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We present mid-infrared (MIR) spectra of HII regions within star-forminggalaxies M83 and M33. Their emission features are compared with Galactic andextragalactic HII regions, HII-type galaxies, starburst galaxies, andSeyfert/LINER type galaxies. Our main results are as follows: (i) the M33 andM83 HII regions lie in between Seyfert/LINER galaxies and HII-type galaxies inthe 7.7/11.3 - 6.2/11.3 plane, while the different sub-samples exhibitingdifferent 7.7/6.2 ratios; (ii) Using the NASA Ames PAH IR Spectroscopicdatabase, we demonstrate that the 6.2/7.7 ratio does not effectively track PAHsize, but the 11.3/3.3 PAH ratio does; (iii) variations on the 17 $\mu$m PAHband depends on object type; however, there is no dependence on metallicity forboth extragalactic HII regions and galaxies; (iv) the PAH/VSG intensity ratiodecreases with the hardness of the radiation field and galactocentric radius(Rg), yet the ionization alone cannot account for the variation seen in all ofour sources; (v) the relative strength of PAH features does not changesignificantly with increasing radiation hardness, as measured through the[NeIII]/[NeII] ratio and the ionization index; (vi) We present PAH SFRcalibrations based on the tight correlation between the 6.2, 7.7, and 11.3$\mu$m PAH luminosities with the 24 $\mu$m luminosity and the combination ofthe 24 $\mu$m and H$\alpha$ luminosity; (vii) Based on the total luminosityfrom PAH and FIR emission, we argue that extragalactic HII regions are moresuitable templates in modeling and interpreting the large scale properties ofgalaxies compared to Galactic HII regions.

PAHs and star formation in the HII regions of nearby galaxies M83 and M33