The cosmic X-ray background: abundance and evolution of hidden black holes. (arXiv:1304.3665v1 [astro-ph.CO])

The cosmic X-ray background: abundance and evolution of hidden black holes. (arXiv:1304.3665v1 [astro-ph.CO]):
The growth of supermassive black holes across cosmic time leaves a radiative
imprint recorded in the X-ray background (XRB). The XRB spectral shape suggests
that a large population of distant, hidden nuclei must exist, which are now
being revealed at higher and higher redshifts by the deepest surveys performed
by Chandra and XMM.

Our current understanding of the XRB emission in terms of AGN population
synthesis models is here reviewed, and the evolutionary path of nuclear
accretion and obscuration, as emerging from the major X-ray surveys, is
investigated. The role of galaxy merging versus secular processes in triggering
nuclear activity is also discussed in the framework of recent galaxy/black hole
co-evolutionary scenarios. Finally, the limits of current instrumentation in
the detection of the most obscured and distant black holes are discussed and
some possible directions to overcome these limits are presented.

Galaxy Formation: Where Do We Stand?. (arXiv:1212.5641v1 [astro-ph.CO])

Galaxy Formation: Where Do We Stand?. (arXiv:1212.5641v1 [astro-ph.CO]):
This paper presents a review of the topic of galaxy formation and evolution,
focusing on basic features of galaxies, and how these observables reveal how
galaxies and their stars assemble over cosmic time. I give an overview of the
observed properties of galaxies in the nearby universe and for those at higher
redshifts up to z~10. This includes a discussion of the major processes in
which galaxies assemble and how we can now observe these - including the merger
history of galaxies, the gas accretion and star formation rates. I show that
for the most massive galaxies mergers and accretion are about equally important
in the galaxy formation process between z = 1-3, while this likely differs for
lower mass systems. I also discuss the mass differential evolution for
galaxies, as well as how environment can affect galaxy evolution, although mass
is the primary criteria for driving evolution. I also discuss how we are
beginning to measure the dark matter content of galaxies at different epochs as
measured through kinematics and clustering. Finally, I review how observables
of galaxies, and the observed galaxy formation process, compares with
predictions from simulations of galaxy formation, finding significant
discrepancies in the abundances of massive galaxies and the merger history. I
conclude by examining prospects for the future using JWST, Euclid, SKA, and the
ELTs in addressing outstanding issues.

Radiative efficiency, variability and Bondi accretion onto massive black holes: from mechanical to quasar feedback in brightest cluster galaxies. (arXiv:1211.5604v1 [astro-ph.CO])

Radiative efficiency, variability and Bondi accretion onto massive black holes: from mechanical to quasar feedback in brightest cluster galaxies. (arXiv:1211.5604v1 [astro-ph.CO]):
We examine unresolved nuclear X-ray sources in 57 brightest cluster galaxies
to study the relationship between nuclear X-ray emission and accretion onto
supermassive black holes (SMBHs). The majority of the clusters in our sample
have prominent X-ray cavities embedded in the surrounding hot atmospheres,
which we use to estimate mean jet power and average accretion rate onto the
SMBHs over the past several hundred Myr. We find that ~50% of the sample have
detectable nuclear X-ray emission. The nuclear X-ray luminosity is correlated
with average accretion rate determined using X-ray cavities, which is
consistent with the hypothesis that nuclear X-ray emission traces ongoing
accretion. The results imply that jets in systems that have experienced recent
AGN outbursts, in the last ~10^7yr, are `on' at least half of the time. Nuclear
X-ray sources become more luminous with respect to the mechanical jet power as
the mean accretion rate rises. We show that nuclear radiation exceeds the jet
power when the mean accretion rate rises above a few percent of the Eddington
rate, where the AGN apparently transitions to a quasar. The nuclear X-ray
emission from three objects (A2052, Hydra A, M84) varies by factors of 2-10 on
timescales of 6 months to 10 years. If variability at this level is a common
phenomenon, it can account for much of the scatter in the relationship between
mean accretion rate and nuclear X-ray luminosity. We find no significant change
in the spectral energy distribution as a function of luminosity in the variable
objects. The relationship between accretion and nuclear X-ray luminosity is
consistent with emission from either a jet, an ADAF, or a combination of the
two, although other origins are possible. We also consider the longstanding
problem of whether jets are powered by the accretion of cold circumnuclear gas
or nearly spherical inflows of hot keV gas.[abridged]

Large Synoptic Survey Telescope: Dark Energy Science Collaboration. (arXiv:1211.0310v1 [astro-ph.CO])

