A Kiloparsec-Scale Binary Active Galactic Nucleus Confirmed by the Expanded Very Large Array

TL;DR

This paper confirms a kiloparsec-scale binary active galactic nucleus using high-resolution radio imaging, demonstrating the presence of two accreting supermassive black holes in merging galaxies at z=0.39.

Contribution

First high-resolution radio confirmation of a kpc-scale binary AGN, clarifying the nature of a double-peaked [O III] AGN system.

Findings

Two compact radio sources coincide with optical nuclei.

Radio emission is powered by accretion, not star formation.

System is a merger of two massive galaxies with sub-Eddington accretion.

Abstract

We report the confirmation of a kpc-scale binary active galactic nucleus (AGN) with high-resolution radio images from the Expanded Very Large Array (EVLA). SDSS J150243.1+111557 is a double-peaked [O III] AGN at z = 0.39 selected from the Sloan Digital Sky Survey. Our previous near-infrared adaptive optics imaging reveals two nuclei separated by 1.4" (7.4 kpc), and our optical integral-field spectroscopy suggests that they are a type-1--type-2 AGN pair. However, these data alone cannot rule out the single AGN scenario where the narrow emission-line region associated with the secondary is photoionized by the broad-line AGN in the primary. Our new EVLA images at 1.4, 5.0, and 8.5 GHz show two steep-spectrum compact radio sources spatially coincident with the optical nuclei. The radio power of the type-2 AGN is an order-of-magnitude in excess of star-forming galaxies with similar extinction-corrected [O II] 3727 luminosities, indicating that the radio emission is powered by accretion. Therefore, SDSS J150243.1+111557 is one of the few confirmed kpc-scale binary AGN systems. Spectral-energy-distribution modeling shows that SDSS J150243.1+111557 is a merger of two ~10^{11} M_sun galaxies. With both black hole masses around 10^8 Msun, the AGNs are accreting at ~10 times below the Eddington limit.