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

TL;DR

This paper reports the discovery of a high-redshift Type Ia supernova with JWST, providing rare data to test for potential luminosity evolution at z>2 and finding no definitive evidence for such evolution.

Contribution

First spectroscopic confirmation of a z>2 SN Ia with JWST, enabling new constraints on luminosity evolution at high redshift.

Findings

SN 2023aeax's luminosity distance aligns with ΛCDM within 0.1σ.

No definitive evidence of luminosity evolution in SN Ia at z>2.

High-redshift SN Ia show peculiar colors but spectra match normal low-z SNe Ia.

Abstract

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 Type Ia supernova (SN Ia; SN $2023$aeax) at $z=2.15$ with JWST, including a NIRCam multi-band light curve. SN $2023$aeax lands at the edge of traditional low-$z$ cosmology cuts because of its blue color (peak rest-frame $B-V\sim-0.3$) but with a normal decline rate ($\Delta m_{15}(B)\sim1.25$), and applying a fiducial standardization with the BayeSN model we find the SN $2023$aeax luminosity distance is in $\sim0.1\sigma$ agreement with $\Lambda$CDM. SN $2023$aeax is only the second spectroscopically confirmed SN Ia in the dark matter-dominated Universe at $z>2$ (the other is SN $2023$adsy), giving it rare leverage to constrain any potential evolution in SN Ia standardized luminosities. Similar to SN $2023$adsy ($B-V\sim0.8)$, SN $2023$aeax 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 $2023$aeax spectrum is well-represented 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 $\sim1\sigma$ distance slope relative to $\Lambda$CDM, though in agreement with recent SN Ia cosmological measurements.