The stellar metallicity distribution in intermediate-latitude fields with BATC and SDSS data

Abstract

Based on Beijing–Arizona–Taiwan–Connecticut (BATC) and Sloan Digital Sky Survey (SDSS) photometric data, we adopt the spectral energy distribution (SED) fitting method to evaluate the metallicity distribution for ∼40 000 main‐sequence stars in the Galaxy. According to the derived photometric metallicities of these sample stars, we find that the metallicity distribution shifts from metal‐rich to metal‐poor with the increase of distance from the Galactic Centre. The mean metallicity is about −1.5 ± 0.2 dex in the outer halo and −1.3 ± 0.1 dex in the inner halo and smoothly decreases from −0.4 to −0.8 in the interval 0 < r≤ 5 kpc. A fluctuation in mean metallicity with Galactic longitude can be found in the interval 4 < r≤ 8 kpc. There is a vertical abundance gradient d[Fe/H]/dz∼−0.21 ± 0.05 dex kpc−1 for the thin disc (z≤ 2 kpc). At a distance 2 < z≤ 5 kpc, where thick‐disc stars dominate, the gradient is about −0.16 ± 0.06 dex kpc−1; this can be interpreted as a mixture of stellar populations with different mean metallicities at all z levels. The vertical metallicity gradient is −0.05 ± 0.04 dex kpc−1 for the halo (z > 5 kpc), so there is little or no metallicity gradient in the halo.

Extinction law at a distance up to 25 kpc toward the Galactic poles

“…However, even for red dwarfs with M Ks ≈ 6 m having Ks ≈ 14 m and, consequently, |Z| ≈ 400 pc, i.e., located behind the bulk of the absorbing layer, the reddening is significant, while the solar metallicity is atypical. According to Peng et al (2012) and Schlesinger et al (2014), who analyzed many studies of the vertical metallicity gradient in the Galaxy, on average, Z = 0.008 at |Z| = 400 pc. For this condition to be met, the isochrones must be shifted so that most of the red dwarfs are between the isochrones Z = 0.005 and 0.015.…”

The stellar metallicity distribution in intermediate-latitude fields

“…This feature may reflect a fluctuation from streams (such as the Monoceros stream) that are accreted from nearby galaxies (Peng et al 2012).…”

“…We find that the vertical abundance gradient for the thin disk (0 < z < 2 kpc) is d −1 is found over the z distance interval 5 < z 15 kpc. Therefore, there is little or no gradient in the halo (Peng et al 2012).…”

A Monte-Carlo Method for Estimating Stellar Photometric Metallicity Distributions

“…The metallicity distribution function (MDF) for stars in the Milky Way is of great importance for revealing the chemical structure of Galactic halo and disk systems, and provides essential clues to the assembly and enrichment history of the Galaxy (Carollo et al 2007(Carollo et al , 2010Peng et al 2012Peng et al , 2013An et al 2013An et al , 2015. Many multi-fiber spectroscopic surveys, including the Sloan Digital Sky Survey (SDSS; York et al 2000), the Radial Velocity Experiment (RAVE; Steinmetz et al 2006), and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST; Deng et al 2012;Zhao et al 2012;Liu et al 2014), have obtained metallicity estimates and other stellar parameters for millions of stars from low-and medium-resolution spectra.…”

“…Ivezić et al (2008) employed SDSS data to derive a metallicity estimator from u − g and g − r colors, and successfully mapped the metallicity distribution of millions of F/G main-sequence stars within a distance of ∼8 kpc from the Sun. Peng et al (2012) also used BATC survey data to estimate the stellar photometric metallicity distribution. Gu et al (2015) obtained a metallicity estimator using SCUSS (Zou et al 2015(Zou et al , 2016) data, which can be applied up to fainter magnitudes due to the use of more accurate SCUSS u-band measurements, and used this estimator to explore the metallicity of the Sagittarius stream in the South Galactic cap.…”