Col(6): \[OIII\] to H$_\beta$ ratio taken from Ho, Filippenko, & Sargent (1997); Col(7): \[OI\] to H$_\alpha$ ratio taken from Ho, Filippenko, & Sargent (1997); Col(8): \[NII\] to H$_\alpha$ ratio taken from Ho, Filippenko, & Sargent (1997); Col(9): \[SII\] to H$_\alpha$ ratio taken from Ho, Filippenko, & Sargent (1997); Col(10): Optical classification of the source; “H” signifies HII region ratios, “T” represents transitional spectra between LINERs and HII regions, and “2” indicates that broad permitted lines were not found in the optical spectrum.]{}

Figure 2 shows the standard optical line ratio diagnostic diagrams (Veilleux & Osterbrock 1987) widely used to classify AGN for the entire H97 sample with our Spitzer sample highlighted. We also show in Figure 2 the theoretical starburst limit line from Kewley et al. 2001. This line represents the maximum line ratios possible from starburst photoionization models using the hardest possible starburst input ionizing radiation field. Note that the majority of galaxies in our sample ($\sim$85-94%, depending on the diagram) have optical line ratios well to the left of this line, indicating that the optical line ratios do not require the presence of [*any*]{} AGN contribution. We point out that the optical spectroscopic classification of a galaxy in 