From hydrodynamics to N-body simulations of star clusters: mergers and
  rotation
  We present a new method to obtain more realistic initial conditions for
N-body simulations of young star clusters. We start from the outputs of
hydrodynamical simulations of molecular cloud collapse, in which star formation
is modelled with sink particles. In our approach, we instantaneously remove gas
from these hydrodynamical simulation outputs to mock the end of the
gas-embedded phase, induced by stellar feedback. We then enforce a realistic
initial mass function by splitting or joining the sink particles based on their
mass and position. Such initial conditions contain more consistent information
on the spatial distribution and the kinematical and dynamical states of young
star clusters, which are fundamental to properly study these systems. For
example, by applying our method to a set of previously run hydrodynamical
simulations, we found that the early evolution of young star clusters is
affected by gas removal and by the early dry merging of sub-structures. This
early evolution can either quickly erase the rotation acquired by our
(sub-)clusters in their embedded phase or "fuel" it by feeding of angular
momentum by sub-structure mergers, before two-body relaxation acts on longer
timescales.
