Investigating Dynamical Properties of Globular Clusters through a Family of Lowered Isothermal Models

TL;DR

This study uses lowered isothermal models called LIMEPY to analyze the dynamical properties of 18 globular clusters, revealing correlations and limitations in modeling clusters with potential black holes.

Contribution

It applies the LIMEPY family of models to fit observational data of globular clusters, providing new insights into their dynamical parameters and evolution.

Findings

LIMEPY models fit most clusters well

Identified concentration-truncation anti-correlation

Highlighted need for models with black holes for some clusters

Abstract

To investigate the dynamical properties of globular clusters, the surface brightness and kinematic data were collected and fitted to a family of lowered isothermal models called LIMEPY models. For 18 studied globular clusters, 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 could describe these clusters well. Among these 18 clusters, NGC 5139, NGC 6388, and NGC 7078 were claimed to be candidates to host intermediate-mass black holes in literature. The models could not appropriately fit the central proper-motion velocity dispersion of NGC 5139 and the slope of 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 centers may need to be considered. Considering NGC 7078, our model with some degree of anisotropy can fit the data. Finally, the strong concentration-truncation anti-correlation and truncation-semimajor-axis correlation were revealed, which could be the observational imprint of the dynamical evolution of globular clusters.