High‐Resolution Tip/Tilt Near‐Infrared Imaging of Warm Ultraluminous Infrared Galaxies

We present high spatial resolution H and K'-band images of a complete sampleof ultraluminous infrared galaxies selected to have warm mid-infrared colorsknown to be characteristic of active galaxies. The extended underlying galaxyis detected in each system, as are tidal features and many of the star-formingknots seen at optical wavelengths. While some of these knots have aconsiderable near-infrared excess, we show that they are likely to havebolometric luminosities more similar to that of the extended starbursts withsimilar optical morphology seen in less far-infrared luminous interactingsystems. We find that each ULIG has increasing contributions at longwavelengths by a very compact source which we identify as an active galacticnucleus. We show that the optical/near-infrared colors of these putative nucleiare much more extreme than the most active starburst IRAS galaxies, yet areidentical to "far-infrared loud" quasars which are in turn similar to opticalquasars combined with large quantities of hot dust. Half of the ULIGs havenuclei with dereddened near-infrared luminosities comparable to those of QSOs,while the other half have dereddened luminosities more similar to Seyferts,although this may be an effect of patchy extinction and scattering.Comment: 36 pages, 8 figures, includes a special style file replacing a AASTEX fil