Arp 220: EXTINCTION AND MERGER-INDUCED STAR FORMATION

We analyze new spatially resolved integral field spectroscopic H- and K-band data at a resolution of 0 ''.3 (100 pc) and reanalyze interferometric CO(2-1) line observations of the prototypical merging system Arp 220. We find that the majority of the K-band luminosity is due to a 10 Myr old starburst, with a significant contribution from an underlying greater than or similar to 1 Gyr old stellar population and a small contribution from stars less than or similar to 8 Myr old. The Calzetti et al. reddening law provides the best fit to photometric data points spanning 0.45-2.12 mu m. Furthermore, estimates of the bolometric luminosity from IRAS fluxes in conjunction with our stellar population analysis indicate that we observe less than 10% of the emitted K-band light. The stellar and CO(2-1) kinematic center of the western nucleus coincides with the compact hot dust emission, indicating that the latter marks the center of the gravitational potential. In the eastern nucleus, the CO(2-1) data are well matched by a model in which the gas orbits around the peak of the dust emission. This, and the similarity of the K-band tracer kinematics, shows that despite the irregular morphology, the eastern nucleus is also a kinematically coherent structure. Comparison of the extinction map with EWCO and EWBr gamma maps indicates that the lower half of the eastern nucleus is significantly more extincted than the upper half, suggesting that the lower half is buried in the larger scale gas disk.