Ionization-induced star formation - III. Effects of external triggering on the initial mass function in clusters

We report on smoothed particle hydrodynamics simulations of the impact on a turbulent ∼2 × 103 M star-forming molecular cloud of irradiation by an external source of ionizing photons. We find that the ionizing radiation has a significant effect on the gas morphology, but a less important role in triggering stars. The rate and morphology of star formation are largely governed by the structure in the gas generated by the turbulent velocity field, and feedback has no discernible effect on the stellar initial mass function. Although many young stars are to be found in dense gas located near an ionization front, most of these objects also form when feedback is absent. Ionization has a stronger effect in diffuse regions of the cloud by sweeping up low-density gas that would not otherwise form stars into gravitationally unstable clumps. However, even in these regions, dynamical interactions between the stars rapidly erase the correlations between their positions and velocities and that of the ionization front.