Tidal debris from Omega Centauri discovered with unsupervised machine learning

Abstract

The gravitational interactions between the Milky Way and in-falling satellites offer a wealth of information about the formation and evolution of our Galaxy. In this paper, we explore the high-dimensionality of the GALAH DR3 plus Gaia eDR3 data set to identify new tidally stripped candidate stars of the nearby star cluster Omega Centauri ($\omega \mathrm{Cen}$). We investigate both the chemical and dynamical parameter space simultaneously, and identify cluster candidates that are spatially separated from the main cluster body, in regions where contamination by halo field stars is high. Most notably, we find candidates for $\omega \mathrm{Cen}$ scattered in the halo extending to more than $50^{\circ }$ away from the main body of the cluster. Using a grid of simulated stellar streams generated with $\omega \mathrm{Cen}$ like orbital properties, we then compare the on sky distribution of these candidates to the models. The results suggest that if $\omega \mathrm{Cen}$ had a similar initial mass as its present day mass, then we can place a lower limit on its time of accretion at t${}_{\mathrm{acc}}>7$ Gyr ago. Alternatively, if the initial stellar mass was significantly larger, as would be expected if $\omega \mathrm{Cen}$ is the remnant core of a dwarf Galaxy, then we can constrain the accretion time to t${}_{\mathrm{acc}}>4$ Gyr ago. Taken together, these results are consistent with the scenario that $\omega \mathrm{Cen}$ is the remnant core of a disrupted dwarf galaxy.

22 pages, 19 figures, 2 tables, accepted for publication in MNRAS

References in corpus (28)

• Array Programming with NumPy
• The Gaia mission
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• galpy: A Python Library for Galactic Dynamics
• The GALAH Survey: Scientific Motivation
• 4MOST: Project overview and information for the First Call for Proposals
• A time-resolved picture of our Milky Way's early formation history
• The GALAH Survey: Observational Overview and Gaia DR1 companion
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• The Global Dynamical Atlas of the Milky Way mergers: Constraints from Gaia EDR3 based orbits of globular clusters, stellar streams and satellite galaxies
• The TESS-HERMES survey Data Release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone
• Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo
• The Parallax of Omega Centauri Measured from Gaia EDR3 and a Direct, Geometric Calibration of the Tip of the Red Giant Branch and the Hubble Constant
• Generation of mock tidal streams
• Identical or fraternal twins? : The chemical homogeneity of wide binaries from Gaia DR2
• The metallicity spread and the age-metallicity relation of Omega Centauri
• The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
• Testing the chemical tagging technique with open clusters
• Prospects for chemically tagging stars in the Galaxy
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• The Gaia-ESO Survey: A globular cluster escapee in the Galactic halo
• Tails and streams around the Galactic globular clusters NGC1851, NGC1904, NGC2298 and NGC2808
• The GALAH survey: Chemical Tagging of Star Clusters and New Members in the Pleiades
• Rotation and Lithium Confirmation of a 500 Parsec Halo for the Open Cluster NGC 2516
• Blind chemical tagging with DBSCAN: prospects for spectroscopic surveys
• The GALAH Survey: Chemically tagging the Fimbulthul stream to the globular cluster $\omega$ Centauri
• The Mg-K anti-correlation in Omega Centauri
• A stellar census in globular clusters with MUSE. A new perspective on the multiple main sequences of $\omega$ Centauri

Cited by in corpus (6)

• A review of unsupervised learning in astronomy
• Identifying substructure associations in the Milky Way halo using chemo-kinematic tagging
• The Nephele ecosystem: stars, globular clusters, and stellar streams associated with the progenitor galaxy of $\omega$ Centauri
• Chemo-dynamical reconstruction of Milky Way globular cluster progenitors: Age-metallicity relations and the universality of multiple stellar populations
• Disruption of a Giant: Spectroscopic Identification of Members in the Periphery and Tidal Tails of $\omega$ Centauri
• Searching for and characterizing halo substructures with the GALAH DR4 survey