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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 TullyFisher 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 S ¼ 0:6 m /b S parameter precisely, where m is the matter density parameter and b S is the bias factor for optical spiral galaxies. At each wavenumber k we estimate S (k) as the ratio of the measured to the derived momentum power over a wide range of scales (0:026 h À1 Mpc P k P 0:157 h À1 Mpc) that spans the linear to the quasi-linear regimes. The estimated S (k) have stable values around 0.5, which demonstrates the constancy of the S parameter at scales down to 40 h À1 Mpc. , 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. Subject headingg s: cosmology: theory -large-scale structure of universe