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

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.