On the Baldwin Effect in Active Galactic Nuclei. I. The Continuum‐Spectrum–Mass Relationship

We suggest that the Baldwin Effect is a result of the spectral dependence ofthe line-driving ionizing continuum on the black hole mass. We derive arelationship between the mass of the central black hole and the broad emissionline luminosity in active galactic nuclei (AGN). Assuming the UV spectrum ofAGN is emitted from an optically thick medium we find an expression for thecharacteristic energy of the ``UV bump'' in terms of the observable luminosityand emission-line width. We show empirically and analytically that the bumpenergy is anti-correlated with the black-hole mass and with the continuumluminosity. Our model reproduces the observed inverse correlation betweenequivalent width and continuum luminosity, yielding an explanation of theBaldwin effect from first principles. The model gives a good fit to the BaldwinEffect of the CIV line for a mean quasar EUV spectrum (Zheng et al. 1997) andfor several model spectra. The model also predicts a correlation between thestrength of the Baldwin Effect (the slope of the equivalent width as a functionof luminosity) and the ionization potential, consistent with recent data.Comment: 19 pages Latex, 2 figures. Accepted for publication in the Astrophysical Journa