Peculiar velocities into the next generation: cosmological parameters from the SFI++ survey

We present cosmological parameter constraints from the SFI++ galaxy peculiar velocity survey, the largest galaxy peculiar velocity sample to date. The analysis is performed by using the gridding method developed in Abate et al. We concentrate on constraining parameters which are affected by the clustering of matter: σ₈ and the growth index γ. Assuming a concordance Λ cold dark matter (ΛCDM) model, we find σ₈= 0.91^+0.22_−0.18 and γ= 0.55^+0.13_−0.14 after marginalizing over Ω_m. These constraints are consistent with, and have constraining power similar to, the same constraints from other current data sets which use different methods. Recently, there have been several claims that the peculiar velocity measurements do not agree with ΛCDM. Instead, we find that, although a higher value of σ₈ and a lower value of Ω_m are preferred, the values are still consistent when compared with Wilkinson Microwave Anisotropy Probe 5 results. We note that although our analysis probes a variety of scales, the constraints will be dominated by the smaller scales, which have the smallest uncertainties. These results show that peculiar velocity analysis is a vital probe of cosmology, providing competitive constraints on parameters such as σ₈. Its sensitivity to the derivative of growth function, particularly down to redshift zero, means that it can provide a vital low redshift anchor on the evolution of structure formation. The importance of utilizing different probes with varying systematics is also an essential requirement for providing a consistency check on the best-fitting cosmological model.