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The origin of diverse alpha-element abundances in galaxy discs

Mackereth, JT, Crain, RA, Schiavon, RP, Schaye, J, Theuns, T and Schaller, M (2018) The origin of diverse alpha-element abundances in galaxy discs. Monthly Notices of the Royal Astronomical Society, 477 (4). pp. 5072-5089. ISSN 0035-8711

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Abstract

Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit a spread in [α/Fe] at fixed [Fe/H], manifest at some locations as a bimodality. The origin of these diverse, and possibly distinct, stellar populations in the Galactic disc is not well understood. We examine the Fe and α-element evolution of 133 Milky Way-like galaxies from the EAGLE simulation, to investigate the origin and diversity of their [α/Fe]–[Fe/H] distributions. We find that bimodal [α/Fe] distributions arise in galaxies whose gas accretion histories exhibit episodes of significant infall at both early and late times, with the former fostering more intense star formation than the latter. The shorter characteristic consumption time-scale of gas accreted in the earlier episode suppresses its enrichment with iron synthesized by Type Ia SNe, resulting in the formation of a high-[α/Fe] sequence. We find that bimodality in [α/Fe] similar to that seen in the Galaxy is rare, appearing in approximately 5 per cent of galaxies in our sample. We posit that this is a consequence of an early gas accretion episode requiring the mass accretion history of a galaxy’s dark matter halo to exhibit a phase of atypically rapid growth at early epochs. The scarcity of EAGLE galaxies exhibiting distinct sequences in the [α/Fe]–[Fe/H] plane may therefore indicate that the Milky Way’s elemental abundance patterns, and its accretion history, are not representative of the broader population of ∼L disc galaxies.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 20 Jul 2018 11:16
Last Modified: 20 Jul 2018 11:16
DOI or Identification number: 10.1093/mnras/sty972
URI: http://researchonline.ljmu.ac.uk/id/eprint/8993

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