Emission-Line Properties of Optically and Radio-selected Complete Quasar Samples

We present spectrophotometry of two complete samples of quasars, one found from the flat radio spectra of the objects and the other from their optical colors. We confirm that the equivalent widths of the major ultraviolet emission lines decrease with increasing continuum luminosity (the "Baldwin effect"), and that the (Lyα + N V)/C IV and λ1909/C IV intensity ratios are also luminosity dependent by virtue of the C IV luminosity dependence. We also show that the Mg II/C IV intensity ratio and possibly the strengths of the blue Fe II emission features and the FWHM of the λ1909 blend are luminosity dependent. These results generally support the Mushotzky and Ferland interpretation of the Baldwin effect in terms of a weak inverse correlation between the continuum luminosity and ionization parameter. Except for the possibility of evolution with look-back time, these luminosity-dependent effects still appear to be a valid way of calibrating quasar luminosities for cosmological tests. Possible differences in the optical spectra which might correlate with the very different radio properties of these two quasar samples are masked by these luminosity-dependent effects. Any future comparison between optical and radio-selected quasars should be made using a fainter sample of optically selected quasars which have luminosities comparable to those of the radio-selected sample.