[Mg/Fe] vs. [Fe/H] distribution of disk stars in several radial distance bins with | Z_GC | ≤ 3 kpc. Gray and black points indicate thin and thick disk stars. A shaded area highlights the metallicity range used to perform a bilinear model fit of the thick disk sequence. The number of thick disk stars used to perform the fit is indicated in parentheses. The best fit model in each radial bin is displayed with red lines. The [Fe/H] location of the knee, together with its error bar, is quoted in each panel and is indicated by an orange error bar. Panels a)–e) subsamples in several Galactocentric radial bins, as indicated in each panel. Panel f) [Fe/H] position of the knee as a function of Galactocentric distance. Box length and height depicts the size of the radial bin and the error bar of the measurement. Panel g) whole thick disk sample, grouping together all the stars in the panels a)–e). Panel h) subsample of RC stars in a radial range where the mean | Z_GC | is approximately constant with R_GC.