  The formation of tidal dwarf galaxies (TDG) inside tidal arms of interacting
disk galaxies has been studied with N-body and N-body/SPH simulations at
different resolutions. In pure N-body simulations no bound objects are formed
at high resolution. At low resolution bound objects can form in tidal tails in
agreement with previous work. We conclude that tidal dwarf galaxies are not
likely to form by pure collisionless collapse in tidal tails. However, the
presence of a sufficiently massive and extended gas component in the progenitor
disk supports the formation of bound stellar objects in the tidal arms. Our
results clearly favor a dissipation supported scenario in which the formation
of TDGs is induced by the local collapse of gas which then triggers the
collapse of the stellar component.
