Dynamical friction in a non-rotating triaxial galaxy: the effect on box orbits

Abstract

We investigate the effect of dynamical friction in the deceleration of globular clusters on box orbits in triaxial potentials, by means of numerical computations in Schwarzschild's self-consistent model. We show that, because of lack of conservation of angular momentum, GCs pass inside the galactic core where they are powerfully decelerated. Typical energy decay times are 10 times shorter than for roundish loop orbits of comparable energy. We also derive an analytic approximation for the energy decay time, and show that it is independent of the detailed shape of the orbit, and of the detailed velocity structure of the underlying galactic model. Also, it scales as |$\propto \,M_\text{GC}^{-1}$|⁠, thus selectively destroying heavier ones. This mechanism thus preferentially acts to destroy heavy GCs, on radial-pointing orbits, in the central regions of galaxies. It is suggested that it may thus be responsible, possibly in conjunction with tidal shocks, for the large core radii and peculiar velocity ellipsoids of GCs observed in several galaxies.