As Fig. 25, but showing He iii. In contrast to our simulation using normal stellar populations (Fig. 24) the clusters dominated by very massive stars can ionize the helium content of the simulation volume within approximately 2 Gyr, completing the reionization at a redshift of about z ~ 2.5. Thus, this scenario based on VMSs as the possible progenitors of IMBHs and SMBHs offers an alternative picture for the as yet unexplained cosmic reionization of helium. In these simulations recombination is not entirely negligible, in particular for helium, where the calculations including recombination yield a number of ionized particles about a factor of two smaller than it would yield for a calculation without recombination.
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