Shedding New Light on Weak Emission-line Quasars in the C IV-Hβ Parameter Space
Brandt, W. N.; Myers, Adam D.; Strauss, Michael A.; Anderson, Scott F.; Fan, Xiaohui; Schneider, Donald P.; Luo, Bin; Trakhtenbrot, Benny; Gallagher, S. C.; Diamond-Stanic, Aleksandar M.; Green, Richard; Netzer, Hagai; Brotherton, Michael S.; Richards, Gordon T.; Plotkin, Richard M.; Ha, Trung; Dix, Cooper; Matthews, Brandon M.; Shemmer, Ohad; Maithil, Jaya; Lira, Paulina; Runnoe, Jessie C.; Wu, Jianfeng
United States, Canada, Chile, China, Israel
Abstract
Weak emission-line quasars (WLQs) are a subset of type 1 quasars that exhibit extremely weak Lyα + N V λ1240 and/or C IV λ1549 emission lines. We investigate the relationship between emission-line properties and accretion rate for a sample of 230 "ordinary" type 1 quasars and 18 WLQs at z < 0.5 and 1.5 < z < 3.5 that have rest-frame ultraviolet and optical spectral measurements. We apply a correction to the Hβ-based black hole mass (M BH) estimates of these quasars using the strength of the optical Fe II emission. We confirm previous findings that WLQs' M BH values are overestimated by up to an order of magnitude using the traditional broad-emission-line region size-luminosity relation. With this M BH correction, we find a significant correlation between Hβ-based Eddington luminosity ratios and a combination of the rest-frame C IV equivalent width and C IV blueshift with respect to the systemic redshift. This correlation holds for both ordinary quasars and WLQs, which suggests that the two-dimensional C IV parameter space can serve as an indicator of accretion rate in all type 1 quasars across a wide range of spectral properties.