Constraining Dark Halo Potentials with Tidal Tails

Abstract

We present an extensive parameter survey to study the influence of halo mass profiles on the development of tidal tails in interacting disk galaxies. We model the galaxies using a fixed exponential disk with a central bulge and vary the halo potential over a range of parameters using both the Hernquist and NFW mass distributions, probing the effect of the halo mass, extent and concentration. We examine the consistency of the results against both observational and theoretical constraints on halo profiles and comment on the failures and weaknesses of different models. Galaxies with rising or flat rotation curves dominated by the halo are inhibited from forming tidal tails unless the halo is abruptly cut off just beyond the disk edge. Conversely, models with declining rotation curves -- resulting either from compact, low mass halos, or from massive disk components in low concentration dark halos -- produce tidal tails very similar to those observed in well-studied interacting systems. As argued by Springel & White (1998), a unifying, quantitative relation for all cases is that the ratio of the escape velocity to the circular velocity at around the solar radius must be v_e/v_c<2.5 for tidal tails to be produced. The galaxy models which appear to fit most of the observational constraints are those which have disk-dominated rotation curves and low concentration halos. We discuss our results in a cosmological context using recent studies which link halo properties to cosmological models.