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Abstract: Based on recent findings of a formation mechanism of substructure in tidaltails by Kuepper, Macleod and Heggie 2008 we investigate a more comprehensiveset of N-body models of star clusters on orbits about a Milky-Way-likepotential. We find that the predicted epicyclic overdensities arise in anytidal tail no matter which orbit the cluster follows as long as the clusterlives long enough for the overdensities to build up.The distance of the overdensities along the tidal tail from the clustercentre depends for circular orbits only on the mass of the cluster and thestrength of the tidal field, and therefore decreases monotonically with time,while for eccentric orbits the orbital motion influences the distance, causinga periodic compression and stretching of the tails and making the distanceoscillate with time. We provide an approximation for estimating the distance ofthe overdensities in this case.We describe an additional type of overdensity which arises in extended tidaltails of clusters on eccentric orbits, when the acceleration of the tidal fieldon the stellar stream is no longer homogeneous. Moreover, we conclude that apericentre passage or a disk shock is not the direct origin of an overdensitywithin a tidal tail. Escape due to such tidal perturbations does not take placeimmediately after the perturbation but is rather delayed and spread over theorbit of the cluster. All observable overdensities are therefore of thementioned two types. In particular, we note that substructured tidal tails donot imply the existence of dark-matter sub-structures in the haloes ofgalaxies.

Author: A.H.W. Kuepper, P. Kroupa, H. Baumgardt, D.C. Heggie

Source: https://arxiv.org/

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