Chemical Diversity in the Ultra-faint Dwarf Galaxy Tucana II

Abstract

We present the first detailed chemical abundance study of the ultra-faint dwarf galaxy Tucana II based on high-resolution Magellan/MIKE spectra of four red giant stars. The metallicity of these stars ranges from [Fe/H] = -3.2 to -2.6, and all stars are low in neutron-capture abundances ([Sr/Fe] and [Ba/Fe] < -1). However, a number of anomalous chemical signatures are present. Three stars are carbon-enhanced, including the most metal-rich star. This star ([Fe/H]=-2.6) shows [Na,$\alpha$,Sc/Fe] < 0, suggesting an extended star formation history with contributions from AGB stars and Type Ia supernovae. The other carbon-enhanced stars have [Fe/H] < -3 and may be consistent with enrichment by faint supernovae, if such supernovae can produce neutron-capture elements. A fourth star with [Fe/H] = -3 is carbon-normal, and exhibits distinct light element abundance ratios from the carbon-enhanced stars. The carbon-normal star implies that at least two distinct nucleosynthesis sources, both possibly associated with Population III stars, contributed to the early chemical enrichment of this galaxy. Despite its very low luminosity, Tucana II shows a diversity of chemical signatures that preclude it from being a simple "one-shot" first galaxy, but still provide a window to star and galaxy formation in the early universe.

arXiv comment6 pages, 2 figures, 1 table, submitted to ApJL

References in corpus (43)

• Astropy: A Community Python Package for Astronomy
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Nucleosynthesis and Evolution of Massive Metal-Free Stars
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• 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
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• R-process enrichment from a single event in an ancient dwarf galaxy
• The YY Isochrones for alpha-element Enhanced Mixtures
• NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. III. Metallicity Distributions of Milky Way Dwarf Satellite Galaxies
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy
• $s$-process production in rotating massive stars at solar and low metallicities
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• The r-process in proto-neutron-star wind revisited
• Pre-galactic metal enrichment - The chemical signatures of the first stars
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• Deriving Stellar Effective Temperatures of Metal-Poor Stars with the Excitation Potential Method
• Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment
• The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars: Black Hole-forming Supernovae with Relativistic Jets
• Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1
• Carbon-enhanced metal-poor stars in dwarf galaxies
• The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies
• Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
• Preserving chemical signatures of primordial star formation in the first low-mass stars
• Are There Any Stars Lacking Neutron-Capture Elements? Evidence from Strontium and Barium
• High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II
• Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy
• The chemical evolution of the Bootes I ultra-faint dwarf galaxy
• Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies
• Chemical signatures of the first star clusters
• Abundance anomalies in metal-poor stars from Population III supernova ejecta hydrodynamics
• Star Formation in Ultrafaint Dwarfs: Continuous or Single-age Bursts?
• A Mass-Dependent Yield Origin of Neutron-Capture Element Abundance Distributions in Ultra-Faint Dwarfs
• A Tale of Tidal Tails in the Milky Way
• Non-LTE iron abundances in cool stars: The role of hydrogen collisions

Cited by in corpus (45)

• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud
• Triangulum II: Not Especially Dense After All
• Chemical Abundances in the Ultra-Faint Dwarf Galaxies Grus I and Triangulum II: Neutron-Capture Elements as a Defining Feature of the Faintest Dwarfs
• Kinematics of Antlia 2 and Crater 2 from The Southern Stellar Stream Spectroscopic Survey (S5)
• The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-Poor Star with an Extreme R-Process Enhancement of [Eu/H] = -0.14
• An extended halo around an ancient dwarf galaxy
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• From actinides to zinc: Using the full abundance pattern of the brightest star in Reticulum II to distinguish between different r-process sites
• Chemical Abundances of new member stars in the Tucana II dwarf galaxy
• Zero-metallicity hypernova uncovered by an ultra metal-poor star in the Sculptor dwarf spheroidal galaxy
• Chemical Abundance Analysis of Tucana III, the Second $r$-process Enhanced Ultra-Faint Dwarf Galaxy
• Ultra-faint dwarf galaxies: unveiling the minimum mass of the first stars
• Chemical Abundance Analysis of Three $\alpha$-Poor, Metal-Poor Stars in the Ultra-Faint Dwarf Galaxy Horologium I
• A Stringent Limit on the Mass Production Rate of $r$-Process Elements in the Milky Way
• The role of faint population III supernovae in forming CEMP stars in ultra-faint dwarf galaxies
• The Origin of r-process Enhanced Metal-Poor Halo Stars In Now-Destroyed Ultra-Faint Dwarf Galaxies
• A CEMP-no star in the ultra-faint dwarf galaxy Pisces II
• Origin of the CEMP-no Group Morphology in the Milky Way
• Stellar metallicities from SkyMapper photometry I: A study of the Tucana II ultra-faint dwarf galaxy
• On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
• Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis
• Detailed chemical abundances of stars in the outskirts of the Tucana II ultra-faint dwarf galaxy
• Formation of the first stars
• How much metals did the first stars provide to the ultra-faint dwarfs?
• Chemical Cartography. II. The Assembly History of the Galactic Stellar Halo Traced by Carbon-Enhanced Metal-Poor Stars
• Tracing Pop III supernovae with extreme energies through the Sculptor dwarf spheroidal galaxy
• Identification of a Group III CEMP-no Star in the Dwarf Spheroidal Galaxy Canes Venatici I
• Highly r-process enhanced stars in ultra-faint dwarf galaxies
• Evidence of First Stars-enriched Gas in High-redshift Absorbers
• The Origin of the Heaviest Metals in Most Ultra-Faint Dwarf Galaxies
• The energy distribution of the first supernovae
• High Resolution Optical Spectroscopy of Stars in the Sylgr Stellar Stream
• Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy
• Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process
• EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations
• Forecasting Chemical Abundance Precision for Extragalactic Stellar Archaeology
• The universality of the rapid neutron-capture process revealed by a possible disrupted dwarf galaxy star
• s-process Enirchment of Ultrafaint Dwarf Galaxies
• The formation of the Milky Way halo and its dwarf satellites: a NLTE-1D abundance analysis. IV. Segue 1, Triangulum II, and Coma Berenices UFDs
• The Pristine Inner Galaxy Survey (PIGS) IX. The largest detailed chemical analysis of very metal-poor stars in the Sagittarius dwarf galaxy
• Analysis of Fermi-LAT data from Tucana-II: Possible constraints on the Dark Matter models with an intriguing hint of a signal
• Stellar halos tracing the assembly of ultra-faint dwarf galaxies
• GRB 160410A: the first Chemical Study of the Interstellar Medium of a Short GRB
• An ancient system hidden in the Galactic plane?