{
  "id": "astro-ph/0411259",
  "version": "v1",
  "published": "2004-11-10T09:09:47.000Z",
  "updated": "2004-11-10T09:09:47.000Z",
  "title": "Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift",
  "authors": [
    "H. Hirashita",
    "A. Ferrara"
  ],
  "comment": "15 pages, 5 figures, accepted for publication in MNRAS",
  "journal": "Mon.Not.Roy.Astron.Soc. 356 (2005) 1529-1541",
  "doi": "10.1111/j.1365-2966.2004.08602.x",
  "categories": [
    "astro-ph"
  ],
  "abstract": "In order to interpret H2 (molecular hydrogen) quasar absorption line observations of damped Ly-alpha systems (DLAs) and sub-DLAs, we model their H2 abundance as a function of dust-to-gas ratio, including H2 self-shielding and dust extinction against dissociating photons. Then, we constrain the physical state of gas by using H2 data. Using H2 excitation data for DLA with H2 detections, we derive a gas density 1.5 < log n [cm^-3] < 2.5, temperature 1.5 < log T [K] < 3, and internal UV radiation field (in units of the Galactic value) 0.5 < log \\chi < 1.5. We then find that the observed relation between molecular fraction and dust-to-gas ratio of the sample is naturally explained by the above conditions. However, it is still possible that H2 deficient DLAs and sub-DLAs with H2 fractions less than ~ 10^-6 are in a more diffuse and warmer state. The efficient photodissociation by the internal UV radiation field explains the extremely small H2 fraction (< 10^-6) observed for \\kappa < 1/30 (\\kappa is the dust-to-gas ratio in units of the Galactic value); H2 self-shielding causes a rapid increase and the large variations of H2 abundance for \\kappa > 1/30. We finally propose an independent method to estimate the star formation rates of DLAs from H2 abundances; such rates are then critically compared with those derived from other proposed methods. The implications for the contribution of DLAs to the cosmic star formation history are briefly discussed.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2004-11-10T09:09:47.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "damped ly-alpha systems",
      "molecular hydrogen",
      "interstellar physics",
      "high-redshift",
      "cosmic star formation history"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "publisher": "Wiley-Blackwell",
      "journal": "J. Finance"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 664158
    }
  }
}