2014MNRAS.438.3263R

With a quasar sample designed for studying orientation effects, we investigate the orientation dependence characteristics of the Civ λ1549 broad emission line in approximately 50 Type 1 quasars with z = 0.1-1.4. Understanding the role that orientation plays in determining the observed ultraviolet spectra in quasars is of interest both for the insight it gives into the physical emitting regions and for its ramifications for the estimation of fundamental properties. Orientation is measured for the sample via radio core dominance. In our analysis we include measurements of the continuum luminosity and the optical-to-X-ray spectral slope, spectral properties commonly included in the suite known as `Eigenvector 1', and the full-width at half-maximum, full-width at one-quarter-maximum, shape, blueshift, and equivalent width of the Civ broad emission line. We also investigate a new prescription that we recently developed for predicting the velocity linewidth of the Hβ broad emission line based on the velocity linewidth of the Civ line and the ratio of continuum-subtracted peak fluxes of Siiv+Oiv] at 1400Å to Civ. We find that, while it is known that orientation does not drive Eigenvector 1, it does affect some properties included in Eigenvector 1. Specifically, we find marginal orientation dependencies for the equivalent width of Civ and the equivalent width ratio of the optical Feii to [Oiii λ5007. Although, in the case of the Civ equivalent width, this may actually be due to an orientation dependence of the ultraviolet continuum luminosity which is found to be marginally significant. The full-width at one-quarter-maximum also shows a marginally significant orientation dependence. Notably, the shape and blueshift of Civ and αox do not depend on orientation. In addition to a correlation analysis of the ultraviolet spectral properties and radio core dominance, we provide composite spectra of edge-on and face-on sources for this sample. In particular, we highlight the orientation dependence of the velocity linewidth predicted for Hβ. We find that this predicted linewidth depends on orientation in a manner similar to the true velocity linewidth of Hβ, where no such dependence is observed for Civ. This is an indication that orientation information concerning the line emitting regions can be extracted from ultraviolet spectra.