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.

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.

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.

We describe a method for estimating physical conditions in the broad line region (BLR) for a significant subsample of Seyfert-1 nuclei and quasars. Several diagnostic ratios based on intermediate (Aliiiλ1860, Siiii]λ1892) and high (Civλ1549, Siivλ1397) ionization lines in the UV spectra of quasars are used to constrain density, ionization and metallicity of the emitting gas. We apply the method to two extreme Population A quasars -the prototypical NLSy1 I Zw 1 and higher z source SDSS J120144.36+011611.6. Under assumptions of spherical symmetry and pure photoionization we infer BLR physical conditions: low ionization (ionization parameter < 10 −2 ), high density (10 12 − 10 13 cm −3 ) and significant metal enrichment. Ionization parameter and density can be derived independently for each source with an uncertainty that is less than ±0.3 dex. We use the product of density and ionization parameter to estimate the BLR radius and derive an estimation of the virial black hole mass (M BH ). Estimates of M BH based on the "photoionization" analysis described in this paper are probably more accurate than those derived from the mass -luminosity correlations widely employed to compute black hole masses for high redshift quasars.

Context. The most highly accreting quasars are of special interest in studies of the physics of active galactic nuclei (AGNs) and host galaxy evolution. Quasars accreting at high rates (L/L Edd ∼ 1) hold promise for use as 'standard candles': distance indicators detectable at very high redshift. However, their observational properties are still largely unknown. Aims. We seek to identify a significant number of extreme accretors. A large sample can clarify the main properties of quasars radiating near L/L Edd ∼ 1 (in this paper they are designated as extreme Population A quasars or simply as extreme accretors) in the Hβ spectral range for redshift 0.8. Methods. We use selection criteria derived from four-dimensional Eigenvector 1 (4DE1) studies to identify and analyze spectra for a sample of 334 candidate sources identified from the SDSS DR7 database. The source spectra were chosen to show a ratio R FeII between the FeII emission blend at λ4570 and Hβ, R FeII > 1. Composite spectra were analyzed for systematic trends as a function of Feii strength, line width, and [Oiii] strength. We introduced tighter constraints on the signal-to-noise ratio (S/N) and R FeII values that allowed us to isolate sources most likely to be extreme accretors. Results. We provide a database of detailed measurements. Analysis of the data allows us to confirm that Hβ shows a Lorentzian function with a full width at half maximum (FWHM) of Hβ ≤ 4000 km s −1 . We find no evidence for a discontinuity at 2000 km s −1 in the 4DE1, which could mean that the sources below this FWHM value do not belong to a different AGN class. Systematic [Oiii] blue shifts, as well as a blueshifted component in Hβ are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of Hβ is still affected by the blueshifted emission; however, the effect is non-negligible if the FWHM Hβ is used as a "virial broadening estimator" (VBE). We emphasize a strong effect of the viewing angle on Hβ broadening, deriving a correction for those sources that shows major disagreement between virial and concordance cosmology luminosity values. Conclusions. The relatively large scatter between concordance cosmology and virial luminosity estimates can be reduced (by an order of magnitude) if a correction for orientation effects is included in the FWHM Hβ value; outflow and sample definition yield relatively minor effects.

Black Hole Mass estimation in quasars, especially at high redshift, involves use of single epoch spectra with s/n and resolution that permit accurate measurement of the width of a broad line assumed to be a reliable virial estimator. Coupled with an estimate of the radius of the broad line region this yields M BH · The radius of the broad line region (BLR) may be inferred from an extrapolation of the correlation between source luminosity and reverberation derived r BLR measures (the so-called Kaspi relation involving about 60 low z sources). We are exploring a different method for estimating r BLR directly from inferred physical conditions in the BLR of each source. We report here on a comparison of r BLR estimates that come from our method and from reverberation mapping. Our "photoionization" method employs diagnostic line intensity ratios in the rest-frame range 1400-2000Å (Aliiiλ1860/ Siiii]λ1892, Civλ1549/Aliiiλ1860) that enable derivation of the product of density and ionization parameter with the BLR 1 cnegrete@inaoep.mx 2 deborah@astro.unam.mx 3 paola.marziani@oapd.inaf.it 4 sulentic@iaa.es -2distance derived from the definition of the ionization parameter. We find good agreement between our estimates of the density, ionization parameter and r BLR and those from reverberation mapping. We suggest empirical corrections to improve the agreement between individual photoionization-derived r BLR values and those obtained from reverberation mapping. The results in this paper can be exploited to estimate black hole masses M BH for large samples of high-z quasars using an appropriate virial broadening estimator. We show that the width of the UV intermediate emission lines are consistent with the width of Hβ, therefore providing a reliable virial broadening estimator that can be measured in large samples of high-z quasars.