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 supernovae 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 alleviate
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.
