A highly-ionized region surrounding SN Refsdal revealed by MUSE

TL;DR

This study uses MUSE spectroscopy to analyze the environment of SN Refsdal at high redshift, revealing a highly-ionized, low-metallicity region likely influenced by previous supernovae or young stars.

Contribution

First detailed spatially-resolved spectroscopic analysis of SN Refsdal's environment at high redshift using MUSE, revealing ionization conditions and environmental properties.

Findings

Detected MgII emission at all SN positions.

Found high [OII]/MgII ratios indicating high ionization and low metallicity.

Observed no [OII] variability over 57 days.

Abstract

Supernova (SN) Refsdal is the first multiply-imaged, highly-magnified, and spatially-resolved SN ever observed. The SN exploded in a highly-magnified spiral galaxy at z=1.49 behind the Frontier Fields Cluster MACS1149, and provides a unique opportunity to study the environment of SNe at high z. We exploit the time delay between multiple images to determine the properties of the SN and its environment, before, during, and after the SN exploded. We use the integral-field spectrograph MUSE on the VLT to simultaneously target all observed and model-predicted positions of SN Refsdal. We find MgII emission at all positions of SN Refsdal, accompanied by weak FeII* emission at two positions. The measured ratios of [OII] to MgII emission of 10-20 indicate a high degree of ionization with low metallicity. Because the same high degree of ionization is found in all images, and our spatial resolution is too coarse to resolve the region of influence of SN Refsdal, we conclude that this high degree of ionization has been produced by previous SNe or a young and hot stellar population. We find no variability of the [OII] line over a period of 57 days. This suggests that there is no variation in the [OII] luminosity of the SN over this period, or that the SN has a small contribution to the integrated [OII] emission over the scale resolved by our observations.