Streaming velocities as a dynamical estimator of Ω

It is well known that estimating the pairwise velocity of galaxies, v 12 , 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 v 12 directly from peculiar velocity samples, which contain redshift-independent distances as well as galaxy redshifts. In contrast to other dynamical measures which determine β ≡ Ω 0.6 σ 8 , this method can provide an estimate of Ω 0.6 σ 8 2 for a range of σ 8 where Ω is the cosmological density parameter, while σ 8 is the standard normalization for the power spectrum of density fluctuations. We demonstrate how to measure this quantity from realistic catalogues.