Chemical Cartography with LAMOST and Gaia Reveal Azimuthal and Spiral Structure in the Galactic Disk

TL;DR

This study maps the metallicity distribution in the Milky Way using LAMOST and Gaia data, revealing radial, vertical, and azimuthal variations linked to spiral arms, enhancing understanding of Galactic structure.

Contribution

It provides the first detailed analysis of azimuthal metallicity variations in the Galactic disk using large spectroscopic and astrometric surveys.

Findings

Radial metallicity gradient of -0.078 dex/kpc in the disk plane.

Vertical metallicity gradient of -0.15 dex/kpc near the Sun.

Detection of azimuthal metallicity variations correlated with spiral arms.

Abstract

Chemical Cartography, or mapping, of our Galaxy has the potential to fully transform our view of its structure and formation. In this work, we use chemical cartography to explore the metallicity distribution of OBAF-type disk stars from the LAMOST survey and a complementary sample of disk giant stars from Gaia DR3. We use these samples to constrain the radial and vertical metallicity gradients across the Galactic disk. We also explore whether there are detectable azimuthal variations in the metallicity distribution on top of the radial gradient. For the OBAF-type star sample from LAMOST, we find a radial metallicity gradient of $\Delta$[Fe/H]/$\Delta$R $\sim -0.078 \pm 0.001$ dex/kpc in the plane of the disk and a vertical metallicity gradient of $\Delta$[Fe/H]/$\Delta$Z $\sim -0.15 \pm 0.01$ dex/kpc in the solar neighborhood. The radial gradient becomes shallower with increasing vertical height while the vertical gradient becomes shallower with increasing Galactocentric radius, consistent with other studies. We also find detectable spatially-dependent azimuthal variations on top of the radial metallicity gradient at the level of $\sim$0.10 dex. Interestingly, the azimuthal variations appear be close to the Galactic spiral arms in one dataset (Gaia DR3) but not the other (LAMOST). These results suggest that there is azimuthal structure in the Galactic metallicity distribution and that in some cases it is co-located with spiral arms.