Testing lowered isothermal models with direct<i>N</i>-body simulations of globular clusters

Abstract

Several self-consistent models have been proposed, aiming at describing the\nphase space distribution of stars in globular clusters. This study explores the\nability of the recently proposed LIMEPY models (Gieles &amp; Zocchi) to reproduce\nthe dynamical properties of direct N-body models of a cluster in a tidal field,\nduring its entire evolution. These dynamical models include prescriptions for\nthe truncation and the degree of radially-biased anisotropy contained in the\nsystem, allowing us to explore the interplay between the role of anisotropy and\ntides in various stages of the life of star clusters. We show that the amount\nof anisotropy in an initially tidally underfilling cluster increases in the\npre-collapse phase, and then decreases with time, due to the effect of the\nexternal tidal field on its spatial truncation. This is reflected in the\ncorrespondent model parameters, and the best-fit models reproduce the main\nproperties of the cluster at all stages of its evolution, except for the phases\nimmediately preceding and following core collapse. We also notice that the\nbest-fit LIMEPY models are significantly different from isotropic King models,\nespecially in the first part of the evolution of the cluster. Our results put\nlimits on the amount of radial anisotropy that can be expected for clusters\nevolving in a tidal field, which is important to understand other factors that\ncould give rise to similar observational signatures, such as the presence of an\nintermediate-mass black hole.\n