On a possible origin for the lack of old star clusters in the Small Magellanic Cloud

TL;DR

This study models the dynamical interactions between the Small and Large Magellanic Clouds to explain the scarcity of old star clusters in the SMC, suggesting many were captured or ejected due to tidal forces.

Contribution

It provides the first detailed numerical simulations exploring how tidal interactions can lead to the loss or capture of star clusters between the Magellanic Clouds.

Findings

Approximately 15% of SMC clusters are captured by the LMC.

20-50% of SMC clusters are ejected into intergalactic space.

Captured clusters tend to be located in the outskirts of the LMC.

Abstract

We model the dynamical interaction between the Small and Large Magellanic Clouds and their corresponding stellar cluster populations. Our goal is to explore whether the lack of old clusters ($\gtrsim 7$ Gyr) in the Small Magellanic Cloud (SMC) can be the result of the capture of clusters by the Large Magellanic Cloud (LMC), as well as their ejection due to the tidal interaction between the two galaxies. For this purpose we perform a suite of numerical simulations probing a wide range of parameters for the orbit of the SMC about the LMC. We find that, for orbital eccentricities $e \geq 0.4$, approximately 15 per cent of the SMC clusters are captured by the LMC. In addition, another 20 to 50 per cent of its clusters are ejected into the intergalactic medium. In general, the clusters lost by the SMC are the less tightly bound cluster population. The final LMC cluster distribution shows a spatial segregation between clusters that originally belonged to the LMC and those that were captured from the SMC. Clusters that originally belonged to the SMC are more likely to be found in the outskirts of the LMC. Within this scenario it is possible to interpret the difference observed between the star field and cluster SMC Age-Metallicity Relationships for ages $\gtrsim 7$ Gyr.