Scl-dE1 GC1: An Extended Globular Cluster in a Low-Luminosity Dwarf
  Elliptical Galaxy
  We report the discovery from Hubble Space Telescope ACS images of an extended
globular cluster, denoted by Scl-dE1 GC1, in the Sculptor Group dwarf
Elliptical galaxy Scl-dE1 (Sc22). The distance of the dE is determined as 4.3
+/- 0.25 Mpc from the I magnitude of the tip of the red giant branch in the
color-magnitude diagram. At this distance the half-light radius of Scl-dE1 GC1
is ~22 pc, placing it among the largest clusters known, particularly for
globular clusters associated with dwarf galaxies. The absolute magnitude of
Scl-dE1 GC1 is Mv = -6.7 and, to within the photometric uncertainties of the
data, the cluster stellar population appears indistinguishable from that of the
dE. We suggest that there may be two modes of globular cluster formation in
dwarf galaxies, a "normal" mode with half-light radii of typically 3 pc, and an
"extended" mode with half-light radii of ~10 pc or more.
