X-ray scaling relations from a complete sample of the richest maxBCG clusters

TL;DR

This study analyzes X-ray and optical data from the richest maxBCG galaxy clusters to understand their ICM-galaxy scaling relations, mass selection effects, and cluster relaxation states, revealing biases and the impact of blending on cluster properties.

Contribution

It provides new insights into the X-ray scaling relations of the richest maxBCG clusters and evaluates the effects of blending, miscentering, and selection biases on these relations.

Findings

Blended systems are skewed into the richest sample.

All optical blended halos are resolved as individual X-ray halos.

Relaxed and cool core fractions are lower than in SZ or X-ray selected samples.

Abstract

We use a complete sample of 38 richest maxBCG clusters to study the ICM-galaxy scaling relations and the halo mass selection properties of the maxBCG algorithm, based on X-ray and optical observations. The clusters are selected from the two largest bins of optical richness in the Planck stacking work with the maxBCG richness $N_{200} \geq 78$. We analyze their Chandra and XMM-Newton data to derive the X-ray properties of the ICM. We then use the distribution of $P(X|N)$, $X=T_X,\ L_X,\ Y_X$, to study the mass selection $P(M|N)$ of maxBCG. Compared with previous works based on the whole richness sample, a significant fraction of blended systems with boosted richness is skewed into this richest sample. Parts of the blended halos are picked apart by the redMaPPer, an updated red-sequence cluster finding algorithm with lower mass scatter. Moreover, all the optical blended halos are resolved as individual X-ray halos, following the established $L_X-T_X$ and $L_X-Y_X$ relations. We further discuss that the discrepancy between ICM-galaxy scaling relations, especially for future blind stacking, can come from several factors, including miscentering, projection, contamination of low mass systems, mass bias and covariance bias. We also evaluate the fractions of relaxed and cool core clusters in our sample. Both are smaller than those from SZ or X-ray selected samples. Moreover, disturbed clusters show a higher level of mass bias than relaxed clusters.