Six More Ultra-Faint Milky Way Companions Discovered in the DECam Local Volume Exploration Survey

Abstract

We report the discovery of six ultra-faint Milky Way satellites discovered through matched-filter searches conducted using Dark Energy Camera (DECam) data processed as part of the second data release of the DECam Local Volume Exploration (DELVE) survey. Leveraging deep Gemini/GMOS-N imaging (for four candidates) as well as follow-up DECam imaging (for two candidates), we characterize the morphologies and stellar populations of these systems. We find that these candidates all share faint absolute magnitudes ($M_V\ge -3.2$ mag) and old, metal-poor stellar populations ($\tau >10$ Gyr, [Fe/H] $<-1.4$ dex). Three of these systems are more extended ($r_{1/2}>15$ pc), while the other three are compact ($r_{1/2}<10$ pc). From these properties, we infer that the former three systems (Boötes V, Leo Minor I, and Virgo II) are consistent with ultra-faint dwarf galaxy classifications, whereas the latter three (DELVE 3, DELVE 4, and DELVE 5) are likely ultra-faint star clusters. Using data from the Gaia satellite, we confidently measure the proper motion of Boötes V, Leo Minor I, and DELVE 4, and tentatively detect a proper motion signal from DELVE 3 and DELVE 5; no signal is detected for Virgo II. We use these measurements to explore possible associations between the newly-discovered systems and the Sagittarius dwarf spheroidal, the Magellanic Clouds, and the Vast Polar Structure, finding several plausible associations. Our results offer a preview of the numerous ultra-faint stellar systems that will soon be discovered by the Vera C. Rubin Observatory and highlight the challenges of classifying the faintest stellar systems.

arXiv comment30 pages, 12 Figures (including Appendix). Submitted to ApJ. We encourage the reader to also review Smith et al. 2022, "Discovery of a new Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V" (arxiv: 2209.08242), who independently present the discovery of one of the candidates reported here. We are working to make code and data products available

