Globular Cluster Systems of Early-type Galaxies in Low-density
  Environments
  Deep images of 10 early-type galaxies in low-density environments have been
obtained with the Advanced Camera for Surveys (ACS) on the Hubble Space
Telescope. The global properties of the globular cluster (GC) systems of the
galaxies have been derived in order to investigate the role of the environment
in galaxy formation and evolution. Using the ACS Virgo Cluster Survey (ACSVCS)
as a high-density counterpart, the similarities and differences between the GC
properties in high- and low-density environments are presented. We find a
strong correlation of the GC mean colours and the degree of colour bimodality
with the host galaxy luminosity in low-density environments, in good agreement
with high-density environments. In contrast, the GC mean colours at a given
host luminosity are somewhat bluer (\Delta(g-z) ~ 0.05) than those for cluster
galaxies, indicating more metal-poor (\Delta[Fe/H] ~ 0.10-0.15) and/or younger
(\Delta age > 2 Gyr) GC systems than those in dense environments. Furthermore,
with decreasing host luminosity, the colour bimodality disappears faster, when
compared to galaxies in cluster environments. Our results suggest that: (1) in
both high- and low-density environments, the mass of the host galaxy has the
dominant effect on GC system properties, (2) the local environment has only a
secondary effect on the history of GC system formation, (3) GC formation must
be governed by common physical processes across a range of environments.
