Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002pasj...54..195t&link_type=abstract
Publications of the Astronomical Society of Japan, vol. 54, pp. 195-207, 2002
Astronomy and Astrophysics
Astronomy
25
Galaxies: Individual (Ngc 253, M 82, Ic 342), Galaxies: Starburst, Ism: Molecules, Molecular Processes, Radio Lines: Galaxies
Scientific paper
The ammonia (J,K) = (1,1), (2,2), (3,3), and (4,4) transitions in the 23.7-24.1GHz region were searched for in nearby galaxies, NGC253 and M82, to study the relation between the molecular abundances and physical conditions. The (1,1), (2,2), and (3,3) emission lines were clearly detected in NGC253, but no lines were found in M82. In NGC253 the shapes of the three emission lines were different from one another. The rotational temperatures obtained in NGC253 were <~ 17 - 50 K, depending on the velocity components. There are two main results: (1) The ortho-to-para abundance ratio was obtained in NGC253 and found to be different depending on the velocity components. The ratio was about 1 for the velocity component where the (2,2)line is detected. On the other hand, the ratio was more than 6 for another velocity component where the (2,2)line is barely detected. This high ratio corresponds to an equilibration tem perature of less than 8K between ortho and para. (2) The abundance of NH3 in NGC253 was found to be about an order of magnitude larger than the upper limit in M82. This result is an additional evidence for the different molecular abundances which were already reported between NGC253 and M82. In addition, the molecular abundances including NH3 in nearby galaxies with rich molecular gas were compared, and we found that the molecular abundance in M82 is systematically peculiar concerning the formation mechanisms of molecules. We discussed factors which cause such a peculiarity in M82.
Kawaguchi Kentarou
Nakai Naomasa
Takano Shuro
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