Probing the early growth of supermassive black holes with the environment of high-redshift quasars

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This work aims at probing the early growth of supermassive black holes in the early universe. Supermassive black holes, which can be over millions of solar masses, are found to be ubiquitous at the center of local massive galaxies, like our Milky Way. How are these monsters formed and evolved? Theoretical works suggest two possible origins: a heavy black hole seed or a typical stellar-mass black hole seed with powerful growth.In this work, thanks to the wide and deep imaging of the Hyper Suprime-Cam Subaru Strategic Program, we constructed a large sample of quasars (i.e., rapidly growing supermassive black holes) over a wide luminosity range at redshift 4 (around 1.5 Gyr after the BigBang). Compared to previous works, this work extends the magnitude coverage of quasar sample towards the deep end by over 2 order of magnitude. The wide magnitude range makes our quasar sample more numerous, and it can provide less-biased view on early growth of supermassive black holes.We estimated their black hole mass and Eddington ratio (which can be used to quantify accretion rate) using Keck/DEIMOS and AAT/AAOmega spectrograph. In this fiscal year, we utilized the information to trace back their possible growth tracks. Results suggest 1) those quasars need a heavy black hole seed to be formed even under the extreme growing mode; and 2) those quasars are tending to "shut-down" their vigorous growth to episodic growth afterwards.