Globular clusters as tracers of the halo assembly of nearby central
  cluster galaxies
  The properties of globular cluster systems (GCSs) in the core of the nearby
galaxy clusters Fornax and Hydra I are presented. In the Fornax cluster we have
gathered the largest radial velocity sample of a GCS system so far, which
enables us to identify photometric and kinematic sub-populations around the
central galaxy NGC 1399. Moreover, ages, metallicities and [alpha/Fe]
abundances of a sub-sample of 60 bright globular clusters (GCs) with high S/N
spectroscopy show a multi-modal distribution in the correlation space of these
three parameters, confirming heterogeneous stellar populations in the halo of
NGC 1399. In the Hydra I cluster very blue GCs were identified. They are not
uniformly distributed around the central galaxies. 3-color photometry including
the U-band reveals that some of them are of intermediate age. Their location
coincides with a group of dwarf galaxies under disruption. This is evidence of
a structurally young stellar halo 'still in formation', which is also supported
by kinematic measurements of the halo light that point to a kinematically
disturbed system. The most massive GCs divide into generally more extended
ultra-compact dwarf galaxies (UCDs) and genuine compact GCs. In both clusters,
the spatial distribution and kinematics of UCDs are different from those of
genuine GCs. Assuming that some UCDs represent nuclei of stripped galaxies, the
properties of those UCDs can be used to trace the assembly of nucleated dwarf
galaxies into the halos of central cluster galaxies. We show via
semi-analytical approaches within a cosmological simulation that only the most
massive UCDs in Fornax-like clusters can be explained by stripped nuclei,
whereas the majority of lower mass UCDs belong to the star cluster family.
