N-body simulations of globular cluster tides

Abstract

We present N-body simulations of globular clusters, in orbits around the Galaxy, in order to study quantitatively and geometrically the tidal effects they encounter. The clusters are modelised with multi-mass King-Michie models (Michie 1963), including mass segregation at initial conditions. The Galaxy is modelled as realistic as possible, with three components: bulge, disk and dark halo. The main finding is that there exist two giant tidal tails around the globuler cluster in permanence along its orbit, whatever this orbit. The length of these tails is of the order of 5 tidal radii, or greater. The escaped stars are distributed radially as a power law in density, with a slope of -4. The tails present substructures, or clumps, that are the relics of the strongest shocks. Due to the compressive disk-shocking, the clusters display a prolate shape which major axis is precessing around the z axis. The tails are preferentially formed by the lowest mass stars, as expected, so that the tidal truncation increases mass segregation. Internal rotation of the cluster increases the mass loss. The flattening of dark matter cannot influence significantly the dynamics of the clusters. The orientation and the strength of the tidal tails are signatures of the last disk crossing, so that observed tidal tails can constrain strongly the cluster orbit and the galactic model (vertical scale of the disc).