Weak line quasars at high redshift: Extremely high accretion rates or anemic broad-line regions?

Abstract

We present Gemini-North K-band spectra of two representative members of the class of high-redshift quasars with exceptionally weak rest-frame ultraviolet emission lines (WLQs), SDSS J114153.34+021924.3 at z = 3.55 and SDSS J123743.08+630144.9 at z = 3.49. In both sources, we detect an unusually weak broad Hβ line and place tight upper limits on the strengths of their [Oiii] lines. Virial, Hβ-based black hole mass determinations indicate normalized accretion rates of L/LEdd= 0 .4 for these sources, which is well within the range observed for typical quasars with similar luminosities and redshifts.We also present high-quality XMM-Newton imaging spectroscopy of SDSS J114153.34+021924.3 and find a hard-X-ray photon index of Γ = 1.91 -0.22+0.24, which supports the virial L/LEdd determination in this source. Our results suggest that theweakness of the broad emission lines inWLQsis not a consequence of an extreme continuum-emission source but instead due to abnormal broad emission line region properties. © 2010 The American Astronomical Society. All rights reserved.