Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS

TL;DR

The paper reports the discovery of Pegasus VII, a dwarf galaxy near M31, characterized by its size, luminosity, and potential tidal interaction, expanding knowledge of satellite galaxies in the Andromeda system.

Contribution

This study introduces Pegasus VII as a newly identified dwarf galaxy in the M31 subgroup, confirmed through multi-telescope imaging and detailed its properties and possible tidal features.

Findings

Pegasus VII has an absolute magnitude of -5.7 mag.

It has a half-light radius of about 177 pc.

The galaxy shows elongation suggestive of tidal interaction.

Abstract

We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group 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 $-5.7 \pm 0.2$ mag and a physical half-light radius of $177^{+36}_{-34}$ 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 $331^{+15}_{-4}$ kpc and a significant elongation ($\epsilon \sim 0.5$) towards 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.