Testing the effect of the progenitor metallicity on the ⁵⁶Ni mass and constraining the progenitor scenarios in Type Ia supernovae

¹ Department of Astronomy, Yonsei University, Seoul 03722, Republic of Korea
² Center for Galaxy Evolution Research, Yonsei University, Seoul 03722, Republic of Korea

^⋆ Corresponding author: ylkim83@yonsei.ac.kr

Received: 2 April 2025
Accepted: 6 September 2025

Abstract

The analytical model found that the intrinsic variation in the initial metallicity of the Type Ia supernova (SN Ia) progenitor stars (Z_progenitor) translates into a 25% variation in the synthesized ⁵⁶Ni mass, and therefore, into a difference of ∼0.2 mag in the observed peak luminosity of SNe Ia. Previous observational studies used the currently observed global gas-phase metallicity of host galaxies, instead of Z_progenitor that was used in the model, and the studies showed a higher scatter in the ⁵⁶Ni mass measurements than the model prediction. We used Z_progenitor of 34 normal SNe Ia and employed recent SN Ia explosion models with various configurations to cover the observed ⁵⁶Ni mass range. Unlike previous studies, which only used samples in the sub-solar range, our sample covers the Z_progenitor range (1/3 Z_⊙ < Z_progenitor < 3 Z_⊙), where most of the Z_progenitor effect occurs. Linear regression returns a slope of 0.02 ± 0.03, which trend is opposite to that of the analytical model, but at at low statistical significance level. A comparison of our sample with SN Ia explosion models on the Z_progenitor–⁵⁶Ni mass diagram allowed us to constrain the progenitor scenarios. We also explored other chemical composition indicators, such as (Fe/H)_progenitor and (α/Fe)_progenitor. For (Fe/H)_progenitor, our sample follows the trend predicted by the analytical models, but at a low significance level (0.4σ). Noticeably, (α/Fe)_progenitor shows the opposite trend and a clear gap. When we split the sample at (α/Fe)_progenitor = 0.35(α/Fe)_⊙, we find a 3σ difference in the weighted means of the ⁵⁶Ni mass. Lastly, the standardized luminosities of SNe Ia in different Z_progenitor groups differed by 0.14 ± 0.09 (1.6σ) mag. We highlight a holistic approach (from the progenitor star to the explosion with SN Ia and host galaxy observational data) to understanding the underlying physics of SNe Ia for a more accurate and precise cosmology.