Presentation #138.10 in the session “AGN and Quasars 1”.
A supermassive black hole binary (SMBHB) is produced as a result of dynamical friction following a major galaxy merger. Though hierarchical merging predicts the existence of a large population of SMBHBs, only one closely separated SMBHB has so far been discovered: in the elliptical galaxy 0402+379 through VLBI observations of dual unresolved, flat spectrum radio cores. Large optical imaging and spectroscopic surveys, such as the SDSS, aid in the identification of large numbers of late-stage galaxy mergers to target for SMBHBs utilizing milliarcsecond VLBI observations. Direct identification of SMBHBs is critical for multi-wavelength follow-up observations to characterize galaxy and SMBH properties, but also for gravitational wave analyses, with pulsar timing arrays (PTAs) such as NANOGrav reaching sufficient sensitivity to robustly search for continuous wave (CW) events and the gravitational wave background (GWB) produced by the ensemble of merging SMBHBs in the last stages of their evolution. In this poster I present a multi-wavelength survey of six spheroidal, post-merger galaxies. Using milliarcsecond Very Long Baseline Array (VLBA) observations, we aim to determine the state of evolution of any SMBH(s) in the core of these merger remnants. We will also characterize the properties of the host galaxies through spatially resolved optical spectra using Gemini Integral Field Unit (IFU) observations and large-scale radio emission using Very Large Array (VLA) observations. Our observational constraints will be used to systematically target gravitational waves produced by the targets in NANOGrav data. I also present the results of one target from the survey which contains a young radio source believed to be a Compact Symmetric Object (CSO).