Speaker
Description
Understanding the formation and evolution of young stars and clusters requires exploring a wide range of environments, from low-density star-forming regions to the most massive stellar nurseries in the Milky Way. As part of the EWOCS (Extended Westerlund 1 and 2 Open Clusters Survey) project, we have used the unprecedented sensitivity of JWST/NIRCam to study, for the first time, the substellar populations of two of the most massive young clusters in the Milky Way: Westerlund 1 and Westerlund 2. With total stellar masses exceeding 30,000 Msun, these clusters provide a unique laboratory to investigate how extreme environments influence the formation of the lowest-mass objects. Theoretical models predict that high stellar densities and strong feedback from massive OB stars may affect brown dwarf formation efficiency, but this has remained largely untested in massive young clusters. In this talk, I will present new JWST/NIRCam results for both clusters. In Westerlund 2, we identify and characterize a large population of brown dwarf candidates reaching into the planetary-mass regime, with indications of a lower disk fraction and reduced substellar demographics compared to nearby low-mass star-forming regions. In Westerlund 1, we statistically derive the first measurement of the (sub)stellar initial mass function down to ~0.05 Msun, revealing an unexpectedly shallow slope, indicating one of the most bottomlight populations of low-mass objects observed in a young cluster. Together, these results provide the first systematic constraints on brown dwarf demographics in the most massive Galactic clusters, suggesting that extreme environments may suppress the formation of the lowest-mass objects. This work offers new insights into the environmental dependence of the initial mass function and establishes key benchmarks for future JWST studies of young clusters across the Milky Way.
