Unveiling a population of galaxies harboring low-mass black holes with X-rays. (arXiv:1305.3826v1 [astro-ph.CO])

Unveiling a population of galaxies harboring low-mass black holes with X-rays. (arXiv:1305.3826v1 [astro-ph.CO]):
We report the discovery of three low-mass black hole candidates residing in
the centers of low-mass galaxies at z<0.3 in the Chandra Deep Field - South
Survey. These black holes are initially identified as candidate active galactic
nuclei based on their X-ray emission in deep Chandra observations.
Multi-wavelength observations are used to strengthen our claim that such
emission is powered by an accreting supermassive black hole. While the X-ray
luminosities are low at L_X ~ 10^40 erg s^-1 (and variable in one case), we
argue that they are unlikely to be attributed to star formation based on
H\alpha or UV-fluxes. Optical spectroscopy with Keck/DEIMOS and VLT/FORS allows
us to (1) measure accurate redshifts, (2) confirm their low stellar host mass,
(3) investigate the source(s) of photo-ionization, and (4) estimate extinction.
With stellar masses of M* < 3*10^9 M_\sun determined from HST/ACS imaging, the
host galaxies are among the lowest mass systems known to host actively
accreting black holes. We estimate BH masses M_BH ~ 2*10^5 M_\sun based on
scaling relations between BH mass and host properties for more luminous
systems. In one case, a broad component of the H\alpha emission-line profile is
detected thus providing a virial mass estimate. Black holes in such low-mass
galaxies are of considerable interest as the low-redshift analogs to the seeds
of the most massive BHs at high redshift which have remained largely elusive to
date. Our study highlights the power of deep X-ray surveys to uncover such
low-mass systems.

Population III Stars and Remnants in High Redshift Galaxies. (arXiv:1305.1325v1 [astro-ph.CO])

Population III Stars and Remnants in High Redshift Galaxies. (arXiv:1305.1325v1 [astro-ph.CO]):
Recent simulations of Population III star formation have suggested that some
fraction form in binary systems, in addition to having a characteristic mass of
tens of solar masses. The deaths of metal-free stars result in the initial
chemical enrichment of the universe and the production of the first
stellar-mass black holes. Here we present a cosmological adaptive mesh
refinement simulation of an overdense region that forms a few 10^9 Msun dark
matter halos and over 13,000 Population III stars by redshift 15. We find that
most halos do not form Population III stars until they reach Mvir ~ 10^7 Msun
because this biased region is quickly enriched from both Population III and
galaxies, which also produce high levels of ultraviolet radiation that suppress
H2 formation. Nevertheless, Population III stars continue to form, albeit in
more massive halos, at a rate of ~ 10^{-4} Msun yr^{-1} Mpc^{-3} at redshift
15. The most massive starless halo has a mass of 7 x 10^7 Msun, which could
host massive black hole formation through the direct gaseous collapse scenario.
We show that the multiplicity of the Population III remnants grows with halo
mass above 10^8 Msun, culminating in 50 remnants located in 10^9 Msun halos on
average. This has implications that high mass X-ray binaries and intermediate
mass black holes that originate from metal-free stars may be abundant in
high-redshift galaxies.

Cosmological growth and feedback from supermassive black holes. (arXiv:1305.0286v1 [astro-ph.CO])

Cosmological growth and feedback from supermassive black holes. (arXiv:1305.0286v1 [astro-ph.CO]):
We develop a simple evolutionary scenario for the growth of supermassive
black holes (BHs), assuming growth due to accretion only, to learn about the
evolution of the BH mass function from $z=3$ to 0 and from it calculate the
energy budgets of different modes of feedback. We tune the parameters of the
model by matching the derived X-ray luminosity function (XLF) with the observed
XLF of active galactic nuclei. We then calculate the amount of comoving kinetic
and bolometric feedback as a function of redshift, derive a kinetic luminosity
function and estimate the amount of kinetic feedback and $PdV$ work done by
classical double Fanaroff-Riley II (FR II) radio sources. We also derive the
radio luminosity function for FR IIs from our synthesized population and set
constraints on jet duty cycles. Around 1/6 of the jet power from FR II sources
goes into $PdV$ work done in the expanding lobes during the time the jet is on.
Anti hierarchical growth of BHs is seen in our model due to addition of an
amount of mass being accreted on to all BHs independent of the BH mass. The
contribution to the total kinetic feedback by active galaxies in a low
accretion, kinetically efficient mode is found to be the most significant at
$z<1.5$. FR II feedback is found to be a significant mode of feedback above
redshifts $z\sim 1.5$, which has not been highlighted by previous studies.

