Mapping the Milky Way with LAMOSTⅠ:method and overview  

作　　者：Chao Liu Yan Xu Jun-Chen Wan Hai-Feng Wang Jeffrey L.Carlin Li-Cai Deng Heidi Jo Newberg Zi-Huang Cao Yong-Hui Hou Yue-Fei Wang Yong Zhang 

机构地区：[1]Key Lab of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China [2]University of the Chinese Academy of Sciences,Beijing 100049,China [3]LSST,933 North Cherry Avenue,Tucson,AZ 85721,USA [4]Department of Physics,Applied Physics and Astronomy,Rensselaer Polytechnic Institute,Troy,NY 12180,USA [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9期81-100,共20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(2014CB845700);the National Natural Science Foundation of China(Grant Nos.11373032 and 11333003);a National Major Scientific Project built by the Chinese Academy of Sciences.Funding for the project has been provided by the project has been provided by the National Development and Reform Commission

摘　　要：We present a statistical method to derive the stellar density profiles of the Milky Way from spectroscopic survey data, taking into account selection effects. We assume the selection function, which can be altered during observations and data reductions, of the spectroscopic survey is based on photometric colors and magnitude. Then the underlying selection function for a line-of-sight can be recovered well by comparing the distribution of the spectroscopic stars in a color-magnitude plane with that of the photometric dataset. Subsequently, the stellar density profile along a line-of-sight can be derived from the spectroscopically measured stellar density profile multiplied by the selection function. The method is validated using Galaxia mock data with two different selection functions. We demonstrate that the derived stellar density profiles reconstruct the true ones well not only for the full set of targets, but also for sub-populations selected from the full dataset. Finally, the method is applied to map the density pro- files for the Galactic disk and halo, using the LAMOST RGB stars. The Galactic disk extends to about R = 19 kpc, where the disk still contributes about 10% to the total stellar surface density. Beyond this radius, the disk smoothly transitions to the halo without any truncation, bending or breaking. Moreover, no over-density corresponding to the Monoceros ring is found in the Galactic anti-center direction. The disk shows moderate north-south asymmetry at radii larger than 12 kpc. On the other hand, the R-Z tomographic map directly shows that the stellar halo is substantially oblate within a Galactocentric radius of 20 kpc and gradually becomes nearly spherical beyond 30 kpc.We present a statistical method to derive the stellar density profiles of the Milky Way from spectroscopic survey data, taking into account selection effects. We assume the selection function, which can be altered during observations and data reductions, of the spectroscopic survey is based on photometric colors and magnitude. Then the underlying selection function for a line-of-sight can be recovered well by comparing the distribution of the spectroscopic stars in a color-magnitude plane with that of the photometric dataset. Subsequently, the stellar density profile along a line-of-sight can be derived from the spectroscopically measured stellar density profile multiplied by the selection function. The method is validated using Galaxia mock data with two different selection functions. We demonstrate that the derived stellar density profiles reconstruct the true ones well not only for the full set of targets, but also for sub-populations selected from the full dataset. Finally, the method is applied to map the density pro- files for the Galactic disk and halo, using the LAMOST RGB stars. The Galactic disk extends to about R = 19 kpc, where the disk still contributes about 10% to the total stellar surface density. Beyond this radius, the disk smoothly transitions to the halo without any truncation, bending or breaking. Moreover, no over-density corresponding to the Monoceros ring is found in the Galactic anti-center direction. The disk shows moderate north-south asymmetry at radii larger than 12 kpc. On the other hand, the R-Z tomographic map directly shows that the stellar halo is substantially oblate within a Galactocentric radius of 20 kpc and gradually becomes nearly spherical beyond 30 kpc.

关 键 词：methods： statistical -- Galaxy structure -- Galaxy disk - Galaxy halo - surveys LAMOST 

分 类 号：P156[天文地球—天文学] P171