TIDAL TALES 2 - THE EFFECT OF DARK-MATTER HALOS ON TIDAL TAIL MORPHOLOGY AND KINEMATICS

We examine the effect of different dark matter halo potentials on the morphology and kinematics of tidal tails in a merger model of NGC 7252 . We find that models of merging galaxies with low halo masses of M-h similar to 4 - 8 Mdisk+bulge(Mdb) can fit the observed morphology and kinematics of the NGC 7252 tails, while galaxies with high-mass halos (M-h similar to 16 - 32 M-db) fail in this respect. In high-mass model s, the deep potential only allows weakly bound disk material (stars or gas) at R greater than or similar to 5 disk scale lengths to be eject ed in tidal tails that tend to fall back onto the parent galaxies befo re the final merger. Galaxies with massive, low-density halos are some what more successful at ejecting tidal debris during mergers, but they still have difficulties recreating the thin, gas-rich tails observed in NGC 7252. Our models suggest upper limits for the dark halo masses in the NGC 7252 progenitor galaxies of roughly M-h less than or simila r to 10 M-db. We note, however, that our calculations have focused on the rather idealized case of the isolated merging of galaxies with dis tinct dark matter halos; calculations that employ more realistic (''co smological'') initial conditions are needed to fully explore the use o f tidal tails in constraining dark matter in galaxies.