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

Figure 6.6: MBE as a function of hydrogen number density for freely-falling
clouds inside minihalos at z ∼ 20. The curves correspond to the evolution
shown in Fig. 6.2, and we adopt the same convention for the lines. Notice
that the BE mass, which gives a rough indication for the final stellar mass,
can decrease by up to a factor of 10, given that a sufficient flux of low-energy
CRs is present.
fragmentation occurs and the BE mass is relevant, at least to zeroth order,
given that star formation is too complex to allow reliable predictions from
simple one-zone models such as considered here (e.g. Larson 2003).
Bearing this caveat in mind, we find that, with a sufficiently strong CR
flux present, the gas density at which the ‘loitering phase’ occurs is increased by
a factor of ∼ 10−100, and the corresponding temperature decreased by a factor
of 2 to 3. Evaluating Equ. (6.37) shows that the BE mass thus decreases by an
order of magnitude down to around 10 M⊙. This is the mass scale of what has
been termed ‘Pop II.5’ stars (e.g. Mackey et al. 2003; Johnson and Bromm
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