An Archival Calibration of JWST/MIRI Prism Wide-Field Slitless Spectroscopy: Methodology, Performance, and a Mid-Infrared Spectral Atlas of Galaxies at z=0-4 in the GOODS-N/S Fields

Through the Low Resolution Spectroscopy (LRS) observing mode of JWST/MIRI, the P750L prism disperses the entire 70" times 110" imager field, turning MIRI into a wide-field slitless spectrograph (WFSS) at 5-14 μ m with spectral resolution R about100. Using archival MIRI LRS data taken in the GOODS-N/S deep fields and calibration programs, we present a complete and precise calibration suite for MIRI WFSS through an AI-assisted agentic workflow under human supervision. The calibration includes flat field, sky background, spectral tracing, wavelength calibration, flux calibration, and the large-scale flux flat (L-flat). We present the methodology of each calibration and quantify its accuracy. As a demonstration, we extract 5-14 μ m slitless spectra of 180 spectroscopically confirmed galaxies at z=0.08 - 3.71 in the GOODS-N/S fields. We detect a large number of polycyclic aromatic hydrocarbon (PAH) bands and atomic lines (including Paschen α out to z=3.71) in individual sources. The PAH 3.3 μ m luminosities correlate with the Paschen α luminosities (measured through NIRCam WFSS) for z about1 galaxies over a about 1.5-dex range, supporting PAH 3.3 μ m as a star-formation-rate tracer out to z about1.6. We release the calibration reference files, reduction scripts, and the mid-infrared spectral atlas. We also present caveats and lessons learned from our archival calibration work. Our empirical sensitivity characterization identifies a noise floor for deep MIRI WFSS integrations (a few ks), whereas shallower integrations exceed the sensitivity predicted by the JWST Exposure Time Calculator. We also provide suggestions for the planning of future MIRI WFSS observing programs.