Abstract
Results from a series of chemical evolution models for the galactic disk (from 4 to 20 kpc) are presented and discussed. In particular, the influence of different forms of the infall and the star formation rate on the chemical and surface density distributions of the gaseous disk are probed. The effects of a metal-dependent initial mass function are also studied. In the models the star formation rate is proportional to a power of both, gas and total (stars plus gas) surface mass densities, Ψ(r,t) ∝ σgasx σtotx-1. An x=1.4 model with an initial mass function independent of time, radius or metallicity, and an infall that settles linearly faster towards the center, gives a present O/H radial distribution more convex than observed but consistent with H II observations. The model overestimates O/H by ~ 0.2 dex, and yields a present surface gas density close to the observational constraints. The model predicts chemical gradients that flatten with time, in disagreement with the observations. Models in which the relative number of very low mass stars (m <= 0.5 Modot) decreases with metallicity tend to improve the agreement with the observed gradient strength and evolution, but all models of this kind fail to reproduce the early chemical history of the solar neighborhood as derived from stellar observations.
