The State of Star Formation and the Intergalactic Medium at z ~ 6

Details The State of Star Formation and the Intergalactic Medium at z ~ 6 The State of Star Formation and the Intergalactic Medium at z ~ 6

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...725..115c&link_type=abstract

The Astrophysical Journal, Volume 725, Issue 1, pp. 115-120 (2010).

Astronomy and Astrophysics

Astronomy

2

Dark Ages, Reionization, First Stars, Intergalactic Medium, Methods: Analytical, Methods: Numerical, Stars: Formation, Stars: Population Iii

Scientific paper

In the context of 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 a lower mass cutoff of >=30 M sun 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 plausibly be fulfilled by continued existence of some pockets of uncontaminated, metal-free gas for star formation. (2) The volume-weighted neutral fraction of the IGM of < f_H I > _V˜ 10^{-4} at z = 5.8 inferred from the SDSS observations of QSO absorption spectra provides enough information to ascertain that reionization is basically complete with at most ~0.1%-1% of IGM that is unionized at z = 5.8. (3) Barring some extreme evolution of the IMF, the neutral fraction of the IGM is expected to rise quickly toward high redshift from the point of H II bubble percolation, with the mean neutral fraction of the IGM expected to reach 6%-12% at z = 6.5, 13%-27% at z = 7.7, and 22%-38% at z = 8.8.

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