Cosmological Impact of Redshift-Dependent Type Ia Supernovae Calibration

TL;DR

This study investigates whether a redshift-dependent calibration correction to Type Ia supernovae affects cosmological measurements, finding it has minimal impact within standard models but can help reconcile data when considering dynamical dark energy.

Contribution

It introduces a phenomenological correction to SNIa magnitudes based on cosmic look-back time and constrains its effects using multiple cosmological datasets.

Findings

No significant evidence for redshift-dependent calibration effects in uncalibrated data.

Including the correction has negligible impact on ΛCDM cosmological parameters.

In dynamical dark energy models, the correction can reduce the Hubble tension to 1.5σ.

Abstract

Type Ia supernovae (SNIa) play a central role in constraining the late-time expansion history of the Universe and are directly implicated in current cosmological tensions. Motivated by the possibility of unaccounted redshift-dependent calibration systematics or new physics, we investigate the impact of a phenomenological correction to SNIa magnitudes that scales with cosmic look-back time. We parameterize this effect with a free amplitude and constrain it using a combination of cosmic microwave background, baryon acoustic oscillation, and SNIa data, considering both $\Lambda$CDM and dynamical dark energy models. Importantly, our parameterization is not intended to serve as a proxy for SNIa progenitor age, as current observations show no significant difference in standardized SNIa brightness between young and old progenitor populations at low redshift. We find no evidence for a redshift-dependent calibration effect when fitting uncalibrated SNIa data, and its inclusion has a negligible impact on cosmological parameters within $\Lambda$CDM, nor does it qualitatively change the inferred dynamics of evolving dark energy. When incorporating a prior on the SNIa absolute magnitude from SH0ES, a nonzero calibration parameter is weakly preferred within $\Lambda$CDM. Interestingly, with dynamical dark energy, the preference of a nonzero calibration parameter increases to $4.3\sigma$, and it can accommodate both the distance ladder and early-Universe constraints, reducing the Hubble tension to $1.5\sigma$, with the best-fit model effectively corresponding to a constant equation of state with $w < -1$. Overall, our results indicate that redshift-dependent SNIa calibration effects, as parameterized here, are not supported by current data within $\Lambda$CDM, but can play a role in reconciling cosmological datasets when combined with extensions to the late-time expansion history.