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

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 log10ion [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.
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Submitted on : Friday, July 1, 2022 - 2:34:30 PM
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Michael V. Maseda, Roland Bacon, Daniel Lam, Jorryt Matthee, Jarle Brinchmann, et al.. Elevated ionizing photon production efficiency in faint high-equivalent-width Lyman-α emitters. Monthly Notices of the Royal Astronomical Society, 2020, 493, pp.5120-5130. ⟨10.1093/mnras/staa622⟩. ⟨insu-03711471⟩

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