Zhang, XuBuder, SvenWu, Ya-QianZhao, Gang2023-09-131674-4527http://hdl.handle.net/1885/299516Estimating ages for a large number of giants is of great importance for studying Galactic evolution. In this work, we determine stellar ages and masses for 556 007 giants from LAMOST Data Release 5 (DR5) with empirical relations estimated from chemical [C/N] abundance ratios. Our sample reveals the two wellknown sequences in the age-[α/M] relation. The high-α sequence is composed of stars older than 8 Gyr and low-α sequence is composed of stars with age ranging from 0 Gyr to 13.8 Gyr. Our sample also shows a flat age-[M/H] relation up until 12 Gyr.We compare these distributions with Galactic Chemical Evolution models for reference. When looking at the spatial distribution of stars in 2 Gyr age bins, we find that young stars are concentrated towards the Galactic plane and older stars extend to higher height above and below the disk. We find a smooth transition of median Galactic height for different age bins, which suggests a strong age-dependence on Galactic scale height.This study is supported by the National Natural Science Foundation of China (Grant Nos. 11988101, 11890694), and National Key R&D Program of China (No. 2019YFA0405502), and China Scholarship Council. X.Z. acknowledges hosting at the Australian National University for part of this research. The Guoshoujing Telescope (the Large sky Area MultiObiject 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 the National Astronomical Observatories, Chinese Academy of Sciences.application/pdfen-AU© 2021 National Astronomical Observatories, CAS and IOP Publishing Ltdstars: fundamental parametersGalaxy: structureGalaxy: evolutionGalaxy: abundances202110.1088/1674-4527/21/9/2162022-07-31