Constraining the galaxy's dark halo with RAVE stars

Piffl, Tilmann; Binney, James, 1950-; McMillan, Paul J.; Steinmetz, Matthias, 1966-; Helmi, A. (Amina), 1970-; Wyse, Rosemary F. G.; Bienaymé, Olivier; Freeman, Ken, 1940-; Gibson, Brad K.; Gilmore, Gerry, 1951-; Grebel, Eva K.; Kordopatis, Georges, 1985-; Navarro, Julio F. (Julio Fernando); Parker, Quentin A.; Reid, Warren A. (Warren Alfred); Seabroke, George; Siebert, Arnaud, 1974-; Watson, Fred (Fred G.); Zwitter, Tomaž

Galaxy : disc; Galaxy : fundamental parameters; Galaxy : halo; Galaxy : kinematics and dynamics; Solar neighbourhood; Galaxy : structure
2014

Journal article


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© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society
Abstract

We use the kinematics of ∼200000 giant stars that lie within ∼1.5 kpc of the plane to measure the vertical profile of mass density near the Sun. We find that the dark mass contained within the isodensity surface of the dark halo that passes through the Sun ((6±0.9)×1010M⊙), and the surface density within 0.9 kpc of the plane ((69±10)M⊙pc−2) are almost independent of the (oblate) halo's axis ratio q. If the halo is spherical, 46 per cent of the radial force on the Sun is provided by baryons, and only 4.3 per cent of the Galaxy's mass is baryonic. If the halo is flattened, the baryons contribute even less strongly to the local radial force and to the Galaxy's mass. The dark-matter density at the location of the Sun is 0.0126q−0.89M⊙pc−3=0.48q−0.89GeVcm−3. When combined with other literature results we find hints for a mildly oblate dark halo with q≃0.8. Our value for the dark mass within the solar radius is larger than that predicted by cosmological dark-matter-only simulations but in good agreement with simulations once the effects of baryonic infall are taken into account. Our mass models consist of three double-exponential discs, an oblate bulge and a Navarro-Frenk-White dark-matter halo, and we model the dynamics of the RAVE stars in the corresponding gravitational fields by finding distribution functions f(J) that depend on three action integrals. Statistical errors are completely swamped by systematic uncertainties, the most important of which are the distance to the stars in the photometric and spectroscopic samples and the solar distance to the Galactic centre. Systematics other than the flattening of the dark halo yield overall uncertainties ∼15 per cent.

Publisher
The University of Hull
Peer reviewed
Yes
Language
English
Extent
1 MB
Identifier
hull:12856

Journal

Journal title
Monthly notices of the Royal Astronomical Society
Publication date
2014
Publisher
Oxford University Press
DOI
10.1093/mnras/stu1948
ISSN (Print)
0035-8711
ISSN (Electronic)
1365-2966
Volume
445
Issue
3
Start page
3133
End page
3151
Notes

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly notices of the Royal Astronomical Society following peer review. The version of record MNRAS (December 11, 2014) 445 (3): 3133-3151 is available online at: http://mnras.oxfordjournals.org/content/445/3/3133.

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