Metallicity and the Universality of the IMF

TL;DR

This paper investigates why the stellar initial mass function (IMF) remains remarkably consistent across different metallicities, showing through simulations and analysis that dust opacity has minimal impact on gas fragmentation and star formation.

Contribution

The study demonstrates that radiation feedback from massive protostars causes the IMF to be largely independent of metallicity, supported by simulations and analytic reasoning.

Findings

Dust opacity has little effect on gas temperature and fragmentation.

IMF variation is minimal despite a 100-fold change in metallicity.

Radiation feedback dominates the star formation process.

Abstract

The stellar initial mass function (IMF), along with the star formation rate, is one of the fundamental properties that any theory of star formation must explain. An interesting feature of the IMF is that it appears to be remarkably universal across a wide range of environments. Particularly, there appears to be little variation in either the characteristic mass of the IMF or its high-mass tail between clusters with different metallicities. Previous attempts to understand this apparent independence of metallicity have not accounted for radiation feedback from high-mass protostars, which can dominate the energy balance of the gas in star-forming regions. We extend this work, showing that the fragmentation of molecular gas should depend only weakly on the amount of dust present, even when the primary heating source is radiation from massive protostars. First, we report a series of core collapse simulations using the ORION AMR code that systematically vary the dust opacity and show explicitly that this has little effect on the temperature or fragmentation of the gas. Then, we provide an analytic argument for why the IMF varies so little in observed star clusters, even as the metallicity varies by a factor of 100.