Multiple supermassive black hole systems: SKA's future leading role

Abstract

This contribution discusses how the SKA will constrain the black hole merger rate at low separations (<<1 kpc). The preliminary evidence that radio-jet triggering is enhanced in dual and triple SMBH systems; negligible dust and gas attenuation at GHz frequencies; and unmatchedsensitivity and angular resolution suggests that the SKA will play a leading role in opening up the low separation parameter space. Identification of galaxies with binary SMBH systems by the SKA will have significant multi-wavelength synergy with current/future facilities such as ALMA, E-ELT, JWST and LSST, all of which will contribute to understanding the astrophysical impact thereof. Also of great importance will be the ability of high brightness temperature sensitivity observations to probe relic emission from precessing jets and hence provide arcsec-scale proxies of close-pair binary SMBH systems that cannot not be spatially resolved by VLBI. If sufficiently massive binaries are found, these may be detectable by directed gravitational wave experiments with pulsar timing arrays. The range of science possible with SMBHs is extensive and the SKA will play a leading role in their discovery, characterization and followup. These different observing modes are therefore expected to usher in the exciting era of multi-messenger astrophysics with a single facility.