COSMOS天区星系团的BO效应

Butcher-Oemler Effect for Galaxy Clusters in COSMOS Field

星系团是宇宙中最大的维里化系统.基于COSMOS天区的测光红移数据,我们获得了一个包含187个星系团的样本,其中包含了大量高红移的星系团,非常适合用来研究星系团中的蓝星系比例随红移的演化效应.利用Subaru望远镜配备的g+、r+和i+波段星等,我们采用了3种颜色判据来挑选蓝星系,均发现星系团中蓝星系的比例随红移显著上升.BO效应的弥散程度还与星系团的富度有关.

Clusters of galaxies are the largest virialized systems in the universe. Based on the photometric redshift database in the COSMOS field, we obtain a sample of 187 clusters, including a number of high-redshift clusters, which facilities the study on the evolution of blue galaxy fraction with cluster redshift. Taking the Subaru g~ ,r＋, i~ magnitudes, we adopt three color criteria to select blue galaxies. A remarkable trend that the blue fration increases with redshifi is found. The scattering of the BO effect is dependent upon the cluster richness.