Stars quenching stars: How photoionization by local sources regulates gas cooling and galaxy formation

Current models of galaxy formation lack an efficient and physically constrained mechanism to regulate star formation (SF) in low and intermediate mass galaxies. We argue that the missing ingredient could be the effect of photoionization by local sources on the gas cooling. We show that the soft X-ray and EUV flux generated by SF is able to efficiently remove the main coolants (e.g. He+, O4+ and Fe8+) from the halo gas via direct photoionization. As a consequence, the cooling and accretion time of the gas surrounding star-forming galaxies may increase by one or two orders of magnitude. For a given halo mass and redshift, the effect is directly related to the value of the star formation rate (SFR). Our results suggest that the existence of a critical SFR above which 'cold' mode accretion is stopped, even for haloes with Mvir well below the critical shock-heating mass suggested by previous studies. The evolution of the critical SFR with redshift, for a given halo mass, resembles the respective steep evolution of the observed SFR for z < 1. This suggests that photoionization by local sources would be able to regulate gas accretion and SF, without the need for additional, strong feedback processes. © 2010 The Author. Journal compilation © 2010 RAS.