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For refcode 1998ApJ...492..521P:
Retrieve 27 NED objects in this reference.
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Copyright by American Astronomical Society. Reproduced by permission
1998ApJ...492..521P Physical Conditions of the Molecular Gas in Seyfert Galaxies PADELI P. PAPADOPOULOS AND E. R. SEAQUIST Department of Astronomy, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8, Canada Received 1997 February 24; accepted 1997 August 22 ABSTRACT We examine the physical conditions of the global molecular gas reservoir in the host galaxies of Seyfert 1 and Seyfert 2 nuclei. To do so, we acquired sensitive ^12^CO, ^13^CO, J = 1-0, and J = 2-1 observations and collected available data from the literature for a sample of 27 Seyfert galaxies. We find that Seyfert galaxies have an average value for the ^12^CO/^13^CO J = 1-0 and J = 2-1 line ratios of <R_10_> = 12 and <R_21_> = 13, respectively, with no discernible dependence on the Seyfert type. The r_12_ = (2-1)/(1-0) line ratio for ^12^CO does not reveal any significant difference between the two types, but Seyfert galaxies as a class seem to have systematically lower values of r_12_ (~0.5-0.7) than do average spirals and starbursts. Moreover, for all the galaxies examined, but especially for Seyfert and starburst galaxies, we find that r_12_ is likely to be smaller as the area of the galaxy sampled by the telescope beam becomes larger. This may be the consequence of a global gas excitation gradient in galaxies where warm (T_kin_ >~ 20 K) gas lies confined, preferably in their central regions (<~1 kpc), while a colder (T_kin_ <~ 10 K), and possibly subthermally excited, gas phase dominates the more extended CO emission in the disk. For Seyfert and starburst galaxies, there are indications that their gas excitation gradients may be quite similar. Examination of the properties of the molecular gas by using the r_12_, R_10_, and R_21_ line ratios reveals that, unless r_12_ <~ 0.6, a single warm gas phase can account for the observed values of these ratios toward the central regions of an average Seyfert and/or starburst galaxy. Subject headings: galaxies: ISM-galaxies: Seyfert-galaxies: starburst- radio lines: galaxies
Retrieve 27 NED objects in this reference.
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