HIGH METAL ENRICHMENTS IN LUMINOUS QUASARS

摘要

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.