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

also pointed out in Smith et al. (2011), our averaging of the accretion rate over
a number of timesteps serves to mimic the buffering of accreted material by
the sub-sink disk. The inputs to our protostellar model are thus necessarily
approximate, as is the protostellar model itself. Nevertheless, it is sufficient
to provide an exploratory picture of how ionizing feedback will affect Pop III
accretion within a cosmological setup.
3.3 Results
3.3.1 Disk Evolution
The gas in both the ‘no-feedback’ and ‘with-feedback’ cases underwent
disk formation, fragmentation, and the emergence of several sinks. We show
the evolution of various disk properties in Figure 3.2. Because of the im-
precision involved in determining which gas particles comprise the disk, for
simplicity we define the disk as consisting of particles with number density
greater than 10 9 cm −3 and with an H2 fraction greater than 10 −3 . This way
the disk only contains cool and dense gas that has not been subject to ion-
ization or significant H2 destruction. From Figure 3.3 we see that the disk
structure is growing in mass well before the first sink forms. This central gas
is already rotationally dominated, as indicated by the low values of χrad in
Figure 3.2, which is the average radial velocity of the gas particles divided by
their average rotational velocity, χrad = vrad/vrot. Velocities are measured with
respect to the center of mass of the disk.
3.3.1.1 No-feedback case
After sink formation, the ‘no-feedback’ disk steadily grows in mass (Fig.
3.3) as angular momentum causes it to expand in radius and become somewhat
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