Size (top) and position angle (bottom) of M 81^∗ as a function of frequency. We plot the data from Table 2. The two lines in the top panel are power-law fits to the shown data. The slopes are  −0.88  ±  0.04, and  −0.89  ±  0.08, respectively, for the major axis and the equivalent diameters of the source. The line in the bottom panel, drawn as a guide, is the function φ = (350 ± 36)° − (30 ± 4)° × (log (ν/Hz)). We did not use the data from Ref. 6 in Table 2 because this is the core component only, and an extended jet component, 1 mas away, was also fitted (in this way, which is therefore not comparable with the other values, which fit core and jet together).