Damping wing-like features in the stacked Ly α forest: Potential neutral hydrogen islands at z < 6

Abstract

Recent quasar absorption line observations suggest that reionization may end as late as z ≈ 5.3. As a means to search for large neutral hydrogen islands at z < 6, we revisit long dark gaps in the Ly β forest in Very Large Telescope/X-Shooter and Keck/Echellette Spectrograph and Imager quasar spectra. We stack the Ly α forest corresponding to both edges of these Ly β dark gaps and identify a damping wing-like extended absorption profile. The average redshift of the stacked forest is z = 5.8. By comparing these observations with reionization simulations, we infer that such a damping wing-like feature can be naturally explained if these gaps are at least partially created by neutral islands. Co..