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arXiv · 2002.11117

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

Michael V. Maseda·Roland Bacon·Daniel Lam·Jorryt Matthee·Jarle Brinchmann·Joop Schaye·Ivo Labbe·Kasper B. Schmidt·Leindert Boogaard·Rychard Bouwens·Sebastiano Cantalupo·Marijn Franx·Takuya Hashimoto·Hanae Inami·Haruka Kusakabe·Guillaume Mahler·Themiya Nanayakkara·Johan Richard·Lutz Wisotzki
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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-alpha emitters from deep VLT/MUSE spectroscopy and directly measure their Halpha 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_star), implying a median Lyman-alpha equivalent width of 249 Angstroms. By combining the Halpha measurement with the UV magnitude we determine the ionizing photon production efficiency, xi_ion, a first for such faint galaxies. The measurement of log (xi_ion [Hz/erg]) = 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-alpha-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4e-4 and 0.008, with light-weighted ages less than 3 Myr.

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Michael V. Maseda, Roland Bacon, Daniel Lam, Jorryt Matthee, Jarle Brinchmann, Joop Schaye, Ivo Labbe, Kasper B. Schmidt, Leindert Boogaard, Rychard Bouwens, Sebastiano Cantalupo, Marijn Franx, Takuya Hashimoto, Hanae Inami, Haruka Kusakabe, Guillaume Mahler, Themiya Nanayakkara, Johan Richard, Lutz Wisotzki. 2020-02-25. Elevated ionizing photon production efficiency in faint high-equivalent-width Lyman-alpha emitters. https://doi.org/10.1093/mnras/staa622

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