Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6
Journal article, 2023
The mean free path of ionizing photons, lambda(mfp), is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of lambda(mfp) from QSO spectra over the redshift range 5 < z < 6, including the first measurements at z similar or equal to 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 similar to 5.5, for which we also acquire new [C II] 158 mu m redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find lambda(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 lambda(mfp) increases steadily and rapidly with time over 5 < z < 6. Notably, we find that lambda(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 lambda(mfp) constraints based on IGM Ly alpha opacity, we find that the evolution of lambda(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.
Author
Yongda Zhu
University of California at Riverside
George D. Becker
University of California at Riverside
Holly M. Christenson
University of California at Riverside
Anson D'Aloisio
University of California at Riverside
Sarah E. I. Bosman
Heidelberg University
Max Planck Society
Tom Bakx
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Valentina D'Odorico
Scuola Normale Superiore di Pisa
Istituto nazionale di astrofisica (INAF)
IFPU—Institute for Fundamental Physics of the Universe
Manuela Bischetti
University of Trieste
Christopher Cain
University of California at Riverside
Frederick B. Davies
Max Planck Society
Rebecca L. Davies
ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
Swinburne University of Technology
Anna-Christina Eilers
Massachusetts Institute of Technology (MIT)
Xiaohui Fan
University of Arizona
Prakash Gaikwad
Max Planck Society
Martin G. Haehnelt
University of Edinburgh
Kavli Institute for Cosmology
Laura C. Keating
University of Edinburgh
Girish Kulkarni
Tata Institute of Fundamental Research
Samuel Lai
Australian National University
Hai-Xia Ma
Nagoya University
Andrei Mesinger
Scuola Normale Superiore di Pisa
Yuxiang Qin
University of Melbourne
ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
Sindhu Satyavolu
Tata Institute of Fundamental Research
Tsutomu T. Takeuchi
The Institute of Statistical Mathematics
Nagoya University
Hideki Umehata
Nagoya University
Jinyi Yang
University of Arizona
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 955 2 115Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.3847/1538-4357/aceef4