Xiaojing Lin, Xiaohui Fan, Feige Wang, Fengwu Sun, Jaclyn B. Champagne, Eiichi Egami, Koki Kakiichi, Jianwei Lyu, Wei Leong Tee, Jinyi Yang, Fuyan Bian, Sarah E. I. Bosman, Zheng Cai, Caitlin M. Casey, Roberto Decarli, Andreas L. Faisst, Steven L. Finkelstein, Seiji Fujimoto, Santosh Harish, Olivier Ilbert, Akio Inoue, Xiangyu Jin, Jeyhan S. Kartaltepe, Dale D. Kocevski, Mingyu Li, Weizhe Liu, Yichen Liu, Jan–Torge Schindler, Marko Shuntov, Takumi S. Tanaka, Marianne Vestergaard, Yunjing Wu, Haowen Zhang, Zijian Zhang
Abstract We report the discovery of 13 broad-line active galactic nuclei (AGNs) at z = 5–8 from the first 10% of JWST Cycle 3 Treasury Program COSMOS-3D. These AGNs are identified by their broad H α or H β emission lines through NIRCam grism slitless spectroscopy. One object at z = 7.646 with broad H β emission has an F444W magnitude of 23.6 mag, making it one of the brightest z > 7.5 broad-line AGNs yet known. Among the 13 AGNs, 10 objects exhibit reddened optical continua with slopes β opt > 0. The remaining three resemble UV-luminous quasars at similar redshift but with β opt less blue than those of typical unobscured quasars. We also obtain MIRI photometry (7.7–18 μ m) for two AGNs and place strong constraints on their rest-frame near-IR spectral energy distribution. We find no significant variability in the rest-frame UV by comparing the COSMOS-3D and COSMOS-Web F115W images taken apart by 60 days in the rest-frame. We compute the H α luminosity function (LF) at z ≈ 5–6 and find potential redshift evolution compared to z ≈ 4–5. We also derive the H β LF at z ∼ 8 by combining our sample with those from the literature. The broad H β emitters in this work suggest a number density 2 orders of magnitude higher than that predicted by the quasar LF based on rest-frame UV-selected samples. As a preview, our work showcases the ability of the COSMOS-3D grism survey to provide a complete view of the properties, growth, and evolution of bright broad-line AGNs at z > 5.