Contour maps of the bulk emission in the same lines as in Fig. 3, obtained by averaging the emission over the velocity interval delimited by the dotted lines in Fig. 3. The background image is the continuum emission shown also in Fig. 1. Contour levels range: from 21.6 to 381.6 in steps of 36 mJy/beam (1σ RMS ≃ 7 mJy/beam) for the K = 2 line; from 22.8 to 402.8 in steps of 38 mJy/beam (1σ RMS ≃ 8 mJy/beam) for the K = 3; from 16.8 to 324.8 in steps of 28 mJy/beam (1σ RMS ≃ 6 mJy/beam) for the K = 4; from 4.5 to 49.5 in steps of 7.5 mJy/beam (1σ RMS ≃ 1.5 mJy/beam) for the K = 2 line of CH₃¹³CN; from 8.7 to 95.7 in steps of 14.5 mJy/beam (1σ RMS ≃ 3 mJy/beam) for the K = 8; and from 8.7 to 153.7 in steps of 14.5 mJy/beam (1σ RMS ≃ 3 mJy/beam) for the K,l = 1,1 line.