Distances to five nearby southern galaxy clusters and the absolute motion of the Local Group

Abstract

We present redshifts and central velocity dispersions derived from observations with the AATs fibre system for galaxies in five nearby southern clusters, Abell 194 (0122–02), Hydra (Abell 1060, 1034–27), Centaurus (1246–41), Pavo II (1842–63) and Klemola 44 (2345–28). Relative distances to these galaxy clusters are derived via the application of the D−σ relation to the early-type galaxies. For the Centaurus cluster we find that the two velocity components (Cen30 and Cen45) lie at the same distance and thus the large peculiar velocity of Cen45 is naturally explained by its infall towards the more massive Cen30 component, as previously advocated by Lucey et al. We find that the rich clusters in our sample have peculiar velocities with respect to the cosmic microwave background (CMB) that are not significantly different from zero. This includes Cen30 for which, from data for 10 galaxies, we find a peculiar motion of only ∼ 200±300 km s−1. Thus our work disagrees with the claim made by Lynden-Bell et al., which is based on data for five galaxies, that Cen30 possesses a large peculiar velocity. The idea of a ‘Great Attractor’ lying beyond the Hydra–Centaurus supercluster is not supported. However, the Centaurus and Hydra clusters themselves will clearly be major attractors in this region. Combining our cluster data with that of Lynden-Bell et al. and Aaronson et al., we derive a motion for the Local Group with respect to this frame of distant rich clusters that is in good agreement with that inferred from the CMB dipole. We find that rich clusters have only small motions with respect to the CMB.