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

X. X. Xue, H. W. Rix, G. Zhao, P. Re Fiorentin, T. Naab, M. Steinmetz, F. C. Van Den Bosch, T. C. Beers, Y. S. Lee, E. F. Bell, C. Rockosi, B. Yanny, H. Newberg, R. Wilhelm, X. Kang, M. C. Smith, Donald P. Schneider

Research output: Contribution to journalArticle

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Abstract

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 Vcir(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, Mvir = 1.0-0.2-0.3 × 10 12 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 Mvir of only ∼1 × 1012 M also (re)opens the question of whether all of the Milky Way's satellite galaxies are on bound orbits.

Original languageEnglish (US)
Pages (from-to)1143-1158
Number of pages16
JournalAstrophysical Journal
Volume684
Issue number2
DOIs
StatePublished - Sep 10 2008

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horizontal branch stars
blue stars
halos
dark matter
kinematics
curves
estimates
galaxies
simulation
radii
galactic evolution
stellar mass
falling
line of sight
baryons
sun
velocity distribution
orbits
stars
profiles

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Xue, X. X. ; Rix, H. W. ; Zhao, G. ; Re Fiorentin, P. ; Naab, T. ; Steinmetz, M. ; Van Den Bosch, F. C. ; Beers, T. C. ; Lee, Y. S. ; Bell, E. F. ; Rockosi, C. ; Yanny, B. ; Newberg, H. ; Wilhelm, R. ; Kang, X. ; Smith, M. C. ; Schneider, Donald P. / 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. In: Astrophysical Journal. 2008 ; Vol. 684, No. 2. pp. 1143-1158.
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title = "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",
abstract = "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 Vcir(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, Mvir = 1.0-0.2-0.3 × 10 12 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 Mvir of only ∼1 × 1012 M⊙ also (re)opens the question of whether all of the Milky Way's satellite galaxies are on bound orbits.",
author = "Xue, {X. X.} and Rix, {H. W.} and G. Zhao and {Re Fiorentin}, P. and T. Naab and M. Steinmetz and {Van Den Bosch}, {F. C.} and Beers, {T. C.} and Lee, {Y. S.} and Bell, {E. F.} and C. Rockosi and B. Yanny and H. Newberg and R. Wilhelm and X. Kang and Smith, {M. C.} and Schneider, {Donald P.}",
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Xue, XX, Rix, HW, Zhao, G, Re Fiorentin, P, Naab, T, Steinmetz, M, Van Den Bosch, FC, Beers, TC, Lee, YS, Bell, EF, Rockosi, C, Yanny, B, Newberg, H, Wilhelm, R, Kang, X, Smith, MC & Schneider, DP 2008, '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', Astrophysical Journal, vol. 684, no. 2, pp. 1143-1158. https://doi.org/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. / Xue, X. X.; Rix, H. W.; Zhao, G.; Re Fiorentin, P.; Naab, T.; Steinmetz, M.; Van Den Bosch, F. C.; Beers, T. C.; Lee, Y. S.; Bell, E. F.; Rockosi, C.; Yanny, B.; Newberg, H.; Wilhelm, R.; Kang, X.; Smith, M. C.; Schneider, Donald P.

In: Astrophysical Journal, Vol. 684, No. 2, 10.09.2008, p. 1143-1158.

Research output: Contribution to journalArticle

TY - JOUR

T1 - 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

AU - Xue, X. X.

AU - Rix, H. W.

AU - Zhao, G.

AU - Re Fiorentin, P.

AU - Naab, T.

AU - Steinmetz, M.

AU - Van Den Bosch, F. C.

AU - Beers, T. C.

AU - Lee, Y. S.

AU - Bell, E. F.

AU - Rockosi, C.

AU - Yanny, B.

AU - Newberg, H.

AU - Wilhelm, R.

AU - Kang, X.

AU - Smith, M. C.

AU - Schneider, Donald P.

PY - 2008/9/10

Y1 - 2008/9/10

N2 - 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 Vcir(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, Mvir = 1.0-0.2-0.3 × 10 12 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 Mvir of only ∼1 × 1012 M⊙ also (re)opens the question of whether all of the Milky Way's satellite galaxies are on bound orbits.

AB - 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 Vcir(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, Mvir = 1.0-0.2-0.3 × 10 12 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 Mvir 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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