Physics
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999pcim.conf...58g&link_type=abstract
The Physics and Chemistry of the Interstellar Medium, Proceedings of the 3rd Cologne-Zermatt Symposium, held in Zermatt, Septemb
Physics
2
Scientific paper
We present new measurements of the ground state fine-structure line of atomic carbon at 492 GHz in a variety of external galaxies, ranging from irregular to spiral, interacting and merging types. Compared to CO(1-0) observed at the same spatial resolution, the CI(1-0) line intensity stays approximatively constant in the different environments, with an average value of the ratio of the line integrated areas of CI(1-0) / CO(1-0) = 0.2 +/- 0.2. However, variations can be found within galaxies or between galaxies: relative to CO lines, CI(1-0) is weaker in galactic nuclei, but stronger in galactic disks, particularly outside star forming regions. This can be understood as a density effect, with CI(1-0) being less biased in excitation towards high density gas than CO. Also in NGC 891, the CI(1-0) emission follows the dust continuum emission at 1.3mm extremely well along the full length of the major axis. Atomic carbon therefore appears to be a reliable tracer of molecular gas in external galaxies. Atomic carbon can contribute significantly to the thermal budget of interstellar gas : the cooling due to C and CO are of the same order of magnitude for most galaxies. CO is generally a more important coolant in starburst galaxies, with intense high-J CO rotational lines. Compared to other fine structure lines, the cooling due to C and CO is usually weak and typically amounts to 2 times 10^{-5} of the FIR continuum or 5% of the CII line. C and CO cooling becomes significant in merger galaxies like Arp 220 where CII is abnormally faint, reaching sim;30% of the gas total.
Gerin Maryvonne
Phillips Thomas G.
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