ray luminosities. We inquire the commonly adopted Gaussianity assumption
on GRBs, QSOs, and BAO. With the joint sample, we fit the flat $\Lambda$ Cold
Dark Matter model with both the Gaussian and the newly discovered likelihoods.
We also investigate the impact of the calibration assumed for \textit{Pantheon}
and \textit{Pantheon +} SNe Ia on this analysis. Remarkably, we show that only
GRBs fulfill the Gaussianity assumption. We achieve small uncertainties on the
matter density parameter $\Omega_M$ and $H_0$. We find $H_0$ values compatible
within 2 $\sigma$ with the one from the Tip of the Red Giant Branch. Finally,
we show that the cosmological results are heavily biased against the arbitrary
calibration choice for SNe Ia. |
Evidence for Widespread AGN Activity among Massive Quiescent Galaxies at
z ~ 2: We quantify the presence of Active Galactic nuclei (AGN) in a mass-complete
(M_* >5e10 M_sun) sample of 123 star-forming and quiescent galaxies at 1.5 < z
< 2.5, using X-ray data from the 4 Ms Chandra Deep Field-South (CDF-S) survey.
41+/-7% of the galaxies are detected directly in X-rays, 22+/-5% with
rest-frame 0.5-8 keV luminosities consistent with hosting luminous AGN
(L_0.5-8keV > 3e42 ergs/s). The latter fraction is similar for star-forming and
quiescent galaxies, and does not depend on galaxy stellar mass, suggesting that
perhaps luminous AGN are triggered by external effects such as mergers. We
detect significant mean X-ray signals in stacked images for both the
individually non-detected star-forming and quiescent galaxies, with spectra
consistent with star formation only and/or a low luminosity AGN in both cases.
Comparing star formation rates inferred from the 2-10 keV luminosities to those
from rest-frame IR+UV emission, we find evidence for an X-ray excess indicative
of low-luminosity AGN. Among the quiescent galaxies, the excess suggests that
as many as 70-100% of these contain low- or high-luminosity AGN, while the
corresponding fraction is lower among star-forming galaxies (43-65%). The
ubiquitous presence of AGN in massive, quiescent z ~ 2 galaxies that we find
provides observational support for the importance of AGN in impeding star
formation during galaxy evolution. | Impacts of the physical data model on the forward inference of initial
conditions from biased tracers: We investigate the impact of each ingredient in the employed physical data
model on the Bayesian forward inference of initial conditions from biased
tracers at the field level. Specifically, we use dark matter halos in a given
cosmological simulation volume as tracers of the underlying matter density
field. We study the effect of tracer density, grid resolution, gravity model,
bias model and likelihood on the inferred initial conditions. We find that the
cross-correlation coefficient between true and inferred phases reacts weakly to
all ingredients above, and is well predicted by the theoretical expectation
derived from a Gaussian model on a broad range of scales. The bias in the
amplitude of the inferred initial conditions, on the other hand, depends
strongly on the bias model and the likelihood. We conclude that the bias model
and likelihood hold the key to an unbiased cosmological inference. Together
they must keep the systematics -- which arise from the sub-grid physics that
are marginalized over -- under control in order to obtain an unbiased
inference. |
Exploring the Impact of Microlensing on Gravitational Wave Signals:
Biases, Population Characteristics, and Prospects for Detection: In this study, we investigate the impact of microlensing on gravitational
wave (GW) signals in the LIGO$-$Virgo sensitivity band. Microlensing caused by
an isolated point lens, with (redshifted) mass ranging from
$M_\mathrm{Lz}\in(1,10^5){\rm M}_\odot$ and impact parameter $y\in (0.01,~5)$,
can result in a maximum mismatch of $\sim 30\%$ with their unlensed
counterparts. When $y<1$, it strongly anti-correlates with the luminosity
distance enhancing the detection horizon and signal-to-noise ratio (SNR).
Biases in inferred source parameters are assessed, with in-plane spin
components being the most affected intrinsic parameters. The luminosity
distance is often underestimated, while sky-localisation and trigger times are
mostly well-recovered. Study of a population of microlensed signals due to an
isolated point lens primarily reveals: (i) using unlensed templates during the
search causes fractional loss ($20\%$ to $30\%$) of potentially identifiable
microlensed signals; (ii) the observed distribution of $y$ challenges the
notion of its high improbability at low values ($y\lesssim 1$), especially for
$y\lesssim 0.1$; (iii) Bayes factor analysis of the population indicates that
certain region in $M_\mathrm{Lz}-y$ parameter space have a higher probability
of being detected and accurately identified as microlensed. Notably, the
microlens parameters for the most compelling candidate identified in previous
microlensing searches, GW200208_130117, fall within a 1-sigma range of the
aforementioned higher probability region. Identifying microlensing signatures
from $M_\mathrm{Lz}<100~$M$_\odot$ remains challenging due to small
microlensing effects at typical SNR values. Additionally, we also examined how
microlensing from a population of microlenses influences the detection of
strong lensing signatures in pairs of GW events, particularly in the
posterior-overlap analysis. | The peak region of the extragalactic background radiation: The Cosmic X-ray background carries the information of cosmic accretion onto
super-massive black holes. The intensity at its peak can be used to constrain
the integrated space density of highly obscured AGNs. Determining the shape and
intensity of the Cosmic X-ray background radiation represents, however, a first
step towards the understanding of the population of Comptonthick AGNs. The
study of AGNs in the local and more distant Universe allows to understand the
whole picture. In this talk, I will review the current understanding of
generation of the Cosmic X-ray background at its peak. I will focus on the
recent measurements of the Cosmic X-ray background and I will discuss the
recent advancements in the understanding of AGNs in both the local and more
distant Universe. Finally, I will also discuss open issues and future
prospects. |
Constraining spatial variations of the fine structure constant using
clusters of galaxies and Planck data: We propose an improved methodology to constrain spatial variations of the
fine structure constant using clusters of galaxies. We use the {\it Planck}
2013 data to measure the thermal Sunyaev-Zeldovich effect at the location of
618 X-ray selected clusters. We then use a Monte Carlo Markov Chain algorithm
to obtain the temperature of the Cosmic Microwave Background at the location of
each galaxy cluster. When fitting three different phenomenological
parameterizations allowing for monopole and dipole amplitudes in the value of
the fine structure constant we improve the results of earlier analysis
involving clusters and the CMB power spectrum, and we also found that the
best-fit direction of a hypothetical dipole is compatible with the direction of
other known anomalies. Although the constraining power of our current datasets
do not allow us to test the indications of a fine-structure constant dipole
obtained though high-resolution optical/UV spectroscopy, our results do
highlight that clusters of galaxies will be a very powerful tool to probe
fundamental physics at low redshift. | Observing low elevation sky and the CMB Cold Spot with BICEP3 at the
South Pole: BICEP3 is a 520 mm aperture on-axis refracting telescope at the South Pole,
which observes the polarization of the cosmic microwave background (CMB) at 95
GHz to search for the B-mode signal from inflationary gravitational waves. In
addition to this main target, we have developed a low-elevation observation
strategy to extend coverage of the Southern sky at the South Pole, where BICEP3
can quickly achieve degree-scale E-mode measurements over a large area. An
interesting E-mode measurement is probing a potential polarization anomaly
around the CMB Cold Spot. During the austral summer seasons of 2018-19 and
2019-20, BICEP3 observed the sky with a flat mirror to redirect the beams to
various low elevation ranges. The preliminary data analysis shows degree-scale
E-modes measured with high signal-to-noise ratio. |
Weak gravitational lensing with the Square Kilometre Array: We investigate the capabilities of various stages of the SKA to perform
world-leading weak gravitational lensing surveys. We outline a way forward to
develop the tools needed for pursuing weak lensing in the radio band. We
identify the key analysis challenges and the key pathfinder experiments that
will allow us to address them in the run up to the SKA. We identify and
summarize the unique and potentially very powerful aspects of radio weak
lensing surveys, facilitated by the SKA, that can solve major challenges in the
field of weak lensing. These include the use of polarization and rotational
velocity information to control intrinsic alignments, and the new area of weak
lensing using intensity mapping experiments. We show how the SKA lensing
surveys will both complement and enhance corresponding efforts in the optical
wavebands through cross-correlation techniques and by way of extending the
reach of weak lensing to high redshift. | Gravity- and temperature-driven phase transitions in a model for
collapsed axionic condensates: We show how to use the cubic-quintic Gross-Pitaevskii-Poisson equation
(cq-GPPE) and the cubic-quintic Stochastic Ginzburg-Landau-Poisson equation
(cq-SGLPE) to investigate the gravitational collapse of a tenuous axionic gas
into a collapsed axionic condensate for both zero and finite temperature $T$.
At $T=0$, we use a Gaussian Ansatz for a spherically symmetric density to
obtain parameter regimes in which we might expect to find compact axionic
condensates. We then go beyond this Ansatz, by using the cq-SGLPE to
investigate the dependence of the axionic condensate on the gravitational
strength $G$ at $T = 0$. We demonstrate that, as $G$ increases, the equilibrium
configuration goes from a tenuous axionic gas, to flat sheets or
$\textit{Zeldovich pancakes}$, cylindrical structures, and finally a spherical
axionic condensate. By varying $G$, we show that there are first-order phase
transitions, as the system goes from one of these structures to the next one;
we find hysteresis loops that are associated with these transitions. We examine
these states and the transitions between these states via the Fourier truncated
cq-GPPE; and we also obtain the thermalized $T > 0$ states from the cq-SGLPE;
the transitions between these states yield thermally driven first-order phase
transitions and their associated hysteresis loops. Finally, we discuss how our
cq-GPPE approach can be used to follow the spatiotemporal evolution of a
rotating axionic condensate and also a rotating binary-axionic-condensate
system; in particular, we demonstrate, in the former, the emergence of vortices
at large angular speeds $\Omega$ and, in the latter, the rich dynamics of the
mergers of the components of this binary system, which can yield vortices in
the process of merging. |
Axion dark matter and the 21-cm signal: It was shown in ref. [1] that cold dark matter axions reach thermal contact
with baryons, and therefore cool them, shortly after the axions thermalize
among themselves and form a Bose-Einstein condensate. The recent observation by
the EDGES collaboration of a baryon temperature at cosmic dawn lower than
expected under "standard" assumptions is interpreted as new evidence that the
dark matter is axions, at least in part. Baryon cooling by dark matter axions
is found to be consistent with the observation of baryon acoustic oscillations. | A simple supergravity model of inflation constrained with Planck 2018
data: We study a model of inflation based on $\mathcal{N}=1$ supergravity
essentially depending on one effective parameter. Under a field transformation
we show that this model turns out to be equivalent to a previously studied
supergravity model known to be ruled out with the original choice of the
parameter. Such parameter measures the slope of the potential at observable
scales. Through a Bayesian parameter estimation, it is shown how this model is
compatible with recent CMB temperature measurements by {\it Planck 2018} giving
rise to a simple, viable, single field model of inflation. The tensor to scalar
ratio constraint is found to be $r_{0.002}<0.065$ with negative running. We
discuss how observables are invariant under the field transformation which
leaves unaltered the slow-roll parameters. As a consequence the use of one
presentation of the model or its field-transformed version is purely a matter
of convenience. |
The behaviour of dark matter associated with 4 bright cluster galaxies
in the 10kpc core of Abell 3827: Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally
bright elliptical galaxies within a core of radius 10kpc. Such corrugation of
the stellar distribution is very rare, and suggests recent formation by several
simultaneous mergers. We map the distribution of associated dark matter, using
new Hubble Space Telescope imaging and VLT/MUSE integral field spectroscopy of
a gravitationally lensed system threaded through the cluster core. We find that
each of the central galaxies retains a dark matter halo, but that (at least)
one of these is spatially offset from its stars. The best-constrained offset is
1.62+/-0.48kpc, where the 68% confidence limit includes both statistical error
and systematic biases in mass modelling. Such offsets are not seen in field
galaxies, but are predicted during the long infall to a cluster, if dark matter
self-interactions generate an extra drag force. With such a small physical
separation, it is difficult to definitively rule out astrophysical effects
operating exclusively in dense cluster core environments - but if interpreted
solely as evidence for self-interacting dark matter, this offset implies a
cross-section sigma/m=(1.7+/-0.7)x10^{-4}cm^2/g x (t/10^9yrs)^{-2}, where t is
the infall duration. | X-ray Emission from Optically Selected Radio-Intermediate and Radio-Loud
Quasars: We present the results of an investigation into the X-ray properties of
radio-intermediate and radio-loud quasars (RIQs and RLQs, respectively). We
combine large, modern optical (e.g., SDSS) and radio (e.g., FIRST) surveys with
archival X-ray data from Chandra, XMM-Newton, and ROSAT to generate an
optically selected sample that includes 188 RIQs and 603 RLQs. This sample is
constructed independently of X-ray properties but has a high X-ray detection
rate (85%); it provides broad and dense coverage of the l-z plane, including at
high redshifts (22% of objects have z=2-5), and it extends to high
radio-loudness values (33% of objects have R*=3-5, using logarithmic units). We
measure the "excess" X-ray luminosity of RIQs and RLQs relative to radio-quiet
quasars (RQQs) as a function of radio loudness and luminosity, and parameterize
the X-ray luminosity of RIQs and RLQs both as a function of optical/UV
luminosity and also as a joint function of optical/UV and radio luminosity.
RIQs are only modestly X-ray bright relative to RQQs; it is only at high values
of radio-loudness (R*>3.5) and radio luminosity that RLQs become strongly X-ray
bright. We find no evidence for evolution in the X-ray properties of RIQs and
RLQs with redshift (implying jet-linked IC/CMB emission does not contribute
substantially to the nuclear X-ray continuum). Finally, we consider a model in
which the nuclear X-ray emission contains both disk/corona-linked and
jet-linked components and demonstrate that the X-ray jet-linked emission is
likely beamed but to a lesser degree than applies to the radio jet. This model
is used to investigate the increasing dominance of jet-linked X-ray emission at
low inclinations. |
Tomographic weak lensing bispectrum: a thorough analysis towards the
next generation of galaxy surveys: We address key points for an efficient implementation of likelihood codes for
modern weak lensing large-scale structure surveys. Specifically, we focus on
the joint weak lensing convergence power spectrum-bispectrum probe and we
tackle the numerical challenges required by a realistic analysis. Under the
assumption of (multivariate) Gaussian likelihoods, we have developed a high
performance code that allows highly parallelised prediction of the binned
tomographic observables and of their joint non-Gaussian covariance matrix
accounting for terms up to the 6-point correlation function and super-sample
effects. This performance allows us to qualitatively address several
interesting scientific questions. We find that the bispectrum provides an
improvement in terms of signal-to-noise ratio (S/N) of about 10% on top of the
power spectrum, making it a non-negligible source of information for future
surveys. Furthermore, we are capable to test the impact of theoretical
uncertainties in the halo model used to build our observables; with presently
allowed variations we conclude that the impact is negligible on the S/N.
Finally, we consider data compression possibilities to optimise future analyses
of the weak lensing bispectrum. We find that, ignoring systematics, 5
equipopulated redshift bins are enough to recover the information content of a
Euclid-like survey, with negligible improvement when increasing to 10 bins. We
also explore principal component analysis and dependence on the triangle shapes
as ways to reduce the numerical complexity of the problem. | Optical spectroscopy of the gamma-ray bright blazars PKS 0447-439 and
PMN J0630-24: The large majority of sources detected by the Fermi Gamma-ray Space Telescope
are blazars, belonging in particular to the blazar subclass of BL Lacertae
objects (BL Lacs). BL Lacs often have featureless optical spectra, which make
it difficult and sometimes impossible to determine their redshifts. This
presents a severe impediment for the use of BL Lacs to measure the spectrum of
the extragalactic background light through its interaction with high-energy
gamma-ray photons. I present here high-quality optical spectroscopy of two of
the brightest gamma-ray blazars, namely, PKS 0447-439 and PMN J0630-24. The
medium-resolution and high signal-to-noise ratio optical spectra show clear
absorption lines, which place these BL Lacs at relatively high redshifts of
z>=1.246 for PKS 0447-439 and z>=1.238 for PMN J0630-24. |
Wavelet Helmholtz decomposition for weak lensing mass map reconstruction: To derive the convergence field from the gravitational shear (gamma) of the
background galaxy images, the classical methods require a convolution of the
shear to be performed over the entire sky, usually expressed thanks to the Fast
Fourier transform (FFT). However, it is not optimal for an imperfect geometry
survey. Furthermore, FFT implicitly uses periodic conditions that introduce
errors to the reconstruction. A method has been proposed that relies on
computation of an intermediate field u that combines the derivatives of gamma
and on convolution with a Green kernel. In this paper, we study the wavelet
Helmholtz decomposition as a new approach to reconstructing the dark matter
mass map. We show that a link exists between the Helmholtz decomposition and
the E/B mode separation. We introduce a new wavelet construction, that has a
property that gives us more flexibility in handling the border problem, and we
propose a new method of reconstructing the dark matter mass map in the wavelet
space. A set of experiments based on noise-free images illustrates that this
Wavelet Helmholtz decomposition reconstructs the borders better than all other
existing methods. | Model selection applied to reconstruction of the Primordial Power
Spectrum: The preferred shape for the primordial spectrum of curvature perturbations is
determined by performing a Bayesian model selection analysis of cosmological
observations. We first reconstruct the spectrum modelled as piecewise linear in
\log k between nodes in k-space whose amplitudes and positions are allowed to
vary. The number of nodes together with their positions are chosen by the
Bayesian evidence, so that we can both determine the complexity supported by
the data and locate any features present in the spectrum. In addition to the
node-based reconstruction, we consider a set of parameterised models for the
primordial spectrum: the standard power-law parameterisation, the spectrum
produced from the Lasenby & Doran (LD) model and a simple variant
parameterisation. By comparing the Bayesian evidence for different classes of
spectra, we find the power-law parameterisation is significantly disfavoured by
current cosmological observations, which show a preference for the LD model. |
Gravitational Microlensing: A parallel, large-data implementation: Gravitational lensing allows us to probe the structure of matter on a broad
range of astronomical scales, and as light from a distant source traverses an
intervening galaxy, compact matter such as planets, stars, and black holes act
as individual lenses. The magnification from such microlensing results in rapid
brightness fluctuations which reveal not only the properties of the lensing
masses, but also the surface brightness distribution in the source. However,
while the combination of deflections due to individual stars is linear, the
resulting magnifications are highly non-linear, leading to significant
computational challenges which currently limit the range of problems which can
be tackled. This paper presents a new and novel implementation of a numerical
approach to gravitational microlensing, increasing the scale of the problems
that can be tackled by more than two orders of magnitude, opening up a new
regime of astrophysically interesting problems. | The Deepest HST Color-Magnitude Diagram of M32: Evidence for
Intermediate-Age Populations: We present the deepest optical color-magnitude diagram (CMD) to date of the
local elliptical galaxy M32. We have obtained F435W and F555W photometry based
on HST ACS/HRC images for a region 110" from the center of M32 and a background
field about 320" away from M32 center. Due to the high resolution of our
Nyquist-sampled images, the small photometric errors, and the depth of our data
we obtain the most detailed resolved photometric study of M32 yet.
Deconvolution of HST images proves to be superior than other standard methods
to derive stellar photometry on extremely crowded HST images. The location of
the strong red clump in the CMD suggests a mean age between 8 and 10 Gyr for
[Fe/H] = -0.2 in M32. We detect for the first time a red giant branch bump and
an asymptotic giant branch bump in M32 which indicate that the mean age of
M32's dominant population at ~2' from its center is between 5 and 10 Gyr. We
see evidence of an intermediate-age population in M32 mainly due to the
presence of bright asymptotic giant branch stars. Our detection of a blue
component of stars (blue plume) may indicate for the first time the presence of
a young stellar population, with ages of the order of 0.5 Gyr, in our M32
field. However, it is likely that the brighter stars of this blue plume belong
to the disk of M31 rather than to M32. The fainter stars populating the blue
plume indicate the presence of stars not younger than 1 Gyr and/or blue
straggler stars in M32. M32's dominant population of 8--10 Gyr implies a
formation redshift of 1 < z_f < 2, precisely when observations of the specific
star formation rates and models of "downsizing" imply galaxies of M32's mass
ought to be forming their stars. Our CMD therefore provides a "ground-truth" of
downsizing scenarios at z=0. Our background field data represent the deepest
optical observations yet of the inner disk and bulge of M31. [Abridged] |
An X-ray underluminous cluster of galaxies in the 4Ms CDFS observations: [Abridged] We use the large public spectroscopic database available in the
GOODS-South field to estimate the dynamical mass and the virialization status
of cluster ClG 0332-2747 at z=0.734. Cluster members selected from their
photometric redshift are used with spectroscopic ones to analyse the galaxy
population of the cluster. In the newly released Chandra 4Ms observations we
detect a faint extended X-ray emission associated to the cluster. Finally, we
compare the optical and X-ray properties of ClG 0332-2747 with the predictions
of a well tested semianalytic model. We estimate the velocity dispersion and
the virial mass considering all 44 spectroscopic members, or 20 red-sequence
members only. We obtain sigma_v=634 +/- 105 Km/s, M_200=3.07
^{+1.57}_{-1.16}~10^{14} M_sun in the former case, and slightly lower values in
the latter case. The cluster appears to have reached the virial equilibrium: it
shows a perfectly Gaussian velocity distribution and no evidence for
substructures. ClG 0332-2747 contains a high fraction of bright red galaxies,
and is dominated by a very massive (1.1 x 10^{12} M_sun) old brightest cluster
galaxy (BCG), suggesting that it formed at an early epoch. We detect a faint
extended X-ray source centered on the BCG, with a total X-ray luminosity of L_X
~ 2 x 10^{42} erg s^-1 (0.1-2.4 keV). This L_X is lower by a factor of ~10-20
than expected according to the M-L_X relation. We provide a possible
explanation of this discrepancy as due to the effects of AGN feedback on the
ICM: the semianalytic model reproduces the M-L_X relation measured from "X-ray
bright" clusters, and it predicts a high scatter at low masses due to heating
and expulsion of the cluster gas. Interestingly, in the model clusters with an
evolved galaxy population like ClG 0332-2747 present the largest scatter in
X-ray luminosity. | Cosmological effects of coupled dark matter: Many models have been studied that contain more than one species of dark
matter and some of these couple the Cold Dark Matter (CDM) to a light scalar
field. In doing this we introduce additional long range forces, which in turn
can significantly affect our estimates of cosmological parameters if not
properly accounted for. It is, therefore, important to study these models and
their resulting cosmological implications. We present a model in which a
fraction of the total cold dark matter density is coupled to a scalar field. We
study the background and perturbation evolution and calculate the resulting
Cosmic Microwave Background anisotropy spectra. The greater the fraction of
dark matter coupled to the scalar field and the stronger the coupling strength,
the greater the deviation of the background evolution from LCDM. Previous work,
with a single coupled dark matter species, has found an upper limit on the
coupling strength of order O(0.1). We find that with a coupling of this
magnitude more than half the dark matter can be coupled to a scalar field
without producing any significant deviations from LCDM. |
Star Formation in the Outer Filaments of NGC 1275: We present photometry of the outer star clusters in NGC 1275, the brightest
galaxy in the Perseus cluster. The observations were taken using the Hubble
Space Telescope Advanced Camera for Surveys. We focus on two stellar regions in
the south and south-east, far from the nucleus of the low velocity system (~22
kpc). These regions of extended star formation trace the H alpha filaments,
drawn out by rising radio bubbles. In both regions bimodal distributions of
colour (B-R)_0 against magnitude are apparent, suggesting two populations of
star clusters with different ages; most of the H alpha filaments show no
detectable star formation. The younger, bluer population is found to be
concentrated along the filaments while the older population is dispersed evenly
about the galaxy. We construct colour-magnitude diagrams and derive ages of at
most 10^8 years for the younger population, a factor of 10 younger than the
young population of star clusters in the inner regions of NGC 1275. We conclude
that a formation mechanism or event different to that for the young inner
population is needed to explain the outer star clusters and suggest that
formation from the filaments, triggered by a buoyant radio bubble either rising
above or below these filaments, is the most likely mechanism. | COSMOPOWER: emulating cosmological power spectra for accelerated
Bayesian inference from next-generation surveys: We present $\it{CosmoPower}$, a suite of neural cosmological power spectrum
emulators providing orders-of-magnitude acceleration for parameter estimation
from two-point statistics analyses of Large-Scale Structure (LSS) and Cosmic
Microwave Background (CMB) surveys. The emulators replace the computation of
matter and CMB power spectra from Boltzmann codes; thus, they do not need to be
re-trained for different choices of astrophysical nuisance parameters or
redshift distributions. The matter power spectrum emulation error is less than
$0.4\%$ in the wavenumber range $k \in [10^{-5}, 10] \, \mathrm{Mpc}^{-1}$, for
redshift $z \in [0, 5]$. $\it{CosmoPower}$ emulates CMB temperature,
polarisation and lensing potential power spectra in the $5\sigma$ region of
parameter space around the $\it{Planck}$ best fit values with an error
$\lesssim 10\%$ of the expected shot noise for the forthcoming Simons
Observatory. $\it{CosmoPower}$ is showcased on a joint cosmic shear and galaxy
clustering analysis from the Kilo-Degree Survey, as well as on a Stage IV
$\it{Euclid}$-like simulated cosmic shear analysis. For the CMB case,
$\it{CosmoPower}$ is tested on a $\it{Planck}$ 2018 CMB temperature and
polarisation analysis. The emulators always recover the fiducial cosmological
constraints with differences in the posteriors smaller than sampling noise,
while providing a speed-up factor up to $O(10^4)$ to the complete inference
pipeline. This acceleration allows posterior distributions to be recovered in
just a few seconds, as we demonstrate in the $\it{Planck}$ likelihood case.
$\it{CosmoPower}$ is written entirely in Python, can be interfaced with all
commonly used cosmological samplers and is publicly available at
https://github.com/alessiospuriomancini/cosmopower . |
Irregular sloshing cold fronts in the nearby merging groups NGC 7618 and
UGC 12491: evidence for Kelvin-Helmholtz instabilities: We present results from two \sim30 ks Chandra observations of the hot
atmospheres of the merging galaxy groups centered around NGC 7618 and UGC
12491. Our images show the presence of arc-like sloshing cold fronts wrapped
around each group center and \sim100 kpc long spiral tails in both groups. Most
interestingly, the cold fronts are highly distorted in both groups, exhibiting
'wings' along the fronts. These features resemble the structures predicted from
non-viscous hydrodynamic simulations of gas sloshing, where Kelvin-Helmholtz
instabilities (KHIs) distort the cold fronts. This is in contrast to the
structure seen in many other sloshing and merger cold fronts, which are smooth
and featureless at the current observational resolution. Both magnetic fields
and viscosity have been invoked to explain the absence of KHIs in these smooth
cold fronts, but the NGC 7618/UGC 12491 pair are two in a growing number of
both sloshing and merger cold fronts that appear distorted. Magnetic fields
and/or viscosity may be able to suppress the growth of KHIs at the cold fronts
in some clusters and groups, but clearly not in all. We propose that the
presence or absence of KHI-distortions in cold fronts can be used as a measure
of the effective viscosity and/or magnetic field strengths in the ICM. | Constraining Galileon Inflation: In this short paper, we present constraints on the Galileon inflationary
model from the CMB bispectrum. We employ a principal-component analysis of the
independent degrees of freedom constrained by data and apply this to the WMAP
9-year data to constrain the free parameters of the model. A simple Bayesian
comparison establishes that support for the Galileon model from bispectrum data
is at best weak. |
Demographics and Physical Properties of Gas Out/Inflows at 0.4 < z < 1.4: We present Keck/LRIS spectra of over 200 galaxies with well-determined
redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet,
low-ionization absorption lines with previously measured masses, luminosities,
colors, and star formation rates to describe the demographics and properties of
galactic flows. Among star-forming galaxies with blue colors, we find a net
blueshift of the FeII absorption greater than 200 km/s (100 km/s) towards 2.5%
(20%) of the galaxies. The fraction of blueshifted spectra does not vary
significantly with stellar mass, color, or luminosity but does decline at
specific star formation rates less than roughly 0.8 Gyr^{-1}. The insensitivity
of the blueshifted fraction to galaxy properties requires collimated outflows
at these redshifts, while the decline in outflow fraction with increasing
blueshift might reflect the angular dependence of the outflow velocity. The low
detection rate of infalling gas, 3 to 6% of the spectra, suggests an origin in
(enriched) streams favorably aligned with our sightline. We find 4 of these 9
infalling streams have projected velocities commensurate with the kinematics of
an extended disk or satellite galaxy. The strength of the MgII absorption
increases with stellar mass, B-band luminosity, and U-B color, trends arising
from a combination of more interstellar absorption at the systemic velocity and
less emission filling in more massive galaxies. Our results provides a new
quantitative understanding of gas flows between galaxies and the circumgalactic
medium over a critical period in galaxy evolution. | The Mg II 2797, 2803 emission in low-metallicity star-forming galaxies
from the SDSS: We present 65 Sloan Digital Sky Survey (SDSS) spectra of 62 star-forming
galaxies with oxygen abundances 12 + logO/H ~ 7.5-8.4. Redshifts of selected
galaxies are in the range z~0.36-0.70. This allows us to detect the redshifted
MgII 2797,2803 emission lines. Our aim is to use these lines for the magnesium
abundance determination. The MgII emission was detected in ~2/3 of the
galaxies. We find that the MgII 2797 emission-line intensity follows a trend
with the excitation parameter x= O^{2+}/O that is similar to that predicted by
CLOUDY photoionised HII region models, suggesting a nebular origin of MgII
emission. The Mg/O abundance ratio is lower by a factor ~2 than the solar
ratio. This is probably the combined effect of interstellar MgII absorption and
depletion of Mg onto dust. However, the effect of dust depletion in selected
galaxies, if present, is small, by a factor of ~2 lower than that of iron. |
Far Ultraviolet Emission in the A2597 and A2204 Brightest Cluster
Galaxies: We use the Hubble Space Telescope ACS/SBC and Very Large Telescope FORS
cameras to observe the Brightest Cluster Galaxies in Abell 2597 and Abell 2204
in the far-ultraviolet (FUV) F150LP and optical U, B, V, R, I Bessel filters.
The FUV and U band emission is enhanced in bright, filamentary structures
surrounding the BCG nuclei. These filaments can be traced out to 20 kpc from
the nuclei in the FUV. Excess FUV and U band light is determined by removing
emission due to the underlying old stellar population and mapped with 1 arcsec
spatial resolution over the central 20 kpc regions of both galaxies. We find
the FUV and U excess emission to be spatially coincident and a stellar
interpretation requires the existence of a significant amount of 10000-50000 K
stars. Correcting for nebular continuum emission and dust intrinsic to the BCG
further increases the FUV to U band emission ratio and implies that stars alone
may not suffice to explain the observations. However, lack of detailed
information on the gas and dust distribution and extinction law in these
systems prevents us from ruling out a purely stellar origin. Non-stellar
processes, such as the central AGN, Scattering, Synchrotron and Bremsstrahlung
emission are investigated and found to not be able to explain the FUV and U
band measurements in A2597. Contributions from non-thermal processes not
treated here should be investigated. Comparing the FUV emission to the optical
H-alpha line emitting nebula shows good agreement on kpc-scales in both A2597
and A2204. In concordance with an earlier investigation by O'Dea et al. (2004)
we find that O-stars can account for the ionising photons necessary to explain
the observed H-alpha line emission. | Complete infrared spectral energy distributions of mm detected quasars
at z>5: We present Herschel far-infrared (FIR) photometry of eleven quasars at
redshift z>5 that have previously been detected at 1.2mm. We perform full
spectral energy distribution (SED) fits over the wavelength range lambda_rest
~0.1-400mu for those objects with good Herschel detections. These fits reveal
the need for an additional far-infrared (FIR) component besides the emission
from a dusty AGN-powered torus. This additional FIR component has temperatures
of T_FIR ~ 40-60K with luminosities of L_(8-1000mu) ~ 10^13 L_sun (accounting
for 25-60% of the bolometric FIR luminosity). If the FIR dust emission is due
to star formation it would suggest star formation rates in excess of 1000 solar
masses per year. We show that at long wavelengths (lambda_rest > 50mu) the
contribution of the AGN-powered torus emission is negligible. This explains how
previous FIR studies of high-redshift quasars that relied on single component
fits to (ground-based) observations at lambda_obs > 350mu reached T_FIR and
L_FIR values similar to our complete SED fits. Stacking the Herschel data of
four individually undetected sources reveals a significant average signal in
the PACS bands but not in SPIRE. The average SED of sources with individual
Herschel detections shows a striking surplus in near- and mid-infrared emission
when compared to common AGN templates. The comparison between two average SEDs
(sources with and without individual Herschel detections) matched in the
UV/optical indicates that for these objects the strength of the MIR emission
may correlate with the strength of the FIR emission. |
Dark Matter Halo Mass Profiles: I provide notes on the NFW, Einasto, Sersic, and other mass profiles which
provide good fits to simulated dark matter halos (S3). I summarize various
published c(M) relations: halo concentration as a function of mass (S1). The
definition of the virial radius is discussed and relations are given to convert
c_vir, M_vir, and r_vir between various defined values of the halo overdensity
(S2). | Does a generalized Chaplygin gas correctly describe the cosmological
dark sector?: Yes, but only for a parameter value that makes it almost coincide with the
standard model. We reconsider the cosmological dynamics of a generalized
Chaplygin gas (gCg) which is split into a cold dark matter (CDM) part and a
dark energy (DE) component with constant equation of state. This model, which
implies a specific interaction between CDM and DE, has a $\Lambda$CDM limit and
provides the basis for studying deviations from the latter. Including matter
and radiation, we use the (modified) CLASS code \cite{class} to construct the
CMB and matter power spectra in order to search for a gCg-based concordance
model that is in agreement with the SNIa data from the JLA sample and with
recent Planck data. The results reveal that the gCg parameter $\alpha$ is
restricted to $|\alpha|\lesssim 0.05$, i.e., to values very close to the
$\Lambda$CDM limit $\alpha =0$. This excludes, in particular, models in which
DE decays linearly with the Hubble rate. |
PBH evaporation, baryon asymmetry,and dark matter: Sufficiently light primordial black holes (PBH) could evaporate in the very
early universe and dilute the preexisting baryon asymmetry and/or the frozen
density of stable relics. The effect is especially strong in the case that PBHs
decayed if and when they dominated the cosmological energy density. The size of
the reduction is first calculated analytically under the simplifying assumption
of the delta-function mass spectrum of PBH and in instant decay approximation.
In the realistic case of exponential decay and for an extended mass spectrum of
PBH the calculations are made numerically. Resulting reduction of the frozen
number density of the supersymmetric relics opens for them a wider window to
become viable dark matter candidate. | Mass Function of Binary Massive Black Holes in Active Galactic Nuclei: If the activity of active galactic nuclei (AGNs) is predominantly induced by
major galaxy mergers, then a significant fraction of AGNs should harbor binary
massive black holes in their centers. We study the mass function of binary
massive black holes in nearby AGNs based on the observed AGN black-hole mass
function and theory of evolution of binary massive black holes interacting with
a massive circumbinary disk in the framework of coevolution of massive black
holes and their host galaxies. The circumbinary disk is assumed to be steady,
axisymmetric, geometrically thin, self-regulated, self-gravitating but
non-fragmenting with a fraction of Eddington accretion rate, which is typically
one tenth of Eddington value. The timescale of orbital decay is {then}
estimated as ~10^8yr for equal mass black-hole, being independent of the black
hole mass, semi-major axis, and viscosity parameter but dependent on the
black-hole mass ratio, Eddington ratio, and mass-to-energy conversion
efficiency. This makes it possible for any binary massive black holes to merge
within a Hubble time by the binary-disk interaction. We find that (1.8+-0.6%)
for the equal mass ratio and (1.6+-0.4%) for the one-tenth mass ratio of the
total number of nearby AGNs have close binary massive black holes with orbital
period less than ten years in their centers, detectable with on-going highly
sensitive X-ray monitors such as Monitor of All-sky X-ray Image and/or
Swift/Burst Alert Telescope. Assuming that all binary massive black holes have
the equal mass ratio, about 20% of AGNs with black hole masses of
10^{6.5-7}M_sun has the close binaries and thus provides the best chance to
detect them. |
The signature of dark energy perturbations in galaxy cluster surveys: All models of dynamical dark energy possess fluctuations, which affect the
number of galaxy clusters in the Universe. We have studied the impact of dark
energy clustering on the number of clusters using a generalization of the
spherical collapse model and the Press-Schechter formalism. Our statistical
analysis is performed in a 7-parameter space using the Fisher matrix method,
for several hypothetical Sunyaev-Zel'dovich and weak lensing (shear maps)
surveys. In some scenarios, the impact of these fluctuations is large enough
that their effect could already be detected by existing instruments such as the
South Pole Telescope, when its data is combined with WMAP and SDSS. Future
observations could go much further and probe the nature of dark energy by
distinguishing between different models on the basis of their perturbations,
not only their expansion histories. | Thermodynamics of the R_h=ct Universe: A Simplification of Cosmic
Entropy: In the standard model of cosmology, the Universe began its expansion with an
anomalously low entropy, which then grew dramatically to much larger values
consistent with the physical conditions at decoupling, roughly 380,000 years
after the Big Bang. There does not appear to be a viable explanation for this
`unnatural' history, other than via the generalized second law of
thermodynamics (GSL), in which the entropy of the bulk, S_bulk, is combined
with the entropy of the apparent (or gravitational) horizon, S_h. This is not
completely satisfactory either, however, since this approach seems to require
an inexplicable equilibrium between the bulk and horizon temperatures. In this
paper, we explore the thermodynamics of an alternative cosmology known as the
R_h=ct universe, which has thus far been highly successful in resolving many
other problems or inconsistencies in LCDM. We find that S_bulk is constant in
this model, eliminating the so-called initial entropy problem simply and
elegantly. The GSL may still be relevant, however, principally in selecting the
arrow of time, given that S_h ~ t^2 in this model. |
Constraints on cosmic string tension imposed by the limit on the
stochastic gravitational wave background from the European Pulsar Timing
Array: We investigate the constraints that can be placed on the cosmic string
tension by using the current Pulsar Timing Array limits on the stochastic
gravitational wave background (SGWB). We have developed a code to compute the
spectrum of gravitational waves (GWs) based on the widely accepted one-scale
model. In its simplest form the one-scale model allows one to vary: (i) the
string tension, G\mu/c^2; (ii) the size of cosmic string loops relative to the
horizon at birth, \alpha; (iii) the spectral index of the emission spectrum, q;
(iv) the cut-off in the emission spectrum, n_*; and (v) the intercommutation
probability, p. The amplitude and slope of the spectrum in the nHz frequency
range is very sensitive to these unknown parameters. We have also investigated
the impact of more complicated scenarios with multiple initial loop sizes, in
particular the 2-\alpha models proposed in the literature and a log-normal
distribution for \alpha. We have computed the constraint on G\mu/c^2 due to the
limit on a SGWB imposed by data from the European Pulsar Timing Array. Taking
into account all the possible uncertainties in the parameters we find a
conservative upper limit of G\mu/c^2<5.3x 10^{-7} which typically occurs when
the loop production scale is close to the gravitational backreaction scale,
\alpha\approx\Gamma G\mu/c^2. Stronger limits are possible for specific values
of the parameters which typically correspond to the extremal cases \alpha\ll
\Gamma G\mu/c^2 and \alpha\gg \Gamma G\mu/c^2. This limit is less stringent
than the previously published limits which are based on cusp emission, an
approach which does not necessarily model all the possible uncertainties. We
discuss the prospects for lowering this limit by two orders of magnitude, or
even a detection of the SGWB, in the very near future in the context of the
Large European Array for Pulsars and the Square Kilometre Array. | Metastable dark energy models in light of Planck 2018: Alleviating the
$H_0$ tension: We investigate the recently introduced metastable dark energy (DE) models
after the final Planck 2018 legacy release. The essence of the present work is
to analyze their evolution at the level of perturbations. Our analyses show
that both the metastable dark energy models considered in this article, are
excellent candidates to alleviate the $H_0$ tension. In particular, for the
present models, Planck 2018 alone can alleviate the $H_0$ tension within 68\%
CL. Along with the final cosmic microwave background data from the Planck 2018
legacy release, we also include external cosmological datasets in order to
asses the robustness of our findings. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS). A precise
measurement of the galaxy stellar mass function and the abundance of massive
galaxies at redshifts 0.5<z<1.3: We measure the evolution of the galaxy stellar mass function from z=1.3 to
z=0.5 using the first 53,608 redshifts of the ongoing VIMOS Public
Extragalactic Survey (VIPERS). We estimate the galaxy stellar mass function at
several epochs discussing in detail the amount of cosmic variance affecting our
estimate. We find that Poisson noise and cosmic variance of the galaxy mass
function in the VIPERS survey are comparable with the statistical uncertainties
of large surveys in the local universe. VIPERS data allow us to determine with
unprecedented accuracy the high-mass tail of the galaxy stellar mass function,
which includes a significant number of galaxies that are usually too rare to
detect with any of the past spectroscopic surveys. At the epochs sampled by
VIPERS, massive galaxies had already assembled most of their stellar mass. We
apply a photometric classification in the (U-V) rest-frame colour to compute
the mass function of blue and red galaxies, finding evidence for the evolution
of their contribution to the total number density budget: the transition mass
above which red galaxies dominate is found to be about 10^10.4 M_sun at z=0.55
and evolves proportionally to (1+z)^3. We are able to trace separately the
evolution of the number density of blue and red galaxies with masses above
10^11.4 M_sun, in a mass range barely studied in previous work. We find that
for such large masses, red galaxies show a milder evolution with redshift, when
compared to objects at lower masses. At the same time, we detect a population
of similarly massive blue galaxies, which are no longer detectable below z=0.7.
These results show the improved statistical power of VIPERS data, and give
initial promising indications of mass-dependent quenching of galaxies at z~1.
[Abridged] | Non-linear matter power spectrum from Time Renormalisation Group:
efficient computation and comparison with one-loop: We address the issue of computing the non-linear matter power spectrum on
mildly non-linear scales with efficient semi-analytic methods. We implemented
M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop
(D1L) limit in a numerical module for the new Boltzmann code CLASS. Our
publicly released module is valid for LCDM models, and optimized in such a way
to run in less than a minute for D1L, or in one hour (divided by number of
nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop
approaches reveals that results depend crucially on the assumed initial
bispectrum at high redshift. When starting from a common assumption, the three
methods give roughly the same results, showing that the partial resumation of
diagrams beyond one loop in the TRG method improves one-loop results by a
negligible amount. A comparison with highly accurate simulations by M. Sato &
T. Matsubara shows that all three methods tend to over-predict non-linear
corrections by the same amount on small wavelengths. Percent precision is
achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1. |
[CII] 158 micron Luminosities and Star Formation Rate in Dusty
Starbursts and AGN: Results are presented for [CII] 158 micron line fluxes observed with the
Herschel PACS instrument in 112 sources with both starburst and AGN
classifications, of which 102 sources have confident detections. Results are
compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and
with L(IR) from IRAS fluxes; AGN/starburst classifications are determined from
equivalent width of the 6.2 micron PAH feature. It is found that the [CII] line
flux correlates closely with the flux of the 11.3 micron PAH feature
independent of AGN/starburst classification, log [f([CII] 158 micron)/f(11.3
micron PAH)] = -0.22 +- 0.25. It is concluded that [CII] line flux measures the
photodissociation region associated with starbursts in the same fashion as the
PAH feature. A calibration of star formation rate for the starburst component
in any source having [CII] is derived comparing [CII] luminosity L([CII]) to
L(IR) with the result that log SFR = log L([CII)]) - 7.08 +- 0.3, for SFR in
solar masses per year and L([CII]) in solar luminosities. The decreasing ratio
of L([CII]) to L(IR) in more luminous sources (the "[CII] deficit") is shown to
be a consequence of the dominant contribution to L(IR) arising from a luminous
AGN component because the sources with largest L(IR) and smallest
L([CII])/L(IR) are AGN. | MeerKLASS: MeerKAT Large Area Synoptic Survey: We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over $\sim
4,000 \, {\rm deg}^2$ for $\sim 4,000$ hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,$\mu$Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged). |
Limits on compact halo objects as dark matter from gravitational
microlensing: Microlensing started with the seminal paper by Paczy\'nski in 1986, first
with observations towards the Large Magellanic Cloud and the galactic bulge.
Since then many other targets have been observed and new applications have been
found. In particular, it turned out to be a powerful method to detect planets
in our galaxy and even in the nearby M31. Here, we will present some results
obtained so far by microlensing without being, however, exhaustive. | Is there a flatness problem in classical cosmology?: I briefly review the flatness problem within the context of classical
cosmology and examine some of the debate in the literature with regard to its
definition and even the question whether it exists. I then present some new
calculations for cosmological models which will collapse in the future;
together with previous work by others for models which will expand forever,
this allows one to examine the flatness problem quantitatively for all
cosmological models. This leads to the conclusion that the flatness problem
does not exist, not only for the cosmological models corresponding to the
currently popular values of lambda_0 and Omega_0 but indeed for all
Friedmann-Lema\^itre models. |
The long-term millimeter activity of active galactic nuclei: We analyze the long-term evolution of the fluxes of six active galactic
nuclei (AGN) - 0923+392, 3C 111, 3C 273, 3C 345, 3C 454.3, and 3C 84 - in the
frequency range 80-267 GHz using archival calibration data of the IRAM Plateau
de Bure Interferometer. Our dataset spans a long timeline of ~14 years with
974-3027 flux measurements per source. We find strong (factors ~2-8) flux
variability on timescales of years for all sources. The flux density
distributions of five out of six sources show clear signatures of bi- or even
multimodality. Our sources show mostly steep (alpha~0.5-1), variable spectral
indices that indicate outflow dominated emission; the variability is most
probably due to optical depth variations. The power spectra globally correspond
to red-noise spectra with five sources being located between the cases of white
and flicker noise and one source (3C 111) being closer to the case of random
walk noise. For three sources the low-frequency ends of their power spectra
appear to be upscaled in spectral power by factors ~2-3 with respect to the
overall powerlaws. In two sources, 3C 454.3 and 3C 84, the 1.3-mm emission
preceeds the 3-mm emission by ~55 and ~300 days, respectively, probably due to
(combinations of) optical depth and emission region geometry effects. We
conclude that the source emission cannot be described by uniform stochastic
emission processes; instead, a distinction of "quiescent" and (maybe multiple)
"flare" states of the source emission appears to be necessary. | Testing the Equivalence Principle with Strong Lensing Time Delay
Variations: Strong lensing time delay measurements provide a valuable and almost
model-independent tool for cosmological investigations. In this work we
recognize that they also carry information on the strength of the gravitational
coupling at the redshift of the lens, and thus could be in principle used to
test the equivalence principle on extragalactic scales. For the case of an
extended lens with a static mass distribution we explicitly derive an
analytical relation between $\dot{G}/G$ and the relative variation of the time
delay. For illustrative purpose, we apply our formula to the light curves of
multiple images of the quasar DES J0408-5354 and simulated ones, which results
in weak constraints on the variation of $\dot{G}/G$ of order $10^{-1}-10^{-2}
\, yr^{-1}$ in the best scenario. Finally, we briefly discuss how those
constraints can be improved in the next future. |
Combined constraints on deviations of dark energy from an ideal fluid
from Euclid and Planck: Cosmological fluids are commonly assumed to be distributed in a spatially
homogeneous way, while their internal properties are described by a perfect
fluid. As such, they influence the Hubble-expansion through their respective
densities and equation of state parameters. The subject of this paper is an
investigation of the fluid-mechanical properties of a dark energy fluid, which
is characterised by its sound speed and its viscosity apart from its equation
of state. In particular, we compute the predicted spectra for the integrated
Sachs-Wolfe effect for our generalised fluid, and compare them with the
corresponding predictions for weak gravitational lensing and galaxy clustering,
which had been computed in previous work. We perform statistical forecasts and
show that the integrated Sachs-Wolfe signal obtained by cross correlating
Euclid galaxies with Planck temperatures, when joined to galaxy clustering and
weak lensing observations, yields a percent sensitivity on the dark energy
sound speed and viscosity. We prove that the iSW effect provides strong
degeneracy breaking for low sound speeds and large differences between the
sound speed and viscosity parameters. | Determining scalar field potential in power-law cosmology with
observational data: In power-law cosmology, we determine potential function of a canonical scalar
field in FLRW universe in presence of barotropic perfect fluid. The combined
WMAP5+BAO+SN dataset and WMAP5 dataset are used here to determine the value of
the potential. The datasets suggest slightly closed universe. If the universe
is closed, the exponents of the power-law cosmology are $q = 1.01$ (WMAP5
dataset) and $q=0.985$ (combined dataset). The lower limits of $a_0$ (closed
geometry) are $5.1\E{26}$ for WMAP5 dataset and $9.85\E{26}$ for the combined
dataset. The domination of the power-law term over the curvature and barotropic
density terms is characterised by the inflection of the potential curve. This
happens when the universe is 5.3 Gyr old for both datasets. |
A new geometrical approach to void statistics: Modelling cosmic voids as spheres in Euclidean space, the notion of a
de-Sitter configuration space is introduced. It is shown that a uniform
distribution over this configuration space yields a power-law approximating the
void size distribution in an intermediate range of volumes, as well as an
estimate for the fractal dimension of the large scale structure. | Probing Cosmic Acceleration by Using the SNLS3 SNIa Dataset: We probe the cosmic acceleration by using the recently released SNLS3 sample
of 472 type Ia supernovae. Combining this type Ia supernovae dataset with the
cosmic microwave background anisotropy data from the Wilkinson Microwave
Anisotropy Probe 7-yr observations, the baryon acoustic oscillation results
from the Sloan Digital Sky Survey data release 7, and the Hubble constant
measurement from the Wide Field Camera 3 on the Hubble Space Telescope, we
measure the dark energy equation of state $w$ and the deceleration parameter
$q$ as functions of redshift by using the Chevallier-Polarski-Linder
parametrization. Our result is consistent with a cosmological constant at
1$\sigma$ confidence level, without evidence for the recent slowing down of the
cosmic acceleration. Furthermore, we consider three binned parametrizations
($w$ is piecewise constant in redshift $z$) based on different binning methods.
The similar results are obtained, i.e., the $\Lambda$CDM model is still nicely
compatible with current observations. |
X-ray Observations of the Chemical Abundances in the Intra-Cluster
Medium: Clusters of galaxies as the largest clearly defined objects in our Universe
are ideal laboratories to study the distribution of the most abundant chemical
elements heavier than hydrogen and helium and the history of their production.
The cluster environment allows us to study the element abundances not only
inside the galaxies, but also in the intergalactic space, the intracluster
medium. Since the intracluster medium is heated to temperatures of several ten
Million degrees, we can study the chemical composition of this medium through
X-ray spectroscopy. Up to 13 heavy elements have been detected by X-ray
spectroscopy so far. The element most easily detected in the X-ray spectra is
iron. In massive galaxy clusters we find a larger mass of heavy elements in the
intracluster medium than in the galaxies. The consideration of the intracluster
medium is therefore vital for an understanding of the complete history of
nucleosynthesis of the heavy elements. The observed abundances for all elements
heavier than nitrogen can roughly be modeled by using two types of sources:
core collapse supernovae and supernovae type Ia. So called cool-core galaxy
clusters show a larger heavy element abundance in the cluster center which
seems to be enriched primarily by products of supernovae of type Ia. The
evidence for observations of an evolution of the heavy element abundance with
redshift has still a moderate significance. | Hubble Space Telescope WFC3 Grism Spectroscopy and Imaging of a Growing
Compact Galaxy at z=1.9: We present HST/WFC3 grism spectroscopy of the brightest galaxy at z>1.5 in
the GOODS-South WFC3 Early Release Science grism pointing, covering the
wavelength range 0.9-1.7 micron. The spectrum is of remarkable quality and
shows the redshifted Balmer lines Hbeta, Hgamma, and Hdelta in absorption at
z=1.902, correcting previous erroneous redshift measurements from the
rest-frame UV. The average rest-frame equivalent width of the Balmer lines is
8+-1 Angstrom, which can be produced by a post-starburst stellar population
with a luminosity-weighted age of ~0.5 Gyr. The M/L ratio inferred from the
spectrum implies a stellar mass of ~4x10^11 Msun. We determine the morphology
of the galaxy from a deep WFC3 F160W image. Similar to other massive galaxies
at z~2 the galaxy is compact, with an effective radius of 2.1+-0.3 kpc.
Although most of the light is in a compact core, the galaxy has two red, smooth
spiral arms that appear to be tidally-induced. The spatially-resolved
spectroscopy demonstrates that the center of the galaxy is quiescent and the
surrounding disk is forming stars, as it shows Hbeta in emission. The galaxy is
interacting with a companion at a projected distance of 18 kpc, which also
shows prominent tidal features. The companion has a slightly redder spectrum
than the primary galaxy but is a factor of ~10 fainter and may have a lower
metallicity. It is tempting to interpret these observations as "smoking gun"
evidence for the growth of compact, quiescent high redshift galaxies through
minor mergers, which has been proposed by several recent observational and
theoretical studies. Interestingly both objects host luminous AGNs, as
indicated by their X-ray luminosities, which implies that these mergers can be
accompanied by significant black hole growth. This study illustrates the power
of moderate dispersion, low background near-IR spectroscopy at HST resolution,
which is now available with the WFC3 grism. |
Spatial Propagation of Weak Lensing Shear Response Corrections: In this paper we show how response function corrections to shear measurements
(e.g. as required by Metacalibration) propagate into cosmic shear power
spectra. We investigate a 2-sphere pixel (also known as HEALpixel') correction
and a forward-modelling approach using simple Gaussian simulations. In the
2-sphere pixel-correction approach we find a free parameter that is the
tolerated condition number of the local response matrices: if this is too large
then this can cause an amplification of the shot noise power spectrum, if too
small it can lead to a loss of area (and a possible selection bias). In
contrast by forward-modelling the power spectrum this choice can be avoided.
This also applies to map-based inference methods using shear-response
calibrated maps. | The Matryoshka Run (II): Time Dependent Turbulence Statistics,
Stochastic Particle Acceleration and Microphysics Impact in a Massive Galaxy
Cluster: We use the Matryoshka run to study the time dependent statistics of
structure-formation driven turbulence in the intracluster medium of a
10$^{15}M_\odot$ galaxy cluster. We investigate the turbulent cascade in the
inner Mpc for both compressional and incompressible velocity components. The
flow maintains approximate conditions of fully developed turbulence, with
departures thereof settling in about an eddy-turnover-time. Turbulent velocity
dispersion remains above $700$ km s$^{-1}$ even at low mass accretion rate,
with the fraction of compressional energy between 10% and 40%. Normalisation
and slope of compressional turbulence is susceptible to large variations on
short time scales, unlike the incompressible counterpart. A major merger occurs
around redshift $z\simeq0$ and is accompanied by a long period of enhanced
turbulence, ascribed to temporal clustering of mass accretion related to
spatial clustering of matter. We test models of stochastic acceleration by
compressional modes for the origin of diffuse radio emission in galaxy
clusters. The turbulence simulation model constrains an important unknown of
this complex problem and brings forth its dependence on the elusive
micro-physics of the intracluster plasma. In particular, the specifics of the
plasma collisionality and the dissipation physics of weak shocks affect the
cascade of compressional modes with strong impact on the acceleration rates. In
this context radio halos emerge as complex phenomena in which a hierarchy of
processes acting on progressively smaller scales are at work. Stochastic
acceleration by compressional modes implies statistical correlation of radio
power and spectral index with merging cores distance, both testable in
principle with radio surveys. |
ISW Imprint of Superstructures on Linear Scales: We build a model for the density and integrated Sachs-Wolfe (ISW) profile of
supervoid and supercluster structures. Our model assumes that fluctuations
evolve linearly from an initial Gaussian random field. We find these
assumptions capable of describing N-body simulations and simulated ISW maps
remarkably well on large scales. We construct an ISW map based on locations of
superstructures identified previously in the SDSS Luminous Red Galaxy sample. A
matched filter analysis of the cosmic microwave background confirms a signal at
the $3.2-\sigma$ confidence level and estimates the radius of the underlying
structures to be $55 \pm 28 ~h^{-1}$Mpc. The amplitude of the signal, however,
is $2-\sigma$ higher than $\Lambda$CDM predictions. | Probing the Mass Assembly and Chemical Evolution of High-z Galaxies with
MASSIV: Understanding the different mechanisms of galaxy assembly at various cosmic
epochs is a key issue for galaxy evolution and formation models. We present
MASSIV (Mass Assembly Survey with SINFONI in VVDS) in this context, an on-going
survey with VLT/SINFONI aiming to probe the kinematics and chemical abundances
of a unique sample of 84 star-forming galaxies selected in the redshift range z
~ 1-2. This large sample, spanning a wide range of stellar masses, is unique at
these high redshifts and statistically representative of the overall galaxy
population. In this paper, we give an overview of the MASSIV survey and then
focus on the spatially-resolved chemical properties of high-z galaxies and
their implication on the process of galaxy assembly. |
On the absence of molecular absorption in high redshift millimetre-band
searches: We have undertaken a search for millimetre-wave band absorption (through the
CO and HCO+ rotational transitions) in the host galaxies of reddened radio
sources (z = 0.405-1.802). Despite the colour selection (optical-near infrared
colours of V - K > 5 in all but one source), no absorption was found in any of
the eight quasars for which the background continuum flux was detected. On the
basis of the previous (mostly intervening) H2 and OH detections, the limits
reached here and in some previous surveys should be deep enough to detect
molecular absorption according to their V - K colours. However, our survey
makes the assumption that the reddening is associated with dust close to the
emission redshift of the quasar and that the narrow millimetre component of
this emission is intercepted by the compact molecular cores. By using the known
millimetre absorbers to define the colour depth and comparing this with the
ultra-violet luminosities of the sources, we find that, even if these
assumptions are valid, only twelve of the forty objects (mainly from this work)
are potentially detectable. This is assuming an excitation temperature of 10 K
at z=0, with the number decreasing with increasing temperatures (to zero
detectable at 100 K). | Constraints on Dark Matter-Baryon Scattering from the Temperature
Evolution of the Intergalactic Medium: The thermal evolution of the intergalactic medium (IGM) can serve as a
sensitive probe of cosmological heat sources and sinks. We employ it to limit
interactions between dark matter and baryons. After reionization the IGM
temperature is set by the balance between photoheating and adiabatic cooling.
