  Aim: To extend the investigations of ultra-compact dwarf galaxies (UCDs)
beyond the well studied Fornax and Virgo clusters. Methods: We measured
spectroscopic redshifts of about 400 compact object candidates with 19.2 < V <
22.4 mag in the central region of the Centaurus galaxy cluster (d=43Mpc), using
VIMOS@VLT. The luminosity range of the candidates covers that of bright
globular clusters (GCs) and of UCDs in Fornax and Virgo. Results: We confirm
the cluster membership of 27 compact objects, covering an absolute magnitude
range -12.2 < M_V < -10.9 mag. We do not find counterparts to the two very
large and bright UCDs in Fornax and Virgo with M_V=-13.5 mag, possibly due to
survey incompleteness. The compact objects' distribution in magnitude and space
is consistent with that of the GC population. Their kinematics and spatial
distribution associate them to the central galaxies rather than to the overall
cluster potential. The compact objects have a mean metallicity consistent with
that of the metal-rich globular cluster sub-population. Compact objects with
high S/N spectra exhibit solar [alpha/Fe] abundances, consistent with typical
dwarf elliptical galaxy values and unlike galactic bulge globular clusters. HST
based size estimates for a sub-sample of eight compact objects reveal the
existence of one very large object with half-light radius r_h around 30 pc,
having M_V=-11.6 mag (~10^7 M_sun). This source shows super-solar [alpha/Fe]
abundances. Seven further sources are only marginally larger than typical GCs
with r_h in the range 4 to 10 pc. Conclusions: We consider the largest compact
object found to be the only bona-fide UCD detected in our study. In order to
improve our understanding of UCDs in Centaurus, a significant increase of our
survey completeness is necessary.
