# Kinematical evolution of tidally limited star clusters: rotational properties

## TL;DR

This study uses N-body simulations to analyze how star clusters' rotational properties evolve over time due to internal relaxation and external tidal effects, revealing persistent rotation even after significant mass loss.

## Contribution

It provides the first detailed simulation-based analysis of the long-term evolution of rotational properties in tidally limited star clusters, linking angular momentum loss to mass loss.

## Key findings

- Rotation decreases as clusters lose mass and evolve.
- Clusters retain measurable rotation even after extensive relaxation.
- Simulation results align with observed kinematic complexity in Galactic globular clusters.

## Abstract

We present the results of a set of N-body simulations following the long-term evolution of the rotational properties of star cluster models evolving in the external tidal field of their host galaxy, after an initial phase of violent relaxation. The effects of two-body relaxation and escape of stars lead to a redistribution of the ordered kinetic energy from the inner to the outer regions, ultimately determining a progressive general loss of angular momentum; these effects are reflected in the overall decline the rotation curve as the cluster evolves and loses stars. We show that all of our models share the same dependence of the remaining fraction of the initial rotation on the fraction of the initial mass lost. As the cluster evolves and loses part of its initial angular momentum, it becomes increasingly dominated by random motions, but even after several tens of relaxation times, and losing a significant fraction of its initial mass, a cluster can still be characterized by a non-negligible ratio of the rotational velocity to the velocity dispersion. This result is in qualitative agreement with the recently observed kinematical complexity which characterizes several Galactic globular clusters.