Measuring the Mass Distribution in Galaxy Clusters

TL;DR

This study compares gravitational lensing and caustic techniques for measuring galaxy cluster mass profiles, finding general agreement within errors and highlighting potential systematic issues and contamination effects.

Contribution

It provides a comparative analysis of two independent methods for galaxy cluster mass estimation, testing their consistency and identifying sources of systematic errors.

Findings

Methods agree within 30% around the virial radius.

Caustic technique overestimates mass at small radii.

Lensing profiles may be contaminated by large-scale structures.

Abstract

Cluster mass profiles are tests of models of structure formation. Only two current observational methods of determining the mass profile, gravitational lensing and the caustic technique, are independent of the assumption of dynamical equilibrium. Both techniques enable determination of the extended mass profile at radii beyond the virial radius. For 19 clusters, we compare the mass profile based on the caustic technique with weak lensing measurements taken from the literature. This comparison offers a test of systematic issues in both techniques. Around the virial radius, the two methods of mass estimation agree to within about 30%, consistent with the expected errors in the individual techniques. At small radii, the caustic technique overestimates the mass as expected from numerical simulations. The ratio between the lensing profile and the caustic mass profile at these radii suggests that the weak lensing profiles are a good representation of the true mass profile. At radii larger than the virial radius, the lensing mass profile exceeds the caustic mass profile possibly as a result of contamination of the lensing profile by large-scale structures within the lensing kernel. We highlight the case of the closely neighboring clusters MS0906+11 and A750 to illustrate the potential seriousness of contamination of the the weak lensing signal by unrelated structures.