An optical/NIR survey of globular clusters in early-type galaxies II.
  Ages of GC systems and the relation to galaxy morphology
  Context: Some photometric studies of extragalactic globular cluster (GC)
systems using the optical and near-infrared colour combination have suggested
the presence of a large fraction of intermediate-age (2-8 Gyrs) GCs. Aims: We
investigate the age distributions of GC systems in 14 E/S0 galaxies. Methods:
We carry out a differential comparison of the (g-z) vs. (g-K) two-colour
diagrams for GC systems in the different galaxies in order to see whether there
are indications of age differences. We also compare the different GC systems
with a few simple stellar population models. Results: No significant difference
is detected in the mean ages of GCs among elliptical galaxies. S0 galaxies on
the other hand, show evidence for younger GCs. Surprisingly, this appears to be
driven by the more metal-poor clusters. The age distribution of GCs in NGC4365
seems to be similar to that of other large ellipticals (e.g. NGC4486, NGC4649).
Padova SSPs with recently released isochrones for old ages (14 Gyrs) show less
of an offset with respect to the photometry than previously published models.
Conclusions: We suggest that E type galaxies assembled most of their GCs in a
shorter and earlier period than S0 type galaxies. The latter galaxy type, seems
to have a more extended period of GC formation/assembly.
