The complex structure of Abell 2345: a galaxy cluster with non-symmetric radio relics

TL;DR

This study investigates the complex internal dynamics and merger history of galaxy cluster Abell 2345 using multi-wavelength data, revealing multiple substructures and a likely ongoing multi-directional merger.

Contribution

It provides a detailed analysis of Abell 2345's internal structure and dynamics, combining optical, radio, and X-ray data to identify multiple subclusters and merger processes.

Findings

Identification of three significant galaxy density peaks.

Detection of complex X-ray surface brightness structure.

Evidence for a multi-directional cluster merger.

Abstract

We aim to obtain new insights into the internal dynamics of the cluster Abell 2345. This cluster exhibits two non-symmetric radio relics well studied through recent, deep radio data. Our analysis is based on redshift data for 125 galaxies acquired at the Telescopio Nazionale Galileo and on new photometric data acquired at the Isaac Newton Telescope. We also use ROSAT/HRI archival X-ray data. We combine galaxy velocities and positions to select 98 cluster galaxies and analyze the internal dynamics of the cluster. We estimate a mean redshift <z>=0.1789 and a LOS velocity dispersion \sigma ~ 1070 km/s. The two-dimensional galaxy distribution reveals the presence of three significant peaks within a region of ~ 1 Mpc (the E, NW, and SW peaks). The spectroscopic catalog confirms the presence of these three clumps. The total mass of the cluster is very uncertain: M~ 2 10^15 solar masses. The E clump well coincides with the main mass peak as recovered from the weak gravitational lensing analysis and is off-set to the east from the BCG by ~ 1.3 arcmin. The ROSAT X-ray data also show a very complex structure, mainly elongated in the E-W direction, with two (likely three) peaks in the surface brightness distribution, which, however, are off-set from the position of the peaks in the galaxy density. The observed phenomenology agrees with the hypothesis that we are looking at a complex cluster merger occurring along two directions: a major merger along the ~ E-W direction (having a component along the LOS) and a minor merger in the western cluster regions along the ~ N-S direction, roughly parallel to the plane of the sky.