Probing the galactic potential with next-generation observations of disk stars

T. Sumi, K. V. Johnston, S. Tremaine, D. N. Spergel, S. R. Majewski

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Our current knowledge of the rotation curve of the Milky Way is remarkably poor compared to other galaxies, limited by the combined effects of extinction and the lack of large samples of stars with good distance estimates and proper motions. Near-future surveys promise a dramatic improvement in the number and precision of astrometric, photometric, and spectroscopic measurements of stars in the Milky Way's disk. We examine the impact of such surveys on our understanding of the Galaxy by "observing" particle realizations of nonaxisymmetric disk distributions orbiting in an axisymmetric halo with appropriate errors and then attempting to recover the underlying potential using a Markov Chain Monte Carlo approach. We demonstrate that the azimuthally averaged gravitational force field in the Galactic plane - and hence, to a lesser extent, the Galactic mass distribution - can be tightly constrained over a large range of radii using a variety of types of surveys so long as the error distribution of the measurements of the parallax, proper motion, and radial velocity are well understood and the disk is surveyed globally. One advantage of our method is that the target stars can be selected nonrandomly in real or apparent-magnitude space to ensure just such a global sample without biasing the results. Assuming that we can always measure the line-of-sight velocity of a star with at least 1kms-1 precision, we demonstrate that the force field can be determined to better than 1% for Galactocentric radii in the range R = 4-20kpc using either: (1) small samples (a few hundred stars) with very accurate trigonometric parallaxes and good proper-motion measurements (uncertainties δp,tri ≲ 10 μas and δ μ ≲ 100 μasyr-1 respectively); (2) modest samples (1000 stars) with good indirect parallax estimates (e.g., uncertainty in photometric parallax δp,phot 10%-20%) and good proper-motion measurements (δμ 100 μasyr-1); or (3) large samples (104 stars) with good indirect parallax estimates and lower accuracy proper-motion measurements (δμ 1masyr -1). We conclude that near-future surveys, like Space Interferometry Mission Lite, Global Astrometric Interferometer for Astrophysics, and VERA, will provide the first precise mapping of the gravitational force field in the region of the Galactic disk.

Original languageEnglish (US)
Pages (from-to)215-229
Number of pages15
JournalAstrophysical Journal
Issue number1
StatePublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Dark matter
  • Galaxy: disk
  • Galaxy: fundamental parameters
  • Galaxy: kinematics and dynamics
  • Methods: data analysis
  • Surveys


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