PACS flux ratios I₁₀₀/I₁₆₀ versus I₇₀/I₁₆₀. The PACS data have been rebinned to ∼250 pc resolution in order to match the HI and ACA CO maps. Heavy curves show the medians in I₁₀₀/I₁₆₀ bins for each galaxy, and the shaded regions indicate 1σ standard deviations. Also shown are the model MBB-T2 flux ratios with γ = 0.14 (the median value for NGC 1705), indicated by the heavy black long-dashed curve. The IR ratios from two MBB models (γ  =  0) are illustrated as a long-dashed (gray) curve with β = 1 (virtually indistinguishable from the MBB-T2 curve), and a short-dashed (black) curve for β = 2. The dot-dashed curve corresponds to the best fit polynomial for the SMC by Leroy et al. (2009). The horizontal lines illustrate the I₁₀₀/I₁₆₀ ratios that would be expected for T_dust = 20 K, 25 K, and 30 K. The line ratios for NGC 625 and NGC 5253 are fairly well approximated by MBBs or MBB-T2 fits, while the polynomial fit by Leroy et al. (2009) is a better approximation for NGC 1705. This fit is roughly equivalent to assuming that only half of the observed 70 μm emission comes from large, “classical” grains, with the other half originating from stochastic heating of small grains.