A Semi-analytic Framework of Population III and Subsequent Galaxy Formation on Cosmological N-body Simulations

TL;DR

This paper introduces a semi-analytic framework for modeling Population III and galaxy formation on cosmological simulations, accounting for feedback effects and streaming velocities, predicting supermassive star formation and high-redshift quasars.

Contribution

The framework self-consistently incorporates Lyman-Werner feedback and streaming velocities, improving modeling of Pop III star formation in cosmological simulations.

Findings

A top-heavy initial mass function for Pop III stars.

Existence of two peaks in Pop III star distribution at different redshifts.

Prediction of supermassive stars in atomic cooling halos at high redshift.

Abstract

We develop a new semi-analytic 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 the Pop III formation. Our model incorporates the Lyman-Werner feedback in a self-consistent way, therefore, the spatial variation of Lyman-Werner feedback naturally emerges. The Pop III mass depends on the properties of a halo as reproducing 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 Mpc/h and enough mass resolution to resolve Pop III-forming halos. A top-heavy initial mass function emerges and two peaks corresponding to the H$_2$ ($20 \lesssim z \lesssim 25$) and atomic cooling halos ($z \lesssim 15$) exist in the distribution. Supermassive stars can be formed in the atomic cooling halos, and the fractions of such supermassive stars increase with the value of streaming velocity. At least an 8 Mpc/h 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 $10^9$ Msun at z=7.5, which is enough to reproduce a high redshift quasar.