VaDAR: Varstrometry for Dual AGN using Radio interferometry

TL;DR

This paper introduces VaDAR, a new method combining Gaia astrometry and radio interferometry to identify dual AGN, demonstrating its effectiveness with a pilot study of 18 quasars and finding a significant fraction likely to be dual AGN or lenses.

Contribution

The paper presents a novel approach using Gaia and VLA data to systematically detect kpc-scale dual AGN, advancing observational techniques in galaxy evolution studies.

Findings

Approximately 39% of targets are candidate dual AGN or lenses.

Radio observations constrain the origin of Gaia astrometric noise.

Method shows promise for systematic dual AGN identification.

Abstract

Binary and dual active galactic nuclei (AGN) are an important observational tool for studying the formation and dynamical evolution of galaxies and supermassive black holes (SMBHs). An entirely new method for identifying possible AGN pairs makes use of the exquisite positional accuracy of Gaia to detect astrometrically-variable quasars, in tandem with the high spatial resolution of the Karl G. Jansky Very Large Array (VLA). We present a new pilot study of radio observations of 18 quasars (0.8 < z < 2.9), selected from the SDSS DR16Q and matched with the Gaia DR3. All 18 targets are identified by their excess astrometric noise in Gaia. We targeted these 18 quasars with the VLA at 2-4 GHz (S-band) and 8-12 GHz (X-band), providing resolutions of 0.65" and 0.2", respectively, in order to constrain the origin of this variability. We combine these data with ancillary radio survey data and perform radio spectral modeling. The new observations are used to constrain the driver of the excess astrometric noise. We find that ~39% of the target sample is likely to be either candidate dual AGN or gravitationally lensed quasars. Ultimately, we use this new strategy to help identify and understand this sample of astrometrically-variable quasars, demonstrate the potential of this method for systematically identifying kpc-scale dual quasars.