Photoionising feedback and the star formation rates in galaxies

Aims. We investigate the effects of ionising photons on accretion and stellar mass growth in a young star forming region, using a Monte Carlo radiation transfer code coupled to a smoothed particle hydrodynamics (SPH) simulation.

Methods. We introduce the framework with which we correct stellar cluster masses for the effects of photoionising (PI) feedback and compare to the results of a full ionisation hydrodynamics code.

Results. We present results of our simulations of star formation in the spiral arm of a disk galaxy, including the effects of photoionising radiation from high mass stars. We find that PI feedback reduces the total mass accreted onto stellar clusters by ≈23% over the course of the simulation and reduces the number of high mass clusters, as well as the maximum mass attained by a stellar cluster. Mean star formation rates (SFRs) drop from SFR_{control = 4.2 × 10^-2 M⊙} yr^-1 to SFR_{MCPI = 3.2 × 10^-2 M⊙} yr^-1 after the inclusion of PI feedback with a final instantaneous SFR reduction of 62%. The overall cluster mass distribution appears to be affected little by PI feedback.

Conclusions. We compare our results to the observed extra-galactic Schmidt-Kennicutt relation and the observed properties of local star forming regions in the Milky Way and find that internal photoionising (PI) feedback is unlikely to reduce SFRs by more than a factor of approximate to 2 and thus may play only a minor role in regulating star formation.