2018ApJS..237...33X

We present a detailed determination and analysis of 3D stellar mass distribution of the Galactic disk for mono-age populations using a sample of 0.93 million main-sequence turnoff and subgiant stars from the LAMOST Galactic Surveys. Our results show the following. (1) All stellar populations younger than 10 Gyr exhibit strong disk flaring, which is accompanied by a dumpy vertical density profile that is best described by a sechⁿ function with index depending on both radius and age. (2) Asymmetries and wave-like oscillations are presented in both the radial and vertical direction, with strength varying with stellar populations. (3) As a contribution by the Local spiral arm, the midplane stellar mass density at solar radius but 400-800 pc (3°-6°) away from the Sun in the azimuthal direction has a value of 0.0594 ± 0.0008 M_☉ pc^–3, which is 0.0164 M_☉ pc^–3 higher than previous estimates at the solar neighborhood. The result raises doubts on the current estimate of local dark matter density. (4) The radial distribution of surface mass density yields a disk scale length evolving from ∼4 kpc for the young populations to ∼2 kpc for the old populations. The overall population exhibits a disk scale length of 2.48 ± 0.05 kpc and a total stellar mass of (3.6 ± 0.1) x 10¹⁰ M_☉ assuming R_☉ = 8.0 kpc, and the value becomes (4.1 ± 0.1) x 10¹⁰ M_☉ if R_☉ = 8.3 kpc. (5) The disk has a peak star formation rate (SFR) changing from 6-8 Gyr ago at the inner part to 4-6 Gyr ago at the outer part, indicating an inside-out assemblage history. The 0-1 Gyr population yields a recent disk total SFR of 1.96 ± 0.12 M_☉ yr^–1.