The Role of the IGIMF in the chemical evolution of the solar neighbourhood

TL;DR

This paper investigates how the integrated galactic initial mass function (IGIMF), which varies with star formation rate, influences the chemical evolution of the solar neighborhood, highlighting the impact of the parameter beta on observable properties.

Contribution

The study applies the IGIMF formalism to a chemical evolution model of the solar neighborhood, exploring the effects of different beta values on chemical and supernova rates, and suggests a fiducial beta of 2.

Findings

Lower beta values lead to flatter IGIMFs with more massive stars.

A beta of 2 best reproduces local observables.

Higher supernova rates and [alpha/Fe] at given metallicity with lower beta.

Abstract

The integrated galactic initial mass function (IGIMF) is computed from the combination of the stellar initial mass function (IMF) and the embedded cluster mass function, described by a power law with index beta. The result of the combination is a time-varying IMF which depends on the star formation rate. We applied the IGIMF formalism to a chemical evolution model for the solar neighbourhood and compared the results obtained by assuming three possible values for beta with the ones obtained by means of a standard, well-tested, constant IMF. In general, a lower absolute value of beta implies a flatter IGIMF, hence a larger number of massive stars, higher Type Ia and II supernova rates, higher mass ejection rates and higher [alpha/Fe] values at a given metallicity. Our suggested fiducial value for beta is 2, since with this value we can account for most of the local observables. We discuss our results in a broader perspective, with some implications regarding the possible universality of the IMF and the importance of the star formation threshold.