The paucity of globular clusters around the field elliptical NGC 7507
  Context: There is strong evidence that globular cluster systems (GCSs) of
massive galaxies are largely assembled by infall/accretion processes.
Therefore, we expect the GCSs of isolated elliptical galaxies to be poor.
Alhough not completely isolated, NGC 7507 is a massive field elliptical galaxy
with an apparently very low dark matter content. Aims: We determine the
richness, the colour distribution, and the structural properties of the GCS of
NGC 7507. Methods: We perform wide-field Washington photometry with data
obtained with the MOSAIC II camera at the 4m-Blanco telescope, CTIO. Results:
The GCS is very poor with S_N ~ 0.6. We identify three subpopulations with
peaks at (C-T1) colours of 1.21, 1.42, and 1.72. The bluest population may
represent the old, metal-poor component. This interpretation is supported by
its shallow density profile. The red population is more concentrated,
resembling the galaxy light. The intermediate-colour population is strongly
peaked in colour and we interpret this population as the signature of a
starburst, whose age depends on the metallicity, but should be quite old, since
no signatures of a merger are identifiable. In addition, we find a main
sequence in the stellar foreground population, which we attribute to the
Sagittarius dwarf tidal stream. Conclusions: The extraordinarily poor GCS of
NGC 7507, a massive elliptical galaxy, is an illustration of how important the
environmental conditions are for producing rich GCSs.
