New distances to galaxies in the Centaurus A group

Abstract

We present Hubble Space Telescope/WFPC2 images of seventeen dwarf galaxies in the Centaurus A group. Their distances derived from the magnitudes of the tip of the red giant branch are 5.2 Mpc (KK112), 3.2 Mpc (ESO 321-014), 3.5 Mpc (KK179), 3.4 Mpc (NGC 5102), 4.6 Mpc (KK200), 3.7 Mpc (ESO 324-024), 4.7 Mpc (KK208), 4.6 Mpc (ESO 444-084), 4.4 Mpc (IC 4316), 4.5 Mpc (NGC 5264), 3.6 Mpc (KK211), 3.6 Mpc (KK213), 3.4 Mpc (ESO 325-011), 3.8 Mpc (KK217), 4.0 Mpc (KK221), 4.8 Mpc (NGC 5408), and 3.6 Mpc (PGC 51659). The galaxies are concentrated in two spatially separated groups around NGC 5128 = Cen A and NGC 5236 = M 83. The Cen A group itself has a mean distance of Mpc, a velocity dispersion of 89 km s-1, a mean projected radius of 263 kpc, an estimated orbital mass of , and an orbital mass-to-blue luminosity ratio of 64 . For the M 83 group we derived a mean distance of Mpc, a velocity dispersion of 62 km s-1, a mean projected radius of 142 kpc, an estimated orbital mass of , and . The M 83 group moves away from the Cen A group, which yields a radius of the zero-velocity surface of the Cen A group of Mpc. The total mass within , agrees with the orbital mass estimate. The centroids of both the groups have very small peculiar velocities, km s-1 (Cen A) and () km s-1 (M 83) with respect to the local Hubble flow with km s-1 Mpc-1.