H66α spectra of the “long slits” (see Fig. 1b). The vertical line marks the systemic velocity of the molecular gas in DR 21, measured from NH₃ (−1.5 km s^-1). Positions S/0, S/5, and N/5 clearly show two velocity components, and are fit with two Gaussians. “Gaussian 1”, the component with the higher velocity, is shown in red, and “Gaussian 2” in blue (see Table 1). Note that in N/5, both Gaussian 1 and 2 are redshifted with respect to the systemic molecular gas velocity.