Improvement of the Richness Estimates of maxBCG Clusters

Minimizing the scatter between cluster mass and accessible observables is an important goal for cluster cosmology. In this work, we introduce a new matched filter richness estimator, and test its performance using the maxBCG cluster catalog. Our new estimator significantly reduces the variance in the L_X -richness relation, from σ_{ln L_X}^2=(0.86± 0.02)^2 to σ_{ln L_X}^2=(0.69± 0.02)^2. Relative to the maxBCG richness estimate, it also removes the strong redshift dependence of the L_X -richness scaling relations, and is significantly more robust to photometric and redshift errors. These improvements are largely due to the better treatment of galaxy color data. We also demonstrate the scatter in the L_X -richness relation depends on the aperture used to estimate cluster richness, and introduce a novel approach for optimizing said aperture which can easily be generalized to other mass tracers.