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 .
Abstract. We present Hubble Space Telescope/WFPC2 images of the galaxies NGC 2366, NGC 2976, NGC 4236, IC 2574, DDO 53, DDO 82, DDO 165, Holmberg I, Holmberg II, Holmberg IX, K52, K73, BK3N, Garland, and A0952+69 in the M 81 complex. Their true distance moduli, derived from the brightness of the tip of the red giant branch, lie in the range of 27. m 52 (NGC 2366) to 28. m 30 (DDO 165), with a median of 27. m 91, which is typical for other known M 81 group members. Using distances and radial velocities of about 50 galaxies in and around the M 81/NGC 2403 complex, we find the radius of the zero-velocity surface of the M 81 group to be R0 = (1.05 ± 0.07) Mpc, which yields a total mass M (R0) = (1.6 ± 0.3) × 10 12 M and a total mass-to-luminosity ratio M (R0)/LB = (38 ± 7) M /L . The total mass within R0 agrees well with the sum of masses estimated via the virial theorem (1.2 × 10 12 M ) and from orbital motions (2.0 × 10 12 M ) of companions around M 81 and NGC 2403. We suggest that most of the dark matter in the group is concentrated around the luminous matter, allowing us to explain the observed asymmetry of the peculiar motions of the M 81 companions. M 81 itself has a peculiar velocity of about 130 km s −1 with respect to the local Hubble flow, but the centroid of the M 81/NGC 2403 complex is almost at rest with respect to Hubble flow (vpec < 35 km s −1 ).
The Faint Irregular Galaxies GMRT Survey (FIGGS) is a Giant Metrewave Radio Telescope (GMRT) based H I imaging survey of a systematically selected sample of extremely faint nearby dwarf irregular galaxies. The primary goal of FIGGS is to provide a comprehensive and statistically robust characterization of the neutral interstellar medium properties of faint, gas-rich dwarf galaxies. The FIGGS galaxies represent the extremely low mass end of the dwarf irregular galaxies population, with a median M B ∼ −13.0 and median H I mass of ∼3 × 10 7 M , extending the baseline in mass and luminosity space for a comparative study of galaxy properties. The H I data are supplemented with observations at other wavelengths. In addition, distances accurate to ∼10 per cent are available for most of the sample galaxies. This paper gives an introduction to FIGGS, describes the GMRT observations and presents the first results from the H I observations. From the FIGGS data, we confirm the trend of increasing H I to optical diameter ratio with decreasing optical luminosity; the median ratio of D H I /D Ho for the FIGGS sample is 2.4. Further, on comparing our data with aperture synthesis surveys of bright spirals, we find at best marginal evidence for a decrease in average surface density with decreasing H I mass. To a good approximation, the discs of gas-rich galaxies, ranging over three orders of magnitude in H I mass, can be described as being drawn from a family with fixed H I average surface density.
Abstract.We present an analysis of Hubble Space Telescope/WFPC2 images of nine nearby galaxies in Sculptor. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical accuracy of ∼12%.