Associations Between QSOs and Groups of Galaxies

Abstract

Evidence that most presently known low-redshift QSOs are associated with groups of galaxies has led to a program aimed at determining the typical properties of these groups. For the 3C273 field, observations of essentially all galaxies with mB ≤ 21.5 over a region 10.1′ (∼1.5 Mpc) in diameter yield four galaxies having redshifts close to that of the QSO. Consideration of the present evidence concerning the richness of groups associated with QSOs leads to the conclusion that, for at least those QSOs that are radio sources, their galactic environment is similar to that of radio galaxies, except that they seldom, if ever, occur in the centers of rich clusters of galaxies.