STATISTICS OF QSO BROAD EMISSION-LINE PROFILES .1. THE C-IV LAMBDA-1549 LINE AND THE LAMBDA-1400 FEATURE

We present the results of a statistical investigation of broad emissio n-line profiles in 123 high-luminosity AGNs using high-quality data in the C IV lambda1549 spectral region, originally obtained for absorpti on-line studies. Several systematic effects are observed: with increas ing line width, the equivalent width and peak-to-continuum intensity r atio of C IV lambda1549 decreases. the ratio of the equivalent width o f the lambda1400 feature to that of C IV lambda1549 increases, the pro file shape of C IV lambda1549 changes from sharply peaked to more flat -topped, the line asymmetry changes, and there is an increase in the m ean wavelength of the lambda1400 feature in the ''rest frame'' defined by the peak of C IV lambda1549. These trends with line width can best be explained in terms of a range of relative strengths of two compone nts making up each broad-line profile. The C IV lambda1549 profile con sists of a ''core'' with a characteristic width of approximately 2000 km s-1 FWHM and an equivalent width that can differ significantly from object to object, plus a broad ''base'' component with a characterist ic width of about 7000 km s-1, blueshifted by approximately 1000 km s- 1 relative to the core, and with a smaller range of equivalent widths. In this intermediate-width emission-line region (ILR) model the core emission arises from a region with a velocity dispersion intermediate between those of the narrow- and broad-line regions. Alternatively, we suggest a ''bipolar'' model consisting of a ''disk'' giving rise pred ominantly to low-ionization lines, plus a co-axial high-ionization out flow. This axisymmetric model incorporates viewing angle and projectio n effects to explain the main line-width correlations. The ''ILR'' mod el seems to provide a more natural explanation of the correlations pre sented here, and of the behavior of other lines reported in the litera ture. We compare the properties of the radio-loud and radio-quiet obje cts and find differences that we interpret as arising from a beamed op tical-UV synchrotron continuum present in the radio-loud objects but a bsent in radio-quiet objects.