1,269 research outputs found
General Hospitals, Specialty Hospitals and Financially Vulnerable Patients
Examines whether specialty hospitals draw well-insured patients away from general and safety-net hospitals, reducing their ability to cross-subsidize less profitable services and uncompensated care, in three cities. Notes challenges and implications
High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?
Observations with the Green Bank Telescope of 21cm HI emission from the
high-velocity cloud Complex H suggest that it is interacting with the Milky
Way. A model in which the cloud is a satellite of the Galaxy in an inclined,
retrograde circular orbit reproduces both the cloud's average velocity and its
velocity gradient with latitude. The model places Complex H at approximately 33
kpc from the Galactic Center on a retrograde orbit inclined about 45 degrees to
the Galactic plane. At this location it has an HI mass > 6 10^6 Msun and
dimensions of at least 10 by 5 kpc. Some of the diffuse HI associated with the
cloud has apparently been decelerated by interaction with Galactic gas. Complex
H has similarities to the dwarf irregular galaxy Leo A and to some compact
high-velocity clouds, and has an internal structure nearly identical to parts
of the Magellanic Stream, with a pressure P/k about 100 cm^{-3} K.Comment: 12 pages includes 4 figures. To be published in Astrophysical Journal
Letters, 1 July 200
Planetary Nebulae Kinematics in M31
We present kinematics of 135 planetary nebulae in M31 from a survey covering
3.9 square degrees and extending out to 15 kpc from the southwest major axis
and more than 20 kpc along the minor axis. The majority of our sample, even
well outside the disk, shows significant rotational support (mean line-of-sight
velocity 116 km/s). We argue that these PN belong to the outer part of M31's
large de Vaucouleurs bulge. Only five PN have velocities clearly inconsistent
with this fast rotating bulge. All five may belong to tidal streams in M31's
outer halo. One is projected on the Northern Spur, and is counter-rotating with
respect to the disk there. Two are projected along the major axis at X=-10 kpc
and have M32-like velocities; they could be debris from that galaxy. The
remaining two halo PN are located near the center of the galaxy and their
velocities follow the gradient found by Ibata et al. (2004), implying that
these PN could belong to the Southern Stream. If M31 has a non-rotating,
pressure-supported halo, we have yet to find it, and it must be a very minor
component of the galaxy.Comment: accepted to ApJ; main body of paper is 36 pages, including 14 figure
The Tully-Fisher Relation and H_not
The use of the Tully-Fisher (TF) relation for the determination of the Hubble
Constant relies on the availability of an adequate template TF relation and of
reliable primary distances. Here we use a TF template relation with the best
available kinematical zero-point, obtained from a sample of 24 clusters of
galaxies extending to cz ~ 9,000 km/s, and the most recent set of Cepheid
distances for galaxies fit for TF use. The combination of these two ingredients
yields H_not = 69+/-5 km/(s Mpc). The approach is significantly more accurate
than the more common application with single cluster (e.g. Virgo, Coma)
samples.Comment: 10 pages, including 2 figures and 1 table; uses AAS LaTex. Submitted
to ApJ Letter
A Very Sensitive 21cm Survey for Galactic High-Velocity HI
Very sensitive HI 21cm observations have been made in 860 directions at dec
>= -43deg in search of weak, Galactic, high-velocity HI emission lines at
moderate and high Galactic latitudes. One-third of the observations were made
toward extragalactic objects. The median 4-sigma detection level is NHI =
8x10^{17} cm^-2 over the 21' telescope beam. High-velocity HI emission is
detected in 37% of the directions; about half of the lines could not have been
seen in previous surveys. The median FWHM of detected lines is 30.3 km/s. High-
velocity HI lines are seen down to the sensitivity limit of the survey implying
that there are likely lines at still lower values of NHI. The weakest lines
have a kinematics and distribution on the sky similar to that of the strong
lines, and thus do not appear to be a new population. Most of the emission
originates from objects which are extended over several degrees; few appear to
be compact sources. At least 75%, and possibly as many as 90%, of the lines are
associated with one of the major high-velocity complexes. The Magellanic Stream
extends at least 10 deg to higher Galactic latitude than previously thought and
is more extended in longitude as well. Although there are many lines with low
column density, their numbers do not increase as rapidly as NHI^-1, so most of
the HI mass in the high-velocity cloud phenomenon likely resides in the more
prominent clouds. The bright HI features may be mere clumps within larger
structures, and not independent objects.Comment: 88 pages includes 22 figures Accepted for Publication in ApJ Suppl.
