The dynamics of the outer parts of omega Centauri
  The multi-object fibre-fed spectrograph AAOmega at the Anglo-Australian
Telescope has been used to establish and measure accurate (<1 kms-1) radial
velocities for a new sample of members in the outer parts of the stellar system
omega Centauri. The new sample more than doubles the number of known members
with precise velocities that lie between 25' and 45' from the cluster center.
Combining this sample with earlier work confirms that the line-of-sight
velocity dispersion of omega Cen remains approximately constant at ~6.5 kms-1
in the outer parts of the cluster, which contain only a small fraction of the
total cluster stellar mass. It is argued that the approximately constant
velocity dispersion in the outer regions is most likely a consequence of
external influences, such as the tidal shock heating that occurs each time
omega Cen crosses the Galactic plane. There is therefore no requirement to
invoke dark matter or non-standard gravitational theories.
