On the Level of Cluster Assembly Bias in SDSS

Understand

Recently, several studies have discovered a strong discrepancy between the large-scale clustering biases of two subsamples of galaxy clusters at the same halo mass, split by their average projected membership distances $R_{\mathrm{mem}}$.

• The level of this discrepancy significantly exceeds the maximum halo assembly bias signal predicted by LCDM.
• In this study, we explore whether some of the clustering bias differences could be caused by biases in $R_{\mathrm{mem}}$ due to projection effects from other systems along the line-of-sight.
• We thoroughly investigate the halo assembly bias of the photometrically-detected redMaPPer clusters in SDSS, by defining a new variant of the average membership distance estimator $\tilde{R}_{\mathrm{mem}}$ that is more robust against projection effects in the cluster membership identification.