Millimeter Interferometer Observations of Infrared Luminous Galaxies: NGC 828 and NGC 6240

Aperture synthesis observations at ~ 7" resolution of the CO emission from two high-luminosity infrared galaxies are presented. The new CO maps provide further morphological and kinematic evidence that the central regions of both galaxies are undergoing merging processes. A secondary molecular gas concentration in NGC 6240 is found approximately 8" (3.9 kpc) northeast of the primary nucleus. The resolved molecular gas distribution of NGC 828 shows a significant asymmetry with respect to the stellar disk. The CO rotation curve of this galaxy exhibits a change of shape on one side of the disk, indicating a possible secondary mass concentration at the 6 cm radio continuum peak. In the nuclei of both NGC 828 and NGC 6240, it is estimated that the volume filling factor of the molecular gas is about 10%. The kinetic energy of the interstellar medium can be dissipated in less than 10^6^ yr, but it can sustain the high luminosity for only a few x 10^-5^ yr. The gas comprises a large fraction of the dynamical mass, probably due to the concentration of gas toward the nuclei during the interactions. The observed gas concentrations are likely to be unstable to large- scale gravitational collapse and will probably lead to nuclear starbursts.