Studying dark gaps in Lyman-α forest transmission with large reionization simulations

The physical conditions of the intergalactic medium (IGM) during the final stages of cosmic reionization (z) correlation in Lyman (Ly) -α transmission flux using extended XQR-30 quasar spectra pose interesting challenges on the reionization end stages. In this work, we investigated the Ly-α forest dark-gap distribution (defined as regions with transmitted flux below 0. 05) as another sensitive tracer of the IGM, using an efficient, large-volume (∼ 1) simulation framework. By constructing a suite of physically motivated model variants (i. e, varying the reionization redshift, IGM temperature, and ionizing-photon mean free path), we generated synthetic sightlines and compared their predicted cumulative distribution of dark gaps with that of observed spectra (at redshift intervals of Δ z=0. 2). We find that most of the models achieve qualitatively consistent agreement with the data. The scenario with a slightly later reionization completion (z∼ 5. 4) provides the closest match, whereas a short, constant mean free path model is disfavored by the data at lower redshifts. These findings give qualitative support for the emerging scenario of reionization end extending to złe5. 7, although they can not rule out a slightly early reionization with enhanced post-ionization ultraviolet (UV) background fluctuations. A similar conclusion arises from the redshift distribution of long dark gap (L) fraction. However, the model variants are still not able to reproduce the observed strong flux correlations at unusually large scales, which remain open for further investigations. are not yet fully understood. Recent reports of unexpectedly large-scale (ge 150 h^ -1 cMpc Gpc 30 h^ -1 cMpc