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

Galaxy clusters at high redshift present a superb opportunity to study galaxy evolution, with large galaxy samples at fixed distances. Several lines of evidence point toward large formation redshifts and passive evolution for cluster elliptical galaxies. At redshifts higher than z ~ 0.8, this picture rests on data from only a handful of rich clusters. We have observed four potential clusters to sample sparser environments in a critical redshift range, 0.8 5) population, significantly redder than the old elliptical population at the cluster redshift. We discuss the implications of our clusters at high redshift and possible differences in environment from richer clusters at similar redshifts selected through X-ray or optical techniques.