2021/01/05 by Peter Zeidler, Elena Sabbi, Antonella Nota +1
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Mass segregation #Radial velocity #Star cluster #Star formation #Stars #Stellar dynamics #Stellar mass #Stellar, planetary, and galactic studies #Velocity dispersion #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.3847/1538-3881/abd6ca
23 pages, 14 figures, 4 tables, accepted to AJ
arxiv created 2021/01/05 · openalex created_date 2021/01/18 · openalex publication_date 2021/02/23 · arxiv updated 2021/03/03 · openalex updated_date 2026/08/05
Abstract Analyzing the dynamical state of nearby young massive star clusters is essential for understanding star cluster formation and evolution during their earliest stages. In this work we analyze the stellar and gas kinematics of the young massive star cluster Westerlund 2 (Wd2) using data from the integral field unit Multi Unit Spectroscopic Explorer (MUSE) and complement them with proper motions from the Gaia DR2. The mean gas radial velocity of 15.9 km s −1 agrees with the assumption that Wd2 is the result of a cloud–cloud collision. The gas motions show the expansion of the H ii region, driven by the radiation from the many OB stars in the cluster center. The velocity profile of the cluster member stars reveals an increasing velocity dispersion with decreasing stellar mass and that the low-mass stars show five distinct velocity groups. Based on their spatial correlation with the cluster’s two clumps, we concluded that this is the imprint of the initial cloud collapse that formed Wd2. A thorough analysis of the dynamical state of Wd2, which determines a dynamical mass range of M dyn,Wd2 = (7.5 ± 1.9) × 10 4 − (4.4 ± 1.1) × 10 5 M ⊙ and exceeds the photometric mass by at least a factor of two, leads to the conclusion that Wd2 is not massive enough to remain gravitationally bound. Additionally we also identify 22 runaway candidates with peculiar velocities between 30 and 546 km s −1 .