The effects of the IMF on the chemical evolution of elliptical galaxies

TL;DR

This study uses a chemical evolution model to analyze how varying initial mass functions (IMFs) influence the observed abundance patterns in elliptical galaxies, challenging previous assumptions about IMF trends with galaxy mass.

Contribution

It introduces a variable IMF model that varies inversely with galaxy mass, improving the fit to observed abundance patterns compared to fixed IMFs.

Findings

A varying IMF from bottom-heavy in low-mass to top-heavy in high-mass galaxies fits data better.

Fixed IMFs fail to reproduce observed abundance trends across galaxy masses.

An inverse IMF trend supports galaxy downsizing and star formation in ellipticals.

Abstract

We describe the use of our chemical evolution model to reproduce the abundance patterns observed in a catalog of elliptical galaxies from the SDSS DR4. The model assumes ellipticals form by fast gas accretion, and suffer a strong burst of star formation followed by a galactic wind which quenches star formation. Models with fixed IMF failed in simultaneously reproducing the observed trends with the galactic mass. So, we tested a varying IMF; contrary to the diffused claim that the IMF should become bottom heavier in more massive galaxies, we find a better agreement with data by assuming an inverse trend, where the IMF goes from being bottom heavy in less massive galaxies to top heavy in more massive ones. This naturally produces a downsizing in star formation, favoring massive stars in largest galaxies. Finally, we tested the use of the Integrated Galactic IMF, obtained by averaging the canonical IMF over the mass distribution function of the clusters where star formation is assumed to take place. We combined two prescriptions, valid for different SFR regimes, to obtain the IGIMF values along the whole evolution of the galaxies in our models. Predicted abundance trends reproduce the observed slopes, but they have an offset relative to the data. We conclude that bottom-heavier IMFs do not reproduce the properties of the most massive ellipticals, at variance with previous suggestions. On the other hand, an IMF varying with galactic mass from bottom-heavier to top-heavier should be preferred