Chemical evolution of two-component galaxies II - Numerical computations

Results provided by analytical models for the chemical evolution of two-component (spheroidal and disk) galaxies based on the instantaneous recycling approximation are compared with numerical results obtained by discarding the cited approximation. The assumptions and general equations used in the calculations are discussed, and the method adopted for the numerical computation is briefly outlined. Some numerical results are reported and compared with the corresponding analytical results for the solar neighborhood and for other galaxies. It is concluded that the analytical models are a zeroth-order approximation for describing the chemical evolution of both the solar neighborhood and other galaxies, that the numerical calculations constitute a first-order approximation, and that the effect of the latter is to lower the gas mass fraction and metallicity by about 25 percent to 50 percent with respect to the corresponding analytical values.