Type IIn supernovae at z ~ 2 from archival data

TL;DR

This paper reports the discovery of three spectroscopically confirmed Type IIn supernovae at redshifts around 2, using archival data, providing insights into massive star formation and initial mass function at high redshift.

Contribution

First detection of Type IIn supernovae at z ~ 2 using archival data, demonstrating their potential to probe early universe star formation.

Findings

Three Type IIn supernovae confirmed at z=0.808, 2.013, 2.357

Number of detections consistent with local stellar initial mass function

Supports non-evolving initial mass function at high redshift

Abstract

Supernovae have been confirmed to redshift z ~ 1.7 for type Ia (thermonuclear detonation of a white dwarf) and to z ~ 0.7 for type II (collapse of the core of the star). The subclass type IIn supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts z ~ 2 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at z ~ 2 for 3 - 5 years after explosion. Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at z ~ 2. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.