Abstract

We study galaxy interactions in the large-scale environment around A2670, a massive (M-200 = 8.5 +/- 1.2 x10(14) M-circle dot) and interacting galaxy cluster at z = 0.0763. We first characterize the environment of the cluster out to 5xR(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 similar to 21 per cent of the cluster galaxies have clear signs of disturbances, with most of those (similar to 60 per cent) likely being disturbed by ram pressure. The number of ram-pressure stripping 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 x 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 x R-200, motivating wide-area studies in larger cluster samples.