Weak-Lensing Characterization of the Dark Matter in 29 Merging Clusters that Exhibit Radio Relics

TL;DR

This study uses weak-lensing analysis of 29 merging galaxy clusters with radio relics to map dark matter distributions, compare mass estimation methods, and identify ideal clusters for studying dark matter and merger dynamics.

Contribution

It provides high-resolution dark matter maps, compares mass estimation techniques, and identifies a subset of clusters optimal for future dark matter and radio relic studies.

Findings

Major mergers with mass ratios below 1:4 are common among clusters with radio relics.

Mass estimates from concentration-mass relations can be biased compared to multi-parameter fits.

BCGs tend to better trace the dark matter peaks than other galaxy features.

Abstract

We present a multiwavelength analysis of 29 merging galaxy clusters that exhibit radio relics. For each merging system, we perform a weak-lensing analysis on Subaru optical imaging. We generate high-resolution mass maps of the dark matter distributions, which are critical for discerning the merging constituents. Combining the weak-lensing detections with X-ray emission, radio emission, and galaxy redshifts, we discuss the formation of radio relics from the past collision. For each subcluster, we obtain mass estimates by fitting a multi-component NFW model with and without a concentration-mass relation. Comparing the two mass estimate techniques, we find that the concentration-mass relation underestimates (overestimates) the mass relative to fitting both parameters for high- (low-) mass subclusters. We compare the mass estimates of each subcluster to their velocity dispersion measurements and find that they preferentially lie below the expected velocity dispersion scaling relation, especially at the low-mass end (~$10^{14}\ M_\odot$). We show that the majority of the clusters that exhibit radio relics are in major mergers with a mass ratio below 1:4. We investigate the position of the mass peak relative to the galaxy luminosity peak, number density peak, and BCG locations and find that the BCG tends to better trace the mass peak position. Finally, we update a golden sample of 8 galaxy clusters that have the simplest geometries and can provide the cleanest picture of the past merger, which we recommend for further investigation to constrain the nature of dark matter and the acceleration process that leads to radio relics.