A Dynamical Fossil in the Ursa Minor Dwarf Spheroidal Galaxy

By J. Kleyna, M. Wilkinson, G. Gilmore, N. Evans. 2003

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The nearby Ursa Minor dwarf spheroidal (UMi dSph) is one of the most dark matter-dominated galaxies known, with a central mass-to-light ratio M/L ~ 70. Somewhat anomalously, it appears to contain morphological substructure in the form of a second peak in the stellar number density. It is often argued that this substructure must be transient, because it could not survive for the ~12 Gyr age of the system, given the crossing time implied by UMi's 8.8 km s-1 internal velocity dispersion. In this Letter, however, we present evidence that the substructure has a cold kinematical signature and argue that UMi's clumpiness could indeed be a primordial artefact. Using numerical simulations, we demonstrate that substructure is incompatible with the cusped dark matter halos predicted by the prevailing cold dark matter (CDM) paradigm but is consistent with an unbound stellar cluster sloshing back and forth within the nearly harmonic potential of a cored dark matter halo. Thus, CDM appears to disagree with observation at the least massive, most dark matter-dominated end of the galaxy mass spectrum.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/762d34f7c29f5fd7d1e1621bbcb581f9f40beb39

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Citations in the corpus

Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf Spheroidal Galaxies (2004, background): “Adding the earlier UMi velocities of Kleyna et al. (2003) produces a dataset with 162 member stars.”
Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy (2005, unknown): “To what extent such mergers may be pervasive in the dSph population remains highly uncertain, although Kleyna et al. (2003; 2004) have detected kinematically distinct substructure in UrsaMinor and Sextans.”
Galactic Searches for Dark Matter (2012, background): “There are also arguments in favor of a core in the Ursa Minor dSph based upon observation of kinematically-cold stellar substructure (Kleyna et al., 2003; Gilmore et al., 2007).”
The all-sky distribution of 511 keV electron-positron annihilation emission (2005, result): “This possibility is indeed indicated by observations of our own Galaxy (Binney & Evans 2001) and dwarf galaxies (Blais-Ouellette et al. 1999; Kleyna et al. 2003).”
The importance of tides for the Local Group dwarf spheroidals (2005, background): “Interestingly, there may be tentative evidence that the UMi dSph has a centrally cored dark matter density profile, rather than a cusp (Kleyna et al. 2003).”
The Orbital Poles of Milky Way Satellite Galaxies: A Rotationally Supported Disk of Satellites (2008, background): “Independent evidence for the existence of cores comes from observations of substructure within the Ursa Minor dwarf (Kleyna et al. 2003) and the location of globular clusters in Fornax (Goerdt et al. 2006; Sánchez-Salcedo et al. 2006).”
Mass loss from dwarf spheroidal galaxies: the origins of shallow dark matter cores and exponential surface brightness profiles (2004, background): “…general about the distribution of dark matter in these galaxies, one recent indirect measurement suggests that Ursa Minor (UMi) has a central, constant-density, dark matter core (Kleyna et al. 2003), similar to those observed in low surface brightness (LSB) galaxies (see, e.g. de Blok et al. 2001).”
STELLAR VELOCITIES IN THE CARINA, FORNAX, SCULPTOR, AND SEXTANS dSph GALAXIES: DATA FROM THE MAGELLAN/MMFS SURVEY (2008, background): “The large data sets also provide information about the velocity distribution in two dimensions, and thus are capable of uncovering kinematic evidence of substructure (Kleyna et al. 2003; Walker et al. 2006b) as well as tidal streaming (Muñoz et al. 2006; Mateo et al. 2008).”
The Observed Properties of Dark Matter on Small Spatial Scales (2007, background): “As Kleyna et al. (2003) show, persistence of the cold structure is possible only if the tidal forces from the UMi central mass gradient are weak.”
The First Cosmic Structures and Their Effects (2004, background): “…(e.g. van den Bosch et al. 2000; Borriello & Salucci 2001; de Blok et al. 2001; van den Bosch & Swaters 2001; de Blok, Bosma & McGaugh 2003; Kleyna et al. 2003), which are sometimes consistent with both a constant density core and an inner cusp, indicating that HI rotation curves do not…”
The spatial distribution of the Milky Way and Andromeda satellite galaxies (2006, background): “The cuspy profile is in disagreement with the density profiles inferred for well-observed MW dSph satellites that are interpreted to be the most dark-matter dominated objects known (Wilkinson et al. 2002; Kleyna et al. 2003), an interpretation that may need revision (Muñoz et al. 2005).”
A METHOD FOR MEASURING (SLOPES OF) THE MASS PROFILES OF DWARF SPHEROIDAL GALAXIES (2011, background): “For example, Kleyna et al. (2003) detect kinematically cold stellar substructure in the Ursa Minor dSph and argue that its survival against tidal disruption is more likely in a cored as opposed to a cusped host potential.”
Dark matter annihilation and decay in dwarf spheroidal galaxies: the classical and ultrafaint dSphs (2015, background): “The nearby dSphs with good data favour dark matter cores over the cusps predicted by pure cold dark matter cosmological simulations (e.g. Kleyna et al. 2003; Goerdt et al. 2006; Battaglia et al. 2008; Walker & Peñarrubia 2011; Cole et al. 2012; Agnello & Evans 2012; Amorisco, Agnello & Evans…”
BARYONS MATTER: WHY LUMINOUS SATELLITE GALAXIES HAVE REDUCED CENTRAL MASSES (2012, background): “…Spano et al. 2008; Trachternach et al. 2008; de Blok et al. 2008; Donato et al. 2009; Oh et al. 2011; Del Popolo 2012), and observed in satellites (Kleyna et al. 2002, 2003; Mashchenko et al. 2005; Goerdt et al. 2006; Strigari et al. 2006; Gilmore et al. 2007; Walker et al. 2009; Strigari et al.…”
Dark matter cores and cusps: the case of multiple stellar populations in dwarf spheroidals (2011, background): “First, Kleyna et al. (2003) discovered kinematically cold substructure in the Ursa Minor dSph.”
Subhaloes in self-interacting galactic dark matter haloes (2012, methodology): “This has been accomplished not just with consideration of multiple stellar components, but also through Schwarzschild modelling (Jardel & Gebhardt 2011) and indirectly based on arguments about survival of cold substructure within Ursa Minor (Kleyna et al. 2003) and the distribution of globular clust”