The Blueshift of the C iv Broad Emission Line in QSOs

Abstract

For the sample from Ge et al. of 87 low-z Palomar-Green quasi-stellar objects (QSOs) and 130 high-z QSOs (0 < z < 5) with H beta-based single-epoch supermassive black hole masses, we perform a uniform decomposition of the C IV lambda 1549 broad-line profile. Based on the rest frame defined by the [O III] lambda 5007 narrow emission line, a medium-strong positive correlation is found between the C IV blueshift and the luminosity at 5100 angstrom or the Eddington ratio L-Bol/L-Edd. A medium-strong negative relationship is found between the C IV blueshift and C IV equivalent width. These results support the postulation where the radiation pressure may be the driver of C IV blueshift. There is a medium-strong correlation between the mass ratio of C IV-based to H beta-based M-BH and the C IV blueshift, which indicates that the bias for C IV-based M-BH is affected by the C IV profile.