The redshift-distance relation. IX - Perturbation of the very nearby velocity field by the mass of the Local Group

The deceleration of the very local cosmological velocity field that is expected as a result of the mass of the Local Group is studied. It is shown that a deceleration may be present in the available data for galaxies and groups of galaxies with distances less than 10 Mpc. The effect is small, near the limit of detection, meaning that the velocity field is very nearly linear. The mass of the Local Group is less than 5×1012Mₛun; from the available data and the deceleration method. The best fit to the data gives MLG = 4×1011Mₛun;, giving a mass-to-light ratio of ≡3. Massive halos with M/L ⪆ 100 for either the Galaxy or for M31 are excluded by the data. The variation of the Hubble v/r ratio with distance is very small beyond 2 Mpc for any reasonable mass of the Local Group. This means that the decelerating effect of the Local Group cannot be invoked to explain any supposed large variation of H with distance locally.