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Aims. We present new VLT ISAAC spectra for 30 quasars, which we combine with previous data to yield a sample of 53 intermediateredshift (z ≈ 0.9-3.0) sources. The sample is used to explore properties of prominent lines in the hβ spectral region of these very luminous quasars. Methods. We compare this data with two large low-redshift (z < 0.8) samples in a search for trends over almost 6dex in source luminosity.Results. We find two major trends: (1) a systematic increase in minimum FWHM hβ with luminosity (discussed in a previous paper).This lower FWHM envelope is best fit by assuming that the narrowest sources radiate near the Eddington limit, show line emission from a virialized cloud distribution, and obey a well-defined broad line region size vs. luminosity relation. (2) A systematic decrease in equivalent width of [oiii]λλ4959, 5007 (from W ≈ 15 to ∼1 Å) with increasing source bolometric luminosity (from log L bol ≈ 43 to log L bol ≈ 49). Other identified trends require differntiating between so-called Population A and Bsources. We generate median composite spectra in six luminosity bins to maximize S /N. Population A sources show reasonably symmetric Lorentzian hβ profiles at all luminosities, while Pop. B sources require two component fits involving an unshifted broad and a redshifted very broad component.Very broad hβ increases in strength with increasing log L bol , while the broad component remains constant, resulting in an apparent "Baldwin effect" with equivalent width decreasing from W ∼ 80 to ∼20 Å over our sample luminosity range. The roughly constant equivalent width shown by the hβ very broad component implies production in optically-thick, photoionized gas. The onset of the redshifted very broad component appears to be a critical change that occurs near the Pop. A-B boundary at FWHM hβ ≈ 4000 km s −1 , which we relate to a critical Eddington ratio (≈0.2 ± 0.1).

We present results of an intensive 2 month campaign of ground-based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution day. The broad Ha and Hb emission [ 1 lines respond to D35% ultraviolet continuum variations with an amplitude of D10% and time delays of 5.6^1.3 days and 5.4^0.8 days, respectively. We interpret this as evidence of variable Balmer line gas D5È6 light days from the central source in this object, widely believed to be a supermassive black hole. The virial mass of the central source implied by line widths and time delays is D106È107 Concomi-M _. tantly, we Ðnd evidence for wavelength-dependent continuum time delays : optical continuum variations lag those at 1315 by 1.0^0.3 days at 4865 to 1.5^0.7 days at 6962 This suggests a stratiÐed A A A. continuum reprocessing region extending several light days from the central source, possibly an accretion disk.

drive the ultraviolet/optical variations. However, the medium energy X-ray NVA is 2-4 times that in the ultraviolet, and the single-epoch, absorption-corrected X-ray/γ-ray luminosity is only about 1/3 that of the ultraviolet/optical/infrared, suggesting that at most ∼1/3 of the total low-energy flux could be reprocessed high-energy emission.The strong wavelength dependence of the ultraviolet NVAs is consistent with an origin in an accretion disk, with the variable emission coming from the hotter inner regions and non-variable emission from the cooler outer regions. These data, when combined with the results of disk fits, indicate a boundary between these regions near a radius of order R ≈ 0.07 lt-day. No interband lag would be expected as reprocessing (and thus propagation between regions) need not occur, and the orbital time scale of ∼1 day is consistent with the observed variability time scale. However, such a model does not immediately explain the good correlation between ultraviolet and X-ray variations.

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.