Probing the origins of the C IV and Fe Kα baldwin effects

Abstract

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 αox, which characterizes the relative X-ray to UV brightness. The EW of the C IVλ1549 emission line is correlated with both αox and luminosity. We find that by regressing l ν(2500) with EW(C IV) and αox, we can obtain tighter correlations than by regressing l ν(2500 ) with only EW(C IV). Both correlation and regression analyses imply that l ν(2500 ) is not the only factor controlling the changes of EW(C IV); αox (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 ) relation and at least 75% of the scatter of the of the EW(C IV)-αox relation. 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 αox 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. © 2009 The American Astronomical Society. All rights reserved.