STATISTICS OF QSO BROAD EMISSION-LINE PROFILES .2. THE C-IV LAMBDA-1549, C-III LAMBDA-1909, AND MG-II LAMBDA-2798 LINES

We present the results of a statistical investigation of broad emission-line profiles in a sample of 85 intermediate redshift QSOs (primarily 0.9 less-than-or-equal-to z less-than-or-equal-to 2.2), split about equally between radio-loud and radio-quiet objects. These emission lines, from the spectra of Steidel & Sargent's Mg II lambda2798 absorption line survey, are reanalyzed in light of new results involving correlations with line width. Some new strong trends are found as line width (FWHM) increases: the ratio of line peak to continuum intensity decreases for C III] lambda1909, the intensity ratio C III] lambda1909/C IV lambda1549 increases, the intensity ratio C III] lambda1909/Mg II lambda2798 decreases, and the peaks of C III] lambda1909 and C IV lambda1549 become increasingly blueshifted relative to the Mg II lambda2798 peak. We present strong, clear differences between the broad emission-line spectra of radio-loud and radio-quiet QSOs. Radio-quiet objects have broader C III] lambda1909 and C IV lambda1549 lines than radio-loud objects, but the distributions of Mg II FWHMs do not differ significantly. The average ratio [FWHM(C III]/FWHM(Mg II)] = 1.59 +/- 0.08 and [FWHM(CIV)/FWHM(Mg II)] = 1.35 +/- 0.09 for radio-quiet objects, but both are consistent with unity (+/- 0.07) for radio-loud objects. The average ratio [FWHM(C III])/FWHM(C IV)] = 1.20 +/- 0.05 for both radio-loud and radio-quiet objects. We interpret these results in terms of the two-component profile that we presented in Paper I: a narrow core (FWHM approximately 2000 km s-1) and a broad base (FWHM approximately 7000 km s-1) blueshifted by approximately 1000 km s-1. The core-to-base ratio determines the FWHM, asymmetry, and line shift. In general, radio-loud objects tend to have larger core-to-base ratios than radio-quiet objects. This scheme reproduces the observed correlations and most C IV lambda1549 and C III] lambda1909 profiles reasonably well, although the broadest C III] lines (FWHM(C III]) > 7000 km s-1, typically radio-quiet objects) require either a base component with a blueshift that increases with line width, or a third extremely broad component with a very large blueshift.