Broad Emission-Line Shifts in Quasars: An Orientation Measure for Radio-Quiet Quasars?

Abstract

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 to Mg II. We confirm previous results that suggest an anti-correlation 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 anti-correlation 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

Hubble Space TelescopeSTIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow‐Line Seyfert 1 Galaxies. I. Data and Analysis

“…This was previously reported in for this sample and has since then been recovered from the Sloan Digital Sky Survey quasars (Richards et al 2002), and a similar correlation was previously noted by Wills et al (1993). The kurtosis is strongly anticorrelated with the asymmetry parameter, implying that the more strongly blueshifted lines have a flattened rather than peaked profile.…”

On the origins of C iv absorption profile diversity in broad absorption line quasars

“…The anti-correlation between the optical-UV slope and the C iv EW is consistent with C iv becoming stronger with a redder αUV. The anticorrelation between the C iv blueshift and its EW (see also Richards et al 2002Richards et al , 2011) is detected here for both the He ii EW and αUV binning. We leave the full analysis of the non-BALQ sample to a separate study (Baskin, in preparation).…”

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

“…Getting the systemic redshift of quasars from emission lines is complicated by the complex physical structure of the broad line regions in which the broad emission lines are emitted. For the bright quasars selected for our composite many of the prominent high-ionization lines visible will arise in hot clouds with high peculiar velocities and will therefore be affected by systematic line shifts (Tytler & Fan 1992;Richards et al 2002b;Gaskell & Goosmann 2013 parameter and fit to the selected region where a weighted minimization of the residuals is done using least squares. The best-fit value and the confidence intervals on the best-fit parameters is determined by resampling the spectrum within the errors and repeating the continuum estimation and the fit on the resampled spectrum 10 000 times.…”