Localizing Gravitational-wave Signals & Identifying Galaxy Hosts with Pulsar Timing Arrays

If the origin of the gravitational-wave background–for which pulsar-timing array (PTAs) collaborations like NANOGrav announced first evidence in 2023–is a population of supermassive black-hole binary systems, then an inevitable consequence is the breakdown in apparent stochasticity of the signal as more pulsars and data are added. Over time, individual binary signals will become resolvable, allowing for single-event characterization following the same qualitative workflow as in LVK and as expected in LISA. But how well can PTAs resolve the origin of a signal, and how is this localization capability tethered to the three-dimensional geometry of the pulsar network, the precision with which the pulsar distances are known, the noise in each pulsar, and the timespan over which a pulsar has been monitored? In this talk, we will explore these factors and present galaxy host ranking protocols based on synthetic data that mirrors the near-future sensitivity of the International Pulsar Timing Array. Understanding the factors governing the angular resolution of a PTA detector, and establishing procedures for host ranking, will be essential to understanding the relationship between supermassive black-hole binaries and their galaxies.