CLUSTER DIPOLE ANALYSIS AS A TEST OF DARK-MATTER MODELS

This work is devoted to the study of the dipole structure in the distr ibution of galaxy clusters and to the constraints that it gives on dar k-matter models. We use simulations of the cluster distribution, based on the Zel'dovich approximation, starting from different dark - matte r models. The aim of our analysis is to check to what extent the obser ved structure of the cluster dipole represents a constraint for DM mod els. Our main results can be summarised as follows. Local Group like o bservers are likely produced in Omega(0)=1 models, quite irrespectivel y of the detailed power-spectrum shape, while they are more rare in th e Omega(0)=0.2 CDM models. Misalignment between the directions of the CMB and cluster dipoles like that observed occurs quite often, althoug h an accurate alignment is not always guaranteed. About 30%, 40% of th e observers measure a misalignment below 20 degrees. The observed clus ter dipole amplitude is more typical in the four high-density (Omega(0 )=1) models than in the low-density (Omega(0)=0.2) ones. Independent e stimates of the cluster biasing factor in the simulations allows to wo rk out the value of Omega(0) from cluster dipoles. It turns out that t he input value (Omega(0)=1 or 0.2) is recovered quite well, thus suppo rting the reliability of cluster dipole to measure the average matter density in the Universe.