The Bimodal Metallicity Distribution of the Cool Circumgalactic Medium at z<1. (arXiv:1302.5424v1 [astro-ph.CO])

The Bimodal Metallicity Distribution of the Cool Circumgalactic Medium at z<1. (arXiv:1302.5424v1 [astro-ph.CO]):
We assess the metal content of the circumgalactic medium (CGM) about galaxies
at z<1 using an HI-selected sample of 27 Lyman limit systems (LLS, defined here
as absorbers with 16.2\lesssimlog N(HI)\lesssim 18.5 observed in absorption
against background QSOs by the Cosmic Origins Spectrograph on-board the {Hubble
Space Telescope. The N(HI) selection avoids metallicity biases inherent in many
previous studies of the low-redshift CGM. We compare the column densities of
weakly ionized metal species (e.g., OII, CII, MgII) to N(HI) in the strongest
HI component of each absorber. We find that the metallicity distribution of the
LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches
peaking at [X/H]simeq1.6 and -0.4 (2.5% and 40% solar metallicities). The cool
CGM probed by these LLS is predominantly ionized. The metal-rich branch of the
population likely traces winds, recycled outflows, and tidally stripped gas;
the metal-poor branch has properties consistent with cold accretion streams
thought to be a major source of fresh gas for star forming galaxies. Both
branches have a nearly equal number of absorbers. Our results thus demonstrate
there is a significant mass of previously-undiscovered cold, metal-poor gas in
the CGM of z<1 galaxies.

A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO])

A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO]):
Modelling AGN feedback in numerical simulations is both technically and
theoretically challenging, with numerous approaches having been published in
the literature. We present a study of five distinct approaches to modelling AGN
feedback within gravitohydrodynamic simulations of major mergers of Milky
Way-sized galaxies. To constrain differences to only be between AGN feedback
models, all simulations start from the same initial conditions and use the same
star formation algorithm. Most AGN feedback algorithms have five key aspects:
black hole accretion rate, energy feedback rate and method, particle accretion
algorithm, black hole advection algorithm, and black hole merger algorithm. All
models follow different accretion histories, with accretion rates that differ
by up to three orders of magnitude at any given time. We consider models with
either thermal or kinetic feedback, with the associated energy deposited
locally around the black hole. Each feedback algorithm modifies the gas
properties near the black hole to different extents. The particle accretion
algorithms usually (but not always) maintain good agreement between the mass
accreted by \dot{M} dt and the mass of gas particles removed from the
simulation. The black hole advection algorithms dampen inappropriate dragging
of the black holes by two-body interactions. Advecting the black hole a limited
distance based upon local mass distributions has many desirably properties. The
black holes merge when given criteria are met, and we find a range of merger
times for different criteria. Using the M_{BH}-\sigma relation as a diagnostic
of the remnants yields three models that lie within the one-sigma scatter of
the observed relation and two that fall below it. The wide variation in
accretion behaviours of the models reinforces the fact that there remains much
to be learnt about the evolution of galactic nuclei. (abridged)

Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO])

Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO]):
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.

Thermodynamics of the Coma Cluster Outskirts. (arXiv:1302.4140v1 [astro-ph.CO])

Thermodynamics of the Coma Cluster Outskirts. (arXiv:1302.4140v1 [astro-ph.CO]):
We present results from a large mosaic of Suzaku observations of the Coma
Cluster, focusing on the thermodynamic properties of the ICM on large scales.
The measured temperature and X-ray brightness profiles are similar along four
relatively undisturbed azimuths probed, with the temperature decreasing from
~8.5 keV at the cluster center to ~2 keV at 2 Mpc. The SW merger boosts the
surface brightness, allowing us to detect X-ray emission out to 2.5 Mpc along
this fifth direction. The X-ray image also reveals two arc-shaped regions with
excess surface brightness towards the east and west of the main cluster core.
These regions appear over-pressured and most likely originate from merger
induced large scale supersonic gas motions. The azimuthally averaged
temperature profile, as well as the deprojected density and pressure profiles
towards the E and NW, all show a sharp drop consistent with an outward
propagating shock front located at the outermost edge of the giant radio halo
observed at 352 MHz with the WSRT and which may be powering this radio
emission. The shape of the entropy profiles along the relatively relaxed E and
NW directions at large radii is consistent with the average profiles of
evolved, well formed cool core clusters, suggesting similar accretion
histories. Our data indicate a flat metal abundance profile at about 0.3 of the
Solar value out to almost the virial radius of Coma, which would favor galactic
winds over ram-pressure stripping as the dominant enrichment mechanism in the
ICM.

