Spatial fluctuations in the spectral shape of the UV background at 2

S. Bolton, James; G. Haehnelt, Martin; Viel, Matteo; F. Carswell, Robert

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.

Citation

S. Bolton, J., G. Haehnelt, M., Viel, M., & F. Carswell, R. (2006). Spatial fluctuations in the spectral shape of the UV background at 2. Monthly Notices of the Royal Astronomical Society, 366(4), 1378-1390. https://doi.org/10.1111/j.1365-2966.2006.09927.x

• Journal Article Type: Article
• Acceptance Date: Nov 23, 2005
• Online Publication Date: Mar 11, 2006
• Publication Date: 2006-03
• Deposit Date: Sep 16, 2019
• Publicly Available Date: Sep 17, 2019
• Journal: Mon.Not.Roy.Astron.Soc.366:1378-1390,2006
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 366
• Issue: 4
• Pages: 1378-1390
• DOI: https://doi.org/10.1111/j.1365-2966.2006.09927.x
• Keywords: Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/2462366
• Publisher URL: https://academic.oup.com/mnras/article/366/4/1378/1126632
• Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2006 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
• Contract Date: Sep 17, 2019