87 research outputs found
Disk mass densities in edge-on spiral galaxies
Very Large Array (VLA) observations of the neutral hydrogen (HI) gas in two nearby edge-on spirals (NGC 4565 and NGC 891) successfully resolve the thickness of the gas layers in both disks over a wide range in radii. The combination of B, C, and D array data produces a 4 arcsec (approx. 200 pc) beam and 21 km s(exp -1) velocity resolution, combined with sensitivity to structures as large as 18 arcmin (approx. 54 kpc). These observations directly constrain the mid-plane disk mass densities, under the assumption of an equilibrium between the thermal pressure of the gas and the gravitational attraction of the disk. The results of a preliminary analysis are given regarding the z-velocity dispersion of the gas, the mass-to-light ratio of the disk in NGC 4565, and the roles of atomic and molecular gases. The data also allow a detailed study of the HI in these galaxies; in general their brightness temperature distributions seem similar to that in the Milky Way. Both galaxies show asymmetric HI extensions beyond the optical disk. In NGC 4565 the extension is a surprisingly abrupt warp, which may bend back to parallel the galactic plane; the velocity structure implies the warp is continuous around the disk
High-Resolution Images of Diffuse Neutral Clouds in the Milky Way. I. Observations, Imaging, and Basic Cloud Properties
A set of diffuse interstellar clouds in the inner Galaxy within a few hundred
pc of the Galactic plane has been observed at an angular resolution of ~1
arcmin combining data from the NRAO Green Bank Telescope and the Very Large
Array. At the distance of the clouds the linear resolution ranges from ~1.9 pc
to ~2.8 pc. These clouds have been selected to be somewhat out of the Galactic
plane and are thus not confused with unrelated emission, but in other respects
they are a Galactic population. They are located near the tangent points in the
inner Galaxy, and thus at a quantifiable distance: kpc
from the Galactic Center, and pc from the Galactic
plane. These are the first images of the diffuse neutral HI clouds that may
constitute a considerable fraction of the ISM. Peak HI column densities range
from cm. Cloud diameters vary between
about 10 and 100 pc, and their HI mass spans the range from less than a hundred
to a few thousands Msun. The clouds show no morphological consistency of any
kind except that their shapes are highly irregular. One cloud may lie within
the hot wind from the nucleus of the Galaxy, and some clouds show evidence of
two distinct thermal phases as would be expected from equilibrium models of the
interstellar medium.Comment: 81 pages, 42 figures, accepted for publication in the Astrophysical
Journal Supplement Serie
The ruff of equatorial emission around the SS433 jets: its spectral index and origin
We present unique radio observations of SS433, using MERLIN, the VLBA, and
the VLA, which allow us to, for the first time, properly image and derive a
meaningful spectral index for the `ruff' of equatorial emission which surrounds
SS433's jet. We interpret this smooth ruff as a wind-like outflow from the
binary.Comment: 4 pages, 4 figures, to appear in Proceedings of the 4th Microquasar
Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodrigue
Spitzer Observations of GX17+2: Confirmation of a Periodic Synchrotron Source
GX17+2 is a low-mass X-ray binary (LMXB) that is also a member of a small family of LMXBs known as "Z-sources" that are believed to have persistent X-ray luminosities that are very close to the Eddington limit. GX17+2 is highly variable at both radio and X-ray frequencies, a feature common to Z-sources. What sets GX17+2 apart is its dramatic variability in the near-infrared, where it changes by ΔK ~ 3 mag. Previous investigations have shown that these brightenings are periodic, recurring every 3.01 days. Given its high extinction (A_V≥9 mag), it has not been possible to ascertain the nature of these events with ground-based observations. We report mid-infrared Spitzer observations of GX17+2 which indicate a synchrotron spectrum for the infrared brightenings. In addition, GX17+2 is highly variable in the mid-infrared during these events. The combination of the large-scale outbursts, the presence of a synchrotron spectrum, and the dramatic variability in the mid-infrared suggest that the infrared brightening events are due to the periodic transit of a synchrotron jet across our line of sight. An analysis of both new, and archival, infrared observations has led us to revise the period for these events to 3.0367 days. We also present new Rossi X-Ray Timing Explorer (RXTE) data for GX17+2 obtained during two predicted infrared brightening events. Analysis of these new data, and data from the RXTE archive, indicates that there is no correlation between the X-ray behavior of this source and the observed infrared brightenings. We examine various scenarios that might produce periodic jet emission
The Fundamental Plane of Black Hole Accretion and its Use as a Black Hole-Mass Estimator
We present an analysis of the fundamental plane of black hole accretion, an
empirical correlation of the mass of a black hole (), its 5 GHz radio
continuum luminosity (), and its 2-10 keV X-ray power-law
continuum luminosity (). We compile a sample of black holes with primary,
direct black hole-mass measurements that also have sensitive,
high-spatial-resolution radio and X-ray data. Taking into account a number of
systematic sources of uncertainty and their correlations with the measurements,
we use Markov chain Monte Carlo methods to fit a mass-predictor function of the
form . Our best-fit results are , , and
with the natural logarithm of the Gaussian intrinsic scatter in the log-mass
direction . This result is a
significant improvement over our earlier mass scaling result because of the
increase in active galactic nuclei sample size (from 18 to 30), improvement in
our X-ray binary sample selection, better identification of Seyferts, and
improvements in our analysis that takes into account systematic uncertainties
and correlated uncertainties. Because of these significant improvements, we are
able to consider potential influences on our sample by including all sources
with compact radio and X-ray emission but ultimately conclude that the
fundamental plane can empirically describe all such sources. We end with advice
for how to use this as a tool for estimating black hole masses.Comment: ApJ Accepted. Online interactive version of Figure 7 available at
http://kayhan.astro.lsa.umich.edu/supplementary_material/fp
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