Molecular gas in the powerful radio nucleus of the ultraluminous infrared galaxy PKS 1345+12

Millimeter CO (1 --> 0) interferometry and high-resolution, Hubble Space Telescope 1.1, 1.6, and 2.2 mu m imaging of the radio compact galaxy PKS 1345+12 are presented. With an infrared luminosity of similar to 2 x 10(12) L., PKS 1345+12 is a prime candidate for studying the link between the ultraluminous infrared galaxy phenomenon and radio galaxies. These new observations probe the molecular gas distribution and obscured nuclear regions of PKS 1345+12 and provide morphological support for the idea that the radio activity in powerful radio galaxies is triggered by the merger of gas-rich galaxies. Two nuclei separated by 2 " (4.0 kpc) are observed in the near-infrared; the extended southeastern nucleus has colors consistent with reddened starlight, and the compact northwestern nucleus has extremely red colors indicative of an optical quasar with a warm dust component. Further, the molecular gas, 3 mn continuum, and radio emission are coincident with the redder nucleus, confirming that the northwestern nucleus is the site of the active galactic nucleus and that the molecular gas is the likely fuel source.