A Sample of Quasars with Strong Nitrogen Emission Lines from the Sloan Digital Sky Survey

TL;DR

This study identifies 293 nitrogen-rich quasars from SDSS, revealing their high nitrogen abundance, strong emission lines, and a significant association with radio activity, suggesting a unique evolutionary stage.

Contribution

First large sample of nitrogen-rich quasars from SDSS, linking nitrogen abundance to radio properties and quasar evolution.

Findings

N-rich quasars constitute about 1.1% of SDSS quasars.

N-rich quasars show stronger Lya and NV emission lines.

High nitrogen abundance correlates with increased radio activity.

Abstract

We report on 293 quasars with strong NIV] lambda 1486 or NIII] lambda 1750 emission lines (rest-frame equivalent width > 3 \AA) at 1.7 < z < 4.0 selected from the Sloan Digital Sky Survey (SDSS) Fifth Data Release. These nitrogen-rich (N-rich) objects comprise ~1.1% of the SDSS quasars. The comparison between the N-rich quasars and other quasars shows that the two quasar subsets share many common properties. We also confirm previous results that N-rich quasars have much stronger Lya and NV lambda 1240 emission lines. Strong nitrogen emission in all ionization states indicates high overall nitrogen abundances in these objects. We find evidence that the nitrogen abundance is closely related to quasar radio properties. The radio-loud fraction in the NIII]-rich quasars is 26% and in the NIV]-rich quasars is 69%, significantly higher than ~8% measured in other quasars with similar redshift and luminosity. Therefore, the high nitrogen abundance in N-rich quasars could be an indicator of a special quasar evolution stage, in which the radio activity is also strong.