The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED)

The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED):
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.

AGN proximity zone fossils and the delayed recombination of metal lines. (arXiv:1303.0019v1 [astro-ph.CO])

AGN proximity zone fossils and the delayed recombination of metal lines. (arXiv:1303.0019v1 [astro-ph.CO]):
We model the time-dependent evolution of metal-enriched intergalactic and
circumgalactic gas exposed to the fluctuating radiation field from an active
galactic nucleus (AGN). We consider diffuse gas densities (n_H=10^-5-10^-3
cm^-3) exposed to the extra-galactic background (EGB) and initially in thermal
equilibrium (T \sim 10^4-10^4.5 K). Once the proximate AGN field turns on,
additional photo-ionisation rapidly ionises the HI and metals. The enhanced AGN
radiation field turns off after a typical AGN lifetime (tau_AGN=1-20 Myr) and
the field returns to the EGB intensity, but the metals remain out of ionisation
equilibrium for timescales that can significantly exceed tau_AGN. We define
this phase as the AGN proximity zone "fossil" phase and show that high
ionisation stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the
abundances of low ions are reduced. In contrast, HI re-equilibrates rapidly
(<<tau_AGN) owing to its low neutral fraction at diffuse densities. We
demonstrate that metal column densities of intervening gas observed in
absorption in quasar sight lines are significantly affected by delayed
recombination for a wide range of densities, metallicities, and AGN strengths,
lifetimes, and duty cycles. We model the exceptionally strong z=0.9 NeVIII
absorbers observed by Tripp et al. (2011) as arising in a possible fossil zone
or near a recently turned-on AGN and we demonstrate that at low redshift even
moderate strength AGN could significantly enhance the high-ion metal columns in
the circumgalactic media of galaxies observed without active AGN. Fossil
proximity zones may be particularly important during the quasar era, z \sim
2-5. AGN proximity zone fossils allow a whole new class of non-equilibrium
solutions that may be applicable to a large fraction of observed metal
absorbers and which could potentially change the inferred physical conditions
and masses of diffuse gases.

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.

Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO])

Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO]):
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using
UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble
Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous
absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph.
CGM warm cloud properties are derived, including volume filling factors of
3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and
metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5
virial radii are metal-bearing and many have velocities consistent with being
bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass
in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total
baryons in massive spirals and comparable to the baryons in their parent galaxy
disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs
(<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon
fraction), suggesting that many of their warm clouds escape. Constant warm
cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3}
K) support the inference that previous COS detections of broad, shallow O VI
and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K)
intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM
clouds cannot account for all the "missing baryons" in spirals, the hot
intra-group gas can, and could account for ~20% of the cosmic baryon census at
z ~ 0 if this hot gas is ubiquitous among spiral groups.

Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO])

Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO]):
In this study we present three-dimensional radiative cooling hydrodynamical
simulations of galactic winds generated particularly in M82-like starburst
galaxies. We have considered intermittent winds induced by SNe explosions
within super star clusters randomly distributed in the central region of the
galaxy and were able to reproduce the observed M82 wind conditions with its
complex morphological outflow structure. We have found that the environmental
conditions in the disk in nearly recent past are crucial to determine whether
the wind will develop a large scale rich filamentary structure, as in M82 wind,
or not. Also, the numerical evolution of the SN ejecta have allowed us to
obtain the abundance distribution over the first 3 kpc extension of the wind
and we have found that the SNe explosions change significantly the metallicity
only of the hot, low-density wind component. Moreover, we have found that the
SN-driven wind transports to outside the disk large amounts of energy, momentum
and gas, but the more massive high-density component reaches only intermediate
altitudes smaller than 1.5 kpc. Therefore, no significant amounts of gas mass
are lost to the IGM and the mass evolution of the galaxy is not much affected
by the starburst events occurring in the nuclear region.

Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO])

Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO]):
We study galaxy super-winds driven in major mergers, using pc-resolution
simulations with detailed models for stellar feedback that can
self-consistently follow the formation/destruction of GMCs and generation of
winds. The models include molecular cooling, star formation at high densities
in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and
radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky
Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in
all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind
mass-loading efficiency (outflow rate divided by SFR) is similar to that in
isolated galaxy counterparts of each merger: it depends more on global galaxy
properties (mass, size, escape velocity) than on the dynamical state of the
merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up
complex morphologies with overlapping, differently-oriented bubbles/shells at a
range of radii. The winds have complex velocity and phase structure, with
material at a range of speeds up to ~1000 km/s, and a mix of molecular,
ionized, and hot gas that depends on galaxy properties and different feedback
mechanisms. These simulations resolve a problem in some 'sub-grid' models,
where simple wind prescriptions can dramatically suppress merger-induced
starbursts. But despite large mass-loading factors (>~10) in the winds, the
peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration
does not act equally, so cold dense gas can still lose angular momentum and
form stars, while blowing out gas that would not have participated in the
starburst in the first place. Considerable wind material is not unbound, and
falls back on the disk at later times post-merger, leading to higher
post-starburst SFRs in the presence of stellar feedback. This may require AGN
feedback to explain galaxy quenching.

The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds. (arXiv:1301.1345v1 [astro-ph.CO])

The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds. (arXiv:1301.1345v1 [astro-ph.CO]):
We use archival UV absorption-line data from HST/STIS to statistically
analyse the absorption characteristics of the high-velocity clouds (HVCs) in
the Galactic halo towards more than 40 extragalactic background sources. We
determine absorption covering fractions of low- and intermediate ions (OI, CII,
SiIII, MgII, FeII, SiIII, CIV, and SiIV) in the range fc = 0.20 - 0.70. For
detailed analysis we concentrate on SiII absorption components in HVCs, for
which we investigate the distribution of column densities, b-values, and radial
velocities. Combining information for SiII and MgII, and using a geometrical
HVC model we investigate the contribution of HVCs to the absorption cross
section of strong MgII absorbers in the local Universe. We estimate that the
Galactic HVCs would contribute on average ~52 % to the total strong MgII cross
section of the Milky Way, if our Galaxy were to be observed from an exterior
vantage point. We further estimate that the mean projected covering fraction of
strong MgII absorption in the Milky Way halo and disc from an exterior vantage
point is fc(sMgII) = 0.31 for a halo radius of R = 61 kpc. These numbers,
together with the observed number density of strong MgII absorbers at low
redshift, indicate that the contribution of infalling gas clouds (i.e., HVC
analogues) in the halos of Milky Way-type galaxies to the cross section of
strong MgII absorbers is <34 %. These findings are in line with the idea that
outflowing gas (e.g., produced by galactic winds) in the halos of more actively
star-forming galaxies dominate the absorption-cross section of strong MgII
absorbers in the local Universe.

The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA])

The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA]):
For early-type galaxies, the ability to sustain a corona of hot, X-ray
emitting gas could have played a key role in quenching their star-formation
history. Yet, it is still unclear what drives the precise amount of hot gas
around these galaxies. By combining photometric and spectroscopic measurements
for the early-type galaxies observed during the Atlas3D integral-field survey
with measurements of their X-ray luminosity based on X-ray data of both low and
high spatial resolution we conclude that the hot-gas content of early-type
galaxies can depend on their dynamical structure. Specifically, whereas slow
rotators generally have X-ray halos with luminosity L_X,gas and temperature T
values that are in line with what is expected if the hot-gas emission is
sustained by the thermalisaton of the kinetic energy carried by the
stellar-mass loss material, fast rotators tend to display L_X,gas values that
fall consistently below the prediction of this model, with similar T values
that do not scale with the stellar kinetic energy as observed in the case of
slow rotators. Considering that fast rotators are likely to be intrinsically
flatter than slow rotators, and that the few L_X,gas-deficient slow rotators
also happen to be relatively flat, the observed L_X,gas deficiency in these
objects would support the hypothesis whereby flatter galaxies have a harder
time in retaining their hot gas. We discuss the implications that a different
hot-gas content could have on the fate of both acquired and internally-produced
gaseous material, considering in particular how the L_X,gas deficiency of fast
rotators would make them more capable to recycle the stellar-mass loss material
into new stars than slow rotators. This is consistent with the finding that
molecular gas and young stars are detected only in fast rotators in the Atlas3D
sample, and that fast rotators tend to dustier than slow rotators. [Abridged]

The COS-Halos Survey: An Empirical Description of the Metal-Line Absorption in the Low-Redshift Circumgalactic Medium. (arXiv:1212.0558v1 [astro-ph.CO])

