Host Galaxies of Intermediate Redshift Radio-Loud and Radio-Quiet Quasars

We have obtained deep images for a sample of 96 radio-loud and radio-quiet quasars at intermediate redshifts (0.4–0.8). Our aim is to compare the properties of the host galaxies and the galaxy environments of the two groups of quasars in a systematic way. To facilitate a direct statistical comparison between radio-loud and radio-quiet objects, we selected pairs of objects with approximately the same redshift and V-magnitude. After analyzing about half the sample we find that there is no systematic difference in the host galaxy luminosities for the two classes of objects. We confirm that radio-loud quasars commonly occur in elliptical type galaxies, with some exceptions, while radio-quiet quasars are found in spiral disks or ellipticals. The optical colours of the host galaxies are bluer than can be expected from passive evolution. At this stage we cannot say if the blue colours are caused by a young stellar population or by light scattered by the ISM of the host galaxy.