The Structure of the Milky Way's Hot Gas Halo. (arXiv:1305.2430v1 [astro-ph.GA])

The Structure of the Milky Way's Hot Gas Halo. (arXiv:1305.2430v1 [astro-ph.GA]):
The Milky Way's million degree gaseous halo contains a considerable amount of
mass that, depending on its structural properties, can be a significant mass
component. In order to analyze the structure of the Galactic halo, we use
XMM-Newton RGS archival data and measure OVII K alpha absorption-line strengths
towards 26 active galactic nuclei (AGN), LMC X-3, and two Galactic sources (4U
1820-30 and X1735-444). We assume a beta-model as the underlying gas density
profile and find best-fit parameters of n_o = 0.46^{+0.74}_{-0.35} cm^-3, r_c =
0.35^{+0.29}_{-0.27} kpc, and beta = 0.71^{+0.13}_{-0.14}. These parameters
result in halo masses ranging between M(18 kpc) = 7.5^{+22.0}_{-4.6} x 10^8
M_sun and M(200 kpc) = 3.8^{+6.0}_{-0.5} x 10^{10} M_sun assuming a gas
metallicity of Z = 0.3 Z_sun, which are consistent with current theoretical and
observational work. The maximum baryon fraction from our halo model of f_b =
0.07^{+0.03}_{-0.01} is significantly smaller than the universal value of f_b =
0.171, implying the mass contained in the Galactic halo accounts for 10 - 50%
of the missing baryons in the Milky Way. We also discuss our model in the
context of several Milky Way observables, including ram pressure stripping in
dwarf spheroidal galaxies, the observed X-ray emission measure in the 0.5 - 2
keV band, the Milky Way's star formation rate, spatial and thermal properties
of cooler gas (~10^5 K) and the observed Fermi bubbles towards the Galactic
center. Although the metallicity of the halo gas is a large uncertainty in our
analysis, we place a lower limit on the halo gas between the Sun and the LMC.
We find that Z >~ 0.2 Z_sun based on the pulsar dispersion measure towards the
LMC.

Neutron Star Masses and Radii from Quiescent Low-Mass X-ray Binaries. (arXiv:1305.3242v1 [astro-ph.HE])

Neutron Star Masses and Radii from Quiescent Low-Mass X-ray Binaries. (arXiv:1305.3242v1 [astro-ph.HE]):
A recent analysis (Guillot et al. 2013) of the thermal spectra of 5 quiescent
low-mass X-ray binaries in globular clusters, in which it was assumed that all
neutron stars have the same radius, determined the radius to be
R=9.1^{+1.3}_{-1.5} km to 90% confidence. However, the masses of the sources
were found to range from 0.86 solar masses to 2.4 solar masses and a
significant amount of the predicted M-R region violates causality and the
existence of a 2 solar mass neutron star. The study determined the amount of
Galactic absorption along the lines-of-sight from fitting the X-ray spectra and
assumed all sources possessed hydrogen atmospheres. We argue, from a Bayesian
analysis, that different interpretations of the data are strongly favored. Our
most-favored model assumes i) the equation of state of neutron star crusts is
well-understood, ii) the high-density equation of state is consistent with
causality and the existence of neutron stars at least as massive as 2 solar
masses, iii) that the Galactic absorption is determined either from the fits in
Guillot et al. (2013) or from independent HI surveys, and iv) that these
objects are well-described by either hydrogen or helium atmospheres. With these
assumptions, the 90% confidence radius range for 1.4 solar mass stars is 11.4
to 12.8 km, and the allowed range for radii of all neutron stars between 1.2
solar masses and 2.0 solar masses is 10.9 to 12.7 km. This result is in much
greater agreement with predictions of the equation of state from both nuclear
experiments and theoretical neutron matter studies than the smaller radii
deduced by Guillot et al. (2013).

