Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An ISO--SWS survey of molecular hydrogen in Starburst and Seyfert
  Galaxies   We present results from a survey of molecular hydrogen emission from a sample
of Starburst and Seyfert galaxies carried out with the Infrared Space
Observatory (ISO). Pure rotational H_2 emission has been detected in a number
of extragalactic objects and a variety of environments. A number of transitions
from S(7) to S(0) are detected in both Starbursts and Seyferts. Using
excitation diagrams we derive temperatures and masses of the ``warm'' molecular
hydrogen. We find that the temperature of the ``warm'' gas is similar in
Starbursts and Seyferts (those Seyferts for which we have firm detections of
the S(0) line) with a value of around T~150 K. This ``warm'' gas accounts for
as much as 10% of the total galactic mass (as probed by CO molecular
observations) in Starbursts. The fraction of ``warm'' gas is overall higher in
Seyferts, ranging between 2--35%. We then investigate the origin of the warm
H_2 emission. Comparison with published theoretical models and Galactic
templates implies that although emission from photodissociation regions (PDR)
alone could explain the emission from Starbursts and Seyferts, most likely a
combination of PDR, shock emission and gas heated by X-rays (mostly for the
Seyferts) is responsible for H_2 excitation in extragalactic environments.
Finally, we find that although PAH and H_2 line emission correlate well in
Starbursts and the large scale emission in AGN, H_2 emission is much stronger
compared to PAH emission in cases where a ``pure'' AGN dominates the energy
output.

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The categories of this paper are: stat
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
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The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: mtrl-th