The Origin of Double-Peaked Narrow Lines in Active Galactic Nuclei I: Very Large Array Detections of Dual AGNs and AGN Outflows

TL;DR

This study uses optical spectroscopy and high-resolution radio observations to distinguish between dual AGNs and outflows as the sources of double-peaked narrow emission lines in active galactic nuclei, revealing that dual AGNs are relatively rare.

Contribution

The paper introduces a new methodology combining optical long-slit spectroscopy with high-resolution VLA radio observations to identify the origins of double-peaked emission lines in AGNs.

Findings

Detected dual AGNs in 3 out of 18 galaxies.

Found that ~75% of double-peaked lines are due to outflows.

Confirmed dual AGNs are about 15% of the sample.

Abstract

We have examined a subset of 18 active galactic nuclei (AGNs) drawn from a sample of 81 galaxies that possess double-peaked narrow optical emission line spectra in the Sloan Digital Sky Survey, have two optical AGN emission components separated by >0.2", and are detected in the Faint Images of the Radio Sky at Twenty-centimeters survey. Without follow-up observations, the sources of the double-peaked narrow emission lines are uncertain, and may be produced by kpc-scale separation dual active supermassive black holes, AGN outflows, or disk rotation. In this work, we propose a new methodology to characterize double-peaked narrow emission-line galaxies based on optical long-slit spectroscopy and high resolution multi-band Very Large Array observations. The nature of the radio emission in the sample galaxies is varied. Of the 18 galaxies, we detect two compact flat-spectrum radio cores with projected spatial separations on the sky between 0.6-1.6 kpc in three galaxies: J1023+3243, J1158+3231, and J1623+0808. The two radio sources are spatially coincident with the two optical components of ionized gas with AGN-like line ratios, which confirms the presence of dual AGNs in these three galaxies. Dual AGNs account for only ~15% (3/18) of the double-peaked AGNs in our sample. Gas kinematics produce ~75% (13/18) of the double-peaked narrow emission lines, distributed in the following way: 7 AGN wind-driven outflows, 5 radio-jet driven outflows, and one rotating narrow-line region. The remaining ~10% (2/18) are ambiguous cases. Our method demonstrates the power of spatially resolved spectroscopy and high resolution radio observations for the identification of AGN outflows and AGN pairs with angular separations as small as 0.18".