On Lyman-limit systems and the evolution of the intergalactic ionizing background

Matthew McQuinn*, S. Peng Oh, Claude André Faucher-Giguère

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


We study the properties of self-shielding intergalactic absorption systems and their implications for the ionizing background. We find that cosmological simulations post-processed with detailed radiative transfer calculations generally are able to reproduce the observed abundance of Lyman-limit systems, and we highlight possible discrepancies between the observations and simulations. This comparison tests cosmological simulations at overdensities of ∼100. Furthermore, we show that the properties of Lyman-limit systems in these simulations, in simple semianalytic arguments, and as suggested by recent observations indicate that a small change in the ionizing emissivity of the sources would have resulted in a much larger change in the amplitude of the intergalactic H I-ionizing background (with this scaling strengthening with increasing redshift). This strong scaling could explain the rapid evolution in the Lyα forest transmission observed at z ≈ 6. Our calculations agree with the suggestion of simpler models that the comoving ionizing emissivity was constant or even increasing from z = 3 to 6. Our calculations also provide a more rigorous estimate than in previous studies for the clumping factor of intergalactic gas after reionization, which we estimate was ≈2-3 at z = 6.

Original languageEnglish (US)
Article number82
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2011


  • cosmology: theory
  • large-scale structure of Universe
  • quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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