The Sloan Digital Sky Survey Reverberation Mapping Project: The C iv Blueshift, Its Variability, and Its Dependence Upon Quasar Properties

Abstract

We use the multi-epoch spectra of 362 quasars from the Sloan Digital Sky Survey Reverberation Mapping project to investigate the dependence of the blueshift of C iv  relative to Mg ii  on quasar properties. We confirm that high-blueshift sources tend to have low C iv  equivalent widths (EWs), and that the low-EW sources span a range of blueshift. Other high-ionization lines, such as He ii , also show similar blueshift properties. The ratio of the line width (measured as both the full width at half maximum and the velocity dispersion) of C iv to that of Mg ii increases with blueshift. Quasar variability enhances the connection between the C iv  blueshift and quasar properties (e.g., EW). The variability of the Mg ii line center (i.e., the wavelength that bisects the cumulative line flux) increases with blueshift. In contrast, the C iv line center shows weaker variability at the extreme blueshifts. Quasars with the high-blueshift C iv lines tend to have less variable continuum emission, when controlling for EW, luminosity, and redshift. Our results support the scenario that high-blueshift sources tend to have large Eddington ratios.