Remnants of Compact Group Type Mergers

Recent simulations by several authors who concentrated on extensive exploration of the merger remnant properties of two equal mass disks have been successful in accounting for several aspects of elliptical structure. However, the projected short merging timescales, typically only several half-mass crossing times, of dense, 4-6 member, low velocity dispersion clusters termed compact groups (CG) make them appealing candidates for elliptical progenitors. Self-consistent, high resolution, multi-component models of compact group type mergers have been simulated. Initially, the systems consist of 6 disk galaxies each with with bulge-disk-halo mass and particle number ratios of .333:1:5.8 and 16384:65536:65536, respectively. As in the case of two merging disks, the remnants evince many properties similar to those observed in ellipticals; light profiles, isophotal shapes, and velocity dispersions are comparable to fiducial elliptical values. The surface densities are fit well by a de Vaucouleurs R(1/4) law over a large range of radius, departing from it only in the very inner regions; and the remnant is supported by anisotropic velocity dispersion for the most part, the spin of the initial disks having been transferred to the halo by dynamical friction. In addition, CG remnants improve over previous models by reproducing the observed result that real ellipticals have angular momentum vectors nearly coincident with the minor axis and by suggesting a method of producing ellipticities that coincide more with the observed clustering around Hubble types n ~ 0-2. A small number of parameters are being varied systematically in order to study consequences of changing the internal structure and orientations of the galaxies. Further study will include analysis of metalicity and color gradients which may be imprinted on the original galaxies and examined in the remnant to elucidate the effect of incomplete violent relaxation. In addition, in order to determine the effects of dissipation, a gaseous component will be added to the disks in the initial progenitors.