Testing Newtonian Gravity with AAOmega: Mass-to-Light Profiles of Four
  Globular Clusters
  Testing Newtonian gravity in the weak-acceleration regime is vital to our
understanding of the nature of the gravitational interaction. It has recently
been claimed that the velocity dispersion profiles of several globular clusters
flatten out at large radii, reminiscent of galaxy rotation curves, even though
globular clusters are thought to contain little or no dark matter. We
investigate this claim, using AAOmega observations of four globular clusters,
namely M22, M30, M53 and M68. M30, one such cluster that has had this claim
made for its velocity dispersion, was included for comparison with previous
studies. We find no statistically significant flattening of the velocity
dispersion at large radii for any of our target clusters and therefore we infer
the observed dynamics do not require that globular clusters are dark matter
dominated, or a modification of gravity. Furthermore, by applying a simple
dynamical model we determine the radial mass-to-light profiles for each
cluster. The isothermal rotations of each cluster are also measured, with M22
exhibiting clear rotation, M68 possible rotation and M30 and M53 lacking any
rotation, within the uncertainties.
