Redshift-space distortions and the real-space clustering of different galaxy types

We study the distortions induced by peculiar velocities on the redshift-space correlation function of galaxies of different morphological types in the Pisces-Perseus redshift survey. Redshift-space distortions affect early and late-type galaxies in different ways. In particular, at small separations the dominant effect comes from virialized cluster cores, where ellipticals are the dominant population. The net result is that a meaningful comparison of the clustering strength of different morphological types can be performed only in real space, i.e., after projecting out the redshift distortions on the two-point correlation function ξ(r_p, π). A power-law fit to the projected function w_p(r_p) on scales smaller than 10 h^-1 Mpc gives r₀ = 8.35_-0.76^+0.75 h^-1 Mpc, γ = 2.05_-0.08^+0.10 for the early-type population, and r₀ = 5.55_-0.45^+0.40 h^-1 Mpc, γ = 1.73_-0.08^+0.07 for spirals and irregulars. These values are derived for a sample luminosity limited to M_Zw ≤ -19.5. We detect a 25% increase of r₀ with luminosity for all types combined, from M_Zw = -19 to -20. In the framework of a simple stable clustering model for the mean streaming of pairs, we estimate σ₁₂(1), the one-dimensional pairwise velocity dispersion between 0 and 1 h^-1 Mpc, to be 865_-165⁺²⁵⁰ km s^-1 for early-type galaxies and 345_-65⁺⁹⁵ km s^-1 for late types. This latter value should be a fair estimate of the pairwise dispersion for "field" galaxies; it is stable with respect to the presence or absence of clusters in the sample, and is consistent with the values found for noncluster galaxies and IRAS galaxies at similar separations.