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Wednesday 10 Nov 2010: Nuclear Star Cluster: Structural and Kinematical Constraints on Their Formation
Markus Hartmann - University of Central Lancashire, UK
Physics, 4th Floor interaction area 11:00-12:00
I present an extensive study of the impact of purely stellar dynamical mergers and accretions on the formation and growth of stellar nuclear clusters (NCs) at the centres of disk galaxies. These simulations seek to explain the morphology and kinematics of observed NCs in late-type spiral galaxies, including the presence of young nuclear cluster disks (NCDs) embedded within some NCs. I present results from two sets of simulations. In the first, I focused on the formation of a NC formed by the multiple mergers of star clusters (SCs). The remnant NCs are consistent with observed scaling relations and they result in oblate systems with boxy shaped isophotes. They are radially biased and have in comparison to the NCs in NGC 4244 and M33 similar amount of rotation. Although the merger reveal structural and kinematical NC comparable to observed, however it fails to reproduce the nuclear cluster disk (NCD) component. These structural components have been found in edge-on NCs and have been connected to the multiple stellar populations, where younger stars less than 100 Myr populate the NCD and the spheroidal component consists of an older population greater than 1 Gyr. The second set of simulations studies the multiple accretion of SCs onto a NC seed like a bare NCD or a migrated super star cluster (SSC) building a nuclear cluster spheroid (NCS). Up to 20 SCs are accreted by the different NC seeds. Unlike the remnant systems in the merger simulations, here the remaining NCs have disky isophotes and comparable rotation as observed in NGC 4244. These findings have important implications to distinguish between the two formation scenarios for NCs: the multiple merger of SCs and accretion of gas with in-situ star formation. The simulations show that the merger scenario can produce rotating oblate NCs and that a subsequent accretion of SCs can build a NCD component as observed in the edge-on late-type spiral galaxies IC 5052, NGC 4206 and NGC 4244.