Left panel: dust temperature T_dust vs. normalized galactocentric distance R/R_opt; right panel: T_dust vs. τ_dust evaluated at 250 μm. As in Fig. 8, points are coded by their oxygen abundance, with filled symbols corresponding to R/R_opt≤ 0.8 and open ones to larger radii. The underlying grayscale shows the two-dimensional density distribution of the data. The dashed lines are unweighted linear regressions to the data points, excluding outliers with T_dust≥ 30 K (in the left panel, T_dust = −2.41 R/R_opt + 21.2).