Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High Velocity Cloud Edges and Mini-HVCs   Arecibo mapping is reported of the neutral hydrogen distribution along
selected directions out from the centers of two small High Velocity Clouds
(HVC), W486 and W491. Both HVCs have a small inner region where the neutral
hydrogen column density N_HI decreases slowly and a larger outer region where
N_HI declines more rapidly, smoothly and exponentially from ~ 2 X 10^19 atoms
cm^-2 down to < 10^18 atoms cm^-2. Line widths, and presumably temperature and
turbulence, do not increase in the outermost regions. Therefore pressure
decreases smoothly, making confinement by dark matter gravity more likely than
confinement by external pressure.
  The more extended HVC, W491, has a superimposed small cloud (which we dub a
``mini-HVC''), offset by 66 km s^-1 in velocity along the line of sight with
peak column density about 5 X 10^18 atoms cm^-2. Preliminary data toward future
mapping of two more HVCs reveals two more mini-HVCs of similarly small size and
central column density a bit less than 1 X 10^19 atoms cm^-2. We suggest that
these three mini-HVCs are not physically associated with the HVCs on which they
are superimposed, but are either very small outlyers of the extended Magellanic
Stream HVC complex or more distant and/or smaller isolated CHVCs.
  The value of N_HI at the point where the neutral and ionized column densities
are equal is ~ 2 X 10^19 atoms cm^-2 for the two mapped HVCs. Therefore the
angular scalelength of the total hydrogen is appreciably larger than the
observed HI scalelength. Previous distance estimates, related to absolute size
and mass of the total hydrogen cloud, may have to be scaled down because of the
undetected, more extended ionized hydrogen.

31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph