The Birth Mass Function of Pop III Stars

TL;DR

This study uses 3D radiation-hydrodynamical simulations to explore the formation, mass distribution, and feedback effects of Population III stars in primordial halos, revealing a top-heavy initial mass function with characteristic masses of 1-10 solar masses.

Contribution

First detailed 3D simulations of Pop III star formation showing multiple stars per halo and a top-heavy IMF with characteristic masses of 1-10 solar masses.

Findings

Multiple stars form in each primordial halo.

Pop III stars have a characteristic mass of 1-10 solar masses.

Stellar feedback influences star formation and final masses.

Abstract

Population III (Pop III) stars ended the cosmic Dark Ages and began early cosmological reionization and chemical enrichment. However, in spite of their importance to the evolution of the early Universe, their properties remain uncertain because of limitations to previous numerical simulations and the lack of any observational constraints. Here we investigate Pop III star formation in five primordial halos with 3D radiation-hydrodynamical cosmological simulations. We find that multiple stars form in each minihalo and that their numbers increase over time, with up to 23 stars forming in one of the halos. Radiative feedback from the stars generates strong outflows, deforms the surrounding protostellar disk, and delays star formation for a few thousand years. Star formation rates vary with halo and depend on mass accretion onto the disk, halo spin number, and the fraction of massive stars in the halo. Stellar masses in our models range from 0.1-37 $\rm M_{\odot}$, and of the 55 stars that form in our models twelve are $\rm > 10~ M_{\odot}$ and most of the others are 1-10 $\rm M_{\odot}$. Our simulations thus suggest that Pop III stars have characteristic masses of 1-10 $\rm M_{\odot}$ and a top-heavy IMF with dN/dM $\propto M_*^{-1.18}$. Up to 70\% of the stars are ejected from their disks by three-body interactions which, along with ionizing UV feedback, limits their final masses.