We have measured the cosmic momentum power spectrum from the peculiar velocities of galaxies in the SFI sample. The SFI catalog contains field spiral galaxies with radial peculiar velocities derived from the I-band Tully-Fisher relation. As a natural measure of the large-scale peculiar velocity field, we use the cosmic momentum field that is defined as the peculiar velocity field weighted by the local number of galaxies. We have shown that the momentum power spectrum can be derived from the density power spectrum for the constant linear biasing of galaxy formation, which makes it possible to estimate the βS = Ω/bS parameter precisely, where Ωm is the matter density parameter and bS is the bias factor for optical spiral galaxies. At each wavenumber k we estimate βS(k) as the ratio of the measured to the derived momentum power over a wide range of scales (0.026 h-1 Mpc k 0.157 h-1 Mpc) that spans the linear to the quasi-linear regimes. The estimated βS(k) have stable values around 0.5, which demonstrates the constancy of the βS parameter at scales down to 40?h-1 Mpc. We have obtained βS = 0.49 or Ωm = 0.30b and the amplitude of the mass fluctuation to be σ8Ω = 0.56. The 68% confidence limits include the cosmic variance. We have also estimated the mass density power spectrum. For example, at k = 0.1047?h Mpc-1 (λ = 60?h-1 Mpc) we measure ΩPδ(k) = 2.51 × 103 (h-1 Mpc)3, which is lower than the high-amplitude power spectra found from the previous maximum likelihood analyses of peculiar velocity samples such as Mark III, SFI, and ENEAR.
展开▼
