VLBI Astrometry of a Recoiling Supermassive Black Hole Candidate

Anisotropic emission of gravitational waves during the merger of a supermassive black hole binary (SMBHB) system may impart a recoil velocity of up to several 1000 km s^-1 on the newly merged supermassive black hole. In the most extreme cases, these supermassive black holes will be ejected from their host galaxy: the so-called “naked” supermassive black holes. In most cases, however, the recoiling black hole will rove the host galaxy, during which time we may observe spatial and/or kinematic signatures of its recoiling nature. Recently, emission line modeling of the Hα+[NII] complex of the AGN in Mrk 1018 (z=0.0424), a changing-look AGN which has changed its spectral class from Type 1 to Type 1.9 and back over a 40-year period, has proposed that the changing-look nature of this source is due to a disruption of the accretion disk around a recoiling supermassive black hole as it passes through pericenter in its orbit. Given the tidally-disturbed morphology of the host galaxy, indicative of a past galaxy merger event, Mrk 1018 is a good candidate to search for the still-elusive recoiling supermassive black hole. Very Long Baseline Interferometry (VLBI), with its superior angular resolution, is a powerful tool with which to search for and monitor pc-scale movement in compact radio AGN over years-long timescales. In this talk I will report on the initial results of a 7-year long VLBI observational campaign on Mrk 1018, during which time any movement due to a gravitational recoil would reveal itself.