New routes in the analysis of composite stellar populations.

The authors describe a new method for synthesizing composite stellar populations. This method takes into account the large metallicity changes occurring along the galaxy evolution, which, near the center can increase up to [Z/Z_sun] ≡ 0.6. Therefore, this method allows to reproduce the spectrum observed in the central regions of massive elliptical galaxies. It can be used to interpret stellar populations in galaxy clusters at large redshifts. The authors illustrate this possibility through the case of Abell 370 at z = 0.374 and find that both their stellar population and their content in heavy elements indicate that cD galaxies result from merging of galaxies quite similar to present-day massive elliptical ones.