We use measurements of the IGM temperature from Lyman-$\alpha$-forest data to
constrain the cross-section $\sigma$ between dark matter and baryons, finding
$\sigma < 10^{-20}$ cm$^2$ for dark-matter masses $m_\chi\leq 1$ GeV. This
provides the first direct constraint on scattering between dark matter and
baryons at redshift $z\sim5$. |
Nurturing Lyman Break Galaxies: Observed link between environment and
spectroscopic features: We examine the effects of magnitude, colour, and Ly-alpha equivalent width
(EW) on the spatial distribution of z~3 Lyman break galaxies (LBGs) and report
significant differences in their auto-correlation functions (ACFs). The results
are obtained using samples of ~10,000-57,000 LBGs from the Canada-France-Hawaii
Telescope Legacy Survey. We find that magnitude has a larger effect on the ACF
amplitude on small scales (<~1 Mpc) and that colour is more influential on
large scales (>~1 Mpc). We find the most significant differences between ACFs
for LBGs with dominant net Ly-alpha EW in absorption (aLBGs) and dominant net
Ly-alpha EW in emission (eLBGs) determined from >~95% pure samples of each
population using a photometric technique calibrated from ~1000 spectra. The
aLBG ACF one-halo term departs from a power law fit near ~1 Mpc, corresponding
to the virial radii of M_DM ~10^13 M_solar haloes, and shows a strong two-halo
term amplitude. In contrast, the eLBG ACF one-halo term departs at ~0.12 Mpc,
suggesting parent haloes of M_DM ~10^11 M_solar, and a two-halo term that
exhibits a `hump' on intermediate scales that we localize to the faintest,
bluest members. We find that the `hump' can be well fit with a model in which a
significant fraction of eLBGs reside on shells. The auto- and cross-correlation
functions indicate that aLBGs are found in massive, group-like haloes and that
eLBGs are found largely on group outskirts and in the field. Ly-alpha is a
tracer of several intrinsic LBG properties, including morphology, implying that
the mechanisms behind the morphology-density relation are in place at z~3 and
that Ly-alpha EW may be a key environment diagnostic. Finally, our results show
that the mass of LBGs has been underestimated because the LBG ACF amplitude is
lower than the true average as a result of the spatial anti-correlation of the
spectral sub-types (abridged). | MOND--particularly as modified inertia: After a succinct review of the MOND paradigm--with its phenomenology, and its
various underlying theories--I concentrate on so called modified inertia (MI)
formulations of MOND, which have so far received only little attention. These
share with all MOND theories the salient MOND predictions, such as
asymptotically flat rotation curves, and the universal mass-asymptotic-speed
relation. My emphasis here is, however, on the fact that MI theories can differ
substantially from their "modified-gravity" (MG) kin in predicting other
phenomena. Because MI theories are non local in time, MOND effects depend on
the full trajectory of a system, not only on its instantaneous state, as in MG
theories. This may lead to rather different predictions for, e.g., the
external-field effect (EFE): A subsystem, such as a globular cluster or a dwarf
galaxy, moving in the field of a mother galaxy, or a galaxy in a cluster, may
be subject to an EFE that depends on the accelerations all along its orbit, not
only on the instantaneous value. And, it is even possible to construct MI
theories with practically no EFE. Other predictions that may differ are also
discussed. Since we do not yet have a full fledged, modified-inertia
formulation, simple, heuristic models have been used to demonstrate these
points. |
Second-order cosmological perturbations in two-field inflation and
predictions for non-Gaussianity: Inflationary predictions for the power spectrum of the curvature perturbation
have been verified to an excellent degree, leaving many models compatible with
observations. In this thesis we studied third-order correlations, that might
allow one to further distinguish between inflationary models. From all the
possible extensions of the standard inflationary model, we chose to study
two-field models with canonical kinetic terms and flat field space. The new
feature is the presence of the so-called isocurvature perturbation. Its
interplay with the adiabatic perturbation outside the horizon gives birth to
non-linearities characteristic of multiple-field models. In this context, we
established the second-order gauge-invariant form of the adiabatic and
isocurvature perturbation and found the third-order action that describes their
interactions. Furthermore, we built on and elaborated the long-wavelength
formalism in order to acquire an expression for the parameter of
non-Gaussianity fNL as a function of the potential of the fields. We next used
this formula to study analytically, within the slow-roll hypothesis, general
classes of potentials and verified our results numerically for the exact
theory. From this study, we deduced general conclusions about the properties of
fNL, its magnitude depending on the characteristics of the field trajectory and
the isocurvature component, as well as its dependence on the magnitude and
relative size of the three momenta of which the three-point correlator is a
function. | Satellite Galaxy Number Density Profiles in the Sloan Digital Sky Survey: We study the spatial distribution of satellite galaxies around isolated
primaries using the Sloan Digital Sky Survey (SDSS) spectroscopic and
photometric galaxy catalogues. We select isolated primaries from the
spectroscopic sample and search for potential satellites in the much deeper
photometric sample. For specific luminosity primaries we obtain robust
statistical results by stacking as many as ~50, 000 galaxy systems. We find no
evidence for any anistropy in the satellite galaxy distribution relative to the
major axes of the primaries. We derive accurate projected number density
profiles of satellites down to 4 magnitudes fainter than their primaries. We
find the normalized satellite profiles generally have a universal form and can
be well fitted by projected NFW profiles. The NFW concentration parameter
increases with decreasing satellite luminosity while being independent of the
luminosity of the primary except for very bright primaries. The profiles of the
faintest satellites show deviations from the NFW form with an excess at small
galactocentric projected distances. In addition, we quantify how the radial
distribution of satellites depends on the colour of the satellites and on the
colour and concentration of their primaries. |
Constraining the Star Formation Histories in Dark Matter Halos: I.
Central Galaxies: Using the self-consistent modeling of the conditional stellar mass functions
across cosmic time by Yang et al. (2012), we make model predictions for the
star formation histories (SFHs) of {\it central} galaxies in halos of different
masses. The model requires the following two key ingredients: (i) mass assembly
histories of central and satellite galaxies, and (ii) local observational
constraints of the star formation rates of central galaxies as function of halo
mass. We obtain a universal fitting formula that describes the (median) SFH of
central galaxies as function of halo mass, galaxy stellar mass and redshift. We
use this model to make predictions for various aspects of the star formation
rates of central galaxies across cosmic time. Our main findings are the
following. (1) The specific star formation rate (SSFR) at high $z$ increases
rapidly with increasing redshift [$\propto (1+z)^{2.5}$] for halos of a given
mass and only slowly with halo mass ($\propto M_h^{0.12}$) at a given $z$, in
almost perfect agreement with the specific mass accretion rate of dark matter
halos. (2) The ratio between the star formation rate (SFR) in the main-branch
progenitor and the final stellar mass of a galaxy peaks roughly at a constant
value, $\sim 10^{-9.3} h^2 {\rm yr}^{-1}$, independent of halo mass or the
final stellar mass of the galaxy. However, the redshift at which the SFR peaks
increases rapidly with halo mass. (3) More than half of the stars in the
present-day Universe were formed in halos with $10^{11.1}\msunh < M_h <
10^{12.3}\msunh$ in the redshift range $0.4 < z < 1.9$. (4) ... [abridged] | The Evolution of an Inhomogeneous Universe: A refined version of a recently introduced method for analysing the dynamics
of an inhomogeneous irrotational dust universe is presented. A fully
non-perturbative numerical computation of the time dependence of volume in this
framework leads to the following results. If the initial state of the universe
is Einstein-de Sitter with small Gaussian perturbations, then there is no
acceleration even though the inhomogeneities strongly affect the evolution. A
universe with a positive background curvature can exhibit acceleration, but not
in conjunction with reasonable values for the Hubble rate. Thus the correct
values for both quantities can be achieved only by introducing a positive
cosmological constant. Possible loopholes to this conclusion are discussed; in
particular, acceleration as an illusion created by peculiarities of light
propagation in an inhomogeneous universe is still possible. Independently of
the cosmological constant question, the present formalism should provide an
important tool for precision cosmology. |
Spectroscopic Cosmological Surveys in the Far-IR: We show the feasibility of spectroscopic cosmological surveys with the SAFARI
instrument onboard of SPICA. The work is done through simulations that make use
of both empirical methods, i.e. the use of observed luminosity functions and
theoretical models for galaxy formation and evolution. The relations assumed
between the line emission to trace AGN and star formation activity have been
derived from the observations of local samples of galaxies. The results
converge to indicate the use of blind spectroscopy with the SAFARI FTS at
various resolutions to study galaxy evolution from the local to the distant
(z~3) Universe. Specifically, two different and independent galaxy evolution
models predict about 7-10 sources to be spectroscopically detected in more than
one line in a 2'x 2'SAFARI field of view, down to the expected flux limits of
SAFARI, with about 20% of sources to be detected at z>2. SPICA-SAFARI will be
therefore excellent at detecting high-z sources and at assessing in a direct
way their nature (e.g whether mainly AGN or Star Formation powered) thanks to
blind spectroscopy. | Galaxy bias from forward models: linear and second-order bias of
IllustrisTNG galaxies: We use field-level forward models of galaxy clustering and the EFT likelihood
formalism to study, for the first time for self-consistently simulated
galaxies, the relations between the linear $b_1$ and second-order bias
parameters $b_2$ and $b_{K^2}$. The forward models utilize all of the
information available in the galaxy distribution up to a given order in
perturbation theory, which allows us to infer these bias parameters with high
signal-to-noise, even from relatively small volumes ($L_{\rm box} = 205{\rm
Mpc}/h$). We consider galaxies from the IllustrisTNG simulations, and our main
result is that the $b_2(b_1)$ and $b_{K^2}(b_1)$ relations obtained from
gravity-only simulations for total mass selected objects are broadly preserved
for simulated galaxies selected by stellar mass, star formation rate, color and
black hole accretion rate. We also find good agreement between the bias
relations of the simulated galaxies and a number of recent estimates for
observed galaxy samples. The consistency under different galaxy selection
criteria suggests that theoretical priors on these bias relations may be used
to improve cosmological constraints based on observed galaxy samples. We do
identify some small differences between the bias relations in the
hydrodynamical and gravity-only simulations, which we show can be linked to the
environmental dependence of the relation between galaxy properties and mass. We
also show that the EFT likelihood recovers the value of $\sigma_8$ to
percent-level from various galaxy samples (including splits by color and star
formation rate) and after marginalizing over 8 bias parameters. This
demonstration using simulated galaxies adds to previous works based on halos as
tracers, and strengthens further the potential of forward models to infer
cosmology from galaxy data. |
The evolution of the low-density HI intergalactic medium from z=3.6 to
0: Data, transmitted flux and HI column density: We present a new, uniform analysis of the HI transmitted flux (F) and HI
column density (N(HI)) distribution in the low-density IGM as a function of
redshift z for 0<z<3.6 using 55 HST/COS FUV (Delta(z)=7.2 at z<0.5), five
HST/STIS+COS NUV (Delta(z)=1.3 at z~1) and 24 VLT/UVES and Keck/HIRES
(Delta(z)=11.6 at 1.7<z<3.6) AGN spectra. We performed a consistent, uniform
Voigt profile analysis to combine spectra taken with different instruments, to
reduce systematics and to remove metal-line contamination. We confirm
previously known conclusions on firmer quantitative grounds in particular by
improving the measurements at z~1. Two flux statistics at 0<F<1, the mean HI
flux and the flux probability distribution function (PDF), show that
considerable evolution occurs from z=3.6 to z=1.5, after which it slows down to
become effectively stable for z<0.5. However, there are large sightline
variations. For the HI column density distribution function (CDDF, f proptional
to N(HI)^(-beta)) at log (N(HI)/1cm^-2)=[13.5, 16.0], beta increases as z
decreases from beta~1.60 at z~3.4 to beta~1.82 at z~0.1. The CDDF shape at
lower redshifts can be reproduced by a small amount of clockwise rotation of a
higher-z CDDF with a slightly larger CDDF normalisation. The absorption line
number per z (dn/dz) shows a similar evolutionary break at z~1.5 as seen in the
flux statistics. High-N(HI) absorbers evolve more rapidly than low-N(HI)
absorbers to decrease in number or cross-section with time. The individual
dn/dz shows a large scatter at a given z. The scatter increases toward lower z,
possibly caused by a stronger clustering at lower z. | Model-independent test for the cosmic distance duality relation with
Pantheon and eBOSS DR16 quasar sample: In this paper, we carry out a new model-independent cosmological test for the
cosmic distance duality relation~(CDDR) by combining the latest five baryon
acoustic oscillations (BAO) measurements and the Pantheon type Ia supernova
(SNIa) sample. Particularly, the BAO measurement from extended Baryon
Oscillation Spectroscopic Survey~(eBOSS) data release~(DR) 16 quasar sample at
effective redshift $z=1.48$ is used, and two methods, i.e. a compressed form of
Pantheon sample and the Artificial Neural Network~(ANN) combined with the
binning SNIa method, are applied to overcome the redshift-matching problem. Our
results suggest that the CDDR is compatible with the observations, and the
high-redshift BAO and SNIa data can effectively strengthen the constraints on
the violation parameters of CDDR with the confidence interval decreasing by
more than 20 percent. In addition, we find that the compressed form of
observational data can provide a more rigorous constraint on the CDDR, and thus
can be generalized to the applications of other actual observational data with
limited sample size in the test for CDDR. |
The Structure and Dynamics of Massive High-$z$ Cosmic-Web Filaments:
Three Radial Zones in Filament Cross-Sections: We analyse the internal structure and dynamics of cosmic-web filaments that
connect massive high-$z$ haloes. Our analysis is based on a high-resolution
AREPO cosmological simulation zooming-in on a volume encompassing three ${\rm
Mpc}$-scale filaments feeding three massive haloes of $\sim
10^{12}\,\text{M}_\odot$ at $z \sim 4$, embedded in a large-scale sheet. Each
filament is surrounded by a cylindrical accretion shock of radius $r_{\rm
shock} \sim 50 \,{\rm kpc}$. The post-shock gas is in virial equilibrium with
the potential well set by an isothermal dark-matter filament. The filament
line-mass is $\sim 9\times 10^8\,\text{M}_\odot\,{\rm kpc}^{-1}$, the gas
fraction within $r_{\rm shock}$ is the universal baryon fraction, and the
virial temperature is $\sim 7\times 10^5 {\rm K}$. In the outer ''thermal'' (T)
zone, $r \geq 0.65 \, r_{\rm shock}$, inward gravity and ram-pressure forces
are over-balanced by outwards thermal pressure forces, decelerating the
inflowing gas expanding the shock outward. In the intermediate ''vortex'' (V)
zone, $0.25 \leq r/ r_{\rm shock} \leq 0.65$, the velocity field is dominated
by a quadrupolar vortex structure due to offset inflow along the sheet through
the post-shock gas. The outwards force is dominated by centrifugal forces
associated with these vortices, with additional contributions from global
rotation and thermal pressure. The shear and turbulent forces associated with
the vortices act inward. The inner ''stream'' (S) zone, $r < 0.25 \, r_{\rm
shock}$, is a dense isothermal core, $T\sim 3 \times 10^4 \, {\rm K}$ and
$n_{\rm H}\sim 0.01 \,{\rm cm^{-3}}$, defining the cold streams that feed
galaxies. The core is formed by an isobaric cooling flow and is associated with
a decrease in outwards forces, though it exhibits both inflows and outflows.
[abridged] | Spectral ageing analysis and dynamical analysis of the double-double
radio galaxy J1548-3216: Using the new low-frequency and high-frequency radio images of this galaxy,
we determined the shape of the spectrum along its lobes and performed the
classical spectral-ageing analysis. On the other hand, we applied the
analytical model of the jet's dynamics, which allowed us to derive the physical
conditions for the source's evolution during the original jet propagation
through the unperturbed IGM, as well as those when the restarted new jet
propagates inside the outer cocoon formed by the old jet material that passed
through the jet terminal shock. The dynamical age estimate of the outer and the
inner lobes is 132+/-28 Myr and ~9+/-4 Myr, respectively. The synchrotron age
in the outer lobes systematically rises from ~25 Myr in the vicinity of the
lobes' edges to about 65-75 Myr in the centre of the old cocoon. These ages
imply an average expansion speed along the jets' axis: (0.012+/-0.003)c in the
outer lobes and (0.058+/-0.025)c in the inner lobes, but the latter speed would
be ~0.25c when they were of age less than 1 Myr. We find that the jet power
during the restarted activity is about ten-fold fainter than that of the
original jet. Similar disproportion is found for the internal pressures and the
magnetic field strengths in the old cocoon and those in the inner lobes. This
disproportion can be effectively reduced by assuming the same equations of
state for the emitting particles and the magnetic fields within the old and the
new lobes. However, we think that our assumption of the non-relativistic
equation of state for the old cocoon and the relativistic one for the new lobes
is more justified. |
Weak-Lensing Mass Measurements of Five Galaxy Clusters in the South Pole
Telescope Survey Using Magellan/Megacam: We use weak gravitational lensing to measure the masses of five galaxy
clusters selected from the South Pole Telescope (SPT) survey, with the primary
goal of comparing these with the SPT Sunyaev--Zel'dovich (SZ) and X-ray based
mass estimates. The clusters span redshifts 0.28 < z < 0.43 and have masses
M_500 > 2 x 10^14 h^-1 M_sun, and three of the five clusters were discovered by
the SPT survey. We observed the clusters in the g'r'i' passbands with the
Megacam imager on the Magellan Clay 6.5m telescope. We measure a mean ratio of
weak lensing (WL) aperture masses to inferred aperture masses from the SZ data,
both within an aperture of R_500,SZ derived from the SZ mass, of 1.04 +/- 0.18.
We measure a mean ratio of spherical WL masses evaluated at R_500,SZ to
spherical SZ masses of 1.07 +/- 0.18, and a mean ratio of spherical WL masses
evaluated at R_500,WL to spherical SZ masses of 1.10 +/- 0.24. We explore
potential sources of systematic error in the mass comparisons and conclude that
all are subdominant to the statistical uncertainty, with dominant terms being
cluster concentration uncertainty and N-body simulation calibration bias.
Expanding the sample of SPT clusters with WL observations has the potential to
significantly improve the SPT cluster mass calibration and the resulting
cosmological constraints from the SPT cluster survey. These are the first WL
detections using Megacam on the Magellan Clay telescope. | Modelling the line-of-sight contribution in substructure lensing: We investigate how Einstein rings and magnified arcs are affected by
small-mass dark-matter haloes placed along the line-of-sight to gravitational
lens systems. By comparing the gravitational signature of line-of-sight haloes
with that of substructures within the lensing galaxy, we derive a mass-redshift
relation that allows us to rescale the detection threshold (i.e. lowest
detectable mass) for substructures to a detection threshold for line-of-sight
haloes at any redshift. We then quantify the line-of-sight contribution to the
total number density of low-mass objects that can be detected through strong
gravitational lensing. Finally, we assess the degeneracy between substructures
and line-of-sight haloes of different mass and redshift to provide a
statistical interpretation of current and future detections, with the aim of
distinguishing between CDM and WDM. We find that line-of-sight haloes
statistically dominate with respect to substructures, by an amount that
strongly depends on the source and lens redshifts, and on the chosen dark
matter model. Substructures represent about 30 percent of the total number of
perturbers for low lens and source redshifts (as for the SLACS lenses), but
less than 10 per cent for high redshift systems. We also find that for data
with high enough signal-to-noise ratio and angular resolution, the non-linear
effects arising from a double-lens-plane configuration are such that one is
able to observationally recover the line-of-sight halo redshift with an
absolute error precision of 0.15 at the 68 per cent confidence level. |
LyAl-Net: A high-efficiency Lyman-$α$ forest simulation with a
neural network: The inference of cosmological quantities requires accurate and large
hydrodynamical cosmological simulations. Unfortunately, their computational
time can take millions of CPU hours for a modest coverage in cosmological
scales ($\approx (100 {h^{-1}}\,\text{Mpc})^3)$). The possibility to generate
large quantities of mock Lyman-$\alpha$ observations opens up the possibility
of much better control on covariance matrices estimate for cosmological
parameters inference, and on the impact of systematics due to baryonic effects.
We present a machine learning approach to emulate the hydrodynamical simulation
of intergalactic medium physics for the Lyman-$\alpha$ forest called LyAl-Net.
The main goal of this work is to provide highly efficient and cheap simulations
retaining interpretation abilities about the gas field level, and as a tool for
other cosmological exploration. We use a neural network based on the U-net
architecture, a variant of convolutional neural networks, to predict the
neutral hydrogen physical properties, density, and temperature. We train the
LyAl-Net model with the Horizon-noAGN simulation, though using only 9% of the
volume. We also explore the resilience of the model through tests of a transfer
learning framework using cosmological simulations containing different baryonic
feedback. We test our results by analysing one and two-point statistics of
emulated fields in different scenarios, as well as their stochastic properties.
