A Semianalytic Framework of Population III and Subsequent Galaxy Formation on Cosmological <i>N</i> -body Simulations

Abstract We develop a new semianalytic framework of Population (Pop) III and subsequent galaxy formation designed to run on dark matter halo merger trees. In our framework, we consider the effect of the Lyman–Werner flux from Pop III and II stars and the dark matter baryon streaming velocity on the critical halo mass for Pop III formation. Our model incorporates the Lyman–Werner feedback in a self-consistent way; therefore, the spatial variation of Lyman–Werner feedback emerges naturally. The Pop III mass depends on the properties of a halo, which is designed to reproduce radiative hydrodynamical simulation results. We perform statistical studies of Pop III stars by applying this framework to high-resolution cosmological N -body simulations with a maximum box size of 16 h −1 Mpc and enough mass resolution to resolve Pop III-forming halos. A top-heavy initial mass function emerges and two peaks corresponding to the H 2 (20 ≲ z ≲ 25) and atomic cooling halos ( z ≲ 15) exist in the distribution. Supermassive stars can be formed in the atomic cooling halos, and the fraction of such supermassive stars increases with the value of streaming velocity. At least an 8 h −1 Mpc simulation box and the self-consistent model for the Lyman–Werner feedback are necessary to correctly model the Pop III formation in the atomic cooling halos. Our model predicts one supermassive star per halo with several 10 9 M ⊙ at z = 7.5, which is enough to reproduce a high-redshift quasar.