2012/08/31 by J. D. Emberson, Rajat M. Thomas, Marcelo A. Alvarez · 1 citation
Physics and Astronomy · #Adiabatic process #Astrophysics #Astrophysics and Cosmic Phenomena #Cosmology and Gravitation Theories #Dark matter #Galaxies: Formation, Evolution, Phenomena #Galaxy #Ionization #Mean free path #Opacity #Physics #Redshift #Reionization #Scattering #Structure formation #Universe #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/763/2/146
published as ApJ, 763:146, 2013 · Accepted for publication in the Astrophysical Journal
openalex publication_date 2013/01/17 · arxiv created 2013/10/18 · arxiv updated 2013/10/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Early in the reionization process, the intergalactic medium (IGM) would have been quite inhomogeneous on small scales, due to the low Jeans mass in the neutral IGM and the hierarchical growth of structure in a cold dark matter universe. This small-scale structure acted as an important sink during the epoch of reionization, impeding the progress of the ionization fronts that swept out from the first sources of ionizing radiation. Here we present results of high-resolution cosmological hydrodynamics simulations that resolve the cosmological Jeans mass of the neutral IGM in representative volumes several Mpc across. The adiabatic hydrodynamics we follow are appropriate in an unheated IGM, before the gas has had a chance to respond to the photoionization heating. Our focus is determination of the resolution required in cosmological simulations in order to sufficiently sample and resolve small-scale structure regulating the opacity of an unheated IGM. We find that a dark matter particle mass of m dm ≲ 50 M ☉ and box size of L ≳ 1 Mpc are required. With our converged results we show how the mean free path of ionizing radiation and clumping factor of ionized hydrogen depend on the ultraviolet background flux and redshift. We find, for example at z = 10, clumping factors typically of 10–20 for an ionization rate of Γ ∼ (0.3–3) × 10 −12 s −1 , with corresponding mean free paths of ∼3–15 Mpc, extending previous work on the evolving mean free path to considerably smaller scales and earlier times.