Photoionization and Triggered Star Formation in SPH simulations
A. Burkert, T. Naab, S. Walch, F. Heitsch
We study the structural evolution of turbulent molecular clouds under the influence of ionizing radiation emitted from a nearby massive star by performing a high-resolution parameter study with the smoothed particle hydrodynamics (SPH) code iVINE. In our simulations, the ionizing radiation enhances the initial turbulent density distribution and thus leads to the formation of pillar-like structures observed adjacent to HII regions in a natural way. Gravitational collapse occurs regularly at the tips of the structures. We find a clear correlation between the initial state of the turbulent cold cloud and the final morphology and physical properties of the structures formed.
The most favorable regime for the formation of pillars is Mach 4–10. Structures and therefore stars only form if the initial density contrast between the high-density unionized gas and the gas that is going to be ionized is lower than the temperature contrast between the hot and the cold gas. The density of the resulting pillars is determined by a pressure equilibrium between the hot and the cold gas. A thorough analysis of the simulations shows that the complex kinematical and geometrical structure of the formed elongated filaments reflects that of observed pillars to an impressive level of detail.
We then continue to show the first results of a novel implementation of ionizing radiation by point-sources into the SPH-code SEREN, employing a Monte-Carlo approach. This approach enables us to simulate the ionization of the turbulent ISM by several massive stars. We present first results on the disruption of molecular clouds by the photoionization of distributed versus clustered O/B stars.