The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood

Duong, L.; Freeman, K. C.; Asplund, M.; Casagrande, L.; Buder, S.; Lind, K.; Ness, M.; Bland-Hawthorn, J.; De Silva, G. M.; D'Orazi, V.; Kos, J.; Lewis, G. F.; Lin, J.; Martell, S. L.; Schlesinger, K.; Sharma, S.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Anguiano, B.; Da Costa, G. S.; Hyde, E.; Horner, J.; Kafle, P. R.; Nataf, D. M.; Reid, W.; Stello, D.; Ting, Y. -S.; Wyse, R. F. G.

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Journal Article

The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood

MPS-Authors

Duong, L.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Freeman, K. C.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Asplund, M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Casagrande, L.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Buder, S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Lind, K.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Ness, M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Bland-Hawthorn, J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

De Silva, G. M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

D'Orazi, V.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Kos, J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Lewis, G. F.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Lin, J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Martell, S. L.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Schlesinger, K.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Sharma, S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Simpson, J. D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Zucker, D. B.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Zwitter, T.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Anguiano, B.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Da Costa, G. S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Hyde, E.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Horner, J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Kafle, P. R.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Nataf, D. M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Reid, W.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Stello, D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Ting, Y. -S.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Wyse, R. F. G.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

External Resource

https://ui.adsabs.harvard.edu/abs/2018MNRAS.476.5216D
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Citation

Duong, L., Freeman, K. C., Asplund, M., Casagrande, L., Buder, S., Lind, K., et al. (2018). The GALAH survey: properties of the Galactic disc(s) in the solar neighbourhood. Monthly Notices of the Royal Astronomical Society, 476, 5216-5232.

Cite as: https://hdl.handle.net/21.11116/0000-0005-CDF6-F

Abstract

Using data from the GALAH pilot survey, we determine properties of the Galactic thin and thick discs near the solar neighbourhood. The data cover a small range of Galactocentric radius (7.9 ≲ R_GC ≲ 9.5 kpc), but extend up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation (at longitude 260° ≤ ℓ ≤ 280°). This allows us to reliably measure the vertical density and abundance profiles of the chemically and kinematically defined `thick' and `thin' discs of the Galaxy. The thin disc (low-α population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/dz = -0.18 ± 0.01 dex kpc^-1, which is broadly consistent with previous studies. In contrast, its vertical α-abundance profile is almost flat, with a gradient of d[α/M]/dz = 0.008 ± 0.002 dex kpc^-1. The steep vertical metallicity gradient of the low-α population is in agreement with models where radial migration has a major role in the evolution of the thin disc. The thick disc (high-α population) has a weaker vertical metallicity gradient d[M/H]/dz = -0.058 ± 0.003 dex kpc^-1. The α-abundance of the thick disc is nearly constant with height, d[α/M]/dz = 0.007 ± 0.002 dex kpc^-1. The negative gradient in metallicity and the small gradient in [α/M] indicate that the high-α population experienced a settling phase, but also formed prior to the onset of major Type Ia supernova enrichment. We explore the implications of the distinct α-enrichments and narrow [α/M] range of the sub- populations in the context of thick disc formation.