On the density structure of galaxy merger remnants

N-body simulations of merging encounters suggest that deviations from the r1/4 law in the brightness profiles of elliptical galaxies at large radius are generated by mergers as well as by passing encounters. These deviations are the transitory result of the radial mixing of particles on to less-bound orbits, and the progressive decay with radius on the local dynamical time-scale. The effective radius (Reff) of merger remnants increases approximately linearly with mass, which indicates that a bright elliptical galaxy formed by the successive amalgamation of similar ‘normal’ ellipticals would move off Kormendy's relation in the |$({R}_\text{eff,}\,\Sigma _\text{e})$|⁠,plane (Σe stands for the effective surface brightness. The location of brightest cluster members in the |$({R}_\text{eff,}\,\Sigma _\text{e})$| plane is thus consistent with the idea that they have experienced several mergers in the past.