Evidence for Local Anisotropy of the Hubble Flow

Abstract

The Universe is accurately isotropic when measured by radio source counts and deep galaxy counts, or by the integrated microwave and X-ray backgrounds. On the other hand, galaxies are distributed in a decidedly clumpy way on scales of a few tens of megaparsecs, and it is natural therefore to ask whether galaxy redshifts show systematic departures from Hubble's law when averaged over similar scales. Discussions of this question have tended to develop along lines fixed by ideas for what might be reasonable patterns of deviations from Hubble's law. If the coherence length of the effect is large enough, it makes sense to expand the redshift field in a power series in distance, just as Oort (55) did for the velocity field in the Galaxy. This has been a convenient approach in theoretical discussions, but so far has proved to be only moderately useful as a framework for analysis of the data, perhaps because one coherence length contains too few independent groups of galaxies. A second framework is based on the thought that the mass concentration in a cluster of galaxies might induce a more or less radial flow toward the cluster in the surrounding field (24). In