Predicting Potential Host Galaxies of Supermassive Black Hole Binaries Based on Stellar Kinematics in Archival IFU Surveys

Abstract: Supermassive black hole binaries (SMBHBs) at the centers of galaxies emit continuous gravitational waves (GWs) at nanohertz frequencies, and ongoing pulsar timing array (PTA) experiments aim to detect the first individual system. Identifying the exact host galaxy of a SMBHB detected in GWs is paramount for a variety of multi-messenger science cases, but it will be challenging due to the large number of candidate galaxies in the sky localization region. Here, we apply recent insights on the distinct characteristics of SMBHB host galaxies to archival galaxy datasets, to predict which nearby massive galaxies are most likely to host SMBHBs detectable by PTAs. Specifically, we use archival galaxy IFU surveys to search for nearby galaxies with distinct stellar kinematic signatures of SMBHB host galaxies, as informed by cosmological simulations. These distinct stellar kinematic signatures, including slow rotation and strong kinematic/photometric misalignments, are a hallmark of recent major galaxy mergers that led to the formation of SMBHBs in these galaxies. We produce a list of nearby massive galaxies that may currently host SMBHBs, ranked by a combination of their host galaxy stellar kinematic properties and their hypothetical GW strain. We discuss how our ranked list can be used (1) for targeted searches for individual sources of continuous GWs by PTAs, (2) to corroborate candidate SMBHBs identified through other approaches, and (3) to select candidate recoiling AGN and closely-separated (<100 pc) dual AGN for telescope follow-up confirmation.