Rotating Globular Clusters

TL;DR

This paper applies advanced axisymmetric rotating models to analyze the internal dynamics and morphology of three globular clusters, revealing the role of rotation and anisotropy in their structure and evolution.

Contribution

It introduces a new family of self-consistent rotating models and demonstrates their effectiveness in interpreting the kinematics and shapes of multiple globular clusters.

Findings

47 Tuc is well explained by the model with rotation accounting for its morphology.

M15's rotation profile and ellipticity are consistent with the model predictions.

Omega Cen's complex kinematics are reproduced, highlighting partial relaxation effects.

Abstract

Internal rotation is considered to play a major role in the dynamics of some globular clusters. However, in only few cases it has been studied by quantitative application of realistic and physically justified global models. Here we present a dynamical analysis of the photometry and three-dimensional kinematics of omega Cen, 47 Tuc, and M15, by means of a recently introduced family of self-consistent axisymmetric rotating models. The three clusters, characterized by different relaxation conditions, show evidence of differential rotation and deviations from sphericity. The combination of line-of-sight velocities and proper motions allows us to determine their internal dynamics, predict their morphology, and estimate their dynamical distance. The well-relaxed cluster 47 Tuc is very well interpreted by our model; internal rotation is found to explain the observed morphology. For M15, we provide a global model in good agreement with the data, including the central behavior of the rotation profile and the shape of the ellipticity profile. For the partially relaxed cluster omega Cen, the selected model reproduces the complex three-dimensional kinematics; in particular the observed anisotropy profile, characterized by a transition from isotropy, to weakly-radial anisotropy, and then to tangential anisotropy in the outer parts. The discrepancy found for the steep central gradient in the observed line-of-sight velocity dispersion profile and for the ellipticity profile is ascribed to the condition of only partial relaxation of this cluster and the interplay between rotation and radial anisotropy.