The reionization history and early metal enrichment inferred from the gamma-ray burst rate

Murakami T.

Yonetoku M.

Umemura M.

Matsubayashi T.

Yamazaki Ryo

Astrophysical Journal

Based on the gamma-ray burst event rate at redshifts of 4 ≤ z ≤ 12 which is assessed by the spectral peak energy-to-luminosity relation recently found by Yonetoku et al., we observationally derive the star formation (SFR) for Population III (Pop. III) stars in a high-redshift universe. As a result, we find that Pop. III stars form continuously at. Using the derived Pop. III SFR, we attempt to estimate the ultraviolet (UV) photon emission rate at in which redshift range no observational information has been hitherto 7 ≤ z ≤ 12 on ionizing radiation intensity. We find that the UV emissivity at can make a noticeable 7 ≤ z ≤ 12 to the early reionization. The maximal emissivity is higher than the level required to keep ionizing the matter (IGM) at. However, if the escape fraction of ionizing photons from Pop. III objects is 7 ≤ z ≤ 12 than 10%, then the IGM can be neutralized at some redshift, which may lead to the double reionization. As the enrichment, the ejection of all metals synthesized in Pop. III objects is marginally consistent with the metallicity, although the confinement of metals in Pop. III objects can reduce the enrichment significantly.

early universe

gamma ryas

bursts

stars

formation

Astronomy. Space sciences [ 440 ]

eng

University of Chicago Press

Copyright (c) 2005 The American Astronomical Society

[DOI] 10.1086/430828

[DOI] http://dx.doi.org/10.1086/430828 isVersionOf