Individual point spectra. Left panel: The location of individual spectra from spiral arms (inter-arm regions) marked by green (blue) circles on top of the spectral curvature map. The size of the circles corresponds to the beam size. Red contours at the total gas-mass density of 8 and 25 M_⊙ pc⁻² define the borders of the spiral arm and inter-arm regions, respectively (Sec. 3.3). Right panel: Non-thermal radio continuum spectra for representative beam-sized regions marked in the left panel. Each spectrum is labeled with its corresponding number. Dotted lines show the power-law fits for frequencies ≥144 MHz. The individual spectra show the same trends as the integrated spectra in Fig. 9.