SPHEREx 3.3 Micron Aromatic Emission in the Magellanic Clouds: Separating Dust Column, Excitation, and Environmental Suppression

Bright emission in the 3.3um unidentified infrared band, often described as an aromatic infrared band, can trace dust column, radiative excitation, or the survival and emissivity of its carriers. We combine SPHEREx maps of the Magellanic Clouds with HERITAGE dust columns, a TIR heating proxy, Brα, Hα, H II-region catalogs, and SAGE 8um imaging. We measure continuum-subtracted 3.3um feature excess, X 3.3, and Brαexcess, X Brα, in matched cells. In each Cloud, a quiescent diffuse baseline depending on dust surface density, Σ d, and TIR/Σ d predicts X 3.3 with R 2=0.628 in the LMC and 0.288 in the SMC. Relative to this expectation, LMC H II interiors are under-luminous by-0.223+0.035-0.040 dex; local-background measurements give-0.153+0.014-0.043 dex despite a total-X 3.3 enhancement of +0.749 dex. SMC H II-region residuals are consistent with zero over its lower-X Brα regime. A matched comparison with stellar-subtracted 8um dust intensity, I 8,dust, shows that column and heating predict I 8,dust more tightly than X 3.3, and that the high-X Brα LMC deficit is stronger for X 3.3 than for I 8,dust. The deficit is therefore selective to the isolated 3.3um feature, not uniform in all aromatic-band-dominated emission. This result suggests that the small aromatic/aliphatic carbonaceous carriers traced by the isolated 3.3um feature are more susceptible to processing in active regions than the larger or differently emitting carbonaceous-grain population dominating the 8um aromatic complexes.