Radio Galaxy–selected Clusters at High Redshift and Associated Extremely Red Object Overdensities

Galaxy clusters at high redshift present a superb opportunity to study galaxyevolution, with large galaxy samples at fixed distances. Several lines ofevidence point towards large formation redshifts and passive evolution forcluster ellipticals. At redshifts larger than z~0.8, this picture rests on datafrom only a handful of rich clusters. We have observed four potential clustersto sample sparser environments in a critical redshift range, 0.8 < z < 1.2. Wecompare the photometric evolution and radial density profiles in our clusterswith more massive clusters studied in a similar manner. We also highlight theoverdense ERO (I-K>5) population, significantly redder than the old ellipticalpopulation at the cluster redshift. We discuss the implications of our clustersat high redshift, and possible differences in environment from richer clustersat similar redshifts selected through X-ray or optical techniques.Comment: 13 pages, 7 figures, accepted in the Astronomical Journal, Oct2000 issu