3,720 research outputs found
Completing HI observations of galaxies II. The Coma Supercluster
High sensitivity 21-cm HI line observations, with an rms noise level of \sim
0.5 mJy, were made of 35 spiral galaxies in the Coma Supercluster, using the
refurbished Arecibo telescope, which resulted in the detection of 25 objects.
These data, combined with the measurements available from the literature,
provide the set of HI data for 94% of all late-type galaxies in the Coma
Supercluster with an apparent photographic magnitude m_p <15.7 mag. We confirm
that the typical scale of HI deficiency around the Coma cluster is 2 Mpc, i.e.
one virial radius. Comparing the HI mass function (HIMF) of cluster with
non-cluster members of the Coma Supercluster we detect a shortage of high HI
mass galaxies among cluster members that can be ascribed to the pattern of HI
deficiency found in rich clusters.Comment: 16 pages, 8 figures, 4 tables. Accepted for publication on A&
Degenerate mixing of plasma waves on cold, magnetized single-species plasmas
In the cold-fluid dispersion relation ω = ω_p/[1+(k_⊥/k_z)^(2]1/2) for Trivelpiece-Gould waves on an infinitely long magnetized plasma cylinder, the transverse and axial wavenumbers appear only in the combination k_⊥/k_z. As a result, for any frequency ω<ω_p, there are infinitely many degenerate waves, all having the same value of k_⊥/k_z. On a cold finite-length plasma column, these degenerate waves reflect into one another at the ends; thus, each standing-wave normal mode of the bounded plasma is a mixture of many degenerate waves, not a single standing wave as is often assumed. A striking feature of the many-wave modes is that the short-wavelength waves often add constructively along resonance cones given by dz/dr = ±(ω_p^2/ω^2-1)^(1/2). Also, the presence of short wavelengths in the admixture for a predominantly long-wavelength mode enhances the viscous damping beyond what the single-wave approximation would predict. Here, numerical solutions are obtained for modes of a cylindrical plasma column with rounded ends. Exploiting the fact that the modes of a spheroidal plasma are known analytically (the Dubin modes), a perturbation analysis is used to investigate the mixing of low-order, nearly degenerate Dubin modes caused by small deformations of a plasma spheroid
Selling mill-run and graded oak lumber
This bulletin reports on School of Forestry Research Project 120, 'Timber Crop'--P. [2].Digitized 2007 AES
Tests on treated fence posts
Cover title.Includes bibliographical references
The First CO Map of a Low Surface Brightness Galaxy
Using the Owens Valley Radio Observatory Millimeter-Wavelength Array (OVRO)
we have obtained the first CO map of a low surface brightness (LSB) galaxy. The
studied galaxy, UGC 01922, was chosen for these observations because both of
its previous CO detection with the IRAM 30m telescope and its classification as
a Malin 1 `cousin' - an LSB galaxy with M_HI > 10^10 Msol. The OVRO map
detected approximately 65% of the CO(1-0) flux found earlier with the single
dish measurements, giving a detected gas mass equivalent to M_H2 = 1.1X10^9
Msol. The integrated gas peak lies at the center of the galaxy and coincides
with both the optical and 1.4 GHz continuum emission peaks. The molecular gas
extends well beyond the OVRO beam size (~4'' or 3 kpc), covering ~25% of the
optical bulge. In all, perhaps the most remarkable aspect of this map is its
unexceptional appearance. Given that it took over ten years to successfully
detect molecular gas in any low surface brightness system, it is surprising
that the appearance and distribution of UGC 01922's CO is similar to what would
be expected for a high surface brightness galaxy in the same morphological
class.Comment: 5 pages, including 3 figures and 3 tables. also available online at
http://www.gb.nrao.edu/~koneil. Accepted by ApJ
Temporal and spatial plasma wave echoes
It is shown that, if a longitudinal wave is excited in a collision-free plasma and Landau-damps away, and later a second wave is excited and also damps away, then a third wave will spontaneously appear in the plasma. This wave appears long after the first two waves have damped away at a time proportional to the interval between the first two waves, and is in that sense an echo. It is also shown that, if a wave is continuously excited at one point in a plasma and a second wave is continuously excited many Landau damping lengths from the first point, then a third wave will spontaneously appear many Landau damping lengths from the second point. Fundamentally, plasma wave echoes are possible because of the reversible nature of Landau damping. However, small-angle Coulomb collisions are very effective in destroying the echo
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