The Growth of Cool Cores and Evolution of Cooling Properties in a Sample of 83 Galaxy Clusters at 0.3 < z < 1.2 Selected from the SPT-SZ Survey. (arXiv:1305.2915v1 [astro-ph.CO])

The Growth of Cool Cores and Evolution of Cooling Properties in a Sample of 83 Galaxy Clusters at 0.3 < z < 1.2 Selected from the SPT-SZ Survey. (arXiv:1305.2915v1 [astro-ph.CO]):
We present first results on the cooling properties derived from Chandra X-ray
observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters
selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope
data. We measure each cluster's central cooling time, central entropy, and mass
deposition rate, and compare to local cluster samples. We find no significant
evolution from z~0 to z~1 in the distribution of these properties, suggesting
that cooling in cluster cores is stable over long periods of time. We also find
that the average cool core entropy profile in the inner ~100 kpc has not
changed dramatically since z ~ 1, implying that feedback must be providing
nearly constant energy injection to maintain the observed "entropy floor" at
~10 keV cm^2. While the cooling properties appear roughly constant over long
periods of time, we observe strong evolution in the gas density profile, with
the normalized central density (rho_0/rho_crit) increasing by an order of
magnitude from z ~ 1 to z ~ 0. When using metrics defined by the inner surface
brightness profile of clusters, we find an apparent lack of classical, cuspy,
cool-core clusters at z > 0.75, consistent with earlier reports for clusters at
z > 0.5 using similar definitions. Our measurements indicate that cool cores
have been steadily growing over the 8 Gyr spanned by our sample, consistent
with a constant, ~150 Msun/yr cooling flow that is unable to cool below
entropies of 10 keV cm^2 and, instead, accumulates in the cluster center. We
estimate that cool cores began to assemble in these massive systems at z ~ 1,
which represents the first constraints on the onset of cooling in galaxy
cluster cores. We investigate several potential biases which could conspire to
mimic this cool core evolution and are unable to find a bias that has a similar
redshift dependence and a substantial amplitude.

The Nuclear Equation of State and Neutron Star Masses. (arXiv:1305.3510v1 [nucl-th])

The Nuclear Equation of State and Neutron Star Masses. (arXiv:1305.3510v1 [nucl-th]):
Neutron stars are valuable laboratories for the study of dense matter. Recent
observations have uncovered both massive and low-mass neutron stars and have
also set constraints on neutron star radii. The largest mass measurements are
powerfully influencing the high-density equation of state because of the
existence of the neutron star maximum mass. The smallest mass measurements, and
the distributions of masses, have implications for the progenitors and
formation mechanisms of neutron stars. The ensemble of mass and radius
observations can realistically restrict the properties of dense matter, and, in
particular, the behavior of the nuclear symmetry energy near the nuclear
saturation density. Simultaneously, various nuclear experiments are
progressively restricting the ranges of parameters describing the symmetry
properties of the nuclear equation of state. In addition, new theoretical
studies of pure neutron matter are providing insights. These observational,
experimental and theoretical constraints of dense matter, when combined, are
now revealing a remarkable convergence.

A Decade-Baseline Study of the Plasma States of Ejecta Knots in Cassiopeia A. (arXiv:1305.1581v1 [astro-ph.HE])

A Decade-Baseline Study of the Plasma States of Ejecta Knots in Cassiopeia A. (arXiv:1305.1581v1 [astro-ph.HE]):
We present the analysis of 21 bright X-ray knots in the Cassiopeia A
supernova remnant from observations spanning 10 yr. We performed a
comprehensive set of measurements to reveal the kinematic and thermal state of
the plasma in each knot, using a combined analysis of two high energy
resolution High Energy Transmission Grating (HETG) and four medium energy
resolution Advanced CCD Imaging Spectrometer (ACIS) sets of spectra. The ACIS
electron temperature estimates agree with the HETG-derived values for
approximately half of the knots studied, yielding one of the first comparisons
between high resolution temperature estimates and ACIS-derived temperatures. We
did not observe the expected spectral evolutionpredicted from the ionization
age and density estimates for each knotin all but three of the knots studied.
The incompatibility of these measurements with our assumptions has led us to
propose a dissociated ejecta model, with the metals unmixed inside the knots,
which could place strong constraints on supernova mixing models.

