The need for accurate redshifts in supernova cosmology

TL;DR

This paper investigates how small systematic redshift errors in supernova measurements can bias cosmological parameters and proposes using supernova data to diagnose local gravitational inhomogeneities.

Contribution

It introduces a method to fit for redshift shifts as free parameters, enabling the diagnosis of local gravitational environments from supernova data.

Findings

Redshift shifts of order 10^{-5} can bias cosmological parameters by about 1%.

Supernova data can be used to probe local gravitational inhomogeneities.

Fitting for redshift shifts helps identify environmental effects on supernova measurements.

Abstract

Recent papers have shown that a small systematic redshift shift ($\Delta z\sim 10^{-5}$) in measurements of type Ia supernovae can cause a significant bias ($\sim$1\%) in the recovery of cosmological parameters. Such a redshift shift could be caused, for example, by a gravitational redshift due to the density of our local environment. The sensitivity of supernova data to redshift shifts means supernovae make excellent probes of inhomogeneities. We therefore invert the analysis, and try to diagnose the nature of our local gravitational environment by fitting for $\Delta z$ as an extra free parameter alongside the usual cosmological parameters.