Average quasar spectra in the context of Eigenvector 1

Recent work has shown that it is possible to systematize quasar spectral diversity in a parameter space called Eigenvector 1 (E1). We present median active galactic nucleus (AGN) spectra for fixed regions of the E1 (optical) parameter space [FWHM(Hbeta) vs. equivalent width ratio R-Fe II = W(Fe II lambda4570)/W(Hbeta)]. Comparison of the median spectra shows considerable differences. We suggest that an E1-driven approach to median/average spectra emphasizes significant differences between AGNs and offers more insights into AGN physics than a single-population median/average spectrum derived from a large and heterogeneous sample of sources. We find that the Hbeta broad component line profile changes along the E1 sequence in FWHM, centroid shift, and profile asymmetry. While objects with FWHM(Hbeta(BC)) less than or similar to 4000 km s(-1) are well fitted by a Lorentz function, AGNs with FWHM(Hbeta(BC)) greater than or similar to 4000 km s(-1) are better fitted if two broad- line components are used: a classical broad-line component and a very broad/redshifted component.