Joint Astrophysics Colloquium

The Search for Distant Galaxy Clusters -
Results from the Red Sequence Cluster Surveys

Erica Ellingson

University of Colorado at Boulder

Massive galaxy clusters at high redshifts are powerful probes of both galaxy and cosmological evolution. In particular, large surveys of distant clusters show promise as probes of dark energy and its equation of state, via the sensitivity of the growth of large scale structure to the history of cosmological expansion. I present results from the Red Sequence Cluster Surveys, wide-field optical surveys for galaxy clusters to z=1. Our highly efficient survey technique isolates the distinct red sequence of galaxies in these clusters, providing both cluster redshifts and a first estimate of mass from the measured cluster richness. Multi-wavelength follow-up of cluster candidates show them to be consistent in general with normal, massive clusters, with a contamination rate of < about 10%. I present X-ray, spectroscopic and weak lensing observations used to calibrate our richness-mass estimate, an analysis of the evolution of the cluster galaxy population, and a preliminary analysis of cosmological constraints from RCS-1, our first 90 square degree survey, which identified about 1000 clusters from redshifts 0.2 to 1.0. These results suggest that the 1000 square degree RCS-2 survey now in progress will provide a robust sample, unprecedented in size, of high redshift clusters for cosmological and cluster evolution studies.