Streaming motions of galaxy clusters within 12000 km/s - V. The peculiar   velocity field
  We analyze in detail the peculiar velocity field traced by 56 clusters within 120 h^-1 Mpc in the Streaming Motions of Abell Clusters (SMAC) sample. The bulk flow of the SMAC sample is 687 +- 203 km/s, toward l = 260 +- 13, b = 0 +- 11. We discuss possible systematic errors and show that no systematic effect is larger than half of the random error. The flow does not drop off significantly with depth, which suggests that it is generated by structures on large scales. In particular, a Great Attractor as originally proposed by Lynden-Bell et al. cannot be responsible for the SMAC bulk flow. The SMAC data suggest infall into an attractor at the location of the Shapley Concentration, but the detection is marginal (at the 90% confidence level). We find that distant attractors in addition to the Shapley Concentration are required to explain the SMAC bulk flow. A comparison with peculiar velocities predicted from the IRAS PSCz redshift survey shows good agreement with a best fit value of Beta_I = Omega^0.6/b_I = 0.39 +- 0.17. However, the PSCz density field is not sufficient to acount for all of the SMAC bulk motion. We also detect, at the 98% confidence level, a residual bulk flow of 372 +- 127 km/s toward l = 273, b = 6 which must be generated by sources not included in the PSCz catalogue, that is, either beyond 200 h^-1 Mpc, in the Zone of Avoidance or in superclusters undersampled by IRAS. Finally, we compare the SMAC bulk flow with other recent measurements. We suggest that a bulk flow of 225 km/s toward l = 300, b = 10 at depths greater than 60 h^-1 Mpc is consistent with all peculiar velocity surveys, when allowance is made for sparse sampling effects. (abridged) 
Michael J. Hudson, Russell J. Smith, John R. Lucey and Enzo Branchini