Volume 627, July 2019
|Number of page(s)||16|
|Published online||18 July 2019|
The mean Hα EW and Lyman-continuum photon production efficiency for faint z ≈ 4−5 galaxies
Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
2 Centre for Astrophysics and SuperComputing, Swinburne, University of Technology, Hawthorn, Victoria 3122, Australia
3 Leibniz-Institut für Astrophysik Postdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
4 Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
5 Department of Astronomy, University of Michigan, 1085 South University Ave, Ann Arbor, MI 48109, USA
Accepted: 20 June 2019
We present the first measurements of the Lyman-continuum photon production efficiency ξion, 0 at z ∼ 4–5 for galaxies fainter than 0.2 L* (−19 mag). ξion, 0 quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of ξion, 0 to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe ξion, 0 to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and ≈300 3 < z < 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6]−[4.5] colors are derived and used to infer the Hα rest-frame equivalent widths, which range from 403 Å to 2818 Å. The derived ξion, 0 is log10(ξion,0/Hz erg−1) = 25.36 ± 0.08 over −20.5 < MUV < −17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that ξion shows no strong dependence on MUV. The ξion, 0 values found in our sample imply that the Lyman-continuum escape fraction for MUV ≈ −19 star-forming galaxies cannot exceed ≈8–20% in the reionization era.
Key words: galaxies: high-redshift / intergalactic medium
© ESO 2019
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