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

Zhu, Yongda; Becker, George D; Bosman, Sarah E I; Cain, Christopher; Keating, Laura C; Nasir, Fahad; D’Odorico, Valentina; Bañados, Eduardo; Bian, Fuyan; Bischetti, Manuela; Bolton, James S; Chen, Huanqing; D’Aloisio, Anson; Davies, Frederick B; Davies, Rebecca L; Eilers, Anna-Christina; Fan, Xiaohui; Gaikwad, Prakash; Greig, Bradley; Haehnelt, Martin G; Kulkarni, Girish; Lai, Samuel; Puchwein, Ewald; Qin, Yuxiang; Ryan-Weber, Emma V; Satyavolu, Sindhu; Spina, Benedetta; Walter, Fabian; Wang, Feige; Wolfson, Molly; Yang, Jinyi

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. Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate the observed damping wing features. Furthermore, this damping wing-like profile implies that the volume-averaged neutral hydrogen fraction must be 〈xH I〉 ≥ 6.1 ± 3.9 per cent at z = 5.8. Our results offer robust evidence that reionization extends below z = 6.

Citation

Zhu, Y., Becker, G. D., Bosman, S. E. I., Cain, C., Keating, L. C., Nasir, F., D’Odorico, V., Bañados, E., Bian, F., Bischetti, M., Bolton, J. S., Chen, H., D’Aloisio, A., Davies, F. B., Davies, R. L., Eilers, A.-C., Fan, X., Gaikwad, P., Greig, B., Haehnelt, M. G., …Yang, J. (2024). Damping wing-like features in the stacked Ly α forest: Potential neutral hydrogen islands at z < 6. Monthly Notices of the Royal Astronomical Society: Letters, 533(1), L49-L56. https://doi.org/10.1093/mnrasl/slae061

• Journal Article Type: Article
• Acceptance Date: Jun 27, 2024
• Online Publication Date: Jun 29, 2024
• Publication Date: 2024-09
• Deposit Date: Jul 8, 2024
• Publicly Available Date: Jul 9, 2024
• Journal: Monthly Notices of the Royal Astronomical Society: Letters
• Electronic ISSN: 1745-3933
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 533
• Issue: 1
• Pages: L49-L56
• DOI: https://doi.org/10.1093/mnrasl/slae061
• Keywords: intergalactic medium, quasars: absorption lines, dark ages, reionization, first stars, large-scale structure of Universe, cosmology: observations
• Public URL: https://nottingham-repository.worktribe.com/output/36876976
• Publisher URL: https://academic.oup.com/mnrasl/advance-article/doi/10.1093/mnrasl/slae061/7701785