@article{76ae2e27bc24462da76bde9c61d0d0d6,
title = "Definitive upper bound on the negligible contribution of quasars to cosmic reionization",
abstract = "Cosmic (hydrogen) reionization marks one of the major phase transitions of the universe at redshift z ≥ 6. During this epoch, hydrogen atoms in the intergalactic medium were ionized by Lyman continuum (LyC) photons. However, it remains challenging to identify the major sources of the LyC photons responsible for reionization. In particular, individual contributions of quasars (or active galactic nuclei) and galaxies are still under debate. Here we construct the far-ultraviolet luminosity function for type 1 quasars at z ≥ 6 that spans 10 magnitudes (−19 ≤ MUV ≤ −29), conclusively showing that quasars made a negligible contribution to reionization. We mainly search for quasars in the low-luminosity range of MUV > −23 mag that is critical for determination of the total LyC photon production of quasars but has been barely explored previously. We find that the quasar population can only provide less than 7% (95% confidence level) of the total photons needed to keep the universe ionized at z = 6.0–6.6. Our result suggests that galaxies, presumably low-luminosity star-forming systems, are the major sources of hydrogen reionization.",
author = "Linhua Jiang and Yuanhang Ning and Xiaohui Fan and Ho, {Luis C.} and Bin Luo and Feige Wang and Jin Wu and Wu, {Xue Bing} and Jinyi Yang and Zheng, {Zhen Ya}",
note = "Funding Information: This research was funded by the Shenzhen Science and Technology Innovation Commission 2020 Basic Research Project (JCYJ20200109110630285); the State Key Laboratory of Space Medicine Fundamentals and Application and the China Astronaut Research and Training Center (SMFA17A02, SMFA18B02, SMFA18B06, SMFA19A01, SMFA19C03), and the Space Medical Experiment Project of China Manned Space Program (HYZHXM01002). There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Funding Information: The following grant information was disclosed by the authors: Shenzhen Science and Technology Innovation Commission 2020 Basic Research Project: JCYJ20200109110630285. State Key Laboratory of Space Medicine Fundamentals and Application and the China Astronaut Research and Training Center: SMFA17A02, SMFA18B02, SMFA18B06, SMFA19A01, SMFA19C03. Space Medical Experiment Project of China Manned Space Program: HYZHXM01002. Publisher Copyright: {\textcopyright} 2022, The Author(s), under exclusive licence to Springer Nature Limited.",
year = "2022",
month = jul,
doi = "10.1038/s41550-022-01708-w",
language = "English (US)",
volume = "6",
pages = "850--856",
journal = "Nature Astronomy",
issn = "2397-3366",
publisher = "Nature Publishing Group",
number = "7",
}