Pre- and post-processing of cluster galaxies out to 5 × R_200: The extreme case of A2670

We study galaxy interactions in the large scale environment around A2670, a massive (M_200 = 8.5 ± 1.2 × 10^14M_⊙) and interacting galaxy cluster at z = 0.0763. We first characterize the environment of the cluster out to 5× R_200 and find a wealth of substructures, including the main cluster core, a large infalling group, and several other substructures. To study the impact of these substructures (pre-processing) and their accretion into the main cluster (post-processing) on the member galaxies, we visually examined optical images to look for signatures indicative of gravitational or hydrodynamical interactions. We find that ∼ 21 cluster galaxies have clear signs of disturbances, with most of those (∼60 candidates found (101) in A2670 is the largest to date for a single system, and while they are more common in the cluster core, they can be found even at > 4 × R_200, confirming cluster influence out to large radii. In support of a pre-processing scenario, most of the disturbed galaxies follow the substructures found, with the richest structures having more disturbed galaxies. Post-processing also seems plausible, as many galaxy-galaxy mergers are seen near the cluster core, which is not expected in relaxed clusters. In addition, there is a comparable fraction of disturbed galaxies in and outside substructures. Overall, our results highlight the complex interplay of gas stripping and gravitational interactions in actively assembling clusters up to 5× R_200, motivating wide-area studies in larger cluster samples.