Constraining Dark Halo Potentials with Tidal Tails

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Abstract
We present an extensive parameter survey of 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 Navarro, Frenk, & White 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. A galaxy with a rising or flat rotation curve dominated by the halo is inhibited from forming a tidal tail 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, 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 ve/vc 2.5 for tidal tails to be produced. The galaxy models that appear to fit most of the observational constraints are those that have disk-dominated rotation curves and low-concentration halos. We discuss our results in a cosmological context using recent studies that link halo properties to cosmological models.
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