{
  "id": "astro-ph/0602586",
  "version": "v1",
  "published": "2006-02-27T14:52:54.000Z",
  "updated": "2006-02-27T14:52:54.000Z",
  "title": "H_2D^+: a light on baryonic dark matter?",
  "authors": [
    "Cecilia Ceccarelli",
    "Carsten Dominik"
  ],
  "comment": "Accepted for publication in ApJ Letters",
  "journal": "Astrophys.J. 640 (2006) L131-L134",
  "doi": "10.1086/503628",
  "categories": [
    "astro-ph"
  ],
  "abstract": "It has been suggested that the dark halos of galaxies are constituted by cloudlets of cold (< 10 K) H_2 and dense (> 10^7$ cm^{-3}) molecular gas. Such gas is extremely difficult to detect, because the classical tracers of molecular gas, CO and/or dust grains, have very low abundances and their emission is exceedingly weak. For this reason, the cloudlet hypothesis remains so far substantially unproven. In this Letter we propose a new method to probe the presence of cold H_2 clouds in galactic halos: the ground transition of ortho-H_2D^+ at 372 GHz. We discuss why the H_2D^+ is abundant under the physical conditions appropriate for the cloudlets, and present a chemical model that predicts the H_2D^+ abundance as function of four key parameters: gas density and metallicity, cosmic ray ionization rate and dust grain size. We conclude that current ground-based instruments might detect the ortho-H_2D^+ line emitted by the cloudlets halo, and prove, therefore, the existence of large quantities of dark baryonic matter around galaxies.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2006-02-27T14:52:54.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "baryonic dark matter",
      "molecular gas",
      "cosmic ray ionization rate",
      "dust grain",
      "cloudlet hypothesis remains"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 711263
    }
  }
}