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.

ISM composition through X-ray spectroscopy of LMXBs. (arXiv:1301.1612v1 [astro-ph.GA])

ISM composition through X-ray spectroscopy of LMXBs. (arXiv:1301.1612v1 [astro-ph.GA]):
The diffuse interstellar medium (ISM) is an integral part of the evolution of
the entire Galaxy. Metals are produced by stars and their abundances are the
direct testimony of the history of stellar evolution. However, the interstellar
dust composition is not well known and the total abundances are yet to be
accurately determined. We probe ISM dust composition, total abundances, and
abundance gradients through the study of interstellar absorption features in
the high-resolution X-ray spectra of Galactic low-mass X-ray binaries (LMXBs).
We use high-quality grating spectra of nine LMXBs taken with XMM-Newton. We
measure the column densities of O, Ne, Mg, and Fe with an empirical model and
estimate the Galactic abundance gradients. The column densities of the neutral
gas species are in agreement with those found in the literature. Solids are a
significant reservoir of metals like oxygen and iron. Respectively, 15-25 % and
65-90 % of the total amount of O I and Fe I is found in dust. The dust amount
and mixture seem to be consistent along all the lines-of-sight (LOS). Our
estimates of abundance gradients and predictions of local interstellar
abundances are in agreement with those measured at longer wavelengths. Our work
shows that X-ray spectroscopy is a very powerful method to probe the ISM. For
instance, on a large scale the ISM appears to be chemically homogeneous showing
similar gas ionization ratios and dust mixtures. The agreement between the
abundances of the ISM and the stellar objects suggests that the local Galaxy is
also chemically homogeneous.

An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO])

An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO]):
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......

RKS Note: Background AGN behind a Galaxy Cluster...

The VMC Survey - VI. Quasars behind the Magellanic system. (arXiv:1207.2492v1 [astro-ph.CO])

The VMC Survey - VI. Quasars behind the Magellanic system. (arXiv:1207.2492v1 [astro-ph.CO]):
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for studies of proper motion and of the
interstellar medium along the line of sight. We search for criteria to identify
candidate QSOs using near-infrared observations from the VISTA survey of the
Magellanic Clouds system (VMC). The VMC survey provides photometry in the YJKs
bands and 12 epochs in the Ks band with unprecedented sensitivity and spatial
resolution. The (Y-J) vs. (J-Ks) diagram has been used to distinguish QSOs from
Milky Way and Magellanic Cloud stars. Then, the slope of variation in the Ks
band has been used to identify a sample of high confidence candidates. These
criteria were developed based on the properties of 117 known QSOs. YJKs
magnitudes and Ks light-curves of known QSOs behind the Magellanic system from
present VMC data are presented. About 75% of them show a slope of variation
>10^-4 mag/day and the shape of the light-curve is in general irregular and
without any clear periodicity. A method to identify QSOs based solely on the
VMC data is proposed using YJKs colours and Ks variability. The number of QSO
candidates found in the South Ecliptic Pole and the 30 Doradus tiles is 22 and
26, respectively, with negligible contamination by young stellar objects,
planetary nebulae, stars and normal galaxies. The high confidence in the nature
of the selected objects is supported by recent studies of possible
contaminants, but remains to be confirmed spectroscopically. In the entire VMC
survey area we expect to find about 1500 QSOs behind the LMC, 600 behind the
SMC, 300 behind the Bridge and 50 behind the Stream areas. The Ks light-curves
can help support investigations of the mechanism responsible for the
variations. (Abridged)