The Extended Main-Sequence Turn-off Clusters of the Large Magellanic Cloud - Missing links in Globular Cluster Evolution

TL;DR

This paper suggests that intermediate-age clusters with extended main-sequence turn-offs in the Large Magellanic Cloud are a phase in cluster evolution linked to chemical properties of ancient globular clusters, driven by observational biases.

Contribution

It proposes that EMSTO clusters are a natural evolutionary phase leading to globular cluster chemical properties, explaining their observed age distribution and chemical variations.

Findings

EMSTO clusters are likely a phase in cluster evolution.

Observational selection effects influence the detection of EMSTO clusters.

EMSTO clusters should show light element abundance variations similar to ancient globular clusters.

Abstract

Recent observations of intermediate age (1 - 3 Gyr) massive star clusters in the Large Magellanic Cloud (LMC) have revealed that the majority possess bifurcated or extended main-sequence turn-off (EMSTO) morphologies. This effect can be understood to arise from subsequent star formation amongst the stellar population with age differences between constituent stars amounting to 50 - 300 Myr. Age spreads of this order are similarly invoked to explain the light element abundance variations witnessed in ancient globular clusters. In this paper we explore the proposition that the clusters exhibiting the EMSTO phenomenon are a general phase in the evolution of massive clusters, one that naturally leads to the particular chemical properties of the ancient globular cluster population. We show that the isolation of EMSTO clusters to intermediate ages is the consequence of observational selection effects. In our proposed scenario, the EMSTO phenomenon is identical to that which establishes the light element abundance variations that are ubiquitous in the ancient globular cluster population. Our scenario makes a strong prediction: EMSTO clusters will exhibit abundance variations in the light elements characteristic of the ancient GC population.