Galactic chemical evolution revisited

TL;DR

This paper critically revisits standard models of galactic chemical evolution, highlighting their limitations and proposing alternative approaches like closed box models and new star formation history derivations based on stellar abundances.

Contribution

It challenges existing assumptions in chemical evolution models and discusses a novel method to derive the galaxy's star formation history from stellar data.

Findings

Thick disk formation was the dominant epoch of star formation.

Standard models rely on oversimplified assumptions about the Galaxy.

A closed box model can approximate galactic chemical evolution.

Abstract

Standard chemical evolution models based on long-term infall are affected by a number of problems, evidenced by the analysis of the most recent data. Among these: (1) models rely on the local metallicity distribution, assuming its shape is valid for the entire Galaxy, which it is not; (2) they assume that the solar vicinity abundance patterns resulted from a unique chemical evolution, which it does not; (3) they assume the disk is a single structure with chemical properties that are a smooth function of the distance to the galactic center, which it is not. Moreover, new results point to a thick disk being as massive as the thin disk, leading to a change of paradigm in the way we see the formation of these structures. I discuss these various issues, and, commenting on Snaith et al. (2014), how a closed box model offers an interesting approximation to the galactic chemical evolution, by providing the conditions in which large amounts of gas are available in the disk at high redshift. The novel way presented in Snaith et al. (2014) to derive SFH from stellar abundances is also discussed, providing a measurement of the SFH of old populations that is valid for the entire Galaxy. The derived SFH shows that the formation of the thick disk has been the dominant epoch of star formation in our Galaxy.