Simulated spectral index maps for field G111.24−1.24 in Fig. A.2. Labels and symbols as in Fig. 1. Panels a–c: spectral index maps (colors) obtained assuming three different source models at the C, Ku, and K bands. Black contours are those of the observed average brightness map for a direct comparison with Fig. A.2. The cross in panels a and b indicate the peak position of the observed C-band emission.