Title: The dynamics of the Galactic disk and the LAMOST survey

Speaker: Chao Liu (NAOC)

Time & Place: Thursday, 3.00pm, April 18th, Lecture Hall, 3rd floor

Abstract: The rotation curve is an important tool to detect the dark matter halo and the mass distributions of other components (e.g., the bulge and the disk) of a galaxy. The Milky Way's rotation curve, which usually measured from the radio sources, e.g., HI, CO etc., is still very uncertain due to the large systematic errors in the distance estimations for the radio sources in the outer disk. In order to map the underlying gravitational potential of the Milky Way, we measured so far the most accurate rotation curve of the Milky Way using more than 4000 red clump stars in the 2nd quadrant of the Galactic disk. It is likely that there is a mass substructure in the outskirt of the Galaxy as well as the disk and the halo components. Except the rotation of the disk stars, their net streaming is also of interest because it reflects the rotating asymmetric components of the potential of the Milky Way, such as the bar and the spiral arms. I will show some new discovered moving groups and patterns in the velocity distributions of the stars either in the solar neighborhood observed by the LAMOST pilot survey or in the outer disk observed by the MMT Hectospec. They may be associated with the resonance of the rotating bar. We expect that, after 5-year survey of the LAMOST, there will be more than 500,000 spectra of the K giants in the disk and around a million of the nearby F/G dwarf stars. These data will constrain the Galactic rotation curve, with which the mass profile of our Galaxy will be accurately mapped from 5 to 20 kpc in Galactocentric radius. Moreover, they will reveal more details of the complicated motions of the disk stars and help to better understand the role that the rotating bar and the spiral arms play in the dynamical evolution of the Galactic disk.