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Creators/Authors contains: "Ma, Hai-Xia"

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  1. Abstract The mean free path of ionizing photons,λmfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements ofλmfpfrom QSO spectra over the redshift range 5 <z< 6, including the first measurements atz≃ 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 nearz∼ 5.5, for which we also acquire new [Cii] 158μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find λ 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 atz= 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate thatλmfpincreases steadily and rapidly with time over 5 <z< 6. Notably, we find thatλmfpdeviates significantly from predictions based on a fully ionized and relaxed IGM as late asz= 5.3. By comparing our results to model predictions and indirectλmfpconstraints based on IGM Lyαopacity, we find that the evolution ofλmfpis consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6. 
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