A self-consistent 3D model of fluctuations in the helium-ionizing background

Abstract

Large variations in the effective optical depth of the He II Ly$\alpha$ forest have been observed at $z\gtrsim 2.7$, but the physical nature of these variations is uncertain: either the Universe is still undergoing the process of He II reionization, or the Universe is highly ionized but the He II-ionizing background fluctuates significantly on large scales. In an effort to build upon our understanding of the latter scenario, we present a novel model for the evolution of ionizing background fluctuations. Previous models have assumed the mean free path of ionizing photons to be spatially uniform, ignoring the dependence of that scale on the local ionization state of the intergalactic medium (IGM). This assumption is reasonable when the mean free path is large compared to the average distance between the primary sources of He II-ionizing photons, $\gtrsim L_{\star }$ quasars. However, when this is no longer the case, the background fluctuations become more severe, and an accurate description of the average propagation of ionizing photons through the IGM requires additionally accounting for the fluctuations in opacity. We demonstrate the importance of this effect by constructing 3D semi-analytic models of the helium ionizing background from $z=2.5$-$3.5$ that explicitly include a spatially varying mean free path of ionizing photons. The resulting distribution of effective optical depths at large scales in the He II Ly$\alpha$ forest is very similar to the latest observations with HST/COS at $2.5\lesssim z\lesssim 3.5$.

10 pages, 7 figures

References in corpus (17)

• An Observational Determination of the Bolometric Quasar Luminosity Function
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Efficient Simulations of Early Structure Formation and Reionization
• Evidence of patchy hydrogen reionization from an extreme Ly$\alpha$ trough below redshift six
• The first ultraviolet quasar stacked spectrum at z=2.4 from WFC3
• HeII Reionization and its Effect on the IGM
• Quasars Are Not Light-Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution
• Voigt Profile Fitting to Quasar Absorption Lines: An Analytic Approximation to the Voigt-Hjerting Function
• The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra
• The History and Morphology of Helium Reionization
• The UV spectrum of HS1700+6416 II. FUSE observations of the HeII Lyman alpha forest
• Photo-heating and the fate of hard photons during the reionisation of HeII by quasars
• The Line-of-Sight Proximity Effect and the Mass of Quasar Host Halos
• The Implications of Gunn-Peterson Troughs in the HeII Lyman-alpha Forest
• Fluctuations in the Ionizing Background During and After Helium Reionization
• AGN-driven helium reionization and the incidence of extended HeIII regions at redshift z>3
• Ultraviolet background fluctuations with clustered sources

Cited by in corpus (1)

• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction