# # Program information file # PROGRAM_ID 2023A038 PROGRAM_TITLE Constraining a Redshift Dependent Type Ia Supernova Mass Step with Improved Stellar Mass Measurements PROGRAM_INV1 Benjamin Rose PROGRAM_INV2 Bhavin Joshi PROGRAM_INV3 Susana Deustua PROGRAM_INV4 Lisa Kelsey PROGRAM_INV5 Erik Peterson PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG Type Ia supernovae [SNIa] are standardizable candles with empirical corrections to their absolute peak magnitude from light-curve shape, observed color, and host-galaxy stellar mass. The host galaxy stellar mass correction, or 'mass step', is an empirical correction with little physical motivation. Further, some evidence suggests SNIa standardization may be better realized using host galaxy star formation rates [SFRs]. If SFR is a better standardization parameter, then the empirical mass step would be redshift dependent. A redshift dependence of the mass step was first measured in 2015. However, a recent paper shows that a redshift bias like this is also possible if one uses only optical host galaxy photometry, a common practice for SNIa host galaxies. Now, the reason for the observed redshift dependence is unknown. This project will disentangle the cause for the redshift-dependent mass step as either an issue of data quality or the need for an SFR correction to SNIa standardization. We propose to build a sample of SNIa host galaxies, with NIR photometry in order to test the redshift-dependent mass step prediction again, while avoiding the bias from using only optical photometry. We will compare a 'low-z' [z ~ 0.02] SNIa sample with a 'high-z' [z ~ 0.2] sample. The low-z SN and host galaxy photometry are already published. The high-z sample [N=124] already has Y-band photometry for 101 galaxies. Using several telescopes, we are proposing to observe 23 host galaxies in Y-band and all 124 galaxies in J and H. Data has recently been taken for over 50 of these targets. We are proposing to observe 20 targets with IRTF. PROGRAM_ABSTRACT_END