Maps of the H₂ (left panel) and CH₃CN (middle panel) density and relative abundance of CH₃CN with respect to H₂ (right panel). The black numbers show the position of the dust cores, and the magenta crosses indicate the position of the newly introduced molecular centers, as shown in Fig. 4 (see also Table A.1). The gray circles indicate the positions and extent of H II regions, where the density of H₂ and CH₃CN is zero. The central region is masked out (transparent hatched area) as the CH₃ CN transitions in this region cannot be reproduced well with the model (see Sect. 6.6).