IGM damping wing constraints on reionisation from covariance reconstruction of two z greater than or similar to 7 QSOs

Bright, high-redshift (z > 6) QSOs are powerful probes of the ionization state of the intervening intergalactic medium (IGM). The detection of Ly α damping wing absorption imprinted in the spectrum of high-z QSOs can provide strong constraints on the epoch of reionization (EoR). In this work, we perform an independent Ly α damping wing analysis of two known z > 7 QSOs; DESJ0252−0503 at z = 7.00 (Wang et al.) and J1007+2115 at z = 7.51 (Yang et al.). For this, we utilize our existing Bayesian framework which simultaneously accounts for uncertainties in: (i) the intrinsic Ly α emission profile (reconstructed from a covariance matrix of measured emission lines; extended in this work to include N v) and (ii) the distribution of ionized (H ii) regions within the IGM using a 1.63 Gpc3 reionization simulation. This approach is complementary to that used in the aforementioned works as it focuses solely redward of Ly α (1218 < λ < 1230 Å) making it more robust to modelling uncertainties while also using a different methodology for (i) and (ii). We find, for an EoR morphology driven by galaxies within Mh ≳ 109 M⊙ haloes, x¯HI=0.64+0.19−0.23 (68 per cent) at z = 7 and x¯HI=0.27+0.21−0.17 at z = 7.51 consistent within 1σ to the previous works above, though both are slightly lower in amplitude. Following the inclusion of N v into our reconstruction pipeline, we perform a reanalysis of ULASJ1120+0641 at z = 7.09 (Mortlock et al.) and ULASJ1342+0928 at z = 7.54 (Bañados et al.) finding x¯HI=0.44+0.23−0.24 at z = 7.09 and x¯HI=0.31+0.18−0.19 at z = 7.54. Finally, we combine the QSO damping wing constraints for all four z ≳ 7 QSOs to obtain a single, unified constraint of x¯HI=0.49+0.11−0.11 at z = 7.29.