Weak lensing magnification of Type Ia Supernovae from the Pantheon sample

TL;DR

This study detects weak lensing effects on Type Ia supernovae using the Pantheon sample, constrains galaxy halo properties, and proposes a modified distance estimator to improve cosmological measurements.

Contribution

It introduces a new estimator for weak lensing convergence using galaxy data, quantifies lensing-induced scatter, and suggests a modified supernova distance measure to enhance cosmological parameter accuracy.

Findings

Correlation between lensing estimator and supernova residuals at 3.6σ significance.

Derived the lensing-induced magnitude scatter as a function of redshift.

Proposed a lensing-inclusive distance modulus for better cosmological constraints.

Abstract

Using data from the Pantheon SN Ia compilation and the Sloan Digital Sky Survey (SDSS), we propose an estimator for weak lensing convergence incorporating positional and photometric data of foreground galaxies. The correlation between this and the Hubble diagram residuals of the supernovae has $3.6\sigma$ significance, and is consistent with weak lensing magnification due to dark matter halos centered on galaxies. We additionally constrain the properties of the galactic haloes, such as the mass-to-light ratio $\Gamma$ and radial profile of the halo matter density $\rho(r)$. We derive a new relationship for the additional r.m.s. scatter in magnitudes caused by lensing, finding $\sigma_{\rm lens} = (0.06 \pm 0.017) (d_{\rm C}(z)/ d_{\rm C}(z=1))^{3/2}$ where $d_{\rm C}(z)$ is the comoving distance to redshift $z$. Hence the scatter in apparent magnitudes due lensing will be of the same size as the intrinsic scatter of SN Ia by $z \sim 1.2$. We propose a modification of the distance modulus estimator for SN Ia to incorporate lensing, which can be easily calculated from observational data. We anticipate this will improve the accuracy of cosmological parameter estimation for high-redshift SN Ia data.