IMF - metallicity: a tight local relation revealed by the CALIFA survey

TL;DR

This study reveals a strong local correlation between the stellar initial mass function and metallicity in early-type galaxies, suggesting metallicity as the key driver of IMF variations and impacting galaxy evolution models.

Contribution

It demonstrates a direct, homogeneous analysis of the IMF-metallicity relation within early-type galaxies using CALIFA survey data, highlighting metallicity as the primary influence on IMF variations.

Findings

IMF becomes more bottom-heavy with increasing metallicity

Local IMF-metallicity relation explains galaxy mass-IMF correlations

Metallicity likely drives IMF variations in early-type galaxies

Abstract

Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies. However, no observations have yet been able to disentangle the physical driver. We analyse here a sample of 24 early-type galaxies drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy towards metal-rich populations. Our result, combined with the galaxy mass-metallicity relation, naturally explains previous claims of a galaxy mass-IMF relation, derived from non-IFU spectra. If we assume that - within the star formation environment of early-type galaxies - metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.