Distribution of gas velocities associated with the outflows in DR21 (left) and Orion KL (right, Bally et al. 2017). Each point shows a local intensity peak of the HCO⁺ emission (above 2 σ) integrated in velocity steps of 5 km s⁻¹. The color of the points signifies the corresponding velocity steps and is the same for the two plots. Background grayscale shows the integrated HCO⁺ (left panel) and CO emission (right panel) over the entire velocity range of the outflows (from −70 to 70 km s⁻¹ for DR21 Main and −100 to 100 km s⁻¹ for Orion KL).