Articulo
Merging instability in groups of galaxies with dark matter
Registro en:
issn:1669-9521
Autor
Navarro, J.
Mosconi, M.
García-Lambas, D.
Institución
Resumen
Several N-body experiments were performed in order to analyze the importance of smoothly distributed dark matter on the merging processes in groups of galaxies. We simulated groups of galaxies as self-gravitating systems of softened point masses with average intergalactic distance (Dₘ) ranging between 10 and 30 in units of the mean galactic half mass radius, and a cluster velocity dispersion to mean galactic internal velocity dispersion ratio (V_cl/σ_g) of about 2. A giant central galaxy ('cannibal') develops in less than a free fall time τ_ff when no background of dark matter is present. Only the galaxies which could acquire escape velocity, and thus leave the system, can avoid merging with the cannibal. This situation arises regardless of the initial dynamical conditions were imposed, which ranged from 'cold' models (all galaxies at rest) to equilibrium models (started with galaxies in virial equilibrium). We also tried initial conditions in which galaxies were moving in random directions with random velocity (rnd models) and found no difference in the time-scale of the process mentioned above. Thus groups of galaxies with no background cannot avoid merging into a single unit in a time-scale (∼ 1 τ_ff) much shorter than the expected life of such systems. The efficiency of the merging process is remarkably diminished when the effects of a massive background are included in the simulations. The more important the background in the dynamics of the system, the longer the system can stand without being cannibalized by a continuously growing galaxy, although keeping similar initial values for Dₘ and V_cl/σ_g. However when such a galaxy has 'eaten' about half of the mass in form of a galaxy, the process accelerates itself and the cannibal is rapidly formed. So, it must be concluded that such a dominant background is actually present if groups of galaxies are, as commonly assumed, older than five crossing times, because systems in which most of the mass is concentrated in galaxies appear to be largely unstable to merging. Asociación Argentina de Astronomía