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arXiv · 2508.21818

First constraints on the local ionization topology in front of two quasars at z ~ 7.5

Timo Kist·Joseph F. Hennawi·Frederick B. Davies·Eduardo Bañados·Sarah E. I. Bosman·Zheng Cai·Anna-Christina Eilers·Xiaohui Fan·Zoltán Haiman·Hyunsung D. Jun·Yichen Liu·Jinyi Yang·Feige Wang
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Abstract

Thus far, Lyman-$α$ damping wings towards quasars have been used to probe the \textit{global} ionization state of the foreground intergalactic medium (IGM). A new parameterization has demonstrated that the damping wing signature also carries \textit{local} information about the distribution of neutral hydrogen (HI) in front of the quasar before it started shining. Leveraging a recently introduced Bayesian \texttt{JAX}-based Hamiltonian Monte Carlo (HMC) inference framework, we derive constraints on the Lorentzian-weighted HI column density $N_\mathrm{HI}^\mathrm{DW}$, the quasar's distance $r_\mathrm{patch}$ to the first neutral patch and its lifetime $t_\mathrm{Q}$ based on JWST/NIRSpec spectra of the two $z \sim 7.5$ quasars J1007+2115 and J1342+0928. After folding in model-dependent topology information, we find that J1007+2115 (and J1342+0928) is most likely to reside in a $\langle x_\mathrm{HI} \rangle = 0.32_{-0.20}^{+0.22}$ ($0.58_{-0.23}^{+0.23}$) neutral IGM while shining for a remarkably short lifetime of $\log_{10} t_\mathrm{Q} /\mathrm{yr} = 4.14_{-0.18}^{+0.74}$ (an intermediate lifetime of $5.64_{-0.43}^{+0.25}$) along a sightline with $\log_{10} N_\mathrm{HI}^\mathrm{DW} /\mathrm{cm}^{-2} = 19.70_{-0.86}^{+0.35}$ ($20.24_{-0.22}^{+0.25}$) and $r_\mathrm{patch} = 28.9_{-14.4}^{+54.0} \,\mathrm{cMpc}$ ($10.9_{-5.9}^{+5.6} \,\mathrm{cMpc}$). In light of the potential presence of local absorbers in the foreground of J1342+0928 as has been recently suggested, we also demonstrate how the Lorentzian-weighted column density $N_\mathrm{HI}^\mathrm{DW}$ provides a natural means for quantifying their contribution to the observed damping wing signal.

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Timo Kist, Joseph F. Hennawi, Frederick B. Davies, Eduardo Bañados, Sarah E. I. Bosman, Zheng Cai, Anna-Christina Eilers, Xiaohui Fan, Zoltán Haiman, Hyunsung D. Jun, Yichen Liu, Jinyi Yang, Feige Wang. 2025-08-29. First constraints on the local ionization topology in front of two quasars at z ~ 7.5. https://doi.org/10.1093/mnras%2Fstaf2219

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