Program: GN-2021A-Q-319

The birth and early growth of supermassive black holes (SMBHs) are among the hottest topics of astronomy and astrophysics today. We are carrying out a spectroscopic survey for high-z quasars based on the Subaru Hyper Suprime-Cam (HSC) imaging data, and have so far identified 93 quasars at 5.6 < z < 7.1. The sample consists mostly of low-luminosity quasars that were overlooked in the past shallower surveys, and thus may represent a new population. In particular, it may include the first, long-anticipated cases of high-z dust-reddened quasars, theoretical models predict that the initial phase of SMBH assembly may happen in dusty environments, while only a small amount of dust extinction makes quasars invisible in the past rest-UV surveys. Our quasars also provide an ideal dataset to explore the high-z host galaxies, that are outshone by and extremely difficult to measure in previously-known luminous quasars. We have started a Gemini/NIRI snapshot imaging survey toward our low-luminosity quasars in the 2020B semester, and here propose to continue the project to complete J- and K-band photometry of the 93 quasars in 2021A. When combined with the optical imaging and spectroscopic data already available, the near-IR magnitudes provide a unique probe of dust reddening and host galaxy contribution. The obtained data will also set the ground for various future programs, exploiting the unprecedented sample of low-luminosity quasars in the early universe.