Temperature profiles as a function of radius for centrally illuminated dusty cores from 12 M_⊙ to 120 M_⊙, following Wilner et al. (1995). The red shaded area shows the interval that corresponds to the sublimation temperature of the ices (120–160 K). The two horizontal black lines represent the range of radii expected for a heating source with a luminosity of 10⁴ L_⊙ (12 M_⊙) and 10⁶ L_⊙ (120 M_⊙). The gray arrow indicates the median size of the methyl formate sources in our sample.