Hierarchical Star Formation in Turbulent Media: Evidence from Young Star
  Clusters
  We present an analysis of the positions and ages of young star clusters in
eight local galaxies to investigate the connection between the age difference
and separation of cluster pairs. We find that star clusters do not form
uniformly but instead are distributed such that the age difference increases
with the cluster pair separation to the 0.25-0.6 power, and that the maximum
size over which star formation is physically correlated ranges from ~200 pc to
~1 kpc. The observed trends between age difference and separation suggest that
cluster formation is hierarchical both in space and time: clusters that are
close to each other are more similar in age than clusters born further apart.
The temporal correlations between stellar aggregates have slopes that are
consistent with turbulence acting as the primary driver of star formation. The
velocity associated with the maximum size is proportional to the galaxy's
shear, suggesting that the galactic environment influences the maximum size of
the star-forming structures.
