Journal Talk 26: Deba Priyo Guha (2026)

Host-Galaxy Stellar Ages of Type Ia Supernovae

Abstract

Type Ia supernovae are our best tools for measuring cosmic distances. After we standardize them, a small scatter still remains, called the Hubble residual. This residual correlates with the host galaxy. If the correlation is driven by the age of the stars, it could bias dark-energy measurements. Son et al. 2025 argue that a local stellar age near the explosion drives this effect.

In this work, we test that claim using the global age of the host galaxy. We measure host ages by fitting the galaxy light with mc-age, using FSPS models and the Nautilus sampler, and we cross-check them with BAGPIPES. We apply this to the Campbell 2013 SDSS sample of 103 supernovae, and to the Carnegie Supernova Project samples, CSP-I and CSP-II.

We then split each sample into young and old hosts, and measure the step in the Hubble residual across the split. We find that the global-age step is small, about mag, below the level. This shows that the global host age does not significantly bias the distances, and it does not support the strong local-age effect claimed by Son et al. 2025.

Presenter: Deba Priyo Guha (M.Sc. (ongoing) in Theoretical Physics, University of Dhaka)

Supervisor: Syed Ashraf Uddin, PhD (Core Member of CASSA; Associate Professor, Department of Physical Sciences, Independent University, Bangladesh)