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 turn-off and subgiant stars from the LAMOST Galactic Surveys .
Our results show ( 1 ) all stellar populations younger than 10 Gyr exhibit strong disk flaring , which is accompanied with a dumpy vertical density profile that is best described by a sech ^ { n } 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 mid-plane stellar mass density at solar radius but 400–800 pc ( 3–6 ^ { \circ } ) away from the Sun in the azimuthal direction has a value of 0.0594 \pm 0.0008 M _ { \odot } /pc ^ { 3 } , which is 0.0164 M _ { \odot } /pc ^ { 3 } higher than previous estimates at the solar neighborhood .
The result causes 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 \sim 4 kpc for the young to \sim 2 kpc for the old populations .
The overall population exhibits a disk scale length of 2.48 \pm 0.05 kpc , and a total stellar mass of 3.6 ( \pm 0.1 ) \times 10 ^ { 10 } M _ { \odot } assuming R _ { \odot } = 8.0 kpc , and the value becomes 4.1 ( \pm 0.1 ) \times 10 ^ { 10 } M _ { \odot } if R _ { \odot } = 8.3 kpc ; ( 5 ) The disk has a peak star formation rate ( SFR ) changing from 6–8 Gyr at the inner 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 \pm 0.12 M _ { \odot } /yr .