Supernovae have been confirmed to redshift z ≈ 1.7 (refs 1, 2) for type Ia (thermonuclear detonation of a white dwarf) and to z ≈ 0.7 (refs 1, 3–5) for type II (collapse of the core of the star). The subclass type IIn (ref. 6) supernovae are luminous7,8,9 core-collapse explosions of massive stars8,9,10,11 and, unlike other types, are very bright in the ultraviolet12,13,14,15, which should enable them to be found optically at redshifts z ≈ 2 and higher14,16. 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 (ref. 14). 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 method14 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 measured17 stellar initial mass function, but not with an evolving initial mass function proposed18,19,20 to explain independent observations at low and high redshift.
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J.C. thanks D. Leonard for discussions. This work was made possible by support from the Gary McCue postdoctoral fellowship and the Center for Cosmology at the University of California, Irvine. We acknowledge support from NSERC and the Royal Society. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from the NSF (grant AST-0071048). The CFHT-LS relies on observations with MegaCam, a joint project of CFHT and CEA/DAPNIA, at the CFHT. We used data products from the Canadian Astronomy Data Centre as part of the CFHT-LS. Both CFHT and the W. M. Keck Observatory are located near the summit of Mauna Kea, Hawai'i. We acknowledge the cultural role that the summit of Mauna Kea has within the indigenous Hawaiian community.
Author Contributions J.C. led the survey design, and performed observations, data reduction and analysis, candidate selection, and data interpretation. M.S. was responsible for the data reduction and analysis of the CFHT-LS yearly stacked images, the supernova light curves, interpretation and key discussions. E.J.B. performed observations and provided observing time, discussions, and input regarding survey design, data analysis and interpretation. J.S.B. provided observing time, performed observations, contributed discussions, and helped in manuscript preparation. R.G.C. was one of the proponents of the CFHT-LS and became the Canadian PI, assembling the team responsible for much of the real-time operation and analysis of the Supernova Legacy Survey. A.G.-Y. provided advice about the analysis and helped prepare the manuscript. E.T. performed spectroscopic observations for two of the z ≈ 2 supernovae.
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Cooke, J., Sullivan, M., Barton, E. et al. Type IIn supernovae at redshift z ≈ 2 from archival data. Nature 460, 237–239 (2009). https://doi.org/10.1038/nature08082
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