Reconstructing the Observed Ionizing Photon Production Efficiency at z ∼ 2 Using Stellar Population Models

The Astrophysical Journal, vol. 889, pp. 180

Abstract

Abstract The ionizing photon production efficiency, ξ ion, is a critical parameter that provides a number of physical constraints to the nature of the early universe, including the contribution of galaxies to the timely completion of the reionization of the universe. Here, we use KECK/MOSFIRE and ZFOURGE multiband photometric data to explore the ξ ion of a population of galaxies at z ∼ 2 with . Our 130 Hα detections show a median of 24.8 ± 0.5 when dust corrected using a Calzetti et al. dust prescription. Our values are typical of mass/magnitude selected ξ ion values observed in the z ∼ 2 universe. Using BPASSv2.2.1 and Starburst99 stellar population models with simple parametric star formation histories (SFH), we find that even with models that account for effects of stellar evolution with binaries/stellar rotation, model galaxies at have low Hα equivalent widths (EWs) and redder colors compared to our z ∼ 2 observed sample. We find that introducing starbursts to the SFHs resolve the tension with the models; however, due to the rapid time evolution of ξ ion, Hα EWs, and rest-frame optical colors, our Monte Carlo simulations of starbursts show that random distributions of starbursts in evolutionary time of galaxies are unlikely to explain the observed distribution. Thus, either our observed sample is specially selected based on their past SFH, or stellar models require additional mechanisms to reproduce the observed high UV luminosity of galaxies for a given production rate of hydrogen ionizing photons.

Authors 10

1. Themiya Nanayakkara corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands; themiyananayakkara@gmail.com

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

2. J. Brinchmann

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

   Affiliation as printed

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

3. Karl Glazebrook

   Swinburne University of Technology

   Affiliation as printed

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

4. R. J. Bouwens Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands; themiyananayakkara@gmail.com

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

5. Lisa J. Kewley

   Australian National University · ASTRO-3D · ARC Centre of Excellence for All-sky Astrophysics

   Affiliation as printed

   ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Canberra, Australian Capital Territory 2611, Australia

   Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia

6. Kim‐Vy Tran

   UNSW Sydney · ASTRO-3D · ARC Centre of Excellence for All-sky Astrophysics · Texas A&M University

   Affiliation as printed

   ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Canberra, Australian Capital Territory 2611, Australia

   Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA

   George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA

   School of Physics, University of New South Wales, Sydney, NSW 2052, Australia

7. David B. Fisher

   Swinburne University of Technology

   Affiliation as printed

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

8. Glenn G. Kacprzak

   Swinburne University of Technology

   Affiliation as printed

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

9. Ivo Labbé

   Swinburne University of Technology

   Affiliation as printed

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

10. Caroline M. S. Straatman

    Ghent University

    Affiliation as printed

    Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium