The Emission-Line Properties of Low-Redshift Quasi-stellar Objects. II. The Relation to Radio Type

We present optical spectrophotometry of 45 quasars in the redshift range 0.045-0.592. These data are combined with the sample of 87 low-redshift quasar and QSO spectra obtained by Boroson & Green for a more extensive investigation of the relation of the properties of the broad Hβ, [O III] λ5007, and optical Fe II emission lines to the objects' radio, optical, and X-ray continuum parameters. We derive a complete correlation matrix for the quasars and perform two-sample tests on the subsamples of flat radio spectrum (FRS) quasars, steep radio spectrum (SRS) quasars, and radio-quiet objects (QSOs). Our principal findings are as follows: 1. We confirm that the width of the Hβ profile at quarter-maximum and half-maximum points is inversely correlated with the ratio of the 6 cm radio core flux to that measured from the optical continuum at 5500 A, which has been argued to be an indicator of the orientation of the objects' radio axis under beaming models. The Hβ profile widths do not correlate strongly with any line or continuum parameter likely to be an indicator of the intrinsic power of the central engine, including the extended radio luminosity. A principal components analysis of the correlation matrix does not reveal any clear trends separate from the dependence of Hβ profile width on the orientation indicator, and we find no evidence of a decrease in the strength of the profile base component in FRS quasars relative to SRS quasars from a simple line deblending procedure. 2. The two-sample tests reveal several strong differences between the quasar and QSO subsamples, including differences between samples closely matched in optical luminosity. While QSOs are statistically closer to FRS quasars than SRS quasars in their emission-line properties, the FRS quasars still have significantly wider and more redward asymmetric Hβ profiles, stronger [O III] λ5007 emission, and weaker optical Fe II emission. The variance of the Hβ profile width and asymmetry parameters is also significantly larger among the combined sample of FRS and SRS quasars than among the QSOs. From the combined quasar and QSO sample, we confirm that there is an inverse correlation between soft X-ray luminosity and the equivalent width of the optical Fe II emission complex in the range ~λλ4434-4684. 3. The Balmer line profiles of several of the quasars show a division into two components, a core of intermediate (~103 km s-1) velocity width, and a very broad (~104 km s-1) base that is typically redshifted with respect to systemic velocity. This supports evidence that the broad-line region is divided into an inner Very Broad Line Region and an outer Intermediate Line Region. A few objects also display unusually strong emission in He II λ4686 and/or He I λ5876, while in other objects these lines are weak or absent. It is presently unclear whether these differences are intrinsic to the objects or else represent transient events caused by the dynamical evolution of the broad-line gas. The results for the quasar sample are consistent with unified models of FRS and SRS quasars and the interpretation that the change in profile widths arises from differing views of a flattened broad-line region with a strong component of planar motion. Under a unified model we estimate the ratio of planar to random BLR motions to be ~7:1. Assuming that the profile width and asymmetry parameters trace the mass of the central black hole, the distributions of these parameters indicate a larger average hole mass and a larger range of hole masses among the quasars than the QSOs, consistent with the model in which quasar black holes are the rapidly spinning product of the coalescence of two or more black holes at the centers of merged galaxies.