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The properties of energetically unbound stars in stellar clusters

Claydon, Ian, Gieles, Mark and Zocchi, A (2017) The properties of energetically unbound stars in stellar clusters Monthly Notices of the Royal Astronomical Society, 466 (4). pp. 3937-3950.

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Several Milky Way star clusters show a roughly flat velocity dispersion profile at large radii, which is not expected from models with a tidal cut-off energy. Possible explanations for this excess velocity include: the effects of a dark matter halo, modified gravity theories and energetically unbound stars inside of clusters. These stars are known as potential escapers (PEs) and can exist indefinitely within clusters which are on circular orbits. Through a series of N-body simulations of star cluster systems, where we vary the galactic potential, orbital eccentricity and stellar mass function, we investigate the properties of the PEs and their effects on the kinematics. We derive a prediction for the scaling of the velocity dispersion at the Jacobi surface due to PEs, as a function of cluster mass, angular velocity of the cluster orbit, and slope of the mass profile of the host galaxy. We see a tentative signal of the mass and orbital velocity dependence in kinematic data of globular clusters from literature. We also find that the fraction of PEs depends sensitively on the galactic mass profile, reaching as high as 40% in the cusp of a Navarro-Frenk-White profile and as the velocity anisotropy also depends on the slope of the galactic mass profile, we conclude that PEs provide an independent way of inferring the properties of the dark matter mass profile at the galactic radius of (globular) clusters in the Gaia-era

Item Type: Article
Subjects : Physics
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Zocchi, A
Date : 12 January 2017
DOI : 10.1093/mnras/stw3309
Copyright Disclaimer : This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords : galaxies: kinematics and dynamics - galaxies: star clusters - methods: analytical - methods: N-body simulations.
Depositing User : Symplectic Elements
Date Deposited : 16 Dec 2016 14:14
Last Modified : 16 Jan 2019 17:10

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