IGM damping wing constraints on the tail end of reionisation from the enlarged XQR-30 sample
arxiv(2024)
摘要
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 reionisation. Given a framework to estimate the intrinsic
(true) Lyα emission of high-z sources, one can infer the ionisation
state of the IGM during reionisation. In this work, we use the enlarged XQR-30
sample of 42 high-resolution and high-SNR QSO 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-ionisation emission line profiles; C IV,
Si IV + O IV] and C III]) and (ii) distribution of ionised regions within the
IGM using synthetic damping wing profiles drawn from a 1.6^3 Gpc^3
reionisation 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 reionisation. 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 x̅_H I <
0.21, 0.20, 0.21 and 0.18 at z = 5.8, 5.95, 6.05 and 6.55. These results
imply reionisation 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.
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