Merging Cluster Collaboration: A Panchromatic Atlas of Radio Relic Mergers

TL;DR

This study analyzes 29 radio relic galaxy cluster mergers to identify substructures, estimate merger dynamics, and find that most mergers occur near the plane of the sky, providing a valuable sample for future detailed studies.

Contribution

It offers a combined photometric and spectroscopic analysis of galaxy cluster mergers, identifying substructures and merger axes orientation, and selects a prime 'gold' sample for further research.

Findings

Most mergers have small line-of-sight velocities, indicating axes are near the plane of the sky.

Substructures align with radio relics and merger shocks in 28 of 29 systems.

Eight systems are identified as a 'gold' sample for detailed follow-up.

Abstract

Golovich et al. 2017b presents an optical imaging and spectroscopic survey of 29 radio relic merging galaxy clusters. In this paper, we study this survey to identify substructure and quantify the dynamics of the mergers. Using a combined photometric and spectroscopic approach, we identify the minimum number of substructures in each system to describe the galaxy populations and estimate the line of sight velocity difference between likely merging subclusters. We find that the line-of-sight velocity components of the mergers are typically small compared with the maximum three dimensional relative velocity (usually $<1000$ km s$^{-1}$ and often consistent with zero). This suggests that the merger axes of these systems are generally in or near the plane of the sky matching findings in magneto-hydrodynamical simulations. In 28 of the 29 systems we identify substructures in the galaxy population aligned with the radio relic(s) and presumed associated merger induced shock. From this ensemble, we identify eight systems to include in a `gold' sample that is prime for further observation, modeling, and simulation study. Additional papers will present weak lensing mass maps and dynamical modeling for each merging system, ultimately leading to new insight into a wide range of astrophysical phenomena at some of the largest scales in the universe.