Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Molecular gas in spiral galaxies: a new warm phase at large
  galactocentric distances?   There is now strong evidence suggesting that the 12CO J = 1-0 transition,
widely used to trace H2 gas, significantly underestimates its mass in
metal-poor regions. In spiral disks such regions are found in large
galactocentric distances where we show that any unaccounted H2 gas phase is
likely to be diffuse (~5-20 cm^-3) and warmer (T(kin) ~ 50-100 K) than the cool
(T(kin) ~ 15-20 K) CO-luminous one. Moreover we find that a high value of the
H2 formation rate on grains, suggested by recent observational work, can
compensate for the reduction of the available grain surface in the metal-poor
part of typical galactic disks and thus enhance this CO-poor H2 component which
may be contributing significantly to the mass and pressure of spiral disks
beyond their optical radius.

31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc