Left: point density diagram of the equivalent width of the Hα nebular emission, W_Hα, versus the light fraction due to populations younger than 32 Myr (x_Y) for 12 540 radial bins of 416 galaxies. The color bar shows the density of data points on a logarithmic scale. White circles trace the mean relation (obtained from the mean W_Hα values in x_Y-bins). The gray line shows the linear fit to all points: W_Hα(Å) = 1.024 + 1.208 x_Y(%). Horizontal lines are drawn at W_Hα = 3 (dashed) and 6 Å (dotted). Vertical lines mark x_Y = 3.4% (the mean x_Y for points with W_Hα< 3 Å; dashed) and x_Y = 4.3% (the mean x_Y for points with W_Hα< 6 Å; dotted). Middle: mean W_Hα radial profiles for galaxies in the seven Hubble type bins. Horizontal lines indicate W_Hα = 3 (dashed), and 6 Å (dotted). Right: radial profile of x_Y in the same Hubble type groups. Horizontal lines indicate x_Y = 3.4 (dashed) and 4.3% (dotted). The dispersion in W_Hα (middle panel) and x_Y (right panel) measured at 1 HLR in Sb galaxies is shown as an error bar. (The corresponding statistical errors are much smaller.)