Revisiting the old end of the Milky Way open cluster age function

Abstract

The age distribution of the open cluster system is a key piece of information to decipher the starformation history of the Milky Way disk. Recently, a remarkable earlier drop of its older end was found, whichcaught our attention. Precisely, we analyzed in detail the population of open clusters older than 1 Gyr locatedinside a circle of 2.0 kpc from the Sun contained in the Milky Way Star Cluster catalog, using the Data Release3.0 of the Gaia survey, and found that it contains a slightly larger old open cluster population with respect to thatwitnessing the earlier drop age distribution. However, there are still some aspects that deserve further attention inorder to undoubtedly handle a statistically complete cluster sample, that allows us to comprehensively know theolder end of the open cluster age distribution function. We discuss some reasons that affect such a completeness,among them, the photometric depth of the database employed, the performance of machine learning techniquesused to recognize open clusters, the cleaning of cluster color-magnitude diagrams from field star contamination,etc.