Mapping infrared enhancements in closely interacting spiral-spiral pairs. I. ISO CAM and ISO SWS observations

Mid-infrared (MIR) imaging and spectroscopic observations are presented for a well-defined sample of eight closely interacting (CLO) pairs of spiral g alaxies that have overlapping disks and show enhanced far-infrared (FIR) em ission. The goal is to study the star formation distribution in CLO pairs, with special emphasis on the role of "overlap starbursts." Observations wer e made with the Infrared Space Observatory (ISO) using the CAM and SWS inst ruments. The ISO CAM maps, tracing the MIR emission of warm dust heated by young massive stars, are compared to new ground-based Ha and R-band images. We identify three possible subgroups in the sample, classified according t o the star formation morphology: (1) advanced mergers (Arp 157, Arp 244, an d Arp 299), (2) severely disturbed systems (Asp 81 and Arp 278), and (3) le ss disturbed systems (Arp 276, KPG 347, and KPG 426). Localized starbursts are detected in the overlap regions in all five pairs of subgroups (1) and (2), suggesting that they are a common property in colliding systems. Excep t for Arp 244, the "overlap starburst" is usually fainter than the major nu clear starburst in CLO pairs. Star formation in "less disturbed systems" is often distributed throughout the disks of both galaxies with no "overlap s tarburst" detected in any of them. These systems also show less enhanced FI R emission, suggesting that they are in an earlier interaction stage when t he direct disk collisions have probably not yet occurred.