Global Properties of Multiple Merger Remnants

Not all the observed properties of elliptical galaxies are reproduced by simulations that seek the origins of early-type galaxies by merging. Here, the merger remnants of small groups of galaxies are contrasted with relics of mergers of pairs of galaxies to determine which process produces objects that best compare to real ellipticals. In both cases, the progenitors consist of self-gravitating disks, halos, and, sometimes, bulges. Pairs of galaxies merge from orbits that initially have zero energy. The systems that produce multiple merger remnants are dense, six- member groups in virial equilibrium with low velocity dispersions. Multiple and pair mergers produce remnants that differ in both their spatial and kinematic properties. Multiple merger remnants have small triaxialities and are most likely to appear nearly round from many viewing angles. They possess cores, with sizes of a few tenths of an effective radius, that are more extended than pair remnant cores, even when bulges are included in the progenitors. In multiple mergers, the spin of all components-halo, disk, and bulge-increases, and, while velocity dispersion dominates in the central regions, υ_r_/σ ~1 outside an effective radius in some projections. The angular momentum and minor axis vectors are aligned for multiple merger remnants. This is unlike the remnants of pair mergers. During merging of multiple progenitors, about half of the orbital angular momentum in each luminous component is converted into internal rotation in that component. Material is prevented from accumulating in the center of multiple merger remnants as efficiently as it does in pair mergers. In previous simulations of pair mergers that include gas, unrealistically steep surface brightness profiles have been produced in the center of the remnants; in multiple mergers, the formation of overdense nuclei may be impeded, thus allowing more successful comparison with real elliptical galaxies.