How probable is the Lyman-alpha damping wing in the spectrum of the redshift z = 5.9896 quasar ULAS J0148+0600?

Fiona, Sawyer,; James S., Bolton,; George D., Becker,; Luke, Conaboy,; Martin G., Haehnelt,; Laura, Keating,; Girish, Kulkarni,; Ewald, Puchwein,

Abstract

The shape of the Ly-𝛼 transmission in the near zone of the redshift 𝑧 = 5.9896 quasar ULAS J0148+0600 (hereafter J0148) is consistent with a damping wing arising from an extended neutral hydrogen island in the diffuse intergalactic medium (IGM). Here we use simulations of late-ending reionisation from Sherwood-Relics to assess the expected incidence of quasars with Ly-𝛼 and Ly-𝛽 absorption similar to the observed J0148 spectrum. We find a late end to reionisation at 𝑧 = 5.3 is a necessary requirement for reproducing a Ly-𝛼 damping wing consistent with J0148. This occurs in ∼ 3 per cent of our simulated spectra for an IGM neutral fraction ⟨𝑥HI⟩ = 0.14 at 𝑧 = 6. However, using standard assumptions for the ionising photon output of J0148, the a priori probability of drawing a simulated quasar spectrum with a Ly-𝛼 damping wing profile and Ly-𝛼 near zone size that simultaneously match J0148 is low, 𝑝 < 10−2. This may indicate that the ionising emission from J0148 is variable on timescales 𝑡 < 105 yr, or alternatively that the Ly-𝛼 transmission in the J0148 near zone is impacted by the transverse proximity effect from nearby star-forming galaxies or undetected quasars. We also predict the IGM temperature should be 𝑇 ∼ 4 × 104 K within a few proper Mpc of the Ly-𝛼 near zone edge due to recent H I and He II photo-heating. Evidence for enhanced thermal broadening in the Ly-𝛼 absorption near the damping wing edge would provide further evidence that the final stages of reionisation are occurring at 𝑧 < 6.

Citation

Fiona, S., James S., B., George D., B., Luke, C., Martin G., H., Laura, K., Girish, K., & Ewald, P. (in press). How probable is the Lyman-alpha damping wing in the spectrum of the redshift z = 5.9896 quasar ULAS J0148+0600?. Monthly Notices of the Royal Astronomical Society,

• Journal Article Type: Article
• Acceptance Date: May 22, 2025
• Deposit Date: Jun 27, 2025
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Keywords: methods: numerical – intergalactic medium – quasars: absorption lines – dark ages, reionisation, first stars
• Public URL: https://nottingham-repository.worktribe.com/output/45161674
• Publisher URL: https://academic.oup.com/mnras