  We present hydrodynamic and magnetohydrodynamic (MHD) simulations of sub
galactic regions including photoionising and supernova feedack. We aim to
improve the initial conditions of our region extraction models by including an
initial population of stars. We also investigate the reliability of extracting
regions in simulations, and show that with a good choice of region, results are
comparable with using a larger region for the duration of our simulations.
Simulations of star formation on molecular cloud scales typically start with a
turbulent cloud of gas, from which stars form and then undergo feedback. In
reality, a typical cloud or region within a galaxy may already include, or
reside near some population of stars containing massive stars undergoing
feedback. We find the main role of a prior population is triggering star
formation, and contributing to gas dynamics. Early time supernova from the
initial population are important in triggering new star formation and driving
gas motions on larger scales above 100 pc, whilst the ionising feedback
contribution from the initial population has less impact, since many members of
the initial population have cleared out gas around them in the prior model. In
terms of overall star formation rates though, the initial population has a
relatively small effect, and the feedback does not for example suppress
subsequent star formation. We find that MHD has a relatively larger impact than
initial conditions, reducing the star formation rate by a factor of 3 at later
times.
