A path towards constraining the evolution of the interstellar medium and outflows in the Milky Way using APOGEE

TL;DR

This paper develops a new chemical evolution model of the Milky Way's interstellar medium and outflows, constrained by APOGEE stellar data, revealing insights into oxygen enrichment and ISM turbulence over the last 6 billion years.

Contribution

It introduces a combined ISM and stellar disc model constrained by APOGEE data, providing novel insights into Galactic outflows and ISM turbulence evolution.

Findings

Modest differential oxygen enrichment in outflows is required.

Elevated ISM gas velocity dispersion over 6 billion years.

Outflow oxygen abundance is higher than local ISM abundance.

Abstract

In recent years, the study of the Milky Way has significantly advanced due to extensive spectroscopic surveys of its stars, complemented by astroseismic and astrometric data. However, it remains disjoint from recent advancements in understanding the physics of the Galactic interstellar medium (ISM). This paper introduces a new model for the chemical evolution of the Milky Way that can be constrained on stellar data, because it combines a state-of-the-art ISM model with a Milky Way stellar disc model. Utilizing a dataset of red clump stars from APOGEE, known for their precise ages and metallicities, we concentrate on the last 6 billion years -- a period marked by Milky Way's secular evolution. We examine the oxygen abundance in the low-$\alpha$ disc stars relative to their ages and birth radii, validating or constraining critical ISM parameters that remain largely unexplored in extragalactic observations. The models that successfully reproduce the radius -- metallicity distribution and the age -- metallicity distribution of stars without violating existing ISM observations indicate a need for modest differential oxygen enrichment in Galactic outflows, meaning that the oxygen abundance of outflows is higher than the local ISM abundance, irrespective of outflow mass loading. The models also suggest somewhat elevated ISM gas velocity dispersion levels over the past 6 billion years compared to galaxies of similar mass. The extra turbulence necessary could result from energy from gas accretion onto the Galaxy, supernovae clustering in the ISM, or increased star formation efficiency per freefall time. This work provides a novel approach to constraining the Galactic ISM and outflows, leveraging the detailed insights available from contemporary Milky Way surveys.