Constraints on black hole fuelling modes from the clustering of X-ray AGN. (arXiv:1305.2200v1 [astro-ph.CO])

Constraints on black hole fuelling modes from the clustering of X-ray AGN. (arXiv:1305.2200v1 [astro-ph.CO]):
We present a clustering analysis of X-ray selected AGN by compiling X-ray
samples from the literature and re-estimating the dark matter (DM) halo masses
of AGN in a uniform manner. We find that moderate luminosity AGN (Lx(2-10
keV)=10^42-10^44 erg/sec) in the z=0-1.3 Universe are typically found in DM
haloes with masses of ~10^13 Msun. We then compare our findings to the
theoretical predictions of the coupled galaxy and black hole formation model
GALFORM. We find good agreement when our calculation includes the hot-halo mode
of accretion onto the central black hole. This type of accretion, which is
additional to the common cold accretion during disk instabilities and galaxy
mergers, is tightly coupled to the AGN feedback in the model. The hot-halo mode
becomes prominent in DM haloes with masses greater than ~10^12.5 Msun, where
AGN feedback typically operates, giving rise to a distinct class of moderate
luminosity AGN that inhabit rich clusters and superclusters. Cold gas fuelling
of the black hole cannot produce the observationally inferred DM halo masses of
X-ray AGN. Switching off AGN feedback in the model results in a large
population of luminous quasars (Lx(2-10 keV) > 10^44 erg/sec) in DM haloes with
masses up to ~10^14 Msun, which is inconsistent with the observed clustering of
quasars. The abundance of hot-halo AGN decreases significantly in the z~3-4
universe. At such high redshifts, the cold accretion mode is solely responsible
for shaping the environment of moderate luminosity AGN. Our analysis supports
two accretion modes (cold and hot) for the fuelling of supermassive black holes
and strongly underlines the importance of AGN feedback in cosmological models
both of galaxy formation and black hole growth.

Turbulence in the SuperModel: Mass Reconstruction with Nonthermal Pressure for Abell 1835. (arXiv:1305.3020v1 [astro-ph.CO])

Turbulence in the SuperModel: Mass Reconstruction with Nonthermal Pressure for Abell 1835. (arXiv:1305.3020v1 [astro-ph.CO]):
The total mass derived from X-ray emission is biased low in a large number of
clusters when compared with the mass estimated via strong and weak lensing.
Suzaku and Chandra observations out to the virial radius report in several
relaxed clusters steep temperature gradients that on assuming pure thermal
hydrostatic equilibrium imply an unphysically decreasing mass profile.
Moreover, the gas mass fraction appears to be inconsistent with the cosmic
value measured from the CMB. Such findings can be interpreted as an evidence
for an additional nonthermal pressure in the outskirts of these clusters. This
nonthermal component may be due to turbulence stirred by residual bulk motions
of extragalactic gas infalling into the cluster. Here we present a SuperModel
analysis of Abell 1835 observed by Chandra out to the virial radius. The
SuperModel formalism can include in the equilibrium a nonthermal component
whose level and distribution are derived imposing that the gas mass fraction
f_{gas} equals the cosmic value at the virial radius. Including such a
nonthermal component, we reconstruct from X rays an increasing mass profile
consistent with the hydrostatic equilibrium also in the cluster outskirts and
in agreement at the virial boundary with the weak lensing value. The increasing
f_{gas} profile confirms that the baryons are not missing but located at the
cluster outskirts.

On the origin of the warm-hot absorbers in the Milky Way's halo. (arXiv:1305.2964v1 [astro-ph.GA])

