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Kinematical fingerprints of star cluster early dynamical evolution
Journal article   Open access

Kinematical fingerprints of star cluster early dynamical evolution

Enrico Vesperini, Anna Lisa Varri, Stephen L. W. McMillan and Stephen E. Zepf
Monthly notices of the Royal Astronomical Society, v 443(1), pp L79-L83
01 Sep 2014
url
https://doi.org/10.1093/mnrasl/slu088View
Published, Version of Record (VoR)Maybe Open Access (Publisher Bronze) Open

Abstract

Astronomy & Astrophysics Physical Sciences Science & Technology
We study the effects of the external tidal field on the violent relaxation phase of star clusters dynamical evolution, with particular attention to the kinematical properties of the equilibrium configurations emerging at the end of this phase. We show that star clusters undergoing the process of violent relaxation in the tidal field of their host galaxy can acquire significant internal differential rotation and are characterized by a distinctive radial variation of the velocity anisotropy. These kinematical properties are the result of the symmetry breaking introduced by the external tidal field in the collapse phase and of the action of the Coriolis force on the orbit of the stars. The resulting equilibrium configurations are characterized by differential rotation, with a peak located between one and two half-mass radii. As for the anisotropy, similar to clusters evolving in isolation, the systems explored in this Letter are characterized by an inner isotropic core, followed by a region of increasing radial anisotropy. However, for systems evolving in an external tidal field, the degree of radial anisotropy reaches a maximum in the cluster intermediate regions and then progressively decreases, with the cluster outermost regions being characterized by isotropy or a mild tangential anisotropy. Young or old but less-relaxed dynamically young star clusters may keep memory of these kinematical fingerprints of their early dynamical evolution.

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