We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the relationship between the 8 \mu m PAH emission , 24 \mu m hot dust emission , and Hii region radiative transfer .
We confirm that in the higher-metallicity Large Magellanic Cloud , PAH destruction is sensitive to optically thin conditions in the nebular Lyman continuum : objects identified as optically thin candidates based on nebular ionization structure show 6 times lower median 8 \mu m surface brightness ( 0.18 mJy arcsec ^ { -2 } ) than their optically thick counterparts ( 1.2 mJy arcsec ^ { -2 } ) .
The 24 \mu m surface brightness also shows a factor of 3 offset between the two classes of objects ( 0.13 vs 0.44 mJy arcsec ^ { -2 } , respectively ) , which is driven by the association between the very small dust grains and higher density gas found at higher nebular optical depths .
In contrast , PAH and dust formation in the low-metallicity Small Magellanic Cloud is strongly inhibited such that we find no variation in either 8 \mu m or 24 \mu m emission between our optically thick and thin samples .
This is attributable to extremely low PAH and dust production together with high , corrosive UV photon fluxes in this low-metallicity environment .
The dust mass surface densities and gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey data support this interpretation .