Abstract Using the Gaia DR3 open cluster catalog, we identified the most massive star in each observed cluster. Examining the mmax-Mcluster relations across different age ranges, we find that as clusters age, the relation gradually deviates from the initial mmax-Mecl relation and eventually exhibits clear age stratification. We conducted N-body simulations for both individual cluster evolution and subcluster coalescence. Four gas expulsion modes were tested for individual clusters, and two scenarios were modeled for cluster coalescence. Under all four gas expulsion modes, the evolution of the mmax-Mcluster relation follows a similar trajectory, differing mainly in evolutionary speed. The coalescence simulations show comparable behavior but align better with the observations, as both exhibit systematically lower mmax-Mcluster relations than individual cluster simulations. This systematically lower observed mmax-Mcluster relation suggests slower cluster mass loss and smaller masses for the most massive stars—both conditions reproduced in the coalescence simulations. Observations also show that clusters older than 5 Myr have most massive stars significantly deviating from the initial mmax-Mecl relation. From this perspective, the coalescence simulations also provide a better match to the observations. In conclusion, the evolution of the mmax-Mecl relation supports subcluster coalescence as a dominant pathway for open cluster formation, consistent with our previous work.
Zhou et al. (Fri,) studied this question.