From globular clusters to the disc: the dual life of our Galaxy

Abstract

The halo and disc globular cluster population can be used as a tracer of the primordial epochs of the Milky Way formation. In this work, literature data of globular clusters ages, chemical abundances, and structural parameters are studied, explicitly focussing on the origin of the known split in the age-metallicity relation of globular clusters. When the alpha-element abundances, which are less strongly affected by the internal light-element spread of globular clusters (Si, Ca), are considered, a very low observational scatter among metal-poor clusters is observed. A plateau at [SiCa/Fe]~0.35 dex, with a dispersion of only 0.05 dex is observed up to a metallicity of about -0.75 dex. Only a few metal-poor clusters in this metallicity interval present low [SiCa/Fe] abundances. Moreover, metal-rich globular clusters show a knee in the [alpha/Fe] versus [Fe/H] plane around [Fe/H] -0.75 dex. As a consequence, if a substantial fraction of galactic globular clusters has an external origin, they have to be mainly formed either in galaxies that are massive enough to ensure high levels of [alpha/Fe] element abundances even at intermediate metallicity, or in lower mass dwarf galaxies accreted by the Milky Way in their early phases of formation. Finally, clusters in the metal-poor branch of the AMR present an anti-correlation of [SiCa/Fe] with the total cluster magnitude, while this is not the case for metal-rich branch clusters. In addition, this lack of faint high-alpha clusters in the young metal-poor population is in contrast with what is observed for old and more metal-poor clusters, possibly reflecting a higher heterogeneity of formation environments at lower metallicity. Accretion of high-mass satellites, as a major contribution to the current Milky Way globular cluster system both in the metal-poor and the metal-intermediate regime is compatible with the observations.

Accepted for publication in A&A on 25/10/2018

References in corpus (20)

• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• The Sausage Globular Clusters
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• Exploring Anticorrelations and Light Element Variations in Northern Globular Clusters Observed by the APOGEE Survey
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• Metallicity and Alpha-Element Abundance Measurement in Red Giant Stars from Medium Resolution Spectra
• Globular Cluster Systems in Giant Ellipticals: the Mass/Metallicity Relation
• Globular Cluster Systems in Brightest Cluster Galaxies: A Near-Universal Luminosity Function?
• The AMBRE project: The thick thin disk and thin thick disk of the Milky Way
• The Alpha-element knee of the Sagittarius Stream
• NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation? Cluster mass and age in the multiple population context
• Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf Spheroidal galaxy?
• The AMBRE Project: Parameterisation of FGK-type stars from the ESO:HARPS archived spectra
• Chemical abundances in the globular clusters NGC 5024 and NGC 5466 from optical and infrared spectroscopy
• Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426
• Stellar abundances and ages for metal-rich Milky Way globular clusters - Stellar parameters and elemental abundances for 9 HB stars in NGC6352
• Chemical Complexity in the Eu-enhanced Monometallic Globular Cluster NGC 5986
• The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366
• High Resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681

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• Origin of the system of globular clusters in the Milky Way
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• JWST/NIRCam Probes Young Star Clusters in the Reionization Era Sunrise Arc
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• The First Billion Years Project: Finding Infant Globular Clusters at z=6
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• Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362
• Clustering clusters: unsupervised machine learning on globular cluster structural parameters
• The $Hubble$ Missing Globular Cluster Survey. I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01
• Trojan globular clusters: radial migration via trapping in bar resonances
• Linking the Internal Properties of Infant Globular Clusters to their Formation Environments
• Globular clusters of the Gaia Enceladus/Sausage -- I. Orbital and dynamical evolution on cosmological timescales