Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...
Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...
Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...
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h = 0.7. To acceler<strong>at</strong>e structure form<strong>at</strong>ion, we chose an artificially enhanced<br />
normaliz<strong>at</strong>ion <strong>of</strong> the power spectrum <strong>of</strong> σ8 = 1.4. We have verified th<strong>at</strong> the<br />
density and velocity fields in the center <strong>of</strong> the minihalo are very similar to<br />
previous simul<strong>at</strong>ions. Even though we used an artificially high value <strong>of</strong> σ8,<br />
the angular momentum pr<strong>of</strong>ile <strong>of</strong> our minihalo just before sink form<strong>at</strong>ion was<br />
still very similar to th<strong>at</strong> <strong>of</strong> other cosmological simul<strong>at</strong>ions which used lower<br />
σ8 values. In particular, the cosmological simul<strong>at</strong>ion <strong>of</strong> Yoshida et al. (2006),<br />
which used σ8 = 0.9, and th<strong>at</strong> <strong>of</strong> Abel et al. (2002), which used σ8 = 0.7,<br />
resulted in minihalo pr<strong>of</strong>iles which were especially similar to ours on the smaller<br />
scales from which the mass <strong>of</strong> the sinks is accreted. This demonstr<strong>at</strong>es th<strong>at</strong> our<br />
realiz<strong>at</strong>ion leads to conditions th<strong>at</strong> are typical for primordial star form<strong>at</strong>ion<br />
(see the discussion in <strong>Stacy</strong> et al. 2010).<br />
To achieve high resolution we employed a standard hierarchical zoom-in<br />
procedure (see <strong>Stacy</strong> et al. 2010 for further details). This involved adding three<br />
additional nested refinement levels <strong>of</strong> length 40, 30, and 20 kpc (comoving)<br />
centered on the site where the first minihalo will form. Each level <strong>of</strong> higher<br />
refinement replaces particles from the lower level with eight child particles<br />
such th<strong>at</strong> in the final simul<strong>at</strong>ion a parent particle is replaced <strong>by</strong> up to 512<br />
child particles. <strong>The</strong> highest-resolution gas particles have a mass <strong>of</strong> mSPH =<br />
0.015 M⊙. <strong>The</strong>refore, the mass resolution <strong>of</strong> the refined simul<strong>at</strong>ion is: Mres <br />
1.5NneighmSPH < ∼ 1 M⊙, where Nneigh 32 is the typical number <strong>of</strong> particles in<br />
the SPH smoothing kernel (e.g. B<strong>at</strong>e and Burkert 1997). <strong>The</strong> main difference<br />
between the current simul<strong>at</strong>ion and th<strong>at</strong> described in <strong>Stacy</strong> et al. (2010) is<br />
th<strong>at</strong> we now record the angular momenta and velocities <strong>of</strong> the sink-accreted<br />
particles before they become incorpor<strong>at</strong>ed into the sinks. This allows us to<br />
track the total spin <strong>of</strong> the sink particles as they grow in mass.<br />
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