The real population of star clusters in the bar of the Large Magellanic Cloud

Abstract

We report results on star clusters located in the South-Eastern half of the Large Magellanic (LMC) bar from Washington $CT_1$ photometry. Using appropriate kernel density estimators we detected 73 star cluster candidates, three of which do not show any detectable trace of star cluster sequences in their colour-magnitude diagrams (CMDs). We did not detect other 38 previously catalogued clusters, which could not be recognized when visually inspecting the $C$ and $T_1$ images either; the distribution of stars in their respective fields do not resemble that of an stellar aggregate. They represent $\sim$ 33 per cent of all catalogued objects located within the analysed LMC bar field. From matching theoretical isochrones to the cluster CMDs cleaned from field star contamination, we derived ages in the range 7.2 < log($t$ yr$^{-1}$) < 10.1. As far as we are aware, this is the first time homogeneous age estimates based on resolved stellar photometry are obtained for most of the studied clusters. We built the cluster frequency (CF) for the surveyed area, and found that the major star cluster formation activity has taken place during the period log($t$ yr$^{-1}$) $\sim$ 8.0 -- 9.0. Since $\sim$ 100 Myr ago, clusters have been formed during few bursting formation episodes. When comparing the observed CF to that recovered from the star formation rate we found noticeable differences, which suggests that field star and star cluster formation histories could have been significantly different.