Dissipationless Formation of Elliptical Galaxies

Abstract

Since the cursory work of van Albada (1982), dissipationless formation of elliptical galaxies has been the subject of several investigations, performed by exploring various sets of initial conditions and with different numerical techniques. It is now well established that dissipationless collapse, starting from initial conditions that are cold enough, produces a final state characterized by a luminosity profile well-fitted by the R 1/4 law of elliptical galaxies (de Vaucouleurs, 1948, 1953). What is much less clear are the details of this process and in particular: what is the influence of inhomogeneities in the initial conditions? how does the final shape relates to the initial conditions? what is the distribution function describing the final system? In order to give an answer to these questions we have performed a large set of N-body simulations by using two-different N-body codes, both based on a spherical harmonics expansion of the gravitational potential and already extensively described in the literature (Londrillo, Messina, 1990; Bertin, Stiavelli, 1989). The use of grids able to resolve the cores, of large numbers of particles (typically 8 × 104), and of small time steps (often 20) half mass crossing times; iii) the final equilibrium system is characterized by positive temperature (Aguilar, Merritt, 1990).