Large Synoptic Survey Telescope: Dark Energy Science Collaboration. (arXiv:1211.0310v1 [astro-ph.CO]):
This white paper describes the LSST Dark Energy Science Collaboration (DESC),
whose goal is the study of dark energy and related topics in fundamental
physics with data from the Large Synoptic Survey Telescope (LSST). It provides
an overview of dark energy science and describes the current and anticipated
state of the field. It makes the case for the DESC by laying out a robust
analytical framework for dark energy science that has been defined by its
members and the comprehensive three-year work plan they have developed for
implementing that framework. The analysis working groups cover five key probes
of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia
supernovae, and strong lensing. The computing working groups span cosmological
simulations, galaxy catalogs, photon simulations and a systematic software and
computational framework for LSST dark energy data analysis. The technical
working groups make the connection between dark energy science and the LSST
system. The working groups have close linkages, especially through the use of
the photon simulations to study the impact of instrument design and survey
strategy on analysis methodology and cosmological parameter estimation. The
white paper describes several high priority tasks identified by each of the 16
working groups. Over the next three years these tasks will help prepare for
LSST analysis, make synergistic connections with ongoing cosmological surveys
and provide the dark energy community with state of the art analysis tools.
Members of the community are invited to join the LSST DESC, according to the
membership policies described in the white paper. Applications to sign up for
associate membership may be made by submitting the Web form at
this http URL with a short statement
of the work they wish to pursue that is relevant to the LSST DESC.

A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates. (arXiv:1210.5679v1 [gr-qc])

A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates. (arXiv:1210.5679v1 [gr-qc]):
Astrophysical black hole candidates are thought to be the Kerr black holes
predicted by General Relativity, but the actual nature of these objects has
still to be proven. The analysis of the electromagnetic radiation emitted by a
geometrically thin and optically thick accretion disk around a black hole
candidate can provide information about the geometry of the space-time around
the compact object and it can thus test the Kerr black hole hypothesis. In this
paper, I present a code based on a ray-tracing approach and capable of
computing some basic properties of thin accretion disks in space-times with
deviations from the Kerr background. The code can be used to fit current and
future X-ray data of stellar-mass black hole candidates and constrain possible
deviations from the Kerr geometry in the spin parameter-deformation parameter
plane.

Investigating the velocity structure and X-ray observable properties of simulated galaxy clusters with PHOX. (arXiv:1210.4158v1 [astro-ph.CO])

Investigating the velocity structure and X-ray observable properties of simulated galaxy clusters with PHOX. (arXiv:1210.4158v1 [astro-ph.CO]):
Non-thermal motions in the intra-cluster medium (ICM) are believed to play a
non-negligible role in the pressure support to the total gravitating mass of
galaxy clusters. Future X-ray missions, such as ASTRO-H and ATHENA, will
eventually allow us to directly detect the signature of these motions from
high-resolution spectra of the ICM. In this paper, we present a study on a set
of clusters extracted from a cosmological hydrodynamical simulation, devoted to
explore the role of non-thermal velocity amplitude in characterising the
cluster state and the relation between observed X-ray properties. In order to
reach this goal, we apply the X-ray virtual telescope PHOX to generate
synthetic observations of the simulated clusters with both Chandra and ATHENA,
the latter used as an example for the performance of very high-resolution X-ray
telescopes. From Chandra spectra we extract global properties, e.g. luminosity
and temperature, and from ATHENA spectra we estimate the gas velocity
dispersion along the line of sight from the broadening of heavy-ion emission
lines (e.g. Fe). We further extend the analysis to the relation between
non-thermal velocity dispersion of the gas and the L_X-T scaling law for the
simulated clusters. Interestingly, we find a clear dependence of slope and
scatter on the selection criterion for the clusters, based on the level of
significance of non-thermal motions. Namely, the scatter in the relation is
significantly reduced by the exclusion of the clusters, for which we estimate
the highest turbulent velocities. Such velocity diagnostics appears therefore
as a promising independent way to identify disturbed clusters, in addition to
the commonly used morphological inspection.

A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc])

A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc]):
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.

Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.

