  We present the results of a survey of radial velocities over a wide region
extending from r~10 arcmin out to r~80 arcmin (~1.5 tidal radii) within the
massive star cluster omega Centauri. The survey was performed with FLAMES@VLT,
to study the velocity dispersion profile in the outer regions of this stellar
system. We derived accurate radial velocities for a sample of 2557 newly
observed stars, identifying 318 bona-fide cluster red giants. Merging our data
with those provided by Pancino et al. (2007), we assembled a final homogeneous
sample of 946 cluster members that allowed us to trace the velocity dispersion
profile from the center out to r~32 arcmin. The velocity dispersion appears to
decrease monotonically over this range, from a central value of sigma_{v}~17.2
Km/s down to a minimum value of sigma_{v}~5.2 Km/s. The observed surface
brightness profile, rotation curve, velocity dispersion profile and ellipticity
profile are simultaneously well reproduced by a simple dynamical model in which
mass follows light, within the classical Newtonian theory of gravitation. The
comparison with an N-body model of the evolution of a system mimicking omega
Cen during the last 10 orbits into the Galactic potential suggests that (a) the
rotation of stars lying in the inner ~20 arcmin of the clusters is not due to
the effects of the tidal field of the Milky Way, as hypothized by other
authors, and (b) the overall observational scenario is still compatible with
the possibility that the outer regions of the cluster are subject to some tidal
stirring.
