Strong progenitor age bias in supernova cosmology – I. Robust andubiquitous evidence from a larger sample of host galaxies in a broaderredshift range

Chul Chung , Seunghyun Park, Junhyuk Son, Hyejeon Cho and Young-Wook Lee

ABSTRACT
Type Ia supernovae (SNe Ia) serve as the most crucial standardizable candles in cosmology, providing direct measurements ofthe Universe’s expansion history. However, it is well known that the post-standardization brightness of SNe Ia is influenced bythe properties of their host galaxies, such as mass and star formation rate, both of which are closely related to progenitor age.In this study, by measuring the stellar population ages of SN host galaxies, we reaffirm the ubiquitous and robust correlationbetween SN Ia luminosity and host age, showing that this host property dependence arises primarily from stellar population ageof the host galaxy. This analysis was conducted using an expanded sample of over 300 hosts across a broad redshift range up toz ∼ 0.4, ensuring sufficientstatisticalsignificance of the result. To quantify the relationship between host age and Hubble residual(HR), we employed two linear regression techniques: LINMIX, which assumes a Gaussian age error, and Bayesian hierarchicallinear regression, which utilizes a full posterior for the age error. Both models demonstrate a robust correlation between hostage and HR, with high statistical significance approaching 5.5σ. While our new regression analyses yield the slopes that aresimilar or slightly shallower compared to our previous results, the significance of these slopes has notably increased. Thesefindings robustly validate our previous suggestions that post-standardization SN Ia luminosity varies with progenitor age, whichis currently not properly accounted for in SN cosmology.

https://doi.org/10.1093/mnras/staf497