Semi-numeric simulations of helium reionization and the fluctuating radiation background

Abstract

Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating He-ionizing background, which may be due to the end of helium reionization of this era. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. We compute the distribution of dark matter halos, ionization state of helium, and density field at z = 3 in broad agreement with recent simulations. Given our speed and flexibility, we investigate a range of ionizing source and active quasar prescriptions. Spanning a large area of parameter space, we find order-of-magnitude fluctuations in the He II ionization rate in the post-reionization regime. During reionization, the fluctuations are even stronger and develop a bimodal distribution, in contrast to semi-analytic models and the hydrogen equivalent. These distributions indicate a low-level ionizing background even at significant He II fractions.

15 pages, 10 figures, MNRAS submitted

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Cited by in corpus (12)

• The Obelisk simulation: galaxies contribute more than AGN to HI reionization of protoclusters
• The accuracy of semi-numerical reionization models in comparison with radiative transfer simulations
• Inhomogeneous Reionization Models in Cosmological Hydrodynamical Simulations
• A self-consistent 3D model of fluctuations in the helium-ionizing background
• Effect of non-equilibrium ionization on derived physical conditions of the high-$z$ intergalactic medium
• Helium Reionization Simulations. I. Modeling Quasars as Radiation Sources
• A Novel Statistical Method for Measuring the Temperature-Density Relation in the IGM Using the $b$-$N_{\text{HI}}$ Distribution of Absorbers in the Ly$\alpha$ Forest
• Helium Reionization Simulations. III. The Helium Lyman-$\alpha$ Forest
• Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure
• Ultraviolet background fluctuations with clustered sources
• Simulating the epoch of Helium Reionization in photon-conserving semi-numerical code SCRIPT
• Measuring photo-ionization rate and mean free path of HeII ionizing photons at $2.5\le z\le 3.6$: Evidence for late and rapid HeII reionization Part-II