Spitzer/MIPS 24um Observations of Galaxy Clusters: An Increasing Fraction of Obscured Star-forming Members from z=0.02 to z=0.83

摘要

We study the mid-infrared properties of 1315 spectroscopically confirmedmembers in eight massive (M>5x10^14 Msun) galaxy clusters covering the redshiftrange from 0.02 to 0.83. The selected clusters all have deep Spitzer MIPS 24umobservations, Hubble and ground-based photometry, and extensive redshiftcatalogs. We observe for the first time an increase in the fraction of clustergalaxies with mid-infrared star formation rates higher than 4 solar masses peryear from 3% at z=0.02 to 13% at z=0.83. This increase is reproduced even whenconsidering only the most massive members (Mstars >4x10^10 Msun). The 24 micronobservations reveal stronger evolution in the fraction of blue/star-formingcluster galaxies than color-selected samples: the number of red but stronglystar-forming cluster galaxies increases with redshift, and combining these withthe optically-defined Butcher-Oemler members increases the total fraction ofblue/star-forming cluster galaxies to ~30% at z=0.83. These results, the firstof our Spitzer/MIPS Infra-Red Cluster Survey (SMIRCS), support earlier studiesindicating the increase in star-forming members is driven by cluster assemblyand galaxy infall, as is expected in the framework of hierarchical formation.