GALAXY VELOCITIES AND SUBSTRUCTURES IN SOUTHERN CLUSTERS - A496 AND SERSIC 40/6, EXAMPLES OF DYNAMIC CUSPS

Estimates of velocity dispersions, mean velocities, and virial masses are given for Sersic 40/6 and A496, based on new observations and published data of 84 and 70 galaxies, respectively. The main optical and x-ray structures together with the velocity field distributions of these clusters are briefly discussed. Both clusters show the presence of density cusps of approximately 0.2 Mpc radius around the central galaxies, having velocity dispersions significantly lower than the clusters overall values that blend smoothly with the cD halo dispersions. In A496 the core galaxies can be considered bound to the cD, forming a dynamical subunit. The core group around the central db in Sersic 40/6 has half its cluster measured dispersion. Although the core dispersion is high, it could be bound if the global high dispersion value is confirmed. An application of the virial theorem using the cD satellite galaxies gives masses of ∼ (2.1 ± 1) × 1014, script M sign⊙ and ∼ (2.5 ± 1) × 1012 script M sign⊙ for the cD galaxies in Sersic 40/6 and A496, respectively. Some consideration is given to the implication for theories of cD formation and evolution. Cooling flows can be affected by the presence of these central dynamical subunits in the inner regions where they control their flow.