PREPRINT
335FDA56-A1D2-4DD7-83BB-581F9BEC24DB

# The chemical signature of the Galactic spiral arms revealed by Gaia DR3

E. Poggio, A. Recio-Blanco, P. A. Palicio, P. Re Fiorentin, P. de Laverny, R. Drimmel, G. Kordopatis, M. G. Lattanzi, M. Schultheis, A. Spagna, E. Spitoni
arXiv:2206.14849

Submitted on 29 June 2022

## Abstract

Taking advantage of the recent Gaia Data Release 3 (DR3), we map chemical inhomogeneities in the Milky Way's disc out to a distance of $\sim$ 4 kpc of the Sun, using different samples of bright giant stars (log($g$) < 1.5 dex, T${}_{\mathrm{e}\mathrm{f}\mathrm{f}}$ \sim 3500-5500 K). We detect remarkable inhomogeneities, which appear to be more prominent and structured for the sample containing stars with relatively hotter effective temperatures. For this sample, we identify three (possibly four) metal-rich elongated features in the Galactic plane, which are located in proximity of the spiral arms in the Galactic disc. When projected onto Galactic radius, those features manifest themselves as statistically significant bumps on top of the observed radial gradients, making the assumption of a linear radial decrease not applicable to this sample. In contrast, the sample containing cooler giants exhibits a relatively smooth decrease as a function of Galactic radius. Considering different slices in Galactic azimuth $\varphi$, the slope of the measured radial metallicity gradient for the cool giants varies gradually from $\sim$-0.05 dex kpc${}^{-1}$ at $\varphi \sim -{20}^{\circ }$ to $\sim$ -0.03 dex kpc${}^{-1}$ at $\varphi \sim {20}^{\circ }$. The strong correlation between the spiral structure of the Galaxy and the observed chemical pattern in the sample with relatively hotter effective temperatures indicates that the spiral arms might be at the origin for the detected chemical inhomogeneities. In this scenario, the spiral arms would leave in the hotter stars a strong signature, which progressively disappears when cooler giants stars are considered.

## Preprint

Comment: 8 pages, 6 figures. Submitted to A&A. We welcome comments, suggestions for missing references, questions, etc

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics