Publication Date:
2019-07-01
Description:
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.
Print ISSN:
0004-6361
Electronic ISSN:
1432-0746
Topics:
Physics
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