Formation of dwarf ellipticals and dwarf irregular galaxies by
  interaction of giant galaxies under environmental influence
  A model is proposed for the formation of gas-rich dwarf irregular galaxies
and gas-poor, rotating dwarf elliptical galaxies following the interaction
between two giant galaxies as a function of space density. The formation of
dwarf galaxies is considered to depend on a random variable, the tidal index
theta, an environmental parameter defined by Karachentsev et al. (2004), such
that for theta less than zero, the formation of dwarf irregular galaxy is
assured whereas for theta greater than zero, the formation of dwarf ellipticals
is preferred. It is found that for particular ranges of the interactive
parameters the model predictions are in good agreement with the observed number
density of the different galaxy types as a function of space density in four
clusters of galaxies. This supports the fact that galaxy interactions do not
all necessarily give rise to the formation of either dwarf irregulars or dwarf
ellipticals. It is also shown that the formation of dwarf irregulars at high
densities is much lower than that of dwarf ellipticals, and that the formation
of the latter reaches a maximum at a particular space density, unlike the
former. This suggests that at high densities many dwarf irregulars are stripped
of their gaseous envelopes to become dwarf elliptical.
