The Galactic rotation curve

The rotation curve is one of the most powerful tools to understand the mass distribution and formation of a disk galaxy. For decades, the rotation curve of the Milky Way was mainly measured from the HI/CO sources. Since 2011, we obtained more than 4000 red clump stars observed from MMT/Hectospec through TAP program. We use the line-of-sight velocities of these stars to derive the rotation curve of The Milky Way between 8 and 14 kpc in Galactiocentric radius. The rotation curve is not flat in the outer disk but increase when R>10 kpc and up to ~250 km/s at ~13 kpc. A normal three-component bulge+disk+halo model alone cannot describe this, but adding a massive ring of 3.22+/-1.12x10^10 Msun at about 11.9+/10.77 kpc provides an excellent empirical fit. Since there is no report of the stellar over-density at such location, a massive dark matter substructure, e.g., a disrupted subhalo or a caustic ring, may be responsible for it. LAMOST and APOGEE/APOGEE-2 will provide complementary information especially off the Galactic mid-plane, allowing better constraint on the mass distribution of the Galactic disk.

Chao Liu (NAOC)
KIAA, 1st floor seminar room
Fri, 2014-08-08 12:00