Optical Surveys for Galaxy Clusters

TL;DR

This paper reviews optical methods for galaxy cluster detection, introduces a new technique using the red sequence to reduce projection errors, and presents preliminary results from the RCS survey showing high efficiency in finding clusters at redshifts 0.5 to 1.4.

Contribution

It introduces a novel 3-D cluster detection method based on the red sequence, improving accuracy over traditional optical surveys.

Findings

RCS effectively detects clusters at 0.5<z<1.4

The survey identified clusters with multiple strong lensing arcs

The new technique reduces projection contamination in optical cluster searches

Abstract

We present a brief review of the history of optical searches of galaxy clusters, starting from that of Abell. The traditional application of this survey method suffers from contamination due to projection of galaxies along the line of sight, which becomes increasingly more severe at higher redshift. The new generation of wide-field CCD imagers has provided a renewed impetus for optical surveys for clusters. We describe a new cluster finding technique using the red sequence of early-type galaxies in galaxy groups and clusters, which eliminates the projection problem by essentially producing a 3-D distribution of red galaxies using two-filter imaging data. The Red-Sequence Cluster Survey (RCS) is a 100 square degree optical survey, carried out using 4m class telescopes, which is optimally designed to search for clusters at $0.5<z<1.4$\ utilizing this technique. We present preliminary results which indicate that the RCS is extremely efficient in detecting galaxy clusters at these redshifts, including a number of clusters with multiple strong lensing arcs.