The COS-Halos Survey: An Empirical Description of the Metal-Line Absorption in the Low-Redshift Circumgalactic Medium. (arXiv:1212.0558v1 [astro-ph.CO]):
We present the equivalent width and column density measurements for low and
intermediate ionization states of the circumgalactic medium (CGM) surrounding
44 low-z, L ~ L* galaxies drawn from the COS-Halos survey. These measurements
are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra
of background quasars within an impact parameter R < 160 kpc to the targeted
galaxies. The data show significant metal-line absorption for 33 of the 44
galaxies, including quiescent systems, revealing the common occurance of a cool
(T ~ 10^{4 - 5} K), metal-enriched CGM. The detection rates and column
densities derived for these metal lines decrease with increasing impact
parameter, a trend we interpret as a declining metal surface density profile
for the CGM. A comparison of the relative column densities of adjacent
ionization states indicates the gas is predominantly ionized. The large surface
density in metals demands a large reservoir of metals and gas in the cool CGM
(very conservatively, M_ CGMcool > 10^9 MSun), which likely traces a distinct
density and/or temperature regime from the highly-ionized CGM traced by OVI
absorption. The large dispersion in absorption strengths (including
non-detections) suggests the cool CGM traces a wide range of densities or a mix
of local ionizing conditions. Lastly, the kinematics inferred from the
metal-line profiles are consistent with the cool CGM being bound to the dark
matters halos hosting the galaxies; this gas may serve as fuel for future
star-formation. Future work will leverage this dataset to provide estimates on
the mass, metallicity, dynamics, and origin of the cool CGM in low-z, L*
galaxies.

Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO])

Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO]):
Luminous X-ray gas coronae in the dark matter halos of massive spiral
galaxies are a fundamental prediction of structure formation models, yet such
coronae remained essentially unexplored. In this paper, for the very first
time, we detect and characterize extended hot X-ray coronae beyond the optical
disks of two normal massive spiral galaxies, NGC1961 and NGC6753. Based on
XMM-Newton X-ray observations, we detect hot gaseous emission extending out to
~60 kpc around both galaxies - well beyond their optical radii. The hot gas,
whose best-fit temperature is kT~0.6 keV and abundance is ~0.1 Solar, appears
to have a fairly uniform distribution, hinting that the quasi-static gas
resides in hydrostatic equilibrium in the potential well of the galaxies. The
bolometric luminosity of the hot gas in the (0.05-0.15)r_200 region, where
r_200 is the virial radius, is ~6e40 erg/s for both NGC1961 and NGC6753. We
derive the baryon mass fractions of NGC1961 and NGC6753 and obtain f_b~0.1,
which values fall short of the cosmic baryon fraction. The detected X-ray
coronae around NGC1961 and NGC6753 offer an excellent basis to probe structure
formation simulations. To this end, the observations are confronted with the
recently developed moving mesh code AREPO and the traditionally used smoothed
particle hydrodynamics code GADGET. The implemented subresolution physics and
the gravity solver are identical in the two codes, but they use different
methods to solve the hydrodynamical equations. We conclude that, while neither
model gives a perfect description, the observed luminosities, gas masses, and
abundances favor the AREPO code. Moreover, the shape of the observed density
profiles are also well reproduced by AREPO within ~0.4r_200. However, neither
model incorporates efficient feedback from supermassive black holes or
supernovae, which could alter the simulated properties of the X-ray coronae.
(abridged)

The baryon budget on the galaxy group/cluster boundary. (arXiv:1212.1613v1 [astro-ph.CO])

The baryon budget on the galaxy group/cluster boundary. (arXiv:1212.1613v1 [astro-ph.CO]):
We present a study of the hot gas and stellar content of 5 optically-selected
poor galaxy clusters, including a full accounting of the contribution from
intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass
analysis with XMM observations. We find weighted mean stellar (including ICL),
gas and total baryon mass fractions within r500 of 0.026+/-0.003, 0.070+/-0.005
and 0.096+/-0.006, respectively, at a corresponding weighted mean M500 of
(1.08_{-0.18}^{+0.21}) x 10^14 Msun. Even when accounting for the intracluster
stars, 4 out of 5 clusters show evidence for a substantial baryon deficit
within r500, with baryon fractions (f_bary) between 50+/-6 to 59+/-8 per cent
of the Universal mean level (i.e. Omega_b / Omega_m); the remaining cluster
having f_bary = 75+/-11 per cent. For the 3 clusters where we can trace the hot
halo to r500 we find no evidence for a steepening of the gas density profile in
the outskirts with respect to a power law, as seen in more massive clusters. We
find that in all cases, the X-ray mass measurements are larger than those
originally published on the basis of the galaxy velocity dispersion (sigma) and
an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased
masses, the stellar fractions (in the range 0.016-0.034, within r500) remain
consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff
(2007), from which our sample is drawn.

