Investigating rotation in young massive clusters by means of hydrodynamical and direct N-body simulations

One of the main open questions of star formation is the process of star clusters aggregation. In my thesis I investigate the kinematical features of embedded star clusters through hydrodynamical and N-body simulations. In particular I focus on the onset of rotation. I started from smoothed-particle-hydrodynamics simulations of turbulence- supported molecular clouds with masses ranging from 10000 M to 200000 Msun . In each simulated cloud a star cluster forms by hierarchical assembly of several sub-clumps; during this process torque is exerted on the parent gas and the stellar component because they accrete on the main cluster structure with non-zero angular momentum. This angular momentum is transferred to the main cluster, which acquires significant rotation. I study the dynamical evolution of the cluster that forms in each cloud using direct summation N-body codes, to see how rotation and ellipticity evolve through time. My simulated star clusters start with large ellipticity (e ∼ 0.7 at t = 3 Myr) and with a rotational velocity Vrot ∼ 5 km s^−1 . During their evolution they tend to become rounder (e ∼ 0.2 at t = 10 Myr) and their rotation signature decreases because of two-body relaxation. Rotation is still apparent at t = 20 Myr, so it decreases on a surprisingly long timescale. This result is a key test to probe the hierarchical formation scenario of star clusters, and might be useful to interpret the observed rotation signature in young massive star clusters (R136, Hénault-Brunet et al. 2012) and in old globular clusters (e.g. Bellazzini et al. 2012).