Formation of ultra-compact blue dwarf galaxies and their evolution into
  nucleated dwarfs
  We propose that there is an evolutionary link between ultra-compact blue
dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on
the results of numerical simulations of dwarf-dwarf merging. We consider the
observational fact that low-mass dwarfs can be very gas-rich, and thereby
investigate the dynamical and chemical evolution of very gas-rich, dissipative
dwarf-dwarf mergers. We find that the remnants of dwarf-dwarf mergers can be
dominated by new stellar populations formed from the triggered starbursts and
consequently can have blue colors and higher metallicities (Z~[0.2-1]Z_sun). We
also find that the remnants of these mergers can have rather high
mass-densities (10^4 M_sun pc^-3) within the central 10 pc and small half-light
radii (40-100 pc). The radial stellar structures of some merger remnants are
similar to those of nucleated dwarfs. Star formation can continue in nuclear
gas disks (R<100 pc) surrounding stellar galactic nuclei (SGNs) so that the
SGNs can finally have multiple stellar populations with different ages and
metallicities. These very compact blue remnants can be identified as UCBDs soon
after merging and as nucleated dwarfs after fading of young stars. We discuss
these results in the context of the origins of metal-rich ultra-compact dwarfs
(UCDs) and SGNs.
