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

L. Duong, K. C. Freeman, M. Asplund, L. Casagrande, S. Buder, K. Lind, M. Ness, J. Bland-Hawthorn, G. M. De Silva, V. D'Orazi, J. Kos, G. F. Lewis, J. Lin, S. L. Martell, K. Schlesinger, S. Sharma, J. D. Simpson, D. B. Zucker, T. Zwitter, B. Anguiano & 9 others G. S. Da Costa, E. Hyde, J. Horner, P. R. Kafle, D. M. Nataf, W. Reid, D. Stello, Y. S. Ting, R. F.G. Wyse

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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 ≲ RGC ≲ 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.

Original languageEnglish
Pages (from-to)5216-5232
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume476
Issue number4
DOIs
Publication statusPublished - 1 Jun 2018

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solar neighborhood
gradients
metallicity
subpopulation
settling
longitude
profiles
supernovae
galaxies
radii

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Duong, L., Freeman, K. C., Asplund, M., Casagrande, L., Buder, S., Lind, K., ... Wyse, R. F. G. (2018). The GALAH survey: Properties of the Galactic disc(s) in the solar neighbourhood. Monthly Notices of the Royal Astronomical Society, 476(4), 5216-5232. https://doi.org/10.1093/MNRAS/STY525
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. / The GALAH survey : Properties of the Galactic disc(s) in the solar neighbourhood. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 476, No. 4. pp. 5216-5232.
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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 ≲ RGC ≲ 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.",
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Duong, L, Freeman, KC, Asplund, M, Casagrande, L, Buder, S, Lind, K, Ness, M, Bland-Hawthorn, J, De Silva, GM, D'Orazi, V, Kos, J, Lewis, GF, Lin, J, Martell, SL, Schlesinger, K, Sharma, S, Simpson, JD, Zucker, DB, Zwitter, T, Anguiano, B, Da Costa, GS, Hyde, E, Horner, J, Kafle, PR, Nataf, DM, Reid, W, Stello, D, Ting, YS & Wyse, RFG 2018, 'The GALAH survey: Properties of the Galactic disc(s) in the solar neighbourhood' Monthly Notices of the Royal Astronomical Society, vol. 476, no. 4, pp. 5216-5232. https://doi.org/10.1093/MNRAS/STY525

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.

In: Monthly Notices of the Royal Astronomical Society, Vol. 476, No. 4, 01.06.2018, p. 5216-5232.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The GALAH survey

T2 - Properties of the Galactic disc(s) in the solar neighbourhood

AU - Duong, L.

AU - Freeman, K. C.

AU - Asplund, M.

AU - Casagrande, L.

AU - Buder, S.

AU - Lind, K.

AU - Ness, M.

AU - Bland-Hawthorn, J.

AU - De Silva, G. M.

AU - D'Orazi, V.

AU - Kos, J.

AU - Lewis, G. F.

AU - Lin, J.

AU - Martell, S. L.

AU - Schlesinger, K.

AU - Sharma, S.

AU - Simpson, J. D.

AU - Zucker, D. B.

AU - Zwitter, T.

AU - Anguiano, B.

AU - Da Costa, G. S.

AU - Hyde, E.

AU - Horner, J.

AU - Kafle, P. R.

AU - Nataf, D. M.

AU - Reid, W.

AU - Stello, D.

AU - Ting, Y. S.

AU - Wyse, R. F.G.

PY - 2018/6/1

Y1 - 2018/6/1

N2 - 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 ≲ RGC ≲ 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.

AB - 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 ≲ RGC ≲ 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.

KW - Galaxy: disc

KW - Galaxy: evolution

KW - Galaxy: formation

KW - Stars: abundances

KW - Surveys

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JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

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