June 200
Reversal-free CaIIH profiles: a challenge for solar chromosphere modeling in quiet inter-network
We study chromospheric emission to understand the temperature stratification
in the solar chromosphere. We observed the intensity profile of the CaIIH line
in a quiet Sun region close to the disk center at the German Vacuum Tower
Telescope. We analyze over 10^5 line profiles from inter-network regions. For
comparison with the observed profiles, we synthesize spectra for a variety of
model atmospheres with a non local thermodynamic equilibrium (NLTE) radiative
transfer code. A fraction of about 25% of the observed CaIIH line profiles do
not show a measurable emission peak in H_{2v} and H_{2r} wavelength bands
(reversal-free). All of the chosen model atmospheres with a temperature rise
fail to reproduce such profiles. On the other hand, the synthetic calcium
profile of a model atmosphere that has a monotonic decline of the temperature
with height shows a reversal-free profile that has much lower intensities than
any observed line profile. The observed reversal-free profiles indicate the
existence of cool patches in the interior of chromospheric network cells, at
least for short time intervals. Our finding is not only in conflict with a
full-time hot chromosphere, but also with a very cool chromosphere as found in
some dynamic simulations.Comment: 8 pages, accepted in A&
Discovery of an extremely red galaxy at z=0.65 with dusty star-formation and nuclear activity
In the course of the follow-up multiwavelength study of a deep radio survey
we have discovered that the milli-Jansky radio source PDFJ011423 is a
low-redshift (z = 0.65) extremely red galaxy (ERG) with K=15.3, R-K = 5.8 and
J-K = 3.1. Optical, infrared and radio photometry, together with optical and
near-infrared spectroscopy, reveal a heavily obscured galaxy (A_V=5-6, from the
observed Balmer decrement) undergoing vigorous star formation and presenting an
active galactic nucleus (AGN). PDFJ011423 is a representative member of the
dusty ERG population, providing a local counterpart for studying more distant
ERGs.Comment: 13 pages (including 2 encapsulated postscript figures), aastex,
accepted for publication in ApJ
Radio-Excess IRAS Galaxies: PMN/FSC Sample Selection
A sample of 178 extragalactic objects is defined by correlating the 60 micron
IRAS FSC with the 5 GHz PMN catalog. Of these, 98 objects lie above the
radio/far-infrared relation for radio-quiet objects. These radio-excess
galaxies and quasars have a uniform distribution of radio excesses and appear
to be a new population of active galaxies not present in previous
radio/far-infrared samples. The radio-excess objects extend over the full range
of far-infrared luminosities seen in extragalactic objects. Objects with small
radio excesses are more likely to have far-infrared colors similar to
starbursts, while objects with large radio excesses have far-infrared colors
typical of pure AGN. Some of the most far-infrared luminous radio-excess
objects have the highest far-infrared optical depths. These are good candidates
to search for hidden broad line regions in polarized light or via near-infrared
spectroscopy. Some low far-infrared luminosity radio-excess objects appear to
derive a dominant fraction of their far-infrared emission from star formation,
despite the dominance of the AGN at radio wavelengths. Many of the radio-excess
objects have sizes likely to be smaller than the optical host, but show
optically thin radio emission. We draw parallels between these objects and high
radio luminosity Compact Steep-Spectrum (CSS) and GigaHertz Peaked-Spectrum
(GPS) objects. Radio sources with these characteristics may be young AGN in
which the radio activity has begun only recently. Alternatively, high central
densities in the host galaxies may be confining the radio sources to compact
sizes. We discuss future observations required to distinguish between these
possibilities and determine the nature of radio-excess objects.Comment: Submitted to AJ. 44 pages, 11 figures. A version of the paper with
higher quality figures is available from
http://www.mso.anu.edu.au/~cdrake/PMNFSC/paperI
SUMSS: A Wide-Field Radio Imaging Survey of the Southern Sky. I. Science goals, survey design and instrumentation
The Molonglo Observatory Synthesis Telescope, operating at 843 MHz with a 5
square degree field of view, is carrying out a radio imaging survey of the sky
south of declination -30 deg. This survey (the Sydney University Molonglo Sky
Survey, or SUMSS) produces images with a resolution of 43" x 43" cosec(Dec.)
and an rms noise level of about 1 mJy/beam. SUMSS is therefore similar in
sensitivity and resolution to the northern NRAO VLA Sky Survey (NVSS; Condon et
al. 1998). The survey is progressing at a rate of about 1000 square degrees per
year, yielding individual and statistical data for many thousands of weak radio
sources. This paper describes the main characteristics of the survey, and
presents sample images from the first year of observation.Comment: 27 pages, 12 figures (figures 2, 8, 10 in jpg format); AJ, in pres
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