Ultra-Compact Dwarfs in the Fossil Group NGC 1132
  Eleven Ultra-Compact Dwarf (UCD) and 39 extended star cluster candidates are
found to be associated with the galaxy NGC 1132. This giant elliptical galaxy
is the remnant of a fossil group. UCD and extended star cluster candidates are
identified through the analysis of their structural parameters, colors, spatial
distribution, and luminosity using deep Hubble Space Telescope observations in
two filters: the F475W (Sloan g) and F850LP (Sloan z). The median effective
radius of these UCDs is r_h=13.0 pc. Two types of UCDs are identified in the
vicinity of NGC 1132, one type shares the same color and luminosity of the
brightest globular clusters and traces the onset of the mass-size relation. The
second kind of UCD is represented by the brightest UCD candidate, a M32-type
object, with an effective radius of r_h=77.1 pc, located at ~6.6 kpc from the
nucleus of NGC 1132. This UCD candidate is likely the remaining nucleus of a
minor merger with the host galaxy. With the exception of a particularly blue
UCD candidate, UCDs are found to extend the mass-metallicity relation found in
globular clusters to higher luminosities. The results of this work support the
growing body of evidence showing that UCDs are not circumscribed to galaxy
clusters as previously thought. UCDs are likely to be a common occurrence in
all environments. The milder tidal field of a fossil group, when compared to a
galaxy cluster, allows UCDs and extended star clusters to survive up to present
time at small galactocentric distances.
