Formation of emission line dots and extremely metal-deficient dwarfs
  from almost dark galaxies
  Recent observations have discovered a number of extremely gas-rich very faint
dwarf galaxies possibly embedded in low-mass dark matter halos. We investigate
star formation histories of these gas-rich dwarf ("almost dark") galaxies both
for isolated and interacting/merging cases. We find that although star
formation rates (SFRs) are very low (<10^-5 M_sun/yr) in the simulated dwarfs
in isolation for the total halo masses (M_h) of 10^8-10^9 M_sun, they can be
dramatically increased to be ~ 10^{-4} M_sun/yr when they interact or merge
with other dwarfs. These interacting faint dwarfs with central compact HII
regions can be identified as isolated emission line dots ("ELdots") owing to
their very low surface brightness envelopes of old stars. The remnant of these
interacting and merging dwarfs can finally develop central compact stellar
systems with very low metallicities (Z/Z_sun<0.1), which can be identified as
extremely metal-deficient ("XMD") dwarfs. These results imply that although
there would exist many faint dwarfs that can be hardly detected in the current
optical observations, they can be detected as isolated ELdots or XMD dwarfs,
when they interact with other galaxies and their host environments. We predict
that nucleated ultra-faint dwarfs formed from merging of almost dark dwarfs can
be identified as globular clusters owing to the very low surface brightness
stellar envelopes, if they are distant objects.
