The SLUGGS Survey: Calcium Triplet-based Spectroscopic Metallicities for
  Over 900 Globular Clusters
  Although the colour distribution of globular clusters in massive galaxies is
well known to be bimodal, the spectroscopic metallicity distribution has been
measured in only a few galaxies. After redefining the calcium triplet
index-metallicity relation, we use our relation to derive the metallicity of
903 globular clusters in 11 early-type galaxies. This is the largest sample of
spectroscopic globular cluster metallicities yet assembled. We compare these
metallicities with those derived from Lick indices finding good agreement. In 6
of the 8 galaxies with sufficient numbers of high quality spectra we find
bimodality in the spectroscopic metallicity distribution. Our results imply
that most massive early-type galaxies have bimodal metallicity, as well as
colour, distributions. This bimodality suggests that most massive galaxies
early-type galaxies experienced two periods of star formation.
