Formation and radiative feedback of first objects and first galaxies

Abstract

Firstly, the formation of first objects driven by dark matter is revisited by high-resolution hydrodynamic simulations. It is revealed that dark matter halos of∼104 M can produce first luminous objectswith the aid of darkmatter cusps. Therefore, themass of first objects is smaller by roughly two orders of magnitude than in the previous prediction. This implies that the number of Population III stars formed in the early universe could be significantly larger than hitherto thought. Secondly, feedback by photo-ionization and photo-dissociation photons in the first objects is explored with radiation hydrodynamic simulations, and it is demonstrated that multiple stars can formin a 105 M halo. Thirdly, the fragmentation of an accretion disk around a primordial protostar is explored with photo-dissociation feedback. As a result, it is found that photo-dissociation can reduce the mass accretion rate onto protostars. Also, protostars as small as 0.8 M may be ejected and evolve while keeping their mass, which might be detected as the "real first stars" in the Galactic halo. Finally, state-of-the-art radiation hydrodynamic simulations are performed to investigate the internal ionization of first galaxies and the escape of ionizing photons. We find that UV feedback by forming massive stars enhances the escape fraction even in a halo as massive as > 6 × 109 M, while it reduces the star formation rate significantly. This may have a momentous impact on cosmic reionization.