Cosmology Seminar- A Reassessment of the Pantheon+ and DES 5YR Calibration Uncertainties: Dovekie

Aims. Type Ia Supernovae (SNe Ia) are crucial tools to measure the accelerating expansion of the universe, today comprising thousands of SNe across multiple telescopes. Accurate measurements of cosmological parameters with SNe Ia require a robust understanding and cross-calibration of the telescopes and filters. The previous best cross-calibration effort, 'Fragilistic', provided cross-calibration for 25 photometric systems, but offered no public code or ability to easily add new surveys. We aim to provide an open-source
cross-calibration solution with an eye to the future, available at https://github.com/bap37/Dovekie/ . Methods. We use the Pan-STARRs (PS1) and Gaia all-sky telescopes to characterise the measured filters from our 11 photometric
systems, using published field stars to, for the first time, derive uncertainties on our filter measurements and modify filters to best
match the data. With these filters, and direct observations of a set of DA white dwarves from Boyd et al. (2024), we simultaneously
cross-calibrate our zeropoints for each filter in each photometric system, and train a new SALT model to propagate these results to
cosmology.
Results. We find improvements to the calibration systematic uncertainty of ×2 for the Pantheon+ (Brout et al. 2022) sample with a new σw(phot) = 0.011, and smaller yet still significant improvements to the DES5YR calibration uncertainty. For our Pantheon+- like sample combined with constraints from Baryonic Acoustic Oscillations and the microwave background radiation, we estimate a reduction in the ΛCDM tension from previously reported 2.5σ to 2σ.