{
  "id": "1601.05803",
  "version": "v1",
  "published": "2016-01-21T21:00:09.000Z",
  "updated": "2016-01-21T21:00:09.000Z",
  "title": "A physical model for the [CII]-FIR deficit in luminous galaxies",
  "authors": [
    "Desika Narayanan",
    "Mark Krumholz"
  ],
  "comment": "16 pages, 9 figures; Submitted to MNRAS, comments welcome",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Observations of ionised carbon at 158 micron ([CII]) from luminous star-forming galaxies at z~0 show that their ratios of [CII] to far infrared (FIR) luminosity are systematically lower than those of more modestly star-forming galaxies. In this paper, we provide a theory for the origin of this so called \"[CII] deficit\" in galaxies. Our model treats the interstellar medium as a collection of clouds with radially-stratified chemical and thermal properties, which are dictated by the clouds' volume and surface densities, as well as the interstellar radiation and cosmic ray fields to which they are exposed. [CII] emission arises from the outer, HI dominated layers of clouds, and from regions where the hydrogen is H2 but the carbon is predominantly C+. In contrast, the most shielded regions of clouds are dominated by CO and produce little [CII] emission. This provides a natural mechanism to explain the observed [CII]-star formation relation: galaxies' star formation rates are largely driven by the surface densities of their clouds. As this rises, so does the fraction of gas in the CO-dominated phase that produces little [CII] emission. Our model further suggests that the apparent offset in the [CII]-FIR relation for high-z sources compared to those at present epoch may arise from systematically larger gas masses at early times: a galaxy with a large gas mass can sustain a high star formation rate even with relatively modest surface density, allowing copious [CII] emission to coexist with rapid star formation.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-01-21T21:00:09.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "physical model",
      "luminous galaxies",
      "high star formation rate",
      "star-forming galaxies",
      "large gas mass"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160105803N"
    }
  }
}