The Hubble flow around the Centaurus A/M83 galaxy complex

We present Hubble Space Telescope ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities V-LG < 550 km s(-1). Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 +/- 0.05 Mpc, a velocity dispersion of 136 km s(-1), a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4-8.1) x 10(12) M-circle dot. This elliptical-dominated group is found to have a relatively high mass-to-light ratio: M/L-B 125 M-circle dot/L-circle dot. For the M83 group we derived a mean distance of 4.79 +/- 0.10 Mpc, a velocity dispersion of 61 km s(-1), a mean harmonic radius of 89 kpc, and an estimated orbital/virial mass of (0.8-0.9) x 10(12) M-circle dot. This spiral-dominated group is found to have a relatively low M/L-B 34 M-circle dot/L-circle dot. The radius of the zero-velocity surface around Cen A lies at R-0 = 1.40 +/- 0.11 Mpc, implying a total mass within R-0 of M-T (6.0 +/- 1.4) x 10(12) M-circle dot. This value is in good agreement with the Cen A orbital/virial mass estimates and provides confirmation of the relatively high M/L-B of this elliptical-dominated group. The centroids of both groups, as well as surrounding field galaxies, have very small peculiar velocities, < 25 km s(-1), with respect to the local Hubble flow with H-0 = 68 km s(-1) Mpc(-1).