The case against large intensity fluctuations in the z ~ 2.5 HeII Lyman-alpha forest

Abstract

Previous studies of the 2.2 < z< 2.7 HeII Lyman-alpha forest measured much larger ionizing background fluctuations than are anticipated theoretically. We re-analyze recent Hubble Space Telescope data from the two HeII sightlines that have been used to make these measurements, HE2347-4342 and HS1700+6416, and find that the vast majority of the absorption is actually consistent with a single HeII photoionization rate. We show that the data constrains the RMS fractional fluctuation level smoothed at 1 Mpc to be < 2 and discuss why other studies had found larger fluctuations. Our measurement is consistent with models in which quasars dominate the z=2.5 metagalactic HeII-ionizing background (but it can accommodate less compelling models), and it suggests that quasars (rather than stars) are the dominant contributor to the HI-ionizing background. We detect a HeII transverse proximity effect that is slightly offset in redshift from a known quasar. Its profile and offset may indicate that the quasar turned on 10 Myr ago.

11 pages, 6 figures, plus appendixes; matches version accepted to MNRAS

References in corpus (16)

• A Catalog of Quasar Properties from SDSS DR7
• An Observational Determination of the Bolometric Quasar Luminosity Function
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII 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
• A Direct Precision Measurement of the Intergalactic Lyman-alpha Opacity at 2<z<4.2
• Through Thick and Thin - HI Absorption in Cosmological Simulations
• The Column Density Distribution and Continuum Opacity of the Intergalactic and Circumgalactic Medium at Redshift <z>=2.4
• Dissecting the properties of optically-thick hydrogen at the peak of cosmic star formation history
• 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
• The Implications of Gunn-Peterson Troughs in the HeII Lyman-alpha Forest
• Fluctuations in the Ionizing Background During and After Helium Reionization
• Fluctuations of the intergalactic UV background towards two lines of sight
• Spatial Correlations in the Helium-Ionizing Background

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• 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
• HST/COS Observations of the Quasar Q0302-003: Probing the He II Reionization Epoch and QSO Proximity Effects