Snake in the Clouds: A new nearby dwarf galaxy in the Magellanic bridge

Abstract

We report the discovery of a nearby dwarf galaxy in the constellation of Hydrus, between the Large and the Small Magellanic Clouds. Hydrus 1 is a mildy elliptical ultra-faint system with luminosity $M_V\sim$ -4.7 and size $\sim$ 50 pc, located 28 kpc from the Sun and 24 kpc from the LMC. From spectroscopy of $\sim$ 30 member stars, we measure a velocity dispersion of 2.7 km/s and find tentative evidence for a radial velocity gradient consistent with 3 km/s rotation. Hydrus 1's velocity dispersion indicates that the system is dark matter dominated, but its dynamical mass-to-light ratio M/L $\sim$ 66 is significantly smaller than typical for ultra-faint dwarfs at similar luminosity. The kinematics and spatial position of Hydrus~1 make it a very plausible member of the family of satellites brought into the Milky Way by the Magellanic Clouds. While Hydrus 1's proximity and well-measured kinematics make it a promising target for dark matter annihilation searches, we find no evidence for significant gamma-ray emission from Hydrus 1. The new dwarf is a metal-poor galaxy with a mean metallicity [Fe/H]=-2.5 and [Fe/H] spread of 0.4 dex, similar to other systems of similar luminosity. Alpha-abundances of Hyi 1 members indicate that star-formation was extended, lasting between 0.1 and 1 Gyr, with self-enrichment dominated by SN Ia. The dwarf also hosts a highly carbon-enhanced extremely metal-poor star with [Fe/H] $\sim$ -3.2 and [C/Fe] $\sim$ +3.0.

