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 −1 . 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 kms −1 , a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4 − 8.1) · 10 12 M ⊙ . This elliptical dominated group is found to have a relatively high mass-to-light ratio: M/L B = 125 M ⊙ /L ⊙ . For the M 83 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 estimated orbital/virial mass of (0.8 − 0.9) · 10 12 M ⊙ . This spiral dominated group is found to have a relatively low M/L B = 34 M ⊙ /L ⊙ . 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) · 10 12 M ⊙ . 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 −1 , with respect to the local Hubble flow with H 0 = 68 km s −1 Mpc −1 .

We use updated data on distances and velocities of galaxies in the proximity of the Local Group (LG) in order to establish properties of the local Hubble flow. For 30 neighbouring galaxies with distances 0.7 < D_LG < 3.0 Mpc, the Local flow is characterized by the Hubble parameter H_loc = (78+/-2) km/(s*Mpc), the mean-square peculiar velocity sigma_v = 25 km/s, corrected for errors of radial velocity measurements (~4 km/s) and distance measurements (~10 km/s), as well as the radius of the zero-velocity surface R_0 = (0.96+/-0.03) Mpc. The minimum value for sigma_v is achieved when the barycenter of the LG is located at the distance D_c = (0.55+/-0.05) D_M31 towards M31 corresponding to the Milky Way-to-M31 mass ratio M_MW / M_M31 ~ 4/5. In the reference frame of the 30 galaxies at 0.7 - 3.0 Mpc, the LG barycenter has a small peculiar velocity ~(24+/-4) km/s towards the Sculptor constellation. The derived value of R_0 corresponds to the total mass M_T(LG) = (1.9+/-0.2) 10^12 M_sun with Omega_m = 0.24 and a topologically flat universe, a value in good agreement with the sum of virial mass estimates for the Milky Way and M31.Comment: 14 pages, 6 figures, 1 table. Accepted for publication in MNRA

Based on high precision measurements of the distances to nearby galaxies with the Hubble telescope, we have determined the radii of the zero velocity spheres for the local group, R 0 = 0.96 ± 0.03Mpc, and for the group of galaxies around M 81/M 82, 0.89 ± 0.05Mpc. These yield estimates of M T = (1.29 ± 0.14) . 10 12 ¤ M and (1.03 ± 0.17) . 10 12 ¤ M , respectively, for the total masses of these groups. The R 0 method allows us to determine the mass ratios for the two brightest members in both groups, as well. By varying the position of the center of mass between the two principal members of a group to obtain minimal scatter in the galaxies on a Hubble diagram, we find mass ratios of 0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81 galaxies, in good agreement with the observed ratios of the luminosities of these galaxies.

We study different incarnations of the Tully-Fisher (TF) relation for the Local Volume (LV) galaxies taken from Updated Nearby Galaxy Catalog. The UNGC sample contains 656 galaxies with W 50 HI-line-width estimates, mostly belonging to low mass dwarfs. Of them, 296 objects have distances measured with accuracy better than 10%. For the sample of 331 LV galaxies having baryonic masses log M bar > 5.8 log M ⊙ we obtain a relation log M bar = 2.49 log W 50 + 3.97 with observed scatter of 0.38 dex. The largest factors affecting the scatter are observational errors in K-band magnitudes and W 50 line widths for the tiny dwarfs, as well as uncertainty of their inclinations. We find that accounting for the surface brightness of the LV galaxies, or their gas fraction, or specific star formation rate, or the isolation index do not reduce essentially the observed scatter on the baryonic TF-diagram. We also notice that a sample of 71 dSph satellites of the Milky Way and M31 with known stellar velocity dispersion σ * tends to follow nearly the same bTF relation, having slightly lower masses than that of late-type dwarfs.

Aims. This work considers the Virgo cluster of galaxies, focusing on its structure, kinematics, and morphological landscape. Our principal aim is to estimate the virial mass of the cluster. For this purpose, we present a sample of 1537 galaxies with radial velocities VLG < 2600 km s −1 situated within a region of ∆SGL = 30 • and ∆SGB = 20 • around M87. About half of the galaxies have distance estimates. Methods. We selected 398 galaxies with distances in a (17 ± 5) Mpc range. Based on their 1D and 2D number-density profiles and their radial velocity dispersions, we made an estimate for the virial mass of the Virgo cluster. Results. We identify the infall of galaxies towards the Virgo cluster core along the Virgo Southern Extension filament. From a 1D profile of the cluster, we obtain the virial mass estimate of (6.3 ± 0.9) × 10 14 M , which is in tight agreement with its mass estimate via the external infall pattern of galaxies.Conclusions. We conclude that the Virgo cluster outskirts between the virial radius and the zero-velocity radius do not contain significant amounts of dark matter beyond the virial radius.