Elevated ionizing photon production efficiency in faint high-equivalent-width Lyman-α emitters

Monthly Notices of the Royal Astronomical Society, vol. 493, pp. 5120–5130

Abstract

ABSTRACT While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic reionization is poorly understood due to a lack of knowledge of their physical properties. We isolate a sample of 35 z ≈ 4–5 continuum-faint Lyman-α emitters from deep VLT/MUSE spectroscopy and directly measure their H α emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than −16 (≈ 0.01 L⋆), implying a median Lyman-α equivalent width of 259 Å. By combining the H α measurement with the UV magnitude, we determine the ionizing photon production efficiency, ξion, a first for such faint galaxies. The measurement of log10 (ξion [Hz erg−1]) = 26.28 ($^{+0.28}_{-0.40}$) is in excess of literature measurements of both continuum- and emission line-selected samples, implying a more efficient production of ionizing photons in these lower luminosity, Lyman-α-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4 × 10−4 and 0.008, with light-weighted ages less than 3 Myr.

Authors 18

1. Michael V. Maseda corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

2. Roland M. Bacon

   Lyon 1 Université · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon

   Affiliation as printed

   Univ Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230, Saint-Genis-Laval, France

3. Daniel Lam Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

4. Jorryt Matthee

   ETH Zurich

   Affiliation as printed

   ETH Zürich, Department of Physics, Wolfgang-Pauli-Str. 27, CH-8093 Zürich, Switzerland

5. J. Brinchmann Aachen Leiden Observatory

   Leiden University · Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto · Leiden Observatory

   Affiliation as printed

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

6. Joop Schaye Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

7. Ivo Labbé

   Swinburne University of Technology

   Affiliation as printed

   Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia

8. Leindert Boogaard Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

9. R. J. Bouwens Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

10. Sebastiano Cantalupo

    ETH Zurich

    Affiliation as printed

    ETH Zürich, Department of Physics, Wolfgang-Pauli-Str. 27, CH-8093 Zürich, Switzerland

11. Marijn Franx Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

12. Takuya Hashimoto

    Waseda University

    Affiliation as printed

    Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan

13. Hanae Inami

    Hiroshima University

    Affiliation as printed

    Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan

14. Haruka Kusakabe

    University of Geneva

    Affiliation as printed

    Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, CH-1290 Versoix, Switzerland

15. Guillaume Mahler

    University of Michigan

    Affiliation as printed

    Department of Astronomy, University of Michigan, 1085 South University Ave., Ann Arbor, MI 48109, USA

16. Themiya Nanayakkara Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands

17. Johan Richard

    Lyon 1 Université · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon

    Affiliation as printed

    Univ Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230, Saint-Genis-Laval, France

18. L. Wisotzki

    Leibniz Institute for Astrophysics Potsdam

    Affiliation as printed

    Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany