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Cosmic Ménage à Trois: The Origin of Satellite Galaxies on Extreme Orbits

By Laura V. Sales, Julio F. Navarro, Mario G. Abadi and Matthias Steinmetz


We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of L ∗ galaxies in a ΛCDM universe. The numerical resolution of the simulations allows us to track in detail the orbits of the ∼ ten brightest satellites around each primary. Most satellites follow conventional orbits; after turning around, they accrete into their host halo and settle on orbits whose apocentric radii are steadily eroded by dynamical friction. As a result, satellites associated with the primary are typically found within its virial radius, rvir, and have velocities consistent with a Gaussian distribution with mild radial anisotropy. However, a number of outliers are also present. We find that a surprising number (about one-third) of satellites identified at z = 0 are on unorthodox orbits, with apocenters that exceed their turnaround radii. These include a number of objects with extreme velocities and apocentric radii at times exceeding ∼ 3.5 rvir (or, e.g., ∼> 1 Mpc when scaled to the Milky Way). This population of satellites on extreme orbits consists typically of the faint member of a satellite pair whose kinship is severed by the tidal field of the primary during first approach. Under the right circumstances, the heavier member of the pair remains bound to th

Year: 2008
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