Star clusters in galaxy cores

Paolo Bianchini, Max-Plank Institute for Astronomy, Heidelberg
Advisors: Florent Renaud, Mark Gieles, Anna-Lisa Varri

Abstract: The distinction between globular clusters and dwarf galaxies has progressively blurred with the recent discoveries of several outer halo extended star clusters, whose size and luminosity are comparable to the one of faint Milky Way satellites. In order to explain the sparse structure of extended clusters, it has been suggested that they formed in dwarf galaxy satellites that later accreted onto the Milky Way. Using N-body simu- lation we test the possibility that a cluster originally formed as compact in the center of a dwarf galaxy could undergo a significant expansion during the accretion process, due to the change of the tidal potential. We show that the cluster gains energy during its early evolution, because of the compressive tidal environment provided by the core region of the dwarf galaxy. When the cluster stops feeling the compressive tides, it ex- periences an expansion. However, we demonstrate that the imprinted expansion is not enough to explain the observed extended structure, since the outcome of this process are always systems more compact than corresponding clusters evolved completely in isolation. We conclude that an accreted origin of extended globular clusters is unlikely to explain their large spatial extent.

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