Power Spectrum of Cosmic Momentum Field Measured from the Sfi Galaxy Sample

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 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 βS = Ω 0.6 m /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 hMpc . k . 0.157 hMpc) that spans the linear to the quasi-linear regimes. The estimated βS(k)’s have stable values around 0.5, which demonstrates the constancy of βS parameter at scales down to 40 h Mpc. We have obtained βS = 0.49 +0.08 −0.05 or Ωm = 0.30 +0.09 −0.05b 5/3 S , and the amplitude of mass fluctuation as σ8Ω 0.6 m = 0.56 +0.27 −0.21. The 68% confidence limits include the cosmic variance. We have also estimated the mass density power spectrum. For example, at k = 0.1047 hMpc (λ = 60 hMpc) we measure Ω m Pδ(k) = (2.51 +0.91 −0.94) × 10 3 (hMpc), which is lower compared to the high-amplitude power spectra found from the previous maximum likelihood analyses of peculiar velocity samples like Mark III, SFI, and ENEAR. Subject headings: cosmology: theory — cosmology: large-scale structure of universe