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

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 Ba~nados, Sarah E. I. Bosman, Zheng Cai, Anna-Christina Eilers, Xiaohui Fan, Zolt’an Haiman, Hyunsung D. Jun, Yichen Liu, Jinyi Yang, Feige Wang
arXiv:2508.21818v1 Announce Type: new
Abstract: Thus far, Lyman-$alpha$ 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.arXiv:2508.21818v1 Announce Type: new
Abstract: Thus far, Lyman-$alpha$ 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.