The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation

TL;DR

This study analyzes the metallicity distribution of G and K dwarfs across various distances from the Galactic plane, providing new constraints for models of the Milky Way's disk formation and evolution.

Contribution

It offers the first bias-corrected MDF for a large, volume-complete sample of G and K dwarfs at different heights, extending previous local studies.

Findings

MDF becomes more metal-poor with increasing distance from the Galactic plane.

Observed MDFs are more metal-poor than those predicted by existing Milky Way models.

K dwarfs are effective tracers of the Galaxy's chemical evolution at larger distances.

Abstract

We present the metallicity distribution function (MDF) for 24,270 G and 16,847 K dwarfs at distances from 0.2 to 2.3 kpc from the Galactic plane, based on spectroscopy from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. This stellar sample is significantly larger in both number and volume than previous spectroscopic analyses, which were limited to the solar vicinity, making it ideal for comparison with local volume-limited samples and Galactic models. For the first time, we have corrected the MDF for the various observational biases introduced by the SEGUE target selection strategy. The SEGUE sample is particularly notable for K dwarfs, which are too faint to examine spectroscopically far from the solar neighborhood. The MDF of both spectral types becomes more metal-poor with increasing |Z|, which reflects the transition from a sample with small [alpha/Fe] values at small heights to one with enhanced [alpha/Fe] above 1 kpc. Comparison of our SEGUE distributions to those of two different Milky Way models reveals that both are more metal-rich than our observed distributions at all heights above the plane. Our unbiased observations of G and K dwarfs provide valuable constraints over the |Z|-height range of the Milky Way disk for chemical and dynamical Galaxy evolution models, previously only calibrated to the solar neighborhood, with particular utility for thin- and thick-disk formation models.