Retrieved IMF vs. TiO2_sdss index values in the centers of the two galaxies NGC3309 (diamonds) and NGC3311 (stars). Solid colored lines are the model values at different metallicity and age 13.5 Gyr. Dashed lines show the same trends when the [Ti/Fe] abundance is subsolar, i.e., −0.3 dex. All other abundances are solar. Points are color-coded as in Figure 6, with darker red in the center and orange in the outskirts. While in the very central regions, TiO2_sdss values indicate a clear gradient for IMF and [Z/H] for NGC3309 and a flat trend for NGC3311 (confirmed by the retrieved results), in the outer regions where the metallicity is lower, it is harder to constrain the IMF, because the same value of TiO2_sdss corresponds to a wide range of IMF.