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 CHFT Deep field, 187 clusters from the Cosmic
Evolution Survey (COSMOS) and 737 clusters from the Spitzer Wide-area InfraRed
Extragalactic survey (SWIRE) field. The redshifts of these clusters are in the
range of 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 colors r'-z' and r^+-m_{3.6\mu m} 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 colors g'-z' and
B-m_{3.6\mu m} of the BCGs at redshifts z>0.8 are systematically bluer than the
passive evolution model for galaxy formed at z_f~2, indicating star formation
in high redshift BCGs.
