Richard de Grijs

Hierarchical star formation in the local Universe

We investigate the hierarchical architecture of star formation in the Magellanic Clouds and contrast our results with recently obtained Galactic star-formation properties. We show that the morphologies of hierarchically nested clusters become increasingly round as we progress to smaller spatial scales, and that this trend reflects a real change in morphology rather than observational artifacts. We propose that this trend reflects young stellar populations transitioning from the fractal state characteristic of newly formed stellar ensembles to the dynamically relaxed state that characterises older bound stellar populations, including open and globular clusters. We find that our hierarchical cluster sample transitions to a dynamically relaxed state at a characteristic size scale of approximately 0.80 pc and a characteristic free-fall time of ≤ 2 Myr. In addition, we explore the clustering properties and stellar luminosity functions of the young, main-sequence stellar populations. Our analysis allows us to conclude that the observed hierarchy is driven by supersonic turbulence.