Quasars and ultraluminous infrared galaxies: At the limit?

We have detected the host galaxies of 16 nearby, radio-quiet quasars using images obtained with the Near-Infrared Camera and MultiObject Spectrometer. We confirm that these luminous quasars tend to live in luminous, early-typ e host galaxies, and we use the host-galaxy magnitudes to refine the lumino sity/host-mass limit inferred from ground-based studies. If quasars obey th e relation M-blackhole/M-spheroid similar to 0.006 found for massive dark o bjects in nonactive galaxies, then our analysis implies that they radiate a t up to similar to 20% of the Eddington rate. An analogous analysis for ult raluminous infrared galaxies shows them to accrete at up to similar Eddingt on fractions, consistent with the hypothesis that some of them an powered b y embedded quasars.