Radial profile of the column density of SMM 1 displayed with logarithmic scale for both axes. The data points represent azimuthally averaged values inside 4″ wide annuli (Fig. 4). The vertical error bars reflect the standard deviation of the azimuthal averaging. The mean radial N(H₂) profile can be fitted by a power-law with between the flat inner core and the “edge”, as indicated by the thick solid line.