Dynamical Modeling of NGC 7252 and the Return of Tidal Material

Abstract

Motivated by recent neutral hydrogen observations with the VLA, we have undertaken an investigation into the interaction that produced the well known merger remnant NGC 7252. Through fully self-consistent N-body simulations, we are able to reproduce the kinematic character of the HI observations quite well, including the velocity reversals observed along each tidal tail. In the simulation these reversals arise from particles which have turned around in their orbit and are moving to smaller radii. The bases of the tails fall back quickly to small pericentric distances, while the more distant regions fall back more slowly to ever increasing pericentric distances. The delayed return of tidally ejected material may extend over many Gyr. The evolution of this merger is followed numerically for 800 h^-1 Myr beyond the best fit time. We find that nearly half of the present tail material, or of order 10^9 h^-2 of neutral hydrogen and 2x10^9 h^-2 of starlight, will return to within 13 h^-1 kpc of the nucleus within this time span. While the collisionless stars of the tails will continue orbiting between their inner and outer turning points, the observations show the HI gas of the tails disappearing upon its return. We discuss this result in light of the lack of central HI in the main body of this merger remnant.Comment: 28 pages of uuencoded, compressed postscript. Accepted to AJ. 9 Postscript figures available upon request from hos@lick.ucsc.edu; postscript text also available from http://ucowww.ucsc.edu/~hos/home.htm

Tides in Colliding Galaxies

“…As a consequence, gaseous tails are more easily produced than stellar ones. Hibbard (1995) used the Very Large Array (VLA) to carry out one of the first systematic study of HI in pairs of galaxies. Observing systems of the so-called Toomre sequence (see Figure 3), he was able to reconstruct the evolution of the gaseous component during a merger.…”

Dynamics of Galaxy Interactions

“…This approach seems to work provided that the galaxy models and their trajectories are cosmologically plausible. One example is NGC 7252, which Hibbard & Mihos (1994) simulated successfully as the result of a direct parabolic encounter of two disk galaxies; an earlier attempt to reproduce this system with a retrograde encounter (Borne & Richstone 1991) required the galaxies to start on implausibly tight circular orbits and proved inconsistent with subsequent HI observations.…”

Star formation triggered by galaxy interactions in modified gravity

“…Numbers of studies in all wavebands have characterised the properties of interacting systems, in particular their star formation activity, with the aim of pinning down the underlying physical processes (e.g. Schombert et al 1990;Hibbard & Mihos 1995;Bournaud et al 2004;Chien et al 2007;Smith et al 2010;Boquien et al 2011;Saintonge et al 2012;Scudder et al 2012). …”