Anisotropies in the Motions and Positions of the Galactic Globular Clusters

Abstract

The velocity ellipsoid for 38 globular clusters with [Fe/H] <= -1.0 is derived and shown to be significantly anisotropic with major axis directed towards low Galactic latitude. Principal axes of the spatial distribution of different groups of clusters are derived and compared with the velocity ellipsoid. The metal poor cluster spatial distribution is significantly flattened along an axis which coincides within the uncertainties with the major axis of the velocity ellipsoid. Given the observed steep age-metallicity relation for metal poor clusters, one speculative interpretation of the data is that an initially flattened filament underwent a relatively rapid initial transverse collapse forming satellite galaxies and metal poor globular clusters while the protogalaxy collapsed and assembled more slowly along the filament acquiring and/or redistributing angular momentum in the process.