Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-08-09
Ap.J., 563, 1 (2001)
Astronomy and Astrophysics
Astrophysics
9 emulateapj pages with 5 embedded postscript figures; accepted for publication in Ap.J. (Dec. 10, 2001 issue)
Scientific paper
10.1086/323691
Observational studies indicate that the intergalactic medium (IGM) is highly ionized up to redshifts just over 6. A number of models have been developed to describe the process of reionization and the effects of the ionizing photons from the first luminous objects. In this paper, we study the impact of an X-ray background, such as high-energy photons from early quasars, on the temperature and ionization of the IGM prior to reionization, before the fully ionized bubbles associated with individual sources have overlapped. X-rays, which have large mean free paths relative to EUV photons, and their photoelectrons can have significant effects on the thermal and ionization balance. We find that hydrogen ionization is dominated by the X-ray photoionization of neutral helium and the resulting secondary electrons. Thus, the IGM may have been warm and weakly ionized prior to full reionization. We examine several related consequences, including the filtering of the baryonic Jeans mass scale, signatures in the cosmic microwave background, and the H$^{-}$-catalyzed production of molecular hydrogen.
Giroux Mark Laird
Shull Michael J.
Venkatesan Aparna
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