Large Fluctuations in the High-Redshift Metagalactic Ionizing Background

Understand

Recent observations have shown that the scatter in opacities among coeval segments of the Lyman-alpha forest increases rapidly at z > 5.

• In this paper, we assess whether the large scatter can be explained by fluctuations in the ionizing background in the post-reionization intergalactic medium.
• We find that matching the observed scatter at z ~ 5.5 requires a short spatially averaged mean free path of < 15 comoving Mpc/h, a factor of > 3 shorter than direct measurements at z ~ 5.2.
• We argue that such rapid evolution in the mean free path is difficult to reconcile with our measurements of the global H I photoionization rate, which stay approximately constant over the interval z ~ 4.8 - 5.5.