Age and mass segregation of multiple stellar populations in galactic   nuclei and their observational signatures
  Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. They are thought to have formed through in-situ star formation following gas inflow to the nucleus of the galaxy and/or through the infall of multiple stellar clusters. Here we study the latter, and explore the composite structure of the NSC, and its relation to the various stellar populations originating from its progenitor infalling clusters. We use N-body simulations of clusters infall, and show that this scenario may produce observational signatures in the form of age segregation: the distribution of the stellar properties (e.g. stellar age and/or metallicity) in the NSCs reflect the infall history of the different clusters. The stellar populations of clusters infalling at different times (dynamical ages), are differentially segregated in the NSC, and are not fully mixed even after few Gyrs of evolution. Moreover, the radial properties of stellar populations in the progenitor cluster are mapped to their radial distribution in the final NSC, potentially leading to efficient mass segregation in NSCs, even those where relaxation times are longer than a Hubble time. Finally, the overall structures of the stellar populations present non-spherical configurations and show significant cluster to cluster population differences. 
Hagai B. Perets and Alessandra Mastrobuono-Battisti
astro-ph.GA astro-ph.SR