Ultra-Compact Dwarfs around NGC 3258 in Antlia
  We present the first compact stellar systems with luminosities in the range
of ultra-compact dwarfs (UCDs), discovered in the Antlia galaxy cluster (-10.5
< M_V < -11.6). The magnitude limit between UCDs and globular clusters (CGs) is
discussed. By means of imaging from VLT (FORS1), CTIO (MOSAIC), and the HST
(ACS) archive, eleven UCDs/bright GCs are selected on the basis of photometry
and confirmed as Antlia members through radial velocities measured on new
GEMINI (GMOS-S) spectra. In addition, nine UCD candidates are identified taking
into account properties derived from their surface brightness profiles. All of
them, members and candidates, are located in the proximity of NGC\,3258, one of
the two brightest elliptical galaxies in the cluster core. Antlia UCDs in this
sample present absolute magnitudes fainter than M_V ~ -11.6 mag and most of
them have colours within the blue GC range, falling only two within the red GC
range. Effective radii measured for the ones lying on the ACS field are in the
range R_eff = 3 - 11 pc and are similar to equivalent objects in other
clusters, obtained from the literature. The UCD sample shares the same
behaviour on the size-luminosity plane: a linear relation between R_eff and M_V
is present for UCDs brighter than M_V ~ -10.5 - -11 mag while no trend is
detected for fainter ones, that have an approximately constant R_eff. The
projected spatial distribution of UCDs, GCs and X-ray emission points to an
ongoing merger between two Antlia groups, dominated by NGC 3258 and NGC 3268.
Nuclei of dwarf elliptical galaxies and blue UCDs share the same locus on the
colour-magnitude diagram, supporting the hypothesis that some blue UCDs may be
remnants of stripped nucleated dwarfs.
