The Chemical Evolution of Iron-Peak Elements with Hypernovae

TL;DR

This study models the chemical evolution of iron-peak elements in the galaxy, highlighting the importance of hypernovae in early star formation and their impact on observed elemental ratios.

Contribution

It introduces a Galactic Chemical Evolution model incorporating hypernova yields and explores hypernova occurrence rates to match observed stellar abundance patterns.

Findings

High hypernova rates in early universe explain observed Zn/Fe ratios.

Including hypernovae with progenitors >= 60 solar masses hinders matching Mn/Fe and Co/Fe evolution.

Updating enrichment models at higher metallicity remains a challenge.

Abstract

We calculate the mean evolution of the iron-peak abundance ratios [(Cr,Mn,Co,Zn)/Fe] in the Galaxy, using modern supernova and hypernova chemical yields and a Galactic Chemical Evolution code that assumes homogeneous chemical evolution. We investigate a range of hypernova occurrence rates and are able to produce a chemical composition that is a reasonable fit to the observed values in metal-poor stars. This requires a hypernova occurence rate that is large (50%) in the early Universe, decreasing throughout evolution to a value that is within present day observational constraints (>~ 1%). A large hypernova occurence rate is beneficial to matching the high [Zn/Fe] observed in the most metal-poor stars, although including hypernovae with progenitor mass >= 60 solar masses is detrimental to matching the observed [(Mn,Co)/Fe] evolution at low [Fe/H]. A significant contribution from HNe seems to be critical for producing supersolar [(Co,Zn)/Fe] at low metallicity, though more work will need to be done in order to match the most extreme values. We also emphasise the need to update models for the enrichment sources at higher metallicity, as the satisfactory recovery of the solar values of [(Cr,Mn,Co,Zn)/Fe] still presents a challenge.