{
  "id": "1405.0405",
  "version": "v1",
  "published": "2014-05-02T14:03:41.000Z",
  "updated": "2014-05-02T14:03:41.000Z",
  "title": "On the Chemical and Structural Evolution of the Galactic Disk",
  "authors": [
    "Daisuke Toyouchi",
    "Masashi Chiba"
  ],
  "comment": "10 pages, 7 figures, Accepted for publication in ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We study the detailed properties of the radial metallicity gradient in the stellar disk of our Galaxy to constrain its chemical and structural evolution. For this purpose we select and analyze $\\sim$ 18,500 disk stars taken from two datasets, the Sloan Digital Sky Survey (SDSS) and the High-Accuracy Radial velocity Planetary Searcher (HARPS). On these surveys we examine the metallicity gradient, $\\Delta$[Fe/H]/$\\Delta R_{\\rm g}$, along the guiding-center radii, $R_{\\rm g}$, of stars and its dependence on the [$\\alpha$/Fe] ratios, to infer the original metallicity distribution of the gas disk from which those stars formed and its time evolution. In both sample sources, the thick-disk candidate stars characterized by high [$\\alpha$/Fe] ratios ([$\\alpha$/Fe] $>$ 0.3 in SDSS, [$\\alpha$/Fe] $>$ 0.2 in HARPS) are found to show a positive $\\Delta$[Fe/H]/$\\Delta R_{\\rm g}$, whereas the thin-disk candidate stars characterized by lower [$\\alpha$/Fe] ratios show a negative one. Furthermore, we find that the relatively young thin-disk population characterized by much lower [$\\alpha$/Fe] ratios ([$\\alpha$/Fe] $<$ 0.2 in SDSS, [$\\alpha$/Fe] $<$ 0.1 in HARPS) shows notably a flattening $\\Delta$[Fe/H]/$\\Delta R_{\\rm g}$ with decreasing [$\\alpha$/Fe], in contrast to the old one with higher [$\\alpha$/Fe] ratios ([$\\alpha$/Fe] $\\sim$ 0.2 in SDSS, [$\\alpha$/Fe] $\\sim$ 0.1 in HARPS). The possible implication for early disk evolution is discussed, in the context of galaxy formation accompanying the rapid infall of primordial gas on the inner disk region, which can generate a positive metallicity gradient, and the subsequent chemical evolution of the disk, which results in a flattening effect of a metallicity gradient at later epochs.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-05-02T14:03:41.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "structural evolution",
      "metallicity gradient",
      "galactic disk",
      "young thin-disk population",
      "high-accuracy radial velocity planetary searcher"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/788/1/89",
      "journal": "The Astrophysical Journal",
      "year": 2014,
      "month": "Jun",
      "volume": 788,
      "number": 1,
      "pages": 89
    },
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2014ApJ...788...89T"
    }
  }
}