The structure of Abell 1351: a bimodal galaxy cluster with peculiar diffuse radio emission

TL;DR

This study investigates the complex internal structure and dynamics of the Abell 1351 galaxy cluster, revealing it as a massive merging system with a peculiar radio halo and evidence of ongoing substructure interactions.

Contribution

It provides a detailed multi-wavelength analysis combining optical and X-ray data to characterize the bimodal, merging nature of Abell 1351, highlighting the connection between cluster dynamics and radio emission.

Findings

Abell 1351 has a high velocity dispersion (~1500 km/s) indicating a massive cluster.

Evidence of bimodality and substructure suggests ongoing merger activity.

The radio halo and relic are linked to the cluster's complex dynamical state.

Abstract

We aim to review the internal structure and dynamics of the Abell 1351 cluster, shown to host a radio halo with a quite irregular shape. Our analysis is based on radial velocity data for 135 galaxies obtained at the Telescopio Nazionale Galileo. We combine galaxy velocities and positions to select 95 cluster galaxy members and analyse the internal dynamics of the whole cluster. We also examine X-ray data retrieved from Chandra and XMM archives. We measure the cluster redshift, <z>=0.325, the line-of-sight (LOS) velocity dispersion, \sigma_v~1500 km/s, and the X-ray temperature, kT~9 keV. From both X-ray and optical data independently, we estimate a large cluster mass, in the 1--4 $10^{15}$ M$_\odot$ range. We attribute the extremely high value of \sigma_v to the bimodality in the velocity distribution. We find evidence of a significant velocity gradient and optical 3D substructure. The X-ray analysis also shows many features in favour of a complex cluster structure, probably supporting an ongoing merger of substructures in Abell 1351. The observational scenario agrees with the presence of two main subclusters in the northern region, each with its brightest galaxy (BCG1 and BCG2), detected as the two most important X-ray substructures with a rest-frame LOS velocity difference of \Delta v~2500 km/s (in the rest frame) and probably being in large part aligned with the LOS. We conclude that Abell 1351 is a massive merging cluster. The details of the cluster structure allow us to interpret the quite asymmetric radio halo as a `normal' halo plus a southern relic, strongly supporting a previous suggestion based only on inspection of radio and preliminary X-ray data.