A Revised SALT2 Surface for Fitting Type Ia Supernova Light Curves

TL;DR

This paper introduces a revised SALT2 model for fitting Type Ia supernova light curves, incorporating new calibration data and focusing on UV region changes, which impacts dark energy measurements.

Contribution

The paper presents SALT2-2021, a new supernova light curve fitting surface with updated calibration and UV modifications, improving dark energy parameter estimates.

Findings

Revised SALT2 alters supernova distance measurements.

Change in dark energy equation of state parameter, Δw = 0.015 ± 0.004.

Highlights importance of reducing systematic uncertainties.

Abstract

We present a revised SALT2 surface (`SALT2-2021') for fitting the light curves of Type Ia supernovae (SNe Ia), which incorporates new measurements of zero-point calibration offsets and Milky Way extinction. The most notable change in the new surface occurs in the UV region. This new surface alters the distance measurements of SNe~Ia, which can be used to investigate the nature of dark energy by probing the expansion history of the Universe. Using the revised SALT2 surface on public data from the first three years of the Dark Energy Survey Supernova Program (combined with an external low-$z$ SNe Ia sample) and combining with cosmic microwave background constraints, we find a change in the dark energy equation of state parameter, $\Delta w = 0.015 \pm 0.004$. This result highlights the continued importance of controlling and reducing systematic uncertainties, particularly with the next generation of supernova analyses aiming to improve constraints on dark energy properties.