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Ejecta, Rings, and Dust in SN 1987A with JWST MIRI/MRS

Sample slices from our 12 MRS sub-band cubes, with the band labels shown in the top-left. The white lines in each pane represent 1.0 arcsec to highlight the increasing size of the FOV, as well as the decreasing spatial resolution from channels 1 to 4. ‘Star 3’ is visible to the lower left of the ER in bands 1A–2A. North is up, east is left. Supernova (SN) 1987A is the nearest supernova in ~400 years. Using the {\em JWST} MIRI Medium Resolution Spectrograph, we spatially resolved the ejecta, equatorial ring (ER) and outer rings in the mid-infrared 12,927 days after the explosion. The spectra are rich in line and dust continuum emission, both in the ejecta and the ring. Broad emission lines (280-380~km~s-1 FWHM) seen from all singly-ionized species originate from the expanding ER, with properties consistent with dense post-shock cooling gas. Narrower emission lines (100-170~km~s-1 FWHM) are seen from species originating from a more extended lower-density component whose high ionization may have been produced by shocks progressing through the ER, or by the UV radiation pulse associated with the original supernova event. The asymmetric east-west dust emission in the ER has continued to fade, with constant temperature, signifying a reduction in dust mass. Small grains in the ER are preferentially destroyed, with larger grains from the progenitor surviving the transition from SN into SNR. The ER is fit with a single set of optical constants, eliminating the need for a secondary featureless hot dust component. We find several broad ejecta emission lines from [Ne~{\sc ii}], [Ar~{\sc ii}], [Fe~{\sc ii}], and [Ni~{\sc ii}]. With the exception of [Fe~{\sc ii}]~25.99µm, these all originate from the ejecta close to the ring and are likely being excited by X-rays from the interaction. The [Fe~{\sc ii}]~5.34µm to 25.99µm line ratio indicates a temperature of only a few hundred K in the inner core, consistent with being powered by 44Ti decay.