Are Complex A and the Orphan stream related?

Abstract

Abstract We consider the possibility that the Galactic neutral hydrogen stream Complex A and the stellar Orphan stream are related, and use this hypothesis to determine possible distances to Complex A and the Orphan stream, and line-of-sight velocities for the latter. The method presented uses our current knowledge of the projected positions of the streams, as well as line-of-sight velocities for Complex A, and we show that a solution exists in which the two streams share the same orbit. If Complex A and the Orphan stream are on this orbit, our calculations suggest the Orphan stream to be at an average distance of 9 kpc, with heliocentric radial velocities of approximately −95 km s−1. Complex A would be ahead of the Orphan stream in the same wrap of the orbit, with an average distance of 4 kpc, which is consistent with the distance constraints determined through interstellar absorption line techniques.