Tides or dark matter sub-halos: Which ones are more attractive?
  Young tidal dwarf galaxies (TDGs) are observed in the tidal debris of
gas-rich interacting galaxies. In contrast to what is generally assumed to be
the case for isolated dwarf galaxies, TDGs are not embedded in their own dark
matter (DM) sub-halo. Hence, they are more sensitive to stellar feedback and
could be disrupted on a short time-scale. Detailed numerical and observational
studies demonstrate that isolated DM-dominated dwarf galaxies can have
lifetimes of more than 10 Gyr. For TDGs that evolve in a tidal field with
compressing accelerations equal to the gravitational acceleration within a DM
sub-halo typical of an isolated dwarf galaxy, a similar survival time is
expected. The tidal acceleration profile depends on the virial mass of the host
galaxy and the distance between the TDG and its host. We analytically compare
the tidal compression to the gravitational acceleration due to either cuspy or
cored DM sub-halos of various virial masses. For example, the tidal field at a
distance of 100 kpc to a host halo of 10^13 Msol can be as stabilizing as a
10^9 Msol DM sub-halo. By linking the tidal field to the equivalent
gravitational field of a DM sub-halo, we can use existing models of isolated
dwarfs to estimate the survivability of TDGs. We show that part of the
unexpectedly high dynamical masses inferred from observations of some TDGs can
be explained by tidal compression and hence TDGs require to contain less
unobservable matter to understand their rotation curves.
