Kinematic substructure in star clusters constrains star cluster formation

TL;DR

This study analyzes the kinematic substructure of 48 young star clusters, finding most support the hierarchical formation model over the monolithic one based on spatial and velocity data.

Contribution

It provides empirical evidence favoring the hierarchical model of star cluster formation through kinematic substructure analysis.

Findings

39 clusters show significant hierarchical substructure

Most clusters are incompatible with the monolithic formation model

Kinematic substructure supports hierarchical formation theory

Abstract

The spatial-kinematic structure of 48 young star clusters and associations is investigated. Moran's $I$ statistic is used to quantify the degree of kinematic substructure in each region, and the results are compared to those expected assuming the hierarchical or monolithic models of star cluster formation. Of the observed regions, 39 are found to have significant kinematic substructure, such that they are compatible with the hierarchical model and incompatible with the monolithic model. This includes multiple regions whose $Q$ parameter shows the region to be centrally concentrated and clustered. The remaining nine are compatible with both models. From this it is concluded that the kinematic substructure of the observed star clusters represents strong evidence in favour the hierarchical model of star cluster formation over the monolithic model.