Mid-Infrared Diagnostics of PAH Processing and Radiation Fields in M33 H II Regions with JWST/MIRI

We present JWST/MIRI (Proposal ID 4297) medium-resolution integral field spectroscopy of five H II regions in the nearby spiral galaxy M33, obtained from the Mikulski Archive for Space Telescopes (MAST). The fully calibrated Level-3 spectral cubes provide continuous wavelength coverage from 6.5 - 20.9 μ m, enabling analysis of polycyclic aromatic hydrocarbon (PAH) emission, ionic fine-structure lines, and warm molecular hydrogen. The spectra show prominent PAH bands at 7.7, 8.6, and 11.3 μ m, multiple H 2 rotational transitions, and hydrogen recombination lines. H 2 rotational diagrams yield warm molecular gas temperatures of about316 - 407 K. The detected [Ne II], [Ne III], [S III], and [S IV] lines yield ionization indices of-1.41 to +0.98. The PAH ionization fraction shows no clear dependence on radiation hardness, consistent with previous Spitzer results. Unlike previous work, we find no clear correlation between the 7.7/11.2 and 8.6/11.2 μ m PAH ratios, while the 7.7/11.2 μ m ratio shows a moderate negative correlation with metallicity, possibly due to our small sample (N=5). The PAH-to-VSG ratio decreases with increasing radiation hardness. We derive the ionization parameter γ, far-ultraviolet radiation field, and PAH charge state, finding a predominantly cationic PAH population (about75%) despite [Ne III]/[Ne II] <1. The lack of a one-to-one correspondence between γ and the 7.7/11.2 μ m ratio suggests that PAH ionization is influenced by additional environmental factors. Given the limited sample, these trends are suggestive rather than statistically definitive.