Peculiar in-plane velocities in the outer disc of the Milky Way  

作　　者：Hai-Jun Tian Chao Liu Jun-Chen Wan You-Gang Wang Qiao Wang Li-Cai Deng Zi-Huang Cao Yong-Hui Hou Yue-Fei Wang Yue Wu Yong-Heng Zhao 

机构地区：[1]China Three Gorges University, Yichang 443002, China [2]Max Planck Institute for Astronomy, K6nigstuhl 17, D-69117 Heidelberg, Germany [3]Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China [4]Key Laboratory of Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China [5]Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042, China

出　　处：《Research in Astronomy and Astrophysics》2017年第11期45-58,共14页天文和天体物理学研究（英文版）

基　　金：supported by the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences (Grant No. XDB09000000);the National Key Basic Research Program of China (Grant 2014CB845700);the National Natural Science Foundation of China (NSFC, Grant Nos. 11503012, U1331202 and U1731124);NSFC (Grant Nos. 11373032 and 11333003);NSFC (Grant Nos. 11390372 and 11633004);NSFC (Grant No. 11403056);The Guo Shou Jing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by National Astronomical Observatories, Chinese Academy of Sciences

摘　　要：We present the peculiar in-plane velocities derived from LAMOST red clump stars, which are purified and separated by a novel approach into two groups with different ages. The samples are mostly contributed around the Galactic anti-center direction so that we are able to map the radial profiles of the radial and azimuthal velocities in the outer disc. From variations of the in-plane velocities with Galactocentric radius for the younger and older populations, we find that both radial and azimuthal velocities are not axisymmetric at 8 〈 R 〈 14 kpc. The two red clump populations show that the mean radial velocity is negative within R - 9 kpc and positive beyond. This is likely because of the perturbation induced by the rotating bar. The cross-zero radius, R -9 kpc, essentially indicates the rough location of the Outer Lindblad Resonance radius. Given the circular speed of 238 km s^-1, the pattern speed of the bar can be approximated as 45 km s^-1 kpc^-1. The young red clump stars show larger mean radial velocity than the old population by about 3km s^-1 between R-9 and 12kpc. This is possibly because the younger population is more sensitive to the perturbation than the older one. The radial profiles of the mean azimuthal velocity for the two populations show an interesting U-shape, i.e. at R 〈 10.Skpc, the azimuthal velocity declines with R by about 10km s^-1, while at R 〉 10.5 kpc it increases with R to 240 - 245 km s^-1. It is not clear why the mean azimuthal velocity shows this U-shape along the Galactic anti-center direction. Moreover, the azimuthal velocity for the younger population is slightly larger than that for the older one and the difference moderately declines with R. Beyond R0-12 kpc, the azimuthal velocities for the two populations are indistinguishable.We present the peculiar in-plane velocities derived from LAMOST red clump stars, which are purified and separated by a novel approach into two groups with different ages. The samples are mostly contributed around the Galactic anti-center direction so that we are able to map the radial profiles of the radial and azimuthal velocities in the outer disc. From variations of the in-plane velocities with Galactocentric radius for the younger and older populations, we find that both radial and azimuthal velocities are not axisymmetric at 8 〈 R 〈 14 kpc. The two red clump populations show that the mean radial velocity is negative within R - 9 kpc and positive beyond. This is likely because of the perturbation induced by the rotating bar. The cross-zero radius, R -9 kpc, essentially indicates the rough location of the Outer Lindblad Resonance radius. Given the circular speed of 238 km s^-1, the pattern speed of the bar can be approximated as 45 km s^-1 kpc^-1. The young red clump stars show larger mean radial velocity than the old population by about 3km s^-1 between R-9 and 12kpc. This is possibly because the younger population is more sensitive to the perturbation than the older one. The radial profiles of the mean azimuthal velocity for the two populations show an interesting U-shape, i.e. at R 〈 10.Skpc, the azimuthal velocity declines with R by about 10km s^-1, while at R 〉 10.5 kpc it increases with R to 240 - 245 km s^-1. It is not clear why the mean azimuthal velocity shows this U-shape along the Galactic anti-center direction. Moreover, the azimuthal velocity for the younger population is slightly larger than that for the older one and the difference moderately declines with R. Beyond R0-12 kpc, the azimuthal velocities for the two populations are indistinguishable.

关 键 词：Galaxy： disc -- Galaxy： structure -- Galaxy： kinematics and dynamics -- Galaxy： stellar content -- stars： kinematics and dynamics 

分 类 号：P15[天文地球—天文学]