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 2 115

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.3847/1538-4357/aceef4

More information

Latest update

10/31/2023