Upper-left panel: a figure showing the W51-IRS2 regions taken from Ginsburg et al. (2017). The emission shown in green is the NACO K-band continuum (Barbosa et al. 2008; Figuerêdo et al. 2008), and these in blue and red are the blue- and redshifted CO 2-1 emission (Ginsburg et al. 2017). The blue contours are the H77α RRL transition detected in Ginsburg et al. (2016), and the white contours are the ALMA 1.3 mm continuum (Ginsburg et al. 2017). Upper-right panel: a zoomed version of the region toward a red dashed box in the upper-left panel. The background is the ALMA 1.3 mm continuum from the project 2015.1.01596.S. The contour levels in white for our VLA K-band continuum are 0.05, 0.10, 0.15, 0.20, 0.40, 0.60, and 0.80 Jy beam⁻¹. The red solid ellipse denotes the W51d2 subregion. Lower panel: a zoomed version of the region toward a red dashed box in the upper-right panel. The background is the ALMA 1.3 mm continuum, with gray contours marking the most luminous objects in this region. The “+” symbols mark the location of the H₂O maser spots. The labels “mrk[number]” are temporary names given by us for studying these objects or subregions that do not even have a name before. Among them, “mrk1”, “mrk2” and “mrk3” are studied in Sections 4.3.1, 4.3.2 and 4.1, respectively.