The milky way tomography with SDSS. III. Stellar kinematics

Nicholas A. Bond, Željko Ivezić, Branimir Sesar, Mario Jurić, Jeffrey A. Munn, Adam Kowalski, Sarah Loebman, Rok Roškar, Timothy C. Beers, Julianne Dalcanton, Constance M. Rockosi, Brian Yanny, Heidi J. Newberg, Carlos Allende Prieto, Ron Wilhelm, Young Sun Lee, Thirupathi Sivarani, Steven R. Majewski, John E. Norris, Coryn A.L. Bailer-JonesPaola Re Fiorentin, David Schlegel, Alan Uomoto, Robert H. Lupton, Gillian R. Knapp, James E. Gunn, Kevin R. Covey, J. Allyn Smith, Gajus Miknaitis, Mamoru Doi, Masayuki Tanaka, Masataka Fukugita, Steve Kent, Douglas Finkbeiner, Tom R. Quinn, Suzanne Hawley, Scott Anderson, Furea Kiuchi, Alex Chen, James Bushong, Harkirat Sohi, Daryl Haggard, Amy Kimball, Rosalie McGurk, John Barentine, Howard Brewington, Mike Harvanek, Scott Kleinman, Jurek Krzesinski, Dan Long, Atsuko Nitta, Stephanie Snedden, Brian Lee, Jeffrey R. Pier, Hugh Harris, Jonathan Brinkmann, Donald P. Schneider

Research output: Contribution to journalArticlepeer-review

172 Scopus citations


We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r < 20 and proper-motion measurements derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry, including ∼170,000 stars with radial-velocity measurements from the SDSS spectroscopic survey. Distances to stars are determined using a photometric-parallax relation, covering a distance range from ∼100pc to 10kpc over a quarter of the sky at high Galactic latitudes (|b|>20°). We find that in the region defined by 1kpc <Z< 5kpc and 3kpc <R< 13kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (<100pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.

Original languageEnglish (US)
Pages (from-to)1-29
Number of pages29
JournalAstrophysical Journal
Issue number1
StatePublished - 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxy: disk
  • Galaxy: halo
  • Galaxy: kinematics and dynamics
  • Galaxy: stellar content
  • Galaxy: structure
  • Methods: data analysis
  • Stars: statistics


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