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

TL;DR

This study reevaluates the age distribution of old open clusters in the Milky Way using Gaia data, revealing a slightly larger population of clusters older than 1 Gyr and discussing factors affecting sample completeness.

Contribution

It provides a detailed analysis of the older end of the open cluster age function using Gaia DR3 data and discusses challenges in achieving a complete, unbiased sample.

Findings

Older open cluster population is slightly larger than previously thought.

Factors like data depth and cluster recognition techniques influence sample completeness.

The study highlights the need for improved methods to accurately characterize the old cluster population.

Abstract

The 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 analyzed 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 in order 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.