The dynamical status of the galaxy cluster Abell 115

TL;DR

This study investigates the dynamical state of galaxy cluster Abell 115, revealing two main substructures in collision, estimating their velocities and masses, and linking the radio relic to the ongoing merger process.

Contribution

The paper provides a detailed dynamical analysis of Abell 115, combining spectroscopic and photometric data to identify substructures and model the merger scenario.

Findings

A115 has a velocity dispersion of 1362 km/s.

Two main substructures, A115N and A115S, differ by ~2000 km/s in LOS velocity.

The cluster mass is estimated at 2.2-3.5 x 10^15 h_70 Msun.

Abstract

We present the results of a new spectroscopic and photometric survey of the hot, binary X-ray cluster A115 at z=0.193, containing a radio relic. We combine galaxy velocity and position information to select 85 galaxies recognized as cluster members (from 115 galaxies observed at TNG telescope), determine global dynamical properties and detect substructures. We find that A115 presents velocity dispersion of sigma_v=1362_{-108}^{+126} km/s. Our analysis confirms the presence of two structures (A115N and A115S) of cluster--type well recognizable in the plane of the sky and shows that they differ of ~2000 km/s in the LOS velocity. We estimate that A115S is slightly dynamically more important than A115N having sigma_v=900-1100 km/s vs sigma_v=750-850 km/s. Moreover, we find evidence for two small groups at low velocities. We estimate a global cluster virial mass of 2.2--3.5 e15 h_70 Msun. Our results agree with a pre--merging scenario where A115N and A115S are colliding with a LOS impact velocity Delta v~1600 km/s.The most likely solution to the two--body problem suggests that the merging axis lies at $\sim 20$ degrees from the plane of the sky and that the cores will cross after ~0.1 Gyr. The radio relic with its largest dimension perpendicular to the merging axis is likely connected to this merger.