Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: CO(1-0), CO(2-1) and Neutral Gas in NGC 6946: Molecular Gas in a
  Late-Type, Gas Rich, Spiral Galaxy   We present "On The Fly" maps of the CO(1-0) and CO(2-1) emission covering a
10' X 10' region of the NGC 6946. Using our CO maps and archival VLA HI
observations we create a total gas surface density map, Sigma_gas, for NGC
6946. The predominantly molecular inner gas disk transitions smoothly into an
atomic outer gas disk, with equivalent atomic and molecular gas surface
densities at R = 3.5' (6 kpc). We estimate that the total H2 mass is 3 X 10^9
Mo, roughly 1/3 of the interstellar hydrogen gas mass, and about 2% of the
dynamical mass of the galaxy at our assumed distance of 6 Mpc. The value of the
CO(2-1)/CO(1-0) line ratio ranges from 0.35 to 2; 50% of the map is covered by
very high ratio, >1, gas. The very high ratios are predominantly from interarm
regions and appear to indicate the presence of wide-spread optically thin gas.
Star formation tracers are better correlated with the total neutral gas disk
than with the molecular gas by itself implying SFR is proportional to
Sigma_gas. Using the 100 FIR and 21 cm continuum from NGC 6946 as star
formation tracers, we arrive at a gas consumption timescale of 2.8 Gyr, which
is relatively uniform across the disk. The high star formation rate at the
nucleus appears to be due to a large accumulation of molecular gas rather than
a large increase in the star formation efficiency. The mid-plane gas pressure
in the outer (R > 10 kpc) HI arms of NGC 6946 is close to the value at the
radial limit (10 kpc) of our observed CO disk. If the mid-plane gas pressure is
a factor for the formation of molecular clouds, these outer HI gas arms should
contain molecular gas which we do not see because they are beyond our detection
limit.

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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga