Investigating dynamical properties of globular clusters through a family of lowered isothermal models

Abstract

ABSTRACT To investigate the dynamical properties of globular clusters, surface brightness and kinematic data were collected and fitted to a family of lowered isothermal models called limepy models. For the 18 globular clusters studied, the amounts of concentration, truncation, and anisotropy were determined. In addition, the cluster mass, half-mass radius, distance, and mass-to-light ratio were also obtained. In general, limepy models can describe these clusters well. Among these 18 clusters, NGC 5139, 6388, and 7078 have been claimed to be candidates for hosting intermediate-mass black holes in the literature. The models could not appropriately fit the central proper-motion velocity dispersion of NGC 5139, nor the slope of the proper-motion velocity dispersion profile of NGC 6388. Thus, more dedicated models with intermediate-mass black holes or a group of stellar-mass black holes at cluster centres may need to be considered. Regarding NGC 7078, our model with some degree of anisotropy can fit the data. Finally, a strong concentration–truncation anticorrelation and a truncation–semimajor-axis correlation were revealed, which could be the observational imprint of the dynamical evolution of globular clusters.