Mapping the Galactic Metallicity Gradient with Open Clusters: The State-of-the-Art and Future Challenges

TL;DR

This study analyzes high-resolution spectroscopic data of 251 open clusters to map the Galactic metallicity gradient, revealing its slope, flattening regions, and comparing it with other spiral galaxies, while discussing future challenges.

Contribution

It provides a homogenized catalogue of open cluster metallicities and orbital parameters, and offers new insights into the Galactic metallicity gradient and its comparison with other galaxies.

Findings

Radial metallicity gradient slope is -0.064 dex/kpc.

Gradient flattens beyond 12.1 kpc from the Galactic center.

Comparison shows similar gradient shapes in other spiral galaxies.

Abstract

In this paper, we make use of data collected for open cluster members by high-resolution spectroscopic surveys and programmes (i.e., APOGEE, Gaia-ESO, GALAH, OCCASO, and SPA). These data have been homogenised and then analysed as a whole. The resulting catalogue contains [Fe/H] and orbital parameters for 251 Galactic open clusters. The slope of the radial metallicity gradient obtained through 175 open clusters with high-quality metallicity determinations is $-$0.064 $\pm$ 0.007 dex kpc$^{-1}$. The radial metallicity distribution traced by open clusters flattens beyond R$_{\rm Gal}$=12.1 $\pm$ 1.1 kpc. The slope traced by open clusters in the [Fe/H]-L$_{\rm z}$ diagram is $-$0.31 $\pm$ 0.02 10$^{3}$ dex km$^{-1}$ kpc$^{-1}$ s, but it flattens beyond L$_{\rm z}$=2769 $\pm$ 177 km kpc s$^{-1}$. In this paper, we also review some high-priority practical challenges around the study of open clusters that will significantly push our understanding beyond the state-of-the-art. Finally, we compare the shape of the galactic radial metallicity gradient to those of other spiral galaxies.