Shellflow. I. The Convergence of the Velocity Field at 6000 Kilometers per Second

Open Access
Publisher Website
Google Scholar
Abstract
We present the first results from the Shellflow program, an all-sky Tully-Fisher (TF) peculiar-velocity survey of 276 Sb-Sc galaxies with redshifts between 4500 and 7000 km s-1. Shellflow was designed to minimize systematic errors between observing runs and between telescopes, thereby removing the possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the data yields a bulk-flow amplitude of Vbulk = 70 km s-1 (1 σ error) with respect to the cosmic microwave background, i.e., consistent with being at rest. At the 95% confidence level, the flow amplitude is -1. Our results are insensitive to which Galactic extinction maps we use, and to the parameterization of the TF relation. The larger bulk motion found in analyses of the Mark III peculiar-velocity catalog are thus likely to be due to nonuniformities between the subsamples making up Mark III. The absence of bulk flow is consistent with the study of Giovanelli and collaborators and flow-field predictions from the observed distribution of IRAS galaxies.