The anatomy of the NGC 5044 group - I. Group membership and dynamics

TL;DR

This study extensively characterizes the NGC 5044 galaxy group, revealing its mass, dynamical state, and evidence of ongoing accretion of smaller groups, thus enhancing understanding of its structure and evolution.

Contribution

It provides a significantly expanded spectroscopic membership catalog and detailed dynamical analysis, clarifying the group's mass, virialization state, and recent accretion activity.

Findings

Group mass estimated at 9.2 x 10^13 solar masses.

Group follows cluster scaling relations in X-ray and velocity.

Evidence of a small, distinct sub-group indicating ongoing accretion.

Abstract

We use a combination of new AAOmega multi-object wide-field spectroscopic observations and literature data to define 111 spectroscopically confirmed members of the massive NGC 5044 group with M_B <= -13.5 mag, providing a three-fold increase in group members over previous analyses of this group. We find the group to have a dynamical mass of 9.2 x 10^13 solar masses, placing it on the border between rich groups and poor clusters. However, comparison to the L_x-sigma and L_x-mass relations shows it more closely follows cluster scaling relations. Using a combination of crossing time, X-ray contours and line-of-sight velocity profile we are able to preclude growth of the NGC 5044 group via major sub-group mergers within the last ~1 Gyr. While the majority of dynamical indicators for the group suggest it is virialised, we find evidence for a small, dynamically distinct sub-group at 1.4 Mpc from the group centre, suggesting that the NGC 5044 group is the dominant structure in its local environment, and is currently accreting smaller groups.