Total masses of the Local Group and M 81 group derived from the local Hubble flow

Abstract

Based on accurate measurements of distances to nearby galaxies made with Hubble Space Telescope, we determined the radii of the zero-velocity surface: R_0 = 0.96+-0.03 Mpc for the Local Group and R_0 = 0.89+-0.05 Mpc for the group of galaxies around M81/M82. This yields the total masses of the groups to be M_T = (1.29+-0.14) 10^{12} M_sun and M_T = (1.03+-0.17) 10^{12} M_sun, respectively. The R_0-method allowed us to determine the mass ratio of the brightest two members in the considered groups. Based on the minimum scatter of galaxies with respect to the Hubble regression, we derived a mass ratio of 0.8 : 1.0 for the Milky Way and Andromeda, and 0.54 : 1.00 for M82 and M81, which is quite close to the ratio of luminosities of these galaxies.