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The oldest and most metal-poor stars in the APOSTLE Local Group simulations

Starkenburg, E and Oman, KA and Navarro, JF and Crain, RA and Fattahi, A and Frenk, CS and Sawala, T and Schaye, J (2017) The oldest and most metal-poor stars in the APOSTLE Local Group simulations. Monthly Notices of the Royal Astronomical Society, 465 (2). pp. 2212-2224. ISSN 0035-8711

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Abstract

We examine the spatial distribution of the oldest and most metal-poor stellar populations of Milky Way-sized galaxies using the A Project Of Simulating The Local Environment (APOSTLE) cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (tform < 0.8 Gyr) and most metal-poor ([Fe/H]<−2.5) stars, both of which increase outwards. The most metalpoor stars form over an extended period of time; half of them form after z = 5.3, and the last 10 per cent after z = 2.8. The age of the metal-poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy’s central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. We investigate the dependence of these results on the assumptions made for metal mixing. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal-poor stars that are very old are systems where metalpoor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 11 Jan 2017 09:36
Last Modified: 06 Sep 2017 16:48
DOI or Identification number: 10.1093/mnras/stw2873
URI: http://researchonline.ljmu.ac.uk/id/eprint/5227

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