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We have produced the next generation of quasar spectral energy distributions (SEDs), essentially updating the work of Elvis et al. (1994) by using high-quality data obtained with several space and ground-based telescopes, including NASA's Great Observatories. We present an atlas of SEDs of 85 optically bright, non-blazar quasars over the electromagnetic spectrum from radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58 radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical spectroscopic data, supplemented with some far-ultraviolet spectra, and more than half also have Spitzer mid-infrared IRS spectra. The X-ray spectral parameters are collected from the literature where available. The radio, far-infrared, and near-infrared photometric data are also obtained from either the literature or new observations. We construct composite spectral energy distributions for radio-loud and radio-quiet objects and compare these to those of Elvis et al., finding that ours have similar overall shapes, but our improved spectral resolution reveals more detailed features, especially in the mid and near-infrared.

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We have performed a spectral principal component analysis (SPCA) for an essentially complete sample of 22 low redshift QSOs with spectral data from Lyα to Hα. SPCA yields a set of independent principal component spectra, each of which represents a set of relationships among QSO continuum and line properties. We find three significant principal components, which account for ∼78% of the total intrinsic variance. The first component, carrying ∼41% of the intrinsic variance, represents Baldwin relationships -anti-correlations between equivalent width of broad emission lines and continuum luminosity. The narrow line core (FWHM ∼2000 km s −1 ) of the broad emission lines dominate this component. The second component, accounting for ∼23% of the intrinsic variance, represents the variations in UV continuum slope, which is probably the result of dust reddening, with possible contributions from starlight. The third principal component is directly related to the Boroson & Green "Eigenvector 1" (their first principal component), clearly showing the anti-correlation between strengths of optical Fe ii and [O iii] λ5007, and other relationships previously found in the Hβ -[O iii] region. This third component shows the expected strong correlation with soft X-ray spectral index. The widths of C iii] λ1909, Mg ii λ2798, and Balmer emission lines are also involved and clearly correlated, relating this component to black hole mass or Eddington accretion ratio. We find an inverse correlation between the strengths of the UV and optical Fe ii blends, as suggested by some photoionization models. We also find correlations of the strengths of several low-ionization UV lines with Fe ii(opt), and a strong positive correlation of C iv λ1549 with [O iii] strength. The wide wavelength coverage of our data enable us to see clearly the relationships between the UV and optical spectra of QSOs. The Baldwin effect and Boroson & Green's Eigenvector 1 relationship are clearly independent. We demonstrate how Baldwin relationships can be derived using our first principal component, virtually eliminating the scatter caused by the third principal component. This rekindles the hope that the Baldwin relationships can be used for cosmological study.