Fourth moments and the dynamics of spherical systems

Abstract

An investigation of the fourth moment of velocity data from the globular cluster Omega Cen demonstrates that useful constraints can be obtained from a dataset of only 300 velocities. The fourth moment of this sample is shown to be inconsistent with an isotropic velocity distribution and suggests that the orbits become predominantly radial at large radii. A more complete analysis of this and other systems awaits larger and more homogeneous samples. 18 refs.