First constraints on the local ionization topology in front of two quasars at <i>z</i> ∼ 7.5

ABSTRACT Thus far, Lyman-$\alpha$ damping wings towards quasars have been used to probe the global ionization state of the foreground intergalactic medium (IGM). A new parametrization has demonstrated that the damping wing signature also carries local information about the distribution of neutral hydrogen (H i) in front of the quasar before it started shining. Leveraging a recently introduced Bayesian jax-based Hamiltonian Monte Carlo inference framework, we derive constraints on the Lorentzian-weighted H i column density $N_\mathrm{H\, {\small I}}^\mathrm{DW}$, the quasar’s distance $r_\mathrm{patch}$ to the first neutral patch, and its lifetime $t_\mathrm{Q}$ based on James Webb Space Telescope (JWST) Near Infrared Spectrograph (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 $\langle x_\mathrm{H\, {\small I}} \rangle = 0.32_{-0.20}^{+0.22}$ ($0.58_{-0.23}^{+0.23}$) 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 $\log _{10} N_\mathrm{H\, {\small I}}^\mathrm{DW}/\mathrm{cm}^{-2}= 19.70_{-0.86}^{+0.35}$ ($20.24_{-0.22}^{+0.25}$) 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 $N_\mathrm{H\, {\small I}}^\mathrm{DW}$ provides a natural means for quantifying their contribution to the observed damping wing signal.