TY - JOUR
T1 - Probing Ultralate Reionization
T2 - Direct Measurements of the Mean Free Path over 5 < z < 6
AU - Zhu, Yongda
AU - Becker, George D.
AU - Christenson, Holly M.
AU - D’Aloisio, Anson
AU - Bosman, Sarah E.I.
AU - Bakx, Tom
AU - D’Odorico, Valentina
AU - Bischetti, Manuela
AU - Cain, Christopher
AU - Davies, Frederick B.
AU - Davies, Rebecca L.
AU - Eilers, Anna Christina
AU - Fan, Xiaohui
AU - Gaikwad, Prakash
AU - Haehnelt, Martin G.
AU - Keating, Laura C.
AU - Kulkarni, Girish
AU - Lai, Samuel
AU - Ma, Hai Xia
AU - Mesinger, Andrei
AU - Qin, Yuxiang
AU - Satyavolu, Sindhu
AU - Takeuchi, Tsutomu T.
AU - Umehata, Hideki
AU - Yang, Jinyi
N1 - Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/10/1
Y1 - 2023/10/1
N2 - 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 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 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.
AB - 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 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 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.
UR - https://www.scopus.com/pages/publications/85174275423
UR - https://www.scopus.com/pages/publications/85174275423#tab=citedBy
U2 - 10.3847/1538-4357/aceef4
DO - 10.3847/1538-4357/aceef4
M3 - Article
AN - SCOPUS:85174275423
SN - 0004-637X
VL - 955
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 115
ER -