• DOI:10.1086/306975
• Corpus ID: 17932350

Radiative Transfer in a Clumpy Universe. III. The Nature of Cosmological Ionizing Sources

@article{Madau1999RadiativeTI,
  title={Radiative Transfer in a Clumpy Universe. III. The Nature of Cosmological Ionizing Sources},
  author={Piero Madau and Francesco Haardt and Martin J. Rees},
  journal={The Astrophysical Journal},
  year={1999},
  volume={514},
  pages={648 - 659}
}

• P. Madau, F. Haardt, M. Rees
• Published 4 September 1998
• Physics
• The Astrophysical Journal

The history of the transition from a neutral intergalactic medium (IGM) to one that is almost fully ionized can reveal the character of cosmological ionizing sources. We study the evolution of the volume filling factors of H II and He III regions in a clumpy IGM and discuss the implications for rival reionization scenarios of the rapid decline observed at z≳3 in the space density of optical and radio-loud quasars and of the large population of star-forming galaxies recently discovered at the same epoch. The hydrogen component in a highly inhomogeneous universe is completely reionized when the number of photons emitted above 1 ryd in one recombination time equals the mean number of hydrogen atoms. If stellar sources are responsible for keeping the IGM ionized at z=5, the rate of star formation at this epoch must be comparable or greater than the one inferred from optical observations of galaxies at z≈3 and the mean metallicity per baryon in the universe ≳0.002 solar. An early generation of stars in dark matter halos with circular velocities, vcirc≈50 km s-1, possibly one of the main sources of UV photons at high z, could be detectable with the Next Generation Space Telescope. Models in which the quasar emissivity declines rapidly at z≳3 predict a late He II reionization epoch, a feature that could explain the recent detection of patchy He II Lyα at z=2.9 by Reimers et al. and the abrupt change observed by Songaila at about the same epoch of the Si IV /C IV ratio, but appear unable to provide the required number of hydrogen-ionizing photons at z≈5.