On the origin of the warm-hot absorbers in the Milky Way's halo. (arXiv:1305.2964v1 [astro-ph.GA]):
Disc galaxies like the Milky Way are expected to be surrounded by massive
coronae of hot plasma that may contain a significant fraction of the so-called
missing baryons. We investigate whether the local (|vLSR|<400 km/s) warm-hot
absorption features observed towards extra-Galactic sources or halo stars are
consistent with being produced by the cooling of the Milky Way's corona. In our
scheme, cooling occurs at the interface between the disc and the corona and it
is triggered by positive supernova feedback. We combine hydrodynamical
simulations with a dynamical 3D model of the galactic fountain to predict the
all-sky distribution of this cooling material, and we compare it with the
observed distribution of detections for different `warm' (SiIII, SiIV, CII,
CIV) and `hot' (OVI) ionised species. The model reproduces the
position-velocity distribution and the column densities of the vast majority of
warm absorbers and about half of OVI absorbers. We conclude that the warm-hot
gas responsible for most of the detections lies within a few kiloparsecs from
the Galactic plane, where high-metallicity material from the disc mixes
efficiently with the hot corona. This process provides an accretion of a few
Mo/yr of fresh gas that can easily feed the star formation in the disc of the
Galaxy. The remaining OVI detections are likely to be a different population of
absorbers, located in the outskirts of the Galactic corona and/or in the
circumgalactic medium of nearby galaxies.

Multi-resonance orbital model of high-frequency quasi-periodic oscillations: possible high-precision determination of black hole and neutron star spin. (arXiv:1305.3552v1 [astro-ph.HE])

Multi-resonance orbital model of high-frequency quasi-periodic oscillations: possible high-precision determination of black hole and neutron star spin. (arXiv:1305.3552v1 [astro-ph.HE]):
Using known frequencies of the twin-peak high-frequency quasiperiodic
oscillations (HF QPOs) and known mass of the central black hole, the black-hole
dimensionless spin can be determined by assuming a concrete version of the
resonance model. However, a wide range of observationally limited values of the
black hole mass implies low precision of the spin estimates. We discuss the
possibility of higher precision of the black hole spin measurements in the
framework of a multi-resonance model inspired by observations of more than two
HF QPOs in the black hole systems, which are expected to occur at two (or more)
different radii of the accretion disc. For the black hole systems we focus on
the special case of duplex frequencies, when the top, bottom, or mixed
frequency is common at two different radii where the resonances occur giving
triple frequency sets. The sets of triple frequency ratios and the related spin
are given. The strong resonance model for "magic" values of the black hole spin
means that two (or more) versions of resonance could occur at the same radius,
allowing cooperative effects between the resonances. For neutron star systems
we introduce a resonant switch model that assumes switching of oscillatory
modes at resonant points. In the case of doubled twin-peak HF QPOs excited at
two different radii with common top, bottom, or mixed frequency, the black hole
spin is given by the triple frequency ratio set. The spin is determined
precisely, but not uniquely, because the same frequency set could correspond to
more than one concrete spin. The black hole mass is given by the magnitude of
the observed frequencies. The resonant switch model puts relevant limits on the
mass and spin of neutron stars, and we expect a strong increase in the fitting
procedure precision when different twin oscillatory modes are applied to data
in the vicinity of different resonant points.

Zooming towards the Event Horizon - mm-VLBI today and tomorrow. (arXiv:1305.2811v1 [astro-ph.HE])

Zooming towards the Event Horizon - mm-VLBI today and tomorrow. (arXiv:1305.2811v1 [astro-ph.HE]):
Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the
opacity barrier of synchrotron self-absorption in AGN and opens the direct view
into sub-pc scale regions not accessible before. Since AGN variability is more
pronounced at short millimeter wavelength, mm-VLBI can reveal structural
changes in very early stages after outbursts. When combined with observations
at longer wavelength, global 3mm and 1mm VLBI adds very detailed information.
This helps to determine fundamental physical properties at the jet base, and in
the vicinity of super-massive black holes at the center of AGN. Here we present
new results from multi-frequency mm-VLBI imaging of OJ287 during a major
outburst. We also report on a successful 1.3mm VLBI experiment with the APEX
telescope in Chile. This observation sets a new record in angular resolution.
It also opens the path towards future mm-VLBI with ALMA, which aims at the
mapping of the black hole event horizon in nearby galaxies, and the study of
the roots of jets in AGN.

