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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abundances <strong>of</strong> HD, which also acts as a cooling agent in low-temper<strong>at</strong>ure pri-<br />
mordial gas (see Johnson and Bromm 2006). However, the presence <strong>of</strong> CRs can<br />
lead to ioniz<strong>at</strong>ion he<strong>at</strong>ing, as well. Whether this direct he<strong>at</strong>ing effect is strong<br />
enough to counter the additional cooling must be determined and will depend<br />
on the high-redshift CR energy density. Similar to our work, Rollinde et al.<br />
(2005, 2006) used models <strong>of</strong> early star form<strong>at</strong>ion to estim<strong>at</strong>e the CR energy<br />
density in the early Universe, constraining it with the observed Li abundances<br />
in metal-poor Galactic halo stars.<br />
In this paper, we will investig<strong>at</strong>e the importance <strong>of</strong> the CR feedback<br />
on Pop III star form<strong>at</strong>ion <strong>by</strong> modeling its effect on the cooling <strong>of</strong> primordial<br />
gas in two cases: collapse within minihaloes, and shocks associ<strong>at</strong>ed with the<br />
virializ<strong>at</strong>ion <strong>of</strong> more massive DM haloes during the l<strong>at</strong>er stages <strong>of</strong> structure<br />
form<strong>at</strong>ion. <strong>The</strong> outline for this paper is as follows. In Chapter 6.2 we discuss<br />
CR acceler<strong>at</strong>ion and propag<strong>at</strong>ion in the high-redshift Universe and how these<br />
might differ from the present-day case. Chapter 6.3 describes the evolution<br />
<strong>of</strong> primordial gas in minihaloes and in virializ<strong>at</strong>ion shocks when accounting<br />
for the effects <strong>of</strong> CRs. For the minihalo case we furthermore discuss how the<br />
fragment<strong>at</strong>ion scale could change for a sufficiently high CR flux. We present<br />
our conclusions in Chapter 6.4.<br />
6.2 Cosmic rays in the high-z Universe<br />
6.2.1 Popul<strong>at</strong>ion III star form<strong>at</strong>ion<br />
Though CR effects will be examined for a range <strong>of</strong> star form<strong>at</strong>ion r<strong>at</strong>es,<br />
the typical Pop III star form<strong>at</strong>ion r<strong>at</strong>e is taken to be th<strong>at</strong> found in Bromm and<br />
Loeb (2006) <strong>at</strong> z 15, which is approxim<strong>at</strong>ely Ψ∗ 2×10 −2 M⊙ yr −1 Mpc −3 in<br />
a comoving volume. This r<strong>at</strong>e was derived using the extended Press-Schechter<br />
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