Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-07-05
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
15 pages, 4 figures, submitted to ApJ Letters
Scientific paper
In the context stellar reionization in the standard cold dark matter model, we analyze observations at z~6 and are able to draw three significant conclusions with respect to star formation and the state of the intergalactic medium (IGM) at z~6. (1) An initial stellar mass function (IMF) more efficient, by a factor of 10-20, in producing ionizing photons than the standard Salpeter IMF is required at z~6. This may be achieved by having either (A) a metal-enriched IMF with and a lower mass cutoff of >= 30Msun or (B) 2-4% of stellar mass being Population III massive metal-free stars at z~6. While there is no compelling physical reason or observational evidence to support (A), (B) could be fulfilled plausibly by continued existence of some pockets of uncontaminated, metal-free gas for star formation. (2) The volume-weighted neutral fraction of the IGM of
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