The Discovery of a Gravitationally Lensed Supernova Ia at Redshift 2.22

TL;DR

This paper reports the discovery of the highest redshift spectroscopically confirmed Type Ia supernova, gravitationally lensed by a distant galaxy cluster, providing insights into supernova properties and lensing effects at z=2.22.

Contribution

It presents the first spectroscopically confirmed SN Ia at z=2.22, strongly lensed by a distant galaxy cluster, with detailed photometric and spectroscopic analysis.

Findings

Highest redshift SN Ia with spectroscopic host redshift

Lensing amplification of 2.8+0.6-0.5 times

SN properties consistent with lower redshift counterparts

Abstract

We present the discovery and measurements of a gravitationally lensed supernova (SN) behind the galaxy cluster MOO J1014+0038. Based on multi-band Hubble Space Telescope and Very Large Telescope (VLT) photometry of the supernova, and VLT spectroscopy of the host galaxy, we find a 97.5% probability that this SN is a SN Ia, and a 2.5% chance of a CC SN. Our typing algorithm combines the shape and color of the light curve with the expected rates of each SN type in the host galaxy. With a redshift of 2.2216, this is the highest redshift SN Ia discovered with a spectroscopic host-galaxy redshift. A further distinguishing feature is that the lensing cluster, at redshift 1.23, is the most distant to date to have an amplified SN. The SN lies in the middle of the color and light-curve shape distributions found at lower redshift, disfavoring strong evolution to z = 2.22. We estimate an amplification due to gravitational lensing of 2.8+0.6-0.5 (1.10 +- 0.23 mag)---compatible with the value estimated from the weak-lensing-derived mass and the mass-concentration relation from LambdaCDM simulations---making it the most amplified SN Ia discovered behind a galaxy cluster.