Cluster dipole analysis as a test of dark matter models

This work is devoted to the study of the dipole structure in the distribution of galaxy clusters and to the constraints that it gives on dark-matter models. We use simulations of the cluster distribution, based on the Zel'dovich approximation, starting from different dark - matter models. The aim of our analysis is to check to what extent the observed structure of the cluster dipole represents a constraint for DM models. Our main results can be summarised as follows. Local Group like observers are likely produced in Omega(0)=1 models, quite irrespectively of the detailed power-spectrum shape, while they are more rare in the Omega(0)=0.2 CDM models. Misalignment between the directions of the CMB and cluster dipoles like that observed occurs quite often, although an accurate alignment is not always guaranteed. About 30%, 40% of the observers measure a misalignment below 20 degrees. The observed cluster 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 estimates of the cluster biasing factor in the simulations allows to work out the value of Omega(0) from cluster dipoles. It turns out that the input value (Omega(0)=1 or 0.2) is recovered quite well, thus supporting the reliability of cluster dipole to measure the average matter density in the Universe.