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.

arXiv commentSubmitted to MNRAS Letters. 6 pages, 4 figures. Comments welcome

References in corpus (59)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• emcee: The MCMC Hammer
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Seventh Data Release of the Sloan Digital Sky Survey
• Overview of the DESI Legacy Imaging Surveys
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models
• 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
• The remnants of galaxy formation from a panoramic survey of the region around M31
• The APOSTLE simulations: solutions to the Local Group's cosmic puzzles
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• The Faintest Dwarf Galaxies
• 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
• The Dark Energy Survey Data Release 1
• A New Milky Way Dwarf Galaxy in Ursa Major
• A Faint New Milky Way Satellite in Bootes
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite?
• The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
• 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
• Discovery of an Unusual Dwarf Galaxy in the Outskirts of the Milky Way
• A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
• There is No Missing Satellites Problem
• The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater
• A quantitative explanation of the observed population of Milky Way satellite galaxies
• The Least Luminous Galaxy: Spectroscopy of the Milky Way Satellite Segue 1
• Pre-reionization Fossils, Ultra-faint Dwarfs and the Missing Galactic Satellite Problem
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• The ACS LCID project. III. The star formation history of the Cetus dSph galaxy: a post-reionization fossil
• PAndAS' progeny: extending the M31 dwarf galaxy cabal
• 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
• PAndAS' cubs: discovery of two new dwarf galaxies in the surroundings of the Andromeda and Triangulum galaxies
• Discovery of two neighboring satellites in the Carina constellation with MagLiteS
• The DECam Local Volume Exploration Survey: Overview and First Data Release
• Where are the Fossils of the First Galaxies? II. True Fossils, Ghost Halos, and the Missing Bright Satellites
• The PAndAS view of the Andromeda satellite system - I. A Bayesian search for dwarf galaxies using spatial and color-magnitude information
• Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
• Lacerta I and Cassiopeia III: Two luminous and distant Andromeda satellite dwarf galaxies found in the 3π Pan-STARRS1 survey
• The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I
• Where are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs
• Abundance matching with the mean star formation rate: there is no missing satellites problem in the Milky Way above ${\mathbf{M}}_{200}\sim 10^9{\mathbf{M}}_{\odot }$
• The abundance of satellites around Milky Way- and M31-like galaxies with the TNG50 simulation: a matter of diversity
• The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda II
• The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy
• The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda III
• Estimating the Mass of the Milky Way Using the Ensemble of Classical Satellite Galaxies
• Perseus I: A distant satellite dwarf galaxy of Andromeda
• Star Formation Histories of Ultra-Faint Dwarf Galaxies: environmental differences between Magellanic and non-Magellanic satellites?
• Sculpting Andromeda -- made-to-measure models for M31's bar and composite bulge: dynamics, stellar and dark matter mass
• Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey
• A rogues gallery of Andromeda's dwarf galaxies I. A predominance of red horizontal branches
• HST Imaging of the Local Volume Dwarf Galaxies Pisces A&B: Prototypes for Local Group Dwarfs
• A peculiar faint satellite in the remote outer halo of M31

Cited by in corpus (12)

• The Hubble Space Telescope Survey of M31 Satellite Galaxies I. RR Lyrae-based Distances and Refined 3D Geometric Structure
• Six More Ultra-Faint Milky Way Companions Discovered in the DECam Local Volume Exploration Survey
• 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
• A detailed star formation history of the distant Milky Way satellite Canes Venatici I: An old dwarf spheroidal forming most of its stars after reionisation