Strong progenitor age bias in supernova cosmology. I. Robust and ubiquitous evidence from a larger sample of host galaxies in a broader redshift range

TL;DR

This study confirms a strong, statistically significant correlation between Type Ia supernova luminosity and the stellar age of their host galaxies across a broad redshift range, highlighting an important factor affecting cosmological measurements.

Contribution

It provides the first robust, statistically significant evidence that host galaxy age influences SN Ia luminosity, using an expanded sample and advanced regression techniques.

Findings

Host galaxy age significantly correlates with SN Ia Hubble residuals.

The correlation remains robust across different regression methods.

The significance of the host age effect has increased with the larger sample.

Abstract

Type Ia supernovae (SNe Ia) serve as the most crucial standardizable candles in cosmology, providing direct measurements of the universe's expansion history. However, it is well-known that the post-standardization brightness of SNe Ia is influenced by the 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 correlation between SN Ia luminosity and host age, showing that this host property dependence arises primarily from stellar population age of the host galaxy. This analysis was conducted using an expanded sample of over 300 hosts across a broad redshift range up to $z \sim 0.4$, ensuring sufficient statistical significance 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 hierarchical linear regression, which utilizes a full posterior for the age error. Both models demonstrate a robust correlation between host age and HR, with high statistical significance approaching $5.5 \sigma$. While our new regression analyses yield the slopes that are similar or slightly shallower compared to our previous results, the significance of these slopes has notably increased. These findings robustly validate our previous suggestions that post-standardization SN Ia luminosity varies with progenitor age, which is currently not properly accounted for in SN cosmology.