Gravitational lensing in the Supernova Legacy Survey (SNLS)

TL;DR

This study investigates gravitational lensing effects on Type Ia supernova brightness in the SNLS, finding tentative evidence of lensing signals and assessing the potential for future detection with larger samples.

Contribution

It provides the first evidence of gravitational lensing in SNLS data and analyzes factors affecting the detection significance.

Findings

Evidence of lensing signal with 2.3 sigma significance

Red/blue galaxy separation improves detection significance

80% probability of 3 sigma detection with full SNLS sample

Abstract

The observed brightness of Type Ia supernovae is affected by gravitational lensing caused by the mass distribution along the line of sight, which introduces an additional dispersion into the Hubble diagram. We look for evidence of lensing in the SuperNova Legacy Survey 3-year data set. We investigate the correlation between the residuals from the Hubble diagram and the gravitational magnification based on a modeling of the mass distribution of foreground galaxies. A deep photometric catalog, photometric redshifts, and well established mass luminosity relations are used. We find evidence of a lensing signal with a 2.3 sigma significance. The current result is limited by the number of SNe, their redshift distribution, and the other sources of scatter in the Hubble diagram. Separating the galaxy population into a red and a blue sample has a positive impact on the significance of the signal detection. On the other hand, increasing the depth of the galaxy catalog, the precision of photometric redshifts or reducing the scatter in the mass luminosity relations have little effect. We show that for the full SuperNova Legacy Survey sample (~400 spectroscopically confirmed Type Ia SNe and ~200 photometrically identified Type Ia SNe), there is an 80% probability of detecting the lensing signal with a 3 sigma significance.