References in corpus (109)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• The Sloan Digital Sky Survey: Technical Summary
• Galactic Stellar and Substellar Initial Mass Function
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The Aquarius Project: the subhalos of galactic halos
• The observed properties of dwarf galaxies in and around the Local Group
• Overview of the DESI Legacy Imaging Surveys
• Mass function of dark matter halos
• Gaia Early Data Release 3: The astrometric solution
• The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Formation and evolution of galaxy dark matter halos and their substructure
• The Faintest Dwarf Galaxies
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• A comprehensive Maximum Likelihood analysis of the structural properties of faint Milky Way satellites
• The Dark Energy Survey Data Release 1
• Internal Dynamics of Globular Clusters
• 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 VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• The Dark Energy Survey Data Release 2
• Tango for three: Sagittarius, LMC, and the Milky Way
• Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
• Assessing the Milky Way Satellites Associated with the Sagittarius Dwarf Spheroidal Galaxy
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• The Dark Energy Survey Image Processing Pipeline
• "Galaxy," Defined
• Accreted versus In Situ Milky Way Globular Clusters
• Pre-reionization Fossils, Ultra-faint Dwarfs and the Missing Galactic Satellite Problem
• Target Selection and Validation of DESI Quasars
• A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• The ACS LCID project. III. The star formation history of the Cetus dSph galaxy: a post-reionization fossil
• The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions
• Target Selection and Validation of DESI Emission Line Galaxies
• Building up the globular cluster system of the Milky Way. The contribution of the Sagittarius galaxy
• Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1
• The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies
• Dark matter substructure and dwarf galactic satellites
• A Magellanic Origin of the DES Dwarfs
• Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud
• Willman 1 - a probable dwarf galaxy with an irregular kinematic distribution
• The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies
• Discovery of two neighboring satellites in the Carina constellation with MagLiteS
• Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• The Caterpillar Project: A Large Suite of Milky Way Sized Halos
• The DECam Local Volume Exploration Survey: Overview and First Data Release
• The Near Infrared Ca II Triplet as Metallicity Indicator: II Extension to extremely metal-poor metallicity regimes
• The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2
• Limit on the LMC mass from a census of its satellites
• Chemical Abundances in the Ultra-Faint Dwarf Galaxies Grus I and Triangulum II: Neutron-Capture Elements as a Defining Feature of the Faintest Dwarfs
• Too Many, Too Few, or Just Right? The Predicted Number and Distribution of Milky Way Dwarf Galaxies
• Tidal Signatures in the Faintest Milky Way Satellites: The Detailed Properties of Leo V, Pisces II and Canes Venatici II
• Identifying true satellites of the Magellanic Clouds
• Revised and new proper motions for confirmed and candidate Milky Way dwarf galaxies
• Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
• A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III
• Gaia EDR3 proper motions of Milky Way dwarfs I: 3D Motions and Orbits
• Proper motions of Milky Way Ultra-Faint satellites with $Gaia$ DR2 $\times$ DES DR1
• A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
• Pristine Dwarf-Galaxy Survey I: A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite
• Modeling the Connection Between Subhalos and Satellites in Milky Way-like Systems
• The DECam Local Volume Exploration Survey Data Release 2
• The First Tidally Disrupted Ultra-Faint Dwarf Galaxy? - Spectroscopic Analysis of the Tucana III Stream
• Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V
• Gaia 1 and 2. A pair of new Galactic star clusters
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• Ships Passing in the Night: Spectroscopic Analysis of Two Ultra-Faint Satellites in the Constellation Carina
• A new Milky Way halo star cluster in the Southern Galactic Sky
• A Hero's Little Horse: Discovery of a Dissolving Star Cluster in Pegasus
• Boötes IV: A New Milky Way Satellite Discovered in the Subaru Hyper Suprime-Cam Survey and Implications for the Missing Satellite Problem
• The Discovery of an Ultra-Faint Star Cluster in the Constellation of Ursa Minor
• Segue 3: An Old, Extremely Low luminosity Star Cluster in the Milky Way's Halo
• On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus III and Tucana V
• Star Formation Histories of Ultra-Faint Dwarf Galaxies: environmental differences between Magellanic and non-Magellanic satellites?
• Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus
• A Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC
• Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey
• Eridanus II: A Fossil from Reionization with an Off-Center Star Cluster
• A Deeper Look at Leo IV: Star Formation History and Extended Structure
• The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
• Nine tiny star clusters in Gaia DR1, PS1 and DES
• Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D$\approx$1.4 Mpc
• Deep Subaru Hyper Suprime-Cam observations of Milky Way satellites Columba I and Triangulum II
• Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Discovery of Three Ultra-faint Dwarf Galaxies
• The Milky Way's stellar streams and globular clusters do not align in a Vast Polar Structure
• The Pristine Dwarf-Galaxy survey -- III. Revealing the nature of the Milky Way globular cluster Sagittarius II
• Stellar mass segregation as separating classifier between globular clusters and ultra-faint dwarf galaxies
• Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda
• A Deeper Look at DES Dwarf Galaxy Candidates: Grus I and Indus II
• Signatures of Tidal Disruption in Ultra-Faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V
• On The Nature of ultra-faint Dwarf Galaxy Candidates II: The case of Cetus II
• Physical characterization of recently discovered globular clusters in the Sagittarius dwarf spheroidal galaxy II. Metallicities, ages and luminosities
• Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
• Short period variability in the globular cluster NGC 419 and the SMC field
• The Elusive Distance Gradient in the Ultra-Faint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View
• Searching for Dwarf Galaxies in $Gaia$ DR2 Phase-Space Data Using Wavelet Transforms

Cited by in corpus (22)

• Forecasts for Galaxy Formation and Dark Matter Constraints from Dwarf Galaxy Surveys
• Metallicity Distribution Functions of 13 Ultra-Faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• Ursa Major III/UNIONS 1: the darkest galaxy ever discovered?
• Discovery of a new Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V
• EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations
• A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Galaxy with DELVE Early Data Release 3
• EDGE-INFERNO: Simulating every observable star in faint dwarf galaxies and their consequences for resolved-star photometric surveys
• Micro galaxies in LCDM
• A census of dwarf galaxy satellites around LMC-mass galaxy NGC 2403
• Mixed Warm Dark Matter Constraints using Milky Way Satellite Galaxy Counts
• The emergence of globular clusters and globular-cluster-like dwarfs
• DELVE-DEEP Survey: The Faint Satellite System of NGC 55
• Ultra-Faint Milky Way Satellites Discovered in Carina, Phoenix, and Telescopium with DELVE Data Release 3
• Dark Star Clusters or Ultra-Faint Dwarf galaxies? Revisiting UMa3/U1
• Stellar Mass Segregation in Dark Matter Halos
• Understanding Stellar Mass-Metallicity and Size Relations in Simulated Ultra-Faint Dwarf Galaxies
• DELVE Milky Way Satellite Galaxy Census I: Satellite Population and Survey Selection Function in DES, DELVE, and Pan-STARRS
• Quantifying the Detectability of Milky Way Satellites with Image Simulations: a Case Study with KiDS
• Chemodynamics of BoötesI with $S^5$: Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints
• DELVE-ing into the Milky Way's Globular Clusters: Assessing extra-tidal features in NGC 5897, NGC 7492, and testing detectability with deeper photometry
• Collisional Dynamics of Stars and Dark Matter in Ultra-Faint Galaxies