Tidal Dwarf Galaxies: Disc Formation at z=0
  Collisional debris around interacting and post-interacting galaxies often
display condensations of gas and young stars that can potentially form
gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent
results on TDGs, which are originally published in Lelli et al. (2015, A&A). We
study a sample of six TDGs around three different interacting systems, using
high-resolution HI observations from the Very Large Array. We find that the HI
emission associated to TDGs can be described by rotating disc models. These
discs, however, would have undergone less than one orbit since the time of the
TDG formation, raising the question of whether they are in dynamical
equilibrium. Assuming that TDGs are in dynamical equilibrium, we find that the
ratio of dynamical mass to baryonic mass is consistent with one, implying that
TDGs are devoid of dark matter. This is in line with the results of numerical
simulations where tidal forces effectively segregate dark matter in the halo
from baryonic matter in the disc, which ends up forming tidal tails and TDGs.
