Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High Resolution Observations of the Near-Infrared Emission from NGC 6822
  Hubble V   We observed Hubble V, the brightest HII region complex in the dwarf irregular
galaxy NGC 6822, at near-infrared (1.8--2.4 um) wavelengths using the Cooled
Grating Spectrometer 4 (CGS4) at the United Kingdom Infra-Red Telescope
(UKIRT). The line emission maps of Hubble V show the typical structure of a
photo-dissociation region (PDR) where an ionized core, traced by compact He I
emission (2.0587 um) and Br_gamma emission (2.1661 um), is surrounded by an
outer layer traced by molecular hydrogen (H_2) emission. The measured line
ratios of H_2 2-1 S(1) (2.2477 um) / 1-0 S(1) (2.1218 um) from 0.2 to 0.6 and
the un-shifted and un-resolved line profiles suggest that the H_2 emission
originates purely from a PDR. By comparing the H_2 results with a PDR model, we
conclude that Hubble V includes dense (10^{4.5} cm^{-3}) and warm PDRs. In this
environment, most of the H_2 molecules are excited by far-UV photons (with a
field strength of 10^{2-4} times that of the average interstellar field),
although collisional processes de-excite H_2 and contribute significantly to
the excitation of the first vibrational level. We expect that Hubble V is in
the early stage of molecular cloud dissolution.

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The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th