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.
@article{arxiv.2002.11117,
title = {Elevated ionizing photon production efficiency in faint high-equivalent-width Lyman-alpha emitters},
author = {Michael V. Maseda and Roland Bacon and Daniel Lam and Jorryt Matthee and Jarle Brinchmann and Joop Schaye and Ivo Labbe and Kasper B. Schmidt and Leindert Boogaard and Rychard Bouwens and Sebastiano Cantalupo and Marijn Franx and Takuya Hashimoto and Hanae Inami and Haruka Kusakabe and Guillaume Mahler and Themiya Nanayakkara and Johan Richard and Lutz Wisotzki},
journal= {arXiv preprint arXiv:2002.11117},
year = {2020}
}
Comments
12 Pages, 6 Figures; Accepted for publication in MNRAS