Internal dynamics of the galaxy cluster Abell 959

TL;DR

This study investigates the internal dynamics of galaxy cluster Abell 959, revealing evidence of substructures, high velocity dispersion, and characteristics indicative of a young, merging, radio-emitting galaxy cluster.

Contribution

The paper provides new insights into Abell 959's internal structure and dynamics using combined optical, X-ray, and lensing data, highlighting its merging state and radio features.

Findings

Detection of a high-velocity NE group ~5' from the center

Identification of an elongated central structure indicating past merger

High velocity dispersion (~1025 km/s) and large virial mass

Abstract

The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still being debated. In this paper we aim to obtain new insights into the internal dynamics of Abell 959, showing evidence of a diffuse radio source, analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 107 galaxies in the cluster field acquired at the Telescopio Nazionale Galileo. We also use photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine galaxy velocities and positions to select 81 galaxies recognized as cluster members and determine global dynamical properties. We analyze the cluster searching for substructures by using several statistical methods. We also study the 2D galaxy distribution in the field of the cluster. We compare our results with those from X-ray and gravitational lensing analyses. We estimate a cluster redshift of z=0.2883 +/- 0.0004. We detect an NE high velocity group at 5' from the cluster center with a relative line--of--sight (LOS) velocity of ~ +1900 km/s with respect to the main system. We also detect a central, dense structure elongated along the SE--NW direction likely connected with the two dominant galaxies and their surrounding cores. This elongated central structure is probably the trace of an old cluster merger. The LOS velocity dispersion of galaxies is very high (1025 (-75/+104) km/s). The virial mass is M(<R=1.48 Mpc)= 1.15 (-0.19/+0.25) Msun. Our results suggest that this cluster is forming along two main directions of mass accretion and show the typical characteristics of radio clusters; i.e., it is very massive and shows a young dynamical state. However, deeper radio observations are needed to clarify the nature of the diffuse radio emission in Abell 959.