The Stellar Populations in spiral disks.III. Constraining their evolutionary histories

We study the old problem of the uniqueness of chemical evolution models by analyzing a set of multiphase models for the galaxy NGC 4303 computed for a variety of plausible physical input parameters. Our aim is to determine if the input parameters may be strongly constrained when nebular abundances and stellar spectral indices radial distributions are used. We run a large number of models (500) for NGC 4303 varying the input parameters. Less than 4% of the models (19) fit the present day observational data within a region of 95% probability. The number of models reduces to ~1% (6) when we also ask them to reproduce the time-averaged abundances represented by the spectral indices. Thus, by proving that only a small fraction of models are favored in reproducing the present day radial abundance distributions and the spectral indices data simultaneously, we show that these spectral indices provide strong time-dependent additional constraints to the possible star formation and chemical histories of spiral disks.