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

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 MB ≤ -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 × 1013 M⊙, placing it on the border between rich groups and poor clusters. However, comparison to the LX-σν and LX-Mass relations shows that it more closely follows the 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 subgroup mergers within the last ∼1 Gyr. While the majority of dynamical indicators for the group suggest it is virialized, we find evidence for a small, dynamically distinct subgroup 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. Show more