Spherical models of star clusters with potential escapers

Abstract

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 halos. 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%. 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 Gaia data in the outskirts of GCs, and, in turn, to formulate meaningful present-day constraints for GC formation scenarios in the early universe.

16 pages, 11 figures, submitted to MNRAS

References in corpus (16)

• A stellar census in globular clusters with MUSE: The contribution of rotation to cluster dynamics studied with 200 000 stars
• N-body modeling of globular clusters: Masses, mass-to-light ratios and intermediate-mass black holes
• Globular cluster number density profiles using Gaia DR2
• The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
• Kinematical fingerprints of star cluster early dynamical evolution
• Towards an N-body Model for the Globular Cluster M4
• Mass models of NGC 6624 without an intermediate-mass black hole
• Stellar envelopes of globular clusters embedded in dark mini-haloes
• The Tidal Tails of 47 Tucanae
• The central dynamics of M3, M13, and M92: Stringent limits on the masses of intermediate-mass black holes
• The Kinematic Richness of Star Clusters I. Isolated Spherical Models with Primordial Anisotropy
• An Approximate Analytic Model of a Star Cluster with Potential Escapers
• A flexible method to evolve collisional systems and their tidal debris in external potentials
• Searching in the dark: the dark mass content of the Milky Way globular clusters NGC288 and NGC6218
• Using globular clusters to test gravity in the weak acceleration regime
• The globular cluster NGC7492 and the Sagittarius tidal stream: together but unmixed

Cited by in corpus (8)

• Radii of Young Star Clusters in Nearby Galaxies
• The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2
• The dynamics of the globular cluster NGC3201 out to the Jacobi radius
• Multimass modelling of Milky Way globular clusters -- I. Implications on their stellar initial mass function above 1 M${}_{\odot }$
• Detecting Globular Cluster Tidal Extensions with Bayesian Inference: I. Analysis of $\omega$ Centauri with Gaia EDR3
• Modes of a stellar system II: non-ergodic systems
• Multiple Stellar Populations outside the tidal radius of NGC1851 through Gaia DR3 XP Spectra
• Hierarchical Bayesian Inference of Globular Cluster Properties