Naval Research Laboratory
VaDAR: Varstrometry for Dual AGN using Radio interferometry
Binary and dual active galactic nuclei (AGN) are an important observational tool for studying the dynamical evolution of galaxies and supermassive black holes (SMBH). However, they are notoriously difficult to unambiguously detect due to current observational limits and biases, and are often identified serendipitously. 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 radio spatial resolution of NRAO’s Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA). Colloquially called varstrometry, this process can be used to measure emission flux, and place limits on source angular size and separation.
We present new radio observations with the VLA 2-4 GHz (S-band) and 8-12 GHz (X-band) of 18 quasars (0.7 < z < 2.9) exhibiting significant positional variability, selected from the SDSS DRQ16 and matched with the Gaia EDR3. In combination with several radio surveys (VLASS, FIRST, etc.), these observations have provided constraints on the origin of the astrometric variability, radio morphology, and other radio properties. We also present preliminary observations of a sub-sample of seven quasars observed with the VLBA at S- and X-bands, providing milliarcsecond scale constraints on the origin of Gaia’s astrometric jitter.