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For refcode 1993ApJ...416...17B:
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1993ApJ...416...17B SIMULATIONS OF COMPACT GROUPS OF GALAXIES: THE EFFECT OF THE DARK MATTER DISTRIBUTION PAUL W. BODE, HALDAN N. COHN, AND PHYLLIS M. LUGGER Astronomy Department, Indiana University, Bloomington, IN 47405 Received 1993 January 27: accepted 1993 April 19 ABSTRACT The dynamical evolution of compact groups, beginning from virial equilibrium, is explored by using self-consistent N-body simulations employing Hernquist's implementatIon of the Barnes-Hut tree algorithm. A total N = 5000 particles is used to represent both galaxies and a smoothly distributed intracluster background (ICB). The ICB mass fraction, {beta}, is varied from 0 to 0.9, with all the models beginning in a virialized state. The first merger occurs near the center of the cluster; the product of this merger is quickly involved in further merging. This process is found to take longer as less of the cluster mass is put into the galaxy halos. For {beta} = 0 the second merger can occur within one dynamical time (~0.4 Gyr), while for {beta} = 0.75 it occurs after two dynamical times. Increasing {beta} from 0.75 to 0.90 delays the onset of merging by a greater amount; merging. begins only after 3-5 dynamical times in the latter case. This delay in merging is consistent with the lengthening of the dynamical friction time scale as galaxy masses are reduced. Stripping of mass from galaxies has less effect than merging does on the evolution. When the projected median separations and line-of-sight velocity dispersions of the models are scaled to be similar to those of Hickson's groups, the crossing times are longer than is observed. The range of values taken on by these parameters shows little dependence on {beta}. The merging histories of models with 10 galaxies behave in a similar fashion to those of the five-galaxy groups. Subject headings: galaxies: clustering - numerical methods
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