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 ratios
vary 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 much
smaller, 10 +- 3, in the southern extended disk of that galaxy. Elsewhere, the
12CO/13CO line ratio is 5-20, typical of spiral galaxies. The line ratio
variation 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 lesser
degree. HCN emission is bright towards each galaxy nucleus and in the
extranuclear region of active star formation; it was not detected in the IC 694
disk, or the eastern part of the overlap region, leading to lower limits of 25
and 20 respectively. By contrast, at the nuclei of IC 694 and NGC 3690 the
ratios are 9 +- 1 and 14 +- 3 respectively. In the western part of the overlap
region it is 11 +- 3.Comment: 16 pages, 4 postscript figures, to appear in ApJ Letter
