A comparison of numerical methods for computing the reionization of intergalacitc hydrogen and helium by a central radiating source

Abstract

We compare numerical methods for solving the radiative transfer equation in the context of the photoionization of intergalactic gaseous hydrogen and helium by a central radiating source. Direct integration of the radiative transfer equation and solutions using photon packets are examined, both for solutions to the time-dependent radiative transfer equation and in the infinite-speed-of-light approximation. The photon packet schemes are found to be more generally computationally efficient than a direct integration scheme. Whilst all codes accurately describe the growth rate of hydrogen and helium ionization zones, it is shown that a fully time-dependent method is required to capture the gas temperature and ionization structure in the near zone of a source when an ionization front expands at a speed close to the speed of light. Applied to Quasi-Stellar Objects in the Epoch of Reionization (EoR), temperature differences as high as $5\times 10^4$ K result in the near-zone for solutions of the time-dependent radiative transfer equation compared with solutions in the infinite-speed-of-light approximation. Smaller temperature differences are found following the nearly full photoionization of helium in gas in which the hydrogen was already ionized and the helium was singly ionized. Variations found in the temperature and ionization structure far from the source, where the gas is predominantly neutral, may affect some predictions for 21-cm EoR experiments.

19 pages, 24 figures, submitted to MNRAS

References in corpus (14)

• Grackle: a Chemistry and Cooling Library for Astrophysics
• HeII Reionization and its Effect on the IGM
• Introducing the THESAN project: radiation-magnetohydrodynamic simulations of the epoch of reionization
• Cosmological Radiative Transfer Codes Comparison Project I: The Static Density Field Tests
• The Sherwood-Relics simulations: overview and impact of patchy reionization and pressure smoothing on the intergalactic medium
• Reionisation scenarios and the temperature of the IGM
• Multi-frequency, thermally coupled radiative transfer with TRAPHIC: Method and tests
• Detecting and Characterizing Young Quasars II: Four Quasars at $z\sim 6$ with Lifetimes $<10^4$ years
• Large scale simulations of H and He reionization and heating driven by stars and more energetic sources
• Estimating the effective lifetime of the $z\sim 6$ quasar population from the composite proximity zone profile
• The Distribution and Evolution of Quasar Proximity Zone Sizes
• Dating individual quasars with the HeII proximity effect
• Observing the redshifted 21 cm signal around a bright QSO at $z\sim 10$
• Galactic wind X-ray heating of the intergalactic medium during the Epoch of Reionization

Cited by in corpus (3)

• Spectral reconstruction for radiation hydrodynamic simulations of galaxy evolution
• The effect of helium reionization on the Lyman-alpha forest hydrogen flux statistics
• The 21-cm signature of X-ray heated halos around galaxies during cosmic dawn