Gas clumping in self-consistent reionization models

Kristian Finlator, S. Peng Oh, Feryal Özel, Romeel Davé

Research output: Contribution to journalArticlepeer-review

105 Scopus citations


We use a suite of cosmological hydrodynamic simulations including a self-consistent treatment for inhomogeneous reionization to study the impact of galactic outflows and photoionization heating on the volume-averaged recombination rate of the intergalactic medium (IGM). By incorporating an evolving ionizing escape fraction and a treatment for self-shielding within Lyman limit systems, we have run the first simulations of 'photon-starved' reionization scenarios that simultaneously reproduce observations of the abundance of galaxies, the optical depth to electron scattering of cosmic microwave background photons τes and the effective optical depth to Lyα absorption at z = 5. We confirm that an ionizing background reduces the clumping factor C by more than 50percent by smoothing moderately overdense (Δ = 1-100) regions. Meanwhile, outflows increase clumping only modestly. The clumping factor of ionized gas is much lower than the overall baryonic clumping factor because the most overdense gas is self-shielded. Photoionization heating further suppresses recombinations if reionization heats gas above the canonical 10000K. Accounting for both effects within our most realistic simulation, C rises from <1 at z > 10 to 3.3 at z = 6. We show that incorporating temperature- and ionization-corrected clumping factors into an analytical reionization model reproduces the numerical simulation's τes to within 10percent. Finally, we explore how many ionizing photons are absorbed during the process of heating filaments by considering the overall photon cost of reionization in analytical models that assume that the IGM is heated at different redshifts. For reionization redshifts of 9-10, cold filaments boost the reionization photon budget by ∼1 photon per hydrogen atom.

Original languageEnglish (US)
Pages (from-to)2464-2479
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Dec 11 2012


  • Cosmology: theory
  • Hydrodynamics
  • Intergalactic medium
  • Methods: numerical
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Gas clumping in self-consistent reionization models'. Together they form a unique fingerprint.

Cite this