We describe the Sloan

We are exploring a spectroscopic unification for all types of broad-line emitting AGNs. The four-dimensional Eigenvector 1 (4DE1) parameter space organizes quasar diversity in a sequence primarily governed by Eddington ratio. This paper considers the role of C iv k1549 measures as 4DE1 diagnostics. We use HST archival spectra for 130 sources with S/N high enough to permit reliable C iv k1549 broad-component measures. We find a C iv k1549 BC profile blueshift that is strongly concentrated among (largely radio-quiet [RQ]) sources with FWHM( H BC ) P 4000 km s À1 (which we call Population A). Narrow-line Seyfert 1 (NLSy1; with FWHM H 2000 km s À1 ) sources belong to this population but do not emerge as a distinct class. The systematic blueshift, widely interpreted as arising in a disk wind/outflow, is not observed in broader line AGNs (including most radio-loud [RL] sources), which we call Population B. We find new correlations involving FWHM(C iv k1549 BC ), C iv k1549 line shift, and equivalent width only among Population A sources. Sulentic et al. suggested C iv k1549 measures enhance an apparent dichotomy between sources with FWHM(H BC ) less and greater than 4000 km s À1 , suggesting that it has more significance in the context of broad-line region structure than the more commonly discussed RL versus RQ dichotomy. Black hole masses computed from FWHM C iv k1549 BC for about 80 AGNs indicate that the C iv k1549 width is a poor virial estimator. Comparison of mass estimates derived from H BC and C iv k1549 reveals that the latter show different and nonlinear offsets for Population A and B sources. A significant number of sources also show narrow-line C iv k1549 emission that must be removed before C iv k1549 BC measures can be made and interpreted effectively. We present a recipe for C iv k1549 narrow-component extraction.

We compare broad emission‐line profiles and estimate line ratios for all major emission lines between Lyα and Hβ in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high‐quality optical and ultraviolet spectra and the possibility of sampling the spectroscopic diversity in the 4D eigenvector 1 (4DE1) context. In the latter sense, each source occupies a region (bin) in the full width at half‐maximum (FWHM)(Hβ) versus Fe iiopt strength plane that is significantly different from the others. High signal‐to‐noise ratio Hβ emission‐line profiles are used as templates for modelling the other lines (Lyα, C ivλ1549, He iiλ1640, Al iiiλ1860, Si iii]λ1892 and Mg iiλ2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids [indicated as a blue component (BLUE), broad component (BC) and very broad component (VBC), respectively]. BC (electron density ne∼ 1012 cm−3, ionization parameter U∼ 10−2 and column density Nc≳ 1023 cm−2) is present in almost all type‐1 quasars and therefore corresponds most closely to the classical broad‐line emitting region (the reverberating component). The bulk of Mg iiλ2800 and Fe ii emission also arises in this region. The BLUE emission (log ne∼ 10, log U∼−1 and log Nc < 23) arises in less optically thick gas; it is often thought to arise in an accretion disc wind. The least understood component involves the VBC (high ionization and large column density), which is found in no more than half (but almost all radio‐loud) type‐1 quasars and luminous Seyfert nuclei. It is perhaps the most distinguishing characteristic of quasars with FWHM (Hβ) ≳ 4000 km s−1 that belong to the so‐called population B of our 4DE1 space. Population A quasars [FWHM (Hβ) ≲ 4000 km s−1] are dominated by BC emission in Hβ and BLUE component emission in C ivλ1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type‐1 quasars.

The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called "main sequence" associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

Broad emission lines in quasars enable us to "resolve" structure and kinematics of the broad line emitting region (BLR) thought to involve an accretion disk feeding a supermassive black hole. Interpretation of broad line measures within the 4DE1 formalism simplifies the apparent confusion among such data by contrasting and unifying properties of so-called high and low accreting Population A and B sources. Hβ serves as an estimator of black hole mass, Eddington ratio and source rest frame, the latter a valuable input for Civλ1549 studies which allow us to isolate the blueshifted wind component. Optical and HST-UV spectra yield Hβ and Civλ1549 spectra for low-luminosity sources while VLT-ISAAC and FORS and TNG-LRS provide spectra for high Luminosity sources. New high S/N data for Civ in high-luminosity quasars are presented here for comparison with the other previously published data. Comparison of Hβ and Civλ1549 profile widths/shifts indicates that much of the emission from the two lines arise in regions with different structure and kinematics. Covering a wide range of luminosity and redshift shows evidence for a correlation between Civλ1549 blueshift and source Eddington ratio, with a weaker trend with source luminosity (similar amplitude outflows are seen over 4 of the 5 dex luminosity range in our combined samples). At low luminosity (z 0.7) only Population A sources show evidence for a significant outflow while at high luminosity the outflow signature begins to appear in Population B quasars as well.