Tidal Interaction as the origin of early-type dwarf galaxies in group
  environment
  We present a sample of dwarf galaxies that suffer ongoing disruption by the
tidal force of nearby massive galaxies. Analysing structural and stellar
population properties using the archival imaging and spectroscopic data from
the Sloan Digital Sky Survey (SDSS), we find that they are likely a `smoking
gun' example of the formation of early-type dwarf galaxies (dEs) in the galaxy
group environment through the tidal stirring. Inner cores of these galaxies are
fairly intact and the observed light profiles are well fitted with the Sersic
functions, while the tidally stretched stellar halos are prominent in the outer
parts. They are all located within the 50 kpc sky-projected distance from the
center of host galaxies and no dwarf galaxies have relative line-of-sight
velocity larger than 205 km/s to their hosts. We derive the Composite Stellar
Population (CSP) properties these galaxies by fitting the SDSS optical spectra
to a multiple-burst composite stellar population model. We find that these
galaxies accumulate a significant fraction of stellar mass within the last 1
Gyr, while they contain a majority stellar population of intermediate age of 2
to 4 Gyr. With these evidences, we argue that tidal stirring, particularly
through the galaxy-galaxy interaction, might have an important role in the
formation and evolution of dEs in the group environment, where the influence of
other gas stripping mechanism might be limited.
