Clustering of luminous red galaxies - II. Small-scale redshift-space distortions

This is the second paper of a series where we study the clustering of luminous red galaxies (LRG) in the recent spectroscopic Sloan Digital Sky Survey (SDSS) data release, DR6, which has 75 000 LRG covering over 1 Gpc 3 h -3 for 0.15 < z < 0.47. Here, we focus on modelling redshift-space distortions in ( , ), the two-point correlation in separate line-of-sight and perpendicular directions, at small scales and in the line-of-sight. We show that a simple Kaiser model for the anisotropic two-point correlation function in redshift space, convolved with a distribution of random peculiar velocities with an exponential form, can describe well the correlation of LRG on all scales. We show that to describe with accuracy the so-called 'fingers-of-God' (FOG) elongations in the radial direction, it is necessary to model the scale dependence of both bias b and the pairwise rms peculiar velocity 12 with the distance. We show how both quantities can be inferred from the ( , ) data. From r 10 Mpc h -1 to r 1 Mpc h -1 , both the bias and 12 are shown to increase by a factor of 2: from b = 2 to 4 and from 12 = 400 to 800 km s -1 . The latter is in good agreement, within a 5 per cent accuracy in the recovered velocities, with direct velocity measurements in dark matter simulations with m = 0.25 and 8 = 0.85.