arXiv commentsubmitted to MNRAS; 21 pages

References in corpus (138)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• emcee: The MCMC Hammer
• The Sloan Digital Sky Survey: Technical Summary
• Galactic Stellar and Substellar Initial Mass Function
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Gaia mission
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Modules for Experiments in Stellar Astrophysics (MESA)
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• Where are the missing galactic satellites?
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• Local Kinematics and the Local Standard of Rest
• The observed properties of dwarf galaxies in and around the Local Group
• The No-U-Turn Sampler: Adaptively Setting Path Lengths in Hamiltonian Monte Carlo
• Astrophysics Source Code Library
• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• Searching for Dark Matter Annihilation from Milky Way Dwarf Spheroidal Galaxies with Six Years of Fermi-LAT Data
• The mass distribution and gravitational potential of the Milky Way
• The Dark Energy Camera
• A new generation of PARSEC-COLIBRI stellar isochrones including the TP-AGB phase
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Observational clues to the progenitors of Type-Ia supernovae
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• A Universal Mass Profile for Dwarf Spheroidal Galaxies?
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Constraining Dark Matter Models from a Combined Analysis of Milky Way Satellites with the Fermi Large Area Telescope
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Near-Field Cosmology with Metal-Poor Stars
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• New Grids of ATLAS9 Model Atmospheres
• A comprehensive Maximum Likelihood analysis of the structural properties of faint Milky Way satellites
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Searching for Dark Matter Annihilation in Recently Discovered Milky Way Satellites with Fermi-LAT
• The Dark Energy Survey Data Release 1
• A New Milky Way Dwarf Galaxy in Ursa Major
• The Observed properties of Dark Matter on small spatial scales
• The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• The Tidal Evolution of Local Group Dwarf Spheroidals
• The Effects of Photoionization on Galaxy Formation - II: Satellites in the Local Group
• The Metamorphosis of Tidally Stirred Dwarf Galaxies
• A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite?
• The Luminosity Function of the Milky Way Satellites
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. III. Metallicity Distributions of Milky Way Dwarf Satellite Galaxies
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with Fermi
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• The RR Lyrae Period-Luminosity Relation. I. Theoretical Calibration
• The Origin of the Magellanic Stream and Its Leading Arm
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• "Skinny Milky Way, Please", says Sagittarius
• The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics and Data Release
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• 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
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• "Galaxy," Defined
• Accurate Stellar Kinematics at Faint Magnitudes: application to the Bootes~I dwarf spheroidal galaxy
• The Relationships Among Compact Stellar Systems: A Fresh View of Ultra Compact Dwarfs
• Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data
• Dwarf galaxy annihilation and decay emission profiles for dark matter experiments
• Precise constraints on the dark matter content of Milky Way dwarf galaxies for gamma-ray experiments
• Dark matter annihilation and decay in dwarf spheroidal galaxies: The classical and ultrafaint dSphs
• Small Dwarf Galaxies Within Larger Dwarfs: Why Some Are Luminous While Most Go Dark
• The Invisibles: A Detection Algorithm to Trace the Faintest Milky Way Satellites
• Deciphering the 3D structure of the old Galactic bulge from the OGLE RR Lyrae stars
• Tidal Tails of Star Clusters
• The upper bound on the lowest mass halo
• Nucleosynthesis and the Inhomogeneous Chemical Evolution of the Carina Dwarf Galaxy
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• A Magellanic Origin of the DES Dwarfs
• The DECam Plane Survey: Optical photometry of two billion objects in the southern Galactic plane
• Line strengths and updated molecular constants for the C2 Swan system
• Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic Stellar History
• On the Efficiency of the Tidal Stirring Mechanism for the Origin of Dwarf Spheroidals: Dependence on the Orbital and Structural Parameters of the Progenitor Disky Dwarfs
• A Comprehensive Search for Dark Matter Annihilation in Dwarf Galaxies
• Indication of Gamma-ray Emission from the Newly Discovered Dwarf Galaxy Reticulum II
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Horologium II: a Second Ultra-faint Milky Way Satellite in the Horologium Constellation
• Willman 1 - a probable dwarf galaxy with an irregular kinematic distribution
• Metallicity and Alpha-Element Abundance Measurement in Red Giant Stars from Medium Resolution Spectra
• The Chemical Composition of Carbon-Rich, Very Metal-Poor Stars: A New Class of Mildly Carbon-Rich Objects Without Excess of Neutron-Capture Elements
• Atomic and Molecular Data for Optical Stellar Spectroscopy
• Clean Kinematic Samples in Dwarf Spheroidals: An Algorithm for Evaluating Membership and Estimating Distribution Parameters When Contamination is Present
• Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1
• Discovery of two neighboring satellites in the Carina constellation with MagLiteS
• Crater 2: An Extremely Cold Dark Matter Halo
• Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1
• Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System with Gaia DR1
• Satellites of LMC-Mass Dwarfs: Close Friendships Ruined by Milky Way Mass Halos
• A new distant Milky Way globular cluster in the Pan-STARRS1 3π survey
• The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies
• The [Fe/H], [C/Fe], and [alpha/Fe] distributions of the Bootes I Dwarf Spheroidal Galaxy
• An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey
• Identifying true satellites of the Magellanic Clouds
• ATLAS lifts the Cup: Discovery of a New Milky Way satellite in Crater
• Systemic Proper Motions of Milky Way Satellites from Stellar Redshifts: the Carina, Fornax, Sculptor and Sextans Dwarf Spheroidals
• Dark matter annihilation and decay from non-spherical dark halos in the Galactic dwarf satellites
• Weak Galactic halo--dwarf spheroidal connection from RR Lyrae stars
• Low Surface Brightness Imaging of the Magellanic System: Imprints of Tidal Interactions between the Clouds in the Stellar Periphery
• A 10 kpc stellar substructure at the edge of the Large Magellanic Cloud: perturbed outer disk or evidence for tidal stripping?
• Discovery of a Faint Outer Halo Milky Way Star Cluster in the Southern Sky
• Magellan/M2FS Spectroscopy of the Reticulum 2 Dwarf Spheroidal Galaxy
• Stellar streams around the Magellanic Clouds
• Simple J-Factors and D-Factors for Indirect Dark Matter Detection
• A Common Origin for Globular Clusters and Ultra-faint Dwarfs in Simulations of the First Galaxies
• On the Run: mapping the escape speed across the Galaxy with SDSS
• Scaling Relations for Dark Matter Annihilation and Decay Profiles in Dwarf Spheroidal Galaxies
• A new low mass for the Hercules dSph: the end of a common mass scale for the dwarfs?
• Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-$s$ stars
• On The Gamma-Ray Emission From Reticulum II and Other Dwarf Galaxies
• Leo V: Spectroscopy of a Distant and Disturbed Satellite
• Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
• A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation
• Search for gamma-ray emission from eight dwarf spheroidal galaxy candidates discovered in Year Two of Dark Energy Survey with Fermi-LAT data
• A model-independent analysis of the Fermi Large Area Telescope gamma-ray data from the Milky Way dwarf galaxies and halo to constrain dark matter scenarios
• A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater
• Accretion of the Magellanic system onto the Galaxy
• Unmixing the Galactic Halo with RR Lyrae tagging
• Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
• Contamination of stellar-kinematic samples and uncertainty about dark matter annihilation profiles in ultrafaint dwarf galaxies: the example of Segue I
• The Hercules satellite: a stellar stream in the Milky Way halo?
• Bayesian Mass Estimates of the Milky Way: including measurement uncertainties with hierarchical Bayes
• Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches
• Exploding Satellites -- The Tidal Debris of the Ultra-Faint Dwarf Galaxy Hercules
• Probing the boundary between star clusters and dwarf galaxies: A MUSE view on the dynamics of Crater/Laevens I
• Proper Motion of Milky Way Dwarf Spheroidals from Line-of-Sight Velocities
• Structured star formation in the Magellanic inter-Cloud region
• A new calibration for the Blue Horizontal Branch
• The Potential of the Dwarf Galaxy Triangulum II for Dark Matter Indirect Detection
• Discovery of a thin stellar stream in the SLAMS survey
• Prospects for Detecting Gamma Rays from Annihilating Dark Matter in Dwarf Galaxies in the Era of DES and LSST
• Chemical abundances of giant stars in the Crater stellar system

Cited by in corpus (77)

