He II reionization and its effect on the intergalactic medium

Matthew McQuinn*, Adam Lidz, Matias Zaldarriaga, Lars Hernquist, Philip F. Hopkins, Suvendra Dutta, Claude André Faucher-Giguère

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

200 Scopus citations


Observations of the intergalactic medium (IGM) suggest that quasars reionize HeII in the IGM at z 3. We have run a set of 190 and 430 comoving Mpc simulations of HeII being reionized by quasars to develop an understanding of the nature of HeII reionization and its potential impact on observables. We find that HeII reionization heats regions in the IGM by as much as 25, 000 K above the temperature that is expected otherwise, with the volume-averaged temperature increasing by 12, 000 K and with large temperature fluctuations on 50 Mpc scales. Much of this heating occurs far from quasars by photons with long mean free path. We find a temperature-density equation of state of γ - 1 0.3 during HeII reionization, but with a wide dispersion in this relation having σT 104 K. HeII reionization by the observed population of quasars cannot produce an inverted relation (γ - 1 < 0). Our simulations are consistent with the observed evolution in the mean transmission of the HeII Lyα forest. We argue that the heat input from HeII reionization is unable to cause the observed depression at z 3.2 in the HI Lyα forest opacity as has been suggested. We investigate how uncertainties in the properties of QSOs and of HeII Lyman limit systems influence our predictions.

Original languageEnglish (US)
Pages (from-to)842-866
Number of pages25
JournalAstrophysical Journal
Issue number2
StatePublished - 2009


  • Cosmology: theory
  • Intergalactic medium

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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