Rapidly Accreting Black Hole of the Lyα-luminous Quasar PSOJ006.1240+39.2219

Abstract

Abstract We present near-infrared 1.1–1.3 and 1.3–1.6 μm spectra of the Lyα-luminous quasar PSO J006.1240+39.2219 at z = 6.617 ± 0.003 obtained with the NIRSPEC spectrograph at the Keck II telescope. The spectra cover the C iv λ1549, C iii] λ1909 emission lines and part of the UV continuum of the quasar. From the NIRSPEC observations of PSO J006.1240+39.2219, we constrain the spectral slope of its UV continuum to be α λ = −1.35 ± 0.26 and measure an absolute magnitude of M 1450 = −25.60. Using the scaling relation between black hole mass, width of the C iv line and ultraviolet continuum luminosity, we derive a black hole mass of (2.19 ± 0.30) × 108 M ⊙, which is consistent but somewhat smaller than the typical black hole masses of z ≳ 6 quasars of similar luminosities. The inferred accretion rate of L Bol/L Edd ≳ 2 indicates that PSO J006.1240+39.2219 is in the phase of the rapid growth of its supermassive black hole characterized by the high N v/C iv line ratio, N v/C iv > 1, and the lower level of ionization of its circumnuclear gas than in other high-redshift luminous quasars. The N v/C iv line ratio of PSO J006.1240+39.2219 implies a relatively high abundance of nitrogen in its circumnuclear gas. This abundance might be produced by the post-starburst population of stars that provide the fuel for black hole accretion.