Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...

we use a ray-tracing scheme to follow the growth of the star’s H ii region once
it has become massive enough to ionize the surrounding gas. We compare this
to a simulation with the same initialization but no radiative feedback. This
allows for a direct evaluation of how radiative feedback alters the mass growth
of Pop III stars, the rate of disk fragmentation, and the formation of additional
stars within the disk. We describe our numerical methodology in Chapter 3.2,
while in Chapter 3.3 we present our results. We conclude in Chapter 3.4.
3.2 Numerical Methodology
3.2.1 Initial Setup
We ran our simulation using GADGET 2, a widely-tested three-dimensional
N-body and SPH code (Springel 2005). We initialized our simulation using a
snapshot from the previous simulation of Stacy et al. (2010). In particular, we
chose the snapshot in which the dense gas in the center of the minihalo has
first reached 10 8 cm −3 . This simulation was originally initialized at z = 100
in a periodic box of length 140 kpc (comoving) using both SPH and DM par-
ticles. This was done in accordance with a ΛCDM cosmology with ΩΛ = 0.7,
ΩM = 0.3, ΩB = 0.04, and H0 = 70 km s −1 Mpc −1 . To accelerate struc-
ture formation, we used an artificially enhanced normalization of the power
spectrum, σ8 = 1.4. As discussed in Stacy et al. (2010), we verified that the
density and velocity fields in the center of the minihalo closely resembled those
in previous simulations. We furthermore found that the angular momentum
profile of the minihalo gas immediately before initial sink formation was very
similar to the cosmological simulations of Abel et al. (2002) and Yoshida et al.
(2006), despite their lower values of σ8 (0.7 and 0.9, respectively).
The high resolution of our simulation was achieved through a standard
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