SPIRE fractional residuals of the DL07 best fits plotted against the normalized radius, R/R_opt. As explained in the text, fractional residuals are defined as (F_ν − F_DL07)/F_ν; 250 μm residuals are shown in the left panel, 350 μm in the middle, and 500 μm in the right. As in Fig. 18, data points are coded by O/H with (red) circles showing 12 + log (O/H)> 8.4, (green) triangles 8.0 <12 + log (O/H)≤ 8.4, and (blue) squares 12 + log (O/H)≤ 8.1. Filled symbols correspond to positions with normalized (to optical radius R_opt) radii within R/R_opt≤ 0.8, and open symbols to larger radii. As in Fig. 18, we show all data with S/N ≥ 3 independently of their ; the DL07 fits with ≤ 2 are indicated by +. The (yellow) dashed lines give the linear regressions described in the text.