paper

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

arXiv:astro-ph/0509740 · doi:10.1086/498258

Abstract

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 β_S = Ω_m^{0.6} / b_S parameter precisely where Ω_m is the matter density parameter and b_S is the bias factor for optical spiral galaxies. At each wavenumber k we estimate β_S(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 β_S(k)'s have stable values around 0.5, which demonstrates the constancy of β_S parameter at scales down to 40 h^{-1}Mpc. We have obtained β_S=0.49_{-0.05}^{+0.08} or Ω_m = 0.30_{-0.05}^{+0.09} b_S^{5/3}, and the amplitude of mass fluctuation as σ_8Ω_m^{0.6}=0.56_{-0.21}^{+0.27}. 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 Ω_m^{1.2} P_δ(k)=(2.51_{-0.94}^{+0.91})\times 10^3 (h^{-1}Mpc)^3, 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.

arXiv comment12 pages, 9 figures, accepted for publication in ApJ

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