Abstract
We tested a chemical evolution model for spiral disks to study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is applied to the Milky Way, M31 and M33. We see that most massive disks seem to have evolved faster and that threshold and efficiency play a very important role in the chemical evolution of spiral disks.
