IRAM 30 m data. Intensity-weighted velocity (color map) of the C¹⁸O J = 2–1 (upper panel), ¹³CO J = 2–1 (middle panel), and H₂CO 3_0,3–2_0,2 (lower panel) lines determined over a small velocity range, [−7.3, −3.5] km s⁻¹, around V_sys = −6.1 km s⁻¹. The plotted region corresponds to the area in which the velocity-integrated emission of the C¹⁸O J = 2–1 line is higherthan 44 Jy beam⁻¹ km s⁻¹, ≈10σ. In each panel, the black contours represent the SCUBA 850 μm continuum (Di Francesco et al. 2008), showing 10 levels increasing logarithmically from 1 to 11.4 Jy beam⁻¹. The white rectangle delimits the region plotted in the upper panel of Fig. 1.