The ensemble average of the emulated Lyman-$\alpha$ forest absorption as a
function of redshift lies within 2.5% of one derived from the full
hydrodynamical simulation. The computation of individual fields from the dark
matter density agrees well with regular physical regimes of cosmological
fields. The results tested on IllustrisTNG100 showed a drastic improvement in
the Lyman-$\alpha$ forest flux without arbitrary rescaling. | Herschel-ATLAS: Modelling the first strong gravitational lenses: We have determined the mass-density radial profiles of the first five strong
gravitational lens systems discovered by the Herschel Astrophysical Terahertz
Large Area Survey (H-ATLAS). We present an enhancement of the semi-linear lens
inversion method of Warren & Dye which allows simultaneous reconstruction of
several different wavebands and apply this to dual-band imaging of the lenses
acquired with the Hubble Space Telescope. The five systems analysed here have
lens redshifts which span a range, 0.22<z<0.94. Our findings are consistent
with other studies by concluding that: 1) the logarithmic slope of the total
mass density profile steepens with decreasing redshift; 2) the slope is
positively correlated with the average total projected mass density of the lens
contained within half the effective radius and negatively correlated with the
effective radius; 3) the fraction of dark matter contained within half the
effective radius increases with increasing effective radius and increases with
redshift. |
Ultraviolet Fe II emission in z ~ 2 quasars: We present spectra of six luminous quasars at z ~ 2, covering rest
wavelengths 1600-3200 A. The fluxes of the UV Fe II emission lines and Mg II
2798 doublet, the line widths of Mg II, and the 3000 A luminosity were obtained
from the spectra. These quantities were compared with those of low-redshift
quasars at z = 0.06 - 0.55 studied by Tsuzuki et al. In a plot of the Fe
II(UV)/Mg II flux ratio as a function of the cental black hole mass, Fe
II(UV)/Mg II in our z ~ 2 quasars is systematically greater than in the
low-redshift quasars. We confermed that luminosity is not responsible for this
excess. It is unclear whether this excess is caused by rich Fe abundance at z ~
2 over low-redshift or by non-abundance effects such as high gas density,
strong radiation field, and high microturbulent velocity. | Probing warm and mixed dark matter models using lensing shift power
spectrum: We argue that the lensing power spectrum of astrometric shift (lensing shift
power spectrum) is a powerful tool of the clustering property of dark matter on
subgalactic scales. First we give the formalism to probe the nature of dark
matter by using the lensing shift power spectrum. Then, leveraging recent
measurements of the lensing shift power spectrum on an angular scale of
approximately $1~$arcsec towards the gravitationally lensed quasar
MG$\,$J0414+0534 at the redshift of $z_S=2.639$, we place constraints on the
mass of warm dark matter (WDM) particles $m_{\rm WDM}$ and their fraction in a
mixed dark matter (MDM) model $r_{\rm WDM}$, in which WDM and cold dark matter
coexist. Although the constraint derived from the above single lensing system
is not as strong as the existing constraints, as we show in this paper, the
lensing shift power spectrum has a great potential to obtain much tighter
constraints on WDM and MDM models through future observations, highlighting the
importance of well-controlled systematic error considerations for achieving
enhanced precision. |
The Atacama Cosmology Telescope: Detection of Sunyaev-Zel'dovich
Decrement in Groups and Clusters Associated with Luminous Red Galaxies: We present a detection of the Sunyaev-Zel'dovich (SZ) decrement associated
with the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey. The
SZ data come from 148 GHz maps of the equatorial region made by the Atacama
Cosmology Telescope (ACT). The LRG sample is divided by luminosity into four
bins, and estimates for the central Sunyaev-Zel'dovich temperature decrement
are calculated through a stacking process. We detect and account for a bias of
the SZ signal due to weak radio sources. We use numerical simulations to relate
the observed decrement to Y200 and clustering properties to relate the galaxy
luminosity bins to mass. We also use a relation between brightest cluster
galaxy luminosity and cluster mass based on stacked gravitational lensing
measurements to estimate the characteristic halo masses. The masses are found
to be around 1e14 M_sun. | H0LiCOW II. Spectroscopic survey and galaxy-group identification of the
strong gravitational lens system HE0435-1223: Galaxies located in the environment or on the line of sight towards
gravitational lenses can significantly affect lensing observables, and can lead
to systematic errors on the measurement of $H_0$ from the time-delay technique.
We present the results of a systematic spectroscopic identification of the
galaxies in the field of view of the lensed quasar HE0435-1223, using the W. M.
Keck, Gemini and ESO-Very Large telescopes. Our new catalog triples the number
of known galaxy redshifts in the vicinity of the lens, expanding to 102 the
number of measured redshifts for galaxies separated by less than 3 arcmin from
the lens. We complement our catalog with literature data to gather redshifts up
to 15 arcmin from the lens, and search for galaxy groups or clusters projected
towards HE0435-1223. We confirm that the lens is a member of a small group that
includes at least 12 galaxies, and find 8 other group candidates near the line
of sight of the lens. The flexion shift, namely the shift of lensed images
produced by high order perturbation of the lens potential, is calculated for
each galaxy/group and used to identify which objects produce the largest
perturbation of the lens potential. This analysis demonstrates that i) at most
three of the five brightest galaxies projected within 12 arcsec of the lens
need to be explicitly used in the lens models, and ii) the groups can be
treated in the lens model as an external tidal field (shear) contribution. |
Optically-passive spirals: The missing link in gradual star formation
suppression upon cluster infall: Galaxies migrate from the blue cloud to the red sequence when their star
formation is quenched. Here, we report on galaxies quenched by environmental
effects and not by mergers or strong AGN as often invoked: They form stars at a
reduced rate which is optically even less conspicuous, and manifest a
transition population of blue spirals evolving into S0 galaxies. These
'optically passive' or 'red spirals' are found in large numbers in the STAGES
project (and by Galaxy Zoo) in the infall region of clusters and groups. | Feeding versus Feedback in NGC4151 probed with Gemini NIFS. II.
Kinematics: We have used the Gemini NIFS to map the gas kinematics of the inner 200x500pc
of the Seyfert galaxy NGC4151 in the Z, J, H and K bands at a resolving power
5000 and spatial resolution of 8pc. The ionised gas emission is most extended
along the known ionisation bi-cone at position angle PA=60-240deg, but is
observed also along its equatorial plane. This indicates that the AGN ionizes
gas beyond the borders of the bi-cone, within a sphere with 1arcsec radius
around the nucleus. The ionised gas has three kinematic components: (1) one
observed at the systemic velocity and interpreted as originating in the galaxy
disk; (2) one outflowing along the bi-cone, with line-of-sight velocities
between -600 and 600 km/s and strongest emission at +/-(100-300)km/s; (3) and
another component due to the interaction of the radio jet with ambient gas. The
mass outflow rate, estimated to be 1 M_Sun/yr along each cone, exceeds the
inferred black hole accretion rate by a factor of 100. There is no evidence in
our data for the gradual acceleration followed by gradual deceleration proposed
by previous modelling of the [OIII] emitting gas. The molecular gas exhiibits
distinct kinematics relative to the ionised gas. Its emission arises in
extended regions approximately perpendicular to the axis of the bi-cone and
along the axis of the galaxy's stellar bar, avoiding the innermost ionised
regions. It does not show an outflowing component, being observed only at
velocities very close to systemic, and is thus consistent with an origin in the
galaxy plane. This hot molecular gas may only be the tracer of a larger
reservoir of colder gas which represents the AGN feeding. |
The Axion Dark Matter eXperiment: The Axion is a particle arising from the Peccei-Quinn solution to the strong
CP problem. Peccei-Quinn symmetry breaking in the early universe could produce
a large number of axions which would still be present today, making the axion a
compelling dark matter candidate. The goal of the Axion Dark Matter eXperiment
(ADMX) is to detect these relic axions through their conversion to photons in a
strong magnetic field. Results are presented from a recent ADMX data-taking,
along with plans for the next phase of ADMX, which will allow the experiment to
explore a significant fraction of the favored dark matter axion mass and
coupling phase space. | Theoretical priors in scalar-tensor cosmologies: Shift-symmetric
Horndeski models: Attempts at constraining theories of late time accelerated expansion often
assume broad priors for the parameters in their phenomenological description.
Focusing on shift-symmetric scalar-tensor theories with standard gravitational
wave speed, we show how a more careful analysis of their dynamical evolution
leads to much narrower priors. In doing so, we propose a simple and accurate
parametrisation of these theories, capturing the redshift dependence of the
equation of state, $w(z)$, and the kinetic braiding parameter, $\alpha_{\rm
B}(z)$, with only two parameters each, and derive their statistical
distribution (a.k.a. theoretical priors) that fit the cosmology of the
underlying model. We have considered two versions of the shift-symmetric model,
one where the energy density of dark energy is given solely by the scalar
field, and another where it also has a contribution from the cosmological
constant. By including current data, we show how theoretical priors can be used
to improve constraints by up to an order of magnitude. Moreover, we show that
shift-symmetric theories without a cosmological constant are observationally
viable. We work up to quartic order in first derivatives of the scalar in the
action and our results suggest this truncation is a good approximation to more
general shift-symmetric theories. This work establishes an actionable link
between phenomenological parameterisations and Lagrangian-based theories, the
two main approaches to test cosmological gravity and cosmic acceleration. |
Cross bispectra and trispectra of the non-linear integrated Sachs-Wolfe
effect and the tracer galaxy density field: In order to investigate possibilities to measure non-Gaussian signatures of
the non-linear iSW effect, we study in this work the family of mixed bispectra
<tau^q gamma^(3-q)> and trispectra <tau^q gamma^(4-q)> between the integrated
Sachs-Wolfe (iSW) temperature perturbation tau and the galaxy over-density
gamma. We use standard Eulerian perturbation theory restricted to tree level
expansion for predicting the cosmic matter field. As expected, the spectra are
found to decrease in amplitude with increasing q. The transition scale between
linear domination and the scales, on which non-linearities take over, moves to
larger scales with increasing number of included iSW source fields q. We derive
the cumulative signal-to-noise ratios for a combination of Planck CMB data and
the galaxy sample of a Euclid-like survey. Including scales down to l_max =
1000 we find sobering values of sigma = 0.83 for the mixed bispectrum and sigma
= 0.19 in case of the trispectrum for q=1. For higher values of q the
polyspectra <tau^2 gamma> and <tau^3 gamma> are found to be far below the
detection limit. | Bayesian inference of cosmic density fields from non-linear,
scale-dependent, and stochastic biased tracers: We present a Bayesian reconstruction algorithm to generate unbiased samples
of the underlying dark matter field from halo catalogues. Our new contribution
consists of implementing a non-Poisson likelihood including a deterministic
non-linear and scale-dependent bias. In particular we present the Hamiltonian
equations of motions for the negative binomial (NB) probability distribution
function. This permits us to efficiently sample the posterior distribution
function of density fields given a sample of galaxies using the Hamiltonian
Monte Carlo technique implemented in the Argo code. We have tested our
algorithm with the Bolshoi $N$-body simulation at redshift $z = 0$, inferring
the underlying dark matter density field from sub-samples of the halo catalogue
with biases smaller and larger than one. Our method shows that we can draw
closely unbiased samples (compatible within 1-$\sigma$) from the posterior
distribution up to scales of about $k$~1 h/Mpc in terms of power-spectra and
cell-to-cell correlations. We find that a Poisson likelihood yields
reconstructions with power spectra deviating more than 10% at $k$=0.2 h/Mpc.
Our reconstruction algorithm is especially suited for emission line galaxy data
for which a complex non-linear stochastic biasing treatment beyond Poissonity
becomes indispensable. |
The Surprisingly Constant Strength of O VI Absorbers over Cosmic Time: O VI absorption is observed in a wide range of astrophysical environments,
including the Local ISM, the disk and halo of the Milky Way, high-velocity
clouds, the Magellanic clouds, starburst galaxies, the intergalactic medium,
damped Lyman-alpha systems, and gamma-ray-burst host galaxies. Here a new
compilation of 775 O VI absorbers drawn from the literature is presented, all
observed at high resolution (instrumental FWHM<20 km/s) and covering the
redshift range z=0-3. In galactic environments [log N(H I)>20], the mean O VI
column density is shown to be insensitive to metallicity, taking a value log
N(O VI)~14.5 for galaxies covering the range -1.6<[O/H]<0. In intergalactic
environments [log N(H I)<17], the mean O VI component column density measured
in datasets of similar sensitivity shows only weak evolution between z=0.2 and
z=2.3, but IGM O VI components are on average almost twice as broad at z=0.2
than at z=2.3. The existence of a characteristic value of log N(O VI) for
galactic O VI absorbers, and the lack of evolution in log N(O VI) for
intergalactic absorbers, lend support to the ``cooling-flow' model of Heckman
et al. (2002), in which all O VI absorbers are created in regions of
initially-hot shock-heated plasma that are radiatively cooling through coronal
temperatures. These regions could take several forms, including conductive,
turbulent, or shocked boundary layers between warm (~10^4 K) clouds and hot
(~10^6 K) plasma, although many such regions would have to be intersected by a
typical galaxy-halo sightline to build up the characteristic galactic N(O VI).
The alternative, widely-used model of single-phase photoionization for
intergalactic O VI is ruled out by kinematic evidence in the majority of IGM O
VI components at low and high redshift. | Is it time to go beyond $Λ$CDM universe?: Concordance $\Lambda$CDM universe is the simplest model that is consistent
with a large variety of cosmological observations till date. But few recent
observations indicate inconsistencies in $\Lambda$CDM model. In this paper, we
consider the combination of recent SnIa+Bao+Cmb+Growth+$H(z)$+$H_{0}$
measurements to revisit the constraints on the dark energy evolution using the
widely studied CPL parametrisation for the dark energy equation of state.
Although the reconstructed behaviour for the dark energy equation of state
confirms the inconsistency of $\Lambda$CDM at $95\%$ confidence level, the
reconstructed $Om$ diagnostic which is a {\it null test} for $\Lambda$CDM,
still allows the concordance $\Lambda$CDM behaviour with a lower range of
$\Omega_{m0}$ than that obtained by Planck-2015. {\it This confirms that
$\Lambda$CDM is still the best choice for the dark energy model}. We also
measure the parameter $S = \sigma_{8}\sqrt{\Omega_{m0}/0.3} = 0.728 \pm 0.023$
which is consistent with its recent measurement by KiDS survey. The confidence
contour in the $\Omega_{m0}-\sigma_{8}$ parameter plane is also fully
consistent with KiDS survey measurement. |
The kinematics of the Local Group in a cosmological context: Recent observations constrained the tangential velocity of M31 with respect
to the Milky Way (MW) to be v_tan<34.4 km/s and the radial velocity to be in
the range v_rad=-109+/- 4.4 km/s (van der Marel et al. 2012). In this study we
use a large volume high resolution N-body cosmological simulation (Bolshoi)
together with three constrained simulations to statistically study this
kinematics in the context of the LCDM. The comparison of the ensembles of
simulated pairs with the observed LG at the 1-sigma level in the uncertainties
has been done with respect to the radial and tangential velocities, the reduced
orbital energy (e_tot), angular momentum (l_orb) and the dimensionless spin
parameter, lambda. Our main results are: (i) the preferred radial and
tangential velocities for pairs in LCDM are v_rad=-80+/-20 km/s, v_tan=50+/-10
km/s, (ii) pairs around that region are 3 to 13 times more common than pairs
within the observational values, (iii) 15%to 24% of LG-like pairs in LCDM have
energy and angular momentum consistent with observations while (iv) 9% to 13%
of pairs in the same sample show similar values in the inferred dimensionless
spin parameter. It follows that within current observational uncertainties the
quasi-conserved quantities that characterize the orbit of the LG, i.e. e_tot,
r_orb and lambda, do not challenge the standard LCDM model, but the model is in
tension with regard to the actual values of the radial and tangential
velocities. This might hint to a problem of the LCDM model to reproduce the
observed LG. | The effect of ram pressure on the star formation, mass distribution and
morphology of galaxies: We investigate the dependence of star formation and the distribution of the
components of galaxies on the strength of ram pressure. Several mock
observations in X-ray, H$\alpha$ and HI wavelength for different ram-pressure
scenarios are presented. By applying a combined N-body/hydrodynamic description
(GADGET-2) with radiative cooling and a recipe for star formation and stellar
feedback 12 different ram-pressure stripping scenarios for disc galaxies were
calculated. Special emphasis was put on the gas within the disc and in the
surroundings. All gas particles within the computational domain having the same
mass resolution. The relative velocity was varied from 100 km/s to 1000 km/s in
different surrounding gas densities in the range from $1\times10^{-28}$ to
$5\times10^{-27}$ g/cm$^3$. The temperature of the surrounding gas was
initially $1\times10^{7}$ K. The star formation of a galaxy is enhanced by more
than a magnitude in the simulation with a high ram-pressure ($5\times10^{-11}$
dyn/cm$^2$) in comparison to the same system evolving in isolation. The
enhancement of the star formation depends more on the surrounding gas density
than on the relative velocity. Up to 95% of all newly formed stars can be found
in the wake of the galaxy out to distances of more than 350 kpc behind the
stellar disc. Continuously stars fall back to the old stellar disc, building up
a bulge-like structure. Young stars can be found throughout the stripped wake
with surface densities locally comparable to values in the inner stellar disc.
Ram-pressure stripping can shift the location of star formation from the disc
into the wake on very short timescales. (Abridged) |
Gravitational wave background from kink-kink collisions on infinite
cosmic strings: We calculate the power spectrum of the stochastic gravitational wave (GW)
background expected from kink-kink collisions on infinite cosmic strings.
Intersections in the cosmic string network continuously generate kinks, which
emit GW bursts by their propagation on curved strings as well as by their
collisions. First, we show that the GW background from kink-kink collisions is
much larger than the one from propagating kinks at high frequencies because of
the higher event rate. We then propose a method to take into account the energy
loss of the string network by GW emission as well as the decrease of kink
number due to the GW backreaction. We find that, even though these effects
reduce the amplitude of the GW background, we can obtain a constraint on the
string tension $G\mu\lesssim 2 \times 10^{-7}$ using the current upper bound on
the GW background by Advanced-LIGO, which is as competitive as the constraint
from cusps on string loops. | The Standardized Candle Method for Type II Plateau Supernovae: In this paper we study the "standardized candle method" using a sample of 37
nearby (z<0.06) Type II plateau supernovae having BVRI photometry and optical
spectroscopy. An analytic procedure is implemented to fit light curves, color
curves, and velocity curves. We find that the V-I color toward the end of the
plateau can be used to estimate the host-galaxy reddening with a precision of
0.2 mag. The correlation between plateau luminosity and expansion velocity
previously reported in the literature is recovered. Using this relation and
assuming a standard reddening law (Rv = 3.1), we obtain Hubble diagrams in the
BVI bands with dispersions of ~0.4 mag. Allowing Rv to vary and minimizing the
spread in the Hubble diagrams, we obtain a dispersion range of 0.25-0.30 mag,
which implies that these objects can deliver relative distances with precisions
of 12-14%. The resulting best-fit value of Rv is 1.4 +/- 0.1. |
Multi-chaotic inflation with and without spectator field: Motivated by the result of Planck+BICEP/Keck recently released, we
investigate the consistency of the multi-field inflation models in terms of the
spectral index $n_s$ and the tensor-to-scalar ratio $r$. In this study, we
focus on double-inflaton models with and without a spectator field. We find
that inflaton with a quadratic potential can become viable when three fields
with a specific hierarchical mass spectrum are realized such that two fields
act as inflatons and the other one is the spectator. We also discuss the
conditions to avoid the fine-tuning, by careful study of how the prediction
depends on the background trajectory in the inflaton-field space. | X-ray power law spectra in active galactic nuclei: X-ray spectra of active galactic nuclei (AGN) are usually described as power
law spectra, characterized by the spectral slope $\alpha$ or photon index
$\Gamma$. Here we discuss the X-ray spectral properties within the framework of
clumpy accretion flows, and estimate the power law slope as a function of the
source parameters. We expect harder spectra in massive objects than in less
massive sources, and steeper spectra in higher accretion rate systems. The
predicted values of the photon index cover the range of spectral slopes
typically observed in Seyfert galaxies and quasars. The overall trends are
consistent with observations, and may account for the positive correlation of
the photon index with Eddington ratio (and the possible anticorrelation with
black hole mass) observed in different AGN samples. Spectral properties are
also closely related to variability properties. We obtain that shorter
characteristic time scales are associated with steeper spectra. This agrees
with the observed `spectral-timing' correlation. |
An estimate of the local ISW signal, and its impact on CMB anomalies: We estimate the local density field in redshift shells to a maximum redshift
of z=0.3, using photometric redshifts for the 2MASS galaxy catalogue, matched
to optical data from the SuperCOSMOS galaxy catalogue. This density-field map
is used to predict the Integrated Sachs-Wolfe (ISW) CMB anisotropies that
originate within the volume at z<0.3. We investigate the impact of this
estimated ISW foreground signal on large-scale anomalies in the WMAP CMB data.
We find that removal of the foreground ISW signal from WMAP data reduces the
significance of a number of reported large-scale anomalies in the CMB,
including the low quadrupole power and the apparent alignment between the CMB
quadrupole and octopole. | An Efficient and Accurate Hybrid Method for Simulating Non-Linear
Neutrino Structure: We present an efficient and accurate method for simulating massive neutrinos
in cosmological structure formation simulations, together with an easy to use
public implementation. Our method builds on our earlier implementation of the
linear response approximation (LRA) for neutrinos, coupled with an N-body code
for cold dark matter particles. The LRA's good behaviour at early times and in
the linear regime is preserved, while better following the non-linear
clustering of neutrinos on small scales. Massive neutrinos are split into
initially "fast" and "slow" components. The fast component is followed
analytically with the LRA all the way to redshift zero. The slow component is
evolved with the LRA only down to a switch-on redshift $z_\nu = 1$, below which
it is followed with the particle method, in order to fully account for its
non-linear evolution. The slow neutrino particles are initialized at $z = 99$
in order to have accurate positions and velocities at the switch-on time, but
are not used to compute the potential until $z \leq 1$, thus avoiding the worst
effect of particle shot noise. We show that our hybrid method matches (and for
small neutrino masses, exceeds) the accuracy of neutrino particle simulations
with substantially lower particle load requirements. |
Visualizing Invisible Dark Matter Annihilation with the CMB and Matter
Power Spectrum: We study the cosmological signatures of Invisibly Annihilating Dark Matter
(IAnDM), where DM annihilates into dark radiation particles that are decoupled
from the Standard Model (SM). In the simple benchmark model we consider here,
such invisible annihilation determines the relic abundance of DM via dark
thermal freeze-out. We demonstrate that IAnDM may reveal itself through
observable, novel signatures that are correlated: scale-dependent $\Delta
N_\text{eff}$ (number of extra effective neutrinos) in the Cosmic Microwave
Background (CMB) spectrum due to DM residual annihilation, while the phase of
acoustic peaks shifts towards the opposite direction relative to that due to SM
neutrinos, resembling the effect due to scattering (fluidlike) thermal dark
radiation; in addition, IAnDM induces modifications to the matter power
spectrum that resemble those due to warm dark matter. Current data are
sensitive to IAnDM with masses up to $\sim200$ keV, while future observations
will improve this reach, especially if the late-time DM annihilation cross
section is enhanced relative to the standard thermal value, which can be
realized in a variety of scenarios. This work also demonstrates a new
possibility of realizing thermal sub-MeV DM with observable signals. | Proper motion and apparent contraction in J0650+6001: We present a multi-epoch and multi-frequency VLBI study of the compact radio
source J0650+6001. In VLBI images the source is resolved into three components.
