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arXiv · 1803.08932

Evidence for Large-Scale Fluctuations in the Metagalactic Ionizing Background Near Redshift Six

George D. Becker·Frederick B. Davies·Steven R. Furlanetto·Matthew A. Malkan·Elisa Boera·Craig Douglass
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Abstract

The observed scatter in intergalactic Lyman-$α$ opacity at $z \lesssim 6$ requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Lyman-$α$ opacity and local density. Here we test these models using Lyman-$α$ emitting galaxies (LAEs) to trace the density field surrounding the longest and most opaque known Lyman-$α$ trough at $z < 6$. Using deep Subaru Hyper Suprime-Cam narrow-band imaging, we find a highly significant deficit of $z \simeq 5.7$ LAEs within 20 Mpc/$h$ of the trough. The results are consistent with a model in which the scatter in Lyman-$α$ opacity near $z \sim 6$ is driven by large-scale UVB fluctuations, and disfavor a scenario in which the scatter is primarily driven by variations in IGM temperature. UVB fluctuations at this epoch present a boundary condition for reionization models, and may help shed light on the nature of the ionizing sources.

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George D. Becker, Frederick B. Davies, Steven R. Furlanetto, Matthew A. Malkan, Elisa Boera, Craig Douglass. 2018-03-23. Evidence for Large-Scale Fluctuations in the Metagalactic Ionizing Background Near Redshift Six. https://doi.org/10.3847/1538-4357%2Faacc73

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