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The mean Hα EW and Lyman-continuum photon production efficiency for faint z ≈ 4-5 galaxies

Abstract : 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 log10ion,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.
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Submitted on : Saturday, July 2, 2022 - 8:12:20 AM
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Daniel Lam, Rychard J. Bouwens, Ivo Labbé, Joop Schaye, Kasper B. Schmidt, et al.. The mean Hα EW and Lyman-continuum photon production efficiency for faint z ≈ 4-5 galaxies. Astronomy and Astrophysics - A&A, EDP Sciences, 2019, 627, ⟨10.1051/0004-6361/201935227⟩. ⟨insu-03711423⟩



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