Testing for Intrinsic SN Ia Luminosity Evolution at z > 2 with JWST

The James Webb Space Telescope (JWST) is opening new frontiers of transient discovery and follow-up at high-redshift. Here we present the discovery of a spectroscopically confirmed SN Ia (SN 2023aeax) at z = 2.15 with JWST, with cadenced NIRCam observations that enable multi-band light curve fitting. SN 2023aeax lands at the edge of traditional low-z cosmology color cuts because of its blue color (peak rest-frame B−V ∼ −0.3), but we still apply a fiducial standardization approach with the BayeSN model and find that the SN2023aeax luminosity distance measurement is in agreement (∼ 0.1σ) with ΛCDM. SN 2023aeax is only the second spectroscopically confirmed SN Ia in the dark matter-dominated Universe at z > 2 (the other is SN 2023adsy), giving it rare leverage to constrain any potential evolution in SN Ia standardized luminosities. Similar to SN2023adsy (B − V ∼ 0.8), SN 2023aeax has a fairly extreme (but opposite) color, which may be due to the small sample size or a secondary factor, such as host galaxy properties. Nevertheless, the SN 2023aeax spectrum is wellrepresented by normal low-z SN Ia spectra and we find no definitive evolution in SN Ia standardization with redshift. Still, the first two spectroscopically confirmed z > 2 SNe Ia have peculiar colors and combine for a ∼ 1σ distance slope relative to ΛCDM, the implications of which require a larger sample and dedicated host galaxy observations to investigate.