Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-07-22
Mon.Not.Roy.Astron.Soc.376:534-548,2007
Astronomy and Astrophysics
Astrophysics
16 pages, 10 figures, most in color. MNRAS, in print. Replaced to match the accepted version. High-quality images and movies c
Scientific paper
10.1111/j.1365-2966.2007.11482.x
Recently, we have presented the first large-scale radiative transfer simulations of reionization. Here we present new simulations which extend the source halo mass range downward to 10^8M_solar, to capture the full range of halo masses thought to be primarily responsible for reionization by their star formation following atomic hydrogen radiative cooling and gravitational collapse. Haloes below about 10^9M_solar, however, are subject to Jeans-mass filtering in the ionized regions, which suppresses their baryonic content and their ability to release ionizing radiation. By including these smaller-mass haloes but accounting for their suppression, too, we find that reionization is ``self-regulating,'' as follows. As the mean ionized fraction rises, so does the fraction of the volume within which suppression occurs. Hence, the degree of suppression is related to the mean ionized fraction. Since low-mass haloes with high emissivity achieve a given mean ionized fraction earlier than do those with low efficiency, Jeans-mass filtering compensates for the difference in the emissivity of the suppressible haloes in these two cases. As a result, in the presence of lower-mass source haloes, reionization begins earlier, but the later stages of reionization and the time of overlap are dictated by the efficiency of the higher-mass haloes, independent of the efficiency of the suppressible, lower-mass haloes. Reionization histories consistent with current observational constraints are shown to be achievable with standard stellar sources in haloes above 10^8M_solar. Neither minihalos nor exotic sources are required, and the phenomenon of ``double reionization'' previously suggested does not occur. (abridged)
Iliev Ilian T.
Mellema Garrelt
Pen U.-L.
Shapiro Paul R.
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