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

calculations, the angular momentum profiles are all quite similar in shape and
amplitude, especially in the innermost region. The central 100 M⊙ that will
later become the star-disk system in our calculation does not differ in angular
momentum from the other two calculations by more than a factor of 2 to 3. In
fact, in this mass range the simulation of Yoshida et al. (2006) tends to have
the highest angular momentum. The initial angular momentum distribution of
the star-forming gas thus seems fairly robust within the range of cosmological
parameter values sampled with these three simulations, and our overall result
should be correspondingly robust. We further note that Clark et al. (2008) find
that their non-cosmological simulation of a primordial gas cloud also resulted
in a profile very similar to the same two cosmological simulations, and upon
extending their calculation through the sink particle method they also found
extensive fragmentation.
However, the generality of our result will be best determined through
a more comprehensive set of simulations, aiming at studying fragmentation
over a range of minihalo spins. We will report on the results in a future work.
Finally, we expect that the effects from protostellar feedback, neglected here,
will likely dominate over those arising from variations in the initial conditions.
Again, this needs to be addressed with improved simulations.
2.6 Summary and Discussion
We have evolved a cosmological simulation until a primordial minihalo
has formed at z 20, and follow the subsequent collapse of the gas in its
center up to densities of n = 10 12 cm −3 . We find that the initial collapse,
leading to the formation of a small hydrostatic core, is very similar to pre-
vious high-resolution work. Subsequently, a disk-like structure grows around
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