November 14th, 2008

This week's paper:

http://arxiv.org/abs/0811.0859
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Unified Rotation Curve of the Galaxy -- Decomposition into de
Vaucouleurs Bulge, Disk, Dark Halo, and the 9-kpc Rotation Dip
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We present a unified rotation curve of the Galaxy re-constructed from
the existing data by re-calculating the distances and velocities for a
set of galactic constants R_0=8 kpc and V_0=200 km/s. We decompose it
into a bulge with de Vaucouleurs-law profile of half-mass scale radius
0.5 kpc and mass 1.8 x 10^{10}M_{sun}, an exponential disk of scale
radius 3.5 kpc of 6.5 x 10^{10}M_{sun}, and an isothermal dark halo of
terminal velocity 200 km/s. The r^{1/4}-law fit was obtained for the
first time for the Milky Way's rotation curve. After fitting by these
fundamental structures, two local minima, or the dips, of rotation
velocity are prominent at radii 3 and 9 kpc. The 3-kpc dip is consistent
with the observed bar. It is alternatively explained by a massive ring
with the density maximum at radius 4 kpc. The 9-kpc dip is clearly
exhibited as the most peculiar feature in the galactic rotation curve.
We explain it by a massive ring of amplitude as large as 0.3 to 0.4
times the disk density with the density peak at radius 11 kpc. This
great ring may be related to the Perseus arm, while no peculiar feature
of HI-gas is associated.