Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6

Journal
Date Issued
2023
Author(s)
Zhu, Yongda
•
Becker, George D.
•
Christenson, Holly M.
•
D'Aloisio, Anson
•
Bosman, Sarah E. I.
•
Bakx, Tom
•
•
•
Cain, Christopher
•
Davies, Frederick B.
•
Davies, Rebecca L.
•
Eilers, Anna-Christina
•
Fan, Xiaohui
•
Gaikwad, Prakash
•
Haehnelt, Martin G.
•
Keating, Laura C.
•
Kulkarni, Girish
•
Lai, Samuel
•
Ma, Hai-Xia
•
•
Qin, Yuxiang
•
Satyavolu, Sindhu
•
Takeuchi, Tsutomu T.
•
Umehata, Hideki
•
Yang, Jinyi
DOI
Abstract
The mean free path of ionizing photons, λ mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of λ mfp 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 mfp increases steadily and rapidly with time over 5 < z < 6. Notably, we find that λ mfp 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 mfp constraints based on IGM Lyα opacity, we find that the evolution of λ mfp 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.
Volume
955
Issue
2
Start page
115
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2023ApJ...955..115Z
Rights
open.access
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