The systematically varying stellar IMF

TL;DR

This paper proposes that the stellar initial mass function (IMF) systematically varies with environmental factors like metallicity and gas density, explaining observed properties of star clusters and galaxies.

Contribution

It introduces a model where the IMF becomes more top-heavy under certain conditions, linking stellar populations to galaxy-wide properties and high-redshift starbursts.

Findings

IMF varies with metallicity and gas density

Explains M/L ratios and LMXB abundance in star clusters

Accounts for galaxy-wide IMF trends with star formation rate

Abstract

Some ultra-compact dwarf galaxies have large dynamical mass to light (M/L) ratios and also appear to contain an overabundance of LMXB sources, and some Milky Way globular clusters have a low concentration and appear to have a deficit of low-mass stars. These observations can be explained if the stellar IMF becomes increasingly top-heavy with decreasing metallicity and increasing gas density of the forming object. The thus constrained stellar IMF then accounts for the observed trend of metallicity and M/L ratio found amongst M31 globular star clusters. It also accounts for the overall shift of the observationally deduced galaxy-wide IMF from top-light to top-heavy with increasing star formation rate amongst galaxies. If the IMF varies similarly to deduced here, then extremely young very massive star-burst clusters observed at a high redshift would appear quasar-like (Jerabkova et al. 2017) .