Systematic Study of Event Horizons and Pathologies of Parametrically Deformed Kerr Spacetimes. (arXiv:1304.7786v2 [gr-qc] UPDATED)

Systematic Study of Event Horizons and Pathologies of Parametrically Deformed Kerr Spacetimes. (arXiv:1304.7786v2 [gr-qc] UPDATED):
In general relativity, all black holes in vacuum are described by the Kerr
metric, which has only two independent parameters: the mass and the spin. The
unique dependence on these two parameters is known as the no-hair theorem. This
theorem may be tested observationally by using electromagnetic or
gravitational-wave observations to map the spacetime around a candidate black
hole and measure potential deviations from the Kerr metric. Several parametric
frameworks have been constructed for tests of the no-hair theorem. Due to the
uniqueness of the Kerr metric, any such parametric framework must violate at
least one of the assumptions of the no-hair theorem. This can lead to
pathologies in the spacetime, such as closed timelike curves or singularities,
which may hamper using the metric in the strong-field regime. In this paper, I
analyze in detail several parametric frameworks and show explicitly the manner
in which they differ from the Kerr metric. I calculate the coordinate locations
of event horizons in these metrics, if any exist, using methods adapted from
the numerical relativity literature. I identify the regions where each
parametric deviation is unphysical as well as the range of coordinates and
parameters for which each spacetime remains a regular extension of the Kerr
metric and is, therefore, suitable for observational tests of the no-hair
theorem.

Pygmies, giants, and skins as laboratory constraints on the equation of state of neutron-rich matter. (arXiv:1305.3202v1 [nucl-th])

Pygmies, giants, and skins as laboratory constraints on the equation of state of neutron-rich matter. (arXiv:1305.3202v1 [nucl-th]):
Laboratory experiments sensitive to the density dependence of the symmetry
energy may place stringent constraints on the equation of state of neutron-rich
matter and, thus, on the structure, dynamics, and composition of neutron stars.
Understanding the equation of state of neutron-rich matter is a central goal of
nuclear physics that cuts across a variety of disciplines. In this contribution
I focus on how laboratory experiments on neutron skins and on both Pygmy and
Giant resonances can help us elucidate the structure of neutron stars.


RKS Note: Clear explanation of nuclear physics situation vis-a-vis neutron star radii.

Testing X-ray Measurements of Galaxy Cluster Gas Mass Fraction Using the Cosmic Distance-Duality Relation. (arXiv:1305.2077v1 [astro-ph.CO])

Testing X-ray Measurements of Galaxy Cluster Gas Mass Fraction Using the Cosmic Distance-Duality Relation. (arXiv:1305.2077v1 [astro-ph.CO]):
We propose a consistency test of some recent X-ray gas mass fraction
($f_{\rm{gas}}$) measurements in galaxy clusters, using the cosmic
distance-duality relation, $\eta_{\rm{theory}}=\dl(1+z)^{-2}/\da$, with
luminosity distance ($\dl$) data from the Union2 compilation of type Ia
supernovae. We set $\eta_{\rm{theory}}\equiv1$, instead of assigning any
redshift parameterizations to it, and constrain the cosmological information
preferred by $f_{\rm{gas}}$ data along with supernova observations. We adopt a
new binning method in the reduction of the Union2 data, in order to minimize
the statistical errors. Four data sets of X-ray gas mass fraction, which are
reported by Allen et al. (2 samples), LaRoque et al. and Ettori et al., are
detailedly analyzed against two theoretical modelings of $f_{\rm{gas}}$. The
results from the analysis of Allen et al.'s samples prove the feasibility of
our method. It is found that the preferred cosmology by LaRoque et al.'s sample
is consistent with its reference cosmology within 1-$\sigma$ confidence level.
However, for Ettori et al.'s $f_{\rm{gas}}$ sample, the inconsistency can reach
more than 3-$\sigma$ confidence level and this dataset shows special preference
to an $\Ol=0$ cosmology.

