{
  "id": "1805.07318",
  "version": "v1",
  "published": "2018-05-18T16:34:03.000Z",
  "updated": "2018-05-18T16:34:03.000Z",
  "title": "The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium",
  "authors": [
    "N. R. Tanvir",
    "J. P. U. Fynbo",
    "A. de Ugarte Postigo",
    "J. Japelj",
    "K. Wiersema",
    "D. Malesani",
    "D. A. Perley",
    "A. J. Levan",
    "J. Selsing",
    "S. B. Cenko",
    "D. A. Kann",
    "B. Milvang-Jensen",
    "E. Berger",
    "Z. Cano",
    "R. Chornock",
    "S. Covino",
    "A. Cucchiara",
    "V. D'Elia",
    "P. Goldoni",
    "A. Gomboc",
    "K. E. Heintz",
    "J. Hjorth",
    "L. Izzo",
    "P. Jakobsson",
    "L. Kaper",
    "T. Kruehler",
    "T. Laskar",
    "M. Myers",
    "S. Piranomonte",
    "G. Pugliese",
    "R. Sanchez-Ramirez",
    "S. Schulze",
    "M. Sparre",
    "E. R. Stanway",
    "G. Tagliaferri",
    "C. C. Thoene",
    "S. Vergani",
    "P. M. Vreeswijk",
    "R. A. M. J. Wijers",
    "D. Watson",
    "D. Xu"
  ],
  "comment": "31 pages",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "The part played by stars in the ionization of the intergalactic medium remains an open question. A key issue is the proportion of the stellar ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst afterglows can be used to determine the neutral hydrogen column-density in their host galaxies and hence the opacity to extreme ultra-violet radiation along the lines-of-sight to the bursts. Thus, making the reasonable assumption that long-duration GRB locations are representative of the sites of massive stars that dominate EUV production, one can calculate an average escape fraction of ionizing radiation in a way that is independent of galaxy size, luminosity or underlying spectrum. Here we present a sample of NH measures for 138 GRBs in the range 1.6<z<6.7 and use it to establish an average escape fraction at the Lyman limit of <fesc>~0.005, with a 98% confidence upper limit of ~0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget of the IGM at z<5, where the bulk of the bursts lie. At higher redshifts, z>5, firm conclusions are limited by the small size of the GRB sample, but any decline in average HI column-density seems to be modest. We also find no indication of a significant correlation of NH with galaxy UV luminosity or host stellar mass, for the subset of events for which these are available. We discuss in some detail a number of selection effects and potential biases. Drawing on a range of evidence we argue that such effects, while not negligible, are unlikely to produce systematic errors of more than a factor ~2, and so would not affect the primary conclusions. Given that many GRB hosts are low metallicity, high specific star-formation rate, dwarf galaxies, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the universe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-05-18T16:34:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "ionizing radiation",
      "massive stars",
      "high specific star-formation rate",
      "gamma-ray burst afterglows",
      "confidence upper limit"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 31,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}