Gas expulsion in highly substructured embedded star clusters
  We investigate the response of initially substructured, young, embedded star
clusters to instantaneous gas expulsion of their natal gas. We introduce
primordial substructure to the stars and the gas by simplistically modelling
the star formation process so as to obtain a variety of substructure
distributed within our modelled star forming regions. We show that, by
measuring the virial ratio of the stars alone (disregarding the gas
completely), we can estimate how much mass a star cluster will retain after gas
expulsion to within 10% accuracy, no matter how complex the background
structure of the gas is, and we present a simple analytical recipe describing
this behaviour. We show that the evolution of the star cluster while still
embedded in the natal gas, and the behavior of the gas before being expelled,
are crucial processes that affect the timescale on which the cluster can evolve
into a virialized spherical system. Embedded star clusters that have high
levels of substructure are subvirial for longer times, enabling them to survive
gas expulsion better than a virialized and spherical system. By using a more
realistic treatment for the background gas than our previous studies, we find
it very difficult to destroy the young clusters with instantaneous gas
expulsion. We conclude that gas removal may not be the main culprit for the
dissolution of young star clusters.
