RECONSTRUCTING POSITIONS AND PECULIAR VELOCITIES OF GALAXY CLUSTERS WITHIN 25,000 KILOMETERS PER SECOND - THE CLUSTER REAL-SPACE DIPOLE

Starting from the observed distribution of Abell/ACO galaxy clusters i n redshift space, we use a two-step procedure to recover their distanc es and peculiar velocities. After statistically correcting for the uno bserved cluster distribution in the zone of avoidance and also for a s mooth absorption at higher latitudes, we use a dynamical iterative alg orithm, based on that published by Strauss & Davis in 1988, to recover the real-space duster positions by minimizing the redshift-space dist ortions. The whole procedure assumes that clusters trace the mass, tha t peculiar velocities are caused by gravity, and that linear perturbat ion theory applies. The amplitude of the cluster dipole measured in re al space turns out to be similar to 23% less than that measured in red shift space. In both cases the dipole direction is aligned with the co smic microwave background dipole within similar to 10 degrees, taking into account the Virgocentric infall component of the Local Group moti on. Using linear theory we obtain beta(c)(=Omega(0)(0.6)/b(c)) approxi mate to 0.21(+/-0.03), where the uncertainty is due to observational e rrors and limitations in the reconstruction procedure, while the intri nsic cosmological variance amounts to similar to 0.07. This beta(c) va lue implies that for a cluster-mass bias parameter of b(c) less than o r similar to 5, a flat universe is not excluded, contrary to previous cluster-dipole z-space analysis. A more stringent determination of bet a(c) will be obtained from the analysis of the peculiar velocity field in a forthcoming paper.