EVOLUTION OF THE NEAR-INFRARED LUMINOSITY FUNCTION IN RICH GALAXY CLUSTERS

We present the K-band (2.2 mu m) luminosity functions (LFs) of the X-r ay-luminous clusters MS1054-0321 (z = 0.823), MS0451-0305 (z = 0.55), Abell 963 (z = 0.206), Abell 665 (z = 0.182) and Abell 1795 (z = 0.063 ) down to absolute magnitudes M-K = -20. Our measurements probe fainte r absolute magnitudes than do any previous studies of the near-infrare d LFs of clusters. All the clusters are found to have similar LFs with in the errors, when the galaxy populations are evolved to redshift z = 0. It is known that the most massive bound systems in the Universe at all redshifts are X-ray-luminous clusters. Therefore, assuming that t he clusters in our sample correspond to a single population seen at di fferent redshifts, the results here imply that not only had the stars in present-day ellipticals in rich clusters formed by z = 0.8, but tha t they existed in as luminous galaxies then as they do today. Addition ally, the clusters have K-band LFs which appear to be consistent with the K-band field LF in the range -24 < M-K < -22, although the uncerta inties in both the field and cluster samples are large.