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Yule-Simpson's paradox in Galactic Archaeology

Minchev, I, Matijevic, G, Hogg, DW, Guiglion, G, Steinmetz, M, Anders, F, Chiappini, C, Martig, M, Queiroz, A and Scannapieco, C (2019) Yule-Simpson's paradox in Galactic Archaeology. Monthly Notices of the Royal Astronomical Society, 487 (3). pp. 3946-3957. ISSN 0035-8711

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Abstract

Simpson’s paradox, or Yule–Simpson effect, arises when a trend appears in different subsets of data but disappears or reverses when these subsets are combined. We describe here seven cases of this phenomenon for chemo-kinematical relations believed to constrain the Milky Way disc formation and evolution. We show that interpreting trends in relations, such as the radial and vertical chemical abundance gradients, the age–metallicity relation, and the metallicity–rotational velocity relation (MVR), can lead to conflicting conclusions about the Galaxy past if analyses marginalize over stellar age and/or birth radius. It is demonstrated that the MVR in RAVE giants is consistent with being always strongly negative, when narrow bins of [Mg/Fe] are considered. This is directly related to the negative radial metallicity gradients of stars grouped by common age (mono-age populations) due to the inside-out disc formation. The effect of the asymmetric drift can then give rise to a positive MVR trend in high-[α/Fe] stars, with a slope dependent on a given survey’s selection function and observational uncertainties. We also study the variation of lithium abundance, A(Li), with [Fe/H] of AMBRE:HARPS dwarfs. A strong reversal in the positive A(Li)–[Fe/H] trend of the total sample is found for mono-age populations, flattening for younger groups of stars. Dissecting by birth radius shows strengthening in the positive A(Li)–[Fe/H] trend, shifting to higher [Fe/H] with decreasing birth radius; these observational results suggest new constraints on chemical evolution models. This work highlights the necessity for precise age estimates for large stellar samples covering wide spatial regions.

Item Type: Article
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: 09 Dec 2019 10:54
Last Modified: 09 Dec 2019 11:00
DOI or Identification number: 10.1093/mnras/stz1239
URI: http://researchonline.ljmu.ac.uk/id/eprint/11871

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