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Chemodynamics of Compact Stellar Systems in NGC 5128: How Similar are Globular Clusters, Ultra-Compact Dwarfs, and Dwarf Galaxies?
Velocity dispersion measurements are presented for several of the mostluminous globular clusters (GCs) in NGC 5128 (Centaurus A) derived fromhigh-resolution spectra obtained with the UVES echelle spectrograph onthe 8.2 m ESO/Very Large Telescope. The measurements are made utilizinga penalized pixel-fitting method that parametrically recoversline-of-sight velocity dispersions. Combining the measured velocitydispersions with surface photometry and structural parameter data fromthe Hubble Space Telescope enables both dynamical masses andmass-to-light ratios to be derived. The properties of these massivestellar systems are similar to those of both massive GCs containedwithin the Local Group and nuclear star clusters and ultra-compact dwarfgalaxies (UCDs). The fundamental plane relations of these clusters areinvestigated in order to fill the apparent gap between the relations ofLocal Group GCs and more massive early-type galaxies. It is found thatthe properties of these massive stellar systems match those of nuclearclusters in dwarf elliptical galaxies and UCDs better than those ofLocal Group GCs, and that all objects share similarly old (gsim8 Gyr)ages, suggesting a possible link between the formation and evolution ofnuclear star clusters in dwarf elliptical galaxies (dE,Ns), UCDs, andmassive GCs. We find a very steep correlation between dynamicalmass-to-light ratio and dynamical mass of the form \Upsilon_{V}^dyn\!\propto \!{\cal M}_dyn^{0.24\pm 0.02} above {\calM}_dyn\!\approx \!2\times 10^6 M sun. Formation scenarios areinvestigated with a chemical abundance analysis using absorption-linestrengths calibrated to the Lick/IDS index system. The results lendsupport to two scenarios contained within a single general formationscheme. Old, massive, super-solar [?/Fe] systems are formed onshort (lsim100 Myr) timescales through the merging of single-collapseGCs which themselves are formed within single, giant molecular clouds.More intermediate- and old-aged (~3-10 Gyr), solar- to sub-solar[?/Fe] systems are formed on much longer (~Gyr) timescales throughthe stripping of dE,Ns in the 1013-1015 Msun potential wells of massive galaxies and galaxy clusters.Based on observations made with ESO Telescopes at the ParanalObservatories under program 69.D-0094 and 69.D-0196.
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