Metallicity gradients in the globular cluster systems of early-type
  galaxies: In-situ and accreted components?
  Massive early-type galaxies typically have two subpopulations of globular
clusters (GCs) which often reveal radial colour (metallicity) gradients.
Collating gradients from the literature, we show that the gradients in the
metal-rich and metal-poor GC subpopulations are the same, within measurement
uncertainties, in a given galaxy. Furthermore, these GC gradients are similar
in strength to the {\it stellar} metallicity gradient of the host galaxy. At
the very largest radii (e.g. greater than 8 galaxy effective radii) there is
some evidence that the GC gradients become flat with near constant mean
metallicity. Using stellar metallicity gradients as a proxy, we probe the
assembly histories of massive early-type galaxies with hydrodynamical
simulations from the Magneticum suite of models. In particular, we measure the
stellar metallicity gradient for the in-situ and accreted components over a
similar radial range as those observed for GC subpopulations. We find that the
in-situ and accreted stellar metallicity gradients are similar but have a
larger scatter than the metal-rich and metal-poor GC subpopulations gradients
in a given galaxy. We conclude that although metal-rich GCs are predominately
formed during the in-situ phase and metal-poor GCs during the accretion phase
of massive galaxy formation, they do not have a strict one-to-one connection.
