Analysis of a Type II Supernova Candidate at <i>z</i> = 3.19 from JWST’s COSMOS-Web Survey

The launch of the James Webb Space Telescope (JWST) has enabled the discovery of a small but increasing sample of high-redshift core-collapse supernovae (CC SNe), which provide new tests of massive star evolution in the early Universe. In this study, we report the analysis of SN 2023aeaf discovered in COSMOS-Web survey observations, which at z = 3.195 has one of the highest SN spectroscopic redshifts to date. Using two epochs of JWST photometry separated by ∼1 month in the rest frame, we photometrically classify SN 2023aeaf by comparing the JWST photometry to spectrophotometric CC SN and Type Ia (SN Ia) models and UV observations of SNe from the Swift telescope, finding that SN 2023aeaf is highly likely to be a Type II SN. A spectrum of the SN+host galaxy was also obtained ∼30 rest-frame days after discovery but shows no clearly identifiable SN features, with H α emission from the host potentially masking emission from the SN. Although the limited photometric coverage prevents strong constraints on the explosion properties, we find that the data are most consistent with a ∼12 M ⊙ progenitor with ∼0.5 M ⊙ of circumstellar material. We next use the host-galaxy spectrum and photometry to model the host spectral energy distribution (SED) using the Prospector Bayesian inference framework. We find that the host is a star-forming galaxy with an sSFR of log 10 ( sSFR / yr − 1 ) = − 10.1 7 − 0.10 + 0.13 , a stellar mass of log ( M ⋆ / M ⊙ ) = 9.0 4 − 0.04 + 0.03 , and a gas-phase metallicity of 12 + log 10 ( O / H ) = 7.82 ± 0.02 . SN 2023aeaf joins a growing sample of early Universe CC SNe with high luminosities, dense circumstellar material (CSM), and low-metallicity environments.