2017MNRAS.467.3255M

Hydrodynamical simulations of turbulent molecular clouds show that star clusters form from the hierarchical merger of several sub-clumps. We run smoothed-particle hydrodynamics simulations of turbulence-supported molecular clouds with mass ranging from 1700 to 43 000 M_☉. We study the kinematic evolution of the main cluster that forms in each cloud. We find that the parent gas acquires significant rotation, because of large-scale torques during the process of hierarchical assembly. The stellar component of the embedded star cluster inherits the rotation signature from the parent gas. Only star clusters with final mass < few x 100 M_☉ do not show any clear indication of rotation. Our simulated star clusters have high ellipticity (∼0.4-0.5 at t = 4 Myr) and are subvirial (Q_vir <= 0.4). The signature of rotation is stronger than radial motions due to subvirial collapse. Our results suggest that rotation is common in embedded massive (>=1000 M_☉) star clusters. This might provide a key observational test for the hierarchical assembly scenario.