Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First results from the Arecibo Galactic HI Survey: the disk/halo
  interface region in the outer Galaxy   The consortium for Galactic studies with the Arecibo L-band Feed Array (ALFA)
is conducting a neutral hydrogen (HI) survey of the whole Arecibo sky
(declination range from -1 to 38 degrees), with high angular (3.5') and
velocity resolution (0.2 km/s). The precursor observations with ALFA of a
region in the Galactic anti-center reveal numerous isolated, small (a few pc in
size), and cold (T_k<400 K) HI clouds at low negative velocities, distinctly
separated from the HI disk emission (`low-velocity clouds', LVCs). These clouds
are most likely located in the transition region between the Galactic disk and
halo (at scale heights of 60--900 pc), yet they have properties of typical cold
neutral clouds. LVCs are colder and, most likely, smaller and less massive than
Lockman's clouds in the disk/halo interface region of the inner Galaxy. Our
observations demonstrate that the cloudy structure of the interface region is
most likely a general phenomenon, not restricted to the inner Galaxy. LVCs have
sizes and radial velocities in agreement with the expectations for clouds
formed in low-temperature fountain flows, although we measure a factor of ten
higher HI column densities. Alternatively, LVCs could represent the final
stages of the infalling intergalactic material in the on-going construction of
the Galaxy.
  In the same dataset at higher negative velocities, we have discovered a
`companion' HI cloud located 50' southwest of CHVC186+19-114. CHVC186+19-114 is
a typical compact high velocity cloud (HVC) with a well-defined core/envelope
structure. The companion cloud has a diameter of only 7'x9', and is one of the
smallest HVCs known, most likely stripped from the main cloud through the
interactions with the halo medium.

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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ex
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
17
The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-alg
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The categories of this paper are: physics
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The categories of this paper are: hep-ph
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The categories of this paper are: stat