A large-scale bulk flow of galaxy clusters

We report first results from the Streaming Motions of Abell Clusters (SMAC) project, an all-sky Fundamental Plane survey of 699 early-type galaxies in 56 clusters between similar to 3000 and similar to 14,000 km s(-1). For this sample, with a median distance of similar to 8000 km s(-1), we find a bulk flow of amplitude 630 +/- 200 km s(-1) toward I = 260 +/- 15 degrees, b = -1 +/-: 12 degrees with respect to the cosmic microwave background. The flow is robust against the effects of individual clusters and data subsets, the choice of Galactic extinction maps, Malmquist bias, and stellar population effects. The direction of the SMAC flow is similar to 90 degrees away from the flow found by Lauer & Postman, but it is in good agreement with the gravity dipole predicted from the distribution of X-ray-luminous clusters. Our detection of a high-amplitude coherent flow on such a large scale argues for excess mass density fluctuation power at wavelengths lambda greater than or similar to 60 h(-1) Mpc, relative to the predictions of currently popular cosmological models.