2016ApJ...826...36G

Based on the Sloan Digital Sky Survey, we develop a new Monte-Carlo-based method to estimate the photometric metallicity distribution function (MDF) for stars in the Milky Way. Compared with other photometric calibration methods, this method enables a more reliable determination of the MDF, particularly at the metal-poor and metal-rich ends. We present a comparison of our new method with a previous polynomial-based approach and demonstrate its superiority. As an example, we apply this method to main-sequence stars with 0.2\lt g-r\lt 0.6 , 6 kpc R . The MDFs for the selected stars within two relatively local intervals (0.8 kpc \lt | Z| \lt 1.2 kpc , 1.5 kpc \lt | Z| \lt 2.5 kpc) can be well-fit by two Gaussians with peaks at [Fe/H] ≃ -0.6 and -1.2, respectively: one associated with the disk system and the other with the halo. The MDFs for the selected stars within two more distant intervals (3 kpc \lt | Z| \lt 5 kpc , 6 kpc \lt | Z| \lt 9 kpc) can be decomposed into three Gaussians with peaks at [Fe/H] ≃ -0.6, -1.4, and -1.9, respectively, where the two lower peaks may provide evidence for a two-component model of the halo: the inner halo and the outer halo. The number ratio between the disk component and halo component(s) decreases with vertical distance from the Galactic plane, which is consistent with the previous literature.