Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II

Abstract

We present Magellan/M2FS, VLT/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8 +/- 0.5 km/s and a velocity dispersion of 3.3 +/- 0.7 km/s. The mass-to-light ratio of Ret II within its half-light radius is 470 +/- 210 Msun/Lsun, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 +/- 0.09 dex, and we identify several extremely metal-poor stars with [Fe/H] < -3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H] = -2.65 +/- 0.07, Ret II matches Segue~1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is log J = 18.8 +/- 0.6 Gev^2/cm^5 within 0.2 degrees, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.

14 pages, 6 figures (4 in color), 2 tables. Accepted for publication in the Astrophysical Journal. Only minor changes from v1

References in corpus (28)

• The Dark Energy Camera
• 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
• Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
• 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
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• 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
• The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics and Data Release
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• 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
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Pre-launch estimates for GLAST sensitivity to Dark Matter annihilation signals
• The Most Dark Matter Dominated Galaxies: Predicted Gamma-ray Signals from the Faintest Milky Way Dwarfs
• Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic Stellar History
• A New Faint Milky Way Satellite Discovered in the Pan-STARRS1 3 pi Survey
• A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus
• Too Many, Too Few, or Just Right? The Predicted Number and Distribution of Milky Way Dwarf Galaxies
• The Very Faint End of the UV Luminosity Function over Cosmic Time: Constraints from the Local Group Fossil Record
• WIMP searches with gamma rays in the Fermi era: challenges, methods and results
• Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal Galaxy
• The LMC geometry and outer stellar populations from early DES data
• Recombination Ghosts in Littrow Configuration: Implications for Spectrographs Using Volume Phase Holographic Gratings
• Precise Radial Velocities of 2046 Nearby FGKM Stars and 131 Standards

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