Tidal Tales Two: The Effect of Dark Matter Halos on Tidal Tail Morphology and Kinematics

Abstract

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 ∼ 4-8 M disk+bulge (M db ) can fit the observed morphology and kinematics of the NGC 7252 tails, while galaxies with high-mass halos (M h ∼ 16-32 M db ) fail in this respect. In high-mass models, the deep potential only allows weakly bound disk material (stars or gas) at R ≳ 5 disk scale lengths to be ejected in tidal tails that tend to fall back onto the parent galaxies before the final merger. Galaxies with massive, low-density halos are somewhat 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 ≲ 10 M db . We note, however, that our calculations have focused on the rather idealized case of the isolated merging of galaxies with distinct dark matter halos; calculations that employ more realistic ("cosmological") initial conditions are needed to fully explore the use of tidal tails in constraining dark matter in galaxies. © 1998. The American Astronomical Society. All rights reserved.