4,085 research outputs found
Cold atomic hydrogen in the inner galaxy
The VLA is used to measure 21 cm absorption in directions with the absolute value of b less than 1 deg., the absolute value of 1 less than 25 deg. to probe the cool atomic gas in the inner galaxy. Abundant H I absorption is detected; typical lines are deep and narrow, sometimes blending in velocity with adjacent features. Unlike 21 cm emission not all allowed velocities are covered: large portions of the l-v diagram are optically thin. Although not similar to H I emission, the absorption shows a striking correspondence with CO emission in the inner galaxy: essentially every strong feature detected in one survey is seen in the other. The provisional conclusion is that in the inner galaxy most cool atomic gas is associated with molecular cloud complexes. There are few or no cold atomic clouds devoid of molecules in the inner galaxy, although these are common in the outer galaxy
A Complete Atlas of HI Absorption toward HII Regions in the Southern Galactic Plane Survey (SGPS1)
We present a complete catalog of H I emission and absorption spectrum pairs,
toward H II regions, detectable within the boundaries of the Southern Galactic
Plane Survey (SGPS I), a total of 252 regions. The catalog is presented in
graphical, numerical and summary formats. We demonstrate an application of this
new dataset through an investigation of the locus of the Near 3kpc Arm.Comment: Accepted for publication by ApJS Feb 6, 2014. Data files and Figure
Set (252 images) to appear in the on-line version of the journa
HI Emission and Absorption in the Southern Galactic Plane Survey
We present preliminary results from the Southern Galactic Plane Survey (SGPS)
Test Region and Parkes data. As part of the pilot project for the Southern
Galactic Plane Survey, observations of a Test Region (325.5 deg < l < 333.5
deg; -0.5 deg < b < 3.5 deg) were completed in December 1998. Single dish
observations of the full survey region (253 deg < l < 358 deg; |b| <1 deg) with
the Parkes Radio Telescope were completed in March 2000. We present a sample of
SGPS HI data with particular attention to the smallest and largest scale
structures seen in absorption and emission, respectively. On the large scale,
we detect many prominent HI shells. On the small scale, we note extremely
compact, cold clouds seen in HI self-absorption. We explore how these two
classes of objects probe opposite ends of the HI spatial power spectrum.Comment: 9 pages, 3 embedded postscript & 4 jpeg figures. Presented at the
Astronomical Society of Australia, Hobart, Tasmania, July 4-7 2000. To appear
in PASA Vol. 18(1
Dark Energy as a Born-Infeld Gauge Interaction Violating the Equivalence Principle
We investigate the possibility that dark energy does not couple to
gravitation in the same way than ordinary matter, yielding a violation of the
weak and strong equivalence principles on cosmological scales. We build a
transient mechanism in which gravitation is pushed away from general relativity
by a Born-Infeld gauge interaction acting as an "Abnormally Weighting" (dark)
Energy. This mechanism accounts for the Hubble diagram of far-away supernovae
by cosmic acceleration and time variation of the gravitational constant while
accounting naturally for the present tests on general relativity.Comment: 5 pages, 3 figures, sequel of Phys. Rev. D 73 023520 (2006), to
appear in Physical Review Letter
A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: I. Observations and Spectra
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the
Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum
sources, located at high (|b| >15deg.) Galactic latitudes. The Declination
coverage of the present survey is Decl. ~ -45deg.. With a mean rms optical
depth of ~0.003, this is the most sensitive Galactic HI 21-cm line absorption
survey to date. To supplement the absorption data, we have extracted the HI
21-cm line emission profiles towards these 102 lines of sight from the Leiden
Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian
fitting analysis to identify the discrete absorption and emission components in
these profiles. In this paper, we present the spectra and the components. A
subsequent paper will discuss the interpretation of these results.Comment: 46 pages, Accepted for publication in Journal of Astrophysics &
Astronom
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
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