Ripples, spirals, rings, and flares: Do they all start from a bombardment of a dwarf?

主讲人 (Speaker): 

刘超

主讲人单位 (Speaker's Institute): 

中国国家天文台

邀请人 (Invited by): 

汤柏添

时间 (Time): 

星期三, 2019/03/20 - 15:00 to 16:00

地点 (Location): 

珠海校区海滨红楼17栋107 (Rm 107, Red House 17)

摘要 (Abstract): 

       The Galactic outer disk was found not in equilibrium in recent years. Interesting features have been discovered from the 3D structure and kinematics of the outer disk: the disk is wobbly and has ring-like features in stellar density; it is significantly flared; significantly  non-axisymmetric motions (also called bulk motions) are found in 3D stellar velocities;  and the disk stars show clear spiral-like patterns in phase space. Many theoretical models favorite that the disk has experienced a bombardment of a dwarf galaxy a few hundreds million years ago. However, more observational features are required to confirm/disconfirm the hypothesis of the  bombardment. 
       Thanks to the millions of the LAMOST stellar spectra, which broadly cover the Galactic outskirt regions, we are able to systematically look at all these disequilibria features with different stellar tracers. With LAMOST RGB stars we find that the Galactic disk is significantly larger than we previously knew. Rich substructures, flares, and warp in the enlarged Galactic disk are unveiled from these data. We find that the Monoceros ring is part of a flare feature, rather than a tidal disrupted substructure. I will also demonstrate how the spiral patterns in the phase space show up and fade away with different ages and at different galactocentric radii. We find that the spiral patterns in different radii actually associate with many kinematic features discovered in R-Z plane.  On the other hand, the azimuthal and radial velocities of the very young OB stars display large-scale ripple features, which is not associated with spiral arms, in the disk plane. It seems that most of these features are likely the consequences of pass-through event of a dwarf galaxy according to the further analysis of test-particle simulations.

主讲人简介 (Speaker's CV): 

Chao Liu got his PhD degree in 2008 at National Astronomical Observatories, CAS (NAOC). Then, after a short visit at Rensselaer Polytechnic Institute, US, he went to Max-Planck Institute of Astronomy, Germany as a postdoc since 2009. During his work in Germany, we was deeply involved in ESA Gaia mission and was responsible for the research and development of the stellar parametrization with Gaia spectrophotometric data. In 2012, he got a professorship at NAOC. He is now also a professor of University of CAS.