A multiwavelength view of the galaxy cluster Abell 523 and its peculiar diffuse radio source

TL;DR

This study provides a comprehensive multiwavelength analysis of galaxy cluster Abell 523, revealing its complex merger state, peculiar radio halo, and deviations from typical cluster scaling relations, highlighting its unique dynamical features.

Contribution

The paper presents new spectroscopic, photometric, X-ray, and radio data to characterize A523's structure, dynamics, and radio emission, revealing its complex merger history and peculiar radio/X-ray properties.

Findings

A523 is a massive, merging galaxy cluster with two subclusters.

The cluster hosts a large, elongated radio halo perpendicular to optical/X-ray elongation.

A523 exhibits a radio/X-ray offset and is underluminous in X-rays or overluminous in radio.

Abstract

We study the structure of the galaxy cluster Abell 523 (A523) at z=0.104 using new spectroscopic data for 132 galaxies acquired at the Telescopio Nazionale Galileo, new photometric data from the Isaac Newton Telescope, and X-ray and radio data from the Chandra and Very Large Array archives. We estimate the velocity dispersion of the galaxy population, sigmaV=949 km/s, and the X-ray temperature of the hot intracluster medium, kT=5.3 keV. We infer that A523 is a massive system: M200 about 7-9 x10E14 Msun. The analysis of the optical data confirms the presence of two subclusters, 0.75 Mpc apart, tracing the SSW-NNE direction and dominated by the two brightest cluster galaxies (BCG1 and BCG2). The X-ray surface brightness is strongly elongated towards the NNE direction, and its peak is clearly offset from both the BCGs. We confirm the presence of a 1.3 Mpc large radio halo, elongated in the ESE-WNW direction and perpendicular to the optical/X-ray elongation. We detect a significant radio/X-ray offset and radio polarization, two features which might be the result of a magnetic field energy spread on large spatial scales. A523 is found consistent with most scaling relations followed by clusters hosting radio haloes, but quite peculiar in the Pradio-LX relation: it is underluminous in the X-rays or overluminous in radio. A523 can be described as a binary head--on merger caught after a collision along the SSW-NNE direction. However, minor optical and radio features suggest a more complex cluster structure, with A523 forming at the crossing of two filaments along the SSW-NNE and ESE-WNW directions.