DES15E2mlf: a spectroscopically confirmed superluminous supernova that exploded 3.5 Gyr after the big bang

We present the Dark Energy Survey (DES) discovery of DES15E2mlf, the most distant superluminous supernova (SLSN) spectroscopically confirmed to date. The light curves and Gemini spectroscopy of DES15E2mlf indicate that it is a Type I superluminous supernova (SLSN-I) at z = 1.861 (a lookback time of similar to 10 Gyr) and peaking at M-AB = -22.3 +/- 0.1 mag. Given the high redshift, our data probe the rest-frame ultraviolet (1400-3500 angstrom) properties of the SN, finding velocity of the C III feature changes by similar to 5600 km s(-1) over 14 d around maximum light. We find the host galaxy of DES15E2mlf has a stellar mass of 3.5(-2.4)(+3.6) x 10(9) M-circle dot, which is more massive than the typical SLSN-I host galaxy.NSF AST-1518052 Alfred P. Sloan Foundation David and Lucile Packard Foundation US National Science Foundation AST-1311862 UK STFC ST/N000919/1 EU-ERC 615929 US Department of Energy US National Science Foundation Ministry of Science and Education of Spain Science and Technology Facilities Council of the United Kingdom Higher Education Funding Council for England National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign Kavli Institute of Cosmological Physics at the University of Chicago Center for Cosmology and Astro-Particle Physics at the Ohio State University Mitchell Institute for Fundamental Physics and Astronomy at Texas AM University Financiadora de Estudos e Projetos Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro Conselho Nacional de Desenvolvimento Cientifico e Tecnologico Ministerio da Ciencia, Tecnologia e Inovacao Deutsche Forschungsgemeinschaft University of California at Santa Cruz University of Cambridge Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid University of Chicago University College London DES-Brazil Consortium University of Edinburgh Eidgenossische Technische Hochschule (ETH) Zurich University of Illinois at Urbana-Champaign Institut de Ciencies de l'Espai (IEEC/CSIC) Institut de Fisica d'Altes Energies Lawrence Berkeley National Laboratory Ludwig-Maximilians Universit at Munchen Excellence Cluster Universe National Optical Astronomy Observatory University of Nottingham Ohio State University University of Pennsylvania University of Portsmouth SLAC National Accelerator Laboratory Stanford University University of Sussex Texas AM University OzDES Membership Consortium National Science Foundation AST-1138766 MINECO AYA2012-39559 ESP2013-48274 FPA2013-47986 Centro de Excelencia Severo Ochoa SEV-2012-0234 European Research Council under the European Unions Seventh Framework Programme 240672 291329 306478 University of Michigan Argonne National Laboratory Fermi National Accelerator Laborator