Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII Dwarf Galaxy in UNIONS

Abstract

We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 subgroup which has been uncovered in the ri photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada–France–Hawaii Telescope and the Gemini-North Telescope. This system has an absolute V -band magnitude of −5.7 ± 0.2 mag and a physical half-light radius of 177 ${}_{-34}^{+36}$ pc, which is characteristic of dynamically confirmed Milky Way satellite dwarf galaxies and about 5 times more extended than the most extended M31 globular clusters. Peg VII lies at a three-dimensional separation from M31 of 331 ${}_{-4}^{+15}$ kpc, and a significant elongation ( ϵ ∼ 0.5) toward the projected direction of M31 could be indicative of a past tidal interaction, but additional investigation into the orbit, star formation history, and whether any gas remains in the galaxy is needed to better understand the evolution of Peg VII.

Keywords

• Dwarf galaxies
• Local Group