Galactic Chemical Evolution: Carbon through Zinc

TLDR

The study calculates the evolution of heavy element abundances from C to Zn in the solar neighborhood using new nucleosynthesis yields. Yields were computed across a range of metallicities and explosion energies, calibrated to supernova light curves and spectra, and applied to model abundance ratios and metallicity distributions for the Galactic bulge, halo, and thick disk. The model reproduces observed abundance patterns—including alpha-element plateaus, Ti underabundance, Zn production via hypernovae, metallicity-driven declines of odd‑Z elements, and iron‑peak trends—and suggests a 1–3 Gyr formation timescale for the thick disk.

Abstract

We calculate the evolution of heavy element abundances from C to Zn in the solar neighborhood adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z=0-Z_\odot) and the explosion energy (normal supernovae and hypernovae), based on the light curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the alpha-elements, O, Mg, Si, S, and Ca show a plateau at [Fe/H] < -1, while Ti is underabundant overall. The observed abundance of Zn ([Zn/Fe] ~ 0) can be explained only by the high energy explosion models, which requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low [Fe/H] is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at -2.5 < [Fe/H] < -1$, and the observed trend at the lower metallicity can be explained by the energy effect. We also show the abundance ratios and the metallicity distribution functions of the Galactic bulge, halo, and thick disk. Our results suggest that the formation timescale of the thick disk is ~ 1-3 Gyr.