Exploring the Systematic Uncertainties of Type Ia Supernovae as Cosmological Probes

TL;DR

This study investigates the systematic uncertainties in using Type Ia supernovae as cosmological tools, focusing on the evolution of key parameters and the impact of flux-averaging on distance measurements.

Contribution

It provides new insights into the redshift evolution of supernova parameters and demonstrates how flux-averaging mitigates systematic effects in cosmological analyses.

Findings

No evidence for evolution of the stretch-luminosity parameter $oldsymbol{ extit{ extalpha}}$ with redshift.

The color-luminosity parameter $oldsymbol{ extbeta}$ varies with redshift when not flux-averaged, but remains constant when flux-averaged.

Flux-averaging significantly influences the derived distance-redshift relation.

Abstract

We explore the systematic uncertainties of using Type Ia supernovae (SNe Ia) as cosmological probes, using the Supernova Legacy Survey Three Year data (SNLS3). We focus on studying the possible evolution of the stretch-luminosity parameter $\alpha$ and the color-luminosity parameter $\beta$, by allowing $\alpha$ and $\beta$ to be function of redshift, $z$. We find no evidence for the redshift evolution of $\alpha$. We find that without flux-averaging SNe, $\beta$ is consistent with being a constant when only statistical uncertainties are included, but it increases significantly with $z$ when systematic uncertainties are also included. The evolution of $\beta$ becomes marginal when all the SNe are flux-averaged, and $\beta$ is consistent with being a constant when only SNe at $z\ge 0.04$ are flux-averaged. Our results are insensitive to the lightcurve fitter used to derive the SNLS3 sample, or the functional form of $\alpha(z)$ and $\beta(z)$ assumed. It is likely that the apparent evolution of $\beta$ with $z$ for SNe without flux-averaging is a consequence of unknown systematic effects; flux-averaging reduces the impact of these effects by averaging them within each redshift bin. Assuming constant $\alpha$ and $\beta$, we find that the flux-averaging of SNe has a significant impact on the distance-redshift relation.