Grand Rotation Curve and Dark-Matter Halo in the Milky Way Galaxy
A grand rotation curve of the Milky Way Galaxy was constructed, which covers a wide range of radius from the Galactic Center to $ \sim$ 1 Mpc, and was deconvolved into bulge, disk, and halo components by least-squares fittings. We determined the masses and scale radii of the bulge and disk to be $ {...
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Veröffentlicht in: | Publications of the Astronomical Society of Japan 2012-08, Vol.64 (4) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | A grand rotation curve of the Milky Way Galaxy was constructed, which covers a wide range of radius from the Galactic Center to
$ \sim$
1 Mpc, and was deconvolved into bulge, disk, and halo components by least-squares fittings. We determined the masses and scale radii of the bulge and disk to be
$ {M_{\rm b}}$
$ =$
(1.652
$ \pm$
0.083)
$ \times$
10
$ ^{10}{\ M_\odot}$
,
$ {a_{\rm b}}$
$ =$
0.522
$ \pm$
0.037 kpc,
$ {M_{\rm d}}$
$ =$
(3.41
$ \pm$
0.41)
$ \times$
10
$ ^{10}{\ M_\odot}$
, and
$ {a_{\rm d}}$
$ =$
3.19
$ \pm$
0.35 kpc. The dark halo was fitted by the Navaro–Frenk–White (NFW) density profile,
$ \rho$
$ =$
$ \rho_0/$
[(
$ R/h$
)(1
$ +$
$ R/h$
)
$ ^2$
], and the fit yielded
$ h$
$ =$
12.5
$ \pm$
0.9 kpc and
$ \rho_0$
$ =$
(1.06
$ \pm$
0.14)
$ \times$
10
$ ^{-2}\ M_{\odot}$
pc
$ ^{-3}$
. The local dark-matter density near the Sun at
$ R_0$
$ =$
8 kpc was estimated to be
$ \rho_0^\odot$
$ =$
(6.12
$ \pm$
0.80)
$ \times$
10
$ ^{-3}\ M_{\odot}$
pc
$ ^{-3}$
$ =$
0.235
$ \pm$
0.030 GeV cm
$ ^{-3}$
. The total mass inside the gravitational boundary of the Galaxy at
$ R$
$ \sim$
385 kpc, a half distance to M 31, was estimated to be
$ {M_{\rm b+d+h}}$
$ =$
(7.03
$ \pm$
1.01)
$ \times$
10
$ ^{11}\ M_{\odot}$
. This leads to a stellar baryon fraction of
$ {M_{\rm b+d}}/{M_{\rm b+d+h}}$
$ =$
0.072
$ \pm$
0.018. Considering the expected baryon fraction in the Local Group, we suggest that baryons in the form of hot gas are filling the dark halo with a temperature of
$ \sim$
10
$ ^{6}$
K and an emission measure of
$ \sim$
10
$ ^{-5}$
pc cm
$ ^{2}$
. Such hot halo gas may share a small fraction of the observed X-ray background emission. |
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ISSN: | 0004-6264 2053-051X |
DOI: | 10.1093/pasj/64.4.75 |