Still non-accelerating: age-bias correction in supernova cosmology is robust to host-progenitor age mapping

TL;DR

This paper re-evaluates the impact of progenitor-age bias on supernova cosmology, showing previous claims of negligible effect are due to methodological issues and that the bias remains significant.

Contribution

The study demonstrates that age-bias correction methods are robust and that previous underestimations were caused by sample selection and dust model assumptions.

Findings

Re-analysis shows the host-age-HR slope was underestimated due to redshift range effects.

Applying the Pantheon+ host-mass correction suppresses the slope, but the dust model is incompatible with galaxy data.

When corrected for these factors, the cosmological impact of age bias remains consistent with prior estimates.

Abstract

We re-examine the claim by Wiseman et al. (2026) that progenitor-age bias has a negligible impact on cosmological inferences from Type Ia supernovae (SNe Ia). We show that their inferred host-age-Hubble residual (HR) slope is severely underestimated because their combined SN Ia sample spans an unusually wide redshift range ($0.04 < z < 0.42$), over which the mean host age evolves by $\sim$\,3 Gyr. As a result, SNe Ia spanning substantial host-age differences are effectively assigned similar HR values prior to regression, artificially flattening the inferred age-HR relation. In addition, their application of the Pantheon+ host-mass correction further suppresses the slope, but the underlying dust model is highly incompatible with the measured dust attenuation curves of galaxies. We also demonstrate that our age bias correction is robust to uncertainties in host-progenitor age mapping arising from different choices of the SN Ia delay-time distribution. The reduced progenitor-age evolution argued by Wiseman et al. (2026) must, by the same logic, be accompanied by a steeper inferred progenitor-age-HR slope. When these two effects are consistently combined in computing the redshift-dependent magnitude correction, the final correction, and hence the resulting cosmological impact, remain largely unchanged from Son et al. (2025).