The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way

Giuseppina Battaglia, Amina Helmi, Heather Morrison, Paul Harding, Edward W. Olszewski, Mario Mateo, Kenneth C. Freeman, John Norris, Stephen A. Shectman

Research output: Contribution to journalArticle

225 Scopus citations

Abstract

We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements, including globular clusters, satellite galaxies, field blue horizontal branch (FHB) stars and red giant stars from the Spaghetti survey. The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc, which allows a reliable determination of the radial velocity dispersion profile out to very large distances. The radial velocity dispersion shows an almost constant value of 120 km s-1 out to 30 kpc and then continuously declines down to 50 km s-1 at about 120 kpc. This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way. For a constant velocity anisotropy, the isothermal profile is ruled out, while both a dark halo following a truncated flat (TF) model of mass 1.2-0.5 +1.8× 1012M and a Navarro, Frenk & White (NFW) profile of mass 0.8-0.2+1.2 × 1012 M and c = 18 are consistent with the data. The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works. We also show how different assumptions for the velocity anisotropy affect the performance of the mass models.x

Original languageEnglish (US)
Pages (from-to)433-442
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume364
Issue number2
DOIs
StatePublished - Dec 1 2005

Keywords

  • Dark matter
  • Galaxy: halo
  • Galaxy: kinematics and dynamics
  • Galaxy: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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