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

Understand

The observed scatter in intergalactic Lyman-$\alpha$ 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-$\alpha$ opacity and local density.
• Here we test these models using Lyman-$\alpha$ emitting galaxies (LAEs) to trace the density field surrounding the longest and most opaque known Lyman-$\alpha$ trough at $z < 6$.