Correlation plot of the NH₃ (1, 1) and (2, 2) linewidths. The straight green dashed line corresponds to equal widths, the red solid line includes the correction for the hyperfine structure of the (2, 2) line Δv_Gauss(2,   2) = 1.15·Δv_HFS(2,   2) + 0.13. The (1, 1) and (2, 2) linewidths are mostly equally distributed around the red solid line, as shown by the contour plot in the top panel. For this upper plot we counted the number of sources in each (1, 1) and (2, 2) linewidth bin of 0.1 km s^-1. The contours give 10 to 90% in steps of 10% of the peak source number per bin, these levels are used for all contour plots in this article.