A COMPARISON OF DYNAMICAL AND MOLECULAR GAS MASSES IN VERY LUMINOUS INFRARED GALAXIES

Observations of the 2.3 mum bands of CO have been used to measure the central stellar velocity dispersions in NGC 1614 and IC 694. K-band images were used to constrain models of the stellar mass distribution. With these data and a spectrum of Arp 220 from the literature, we have determined the total mass within the central regions of all three galaxies. The central molecular gas masses inferred from (CO)-C-12 J = 1-0 fluxes are larger than the total masses determined from stellar kinematics. Subtraction of the likely stellar mass from the total mass yields upper limits for the H-2 mass that are 4-10 times less than the previously reported masses. This result supports other arguments that the I(CO)/M(H-2) ratio is not the same in ultraluminous galaxies as it is in Milky Way giant molecular clouds.