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

Simon E. T. Smith; Alan W. McConnachie; Stephen Gwyn; Christian R. Hayes; Massimiliano Gatto; Ken Chambers; Jean-Charles Cuillandre; Michael J. Hudson; Eugene Magnier; Nicolas Martin; Julio Navarro

arXiv · 2502.09792

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

Simon E. T. Smith·Alan W. McConnachie·Stephen Gwyn·Christian R. Hayes·Massimiliano Gatto·Ken Chambers·Jean-Charles Cuillandre·Michael J. Hudson·Eugene Magnier·Nicolas Martin·Julio Navarro

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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.

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Simon E. T. Smith, Alan W. McConnachie, Stephen Gwyn, Christian R. Hayes, Massimiliano Gatto, Ken Chambers, Jean-Charles Cuillandre, Michael J. Hudson, Eugene Magnier, Nicolas Martin, Julio Navarro. 2025-02-13. Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS. https://arxiv.org/abs/2502.09792

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