Streaming Velocities as a Dynamical Estimator of Ω

It is well known that estimating the mean pairwise velocity of galaxies v12 from the redshift space galaxy correlation function is difficult because this method is highly sensitive to the assumed model of the pairwise velocity dispersion. Here we propose an alternative method to estimate v12 directly from peculiar velocity samples, which contain redshift-independent distances as well as galaxy redshifts. In contrast to other dynamical measures which determine β≡Ω0.6σ8, this method can provide an estimate of Ω0.6σ28 for a range of σ8, where Ω is the cosmological density parameter, while σ8 is the standard normalization for the power spectrum of density fluctuations. We demonstrate how to measure this quantity from realistic catalogs.