Discovery of two spectroscopically peculiar, low-luminosity quasars at z ~ 4

Abstract

We report the discovery of two low-luminosity quasars at z ~ 4, both of which show prominent N iv] λ1486 emission. This line is extremely rare in quasar spectra at any redshift; detecting it in two 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] λ1486 emission in a high-redshift quasar may thus be understood in the context of coformation and early coevolution 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 nondetection (and possibly even broad absorption) of N v λ1240 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.

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