Keck spectroscopy of gravitationally lensed z ≃ 4 galaxies: Improved constraints on the escape fraction of ionizing photons

Tucker A. Jones, Richard S. Ellis, Matthew A. Schenker, Daniel P Stark

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

The fraction of ionizing photons that escape from young star-forming galaxies is one of the largest uncertainties in determining the role of galaxies in cosmic reionization. Yet traditional techniques for measuring this fraction are inapplicable at the redshifts of interest due to foreground screening by the Lyα forest. In an earlier study, we demonstrated a reduction in the equivalent width of low-ionization absorption lines in composite spectra of Lyman break galaxies at z ≃ 4 compared to similar measures at z ≃ 3. This might imply a lower covering fraction of neutral gas and hence an increase with redshift in the escape fraction of ionizing photons. However, our spectral resolution was inadequate to differentiate between several alternative explanations, including changes with redshift in the outflow kinematics. Here we present higher quality spectra of three gravitationally lensed Lyman break galaxies at z ≃ 4 with a spectral resolution sufficient to break this degeneracy of interpretation. We present a method for deriving the covering fraction of low-ionization gas as a function of outflow velocity and compare the results with similar quality data taken for galaxies at lower redshift. We find an interesting but tentative trend of lower covering fractions of low-ionization gas for galaxies with strong Lyα emission. In combination with the demographic trends of Lyα emission with redshift from our earlier work, our results provide new evidence for a reduction in the average H I covering fraction, and hence an increase in the escape fraction of ionizing radiation from Lyman break galaxies, with redshift.

Original languageEnglish (US)
Article number52
JournalAstrophysical Journal
Volume779
Issue number1
DOIs
StatePublished - Dec 10 2013

Fingerprint

escape
ionization
spectroscopy
galaxies
spectral resolution
photons
outflow
gas
demographic trend
coverings
gas ionization
data quality
kinematics
trends
neutral gases
ionizing radiation
screening
stars
composite materials
ionising radiation

Keywords

  • dark ages, reionization, first stars
  • galaxies: evolution
  • galaxies: formation
  • galaxies: ISM

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Keck spectroscopy of gravitationally lensed z ≃ 4 galaxies : Improved constraints on the escape fraction of ionizing photons. / Jones, Tucker A.; Ellis, Richard S.; Schenker, Matthew A.; Stark, Daniel P.

In: Astrophysical Journal, Vol. 779, No. 1, 52, 10.12.2013.

Research output: Contribution to journalArticle

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