The Stellar Metallicity Distribution of the Galactic Halo Based on SCUSS and SDSS Data

Abstract

Abstract Based on the Sloan Digital Sky Survey and South Galactic Cap u-band Sky Survey (SCUSS), we simulate the photometric metallicity distribution functions (MDFs) of stars in the Galactic halo. The photometric metallicity of stars was estimated by a new Monte-Carlo method. Due to the use of a more reliable metallicity calibration method and more accurate u-band deep measurements from SCUSS, we can obtain more accurate MDFs of a large sample of distant stars in the Galactic halo. In this study, we select 78,092 F/G main-sequence turnoff stars (MSTO) in the south Galactic cap, with 0.2 < (g − r)0 < 0.4, as tracers of the stellar MDFs in the Galactic halo. The sample stars are divided into two height intervals above the Galactic plane: −8 < z < −4 kpc and −12 < z < −8 kpc. The MDFs of selected stars in each interval are well fit by a three-Gaussian model, with peaks at [Fe/H] ≈ −0.63, −1.45, and −2.0. The two metal-poor components correspond to the inner halo and outer halo, respectively. The fraction of the metal-rich component, which may be contributed by the substructure (such as Sagittarius stream or other streams) is about 10%. With limited kinematic estimation, we find the correlations between metallicity and kinematics. Our results provide additional supporting evidence of duality of the Galactic halo.