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Molecular line CO (2→1) observations of ultraluminous IRAS galaxies

Rigopoulou, D.; Lawrence, A.; White, G. J.; Rowan-Robinson, M. and Church, S. E. (1996). Molecular line CO (2→1) observations of ultraluminous IRAS galaxies. Astronomy & Astrophysics, 305 pp. 747–755.

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CO (J=2→1) observations of six ultraluminous IRAS galaxies are presented. Four of these galaxies have no previous CO J=2→1 data and two have no previous CO detections at all. Based on these observations, molecular hydrogen masses are estimated and range from 5x109 to 1.8x1010 M. The present data follow the well established correlation that exists between the infrared luminosity LIR and the molecular mass content. The high values of the LIR/MH2 suggest either an increased star formation efficiency and / or an additional source of luminosity such as an active nucleus. The ratio R=(J=2→1)/(J=1→0) between the J=2→1 and 1→0 line temperatures, is examined next using our J=2→1 intensities and other published CO J=1→0 data. For Arp 220, Mrk 231, Mrk 273 R lies in the range 0.7 to 1.1; for IRAS 05189 the CO intensity and the ratio R were both found to have extremely low values. The low values of R≤1 found for all galaxies, suggest that the line profiles are dominated by emission coming from optically thick thermalized CO. Finally the line profiles are examined and compared to published models concerning the distribution and kinematics of the gas. Assuming that the CO is distributed in a disk as in normal spiral galaxies, then this region is probably concentrated towards the center of the galaxies.

Item Type: Journal Article
Copyright Holders: 1996 European Southern Observatory
ISSN: 1432-0746
Keywords: galaxies; radio lines
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 32704
Depositing User: Glenn White
Date Deposited: 22 Mar 2012 12:08
Last Modified: 27 Oct 2014 23:30
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