Radio-Selected Binary Active Galactic Nuclei from the Very Large Array Stripe 82 Survey

TL;DR

This study uses high-resolution radio imaging from the VLA Stripe 82 survey to identify and analyze a large sample of binary active galactic nuclei, providing insights into galaxy mergers and black hole growth.

Contribution

It presents a new method of identifying binary AGNs using radio imaging, expanding the sample beyond optical surveys and aiding understanding of black hole accretion triggers.

Findings

Identified 52 binary AGN candidates within 10 kpc separations.

Approximately 60% of candidates are expected to be confirmed with full spectroscopic data.

Radio surveys effectively complement optical methods for finding binary AGNs.

Abstract

Galaxy mergers play an important role in the growth of galaxies and their supermassive black holes. Simulations suggest that tidal interactions could enhance black hole accretion, which can be tested by the fraction of binary active galactic nuclei (AGNs) among galaxy mergers. But determining the fraction requires a statistical sample of binaries. We have identified kpc-scale binary AGNs directly from high-resolution radio imaging. Inside the 92 square deg covered by the high-resolution Very Large Array survey of the Sloan Digital Sky Survey (SDSS) Stripe 82 field, we identified 22 grade A and 30 grade B candidates of binary radio AGNs with angular separations less than 5" (10 kpc at z = 0.1). Eight of the candidates have optical spectra for both components from the SDSS spectroscopic surveys and our Keck program. Two grade B candidates are projected pairs, but the remaining six candidates are all compelling cases of binary AGNs based on either emission line ratios or the excess in radio power compared to the H-alpha-traced star formation rate. Only two of the six binaries were previously discovered by an optical spectroscopic search. Based on these results, we estimate that ~60% of our binary candidates would be confirmed once we obtain complete spectroscopic information. We conclude that wide-area high-resolution radio surveys offer an efficient method to identify large samples of binary AGNs. These radio-selected binary AGNs complement binaries identified at other wavelengths and are useful for understanding the triggering mechanisms of black hole accretion.