{
  "id": "2011.01189",
  "version": "v1",
  "published": "2020-11-02T18:29:00.000Z",
  "updated": "2020-11-02T18:29:00.000Z",
  "title": "Exploring the Galaxy's halo and very metal-weak thick disk with SkyMapper and Gaia DR2",
  "authors": [
    "G. Cordoni",
    "G. S. Da Costa",
    "D. Yong",
    "A. D. Mackey",
    "A. F. Marino",
    "S. Monty",
    "T. Nordlander",
    "J. E. Norris",
    "M. Asplund",
    "M. S. Bessell",
    "A. R. Casey",
    "A. Frebel",
    "K. Lind",
    "S. J. Murphy",
    "B. P. Schmidt",
    "X. D. Gao",
    "T. Xylakis-Dornbusch",
    "A. M. Amarsi",
    "A. P. Milone"
  ],
  "comment": "23 pages, 15 figures, accepted for publication in MNRAS",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "In this work we combine spectroscopic information from the \\textit{SkyMapper survey for Extremely Metal-Poor stars} and astrometry from Gaia DR2 to investigate the kinematics of a sample of 475 stars with a metallicity range of $ -6.5 \\leq \\rm [Fe/H] \\leq -2.05$ dex. Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the \\textit{Gaia Sausage} and \\textit{Gaia Sequoia} accretion events, respectively. The most metal-poor of these candidates have metallicities of $\\rm [Fe/H]=-3.31$ and $\\rm [Fe/H]=-3.74$, respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events. We also find, consistent with other studies, that $\\sim$21\\% of the sample have orbits that remain confined to within 3~kpc of the Galactic plane, i.e., |Z$_{max}$| $\\leq$ 3~kpc. Of particular interest is a sub-sample ($\\sim$11\\% of the total) of low |Z$_{max}$| stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H] = --4.30 and the sub-sample is best interpreted as the very low-metallicity tail of the metal-weak thick disk population. The low |Z$_{max}$|, low eccentricity stars with retrograde orbits are likely accreted, while the low |Z$_{max}$|, high eccentricity pro- and retrograde stars are plausibly associated with the \\textit{Gaia Sausage} system. We find that a small fraction of our sample ($\\sim$4\\% of the total) is likely escaping from the Galaxy, and postulate that these stars have gained energy from gravitational interactions that occur when infalling dwarf galaxies are tidally disrupted.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-11-02T18:29:00.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "gaia dr2",
      "galaxys halo",
      "accretion events",
      "low-metallicity tail",
      "metal-weak thick disk population"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 23,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}