The Stellar Populations of Spiral Disks. III. Constraining Their Evolutionary Histories

We study the old problem of the uniqueness of chemical evolution models byanalyzing a set of multiphase models for the galaxy NGC 4303 computed for avariety of plausible physical input parameters. Our aim is to determine if the input parameters may be strongly constrainedwhen nebular abundances and stellar spectral indices radial distributions areused. We run a large number of models (500) for NGC 4303 varying the inputparameters. Less than 4% of the models (19) fit the present day observationaldata 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 representedby the spectral indices. Thus, by proving that only a small fraction of modelsare favored in reproducing the present day radial abundance distributions andthe spectral indices data simultaneously, we show that these spectral indicesprovide strong time-dependent additional constraints to the possible starformation and chemical histories of spiral disks.