Central oxygen abundance as a function of central surface brightness of the disk in the ﹩W1﹩ band. The dotted line in each panel shows the simple relation (Equation (7)). Panel a shows the subdivision of our sample of galaxies into three subsamples according to the value of disk scale length h_W1. The solid line corresponds to the parametric relation O/H = ﹩f({{{\rm \Sigma}}_{{{L}_{W1}}}},{{h}_{W1}})﹩ (Equation (8)) for h_W1 = 1 kpc. The dashed line is the relation for h_W1 = 7 kpc. Typical errors are shown by the cross in the lower left corner. Panel b shows the subdivision of our sample of galaxies into three subsamples according to the value of the bulge contribution f_B to the total galaxy luminosity. The solid line corresponds the parametric relation O/H = ﹩f({{{\rm \Sigma}}_{{{L}_{W1}}}},{{f}_{B}})﹩ (Equation (9)) for f_B = 0. The dashed line shows the corresponding relation for f_B = 1. Panel c shows the subdivision of our sample of galaxies into three subsamples according to the morphological T type. The solid line corresponds to the parametric relation O/H = ﹩f({{{\rm \Sigma}}_{{{L}_{W1}}}},T)﹩ (Equation (10)) for T = 1. The dashed line represents the relation for T = 7.