On the origin of the C IV Baldwin effect in AGN

The origin of the luminosity dependence of the equivalent width (EW) of broad emission lines in AGN (the Baldwin effect) is not firmly established yet. We explore this question for the broad C IV \lambda 1549 line using the Boroson & Green sample of the 87 z < 0.5 Bright Quasar Survey (BQS) quasars. Useful UV spectra of the C IV region are available for 81 of the objects, which are used to explore the dependence of the C IV EW on various emission properties. We confirm earlier results on the strong correlations of the C IV EW with some of the emission parameters which define the Boroson & Green Eigenvector 1, and with the optical to X-ray slope \alpha_ox. In addition, we find a strong correlation of the C IV EW with the relative accretion rate, L/L_Edd. Since L/L_Edd drives some of the Eigenvector 1 correlations, it may be the primary physical parameter which drives the Baldwin effect for C IV.