Journal
ASTROPHYSICAL JOURNAL
Volume 849, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/aa9120
Keywords
Galaxy: halo; Galaxy: kinematics and dynamics; stars: variables: RR Lyrae
Categories
Funding
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy Office of Science
- University of Arizona
- Brazilian Participation Group
- Brookhaven National Laboratory, Carnegie Mellon University
- University of Florida
- French Participation Group
- German Participation Group
- Harvard University
- Instituto de Astrofisica de Canarias
- Michigan State/Notre Dame/JINA Participation Group
- Johns Hopkins University
- Lawrence Berkeley National Laboratory
- Max Planck Institute for Astrophysics
- Max Planck Institute for Extraterrestrial Physics
- New Mexico State University
- New York University
- Ohio State University
- Pennsylvania State University
- University of Portsmouth
- Princeton University
- Spanish Participation Group
- University of Tokyo
- University of Utah
- Vanderbilt University
- University of Virginia
- University of Washington
- Yale University
- National Aeronautics and Space Administration
- NSF [AST-0908139]
- Caltech Summer Undergraduate Research Fellowship (SURF) program
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RR Lyrae stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way (MW). This is because they are easy to find in the light-curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112. RR Lyr stars beyond 50 kpc in the outer halo of the MW, excluding the Sgr streams, for which we have obtained moderate-resolution spectra with Deimos on the Keck II Telescope. Four of these have distances exceeding 100 kpc. These were selected from a much larger set of 447. candidate RR Lyr stars that were datamined using machine-learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112. RR Lyr stars we determine the radial velocity dispersion in the outer halo of the MW to be similar to 90 km s(-1) at 50. kpc, falling to about 65 km s(-1) near 100. kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447. candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as r(--4).
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