The Lick index  ⟨ Fe ⟩  is plotted against Mg b for the integrated spectra of the two inner fields F42 (box, in red) and F56 (open star, in blue). Two families of tracks from Thomas et al. (2003) for [α/Fe] of 0.3 (open symbols) and 0.0 (filled symbols) are shown for metallicity [Z] of  −1.35, −0.33, 0.0 and 0.35 by lines with points. The lower set of four lines have [α/Fe] = 0.3, and the upper ones [α/Fe] = 0. Models with  [Z]  = 0.35 are indicated in black,  [Z]  = 0.0 in orange,  [Z]  =  −0.33 in green and  [Z]  =  −1.35 in magenta. The ages in Gyr along each track are indicated.