Dwarf Galaxies and Globular Clusters in High Velocity Hydrogen Streams

Abstract

The dwarf spheroidal galaxies Draco and Ursa Minor lie in a stream of high velocity clouds, while Sculptor lies within 3° of the Magellanic stream. Of the distant diffuse globular clusters, Palomar 13 lies in the tail of the Magellanic stream, while Palomar 1 lies in another prominent northern stream. Four farther distant globulars of concentration class XII appear to be unrelated. Using the known distances to the optical objects, the parallaxes due to the offset of the Sun from galactic centre are calculated. Not only the Magellanic stream, but also Sculptor and the Draco–Ursa Minor stream are then seen to lie in a plane which is presumably the plane of the orbit of the Magellanic Clouds about the galactic centre. By demanding that all points of the Magellanic stream be precisely in the plane defined by the galactic centre Palomar 13 and the centre of the mass of the Magellanic Clouds, the distances to all points of the stream are calculated from parallax. With both radial velocities and distances known to so many points on the stream, it seems likely that dynamical modelling will yield a much more accurate total mass for the Galaxy.