Astrometric Constraints on a Massive Black Hole Binary in NGC,4472

In an EHT study of a Jy-level target, Safarzadeh et al. (2019) show how astrometric monitoring could constrain massive black hole binaries with the wide separations that make them long-lived against gravitational wave losses, and with the small mass ratios expected from merged satellite galaxies. With this ngVLA study, we show how such frontier topics could be explored for the more numerous mJy-level targets, such as NGC,4472. We also discuss how ngVLA astrometric monitoring could test the upper limits from pulsar timing arrays on gravitational waves from NGC,4472.