Abstract
We study the old problem of the uniqueness of chemical evolution models. We showed in (Molla 1999) that multiphase models for three Virgo cluster galaxies were able to reproduce the observed radial distributions of spectral indices Mg2 and Fe52. But those models may fit the present-epoch radial distributions with different star formation histories (Tosi 1996). The two spectral indices above are in turn affected by the well known age--metallicity degeneracy which prevents the disentangling of age and metallicity for single stellar populations. In this work we face both issues by analyzing a set of multiphase models for the Virgo galaxy NGC~4303.
