The metallicity distribution of the stars in elliptical galaxies

Abstract

Elliptical galaxies probably host the most metal rich stellar populations in the Universe. The processes leading to both the formation and the evolution of such stars are discussed by means of a new multi-zone photo-chemical evolution model, taking into account detailed nucleosynthetic yields, feedback from supernovae, Pop III stars and an initial infall episode. Moreover, the radial variations in the metallicity distribution of these stars are investigated by means of G-dwarf-like diagrams. By comparing model predictions with observations, we derive a picture of galaxy formation in which the higher is the mass of the galaxy, the shorter are the infall and the star formation timescales. Therefore, the stellar component of the most massive and luminous galaxies might attain a metallicity Z > Z_sun in only 0.5 Gyr. Each galaxy is created outside-in, i.e. the outermost regions accrete gas, form stars and develop a galactic wind very quickly, compared to the central core in which the star formation can last up to ~1.3 Gyr. This finding will be discussed at the light of recent observations of the galaxy NGC 4697 which clearly show a strong radial gradient in the mean stellar [<Mg/Fe>] ratio.