A Nicmos Imaging Study of Quasar Host Galaxy Evolution

Abstract

We summarise the results of a major HST/NICMOS programme designed to investigate the cosmological evolution of quasar host galaxies from z=2 to the present day. At z = 1 we have been able to establish host-galaxy luminosities and scalelengths and, apart from simple passive stellar evolution, we find little difference between these galaxies and the elliptical hosts of low-redshift quasars of comparable nuclear output implying that the hosts are virtually fully assembled by z = 1. At z 2 the host galaxies are harder to detect, but we have been able to derive host luminosities. We find evidence that the difference between RQQ and RLQ hosts appears to grow with increasing redshift, with the RLQ hosts remaining consistent with passive evolution while the RQQ hosts appear to show a (modest) drop in mass. Possible physical causes of this effect are briefly discussed.