–
Ottobre 15, 2025
The Lyman-alpha forest in high-redshift quasar spectra is a key
observational tool to study the tail end of the Epoch of Reionization
(EoR). In particular, the presence of Gunn-Peterson troughs with lengths
up to ~100 comoving Mpc suggests the existence of extended neutral
regions and large-scale correlations in the intergalactic medium (IGM)
near the reionization <a href="http://boundary.
I" target="_blank" title="boundary.
I">boundary.
I will present two complementary results from high-S/N, high-resolution
quasar spectra from the XQR-30 sample and additional VLT/X-Shooter and
Keck/ESI data, that address both the ionization state and the coherence
scale of the IGM at 5 < z < 6. First, by stacking Lyman-alpha forest
dark-gap edges adjacent to Gunn–Peterson troughs, we detect a stochastic
damping-wing signal at z ~ 5.6 and infer a model-independent neutral
fraction of x_HI = 0.19 ± 0.07 (1σ) with x_HI < 0.44 at z = 5.9,
demonstrating the presence of neutral islands close to the end of
reionization and favoring a late-and-slow scenario. Second, we measure
the redshift-dependent correlation length of Lyman-alpha transmission by
fitting the flux-correlation matrix with an MCMC framework and
benchmarking against 1.5 Gpc³ reionization lightcones. We find strong,
rapidly increasing correlations toward higher redshift, from L ≤ 26.5
(68.5) Mpc (1σ/2σ) at z = 5.0 to L = 253 (+273/-42) Mpc at z = 6.1,
exceeding <60 Mpc predicted by current simulations incorporating UV
background fluctuations and neutral islands. These results jointly imply
(i) substantial residual neutrality at 5.6 < z < 6 and (ii) IGM
coherence on >200 Mpc scales at z ~ 6, setting hard requirements on
simulation volumes and suggesting missing large-scale physics in
standard EoR <a href="http://models.
" target="_blank" title="models.
">models.