Are Hubble Residuals a Product of Poor Mass Estimates? Improving Supernova Ia Host Galaxy Characterizations

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Type Ia supernovae (SNIa) are extraordinary cosmological distance indicators that were used in the discovery of the accelerated expansion of the universe and are now being used for precision measurements of the equation of state of dark energy. SNIa properties now curiously show trends with host galaxy properties, which complicates their use as clean predictors of distance. At present, it is not clear if these trends are indicating something physical, or if they are simply a manifestation of insufficient data and the methods that are used to measure galaxy properties. This project will revisit these trends, making use of the more extensive multi-wavelength datasets that are now available, and improved methods for characterizing galaxy masses and other properties. The team at Johns Hopkins University will enlist undergraduate interns from Baltimore-area schools, with a focus on students from underrepresented and underserved backgrounds, to participate in the archival data recovery, galaxy characterization, and publication of the final catalogs.The main goal of this program is to test the much-debated existence and magnitude of Hubble residuals, excesses in corrected SNIa peak luminosities that appear to correlate with host galaxy masses. The team will compile an extensive multi-wavelength dataset from available and soon to be available infrared archives, leveraging existing optical data to recover the best available star-formation histories from non-parametric fitting, and more accurately determine stellar masses and star-formation rates for SNIa host galaxies from the Pantheon+ sample, which is a large compilation of several past SNIa surveys. Using this complete and robust catalog of host characteristics, the team will revisit Hubble residuals and their implications for cosmological analyses. In addition, this project will allow the first estimation of SNIa delay-time distributions as a function of host mass, and over a wide redshift range, and thus test the hypothesis, implied by the Hubble residuals, that SNIa are the products of more than one dominant progenitor mechanism.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.