Tracing the Orbits of Supermassive Black Hole Binaries in MASSIVE Survey Galaxies

The central regions of massive early-type galaxies commonly show shallow stellar-density profiles. Theory, models, and simulations suggest that such cores could arise from stellar scouring by supermassive black hole (SMBH) binaries. However, astrophysical settings that offer quantitative tests of this picture are lacking. A direct way to identify such a setting would be to trace the orbit of one or both members of an SMBH binary in a stellar core. Here, we study the viability of tracing such orbits on subparsec scales via astrometric monitoring with the next-generation Very Large Array (ngVLA) at 80 GHz. We focus on galaxies in the MASSIVE survey with stellar-dynamical constraints on the masses of their putative SMBH binaries. To optimize the monitoring outcomes, we first vet each galaxy near 80 GHz for its compactness, persistence, radio spectral shape, signal-to-noise ratio, and phase calibrator availability. Given each galaxy’s distance and SMBH binary mass, we then quantify the binary-orbit parameters accessible via astrometric monitoring with the long-baseline stations of the ngVLA.

The NRAO is a facility of the NSF, operated under cooperative agreement by AUI. The ngVLA is a design and development project of the NSF operated under cooperative agreement by AUI. Part of this research was carried out at JPL/Caltech, under a contract with NASA.