Using a sample of 3814 quasars from the Early Data Release of the Sloan Digital Sky Survey, we confirm that high-ionization, broad emission lines, such as C IV, are significantly blueshifted with respect to low-ionization, broad emission lines, such as Mg II, which are thought to be close to the systemic redshift. We examine the velocity shifts of the Mg II and C IV emission lines with respect to [O III] and Mg II, respectively. C IV emission-line peaks have a range of shifts from a redshift of 500 km s-1 to blueshifts well in excess of 2000 km s-1 as compared with Mg n. We confirm previous results that suggest an anticorrelation between the shift of the C IV emission-line peak and the rest equivalent width of the C IV emission line. Furthermore, by creating composite quasar spectra as a function of C IV shift, we are able to study in detail the profiles of the line as a function of velocity shift. We find that the apparent shift of the C IV emission-line peak is not a shift so much as it is a lack of flux in the red wing for the composite with the largest apparent shift. This observation should strongly constrain models for the broad emission-line region in quasars. The emission-line blueshift and equivalent width of C IV are also discussed in light of the well-known anticorrelation between the equivalent width of C IV emission and continuum luminosity, otherwise known as the Baldwin effect. We further discuss the C IV emission-line shift as a function of other quasar properties, such as spectral index, radio and X-ray detection. We find a possible correlation between the C IV emission-line shifts and the radio properties of the quasars, which is suggestive of orientation as the cause of the C IV velocity shifts. Finally, we explore whether the C IV emission-line blueshifts correlate with the presence of broad absorption line absorption troughs or with narrow, "associated" absorption, and how these might be related to orientation.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science