A hidden link in the LMC star cluster formation history

Abstract

The age distribution function of star clusters in the Large Magellanic Cloud (LMC) is known to present a feature called the cluster age gap, a period of time from ~ 4 to 11 Gyr ago with a remarkable small number of clusters identified. In this work we performed an in-depth analysis of three recently catalogued age gap cluster candidates with the aim of confirming their physical nature. We used GEMINI@GMOS g,i photometry centred on the objects to build colour-magnitude diagrams from which we recognised their main features. We also performed an automatic search of stellar overdensities using Gaussian mixture model techniques and analysed the corresponding colour-magnitude diagrams similarly as performed for the aforementioned candidates. The present GEMINI data sets would seem to discard any strong evidence of these object being real clusters, and rather support the possibility of the result of stellar density variations of the LMC field star distribution. These three objects, in addition to other 17 new identified candidates, are placed in the LMC outermost disc in a limited region toward the southwest from the LMC centre. They had embraced the possibility to answer the long-time conundrum about the absence of LMC age gap clusters. From an statistical approach, combined with the knowledge of the expected LMC age-metallicity relationship, and recent simulations of the interaction between the LMC and the Milky Way, we provide not only evidence against the physical nature of the studied objects, but also an interpretation on the lack of identification of more LMC age gap clusters.