• The Faintest Dwarf Galaxies
• Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
• Milky Way Satellite Census. II. Galaxy--Halo Connection Constraints Including the Impact of the Large Magellanic Cloud
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• The large-scale structure of the halo of the Andromeda galaxy II. Hierarchical structure in the Pan-Andromeda Archaeological Survey
• The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions
• Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1
• Constraints on Dark Matter Microphysics from the Milky Way Satellite Population
• Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-Faint Galaxies
• The Gas Content and Stripping of Local Group Dwarf Galaxies
• The Lazy Giants: APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic Clouds
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• The DECam Local Volume Exploration Survey: Overview and First Data Release
• Limit on the LMC mass from a census of its satellites
• The faint end of the Centaurus A satellite luminosity function
• Revised and new proper motions for confirmed and candidate Milky Way dwarf galaxies
• A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III
• Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
• The M101 Satellite Luminosity Function and the Halo to Halo Scatter Among Local Volume Hosts
• Wide-Field Survey of Dwarf Satellite Systems Around 10 Hosts in the Local Volume
• 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
• Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites
• Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V
• The Suppression of Star Formation on the Smallest Scales: What Role Does Environment Play?
• The mass of our Galaxy from satellite proper motions in the Gaia era
• An Updated SMC and Magellanic Bridge Catalog of Star Clusters, Associations and Related Objects
• Structure Formation Models Weaken Limits on WIMP Dark Matter from Dwarf Spheroidal Galaxies
• How low does it go? Too few Galactic satellites with standard reionization quenching
• Search for RR Lyrae stars in DES ultra-faint systems: Grus I, Kim 2, Phoenix II, and Grus II
• Dark and luminous satellites of LMC-mass galaxies in the FIRE simulations
• Star Formation Histories of Ultra-Faint Dwarf Galaxies: environmental differences between Magellanic and non-Magellanic satellites?
• A Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC
• Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus
• VLT Spectroscopy of Ultra-Faint Dwarf Galaxies. 1. Boötes I, Leo IV, Leo V
• Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey
• The velocity anisotropy of the Milky Way satellite system
• Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter
• Orbital evidences for dark-matter-free Milky Way dwarf spheroidal galaxies
• Effective $J$-factors for Milky Way dwarf spheroidal galaxies with velocity-dependent annihilation
• Gaia RR Lyrae Stars in Nearby Ultra-Faint Dwarf Satellite Galaxies
• Satellites of Satellites: The Case for Carina and Fornax
• The Magellanic Edges Survey I. Description and First Results
• Identification of RR Lyrae stars in multiband, sparsely-sampled data from the Dark Energy Survey using template fitting and Random Forest classification
• The assembly history of the Galactic inner halo inferred from alpha-patterns
• Spectroscopic analysis of Milky Way outer halo satellites: Aquarius II and Bootes II
• A panoramic view of the Local Group dwarf galaxy NGC 6822
• HST resolves stars in a tiny body falling on the dwarf galaxy DDO 68
• Magellan/M2FS and MMT/Hectochelle Spectroscopy of Dwarf Galaxies and Faint Star Clusters within the Galactic Halo
• Sizing from the Smallest Scales: The Mass of the Milky Way
• The Luminosity Functions and Redshift Evolution of Satellites of Low-Mass Galaxies in the COSMOS Survey
• A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II
• Matching the mass function of Milky Way satellites in competing dark matter models
• The Elusive Distance Gradient in the Ultra-Faint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View
• H$\alpha$ Distances to the Leading Arm of the Magellanic Stream
• OGLE-ing the Magellanic System: Cepheids in the Bridge
• The abundance of satellite galaxies in the inner region of $\Lambda$CDM Milky Way sized haloes
• Discovery of a Rare Group of Dwarf Galaxies in the Local Universe
• Ghostly Stellar Haloes and their Relationship to Ultra-faint Dwarfs
• Anticipating the XRISM search for the decay of resonantly produced sterile neutrino dark matter
• No globular cluster progenitors in Milky Way satellite galaxies
• The Smallest Scale of Hierarchy Survey (SSH) III. Dwarf-dwarf satellite merging phenomena in the low-mass regime
• Residual velocities of Small Magellanic Cloud star clusters
• The Hierarchical Structure of Galactic Haloes: Classification and characterisation with Halo-OPTICS
• The YMCA (Yes, Magellanic Clouds Again) survey: probing the outer regions of the Magellanic system with VST
• Unlocking Discovery Potential for Decaying Dark Matter and Faint X-ray Sources with XRISM
• Destruction of the central black hole gas reservoir through head-on galaxy collisions
• Cosmological prior for the $J$-factor estimation of dwarf spheroidal galaxies
• Densities and mass assembly histories of the Milky Way satellites are not a challenge to $\Lambda$CDM
• DELVE Milky Way Satellite Galaxy Census I: Satellite Population and Survey Selection Function in DES, DELVE, and Pan-STARRS
• Chemodynamics of BoötesI with $S^5$: Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints
• Forward-modelling the Luminosity, Distance, and Size distributions of the Milky Way Satellites
• Identification of high-energy astrophysical point sources via hierarchical Bayesian nonparametric clustering
• A search for stellar structures around nine outer halo globular clusters in the Milky Way
• Magellan/IMACS spectroscopy of Grus I: A low metallicity ultra-faint dwarf galaxy