Variation of Molecular Line Ratios and Cloud Properties in the Arp 299 Galaxy Merger

High resolution observations of 12CO (2.''3), 13CO (3.''9), and HCN (5.''4)J=1--0 in the galaxy merger Arp 299 (IC 694 and NGC 3690) show the line ratiosvary dramatically across the system. The 12CO/13CO ratio is unusually large, 60+- 15, at the IC 694 nucleus, where 12CO emission is very strong, and muchsmaller, 10 +- 3, in the southern extended disk of that galaxy. Elsewhere, the12CO/13CO line ratio is 5-20, typical of spiral galaxies. The line ratiovariation in the overlap between the two galaxies is smaller, ranging from 10+- 3 in the east to 20 +- 4 in the west. The 12CO/HCN line ratio also varies across Arp 299, although to a lesserdegree. HCN emission is bright towards each galaxy nucleus and in theextranuclear region of active star formation; it was not detected in the IC 694disk, or the eastern part of the overlap region, leading to lower limits of 25and 20 respectively. By contrast, at the nuclei of IC 694 and NGC 3690 theratios are 9 +- 1 and 14 +- 3 respectively. In the western part of the overlapregion it is 11 +- 3.Comment: 16 pages, 4 postscript figures, to appear in ApJ Letter