Supermassive black holes in the early universe

We analyzed spectra of 15 luminous high-redshift quasars (3.3<z<5.1) and we derived black hole masses that are based on Hβ, MgII, and CIV emission lines, in the range of 2×10⁸<M_bh<4×10¹⁰ M_⊙. Assuming exponential growth of the black holes we estimated that it takes about several 100 Myr up to 1 Gyr to accumulate the observed black hole masses, i.e., most of the SMBHs that power these quasars at high-redshifts, started to grow at z ≃ 5 {to} 10.