On the rotation of nuclear star clusters formed by cluster-inspirals
  Nuclear Star Clusters (NSCs) are commonly observed in the centres of most
galactic nuclei, including our own Milky Way. While their study can reveal
important information about the build-up of the innermost regions of galaxies,
the physical processes that regulate their formation are still poorly
understood. NSCs might have been formed through gas infall and subsequent in
situ star formation, and/or through the infall and merging of multiple star
clusters into the centre of the galaxy. Here, we investigate the viability of
the latter, by studying direct N-body simulations of inspiralling clusters to
the centre of a Milky-Way-like nuclear bulge that hosts a massive black hole.
We find that the NSC that forms through this process can show both
morphological and kinematical properties that make it comparable with
observations of the Milky Way NSC, including significant rotation- a fact that
has been so far attributed mainly to gas infall. We explore its kinematic
evolution, to see if and how the merger history can imprint fossil records on
its dynamical structure. Moreover, we study the effect of stellar foreground
contamination in the line-of-sight kinematics of the NSC. Our study shows that
no fine tuning of the orientation of the infalling globular clusters is
necessary to result in a rotating NSC. We suggest that cluster-inspiral is a
viable mechanism for the formation of rotating NSCs.
