Near-infrared Adaptive Optics Imaging of High-redshift Quasars

The properties of high-redshift quasar host galaxies are studied in order to investigate the connection between galaxy evolution, nuclear activity, and the formation of supermassive black holes. We combine new near-IR observations of three high-redshift quasars (2 < z < 3), obtained at the ESOVery Large Telescope equipped with adaptive optics, with selected data from the literature. For the three new objects we were able to detect and characterize the properties of the host galaxy, found to be consistent with those of massive elliptical galaxies of MR 24:7 for the one radio-loud quasar, andMR 23:8 for the two radio-quiet quasars. When combined with existing data at lower redshift, these new observations depict a scenario where the host galaxies of radio-loud quasars are seen to follow the expected trend of luminous ( 5L ) elliptical galaxies undergoing passive evolution. This trend is remarkably similar to that followed by radio galaxies at z > 1:5. Radio-quiet quasar hosts also follow a similar trend but at a lower average luminosity ( 0.5 mag dimmer). The data indicate that quasar host galaxies are already fully formed at epochs as early as 2 Gyr after the big bang and then passively fade in luminosity to the present epoch. Subject headinggs: galaxies: active — galaxies: evolution — infrared: galaxies — quasars: general