Quasars with super-metal-rich emission-line regions

We study the degree of chemical enrichment in the broad emission line regions (BELRs) of two QSOs with unusually strong nitrogen emission lines. The N v lambda 1240/C iv lambda 1549 intensity ratio is often used as a metallicity indicator for QSOs. The validity of this approach can be tested by studying objects in which the N iv] and N iii] lines, in addition to N v, are unusually strong and easily measurable. If all of these ionization states of nitrogen point to the same metallicity, it implies that the large N v strengths observed in most QSOs are not due to some peculiarity of the Nv lambda 1240 line. This test had previously been applied to Q0353-383, a QSO long known to have extremely strong N iii] and N iv] lines, with the result supporting high metallicity in that object. Here we make the same check in two other QSOs with very strong nitrogen lines, as a step toward using such QSOs to better probe the early chemical enrichment histories of their host galaxies. J1254+0241 has a metallicity of about 10 times solar, with good agreement between the abundance results from different line ratios. J1546+5253 has a more moderate metallicity, about 5 times solar, but the abundances determined from different line ratios show a much wider scatter than they do for J1254+0241 or Q0353- 383. This QSO also has an unusual low-ionization emission line spectrum similar to some low-ionization BAL QSOs and to the unusual AGN I Zw 1. We attribute the peculiarities in its spectrum to some combination of unusual structure and/or unusual physical conditions in its BELR. Our results further affirm the validity of the N v/C iv ratio as an abundance indicator in QSOs.