Stellar initial mass function variation in massive early-type galaxies: the potential role of the deuterium abundance

TL;DR

This paper explores how variations in deuterium abundance in star-forming regions may influence the initial mass function in massive early-type galaxies, potentially explaining observed bottom-heavy IMFs.

Contribution

It proposes that deuterium abundance in star-forming clouds affects the IMF, linking chemical composition to stellar mass distribution in galaxies.

Findings

Deuterium-poor gas leads to lower-mass stars at formation.

Deuterium abundance variations correlate with IMF variations in galaxy centers.

Stellar mass loss is deuterium-free and influences star formation over time.

Abstract

The observed stellar initial mass function (IMF) appears to vary, becoming bottom-heavy in the centres of the most massive, metal-rich early-type galaxies. It is still unclear what physical processes might cause this IMF variation. In this paper, we demonstrate that the abundance of deuterium in the birth clouds of forming stars may be important in setting the IMF. We use models of disc accretion onto low-mass protostars to show that those forming from deuterium-poor gas are expected to have zero-age main sequence masses significantly lower than those forming from primordial (high deuterium fraction) material. This deuterium abundance effect depends on stellar mass in our simple models, such that the resulting IMF would become bottom-heavy - as seen in observations. Stellar mass loss is entirely deuterium-free and is important in fuelling star formation across cosmic time. Using the EAGLE simulation we show that stellar mass loss-induced deuterium variations are strongest in the same regions where IMF variations are observed: at the centres of the most massive, metal-rich, passive galaxies. While our analysis cannot prove that the deuterium abundance is the root cause of the observed IMF variation, it sets the stage for future theoretical and observational attempts to study this possibility.