Lensing and Supernovae: Quantifying The Bias on the Dark Energy Equation of State

TL;DR

This study quantifies the bias introduced by gravitational lensing on supernova-based measurements of dark energy, finding it to be negligible for large datasets and thus not a significant systematic concern.

Contribution

The paper provides a detailed analysis of lensing bias on the dark energy equation of state using mock supernova samples, demonstrating its minimal impact on future cosmological measurements.

Findings

Lensing bias on dark energy EOS is less than 0.5% for datasets with over 2,000 SNe.

Removing highly magnified SNe increases bias to about 0.8%.

Lensing systematic can be ignored given current measurement uncertainties.

Abstract

The gravitational magnification and demagnification of Type Ia supernovae (SNe) modify their positions on the Hubble diagram, shifting the distance estimates from the underlying luminosity-distance relation. This can introduce a systematic uncertainty in the dark energy equation of state (EOS) estimated from SNe, although this systematic is expected to average away for sufficiently large data sets. Using mock SN samples over the redshift range $0 < z \leq 1.7$ we quantify the lensing bias. We find that the bias on the dark energy EOS is less than half a percent for large datasets ($\gtrsim$ 2,000 SNe). However, if highly magnified events (SNe deviating by more than 2.5$\sigma$) are systematically removed from the analysis, the bias increases to $\sim$ 0.8%. Given that the EOS parameters measured from such a sample have a 1$\sigma$ uncertainty of 10%, the systematic bias related to lensing in SN data out to $z \sim 1.7$ can be safely ignored in future cosmological measurements.