The Black Hole Masses and Eddington Ratios of Type 2 Quasars

Abstract

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 ] λ 5007 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 ] λλ 3726, 3729, [S ii ] λλ 6716, 6731, and [O iii ] λ 5007, 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  ≈ 10 6.5 to 10 10.4 M ⊙ (median 10 8.2 M ⊙ ). Type 2 quasars have characteristically large Eddington ratios ( L bol / L Edd  ≈ 10 −2.9 –10 1.8 ; 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.