Spectral index maps for all five frequency pairs, computed following Sect. 3.3, plotted over the higher-frequency contours. In each panel, the common beam for the two frequencies is plotted as a black circle in the bottom left corner, and a size scale reference of 1 pc is in the top right corner. The frequency pairs are color-coded from the lowest (5 − 8.4 GHz) to the highest (43.8 − 87.6 GHz), going from red to blue. The color map is chosen from a colour-vision deficiency-friendly package (Crameri 2023).