DJ.1.02 — Encounter Dynamics and Tidal Response as Functions of Galaxy Structure

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Aug 7th at 10:55 AM until 11:15 AM

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Author(s): Joshua Edward Barnes1

Institution(s): 1. University of Hawaii at Manoa

Tidal interactions between disk galaxies are known to depend on galaxy structure, but the details of this relationship are incompletely understood. I have constructed a three-parameter grid of bulge/disk/halo models broadly consistent with ΛCDM, and simulated an extensive series of encounters using these models. Halo mass and extent strongly influence the dynamics of orbit evolution. In close encounters, the transfer of angular momentum mediated by the dynamical response of massive, extended halos can actually reverse the direction of orbital motion of the central galaxies following their first passage. Tidal response is strongly correlated with the ratio ve/vc of escape to circular velocity within the participating disks. Moreover, the same ratio also correlates with the rate at which tidal tails are reaccreted by their galaxies of origin; consequently, merger remnants with prominent ``twin tails'', such as NGC 7252, are hard to reproduce unless (ve/vc)2 ≤ 5.5. The tidal morphology of an interacting system can provide useful constraints on progenitor structure. In particular, encounters in which halo dynamics reverses orbital motion exhibit a distinctive morphology which may be recognized observationally. Detailed models attempting to reproduce observations of interacting galaxies should explore the likely range of progenitor structures along with the encounter parameters.