The anatomy of the NGC5044 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 M_B <= -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 × 10¹³M_solar, placing it on the border between rich groups and poor clusters. However, comparison to the L_X-σ_ν and L_X-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 NGC5044 group via major subgroup 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 subgroup 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.