Kinematical evolution of tidally limited star clusters: rotational properties

Abstract

We present the results of a set of N-body simulations following the long-term\nevolution of the rotational properties of star cluster models evolving in the\nexternal tidal field of their host galaxy, after an initial phase of violent\nrelaxation. The effects of two-body relaxation and escape of stars lead to a\nredistribution of the ordered kinetic energy from the inner to the outer\nregions, ultimately determining a progressive general loss of angular momentum;\nthese effects are reflected in the overall decline the rotation curve as the\ncluster evolves and loses stars.\n We show that all of our models share the same dependence of the remaining\nfraction of the initial rotation on the fraction of the initial mass lost. As\nthe cluster evolves and loses part of its initial angular momentum, it becomes\nincreasingly dominated by random motions, but even after several tens of\nrelaxation times, and losing a significant fraction of its initial mass, a\ncluster can still be characterized by a non-negligible ratio of the rotational\nvelocity to the velocity dispersion. This result is in qualitative agreement\nwith the recently observed kinematical complexity which characterizes several\nGalactic globular clusters.\n