The Structural Evolution of Forming and Early Stage Star Clusters

TL;DR

This study investigates how the spatial distribution of stars in young clusters becomes smoother over time, revealing the effects of dynamical processes in early cluster evolution.

Contribution

It provides empirical evidence of the correlation between substructure dissipation and dynamical age in young star clusters, using statistical analysis of observational data.

Findings

Smoother stellar distributions are found closer to cluster centers.

Higher surface density regions show less substructure.

Dissipation of substructure occurs rapidly in young clusters.

Abstract

We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young ($\sim$1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) Survey and the statistical analysis of the Angular Dispersion Parameter, $\delta_{\rm ADP}$. We find statistically significant correlation between $\delta_{\rm ADP}$ and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters.