Modeling the Evolution of Disk Galaxies. II. Yields of Massive Stars

Abstract

Checking stellar yields with galactic chemical evolution models is an important test of stellar nucleosynthesis simulations. This is generally done by applying a very simple galactic model with a large number of free parameters. It is, however, at least questionable whether such a model can serve as a dependable test of stellar nucleosynthesis. A self-consistent galactic model, on the other hand, can be used to determine yields that are consistent with the galactic chemical evolution. The chemodynamical model introduced in this paper includes a detailed description of the stellar metal-dependent enrichment and serves to determine the chemical yields of massive stars. It shows that the metal dependency of stellar nucleosynthesis, gas flows in the galaxy, mixing processes in the interstellar medium, and the energy release of supernovae (SNe) have a great influence on the distribution of chemical elements. From the chemodynamical model and the observed evolution of [α/Fe], I find that on average, one out of 195 intermediate-mass stars explodes as a SN of Type Ia. This yields a ratio of Type Ia SN to Type II + Ib SN of 1:8.5. Furthermore, the model predicts present SN rates in our Galaxy for Types Ia and II + Ib of 1/107 yr and 1/41 yr, respectively. I present Galactic yields of 23 different chemical elements from C to Ni. One important result is that the yields of Cr, Fe, and Ni are a factor of 2 too high, and odd-z element yields are systematically underestimated in the nucleosynthesis models of massive stars. A comparison of the stellar with the Galactic yields suggests that the lower mass limit for stars to become Type II SNe may be 11 M☉, and that the core collapse of stars more massive than 30-40 M☉ produces a black hole. The model predicts 1.2-1.5 × 109 stellar remnants of massive stars (neutron stars and black holes) in our Galaxy.