Constraints on Hydrodynamical Subgrid Models from Quasar Absorption Line Studies of the Simulated Circumgalactic Medium. (arXiv:1212.2965v1 [astro-ph.GA])

Constraints on Hydrodynamical Subgrid Models from Quasar Absorption Line Studies of the Simulated Circumgalactic Medium. (arXiv:1212.2965v1 [astro-ph.GA]):
Cosmological hydrodynamical simulations of galaxy evolution are increasingly
able to produce realistic galaxies, but the largest hurdle remaining is in
constructing subgrid models that accurately describe the behavior of stellar
feedback. As an alternate way to test and calibrate such models, we propose to
focus on the circumgalactic medium. To do so, we generate a suite of
adaptive-mesh refinement (AMR) simulations for a Milky-Way-massed galaxy run to
z=0, systematically varying the feedback implementation. We then post-process
the simulation data to compute the absorbing column density for a wide range of
common atomic absorbers throughout the galactic halo, including H I, Mg II, Si
II, Si III, Si IV, C IV, N V, O VI, and O VII. The radial profiles of these
atomic column densities are compared against several quasar absorption line
studies, to determine if one feedback prescription is favored. We find that
although our models match some of the observations (specifically those ions
with lower ionization strengths), it is particularly difficult to match O VI
observations. There is some indication that the models with increased feedback
intensity are better matches. We demonstrate that sufficient metals exist in
these halos to reproduce the observed column density distribution in principle,
but the simulated circumgalactic medium lacks significant multiphase
substructure and is generally too hot. Furthermore, we demonstrate the failings
of inflow-only models (without energetic feedback) at populating the CGM with
adequate metals to match observations even in the presence of multiphase
structure. Additionally, we briefly investigate the evolution of the CGM from
z=3 to present. Overall, we find that quasar absorption line observations of
the gas around galaxies provide a new and important constraint on feedback
models.

Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO])

Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO]):
In a sample of elliptical galaxies that span a large range of mass, a
previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically
decrease with increasing elliptical galaxy mass. Metallicity mixtures, age
effects, stellar chromospheric emission effects, and low-mass initial mass
function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less
than 0.3 dex is sufficient to blanket all observations. Feature gradients
within galaxies imply a global Ca deficit rather than a radius-dependent
phenomenon. Some, but not all, Type II supernova nucleosynthetic yield
calculations indicate a decreasing Ca/Fe yield ratio in more massive
supernovae, lending possible support to the hypothesis that more massive
elliptical galaxies have an IMF that favors more massive stars. No Type II
supernova nucleosynthetic yield calculations show significant leverage in the
Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems
unlikely that the Ca behavior can be explained as a built-in metallicity
effect, and this argues against explanations that vary only the Type II to Type
Ia supernova enrichment ratio.

X-ray measurement of the elemental abundances at the outskirts of the Perseus cluster with Suzaku. (arXiv:1211.4712v1 [astro-ph.CO])

X-ray measurement of the elemental abundances at the outskirts of the Perseus cluster with Suzaku. (arXiv:1211.4712v1 [astro-ph.CO]):
We report on the abundance of metals (Mg and Fe) in the intracluster medium
(ICM) at the outskirts (0.2 r200 - 0.8 r200) of the Perseus cluster. The X-ray
spectra were obtained in the Suzaku/XIS mapping observations of this region. We
employ single temperature models to fit all the X-ray spectra. The ICM
temperature smoothly decreases toward the outer region from 6 keV to 4 keV. The
Fe abundance is uniformly distributed at the outskirts (~0.3 solar). The Mg
abundance is ~1 solar at the outskirts. The solar ratios of Mg/Fe of the
outskirts region (Mg/Fe ~4) are a factor of 4 larger than those of the central
region. Various systematic effects, including the spatial fluctuations in the
cosmic X-ray background, are taken into account and evaluated. These our
results have not changed significantly.

Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey. (arXiv:1211.5140v1 [astro-ph.CO])

Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey. (arXiv:1211.5140v1 [astro-ph.CO]):
We place general constraints on the luminosity and mass of hot X-ray emitting
gas residing in extended "hot halos" around nearby massive galaxies. We examine
stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog
(2MVIG), as well as subsets of this sample based on galaxy morphology and
K-band luminosity. We detect X-ray emission at high confidence (ranging up to
nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc
is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the
early-type galaxies are more than twice as luminous as the late-type galaxies.
Using a spatial analysis, we also find evidence for extended emission around
five out of seven subsamples (the full sample, the luminous galaxies,
early-type galaxies, luminous late-type galaxies, and luminous early-type
galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively.
Several additional lines of evidence also support this conclusion and suggest
that about 1/2 of the total emission is extended, and about 1/3 of the extended
emission comes from hot gas. For the sample of luminous galaxies, which has the
strongest evidence for extended emission, the average hot gas mass is 4x10^9
Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.

Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-Velocity Cloud Complex A. (arXiv:1211.1973v1 [astro-ph.GA])

Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-Velocity Cloud Complex A. (arXiv:1211.1973v1 [astro-ph.GA]):
The high-velocity cloud (HVC) Complex A is a probe of the physical conditions
in the Galactic halo. The kinematics, morphology, distance, and metallicity of
Complex A indicate that it represents new material that is accreting onto the
Galaxy. We present Wisconsin H-alpha Mapper (WHAM) kinematically resolved
observations of Complex A over the velocity range of -250 to -50 km/s in the
local standard of rest reference frame. These observations include the first
full H-alpha intensity map of Complex A across (l, b) = (124, 18) to (171, 53)
and deep targeted observations in H-alpha, [S II]6716, [N II]6584, and [O
I]6300 towards regions with high H I column densities, background quasars, and
stars. The H-alpha data imply that the masses of neutral and ionized material
in the cloud are similar, both being greater than a million solar masses. We
find that the Bland-Hawthorn & Maloney (1999, 2001) model for the intensity of
the ionizing radiation near the Milky Way is consistent with the known distance
of the high-latitude part of Complex A and an assumed cloud geometry that puts
the lower-latitude parts of the cloud at a distance of 7 to 8 kpc. This
compatibility implies a 5% ionizing photon escape fraction from the Galactic
disk. We also provide the nitrogen and sulfur upper abundance solutions for a
series of temperatures, metallicities, and cloud configurations for purely
photoionized gas; these solutions are consistent with the sub-solar abundances
found by previous studies, especially for temperatures above 10,000 K or for
gas with a high fraction of singly-ionized nitrogen and sulfur.

Chandra View of the Warm-Hot IGM toward 1ES 1553+113: Absorption Line Detections and Identifications (Paper I). (arXiv:1210.7177v1 [astro-ph.CO])

Chandra View of the Warm-Hot IGM toward 1ES 1553+113: Absorption Line Detections and Identifications (Paper I). (arXiv:1210.7177v1 [astro-ph.CO]):
About 30-40 percent of the expected number of baryons is still missing in the
local Universe (z \lesssim 0.4). They are predicted to be hiding in a web of
intergalactic gas at temperatures of about 10^5-10^7 K (the WHIM). Detecting
this matter has had limited success so far, because of its low-density and high
temperature, which makes it difficult to detect with current far-ultraviolet
and X-ray instrumentation.

Here we present the first results from our pilot 500 ks Chandra-LETG
observation of the soft X-ray brightest source in the z > 0.4 sky, the blazar
1ES 1553+113. We identify a total of 11 possible absorption lines, with
single-line statistical significances between 2.2-4.1 sigma. Six of these lines
are detected at high significance (3.6 < \sigma < 4.1), while the remaining
five are regarded as marginal detections in association with either other X-ray
lines detected at higher significance and/or FUV signposts. Three of these
lines are consistent with metal absorption at z~0. The remaining 8 lines may be
imprinted by intervening absorbers and are all consistent with being
high-ionization counterparts of FUV HI and/or OVI IGM signposts. In particular,
four of these eight absorption lines (4.1\sigma, 4.1\sigma, 3.8\sigma and
2.7\sigma), are identified as CV and CVI absorbers belonging to two WHIM
systems at z_X = 0.312 and z_X = 0.133, which also produce broad HI and OVI
absorption in the FUV. The true statistical significances of these two X-ray
absorption systems, after properly accounting for the number of redshift
trials, are 5.8\sigma and 3.8\sigma.

