Ionizing feedback from massive stars in massive clusters III: Disruption
  of partially unbound clouds
  We extend our previous SPH parameter study of the effects of photoionization
from O-stars on star-forming clouds to include initially unbound clouds. We
generate a set of model clouds in the mass range $10^{4}-10^{6}$M$_{\odot}$
with initial virial ratios $E_{\rm kin}/E_{\rm pot}$=2.3, allow them to form
stars, and study the impact of the photoionizing radiation produced by the
massive stars. We find that, on the 3Myr timescale before supernovae are
expected to begin detonating, the fractions of mass expelled by ionizing
feedback is a very strong function of the cloud escape velocities. High-mass
clouds are largely unaffected dynamically, while lower-mass clouds have large
fractions of their gas reserves expelled on this timescale. However, the
fractions of stellar mass unbound are modest and significant portions of the
unbound stars are so only because the clouds themselves are initially partially
unbound. We find that ionization is much more able to create well-cleared
bubbles in the unbound clouds, owing to their intrinsic expansion, but that the
presence of such bubbles does not necessarily indicate that a given cloud has
been strongly influenced by feedback. We also find, in common with the bound
clouds from our earlier work, that many of the systems simulated here are
highly porous to photons and supernova ejecta, and that most of them will
likely survive their first supernova explosions.
