High-quality UV & X-ray quasar spectral data

The clarity of these correlations is improved when (1) using CIV broad emission line equivalent width (EQW) and blueshift (relative to systemic) values calculated from high signal-to-noise ratio reconstructions of optical/UV spectra and (2) removing quasars expected to be absorbed based on their UV/X-ray spectral slopes.

In addition to using the traditional CIV parameter space measures of CIV EQW and blueshift, we define a "CIV_{\parallel}_ distance" along a best-fit polynomial curve that incorporates information from both CIV parameters. We find that the CIV_{\parallel}_ distance is linearly correlated with both the optical-to-X-ray slope, {alpha}_ox_, and broad-line HeII EQW, which are known spectral energy distribution indicators, but does not require X-ray or high spectral resolution UV observations to compute.