The origin of the chemical elements in cluster cores. (arXiv:1210.1093v1 [astro-ph.CO])

The origin of the chemical elements in cluster cores. (arXiv:1210.1093v1 [astro-ph.CO]):
Metals play a fundamental role in ICM cooling processes in cluster cores
through the emission of spectral lines. But when and how were these metals
formed and distributed through the ICM? The X-ray band has the unique property
of containing emission lines from all elements from carbon to zinc within the
0.1-10 keV band. Using XMM-Newton, the abundances of about 11 elements are
studied, which contain valuable information about their origin. Most elements
were formed in type Ia and core-collapse supernovae, which have very different
chemical yields. Massive stars and AGB stars also contribute by providing most
of the carbon and nitrogen in the ICM. Because feedback processes suppress star
formation in the cluster centre, the element abundances allow us to directly
probe the star formation history of the majority of stars that are thought to
have formed between z=2-3. The spatial distribution in the core and the
evolution with redshift also provide information about how these elements are
transported from the member galaxies to the ICM. I review the current progress
in chemical enrichment studies of the ICM and give an outlook to the future
opportunities provided by XMM-Newton's successors, like Astro-H.

The evolution of active galactic nuclei and their spins. (arXiv:1210.1025v1 [astro-ph.HE])

The evolution of active galactic nuclei and their spins. (arXiv:1210.1025v1 [astro-ph.HE]):
Massive black holes (MBHs) in contrast to stellar mass black holes are
expected to substantially change their properties over their lifetime. MBH
masses increase by several order of magnitude over the Hubble time, as
illustrated by Soltan's argument. MBH spins also must evolve through the series
of accretion and mergers events that grow the MBH's masses. We present a simple
model that traces the joint evolution of MBH masses and spins across cosmic
time. Our model includes MBH-MBH mergers, merger-driven gas accretion,
stochastic fueling of MBHs through molecular cloud capture, and a basic
implementation of accretion of recycled gas. This approach aims at improving
the modeling of low-redshift MBHs and AGN, whose properties can be more easily
estimated observationally. Despite the simplicity of the model, it captures
well the global evolution of the MBH population from z\sim6 to today. Under our
assumptions, we find that the typical spin and radiative efficiency of MBHs
decrease with cosmic time because of the higher incidence of stochastic
processes in gas-rich galaxies and MBH-MBH mergers in gas-poor galaxies. At z=0
the spin distribution in gas-poor galaxies peaks at spins 0.4-0.8, and it is
not strongly mass dependent. MBHs in gas-rich galaxies have a more complex
evolution, with low-mass MBHs at low redshift having low spins, and spins
increasing at larger masses and redshifts. We also find that at z>1 MBH spins
are on average highest in high luminosity AGN, while at lower redshifts these
differences disappear.

Black Holes in the Early Universe. (arXiv:1209.2243v1 [astro-ph.CO])

Black Holes in the Early Universe. (arXiv:1209.2243v1 [astro-ph.CO]):
The existence of massive black holes was postulated in the sixties, when the
first quasars were discovered. In the late nineties their reality was proven
beyond doubt, in the Milky way and a handful nearby galaxies. Since then,
enormous theoretical and observational efforts have been made to understand the
astrophysics of massive black holes. We have discovered that some of the most
massive black holes known, weighing billions of solar masses, powered luminous
quasars within the first billion years of the Universe. The first massive black
holes must therefore have formed around the time the first stars and galaxies
formed. Dynamical evidence also indicates that black holes with masses of
millions to billions of solar masses ordinarily dwell in the centers of today's
galaxies. Massive black holes populate galaxy centers today, and shone as
quasars in the past; the quiescent black holes that we detect now in nearby
bulges are the dormant remnants of this fiery past. In this review we report on
basic, but critical, questions regarding the cosmological significance of
massive black holes. What physical mechanisms lead to the formation of the
first massive black holes? How massive were the initial massive black hole
seeds? When and where did they form? How is the growth of black holes linked to
that of their host galaxy? Answers to most of these questions are work in
progress, in the spirit of these Reports on Progress in Physics.

Narrow Atomic Features from Rapidly Spinning Neutron Stars. (arXiv:1209.0768v1 [astro-ph.HE])

Narrow Atomic Features from Rapidly Spinning Neutron Stars. (arXiv:1209.0768v1 [astro-ph.HE]):
Neutron stars spinning at moderate rates (~300-600Hz) become oblate in shape
and acquire a nonzero quadrupole moment. In this paper, we calculate profiles
of atomic features from such neutron stars using a ray-tracing algorithm in the
Hartle-Thorne approximation. We show that line profiles acquire cores that are
much narrower than the widths expected from pure Doppler effects for a large
range of observer inclinations. As a result, the effects of both the oblateness
and the quadrupole moments of neutron stars need to be taken into account when
aiming to measure neutron star radii from rotationally broadened lines.
Moreover, the presence of these narrow cores substantially increases the
likelihood of detecting atomic lines from rapidly spinning neutron stars.

