Bottom panels: blueshifted (blue solid contours) and redshifted (red dashed contours) ¹³CO (1–0) (left) and ¹³CO (2–1) (right) averaged emission overlaid on the 1.4 mm continuum emission (grayscale) towards G19 and G29, respectively. The velocity intervals for which the blueshifted and redshifted emission have been averaged are indicated in blue and red dotted vertical lines in the corresponding upper spectra. Contour levels are 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35 Jy beam^-1 (1σ ≃ 7 mJy beam^-1) for the ¹³CO (1–0) blueshifted emission and 0.15, 0.2, 0.25, 0.3, and 0.35 Jy beam^-1 (1σ ≃ 50 mJy beam^-1) for the ¹³CO (1–0) redshifted emission (G19), and 0.03, 0.09, 0.15, 0.27, 0.39, and 0.51 Jy beam^-1 (1σ ≃ 7 mJy beam^-1) for the ¹³CO (2–1) blueshifted emission and 0.03, 0.06, 0.09, 0.15, 0.3 and 0.45 Jy beam^-1 (1σ ≃ 7 mJy beam^-1) for the ¹³CO (2–1) redshifted emission (G29). Grayscale contours for the continuum emission are the same as in Fig. 1. The synthesized beam is shown in the lower righthand corner. The white cross marks the position of the 1.4 mm continuum emission peak. Top panels: ¹³CO (1–0) and (2–1) spectra taken towards the 1.4 mm continuum emission peak of the G19 (left) and G29 (right) cores. The dashed vertical line indicates the systemic velocity of each core.