Properties of Early-Type, Dry Galaxy Mergers and the Origin of Massive Elliptical Galaxies

The luminosity dependence of kinematic and isophotal properties of elliptical galaxies is investigated using numerical simulations of galaxy merging, combined with semianalytical models of hierarchical structure formation. Mergers of spiral galaxies as the only formation mechanism for elliptical galaxies can reproduce neither the kinematic and photometric properties of very massive elliptical galaxies nor the change from rotationally flattened, disky systems to anisotropic, boxy systems with increasing luminosity. We present numerical simulations showing that binary mergers of early-type galaxies open an additional channel for the formation of anisotropic, slowly rotating, boxy elliptical galaxies. Including this channel in a semianalytical model, we can successfully reproduce the observed trend that more luminous giant elliptical galaxies are more boxy and less flattened by rotation. This trend can be more strongly reproduced by suppressing residual gas infall and star formation for galaxies with stellar bulge masses M* ≥ 3 × 1010 M☉. Hence we propose that mergers of early-type galaxies play an important role in the assembly of massive elliptical galaxies.

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