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

arXiv · 2502.03085

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

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Abstract

The shape of the Ly-$\alpha$ transmission in the near zone of the redshift $z=5.9896$ quasar ULAS J0148$+$0600 (hereafter J0148) is consistent with a damping wing arising from an extended neutral hydrogen island in the diffuse intergalactic medium (IGM). Here we use simulations of late-ending reionisation from Sherwood-Relics to assess the expected incidence of quasars with Ly-$\alpha$ and Ly-$\beta$ 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-$\alpha$ damping wing consistent with J0148. This occurs in $\sim3$ per cent of our simulated spectra for an IGM neutral fraction $\langle x_{\rm HI}\rangle=0.14$ 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-$\alpha$ damping wing profile \emph{and} Ly-$\alpha$ 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 $t<10^{5}\rm\,yr$, or alternatively that the Ly-$\alpha$ 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 $T\sim 4\times 10^{4}\rm\,K$ within a few proper Mpc of the Ly-$\alpha$ near zone edge due to recent H$\,\rm \scriptstyle I$ and He$\,\rm \scriptstyle II$ photo-heating. Evidence for enhanced thermal broadening in the Ly-$\alpha$ absorption near the damping wing edge would provide further evidence that the final stages of reionisation are occurring at $z<6$.

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Fiona Sawyer, James S. Bolton, George D. Becker, Luke Conaboy, Martin G. Haehnelt, Laura Keating, Girish Kulkarni, Ewald Puchwein. 2025-02-05. How probable is the Lyman-$\alpha$ damping wing in the spectrum of the redshift z = 5.9896 quasar ULAS J0148+0600?. https://arxiv.org/abs/2502.03085

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