On the Formation of Boxy and Disky Elliptical Galaxies

Abstract

N-body simulations of major spiral-spiral mergers with different mass ratios q <= 4:1 are presented. All mergers lead to spheroidal stellar systems with de Vaucouleurs-like surface density profiles, resembling elliptical galaxies. The internal dynamical structure of the remnants does however depend critically on the adopted mass ratio. Equal-mass mergers with q <= 2:1 form radially anisotropic, slowly rotating systems with preferentially boxy isophotes. Unequal-mass mergers with q > 2:1 result in the formation of rotationally supported ellipticals with disky isophotes and small minor axis rotation. Projection effects lead in general to a large scatter in the kinematical and isophotal properties. If the observed dichotomy between boxy and disky ellipticals is a result of different mass ratios of the merger components massive ellipticals must have formed preferentially from equal-mass mergers in contrast to low-mass ellipticals which had to form from unequal-mass mergers.