Host galaxies of quasars and their association with galaxy clusters

Seventeen quasars with redshifts ranging from 0.044 to 0.828 have been observed through an r filter using a CCD detector at the Cassegrain focus of the 2.2 m telescope of the Max-Planck-Institut fuer Astronomie. Counts of faint galaxies in the vicinity of the quasar images indicate that quasars are usually located in groups or clusters of galaxies which are dominated by the luminosity contribution of the quasar host galaxy. It is concluded that most of the radio quasars are central events in galaxies which are more luminous and larger on average than normal elliptical and spiral galaxies. It is suggested that most radio-loud quasars are situated in giant elliptical galaxies in which a considerable amount of hot gas and young stars may be present owing to recent collisions or tidal interaction with nearby cluster members.