Galaxy Clusters at High Redshift and Evolution of Brightest Cluster Galaxies

Identification of high-redshift clusters is important for studies of cosmology and cluster evolution. Using photometric redshifts of galaxies, we identify 631 clusters from the Canada-France-Hawaii Telescope (CFHT) wide field, 202 clusters from the CFHT deep field, 187 clusters from the Cosmic Evolution Survey (COSMOS) field, and 737 clusters from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE) field. The redshifts of these clusters are in the range 0.1 <~ z <~ 1.6. Merging these cluster samples gives 1644 clusters in the four survey fields, of which 1088 are newly identified and more than half are from the large SWIRE field. Among 228 clusters of z >= 1, 191 clusters are newly identified, and most of them from the SWIRE field. With this large sample of high-redshift clusters, we study the color evolution of the brightest cluster galaxies (BCGs). The r' - z' and r ⁺ - m _{3.6 μm} colors of the BCGs are consistent with a stellar population synthesis model in which the BCGs are formed at redshift z_f >= 2 and evolved passively. The g' - z' and B - m _{3.6 μm} colors of the BCGs at redshifts z > 0.8 are systematically bluer than the passive evolution model for galaxies formed at z_f ~ 2, indicating star formation in high-redshift BCGs.