Does Concentration Drive the Scatter in the Stellar-to-Halo Mass Relation of Galaxy Clusters?

Abstract

Concentration is one of the key dark matter halo properties that could drive the scatter in the stellar-to-halo mass relation of massive clusters. We derive robust photometric stellar masses for a sample of brightest central galaxies (BCGs) in SDSS redMaPPer clusters at $0.17<z<0.3$, and split the clusters into two equal-halo mass subsamples by their BCG stellar mass $M_{\ast }$. The weak lensing profiles $\hat{I}”\hat{I}\pounds$ of the two cluster subsamples exhibit different slopes on scales below 1 M$pc/h$. To interpret such discrepancy, we perform a comprehensive Bayesian modelling of the two $\hat{I}”\hat{I}\pounds$ profiles by including different levels of miscentring effects between the two subsamples as informed by X-ray observations. We find that the two subsamples have the same average halo mass of $1.74\times 10^{14}{M}_{\odot }/h$, but the concentration of the low-$M_{\ast }$ clusters is $5.87_{-0.60}^{+0.77}$, $\sim 1.5\ddot{I}ƒ$ smaller than that of their high-$M_{\ast }$ counterparts~($6.95_{-0.66}^{+0.78}$). Furthermore, both cluster weak lensing and cluster-galaxy cross-correlations indicate that the large-scale bias of the low-$M_{\ast }$, low-concentration clusters are $\sim 10\%$ higher than that of the high-$M_{\ast }$, high-concentration systems, hence possible evidence of the cluster assembly bias effect. Our results reveal a remarkable physical connection between the stellar mass within 20{-}30 k$pc/h$, the dark matter mass within $\sim$ 200 k$pc/h$, and the cosmic overdensity on scales above 10 M$pc/h$, enabling a key observational test of theories of co-evolution between massive clusters and their central galaxies.

12 pages, 6 figures, matched to the published version in MNRAS