Orbital masses of nearby luminous galaxies

Abstract

We use observational properties of galaxies accumulated in the Updated Nearby Galaxy Catalog to derive a dark matter mass of luminous galaxies via motions of their companions. The data on orbital-to-stellar mass ratio are presented for 15 luminous galaxies situated within 11 Mpc from us: the Milky Way, M31, M81, NGC5128, IC342, NGC253, NGC4736, NGC5236, NGC6946, M101, NGC4258, NGC4594, NGC3115, NGC3627 and NGC3368, as well as for a composit suite around other nearby galaxies of moderate and low luminosity. The typical ratio for them is M_{orb}/M* = 31, corresponding to the mean local density of matter Omega_m = 0.09, i.e 1/3 of the global cosmic density. This quantity seems to be rather an upper limit of dark matter density, since the peripheric population of the suites may suffer from the presence of fictitious unbound members. We notice that the Milky Way and M31 haloes have lower dimensions and lower stellar masses than those of other 13 nearby luminous galaxies. However, the dark-to-stellar mass ratio for both the Milky Way and M31 is the typical one for other neighboring luminous galaxies. The distortion in the Hubble flow, observed around the Local Group and five other neighboring groups yields their total masses within the radius of zero velocity surface,R_0, which are slightly lower than the orbital and virial values. This difference may be due to the effect of dark energy, producing a kind of "mass defect" within R_0.