Upper-left panel: same as the detection result of the distribution of H₂O maser spots in W51e2 in Figure 6, with names of different regions being marked. Upper-right panel: a zoomed map of the distribution of H₂O maser spots, corresponding to the region marked with a gray dashed box in the upper-left panel. Lower-left panel: the 1.3 mm continuum, SiO J = 5–4, and HC₃N J = 24–23 emissions in the W51e2 region. For orange contours, the start, step, and end levels are 0.06, 0.01, and 0.10 Jy beam⁻¹, respectively. For cyan contours, the start, step, and end levels are 0.10, 0.10, and 0.50 Jy beam⁻¹, respectively. Lower middle panel: a cartoon taken from Li et al. (2013), which is used to indicate the turbulent entrainment origin of protostellar outflows. In this figure, the p_wind and p_envelope represent the ram pressure of the wind and the envelope. Lower-right panel: a cartoon taken from López-Vázquez et al. (2024), which is used to indicate the multilayer outflows driven by disk winds of source HH 30.