Spatial Correlations in the Helium-Ionizing Background

Abstract

After quasars ionize intergalactic HeII at z~3, a large radiation field builds up above the HeII ionization edge. Unlike the background responsible for HI ionizations, this field should be highly variable, thanks to the scarcity of bright quasars and the relatively short attenuation lengths (~50 Mpc) of these high-energy photons. Recent observations of the HeII and HI Lyman-alpha forests show that this background does indeed vary strongly, with substantial fluctuations on scales as small as ~2 Mpc. Here we show that such spatial fluctuation scales are naturally expected in any model in which the sources are as rare as bright quasars, so long as the attenuation length is relatively small. The correlation length itself is comparable to the attenuation length (~10 Mpc) for the most plausible physical scenarios, but we find order-of-magnitude fluctuations on all scales smaller than ~6 Mpc. Moreover, aliasing along the one-dimensional skewers probed by the HeII and HI Lyman-alpha forests exaggerates these variations, so that order-of-magnitude fluctuations should be observed on all scales smaller than ~20 Mpc. Complex radiative transfer is therefore not required to explain the observed fluctuations, at least at the level of current data.

6 pages, 3 figures, submitted to ApJ

References in corpus (39)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Halo Models of Large Scale Structure
• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data
• 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
• An Observational Determination of the Bolometric Quasar Luminosity Function
• Radiative Transfer in a Clumpy Universe: III. The Nature of Cosmological Ionizing Sources
• The 2dF QSO Redshift Survey - I. The Optical QSO Luminosity Function
• The Rest-Frame Extreme Ultraviolet Spectral Properties of QSOs
• The Opacity of the Lyman Alpha Forest and Implications for Omega_{baryon} and the Ionizing Background
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• HeII Reionization and its Effect on the IGM
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6
• A Composite Extreme Ultraviolet QSO Spectrum from the Far Ultraviolet Spectroscopic Explorer
• The Lyman-alpha forest opacity and the metagalactic hydrogen ionization rate at z~2-4
• Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
• 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
• A Study of the Reionization History of Intergalactic Helium with FUSE and VLT
• Ionizing radiation fluctuations and large-scale structure in the Lyman-alpha forest
• The effects of UV background correlations on LyA forest flux statistics
• The Fluctuating Intergalactic Radiation Field at Redshifts z = 2.3-2.9 from He II and H I Absorption towards HE 2347-4342
• Caught in the act: a helium-reionizing quasar near the line of sight to Q0302-003
• The History and Morphology of Helium Reionization
• Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9
• UV Radiative Feedback During the Advanced Stages of Reionization
• The Epoch of Helium Reionization
• The UV spectrum of HS1700+6416 II. FUSE observations of the HeII Lyman alpha forest
• Constraints on the UV metagalactic emissivity using the LyA forest
• Reionisation scenarios and the temperature of the IGM
• Spatial fluctuations in the spectral shape of the UV background at 2<z<3 and the reionization of helium
• Quasars near the line of sight towards Q 0302-003 and the transverse proximity effect
• Radiative Transfer Effects on the Lya Forest
• The ionizing background at the end of overlap
• The transverse proximity effect in spectral hardness on the line of sight towards HE 2347-4342
• A High Yield of New Sightlines for the Study of Intergalactic Helium: Far-UV-Bright Quasars from SDSS, GALEX, and HST
• Fluctuations of the intergalactic UV background towards two lines of sight
• The HeII Lyman alpha forest and the thermal state of the IGM

Cited by in corpus (8)

• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Models of the Thermal Evolution of the Intergalactic Medium After Reionization
• The Signatures of Large-scale Temperature and Intensity Fluctuations in the Lyman-alpha Forest
• The evolution of the helium-ionizing background at z ~ 2-3
• Large-Scale Fluctuations in the HeII Lyman-alpha Forest and HeII Reionization
• The case against large intensity fluctuations in the z ~ 2.5 HeII Lyman-alpha forest
• The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon
• Constraints on Quasar Lifetimes and Beaming from the HeII Lyman-alpha Forest