Ranking Host Galaxies of Supermassive Black Hole Binaries Found by PTAs

Supermassive black hole binaries (SMBHBs) are expected to be promising multi-messenger sources, producing nanohertz gravitational waves (GWs) detectable with pulsar timing arrays (PTAs) and electromagnetic (EM) emission coming from the gaseous post-merger environment. Here we focus specifically on the identification of the SMBHB’s host galaxy as the EM counterpart, a task which continues to be challenging due the poor localization capability of PTAs. In this talk, we start with the localization region obtained from the GW analysis and present a probabilistic ranking scheme for hosts that lie within the region. We incorporate sky, distance, and mass information from the GW posteriors and galaxy catalogs. We also present examples which include EM frequency constraints, which could be derived for some SMBHB candidates. In particular, we discuss how the ranking is impacted when including this frequency information.