The Anatomy of the NGC 5044 Group I: Group Membership and Dynamics

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 NGC5044 group with MB ≤ −13.5mag, providing a three-fold increase in group members over previous analyses of this group. We find the group to have a dynamical mass of 9.2×10 M⊙, placing it on the border between rich groups and poor clusters. However, comparison to the LX–σν and LX–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 NGC5044 group via major sub-group mergers within the last ∼1Gyr. While the majority of dynamical indicators for the group suggest it is virialized, we find evidence for a small, dynamically distinct sub-group at 1.4Mpc from the group centre, suggesting that the NGC5044 group is the dominant structure in its local environment, and is currently accreting smaller groups.