WoU-MMA: Mapping the host galaxies of low-frequency gravitational-wave sources

Gravitational waves are a fundamental prediction of Einstein’s description of gravity as warped spacetime. Just like electromagnetic waves, there is a spectrum of gravitational-wave signals that can originate from a plethora of sources. While gravitational waves have been observed with Earth-based detectors from mergers of black holes similar in mass to the Sun, the mergers of more massive black holes remain elusive. However, by harnessing precision timing campaigns of pulsars in the Milky Way, we are getting closer to forging Galaxy-scale detectors that can measure gravitational-wave signals from the most massive black holes in the Universe. This research team will create a catalog of galaxies that might contain such pairs of massive black holes. This will allow researchers to reference likely sky-locations found by gravitational-wave searches back to this catalog and determine the origin of the signal much more precisely. This project will fund the training of two graduate students in multi-messenger science. It will result in a student-developed web-tool for the inspection and filtering of candidate host-galaxies of gravitational-wave signals from SMBHBs. This web-tool will be tested and improved as an integrated activity for the NANOGrav Student Teams of Astrophysics ResearcherS (STARS) program. Located at Vanderbilt University and UC Berkeley, the team will forge pathways to the multi-messenger discovery of supermassive black-hole binary (SMBHB) systems and construct observationally-driven models of the low-frequency stochastic gravitational wave (GW) background. This work is based on two massive-galaxy catalogs derived from the Wide-field Infrared Survey Explorer; one catalog is all-sky but only complete out to z<0.45, the other probes z<1 but with only partial sky coverage. At UC Berkeley, team members will conduct a program of augmentation and enhancement to provide crucial data for multi-messenger studies, including galaxy stellar masses and resident supermassive blackhole masses. At Vanderbilt, team members will conduct a realistic program of simulated discoveries of individual SMBHBs in near-future pulsar-timing array campaigns, followed by the filtering of potential host galaxies that are contained within the GW statistical localization regions. This will result in a set of host ranking protocols based on galaxy and GW-inferred SMBHB properties. In the project’s final stage, the full team will combine their expertise to populate galaxies in the enhanced catalogs with SMBHBs according to statistical weights. They will use these to make maps of the GW-sky, study the anisotropy of the ensemble background signal’s angular power distribution, and explore its effect on near-future signal detection prospects. This award addresses/advances the goals of the Windows on the Universe Big Idea. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.