Molecular Gas Distribution in Double-Nucleus Ultraluminous Infrared Galaxies

Millimeter (CO) observations of 5 double-nucleus ultraluminous infrared galaxy (ULIG) mergers are presented. With nuclear separations of 3 − 5 kpc, these galaxies are in the “intermediate” stages of the merger process. A preliminary comparison of the distribution of molecular gas (the likely fuel source for both starbursts and active galactic nuclei: AGN) shows a tendency for molecular gas to be associated with the AGN nucleus of ULIGs with “warm”, Seyfert-like infrared colors (f25μm/f60μm ≥ 0.20) and associated with both stellar nuclei of ULIGs with “cool” infrared colors (f25μm/f60μm < 0.2). Studies of ULIGs with a wide range of nuclear separations using the high resolution and increased sensitivity of ALMA will provide a larger statistical sample with which the gas distribution, molecular gas masses, and densities can be determined as a function of the evolutionary stage, starburst and AGN activity, and lookback time.