The central component shows a flat spectrum, suggesting the presence of the
core, while the two outer regions, with a steeper spectral index, display a
highly asymmetric flux density. The time baseline of the observations
considered to derive the source expansion covers about 15 years. During this
time interval, the distance between the two outer components has increased by
0.28+/-0.13 mas, that corresponds to an apparent separation velocity of
0.39c+/-0.18c and a kinematic age of 360+/-170 years. On the other hand, a
multi-epoch monitoring of the separation between the central and the southern
components points out an apparent contraction of about 0.29+/-0.02 mas,
corresponding to an apparent contraction velocity of 0.37c+/-0.02c. Assuming
that the radio structure is intrinsically symmetric, the high flux density
ratio between the outer components can be explained in terms of Doppler beaming
effects where the mildly relativistic jets are separating with an intrinsic
velocity of 0.43c+/-0.04c at an angle between 12 and 28 degrees to the line of
sight. In this context, the apparent contraction may be interpreted as a knot
in the jet that is moving towards the southern component with an intrinsic
velocity of 0.66c+/-0.03c, and its flux density is boosted by a Doppler factor
of 2.0. |
Tracing The Sound Horizon Scale With Photometric Redshift Surveys: We propose a new method for cosmological parameters extraction using the
baryon acoustic oscillation scale as a standard ruler in deep galaxy surveys
with photometric determination of redshifts. The method consists in a simple
empirical parametric fit to the angular 2-point correlation function w(theta).
It is parametrized as a power law to describe the continuum plus a Gaussian to
describe the BAO bump. The location of the Gaussian is used as the basis for
the measurement of the sound horizon scale. This method, although simple,
actually provides a robust estimation, since the inclusion of the power law and
the use of the Gaussian removes the shifts which affect the local maximum. We
discuss the effects of projection bias, non-linearities, redshift space
distortions and photo-z precision, and apply our method to a mock catalog of
the Dark Energy Survey, built upon a large N-body simulation provided by the
MICE collaboration. We discuss the main systematic errors associated to our
method and show that they are dominated by the photo-z uncertainty. | Warm inflationary model in loop quantum cosmology: A warm inflationary universe model in loop quantum cosmology is studied. In
general we discuss the condition of inflation in this framework. By using a
chaotic potential, $V(\phi)\propto \phi^2$, we develop a model where the
dissipation coefficient $\Gamma=\Gamma_0=$ constant. We use recent astronomical
observations for constraining the parameters appearing in our model. |
Nonhelical inverse transfer of a decaying turbulent magnetic field: In the presence of magnetic helicity, inverse transfer from small to large
scales is well known in magnetohydrodynamic (MHD) turbulence and has
applications in astrophysics, cosmology, and fusion plasmas. Using high
resolution direct numerical simulations of magnetically dominated
self-similarly decaying MHD turbulence, we report a similar inverse transfer
even in the absence of magnetic helicity. We compute for the first time
spectral energy transfer rates to show that this inverse transfer is about half
as strong as with helicity, but in both cases the magnetic gain at large scales
results from velocity at similar scales interacting with smaller-scale magnetic
fields. This suggests that both inverse transfers are a consequence of a
universal mechanisms for magnetically dominated turbulence. Possible
explanations include inverse cascading of the mean squared vector potential
associated with local near two-dimensionality and the shallower $k^2$
subinertial range spectrum of kinetic energy forcing the magnetic field with a
$k^4$ subinertial range to attain larger-scale coherence. The inertial range
shows a clear $k^{-2}$ spectrum and is the first example of fully isotropic
magnetically dominated MHD turbulence exhibiting weak turbulence scaling. | Radio Continuum Surveys with Square Kilometre Array Pathfinders: In the lead-up to the Square Kilometre Array (SKA) project, several
next-generation radio telescopes and upgrades are already being built around
the world. These include APERTIF (The Netherlands), ASKAP (Australia), eMERLIN
(UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), Meerkat
(South Africa), and the Murchison Widefield Array (MWA). Each of these new
instruments has different strengths, and coordination of surveys between them
can help maximise the science from each of them. A radio continuum survey is
being planned on each of them with the primary science objective of
understanding the formation and evolution of galaxies over cosmic time, and the
cosmological parameters and large-scale structures which drive it. In pursuit
of this objective, the different teams are developing a variety of new
techniques, and refining existing ones. Here we describe these projects, their
science goals, and the technical challenges which are being addressed to
maximise the science return. |
Constraining primordial non-Gaussianity from DESI quasar targets and
Planck CMB lensing: We detect the cross-correlation between 2.7 million DESI quasar targets
across 14,700 deg$^2$ (180 quasars deg$^{-2}$) and Planck 2018 CMB lensing at
$\sim$30$\sigma$. We use the cross-correlation on very large scales to
constrain local primordial non-Gaussianity via the scale dependence of quasar
bias. The DESI quasar targets lie at an effective redshift of 1.51 and are
separated into four imaging regions of varying depth and image quality. We
select quasar targets from Legacy Survey DR9 imaging, apply additional flux and
photometric redshift cuts to improve the purity and reduce the fraction of
unclassified redshifts, and use early DESI spectroscopy of 194,000 quasar
targets to determine their redshift distribution and stellar contamination
fraction (2.6%). Due to significant excess large-scale power in the quasar
autocorrelation, we apply weights to mitigate contamination from imaging
systematics such as depth, extinction, and stellar density. We use realistic
contaminated mocks to determine the greatest number of systematic modes that we
can fit, before we are biased by overfitting and spuriously remove real power.
We find that linear regression with one to seven imaging templates removed per
region accurately recovers the input cross-power, $f_{\textrm{NL}}$ and linear
bias. As in previous analyses, our $f_{\textrm{NL}}$ constraint depends on the
linear primordial non-Gaussianity bias parameter, $b_{\phi} = 2(b - p)\delta_c$
assuming universality of the halo mass function. We measure $f_{\textrm{NL}} =
-26^{+45}_{-40}$ with $p=1.6$ $(f_{\textrm{NL}} = -18^{+29}_{-27}$ with
$p=1.0$), and find that this result is robust under several systematics tests.
Future spectroscopic quasar cross-correlations with Planck lensing lensing can
tighten the $f_{\textrm{NL}}$ constraints by a factor of 2 if they can remove
the excess power on large scales in the quasar auto power spectrum. | The High Redshift Integrated Sachs-Wolfe Effect: In this paper we rely on the quasar (QSO) catalog of the Sloan Digital Sky
Survey Data Release Six (SDSS DR6) of about one million photometrically
selected QSOs to compute the Integrated Sachs-Wolfe (ISW) effect at high
redshift, aiming at constraining the behavior of the expansion rate and thus
the behaviour of dark energy at those epochs. This unique sample significantly
extends previous catalogs to higher redshifts while retaining high efficiency
in the selection algorithm. We compute the auto-correlation function (ACF) of
QSO number density from which we extract the bias and the stellar
contamination. We then calculate the cross-correlation function (CCF) between
QSO number density and Cosmic Microwave Background (CMB) temperature
fluctuations in different subsamples: at high z>1.5 and low z<1.5 redshifts and
for two different choices of QSO in a conservative and in a more speculative
analysis. We find an overall evidence for a cross-correlation different from
zero at the 2.7\sigma level, while this evidence drops to 1.5\sigma at z>1.5.
We focus on the capabilities of the ISW to constrain the behaviour of the dark
energy component at high redshift both in the \LambdaCDM and Early Dark Energy
cosmologies, when the dark energy is substantially unconstrained by
observations. At present, the inclusion of the ISW data results in a poor
improvement compared to the obtained constraints from other cosmological
datasets. We study the capabilities of future high-redshift QSO survey and find
that the ISW signal can improve the constraints on the most important
cosmological parameters derived from Planck CMB data, including the high
redshift dark energy abundance, by a factor \sim 1.5. |
Another look to distortions of the CMB spectrum: We review aspects of Cosmic Microwave Background (CMB) spectral distortions
which do not appear to have been fully explored in the literature. In
particular, implications of recent evidences of heating of the intergalactic
medium (IGM) by feedback from active galactic nuclei are investigated. Taking
also into account the IGM heating associated to structure formation, we argue
that values of the y parameter of several*10^(-6), i.e. a factor of a few below
the COBE/FIRAS upper limit, are to be expected. The Compton scattering by the
re-ionized plasma also re-processes primordial distortions, adding a y-type
contribution. Hence no pure Bose-Einstein-like distortions are to be expected.
An assessment of Galactic and extragalactic foregrounds, taking into account
the latest results from the Planck satellite as well as the contributions from
the strong CII and CO lines from star-forming galaxies, demonstrates that a
foreground subtraction accurate enough to fully exploit the PIXIE sensitivity
will be extremely challenging. Motivated by this fact we also discuss methods
to detect spectral distortions not requiring absolute measurements and show
that accurate determinations of the frequency spectrum of the CMB dipole
amplitude may substantially improve over COBE/FIRAS limits on distortion
parameters. Such improvements may be at reach of next generation CMB anisotropy
experiments. The estimated amplitude of the Cosmic Infrared Background (CIB)
dipole might be detectable by careful analyses of Planck maps at the highest
frequencies. Thus Planck might provide interesting constraints on the CIB
intensity, currently known with a ~30% uncertainty. | Isolating the Lyman Alpha Forest BAO Anomaly: A 2.5-3 sigma discrepancy has been reported between the baryonic acoustic
oscillation peak (BAO) in the Lyman $\alpha$ forest at $z\sim 2.34$ and the
best fit Planck $\Lambda$CDM cosmology. To isolate the origin of the tension,
we consider unanchored BAO, in which the standard BAO ruler is not calibrated,
eliminating any dependence on cosmology before redshift $z\sim 2.34$. We
consider BOSS BAO measurements at $z\sim 0.32$, 0.57 and 2.34, using the full
2-dimensional constraints on the angular and line of sight BAO scale, as well
as isotropic BAO measurements by 6dF and SDSS at $z\sim 0.106$ and $z\sim
0.15$. We find that the $z>0.43$ data alone is in 2.9 sigma of tension with
$\Lambda$CDM with or without the Planck best fit values of the mass fraction
$\Omega_m$ and the BAO scale $r_d H_0$, indicating that the tension arises not
from the $\Lambda$CDM parameters but from the dark energy evolution itself at
0.57<z<2.34. This conclusion is supported when the acoustic scale measured by
the CMB is included, which further increases the tension and excludes a
solution with a constant dark energy equation of state. Including the low $z$
BAO data, which is itself consistent with $\Lambda$CDM, reduces the tension to
just over 2 sigma, however in this case a CPL parametrization of the dark
energy evolution yields only a modest improvement. |
Median statistics estimates of Hubble and Newton's Constant: Robustness of any statistics depends upon the number of assumptions it makes
about the measured data. We point out the advantages of median statistics using
toy numerical experiments and demonstrate its robustness, when the number of
assumptions we can make about the data are limited. We then apply the median
statistics technique to obtain estimates of two constants of nature, Hubble
Constant ($H_0$) and Newton's Gravitational Constant($G$), both of which show
significant differences between different measurements. For $H_0$, we update
the analysis done by Chen and Ratra (2011) and Gott et al. (2001) using $576$
measurements. We find after grouping the different results according to their
primary type of measurement, the median estimates are given by
$H_0=72.5^{+2.5}_{-8}$ km/sec/Mpc with errors corresponding to 95% c.l.
(2$\sigma$) and $G=6.674702^{+0.0014}_{-0.0009} \times 10^{-11} \mathrm{N
m^{2}kg^{-2}}$ corresponding to 68% c.l. (1$\sigma$). | Using the topology of large-scale structure in the WiggleZ Dark Energy
Survey as a cosmological standard ruler: We present new and accurate measurements of the cosmic distance-redshift
relation, spanning 0.2 < z < 1, using the topology of large-scale structure as
a cosmological standard ruler. Our results derive from an analysis of the
Minkowski functionals of the density field traced by the WiggleZ Dark Energy
Survey. The Minkowski functionals are a set of statistics which completely
describe the topological nature of each isodensity surface within the field, as
a function of the density value. Given the shape of the underlying matter power
spectrum, measured by fluctuations in the Cosmic Microwave Background
radiation, the expected amplitudes of the Minkowski functionals are specified
as an excursion set of a Gaussian random field, with minimal non-Gaussian
corrections for the smoothing scales > 10 Mpc/h considered in this analysis.
The measured amplitudes then determine the cosmic distance D_V(z), which we
obtain with 3-7% accuracies in six independent redshift slices, with the
standard ruler originating in the known curvature of the model power spectrum
at the smoothing scale. We introduce a new method for correcting the
topological statistics for the sparse-sampling of the density field by the
galaxy tracers, and validate our overall methodology using mock catalogues from
N-body simulations. Our distance measurements are consistent with standard
models which describe the cosmic expansion history, and with previous analyses
of baryon acoustic oscillations (BAOs) detected by the WiggleZ Survey, with the
topological results yielding a higher distance precision by a factor of 2.
However, the full redshift-space power-spectrum shape is required to recover
the topological distances, in contrast to the preferred length scale imprinted
by BAOs, which is determined by simpler physics. |
Interpretation of the Extragalactic Radio Background: We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon
flight of the ARCADE 2 instrument, along with previous measurements at other
frequencies, to constrain models of extragalactic emission. Such emission is a
combination of the Cosmic Microwave Background (CMB) monopole, Galactic
foreground emission, the integrated contribution of radio emission from
external galaxies, any spectral distortions present in the CMB, and any other
extragalactic source. After removal of estimates of foreground emission from
our own Galaxy, and the estimated contribution of external galaxies, we present
fits to a combination of the flat-spectrum CMB and potential spectral
distortions in the CMB. We find 2 sigma upper limits to CMB spectral
distortions of mu < 5.8 x 10^{-5} and Y_ff < 6.2 x 10^{-5}. We also find a
significant detection of a residual signal beyond that which can be explained
by the CMB plus the integrated radio emission from galaxies estimated from
existing surveys. After subtraction of an estimate of the contribution of
discrete radio sources, this unexplained signal is consistent with
extragalactic emission in the form of a power law with amplitude 1.06 \pm 0.11
K at 1 GHz and a spectral index of -2.56 \pm 0.04. | The impact of a new median statistics $H_0$ prior on the evidence for
dark radiation: Recent analyses that include cosmic microwave background (CMB) anisotropy
measurements from the Atacama Cosmology Telescope and the South Pole Telescope
have hinted at the presence of a dark radiation component at more than two
standard deviations. However, this result depends sensitively on the assumption
of an HST prior on the Hubble constant, where $H_0=73.8\pm2.4$ km/s/Mpc at 68%
c.l.. From a median statistics (MS) analysis of 537 non-CMB $H_0$ measurements
from Huchra's compilation we derive $H_0=68 \pm2.8$ km/s/Mpc at 68% c.l., in
good agreement with the results of a recent analysis of the full Huchra list of
$H_0$ measurements. This result is also fully consistent with the value of
$H_0=69.7\pm2.5$ km/s/Mpc at 68% c.l. obtained from CMB measurements under
assumption of the standard $\Lambda$CDM model. We show that with the MS $H_0$
prior the evidence for dark radiation is weakened to $\sim 1.2$ standard
deviations. Parametrizing the dark radiation component through the effective
number of relativistic degrees of freedom $N_{eff}$, we find
$N_{eff}=3.98\pm0.37$ at 68% c.l. with the HST prior and $N_{eff}=3.52\pm0.39$
at 68% c.l. with the MS prior. We also discuss the implications for current
limits on neutrino masses and on primordial Helium abundances. |
Ultraviolet variability of quasars: dependence on the accretion rate: We compiled a catalogue of about 4000 SDSS quasars including individual
estimators V for the variability strength, virial black hole masses M, and mass
accretion rates dM/dt from the Davis-Laor scaling relation. We confirm
significant anti-correlations between V and dM/dt, the Eddington ratio, and the
bolometric luminosity L, respectively. A weak, statistically not significant
positive trend is indicated for the dependence of V on M. As a side product, we
find a strong correlation of the radiative efficiency with M and show that this
trend is most likely produced by selection effects in combination with the mass
errors and the use of the scaling relation for dM/dt. The anti-correlations
found for V cannot be explained in such a way. The strongest anti-correlation
is found with dM/dt. However, it is difficult to decide which of the quantities
(L, Eddington ratio, dM/dt) is intrinsically correlated with V and which of the
observed correlations are produced by the relations between these quantities. A
V-dM/dt anti-correlation is qualitatively expected for the strongly
inhomogeneous accretion disks. We argue that several observed variability
properties are not adequately explained by the simple multi-temperature
black-body model of a standard disk and suggest to check whether the strongly
inhomogeneous disk model is capable of reproducing these observations better. | Multi-probe analysis of the galaxy cluster CL J1226.9+3332: hydrostatic
mass and hydrostatic-to-lensing bias: We present a multi-probe analysis of the well-known galaxy cluster CL
J1226.9+3332 as a proof of concept for multi-wavelength studies within the
framework of the NIKA2 Sunyaev-Zeldovich Large Program (LPSZ). CL J1226.9+3332
is a massive and high redshift (z = 0.888) cluster that has already been
observed at several wavelengths. A joint analysis of the thermal SZ (tSZ)
effect at millimeter wavelength with the NIKA2 camera and in X-ray with the
XMM-Newton satellite permits the reconstruction of the cluster thermodynamical
properties and mass assuming hydrostatic equilibrium. We test the robustness of
our mass estimates against different definitions of the data analysis transfer
function. Using convergence maps reconstructed from the data of the CLASH
program we obtain estimates of the lensing mass, which we compare to the
estimated hydrostatic mass. This allows us to measure the
hydrostatic-to-lensing mass bias and the associated systematic effects related
to the NIKA2 measurement. We obtain M500HSE = (7.65 +- 1.03) 1014 Msun and
M500lens = (7.35 +- 0.65) 1014 Msun, which implies a HSE-to-lensing bias
consistent with 0 within 20 percent. |
H2 formation and excitation in the Stephan's Quintet galaxy-wide
collision: Context. The Spitzer Space Telescope has detected a powerful (L(H2)~10^41 erg
s-1) mid-infrared H2 emission towards the galaxy-wide collision in the
Stephan's Quintet (SQ) galaxy group. This discovery was followed by the
detection of more distant H2-luminous extragalactic sources, with almost no
spectroscopic signatures of star formation. These observations set molecular
gas in a new context where one has to describe its role as a cooling agent of
energetic phases of galaxy evolution. Aims. The SQ postshock medium is observed
to be multiphase, with H2 gas coexisting with a hot (~ 5 10^6 K), X-ray
emitting plasma. The surface brightness of H2 lines exceeds that of the X-rays
and the 0-0 S(1) H2 linewidth is ~ 900 km s-1, of the same order of the
collision velocity. These observations raise three questions we propose to
answer: (i) Why H2 is present in the postshock gas ? (ii) How can we account
for the H2 excitation ? (iii) Why H2 is a dominant coolant ? Methods. We
consider the collision of two flows of multiphase dusty gas. Our model
quantifies the gas cooling, dust destruction, H2 formation and excitation in
the postshock medium. Results. (i) The shock velocity, the post-shock
temperature and the gas cooling timescale depend on the preshock gas density.
The collision velocity is the shock velocity in the low density volume filling
intercloud gas. This produces a ~ 5 10^6 K, dust-free, X-ray emitting plasma.
