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Origin of the metallicity distribution in the thick disc

Miranda, M. S.; Pilkington, K.; Gibson, B. K.; Brook, C. B.; Sánchez-Blázquez, P.; Minchev, I.; Few, C. G.; Smith, R.; Domínguez-Tenreiro, R.; Obreja, A.; Bailin, J.; Stinson, G. S.


M. S. Miranda

K. Pilkington

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Professor Brad Gibson
Head of Dept, Physics & Maths; Director, E.A. Milne Centre for Astrophysics

C. B. Brook

P. Sánchez-Blázquez

I. Minchev

R. Smith

R. Domínguez-Tenreiro

A. Obreja

J. Bailin

G. S. Stinson


Using a suite of cosmological chemodynamical disc galaxy simulations, we assess how (a) radial metallicity gradients evolve with scaleheight; (b) the vertical metallicity gradients change through the thick disc; and (c) the vertical gradient of the stellar rotation velocity varies through the disc. We compare with the Milky Way to search for analogous trends. Methods. We analyse five simulated spiral galaxies with masses comparable to the Milky Way. The simulations span a range of star formation and energy feedback strengths and prescriptions, particle-and grid-based hydrodynamical implementations, as well as initial conditions/assembly history. Disc stars are identified initially via kinematic decomposition, with a posteriori spatial cuts providing the final sample from which radial and vertical gradients are inferred. Results. Consistently, we find that the steeper, negative, radial metallicity gradients seen in the mid-plane flatten with increasing height away from the plane. In simulations with stronger (and/or more spatially-extended) feedback, the negative radial gradients invert, becoming positive for heights in excess of ∼1 kpc. Such behaviour is consistent with that inferred from recent observations. Our measurements of the vertical metallicity gradients show no clear correlation with galactocentric radius, and are in good agreement with those observed in the Milky Way's thick disc (locally). Each of the simulations presents a decline in rotational velocity with increasing height from the mid-plane, although the majority have shallower kinematic gradients than that of the Milky Way. Conclusions. Simulations employing stronger/more extended feedback prescriptions possess radial and vertical metallicity and kinematic gradients more in line with recent observations. The inverted, positive, radial metallicity gradients seen in the simulated thick stellar discs originate in a population of younger, more metal-rich, stars formed in situ, superimposed upon a background population of older migrators from the inner disc; the contrast provided by the former increases radially, due to the inside-out growth of the disc. A similar behaviour may be responsible for the same flattening as seen in the radial gradients with scaleheight in the Milky Way.


Miranda, M. S., Pilkington, K., Gibson, B. K., Brook, C. B., Sánchez-Blázquez, P., Minchev, I., …Stinson, G. S. (2016). Origin of the metallicity distribution in the thick disc. Astronomy and Astrophysics, 587, Article A10.

Acceptance Date Dec 13, 2015
Online Publication Date Feb 11, 2016
Publication Date Mar 1, 2016
Deposit Date Mar 31, 2016
Publicly Available Date Oct 27, 2022
Journal Astronomy & astrophysics
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 587
Article Number A10
Keywords Galaxies -- abundancies; Galaxies -- evolution; Galaxies -- formation; Galaxy -- disc; Methods -- numerical
Public URL
Publisher URL
Additional Information Copy of article first published in: Astronomy & astrophysics, 2016, v.587


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