Reconstruction of Radio Relics and X-Ray Tails in an Off-axis Cluster Merger: Hydrodynamical Simulations of A115

Abstract

Although a merging galaxy cluster is a useful laboratory to study many important astrophysical processes and fundamental physics, only limited interpretations are possible without careful analysis of the merger scenario. However, the study is demanding because a thorough comparison of multiwavelength observations with detailed numerical simulations is required. In this paper, we present such a study for the off-axis binary merger A115. The system possesses a number of remarkable observational features, but no convincing merger scenario explaining the shape and location of the radio relic in harmony with the orientation of the cometary X-ray tails has been presented. Our hydrodynamical simulation with adaptive mesh refinement suggests that the cometary X-ray tail of A115 might be a slingshot tail that can arise similar to 0.3 Gyr after the impact, before the two subclusters reach their apocenters. This scenario can predict the location and orientation of the giant radio relic, which is parallel to the northern X-ray tail. In addition, our study indicates that diffusive shock acceleration alone cannot generate the observed radio power unless aided by stronger magnetic fields and/or more significant presence of fossil electrons.