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    Discovery of a Dynamical Cold Point in the Heart of the Sagittarius dSph Galaxy With Observations from the APOGEE Project

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    Date
    2013-11
    Author
    Majewski, Steven R.
    Hasselquist, Sten
    Lokas, Ewa L.
    Nidever, David L.
    Frinchaboy, Peter M.
    Garcia Perez, Ana E.
    Johnston, Kathryn V.
    Meszaros, Szabolcs
    Shetrone, Matthew
    Allende Prieto, Carlos
    Beaton, Rachael L.
    Beers, Timothy C.
    Bizyaev, Dmitry
    Cunha, Katia
    Damke, Guillermo
    Ebelke, Garrett
    Eisenstein, Daniel J.
    Hearty, Fred
    Holtzman, Jon
    Johnson, Jennifer A.
    Law, David R.
    Malanushenko, Viktor
    Malanushenko, Elena
    O'Connell, Robert W.
    Oravetz, Daniel
    Pan, Kaike
    Schiavon, Ricardo P.
    Schneider, Donald P.
    Simmons, Audrey
    Skrutskie, Michael F.
    Smith, Verne V.
    Wilson, John C.
    Zasowski, Gail
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    Abstract
    The dynamics of the core of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy are explored using high-resolution (R similar to 22,500), H-band, near-infrared spectra of over 1000 giant stars in the central 3 deg(2) of the system, of which 328 are identified as Sgr members. These data, among some of the earliest observations from the Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the largest published sample of high resolution Sgr dSph spectra to date, reveal a distinct gradient in the velocity dispersion of Sgr from 11 to 14 km s(-1) for radii > 0 degrees.8 from center to a dynamical cold point of 8 km s(-1) in the Sgr center-a trend differing from that found in previous kinematical analyses of Sgr over larger scales that suggests a more or less flat dispersion profile at these radii. Well-fitting mass models with either cored and cusped dark matter distributions can be found to match the kinematical results, although the cored profile succeeds with significantly more isotropic stellar orbits than required for a cusped profile. It is unlikely that the cold point reflects an unusual mass distribution. The dispersion gradient may arise from variations in the mixture of populations with distinct kinematics within the dSph; this explanation is suggested (e. g., by detection of a metallicity gradient across similar radii), but not confirmed, by the present data. Despite these remaining uncertainties about their interpretation, these early test data (including some from instrument commissioning) demonstrate APOGEE's usefulness for precision dynamical studies, even for fields observed at extreme airmasses.
    Department
    McDonald Observatory
    Subject
    galaxies: dwarf
    galaxies: individual (sagittarius dsph)
    galaxies:
    interactions
    galaxies: kinematics and dynamics
    galaxies: stellar
    content
    galaxies: structure
    dwarf spheroidal galaxy
    dark-matter distribution
    sky survey view
    milky-way
    globular-clusters
    radial-velocities
    acs survey
    kinematics
    evolution
    stars
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/43074
    Citation
    Majewski, Steven R., Sten Hasselquist, Ewa L. ?okas, David L. Nidever, Peter M. Frinchaboy, Ana E. García Pérez, Kathryn V. Johnston et al. "Discovery of a Dynamical Cold Point in the Heart of the Sagittarius dSph Galaxy with Observations from the APOGEE Project." The Astrophysical Journal Letters, Vol. 777, No. 1 (Nov., 2013): L13.
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