Spatial fluctuations in the spectral shape of the UV background at 2<z<3 and the reionization of helium

Abstract

The low density hydrogen and helium in the IGM probed by QSO absorption lines is sensitive to the amplitude and spectral shape of the metagalactic UV background. We use realistic HI and HeII Ly-alpha forest spectra, constructed from state-of-the-art hydrodynamical simulations of a Lambda-CDM Universe, to confirm the reliability of using line profile fitting techniques to infer the ratio of the metagalactic HI and HeII ionization rates. We further show that the large spatial variations and the anti-correlation with HI absorber density observed in the ratio of the measured HeII to HI column densities can be explained in a model where the HI ionization rate is dominated by the combined UV emission from young star forming galaxies and QSOs and the HeII ionization rate is dominated by emission from QSOs only. In such a model the large fluctuations in the column density ratio are due to the small number of QSOs expected to contribute at any given point to the HeII ionization rate. A significant contribution to UV emission at the HeII photoelectric edge from hot gas in galaxies and galaxy groups would decrease the expected fluctuations in the column density ratio. Consequently, this model appears difficult to reconcile with the large increase in HeII opacity fluctuations towards higher redshift. Our results further strengthen previous suggestions that observed HeII Ly-alpha forest spectra at z~2-3.5 probe the tail end of the reionization of HeII by QSOs.

14 pages, 7 figures, accepted for publication in MNRAS. Minor changes to submitted version, most notably an extra section (5.2) and figure (fig.6)

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Cited by in corpus (48)

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• The Physics of the Intergalactic Medium
• The Evolution of the Intergalactic Medium
• The Direct Detection of Lyman-Continuum Emission from Star-forming Galaxies at z~3
• HeII Reionization and its Effect on the IGM
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest
• Evolution of the Quasar Luminosity Function Over 3 < z < 5 in the COSMOS Survey Field
• Early and Extended Helium Reionization Over More Than 600 Million Years of Cosmic Time
• The first (nearly) model-independent constraint on the neutral hydrogen fraction at z~5--6
• The History and Morphology of Helium Reionization
• GALEX far-UV color selection of UV-bright high-redshift quasars
• Scale-dependent bias in the BAO-scale intergalactic neutral hydrogen
• The UV spectrum of HS1700+6416 II. FUSE observations of the HeII Lyman alpha forest
• Reionisation scenarios and the temperature of the IGM
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• Intergalactic Lyman continuum photon budget in the past 5 billion years
• Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies
• Statistical Detection of the HeII Transverse Proximity Effect: Evidence for Sustained Quasar Activity for $>$25 Million Years
• The transverse proximity effect in spectral hardness on the line of sight towards HE 2347-4342
• The Inhomogeneous Ionizing Background Following Reionization
• Spectral shape of the UV ionizing background and HeII absorption at redshifts 1.8 < z < 2.9
• Lyman Limit Systems in Cosmological Simulations
• The impact of helium reionization on the structure of the intergalactic medium
• The evolution of the helium-ionizing background at z ~ 2-3
• Fluctuations in the Ionizing Background During and After Helium Reionization
• Toward an internally consistent astronomical distance scale
• Large-Scale Fluctuations in the HeII Lyman-alpha Forest and HeII Reionization
• The distribution of Lyman-limit absorption systems during and after reionization
• The Effect of Fluctuations on the Helium-Ionizing Background
• Fluctuations of the intergalactic UV background towards two lines of sight
• The case against large intensity fluctuations in the z ~ 2.5 HeII Lyman-alpha forest
• The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon
• On the importance of high redshift intergalactic voids
• Constraints on Quasar Lifetimes and Beaming from the HeII Lyman-alpha Forest
• Efficient adiabatic hydrodynamical simulations of the high-redshift intergalactic medium
• Cosmic Variance In the Transparency of the Intergalactic Medium After Reionization
• Probing the environment of high-z quasars using the proximity effect in projected quasar pairs
• The Imprint of Cosmic Reionization on Galaxy Clustering
• The HeII Lyman alpha forest and the thermal state of the IGM
• Semi-numeric simulations of helium reionization and the fluctuating radiation background
• Spatial Correlations in the Helium-Ionizing Background
• Log-Poisson Non-Gaussianity of Ly$\alpha$ Transmitted Flux Fluctuations at High Redshift
• Three- and two-point spatial correlations of IGM at $z\sim 2$: Cloud based analysis using simulations
• UV background fluctuations traced by metal ions at $z\approx 3$
• Ultraviolet background fluctuations with clustered sources