{
  "id": "1803.03655",
  "version": "v1",
  "published": "2018-03-09T19:01:28.000Z",
  "updated": "2018-03-09T19:01:28.000Z",
  "title": "Accurately predicting the escape fraction of ionizing photons using restframe ultraviolet absorption lines",
  "authors": [
    "J. Chisholm",
    "S. Gazagnes",
    "D. Schaerer",
    "A. Verhamme",
    "J. R. Rigby",
    "M. Bayliss",
    "K. Sharon",
    "M. Gladders",
    "H. Dahle"
  ],
  "comment": "12 pages, 5 figures. Resubmitted to A&A. Comments welcome",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high-redshifts. Without methods to indirectly measure the escape fraction of high-redshift galaxies, it is unlikely that we will know what reionized the universe. Here, we analyze the far-ultraviolet H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within $1.4\\sigma$) using both the H I and the Si II absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Ly$\\alpha$ escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame ultraviolet spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions ($f_\\text{esc}\\le 1$%), but eleven have escape fractions $>1$%. The methods presented here will measure the escape fractions of high-redshift galaxies, enabling future telescopes to determine whether star-forming galaxies reionized the early universe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-03-09T19:01:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "escape fraction",
      "restframe ultraviolet absorption lines",
      "ionizing photons",
      "high-redshift galaxy",
      "accurately predict"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}