  We present HST/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. Distances are determined based on the luminosities of stars at the tip of
the red giant branch that range from 3.0 Mpc to 6.5 Mpc. The galaxies are
concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83
(NGC 5236). The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a
velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an
estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun. This elliptical
dominated group is found to have a relatively high mass-to-light ratio: M/L_B =
125 M_sun/L_sun. For the M 83 group we derived a mean distance of 4.79 +/-0.10
Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and
estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun. This spiral
dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun. 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_sun. This
value is in good agreement with the Cen A virial/orbital mass estimates and
provides confirmation of the relatively high M/L_B of this elliptical-dominated
group. The centroids of both the groups, as well as surrounding field galaxies,
have very small peculiar velocities, < 25 km/s, with respect to the local
Hubble flow with H_0 = 68 km/s/Mpc.
