IAU Symposium Abstract S186-070T

A High Resolution, Multi-transition Study of the Merger Arp 299 -- Dramatic Changes in Molecular Cloud Properties Across the System.

S. Aalto1,3, S.Radford2, N. Scoville3, and S. Sargent4
1 Onsala Observatory, Sweden < susanne@oso.chalmers.se >
2 NRAO, USA < sradford@nrao.edu >
3 Caltech, USA < nzs@astro.caltech.edu >
4 Caltech, USA < afs@astro.caltech.edu >

High resolution OVRO observations of CO 1-0, 2-1; 13CO 1-0, 2-1, and HCN 1-0 of the merger Arp 299 (IC 694 and NGC 3690) show the line ratios vary dramatically across the system. The CO/13CO 1-0 ratio is unusually large, 60, at the IC 694 nucleus, where CO emission is very strong, and much smaller, 10, in the southern extended disk of that galaxy. The large ratio can primarily be attributed to a low to moderate optical depth in the CO 1-0 line at the nucleus of IC 694. These results demonstrate that there is no general lack of 13CO in this merger, as was first indicated by single dish studies. Instead, relatively faint 13CO emission is confined to small regions of very high CO surface brightness. These data support the hypothesis that unusually high CO/13CO 1-0 intensity ratios are associated with extremely compact molecular distributions in the nuclei of merging galaxies. We will use multi transition information to present a model of the physical conditions of the molecular gas at the nucleus of IC 694, as well as an estimate of molecular abundances. Furthermore, we will discuss molecular dynamics in this fairly early merger, and focus on the dynamics and distribution of the gas in the compact molecular nucleus of IC 694.