PHYSICS OF GALACTIC COLLIDERS: HIGH-SPEED SATELLITES IN ΛCDM VERSUS MONDIAN COSMOLOGY

The statistics of high-speed satellite galaxies, as reported in the recent literature, can be a powerful diagnosis of the depth of the potential well of the host halo, and hence discriminate between competing gravitational theories. Naively one expects that high-speed satellites are more common in modified Newtonian dynamics (MOND) than in cold dark matter (CDM) since an isolated MONDian system has an infinite potential well, while CDM halos have finite potential wells. In this Letter, we report on an initial test of this hypothesis in the context of the first generation of cosmological simulations utilizing a rigorous MONDian Poisson solver. We find that such high-speed encounters are approximately a factor of 4 more common in MOND than in the concordance Lambda CDM model of cosmic structure formation.