VaDAR: Varstrometry for Dual AGN Using Radio Interferometry

Abstract

Binary and dual active galactic nuclei (AGNs) are an important observational tool for studying the formation and dynamical evolution of galaxies and supermassive black holes. 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 Sloan Digital Sky Survey 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 ∼44% 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, demonstrating the potential of this method for systematically identifying kiloparsec-scale dual quasars.

Prevalence of Compact Nuclear Radio Emission in Post-merger Galaxies and Its Origin

“…Gaiaʼs superb astrometric precision has enabled a number of searches for DAGNs and SMBHBs candidates that utilize astrometric variability induced by photocenter pseudo-motion of the unresolved SMBH pair, or varstrometry (Hwang et al 2020;Shen et al 2021;Chen et al 2022;Schwartzman et al 2024). This technique is particularly powerful for systems with z > 0.5, as Gaiaʼs astrometry is optimized for compact sources (Makarov & Secrest 2022).…”