Highly ionized region surrounding SN Refsdal revealed by MUSE

¹ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: karman@astro.rug.nl
² Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
³ INAF–Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
⁴ University Observatory Munich, Scheinerstrasse 1, 81679 Munich, Germany
⁵ Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, via Saragat 1, 44122 Ferrara, Italy
⁶ Department of Physics and Astronomy, University of Bologna, 6/2, Viale Berti Pichat, 40127 Bologna, Italy
⁷ Institut d’Astrophysique de Paris, UMR7095 CNRS-Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁸ INAF–Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁹ Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
¹⁰ Department of Physics and Astronomy, University of South Carolina, 712 Main St., Columbia, SC 29208, USA
¹¹ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
¹² Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA

Received: 24 September 2015
Accepted: 9 November 2015

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 Mg ii emission at all positions of SN Refsdal, accompanied by weak Fe ii* emission at two positions. The measured ratios of [O ii] to Mg ii 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 [O ii] line over a period of 57 days. This suggests that there is no variation in the [O ii] luminosity of the SN over this period, or that the SN has a small contribution to the integrated [O ii] emission over the scale resolved by our observations.