The HectoMAP Cluster Survey - I. redMaPPer Clusters

TL;DR

This study uses the HectoMAP redshift survey to validate and analyze redMaPPer galaxy cluster candidates, demonstrating the effectiveness of scaled richness as a mass proxy and assessing catalog purity and completeness.

Contribution

It provides spectroscopic validation of redMaPPer clusters, evaluates the scaled richness as a mass proxy, and assesses catalog purity and completeness using dense redshift data.

Findings

Scaled richness correlates tightly with spectroscopic richness.

RedMaPPer purity exceeds 90% at low richness.

Some massive clusters are missing from the catalog.

Abstract

We use the dense HectoMAP redshift survey to explore the properties of 104 redMaPPer cluster candidates. The redMaPPer systems in HectoMAP cover the full range of richness and redshift (0.08 $< z <$ 0.60). Fifteen systems included in the Subaru/Hyper Suprime-Cam public data release are bona fide clusters. The median number of spectroscopic members per cluster is $\sim20$. We include redshifts of 3547 member candidates listed in the redMaPPer catalog whether they are cluster members or not. We evaluate the redMaPPer membership probability spectroscopically. The scaled richness ({\lambda}rich/S) provided by redMaPPer correlates tightly with the spectroscopic richness regardless of the cluster redshift and appears to be a better mass proxy than the original richness, {\lambda}rich. The purity (number of real systems) in redMaPPer exceeds 90% even at the lowest richness; however, there is some incompleteness. Five massive galaxy clusters (M $\gtrsim 2 \times 10^{13}$ M$_{\odot}$) associated with X-ray emission in the HectoMAP region are missing from the catalog.