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Date and Time of the Query: 2019-06-18 T11:06:46 PDT
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For refcode 2002PASJ...54..195T:
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Copyright by Astronomical Society of Japan. 2002PASJ...54..195T Observations of Ammonia in External Galaxies I. NGC 253 and M 82 Shuro TAKANO, Naomasa NAKAI, and Kentarou KAWAGUCHI Nobeyama Radio Observatory (NRO), 2 Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305 stakano@nro.nao.ac.jp (Received 2000 August 9; accepted 2002 January 29) Abstract The ammonia (J,K) = (1,1), (2,2), (3,3), and (4,4) transitions in the 23.7-24.1 GHz region were searched for in nearby galaxies, NGC 253 and M 82, 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 NGC 253, but no lines were found in M 82. In NGC 253 the shapes of the three emission lines were different from one another. The rotational temperatures obtained in NGC 253 were <~ 17-50 K, depending on the velocity components. There are two main results: (1) The ortho-to-para abundance ratio was obtained in NGC 253 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 temperature of less than 8 K between ortho and para. (2) The abundance of NH_3_ in NGC 253 was found to be about an order of magnitude larger than the upper limit in M 82. This result is an additional evidence for the different molecular abundances which were already reported between NGC 253 and M 82. In addition, the molecular abundances including NH_3_ in nearby galaxies with rich molecular gas were compared, and we found that the molecular abundance in M 82 is systematically peculiar concerning the formation mechanisms of molecules. We discussed factors which cause such a peculiarity in M 82. Key Words: galaxies: individual (NGC 253, M 82, IC 342) - galaxies: starburst - ISM: molecules - molecular processes - radio lines: galaxies
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