Astronomical Models of PAHs and Dust

Physical dust models which include a PAH component are quite successful in reproducing the measured extinction vs. wavelength in the Milky Way, the infrared (IR) emission observed from Milky Way regions and other galaxies, and a number of other observational constraints. Many of the adopted PAH properties are necessarily highly idealized. The observed variations in the 7.7 μ m/11.3 μ m band ratio can be reproduced by varying the PAH ionization balance. Changing the spectrum of the starlight heating the PAHs affects the overall strength of the PAH emission (relative to total IR), but has relatively little effect on the 7.7 μ m/11.3 μ m band ratio.