Zhu, YongdaYongdaZhuBecker, George D.George D.BeckerChristenson, Holly M.Holly M.ChristensonD'Aloisio, AnsonAnsonD'AloisioBosman, Sarah E. I.Sarah E. I.BosmanBakx, TomTomBakxD'ODORICO, ValentinaValentinaD'ODORICOBISCHETTI, ManuelaManuelaBISCHETTICain, ChristopherChristopherCainDavies, Frederick B.Frederick B.DaviesDavies, Rebecca L.Rebecca L.DaviesEilers, Anna-ChristinaAnna-ChristinaEilersFan, XiaohuiXiaohuiFanGaikwad, PrakashPrakashGaikwadHaehnelt, Martin G.Martin G.HaehneltKeating, Laura C.Laura C.KeatingKulkarni, GirishGirishKulkarniLai, SamuelSamuelLaiMa, Hai-XiaHai-XiaMaMesinger, AndreiAndreiMesingerQin, YuxiangYuxiangQinSatyavolu, SindhuSindhuSatyavoluTakeuchi, Tsutomu T.Tsutomu T.TakeuchiUmehata, HidekiHidekiUmehataYang, JinyiJinyiYang2024-11-082024-11-0820230004-637Xhttp://hdl.handle.net/20.500.12386/35374The mean free path of ionizing photons, λ <SUB>mfp</SUB>, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of λ <SUB>mfp</SUB> from QSO spectra over the redshift range 5 < z < 6, including the first measurements at z ≃ 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs near z ~ 5.5, for which we also acquire new [C II] 158 μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find ${\lambda }_{\mathrm{mfp}}={9.33}_{-1.80}^{+2.06}$ , ${5.40}_{-1.40}^{+1.47}$ , ${3.31}_{-1.34}^{+2.74}$ , and ${0.81}_{-0.48}^{+0.73}$ pMpc at z = 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate that λ <SUB>mfp</SUB> increases steadily and rapidly with time over 5 < z < 6. Notably, we find that λ <SUB>mfp</SUB> deviates significantly from predictions based on a fully ionized and relaxed IGM as late as z = 5.3. By comparing our results to model predictions and indirect λ <SUB>mfp</SUB> constraints based on IGM Lyα opacity, we find that the evolution of λ <SUB>mfp</SUB> is consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6.STAMPAenArticle10.3847/1538-4357/aceef42-s2.0-85174275423https://iopscience.iop.org/article/10.3847/1538-4357/aceef4https://api.elsevier.com/content/abstract/scopus_id/851742754232023ApJ...955..115ZFIS/05 - ASTRONOMIA E ASTROFISICA