RECONSTRUCTING POSITIONS AND PECULIAR VELOCITIES OF GALAXY CLUSTERS WITHIN 25,000 KILOMETERS PER SECOND - THE BULK VELOCITY

Using a dynamical three-dimensional reconstruction procedure, we estim ate the peculiar velocities of R greater than or equal to 0 Abell/ACO galaxy clusters from their measured redshift within 25,000 km s(-1). T he reconstruction algorithm relies on the linear gravitational instabi lity hypothesis, assumes linear biasing, and requires an input value o f the cluster beta-parameter (beta(c) = Omega(0)(0.6)/b(c)), which we estimated in Branchini & Plionis to be beta(c) similar or equal to 0.2 1. The resulting cluster velocity field is dominated by a large-scale streaming motion along the Perseus-Pisces/Great Attractor baseline dir ected toward the Shapley concentration, in qualitative agreement with the galaxy velocity field on smaller scales. Fitting the predicted clu ster peculiar velocities to a dipole term, in the Local Group frame an d within a distance of similar to 18,000 km s(-1), we recover extremel y well both the Local Group velocity and direction, in disagreement wi th the Lauer & Postman observation. However, we find a similar to 6% p robability that their observed velocity field could be a realization o f our corresponding one, if the latter is convolved with their large d istance-dependent errors. Our predicted cluster bulk velocity amplitud e agrees well with that deduced by the POTENT and the da Costa et al. analyses of observed galaxy motions at similar to 5000-6000 km s(-1); it decreases thereafter, while, at the Lauer & Postman limiting depth (similar to 15,000 km s(-1)), its amplitude is similar to 150 km s(-1) , in comfortable agreement with most cosmological models.