Extreme star formation in the interacting galaxy Arp 299 (IC 694+NGC 3690)

We present a comprehensive study of the star formation properties of the in frared luminous galaxy Arp 299 (IC 694 + NGC 3690), The observations includ e Hubble Space Telescope (HST) NICMOS imaging and Multiple Mirror Telescope optical and near-infrared spectroscopy together with HST archival data. We correct the galaxy parameters for extinction and use the results as bounda ry conditions for evolutionary starburst models. These models and other arg uments show that Arp 299 has been going through a broad variety of interact ion-induced star formation for the last similar to 15 Myr. In addition to n uclear starbursts in the two colliding galaxies, there are nearby luminous star-forming regions that may be the result of molecular clouds breaking up and starting to form massive stars as they approach the nuclear potential. Two regions near the interaction region have very recently formed massive stars (similar to 4 Myr old). One of these regions in particular appears to have undergone a starburst of very short duration, in contrast with the 5- 10 Myr durations that are typical of nuclear events. These regions will pro bably form gravitationally bound new dwarf galaxies, although they are clos e enough to the more massive original galaxies that they will probably even tually be subsumed into them. In addition, we find 19 H n regions at least as energetic as 30 Doradus, and 21 older star clusters that likely are the products of similar H n regions formed in the past. This population of supe rgiant H n regions is unprecedented in normal galaxies and emphasizes that the effects of the interaction propagate through the entire pair of galaxie s.