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Spherical models of star clusters with potential escapers

Claydon, Ian, Gieles, Mark, Varri, Anna Lisa, Heggie, Douglas C and Zocchi, Alice (2019) Spherical models of star clusters with potential escapers Monthly Notices of the Royal Astronomical Society, 487 (1). pp. 147-160.

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An increasing number of observations of the outer regions of globular clusters (GCs) have shown a flattening of the velocity dispersion profile and an extended surface density profile. Formation scenarios of GCs can lead to different explanations of these peculiarities, therefore the dynamics of stars in the outskirts of GCs are an important tool in tracing back the evolutionary history and formation of star clusters. One possible explanation for these features is that GCs are embedded in dark matter haloes. Alternatively, these features are the result of a population of energetically unbound stars that can be spatially trapped within the cluster, known as potential escapers (PEs). We present a prescription for the contribution of these energetically unbound members to a family of self-consistent, distribution function-based models, which, for brevity, we call the Spherical Potential Escapers Stitched (SPES) models. We show that, when fitting to mock data of bound and unbound stars from an N-body model of a tidally limited star cluster, the SPES models correctly reproduce the density and velocity dispersion profiles up to the Jacobi radius, and they are able to recover the value of the Jacobi radius itself to within 20 per cent. We also provide a comparison to the number density and velocity dispersion profiles of the Galactic cluster 47 Tucanae. Such a case offers a proof of concept that an appropriate modelling of PEs is essential to accurately interpret current and forthcoming Gaia data in the outskirts of GCs, and, in turn, to formulate meaningful present-day constraints for GC formation scenarios in the early Universe.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Varri, Anna Lisa
Heggie, Douglas C
Zocchi, Alice
Date : 4 May 2019
Funders : Royal Society, European Research Council, Carnegie Trust for the Universities of Scotland
DOI : 10.1093/mnras/stz1109
Grant Title : University Research Fellowship
Copyright Disclaimer : This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (
Uncontrolled Keywords : Methods: analytical. Methods: numerical. Stars: kinematics and dynamics. Globular clusters: general. Open clusters and associations: general. Galaxies: star clusters: general.
Depositing User : Clive Harris
Date Deposited : 12 Jun 2019 07:46
Last Modified : 12 Jun 2019 07:46

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