The shock velocity is smaller in clouds. We show that gas heated to
temperatures less than 10^6 K cools, keeps its dust content and becomes H2
within the SQ collision age (~ 5 10^6 years). (ii) Since the bulk kinetic
energy of the H2 gas is the dominant energy reservoir, we consider that the H2
emission is powered by the dissipation of kinetic turbulent energy. (Abridged) | Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Two-point
Correlation Functions: We perform a blinded cosmology analysis with cosmic shear two-point
correlation functions (2PCFs) measured from more than 25 million galaxies in
the Hyper Suprime-Cam three-year shear catalog in four tomographic redshift
bins ranging from 0.3 to 1.5. After conservative masking and galaxy selection,
the survey covers 416 deg$^2$ of the northern sky with an effective galaxy
number density of 15 arcmin$^{-2}$ over the four redshift bins. The 2PCFs
adopted for cosmology analysis are measured in the angular range: $7.1 <
\theta/{\rm arcmin} < 56.6$ for $\xi_+$ and $31.2 <\theta/{\rm arcmin} < 248$
for $\xi_-$, with a total signal-to-noise ratio of 26.6. We apply a
conservative, wide, flat prior on the photometric redshift errors on the last
two tomographic bins, and the relative magnitudes of the cosmic shear amplitude
across four redshift bins allow us to calibrate the photometric redshift
errors. With this flat prior on redshift errors, we find $\Omega_{\rm
m}=0.256_{-0.044}^{+0.056}$ and $S_8\equiv \sigma_8 \sqrt{\Omega_{\rm
m}/0.3}=0.769_{-0.034}^{+0.031}$ (both 68\% CI) for a flat $\Lambda$ cold dark
matter cosmology. We find, after unblinding, that our constraint on $S_8$ is
consistent with the Fourier space cosmic shear and the 3$\times$2pt analyses on
the same HSC dataset. We carefully study the potential systematics from
astrophysical and systematic model uncertainties in our fiducial analysis using
synthetic data, and report no biases (including projection bias in the
posterior space) greater than $0.5\sigma$ in the estimation of $S_8$. Our
analysis hints that the mean redshifts of the two highest tomographic bins are
higher than initially estimated. In addition, a number of consistency tests are
conducted to assess the robustness of our analysis. Comparing our result with
Planck-2018 cosmic microwave background observations, we find a ~$2\sigma$
tension for the $\Lambda$CDM model. |
The gravitationally lensed, luminous infrared galaxy IRAS F10214+4724
observed with XMM-Newton: We report on a short XMM-Newton observation of the gravitationally-lensed,
luminous infrared galaxy IRAS F10214+4724 at z=2.3. A faint X-ray source is
detected at 4 sigma. The observed 0.5-2 keV (1.7-6.6 keV in the rest-frame)
flux is 1.3e-15 erg/s/cm2 and the spectral slope in the rest-frame 1-10 keV
band is Gamma~2. These results agree with those obtained from the Chandra X-ray
Observatory, given the large uncertainties in both measurements. While possible
evidence for excess emission above 5 keV is seen, we suspect this excess might
be either spurious or not related to the infrared galaxy. | Absorption signatures of warm-hot gas at low redshift: OVI: We investigate the origin and physical properties of OVI absorbers at low
redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations
from the OverWhelmingly Large Simulations (OWLS) project. Intervening OVI
absorbers are believed to trace shock-heated gas in the Warm-Hot Intergalactic
Medium (WHIM) and may thus play a key role in the search for the missing
baryons in the present-day Universe. When compared to observations, the
predicted distributions of the different OVI line parameters (column density,
Doppler parameter, rest equivalent width) from our simulations exhibit a lack
of strong OVI absorbers. This suggests that physical processes on sub-grid
scales (e.g. turbulence) may strongly influence the observed properties of OVI
systems. We find that the intervening OVI absorption arises mainly in highly
metal-enriched (0.1 << Z/Z_sun < 1) gas at typical overdensities of 1 <<
rho/<rho> < 100. One third of the OVI absorbers in our simulation are found to
trace gas at temperatures T < 10^5 K, while the rest arises in gas at higher
temperatures around T =10^5.3 K. The OVI resides in a similar region of
(rho,T)-space as much of the shock-heated baryonic matter, but the vast
majority of this gas has a lower metal content and does not give rise to
detectable OVI absorption As a consequence of the patchy metal distribution,
OVI absorbers in our simulations trace only a very small fraction of the cosmic
baryons (<2 percent) and the cosmic metals. Instead, these systems presumably
trace previously shock-heated, metal-rich material from galactic winds that is
now cooling. The common approach of comparing OVI and HI column densities to
estimate the physical conditions in intervening absorbers from QSO observations
may be misleading, as most of the HI (and most of the gas mass) is not
physically connected with the high-metallicity patches that give rise to the
OVI absorption. |
The evolution of CMB spectral distortions in the early Universe: The energy spectrum of the cosmic microwave background (CMB) allows
constraining episodes of energy release in the early Universe. In this paper we
revisit and refine the computations of the cosmological thermalization problem.
For this purpose a new code, called CosmoTherm, was developed that allows
solving the coupled photon-electron Boltzmann equation in the expanding,
isotropic Universe for small spectral distortion in the CMB. We explicitly
compute the shape of the spectral distortions caused by energy release due to
(i) annihilating dark matter; (ii) decaying relict particles; (iii) dissipation
of acoustic waves; and (iv) quasi-instantaneous heating. We also demonstrate
that (v) the continuous interaction of CMB photons with adiabatically cooling
non-relativistic electrons and baryons causes a negative mu-type CMB spectral
distortion of DI_nu/I_nu ~ 10^{-8} in the GHz spectral band. We solve the
thermalization problem including improved approximations for the double Compton
and Bremsstrahlung emissivities, as well as the latest treatment of the
cosmological recombination process. At redshifts z <~ 10^3 the matter starts to
cool significantly below the temperature of the CMB so that at very low
frequencies free-free absorption alters the shape of primordial distortions
significantly. In addition, the cooling electrons down-scatter CMB photons
introducing a small late negative y-type distortion at high frequencies. We
also discuss our results in the light of the recently proposed CMB experiment
Pixie, for which CosmoTherm should allow detailed forecasting. Our current
computations show that for energy injection because of (ii) and (iv) Pixie
should allow to improve existing limits, while the CMB distortions caused by
the other processes seem to remain unobservable with the currently proposed
sensitivities and spectral bands of Pixie. | Nonlinear relativistic corrections to cosmological distances, redshift
and gravitational lensing magnification. I - Key results: The next generation of telescopes will usher in an era of precision
cosmology, capable of determining the cosmological model to beyond the percent
level. For this to be effective, the theoretical model must be understood to at
least the same level of precision. A range of subtle relativistic effects
remain to be explored theoretically, and offer the potential for probing
general relativity in this new regime. We present the distance-redshift
relation to second order in cosmological perturbation theory for a general dark
energy model. This relation determines the magnification of sources at high
precision, as well as redshift space distortions in the mildly non-linear
regime. We identify a range of new lensing effects, including:
double-integrated and nonlinear integrated Sach-Wolfe contributions, transverse
Doppler effects, lensing from the induced vector mode and gravitational wave
backgrounds, in addition to lensing from the second-order potential.
Modifications to Doppler lensing from redshift-space distortions are
identified. Finally, we find a new double-coupling between the density
fluctuations integrated along the line of sight, and gradients in the density
fluctuations coupled to transverse velocities along the line of sight. These
can be large and thus offer important new probes of gravitational lensing and
general relativity. This paper accompanies arXiv:1402.1933, where a
comprehensive derivation is given. |
Super-horizon second-order perturbations for cosmological random
fluctuations and the Hubble-constant problem: The super-horizon second-order density perturbations corresponding to
cosmological random fluctuations are considered, their non-vanishing spatial
average is shown to be useful in solving the serious problem on the
cosmological tension between measured Hubble constants at present and those at
the early stage, and the difference from previous works on the backreaction is
discussed. | Testing the accuracy of clustering redshift with simulations: We explore the accuracy of the clustering-based redshift inference within the
MICE2 simulation. This method uses the spatial clustering of galaxies between a
spectroscopic reference sample and an unknown sample. The goal of this study is
to give a preview of the redshift accuracy one can reach with this method. To
do so, we first highlight the requirements of this technique in term of number
of objects in both the reference and unknown samples. We also confirm that this
method does not require a representative spectroscopic sample for calibration.
We estimate that a density of spectroscopic objects of $10^{-5}$
arcmin$^{-2}$ per redshift bin of width $\delta z = 0.01$ over $9000 \
\text{deg}^{2}$ allows to reach 0.1 \% accuracy in the mean redshift for a
galaxy density compatible with next generation of cosmological surveys. This
number is compatible with the density of the Quasi Stellar Objects in BOSS.
Second we demonstrate our ability to measure individual redshifts for galaxies
independently from the photometric redshifts procedure. The resulting
individual clustering redshifts have a bias=$-0.001$, an outlier fraction of
$\eta=3.57\%$ and a scatter of $\sigma=0.027$ to $i<25$. The advantage of this
procedure is threefold: i) it allows the use of clustering redshifts for any
field in astronomy, ii) it allows the possibility to combine photometric and
clustering based redshifts to get an improved redshift estimation, iii) it
allows the use of cluster-$z$ to define tomographic bins for weak lensing.
Finally we explore this last option and build 5 clustering redshift selected
tomographic bins from redshift 0.2 to 1. We found a bias on the mean redshift
estimate of $0.002$ per bin. |
Emergence of a Broad-Absorption-Line Outflow in the Narrow-line Seyfert
1 Galaxy WPVS 007: We report results from a 2003 FUSE observation, and reanalysis of a 1996 HST
observation of the unusual X-ray transient Narrow-line Seyfert 1 galaxy WPVS
007. The HST FOS spectrum revealed mini-BALs with V_max ~ 900 km s^-1 and FWHM
~ 550 km s^-1. The FUSE spectrum showed that an additional BAL outflow with
V_max ~ 6000 km s^-1 and FWHM ~ 3400 km s^-1 had appeared. WPVS 007 is a
low-luminosity object in which such a high velocity outflow is not expected;
therefore, it is an outlier on the M_V/V_max relationship. Template spectral
fitting yielded apparent ionic columns, and a Cloudy analysis showed that the
presence of PV requires a high ionization parameter log(U) >= 0 and high column
density log(N_H) >= 23 assuming solar abundances and a nominal SED for
low-luminosity NLS1s with alpha_ox=-1.28. A recent long Swift observation
revealed the first hard X-ray detection and an intrinsic (unabsorbed) alpha_ox
~ -1.9$. Using this SED in our analysis yielded lower column density
constraints (log(N_H) >= 22.2 for Z=1, or log(N_H) >= 21.6 if Z=5). The X-ray
weak continuum, combined with X-ray absorption consistent with the UV lines,
provides the best explanation for the observed Swift X-ray spectrum. The large
column densities and velocities implied by the UV data in any of these
scenarios could be problematic for radiative acceleration. We also point out
that since the observed PV absorption can be explained by lower total column
densities using an intrinsically X-ray weak spectrum, we might expect to find
PV absorption preferentially more often (or stronger) in quasars that are
intrinsically X-ray weak. | Observational Upper Bound on the Cosmic Abundances of Negative-mass
Compact Objects and Ellis Wormholes from the Sloan Digital Sky Survey Quasar
Lens Search: The latest result in the Sloan Digital Sky Survey Quasar Lens Search (SQLS)
has set the first cosmological constraints on negative-mass compact objects and
Ellis wormholes. There are no multiple images lensed by the above two exotic
objects for $\sim 50000$ distant quasars in the SQLS data. Therefore, an upper
bound is put on the cosmic abundances of these lenses. The number density of
negative mass compact objects is $n<10^{-8} (10^{-4}) h^3 {\rm Mpc}^{-3}$ at
the mass scale $|M| > 10^{15} (10^{12}) M_\odot$, which corresponds to the
cosmological density parameter $|\Omega| < 10^{-4}$ at the galaxy-scale mass
range $|M|=10^{12-15}M_\odot$. The number density of the Ellis wormhole is
$n<10^{-4} h^3 {\rm Mpc}^{-3}$ for a range of the throat radius $a =
10^{1-4}$pc, which is much smaller than the Einstein ring radius. |
The Bluedisks project, a study of unusually HI-rich galaxies: I. HI
Sizes and Morphology: We introduce the "Bluedisk" project, a large program at the Westerbork
Synthesis Radio Telescope (WSRT) that has mapped the HI in a sample of 23
nearby galaxies with unusually high HI mass fractions, along with a
similar-sized sample of control galaxies matched in stellar mass, size,
inclination and redshift. This paper presents the sample selection,
observational set-up, data reduction strategy, and a first analysis of the
sizes and structural properties of the HI disks. We find that the HI-rich
galaxies lie on the same HI mass versus HI size relation as normal spiral
galaxies, extending it to total HI masses of $2 \times 10^{10} M_{\odot}$ and
radii R1 of $\sim 100$ kpc (where R1 is defined as the radius where the HI
column density reaches 1 $M_{\odot}$ pc$^{-2}$). HI-rich galaxies have
significantly larger values of HI-to-optical size ratio at fixed stellar mass,
concentration index, stellar and star formation rate surface density compared
to the control sample. The disks of HI-rich galaxies are also significantly
more clumpy (i.e. have higher HI Gini and $\Delta$Area coefficient) than those
of normal spirals. There is no evidence that the disks of HI-rich galaxies are
more disturbed: HI-rich galaxies exhibit no difference with respect to control
samples in their distributions of HI asymmetry indices or optical/HI disk
position angle differences. In fact, the center of the HI distribution
corresponds more closely with the center of the optical light in the HI-rich
galaxies than in the controls. All these results argue against a scenario in
which new gas has been brought in by mergers. It is possible that they may be
more consistent with cooling from a surrounding quasi-static halo of warm/hot
gas. | The kinematic of HST-1 in the jet of M87: Aims: We aim to constrain the structural variations within the HST-1 region
downstream of the radio jet of M87, in general as well as in connection to the
episodes of activity at very high energy (VHE). Methods: We analyzed and
compared 26 VLBI observations of the M87 jet, obtained between 2006 and 2011
with the Very Long Baseline Array (VLBA) at 1.7 GHz and the European VLBI
Network (EVN) at 5 GHz. Results: HST-1 is detected at all epochs; we
model-fitted its complex structure with two or more components, the two
outermost of which display a significant proper motion with a superluminal
velocity around ~4c. The motion of a third feature that is detected upstream is
more difficult to characterize. The overall position angle of HST-1 has changed
during the time of our observations from -65deg to -90deg, while the structure
has moved by over 80 mas downstream. Our results on the component evolution
suggest that structural changes at the upstream edge of HST-1 can be related to
the VHE events. |
Interpreting deep learning models for weak lensing: Deep Neural Networks (DNNs) are powerful algorithms that have been proven
capable of extracting non-Gaussian information from weak lensing (WL) data
sets. Understanding which features in the data determine the output of these
nested, non-linear algorithms is an important but challenging task. We analyze
a DNN that has been found in previous work to accurately recover cosmological
parameters in simulated maps of the WL convergence ($\kappa$). We derive
constraints on the cosmological parameter pair $(\Omega_m,\sigma_8)$ from a
combination of three commonly used WL statistics (power spectrum, lensing
peaks, and Minkowski functionals), using ray-traced simulated $\kappa$ maps. We
show that the network can improve the inferred parameter constraints relative
to this combination by $20\%$ even in the presence of realistic levels of shape
noise. We apply a series of well established saliency methods to interpret the
DNN and find that the most relevant pixels are those with extreme $\kappa$
values. For noiseless maps, regions with negative $\kappa$ account for
$86-69\%$ of the attribution of the DNN output, defined as the square of the
saliency in input space. In the presence of shape nose, the attribution
concentrates in high convergence regions, with $36-68\%$ of the attribution in
regions with $\kappa > 3 \sigma_{\kappa}$. | Faint Companions of Isolated 2MIG Galaxies: We present the results of a search for companions around the isolated
galaxies from the 2MIG catalog. Among 3227 2MIG galaxies we detected 125
objects with a total of 214 neighbors having radial velocity differences of
Delta V < 500 km/s and projected separations of R_p < 500 kpc relative to the
2MIG galaxies. The median luminosity of the companions is 1/25 of the
luminosity of catalog galaxies, which has little effect on the dynamic
isolation of the latter. The median ratio of the orbital mass to the
K-luminosity determined from 60 companions of E and S0 2MIG galaxies, 63
M_sun/L_sun, is signficantly greater than that found from the spiral galaxy
companions (17 M_sun/L_sun). We note that a fraction of 2MIG galaxies with
companions may be a part of low-contrast diffuse structures: clouds and
filaments. |
Post-inflationary preheating with weak coupling: Particle production in the background of an external classical oscillating
field is a key process describing the stage of preheating after inflation. For
sufficiently strong couplings between the inflaton and matter fields, this
process is known to proceed non-perturbatively. Parametric resonance plays
crucial role for bosonic fields in this case, and the evolution of the
occupation numbers for fermions is non-perturbative as well. In the Minkowski
space, parametric resonance for bosons and non-perturbative effects for
fermions would still persist even in the case of weak coupling. In particular,
the energy density of created bosons would grow exponentially with time.
However, the situation is quite different in the expanding universe. We give a
simple demonstration how the conditions of the expanding universe,
specifically, redshift of the field modes, lead to the usual perturbative
expressions for particle production by an oscillating inflaton in the case of
weak couplings. The results that we obtain are relevant and fully applicable to
the Starobinsky model of inflation. | Higher Order Statistics for Three-dimensional Shear and Flexion: We introduce a collection of statistics appropriate for the study of
spinorial quantities defined in three dimensions, focussing on applications to
cosmological weak gravitational lensing studies in 3D. In particular, we
concentrate on power spectra associated with three- and four-point statistics,
which have the advantage of compressing a large number of typically very noisy
modes into a convenient data set. It has been shown previously by \cite{MuHe09}
that, for non--Gaussianity studies in the microwave background, such
compression can be lossless for certain purposes, so we expect the statistics
we define here to capture the bulk of the cosmological information available in
these higher-order statistics. We consider the effects of a sky mask and noise,
and use Limber's approximation to show how, for high-frequency angular modes,
confrontation of the statistics with theory can be achieved efficiently and
accurately. We focus on scalar and spinorial fields including convergence,
shear and flexion of 3D weak lensing, but many of the results apply for general
spin fields. |
The view from the boundary: a new void stacking method: We introduce a new method for stacking voids and deriving their profile that
greatly increases the potential of voids as a tool for precision cosmology.
Given that voids are highly non-spherical and have most of their mass at their
edge, voids are better described relative to their boundary rather than
relative to their centre, as in the conventional spherical stacking approach.
The boundary profile is obtained by computing the distance of each volume
element from the void boundary. Voids can then be stacked and their profiles
computed as a function of this boundary distance. This approach enhances the
weak lensing signal of voids, both shear and convergence, by a factor of two
when compared to the spherical stacking method. It also results in steeper void
density profiles that are characterised by a very slow rise inside the void and
a pronounced density ridge at the void boundary. The resulting boundary density
profile is self-similar when rescaled by the thickness of the density ridge,
implying that the average rescaled profile is independent of void size. The
boundary velocity profile is characterized by outflows in the inner regions
whose amplitude scales with void size, and by a strong inflow into the
filaments and walls delimiting the void. This new picture enables a
straightforward discrimination between collapsing and expanding voids both for
individual objects as well as for stacked samples. | Cosmic Structure and Dynamics of the Local Universe: We present a cosmography analysis of the Local Universe based on the recently
released Two-Micron All-Sky Redshift Survey (2MRS). Our method is based on a
Bayesian Networks Machine Learning algorithm (the Kigen-code) which
self-consistently samples the initial density fluctuations compatible with the
observed galaxy distribution and a structure formation model given by second
order Lagrangian perturbation theory (2LPT). From the initial conditions we
obtain an ensemble of reconstructed density and peculiar velocity fields which
characterize the local cosmic structure with high accuracy unveiling nonlinear
structures like filaments and voids in detail. Coherent redshift space
distortions are consistently corrected within 2LPT. From the ensemble of
cross-correlations between the reconstructions and the galaxy field and the
variance of the recovered density fields we find that our method is extremely
accurate up to k ~ 1 h Mpc^-1 and still yields reliable results down to scales
of about 3-4 h^-1 Mpc. The motion of the local group we obtain within ~ 80 h^-1
Mpc (v_LG=522+-86 km s^-1, l_LG=291^o +- 16^o, b_LG=34^o+-8^o) is in good
agreement with measurements derived from the CMB and from direct observations
of peculiar motions and is consistent with the predictions of LambdaCDM. |
The Thermal Proximity Effect: A New Probe of He II Reionization History
and the Quasar Lifetime: Despite decades of effort, the timing and duration of He II reionization, as
well as its morphology and the properties of the quasars believed to drive it,
are still not well constrained. In this paper we present a new method to study
both He II reionization and quasars via the thermal proximity effect -- the
photoelectric heating of the intergalactic medium around quasars when their
hard radiation doubly ionizes helium. We post-process a SPH simulation with 1D
radiative calculations, and study how the thermal proximity effect depends on
the amount of singly ionized helium, $x_{\rm HeII,0}$, which prevailed in the
IGM before the quasar turned on, and the characteristic lifetime $t_{\rm Q}$
for which quasars shine. We find that the amplitude of the temperature boost in
the quasar environment depends on $x_{\rm HeII,0}$, with a characteristic value
of $\Delta T \simeq 10^4\,{\rm K}$ for an initially singly ionized IGM ($x_{\rm
HeII,0} = 1.0$), whereas the size of the thermal proximity zone is sensitive to
quasar lifetime $t_{\rm Q}$, with typical sizes of ~100 cMpc for luminous
quasars shining for $t_{\rm Q}=10^8$ yr. This temperature boost is manifest as
a change in the thermal broadening of H I absorption lines near the quasar. We
introduce a new method based on measuring the Ly$\alpha$ forest power spectrum
as a function of distance from the quasar, and conduct Bayesian MCMC analysis
to demonstrate that the thermal proximity effect should be easily detectable.
