Linear Redshift Distortions: A Review

Redshift maps of galaxies in the Universe are distorted by the peculiar velocities of galaxies along the line of sight. The amplitude of the distortions on large, linear scales yields a measurement of the linear redshift distortion parameter, which is $\beta \approx \Omega_0^{0.6}/b$ in standard cosmology with cosmological density $\Omega_0$ and light-to-mass bias $b$. All measurements of $\beta$ from linear redshift distortions published up to mid 1997 are reviewed. The average and standard deviation of the reported values is $\beta_{optical} = 0.52 \pm 0.26$ for optically selected galaxies, and $\beta_{IRAS} = 0.77 \pm 0.22$ for IRAS selected galaxies. The implied relative bias is $b_{optical}/b_{IRAS} \approx 1.5$. If optical galaxies are unbiased, then $\Omega_0 = 0.33^{+0.32}_{-0.22}$, while if IRAS galaxies are unbiased, then $\Omega_0 = 0.63^{+0.35}_{-0.27}$.