SIMBAD references

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(Hβ) vs. equivalent width ratio R_FeII_=W(Fe II λ4570)/W(Hβ)]. 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 Hβ broad component line profile changes along the E1 sequence in FWHM, centroid shift, and profile asymmetry. While objects with FWHM(Hβ<sub>BC</sub>)≲4000 km.s<sup>–1</sup> are well fitted by a Lorentz function, AGNs with FWHM(Hβ<sub>BC</sub>)≳4000 km.s<sup>–1</sup> are better fitted if two broad-line components are used: a ``classical'' broad-line component and a very broad/redshifted component.