Short-spacing corrected spectral index maps of NGC 891 and corresponding error maps. a: 1.5 GHz in-band total spectral index. b: 1.5 GHz in-band non-thermal spectral index. c: 1.5 GHz in-band spectral index error. d: 6 GHz in-band total spectral index. e: 6 GHz in-band non-thermal spectral index. f: 6 GHz in-band spectral index error. g: Total spectral index between 1.5 and 6 GHz. h: Non-thermal spectral index between 1.5 and 6 GHz. i: Error of spectral index between 1.5 and 6 GHz. The angular resolution in each panel is 12″ FWHM (black circles). All maps extend to the 5σ level in the corresponding total intensity images. The black contours in the in-band maps are placed at the 30σ level, where the maps were cut off before creating the scatter plot in Fig. 14a; see text for details.