Abundance gradients and their evolution in the Milky Way disk

TL;DR

This paper models the chemical evolution of the Milky Way disk, successfully reproducing observed abundance profiles of multiple elements and analyzing the roles of different stellar sources and formation schemes.

Contribution

It introduces a simple chemical evolution model that explains the abundance gradients and their evolution, highlighting the roles of massive and intermediate-mass stars.

Findings

Massive star yields reproduce most abundance profiles.

Carbon and nitrogen require additional sources beyond massive stars.

Inside-out formation leads to steeper past abundance profiles.

Abstract

Based on a simple, but fairly successful, model of the chemical evolution of the Milky Way disk, we study the evolution of the abundances of the elements He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for massive stars with and without mass loss. We find that most observed abundance profiles are correctly reproduced by massive star yields, but C and N require supplementary sources. We argue that massive, mass losing stars can totally account for the abundance profile of C, while intermediate mass stars are the main source of N; in both cases, some conflict with corresponding data on extragalactic HII regions arises, at least if current observations in the Galaxy are taken at face value. The observed behaviour of Al is marginally compatible with current massive star yields, which probably overestimate the ``odd-even'' effect. We also find that the adopted ``inside-out'' formation scheme for the Milky Way disk produce abundance profiles steeper in the past. The corresponding abundance scatter is smaller in the inner disk than in the outer regions for a given interval of Galactic age.