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We recently discussed an Eigenvector 1 (E1) parameter space that provides optimal discrimination between the principal classes of broad-line active galactic nuclei (AGNs). In this paper we begin a search for the most important physical parameters that are likely to govern correlations and data point distribution in E1 space. We focus on the principal optical parameter plane involving the width of the Hb broad component and the equivalent width ratio between the Fe II blend at 4570We show that the observed correlation for radio-quiet sources can be accounted for if it is Hb BC . primarily driven by the ratio of AGN luminosity to black hole mass (L /M P Eddington ratio) convolved with source orientation. L /M apparently drives the radio-quiet correlation only for FWHM(Hb) [ 4000 km s~1, which includes narrow-line Seyfert 1 galaxies and can be said to deÐne an AGN "" main sequence.ÏÏ Source orientation plays an increasingly important role as increases. We also FWHM(Hb BC ) argue that AGNs lying outside the radio-quiet main sequence, and speciÐcally those with optical Fe II much stronger than expected for a given may all be broad absorption line QSOs.

[LaTeX removed] Recent work has shown that it is possible to systematize quasar spectral diversity in a parameter space called ``Eigenvector 1'' (E1). We present median AGN spectra for fixed regions of the E1 (optical) parameter space (FWHM(H-beta) vs. equivalent width ratio RFE=W(FeII4570)/W(H-beta). Comparison of the median spectra for different regions show considerable differences. We suggest that an E1-driven approach to median/average spectra emphasizes significant differences between AGN, and offers more insights into AGN physics and dynamics than a single population median/average derived from a large and heterogeneous sample of sources. We find that the H-beta broad component line profile changes in shape along the E1 sequence both in average centroid shift and asymmetry. While objects with FWHM(H-beta)< 4000 km/s are well fitted by a Lorentz function, AGN with FWHM(H-beta)> 4000 km/s are well fitted if two broad line components are used: a broad (the "classical" broad line component) and a very broad/redshifted component.Comment: 1 table + 3 figures, accepted for publication in ApJ

We compute the virial mass (M) of the central black hole and the luminosity‐to‐mass (L/M) ratio of ≈300 low‐z quasars and luminous type 1 Seyfert nuclei. We analyse the following: (1) whether radio‐quiet and radio‐loud objects show systematic differences in terms of M and L/M; (2) the influence of M and L/M on the shape of the Hβ broad component line profile; and (3) the significance of the so‐called ‘blue outliers’, i.e. sources showing a significant blueshift of the [O iii]λλ4959,5007 lines with respect to the narrow component of Hβ, which is used as an estimator of the quasar reference frame. We show that M and L/M distributions for radio‐quiet and radio‐loud sources are probably different for samples matched in luminosity and redshift, in the sense that radio‐quiet sources have systematically smaller masses and larger L/M. However, the L/M ratio distributions become indistinguishable if 8.5 < log M < 9.5. Line profile comparisons for median spectra computed over narrow ranges of M and L/M indicate that a Lorentz function provides a better fit for higher L/M sources and a double Gaussian for lower L/M values. A second (redshifted) Gaussian component at low L/M appears as a red asymmetry frequently observed in radio‐loud and radio‐quiet sources with broader (full width at half‐maximum ≳4000 km s−1) Hβ broad component profiles. This component becomes stronger in larger mass and lower L/M sources. No specific influence of radio loudness on the Hβ broad component profile is detected, although equivalent widths of Hβ broad component and especially of [O iii]λλ4959,5007 are larger for radio‐loud sources. We identify five more ‘blue outlier’ sources. Since these sources are, on average, one magnitude brighter than other active galactic nuclei with similar mass, their resulting Eddington ratio is 2–3 times higher. We hint at evolutionary effects that explain some of these results, and reinforce the ‘eigenvector 1’ correlations.