Multiple populations within globular clusters in Early-type galaxies Exploring their effect on stellar initial mass function estimates

TL;DR

This study investigates how multiple stellar populations within globular clusters affect the integrated spectral features and mass-to-light ratios of early-type galaxies, concluding they are unlikely to cause observed IMF variations but may influence chemical signatures.

Contribution

The paper develops new stellar population models incorporating helium variations and initial-final mass relations to assess globular cluster effects on galaxy properties.

Findings

Multiple populations unlikely to cause IMF-sensitive line variations.

Globular cluster populations may explain some chemical patterns in galaxy centers.

Models suggest minimal impact on galaxy mass-to-light ratio variations.

Abstract

It is now well-established that most (if not all) ancient globular clusters host multiple popula- tions, that are characterised by distinct chemical features such as helium abundance variations along with N-C and Na-O anti-correlations, at fixed [Fe/H]. These very distinct chemical fea- tures are similar to what is found in the centres of the massive early-type galaxies and may influence measurements of the global properties of the galaxies. Additionally, recent results have suggested that M/L variations found in the centres of massive early-type galaxies might be due to a bottom-heavy stellar initial mass function. We present an analysis of the effects of globular cluster-like multiple populations on the integrated properties of early-type galaxies. In particular, we focus on spectral features in the integrated optical spectrum and the global mass-to-light ratio that have been used to infer variations in the stellar initial mass function. To achieve this we develop appropriate stellar population synthesis models and take into account, for the first time, an initial-final mass relation which takes into consideration a varying He abundance. We conclude that while the multiple populations may be present in massive early-type galaxies, they are likely not responsible for the observed variations in the mass- to-light ratio and IMF sensitive line strengths. Finally, we estimate the fraction of stars with multiple populations chemistry that come from disrupted globular clusters within massive ellipticals and find that they may explain some of the observed chemical patterns in the centres of these galaxies.