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 ≤ M_UV ≤ −29), conclusively showing that quasars made a negligible contribution to reionization. We mainly search for quasars in the low-luminosity range of M_UV > −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.

宇宙（氢）再电离标志着宇宙在红移z  ≥ 6 处的主要相变之一。在这一时期，星际介质中的氢原子被莱曼连续谱 (LyC) 光子电离。然而，确定负责再电离的 LyC 光子的主要来源仍然具有挑战性。特别是，类星体（或活动星系核）和星系的个体贡献仍在争论中。在这里，我们构建了z ≥ 6的 1 型类星体的远紫外光度函数 ，跨越 10 个星等（-19 ≤  M _UV  ≤ -29），最终表明类星体对再电离的贡献可以忽略不计。我们主要寻找M _{UV低光度范围内的类星体} > -23 等，这对于确定类星体的总 LyC 光子产生至关重要，但以前几乎没有被探索过。我们发现类星体群体只能提供不到 7%（95% 的置信水平）将宇宙电离在z  = 6.0–6.6 所需的总光子。我们的结果表明，星系，可能是低光度恒星形成系统，是氢再电离的主要来源。