  Among the various phenomena observed in interacting galaxies is the ejection
due to tidal forces of material into the intergalactic medium and its
subsequent rearranging which can lead to the formation of self-gravitating
tidal dwarf galaxies
  (TDGs). We investigate this process with a detailed multiwavelength study of
the interacting system Arp 245 (NGC 2992/3) and a numerical model of the
collision.
  The system is observed at an early stage of the interaction, about 100 Myr
after perigalacticon, though at a time when tidal tails have already developed.
  Our HI map shows prominent counterparts to the optical tails. Whereas the
stellar and gaseous components of the plume that originates from NGC 2992
match, the stellar and HI tails emanating from NGC 2993 have a different
morphology. In particular, the HI forms a ring, a feature that has been
successfully reproduced by our numerical simulations. The HI emission in the
system as a whole peaks at the tip of the NGC 2992 tail where a gas reservoir
of about
  10^9 Msun, about 60% of the HI towards NGC 2992, coincides with a
star-forming optical condensation,
  A245N. The latter tidal object exhibits properties ranging between those of
dwarf irregular galaxies (structural parameters, gas content, star formation
rate) and those of spiral disks
  (metallicity, star formation efficiency, stellar population). Prompted by the
questions raised for this particular object, we discuss some issues related to
the definition and identification of TDGs (abridged)
