Measuring the Mean and Scatter of the X-Ray Luminosity-Optical Richness Relation for maxBCG Galaxy Clusters

Abstract

Determining the scaling relations between galaxy cluster observables requires large samples of uniformly observed clusters. We measure the mean X-ray luminosity-optical richness (L¯X-N¯200) relation for an approximately volume-limited sample of more than 17,000 optically selected clusters from the maxBCG catalog spanning the redshift range 0.1) relation for an approximately volume-limited sample of more than 17,000 optically selected clusters from the maxBCG catalog spanning the redshift range 0.1) relation for an approximately volume-limited sample of more than 17,000 optically selected clusters from the maxBCG catalog spanning the redshift range 0.1X-N200 relation, we measure ?lnL=0.86+/-0.03 at fixed N200. This scatter is large enough to significantly bias the mean stacked relation. The corrected median relation can be parameterized by L'X=e?(N¯200/40)?x1042 h-2 ergs s-1, where ?=3.57+/-0.08 and ?=1.82+/-0.05. We find that X-ray-selected clusters are significantly brighter than optically selected clusters at a given optical richness. This selection bias explains the apparently X-ray-underluminous nature of optically selected cluster catalogs.