The Implications of Gunn-Peterson Troughs in the HeII Lyman-alpha Forest

Abstract

Many experts believe that the z ~ 3 HeII Ly-alpha forest will suffer from the same saturation issues as the z ~ 6 HI Ly-alpha forest and, therefore, will not be a sensitive probe of HeII reionization. However, there are several factors that make HeII Ly-alpha absorption more sensitive than HI Ly-alpha. We show that observations of HeII Ly-alpha and Ly-beta Gunn-Peterson troughs can provide a relatively model-independent constraint on the volume-averaged HeII fraction of x_HeII >~ 0.1. This bound derives from first using the most underdense regions in the HeII forest to constrain the local HeII fraction and, then, assuming photoionization equilibrium with the maximum allowed photoionization rate to calculate the ionization state of nearby gas. It is possible to evade this constraint by a factor of ~2, but only if the HeII were reionized recently. We argue that HeII Ly-alpha Gunn-Peterson troughs observed in the spectra of Q0302-003 and HE2347-4342 signify the presence of >~ 10 comoving Mpc patches in which x_HeII > 0.03. This is a factor of 20 improvement over previous constraints from these spectra and 100 times stronger than the tightest constraint on the HI volume-filling fraction from the z>6 HI Lyman forest.

arXiv comment5 pages, 4 figures, includes some supplementary text not in ApJ Letter version

References in corpus (18)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Radiative Transfer in a Clumpy Universe: II. The Utraviolet Extragalactic Background
• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• Reionization of the Inhomogeneous Universe
• Probing the Universe with the Lyman-alpha Forest: I. Hydrodynamics of the Low Density IGM
• HeII Reionization and its Effect on the IGM
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• A Direct Precision Measurement of the Intergalactic Lyman-alpha Opacity at 2<z<4.2
• The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6
• The Lyman-alpha forest opacity and the metagalactic hydrogen ionization rate at z~2-4
• A Measurement of the Temperature-Density Relation in the Intergalactic Medium Using a New Lyman-alpha Absorption Line Fitting Method
• The High-Redshift He II Gunn-Peterson Effect: Implications and Future Prospects
• The Fluctuating Intergalactic Radiation Field at Redshifts z = 2.3-2.9 from He II and H I Absorption towards HE 2347-4342
• Resolving the Helium Lyman-$\alpha$ Forest: Mapping Intergalactic Gas and Ionizing Radiation at $z\approx 3$
• The Influence of the Photoionizing Radiation Spectrum on Metal-Line Ratios in Ly alpha Forest Clouds
• Mapping Low-Density Intergalactic Gas: a Third Helium Lyman-alpha Forest
• Quasars near the line of sight towards Q 0302-003 and the transverse proximity effect
• Fluctuations of the intergalactic UV background towards two lines of sight

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• Statistical Detection of the HeII Transverse Proximity Effect: Evidence for Sustained Quasar Activity for $>$25 Million Years
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• The He II Post-Reionization Epoch: HST/COS Observations of the Quasar HS1700+6416
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• Modeling the HeII Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration
• Cosmological Constraints from the eBOSS Lyman-$\alpha$ Forest using the PRIYA Simulations
• The case against large intensity fluctuations in the z ~ 2.5 HeII Lyman-alpha forest
• New Evidence for Extended HeII Reionization at z>3.5 from HeII Lyman Alpha and Beta Transmission Spikes
• The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon
• HST Spectral Observations near the He II Ly-alpha Break: Implications for He II Reionization
• He II Lyβ Gunn-Peterson Absorption: New HST Observations, and Theoretical Expectations
• Constraining the epoch of reionization from the observed properties of the high-z Universe
• LyMAS reloaded: improving the predictions of the large-scale Lyman-α forest statistics from dark matter density and velocity fields
• Carbon ionization states and the cosmic far-UV background with HeII absorption
• The HeI 584 A Forest as a Diagnostic of Helium Reionization
• Probing Inhomogeneity in the Helium Ionizing UV Background
• Cosmic reionization of hydrogen and helium: contribution from both mini-quasars and stars
• UV background fluctuations traced by metal ions at $z\approx 3$
• HeII Ly$\alpha$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization