The Birth Mass Function of Pop III Stars
  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.
