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

Abstract

Age distribution of the open cluster system is a key piece of information to decipher the star-formation history of the milky way disk. Recently, a remarkable earlier drop of its older end was found, which caught our attention. Precisely, we analysed in detail the population of open clusters older than 1 Gyr located inside a circle of 2.0 kpc from the Sun contained in the milky way star-cluster catalog, using the data release 3.0 of the Gaia survey, and found that it contains a slightly larger old open-cluster population with respect to that witnessing the earlier drop age distribution. However, there are still some aspects that deserve further attention to undoubtedly handle a statistically complete cluster sample, that allows us to comprehensively know the older 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 techniques used to recognize open clusters, the cleaning of cluster color–magnitude diagrams from field star contamination, etc.