The Formation and Evolution of Massive Black Holes

The past 10 years have witnessed a change of perspective in the way astrophysicists think about massive black holes (MBHs), which are now considered to have a major role in the evolution of galaxies. This appreciation was driven by the realization that black holes of millions solar masses and above reside in the center of most galaxies, including the Milky Way. MBHs also powered active galactic nuclei known to exist just a few hundred million years after the Big Bang. Here, I summarize the current ideas on the evolution of MBHs through cosmic history, from their formation about 13 billion years ago to their growth within their host galaxies

Identifying the Baryons in a Multiphase Intergalactic Medium. (arXiv:1208.3249v1 [astro-ph.CO])

Identifying the Baryons in a Multiphase Intergalactic Medium. (arXiv:1208.3249v1 [astro-ph.CO]):
In this white paper, we summarize current observations of the baryon census
at low redshift (Shull, Smith, & Danforth 2012). Measurements of Lya, O-VI, and
broad Lya absorbers, together with more careful corrections for metallicity and
ionization fraction, can now account for approximately 60% of the baryons in
the intergalactic medium (IGM). An additional 5 +/- 3% may reside in the
circumgalactic medium (CGM), 7 +/- 2% in galaxies, and 4 +/- 1.5% in clusters.
This still leaves a substantial fraction, 29 +/- 13%, unaccounted for. We
suggest improvements in measuring the baryons in major components of the IGM
and CGM with future Ultraviolet and X-ray spectrographs. These missions could
find and map the missing baryons, the fuel for the formation and chemical
evolution of galaxies.

Origin of the X-ray disc-reflection steep radial emissivity. (arXiv:1208.0360v1 [astro-ph.HE])

Origin of the X-ray disc-reflection steep radial emissivity. (arXiv:1208.0360v1 [astro-ph.HE]):
X-ray reflection off the accretion disc surrounding a black hole, together
with the associated broad iron K$\alpha$ line, has been widely used to
constrain the innermost accretion-flow geometry and black hole spin. Some
recent measurements have revealed steep reflection emissivity profiles in a
number of active galactic nuclei and X-ray binaries. We explore the physically
motivated conditions that give rise to the observed steep disc-reflection
emissivity profiles. We perform a set of simulations based on the configuration
of a possible future high-resolution X-ray mission. Computations are carried
out for typical X-ray bright Seyfert-1 galaxies. We find that steep emissivity
profiles with $q\sim 4-5$ (where the emissivity is $\epsilon (r) \propto
r^{-q}$) are produced considering either i) a lamp-post scenario where a
primary compact X-ray source is located close to the black hole, or ii) the
radial dependence of the disc ionisation state. We also highlight the role of
the reflection angular emissivity: the radial emissivity index $q$ is
overestimated when the standard limb-darkening law is used to describe the
data. Very steep emissivity profiles with $q \geq 7$ are naturally obtained by
applying reflection models that take into account radial profile $\xi (r)$ of
the disc ionisation induced by a compact X-ray source located close to the
central black hole.

Toward an accurate mass function for precision cosmology. (arXiv:1206.5302v1 [astro-ph.CO])

Toward an accurate mass function for precision cosmology. (arXiv:1206.5302v1 [astro-ph.CO]):
Cosmological surveys aim to use the evolution of the abundance of galaxy
clusters to accurately constrain the cosmological model. In the context of
LCDM, we show that it is possible to achieve the required percent level
accuracy in the halo mass function with gravity-only cosmological simulations,
and we provide simulation start and run parameter guidelines for doing so. Some
previous works have had sufficient statistical precision, but lacked robust
verification of absolute accuracy. Convergence tests of the mass function with,
for example, simulation start redshift can exhibit false convergence of the
mass function due to counteracting errors, potentially misleading one to infer
overly optimistic estimations of simulation accuracy. Percent level accuracy is
possible if initial condition particle mapping uses second order Lagrangian
Perturbation Theory, and if the start epoch is between 10 and 50 expansion
factors before the epoch of halo formation of interest. The mass function for
halos with fewer than ~1000 particles is highly sensitive to simulation
parameters and start redshift, implying a practical minimum mass resolution
limit due to mass discreteness. The narrow range in converged start redshift
suggests that it is not presently possible for a single simulation to capture
accurately the cluster mass function while also starting early enough to model
accurately the numbers of reionisation era galaxies, whose baryon feedback
processes may affect later cluster properties. Ultimately, to fully exploit
current and future cosmological surveys will require accurate modeling of
baryon physics and observable properties, a formidable challenge for which
accurate gravity-only simulations are just an initial step.