Stellar Yields and Chemical Evolution -- I. Abundance Ratios and Delayed Mixing in the Solar Neighbourhood

Abstract

We analyse two recent computations of type II supernova nucleosynthesis by Woosley & Weaver (1995, hereafter WW95) and Thielemann, Nomoto, & Hashimoto (1996, hereafter TNH96), focusing on the ability to reproduce the observed [Mg/Fe]-ratios in various galaxy types. We show that the yields of oxygen and total metallicity are in good agreement. However, TNH96-models produce more magnesium in the intermediate and less iron in the upper mass range of type II supernovae than WW95-models. To investigate the significance of these discrepancies for chemical evolution, we calculate Simple Stellar Population-yields for both sets of models and different IMF slopes. We conclude that the Mg-yields of WW95 do not suffice to explain the [Mg/Fe] overabundance neither in giant elliptical galaxies and bulges nor in metal-poor stars in the solar neighbourhood and the galactic halo. Calculating the chemical evolution in the solar neighbourhood according to the standard infall-model (e.g. Matteucci & Greggio 1986; Timmes, Woosley, & Weaver 1995; Yoshii, Tsujimoto, & Nomoto 1995), we find that using WW95 and TNH96 nucleosynthesis, the solar magnesium abundance is underestimated by 29 and 7 per cent, respectively.We include the relaxation of the instantaneous mixing approximation in chemical evolution models by splitting the gas component into two different phases. In additional simulations of the chemical evolution in the solar neighbourhood, we discuss various timescales for the mixing of the stellar ejecta with the interstellar medium. We find that a delay of the order of 10 8 years leads to a better fit of the observational data in the [Mg/Fe]-[Fe/H] diagram without destroying the agreement with solar element abundances and the age-metallicity relation.

The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution

“…The most likely explanation for this discrepancy is that the magnesium production with respect to oxygen in both the K06 and CL04 CCSNe yields are underestimated. The underestimation of Mg in CCSNe yields has been highlighted in Thomas et al (1998). A similar underestimated Mg/O ratio is also reported in other chemical evolution models in the literature (Sukhbold et al 2016;Rybizki et al 2017;Limongi & Chieffi 2018).…”

A primer on hierarchical galaxy formation: the semi-analytical approach

“…Their super solar total metallicities and Mg/Fe ratios are described as α-enhancement. The observed trend in Mg line strength and velocity dispersion can be reproduced with a standard IMF in a single burst model, if the timescale of the burst is an appropriate function of galaxy mass (Thomas et al 1998). In this simple picture, all the stars in the elliptical form in a single burst at high redshift which is terminated by the ejection of gas in a wind (Larson 1974(Larson , 1975.…”

The Evolution of Oxygen and Magnesium in the Bulge and Disk of the Milky Way

“…In particular, the yields from stars in the range 10-20 M were increased in order to fit the observed Mg absolute solar abundance. The well-known problem of low Mg yields has been discussed by others (e.g., Thomas et al 1998). The yields for SNe Ia, which are assumed to originate from single-degenerate systems, are taken from Iwamoto et al (1999).…”