The Structural Evolution of Forming and Early Stage Star 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, ${\delta }_{\mathrm{ADP}}$. We find statistically significant correlation between ${\delta }_{\mathrm{ADP}}$ 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.

ApJ accepted, 7 pages, 5 figures

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• The Structure of the Young Star Cluster NGC 6231. I. Stellar Population
• The stellar content of the infalling molecular clump G286.21+0.17
• The evolution of protoplanetary disc radii and disc masses in star-forming regions
• Report on Optimal Substructure Techniques for Stellar, Gas and Combined Samples
• The Great Planetary Heist: Theft and capture in star-forming regions