2017ApJ...846...57I

We present the result of our spectroscopic follow-up observation for faint quasar candidates at z ∼ 5 in part of the Canada-France-Hawaii Telescope Legacy Survey wide field. We select nine photometric candidates and identify three z ∼ 5 faint quasars, one z ∼ 4 faint quasar, and a late-type star. Since two faint quasar spectra show the C IV emission line without suffering from a heavy atmospheric absorption, we estimate their black hole masses (M_BH) and Eddington ratios (L/L_Edd). The inferred logM_BH are 9.04 ± 0.14 and 8.53 ± 0.20, respectively. In addition, the inferred log(L/L_Edd) are -1.00 ± 0.15 and -0.42 ± 0.22, respectively. If we adopt that L/L_Edd=constant or∝(1+z)², the seed black hole masses (M_seed) of our z ∼ 5 faint quasars are expected to be 10⁵ M_☉ in most cases. We also compare the observational results with a mass accretion model, where angular momentum is lost due to supernova explosions. Accordingly, M_BH of the z ∼ 5 faint quasars in our sample can be explained even if M_seed is ∼10³ M_☉. Since z ∼ 6 luminous qusars and our z ∼ 5 faint quasars are not on the same evolutionary track, z ∼ 6 luminous quasars and our z ∼ 5 quasars are not the same populations but different populations, due to the difference of a period of the mass supply from host galaxies. Furthermore, we confirm that one can explain M_BH of z ∼ 6 luminous quasars and our z ∼ 5 faint quasars even if their seed black holes are formed at z ∼ 7.