{
  "id": "1801.01514",
  "version": "v1",
  "published": "2018-01-04T19:09:19.000Z",
  "updated": "2018-01-04T19:09:19.000Z",
  "title": "The GALAH survey: properties of the Galactic disk(s) in the solar neighbourhood",
  "authors": [
    "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",
    "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"
  ],
  "comment": "16 pages, 15 figures",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Using data from the GALAH pilot survey, we determined properties of the Galactic thin and thick disk near the solar neighbourhood. The data cover a small range of Galactocentric radius ($7.9 \\leq R_\\mathrm{GC} \\leq 9.5$ kpc), but extends up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation. This allows us to measure reliably the vertical density and abundance profiles of the chemically and kinematically defined `thick' and `thin' disks of the Galaxy. We found scale heights of $0.40 \\pm 0.02$ kpc and $0.81 \\pm 0.04$ kpc for the low- and high-$\\alpha$ populations, respectively. The thin disk (low-$\\alpha$ population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/d$z=-0.18 \\pm 0.01$ dex kpc$^{-1}$, which is broadly consistent with previous studies. In contrast, its vertical $\\alpha$-abundance profile is almost flat, with a gradient of d[$\\alpha$/M]/d$z$ = $0.008 \\pm 0.002$ dex kpc$^{-1}$. The steep metallicity gradient of the low-$\\alpha$ population seems consistent with various radial migration predictions and further confirms that migration plays an important role in the evolution of the thin disk. The thick disk (high-$\\alpha$ population) has a weaker vertical metallicity gradient d[M/H]/d$z = -0.058 \\pm 0.003$ dex kpc$^{-1}$. The $\\alpha$-abundance of the thick disk is nearly constant with height, d[$\\alpha$/M]/d$z$ = $0.007 \\pm 0.002$ dex kpc$^{-1}$. The negative gradient in metallicity and the small gradient in [$\\alpha$/M] indicate that the high-$\\alpha$ population experienced a settling phase, but also formed prior to the onset of major SNeIa enrichment. We explore the implications of the distinct $\\alpha$-enrichments and narrow [$\\alpha$/M] range of the sub-populations in the context of thick disk formation.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-01-04T19:09:19.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "solar neighbourhood",
      "galactic disk",
      "dex kpc",
      "galah survey",
      "thick disk"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}