All-sky Kinematics and Chemistry of Monoceros Stellar Overdensity

TL;DR

This study combines multi-source data to analyze the Monoceros stellar overdensity's kinematic and chemical properties, revealing its similarity to the Galactic thin disk and suggesting an in situ formation.

Contribution

Introduces a new method for selecting and analyzing Monoceros stars across both hemispheres using combined data and simulations, providing first detailed chemical characterization.

Findings

Monoceros stars have azimuthal velocities between 200 and 250 km/s.

The structure's chemical properties resemble those of the Galactic thin disk.

Northern and southern Monoceros regions have indistinguishable chemical compositions.

Abstract

We explore the kinematic and chemical properties of Monoceros stellar overdensity by combining data from 2MASS, WISE, APOGEE, and $\text{Gaia}$. Monoceros is a structure located towards the Galactic anticenter and close to the disk. We identified that its stars have azimuthal velocity in the range of $200 < v_{\phi}\,{\rm(km\,s^{-1})}< 250$. Combining their kinematics and spatial distribution, we designed a new method to select stars from this overdensity. This method allows us to easily identify the structure in both hemispheres and estimate their distances. Our analysis was supported by comparison with simulated data from the entire sky generated by $\texttt{Galaxia}$ code. Furthermore, we characterized, for the first time, the Monoceros overdensity in several chemical-abundance spaces. Our results confirm its similarity to stars found in the thin disk of the Galaxy and suggest an $\textit{in situ}$ formation. Furthermore, we demonstrate that the southern (Mon-S) and northern (Mon-N) regions of Monoceros exhibit indistinguishable chemical compositions.