The Massive and Distant Clusters of WISE Survey (MaDCoWS): Stellar Mass Fractions of Infrared-Selected Galaxy Clusters at z~1

Galaxy clusters are the most massive gravitationally-bound objects in the universe and are excellent tools to study both cosmology and galaxy evolution. Whereas many cluster surveys identify clusters via signatures of their intracluster medium (ICM) in either X-ray or SZ, the complementary Massive and Distant Clusters of WISE Survey (MaDCoWS) uses infrared WISE data to find the most significant galaxy overdensities at z ~ 1. Follow-up SZ observations have provided ICM confirmation of more than twenty MaDCoWS clusters --- including MOO J1142+1527, the most massive cluster detected by any method above z = 1.15 --- while follow-up Chandra observations have also revealed a significant fraction of MaDCoWS clusters to be merging systems. Using SZ-based masses from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and measuring the stellar mass from Spitzer/IRAC 3.6 micron images, we have measured the stellar mass fraction (f_*) for twelve of these infrared-selected clusters, spanning a mass range of ~2--6×10¹⁴ M_⊙ and a redshift range from 0.93--1.32 for both merging and non-merging systems. Comparing these stellar mass fractions to those identically measured in a sample of ICM-selected clusters with similar masses and redshifts from the South Pole Telescope (SPT)-SZ Survey, we found no significant difference in mean f_* between the two selection methods. We did, however, find a larger scatter in f_* for the IR-selected MaDCoWS clusters, as expected. Our ongoing work with these clusters includes making improved measurements of f_* using deeper IRAC data and extending the sample with mass measurements from new SZ observations.