KMHK 1762: Another star cluster in the Large Magellanic Cloud age gap

TL;DR

This study re-analyzed the age of the star cluster KMHK 1762 in the Large Magellanic Cloud, revealing it is approximately 5.5 billion years old and confirming it as part of the rare star clusters within the galaxy's age gap.

Contribution

The paper provides a more accurate age estimate for KMHK 1762 using deep photometry and Gaia data, identifying it as the third confirmed star cluster in the LMC's age gap.

Findings

KMHK 1762 is approximately 5.5 Gyr old.

It is the third confirmed star cluster in the LMC's age gap.

The age gap may be due to observational biases.

Abstract

The star cluster (SC) age distribution of the Large Magellanic Cloud (LMC) exhibits a gap from $\sim$ 4 to 10 Gyr ago, with an almost total absence of SCs. Within this age gap, only two confirmed SCs have been identified hitherto. Nonetheless, the star field counterpart does not show the same characteristics, making the LMC a peculiar galaxy where star formation history and cluster formation history appear to differ significantly. We re-analyzed the color-magnitude diagram (CMD) of the KMHK 1762 SC by using the deep optical photometry provided by the "Yes, Magellanic Clouds Again" survey, to robustly assess its age. First, we partially removed foreground and/or field stars by means of parallaxes and proper motions obtained from the {\it Gaia} Early Data Release 3. Then, we applied the Automated Stellar Cluster Analysis package to the cleaned photometric catalogue to identify the isochrone that best matches the CMD of KMHK 1762. The estimated age of KMHK 1762 is $\log (t) = 9.74 \pm 0.15$ dex ($\sim$5.5 Gyr), that is more than 2 Gyr older than the previous estimation which was obtained with shallower photometry. This value makes KMHK 1762 the third confirmed age gap SC of the LMC. The physical existence of a quiescent period of the LMC SC formation is questioned. We suggest it can be the result of an observational bias, originated by the combination of shallow photometry and limited investigation of the LMC periphery.