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

Abstract

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. (2008). We concentrate on constraining parameters which are affected by the clustering of matter: sigma_8 and the growth index gamma. Assuming a concordance LCDM model we find sigma_8=0.91+0.22-0.18 and gamma=0.55+0.13-0.14 after marginalising over Omega_m. These constraints are consistent with, and have similar constraining power 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 LCDM. We find instead although a higher value of sigma_8 and a lower value of Omega_m are preferred, the values are still consistent when compared with WMAP5. 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 sigma_8. Its sensitivity to the derivative of growth function, particularly down to redshift zero, means it can provide a vital low redshift anchor on the evolution of structure formation. The importance of utilising different probes with varying systematics is also an essential requirement for providing a consistency check on the best-fitting cosmological model.