Formation and Radiative Feedback of First Objects and First Galaxies

TL;DR

This paper uses advanced simulations to study the formation, feedback, and evolution of the first stars and galaxies, revealing smaller initial objects, multiple star formation, and significant effects on cosmic reionization.

Contribution

It provides new insights into the mass scale of first objects, star formation processes, and ionizing photon escape, improving understanding of early universe evolution.

Findings

First objects can form in dark matter haloes of ~10^4 M_sun.

Multiple stars can form in 10^5 M_sun haloes due to feedback.

UV feedback influences ionizing photon escape and star formation rates.

Abstract

First, the formation of first objects driven by dark matter is revisited by high-resolution hydrodynamic simulations. It is revealed that dark matter haloes of ~10^4M_sun can produce first luminous objects with the aid of dark matter cusps. Therefore, the mass of first objects is smaller by roughly two orders of magnitude than in the previous prediction. This implies that the number of Pop III stars formed in the early universe could be significantly larger than hitherto thought. Secondly, the 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 form in a 10^5M_sun 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 the photo-dissociation can reduce the mass accretion rate onto protostars. Also, protostars as small as 0.8M_sun may be ejected and evolve with keeping their mass, which might be detected as "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* 10^9M_sun, while it reduces the star formation rate significantly. This may have a momentous impact on the cosmic reionization.