The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X

Abstract

Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey (SDSS - York et al. 2000). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo). Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity histogram for this field confirms three populations of stars along the sight line: foreground Milky Way dwarfs at small negative velocities, M31 halo red giants over a broad range of velocities, and a very cold velocity ``spike'' consisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By carefully considering both the random and systematic velocity errors of these stars (e.g., through duplicate star measurements), we derive an intrinsic velocity dispersion of just sigma_v = 3.9 +/- 1.2 km/s for And X, which for its size, implies a minimum mass-to-light ratio of M/L =37^{+26}_{-19} assuming the mass traces the light. Based on the clean sample of member stars, we measure the median metallicity of And X to be [Fe/H] = -1.93 +/- 0.11, with a slight radial metallicity gradient. The dispersion in metallicity is large, sigma([Fe/H]) = 0.48, possibly hinting that the galaxy retained much of its chemical enrichment products. We discuss the potential for better understanding the formation and evolution mechanisms for M31's system of dSphs through (current) kinematic and chemical abundance studies, especially in relation to the Milky Way sample. (abridged version)

Accepted for Publication in Astrophys. J. 14 pages including 7 figures and 2 tables (journal format)

References in corpus (18)

• 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
• A common mass scale for satellite galaxies of the Milky Way
• The Observed properties of Dark Matter on small spatial scales
• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy
• The Cold Dark Matter Halos of Local Group Dwarf Spheroidals
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• Complexity on Small Scales III: Iron and alpha Element Abundances in the Carina Dwarf Spheroidal Galaxy
• A trio of new Local Group galaxies with extreme properties
• Exploring Halo Substructure with Giant Stars X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy
• The mass and velocity anisotropy of the Carina, Fornax, Sculptor and Sextans dwarf spheroidal galaxies
• A New Method for Isolating M31 Red Giant Stars: The Discovery of Stars out to a Radial Distance of 165 Kiloparsecs
• Andromeda XVII: A New Low Luminosity Satellite of M31
• The Extended Star Formation History of the Andromeda Spheroid at Twenty One Kiloparsecs on the Minor Axis

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• Global Properties of M31's Stellar Halo from the SPLASH Survey: II. Metallicity Profile
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• Elemental Abundances in M31: The Kinematics and Chemical Evolution of Dwarf Spheroidal Satellite Galaxies
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• Elemental Abundances in M31: A Comparative Analysis of Iron and Alpha Element Abundances in the Outer Disk, Giant Stellar Stream, and Inner Halo of M31
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• Global Properties of M31's Stellar Halo from the SPLASH Survey: III. Measuring the Stellar Velocity Dispersion Profile
• Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-Resolution Resolved Stellar Spectroscopy in the Stellar Halo
• Elemental abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra
• A Deep Photometric Look at Two of Andromeda's Dwarf Spheroidals: X and XVII
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• Measuring Detailed Chemical Abundances From Co-added Medium Resolution Spectra I. Tests using Milky Way dwarf spheroidal galaxies and globular clusters
• Satellites in the Local Group and Other Nearby Groups
• Recent Results from SPLASH: Chemical Abundances and Kinematics of Andromeda's Stellar Halo