Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991a%26a...249..323a&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 249, no. 2, Sept. 1991, p. 323-326.
Astronomy and Astrophysics
Astrophysics
78
Carbon Isotopes, Carbon Monoxide, Interacting Galaxies, Molecular Clouds, Galactic Evolution, Interstellar Matter, Milky Way Galaxy
Scientific paper
The J = 1-0 transitions of CO-12 and CO-13 are observed in 21 galaxies. Unusually large CO-12/CO-13 (1-0) intensity ratios of more than 20 are measured in four merging galaxies: NGC 3256, NGC 1614, Arp 220 (IC 4553) and Arp 299 (IC 694 and NGC 3690). All four are warm and luminous in the infrared. The ratio in the rest of the objects, which display a variety of morphologies, is well concentrated around a mean value of 11. The large CO-12/CO-13 intensity ratios reflect a decrease in mean optical depth of molecular clouds that have been disturbed by powerful tidal forces or by a starburst triggered in the merging process. The intensity ratio of about 11 is a factor of about 2 times larger than that of giant molecular clouds in the Galactic disk, leading to the conclusion that the Galactic disk is a poor model for some extragalactic molecular emission. Since nuclear CO emission dominates in several of the sample galaxies, a comparison with the molecular clouds of the Galactic center may be more appropriate.
Aalto Samuli
Black John Harry
Booth Roy S.
Johansson Lars E. B.
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