A Monte-Carlo Method for Estimating Stellar Photometric Metallicity Distributions

Abstract

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 metalrich 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 < -< g r 0.2 0.6, 6 kpc < R < 9 kpc, and in different intervals in height above the plane, Z | |. The MDFs for the selected stars within two relatively local intervals (0.8 kpc < < Z 1.2 kpc | | , 1.5 kpc < < Z 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 < < Z 5 kpc | | , 6 kpc < < Z 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.

Element abundance analysis of the metal-rich stellar halo and high-velocitythick disk in the galaxy

“…For example, the inner-halo is mainly distributed at distances up to 10−15 kpc from the Galactic center, and the mean metallicity of the inner-halo range from [Fe/H] ∼ −1.2 dex to −1.7 dex. The outer-halo is mainly distributed at distances up to 15−20 kpc from the Galactic center, and the mean metallicity of the outer-halo range from [Fe/H] ∼ −1.9 dex to −2.3 dex (e.g., Carollo et al 2007;An et al , 2015Zuo et al 2017;Gu et al 2015Gu et al , 2016Gu et al , 2019Liu et al 2018). Studies of the detailed chemical abundances and ages of halo stars have sought to place further constraints on the structure and formation of the Galactic halo (Naidu et al 2020;S ¸ahin & Bilir 2020).…”

Existence of the Metal-Rich Stellar Halo and High-velocity Thick Disk in the Galaxy

“…In the spatial distribution, the inner halo component dominates at distances up to 10−15 kpc from the Galactic center, while the outer-halo component dominates in the region beyond 15 − 20 kpc (Carollo et al 2007). The mean metallicity of the inner-halo range from [Fe/H] ∼ −1.2 to −1.7, while the outer-halo is from [Fe/H] ∼ −1.9 to −2.3 (e.g., Carollo et al 2007;An et al 2013An et al , 2015Zuo et al 2017;Gu et al 2015Gu et al , 2016Gu et al , 2019Liu et al 2018), which may depend on the distance of the sample stars.…”