Abell 1758N from an optical point of view: new insights on a merging cluster with diffuse radio emission

TL;DR

This study investigates the internal dynamics of the merging galaxy cluster Abell 1758N using new redshift data, revealing its bimodal structure, velocity dispersions, and mass, thereby providing new insights into its merging state and radio emissions.

Contribution

The paper provides the first detailed dynamical analysis of Abell 1758N combining new redshift data with optical and archival imaging, clarifying its bimodal structure and merging status.

Findings

Abell 1758N has a high velocity dispersion of ~1300 km/s.

The cluster exhibits a bimodal structure with two subclusters.

The total mass of Abell 1758N is estimated at 2-3 x 10^15 solar masses.

Abstract

We seek to explore the internal dynamics of the cluster Abell 1758N, which has been shown to host a radio halo and two relics, and is known to be a merging bimodal cluster. Our analysis is mainly based on new redshift data for 137 galaxies acquired at the Telescopio Nazionale Galileo, only four of which have redshifts previously listed in the literature. We also used photometric data from the Sloan Digital Sky Survey and from the Canada-France-Hawaii Telescope archive. We combined galaxy velocities and positions to select 92 cluster galaxies and analyzed the internal cluster dynamics. We estimate a cluster redshift of <z>=0.2782 and quite a high line-of-sight (LOS) velocity dispersion of ~ 1300 km/s. Our 2D analysis confirms the presence of a bimodal structure along the NW-SE direction. We add several pieces of information to the previous merging scenario: the two subclusters (here A1758N(NW) and A1758N(SE)) cannot be separated in the velocity analyses and we deduce a small LOS velocity difference of ~300 km/s in the cluster rest-frame. The velocity information successfully shows that A1758N is surrounded by two small groups and active galaxies infalling onto, or escaping from, the cluster. Removing the two groups, we estimate ~1000 km/s and ~800 km/s for the velocity dispertions of A1758N(NW) and A1758N(SE), respectively. We find that Abell 1758N is a very massive cluster with a range of M=2-3 10^15 solar masses, depending on the adopted model. As expected for clusters that host powerful, extended, diffuse radio emissions, Abell 1758N is a major cluster merger just forming a massive system.