The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from the Kinematics of ~2400 SDSS Blue Horizontal-Branch Stars

doi:10.1086/589500

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The Astrophysical Journal Volume 684 Number 2 Create an alert RSS this journal

X. X. Xue et al. 2008 ApJ 684 1143 doi:10.1086/589500

The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from the Kinematics of ~2400 SDSS Blue Horizontal-Branch Stars

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X. X. Xue^1,2,3, H. W. Rix², G. Zhao¹, P. Re Fiorentin^2,4, T. Naab⁵, M. Steinmetz⁶, F. C. van den Bosch², T. C. Beers⁷, Y. S. Lee⁷, E. F. Bell², C. Rockosi⁸, B. Yanny⁹, H. Newberg¹⁰, R. Wilhelm¹¹, X. Kang², M. C. Smith¹² and D. P. Schneider¹³

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¹ National Astronomical Observatories, CAS, 20A Datun Road, Chaoyang District, 100012 Beijing, China
² Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
³ Graduate University of the Chinese Academy of Sciences, 19A Yuquan Road, Shijingshan District, 100049 Beijing, China
⁴ Department of Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
⁵ Universität Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany
⁶ Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Department of Physics and Astronomy, CSCE (Center for the Study of Cosmic Evolution), and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824
⁸ Lick Observatory/University of California, Santa Cruz, CA 95060
⁹ Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510-5011
¹⁰ Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180
¹¹ Department of Physics and Astronomy, Texas Tech University, Lubbock, TX 79409
¹² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹³ Department of Astronomy and Astrophysics, Pennsylvania State University, 504 Davey Laboratory, University Park, PA 16802

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Abstract References Cited By

We derive new constraints on the mass of the Milky Way's dark matter halo, based on 2401 rigorously selected blue horizontal-branch halo stars from SDSS DR6. This sample enables construction of the full line-of-sight velocity distribution at different galactocentric radii. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way. This procedure results in an estimate of the Milky Way's circular velocity curve to ~60 kpc, which is found to be slightly falling from the adopted value of 220 km s⁻¹ at the Sun's location, and implies M(< 60 kpc) = (4.0 ± 0.7) × 10¹¹ M. The radial dependence of V_cir(r) , derived in statistically independent bins, is found to be consistent with the expectations from an NFW dark matter halo with the established stellar mass components at its center. If we assume that an NFW halo profile of characteristic concentration holds, we can use the observations to estimate the virial mass of the Milky Way's dark matter halo, M_vir = 1.0^{+ 0.3}_−0.2 × 10¹² M, which is lower than many previous estimates. We have checked that the particulars of the cosmological simulations are unlikely to introduce systematics larger than the statistical uncertainties. This estimate implies that nearly 40% of the baryons within the virial radius of the Milky Way's dark matter halo reside in the stellar components of our Galaxy. A value for M_vir of only ~1 × 10¹² M also (re)opens the question of whether all of the Milky Way's satellite galaxies are on bound orbits.

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The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from the Kinematics of ~2400 SDSS Blue Horizontal-Branch Stars

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