Merging and stripping of haloes in binary galaxy systems

Abstract

N-body experiments of the collision of two systems composed of an isothermal halo surrounding a central particle with 5–10 per cent of the halo's mass are performed. The presence of the core slightly suppresses the interaction on the first crossing. Subsequent orbits decay, but on a timescale longer than dynamical friction would predict. The halo density beyond the softening radius of the core is reduced from the initial value by an average of about 30 per cent. The density distribution, in the vicinity of the cores, becomes shallower at maximum orbital separation. The orbital dynamics of the cores after the first crossing are well represented by a force given by a mass which increases linearly with radius, with the core particles on almost radial orbits. Integrated H I profiles used as indicators of rotation curves are consistent with the operation of this process.