Leo V: A Companion of a Companion of the Milky Way Galaxy?

Abstract

We report the discovery of a new Milky Way satellite in the constellation Leo, identified in data from the Sloan Digital Sky Survey. It lies at a distance of ~180 kpc, and is separated by 3° from another recent discovery, Leo IV. We present follow-up imaging from the Isaac Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at the Multiple Mirror Telescope. Leo V's heliocentric velocity is ~173.3 ± 3.1 km s⁻¹, offset by ~40 km s⁻¹ from that of Leo IV. A simple interpretation of the kinematic data is that both objects may lie on the same stream, although the implied orbit is only modestly eccentric (e ~ 0.2)