Spectral index distributions for the cross-matched MGCLS compact sources, using data from the MGCLS (1.28 GHz), NVSS (1.4 GHz), SUMSS (843 MHz), and TGSS (148 MHz) catalogues. Left to right: distributions for MGCLS sources with flux density measurements at two, three, and four frequencies, respectively. The number of compact sources, N_s, and the median spectral index, , are indicated in the upper right corner of each panel, and the respective median spectral indices are indicated by vertical dashed lines.