The Baldwin Effect and Black Hole Accretion: A Spectral Principal Component Analysis of a Complete Quasar Sample

A unique set of UV-optical spectrograms of 22 low redshift QSOs areinvestigated using principal component analysis. We find three significantprincipal components over the broad wavelength range from Ly\alpha to H\alpha.They together account for about 78% of the sample intrinsic variance. Wepresent strong arguments that the first principal component represents theBaldwin effect, relating equivalent widths to the luminosity (i.e. accretionrate), but only emission-line cores are involved. The second componentrepresents continuum variations, probably dominated by intrinsic reddening. Thethird principal component directly relates QSO UV properties to the opticalprincipal component 1 found by Boroson & Green (1992). It is the primary causeof scatter in the Baldwin relationships. It is also directly related to broademission-line width and soft X-ray spectral index, and therefore probablydriven by Eddington accretion ratio. We demonstrate how Baldwin relationshipscan be derived using our first principal component, virtually eliminating thescatter caused by the third principal component. This rekindles the hope thatthe Baldwin relationships can be used for cosmological study.Comment: 35 pages, 13 figures, AASTEX, accepted for publication in Ap