On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO])

On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO]):
The Milky Way appears to be missing baryons, as the observed mass in stars
and gas is well below the cosmic mean. One possibility is that a substantial
fraction of the Galaxy's baryons are embedded within an extended,
million-degree hot halo, an idea supported indirectly by observations of warm
gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray
observations have established that hot gas does exist in our Galaxy beyond the
local hot bubble; however, it may be distributed in a hot disk configuration.
Moreover, recent investigations into the X-ray constraints have suggested that
any Galactic corona must be insignificant. Here we re-examine the observational
data, particularly in the X-ray and radio bands, in order to determine whether
it is possible for a substantial fraction of the Galaxy's baryons to exist in ~
10^6 K gas. In agreement with past studies, we find that a baryonically closed
halo is clearly ruled out if one assumes that the hot corona is distributed
with a cuspy NFW profile. However, if the hot corona of the galaxy is in an
extended, low-density distribution with a large central core, as expected for
an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10^11
M_sun of material, possibly accounting for all of the missing Galactic baryons.
We briefly discuss some potential avenues for discriminating between a massive,
extended hot halo and a local hot disk.

Ionized Gas in the First 10 Kiloparsecs of the Interstellar Galactic Halo: Metal Ion Fractions. (arXiv:1209.4640v1 [astro-ph.GA])

Ionized Gas in the First 10 Kiloparsecs of the Interstellar Galactic Halo: Metal Ion Fractions. (arXiv:1209.4640v1 [astro-ph.GA]):
We present direct measures of the ionization fractions of several sulfur ions
in the Galactic warm ionized medium (WIM). We obtained high resolution
ultraviolet absorption line spectroscopy of post-asymptotic giant branch stars
in the the globular clusters Messier 3 [(l,b)=(42.2, +78.7); d=10.2 kpc, z=10.0
kpc] and Messier 5 [(l,b)=(3.9, +46.8); d=7.5 kpc, z = +5.3 kpc] with the
Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure,
or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H
I. These clusters also house millisecond pulsars, whose dispersion measures
give an electron column density from which we infer the H II column in these
directions. We find fractions of S+2 in the WIM for the M 3 and M 5 sight lines
x(S+2) = N(S+2)/N(S) = 0.33+/-0.07 and 0.47+/-0.09, respectively, with
variations perhaps related to location. With negligible quantities of the
higher ionization states, we conclude S+ and S+2 account for all of the S in
the WIM. We extend the methodology to study the ion fractions in the warm and
hot ionized gas of the Milky Way, including the high ions Si+3, C+3, N+4, and
O+5. The vast majority of the Galactic ionized gas is warm (T ~ 10^4 K) and
photoionized (the WIM) or very hot (T > 4x10^5 K) and collisionally ionized.
The common tracer of ionized gas beyond the Milky Way, O+5, traces <1% of the
total ionized gas mass of the Milky Way.

Warm-hot gas in groups and galaxies toward H2356-309. (arXiv:1209.4080v1 [astro-ph.CO])

Warm-hot gas in groups and galaxies toward H2356-309. (arXiv:1209.4080v1 [astro-ph.CO]):
We present a detailed analysis of the galaxy and group distributions around
three reported X-ray absorption line systems in the spectrum of the quasar
H2356-309. Previous studies associated these absorbers with known large-scale
galaxy structures (i.e., walls and filaments) along the line of sight. Such
absorption lines typically trace 10^{5-7} K gas, and may be evidence of the
elusive warm-hot intergalactic medium (WHIM) thought to harbor the bulk of the
low-redshift "missing baryons;" alternatively, they may be linked to individual
galaxies or groups in the filaments. Here we combine existing galaxy survey
data with new, highly complete multi-object Magellan spectroscopy to
investigate the detailed galaxy distribution near each absorber. All of these
three absorption systems nominally lie within the virial radii of nearby
galaxies and/or groups, and could therefore arise in these virialized
structures rather than (or in addition to) the WHIM. However, we find no
additional galaxies near a fourth "void" absorber recently reported by
Zappacosta et al., suggesting that this system may indeed trace gas
unassociated with any individual halo. We therefore conclude that most X-ray
absorbers are coincident with galaxy and/or group environments, though some
could still trace the large-scale filamentary WHIM gas predicted by
simulations.