The G-dwarf problem in the Galactic spheroid

Abstract

Using two alternative [O/H]-[Fe/H] dependences, the empirical oxygen abundance distribution (EGD) is deduced from two different samples of old objects, available in the literature. Under the assumption that each distribution (with the addition of a third one previously known) is typical for the corresponding subsystem, the EGD of the Galactic spheroid is determined weighting by mass. A fit to the data is provided by simple models of chemical evolution implying both homogeneous and inhomogeneous mixing, where star formation is inhibited during halo formation and enhanced during bulge formation, with respect to the disk. The theoretical oxygen abundance distribution (TGD) is first determined for the halo and the bulge separately, and then for the Galactic spheroid weighting by mass. Simple models implying inhomogeneous mixing are able to fit an empirical age-metallicity relation (EAMR) recently determined from a homogeneous sample of globular clusters, which shows a non monotonic trend characterized by large dispersion. Some possible implications related to the formation of Galactic spheroid and disk are also discussed.