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

the existence of a pressure deficit around the sink that otherwise would yield
an artificially high accretion rate (see Bromm et al. 2002; Martel et al. 2006).
However, the sink can still evolve in position and velocity due to gravitational
and hydrodynamical interactions.
The sink particle method is very useful for various reasons. It elimi-
nates the need to incorporate chemistry, hydrodynamics and radiative transfer
at extremely high densities (n > 10 12 cm −3 ). More importantly, by stopping
the density growth at n > 10 12 cm −3 , the method allows the evolution of
the region of interest to be followed for many dynamical times. Without the
sink particle method, this would be computationally challenging because the
increasing density would lead to prohibitively small numerical timesteps, a
problem sometimes called ‘Courant myopia’. Finally, the sink particle method
allows for a direct measurement of the angular momentum growth and the
accretion rate onto the high-density region instead of having to indirectly ex-
trapolate this from the instantaneous density and velocity profiles at the end
of the simulation (e.g. Abel et al. 2002; Yoshida et al. 2006).
4.3 Results
4.3.1 Sink Growth and Angular Momentum
4.3.1.1 Accretion Rate
The first minihalo within the cosmological box forms at z 20. The
subsequent evolution of the central region of the minihalo to densities of n =
10 12 cm −3 is described in Stacy et al. (2010). The growth of the first sink
that forms, which will be referred to as sink A, is similar to that found in
Bromm and Loeb (2004) as well as Stacy et al. (2010). The mass growth
is especially similar to that in Stacy et al. (2010) for the first few hundred
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