2009ApJ...702..767W

We use UV/optical and X-ray observations of 272 radio-quiet Type 1 active galactic nuclei and quasars to investigate the C IV Baldwin Effect (BEff). The UV/optical spectra are drawn from the Hubble Space Telescope, International Ultraviolet Explorer and Sloan Digital Sky Survey archives. The X-ray spectra are from the Chandra and XMM-Newton archives. We apply correlation and partial-correlation analyses to the equivalent widths (EWs), continuum monochromatic luminosities, and α_ox, which characterizes the relative X-ray to UV brightness. The EW of the C IV λ1549 emission line is correlated with both α_ox and luminosity. We find that by regressing l_ν(2500 Å) with EW(C IV) and α_ox, we can obtain tighter correlations than by regressing l _ν(2500 Å) with only EW(C IV). Both correlation and regression analyses imply that l_ν(2500 Å) is not the only factor controlling the changes of EW(C IV); α_ox(or, equivalently, the soft X-ray emission) plays a fundamental role in the formation and variation of C IV. Variability contributes at least 60% of the scatter of the EW(C IV)-l_ν(2500 Å) relation and at least 75% of the scatter of the of the EW(C IV)-α_oxrelation. In our sample, narrow Fe Kα 6.4 keV emission lines are detected in 50 objects. Although narrow Fe Kα exhibits a BEff similar to that of C IV, its EW has almost no dependence on either α_ox or EW(C IV). This suggests that the majority of narrow Fe Kα emission is unlikely to be produced in the broad emission-line region. We do find suggestive correlations between the emission-line luminosities of C IV and Fe Kα, which could be potentially used to estimate the detectability of the Fe Kα line of quasars from rest-frame UV spectroscopic observations.