CLUSTERING DUE TO CLUSTER GALAXIES

This paper presents a calculation of the contribution that galaxies in clusters make towards the clustering exhibited by all galaxies. It is shown that, within observational uncertainties, cluster galaxies may be responsible for all the clustering measured by the galaxy-galaxy correlation function, xi-gg(r). This extends Peebles's result that cluster galaxies make a significant contribution to the two-point function on a scale of 1 h-1 Mpc. (h is the value of Hubble's constant in units of 100 km s-1 Mpc-1.) This then accounts for the apparent paradox that the two-point correlation function in redshift space is elongated along the line-of-sight on scales where xi-gg(r) is significantly less than unity. It has previously been argued that the elongation is a direct indication of non-linear dynamical effects. This result also suggests that n-point correlation functions do little more than probe cluster structure on scales up to 10 h-1 Mpc. The variance of the galaxy density field is also considered and used to place constraints on the amplitude of the cluster-galaxy cross-correlation function.