An Improved Cluster Richness Estimator

TL;DR

This paper presents a new matched filter richness estimator that reduces scatter in the L_X-richness relation, improves robustness to errors, and optimizes aperture size for better cluster mass estimation.

Contribution

A novel matched filter richness estimator that decreases variance and redshift dependence, enhancing cluster mass proxies in cosmology.

Findings

Reduces variance in L_X-richness relation from 0.86 to 0.69.

Removes redshift dependence of richness scaling relations.

Improves robustness to photometric and redshift errors.

Abstract

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 \sigma_{\ln L_X}^2=(0.86\pm0.02)^2 to \sigma_{\ln L_X}^2=(0.69\pm0.02)^2. Relative to the maxBCG richness estimate, it also removes the strong redshift dependence of the richness scaling relations, and is significantly more robust to photometric and redshift errors. These improvements are largely due to our more sophisticated 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 be easily generalized to other mass tracers.