The Structural Evolution of Forming and Early Stage Star Clusters
  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.
