High metal enrichments in luminous quasars

We discuss observations of the broad emission line in luminous intermediate redshift quasars, with emphasis on Q0207-398. This object has relatively sharp lines, allowing us to deconvolve the profiles into distinct components. In this paper we examine the high ionization region, which we show must be matter-bounded, partially transparent to ionizing radiation. We measure a large N V λ1240/He II λ1640 ratio in Q0207 - 398, but detailed calculations predict this ratio to be ∼1 for standard cloud properties. We show that no choice of incident continuum, ionizing photon flux, density, or even the appeal to nonradiative energy sources, can reproduce the observed N V, C IV, O VI, He II spectrum with solar abundances. The intensity of the N V line is sensitive to the abundance of the gas because the abundance of nitrogen, a secondary element, goes up roughly as the square of the metallicity. The lowest metallicity capable of reproducing the N V spectrum in Q0207-398 is Z ≈ 5 Z_⊙, consistent with that inferred to exist in the cores of massive galaxies after epochs of rapid star formation. Our final model of the high-ionization emission region is one with many properties similar to those inferred for broad absorption-line QSO absorption-line clouds.