The Hierarchical Distribution of the Young Stellar Clusters in Six Local
  Star Forming Galaxies
  We present a study of the hierarchical clustering of the young stellar
clusters in six local (3--15 Mpc) star-forming galaxies using Hubble Space
Telescope broad band WFC3/UVIS UV and optical images from the Treasury Program
LEGUS (Legacy ExtraGalactic UV Survey). We have identified 3685 likely clusters
and associations, each visually classified by their morphology, and we use the
angular two-point correlation function to study the clustering of these stellar
systems. We find that the spatial distribution of the young clusters and
associations are clustered with respect to each other, forming large, unbound
hierarchical star-forming complexes that are in general very young. The
strength of the clustering decreases with increasing age of the star clusters
and stellar associations, becoming more homogeneously distributed after ~40--60
Myr and on scales larger than a few hundred parsecs. In all galaxies, the
associations exhibit a global behavior that is distinct and more strongly
correlated from compact clusters. Thus, populations of clusters are more
evolved than associations in terms of their spatial distribution, traveling
significantly from their birth site within a few tens of Myr whereas
associations show evidence of disruption occurring very quickly after their
formation. The clustering of the stellar systems resembles that of a turbulent
interstellar medium that drives the star formation process, correlating the
components in unbound star-forming complexes in a hierarchical manner,
dispersing shortly after formation, suggestive of a single, continuous mode of
star formation across all galaxies.
