Stellar mass distribution and star formation history of the Galactic disk revealed by mono-age stellar populations from LAMOST

Abstract

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 $sec{h}^n$ 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 ({\rm 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 {\rm SFR} of $1.96\pm 0.12$\,$M_{\odot }$/yr.

37 pages, 26 figures, 8 tables; Accepted for publication in ApJ supplement