Representative SEDs in various parts of M 31. The solid line shows the fit of the modified blackbody with β = 2 to the full flux densities (shown in red), and the dashed line shows the fit to the rescaled flux densities (shown in blue). Only the filled data points are used in the fits. The fit parameters are discussed in the text. Top row: a) the SED of a pixel in the nuclear region (00^h42^m30^s, +41°09′); b) the northern edge of the 10 kpc ring (00^h45^m40^s, +41°54′); c) the bright pixel in the southern end of M 31 (00^h40^m45^s, +40°39′). Bottom row, outer spiral arms: d) 14.8 kpc arm (00^h39^m53^s, +40°23′); e) 22 kpc arm (00^h37^m43^s, +39°58′); and f) 26 kpc arm (00^h36^m52^s, +39°43′). The last two SEDs also show a variable β_dust fit with a dotted line.