Near-infrared adaptive optics imaging of QSO host galaxies

We report near-infrared (primarily H band) adaptive optics (AO) imaging with the Gemini-N and Subaru Telescopes, of a representative sample of 32 nearby (z < 0.3) QSOs selected from the Palomar-Green (PG) Bright Quasar Survey (BQS), in order to investigate the properties of the host galaxies. Two-dimensional modeling and visual inspection of the images shows that ∼36% of the hosts are ellipticals, ∼39% contain a prominent disk component, and ∼25% are of undetermined type. Thirty percent show obvious signs of disturbance. The mean MH(host) = -24.82 (2.1L _H*), with a range -23.5 to -26.5 (∼0.63Z, _H*, to 10L _H*). At <L _H*, all hosts have a dominant disk component, while at >2L _H* most are ellipticals. "Disturbed" hosts are found at all M _H(host), while "strongly disturbed" hosts appear to favor the more luminous hosts. Hosts with prominent disks have less luminous QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in mergers (which presumably shortly will be ellipticals). At z < 0.13, where our sample is complete at B band, we find no clear correlation between M _B(QSO) and M _H(host). However, at z > 0.15, the more luminous QSOs (M _B < -24.7), and four of five of the radio-loud QSOs, have the most luminous H-band hosts (>7L _H*) , most of which are ellipticals. Finally, we find a strong correlation between the "infrared excess," L _IR/L _BB, of QSOs with host type and degree of disturbance. Disturbed and strongly disturbed hosts and hosts with dominant disks have L _IR/L _BB twice that of nondisturbed and elliptical hosts, respectively. QSOs with disturbed and strongly disturbed hosts are also found to have morphologies and mid/far-infrared colors that are similar to what is found for "warm" ultraluminous infrared galaxies, providing further evidence for a possible evolutionary connection between both classes of objects.