Eddington Accretion and QSO Emission Lines at z ~2

Abstract

Broad absorption line (BAL) QSOs have been suggested to be youthful superaccretors based on their powerful radiatively driven absorbing outflows and often reddened continua. To test this hypothesis, we observed near-IR spectra of the Hβ region for 11 bright BAL QSOs at redshift z ~ 2. We measured these and literature spectra for six BAL QSOs and 13 radio-loud and seven radio-quiet non-BAL QSOs. Using the luminosity and Hβ broad line width to derive black hole mass and accretion rate, we find that both BAL and non-BAL QSOs at z ~ 2 tend to have higher L/LEdd than those at low z—probably a result of selecting the brightest QSOs. However, we find that the high-z QSOs, in particular the BAL QSOs, have extremely strong Fe II and very weak [O III], extending the inverse relationship found for low-z QSOs. This suggests that, even while radiating near LEdd, the BAL QSOs have a more plentiful fuel supply than non-BAL QSOs. Comparison with low-z QSOs shows for the first time that the inverse Fe II-[O III] relationship is indeed related to L/LEdd, rather than black hole mass.