Inhomogeneous HeII reionization in Hydrodynamic Simulations

Abstract

The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 < z < 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for large volumes, the physics of HeII reionization is often approximated by a uniform UV background model that does not capture the patchiness of reionization. We have devised a model that implements the effects of HeII reionization using semi-analytic calculations of the thermal state of intergalactic gas-- a way to bypass a full radiative transfer simulation while still realizing the physics of HeII reionization that affects observables such as the Lyman alpha forest. Here we present a publicly-available code that flexibly models inhomogeneous HeII reionization in simulations at a negligible computational cost. Because many of the parameters of HeII reionization are uncertain, our model is customizable from a set of free parameters. We show results from this code in MP-Gadget, where this model is implemented. We demonstrate the resulting temperature evolution and temperature-density relation of intergalactic gas-- consistent with recent measurements and previous radiative transfer simulations. We show that the impact of HeII reionization gives rise to subtle signatures in the one-dimensional statistics of the Lyman alpha forest at the level of several per cent, in agreement with previous findings. The flexible nature of these simulations are ideal for studies of HeII reionization and future observations of the HeII Lyman alpha forest.

11 pages, 10 figures

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• Inferring the Thermal History of the Intergalactic Medium from the Properties of the Hydrogen and Helium Lyman-alpha Forest
• PRIYA: A New Suite of Lyman-alpha Forest Simulations for Cosmology
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• Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure
• Separating the memory of reionization from cosmology in the Ly$\alpha$ forest power spectrum at the post-reionization era
• The long-lasting effect of X-ray preheating in the post-reionization intergalactic medium
• Effect of Separate Initial Conditions on the Lyman-$\alpha$ Forest in Simulations
• Constraining the Temperature-Density Relation of the Inter-Galactic Medium from Analytically Modeling Lyman-alpha Forest Absorbers
• Simulating the epoch of Helium Reionization in photon-conserving semi-numerical code SCRIPT
• Reionization relics in the cross-correlation between the Ly$\alpha$ forest and 21 cm intensity mapping in the post-reionization era
• 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
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