JWST Observations of SN 2024ggi. I. Interpretation and Model Comparison of the Type II Supernova 2024ggi at 55 Days past Explosion

We present panchromatic 0.4–21 μm observations of the nearby (∼7.2 Mpc) Type II supernova (SN) 2024ggi, obtained during the plateau phase at ∼55 days past explosion. Our data set includes JWST spectra spanning 1.7–14 μm, mid-infrared (MIR) imaging at 7.7 and 21 μm, and near-simultaneous ground-based optical and near-infrared (NIR) spectra covering 0.32−1.8 μm. The NIR and MIR spectral features of SN 2024ggi are dominated by H i emission. We present line IDs and a toy PHOENIX/1D model that reproduces the observations well, especially the continuum redward of 0.9 μm. We compare SN 2024ggi to SN 2022acko and SN 2023ixf, two other Type II SNe that were also observed by JWST, and highlight key similarities and differences in their spectral features. No evidence for a MIR excess or dust is found at these epochs, with the model matching the observed flux out to 21 μm. We discuss the model’s shortcomings, focusing on the density profile, which suppresses line blanketing and produces features in the optical that are too narrow. Our results show the power of panchromatic studies in both exploring the nature of the SN ejecta and constraining detailed models of SNe.