Discovery of Two Spectroscopically Peculiar, Low-Luminosity Quasars at z~4

TL;DR

This paper reports the discovery of two rare, low-luminosity quasars at z~4 exhibiting unusual N IV] emission, suggesting potential links to early galaxy formation or unique AGN evolutionary stages.

Contribution

It presents the identification of two low-luminosity, high-redshift quasars with rare spectral features, expanding understanding of early quasar and galaxy co-evolution.

Findings

Detection of N IV] 1486A emission in 2 out of 23 quasars (~9%)

Possible connection between N IV] emission and early starburst activity

Implications for early stages of quasar evolution or galaxy formation

Abstract

We report the discovery of two low-luminosity quasars at z~4, both of which show prominent N IV] 1486A emission. This line is extremely rare in quasar spectra at any redshift; detecting it in two out of a sample of 23 objects (i.e., ~ 9% of the sample) is intriguing and is likely due to the low-luminosity, high-redshift quasar sample we are studying. This is still a poorly explored regime, where contributions from associated, early starbursts may be significant. One interpretation of this line posits photoionization by very massive young stars. Seeing N IV] 1486A emission in a high-redshift quasar may thus be understood in the context of co-formation and early co-evolution of galaxies and their supermassive black holes. Alternatively, we may be seeing a phenomenon related to the early evolution of quasar broad emission line regions. The non-detection (and possibly even broad absorption) of N V 1240A line in the spectrum of one of these quasars may support that interpretation. These two objects may signal a new faint quasar population or an early AGN evolutionary stage at high redshifts.