On the Origin of Dynamically Cold Rings around the Milky Way

Abstract

We present a scenario for the production of dynamically cold ringsaround the Milky Way via a high-eccentricity, flyby encounter. Theseinitial conditions are more cosmologically motivated than thoseconsidered in previous works. We find that the encounters we examinegenerically produce a series of nearly dynamically cold ringlikefeatures on low-eccentricity orbits that persist over timescales of ~2-4Gyr via the tidal response of the primary galaxy to the close passage ofthe satellite. Moreover, they are both qualitatively and quantitativelysimilar to the distribution, kinematics, and stellar population of theMonoceros Ring. Therefore, we find that a high-eccentricity flyby by asatellite galaxy represents a cosmologically appealing scenario forforming kinematically distinct ringlike features around the Milky Way.