Yule-Simpson’s paradox in Galactic Archaeology

Minchev, Ivan; Matijevič, G.; Guiglion, G.; Steinmetz, Matthias; Anders, F.; Chiappini, Cristina; Martig, Marie; Queiroz, A. B. A.; Scannapieco, Cecilia

doi:10.1093/mnras/stz1239

Cited by 43 publications

(36 citation statements)

References 105 publications

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“…As inferred from earlier figures, the proto-disc and starburstdisc components occupy a common region in rotation velocitymetallicity space at all locations in real space. Their distribution follows a positive slope, which is often discussed to be associated with the inside-out formation of the thick disc in the context of an isolated galaxy formation scenario (Schönrich & McMillan 2017;Kawata et al 2018;Minchev et al 2019). In our simulation, however, the positive relation between metallicity and rotation velocity is built up by mergers: as the proto-disc evolves and self-enriches prior to the GES merger, multiple smaller mergers impart dynamical heating such that the older, relatively metal-poor proto-disc stars are heated more relative to the younger, more metal-rich stars, thus establishing the positive trend in rotation velocity-metallicity space for this component.…”

Section: The Rotation Velocity-metallicity Planementioning

confidence: 99%

The dual origin of the Galactic thick disc and halo from the gas-rich Gaia–Enceladus Sausage merger

Grand

Kawata

Belokurov

et al. 2020

Monthly Notices of the Royal Astronomical Society

115

106

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We analyse a set of cosmological magneto-hydrodynamic simulations of the formation of Milky Way-mass galaxies identified to have a prominent radially anisotropic stellar halo component similar to the so-called “Gaia Sausage” found in the Gaia data. We examine the effects of the progenitor of the Sausage (the Gaia-Enceladus-Sausage, GES) on the formation of major galactic components analogous to the Galactic thick disc and inner stellar halo. We find that the GES merger is likely to have been gas-rich and contribute 10-50$\%$ of gas to a merger-induced centrally concentrated starburst that results in the rapid formation of a compact, rotationally supported thick disc that occupies the typical chemical thick disc region of chemical abundance space. We find evidence that gas-rich mergers heated the proto-disc of the Galaxy, scattering stars onto less-circular orbits such that their rotation velocity and metallicity positively correlate, thus contributing an additional component that connects the Galactic thick disc to the inner stellar halo. We demonstrate that the level of kinematic heating of the proto-galaxy correlates with the kinematic state of the population before the merger, the progenitor mass and orbital eccentricity of the merger. Furthermore, we show that the mass and time of the merger can be accurately inferred from local stars on counter-rotating orbits.

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Section: The Rotation Velocity-metallicity Planementioning

confidence: 99%

The dual origin of the Galactic thick disc and halo from the gas-rich Gaia–Enceladus Sausage merger

Grand

Kawata

Belokurov

et al. 2020

Monthly Notices of the Royal Astronomical Society

115

106

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“…Therefore, the global thick discs' scale heights are going to be flattened by the MAPs that dominate the surface density at each radius, which are not the ones that flare the most. This is an example of a Yule-Simpson's paradox, characterized as 'weak' by Minchev et al (2019).…”

Section: Flaring Of Maps Flaring Of Thick Discs and Bimodalitymentioning

confidence: 99%

On the flaring of thick discs of galaxies: insights from simulations

Cruz

Martig

Minchev

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Using simulated galaxies in their cosmological context, we analyse how the flaring of mono-age populations (MAPs) influences the flaring and the age structure of geometrically defined thick discs. We also explore under which circumstances the geometric thin and thick discs are meaningfully distinct components, or are part of a single continuous structure as in the Milky Way. We find that flat thick discs are created when MAPs barely flare or have low surface density at the radius where they start flaring. When looking at the vertical distribution of MAPs, these galaxies show a continuous thin/thick structure. They also have radial age gradients and tend to have quiescent merger histories. Those characteristics are consistent with what is observed in the Milky Way. Flared thick discs, on the other hand, are created when the MAPs that flare have a high surface density at the radius where they start flaring. The thick discs’ scale heights can either be dominated by multiple MAPs or just a few, depending on the mass and scale height distribution of the MAPs. In a large fraction of these galaxies, thin and thick discs are clearly distinct structures. Finally, flared thick discs have diverse radial age gradients and merger histories, with galaxies that are more massive or that have undergone massive mergers showing flatter age radial gradients in their thick disc.

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“…Yong et al (2012) find a similar trend for [Al/Fe] of 0.03 ± 0.01 dex/kpc; for [Na/Fe], however, they find a flat trend with significant scatter. Minchev et al (2019) discuss the effect that sample selection can have on measured abundance gradients, in particular the bias introduced by most samples containing a majority of young clusters. To more accurately compare to previous work, and provide more meaningful comparisons for galactic evolution models, in this section we compare mono-age samples.…”

Section: "Odd-z" Gradientsmentioning

confidence: 99%