A JWST near- and mid-infrared nebular spectrum of the type Ia Supernova 2021aefx

Lindsey A. Kwok et al.We present JWST near-infrared (NIR) and mid-infrared (MIR) spectroscopic observations of the nearby normal Type Ia supernova (SN) SN 2021aefx in the nebular phase at +255 days past maximum light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument observations, combined with ground-based optical data from the South African Large Telescope, constitute the first complete optical+NIR+MIR nebular SN Ia spectrum covering 0.3–14 μm. This spectrum unveils the previously unobserved 2.5−5 μm region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. The data show a significant improvement in sensitivity and resolution compared to previous Spitzer MIR data. We identify numerous NIR and MIR nebular emission lines from iron-group elements as well as lines from the intermediate-mass element argon. The argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia models. We present fits to simple geometric line profiles to features beyond 1.2 μm and find that most lines are consistent with Gaussian or spherical emission distributions, while the [Ar iii] 8.99 μm line has a distinctively flat-topped profile indicating a thick spherical shell of emission. Using our line profile fits, we investigate the emissivity structure of SN 2021aefx and measure kinematic properties. Continued observations of SN 2021aefx and other SNe Ia with JWST will be transformative to the study of SN Ia composition, ionization structure, density, and temperature, and will provide important constraints on SN Ia progenitor and explosion models.L.A.K. acknowledges support by NASA FINESST fellowship 80NSSC22K1599. T.S. is supported by the NKFIH/OTKA FK-134432 grant of the National Research, Development and Innovation (NRDI) Office of Hungary, the János Bolyai Research Scholarship of the Hungarian Academy of Sciences, and the New National Excellence Program (UNKP-22-5) of the Ministry for Innovation and Technology of Hungary from the source of NRDI Fund. D.J.S. is supported by NSF grants AST-1821987, 1813466, 1908972, and 2108032, and by the Heising-Simons Foundation under grant No. 2020-1864. K.M. acknowledges support from the Japan Society for the Promotion of Science (JSPS) KAKENHI grants JP18H05223 and JP20H00174. L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) “Investing in your future” under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016, and the program Unidad de Excelencia María de Maeztu CEX2020-001058-M. K.M. and M.D. are funded by the EU H2020 ERC grant No. 758638. J.P.H. acknowledges support from the George A. and Margaret M. Downsbrough bequest. C.L. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant No. DGE-2233066. A.F. acknowledges support by the European Research Council (ERC) under the European Unionʼs Horizon 2020 research and innovation program (ERC advanced grant KILONOVA No. 885281).Peer reviewe