PRIMUS: Infrared and X-ray AGN Selection Techniques at 0.2<z<1.2. (arXiv:1302.2920v1 [astro-ph.CO])

PRIMUS: Infrared and X-ray AGN Selection Techniques at 0.2<z<1.2. (arXiv:1302.2920v1 [astro-ph.CO]):
We present a study of Spitzer/IRAC and X-ray active galactic nuclei (AGNs)
selection techniques in order to quantify the overlap, uniqueness,
contamination, and completeness of each. We investigate how the overlap and
possible contamination of the samples depends on the IR and X-ray depths. We
use Spitzer/IRAC imaging, Chandra and XMM X-ray imaging, and PRism MUlti-object
Survey (PRIMUS) spectroscopic redshifts to construct galaxy and AGN samples at
0.2<z<1.2 over 8 deg^2. We construct samples over a wide range of IRAC flux
limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare
IR-AGN samples defined using the IRAC color selection of Stern et al. and
Donley et al. with X-ray detected AGN samples. For roughly similar depth IR and
X-ray surveys, we find that ~75% of IR-AGN are identified as X-ray AGN. This
fraction increases to ~90% when comparing against the deepest X-ray data,
indicating that only ~10% of IR-selected AGN may be heavily obscured. The
IR-AGN selection proposed by Stern et al. suffers from contamination by
star-forming galaxies at various redshifts when using deeper IR data, though
the selection technique works well for shallow IR data. While similar overall,
the IR-AGN samples preferentially contain more luminous AGN, while the X-ray
AGN samples preferentially contain lower specific accretion rate AGN, where the
host galaxy light dominates at IR wavelengths. The host galaxy populations of
the IR and X-ray AGN samples have similar restframe colors and stellar masses;
both selections identify AGN in blue, star-forming and red, quiescent galaxies.

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?. (arXiv:1302.3442v1 [astro-ph.HE])

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?. (arXiv:1302.3442v1 [astro-ph.HE]):
It is believed that jets emerging from blazars (Flat Spectrum Radio Quasars
(FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually
exhibit lower luminosity and harder power law spectra at gamma-ray energies
than FSRQs. It was argued previously that the difference in accretion rates is
mainly responsible for the large observed luminosity mismatch between them.
However, when intrinsic luminosities are derived by correcting for beaming
effects, this mismatch is significantly reduced. We show that spin plays an
important role to reveal the dichotomy of luminosity distributions between BL
Lacs and FSRQs, suggesting BL Lacs to be low luminous and slow rotators
compared to FSRQs.

Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows. (arXiv:1302.3067v1 [astro-ph.HE])

Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows. (arXiv:1302.3067v1 [astro-ph.HE]):
We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion
disks formed by the Type II collapsars and outflows launched from these disks.
We deal with accretion disks having relatively low accretion rates: 0.001 M_sun
s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection
dominated. We report the synthesis of several unusual nuclei like 31P, 39K,
43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and
copper in the disk. We also confirm that isotopes of iron, cobalt, nickel,
argon, calcium, sulphur and silicon get synthesized in the disk, as shown by
previous authors. Much of these heavy elements thus synthesized are ejected
from the disk and survive in the outflows. Indeed, emission lines of many of
these heavy elements have been observed in the X-ray afterglows of several
GRBs.