The Kinematic State of the Local Volume

Abstract

The kinematics of galaxies with 10 megaparsecs (10 Mpc) of the Milky Way is investigated using published distances and radial velocities. With respect to the average Hubble flow (isotropic or simple anisotropic), there is NO systematic relation between peculiar velocity dispersion and absolute magnitude over a range of 10 magnitudes; neither is there any apparent variation with galaxy type or between field and cluster members. There are several possible explanations for the lack of variation, though all have difficulties: either there is no relationship between light and mass on these scales, or the peculiar velocities are not produced by gravitational interaction, or the background dynamical picture is wrong in some systematic way. The extremely cold local flow of 40-60 km/s dispersion reported by some authors is shown to be an artifact of sparse data, a velocity dispersion of over 100 km/s being closer to the actual value. Galaxies with a high (positive) radial velocity have been selected against in studies of this volume, biasing numerical results.

arXiv commentaastex preprint, 40 figures, accepted by ApJ. Miscalculation of absolute magnitudes corrected. No significant changes in conclusions

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