Ages and kinematics of chemically selected, accreted Milky Way halo stars

Abstract

We exploit the [Mg/Mn]-[Al/Fe] chemical abundance plane to help identify nearby halo stars in the 14th data release from the APOGEE survey that have been accreted on to the Milky Way. Applying a Gaussian Mixture Model, we find a `blob' of 856 likely accreted stars, with a low disc contamination rate of ~7%. Cross-matching the sample with the second data release from Gaia gives us access to parallaxes and apparent magnitudes, which place constraints on distances and intrinsic luminosities. Using a Bayesian isochrone pipeline, this enables us to estimate new ages for the accreted stars, with typical uncertainties of ~20%. Our new catalogue is further supplemented with estimates of orbital parameters. The blob stars span a metallicities between -0.5 to -2.5, and [Mg/Fe] between -0.1 to 0.5. They constitute ~30% of the metal-poor ([Fe/H] < -0.8) halo at metallicities of ~-1.4. Our new ages are mainly range between 8 to 13 Gyr, with the oldest stars the metal-poorest, and with the highest [Mg/Fe] abundance. If the blob stars are assumed to belong to a single progenitor, the ages imply that the system merged with our Milky Way around 8 Gyr ago and that star formation proceeded for ~5 Gyr. Dynamical arguments suggest that such a single progenitor would have a total mass of ~1011Msun, similar to that found by other authors using chemical evolution models and simulations. Comparing the scatter in the [Mg/Fe]-[Fe/H] plane of the blob stars to that measured for stars belonging to the Large Magellanic Cloud suggests that the blob does indeed contain stars from only one progenitor.

14 pages, 9 figures, 2 tables, submitted to MNRAS. Comments welcome!

References in corpus (31)

• Galactic chemical evolution: Carbon through Zinc
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• Two Stellar Components in the Halo of the Milky Way
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The accretion origin of the Milky Way's stellar halo
• The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream
• The Dual Origin of Stellar Halos
• The stellar mass-halo mass relation of isolated field dwarfs: a critical test of $\Lambda$CDM at the edge of galaxy formation
• Constraining the Galaxy's dark halo with RAVE stars
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• Kinematics of the stellar halo and the mass distribution of the Milky Way using BHB stars
• Building Late-Type Spiral Galaxies by In-Situ and Ex-Situ Star Formation
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• New H-band Stellar Spectral Libraries for the SDSS-III/APOGEE survey
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• PLATO as it is: a legacy mission for Galactic archaeology
• The mechanics of tidal streams
• A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?
• Binary stars in the Galactic thick disc
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution
• The K2-HERMES Survey: Age and Metallicity of the Thick Disc
• Constraining Metallicity-dependent Mixing and Extra Mixing using [C/N] in Alpha-Rich Field Giants
• Disentangling the Galactic Halo with APOGEE: II. Chemical and Star Formation Histories for the Two Distinct Populations
• Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars
• Metallicity Bias in the Kinematics of the Milky Way Stellar Halo
• Does SEGUE/SDSS indicate a dual Galactic halo?
• On the Relative Ages of the $\alpha$-Rich and $\alpha$-Poor Stellar Populations in the Galactic Halo
• The K2 Galactic Caps Project -- Going Beyond the \textit{Kepler} Field and Ageing the Galactic Disc

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