Physical conditions along the DR21 Main outflow: CO excitation temperature (top) and gas densities (bottom). The CO excitation temperature is obtained from the ratio of CO 14–13 and 16–15 lines at 185.99 μm and 162.81 μm, respectively (see Sect. 4.2.1). A typical errorbar is shown for the offset of 80^′′. The H₂, H, and e densities are estimated assuming the oxygen column density of 10¹⁷ cm⁻², in regions where sufficient agreement with observations was found (Sect. 4.2.2). The gas temperature of 300 K, consistent with T_rot(CO), was further assumed for the H₂ and H emitting gas. The vertical lines show the ranges of densities in agreement with models, whereas the symbols refer to the average values at a given offset.