2010ApJ...712.1191T

Velocity dispersion measurements are presented for several of the most luminous globular clusters (GCs) in NGC 5128 (Centaurus A) derived from high-resolution spectra obtained with the UVES echelle spectrograph on the 8.2 m ESO/Very Large Telescope. The measurements are made utilizing a penalized pixel-fitting method that parametrically recovers line-of-sight velocity dispersions. Combining the measured velocity dispersions with surface photometry and structural parameter data from the Hubble Space Telescope enables both dynamical masses and mass-to-light ratios to be derived. The properties of these massive stellar systems are similar to those of both massive GCs contained within the Local Group and nuclear star clusters and ultra-compact dwarf galaxies (UCDs). The fundamental plane relations of these clusters are investigated in order to fill the apparent gap between the relations of Local Group GCs and more massive early-type galaxies. It is found that the properties of these massive stellar systems match those of nuclear clusters in dwarf elliptical galaxies and UCDs better than those of Local Group GCs, and that all objects share similarly old (≳8 Gyr) ages, suggesting a possible link between the formation and evolution of nuclear star clusters in dwarf elliptical galaxies (dE,Ns), UCDs, and massive GCs. We find a very steep correlation between dynamical mass-to-light ratio and dynamical mass of the form Υ_V^dyn¡∝¡M_dyn^0.24±0.02 above {M_dyn¡~¡2×10^6} M_☉. Formation scenarios are investigated with a chemical abundance analysis using absorption-line strengths calibrated to the Lick/IDS index system. The results lend support to two scenarios contained within a single general formation scheme. Old, massive, super-solar [α/Fe] systems are formed on short (≲100 Myr) timescales through the merging of single-collapse GCs which themselves are formed within single, giant molecular clouds. More intermediate- and old-aged (∼3-10 Gyr), solar- to sub-solar [α/Fe] systems are formed on much longer (∼Gyr) timescales through the stripping of dE,Ns in the 10¹³-10¹⁵ M_☉ potential wells of massive galaxies and galaxy clusters.