On the stellar populations of massive galaxies

In this Letter, we analyse the predicted physical properties of massive galaxies, in the framework of recent semi-analytic models of galaxy formation. All models considered account for winds driven by supernova explosions and suppression of gas condensation at the centre of relatively massive haloes by active galactic nuclei (AGN). We show that while these models successfully reproduce the old stellar populations observed for massive galaxies, they fail in reproducing their observed chemical abundances. This problem is alleviated but still present if AGN feedback is completely switched off. Moreover, in this case, model predictions fail in accounting for the old stellar ages of massive galaxies. We argue that the difficulty of semi-analytical models in simultaneously reproducing the observed ages and metallicities of massive galaxies signals a fundamental problem with the schemes that are currently adopted to model star formation, feedback and related recycling of gas and metals.