The PG X-ray QSO sample: Links between the ultraviolet-X-ray continuum and emission lines

Two sets of relationships relate QSO UV to soft X-ray continua with the broad-line region. These are (i) the Baldwin relationships, which are inverse relationships between the broad-line equivalent width and the continuum luminosity, and (ii) Boroson & Green's optical "Principal Component 1" relationships, linking steeper soft Xray spectra with narrower H beta emission, stronger HP blue wings, stronger optical Fe II emission, and weaker [O III] lambda 5007 lines. In order to understand these relationships, we extended the spectra into the UV for 22 QSOs with high-quality soft X-ray spectra. These are from the complete sample of QSOs from the Bright Quasar Survey for which Laor et al. demonstrated strong luminosity and X-ray-optical Principal Component 1 relationships. We show that these extend to a whole new set of UV relationships: Principal Component 1 (in the sense of steeper X-ray spectra) is related to narrower C III] lambda 1909 lines, larger Si III] lambda 1892/C III] lambda 1909 ratios (a high-density indicator), stronger low-ionization lines, and weaker C IV lambda 1549 but stronger N V lambda 1240 lines. We speculate that high accretion rates are linked to high columns of dense (similar to 10(11) cm(-3)), nitrogen-enhanced, low-ionization gas from nuclear starbursts. Line width, inverse Fe II-[O III] and inverse Fe II-C IV relationships hint at the geometrical arrangement of this gas. These Principal Component 1 relationships appear to be independent of luminosity and therefore of the Baldwin relationships.