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.

Madau, P., Haardt, F., Rees, M. (1999). Radiative Transfer in a Clumpy Universe. III. The Nature of Cosmological Ionizing Sources. THE ASTROPHYSICAL JOURNAL, 514(2 Part 1), 648-659 [10.1086/306975].

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

Madau, P;
1999

Abstract

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.
Articolo in rivista - Articolo scientifico
Diffuse radiation; Intergalactic medium; Radiative transfer;
English
1999
514
2 Part 1
648
659
none
Madau, P., Haardt, F., Rees, M. (1999). Radiative Transfer in a Clumpy Universe. III. The Nature of Cosmological Ionizing Sources. THE ASTROPHYSICAL JOURNAL, 514(2 Part 1), 648-659 [10.1086/306975].
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/452787
Citazioni
  • Scopus 623
  • ???jsp.display-item.citation.isi??? 653
Social impact