Cluster Abell 520: a perspective based on member galaxies. A cluster forming at the crossing of three filaments?

TL;DR

This study analyzes galaxy velocities and positions in Abell 520 to understand its complex structure, suggesting it is forming at the intersection of three filaments, which may explain the observed dark core.

Contribution

It provides a detailed dynamical analysis of Abell 520 using new and existing redshift data, revealing its filamentary structure and its impact on dark matter observations.

Findings

Abell 520 is a complex, merging cluster.

The cluster is forming at the intersection of three filaments.

A filament aligned with the line of sight may explain the dark core.

Abstract

The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still debated. An interesting case is the rich, merging cluster Abell 520, containing a radio halo. A recent gravitational analysis has shown in this cluster the presence of a massive dark core suggested to be a possible problem for the current cold dark matter paradigm. We aim to obtain new insights into the internal dynamics of Abell 520 analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 293 galaxies in the cluster field obtained combining new redshift data for 86 galaxies acquired at the TNG with data obtained by CNOC team and other few data from the literature. We also use new photometric data obtained at the INT telescope. We combine galaxy velocities and positions to select 167 cluster members around z~0.201. We analyze the cluster structure using the weighted gap analysis, the KMM method, the Dressler-Shectman statistics and the analysis of the velocity dispersion profiles. We compare our results with those from X-ray, radio and gravitational lensing analyses. We find that Abell 520 is definitely a very complex system. Our results suggest that we are looking at a cluster forming at the crossing of three filaments of the large scale structure. In particular, we detect a filament aligned with the LOS and projected onto the center of the forming cluster. It might explain the apparent massive dark core shown by gravitational lensing analysis.