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

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 $⟨x_{\mathrm{HI}}⟩=0.32_{-0.20}^{+0.22}$ ($0.58_{-0.23}^{+0.23}$) 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.

submitted to MNRAS

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