Velocity Dispersions in Clusters of Galaxies

Extract

31 redshifts have been obtained for A1367, 34 for A262 and 61 for the Centaurus cluster (HMS 1247-4102). Full details of this work have been and will be presented in M.N.R.A.S. Both A1367 and A262 are spiral-rich in Oemler’s classification, while Centaurus is intermediate in type between spiral-rich and poor. In all 3 cases, the distributions of E and L galaxies are centrally concentrated, whilst the spirals are distributed in a more extensive and ragged fashion. The mean corrected redshifts and velocity dispersions for 2 morphological subsets are given in Table I. There is no significant difference in the mean velocities of the 2 subsets for each cluster. However, the velocity dispersions for the spirals are significantly greater than those for the E,L galaxies in both A1367 and A262. The differences in velocity dispersions of the 2 subsets for Centaurus are not statistically significant. Gott and Gunn have suggested that irregular clusters of the sort presently described have not undergone collapse. However, all 3 clusters show morphological separation and are x-ray sources. This is consistent with a collapsed core surrounded by a shell of infailing spirals.