Identification of Outflows and Candidate Dual Active Galactic Nuclei in SDSS Quasars at z=0.8-1.6

TL;DR

This study analyzes high-redshift quasars with double-peaked emission lines to identify potential outflows or dual active galactic nuclei, extending previous low-redshift findings and exploring their kinematic origins.

Contribution

It introduces a method to select and analyze high-redshift quasars with double-peaked lines, providing evidence for outflows and dual AGN candidates at z=0.8-1.6.

Findings

Correlation between line-splitting and line-width similar to low-redshift studies.

Velocity-splittings correlate with quasar Eddington ratio.

Anti-correlation between velocity-offset ratio and luminosity ratio suggests dual AGN presence.

Abstract

We present a sample of 131 quasars from the Sloan Digital Sky Survey at redshifts 0.8<z<1.6 with double peaks in either of the high-ionization narrow emission lines [NeV]3426 or [NeIII]3869. These sources were selected with the intention of identifying high-redshift analogs of the z<0.8 active galactic nuclei (AGN) with double-peaked [OIII]5007 lines, which might represent AGN outflows or dual AGN. Lines of high-ionization potential are believed to originate in the inner, highly photoionized portion of the narrow line region (NLR), and we exploit this assumption to investigate the possible kinematic origins of the double-peaked lines. For comparison, we measure the [NeV]3426 and [NeIII]3869 double peaks in low-redshift (z<0.8) [OIII]-selected sources. We find that [NeV]3426 and [NeIII]3869 show a correlation between line-splitting and line-width similar to that of [OIII]5007 in other studies; and the velocity-splittings are correlated with the quasar Eddington ratio. These results suggest an outflow origin for at least a subset of the double-peaks, allowing us to study the high-ionization gas kinematics around quasars. However, we find that a non-neligible fraction of our sample show no evidence for an ionization stratification. For these sources, the outflow scenario is less compelling, leaving the dual AGN scenario as a viable possibility. Finally, we find that our sample shows an anti-correlation between the velocity-offset ratio and luminosity ratio of the components, which is a potential dynamical argument for the presence of dual AGN. Therefore, this study serves as a first attempt at extending the selection of candidate dual AGN to higher redshifts.