Velocity Dipoles in Cold Dark Matter Cosmologies

Galaxy velocity dipoles are calculated in the frame of a cold dark matter scenario for galaxy formation, allowing the primordial spectral index n and the density parameter Omega0 to take values smaller than the standard ones n = 1, Omega = 1. Different values for the bias parameter b are also considered. Constraints on n, Omega0, and b are obtained by applying a maximum likelihood test to velocity dipoles deduced from a sample of elliptical galaxies, a sample of spiral galaxies, and the motion of the Local Group. The observed galaxy bulk flows favor a flat, or nearly flat, model with a low value for the spectral index and a modest amount of bias.