The mass-concentration relation in lensing clusters: the role of statistical biases and selection effects

TL;DR

This paper examines the mass-concentration relation in galaxy clusters, addressing biases and selection effects, and finds that correcting these biases aligns observations with the predictions of the $\\Lambda$CDM model.

Contribution

It provides a critical revision of observed mass-concentration relations in multiple cluster samples, incorporating bias corrections and theoretical models to resolve previous tensions.

Findings

Bias correction reduces tension with $\\Lambda$CDM predictions.

Sample-dependent normalization and slope of the relation.

Selection effects significantly influence observed relations.

Abstract

The relation between mass and concentration of galaxy clusters traces their formation and evolution. Massive lensing clusters were observed to be over-concentrated and following a steep scaling in tension with predictions from the concordance $\Lambda$CDM paradigm. We critically revise the relation in the CLASH, the SGAS, the LOCUSS, and the high-redshift samples of weak lensing clusters. Measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. We corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant BCG and, mostly, selection effects in the observed sample. The normalisation, the slope and the scatter of the expected relation are strongly sample-dependent. For the considered samples, the predicted slope is much steeper than that of the underlying relation characterising dark-matter only clusters. We found that the correction for statistical and selection biases in observed relations mostly solve the tension with the $\Lambda$CDM model.