Branchini Enzo, Plionis Manolis
Astrophysical Journal v.460, p.569
Publication year: 1996


Starting from the observed distribution of Abell/ACO galaxy clusters in redshift space, we use a two-step procedure to recover their distances and peculiar velocities. After statistically correcting for the unobserved cluster distribution in the zone of avoidance and also for a smooth absorption at higher latitudes, we use a dynamical iterative algorithm, based on that published by Strauss & Davis in 1988, to recover the real-space cluster positions by minimizing the redshift-space distortions. The whole procedure assumes that clusters trace the mass, that peculiar velocities are caused by gravity, and that linear perturbation theory applies. The amplitude of the cluster dipole measured in real space turns out to be ~23% less than that measured in redshift space. In both cases the dipole direction is aligned with the cosmic microwave background dipole within ~10^deg^, taking into account the Virgocentric infall component of the Local Group motion. Using linear theory we obtain β_c_( = {OMEGA}_0_^0.6^/b_c_) ~ 0.21(+/- 0.03), where the uncertainty is due to observational errors and limitations in the reconstruction procedure, while the intrinsic cosmological variance amounts to ~0.07. This β_c_ value implies that for a cluster-mass bias parameter of b_c_ <~ 5, a flat universe is not excluded, contrary to previous cluster-dipole z-space analysis. A more stringent determination of β_c_ will be obtained from the analysis of the peculiar velocity field in a forthcoming paper.