For a mock dataset of 50 quasars at z~4, we predict that one can measure
$x_{\rm HeII,0}$ to a precision $\approx 0.04$, and $t_{\rm Q}$ to a precision
of $\approx 0.1$ dex. By applying our formalism to existing high-resolution
Ly$\alpha$ forest spectra of quasars at $3.1 \lesssim z \lesssim 5.0$, one
should be able to detect the thermal proximity effect, and reconstruct the full
reionization history of He II. | Almanac: Weak Lensing power spectra and map inference on the masked
sphere: We present a field-based signal extraction of weak lensing from noisy
observations on the curved and masked sky. We test the analysis on a simulated
Euclid-like survey, using a Euclid-like mask and noise level. To make optimal
use of the information available in such a galaxy survey, we present a Bayesian
method for inferring the angular power spectra of the weak lensing fields,
together with an inference of the noise-cleaned tomographic weak lensing shear
and convergence (projected mass) maps. The latter can be used for field-level
inference with the aim of extracting cosmological parameter information
including non-gaussianity of cosmic fields. We jointly infer all-sky $E$-mode
and $B$-mode tomographic auto- and cross-power spectra from the masked sky, and
potentially parity-violating $EB$-mode power spectra, up to a maximum multipole
of $\ell_{\rm max}=2048$. We use Hamiltonian Monte Carlo sampling, inferring
simultaneously the power spectra and denoised maps with a total of $\sim 16.8$
million free parameters. The main output and natural outcome is the set of
samples of the posterior, which does not suffer from leakage of power from $E$
to $B$ unless reduced to point estimates. However, such point estimates of the
power spectra, the mean and most likely maps, and their variances and
covariances, can be computed if desired. |
An X-ray/optical study of the complex dynamics of the core of the
massive intermediate-redshift cluster MACSJ0717.5+3745: Using CHANDRA, we investigate the spatial temperature distribution of the
intracluster medium (ICM) within 700 kpc of the center of the massive merging
cluster MACSJ0717.5+3745 at z=0.55. Combining the X-ray evidence with
information about the distribution and velocities of the cluster galaxies near
the core provides us with a snapshot of the three-dimensional geometry and
dynamics of one of the most complex cluster studied to date. We find
MACSJ0717.5+3745 to be an active triple merger with ICM temperatures exceeding
20 keV. Although radial velocity information and X-ray/optical offsets indicate
that all three mergers proceed along distinctly different directions, the
partial alignment of the merger axes points to a common origin in the
large-scale filament south-east of the cluster core. Clear decrements in the
ICM temperature observed near two of these subclusters identify the respective
X-ray surface brightness peaks as remnants of cool cores; the compactness and
low temperature of 5.7 keV of one of these features suggest that the respective
merger, a high-velocity collision at 3,000 km/s, is still in its very early
stages. Looking beyond the triple merger, we find the large-scale filament to
not only provide a spatial as well as temporal arrow for the interpretation of
the dynamics of the merger events near the cluster core; we also find
tantalizing, if circumstantial, evidence for direct, large-scale heating of the
ICM by contiguous infall of low-density gas from the filament. | Evidence for a pressure discontinuity at the position of the Coma relic
from Planck Sunyaev-Zel'dovich effect data: Radio relics are Mpc-scale diffuse synchrotron sources found in galaxy
cluster outskirts. They are believed to be associated with large-scale shocks
propagating through the intra-cluster medium, although the connection between
radio relics and the cluster merger shocks is not yet proven conclusively. We
present a first tentative detection of a pressure jump in the well-known relic
of the Coma cluster through Sunyaev-Zel'dovich (SZ) effect imaging.The SZE data
are extracted from the first public all-sky data release of Planck and we use
high-frequency radio data at 2.3 GHz to constrain the shock-front geometry. The
SZE data provide evidence for a pressure discontinuity, consistent with the
relic position, without requiring any additional prior on the shock-front
location. The derived Mach number M = 2.9 (+0.8/-0.6) is consistent with X-ray
and radio results. A high-pressure "filament" without any pressure
discontinuity is disfavoured by X-ray measurements and a "sub-cluster" model
based on the infalling group NGC 4839 can be ruled out considering the
published mass estimates for this group. These results signify a first attempt
towards directly measuring the pressure discontinuity for a radio relic and the
first SZ-detected shock feature observed near the virial radius of a galaxy
cluster. |
Patterns of primary beam non-redundancy in close-packed 21 cm array
observations: Radio interferometer arrays such as HERA consist of many close-packed dishes
arranged in a regular pattern, giving rise to a large number of `redundant'
baselines with the same length and orientation. Since identical baselines
should see an identical sky signal, this provides a way of finding a relative
gain/bandpass calibration without needing an explicit sky model. In reality,
there are many reasons why baselines will not be exactly identical, giving rise
to a host of effects that spoil the redundancy of the array and induce spurious
structure in the calibration solutions if not accounted for. In this paper, we
seek to build an understanding of how differences in the primary beam response
between antennas affect redundantly-calibrated interferometric visibilities and
their resulting frequency (delay-space) power spectra. We use simulations to
study several generic types of primary beam variation, including differences in
the width of the main lobe, the angular and frequency structure of the
sidelobes, and the beam ellipticity and orientation. For all of these types, we
find that additional temporal structure is induced in the gain solutions,
particularly when bright point sources pass through the beam. In comparison,
only a low level of additional spectral structure is induced. The temporal
structure modulates the cosmological 21cm power spectrum, but only at the level
of a few percent in our simulations. We also investigate the possibility of
signal loss due to decoherence effects when non-redundant visibilities are
averaged together, finding that the decoherence is worst when bright point
sources pass through the beam, and that its magnitude varies significantly
between baseline groups and types of primary beam variation. Redundant
calibration absorbs some of the decoherence effect however, reducing its impact
compared to if the visibilities were perfectly calibrated. | An AzTEC 1.1 mm survey of the GOODS-N field -- II. Multi-wavelength
identifications and redshift distribution: We present results from a multi-wavelength study of 29 sources (false
detection probabilities <5%) from a survey of the Great Observatories Origins
Deep Survey-North field at 1.1mm using the AzTEC camera. Comparing with
existing 850um SCUBA studies in the field, we examine differences in the source
populations selected at the two wavelengths. The AzTEC observations uniformly
cover the entire survey field to a 1-sigma depth of ~1mJy. Searching deep
1.4GHz VLA, and Spitzer 3--24um catalogues, we identify robust counterparts for
21 1.1mm sources, and tentative associations for the remaining objects. The
redshift distribution of AzTEC sources is inferred from available spectroscopic
and photometric redshifts. We find a median redshift of z=2.7, somewhat higher
than z=2.0 for 850um-selected sources in the same field, and our lowest
redshift identification lies at a spectroscopic redshift z=1.1460. We measure
the 850um to 1.1mm colour of our sources and do not find evidence for `850um
dropouts', which can be explained by the low-SNR of the observations. We also
combine these observed colours with spectroscopic redshifts to derive the range
of dust temperatures T, and dust emissivity indices $\beta$ for the sample,
concluding that existing estimates T~30K and $\beta$~1.75 are consistent with
these new data. |
Redshift-Space Enhancement of Line-of-Sight Baryon Acoustic Oscillations
in the SDSS Main-Galaxy Sample: We show that redshift-space distortions of galaxy correlations have a strong
effect on correlation functions with distinct, localized features, like the
signature of the baryon acoustic oscillations (BAO). Near the line of sight,
the features become sharper as a result of redshift-space distortions. We
demonstrate this effect by measuring the correlation function in Gaussian
simulations and the Millennium Simulation. We also analyze the SDSS DR7
main-galaxy sample (MGS), splitting the sample into slices 2.5 degrees on the
sky in various rotations. Measuring 2D correlation functions in each slice, we
do see a sharp bump along the line of sight. Using Mexican-hat wavelets, we
localize it to (110 +/- 10) Mpc/h. Averaging only along the line of sight, we
estimate its significance at a particular wavelet scale and location at 2.2
sigma. In a flat angular weighting in the (pi,r_p) coordinate system, the noise
level is suppressed, pushing the bump's significance to 4 sigma. We estimate
that there is about a 0.2% chance of getting such a signal anywhere in the
vicinity of the BAO scale from a power spectrum lacking a BAO feature. However,
these estimates of the significances make some use of idealized Gaussian
simulations, and thus are likely a bit optimistic. | ${\rm S{\scriptsize IM}BIG}$: A Forward Modeling Approach To Analyzing
Galaxy Clustering: We present the first-ever cosmological constraints from a simulation-based
inference (SBI) analysis of galaxy clustering from the new ${\rm S{\scriptsize
IM}BIG}$ forward modeling framework. ${\rm S{\scriptsize IM}BIG}$ leverages the
predictive power of high-fidelity simulations and provides an inference
framework that can extract cosmological information on small non-linear scales,
inaccessible with standard analyses. In this work, we apply ${\rm S{\scriptsize
IM}BIG}$ to the BOSS CMASS galaxy sample and analyze the power spectrum,
$P_\ell(k)$, to $k_{\rm max}=0.5\,h/{\rm Mpc}$. We construct 20,000 simulated
galaxy samples using our forward model, which is based on high-resolution ${\rm
Q{\scriptsize UIJOTE}}$ $N$-body simulations and includes detailed survey
realism for a more complete treatment of observational systematics. We then
conduct SBI by training normalizing flows using the simulated samples and infer
the posterior distribution of $\Lambda$CDM cosmological parameters: $\Omega_m,
\Omega_b, h, n_s, \sigma_8$. We derive significant constraints on $\Omega_m$
and $\sigma_8$, which are consistent with previous works. Our constraints on
$\sigma_8$ are $27\%$ more precise than standard analyses. This improvement is
equivalent to the statistical gain expected from analyzing a galaxy sample that
is $\sim60\%$ larger than CMASS with standard methods. It results from
additional cosmological information on non-linear scales beyond the limit of
current analytic models, $k > 0.25\,h/{\rm Mpc}$. While we focus on $P_\ell$ in
this work for validation and comparison to the literature, ${\rm S{\scriptsize
IM}BIG}$ provides a framework for analyzing galaxy clustering using any summary
statistic. We expect further improvements on cosmological constraints from
subsequent ${\rm S{\scriptsize IM}BIG}$ analyses of summary statistics beyond
$P_\ell$. |
Scalar field description of a parametric model of dark energy: We investigate theoretical and observational aspects of a time-dependent
parameterization for the dark energy equation of state (EoS) $w(z)$, which is a
well behaved function of the redshift $z$ over the entire cosmological
evolution, i.e., $z \in [-1,\infty)$. By using a theoretical algorithm of
constructing the quintessence potential directly from the effective EoS
parameter, we derive and discuss the general features of the resulting
potential for this $w(z)$ function. Since the parameterization here discussed
allows us to divide the parametric plane in defined regions associated to
distinct classes of dark energy models, we use the most recent observations
from type Ia supernovae, baryon acoustic oscillation peak and Cosmic Microwave
Background shift parameter to check which class is observationally prefered. We
show that the largest portion of the confidence contours lies into the region
corresponding to a possible crossing of the so-called phanton divide line at
some point of the cosmic evolution. | Search for X-Ray Emission Associated with the Shapley Supercluster with
Suzaku: Suzaku performed observations of 3 regions in and around the Shapley
supercluster: a region located between A3558 and A3556, at ~0.9 times the
virial radii of both clusters, and two other regions at 1{\deg}and 4{\deg}away
from the first pointing. The 4{\deg}-offset observation was used to evaluate
the Galactic foreground emission. We did not detect significant redshifted
Oxygen emission lines (O VII and O VIII) in the spectra of all three pointings,
after subtracting the contribution of foreground and background emission. An
upper limit for the redshifted O VIII Ka line intensity of the warm-hot
intergalactic medium (WHIM) is 1.5 \times 10^-7 photons s^-1 cm^-2 arcmin^-2,
which corresponds to an overdensity of ~380 (Z/0.1 Z_solar)^{-1/2} (L/3
Mpc)^{-1/2}, assuming T=3\times10^6 K. We found excess continuum emission in
the 1{\deg}-offset and on-filament regions, represented by thermal models with
kT ~1 keV and ~2 keV, respectively. The redshifts of both 0 and that of the
supercluster (0.048) are consistent with the observed spectra. The ~1 keV
emission can be also fitted with Ne-rich Galactic (zero redshift) thin thermal
emission. Radial intensity profile of 2 keV component suggests contribution
from A3558 and A3556, but with significant steepening of the intensity slope in
the outer region of A3558. Finally, we summarized the previous Suzaku search
for the WHIM and discussed the feasibility of constraining the WHIM. An
overdensity of < 400 can be detectable using O VII and O VIII emission lines in
a range of 1.4\times10^6 K < T < 5\times10^6 K or a continuum emission in a
relatively high temperature range T > 5\times10^6 K with the Suzaku XIS. The
non detection with Suzaku suggests that typical line-of-sight average
overdensity is < 400. |
Nuclear and Extended Spectra of NGC 1068 - I: Hints from Near-Infrared
Spectroscopy: We report the first simultaneous zJHK spectroscopy on the archetypical
Seyfert 2 Galaxy NGC 1068 covering the wavelength region 0.9 to 2.4 micron. The
slit, aligned in the NS direction and centred in the optical nucleus, maps a
region 300 pc in radius at sub-arcsec resolution, with a spectral resolving
power of 360 km s^-1. This configuration allow us to study the physical
properties of the nuclear gas including that of the north side of the
ionization cone, map the strong excess of continuum emission in the K-band and
attributed to dust and study the variations, both in flux and profile, in the
emission lines. Our results show that (1) Mid- to low-ionization emission lines
are splitted into two components, whose relative strengths vary with the
position along the slit and seem to be correlated with the jet. (2) The coronal
lines are single-peaked and are detected only in the central few hundred of
parsecs from the nucleus. (3) The absorption lines indicate the presence of
intermediate age stellar population, which might be a significant contributor
to the continuum in the NIR spectra. (4) Through some simple photoionization
models we find photoionization as the main mechanism powering the emitting gas.
(5) Calculations using stellar features point to a mass concentration inside
the 100 - 200 pc of about 10^10 solar masses. | Constraining Baryonic Physics with DES Y1 and Planck data -- Combining
Galaxy Clustering, Weak Lensing, and CMB Lensing: We constrain cosmology and baryonic feedback scenarios with a joint analysis
of weak lensing, galaxy clustering, cosmic microwave background (CMB) lensing,
and their cross-correlations (so-called 6$\times$2) using data from the Dark
Energy Survey (DES) Y1 and the Planck satellite mission. Noteworthy features of
our 6$\times$2 pipeline are: We extend CMB lensing cross-correlation
measurements to a band surrounding the DES Y1 footprint (a $\sim 25\%$ gain in
pairs), and we develop analytic covariance capabilities that account for
different footprints and all cross-terms in the 6$\times$2 analysis. We also
measure the DES Y1 cosmic shear two-point correlation function (2PCF) down to
$0.^\prime 25$, but find that going below $2.^\prime 5$ does not increase
cosmological information due to shape noise. We model baryonic physics
uncertainties via the amplitude of Principal Components (PCs) derived from a
set of hydro-simulations. Given our statistical uncertainties, varying the
first PC amplitude $Q_1$ is sufficient to model small-scale cosmic shear 2PCF.
For DES Y1+Planck 6$\times$2 we find $S_8=0.799\pm0.016$, comparable to the
5$\times$2 result of DES Y3+SPT/Planck $S_8=0.773\pm0.016$. Combined with our
most informative cosmology priors -- baryon acoustic oscillation (BAO), big
bang nucleosynthesis (BBN), type Ia supernovae (SNe Ia), and Planck 2018
EE+lowE, we measure $S_8=0.817\pm 0.011$. Regarding baryonic physics
constraints, our 6$\times$2 analysis finds $Q_1=2.8\pm1.8$. Combined with the
aforementioned priors, it improves the constraint to $Q_1=3.5\pm1.3$. For
comparison, the strongest feedback scenario considered in this paper, the
cosmo-OWLS AGN ($\Delta T_\mathrm{heat}=10^{8.7}$ K), corresponds to
$Q_1=5.84$. |
The Dependence of Star Formation Rates on Stellar Mass and Environment
at z~0.8: We examine the star formation rates (SFRs) of galaxies in a redshift slice
encompassing the z=0.834 cluster RX J0152.7-1357. We used a low-dispersion
prism in the Inamori Magellan Areal Camera and Spectrograph (IMACS) to identify
galaxies with z<23.3 AB mag in diverse environments around the cluster out to
projected distances of ~8 Mpc from the cluster center. We utilize a
mass-limited sample (M>2x10^{10} M_sun) of 330 galaxies that were imaged by
Spitzer MIPS at 24 micron to derive SFRs and study the dependence of specific
SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show
a strong decrease with increasing local density, similar to the relation at
z~0. Our result contrasts with other work at z~1 that find the SFR-density
trend to reverse for luminosity-limited samples. These other results appear to
be driven by star-formation in lower mass systems (M~10^{10} M_sun). Our
results imply that the processes that shut down star-formation are present in
groups and other dense regions in the field. Our data also suggest that the
lower SFRs of galaxies in higher density environments may reflect a change in
the ratio of star-forming to non-star-forming galaxies, rather than a change in
SFRs. As a consequence, the SFRs of star-forming galaxies, in environments
ranging from small groups to clusters, appear to be similar and largely
unaffected by the local processes that truncate star-formation at z~0.8. | A High Signal-to-Noise Ratio Composite Spectrum of Gamma-ray Burst
Afterglows: We present a composite spectrum of 60 long duration gamma-ray burst (GRB)
afterglows with redshifts in the range 0.35<z<6.7 observed with low resolution
optical spectra. The composite spectrum covers the wavelength range 700-6600 A
in the rest frame and has a mean signal-to-noise ratio of 150 per 1 A pixel and
reaches a maximum of ~300 in the range 2500-3500 A. Equivalent widths are
measured from metal absorption lines from the Lya line to ~5200 A, and
associated metal and hydrogen lines are identified between the Lyman break and
Lya line. The average transmission within the Lyman forest is consistent with
that found along quasar lines of sight. We find a temporal variation in fine
structure lines when dividing the sample into bursts observed within 2 hours
from their trigger and those observed later. Other lines in the predominantly
neutral gas show variations too, but this is most likely a random effect caused
by weighting of individual strong absorption lines and which mimics a temporal
variation. Bursts characterized with high or low prompt GRB energy release
produce afterglows with similar absorption line strengths, and likewise for
bursts with bright or faint optical afterglows. Bursts defined as dark from
their optical to X-ray spectral index have stronger absorption lines relative
to the optically bright bursts. The composite spectrum has strong CaII and MgII
absorption lines as commonly found in dusty galaxies, however, we find no
evidence for dust or a significant molecular content based on the non-detection
of diffuse interstellar bands. Compared to starburst galaxy spectra, the GRB
composite has much stronger fine structure lines, while metal absorption lines
are weaker. |
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