Overlay of the 25 GHz continuum emission (gray scale and white contours) and the integrated intensities of the quasi-thermal (6,6) and (10,10) lines of ammonia (taken from Goddi et al. 2015). The (6,6) contours show the elongated dense molecular environment at the southern boundary of the H II region W51d. The location of main molecular hotspots, W51N4, W51d2, W51N2, and W51-North (from west to east), are indicated. For more details, see Goddi et al. (2015).