Pristine Dwarf-Galaxy Survey I: A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite

Abstract

We present a detailed study of the faint Milky Way satellite Draco II (Dra II) from deep CFHT/MegaCam broadband $g$ and $i$ photometry and narrow-band metallicity-sensitive CaHK observations, along with follow-up Keck II/DEIMOS multi-object spectroscopy. Forward modeling of the deep photometry allows us to refine the structural and photometric properties of Dra II: the distribution of stars in colour-magnitude space implies Dra II is old (13.5 $\pm 0.5$ Gyr), very metal poor, very faint ($L_V=180_{-72}^{+124}{L}_{\odot }$), and at a distance $d=21.5\pm 0.4$ kpc. The narrow-band, metallicity-sensitive CaHK Pristine photometry confirms this very low metallicity ([Fe/H]$=-2.7\pm 0.1$ dex). Even though our study benefits from a doubling of the spectroscopic sample size compared to previous investigations, the velocity dispersion of the system is still only marginally resolved (${\sigma }_{vr}<5.9$ km s${}^{-1}$ at the 95 per cent confidence level) and confirms that Dra II is a dynamically cold stellar system with a large recessional velocity ($⟨v_r⟩=-342.5_{-1.2}^{+1.1}$ km s${}^{-1}$). We further show that the spectroscopically confirmed members of Dra~II have a mean proper motion of $({\mu }_{\alpha }^{\ast },{\mu }_{\delta })=(1.26\pm 0.27,0.94\pm 0.28)$ mas yr${}^{-1}$ in the Gaia DR2 data, which translates to an orbit with a pericenter and an apocenter of $21.3_{-1.0}^{+0.7}$ and $153.8_{-34.7}^{+56.7}$ kpc, respectively. Taken altogether, these properties favour the scenario of Dra~II being a potentially disrupting dwarf galaxy. The low-significance extra-tidal features we map around the satellite tentatively support this scenario.

arXiv commentAccepted for publication in MNRAS

References in corpus (71)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Sloan Digital Sky Survey: Technical Summary
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The observed properties of dwarf galaxies in and around the Local Group
• Stellar mass-to-light ratios and the Tully-Fisher relation
• The Dartmouth Stellar Evolution Database
• galpy: A Python Library for Galactic Dynamics
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• The Pan-STARRS1 Photometric System
• 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 Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• Resolved Massive Star Clusters in the Milky Way and its Satellites: Brightness Profiles and a Catalogue of Fundamental Parameters
• Intrinsic iron spread and a new metallicity scale for Globular Clusters
• A Universal Mass Profile for Dwarf Spheroidal Galaxies?
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• 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
• A comprehensive Maximum Likelihood analysis of the structural properties of faint Milky Way satellites
• A New Milky Way Dwarf Galaxy in Ursa Major
• A Faint New Milky Way Satellite in Bootes
• The Tidal Evolution of Local Group Dwarf Spheroidals
• A New Milky Way Dwarf Satellite in Canes Venatici
• A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite?
• Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)
• A Curious New Milky Way Satellite in Ursa Major
• Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultra-Faint Dwarf Spheroidal Satellite Galaxies
• A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
• The large-scale structure of the halo of the Andromeda Galaxy Part I: global stellar density, morphology and metallicity properties
• The Pristine survey I: Mining the Galaxy for the most metal-poor stars
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• A quantitative explanation of the observed population of Milky Way satellite galaxies
• The nucleus of the Sagittarius dSph galaxy and M54: a window on the process of galaxy nucleation
• "Galaxy," Defined
• Segue 2: A Prototype of the Population of Satellites of Satellites
• The two metallicity groups of the globular cluster M22: a chemical perspective
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. II. Catalog of Stars in Milky Way Dwarf Satellite Galaxies
• Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way
• Chemical Enrichment in the Faintest Galaxies: the Carbon and Iron Abundance Spreads in the Boötes I Dwarf Spheroidal Galaxy and the Segue 1 System
• Na-O Anticorrelation And HB I. The Na-O anticorrelation in NGC 2808
• Multiple stellar populations in the globular cluster NGC 1851
• The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies
• Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic Stellar History
• M 54 + Sagittarius = omega Centauri
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Willman 1 - a probable dwarf galaxy with an irregular kinematic distribution
• The discovery of two extremely low luminosity Milky Way globular clusters
• The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies
• A new distant Milky Way globular cluster in the Pan-STARRS1 3π survey
• The globular cluster NGC 2419: a crucible for theories of gravity
• Revisiting the influence of unidentified binaries on velocity dispersion measurements in ultra-faint stellar systems
• The Comparative Chemical Evolution of an Isolated Dwarf Galaxy: A VLT and Keck Spectroscopic Survey of WLM
• Na-O Anticorrelation and Horizontal Branches. V. The Na-O anticorrelation in NGC 6441 from Giraffe spectra
• Discovery of a Faint Old Stellar System at 150 kpc
• Discovery of a Faint Outer Halo Milky Way Star Cluster in the Southern Sky
• Current velocity data on dwarf galaxy NGC1052-DF2 do not constrain it to lack dark matter
• Na-O Anticorrelation and HB. VI. The chemical composition of the peculiar bulge globular cluster NGC 6388
• Planet-disc evolution and the formation of Kozai-Lidov planets
• NGC 2419 -- Another Remnant of Accretion by the Milky Way
• 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
• The Pristine survey III: Spectroscopic confirmation of an efficient search for extremely metal-poor stars
• Digging deeper into the Southern skies: a compact Milky-Way companion discovered in first-year Dark Energy Survey data
• The Discovery of an Ultra-Faint Star Cluster in the Constellation of Ursa Minor
• On the nature of ultra-faint dwarf galaxy candidates I: DES1, Eridanus III and Tucana V
• A chemical confirmation of the faint Bootes II dwarf Spheroidal Galaxy
• Kim 3: an Ultra-faint Star Cluster in the Constellation of Centaurus
• SMASH 1: a very faint globular cluster disrupting in the outer reaches of the LMC?
• Galactic Globular and Open Cluster Fiducial Sequences in the Pan-STARRS1 Photometric System

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• The Elusive Distance Gradient in the Ultra-Faint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View
• Destruction of the central black hole gas reservoir through head-on galaxy collisions
• Densities and mass assembly histories of the Milky Way satellites are not a challenge to $\Lambda$CDM
• Stellar Mass Segregation in Dark Matter Halos
• DELVE Milky Way Satellite Galaxy Census I: Satellite Population and Survey Selection Function in DES, DELVE, and Pan-STARRS
• Forward-modelling the Luminosity, Distance, and Size distributions of the Milky Way Satellites
• Magellan/IMACS spectroscopy of Grus I: A low metallicity ultra-faint dwarf galaxy
• Willman 1 Revisited: The Kinematics, Chemistry, and Orbital Properties of a Potentially-Disrupting Dwarf Galaxy