QSO Hosts and Environments at z = 0.9-4.2: JHK Images with Adaptive Optics

We have observed nine QSOs with redshifts of 0.85 to 4.16 at near-infrared wavelengths with PUEO, the Adaptive Optics (AO) Bonnette of the Canada-France-Hawaii Telescope. Exposure times ranged from 1500 to 24,000 s (mostly near 7000 s) in the J, H, and/or K bands with pixels 0.″035 on the sky. The FWHMs of the co-added images at the location of the quasars are typically 0.″16. Including another QSO published previously, we find associated QSO structure in at least eight of 10 objects, including the QSO at z = 4.16. The structures seen in all cases include long, faint features that appear to be tidal tails. In four cases we have also resolved the QSO host galaxies, but we find them to be smooth and symmetric. Future point-spread function removal may expand this result. Of the nine objects (including one object previously reported) with more extended structure, five are radio-loud, and all but one of these appear to be in a dense, small group of compact galaxy companions. The radio-quiet objects do not occupy the same dense environments as seen in the near-infrared. In this small sample we do not find any apparent trends of these properties with redshift over the range 0.8 < z < 2.4. The colors of the host galaxies and companions are consistent with young stellar populations at the QSO redshift. Our observations suggest that AO observations in the visible region will exhibit luminous signatures of the substantial star formation activity that must be occurring.