Galactic Stellar Populations from Photometric Metallicity Distribution Functions
Abstract
Based on Sloan Digital Sky Survey photometric data, Gu developed a new Monte-Carlo-based method for estimating the stellar metallicity distribution functions (MDFs). This method enables a more reliable determination of MDFs compared with the conventional polynomial-based methods. In this work, MDF determined from the method are well fit by a three-Gaussian model, with peaks at [Fe/H] = -0.68, -1.38, and -1.90, associated with the thick disk, the inner halo, and the outer halo, respectively. The vertical metallicity gradient within 1 < Z < 5 kpc is d< [{Fe}/{{H}}]> /{dZ}≈ -0.19 {dex}\cdot {kpc}}-1 around R = 8.25 kpc. But the mean radial gradient is almost negligible. The density profile of the thick disk is fitted with a modified double exponential law decaying to a constant at far distance. The scale height and scale length thus estimated are H ≈ 1.13 kpc and L ≈ 3.63 kpc, which are consistent with the results determined from star-count methods in previous studies. The halos are described with a two-axial power-law ellipsoid, and the axis ratios of both the inner halo and the outer halo, inferred from stellar number density in the R-Z plane, are q ih ≈ 0.49 and q oh ≈ 0.61, respectively. It also manifests that the outer halo is more spherical than the inner halo. Moreover, the halo power-law indices estimated are n ih ≈ 3.4 and n oh ≈ 3.1, indicating that the stellar number density of the inner halo changes more steeply than that of outer halo.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2019
- DOI:
- 10.3847/1538-4357/ab2050
- arXiv:
- arXiv:1905.02880
- Bibcode:
- 2019ApJ...877...83G
- Keywords:
-
- Galaxy: abundances;
- Galaxy: disk;
- Galaxy: fundamental parameters;
- Galaxy: halo;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 10 pages, 12 figures, Accepted for publication in ApJ