SN 2023adsy -- a normal Type Ia Supernova at z=2.9, discovered by JWST

Abstract: Supernovae (SNe) discovered in high-redshift (z > 2) galaxies by the James Webb Space Telescope (JWST) provide a unique opportunity to extend the Hubble-diagram beyond z~1.5 and constrain the cosmic Star Formation Rate in the early Universe. SN~2023adsy, a Type Ia supernova discovered by JWST at z=2.9, was found to be a peculiar event, being extremely red and faint, but showing very similar rest-frame light curve decline rate to the majority of low-redshift SNe Ia. We examine whether the red color and faint peak magnitude could also be explained by significant reddening/extinction due to dust within the host galaxy. We use the light curve fitter SALT3-NIR with templates extended to the near-infrared, to re-fit the published NIRCam photometry, assuming a "normal" SN Ia and Milky-Way dust extinction law. NIRCam photometry of the host galaxy taken before the SN discovery is also examined by comparing its Spectral Energy Distribution with galaxy templates. The NIRCam photometry can be fit reasonably well with a slowly declining, but otherwise "normal" SN Ia template suffering significant reddening ($E(B-V)_{host} \gtrsim 0.5$ mag). Photometry of the host galaxy suggests a blue, star-forming galaxy, where the presence of significant amount of dust cannot be ruled out. Comparison of the inferred luminosity distance with the prediction of the $\Lambda$CDM cosmology on the Hubble-diagram suggests no significant evolution of the SN Ia peak luminosity at z>2 redshifts. It is also shown that the discovery of a single SN Ia between 2 < z < 3 within the area of the JADES survey during 1 year is consistent with the current estimates for the SN Ia rates at such redshifts.