The evolution of galaxies in clusters. V - A study of populations since Z approximately equal to 0.5

Abstract

The evolution of the colors of cluster galaxies since redshift of about 0.5 is studied using photometry of 33 clusters. In each cluster, those galaxies brighter than M(v) = -20 which are within the circular area containing the inner 30 percent of the total cluster population are selected. From the distribution of these galaxies in the color-magnitude plane, the fraction of galaxies whose rest-frame B-V colors are at least 0.2 mag bluer than the ridge line of the early-type galaxies at that magnitude is determined. It is found that low-redshift compact clusters form a very homogeneous group of objects with cores essentially devoid of blue galaxies. At redshifts greater than 0.1, compact clusters have significant numbers of blue galaxies, the fraction increasing with redshift. The colors of spiral galaxies in the cores of nearby clusters tend to be redder than those of spirals in the field.