A simple two-component description of energy equipartition and mass segregation for anisotropic globular clusters

Abstract

In weakly collisional stellar systems such as some globular clusters, partial energy equipartition and mass segregation are expected to develop as a result of the cumulative effect of stellar encounters even in systems initially characterized by star-mass independent density and energy distributions. In parallel, numerical simulations have demonstrated that radially-biased pressure anisotropy slowly builds up in realistic models of globular clusters from initial isotropic conditions, leading to anisotropy profiles that, to some extent, mimic those resulting from incomplete violent relaxation known to be relevant to elliptical galaxies. In this paper we consider a set of realistic simulations realized by means of Monte Carlo methods and analyze them by means of self-consistent two-component models. For the purpose, we refer to an underlying distribution function, originally conceived to describe elliptical galaxies, that has been recently truncated and adapted to the context of globular clusters. The two components are meant to represent light stars (combining all main sequence stars) and heavy stars (giants, dark remnants, and binaries). We show that this conceptually simple family of two-component truncated models provides a reasonable description of simulated density, velocity dispersion, and anisotropy profiles, especially for the most relaxed systems, with the capability to express quantitatively the attained levels of energy equipartition and mass segregation. In contrast, two-component isotropic models based on the King distribution function do not offer a comparably satisfactory representation of the simulated globular clusters. With this work we provide a new reliable diagnostic tool applicable to nonrotating globular clusters that are characterized by significant gradients in the local value of the mass-to-light ratio, beyond the commonly used one-component dynamical models.

18 pages, 18 figures, 7 tables. Accepted for publication in Astronomy & Astrophysics

References in corpus (12)

• A stellar census in globular clusters with MUSE: The contribution of rotation to cluster dynamics studied with 200 000 stars
• Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. I. Sample Selection, Data Reduction and NGC 7078 Results
• Hubble Space Telescope proper motion (HSTPROMO) catalogs of Galactic globular clusters. II. Kinematic profiles and maps
• The eye of Gaia on globular clusters kinematics: internal rotation
• Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. V. The rapid rotation of 47 Tuc traced and modeled in three dimensions
• Differences in the rotational properties of multiple stellar populations in M 13: a faster rotation for the "extreme" chemical subpopulation
• The Gaia-ESO Survey: Kinematics of seven Galactic globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XVIII. Proper-motion kinematics of multiple stellar populations in the core regions of NGC 6352
• A study of rotating globular clusters - the case of the old, metal-poor globular cluster NGC 4372
• The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2
• On the Link Between Energy Equipartition and Radial Variation in the Stellar Mass Function of Star Clusters
• Characterization of the velocity anisotropy of accreted globular clusters

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