The hunt for the Milky Way's accreted disc

Abstract

The Milky Way is expected to host an accreted disc of stars and dark matter. This forms as massive >1:10 mergers are preferentially dragged towards the disc plane by dynamical friction and then tidally shredded. The accreted disc likely contributes only a tiny fraction of the Milky Way's thin and thick stellar disc. However, it is interesting because: (i) its associated `dark disc' has important implications for experiments hoping to detect a dark matter particle in the laboratory; and (ii) the presence or absence of such a disc constrains the merger history of our Galaxy. In this work, we develop a chemo-dynamical template to hunt for the accreted disc. We apply our template to the high-resolution spectroscopic sample from Ruchti et al. (2011), finding at present no evidence for accreted stars. Our results are consistent with a quiescent Milky Way with no >1:10 mergers since the disc formed and a correspondingly light `dark disc'. However, we caution that while our method can robustly identify accreted stars, our incomplete stellar sample makes it more challenging to definitively rule them out. Larger unbiased stellar samples will be required for this.

14 pages; 8 figures; 1 table. Accepted for publication in MNRAS

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Cited by in corpus (14)

• The origin of the Milky Way globular clusters
• The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc
• Bringing the Galaxy's dark halo to life
• Gaia-DR2 extended kinematical maps. Part II: Dynamics in the Galactic disk explaining radial and vertical velocities
• The Size of Star Clusters Accreted by the Milky Way
• NGC 5746: formation history of a massive disc-dominated galaxy
• The kinematics of local thick discs do not support an accretion origin
• Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2
• An old, metal-rich accreted stellar component in the Milky Way stellar disk
• The effect of secular galactic growth on the evolution of star clusters
• Dependence of Galactic Halo Kinematics on the Adopted Galactic Potential
• Metallicity Gradient of the Thick Disc Progenitor at High Redshift
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data II. Chrono-chemo-kinematics of the disc
• Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction