The effect of photoionising feedback on the shaping of
  hierarchically-forming stellar clusters
  We use two hydrodynamical simulations (with and without photoionising
feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing
global hierarchical collapse (GHC), to study the effect of the feedback on the
structural and kinematic properties of the gas and the stellar clusters formed
in the clouds. During this early stage, the evolution of the two simulations is
very similar (implying that the feedback from low mass stars does not affect
the cloud-scale evolution significantly) and the star-forming region accretes
faster than it can convert gas to stars, causing the instantaneous measured
star formation efficiency (SFE) to remain low even in the absence of
significant feedback. Afterwards, the ionising feedback first destroys the
filamentary supply to star-forming hubs and ultimately removes the gas from it,
thus first reducing the star formation (SF) and finally halting it. The
ionising feedback also affects the initial kinematics and spatial distribution
of the forming stars, because the gas being dispersed continues to form stars,
which inherit its motion. In the non-feedback simulation, the groups remain
highly compact and do not mix, while in the run with feedback, the gas
dispersal causes each group to expand, and the cluster expansion thus consists
of the combined expansion of the groups. Most secondary star-forming sites
around the main hub are also present in the non-feedback run, implying a
primordial rather than triggered nature. We do find one example of a peripheral
star-forming site that appears only in the feedback run, thus having a
triggered origin. However, this appears to be the exception rather than the
rule, although this may be an artifact of our simplified radiative transfer
scheme.
