A probabilistic formulation of evolutionary synthesis models: implications for SED fittings

Evolutionary synthesis models (ESM) have been extensively used to obtain the star formation history in galaxies by means of SED fitting. Implicit in this use of ESM is that (a) for given evolutionary parameters, the shape of the SED is fixed whatever the size of the observed cluster (b) all regions of the observed SED have the same weight in the fit. However, Nature does not follow these two assumptions, as is implied by the existence of Surface Brightness Fluctuations in galaxies and as can be shown by simple logical arguments.Comment: 2 pages, 2 figure, going to be published in the proceedings of the IAU Symp. 241, "Stellar Populations as Building Blocks of Galaxies