{
  "id": "1709.03993",
  "version": "v1",
  "published": "2017-09-12T18:00:29.000Z",
  "updated": "2017-09-12T18:00:29.000Z",
  "title": "CO line emission from galaxies in the Epoch of Reionization",
  "authors": [
    "L. Vallini",
    "A. Pallottini",
    "A. Ferrara",
    "S. Gallerani",
    "E. Sobacchi",
    "C. Behrens"
  ],
  "comment": "16 pages, 14 figures, accepted for publication in MNRAS",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We study the CO line luminosity ($L_{\\rm CO}$), the shape of the CO Spectral Line Energy Distribution (SLED), and the value of the CO-to-$\\rm H_2$ conversion factor in galaxies in the Epoch of Reionization (EoR). To this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution ($30\\, \\rm{pc}$), cosmological simulation of a main-sequence ($M_{*}\\approx10^{10}\\, \\rm{M_{\\odot}}$, $SFR\\approx 100\\,\\rm{M_{\\odot}\\, yr^{-1}}$) galaxy, \"Alth{\\ae}a\", at $z\\approx6$. We find that the CO emission traces the inner molecular disk ($r\\approx 0.5 \\,\\rm{kpc}$) of Alth{\\ae}a with the peak of the CO surface brightness co-located with that of the [CII] 158$\\rm \\mu m$ emission. Its $L_{\\rm CO(1-0)}=10^{4.85}\\, \\rm{L_{\\odot}}$ is comparable to that observed in local galaxies with similar stellar mass. The high ($\\Sigma_{gas} \\approx 220\\, \\rm M_{\\odot}\\, pc^{-2}$) gas surface density in Alth{\\ae}a, its large Mach number (\\mach$\\approx 30$), and the warm kinetic temperature ($T_{k}\\approx 45 \\, \\rm K$) of GMCs yield a CO SLED peaked at the CO(7-6) transition, i.e. at relatively high-$J$, and a CO-to-$\\rm H_2$ conversion factor $\\alpha_{\\rm CO}\\approx 1.5 \\, \\rm M_{\\odot} \\rm (K\\, km\\, s^{-1}\\, pc^2)^{-1} $ lower than that of the Milky Way. The ALMA observing time required to detect (resolve) at 5$\\sigma$ the CO(7-6) line from galaxies similar to Alth{\\ae}a is $\\approx13$ h ($\\approx 38$ h).",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-09-12T18:00:29.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "line emission",
      "reionization",
      "conversion factor",
      "spectral line energy distribution",
      "warm kinetic temperature"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}