Redshift space clustering of galaxies and cold dark matter model

The distortion effect of peculiar velocities on the power spectrum and correlation function of galaxies in redshift space is investigated over a large range of scales, from ∼1 to 400 h^-1 Mpc, using large-scale computer simulations of cold dark matter models. The results are compared with observations of optical and IRAS galaxies. The distortion effect is observed to be large; it significantly changes the shape of the power spectrum. For Ω= 1, the redshift space power spectrum is enhanced by a factor of nearly 2 over the real space spectrum on large scales, and is decreased by a factor of about 5 on small scales, resulting in a considerably steeper spectrum in redshift space than in real space. A direct comparison of observations and simulations in redshift space reveals that, contrary to previous suggestions, the power spectrum of IRAS galaxies, as well as optical galaxies, is consistent with the spectrum of the standard cold dark matter (CDM) model. The problems that an Ω=1 CDM model currently faces, such as too large perculiar velocities on small scales, may be related more to the high value of Ω in the model rather than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data. It appears that the redshift-space power spectrum alone is rather insensitive to Ω for CDM models for scales ≤ 200 h^-1 Mpc.