The impacts of ultraviolet radiation feedback on galaxies during the epoch of reionization

We explore the impacts of ultraviolet (UV) radiation feedback on galaxies during the epoch of reionization by cosmological simulations in which hydrodynamics and the transfer of the H and He ionizing photons are consistently coupled. Moreover, we take into account H-2 non-equilibrium chemistry, including photodissociation. The most striking feature of the simulations is a high spatial resolution for the radiative transfer (RT) calculation which enables us to start considering not only external UV feedback processes but also internal UV feedback processes in each galaxy. We find that the star formation is significantly suppressed due to the internal UV and supernova (SN) feedback. In low-mass galaxies with M < 10(9) M-circle dot, a large amount of gas is evacuated by photoevaporation as previous studies have shown, which results in the suppression of star formation. Surprisingly, star formation in massive haloes is also strongly suppressed despite the fact that these haloes hardly lose any gas by photoevaporation. The suppression of star formation in massive haloes is mainly caused by the following two factors: (i) small-scale clumpy structures in the galaxies are smoothened by the internal feedback; (ii) although the dense gas in the galaxies is mostly neutral, the H-2 formation and cooling processes are disturbed by mild photoheating. Photodissociating radiations actually suppress star formation, but the magnitude of the effect is not so large in massive galaxies. Even though our simulation volume is too small to be a representative patch of the Universe during reionization, we find that our simulated star formation rate densities and HI fractions at z similar to 6-7 are consistent with those found in observations.