THE CONNECTION between REDDENING, GAS COVERING FRACTION, and the ESCAPE of IONIZING RADIATION at HIGH REDSHIFT

Naveen A. Reddy, Charles C. Steidel, Max Pettini, Milan Bogosavljevic, Alice E. Shapley

    Research output: Contribution to journalArticle

    Abstract

    Using a large sample of spectroscopically confirmed z ∼ 3 galaxies, we establish an empirical relationship between reddening (E (B - V)), neutral gas covering fraction ( fcov (H I)), and the escape of ionizing (Lyman continuum, LyC) photons. Our sample includes 933 galaxies at z ∼ 3, 121 of which have deep spectroscopic observations (≲7 hr) at 850 ≳ lrest ≳ 1300 A with the Low Resolution Imaging Spectrograph on Keck. The high covering fraction of outflowing optically thick H I indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of LyC photons. By modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by H I and reddened by a line-of-sight extinction, we derive an empirical relationship between E (B - V) and fcov (H I). Galaxies with redder UV continua have larger covering fractions of H I characterized by higher line-of-sight extinctions. We develop a model which connects the ionizing escape fraction with E (B - V), and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. Alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic LyC-to-UV flux density ratio to be 〈S (900 A) S (1500 A)〉 int ≲ 0.20, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. Last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from highredshift galaxies.

    Original languageEnglish (US)
    Article number108
    JournalAstrophysical Journal
    Volume828
    Issue number2
    DOIs
    StatePublished - Sep 10 2016

    Fingerprint

    coverings
    escape
    galaxies
    continuums
    extinction
    gases
    gas
    line of sight
    dust
    stellar spectra
    composite materials
    stellar winds
    neutral gases
    photons
    ionizing radiation
    modeling
    spectrographs
    depletion
    flux density
    attenuation

    Keywords

    • dark ages, reionization, first stars
    • dust, extinction
    • galaxies: evolution
    • galaxies: formation
    • galaxies: high-redshift
    • galaxies: ISM

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    THE CONNECTION between REDDENING, GAS COVERING FRACTION, and the ESCAPE of IONIZING RADIATION at HIGH REDSHIFT. / Reddy, Naveen A.; Steidel, Charles C.; Pettini, Max; Bogosavljevic, Milan; Shapley, Alice E.

    In: Astrophysical Journal, Vol. 828, No. 2, 108, 10.09.2016.

    Research output: Contribution to journalArticle

    Reddy, Naveen A. ; Steidel, Charles C. ; Pettini, Max ; Bogosavljevic, Milan ; Shapley, Alice E. / THE CONNECTION between REDDENING, GAS COVERING FRACTION, and the ESCAPE of IONIZING RADIATION at HIGH REDSHIFT. In: Astrophysical Journal. 2016 ; Vol. 828, No. 2.
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    AU - Steidel, Charles C.

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    AU - Bogosavljevic, Milan

    AU - Shapley, Alice E.

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    KW - galaxies: formation

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    KW - galaxies: ISM

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