2016ApJ...819...65S

We present a sample of resolved galactic H ii regions and photodissociation regions (PDRs) observed with the Spitzer infrared spectrograph in spectral mapping mode between the wavelengths of 5-15 µm. For each object we have spectral maps at a spatial resolution of ∼4" in which we have measured all of the mid-infrared emission and absorption features. These include the polycyclic aromatic hydrocarbon (PAH) emission bands, primarily at 6.2, 7.7, 8.6, 11.2, and 12.7 µm, as well as the spectral emission lines of neon and sulfur and the absorption band caused by silicate dust at around 9.8 µm. In this work we describe the data in detail, including the data reduction and measurement strategies, and subsequently present the PAH emission band intensity correlations for each of the objects and the sample as a whole. We find that there are distinct differences between the sources in the sample, with two main groups: the first comprising the H ii regions and the second the reflection nebulae (RNe). Three sources–the reflection nebula NGC 7023, the Horsehead nebula PDR (an interface between the H ii region IC 434 and the Orion B molecular cloud), and M17–resist this categorization, with the Horsehead PDR points mimicking the RNe and the NGC 7023 fluxes displaying a unique bifurcated appearance in our correlation plots. These discrepancies seem to be due to the very low radiation field experienced by the Horsehead PDR and the very clean separation between the PDR environment and a diffuse environment in the NGC 7023 observations.