The Black Hole Masses and Eddington Ratios of Type 2 Quasars

摘要

Type?2 quasars are an important constituent of active galaxies, possibly representing the evolutionary precursors of traditionally studied type?1 quasars. We characterize the black hole (BH) mass (M BH) and Eddington ratio (L bol/L Edd) for 669 type?2 quasars selected from the Sloan Digital Sky Survey, using BH masses estimated from the M BH–σ * relation and bolometric corrections scaled from the extinction-corrected [O iii] λ5007 luminosity. When stellar velocity dispersions cannot be measured directly from the spectra, we estimate them from the core velocity dispersions of the narrow emission lines [O ii] λλ3726, 3729, [S ii] λλ6716, 6731, and [O iii] λ5007, which are shown to trace the gravitational potential of the stars. Energy input from the active nucleus still imparts significant perturbations to the gas kinematics, especially to high-velocity, blueshifted wings. Nonvirial motions in the gas become most noticeable in systems with high Eddington ratios. The BH masses of our sample of type?2 quasars range from M BH?≈?106.5 to 1010.4 M ⊙ (median 108.2 M ⊙). Type?2 quasars have characteristically large Eddington ratios (L bol/L Edd?≈?10?2.9–101.8; median 10?0.7), slightly higher than in type?1 quasars of similar redshift; the luminosities of ~20% of the sample formally exceed the Eddington limit. The high Eddington ratios may be consistent with the notion that obscured quasars evolve into unobscured quasars.