On the G-dwarf abundance distribution in the solar cylinder.

The oxygen abundance distribution of G-dwarfs in the solar cylinder is obtained using the G-dwarf data of Pagel and Patchett as local normalization and two different types of models of the local, vertical structure of the galactic disc. One is the model of Norris and Ryan and the other is obtained using the Polak-Ribiere method to fit the data of Kuijken and Gilmore. The results are compared to simple, chemical evolution models characterized by an exponentially decreasing infall rate, simple star-formation laws of the type dΣ_*/dt ∝ Σ^N_g and no radial flows. Infall time-scales of t_i = 3-4.5 and 4-6 Gyr are deduced from the comparison for the two sets of models with an estimated uncertainty on t_i of ≡1.5 Gyr. The infall time-scales obtained in the analysis compare well with the empirically determined halo formation time-scale of ≡3 Gyr found by Schuster and Nissen, strongly suggesting that the formation of the halo and disc were coupled processes in the sense that the halo stars formed out of the gas, which later became the galactic disc.