Program: GS-2022A-Q-324

Type Ia supernovae (SNe Ia) are one of the best probes to constrain the nature of dark energy. Recent surveys have observed such a large number of high-z SNe Ia that cosmological constraints are now limited by systematics and the relatively small number of low-z SNe. Our Young Supernova Experiment (YSE) is constructing an unbiased, high-fidelity low-z SN Ia sample in the Pan-STARRS1 natural system to improve SN cosmology constraints. This sample will (1) quadruple the number of cosmologically useful low-z SNe Ia, (2) be unique in its photometric calibration precision, and (3) be the largest low-z SN Ia sample observed with the same system as a high-z sample. Our program will yield the SN Ia sample that will anchor high-z supernovae from the Vera C. Rubin Observatory and will fulfill the Nancy Grace Roman Space Telescope low-z SN Ia requirement. Our homogeneous low-z sample will minimize the largest systematic error sources and with it, we will acquire a state-of-the-art constraint on the equation-of-state parameter of dark energy, w, to better than 3%. We propose to use Gemini/GMOS spectroscopy to characterize the cosmological sample and study the poorly constrained early-time evolution of SNe Ia, to understand their progenitors and explosion physics.