Two Populations of Carbon-Enhanced Metal-Poor Stars in the Disk System of the Milky Way

TL;DR

This study identifies two distinct populations of carbon-enhanced metal-poor stars in the Milky Way's disk, revealing insights into the galaxy's formation history through chemo-dynamical analysis.

Contribution

It provides the first chemo-dynamical characterization of CEMP stars in the Milky Way disk, linking them to different galactic components and formation scenarios.

Findings

Mildly prograde CEMP stars likely originate from ex-situ inner-halo populations.

Strongly prograde CEMP stars are associated with the metal-weak thick disk.

Results suggest diverse formation pathways for CEMP stars in the Milky Way.

Abstract

We present a chemo-dynamical analysis of low-resolution ($R \sim 1300$) spectroscopy of stars from the AAOmega Evolution of Galactic Structure (AEGIS) survey, focusing on two key populations of carbon-enhanced metal-poor (CEMP) stars within the disk system of the Milky Way: a mildly prograde population ($L_z < 1000\,$kpc$\,$km$\,$s$^{-1}$) and a strongly prograde ($L_z > 1000\,$kpc$\,$km$\,$s$^{-1}$) population. Based on their chemical and kinematic characteristics, and on comparisons with similar populations found in the recent literature, we tentatively associate the former with an ex-situ inner-halo population originating from either the $Gaia$ Sausage or $Gaia$-Enceladus. The latter population is linked to the metal-weak thick-disk (MWTD). We discuss their implications in the context of the formation history of the Milky Way.