Abstract
We present a new semi-analytic model of the formation of the first stars. Our
method takes dark matter halo merger trees (including 3-dimensional spatial
information) from cosmological N-body simulations as input and applies analytic
prescriptions to compute both the Population III (Pop III) and metal-enriched
star formation histories. We have developed a novel method to accurately
compute the major feedback processes affecting Pop III star formation: H$_2$
photodissociation from Lyman-Werner (LW) radiation, suppression of star
formation due to inhomogeneous reionization, and metal enrichment via
supernovae winds. Our method utilizes a grid-based approach relying on fast
Fourier transforms (FFTs) to rapidly track the LW intensity, ionization
fraction, and metallicity in 3-dimensions throughout the simulation box. We
present simulations for a wide range of astrophysical model parameters from
$z30-6$. Initially long-range LW feedback and local metal enrichment
and reionization feedback dominate. However, for $z 15$ we find that
the star formation rate density (SFRD) of Pop III stars is impacted by the
combination of external metal enrichment (metals from one halo polluting other
pristine halos) and inhomogeneous reionization. We find that the interplay of
these processes is particularly important for the Pop III SFRD at $z łesssim
10$. Reionization feedback delays star formation long enough for metal bubbles
to reach halos that would otherwise form Pop III stars. Including these effects
can lead to more than an order of magnitude decrease in the Pop III SFRD at
$z=6$ compared to LW feedback alone.
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