Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

By M. Wilkinson, J. Kleyna, N. Evans, G. Gilmore, M. Irwin, E. Cambridge, Hawaii, Basel. 2004

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We present projected velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal galaxies based on 207 and 162 discrete stellar velocities, respectively. Both profiles show a sharp decline in the velocity dispersion outside ~30' (Draco) and ~40' (UMi). New deep photometry of Draco reveals a break in the light profile at ~25'. These data imply the existence of a kinematically cold population in the outer parts of both galaxies. Possible explanations of both the photometric and the kinematic data in terms of both equilibrium and nonequilibrium models are discussed in detail. We conclude that these data challenge the picture of dwarf spheroidal galaxies as simple, isolated stellar systems.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/5a934fae635e3677e32b2920905dd4393ce60281

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Complexity on Small Scales: The Metallicity Distribution of the Carina Dwarf Spheroidal Galaxy (2005, background): “Because of their high velocity dispersion, their velocity dispersion profiles, their morphology and their lack of depth extent many dSphs are believed to be dominated by dark matter (e.g., Mateo 1997; Odenkirchen et al. 2001; Klessen, Grebel, & Harbeck 2003; Wilkinson et al. 2004).”
The Observed Properties of Dark Matter on Small Spatial Scales (2007, background): “…I, Leo II, Sextans, and Sculptor dSph’s have been mapped to the (rather poorly defined concept of an) optical edge (Mateo 1997; Kleyna et al. 2002; Wilkinson et al. 2004, 2006;Muñoz et al. 2005; Sohn et al. 2007; Koch et al. 2007b; Battaglia et al. 2006; Walker et al. 2006)—see Figure 2 for a…”
Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies (2007, methodology): “…et al. (2007) show that dSph masses within r ≤ 600 pc (M600) are constrained robustly by kinematic 5 We have not included the unpublished data of Wilkinson et al. (2004) or Muñoz et al. (2005) in our calculations of the velocity dispersion profiles of Draco. dSph Velocity Dispersion Profiles…”
On the Accretion Origin of a Vast Extended Stellar Disk around the Andromeda Galaxy (2005, methodology): “The radial velocities were measured by cross-correlating against a model template with Gaussian functions at the rest-frame wavelength positions of the Ca II triplet lines (the technique used is similar to that discussed by Wilkinson et al. 2004).”
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters (2018, background): “Hargreaves et al. (1994), Olszewski et al. (1995, 1996), Wilkinson et al. (2004) and Muñoz et al. (2005) led subsequent spectroscopic campaigns, collecting hundreds of radial velocity measurements over the following decade.”
A METHOD FOR MEASURING (SLOPES OF) THE MASS PROFILES OF DWARF SPHEROIDAL GALAXIES (2011, background): “Many dSph kinematic studies (e.g., Wilkinson et al. 2004; Strigari et al. 2006, 2008; Koch et al. 2007; Łokas 2009; Walker et al. 2009a; Battaglia et al. 2008a, 2011) rely instead on the Jeans equations, obtained by integrating the CBE over velocity space.”
Exploring Halo Substructure with Giant Stars. XI. The Tidal Tails of the Carina Dwarf Spheroidal Galaxy and the Discovery of Magellanic Cloud Stars in the Carina Foreground (2006, background): “While this is partly due to technical differences in interpretation of even the same databases (e.g., Wilkinson et al. 2004, Łokas et al. 2005, Muñoz et al. 2005), in general most studies are finding flat dSph velocity dispersion profiles to be the norm.”
A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY (2010, background): “…that the stars beyond ∼ 8′ from the center of the galaxy have been stripped, we caution that apparent features in other data sets of similar size (or even larger) have often disappeared when larger samples of velocity measurements become available (Wilkinson et al. 2004; Kleyna et al. 2004).”
STELLAR VELOCITIES IN THE CARINA, FORNAX, SCULPTOR, AND SEXTANS dSph GALAXIES: DATA FROM THE MAGELLAN/MMFS SURVEY (2008, background): “…reaching hundreds of stars per dSph, velocity dispersion profiles are now available for all of the brighter MW dSphs (Kleyna et al. 2002, 2004; Wilkinson et al. 2004; Muñoz et al. 2005, 2006; Sohn et al. 2007; Walker et al. 2006a, 2006b, 2007b; Battaglia et al. 2006; Mateo et al. 2008; Koch…”
A UNIVERSAL MASS PROFILE FOR DWARF SPHEROIDAL GALAXIES? (2009, background): “Meaningful constraints on γ require more sophisticated analyses that incorporate realistic models 7 Wilkinson et al. (2004) and Kleyna et al. (2004) report sharp declines at large radii in Ursa Minor and Sextans, but these features are not reproduced either in our data sets or in those of Muñoz et…”
The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy (2006, background): “…is much higher than is typical for globular clusters, which have mass-to-light ratiosin the range 1-3 (e.g. McLaughlin & van der Marel 2005), but considerably lower than that found for many other dSphs such as Draco and Ursa Minor (M/L > 100 (M/LV)⊙, e.g. Kleyna et al. 2003; Wilkinson et al. 2004).”
Simultaneous ram pressure and tidal stripping; how dwarf spheroidals lost their gas (2005, background): “Journal compilation C© 2006 RAS, MNRAS 369, 1021–1038 Downloaded from https://academic.oup.com/mnras/article-abstract/369/3/1021/1225729 by guest on 29 July 2018 observed for Draco, and the amount of gas that needs to be turned into stars is non-negligible, ∼6 × 106 M ; if we sum such mass to the re”
The importance of tides for the Local Group dwarf spheroidals (2005, background): “This hypothesis was presented in Wilkinson et al. (2004) and formed one of the motivations for this current work.”
The Kinematic Status and Mass Content of the Sculptor Dwarf Spheroidal Galaxy (2008, background): “In some cases a number of spatial and kinematic substructures have been observed (e.g., Wilkinson et al. 2004; Coleman et al. 2005; Battaglia 2007, hereafter B07), which are perhaps the remnants of accreted subunits (stellar clusters or smaller galaxies).”
Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy (2005, unknown): “Comparison with Draco and Ursa Minor Velocity dispersion profiles extending to the limits of the stellar distributions are now available for the dSphs Fornax, Ursa Minor, and Draco (Kleyna et al. 2002; Wilkinson et al. 2004, hereafter, WK04;, Muñoz et al. 2005).”
The Cold Dark Matter Halos of Local Group Dwarf Spheroidals (2007, background): “…between orbital shapes, their radial dependence, and the overall mass profile (Wilkinson et al. 2002, Kazantzidis et al. 2004, Mashchenko et al. 2006, Kleyna et 2004, Tolstoy et al. 2004, Wilkinson et al. 2004, Muñoz et al. 2005, 2006, Wang et al. 2005, Walker et al. 2006a,b, Sohn et al. 2006).”
Redefining the Missing Satellites Problem (2007, methodology): “…the primary constraints come from the velocity dispersion of ∼ 200 stars in the population of dark matter dominated dwarf spheroidal galaxies (dSphs) (Wilkinson et al. 2004; Lokas et al. 2005; Munoz et al. 2005, 2006; Westfall et al. 2006; Walker et al. 2005, 2006; Sohn et al. 2006; Gilmore et al.…”
Two Distinct Ancient Components in the Sculptor Dwarf Spheroidal Galaxy: First Results from the Dwarf Abundances and Radial Velocities Team (2004, background): “The radial velocity studies of Wilkinson et al. (2004) and Kleyna et al. (2004) have also considered the possibility that kinematically distinct components exist in Ursa Minor, Draco, and Sextans.”