# Chemo-dynamical properties of the Anticenter Stream: a surviving disc fossil from a past satellite interaction

## TL;DR

The paper investigates the Anticenter Stream using Gaia DR2 and spectroscopic data, revealing its distinct properties and origin as a tidal tail from a past satellite interaction, serving as a fossil record of the Galactic disc.

## Contribution

It provides new kinematic, metallicity, and age data for the ACS, supporting its origin as a satellite debris and highlighting its potential to constrain Galactic potential models.

## Key findings

- ACS is kinematically and spatially distinct from Monoceros
- ACS is more metal-poor and older than Monoceros
- ACS likely originated from a tidal tail of the Sagittarius dwarf

## Abstract

Using Gaia DR2, we trace the Anticenter Stream (ACS) in various stellar populations across the sky and find that it is kinematically and spatially decoupled from the Monoceros Ring. Using stars from {\sc lamost} and {\sc segue}, we show that the ACS is systematically more metal-poor than Monoceros by $0.1$ dex with indications of a narrower metallicity spread. Furthermore, the ACS is predominantly populated of old stars ($\sim 10\,\rm{Gyr}$), whereas Monoceros has a pronounced tail of younger stars ($6-10\, \rm{Gyr}$) as revealed by their cumulative age distributions. Put togehter, all of this evidence support predictions from simulations of the interaction of the Sagittarius dwarf with the Milky Way, which argue that the Anticenter Stream (ACS) is the remains of a tidal tail of the Galaxy excited during Sgr's first pericentric passage after it crossed the virial radius, whereas Monoceros consists of the composite stellar populations excited during the more extended phases of the interaction. We suggest that the ACS can be used to constrain the Galactic potential, particularly its flattening, setting strong limits on the existence of a dark disc. Importantly, the ACS can be viewed as a stand-alone fossil of the chemical enrichment history of the Galactic disc.