Multivariate analysis of globular cluster systems in early-type galaxies

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Abstract
We use multivariate statistical analysis to study the relation between the globular cluster content of early-type galaxies and a number of their observed properties. The number of globular clusters scales non-linearly with galaxy luminosity and virial mass. Both the total number of clusters and their specific frequency correlate with metallicity, internal velocity anisotropy, isophotal shape parameters and, possibly, X-ray luminosity of the host galaxy. We observe that the properties of the globular cluster systems, to a large extent, are correlated with the so-called Fundamental Plane of early-type galaxies, although a residual amount of variability in the number and specific frequency of globulars remains. This residual scatter correlates with the variables which reflect velocity anisotropy and isophotal shape. These results imply that the mechanisms of formation of the globular clusters are closely tied to those operating during the formation and evolution of their host galaxies. We also briefly investigate the properties of globular cluster systems in low surface brightness dwarf galaxies and compare them to those of large ellipticals. Possible theoretical implications of our results are discussed and we conclude that the formation of globular clusters in early-type galaxies was, at least partially, driven by dissipative interactions and merging, most of which possibly took place at early epochs.

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