Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk

TL;DR

This paper presents evidence of a large-scale positive correlation between rotation velocity and metallicity in the Galactic thick disk, based on Gaia and APOGEE data, providing constraints for galaxy formation theories.

Contribution

It provides the first extensive observational confirmation of a positive rotation-metallicity correlation in the thick disk across 8 kpc, informing galaxy formation models.

Findings

Thick disk shows a positive velocity-metallicity correlation.

Radial metallicity gradients are re-derived with high precision.

The correlation persists over an 8 kpc range.

Abstract

This study is based on high quality astrometric and spectroscopic data from the most recent releases by Gaia and APOGEE. We select $58\,882$ thin and thick disk red giants, in the Galactocentric (cylindrical) distance range $5 < R < 13$~kpc and within $|z| < 3$~kpc, for which full chemo-kinematical information is available. Radial chemical gradients, $\partial \rm{[M/H]} / \partial \rm{R}$, and rotational velocity-metallicity correlations, $\partial V_\phi / \partial \rm{[M/H]}$, are re-derived firmly uncovering that the thick disk velocity-metallicity correlation maintains its positiveness over the $8$~kpc range explored. This observational result is important as it sets experimental constraints on recent theoretical studies on the formation and evolution of the Milky Way disk and on cosmological models of Galaxy formation.