アブストラクト：
"We present the latest results obtained from a semi-analytic model of galaxy formation related to the growth history of SMBHs at z < 8. We focus on (1) the growth timescale (AGN lifetime) and (2) Eddington ratio distribution function. For the growth timescale, we find that the growth timescale of less-luminous AGNs could be longer than that of quasars, namely > 10^7 yr. This result implies that even if AGNs are triggered only by mergers of galaxies, we could explain the faint end slope of AGN luminosity functions. For the Eddington ratio distribution, we find that super-Eddington accreting growth should be important for less massive SMBHs (it always means less luminous AGNs) at higher redshift although they are elusive due to the current observational limitations. We show the evolution of the distribution function from z ~ 8 with varying the sample selection to show the importance of deep surveys of less-luminous AGNs in the future."