WEAK LINE QUASARS AT HIGH REDSHIFT: EXTREMELY HIGH ACCRETION RATES OR ANEMIC BROAD-LINE REGIONS?

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 H beta line and place tight upper limits on the strengths of their [O III] lines. Virial, H beta-based black hole mass determinations indicate normalized accretion rates of L/L-Edd = 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 Gamma = 1.91(-0.22)(+0.24) which supports the virial L/L-Edd determination in this source. Our results suggest that the weakness of the broad emission lines in WLQsis not a consequence of an extreme continuum-emission source but instead due to abnormal broad emission line region properties.