Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda

Abstract

We report the discovery of an ultra-faint dwarf in the constellation of Pegasus. Pegasus~V (Peg~V) was initially identified in the public imaging data release of the DESI Legacy Imaging Surveys and confirmed with deep imaging from Gemini/GMOS-N. The colour-magnitude diagram shows a sparse red giant branch (RGB) population and a strong over-density of blue horizontal branch stars. We measure a distance to Peg~V of $D=692_{-31}^{+33}$~kpc, making it a distant satellite of Andromeda with $M_V=-6.3\pm 0.2$ and a half-light radius of $r_{\mathrm{half}}=89\pm 41$~pc. It is located $\sim 260$~kpc from Andromeda in the outskirts of its halo. The RGB is well-fit by a metal-poor isochrone with [Fe/H]$=-3.2$, suggesting it is very metal poor. This, combined with its blue horizontal branch could imply that it is a reionisation fossil. This is the first detection of an ultra-faint dwarf outside the deep Pan-Andromeda Archaeological Survey area, and points to a rich, faint satellite population in the outskirts of our nearest neighbour.

Submitted to MNRAS Letters. 6 pages, 4 figures. Comments welcome

References in corpus (18)

• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• The Invisibles: A Detection Algorithm to Trace the Faintest Milky Way Satellites
• Leo V: A Companion of a Companion of the Milky Way Galaxy
• The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies
• A trio of new Local Group galaxies with extreme properties
• The DECam Local Volume Exploration Survey: Overview and First Data Release
• Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
• The abundance of satellites around Milky Way- and M31-like galaxies with the TNG50 simulation: a matter of diversity
• The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy
• Star Formation Histories of Ultra-Faint Dwarf Galaxies: environmental differences between Magellanic and non-Magellanic satellites?
• Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey
• HST Imaging of the Local Volume Dwarf Galaxies Pisces A&B: Prototypes for Local Group Dwarfs

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• The Hubble Space Telescope Survey of M31 Satellite Galaxies I. RR Lyrae-based Distances and Refined 3D Geometric Structure
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• Pegasus W: An Ultra-Faint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization
• Discovery of a new Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V
• The PAndAS View of the Andromeda Satellite System. IV Global properties
• Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
• Observational Signatures of Massive Black Hole Progenitor Pathways: Could Leo I a Smoking Gun?
• Andromeda's asymmetric satellite system as a challenge to cold dark matter cosmology
• Andromeda XXXV: The Faintest Dwarf Satellite of the Andromeda Galaxy
• Environmental Quenching of Low Surface Brightness Galaxies near Milky Way mass Hosts
• Chemodynamics of BoötesI with $S^5$: Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints