The Effect of Weak Lensing on Distance Estimates from Supernovae

TL;DR

This study investigates how weak gravitational lensing affects supernova distance measurements, demonstrating that incorporating lensing into models can improve accuracy and will be crucial for future cosmological surveys.

Contribution

The paper introduces a new parameter in the SALT2 method to account for lensing effects, improving supernova distance estimates and providing the first empirical detection of lensing influence on supernova residuals.

Findings

Lensing correlation with residuals is consistent with predictions at 1.7sigma.

Inclusion of lensing parameter improves distance estimates.

Lensing effects are marginally detected but will be significant in future surveys.

Abstract

Using a sample of 608 Type Ia supernovae from the SDSS-II and BOSS surveys, combined with a sample of foreground galaxies from SDSS-II, we estimate the weak lensing convergence for each supernova line-of-sight. We find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (at a significance of 1.7sigma. Strong correlations are also found between the residuals and supernova nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4sigma. We show for the first time that distance estimates from supernovae can be improved when lensing is incorporated by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using CMB data from WMAP7, H0 data from HST and SDSS BAO measurements, we find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Omega_m and w are unaffected. The lensing of supernovae, while only seen at marginal significance in this low redshift sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics dominated.