The shocked outflow in NGC 4051 - momentum-driven feedback, UFO's and warm absorbers. (arXiv:1305.2046v1 [astro-ph.HE])

The shocked outflow in NGC 4051 - momentum-driven feedback, UFO's and warm absorbers. (arXiv:1305.2046v1 [astro-ph.HE]):
An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009
revealed an unusually rich absorption spectrum with outflow velocities, in both
RGS and EPIC spectra, up to ~ 9000 km/s (Pounds and Vaughan 2011). Evidence was
again seen for a fast ionised wind with velocity ~ 0.12c (Tombesi 2010, Pounds
and Vaughan 2012). Detailed modelling with the XSTAR photoionisation code now
confirms the general correlation of velocity and ionisation predicted by mass
conservation in a Compton-cooled shocked wind (King 2010). We attribute the
strong column density gradient in the model to the addition of strong two-body
cooling in the later stages of the flow, causing the ionisation (and velocity)
to fall more quickly, and confining the lower ionisation gas to a narrower
region. The column density and recombination timescale of the highly ionised
flow component, seen mainly in Fe K lines, determine the primary shell
thickness which, when compared with the theoretical Compton cooling length,
determines a shock radius of ~ 10^17 cm. Variable radiative recombination
continua (RRC) provide a key to scaling the lower ionisation gas, with the RRC
flux then allowing a consistency check on the overall flow geometry. We
conclude that the 2009 observation of NGC 4051 gives strong support to the idea
that a fast, highly ionised wind, launched from the vicinity of the
supermassive black hole, will lose much of its mechanical energy after shocking
against the ISM at a sufficiently small radius for strong Compton cooling.
However, the total flow momentum will be conserved, retaining the potential for
a powerful AGN wind to support momentum-driven feedback (King 2003; 2005). We
speculate that the `warm absorber' components often seen in AGN spectra result
from accumulation of shocked wind and ejected ISM.

Discrete clouds of neutral gas between the galaxies M31 and M33. (arXiv:1305.1631v1 [astro-ph.CO])

Discrete clouds of neutral gas between the galaxies M31 and M33. (arXiv:1305.1631v1 [astro-ph.CO]):
Spiral galaxies must acquire gas to maintain their observed level of star
formation beyond the next few billion years (Leroy et al. 2008). A source of
this material may be the gas that resides between galaxies, but our
understanding of the state and distribution of this gas is incomplete (Shull et
al. 2012). Radio observations (Braun & Thilker 2004) of the Local Group of
galaxies have revealed hydrogen gas extending from the disk of the galaxy M31
at least halfway to M33. This feature has been interpreted to be the neutral
component of a condensing intergalactic filament (Dav\'e et al. 2001) which
would be able to fuel star formation in M31 and M33, but simulations suggest
that such a feature could also result from an interaction between both galaxies
within the past few billion years (Bekki 2008). Here we report radio
observations showing that about 50 per cent percent of this gas is composed of
clouds, while the rest is distributed in an extended, diffuse component. The
clouds have velocities comparable to those of M31 and M33, and have properties
suggesting they are unrelated to other Local Group objects. We conclude that
the clouds are likely to be transient condensations of gas embedded in an
intergalactic filament and are therefore a potential source of fuel for future
star formation in M31 and M33.

Inner Accretion Disk Edges in a Kerr-Like Spacetime. (arXiv:1304.8106v1 [gr-qc])

Inner Accretion Disk Edges in a Kerr-Like Spacetime. (arXiv:1304.8106v1 [gr-qc]):
According to the no-hair theorem, astrophysical black holes are uniquely
described by the Kerr metric. In order to test this theorem with observations
in either the electromagnetic or gravitational-wave spectra, several Kerr-like
spacetimes have been constructed which describe potential deviations from the
Kerr spacetime in parametric form. For electromagnetic tests of the no-hair
theorem, such metrics allow for the proper modeling of the accretions flows
around candidate black holes and the radiation emitted from them. In many of
these models, the location of the inner edge of the accretion disk is of
special importance. This inner edge is often taken to coincide with the
innermost stable circular orbit (ISCO), which can serve as a direct probe of
the spin and the deviation from the Kerr metric. In certain cases, however, an
ISCO does not exist, and the inner edge of an accretion disk is instead
determined by an instability against small perturbations in the direction
vertical to the disk. In this paper, I analyze the properties of accretion
disks in the Kerr-like metric proposed by Johannsen and Psaltis (2011), whose
inner edges are located at the radii where this vertical instability occurs. I
derive expressions of the energy and axial angular momentum of disk particles
that move on circular equatorial orbits and calculate the locations of the
inner disk edges. As a possible observable of such accretion disks, I simulate
profiles of relativistically broadened iron lines and show that they depend
significantly on the values of the spin and the deviation parameter.