Deconstructing the Antlia cluster core

TL;DR

This study investigates the complex structure of the Antlia galaxy cluster, revealing multiple galaxy groups at different velocities and suggesting a significant extension along the line of sight, which explains its high velocity dispersion.

Contribution

It provides new spectroscopic data and identifies distinct galaxy groups within Antlia, clarifying its kinematic substructure and challenging previous notions of its uniformity.

Findings

Identification of three galaxy groups at different velocities

Large radial velocity dispersion due to line-of-sight extension

Spectroscopic confirmation of cluster substructure

Abstract

The present literature does not give a satisfactory answer to the question about the nature of the "Antlia galaxy cluster". The radial velocities of galaxies found in the region around the giant ellipticals NGC 3258/3268 range from about 1000 km/s to 4000 km/s. We characterise this region and its possible kinematical and population substructure. We have obtained VLT--VIMOS multi-object spectra of the galaxy population in the inner part of the Antlia cluster and measure radial velocities for 45 potential members. We supplement our galaxy sample with literature data, ending up with 105 galaxy velocities. We find a large radial velocity dispersion for the entire sample as reported in previous papers. However, we find three groups at about 1900 km/s, 2800 km/s, and 3700 km/s, which we interpret as differences in the recession velocities rather than peculiar velocities. The high radial velocity dispersion of galaxies in the Antlia region reflects a considerable extension along the line of sight.