IGM damping wing constraints on the tail end of reionization from the enlarged XQR-30 sample

ABSTRACT The attenuation of Lyα photons by neutral hydrogen in the intergalactic medium (IGM) at z ≳ 5 continues to be a powerful probe for studying the epoch of reionization. Given a framework to estimate the intrinsic (true) Lyα emission of high-z sources, one can infer the ionization state of the IGM during reionization. In this work, we use the enlarged XQR-30 sample of 42 high-resolution and high signal-to-noise quasar spectra between 5. 8 \, z \, 6. 6 obtained with VLT/X-shooter to place constraints on the IGM neutral fraction. This is achieved using our existing Bayesian QSO reconstruction framework which accounts for uncertainties such as the: (i) posterior distribution of predicted intrinsic Lyα emission profiles (obtained via covariance matrix reconstruction of the Lyα and N v emission lines from unattenuated high-ionization emission line profiles; C iv, Si iv + O iv], and C iii]) and (ii) distribution of ionized regions within the IGM using synthetic damping wing profiles drawn from a 1. 63 Gpc3 reionization simulation. Following careful quality control, we used 23 of the 42 available QSOs to obtain constraints/limits on the IGM neutral fraction during the tail-end of reionization. Our median and 68th percentile constraints on the IGM neutral fraction are: 0. 20+0. 14 -0. 12 and 0. 29+0. 14 -0. 13 at z = 6. 15 and 6. 35. Further, we also report 68th percentile upper limits of x₇\, ₈{} 0. 21, 0. 20, 0. 21, and 0. 18 at z = 5. 8, 5. 95, 6. 05, and 6. 55. These results imply reionization is still ongoing at 5. 8 \, z \, 6. 55, consistent with previous results from XQR-30 (dark fraction and Lyα forest) along with other observational probes considered in the literature.