Luminous Ir Galaxies in a Merger Sequence: Bima Co Imaging

The power output in luminous infrared galaxies (LIGs, LIR,(,1011L 8 , Hi, == 75 km s-l Mpc1) can approach the bolometric luminosity of quasars and can be provided by either starbursts or dust-enshouded QSOs, or both. Most LIGs appear to comprise of mergers of gas-rich galaxies. So, intense bursts of star formation apparently result from interaction and merging of galaxies, but the exact physical processes involved in collecting the large amount of gas involved and in initiating the starbursts are not well understood. In order to trace observationally the conditions in the interstellar medium (ISM) that lead to starbursts, we have used the newly expanded Berkeley-Illinois-Maryland Association (BIMA) millimeter-wave array to map the molecular ISM in a sample of LIGs chosen to represent different phases of the interacting/merging process. Most importantly, a few LIGs in the sample might be in a "pre-starburst" phase, so they provide an ideal laboratory for studying the conditions leading to starbursts (Lo, Gao & Gruendl 1997). Our emphasis is on the widely separated LIGs at early/intermediate stages of interaction for this reason, and also for complementary studies to previous CO imaging studies that have concentrated on relatively advanced merger systems (Scoville et al. 1991; Downes & Solomon 1997) in which the ISM has already been highly disrupted by the interaction and starbursts.