Modeling the kinematics of globular cluster systems

TL;DR

This paper develops a model for globular cluster systems that combines formation, evolution, and kinematic data, calibrated with observations and applied to simulations to understand their origins and properties.

Contribution

It introduces a new model linking GC properties to galaxy formation, incorporating both in-situ and ex-situ clusters based on simulation data.

Findings

Ex-situ clusters dominate in outer galaxy regions.

Metallicity decreases outward due to accreted, metal-poor clusters.

Ex-situ GCs exhibit higher velocity dispersions and orbital actions.

Abstract

Globular clusters (GCs) are old massive star clusters that serve as `fossils' of galaxy formation. The advent of Gaia observatory has enabled detailed kinematics studies of the Galactic GCs and revolutionized our understanding of the connections between GC properties and galaxy assembly. However, lack of kinematic measurements of extragalactic GCs limits the sample size of GC systems that we can fully study. In this work, we present a model for GC formation and evolution, which includes positional and kinematic information of individual GCs by assigning them to particles in the Illustris TNG50-1 simulation based on age and location. We calibrate the three adjustable model parameters using observed properties of the Galactic and extragalactic GC systems, including the distributions of position, systemic velocity, velocity dispersion, anisotropy parameter, orbital actions, and metallicities. We also analyze the properties of GCs from different origins. In outer galaxy, ex-situ clusters are more dominant than the clusters formed in-situ. This leads to the GC metallicities decreasing outwards due to the increasing abundance of accreted, metal-poor clusters. We also find the ex-situ GCs to have greater velocity dispersions and orbital actions, in agreement with their accretion origin.